WO2024096075A1 - Iron-containing lithium polysulfide - Google Patents

Iron-containing lithium polysulfide Download PDF

Info

Publication number
WO2024096075A1
WO2024096075A1 PCT/JP2023/039491 JP2023039491W WO2024096075A1 WO 2024096075 A1 WO2024096075 A1 WO 2024096075A1 JP 2023039491 W JP2023039491 W JP 2023039491W WO 2024096075 A1 WO2024096075 A1 WO 2024096075A1
Authority
WO
WIPO (PCT)
Prior art keywords
iron
lithium
sulfide
polysulfide
atomic
Prior art date
Application number
PCT/JP2023/039491
Other languages
French (fr)
Japanese (ja)
Inventor
友成 竹内
比夏里 栄部
美紗恵 乙山
健太郎 倉谷
Original Assignee
国立研究開発法人産業技術総合研究所
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by 国立研究開発法人産業技術総合研究所 filed Critical 国立研究開発法人産業技術総合研究所
Publication of WO2024096075A1 publication Critical patent/WO2024096075A1/en

Links

Images

Classifications

    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G49/00—Compounds of iron
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0561—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of inorganic materials only
    • H01M10/0562—Solid materials
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates

Definitions

  • the present invention relates to iron-containing lithium polysulfide and a method for producing the same.
  • lithium-ion secondary batteries used in them are increasingly required to have higher capacities.
  • the capacity of the positive electrode has been slower than that of the negative electrode, and even the high-capacity Li(Ni,Mn,Co) O2 -based materials that have been actively researched and developed recently have a capacity of about 250 to 300 mAh/g.
  • sulfur has a high theoretical capacity of approximately 1670 mAh/g, making it one of the promising candidates for a high-capacity electrode material.
  • elemental sulfur does not contain lithium, lithium or an alloy containing lithium must be used for the negative electrode, which has the disadvantage that the range of options for the negative electrode is narrow.
  • lithium sulfide contains lithium, so alloys such as graphite and silicon can be used for the negative electrode, dramatically expanding the range of negative electrode options and avoiding the risk of short circuits caused by dendrite formation when using metallic lithium.
  • lithium sulfide has poor electrical conductivity (see, for example, Non-Patent Document 1 below).
  • a method for improving electrical conductivity a method of forming a bond with a hetero element so that sulfur atoms are not liberated during Li insertion and desorption reactions is considered.
  • a transition metal element capable of imparting electrical conductivity to insulating lithium sulfide is suitable, and examples thereof include compounds such as Li x Fe y S z described in Patent Documents 1 and 2.
  • a method of introducing a typical element and forming a bond between sulfur and the transition metal and the typical element to stabilize the framework structure is also considered.
  • An example of a lithium sulfide complex into which multiple hetero elements (transition metal element, typical element) are introduced is a lithium-iron-phosphorus-sulfur-carbon complex (see, for example, Patent Document 3).
  • the present invention was made in consideration of the current state of the prior art described above, and its main objective is to provide a new material that has a high lithium sulfide utilization rate, a high capacity, good rate characteristics, and excellent charge/discharge characteristics in a compound mainly composed of lithium sulfide that is useful as a positive electrode active material for lithium ion secondary batteries.
  • an iron-containing lithium polysulfide containing lithium sulfide (Li 2 S) as a main phase having a crystallite size of 50 nm or less calculated from the half-width of the diffraction peak based on the (111) plane of Li 2 S obtained by powder X-ray diffraction, and having a Li content of 50 to 70 atomic %, an Fe content of 2 to 12 atomic %, an S content of 20 to 40 atomic %, a C content of 0 to 5 atomic %, and a halogen content of 0 to 0.8 atomic %, improves the utilization rate of lithium sulfide and becomes a high-capacity material, and further, has a low amount of impurities and improves electrical conductivity, while the free sulfur is greatly reduced by the formation of bonds between sulfur and iron, thereby improving the rate characteristics.
  • Li 2 S lithium polysulfide containing lithium sulfide
  • the iron-containing lithium polysulfide can be obtained, for example, by passing a direct current pulse current through a mixture containing a lithium-containing compound, an iron-containing compound, and a sulfur-containing compound to heat and react by current sintering, subjecting the resulting product to a first mechanical milling process, and then subjecting the product to a second mechanical milling process with a predetermined metal sulfide.
  • a direct current pulse current through a mixture containing a lithium-containing compound, an iron-containing compound, and a sulfur-containing compound to heat and react by current sintering, subjecting the resulting product to a first mechanical milling process, and then subjecting the product to a second mechanical milling process with a predetermined metal sulfide.
  • this method not only is a mixture of lithium sulfide and iron sulfide in which the reaction at the atomic level has progressed appropriately formed, but a small amount of iron sulfide is also contained, resulting in improved electrical conductivity and improved
  • An iron-containing lithium polysulfide containing lithium, iron, and sulfur as constituent elements Contains lithium sulfide (Li 2 S) as a main phase;
  • the crystallite size calculated from the half-width of the diffraction peak based on the (111) plane of Li 2 S obtained by powder X-ray diffraction is 50 nm or less, and
  • the iron-containing lithium polysulfide has a Li content of 50 to 70 atomic %, an Fe content of 2 to 12 atomic %, an S content of 20 to 40 atomic %, a C content of 0 to 5 atomic %, and a halogen content of 0 to 0.8 atomic %, relative to 100 atomic % of the total amount of the iron-containing lithium polysulfide.
  • Item 2 The iron-containing lithium polysulfide according to Item 1, wherein the abundance ratio of lithium sulfide (Li 2 S) is 70 mol % or more based on the iron-containing lithium polysulfide as estimated by Rietveld analysis.
  • Item 3 The iron-containing lithium polysulfide according to item 1 or 2, further comprising an iron sulfide (FeS) phase.
  • FeS iron sulfide
  • Item 4 The iron-containing lithium polysulfide according to any one of Items 1 to 3, having an electrical conductivity of 10 -3 to 10 -6 S/cm at 25° C.
  • Item 5 The iron-containing lithium polysulfide according to any one of claims 1 to 4, which is for use in a lithium-ion secondary battery.
  • Item 6 The iron-containing lithium polysulfide according to any one of items 1 to 5, which is used as a positive electrode active material for a lithium-ion secondary battery.
  • Item 7 A method for producing the iron-containing lithium polysulfide according to any one of items 1 to 6, comprising the steps of: (3) A production method comprising a step of mechanically milling a mixture containing a lithium-containing compound, an iron-containing compound, and a sulfur-containing compound; a heat-treated product of the mixture; or a mechanically milled product of the heat-treated product of the mixture, and a metal sulfide having an electrical conductivity of 10 ⁇ 3 S/cm or more.
  • Item 8 Before the step (3), (2) The method according to item 7, further comprising subjecting a mixture containing a lithium-containing compound, an iron-containing compound, and a sulfur-containing compound, or a heat-treated product of the mixture, to mechanical milling.
  • Item 9 Prior to the step (2), (1) The method according to item 8, further comprising a step of heating a mixture containing a lithium-containing compound, an iron-containing compound, and a sulfur-containing compound.
  • step (1) is a step of passing a direct current pulse current through the mixture to heat and react the mixture.
  • Item 11 The manufacturing method according to any one of items 7 to 10, wherein steps (1) to (3) are carried out in a non-oxidizing atmosphere.
  • a positive electrode active material for a lithium ion secondary battery comprising the iron-containing lithium polysulfide according to any one of items 1 to 6.
  • Item 13 A lithium ion secondary battery having as a component the positive electrode active material for lithium ion secondary batteries described in Item 12.
  • An all-solid-state lithium ion secondary battery comprising, as components, the positive electrode active material for a lithium ion secondary battery described in Item 13 and a lithium ion conductive solid electrolyte.
  • the iron-containing lithium polysulfide of the present invention is a fine particle having a crystallite size of 50 nm or less, contains lithium sulfide (Li 2 S) as a main phase, and has additive elements adjusted within a specific composition range, and combined with a small amount of impurities, the utilization rate of lithium sulfide is high, and the high capacity characteristics inherent to lithium sulfide can be fully exhibited, and the electrical conductivity is improved, resulting in a positive electrode active material with excellent rate characteristics.
  • Li 2 S lithium sulfide
  • the iron-containing lithium polysulfide of the present invention is a highly useful material as a positive electrode active material for lithium secondary batteries, such as non-aqueous electrolyte lithium ion secondary batteries and all-solid-state lithium ion secondary batteries.
  • the manufacturing method of the present invention makes it relatively easy to manufacture composites with such excellent performance.
  • FIG. 2 is a schematic diagram of an example of an electric current sintering apparatus.
  • 1 shows X-ray diffraction patterns of samples obtained in Examples 1 and 2 and Comparative Examples 1 and 2.
  • 1 shows initial discharge curves at a current density of 0.13 to 1.3 mA/cm 2 of all-solid-state lithium ion secondary batteries using the samples obtained in Examples 1 and 2 and Comparative Examples 1 and 2 as positive electrode active materials.
  • 1 shows X-ray diffraction patterns of samples obtained in Example 3 and Comparative Example 3.
  • 1 shows initial discharge curves at a current density of 0.13 to 1.3 mA/ cm2 of all-solid-state lithium ion secondary batteries using the samples obtained in Example 3 and Comparative Example 3 as positive electrode active materials.
  • 1 shows X-ray diffraction patterns of samples obtained in Example 4 and Comparative Example 4.
  • 1 shows initial discharge curves at a current density of 0.13 to 1.3 mA/ cm2 of all-solid-state lithium ion secondary batteries using the samples obtained in Example 4 and Comparative Example 4 as positive electrode active materials.
  • 1 shows X-ray diffraction patterns of samples obtained in Example 5 and Comparative Example 5.
  • 1 shows initial discharge curves at a current density of 0.13 to 1.3 mA/ cm2 of all-solid-state lithium ion secondary batteries using the samples obtained in Example 5 and Comparative Example 5 as positive electrode active materials.
  • 1 shows X-ray diffraction patterns of samples obtained in Example 6 and Comparative Example 6.
  • 1 shows initial discharge curves at a current density of 0.13 to 1.3 mA/ cm2 of all-solid-state lithium ion secondary batteries using the samples obtained in Example 6 and Comparative Example 6 as positive electrode active materials.
  • lithium ion secondary battery is a concept that also includes “metal lithium secondary batteries” that use metallic lithium as the negative electrode material.
  • lithium ion secondary battery refers to both “nonaqueous lithium ion secondary batteries” that use a nonaqueous electrolyte and “all-solid-state lithium ion secondary batteries” that use a solid electrolyte.
  • the iron-containing lithium polysulfide of the present invention is an iron-containing lithium polysulfide containing lithium, iron and sulfur as constituent elements, containing lithium sulfide (Li 2 S) as a main phase, and having a crystallite size calculated from the half-width of the diffraction peak based on the (111) plane of Li 2 S obtained by powder X-ray diffraction of 50 nm or less, and the total amount of the iron-containing lithium polysulfide is taken as 100 atomic %, and the Li content is 50 to 70 atomic %, the Fe content is 2 to 12 atomic %, the S content is 20 to 40 atomic %, the C content is 0 to 5 atomic %, and the halogen content is 0 to 0.8 atomic %.
  • Li 2 S lithium sulfide
  • Such iron-containing lithium polysulfide of the present invention has a high utilization rate of lithium sulfide, can fully exhibit the high capacity characteristics inherent to lithium sulfide, has improved electrical conductivity, and is a material that becomes a positive electrode active material having excellent rate characteristics, and is particularly useful as a positive electrode active material for lithium ion secondary batteries.
  • the initial discharge capacity at an applied current of 0.13 mA/ cm2 when taken as 100%, the initial discharge capacity at an applied current of 1.3 mA/ cm2 can be 60 to 95%, preferably 70 to 90%. In this specification, the presence of such a characteristic is sometimes referred to as "having excellent rate characteristics".
  • the iron-containing lithium polysulfide of the present invention has a main phase consisting of lithium sulfide.
  • the amount of lithium sulfide phase is preferably 70 mol% or more, more preferably 80 mol% or more, and even more preferably 85 mol% or more, based on the entire iron-containing lithium polysulfide of the present invention (100 mol%).
  • the upper limit of the amount of lithium sulfide phase is not particularly limited, but is usually 100 mol%.
  • the iron-containing lithium polysulfide of the present invention may contain up to 30 mol% (particularly up to 20 mol%, and even more preferably up to 15 mol%) of other crystals in addition to the lithium sulfide crystal phase, and at this content, the effect on the charge and discharge characteristics is limited.
  • the iron-containing lithium polysulfide of the present invention contains a small amount (0.1 to 15 mol%, preferably 0.5 to 10 mol%) of iron sulfide (FeS) phase, it is possible to further improve the capacity and rate characteristics.
  • the amount present in the composite is estimated using the Rietveld analysis method of normal X-ray diffraction data. The Rietveld method is described in detail in the following non-patent literature (F. Izumi and T. Ikeda, Mater Sci. Forum, 321-324, 198 (2000)).
  • iron-containing lithium polysulfide of the present invention iron atoms are arranged within the lithium sulfide crystal lattice to form Fe-S bonds, and since it contains Fe and has a reduced amount of impurities, it is conductive to the inside, has a high electrode utilization rate (particularly the positive electrode utilization rate), and can more fully demonstrate the high capacity characteristics that lithium sulfide inherently possesses. Furthermore, when the manufacturing method of the present invention described below is adopted, a metastable phase of iron-containing lithium polysulfide is formed, which is then refined by mechanical milling to form submicron particles, making it possible to stabilize the iron-containing lithium polysulfide that is inherently a metastable phase.
  • the iron-containing lithium polysulfide of the present invention having the above-mentioned characteristics preferably has the added element iron atoms arranged within the lithium sulfide crystal lattice to form Fe-S bonds, which further suppresses the presence of free sulfur and provides good electrical conductivity, making it easier to exhibit excellent capacity and rate characteristics.
  • the iron-containing lithium polysulfide of the present invention preferably has a stabilized metastable phase in which iron atoms are introduced into the lithium sulfide crystal lattice.
  • the iron-containing lithium polysulfide of the present invention preferably consists of submicron or smaller crystallites because the metastable phase of iron-containing lithium polysulfide is stable. More specifically, the crystallite size of the iron-containing lithium polysulfide of the present invention is preferably 50 nm or less, more preferably 40 nm or less (particularly 1 to 30 nm).
  • the crystallites can be refined by the mechanical milling process.
  • the crystallite size of the iron-containing lithium polysulfide of the present invention is a value calculated based on the Scherrer formula from the half-width of the diffraction peak based on the (111) plane that shows the maximum intensity of the peak of lithium sulfide observed as the main phase in powder X-ray diffraction measurement.
  • the ratio of each element in the iron-containing lithium polysulfide of the present invention is not particularly limited, but it is preferable that there is an amount of Fe sufficient to form Fe-S bonds to the extent that free sulfur is not generated, that there is an amount of Li sufficient to provide a theoretical capacity of 600 mAh/g or more estimated from the amount of Li contained, and that there is an amount of Fe sufficient to ensure electrical conductivity.
  • the amount of impurities such as carbon is too large, the capacity, cycle characteristics, and rate characteristics will deteriorate.
  • the total amount of the lithium sulfide-iron-carbon composite of the present invention formed is 100 atomic %, and that the Li content is 50 to 70 atomic % (particularly 51 to 60 atomic %), the Fe content is 2 to 12 atomic % (particularly 4 to 11 atomic %), the S content is 20 to 40 atomic % (particularly 30 to 39 atomic %), the C content is 0 to 5 atomic % (particularly 0 to 3 atomic %), and the halogen content is 0 to 0.8 atomic % (particularly 0 to 0.5 atomic %).
  • the composite does not contain carbon or halogen (both the C content and the halogen content are 0 atomic %).
  • the iron-containing lithium polysulfide of the present invention as described above can have improved electrical conductivity, and specifically, the electrical conductivity of the iron-containing lithium polysulfide of the present invention can be set to 10 ⁇ 3 to 10 ⁇ 6 S/cm, preferably 10 ⁇ 3 to 3 ⁇ 10 ⁇ 6 S/cm, at 25° C.
  • the electrical conductivity of the iron-containing lithium polysulfide of the present invention is measured by compressing the powder at 300 MPa and measuring the current when a voltage is applied.
  • the iron-containing lithium polysulfide of the present invention is not particularly limited, but may be produced by the following method: (3) It can be obtained by a manufacturing method including a step of subjecting a mixture containing a lithium-containing compound, an iron-containing compound, and a sulfur-containing compound, a heat-treated product of the mixture, or a mechanically milled product of the heat-treated product of the mixture, and a metal sulfide having an electrical conductivity of 10 ⁇ 3 S/cm or more to mechanical milling.
  • the particles are refined, and the metastable phase in which iron atoms are incorporated into the lithium sulfide phase is stabilized, while the electrical conductivity can be particularly improved.
  • the production method of the present invention further includes the steps of: (2) It is preferable to include a step of subjecting a mixture containing a lithium-containing compound, an iron-containing compound, and a sulfur-containing compound, or a heat-treated product of the mixture, to a mechanical milling treatment, whereby the particles are refined before the step (3), and the metastable phase in which iron atoms are incorporated into the lithium sulfide phase is stabilized, making it easier to improve the electrical conductivity.
  • the production method of the present invention further includes, before the step (2), It is preferable to include a step (1) of heating a mixture containing a lithium-containing compound, an iron-containing compound, and a sulfur-containing compound, whereby the reaction can be moderately advanced by heating, and the electrical conductivity can be easily further improved by the subsequent steps (2) and (3).
  • a step (1) of heating a mixture containing a lithium-containing compound, an iron-containing compound, and a sulfur-containing compound whereby the reaction can be moderately advanced by heating, and the electrical conductivity can be easily further improved by the subsequent steps (2) and (3).
  • the types of lithium-containing compounds, iron-containing compounds, and sulfur-containing compounds are not particularly limited, and three or more types of compounds containing one type each of the elements lithium, iron, and sulfur can be mixed and used, or a compound containing two or more types of elements selected from lithium, iron, and sulfur can be used as part of the raw material.
  • These raw material compounds are preferably compounds that do not contain metal elements other than lithium and iron, or carbon.
  • the elements contained in the raw material compounds other than lithium, iron, and sulfur are released or volatilized by heat treatment.
  • raw material compounds include lithium-containing compounds such as lithium sulfide (Li 2 S) and lithium hydroxide (LiOH), iron-containing compounds such as metallic iron (Fe), iron sulfide (FeS, FeS 2 , etc.), and iron sulfate (FeSO 4 ), and sulfur-containing compounds such as sulfur (S), lithium sulfide (Li 2 S), and iron sulfide (FeS, FeS 2 , etc.).
  • lithium-containing compounds such as lithium sulfide (Li 2 S) and lithium hydroxide (LiOH)
  • iron-containing compounds such as metallic iron (Fe), iron sulfide (FeS, FeS 2 , etc.
  • iron sulfate FeSO 4
  • sulfur-containing compounds such as sulfur (S), lithium sulfide (Li 2 S), and iron sulfide (FeS, FeS 2 , etc.
  • lithium sulfide Li 2 S
  • iron sulfide FeS, FeS 2
  • Li 2 S lithium sulfide
  • FeS, FeS 2 iron sulfide
  • these raw material compounds are preferably in the form of a powder with an average particle size of about 0.1 to 100 ⁇ m.
  • the average particle size of the raw material compounds is determined by the value at which the cumulative frequency distribution is 50% when particle size distribution is measured using a dry laser diffraction/scattering method.
  • the mixing ratio of the raw materials consisting of the lithium-containing compound, the iron-containing compound, and the sulfur-containing compound is not particularly limited, but it is preferable that in the final product, the iron-containing lithium polysulfide of the present invention, there is an amount of Fe that is sufficient to easily form Fe-S bonds to the extent that free sulfur is not generated, there is an amount of Li that is sufficient to easily achieve a theoretical capacity estimated from the amount of Li of about 600 mAh/g or more, and there is an amount of Fe that ensures electrical conductivity and is unlikely to deteriorate in capacity and rate characteristics.
  • the mixing ratio of the raw materials so that the Li content is 50 to 70 atomic % (particularly 51 to 60 atomic %), the Fe content is 2 to 12 atomic % (particularly 4 to 11 atomic %), the S content is 20 to 40 atomic % (particularly 30 to 39 atomic %), the C content is 0 to 5 atomic % (particularly 0 to 3 atomic %), and the halogen content is 0 to 0.8 atomic % (particularly 0 to 0.5 atomic %).
  • the mixing ratio of the raw material compounds can be adjusted so that the ratio of each element contained in the raw material compounds is the same as the ratio of each element in the desired iron-containing lithium polysulfide of the present invention.
  • Step (1) it is preferable to first subject the mixture containing the lithium-containing compound, the iron-containing compound, and the sulfur-containing compound to a heat treatment.
  • the heating method is not particularly limited, it is preferable to perform electric sintering from the viewpoint of easily obtaining a mixture of lithium sulfide and iron sulfide in which the reaction at the atomic level has progressed appropriately by the heating reaction.
  • step (1) When electric sintering is performed in step (1), specifically, the raw material mixture described above is filled into a conductive mold (conductive container), and a current, preferably a direct current pulse current, is passed through the conductive mold (conductive container) (a method known as discharge plasma sintering, pulsed electric current sintering, plasma activated sintering, etc.), which heats the conductive mold (conductive container) with Joule heat, heating the raw material mixture in the conductive mold (conductive container), causing the elements to diffuse and move, making it possible to suitably produce an intermediate in which the elements are mixed together at the atomic level.
  • a current preferably a direct current pulse current
  • the atmosphere during this electric sintering process is preferably a non-oxidizing atmosphere.
  • the electric sintering process may be performed under normal pressure, but it is preferable to perform the electric sintering process under pressure.
  • a conductive container is filled with a raw material mixture containing the raw materials lithium-containing compound, iron-containing compound, and sulfur-containing compound, and a pulsed ON-OFF direct current is preferably passed through the container while applying pressure, preferably in a non-oxidizing atmosphere.
  • the material of the conductive mold is not particularly limited as long as it is conductive, and in addition to those made of carbon, iron, iron oxide, aluminum, tungsten carbide, etc., those made of a mixture of carbon and/or iron oxide and silicon nitride can also be suitably used.
  • the electric sintering treatment is preferably performed in an inert gas atmosphere such as Ar or N2 , or in a reducing atmosphere such as H2 , etc.
  • the pressure can be reduced so that the oxygen concentration is sufficiently low, for example, the oxygen partial pressure can be reduced to 20 Pa or less (particularly 1 to 20 Pa).
  • the inside of the container can be made into a non-oxidizing atmosphere.
  • the conductive mold (conductive container) does not have to be completely sealed, and when an incompletely sealed container is used, the container can be placed in a reaction chamber and the inside of the reaction chamber can be made into a non-oxidizing atmosphere. This makes it possible to carry out the heating reaction of the raw material mixture described above in a non-oxidizing atmosphere.
  • the conductive container is heated by Joule heat, and the raw materials in the container are heated, causing the starting materials to react with each other and forming an intermediate in which the atoms are mixed together.
  • the desired intermediate can be produced in a short time of less than 30 minutes, so there is little loss of easily volatile elements such as Li and S, and an intermediate with a composition ratio close to the raw material mixture ratio can be obtained.
  • the heating temperature in the electric sintering process is usually preferably 400 to 1200°C, more preferably 500 to 1100°C, from the viewpoints of more thoroughly interdiffusing the constituent elements to facilitate mixing at the atomic level, reducing sulfur that is not bonded to transition metals and typical elements (free sulfur) and facilitating high capacity, and suppressing loss due to volatilization of elements such as Li and S and facilitating high capacity.
  • the time for holding within the above heating temperature range is preferably 0 to 30 minutes from the viewpoints of easily suppressing loss due to volatilization of elements such as Li and S and facilitating high capacity, and once the temperature range is reached, the electric current can be immediately stopped (i.e., the holding time at the above heating temperature is set to 0) and the material can be left to cool.
  • the pressure to be applied when compressing the raw material powder is preferably, for example, 5 to 60 MPa, and more preferably 10 to 50 MPa, from the viewpoint of making it easier to strengthen contact between the raw material compounds, to facilitate sufficient atomic diffusion during heating, and to facilitate sufficient reaction between atoms in the raw material compounds.
  • the product has a composition with a low melting point, it is also possible to heat without applying pressure (atmospheric pressure). From this viewpoint, and taking into consideration the case where the product has a composition with a low melting point, the pressure to be applied when compressing the raw material powder can be 0.1 to 60 MPa, and preferably 0.1 to 50 MPa.
  • the device for electric sintering is not particularly limited as long as it is capable of heating, cooling, pressurizing, etc. the raw material mixture and can apply the current required for discharge.
  • a commercially available electric sintering device discharge plasma sintering device
  • Such an electric sintering device and its principle are disclosed, for example, in JP-A-10-251070.
  • Figure 1 shows a schematic diagram of an electric sintering device. Note that the electric sintering device is not limited to the device described below.
  • the electric sintering apparatus 1 shown in Figure 1 has a sintering die (electronically conductive container) 3 in which a sample 2 is loaded, and a pair of upper and lower punches 4 and 5.
  • the punches 4 and 5 are supported by punch electrodes 6 and 7, respectively, and a pulse current can be supplied to the sample 2 loaded in the sintering die 3 via these punch electrodes 6 and 7 while applying pressure as necessary.
  • the material of the sintering die 3 is not limited, and examples include carbon materials such as graphite.
  • the electric current section including the conductive container 3, electric current punches 4 and 5, and punch electrodes 6 and 7 is housed in a water-cooled vacuum chamber 8, and the interior of the chamber can be adjusted to a predetermined atmosphere by an atmosphere control mechanism 15. Therefore, it is preferable to use the atmosphere control mechanism 15 to adjust the interior of the chamber to a non-oxidizing atmosphere.
  • the control device 12 drives and controls the pressurizing mechanism 13, the pulse power supply 11, the atmosphere control mechanism 15, the water cooling mechanisms 16 and 10, and the temperature measuring device 17.
  • the control device 12 drives the pressurizing mechanism 13 so that the punch electrodes 6 and 7 pressurize the raw material mixture at a predetermined pressure.
  • the pulse current applied for heating can be, for example, a pulsed (ON-OFF switching) direct current with a pulse width of about 2-3 milliseconds and a cycle of about 3-300 Hz.
  • the specific current value varies depending on the type and size of the conductive mold (conductive container), but it is preferable to determine the specific current value so that the temperature range is as described above. For example, when a graphite mold material with an inner diameter of 15 mm is used, 200-1000 A is preferable, and when a graphite mold material with an inner diameter of 100 mm is used, 1000-8000 A is preferable.
  • the raw material mixture filled in the conductive container 3 described above can be pressurized via punch electrodes 6 and 7.
  • Step (2) a mixture containing a lithium-containing compound, an iron-containing compound and a sulfur-containing compound, or a heat-treated product of the mixture, is subjected to a mechanical milling treatment to mix, pulverize and react with each other.
  • the raw material powders When using a mixture containing a lithium-containing compound, an iron-containing compound, and a sulfur-containing compound, the raw material powders can be mixed and then subjected to mechanical milling. When using a heat-treated product of the mixture, the product obtained in the above-mentioned step (1) can be used.
  • Mechanical milling is a method in which raw materials are milled and mixed while mechanical energy is applied to them to cause a reaction. According to this method, the raw materials are milled and mixed by applying mechanical impact and friction, which causes the compounds contained in the raw materials to come into vigorous contact with each other and be finely divided, making it easy to obtain a metastable phase.
  • the above-mentioned mechanical milling process forms metastable iron-containing lithium polysulfide, which is difficult to produce by heat treatment alone, while also finely dividing it so that it exists stably.
  • Mechanical milling devices that can be used include, for example, ball mills, vibration mills, turbo mills, and disk mills, with ball mills being preferred.
  • the mechanical milling treatment is easy to suppress the oxidation of sulfides, it is preferable to perform the treatment in a non-oxidizing atmosphere, for example, in an inert gas atmosphere such as Ar or N2 , or in a reducing atmosphere such as H2 .
  • the treatment can be performed in a reduced pressure state in which the oxygen concentration is sufficiently low, for example, the oxygen partial pressure can be reduced to 20 Pa or less (particularly 1 to 20 Pa).
  • the rotation speed during mechanical milling is preferably 200 to 600 rpm, more preferably 250 to 550 rpm, to prevent sulfur from volatilizing and to facilitate the formation of a composite with a high desired sulfur content.
  • the temperature during mechanical milling is preferably 200°C or less, more preferably 20 to 100°C, to prevent sulfur from volatilizing and to facilitate the formation of a composite with a high desired sulfur content.
  • step (3) Second mechanical milling step (step (3))
  • a mixture containing a lithium-containing compound, an iron-containing compound, and a sulfur-containing compound; a heat-treated product of the mixture; or a mechanically milled product of the heat-treated product of the mixture, and a metal sulfide having an electrical conductivity of 10 ⁇ 3 S/cm or more are subjected to a mechanical milling treatment, and then mixed, pulverized, and reacted with each other to obtain the iron-containing lithium polysulfide of the present invention.
  • the raw material powders When using a mixture containing a lithium-containing compound, an iron-containing compound, and a sulfur-containing compound, the raw material powders can be mixed and then subjected to mechanical milling with a metal sulfide having an electrical conductivity of 10 ⁇ 3 S/cm or more.
  • a heat-treated product of the mixture the product obtained in the above-mentioned step (1) and a metal sulfide having an electrical conductivity of 10 ⁇ 3 S/cm or more can be used.
  • the product obtained in the above-mentioned step (2) can be used.
  • step (1) or step (2) when the above-mentioned step (1) or step (2) is adopted, if the product already contains a metal sulfide having an electrical conductivity of 10 ⁇ 3 S/cm or more in the amount to be added described later, it is not necessary to add a new metal sulfide.
  • a sulfide having a high electrical conductivity such as iron sulfide is used as a raw material, if the peak in the X-ray diffraction spectrum disappears in the milling step of step (2), that is, if mechanical milling is performed to the extent that the sulfide phase cannot be identified, or if the content of the sulfide phase is reduced as a result of the milling step of step (2), a separate metal sulfide must be added.
  • the electrical conductivity of the usable metal sulfide is not particularly limited, but from the viewpoints of easily improving the utilization rate of lithium sulfide, easily allowing the inherent high capacity property of lithium sulfide to be fully exhibited, and easily having excellent rate characteristics, it is preferably 10 3 to 10 -3 S/cm, and more preferably 10 3 to 10 -2 S/cm.
  • the electrical conductivity of the metal sulfide is measured by compacting the powder at about 300 MPa and measuring the amount of current when a voltage is applied.
  • Metal sulfides having such electrical conductivity are not particularly limited, but examples thereof include iron-containing lithium polysulfides ( Li2FeS2 , etc.; however, different from the products of steps (1) and ( 2 )), iron sulfides (FeS, FeS2 , etc.), molybdenum sulfides ( MoS2 , Mo6S8 , etc.), copper sulfides (CuS, etc.), etc. These metal sulfides can be used alone or in combination of two or more.
  • the amount of the metal sulfide added is not particularly limited, but from the viewpoint of making it easier to improve the utilization rate of lithium sulfide, to make it easier to fully utilize the high capacity characteristics inherent to lithium sulfide, and to make it easier to have excellent rate characteristics, the metal sulfide can be added in an amount of 3 to 25 mass%, preferably 5 to 20 mass%, of 100 mass% of the total amount of the intermediate obtained in step (2) and the metal sulfide.
  • Mechanical milling devices that can be used include, for example, ball mills, vibration mills, turbo mills, and disk mills, with ball mills being preferred.
  • the mechanical milling treatment is easy to suppress the oxidation of sulfides, it is preferable to perform the treatment in a non-oxidizing atmosphere, for example, in an inert gas atmosphere such as Ar or N2 , or in a reducing atmosphere such as H2 .
  • the treatment can be performed in a reduced pressure state in which the oxygen concentration is sufficiently low, for example, the oxygen partial pressure can be reduced to 20 Pa or less (particularly 1 to 20 Pa).
  • the rotation speed during mechanical milling is preferably 200 to 600 rpm, more preferably 250 to 550 rpm, to prevent sulfur from volatilizing and to facilitate the formation of a composite with a high desired sulfur content.
  • the temperature during mechanical milling is preferably 100°C or less, more preferably 20 to 80°C, to prevent sulfur from volatilizing and to facilitate the formation of a composite with a high desired sulfur content.
  • Lithium-ion secondary battery The iron-containing lithium polysulfide of the present invention can be effectively used as a positive electrode active material for lithium primary batteries, lithium ion secondary batteries (metal lithium secondary batteries, etc.) by utilizing the excellent properties described above.
  • the iron-containing lithium polysulfide of the present invention is a material containing lithium in its structure, it is a material that can be charged and discharged, and has a high capacity and excellent rate characteristics, so it is useful as a positive electrode active material for lithium ion secondary batteries.
  • the lithium ion secondary battery using the iron-containing lithium polysulfide of the present invention as a positive electrode active material may be a non-aqueous electrolyte lithium ion secondary battery that uses a non-aqueous solvent-based electrolyte as the electrolyte, or may be an all-solid-state lithium ion secondary battery that uses a lithium ion conductive solid electrolyte.
  • the structure of the non-aqueous electrolyte lithium ion secondary battery and the all-solid-state lithium ion secondary battery can be the same as that of a known lithium ion secondary battery, except that the iron-containing lithium polysulfide of the present invention is used as the positive electrode active material.
  • a non-aqueous electrolyte lithium ion secondary battery can have the same basic structure as a known non-aqueous electrolyte lithium ion secondary battery, except that the iron-containing lithium polysulfide of the present invention described above is used as the positive electrode active material.
  • the iron-containing lithium polysulfide of the present invention described above can be used as the positive electrode active material, and a positive electrode mixture containing a conductive material and a binder can be supported on a positive electrode current collector such as Al, Ni, stainless steel, or carbon cloth.
  • a positive electrode current collector such as Al, Ni, stainless steel, or carbon cloth.
  • the conductive material for example, carbon materials such as graphite, cokes, carbon black, and acicular carbon can be used.
  • Both lithium-containing and lithium-free materials can be used for the negative electrode.
  • non-sinterable carbon, and lithium metal, tin, silicon, and alloys containing these, and SiO, etc. can also be used.
  • These negative electrode active materials can also be supported on a negative electrode current collector made of Al, Cu, Ni, stainless steel, carbon, etc., using conductive materials, binders, etc. as necessary.
  • Separators can be made of materials such as polyolefin resins, such as polyethylene and polypropylene, fluororesins, nylon, aromatic aramid, and inorganic glass, and can be in the form of porous membranes, nonwoven fabrics, woven fabrics, etc.
  • the solvent for the non-aqueous electrolyte may be a solvent known as a solvent for non-aqueous solvent-based secondary batteries, such as a carbonate compound, an ether compound, a nitrile compound, or a sulfur-containing compound.
  • all-solid-state lithium-ion secondary batteries can have the same structure as known all-solid-state lithium-ion secondary batteries, except that the iron-containing lithium polysulfide of the present invention is used as the positive electrode active material.
  • examples of the lithium ion conductive solid electrolyte that can be used include polymer-based solid electrolytes such as polyethylene oxide-based polymer compounds, polymer compounds containing at least one of a polyorganosiloxane chain and a polyoxyalkylene chain, as well as sulfide-based solid electrolytes and oxide-based solid electrolytes.
  • the iron-containing lithium polysulfide of the present invention can be used as the positive electrode active material, and a positive electrode mixture containing a conductive material, a binder, and a solid electrolyte can be supported on a positive electrode current collector such as Ti, Al, Ni, stainless steel, etc.
  • a positive electrode current collector such as Ti, Al, Ni, stainless steel, etc.
  • carbon materials such as graphite, cokes, carbon black, and acicular carbon can be used, as in non-aqueous solvent-based lithium-ion secondary batteries.
  • both lithium-containing and lithium-free materials can be used.
  • lithium metal, tin, silicon and alloys containing these, SiO, etc. can be used.
  • These negative electrode active materials can also be supported on a negative electrode current collector made of Al, Cu, Ni, stainless steel, carbon, etc., using the above-mentioned conductive materials, binders, etc., as necessary.
  • non-aqueous electrolyte lithium-ion secondary battery and the all-solid-state lithium-ion secondary battery there are no particular limitations on the shape of the non-aqueous electrolyte lithium-ion secondary battery and the all-solid-state lithium-ion secondary battery, and they may be cylindrical, rectangular, etc.
  • Li 2 S lithium sulfide
  • FeS iron sulfide
  • the graphite mold filled with the raw materials was then placed in an electric sintering machine.
  • the graphite mold and the electric parts, including the electrode parts, were placed in a vacuum chamber, which was evacuated to a vacuum (approximately 20 Pa) and then filled with high-purity argon gas (oxygen concentration approximately 0.2 ppm) up to atmospheric pressure.
  • the raw material packed in the graphite mold was pressurized at approximately 30 MPa while a DC pulse current of approximately 600 A (pulse width 2.5 ms, cycle 28.6 Hz) was applied.
  • the area near the graphite mold was heated at a temperature increase rate of approximately 200°C/min, and reached 600°C 3 minutes after the start of application of the pulse current.
  • the current application and pressure were then immediately stopped and the material was allowed to cool naturally.
  • the graphite jig was transferred to a glove box with an argon gas atmosphere with a dew point of -80°C, and the reaction product of lithium sulfide and iron sulfide was removed from the mold and crushed in a mortar. It was then placed in a zirconia pot under an argon gas atmosphere and processed by mechanical milling at 400 rpm for 20 hours using a planetary ball mill (model P-7) manufactured by Fritsch Japan Co., Ltd.
  • Li 2 FeS 2 prepared by mixing commercially available Li 2 S and FeS in a 1:1 molar ratio and then heating in an electric sintering machine at 1000°C for 1 minute, electrical conductivity 10 -2 S/cm (25°C)
  • Li 8 FeS 5 Li 8 FeS 5
  • the ratios (atomic %) of each element in the obtained sample were Li 52%, Fe 11%, and S 37%.
  • the obtained sample did not contain carbon or halogen.
  • the electrical conductivity of the obtained sample was measured by compacting it at 300 MPa and measuring the current value when a voltage was applied, and the result was 4.4 ⁇ 10 ⁇ 4 S/cm, which was dramatically improved compared to the electrical conductivity of Li 8 FeS 5 before it was composited with Li 2 FeS 2 (Comparative Example 1), which was 1.1 ⁇ 10 ⁇ 5 S/cm.
  • the X-ray diffraction pattern of the obtained sample showed a peak derived from low-crystalline lithium sulfide (Li 2 S) as the main phase, and a peak derived from iron sulfide (FeS) was also observed. That is, the abundance ratio of lithium sulfide (Li 2 S) estimated by Rietveld analysis was 96 mol%, and the abundance ratio of iron sulfide (FeS) was 4 mol%. In addition, the crystallite size estimated from the half-width of the diffraction peak based on the (111) plane of lithium sulfide was 20 nm. From the above, by this method, an iron-containing lithium polysulfide in which the main phase is lithium sulfide and the crystallite size is 50 nm or less could be produced.
  • the obtained iron-containing lithium polysulfide was used as the positive electrode active material, indium metal was used as the negative electrode, and an argyrodite-type sulfide-based solid electrolyte was used as the electrolyte to assemble an all-solid-state lithium-ion secondary battery, and charge/discharge tests were conducted.
  • the above-mentioned iron-containing lithium polysulfide, argyrodite-type sulfide-based solid electrolyte, and acetylene black were mixed in a mass ratio of 4:5:1 to form a positive electrode composite, and a pellet battery with a diameter of 10 mm was produced by pressure molding the positive electrode composite/argyrodite-type sulfide-based solid electrolyte/lithium indium foil.
  • a charge/discharge test was performed by starting charging with constant current measurement in the range of 3.0 V to 1.0 V. The current density was 0.13 mA/ cm2 for charging and 0.13 to 1.3 mA/ cm2 for discharging.
  • the initial discharge capacity was 520mAh/g when the discharge current density was low (0.13mA/ cm2 ), 500mAh/g when it was 0.25mA/ cm2 , 480mAh/g when it was 0.64mA/ cm2 , and 450mAh/g when it was high current density (1.3mA/ cm2 ).
  • the initial discharge capacity at high current density (1.3mA/ cm2 ) was as high as 86% of the initial discharge capacity at low current density (0.13mA/ cm2 ), and it can be understood that a positive electrode active material with excellent capacity and rate characteristics was obtained.
  • Example 2 An iron-containing lithium polysulfide was obtained in the same manner as in Example 1, except that the mechanical milling time of the reaction product of lithium sulfide and iron sulfide (Li 8 FeS 5 ) and Li 2 FeS 2 was set to 2 hours.
  • the ratios (atomic %) of each element in the obtained sample were Li 52%, Fe 11%, and S 37%.
  • the obtained sample did not contain carbon or halogen.
  • the powder was compressed at 300 MPa and the current value when a voltage was applied was measured, which was 4.0 ⁇ 10 ⁇ 4 S/cm, which was dramatically improved compared to the electrical conductivity of Li 8 FeS 5 before being composited with Li 2 FeS 2 (Comparative Example 1), which was 1.1 ⁇ 10 ⁇ 5 S/cm.
  • the X-ray diffraction pattern of the obtained sample showed a peak derived from low-crystalline lithium sulfide (Li 2 S) as the main phase, and a peak derived from iron sulfide (FeS) was also observed. That is, the abundance ratio of lithium sulfide (Li 2 S) estimated by Rietveld analysis was 91 mol %, and the abundance ratio of iron sulfide (FeS) was 9 mol %. In addition, the crystallite size estimated from the half-width of the diffraction peak based on the (111) plane of lithium sulfide was 18 nm. From the above, by this method, an iron-containing lithium polysulfide in which the main phase is lithium sulfide and the crystallite size is 50 nm or less could be produced.
  • the obtained iron-containing lithium polysulfide was used as the positive electrode active material, indium metal was used as the negative electrode, and an argyrodite-type sulfide-based solid electrolyte was used as the electrolyte to assemble an all-solid-state lithium-ion secondary battery, and charge/discharge tests were conducted.
  • the above-mentioned iron-containing lithium polysulfide, argyrodite-type sulfide-based solid electrolyte, and acetylene black were mixed in a mass ratio of 4:5:1 to form a positive electrode composite, and a pellet battery with a diameter of 10 mm was produced by pressure molding the positive electrode composite/argyrodite-type sulfide-based solid electrolyte/lithium indium foil.
  • a charge/discharge test was performed by starting charging with constant current measurement in the range of 3.0 V to 1.0 V. The current density was 0.13 mA/ cm2 for charging and 0.13 to 1.3 mA/ cm2 for discharging.
  • the initial discharge capacity was 510 mAh/g when the discharge current density was low (0.13 mA/ cm2 ), 500 mAh/g when it was 0.25 mA/ cm2 , 480 mAh/g when it was 0.64 mA/ cm2 , and 450 mAh/g when it was high current density (1.3 mA/ cm2 ).
  • the initial discharge capacity at high current density was as high as 88% of the initial discharge capacity at low current density (0.13 mA/ cm2 ), and it can be understood that a positive electrode active material excellent in capacity and rate characteristics was obtained.
  • Comparative Example 1 An iron-containing lithium polysulfide was obtained in the same manner as in Example 1, except that Li2FeS2 was not added to the reaction product ( Li8FeS5 ) of lithium sulfide and iron sulfide , and the subsequent mechanical milling treatment was not performed. Specifically, an iron-containing lithium polysulfide was obtained as follows.
  • Li 2 S lithium sulfide
  • FeS iron sulfide
  • the graphite mold filled with the raw materials was then placed in an electric sintering machine.
  • the graphite mold and the electric parts, including the electrode parts, were placed in a vacuum chamber, which was evacuated to a vacuum (approximately 20 Pa) and then filled with high-purity argon gas (oxygen concentration approximately 0.2 ppm) up to atmospheric pressure.
  • the raw material packed into the graphite mold was pressurized at approximately 30 MPa while a DC pulse current of approximately 600 A (pulse width 2.5 ms, cycle 28.6 Hz) was applied.
  • the area near the graphite mold was heated at a temperature increase rate of approximately 200°C/min, and reached 600°C 3 minutes after the start of application of the pulse current.
  • the current application and pressure were then immediately stopped and the material was allowed to cool naturally.
  • the graphite jig was transferred to a glove box with an argon gas atmosphere with a dew point of -80°C, and the reaction product of lithium sulfide and iron sulfide was removed from the mold and crushed in a mortar. It was then placed in a zirconia pot under an argon gas atmosphere and processed by mechanical milling at 400 rpm for 20 hours using a planetary ball mill (model P-7) manufactured by Fritsch Japan Co., Ltd.
  • the ratios (atomic %) of each element in the obtained sample were Li 57%, Fe 7%, and S 36%.
  • the obtained sample did not contain carbon or halogens.
  • the powder was compressed at 300 MPa and the current value was measured by applying a voltage, resulting in a value of 1.1 ⁇ 10 ⁇ 5 S/cm, which was lower than that of Examples 1 and 2.
  • the X-ray diffraction pattern of the obtained sample was composed of peaks derived from low-crystalline lithium sulfide (Li 2 S) as the main phase, and no other peaks were observed.
  • the abundance ratio of lithium sulfide (Li 2 S) estimated by Rietveld analysis was 100 mol %.
  • the crystallite size estimated from the half-width of the diffraction peak based on the (111) plane of lithium sulfide was 26 nm.
  • the obtained iron-containing lithium polysulfide was used as the positive electrode active material, indium metal was used as the negative electrode, and an argyrodite-type sulfide-based solid electrolyte was used as the electrolyte to assemble an all-solid-state lithium-ion secondary battery, and charge/discharge tests were conducted.
  • the above-mentioned iron-containing lithium polysulfide, argyrodite-type sulfide-based solid electrolyte, and acetylene black were mixed in a mass ratio of 4:5:1 to form a positive electrode composite, and a pellet battery with a diameter of 10 mm was produced by pressure molding the positive electrode composite/argyrodite-type sulfide-based solid electrolyte/lithium indium foil.
  • a charge/discharge test was performed by starting charging with constant current measurement in the range of 3.0 V to 1.0 V. The current density was 0.13 mA/ cm2 for charging and 0.13 to 1.3 mA/ cm2 for discharging.
  • the initial discharge capacity was 490mAh/g when the discharge current density was low (0.13mA/ cm2 ), 430mAh/g when it was 0.25mA/ cm2 , 280mAh/g when it was 0.64mA/ cm2 , and 140mAh/g when it was high current density (1.3mA/ cm2 ).
  • the initial discharge capacity at high current density (1.3mA/ cm2 ) was only 28% of the initial discharge capacity at low current density (0.13mA/ cm2 ), and a positive electrode active material with particularly excellent rate characteristics was not obtained.
  • Comparative Example 2 An iron-containing lithium polysulfide was obtained in the same manner as in Example 1, except that the mechanical milling time of the reaction product of lithium sulfide and iron sulfide (Li 8 FeS 5 ) and Li 2 FeS 2 was set to 0 hours (the reaction product of lithium sulfide and iron sulfide (Li 8 FeS 5 ) and Li 2 FeS 2 were mixed, but the mechanical milling process was not performed).
  • the ratios (atomic %) of each element in the obtained sample were Li 52%, Fe 11%, and S 37%.
  • the obtained sample did not contain carbon or halogens.
  • the powder was compressed at 300 MPa and the current value was measured by applying a voltage, resulting in a value of 1.0 ⁇ 10 ⁇ 5 S/cm, which was lower than that of Examples 1 and 2.
  • the X-ray diffraction pattern of the obtained sample was composed of low-crystalline lithium sulfide (Li 2 S) and low-crystalline Li 2 FeS 2 , as shown in Figure 2. That is, the abundance ratio of lithium sulfide (Li 2 S) estimated by Rietveld analysis was 86 mol%, and the abundance ratio of Li 2 FeS 2 was 14 mol%. In addition, the crystallite size estimated from the half-width of the diffraction peak based on the (111) plane of lithium sulfide was 26 nm.
  • the obtained iron-containing lithium polysulfide was used as the positive electrode active material, indium metal was used as the negative electrode, and an argyrodite-type sulfide-based solid electrolyte was used as the electrolyte to assemble an all-solid-state lithium-ion secondary battery, and charge/discharge tests were conducted.
  • the above-mentioned iron-containing lithium polysulfide, argyrodite-type sulfide-based solid electrolyte, and acetylene black were mixed in a mass ratio of 4:5:1 to form a positive electrode composite, and a pellet battery with a diameter of 10 mm was produced by pressure molding the positive electrode composite/argyrodite-type sulfide-based solid electrolyte/lithium indium foil.
  • a charge/discharge test was performed by starting charging with a constant current measurement in the range from the initial voltage to 1.0 V. The current density was 0.13 mA/ cm2 for charging and 0.13 to 1.3 mA/ cm2 for discharging.
  • the initial discharge capacity was 470 mAh/g when the discharge current density was low (0.13 mA/ cm2 ), 410 mAh/g when it was 0.25 mA/ cm2 , 380 mAh/g when it was 0.64 mA/ cm2 , and 250 mAh/g when it was high current density (1.3 mA/ cm2 ).
  • the initial discharge capacity at high current density (1.3 mA/ cm2 ) was only 54% of the initial discharge capacity at low current density (0.13 mA/ cm2 ), and a positive electrode active material with particularly excellent rate characteristics was not obtained.
  • Li 2 S lithium sulfide
  • FeS iron sulfide
  • the graphite mold filled with the raw materials was then placed in an electric sintering machine.
  • the graphite mold and the electric parts, including the electrode parts, were placed in a vacuum chamber, which was evacuated to a vacuum (approximately 20 Pa) and then filled with high-purity argon gas (oxygen concentration approximately 0.2 ppm) up to atmospheric pressure.
  • the raw material filled in the graphite mold was pressurized at about 30 MPa while applying a DC pulse current of about 600 A (pulse width 2.5 milliseconds, period 28.6 Hz).
  • the vicinity of the graphite mold was heated at a temperature increase rate of about 200°C/min, and reached 600°C 3 minutes after the start of the pulse current application.
  • the current application and pressure were immediately stopped and the mixture was allowed to cool naturally to produce Li10FeS6 .
  • the graphite jig was transferred to a glove box in an argon gas atmosphere with a dew point of -80°C, and the reaction product of lithium sulfide and iron sulfide (Li 10 FeS 6 ) was removed from the mold material.
  • the ratio (atomic %) of each element in the obtained sample was Li 56%, Fe 8%, and S 36%.
  • the obtained sample did not contain carbon or halogens.
  • the X-ray diffraction pattern of the obtained sample was composed of low-crystalline lithium sulfide (Li 2 S) and iron sulfide (FeS) as shown in Fig. 4, and the abundance ratio of lithium sulfide (Li 2 S) was 94 mol % and the abundance ratio of FeS was 6 mol % as determined by Rietveld analysis.
  • the crystallite size calculated from the half-width of the diffraction peak based on the (111) plane of lithium sulfide was 23 nm.
  • the obtained iron-containing lithium polysulfide was used as the positive electrode active material, indium metal was used as the negative electrode, and an argyrodite-type sulfide-based solid electrolyte was used as the electrolyte to assemble an all-solid-state lithium-ion secondary battery, and charge/discharge tests were conducted.
  • the above-mentioned iron-containing lithium polysulfide, argyrodite-type sulfide-based solid electrolyte, and acetylene black were mixed in a mass ratio of 4:5:1 to form a positive electrode composite, and a pellet battery with a diameter of 10 mm was fabricated by pressure molding the positive electrode composite/argyrodite-type sulfide-based solid electrolyte/lithium indium foil.
  • a charge/discharge test was performed by starting charging with constant current measurement in the range of 1.0 to 3.0 V. The current density was 0.13 mA/cm 2 for charging and 0.13 to 1.3 mA/cm 2 for discharging.
  • the initial discharge capacity was about 620 mAh/g at a low discharge current density (0.13 mA/ cm2 ), about 540 mAh/g at 0.25 mA/ cm2 , about 510 mAh/g at 0.64 mA/ cm2 , and about 430 mAh/g at a high current density (1.3 mA/ cm2 ). That is, the discharge capacity at a high current density (1.3 mA/ cm2 ) was as high as about 70% of that at a low current density (0.13 mA/ cm2 ), and an electrode material with excellent rate characteristics was obtained.
  • Comparative Example 3 A sample was prepared in exactly the same manner as in Example 3, except that the mechanical milling time of the reaction product of lithium sulfide and iron sulfide (Li 10 FeS 6 ) and Li 2 FeS 2 was 0 hours (the reaction product of lithium sulfide and iron sulfide (Li 10 FeS 6 ) and Li 2 FeS 2 were mixed, but mechanical milling was not performed).
  • the ratios (atomic %) of each element in the obtained sample were Li 56%, Fe 8%, and S 36%, the same as in Example 3.
  • the obtained sample did not contain carbon or halogens.
  • the X-ray diffraction pattern of the obtained sample was composed of crystalline lithium sulfide (Li 2 S) and crystalline Li 2 FeS 2 , and the abundance ratio of lithium sulfide (Li 2 S) obtained by Rietveld analysis was 87 mol %, and the abundance ratio of Li 2 FeS 2 was 13 mol %.
  • the crystallite size calculated from the half width of the diffraction peak based on the (111) plane of lithium sulfide was 106 nm.
  • the obtained composite powder was assembled into an all-solid-state battery in the same manner as in Example 3, and a charge/discharge test was performed.
  • the initial (first cycle) discharge curve is shown in Fig. 5, and the initial discharge capacity was only a low discharge capacity of about 150 mAh/g at a low discharge current density (0.13 mA/ cm2 ), about 140 mAh/g at a current density of 0.25 mA/ cm2 , about 130 mAh/g at a current density of 0.64 mA/ cm2 , and about 120 mAh/ g at a high current density (1.3 mA/ cm2 ). It was found that an electrode material excellent in both capacity and rate characteristics cannot be obtained by simply mixing Li10FeS6 with Li2FeS2 .
  • Li 2 S lithium sulfide
  • FeS iron sulfide
  • Mo 6 S 8 Cu 2 Mo 6 S 8 was synthesized by heat treating a powder of MoS 2 , Mo, and CuS mixed in a molar ratio of 3:3:2 at 1000°C under an argon gas atmosphere, and this was then immersed in 5 mol/L HCl for 1 hour to dissolve Cu to produce Mo 6 S 8 ), which was then used to prepare a reaction product of lithium sulfide and iron sulfide: Mo 6 S 8.
  • the mixture was mixed in a mortar so that the ratio of the powder to the powder was 8:2 (mass ratio), placed in a zirconia pot under an argon gas atmosphere, and processed by mechanical milling at 400 rpm for 40 hours using a planetary ball mill (model P-7) manufactured by Fritsch Japan Co., Ltd.
  • the ratios (atomic %) of each element in the obtained sample were Li 55%, Fe 5%, S 37%, and Mo 3%.
  • the obtained sample did not contain carbon or halogen.
  • the powder was compressed at 300 MPa and the current value was measured by applying a voltage, which was 3.5 ⁇ 10 ⁇ 4 S/cm, which was dramatically improved compared to the electrical conductivity of Comparative Example 4, which was not subjected to mechanical milling, which was less than 10 ⁇ 8 S/cm (immeasurable).
  • the X-ray diffraction pattern of the obtained sample showed a peak derived from low-crystalline lithium sulfide (Li 2 S) as the main phase, and no peak derived from iron sulfide (FeS) was observed.
  • the abundance ratio of lithium sulfide (Li 2 S) estimated by Rietveld analysis was 100 mol%.
  • the crystallite size calculated from the half-width of the diffraction peak based on the (111) plane of lithium sulfide was 17 nm.
  • the obtained iron-containing lithium polysulfide was used as the positive electrode active material, indium metal was used as the negative electrode, and an argyrodite-type sulfide-based solid electrolyte was used as the electrolyte to assemble an all-solid-state lithium-ion secondary battery, and charge/discharge tests were conducted.
  • the above-mentioned iron-containing lithium polysulfide, argyrodite-type sulfide-based solid electrolyte, and acetylene black were mixed in a mass ratio of 4:5:1 to form a positive electrode composite, and a pellet battery with a diameter of 10 mm was produced by pressure molding the positive electrode composite/argyrodite-type sulfide-based solid electrolyte/lithium indium foil.
  • a charge/discharge test was performed by starting charging with constant current measurement in the range of 3.0 V to 1.0 V. The current density was 0.13 mA/ cm2 for charging and 0.13 to 1.3 mA/ cm2 for discharging.
  • the initial discharge capacity was 520 mAh/g when the discharge current density was low (0.13 mA/ cm2 ), 500 mAh/g when it was 0.25 mA/ cm2 , 480 mAh/g when it was 0.64 mA/ cm2 , and 420 mAh/g when it was high current density (1.3 mA/ cm2 ).
  • the initial discharge capacity at high current density was as high as 81% of the initial discharge capacity at low current density (0.13 mA/ cm2 ), and it can be understood that a positive electrode active material excellent in capacity and rate characteristics was obtained.
  • Comparative Example 4 A sample was prepared in exactly the same manner as in Example 4, except that the mechanical milling time of the reaction product of lithium sulfide and iron sulfide with Mo6S8 was set to 0 hours (the reaction product of lithium sulfide and iron sulfide was mixed with Mo6S8 , but mechanical milling was not performed).
  • the ratios (atomic %) of the elements in the obtained sample were Li 55%, Fe 5%, S 37%, and Mo 3%, similar to those in Example 4.
  • the obtained sample did not contain carbon or halogens.
  • the powder was compacted at 300 MPa and the current value was measured by applying a voltage, resulting in a value of less than 10 ⁇ 8 S/cm (immeasurable), which was dramatically lower than that in Example 4.
  • the X-ray diffraction pattern of the obtained sample was composed of crystalline lithium sulfide (Li 2 S), crystalline Mo 6 S 8 , and crystalline iron sulfide (FeS) as shown in Fig. 6, and the abundance ratio of lithium sulfide (Li 2 S) was 82 mol%, the abundance ratio of Mo 6 S 8 was 2 mol%, and the abundance ratio of iron sulfide (FeS) was 16 mol% as determined by Rietveld analysis.
  • the crystallite size calculated from the half-width of the diffraction peak based on the (111) plane of lithium sulfide was 80 nm.
  • the obtained composite powder was assembled into an all-solid-state battery in the same manner as in Example 4, and a charge/discharge test was performed.
  • the initial (first cycle) discharge curve is shown in Fig. 7, and the initial discharge capacity was only a low discharge capacity of about 110 mAh/g at a low discharge current density (0.13 mA/ cm2 ), about 100 mAh/g at a current density of 0.25 mA/ cm2 , about 90 mAh/g at a current density of 0.64 mA/ cm2 , and about 70 mAh/g at a high current density (1.3 mA/ cm2 ).
  • Li 2 S lithium sulfide
  • FeS iron sulfide
  • MoS 2 manufactured by Kojundo Chemical Laboratory Co., Ltd., model number: MOI06PB
  • a mortar at room temperature 25°C
  • the reactant of lithium sulfide and iron sulfide:MoS 2 8:2 (mass ratio)
  • the mixture was placed in a zirconia pot under an argon gas atmosphere and subjected to mechanical milling at 400 rpm for 20 hours using a planetary ball mill (model P-7) manufactured by Fritsch Japan Co., Ltd., to prepare a sample.
  • the ratios (atomic %) of each element in the obtained sample were Li 54%, Fe 5%, S 38%, and Mo 3%.
  • the obtained sample did not contain carbon or halogen.
  • the powder was compressed at 300 MPa and the current value was measured by applying a voltage, which was 3.4 ⁇ 10 -3 S/cm, which was dramatically improved compared to the electrical conductivity of Comparative Example 5, which was not subjected to mechanical milling, which was less than 10 -8 S/cm (immeasurable).
  • the X-ray diffraction pattern of the obtained sample was composed of low-crystalline lithium sulfide (Li 2 S) and iron sulfide (FeS) as shown in Fig. 8, and the abundance ratio of lithium sulfide (Li 2 S) estimated by Rietveld analysis was 91 mol%, the abundance ratio of MoS 2 was 0 mol%, and the abundance ratio of iron sulfide (FeS) was 9 mol%.
  • the crystallite size calculated from the half-width of the diffraction peak based on the (111) plane of lithium sulfide was 19 nm.
  • the obtained iron-containing lithium polysulfide was used as the positive electrode active material, indium metal was used as the negative electrode, and an argyrodite-type sulfide-based solid electrolyte was used as the electrolyte to assemble an all-solid-state lithium-ion secondary battery, and charge/discharge tests were conducted.
  • the above-mentioned iron-containing lithium polysulfide, argyrodite-type sulfide-based solid electrolyte, and acetylene black were mixed in a mass ratio of 4:5:1 to form a positive electrode composite, and a pellet battery with a diameter of 10 mm was produced by pressure molding the positive electrode composite/argyrodite-type sulfide-based solid electrolyte/lithium indium foil.
  • a charge/discharge test was performed by starting charging with constant current measurement in the range of 3.0 V to 1.0 V. The current density was 0.13 mA/ cm2 for charging and 0.13 to 1.3 mA/ cm2 for discharging.
  • the initial (first cycle) discharge curve is shown in Figure 9, and the initial discharge capacity was about 660 mAh/g at a low discharge current density (0.13 mA/ cm2 ), about 620 mAh/g at 0.25 mA/ cm2 , about 600 mAh/g at 0.64 mA/ cm2 , and about 560 mAh/g at a high current density (1.3 mA/ cm2 ). That is, the discharge capacity at a high current density (1.3 mA/ cm2 ) was as high as about 86% of that at a low current density (0.13 mA/ cm2 ), and an electrode material with excellent rate characteristics was obtained.
  • Comparative Example 5 A sample was prepared in the same manner as in Example 5 except that the mechanical milling treatment time of the reaction product of lithium sulfide and iron sulfide with MoS2 was 0 hours (the reaction product of lithium sulfide and iron sulfide was mixed with MoS2 , but the mechanical milling treatment was not performed).
  • the ratios (atomic %) of the elements in the obtained sample were Li 54%, Fe 5%, S 38%, and Mo 3%, similar to those in Example 5.
  • the obtained sample did not contain carbon or halogens.
  • the powder was compressed at 300 MPa and the current value was measured by applying a voltage, resulting in a value of less than 10 ⁇ 8 S/cm (impossible to measure), which was dramatically lower than that of Example 5.
  • the X-ray diffraction pattern of the obtained sample was composed of crystalline lithium sulfide (Li 2 S), iron sulfide (FeS) and MoS 2 , and the abundance ratio of lithium sulfide (Li 2 S) was 77 mol%, the abundance ratio of Mo 6 S 8 was 8 mol%, and the abundance ratio of iron sulfide (FeS) was 15 mol%, as determined by Rietveld analysis, as shown in Figure 8.
  • the crystallite size calculated from the half-width of the diffraction peak based on the (111) plane of lithium sulfide was 84 nm.
  • the obtained composite powder was assembled into an all-solid-state battery in the same manner as in Example 5, and a charge/discharge test was performed.
  • the results are shown in Fig. 9, and the initial discharge capacity was only low at about 3 mAh/g at a low discharge current density (0.13 mA/ cm2 ), about 3 mAh/g at a current density of 0.25 mA/ cm2 , about 2 mAh/g at a current density of 0.64 mA/ cm2 , and about 2 mAh/g at a high current density (1.3 mA/ cm2 ). It was found that an electrode material excellent in both capacity and rate characteristics cannot be obtained by simply mixing MoS2 .
  • Li 2 S lithium
  • the ratios (atomic %) of each element in the obtained sample were Li 54%, Fe 5%, S 37%, and Cu 4%.
  • the obtained sample did not contain carbon or halogen.
  • the powder was compacted at 300 MPa and the current value was measured by applying a voltage, which was 1.6 ⁇ 10 ⁇ 6 S/cm, which was dramatically improved compared to the electrical conductivity of Comparative Example 6, which was not subjected to mechanical milling, which was less than 10 ⁇ 8 S/cm (immeasurable).
  • the X-ray diffraction pattern of the obtained sample was composed of low-crystalline lithium sulfide (Li 2 S), and the abundance ratio of lithium sulfide (Li 2 S) obtained by Rietveld analysis was 100 mol % as shown in Fig. 10.
  • the crystallite size calculated from the half-width of the diffraction peak based on the (111) plane of lithium sulfide was 23 nm.
  • the obtained iron-containing lithium polysulfide was used as the positive electrode active material, indium metal was used as the negative electrode, and an argyrodite-type sulfide-based solid electrolyte was used as the electrolyte to assemble an all-solid-state lithium-ion secondary battery, and charge/discharge tests were conducted.
  • the above-mentioned iron-containing lithium polysulfide, argyrodite-type sulfide-based solid electrolyte, and acetylene black were mixed in a mass ratio of 4:5:1 to form a positive electrode composite, and a pellet battery with a diameter of 10 mm was produced by pressure molding the positive electrode composite/argyrodite-type sulfide-based solid electrolyte/lithium indium foil.
  • a charge/discharge test was performed by starting charging with constant current measurement in the range of 3.0 V to 1.0 V. The current density was 0.13 mA/ cm2 for charging and 0.13 to 1.3 mA/ cm2 for discharging.
  • the initial (first cycle) discharge curve is shown in Figure 11, and the initial discharge capacity was about 550 mAh/g at a low discharge current density (0.13 mA/ cm2 ), about 490 mAh/g at 0.25 mA/ cm2 , about 450 mAh/g at 0.64 mA/ cm2 , and about 380 mAh/g at 1.3 mA/ cm2 . That is, the discharge capacity at a high current density (1.3 mA/ cm2 ) was as high as about 70% of that at a low current density (0.13 mA/ cm2 ), and an electrode material with excellent rate characteristics was obtained.
  • Comparative Example 6 A sample was prepared in the same manner as in Example 6, except that the mechanical milling treatment time of the reaction product of lithium sulfide and iron sulfide and CuS was 0 hours (the reaction product of lithium sulfide and iron sulfide and CuS were mixed, but the mechanical milling treatment was not performed).
  • the ratios (atomic %) of the elements in the obtained sample were Li 54%, Fe 5%, S 37%, and Cu 4%, similar to Example 6.
  • the obtained sample did not contain carbon or halogens.
  • the powder was compressed at 300 MPa and the current value was measured by applying a voltage, resulting in a value of less than 10 ⁇ 8 S/cm (impossible to measure), which was dramatically lower than that of Example 6.
  • the X-ray diffraction pattern of the obtained sample was composed of crystalline lithium sulfide (Li 2 S), iron sulfide (FeS) and CuS, and the abundance ratio of lithium sulfide (Li 2 S) was 73 mol %, the abundance ratio of CuS was 12 mol %, and the abundance ratio of iron sulfide (FeS) was 15 mol % as determined by Rietveld analysis, as shown in Figure 10.
  • the crystallite size calculated from the half-width of the diffraction peak based on the (111) plane of lithium sulfide was 86 nm.
  • the obtained composite powder was assembled into an all-solid-state battery in the same manner as in Example 6, and a charge/discharge test was performed. The results are shown in FIG. 11.
  • the initial discharge capacity was only about 7 mAh/g at a low discharge current density (0.13 mA/cm 2 ), and was about 4 mAh/g at a current density of 0.25 mA/cm 2 , about 3 mAh/g at 0.64 mA/cm 2 , and about 3 mAh/g at 1.3 mA/cm 2 .
  • an electrode material excellent in both capacity and rate characteristics cannot be obtained by simply mixing CuS with the reaction product of lithium sulfide and iron sulfide.

Landscapes

  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • General Chemical & Material Sciences (AREA)
  • Inorganic Chemistry (AREA)
  • Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Organic Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • General Physics & Mathematics (AREA)
  • Battery Electrode And Active Subsutance (AREA)

Abstract

In the present invention, iron-containing lithium polysulfide contains lithium, iron, and sulfur as constituent elements, wherein: lithium sulfide (Li2S) is included as the main phase; the crystallite size that is calculated from the half-width of a diffraction peak that is based on the (111) plane of the Li2S obtained by powder X-ray diffraction is 50 nm or less; and, taking the total iron-containing lithium polysulfide content to be 100 at%, the Li content is 50–70 at%, the Fe content is 2–12 at%, the S content is 20–40 at%, the C content is 0–5 at%, and the halogen content is 0–0.8 at%. In a compound that has lithium sulfide as a main component and is useful as a positive electrode active material for a lithium-ion secondary battery, said iron-containing lithium polysulfide is a material that has a high lithium sulfide use rate, high capacitance, and excellent rate properties.

Description

鉄含有多硫化リチウムIron-containing lithium polysulfide
　本発明は、鉄含有多硫化リチウム及びその製造方法に関する。 The present invention relates to iron-containing lithium polysulfide and a method for producing the same.
　近年の携帯電子機器、ハイブリッド車等の高性能化により、それに用いられる二次電池（特にリチウムイオン二次電池）は益々高容量化が求められるようになっている。現行のリチウムイオン二次電池では負極に比べて正極の高容量化が遅れており、最近盛んに研究開発されている高容量型のＬｉ（Ｎｉ，Ｍｎ，Ｃｏ）Ｏ２系材料でも２５０～３００ｍＡｈ／ｇ程度である。 In recent years, the performance of portable electronic devices, hybrid vehicles, etc. has improved, and secondary batteries (especially lithium-ion secondary batteries) used in them are increasingly required to have higher capacities. In current lithium-ion secondary batteries, the capacity of the positive electrode has been slower than that of the negative electrode, and even the high-capacity Li(Ni,Mn,Co) O2 -based materials that have been actively researched and developed recently have a capacity of about 250 to 300 mAh/g.
　一方、硫黄は理論容量が約１６７０ｍＡｈ／ｇと高く、高容量電極材料の有望な候補の一つである。しかしながら、硫黄単体はリチウムを含有していないので、負極にリチウム又はリチウムを含む合金等を用いなければならず、負極の選択幅が狭いという欠点がある。 On the other hand, sulfur has a high theoretical capacity of approximately 1670 mAh/g, making it one of the promising candidates for a high-capacity electrode material. However, since elemental sulfur does not contain lithium, lithium or an alloy containing lithium must be used for the negative electrode, which has the disadvantage that the range of options for the negative electrode is narrow.
　これに対して、硫化リチウムはリチウムを含有しているので、負極に黒鉛やシリコン等の合金類を用いることができ、負極の選択幅が飛躍的に広がるとともに、金属リチウム使用によるデンドライト生成が引き起こす短絡等の危険性を回避できる。しかしながら、硫化リチウムは、電気伝導性に乏しい（例えば、下記非特許文献１参照）。 In contrast, lithium sulfide contains lithium, so alloys such as graphite and silicon can be used for the negative electrode, dramatically expanding the range of negative electrode options and avoiding the risk of short circuits caused by dendrite formation when using metallic lithium. However, lithium sulfide has poor electrical conductivity (see, for example, Non-Patent Document 1 below).
　電気伝導性を改善する方法として、Ｌｉ挿入及び脱離反応の際に硫黄原子が遊離しないよう異種元素との結合を形成する方法が考えられる。そのためには、異種元素を硫化リチウムに導入した化合物を作製する必要がある。添加する異種元素としては、絶縁性の硫化リチウムに導電性を付与することのできる遷移金属元素が適しており、例えば、特許文献１及び２に記載の、ＬｉｘＦｅｙＳｚ等の化合物等が挙げられる。このような遷移金属元素の導入による硫黄元素の遊離抑制、及び導電性付与により、硫化リチウムの利用率向上を図ることができる。また、典型元素を導入し、硫黄及び遷移金属と典型元素の間に結合を形成して骨格構造を安定化させる方法も考えられる。複数の異種元素（遷移金属元素、典型元素）を導入した硫化リチウム複合体の例として、リチウム－鉄－リン－硫黄－炭素複合体がある（例えば、特許文献３参照）。 As a method for improving electrical conductivity, a method of forming a bond with a hetero element so that sulfur atoms are not liberated during Li insertion and desorption reactions is considered. For this purpose, it is necessary to prepare a compound in which a hetero element is introduced into lithium sulfide. As the hetero element to be added, a transition metal element capable of imparting electrical conductivity to insulating lithium sulfide is suitable, and examples thereof include compounds such as Li x Fe y S z described in Patent Documents 1 and 2. By suppressing the liberation of sulfur element by introducing such a transition metal element and imparting electrical conductivity, it is possible to improve the utilization rate of lithium sulfide. In addition, a method of introducing a typical element and forming a bond between sulfur and the transition metal and the typical element to stabilize the framework structure is also considered. An example of a lithium sulfide complex into which multiple hetero elements (transition metal element, typical element) are introduced is a lithium-iron-phosphorus-sulfur-carbon complex (see, for example, Patent Document 3).
国際公開第２０１０／０８４８０８号International Publication No. 2010/084808 国際公開第２０１５／０３７５９８号International Publication No. 2015/037598 国際公開第２０１６／０８０４４３号International Publication No. 2016/080443
　しかしながら、上記した従来の硫化物においても、電気伝導度の点では十分とは言えず、電池の出力特性の向上を目的に、電気伝導度及びエネルギー密度をさらに向上させ、結果として、容量及びレート特性を向上させることが求められている。 However, even the conventional sulfides mentioned above do not have sufficient electrical conductivity, and there is a demand to further improve electrical conductivity and energy density, thereby improving the capacity and rate characteristics, in order to improve the output characteristics of the battery.
　本発明は、上記した従来技術の現状に鑑みてなされたものであり、その主な目的は、リチウムイオン二次電池用正極活物質として有用な硫化リチウムを主成分とする化合物において、硫化リチウムの利用率が高く、高容量を有し、更に、良好なレート特性を有する、優れた充放電特性を有する新規な材料を提供することである。 The present invention was made in consideration of the current state of the prior art described above, and its main objective is to provide a new material that has a high lithium sulfide utilization rate, a high capacity, good rate characteristics, and excellent charge/discharge characteristics in a compound mainly composed of lithium sulfide that is useful as a positive electrode active material for lithium ion secondary batteries.
　本発明者らは、上記した目的を達成すべく鋭意研究を重ねてきた。その結果、硫化リチウム（Ｌｉ２Ｓ）を主相として含み、粉末Ｘ線回折によって得られたＬｉ２Ｓの（１１１）面に基づく回折ピークの半価幅から算出される結晶子サイズが５０ｎｍ以下であり、且つ、Ｌｉ含有量が５０～７０原子％、Ｆｅ含有量が２～１２原子％、Ｓ含有量が２０～４０原子％、Ｃ含有量が０～５原子％、ハロゲン含有量が０～０．８原子％である鉄含有多硫化リチウムは、硫化リチウムの利用率が向上して高容量の材料となり、さらに、不純物量が少なく電気伝導度が向上しつつ、硫黄と鉄の結合が形成されることによって遊離硫黄が大幅に減少するために、レート特性も向上することを見出した。鉄含有多硫化リチウムは、例えば、リチウム含有化合物、鉄含有化合物、及び硫黄含有化合物を含む混合物に対して、直流パルス電流を通電して通電焼結処理によって加熱反応させた後、得られた生成物を第一メカニカルミリング処理した後、さらに、所定の金属硫化物と第二メカニカルミリング処理することにより得られる。この方法によれば、原子レベルでの反応が適度に進行した硫化リチウムと硫化鉄との混合物が形成されるのみならず、鉄硫化物も少量含まれることとなり、結果として、電気伝導度を向上させ、容量及びレート特性を改善することができる。本発明は、これらの知見に基づいて更に研究を重ねた結果、完成されたものである。即ち、本発明は、以下構成を包含する。 The present inventors have conducted extensive research to achieve the above-mentioned object. As a result, they have found that an iron-containing lithium polysulfide containing lithium sulfide (Li 2 S) as a main phase, having a crystallite size of 50 nm or less calculated from the half-width of the diffraction peak based on the (111) plane of Li 2 S obtained by powder X-ray diffraction, and having a Li content of 50 to 70 atomic %, an Fe content of 2 to 12 atomic %, an S content of 20 to 40 atomic %, a C content of 0 to 5 atomic %, and a halogen content of 0 to 0.8 atomic %, improves the utilization rate of lithium sulfide and becomes a high-capacity material, and further, has a low amount of impurities and improves electrical conductivity, while the free sulfur is greatly reduced by the formation of bonds between sulfur and iron, thereby improving the rate characteristics. The iron-containing lithium polysulfide can be obtained, for example, by passing a direct current pulse current through a mixture containing a lithium-containing compound, an iron-containing compound, and a sulfur-containing compound to heat and react by current sintering, subjecting the resulting product to a first mechanical milling process, and then subjecting the product to a second mechanical milling process with a predetermined metal sulfide. According to this method, not only is a mixture of lithium sulfide and iron sulfide in which the reaction at the atomic level has progressed appropriately formed, but a small amount of iron sulfide is also contained, resulting in improved electrical conductivity and improved capacity and rate characteristics. The present invention has been completed as a result of further research based on these findings. That is, the present invention includes the following configurations.
　項１．リチウム、鉄及び硫黄を構成元素として含む鉄含有多硫化リチウムであって、
硫化リチウム（Ｌｉ２Ｓ）を主相として含み、
粉末Ｘ線回折によって得られたＬｉ２Ｓの（１１１）面に基づく回折ピークの半価幅から算出される結晶子サイズが５０ｎｍ以下であり、且つ、
前記鉄含有多硫化リチウムの総量を１００原子％として、Ｌｉ含有量が５０～７０原子％、Ｆｅ含有量が２～１２原子％、Ｓ含有量が２０～４０原子％、Ｃ含有量が０～５原子％、ハロゲン含有量が０～０．８原子％である、鉄含有多硫化リチウム。 Item 1. An iron-containing lithium polysulfide containing lithium, iron, and sulfur as constituent elements,
Contains lithium sulfide (Li 2 S) as a main phase;
The crystallite size calculated from the half-width of the diffraction peak based on the (111) plane of Li 2 S obtained by powder X-ray diffraction is 50 nm or less, and
The iron-containing lithium polysulfide has a Li content of 50 to 70 atomic %, an Fe content of 2 to 12 atomic %, an S content of 20 to 40 atomic %, a C content of 0 to 5 atomic %, and a halogen content of 0 to 0.8 atomic %, relative to 100 atomic % of the total amount of the iron-containing lithium polysulfide.
　項２．前記鉄含有多硫化リチウムを基準として、Ｒｉｅｔｖｅｌｄ解析により見積もられた硫化リチウム（Ｌｉ２Ｓ）の存在比が７０モル％以上である、項１に記載の鉄含有多硫化リチウム。 Item 2. The iron-containing lithium polysulfide according to Item 1, wherein the abundance ratio of lithium sulfide (Li 2 S) is 70 mol % or more based on the iron-containing lithium polysulfide as estimated by Rietveld analysis.
　項３．さらに、硫化鉄（ＦｅＳ）相を有する、項１又は２に記載の鉄含有多硫化リチウム。 Item 3. The iron-containing lithium polysulfide according to item 1 or 2, further comprising an iron sulfide (FeS) phase.
　項４．２５℃における電気伝導度が１０－３～１０－６Ｓ／ｃｍである、項１～３のいずれか１項に記載の鉄含有多硫化リチウム。 Item 4. The iron-containing lithium polysulfide according to any one of Items 1 to 3, having an electrical conductivity of 10 -3 to 10 -6 S/cm at 25° C.
　項５．リチウムイオン二次電池用である、請求項１～４のいずれか１項に記載の鉄含有多硫化リチウム。 Item 5. The iron-containing lithium polysulfide according to any one of claims 1 to 4, which is for use in a lithium-ion secondary battery.
　項６．リチウムイオン二次電池の正極活物質用である、項１～５のいずれか１項に記載の鉄含有多硫化リチウム。 Item 6. The iron-containing lithium polysulfide according to any one of items 1 to 5, which is used as a positive electrode active material for a lithium-ion secondary battery.
　項７．項１～６のいずれか１項に記載の鉄含有多硫化リチウムの製造方法であって、
（３）リチウム含有化合物、鉄含有化合物及び硫黄含有化合物を含む混合物；前記混合物の加熱処理物；又は前記混合物の加熱生成物のメカニカルミリング処理物と、電気伝導度が１０－３Ｓ／ｃｍ以上である金属硫化物とを、メカニカルミリング処理する工程
を備える、製造方法。 Item 7. A method for producing the iron-containing lithium polysulfide according to any one of items 1 to 6, comprising the steps of:
(3) A production method comprising a step of mechanically milling a mixture containing a lithium-containing compound, an iron-containing compound, and a sulfur-containing compound; a heat-treated product of the mixture; or a mechanically milled product of the heat-treated product of the mixture, and a metal sulfide having an electrical conductivity of 10 −3 S/cm or more.
　項８．前記工程（３）の前に、さらに、
（２）リチウム含有化合物、鉄含有化合物及び硫黄含有化合物を含む混合物；又は前記混合物の加熱処理物を、メカニカルミリング処理する工程
を備える、項７に記載の製造方法。 Item 8. Before the step (3),
(2) The method according to item 7, further comprising subjecting a mixture containing a lithium-containing compound, an iron-containing compound, and a sulfur-containing compound, or a heat-treated product of the mixture, to mechanical milling.
　項９．前記工程（２）の前に、さらに、
（１）リチウム含有化合物、鉄含有化合物及び硫黄含有化合物を含む混合物を加熱する工程
を備える、項８に記載の製造方法。 Item 9. Prior to the step (2),
(1) The method according to item 8, further comprising a step of heating a mixture containing a lithium-containing compound, an iron-containing compound, and a sulfur-containing compound.
　項１０．前記工程（１）が、前記混合物に対して、直流パルス電流を通電して該混合物を加熱反応させる工程である、項９に記載の製造方法。 Item 10. The method according to item 9, wherein step (1) is a step of passing a direct current pulse current through the mixture to heat and react the mixture.
　項１１．前記工程（１）～（３）を、非酸化性雰囲気下において行う、項７～１０のいずれか１項に記載の製造方法。 Item 11. The manufacturing method according to any one of items 7 to 10, wherein steps (1) to (3) are carried out in a non-oxidizing atmosphere.
　項１２．項１～６のいずれか１項に記載の鉄含有多硫化リチウムを含むリチウムイオン二次電池用正極活物質。 Item 12. A positive electrode active material for a lithium ion secondary battery, comprising the iron-containing lithium polysulfide according to any one of items 1 to 6.
　項１３．項１２に記載のリチウムイオン二次電池用正極活物質を構成要素とするリチウムイオン二次電池。 Item 13. A lithium ion secondary battery having as a component the positive electrode active material for lithium ion secondary batteries described in Item 12.
　項１４．項１３に記載のリチウムイオン二次電池用正極活物質と、リチウムイオン伝導性固体電解質とを、構成要素として含む、全固体リチウムイオン二次電池。 Item 14. An all-solid-state lithium ion secondary battery comprising, as components, the positive electrode active material for a lithium ion secondary battery described in Item 13 and a lithium ion conductive solid electrolyte.
　本発明の鉄含有多硫化リチウムは、結晶子サイズが５０ｎｍ以下という微細化された粒子であり、硫化リチウム（Ｌｉ２Ｓ）を主相として含み、添加元素を特定の組成の範囲内に調整しており不純物量が少ないことも相まって、硫化リチウムの利用率が高く、硫化リチウムが本来有する高容量の特性を充分に発揮することができるとともに、電気伝導度が向上し、レート特性に優れた正極活物質となる。 The iron-containing lithium polysulfide of the present invention is a fine particle having a crystallite size of 50 nm or less, contains lithium sulfide (Li 2 S) as a main phase, and has additive elements adjusted within a specific composition range, and combined with a small amount of impurities, the utilization rate of lithium sulfide is high, and the high capacity characteristics inherent to lithium sulfide can be fully exhibited, and the electrical conductivity is improved, resulting in a positive electrode active material with excellent rate characteristics.
　このため、本発明の鉄含有多硫化リチウムは、非水電解質リチウムイオン二次電池、全固体型リチウムイオン二次電池等のリチウム二次電池用の正極活物質として有用性の高い物質である。 For this reason, the iron-containing lithium polysulfide of the present invention is a highly useful material as a positive electrode active material for lithium secondary batteries, such as non-aqueous electrolyte lithium ion secondary batteries and all-solid-state lithium ion secondary batteries.
　また、本発明の製造方法によれば、この様な優れた性能を有する複合体を、比較的容易に製造できる。 Furthermore, the manufacturing method of the present invention makes it relatively easy to manufacture composites with such excellent performance.
通電焼結装置の一例の概略図である。FIG. 2 is a schematic diagram of an example of an electric current sintering apparatus. 実施例１～２及び比較例１～２で得られた試料のＸ線回折パターンである。1 shows X-ray diffraction patterns of samples obtained in Examples 1 and 2 and Comparative Examples 1 and 2. 実施例１～２及び比較例１～２で得られた試料を正極活物質とする全固体リチウムイオン二次電池の電流密度０．１３～１．３ｍＡ／ｃｍ２における初回放電曲線である。1 shows initial discharge curves at a current density of 0.13 to 1.3 mA/cm 2 of all-solid-state lithium ion secondary batteries using the samples obtained in Examples 1 and 2 and Comparative Examples 1 and 2 as positive electrode active materials. 実施例３及び比較例３で得られた試料のＸ線回折パターンである。1 shows X-ray diffraction patterns of samples obtained in Example 3 and Comparative Example 3. 実施例３及び比較例３で得られた試料を正極活物質とする全固体リチウムイオン二次電池の電流密度０．１３～１．３ｍＡ／ｃｍ２における初回放電曲線である。1 shows initial discharge curves at a current density of 0.13 to 1.3 mA/ cm2 of all-solid-state lithium ion secondary batteries using the samples obtained in Example 3 and Comparative Example 3 as positive electrode active materials. 実施例４及び比較例４で得られた試料のＸ線回折パターンである。1 shows X-ray diffraction patterns of samples obtained in Example 4 and Comparative Example 4. 実施例４及び比較例４で得られた試料を正極活物質とする全固体リチウムイオン二次電池の電流密度０．１３～１．３ｍＡ／ｃｍ２における初回放電曲線である。1 shows initial discharge curves at a current density of 0.13 to 1.3 mA/ cm2 of all-solid-state lithium ion secondary batteries using the samples obtained in Example 4 and Comparative Example 4 as positive electrode active materials. 実施例５及び比較例５で得られた試料のＸ線回折パターンである。1 shows X-ray diffraction patterns of samples obtained in Example 5 and Comparative Example 5. 実施例５及び比較例５で得られた試料を正極活物質とする全固体リチウムイオン二次電池の電流密度０．１３～１．３ｍＡ／ｃｍ２における初回放電曲線である。1 shows initial discharge curves at a current density of 0.13 to 1.3 mA/ cm2 of all-solid-state lithium ion secondary batteries using the samples obtained in Example 5 and Comparative Example 5 as positive electrode active materials. 実施例６及び比較例６で得られた試料のＸ線回折パターンである。1 shows X-ray diffraction patterns of samples obtained in Example 6 and Comparative Example 6. 実施例６及び比較例６で得られた試料を正極活物質とする全固体リチウムイオン二次電池の電流密度０．１３～１．３ｍＡ／ｃｍ２における初回放電曲線である。1 shows initial discharge curves at a current density of 0.13 to 1.3 mA/ cm2 of all-solid-state lithium ion secondary batteries using the samples obtained in Example 6 and Comparative Example 6 as positive electrode active materials.
　本明細書において、数値範囲を「Ａ～Ｂ」で表示する場合、Ａ以上Ｂ以下を意味する。 In this specification, when a numerical range is expressed as "A to B," it means A or more and B or less.
　また、「含有」は、「含む（comprise）」、「実質的にのみからなる（consist essentially of）」及び「のみからなる（consist of）」のいずれも包含する。 In addition, "contain" includes any of the terms "comprise," "consist essentially of," and "consist of."
　本発明において、「リチウムイオン二次電池」とは、負極材料として金属リチウムを用いた「金属リチウム二次電池」も包含する概念である。また、本発明において、「リチウムイオン二次電池」とは、非水電解液を使用した「非水リチウムイオン二次電池」と固体電解質を使用した「全固体リチウムイオン二次電池」の双方を意味する。 In the present invention, the term "lithium ion secondary battery" is a concept that also includes "metal lithium secondary batteries" that use metallic lithium as the negative electrode material. In addition, in the present invention, the term "lithium ion secondary battery" refers to both "nonaqueous lithium ion secondary batteries" that use a nonaqueous electrolyte and "all-solid-state lithium ion secondary batteries" that use a solid electrolyte.
　１．鉄含有多硫化リチウム
　本発明の鉄含有多硫化リチウムは、リチウム、鉄及び硫黄を構成元素として含む鉄含有多硫化リチウムであって、硫化リチウム（Ｌｉ２Ｓ）を主相として含み、粉末Ｘ線回折によって得られたＬｉ２Ｓの（１１１）面に基づく回折ピークの半価幅から算出される結晶子サイズが５０ｎｍ以下であり、且つ、前記鉄含有多硫化リチウムの総量を１００原子％として、Ｌｉ含有量が５０～７０原子％、Ｆｅ含有量が２～１２原子％、Ｓ含有量が２０～４０原子％、Ｃ含有量が０～５原子％、ハロゲン含有量が０～０．８原子％である。このような本発明の鉄含有多硫化リチウムは、硫化リチウムの利用率が高く、硫化リチウムが本来有する高容量の特性を充分に発揮することができるとともに、電気伝導度が向上し、優れたレート特性を有する正極活物質となる材料であり、リチウムイオン二次電池の正極活物質用途として特に有用である。 1. Iron-containing lithium polysulfide The iron-containing lithium polysulfide of the present invention is an iron-containing lithium polysulfide containing lithium, iron and sulfur as constituent elements, containing lithium sulfide (Li 2 S) as a main phase, and having a crystallite size calculated from the half-width of the diffraction peak based on the (111) plane of Li 2 S obtained by powder X-ray diffraction of 50 nm or less, and the total amount of the iron-containing lithium polysulfide is taken as 100 atomic %, and the Li content is 50 to 70 atomic %, the Fe content is 2 to 12 atomic %, the S content is 20 to 40 atomic %, the C content is 0 to 5 atomic %, and the halogen content is 0 to 0.8 atomic %. Such iron-containing lithium polysulfide of the present invention has a high utilization rate of lithium sulfide, can fully exhibit the high capacity characteristics inherent to lithium sulfide, has improved electrical conductivity, and is a material that becomes a positive electrode active material having excellent rate characteristics, and is particularly useful as a positive electrode active material for lithium ion secondary batteries.
　このような本発明の鉄含有多硫化リチウムによれば、例えば、電流印加０．１３ｍＡ／ｃｍ２での初期放電容量の値を１００％とした場合に、電流印加１．３ｍＡ／ｃｍ２での初期放電容量の値を６０～９５％、好ましくは７０～９０％とすることが可能である。本明細書においては、このような特性を示すことを、「優れたレート特性を有する」ということがある。 According to such an iron-containing lithium polysulfide of the present invention, for example, when the initial discharge capacity at an applied current of 0.13 mA/ cm2 is taken as 100%, the initial discharge capacity at an applied current of 1.3 mA/ cm2 can be 60 to 95%, preferably 70 to 90%. In this specification, the presence of such a characteristic is sometimes referred to as "having excellent rate characteristics".
　本発明の鉄含有多硫化リチウムは、粉末Ｘ線回折測定において、主相が硫化リチウムからなる。硫化リチウム相の存在量は、本発明の鉄含有多硫化リチウム全体を基準（１００モル％）として７０モル％以上が好ましく、８０モル％以上がより好ましく、８５モル％以上がさらに好ましい。なお、硫化リチウム相の存在量の上限値は、特に制限されるわけではないが、通常、１００モル％である。また、本発明の鉄含有多硫化リチウムは、硫化リチウムの結晶相以外に他の結晶が３０モル％まで（特に２０モル％まで、さらには１５モル％まで）なら含まれていてもよく、この程度の含有量であれば充放電特性に与える影響は限定的である。特に、本発明の鉄含有多硫化リチウムに少量（０．１～１５モル％、好ましくは０．５～１０モル％）の硫化鉄（ＦｅＳ）相が含まれる場合には、容量及びレート特性をさらに向上させることも可能である。なお、複合体中における存在量については、通常のＸ回折データのＲｉｅｔｖｅｌｄ解析法等を用いて見積もる。Ｒｉｅｔｖｅｌｄ法については、下記の非特許文献（F. Izumi and T. Ikeda, Mater Sci. Forum, 321-324, 198 (2000).）に詳細な記述がある。 In the powder X-ray diffraction measurement, the iron-containing lithium polysulfide of the present invention has a main phase consisting of lithium sulfide. The amount of lithium sulfide phase is preferably 70 mol% or more, more preferably 80 mol% or more, and even more preferably 85 mol% or more, based on the entire iron-containing lithium polysulfide of the present invention (100 mol%). The upper limit of the amount of lithium sulfide phase is not particularly limited, but is usually 100 mol%. In addition, the iron-containing lithium polysulfide of the present invention may contain up to 30 mol% (particularly up to 20 mol%, and even more preferably up to 15 mol%) of other crystals in addition to the lithium sulfide crystal phase, and at this content, the effect on the charge and discharge characteristics is limited. In particular, when the iron-containing lithium polysulfide of the present invention contains a small amount (0.1 to 15 mol%, preferably 0.5 to 10 mol%) of iron sulfide (FeS) phase, it is possible to further improve the capacity and rate characteristics. The amount present in the composite is estimated using the Rietveld analysis method of normal X-ray diffraction data. The Rietveld method is described in detail in the following non-patent literature (F. Izumi and T. Ikeda, Mater Sci. Forum, 321-324, 198 (2000)).
　この様な本発明の鉄含有多硫化リチウムでは、鉄原子は硫化リチウム結晶格子内に配置してＦｅ－Ｓ結合を形成し、Ｆｅを含むうえに不純物量が低減されているために内部まで導電性が付与されており、電極利用率（特に正極利用率）が高く、硫化リチウムが本来有する高容量の特性をより十分に発揮することができる。また、後述する本発明の製造方法を採用する場合には。準安定相である鉄含有多硫化リチウムが形成され、これがメカニカルミリング法により微細化されてサブミクロンの粒子となり、本来準安定相である鉄含有多硫化リチウムを安定化させることも可能である。 In such iron-containing lithium polysulfide of the present invention, iron atoms are arranged within the lithium sulfide crystal lattice to form Fe-S bonds, and since it contains Fe and has a reduced amount of impurities, it is conductive to the inside, has a high electrode utilization rate (particularly the positive electrode utilization rate), and can more fully demonstrate the high capacity characteristics that lithium sulfide inherently possesses. Furthermore, when the manufacturing method of the present invention described below is adopted, a metastable phase of iron-containing lithium polysulfide is formed, which is then refined by mechanical milling to form submicron particles, making it possible to stabilize the iron-containing lithium polysulfide that is inherently a metastable phase.
　上記した特徴を有する本発明の鉄含有多硫化リチウムは、添加元素である鉄原子が硫化リチウム結晶格子内に配置してＦｅ－Ｓ結合を形成していることが好ましく、これにより、遊離硫黄の存在がさらに抑制されやすいうえに良好な導電性が付与されており、優れた容量及びレート特性を発揮しやすい。 The iron-containing lithium polysulfide of the present invention having the above-mentioned characteristics preferably has the added element iron atoms arranged within the lithium sulfide crystal lattice to form Fe-S bonds, which further suppresses the presence of free sulfur and provides good electrical conductivity, making it easier to exhibit excellent capacity and rate characteristics.
　また、本発明の鉄含有多硫化リチウムは、鉄原子が硫化リチウム結晶格子内に導入された準安定相が安定化されていることが好ましい。本発明の鉄含有多硫化リチウムは、準安定相である鉄含有多硫化リチウムが安定的に存在するため、サブミクロン以下の結晶子からなることが好ましい。より具体的には、本発明の鉄含有多硫化リチウムの結晶子サイズは、５０ｎｍ以下が好ましく、４０ｎｍ以下（特に１～３０ｎｍ）がより好ましい。後述の製造方法のように、メカニカルミリング処理を含む製造方法により本発明の鉄含有多硫化リチウムが製造された場合には、メカニカルミリング処理により、結晶子を微細化することが可能である。なお、本発明の鉄含有多硫化リチウムの結晶子サイズは、粉末Ｘ線回折測定において主相として観測される硫化リチウムのピークの最高強度を示す（１１１）面に基づく回折ピークの半価幅から、Ｓｃｈｅｒｒｅｒの式に基づいて算出される値である。 Furthermore, the iron-containing lithium polysulfide of the present invention preferably has a stabilized metastable phase in which iron atoms are introduced into the lithium sulfide crystal lattice. The iron-containing lithium polysulfide of the present invention preferably consists of submicron or smaller crystallites because the metastable phase of iron-containing lithium polysulfide is stable. More specifically, the crystallite size of the iron-containing lithium polysulfide of the present invention is preferably 50 nm or less, more preferably 40 nm or less (particularly 1 to 30 nm). When the iron-containing lithium polysulfide of the present invention is produced by a production method including a mechanical milling process, as in the production method described below, the crystallites can be refined by the mechanical milling process. The crystallite size of the iron-containing lithium polysulfide of the present invention is a value calculated based on the Scherrer formula from the half-width of the diffraction peak based on the (111) plane that shows the maximum intensity of the peak of lithium sulfide observed as the main phase in powder X-ray diffraction measurement.
　さらに、本発明の鉄含有多硫化リチウムにおける各元素の存在割合については、特に限定的ではないが、遊離硫黄が生じない程度にＦｅ－Ｓ結合が形成できるだけのＦｅ量が存在し、含有Ｌｉ量から見積もられる理論容量が６００ｍＡｈ／ｇ以上であるだけのＬｉ量が存在し、導電性を確保できるだけのＦｅ量が存在することが好ましい。また、炭素等をはじめとする不純物量が多すぎると、容量もサイクル特性もレート特性も劣化する。このような観点から、形成される本発明の硫化リチウム－鉄－炭素複合体の総量を１００原子％として、Ｌｉ含有量は５０～７０原子％（特に５１～６０原子％）、Ｆｅ含有量は２～１２原子％（特に４～１１原子％）、Ｓ含有量は２０～４０原子％（特に３０～３９原子％）、Ｃ含有量は０～５原子％（特に０～３原子％）、ハロゲン含有量は０～０．８原子％（特に０～０．５原子％）であることが好ましい。なかでも、炭素及びハロゲンを含まない（Ｃ含有量及びハロゲン含有量がともに０原子％である）ことが特に好ましい。 Furthermore, the ratio of each element in the iron-containing lithium polysulfide of the present invention is not particularly limited, but it is preferable that there is an amount of Fe sufficient to form Fe-S bonds to the extent that free sulfur is not generated, that there is an amount of Li sufficient to provide a theoretical capacity of 600 mAh/g or more estimated from the amount of Li contained, and that there is an amount of Fe sufficient to ensure electrical conductivity. In addition, if the amount of impurities such as carbon is too large, the capacity, cycle characteristics, and rate characteristics will deteriorate. From this perspective, it is preferable that the total amount of the lithium sulfide-iron-carbon composite of the present invention formed is 100 atomic %, and that the Li content is 50 to 70 atomic % (particularly 51 to 60 atomic %), the Fe content is 2 to 12 atomic % (particularly 4 to 11 atomic %), the S content is 20 to 40 atomic % (particularly 30 to 39 atomic %), the C content is 0 to 5 atomic % (particularly 0 to 3 atomic %), and the halogen content is 0 to 0.8 atomic % (particularly 0 to 0.5 atomic %). Among them, it is particularly preferable that the composite does not contain carbon or halogen (both the C content and the halogen content are 0 atomic %).
　なお、Ｌｉ量を理論容量が６００ｍＡｈ／ｇ以上となる量とした理由については、酸化物系の高容量材料Ｌｉ（Ｎｉ，Ｍｎ，Ｃｏ）Ｏ２が最大値として３００ｍＡｈ／ｇ×４Ｖ＝１２００Ｗｈ／ｋｇのエネルギー密度を有するため、それと同程度の硫黄系材料（電圧２Ｖ）として６００ｍＡｈ／ｇ以上あれば十分と判断したことによる。 The reason why the amount of Li is set to an amount that results in a theoretical capacity of 600 mAh/g or more is that the oxide-based high-capacity material Li(Ni,Mn,Co) O2 has a maximum energy density of 300 mAh/g×4V=1200 Wh/kg, and it was determined that a sulfur-based material (voltage 2V) of 600 mAh/g or more is sufficient for the same level.
　以上のような本発明の鉄含有多硫化リチウムは、電気伝導度を向上させることができ、具体的には、本発明の鉄含有多硫化リチウムの電気伝導度は、２５℃において、１０－３～１０－６Ｓ／ｃｍ、好ましくは１０－３～３×１０－６Ｓ／ｃｍとすることができる。本発明の鉄含有多硫化リチウムの電気伝導度は、粉末を３００ＭＰａで加圧成形し、電圧印加時の電流を測定することにより測定する。 The iron-containing lithium polysulfide of the present invention as described above can have improved electrical conductivity, and specifically, the electrical conductivity of the iron-containing lithium polysulfide of the present invention can be set to 10 −3 to 10 −6 S/cm, preferably 10 −3 to 3×10 −6 S/cm, at 25° C. The electrical conductivity of the iron-containing lithium polysulfide of the present invention is measured by compressing the powder at 300 MPa and measuring the current when a voltage is applied.
　２．鉄含有多硫化リチウムの製造方法
　本発明の鉄含有多硫化リチウムは、特に制限されないが、
（３）リチウム含有化合物、鉄含有化合物及び硫黄含有化合物を含む混合物；前記混合物の加熱処理物；又は前記混合物の加熱生成物のメカニカルミリング処理物と、電気伝導度が１０－３Ｓ／ｃｍ以上である金属硫化物とを、メカニカルミリング処理する工程
を備える製造方法によって得ることができる。この方法によれば、所定の金属硫化物とメカニカルミリング処理することによって、粒子が微細化されて、鉄原子が硫化リチウム相内に取り込まれた準安定相が安定化されつつ、電気伝導度を特に向上させることができる。 2. Method for Producing Iron-Containing Lithium Polysulfide The iron-containing lithium polysulfide of the present invention is not particularly limited, but may be produced by the following method:
(3) It can be obtained by a manufacturing method including a step of subjecting a mixture containing a lithium-containing compound, an iron-containing compound, and a sulfur-containing compound, a heat-treated product of the mixture, or a mechanically milled product of the heat-treated product of the mixture, and a metal sulfide having an electrical conductivity of 10 −3 S/cm or more to mechanical milling. According to this method, by subjecting a predetermined metal sulfide to mechanical milling, the particles are refined, and the metastable phase in which iron atoms are incorporated into the lithium sulfide phase is stabilized, while the electrical conductivity can be particularly improved.
　なお、本発明の製造方法は、工程（３）の前に、さらに、
（２）リチウム含有化合物、鉄含有化合物及び硫黄含有化合物を含む混合物；又は前記混合物の加熱処理物を、メカニカルミリング処理する工程
を備えることが好ましい。これにより、上記工程（３）の前に、粒子が微細化されて、鉄原子が硫化リチウム相内に取り込まれた準安定相が安定化され、電気伝導度を向上させやすい。 In addition, the production method of the present invention further includes the steps of:
(2) It is preferable to include a step of subjecting a mixture containing a lithium-containing compound, an iron-containing compound, and a sulfur-containing compound, or a heat-treated product of the mixture, to a mechanical milling treatment, whereby the particles are refined before the step (3), and the metastable phase in which iron atoms are incorporated into the lithium sulfide phase is stabilized, making it easier to improve the electrical conductivity.
　また、本発明の製造方法は、工程（２）の前に、さらに、
（１）リチウム含有化合物、鉄含有化合物及び硫黄含有化合物を含む混合物を加熱する工程
を備えることが好ましい。これにより、加熱によって適度に反応を進行させ、続く工程（２）及び（３）によって、電気伝導度をさらに向上させやすい。
以下、この方法について具体的に説明する。 In addition, the production method of the present invention further includes, before the step (2),
It is preferable to include a step (1) of heating a mixture containing a lithium-containing compound, an iron-containing compound, and a sulfur-containing compound, whereby the reaction can be moderately advanced by heating, and the electrical conductivity can be easily further improved by the subsequent steps (2) and (3).
This method will now be described in detail.
　（２－１）原料粉末
　本発明では、原料として、リチウム含有化合物、鉄含有化合物及び硫黄含有化合物を用いる。 (2-1) Raw Material Powder In the present invention, a lithium-containing compound, an iron-containing compound, and a sulfur-containing compound are used as raw materials.
　リチウム含有化合物、鉄含有化合物及び硫黄含有化合物の各化合物の種類については特に限定的ではなく、リチウム、鉄及び硫黄の各元素を一種類ずつ含む３種類又はそれ以上の種類の化合物を混合して用いることもでき、あるいは、リチウム、鉄及び硫黄の内の２種類又はそれ以上の元素を同時に含む化合物を原料の一部として用いることもできる。 The types of lithium-containing compounds, iron-containing compounds, and sulfur-containing compounds are not particularly limited, and three or more types of compounds containing one type each of the elements lithium, iron, and sulfur can be mixed and used, or a compound containing two or more types of elements selected from lithium, iron, and sulfur can be used as part of the raw material.
　これらの原料化合物は、リチウム及び鉄以外の金属元素や、炭素元素を含まない化合物であることが好ましい。また、原料化合物中に含まれるリチウム、鉄及び硫黄の各元素以外の元素については、熱処理により離脱又は揮発していくものが好ましい。 These raw material compounds are preferably compounds that do not contain metal elements other than lithium and iron, or carbon. In addition, it is preferable that the elements contained in the raw material compounds other than lithium, iron, and sulfur are released or volatilized by heat treatment.
　この様な原料化合物の具体例としては、例えば、リチウム含有化合物として、硫化リチウム（Ｌｉ２Ｓ）、水酸化リチウム（ＬｉＯＨ）等を例示でき、鉄含有化合物として、金属鉄（Ｆｅ）、硫化鉄（ＦｅＳ、ＦｅＳ２等）、硫酸鉄（ＦｅＳＯ４）等を例示でき、硫黄含有化合物として、硫黄（Ｓ）、硫化リチウム（Ｌｉ２Ｓ）、硫化鉄（ＦｅＳ、ＦｅＳ２等）等を例示できる。この中で、特に生成物である本発明の鉄含有多硫化リチウムの構成元素のみからなり、最小限の原料数で反応させることのできる硫化リチウム（Ｌｉ２Ｓ）、及び硫化鉄（ＦｅＳ、ＦｅＳ２）の組み合わせが好ましい。 Specific examples of such raw material compounds include lithium-containing compounds such as lithium sulfide (Li 2 S) and lithium hydroxide (LiOH), iron-containing compounds such as metallic iron (Fe), iron sulfide (FeS, FeS 2 , etc.), and iron sulfate (FeSO 4 ), and sulfur-containing compounds such as sulfur (S), lithium sulfide (Li 2 S), and iron sulfide (FeS, FeS 2 , etc.). Among these, a combination of lithium sulfide (Li 2 S) and iron sulfide (FeS, FeS 2 ) is particularly preferred, which consists only of the constituent elements of the iron-containing lithium polysulfide of the present invention, which is the product, and can be reacted with a minimum number of raw materials.
　これら原料化合物の形状については特に限定はないが、平均粒径０．１～１００μｍ程度の粉末状であることが好ましい。ただし、メカニカルミリング工程があるため、原料化合物のサイズには特に限定はなく、粒径の大きな原料化合物を使用することもできるし、必要に応じて乳鉢等で粉砕することにより、平均粒径を制御することもできる。なお、原料化合物の平均粒径は、乾式のレーザー回折・散乱法による粒度分布測定で、累積度数分布が５０％となる値により求める。 There are no particular limitations on the shape of these raw material compounds, but they are preferably in the form of a powder with an average particle size of about 0.1 to 100 μm. However, because a mechanical milling process is used, there are no particular limitations on the size of the raw material compounds, and raw material compounds with large particle sizes can be used, and the average particle size can be controlled by grinding in a mortar, etc., as necessary. The average particle size of the raw material compounds is determined by the value at which the cumulative frequency distribution is 50% when particle size distribution is measured using a dry laser diffraction/scattering method.
　リチウム含有化合物、鉄含有化合物及び硫黄含有化合物からなる原料の混合割合については、特に限定的ではないが、最終生成物である本発明の鉄含有多硫化リチウムにおいて、遊離硫黄が生じない程度にＦｅ－Ｓ結合が形成しやすいだけのＦｅ量が存在し、Ｌｉ量から見積もられる理論容量が６００ｍＡｈ／ｇ程度以上となりやすいだけのＬｉ量が存在し、導電性を確保し容量及びレート特性を劣化しにくいだけのＦｅが存在することが好ましい。このような観点から、原料の混合割合については、Ｌｉ含有量は５０～７０原子％（特に５１～６０原子％）、Ｆｅ含有量は２～１２原子％（特に４～１１原子％）、Ｓ含有量は２０～４０原子％（特に３０～３９原子％）、Ｃ含有量は０～５原子％（特に０～３原子％）、ハロゲン含有量が０～０．８原子％（特に０～０．５原子％）となるように調整することが好ましい。原料化合物の混合比率については、原料化合物に含まれる各元素の比率が、目的とする本発明の鉄含有多硫化リチウム中の各元素の比率と同一となるように調整することができる。 The mixing ratio of the raw materials consisting of the lithium-containing compound, the iron-containing compound, and the sulfur-containing compound is not particularly limited, but it is preferable that in the final product, the iron-containing lithium polysulfide of the present invention, there is an amount of Fe that is sufficient to easily form Fe-S bonds to the extent that free sulfur is not generated, there is an amount of Li that is sufficient to easily achieve a theoretical capacity estimated from the amount of Li of about 600 mAh/g or more, and there is an amount of Fe that ensures electrical conductivity and is unlikely to deteriorate in capacity and rate characteristics. From this perspective, it is preferable to adjust the mixing ratio of the raw materials so that the Li content is 50 to 70 atomic % (particularly 51 to 60 atomic %), the Fe content is 2 to 12 atomic % (particularly 4 to 11 atomic %), the S content is 20 to 40 atomic % (particularly 30 to 39 atomic %), the C content is 0 to 5 atomic % (particularly 0 to 3 atomic %), and the halogen content is 0 to 0.8 atomic % (particularly 0 to 0.5 atomic %). The mixing ratio of the raw material compounds can be adjusted so that the ratio of each element contained in the raw material compounds is the same as the ratio of each element in the desired iron-containing lithium polysulfide of the present invention.
　なお、Ｌｉ量を理論容量が６００ｍＡｈ／ｇ以上となる量とした理由については、酸化物系の高容量材料Ｌｉ（Ｎｉ，Ｍｎ，Ｃｏ）Ｏ２が最大値として３００ｍＡｈ／ｇ×４Ｖ＝１２００Ｗｈ／ｋｇのエネルギー密度を有するため、それと同程度の硫黄系材料（電圧２Ｖ）として６００ｍＡｈ／ｇ以上あれば十分と判断したことによる。 The reason why the amount of Li is set to an amount that results in a theoretical capacity of 600 mAh/g or more is that the oxide-based high-capacity material Li(Ni,Mn,Co) O2 has a maximum energy density of 300 mAh/g×4V=1200 Wh/kg, and it was determined that a sulfur-based material (voltage 2V) of 600 mAh/g or more is sufficient for the same level.
　（２－２）工程（１）
　工程（１）を採用する場合、まず、リチウム含有化合物、鉄含有化合物及び硫黄含有化合物を含む混合物に対して、加熱処理を施すことが好ましい。加熱方法は特に制限されるわけではないが、加熱反応によって原子レベルでの反応が適度に進行した硫化リチウムと硫化鉄の混合物を得やすい観点から、通電焼結を行うことが好ましい。 (2-2) Step (1)
When the step (1) is adopted, it is preferable to first subject the mixture containing the lithium-containing compound, the iron-containing compound, and the sulfur-containing compound to a heat treatment. Although the heating method is not particularly limited, it is preferable to perform electric sintering from the viewpoint of easily obtaining a mixture of lithium sulfide and iron sulfide in which the reaction at the atomic level has progressed appropriately by the heating reaction.
　工程（１）において通電焼結を行う場合、具体的には、上記した原料混合物を、導電性を有する型（導電性容器）に充填し、該導電性を有する型（導電性容器）に、好ましくは直流パルス電流を通電すること（放電プラズマ焼結法、パルス通電焼結法、プラズマ活性化焼結法等と呼ばれる方法）により、ジュール熱による導電性を有する型（導電性容器）の加熱が起こり、導電性を有する型（導電性容器）内の原料混合物が加熱されて、各元素が拡散移動し、原子レベルで各元素が相互に混合した中間体を好適に作製することができる。 When electric sintering is performed in step (1), specifically, the raw material mixture described above is filled into a conductive mold (conductive container), and a current, preferably a direct current pulse current, is passed through the conductive mold (conductive container) (a method known as discharge plasma sintering, pulsed electric current sintering, plasma activated sintering, etc.), which heats the conductive mold (conductive container) with Joule heat, heating the raw material mixture in the conductive mold (conductive container), causing the elements to diffuse and move, making it possible to suitably produce an intermediate in which the elements are mixed together at the atomic level.
　この通電焼結処理の際の雰囲気は、非酸化性雰囲気下とすることが好ましい。また、常圧下に通電焼結処理を施してもよいが、加圧下に通電焼結処理を施すことが好ましい。 The atmosphere during this electric sintering process is preferably a non-oxidizing atmosphere. Also, the electric sintering process may be performed under normal pressure, but it is preferable to perform the electric sintering process under pressure.
　具体的な方法としては、導電性を有する容器に原料とするリチウム含有化合物、鉄含有化合物及び硫黄含有化合物を含む原料混合物を充填し、好ましくは非酸化性雰囲気下において、加圧しながらパルス状のＯＮ－ＯＦＦ直流電流を通電することが好ましい。 As a specific method, a conductive container is filled with a raw material mixture containing the raw materials lithium-containing compound, iron-containing compound, and sulfur-containing compound, and a pulsed ON-OFF direct current is preferably passed through the container while applying pressure, preferably in a non-oxidizing atmosphere.
　導電性を有する型（導電性容器）の材質としては、導電性を有するものであれば特に限定されず、炭素、鉄、酸化鉄、アルミニウム、タングステンカーバイド等から形成されているものの他、炭素及び／又は酸化鉄に窒化珪素を混合した混合物等から形成されているものも好適に使用できる。 The material of the conductive mold (conductive container) is not particularly limited as long as it is conductive, and in addition to those made of carbon, iron, iron oxide, aluminum, tungsten carbide, etc., those made of a mixture of carbon and/or iron oxide and silicon nitride can also be suitably used.
　通電焼結処理は、硫化物の酸化をより抑制するため、例えば、Ａｒ、Ｎ２等の不活性ガス雰囲気下、Ｈ２等の還元性雰囲気下等で行うことが好ましい。また、酸素濃度が十分に低い減圧状態、例えば、酸素分圧が、２０Ｐａ以下（特に１～２０Ｐａ）の減圧下とすることもできる。 In order to further suppress the oxidation of sulfides, the electric sintering treatment is preferably performed in an inert gas atmosphere such as Ar or N2 , or in a reducing atmosphere such as H2 , etc. In addition, the pressure can be reduced so that the oxygen concentration is sufficiently low, for example, the oxygen partial pressure can be reduced to 20 Pa or less (particularly 1 to 20 Pa).
　具体的な処理としては、導電性を有する型（導電性容器）として十分な密閉状態を確保できる容器を用いる場合には、該容器内を非酸化性雰囲気とすることができる。また、導電性を有する型（導電性容器）は完全な密閉状態でなくてもよく、不完全な密閉状態の容器を用いる場合には、該容器を反応室内に収容して、該反応室内を非酸化性雰囲気とすることができる。これにより、上記した原料混合物の加熱反応を非酸化性雰囲気下で行うことが可能である。この場合、例えば、反応室内を０．０１ＭＰａ以上（特に０．０５～０．２ＭＰａ）の不活性ガス雰囲気、還元性ガス雰囲気等とすることが好ましい。 As a specific treatment, when a container that can ensure a sufficiently sealed state is used as the conductive mold (conductive container), the inside of the container can be made into a non-oxidizing atmosphere. Furthermore, the conductive mold (conductive container) does not have to be completely sealed, and when an incompletely sealed container is used, the container can be placed in a reaction chamber and the inside of the reaction chamber can be made into a non-oxidizing atmosphere. This makes it possible to carry out the heating reaction of the raw material mixture described above in a non-oxidizing atmosphere. In this case, for example, it is preferable to make the inside of the reaction chamber into an inert gas atmosphere of 0.01 MPa or more (particularly 0.05 to 0.2 MPa), a reducing gas atmosphere, etc.
　導電性容器に上記した原料混合物を充填した状態で直流パルス電流を印加することにより、ジュール熱による導電性容器の加熱が起こり、容器内の原料が加熱されて出発原料同士が反応して、各原子が相互に混合した中間体が形成され得る。この方法では、３０分以下という短時間で目的とする中間体を製造できるので、揮発し易いＬｉやＳ等の欠損が少なく、原料混合比に近い組成比の中間体を得ることができる。 By applying a direct current pulse current to a conductive container filled with the above-mentioned raw material mixture, the conductive container is heated by Joule heat, and the raw materials in the container are heated, causing the starting materials to react with each other and forming an intermediate in which the atoms are mixed together. With this method, the desired intermediate can be produced in a short time of less than 30 minutes, so there is little loss of easily volatile elements such as Li and S, and an intermediate with a composition ratio close to the raw material mixture ratio can be obtained.
　通電焼結工程での加熱温度は、通常、各構成元素をより十分に相互拡散させて原子レベルで相互に混合しやすくするとともに、遷移金属及び典型元素と結合しない硫黄（遊離硫黄）を低減しやすく高容量としやすいとともに、Ｌｉ、Ｓ等の元素の揮発による欠損を抑制しやすく高容量としやすい観点から、４００～１２００℃が好ましく、５００～１１００℃がより好ましい。上記した加熱温度範囲に保持する時間については、Ｌｉ、Ｓ等の元素の揮発による欠損を抑制しやすく高容量としやすい観点から、０～３０分が好ましく、上記した温度範囲に到達すれば、直ちに通電を停止して（つまり、上記した加熱温度における保持時間を０として）放冷することもできる。 The heating temperature in the electric sintering process is usually preferably 400 to 1200°C, more preferably 500 to 1100°C, from the viewpoints of more thoroughly interdiffusing the constituent elements to facilitate mixing at the atomic level, reducing sulfur that is not bonded to transition metals and typical elements (free sulfur) and facilitating high capacity, and suppressing loss due to volatilization of elements such as Li and S and facilitating high capacity. The time for holding within the above heating temperature range is preferably 0 to 30 minutes from the viewpoints of easily suppressing loss due to volatilization of elements such as Li and S and facilitating high capacity, and once the temperature range is reached, the electric current can be immediately stopped (i.e., the holding time at the above heating temperature is set to 0) and the material can be left to cool.
　原料粉末を加圧する際の圧力としては、原料化合物同士の接触を強くしやすく加熱時の原子相互拡散を十分にしやすく、原料化合物における原子相互間の反応を十分としやすい観点から、例えば、５～６０ＭＰａが好ましく、１０～５０ＭＰａがより好ましい。なお、生成物の融点が低い組成の場合は、無加圧（大気圧）で加熱することも可能である。この観点から、生成物の融点が低い組成の場合も考慮すると、原料粉末を加圧する際の圧力は、０．１～６０ＭＰａ、好ましくは０．１～５０ＭＰａとすることも可能である。 The pressure to be applied when compressing the raw material powder is preferably, for example, 5 to 60 MPa, and more preferably 10 to 50 MPa, from the viewpoint of making it easier to strengthen contact between the raw material compounds, to facilitate sufficient atomic diffusion during heating, and to facilitate sufficient reaction between atoms in the raw material compounds. Note that if the product has a composition with a low melting point, it is also possible to heat without applying pressure (atmospheric pressure). From this viewpoint, and taking into consideration the case where the product has a composition with a low melting point, the pressure to be applied when compressing the raw material powder can be 0.1 to 60 MPa, and preferably 0.1 to 50 MPa.
　通電焼結を行う装置としては、原料混合物を加熱、冷却、加圧等することが可能であり、放電に必要な電流を印加できるものであれば特に限定されない。例えば、市販の通電焼結装置（放電プラズマ焼結装置）を使用できる。このような通電焼結装置及びその原理は、例えば、特開平１０－２５１０７０号公報等に開示されている。 The device for electric sintering is not particularly limited as long as it is capable of heating, cooling, pressurizing, etc. the raw material mixture and can apply the current required for discharge. For example, a commercially available electric sintering device (discharge plasma sintering device) can be used. Such an electric sintering device and its principle are disclosed, for example, in JP-A-10-251070.
　以下に通電焼結装置の模式図を示した図１を参考にしながら、通電焼結を行う場合の具体例を説明する。なお、通電焼結装置は、以下に説明する装置のみに限られない。 Below, a specific example of electric sintering will be described with reference to Figure 1, which shows a schematic diagram of an electric sintering device. Note that the electric sintering device is not limited to the device described below.
　図１に示す通電焼結装置１においては、試料２が装填される焼結ダイ（電子伝導性容器）３と上下一対のパンチ４及び５とを有する。パンチ４及び５は、それぞれパンチ電極６及び７に支持されており、このパンチ電極６及び７を介して、焼結ダイ３に装填された試料２に必要に応じて加圧しながらパルス電流を供給することができる。焼結ダイ３の素材は限定されず、例えば、黒鉛等の炭素材料が挙げられる。 The electric sintering apparatus 1 shown in Figure 1 has a sintering die (electronically conductive container) 3 in which a sample 2 is loaded, and a pair of upper and lower punches 4 and 5. The punches 4 and 5 are supported by punch electrodes 6 and 7, respectively, and a pulse current can be supplied to the sample 2 loaded in the sintering die 3 via these punch electrodes 6 and 7 while applying pressure as necessary. The material of the sintering die 3 is not limited, and examples include carbon materials such as graphite.
　図１に示す通電焼結装置では、上記した導電性容器３、通電用パンチ４及び５、パンチ電極６及び７を含む通電部は、水冷真空チャンバー８に収容されており、チャンバー内は、雰囲気制御機構１５による所定の雰囲気に調整することができる。したがって、雰囲気制御機構１５を利用して、チャンバー内を非酸化性雰囲気に調整することが好ましい。 In the electric sintering apparatus shown in FIG. 1, the electric current section including the conductive container 3, electric current punches 4 and 5, and punch electrodes 6 and 7 is housed in a water-cooled vacuum chamber 8, and the interior of the chamber can be adjusted to a predetermined atmosphere by an atmosphere control mechanism 15. Therefore, it is preferable to use the atmosphere control mechanism 15 to adjust the interior of the chamber to a non-oxidizing atmosphere.
　制御装置１２は、加圧機構１３、パルス電源１１、雰囲気制御機構１５、水冷却機構１６及び１０、並びに温度計測装置１７を駆動制御する。制御装置１２は加圧機構１３を駆動し、パンチ電極６及び７が所定の圧力で原料混合物を加圧するよう構成されている。 The control device 12 drives and controls the pressurizing mechanism 13, the pulse power supply 11, the atmosphere control mechanism 15, the water cooling mechanisms 16 and 10, and the temperature measuring device 17. The control device 12 drives the pressurizing mechanism 13 so that the punch electrodes 6 and 7 pressurize the raw material mixture at a predetermined pressure.
　加熱のために印加するパルス電流は、例えばパルス幅２～３ミリ秒程度で、周期は３～３００Ｈｚ程度のパルス状の（ＯＮ－ＯＦＦをスイッチングする）直流電流を用いることができる。具体的な電流値は導電性を有する型（導電性容器）の種類、大きさ等により異なるが、上記した温度範囲となるように、具体的な電流値を決めることが好ましい。例えば、内径１５ｍｍの黒鉛型材を用いた場合には２００～１０００Ａ、内径１００ｍｍの黒鉛型材を用いた場合には１０００～８０００Ａが好ましい。通電焼結処理時は、型材温度をモニターしながら電流値を増減させ、所定の温度を管理できるように電流値を制御することが好ましい。 The pulse current applied for heating can be, for example, a pulsed (ON-OFF switching) direct current with a pulse width of about 2-3 milliseconds and a cycle of about 3-300 Hz. The specific current value varies depending on the type and size of the conductive mold (conductive container), but it is preferable to determine the specific current value so that the temperature range is as described above. For example, when a graphite mold material with an inner diameter of 15 mm is used, 200-1000 A is preferable, and when a graphite mold material with an inner diameter of 100 mm is used, 1000-8000 A is preferable. During the electric sintering process, it is preferable to increase or decrease the current value while monitoring the mold material temperature, and to control the current value so that the specified temperature can be maintained.
　原料混合物を加圧した状態とするためには、例えば、上記した導電性容器３に充填した原料混合物をパンチ電極６及び７を介して加圧することができる。 To pressurize the raw material mixture, for example, the raw material mixture filled in the conductive container 3 described above can be pressurized via punch electrodes 6 and 7.
　（２－３）工程（２）
　工程（２）を採用する場合、リチウム含有化合物、鉄含有化合物及び硫黄含有化合物を含む混合物；又は前記混合物の加熱処理物を、メカニカルミリング処理を施し、混合、粉砕及び反応させる。 (2-3) Step (2)
When the step (2) is adopted, a mixture containing a lithium-containing compound, an iron-containing compound and a sulfur-containing compound, or a heat-treated product of the mixture, is subjected to a mechanical milling treatment to mix, pulverize and react with each other.
　なお、リチウム含有化合物、鉄含有化合物及び硫黄含有化合物を含む混合物を使用する場合は、各原料粉末を混合した後にメカニカルミリング処理を施すことができ、また、前記混合物の加熱処理物を使用する場合は、上記した工程（１）で得られた生成物を使用することができる。 When using a mixture containing a lithium-containing compound, an iron-containing compound, and a sulfur-containing compound, the raw material powders can be mixed and then subjected to mechanical milling. When using a heat-treated product of the mixture, the product obtained in the above-mentioned step (1) can be used.
　メカニカルミリング法は、機械的エネルギーを付与しながら原料を摩砕混合し反応させる方法であり、この方法によれば、原料に機械的な衝撃や摩擦を与えて摩砕混合することによって、原料に含まれる各化合物が激しく接触して微細化されるため、準安定相が得られやすい。本発明では、上記したメカニカルミリング処理により、熱処理だけでは作製が困難な準安定鉄含有多硫化リチウムを形成しつつ、微細化して安定的に存在させることができる。 Mechanical milling is a method in which raw materials are milled and mixed while mechanical energy is applied to them to cause a reaction. According to this method, the raw materials are milled and mixed by applying mechanical impact and friction, which causes the compounds contained in the raw materials to come into vigorous contact with each other and be finely divided, making it easy to obtain a metastable phase. In the present invention, the above-mentioned mechanical milling process forms metastable iron-containing lithium polysulfide, which is difficult to produce by heat treatment alone, while also finely dividing it so that it exists stably.
　メカニカルミリング装置としては、例えば、ボールミル、振動ミル、ターボミル、ディスクミル等を用いることができ、中でもボールミルが好ましい。 Mechanical milling devices that can be used include, for example, ball mills, vibration mills, turbo mills, and disk mills, with ball mills being preferred.
　メカニカルミリング処理は、硫化物の酸化を抑制しやすいため、非酸化性雰囲気下、例えば、Ａｒ、Ｎ２等の不活性ガス雰囲気下、Ｈ２等の還元性雰囲気下等で行うことが好ましい。また、酸素濃度が十分に低い減圧状態、例えば、酸素分圧が、２０Ｐａ以下（特に１～２０Ｐａ）の減圧下とすることもできる。 Since the mechanical milling treatment is easy to suppress the oxidation of sulfides, it is preferable to perform the treatment in a non-oxidizing atmosphere, for example, in an inert gas atmosphere such as Ar or N2 , or in a reducing atmosphere such as H2 . In addition, the treatment can be performed in a reduced pressure state in which the oxygen concentration is sufficiently low, for example, the oxygen partial pressure can be reduced to 20 Pa or less (particularly 1 to 20 Pa).
　メカニカルミリングを行う際の回転数については、硫黄の揮発が生じにくくし、目的とする硫黄の含有比率が高い複合体を形成しやすくするため、２００～６００ｒｐｍが好ましく、２５０～５５０ｒｐｍがより好ましい。 The rotation speed during mechanical milling is preferably 200 to 600 rpm, more preferably 250 to 550 rpm, to prevent sulfur from volatilizing and to facilitate the formation of a composite with a high desired sulfur content.
　メカニカルミリングを行う際の温度については、硫黄の揮発が生じにくくし、目的とする硫黄の含有比率が高い複合体を形成しやすくするため、２００℃以下が好ましく、２０～１００℃がより好ましい。 The temperature during mechanical milling is preferably 200°C or less, more preferably 20 to 100°C, to prevent sulfur from volatilizing and to facilitate the formation of a composite with a high desired sulfur content.
　メカニカルミリング時間については、特に限定的ではないが、得られる複合体の結晶子サイズが、５０ｎｍ以下となるまでメカニカルミリング処理を行うことが好ましい。 There are no particular limitations on the mechanical milling time, but it is preferable to carry out the mechanical milling process until the crystallite size of the resulting composite is 50 nm or less.
　（２－４）第二メカニカルミリング工程（工程（３））
　工程（３）では、リチウム含有化合物、鉄含有化合物及び硫黄含有化合物を含む混合物；前記混合物の加熱処理物；又は前記混合物の加熱生成物のメカニカルミリング処理物と、電気伝導度が１０－３Ｓ／ｃｍ以上である金属硫化物とを、メカニカルミリング処理を施し、混合、粉砕及び反応させることで、本発明の鉄含有多硫化リチウムを得ることができる。 (2-4) Second mechanical milling step (step (3))
In step (3), a mixture containing a lithium-containing compound, an iron-containing compound, and a sulfur-containing compound; a heat-treated product of the mixture; or a mechanically milled product of the heat-treated product of the mixture, and a metal sulfide having an electrical conductivity of 10 −3 S/cm or more are subjected to a mechanical milling treatment, and then mixed, pulverized, and reacted with each other to obtain the iron-containing lithium polysulfide of the present invention.
　なお、リチウム含有化合物、鉄含有化合物及び硫黄含有化合物を含む混合物を使用する場合は、各原料粉末を混合した後に電気伝導度が１０－３Ｓ／ｃｍ以上である金属硫化物とメカニカルミリング処理を施すことができ、また、前記混合物の加熱処理物を使用する場合は、上記した工程（１）で得られた生成物と電気伝導度が１０－３Ｓ／ｃｍ以上である金属硫化物とを使用することができ、また、前記混合物の加熱生成物のメカニカルミリング処理物を使用する場合は、上記した工程（２）で得られた生成物を使用することができる。 When using a mixture containing a lithium-containing compound, an iron-containing compound, and a sulfur-containing compound, the raw material powders can be mixed and then subjected to mechanical milling with a metal sulfide having an electrical conductivity of 10 −3 S/cm or more. When using a heat-treated product of the mixture, the product obtained in the above-mentioned step (1) and a metal sulfide having an electrical conductivity of 10 −3 S/cm or more can be used. When using a mechanically milled product of the heat-treated product of the mixture, the product obtained in the above-mentioned step (2) can be used.
　なお、上記した工程（１）や工程（２）を採用する場合において、当該生成物中に、電気伝導度が１０－３Ｓ／ｃｍ以上の金属硫化物を、後述する添加量程度に既に含んでいる場合は新たに金属硫化物を加えなくてもよい。本発明では、原料として、硫化鉄等の電気伝導度の高い硫化物を使用している場合であっても、工程（２）のミリング工程においてＸ線回折スペクトルにおけるピークが消失する、つまり、当該硫化物相が同定できないほどにまでメカニカルミリングを施すような場合や、工程（２）のミリング工程の結果当該硫化物相の含有量が少なくなる場合は、別途、金属硫化物の添加が必要である。 In addition, when the above-mentioned step (1) or step (2) is adopted, if the product already contains a metal sulfide having an electrical conductivity of 10 −3 S/cm or more in the amount to be added described later, it is not necessary to add a new metal sulfide. In the present invention, even if a sulfide having a high electrical conductivity such as iron sulfide is used as a raw material, if the peak in the X-ray diffraction spectrum disappears in the milling step of step (2), that is, if mechanical milling is performed to the extent that the sulfide phase cannot be identified, or if the content of the sulfide phase is reduced as a result of the milling step of step (2), a separate metal sulfide must be added.
　使用できる金属硫化物の電気伝導度は、特に制限されるわけではないが、硫化リチウムの利用率を向上させやすく、硫化リチウムが本来有する高容量の特性を充分に発揮させやすく、優れたレート特性を有しやすい観点から、１０３～１０－３Ｓ／ｃｍが好ましく、１０３～１０－２Ｓ／ｃｍがより好ましい。金属硫化物の電気伝導度は、粉末を３００ＭＰａ程度で圧粉成型し、電圧印加時の電流量を測定することにより測定する。 The electrical conductivity of the usable metal sulfide is not particularly limited, but from the viewpoints of easily improving the utilization rate of lithium sulfide, easily allowing the inherent high capacity property of lithium sulfide to be fully exhibited, and easily having excellent rate characteristics, it is preferably 10 3 to 10 -3 S/cm, and more preferably 10 3 to 10 -2 S/cm. The electrical conductivity of the metal sulfide is measured by compacting the powder at about 300 MPa and measuring the amount of current when a voltage is applied.
　このような電気伝導度を有する金属硫化物としては、特に制限されるわけではないが、例えば、鉄含有多硫化リチウム（Ｌｉ２ＦｅＳ２等；ただし、工程（１）及び（２）の生成物とは異なる）、硫化鉄（ＦｅＳ、ＦｅＳ２等）、硫化モリブデン（ＭｏＳ２、Ｍｏ６Ｓ８等）、硫化銅（ＣｕＳ等）等が挙げられる。これらの金属硫化物は、単独で用いることもでき、２種以上を組合せて用いることもできる。 Metal sulfides having such electrical conductivity are not particularly limited, but examples thereof include iron-containing lithium polysulfides ( Li2FeS2 , etc.; however, different from the products of steps (1) and ( 2 )), iron sulfides (FeS, FeS2 , etc.), molybdenum sulfides ( MoS2 , Mo6S8 , etc.), copper sulfides (CuS, etc.), etc. These metal sulfides can be used alone or in combination of two or more.
　工程（３）において、上記した金属硫化物の添加量は、特に制限されるわけではないが、硫化リチウムの利用率を向上させやすく、硫化リチウムが本来有する高容量の特性を充分に発揮させやすく、優れたレート特性を有しやすい観点から、工程（２）で得られた中間体と、上記した金属硫化物との合計量を１００質量％として、上記した金属硫化物が３～２５質量％、好ましくは５～２０質量％となるように添加することができる。 In step (3), the amount of the metal sulfide added is not particularly limited, but from the viewpoint of making it easier to improve the utilization rate of lithium sulfide, to make it easier to fully utilize the high capacity characteristics inherent to lithium sulfide, and to make it easier to have excellent rate characteristics, the metal sulfide can be added in an amount of 3 to 25 mass%, preferably 5 to 20 mass%, of 100 mass% of the total amount of the intermediate obtained in step (2) and the metal sulfide.
　メカニカルミリング装置としては、例えば、ボールミル、振動ミル、ターボミル、ディスクミル等を用いることができ、中でもボールミルが好ましい。 Mechanical milling devices that can be used include, for example, ball mills, vibration mills, turbo mills, and disk mills, with ball mills being preferred.
　メカニカルミリング処理は、硫化物の酸化を抑制しやすいため、非酸化性雰囲気下、例えば、Ａｒ、Ｎ２等の不活性ガス雰囲気下、Ｈ２等の還元性雰囲気下等で行うことが好ましい。また、酸素濃度が十分に低い減圧状態、例えば、酸素分圧が、２０Ｐａ以下（特に１～２０Ｐａ）の減圧下とすることもできる。 Since the mechanical milling treatment is easy to suppress the oxidation of sulfides, it is preferable to perform the treatment in a non-oxidizing atmosphere, for example, in an inert gas atmosphere such as Ar or N2 , or in a reducing atmosphere such as H2 . In addition, the treatment can be performed in a reduced pressure state in which the oxygen concentration is sufficiently low, for example, the oxygen partial pressure can be reduced to 20 Pa or less (particularly 1 to 20 Pa).
　メカニカルミリングを行う際の回転数については、硫黄の揮発が生じにくくし、目的とする硫黄の含有比率が高い複合体を形成しやすくするため、２００～６００ｒｐｍが好ましく、２５０～５５０ｒｐｍがより好ましい。 The rotation speed during mechanical milling is preferably 200 to 600 rpm, more preferably 250 to 550 rpm, to prevent sulfur from volatilizing and to facilitate the formation of a composite with a high desired sulfur content.
　メカニカルミリングを行う際の温度については、硫黄の揮発が生じにくくし、目的とする硫黄の含有比率が高い複合体を形成しやすくするため、１００℃以下が好ましく、２０～８０℃がより好ましい。 The temperature during mechanical milling is preferably 100°C or less, more preferably 20 to 80°C, to prevent sulfur from volatilizing and to facilitate the formation of a composite with a high desired sulfur content.
　メカニカルミリング時間については、特に限定的ではないが、得られる複合体の結晶子サイズが、５０ｎｍ以下となるまでメカニカルミリング処理を行うことが好ましい。 There are no particular limitations on the mechanical milling time, but it is preferable to carry out the mechanical milling process until the crystallite size of the resulting composite is 50 nm or less.
　３．リチウムイオン二次電池
　本発明の鉄含有多硫化リチウムは、上記した優れた特性を利用して、リチウム一次電池、リチウムイオン二次電池（金属リチウム二次電池等）等の正極活物質として有効に利用できる。特に、本発明の鉄含有多硫化リチウムは、構造中にリチウムを含有する材料であるため、充電から充放電を行うことができる材料であり、しかも、高容量で、優れたレート特性を有することから、リチウムイオン二次電池用の正極活物質として有用である。本発明の鉄含有多硫化リチウムを正極活物質として使用するリチウムイオン二次電池は、電解質として非水溶媒系電解液を用いる非水電解質リチウムイオン二次電池であってもよく、或いは、リチウムイオン伝導性の固体電解質を用いる全固体型リチウムイオン二次電池であってもよい。 3. Lithium-ion secondary battery The iron-containing lithium polysulfide of the present invention can be effectively used as a positive electrode active material for lithium primary batteries, lithium ion secondary batteries (metal lithium secondary batteries, etc.) by utilizing the excellent properties described above. In particular, since the iron-containing lithium polysulfide of the present invention is a material containing lithium in its structure, it is a material that can be charged and discharged, and has a high capacity and excellent rate characteristics, so it is useful as a positive electrode active material for lithium ion secondary batteries. The lithium ion secondary battery using the iron-containing lithium polysulfide of the present invention as a positive electrode active material may be a non-aqueous electrolyte lithium ion secondary battery that uses a non-aqueous solvent-based electrolyte as the electrolyte, or may be an all-solid-state lithium ion secondary battery that uses a lithium ion conductive solid electrolyte.
　非水電解質リチウムイオン二次電池及び全固体型リチウムイオン二次電池の構造は、本発明の鉄含有多硫化リチウムを正極活物質として用いること以外は、公知のリチウムイオン二次電池と同様とすることができる。 The structure of the non-aqueous electrolyte lithium ion secondary battery and the all-solid-state lithium ion secondary battery can be the same as that of a known lithium ion secondary battery, except that the iron-containing lithium polysulfide of the present invention is used as the positive electrode active material.
　例えば、非水電解質リチウムイオン二次電池については、上記した本発明の鉄含有多硫化リチウムを正極活物質として使用する他は、基本的な構造は、公知の非水電解質リチウムイオン二次電池と同様とすることができる。 For example, a non-aqueous electrolyte lithium ion secondary battery can have the same basic structure as a known non-aqueous electrolyte lithium ion secondary battery, except that the iron-containing lithium polysulfide of the present invention described above is used as the positive electrode active material.
　正極については、上記した本発明の鉄含有多硫化リチウムを正極活物質として用い、導電材とバインダーとを含む正極合剤をＡｌ、Ｎｉ、ステンレス、カーボンクロス等の正極集電体に担持させることができる。導電材としては、例えば、黒鉛、コークス類、カーボンブラック、針状カーボン等の炭素材料を用いることができる。 For the positive electrode, the iron-containing lithium polysulfide of the present invention described above can be used as the positive electrode active material, and a positive electrode mixture containing a conductive material and a binder can be supported on a positive electrode current collector such as Al, Ni, stainless steel, or carbon cloth. As the conductive material, for example, carbon materials such as graphite, cokes, carbon black, and acicular carbon can be used.
　負極としては、リチウムを含有する材料とリチウムを含有しない材料共に用いることが可能である。例えば、黒鉛、難焼結性炭素、リチウム金属等の他、スズ、シリコン及びこれらを含む合金や、ＳｉＯ等も用いることができる。これらの負極活物質についても、必要に応じて、導電材、バインダー等を用いて、Ａｌ、Ｃｕ、Ｎｉ、ステンレス、カーボン等からなる負極集電体に担持させることができる。 Both lithium-containing and lithium-free materials can be used for the negative electrode. For example, in addition to graphite, non-sinterable carbon, and lithium metal, tin, silicon, and alloys containing these, and SiO, etc. can also be used. These negative electrode active materials can also be supported on a negative electrode current collector made of Al, Cu, Ni, stainless steel, carbon, etc., using conductive materials, binders, etc. as necessary.
　セパレータとしては、例えば、ポリエチレン、ポリプロピレン等のポリオレフィン樹脂、フッ素樹脂、ナイロン、芳香族アラミド、無機ガラス等の材質からなり、多孔質膜、不織布、織布等の形態の材料を用いることができる。 Separators can be made of materials such as polyolefin resins, such as polyethylene and polypropylene, fluororesins, nylon, aromatic aramid, and inorganic glass, and can be in the form of porous membranes, nonwoven fabrics, woven fabrics, etc.
　非水電解質の溶媒としては、カーボネート化合物、エーテル化合物、ニトリル化合物、含硫黄化合物等の非水溶媒系二次電池の溶媒として公知の溶媒を用いることができる。 The solvent for the non-aqueous electrolyte may be a solvent known as a solvent for non-aqueous solvent-based secondary batteries, such as a carbonate compound, an ether compound, a nitrile compound, or a sulfur-containing compound.
　また、全固体型リチウムイオン二次電池についても、本発明の鉄含有多硫化リチウムを正極活物質として用いる以外は、公知の全固体型リチウムイオン二次電池と同様の構造とすることができる。 Furthermore, all-solid-state lithium-ion secondary batteries can have the same structure as known all-solid-state lithium-ion secondary batteries, except that the iron-containing lithium polysulfide of the present invention is used as the positive electrode active material.
　この場合、リチウムイオン伝導性固体電解質としては、例えば、ポリエチレンオキサイド系の高分子化合物、ポリオルガノシロキサン鎖及びポリオキシアルキレン鎖の少なくとも一種を含む高分子化合物等のポリマー系固体電解質の他、硫化物系固体電解質、酸化物系固体電解質等を用いることができる。 In this case, examples of the lithium ion conductive solid electrolyte that can be used include polymer-based solid electrolytes such as polyethylene oxide-based polymer compounds, polymer compounds containing at least one of a polyorganosiloxane chain and a polyoxyalkylene chain, as well as sulfide-based solid electrolytes and oxide-based solid electrolytes.
　全固体型リチウムイオン二次電池の正極については、例えば、本発明の鉄含有多硫化リチウムを正極活物質として用い、導電材、バインダー及び固体電解質を含む正極合剤をＴｉ、Ａｌ、Ｎｉ、ステンレス等の正極集電体に担持させることができる。導電材については、非水溶媒系リチウムイオン二次電池と同様に、例えば、黒鉛、コークス類、カーボンブラック、針状カーボン等の炭素材料を用いることができる。 For the positive electrode of an all-solid-state lithium-ion secondary battery, for example, the iron-containing lithium polysulfide of the present invention can be used as the positive electrode active material, and a positive electrode mixture containing a conductive material, a binder, and a solid electrolyte can be supported on a positive electrode current collector such as Ti, Al, Ni, stainless steel, etc. For the conductive material, carbon materials such as graphite, cokes, carbon black, and acicular carbon can be used, as in non-aqueous solvent-based lithium-ion secondary batteries.
　負極としては、リチウムを含有する材料とリチウムを含有しない材料共に用いることが可能である。例えば、黒鉛、難焼結性炭素等の他、リチウム金属、スズ、シリコン及びこれらを含む合金等や、ＳｉＯ等を用いることができる。これらの負極活物質についても、必要に応じて、上記した導電材、バインダー等を用いて、Ａｌ、Ｃｕ、Ｎｉ、ステンレス、カーボン等からなる負極集電体に担持させることができる。 As the negative electrode, both lithium-containing and lithium-free materials can be used. For example, in addition to graphite and non-sinterable carbon, lithium metal, tin, silicon and alloys containing these, SiO, etc. can be used. These negative electrode active materials can also be supported on a negative electrode current collector made of Al, Cu, Ni, stainless steel, carbon, etc., using the above-mentioned conductive materials, binders, etc., as necessary.
　非水電解質リチウムイオン二次電池及び全固体型リチウムイオン二次電池の形状についても特に限定はなく、円筒型、角型等のいずれであってもよい。 There are no particular limitations on the shape of the non-aqueous electrolyte lithium-ion secondary battery and the all-solid-state lithium-ion secondary battery, and they may be cylindrical, rectangular, etc.
　以下に実施例及び比較例を示して本発明を具体的に説明する。ただし、本発明は、以下の実施例のみに限定されないことは、言うまでもない。 The present invention will be specifically explained below with reference to examples and comparative examples. However, it goes without saying that the present invention is not limited to the following examples.
　実施例１
　市販の硫化リチウム（Ｌｉ２Ｓ）（（株）高純度化学研究所製、型番：ＬＩＩ０６ＰＢ）と硫化鉄（ＦｅＳ）（Ａｌｆａ　Ａｅｓａｒ製、型番：１４０２４）を、モル比がＬｉ２Ｓ：ＦｅＳ＝４：１となるよう、アルゴンガス雰囲気のグローブボックス内（露点－８０℃）で秤量し、乳鉢で充分に混合後、内径１５ｍｍの黒鉛型材に充填した。 Example 1
Commercially available lithium sulfide (Li 2 S) (manufactured by Kojundo Chemical Laboratory Co., Ltd., model number: LII06PB) and iron sulfide (FeS) (manufactured by Alfa Aesar, model number: 14024) were weighed in a glove box (dew point: −80° C.) in an argon gas atmosphere so that the molar ratio was Li 2 S:FeS = 4:1, and then thoroughly mixed in a mortar and filled into a graphite mold material with an inner diameter of 15 mm.
　次いで、原料を充填した黒鉛型材を通電焼結機に収容した。黒鉛型材及び電極部分を含む通電部分については、真空チャンバー内に収容されており、チャンバー内は、真空（約２０Ｐａ）脱気後、高純度アルゴンガス（酸素濃度約０．２ｐｐｍ）を大気圧まで充填した。 The graphite mold filled with the raw materials was then placed in an electric sintering machine. The graphite mold and the electric parts, including the electrode parts, were placed in a vacuum chamber, which was evacuated to a vacuum (approximately 20 Pa) and then filled with high-purity argon gas (oxygen concentration approximately 0.2 ppm) up to atmospheric pressure.
　その後、黒鉛型材に充填された原料を約３０ＭＰａで加圧しながら約６００Ａの直流パルス電流（パルス幅２．５ミリ秒、周期２８．６Ｈｚ）を印加した。黒鉛型材近傍は約２００℃／分の昇温速度で加熱され、パルス電流印加開始３分後に６００℃に到達した。その後、直ちに電流印加及び加圧を停止して自然放冷した。 Then, the raw material packed in the graphite mold was pressurized at approximately 30 MPa while a DC pulse current of approximately 600 A (pulse width 2.5 ms, cycle 28.6 Hz) was applied. The area near the graphite mold was heated at a temperature increase rate of approximately 200°C/min, and reached 600°C 3 minutes after the start of application of the pulse current. The current application and pressure were then immediately stopped and the material was allowed to cool naturally.
　室温（２５℃）まで冷却後、黒鉛治具を露点－８０℃のアルゴンガス雰囲気のグローブボックスに移し、硫化リチウムと硫化鉄との反応物を型材から取り出し、乳鉢で粉砕した後、アルゴンガス雰囲気下でジルコニア製ポットに入れ、フリッチュ・ジャパン株式会社（株）製の遊星ボールミル（型式Ｐ－７）を用い、メカニカルミリング法により、４００ｒｐｍで２０時間処理した。 After cooling to room temperature (25°C), the graphite jig was transferred to a glove box with an argon gas atmosphere with a dew point of -80°C, and the reaction product of lithium sulfide and iron sulfide was removed from the mold and crushed in a mortar. It was then placed in a zirconia pot under an argon gas atmosphere and processed by mechanical milling at 400 rpm for 20 hours using a planetary ball mill (model P-7) manufactured by Fritsch Japan Co., Ltd.
　その後、室温（２５℃）で、Ｌｉ２ＦｅＳ２（市販のＬｉ２ＳとＦｅＳを１：１モル比で混合後、通電焼結機で１０００℃、１分加熱により作製、電気伝導度１０－２Ｓ／ｃｍ（２５℃））を、硫化リチウムと硫化鉄との反応物（Ｌｉ８ＦｅＳ５）：Ｌｉ２ＦｅＳ２＝６：４（質量比）となるように乳鉢で混合し、アルゴンガス雰囲気下でジルコニア製ポットに入れ、フリッチュ・ジャパン株式会社（株）製の遊星ボールミル（型式Ｐ－７）を用い、メカニカルミリング法により、４００ｒｐｍで１時間処理した。 Then, at room temperature (25°C), Li 2 FeS 2 (prepared by mixing commercially available Li 2 S and FeS in a 1:1 molar ratio and then heating in an electric sintering machine at 1000°C for 1 minute, electrical conductivity 10 -2 S/cm (25°C)) was mixed in a mortar to give a reaction product of lithium sulfide and iron sulfide (Li 8 FeS 5 ):Li 2 FeS 2 = 6:4 (mass ratio), placed in a zirconia pot under an argon gas atmosphere, and processed by mechanical milling at 400 rpm for 1 hour using a planetary ball mill (model P-7) manufactured by Fritsch Japan Co., Ltd.
　得られた試料の各元素の比率（原子％）は、Ｌｉ５２％、Ｆｅ１１％、Ｓ３７％であった。なお、得られた試料には、炭素やハロゲンは含まれていなかった。また、得られた試料の電気伝導度を測定するために３００ＭＰａで圧粉成型し電圧印加時の電流値を測定することにより測定したところ、４．４×１０－４Ｓ／ｃｍであり、Ｌｉ２ＦｅＳ２と複合化する前（比較例１）のＬｉ８ＦｅＳ５の電気伝導度である１．１×１０－５Ｓ／ｃｍと比較して劇的に向上していた。 The ratios (atomic %) of each element in the obtained sample were Li 52%, Fe 11%, and S 37%. The obtained sample did not contain carbon or halogen. In addition, the electrical conductivity of the obtained sample was measured by compacting it at 300 MPa and measuring the current value when a voltage was applied, and the result was 4.4×10 −4 S/cm, which was dramatically improved compared to the electrical conductivity of Li 8 FeS 5 before it was composited with Li 2 FeS 2 (Comparative Example 1), which was 1.1×10 −5 S/cm.
　得られた試料のＸ線回折パターンは、図２に示す通り、主相として低結晶性硫化リチウム（Ｌｉ２Ｓ）由来のピークが認められ、それ以外に硫化鉄（ＦｅＳ）由来のピークが認められた。つまり、Ｒｉｅｔｖｅｌｄ解析により見積もられた硫化リチウム（Ｌｉ２Ｓ）の存在比は９６モル％、硫化鉄（ＦｅＳ）の存在比は４モル％であった。また、硫化リチウムの（１１１）面に基づく回折ピークの半価幅から見積もった結晶子サイズは２０ｎｍであった。以上から、本手法により、主相が硫化リチウムであり、その結晶子サイズが５０ｎｍ以下である鉄含有多硫化リチウムが作製できた。 As shown in FIG. 2, the X-ray diffraction pattern of the obtained sample showed a peak derived from low-crystalline lithium sulfide (Li 2 S) as the main phase, and a peak derived from iron sulfide (FeS) was also observed. That is, the abundance ratio of lithium sulfide (Li 2 S) estimated by Rietveld analysis was 96 mol%, and the abundance ratio of iron sulfide (FeS) was 4 mol%. In addition, the crystallite size estimated from the half-width of the diffraction peak based on the (111) plane of lithium sulfide was 20 nm. From the above, by this method, an iron-containing lithium polysulfide in which the main phase is lithium sulfide and the crystallite size is 50 nm or less could be produced.
　得られた鉄含有多硫化リチウムを正極活物質に用い、負極にインジウム金属、電解質にアルジロダイト型硫化物系固体電解質を用いて全固体リチウムイオン二次電池を組み上げ、充放電試験を行った。 The obtained iron-containing lithium polysulfide was used as the positive electrode active material, indium metal was used as the negative electrode, and an argyrodite-type sulfide-based solid electrolyte was used as the electrolyte to assemble an all-solid-state lithium-ion secondary battery, and charge/discharge tests were conducted.
　正極については、上記した鉄含有多硫化リチウムと、アルジロダイト型硫化物系固体電解質と、アセチレンブラックとを、質量比４：５：１で混合して正極合材として用い、正極合材／アルジロダイト型硫化物系固体電解質／リチウムインジウム箔を加圧成型することにより直径１０ｍｍのペレット電池を作製した。これを、３．０Ｖから１．０Ｖまでの範囲内での定電流測定で充電開始により充放電試験を行った。なお、電流密度は、充電においては０．１３ｍＡ／ｃｍ２とし、放電においては０．１３～１．３ｍＡ／ｃｍ２とした。 For the positive electrode, the above-mentioned iron-containing lithium polysulfide, argyrodite-type sulfide-based solid electrolyte, and acetylene black were mixed in a mass ratio of 4:5:1 to form a positive electrode composite, and a pellet battery with a diameter of 10 mm was produced by pressure molding the positive electrode composite/argyrodite-type sulfide-based solid electrolyte/lithium indium foil. A charge/discharge test was performed by starting charging with constant current measurement in the range of 3.0 V to 1.0 V. The current density was 0.13 mA/ cm2 for charging and 0.13 to 1.3 mA/ cm2 for discharging.
　初回（１サイクル目）放電曲線は図３に示すとおり、初回放電容量は、放電電流密度が低電流密度（０．１３ｍＡ／ｃｍ２）の場合で５２０ｍＡｈ／ｇ、０．２５ｍＡ／ｃｍ２の場合で５００ｍＡｈ／ｇ、０．６４ｍＡ／ｃｍ２の場合で４８０ｍＡｈ／ｇ、高電流密度（１．３ｍＡ／ｃｍ２）の場合で４５０ｍＡｈ／ｇであった。つまり、高電流密度（１．３ｍＡ／ｃｍ２）における初回放電容量は、低電流密度（０．１３ｍＡ／ｃｍ２）における初回放電容量の８６％という高い値を示し、容量及びレート特性に優れた正極活物質が得られたことが理解できる。 As shown in Fig. 3, the initial discharge capacity was 520mAh/g when the discharge current density was low (0.13mA/ cm2 ), 500mAh/g when it was 0.25mA/ cm2 , 480mAh/g when it was 0.64mA/ cm2 , and 450mAh/g when it was high current density (1.3mA/ cm2 ). In other words, the initial discharge capacity at high current density (1.3mA/ cm2 ) was as high as 86% of the initial discharge capacity at low current density (0.13mA/ cm2 ), and it can be understood that a positive electrode active material with excellent capacity and rate characteristics was obtained.
　実施例２
　硫化リチウムと硫化鉄との反応物（Ｌｉ８ＦｅＳ５）と、Ｌｉ２ＦｅＳ２とのメカニカルミリング時間を２時間とする他は、実施例１と同様に、鉄含有多硫化リチウムを得た。 Example 2
An iron-containing lithium polysulfide was obtained in the same manner as in Example 1, except that the mechanical milling time of the reaction product of lithium sulfide and iron sulfide (Li 8 FeS 5 ) and Li 2 FeS 2 was set to 2 hours.
　得られた試料の各元素の比率（原子％）は、Ｌｉ５２％、Ｆｅ１１％、Ｓ３７％であった。なお、得られた試料には、炭素やハロゲンは含まれていなかった。また、得られた試料の電気伝導度を測定するために粉末を３００ＭＰａで圧粉成型し、電圧印加時の電流値を測定することにより測定したところ、４．０×１０－４Ｓ／ｃｍであり、Ｌｉ２ＦｅＳ２と複合化する前（比較例１）のＬｉ８ＦｅＳ５の電気伝導度である１．１×１０－５Ｓ／ｃｍと比較して劇的に向上していた。 The ratios (atomic %) of each element in the obtained sample were Li 52%, Fe 11%, and S 37%. The obtained sample did not contain carbon or halogen. In order to measure the electrical conductivity of the obtained sample, the powder was compressed at 300 MPa and the current value when a voltage was applied was measured, which was 4.0×10 −4 S/cm, which was dramatically improved compared to the electrical conductivity of Li 8 FeS 5 before being composited with Li 2 FeS 2 (Comparative Example 1), which was 1.1×10 −5 S/cm.
　得られた試料のＸ線回折パターンは、図２に示す通り、主相として低結晶性硫化リチウム（Ｌｉ２Ｓ）由来のピークが認められ、それ以外に硫化鉄（ＦｅＳ）由来のピークが認められた。つまり、Ｒｉｅｔｖｅｌｄ解析により見積もられた硫化リチウム（Ｌｉ２Ｓ）の存在比は９１モル％、硫化鉄（ＦｅＳ）の存在比は９モル％であった。また、硫化リチウムの（１１１）面に基づく回折ピークの半価幅から見積もった結晶子サイズは１８ｎｍであった。以上から、本手法により、主相が硫化リチウムであり、その結晶子サイズが５０ｎｍ以下である鉄含有多硫化リチウムが作製できた。 As shown in FIG. 2, the X-ray diffraction pattern of the obtained sample showed a peak derived from low-crystalline lithium sulfide (Li 2 S) as the main phase, and a peak derived from iron sulfide (FeS) was also observed. That is, the abundance ratio of lithium sulfide (Li 2 S) estimated by Rietveld analysis was 91 mol %, and the abundance ratio of iron sulfide (FeS) was 9 mol %. In addition, the crystallite size estimated from the half-width of the diffraction peak based on the (111) plane of lithium sulfide was 18 nm. From the above, by this method, an iron-containing lithium polysulfide in which the main phase is lithium sulfide and the crystallite size is 50 nm or less could be produced.
　得られた鉄含有多硫化リチウムを正極活物質に用い、負極にインジウム金属、電解質にアルジロダイト型硫化物系固体電解質を用いて全固体リチウムイオン二次電池を組み上げ、充放電試験を行った。 The obtained iron-containing lithium polysulfide was used as the positive electrode active material, indium metal was used as the negative electrode, and an argyrodite-type sulfide-based solid electrolyte was used as the electrolyte to assemble an all-solid-state lithium-ion secondary battery, and charge/discharge tests were conducted.
　正極については、上記した鉄含有多硫化リチウムと、アルジロダイト型硫化物系固体電解質と、アセチレンブラックとを、質量比４：５：１で混合して正極合材として用い、正極合材／アルジロダイト型硫化物系固体電解質／リチウムインジウム箔を加圧成型することにより直径１０ｍｍのペレット電池を作製した。これを、３．０Ｖから１．０Ｖまでの範囲内での定電流測定で充電開始により充放電試験を行った。なお、電流密度は、充電においては０．１３ｍＡ／ｃｍ２とし、放電においては０．１３～１．３ｍＡ／ｃｍ２とした。 For the positive electrode, the above-mentioned iron-containing lithium polysulfide, argyrodite-type sulfide-based solid electrolyte, and acetylene black were mixed in a mass ratio of 4:5:1 to form a positive electrode composite, and a pellet battery with a diameter of 10 mm was produced by pressure molding the positive electrode composite/argyrodite-type sulfide-based solid electrolyte/lithium indium foil. A charge/discharge test was performed by starting charging with constant current measurement in the range of 3.0 V to 1.0 V. The current density was 0.13 mA/ cm2 for charging and 0.13 to 1.3 mA/ cm2 for discharging.
　初回（１サイクル目）放電曲線は図３に示すとおり、初回放電容量は、放電電流密度が低電流密度（０．１３ｍＡ／ｃｍ２）の場合で５１０ｍＡｈ／ｇ、０．２５ｍＡ／ｃｍ２の場合で５００ｍＡｈ／ｇ、０．６４ｍＡ／ｃｍ２の場合で４８０ｍＡｈ／ｇ、高電流密度（１．３ｍＡ／ｃｍ２）の場合で４５０ｍＡｈ／ｇであった。つまり、高電流密度（１．３ｍＡ／ｃｍ２）における初回放電容量は、低電流密度（０．１３ｍＡ／ｃｍ２）における初回放電容量の８８％という高い値を示し、容量及びレート特性に優れた正極活物質が得られたことが理解できる。 As shown in Fig. 3, the initial discharge capacity was 510 mAh/g when the discharge current density was low (0.13 mA/ cm2 ), 500 mAh/g when it was 0.25 mA/ cm2 , 480 mAh/g when it was 0.64 mA/ cm2 , and 450 mAh/g when it was high current density (1.3 mA/ cm2 ). In other words, the initial discharge capacity at high current density (1.3 mA/ cm2 ) was as high as 88% of the initial discharge capacity at low current density (0.13 mA/ cm2 ), and it can be understood that a positive electrode active material excellent in capacity and rate characteristics was obtained.
　比較例１
　硫化リチウムと硫化鉄との反応物（Ｌｉ８ＦｅＳ５）に対して、Ｌｉ２ＦｅＳ２を添加せず、また、その後のメカニカルミリング処理を行わなかったこと以外は実施例１と同様に、鉄含有多硫化リチウムを得た。具体的には、以下のとおり、鉄含有多硫化リチウムを得た。 Comparative Example 1
An iron-containing lithium polysulfide was obtained in the same manner as in Example 1, except that Li2FeS2 was not added to the reaction product ( Li8FeS5 ) of lithium sulfide and iron sulfide , and the subsequent mechanical milling treatment was not performed. Specifically, an iron-containing lithium polysulfide was obtained as follows.
　市販の硫化リチウム（Ｌｉ２Ｓ）（（株）高純度化学研究所製、型番：ＬＩＩ０６ＰＢ）と硫化鉄（ＦｅＳ）（Ａｌｆａ　Ａｅｓａｒ製、型番：１４０２４）を、モル比がＬｉ２Ｓ：ＦｅＳ＝４：１となるよう、アルゴンガス雰囲気のグローブボックス内（露点－８０℃）で秤量し、乳鉢で充分に混合後、内径１５ｍｍの黒鉛型材に充填した。 Commercially available lithium sulfide (Li 2 S) (manufactured by Kojundo Chemical Laboratory Co., Ltd., model number: LII06PB) and iron sulfide (FeS) (manufactured by Alfa Aesar, model number: 14024) were weighed in a glove box (dew point: −80° C.) in an argon gas atmosphere so that the molar ratio was Li 2 S:FeS = 4:1, and then thoroughly mixed in a mortar and filled into a graphite mold material with an inner diameter of 15 mm.
　次いで、原料を充填した黒鉛型材を通電焼結機に収容した。黒鉛型材及び電極部分を含む通電部分については、真空チャンバー内に収容されており、チャンバー内は、真空（約２０Ｐａ）脱気後、高純度アルゴンガス（酸素濃度約０．２ｐｐｍ）を大気圧まで充填した。 The graphite mold filled with the raw materials was then placed in an electric sintering machine. The graphite mold and the electric parts, including the electrode parts, were placed in a vacuum chamber, which was evacuated to a vacuum (approximately 20 Pa) and then filled with high-purity argon gas (oxygen concentration approximately 0.2 ppm) up to atmospheric pressure.
　その後、黒鉛型材に充填された原料を約３０ＭＰａで加圧しながら約６００Ａの直流パルス電流（パルス幅２．５ミリ秒、周期２８．６Ｈｚ）を印加した。黒鉛型材近傍は約２００℃／分の昇温速度で加熱され、パルス電流印加開始３分後に６００℃に到達した。その後、直ちに電流印加及び加圧を停止して自然放冷した。 Then, the raw material packed into the graphite mold was pressurized at approximately 30 MPa while a DC pulse current of approximately 600 A (pulse width 2.5 ms, cycle 28.6 Hz) was applied. The area near the graphite mold was heated at a temperature increase rate of approximately 200°C/min, and reached 600°C 3 minutes after the start of application of the pulse current. The current application and pressure were then immediately stopped and the material was allowed to cool naturally.
　室温（２５℃）まで冷却後、黒鉛治具を露点－８０℃のアルゴンガス雰囲気のグローブボックスに移し、硫化リチウムと硫化鉄との反応物を型材から取り出し、乳鉢で粉砕した後、アルゴンガス雰囲気下でジルコニア製ポットに入れ、フリッチュ・ジャパン株式会社（株）製の遊星ボールミル（型式Ｐ－７）を用い、メカニカルミリング法により、４００ｒｐｍで２０時間処理した。 After cooling to room temperature (25°C), the graphite jig was transferred to a glove box with an argon gas atmosphere with a dew point of -80°C, and the reaction product of lithium sulfide and iron sulfide was removed from the mold and crushed in a mortar. It was then placed in a zirconia pot under an argon gas atmosphere and processed by mechanical milling at 400 rpm for 20 hours using a planetary ball mill (model P-7) manufactured by Fritsch Japan Co., Ltd.
　得られた試料の各元素の比率（原子％）は、Ｌｉ５７％、Ｆｅ７％、Ｓ３６％であった。なお、得られた試料には、炭素やハロゲンは含まれていなかった。また、得られた試料の電気伝導度を測定するために粉末を３００ＭＰａで圧粉成型し、電圧印加で電流値を測定することにより測定したところ、１．１×１０－５Ｓ／ｃｍと実施例１～２と比較して低い値であった。 The ratios (atomic %) of each element in the obtained sample were Li 57%, Fe 7%, and S 36%. The obtained sample did not contain carbon or halogens. In order to measure the electrical conductivity of the obtained sample, the powder was compressed at 300 MPa and the current value was measured by applying a voltage, resulting in a value of 1.1×10 −5 S/cm, which was lower than that of Examples 1 and 2.
　得られた試料のＸ線回折パターンは、図２に示す通り、主相として低結晶性硫化リチウム（Ｌｉ２Ｓ）由来のピークからなり、それ以外にピークは認められなかった。つまり、Ｒｉｅｔｖｅｌｄ解析により見積もられた硫化リチウム（Ｌｉ２Ｓ）の存在比は１００モル％であった。また、硫化リチウムの（１１１）面に基づく回折ピークの半価幅から見積もった結晶子サイズは２６ｎｍであった。 As shown in Fig. 2, the X-ray diffraction pattern of the obtained sample was composed of peaks derived from low-crystalline lithium sulfide (Li 2 S) as the main phase, and no other peaks were observed. In other words, the abundance ratio of lithium sulfide (Li 2 S) estimated by Rietveld analysis was 100 mol %. In addition, the crystallite size estimated from the half-width of the diffraction peak based on the (111) plane of lithium sulfide was 26 nm.
　得られた鉄含有多硫化リチウムを正極活物質に用い、負極にインジウム金属、電解質にアルジロダイト型硫化物系固体電解質を用いて全固体リチウムイオン二次電池を組み上げ、充放電試験を行った。 The obtained iron-containing lithium polysulfide was used as the positive electrode active material, indium metal was used as the negative electrode, and an argyrodite-type sulfide-based solid electrolyte was used as the electrolyte to assemble an all-solid-state lithium-ion secondary battery, and charge/discharge tests were conducted.
　正極については、上記した鉄含有多硫化リチウムと、アルジロダイト型硫化物系固体電解質と、アセチレンブラックとを、質量比４：５：１で混合して正極合材として用い、正極合材／アルジロダイト型硫化物系固体電解質／リチウムインジウム箔を加圧成型することにより直径１０ｍｍのペレット電池を作製した。これを、３．０Ｖから１．０Ｖまでの範囲内での定電流測定で充電開始により充放電試験を行った。なお、電流密度は、充電においては０．１３ｍＡ／ｃｍ２とし、放電においては０．１３～１．３ｍＡ／ｃｍ２とした。 For the positive electrode, the above-mentioned iron-containing lithium polysulfide, argyrodite-type sulfide-based solid electrolyte, and acetylene black were mixed in a mass ratio of 4:5:1 to form a positive electrode composite, and a pellet battery with a diameter of 10 mm was produced by pressure molding the positive electrode composite/argyrodite-type sulfide-based solid electrolyte/lithium indium foil. A charge/discharge test was performed by starting charging with constant current measurement in the range of 3.0 V to 1.0 V. The current density was 0.13 mA/ cm2 for charging and 0.13 to 1.3 mA/ cm2 for discharging.
　初回放電曲線は図３に示すとおり、初回放電容量は、放電電流密度が低電流密度（０．１３ｍＡ／ｃｍ２）の場合で４９０ｍＡｈ／ｇ、０．２５ｍＡ／ｃｍ２の場合で４３０ｍＡｈ／ｇ、０．６４ｍＡ／ｃｍ２の場合で２８０ｍＡｈ／ｇ、高電流密度（１．３ｍＡ／ｃｍ２）の場合で１４０ｍＡｈ／ｇであった。つまり、高電流密度（１．３ｍＡ／ｃｍ２）における初回放電容量は、低電流密度（０．１３ｍＡ／ｃｍ２）における初回放電容量の２８％しか得られず、特にレート特性に優れた正極活物質は得られなかった。 As shown in Fig. 3, the initial discharge capacity was 490mAh/g when the discharge current density was low (0.13mA/ cm2 ), 430mAh/g when it was 0.25mA/ cm2 , 280mAh/g when it was 0.64mA/ cm2 , and 140mAh/g when it was high current density (1.3mA/ cm2 ). In other words, the initial discharge capacity at high current density (1.3mA/ cm2 ) was only 28% of the initial discharge capacity at low current density (0.13mA/ cm2 ), and a positive electrode active material with particularly excellent rate characteristics was not obtained.
　比較例２
　硫化リチウムと硫化鉄との反応物（Ｌｉ８ＦｅＳ５）とＬｉ２ＦｅＳ２とのメカニカルミリング時間を０時間とする（硫化リチウムと硫化鉄との反応物（Ｌｉ８ＦｅＳ５）とＬｉ２ＦｅＳ２とを混合するが、メカニカルミリング処理を行わない）こと以外は実施例１と同様に、鉄含有多硫化リチウムを得た。 Comparative Example 2
An iron-containing lithium polysulfide was obtained in the same manner as in Example 1, except that the mechanical milling time of the reaction product of lithium sulfide and iron sulfide (Li 8 FeS 5 ) and Li 2 FeS 2 was set to 0 hours (the reaction product of lithium sulfide and iron sulfide (Li 8 FeS 5 ) and Li 2 FeS 2 were mixed, but the mechanical milling process was not performed).
　得られた試料の各元素の比率（原子％）は、Ｌｉ５２％、Ｆｅ１１％、Ｓ３７％であった。なお、得られた試料には、炭素やハロゲンは含まれていなかった。また、得られた試料の電気伝導度を測定するために粉末を３００ＭＰａで圧粉成型し、電圧印加で電流値を測定することにより測定したところ、１．０×１０－５Ｓ／ｃｍと実施例１～２と比較して低い値であった。 The ratios (atomic %) of each element in the obtained sample were Li 52%, Fe 11%, and S 37%. The obtained sample did not contain carbon or halogens. In order to measure the electrical conductivity of the obtained sample, the powder was compressed at 300 MPa and the current value was measured by applying a voltage, resulting in a value of 1.0×10 −5 S/cm, which was lower than that of Examples 1 and 2.
　得られた試料のＸ線回折パターンは、図２に示す通り、低結晶性硫化リチウム（Ｌｉ２Ｓ）及び低結晶性Ｌｉ２ＦｅＳ２からなるものであった。つまり、Ｒｉｅｔｖｅｌｄ解析により見積もられた硫化リチウム（Ｌｉ２Ｓ）の存在比は８６モル％、Ｌｉ２ＦｅＳ２の存在比は１４モル％であった。また、硫化リチウムの（１１１）面に基づく回折ピークの半価幅から見積もった結晶子サイズは２６ｎｍであった。 The X-ray diffraction pattern of the obtained sample was composed of low-crystalline lithium sulfide (Li 2 S) and low-crystalline Li 2 FeS 2 , as shown in Figure 2. That is, the abundance ratio of lithium sulfide (Li 2 S) estimated by Rietveld analysis was 86 mol%, and the abundance ratio of Li 2 FeS 2 was 14 mol%. In addition, the crystallite size estimated from the half-width of the diffraction peak based on the (111) plane of lithium sulfide was 26 nm.
　得られた鉄含有多硫化リチウムを正極活物質に用い、負極にインジウム金属、電解質にアルジロダイト型硫化物系固体電解質を用いて全固体リチウムイオン二次電池を組み上げ、充放電試験を行った。 The obtained iron-containing lithium polysulfide was used as the positive electrode active material, indium metal was used as the negative electrode, and an argyrodite-type sulfide-based solid electrolyte was used as the electrolyte to assemble an all-solid-state lithium-ion secondary battery, and charge/discharge tests were conducted.
　正極については、上記した鉄含有多硫化リチウムと、アルジロダイト型硫化物系固体電解質と、アセチレンブラックとを、質量比４：５：１で混合して正極合材として用い、正極合材／アルジロダイト型硫化物系固体電解質／リチウムインジウム箔を加圧成型することにより直径１０ｍｍのペレット電池を作製した。これを、初期電圧から１．０Ｖまでの範囲内での定電流測定で充電開始により充放電試験を行った。なお、電流密度は、充電においては０．１３ｍＡ／ｃｍ２とし、放電においては０．１３～１．３ｍＡ／ｃｍ２とした。 For the positive electrode, the above-mentioned iron-containing lithium polysulfide, argyrodite-type sulfide-based solid electrolyte, and acetylene black were mixed in a mass ratio of 4:5:1 to form a positive electrode composite, and a pellet battery with a diameter of 10 mm was produced by pressure molding the positive electrode composite/argyrodite-type sulfide-based solid electrolyte/lithium indium foil. A charge/discharge test was performed by starting charging with a constant current measurement in the range from the initial voltage to 1.0 V. The current density was 0.13 mA/ cm2 for charging and 0.13 to 1.3 mA/ cm2 for discharging.
　初回（１サイクル目）放電曲線は図３に示すとおり、初回放電容量は、放電電流密度が低電流密度（０．１３ｍＡ／ｃｍ２）の場合で４７０ｍＡｈ／ｇ、０．２５ｍＡ／ｃｍ２の場合で４１０ｍＡｈ／ｇ、０．６４ｍＡ／ｃｍ２の場合で３８０ｍＡｈ／ｇ、高電流密度（１．３ｍＡ／ｃｍ２）の場合で２５０ｍＡｈ／ｇであった。つまり、高電流密度（１．３ｍＡ／ｃｍ２）における初回放電容量は、低電流密度（０．１３ｍＡ／ｃｍ２）における初回放電容量の５４％しか得られず、特にレート特性に優れた正極活物質は得られなかった。 As shown in Fig. 3, the initial discharge capacity was 470 mAh/g when the discharge current density was low (0.13 mA/ cm2 ), 410 mAh/g when it was 0.25 mA/ cm2 , 380 mAh/g when it was 0.64 mA/ cm2 , and 250 mAh/g when it was high current density (1.3 mA/ cm2 ). In other words, the initial discharge capacity at high current density (1.3 mA/ cm2 ) was only 54% of the initial discharge capacity at low current density (0.13 mA/ cm2 ), and a positive electrode active material with particularly excellent rate characteristics was not obtained.
　実施例３
　市販の硫化リチウム（Ｌｉ２Ｓ）（（株）高純度化学研究所製、型番：ＬＩＩ０６ＰＢ）と硫化鉄（ＦｅＳ）（Ａｌｆａ　Ａｅｓａｒ製、型番：１４０２４）を、モル比がＬｉ２Ｓ：ＦｅＳ＝５：１となるよう、アルゴンガス雰囲気のグローブボックス内（露点－８０℃）で秤量し、乳鉢で充分に混合後、内径１５ｍｍの黒鉛型材に充填した。 Example 3
Commercially available lithium sulfide (Li 2 S) (manufactured by Kojundo Chemical Laboratory Co., Ltd., model number: LII06PB) and iron sulfide (FeS) (manufactured by Alfa Aesar, model number: 14024) were weighed in a glove box (dew point: −80° C.) in an argon gas atmosphere so that the molar ratio was Li 2 S:FeS = 5:1, and then thoroughly mixed in a mortar and filled into a graphite mold material with an inner diameter of 15 mm.
　次いで、原料を充填した黒鉛型材を通電焼結機に収容した。黒鉛型材及び電極部分を含む通電部分については、真空チャンバー内に収容されており、チャンバー内は、真空（約２０Ｐａ）脱気後、高純度アルゴンガス（酸素濃度約０．２ｐｐｍ）を大気圧まで充填した。 The graphite mold filled with the raw materials was then placed in an electric sintering machine. The graphite mold and the electric parts, including the electrode parts, were placed in a vacuum chamber, which was evacuated to a vacuum (approximately 20 Pa) and then filled with high-purity argon gas (oxygen concentration approximately 0.2 ppm) up to atmospheric pressure.
　その後、黒鉛型材に充填された原料を約３０ＭＰａで加圧しながら約６００Ａの直流パルス電流（パルス幅２．５ミリ秒、周期２８．６Ｈｚ）を印加した。黒鉛型材近傍は約２００℃／分の昇温速度で加熱され、パルス電流印加開始３分後に６００℃に到達した。その後、直ちに電流印加及び加圧を停止して自然放冷しＬｉ１０ＦｅＳ６を作製した。 Then, the raw material filled in the graphite mold was pressurized at about 30 MPa while applying a DC pulse current of about 600 A (pulse width 2.5 milliseconds, period 28.6 Hz). The vicinity of the graphite mold was heated at a temperature increase rate of about 200°C/min, and reached 600°C 3 minutes after the start of the pulse current application. Then, the current application and pressure were immediately stopped and the mixture was allowed to cool naturally to produce Li10FeS6 .
　室温（２５℃）まで冷却後、黒鉛治具を露点－８０℃のアルゴンガス雰囲気のグローブボックスに移し、硫化リチウムと硫化鉄との反応物（Ｌｉ１０ＦｅＳ６）を型材から取り出し、Ｌｉ２ＦｅＳ２（市販のＬｉ２ＳとＦｅＳを１：１モル比で混合後、通電焼結機で１０００℃、１分加熱により作製、電気伝導度１０－２Ｓ／ｃｍ（２５℃））を、Ｌｉ１０ＦｅＳ６：Ｌｉ２ＦｅＳ２＝８：２（質量比）となるように乳鉢で混合し、アルゴンガス雰囲気下でジルコニア製ポットに入れ、フリッチュ・ジャパン株式会社（株）製の遊星ボールミル（型式Ｐ－７）を用い、メカニカルミリング法により、４００ｒｐｍで２時間メカニカルミリング処理して試料を得た。 After cooling to room temperature (25°C), the graphite jig was transferred to a glove box in an argon gas atmosphere with a dew point of -80°C, and the reaction product of lithium sulfide and iron sulfide (Li 10 FeS 6 ) was removed from the mold material. Li 2 FeS 2 (prepared by mixing commercially available Li 2 S and FeS in a 1:1 molar ratio and then heating at 1000°C for 1 minute in an electric sintering machine, electrical conductivity 10 -2 S/cm (25°C)) was mixed in a mortar to Li 10 FeS 6 :Li 2 FeS 2 = 8:2 (mass ratio), placed in a zirconia pot under an argon gas atmosphere, and mechanically milled for 2 hours at 400 rpm using a planetary ball mill (model P-7) manufactured by Fritsch Japan Co., Ltd. to obtain a sample.
　得られた試料の各元素の比率（原子％）は、Ｌｉ５６％、Ｆｅ８％、Ｓ３６％であった。なお、得られた試料には、炭素やハロゲンは含まれていなかった。 The ratio (atomic %) of each element in the obtained sample was Li 56%, Fe 8%, and S 36%. The obtained sample did not contain carbon or halogens.
　得られた試料のＸ線回折パターンは、図４に示す通り、低結晶性硫化リチウム（Ｌｉ２Ｓ）及び硫化鉄（ＦｅＳ）から成り、Ｒｉｅｔｖｅｌｄ解析から求めた硫化リチウム（Ｌｉ２Ｓ）の存在比は９４モル％、ＦｅＳの存在比は６モル％であった。また、硫化リチウムの（１１１）面に基づく回折ピークの半値幅から算出される結晶子サイズは２３ｎｍであった。 The X-ray diffraction pattern of the obtained sample was composed of low-crystalline lithium sulfide (Li 2 S) and iron sulfide (FeS) as shown in Fig. 4, and the abundance ratio of lithium sulfide (Li 2 S) was 94 mol % and the abundance ratio of FeS was 6 mol % as determined by Rietveld analysis. The crystallite size calculated from the half-width of the diffraction peak based on the (111) plane of lithium sulfide was 23 nm.
　得られた鉄含有多硫化リチウムを正極活物質に用い、負極にインジウム金属、電解質にアルジロダイト型硫化物系固体電解質を用いて全固体リチウムイオン二次電池を組み上げ、充放電試験を行った。 The obtained iron-containing lithium polysulfide was used as the positive electrode active material, indium metal was used as the negative electrode, and an argyrodite-type sulfide-based solid electrolyte was used as the electrolyte to assemble an all-solid-state lithium-ion secondary battery, and charge/discharge tests were conducted.
　正極については、上記した鉄含有多硫化リチウムと、アルジロダイト型硫化物系固体電解質と、アセチレンブラックとを、質量比４：５：１で混合して正極合材として用い、正極合材／アルジロダイト型硫化物系固体電解質／リチウムインジウム箔を加圧成型することにより直径１０ｍｍのペレット電池を作製した。これを、１．０～３．０Ｖの範囲内での定電流測定で充電開始により充放電試験を行った。なお、電流密度は、充電については０．１３ｍＡ／ｃｍ２、放電については０．１３～１．３ｍＡ／ｃｍ２とした。 For the positive electrode, the above-mentioned iron-containing lithium polysulfide, argyrodite-type sulfide-based solid electrolyte, and acetylene black were mixed in a mass ratio of 4:5:1 to form a positive electrode composite, and a pellet battery with a diameter of 10 mm was fabricated by pressure molding the positive electrode composite/argyrodite-type sulfide-based solid electrolyte/lithium indium foil. A charge/discharge test was performed by starting charging with constant current measurement in the range of 1.0 to 3.0 V. The current density was 0.13 mA/cm 2 for charging and 0.13 to 1.3 mA/cm 2 for discharging.
　初回（１サイクル目）放電曲線は図５に示す通り、初回放電容量は、放電電流密度が低電流密度（０．１３ｍＡ／ｃｍ２）において約６２０ｍＡｈ／ｇ、０．２５ｍＡ／ｃｍ２において約５４０ｍＡｈ／ｇ、０．６４ｍＡ／ｃｍ２において約５１０ｍＡｈ／ｇ、高電流密度（１．３ｍＡ／ｃｍ２）において約４３０ｍＡｈ／ｇの放電容量が得られた。すなわち、高電流密度（１．３ｍＡ／ｃｍ２）での放電容量は低電流密度（０．１３ｍＡ／ｃｍ２）での約７０％もの高い値を示し、レート特性に優れた電極材料が得られた。 As shown in Fig. 5, the initial discharge capacity was about 620 mAh/g at a low discharge current density (0.13 mA/ cm2 ), about 540 mAh/g at 0.25 mA/ cm2 , about 510 mAh/g at 0.64 mA/ cm2 , and about 430 mAh/g at a high current density (1.3 mA/ cm2 ). That is, the discharge capacity at a high current density (1.3 mA/ cm2 ) was as high as about 70% of that at a low current density (0.13 mA/ cm2 ), and an electrode material with excellent rate characteristics was obtained.
　比較例３
　硫化リチウムと硫化鉄との反応物（Ｌｉ１０ＦｅＳ６）とＬｉ２ＦｅＳ２とのメカニカルミリング時間を０時間とする（硫化リチウムと硫化鉄との反応物（Ｌｉ１０ＦｅＳ６）とＬｉ２ＦｅＳ２とを混合するが、メカニカルミリング処理を行わない）こと以外は実施例３と全く同様にして試料を作製した。 Comparative Example 3
A sample was prepared in exactly the same manner as in Example 3, except that the mechanical milling time of the reaction product of lithium sulfide and iron sulfide (Li 10 FeS 6 ) and Li 2 FeS 2 was 0 hours (the reaction product of lithium sulfide and iron sulfide (Li 10 FeS 6 ) and Li 2 FeS 2 were mixed, but mechanical milling was not performed).
　得られた試料の各元素の比率（原子％）は、実施例３と同様、Ｌｉ５６％、Ｆｅ８％、Ｓ３６％であった。なお、得られた試料には、炭素やハロゲンは含まれていなかった。 The ratios (atomic %) of each element in the obtained sample were Li 56%, Fe 8%, and S 36%, the same as in Example 3. The obtained sample did not contain carbon or halogens.
　得られた試料のＸ線回折パターンは、図４に示す通り、結晶性硫化リチウム（Ｌｉ２Ｓ）及び結晶性Ｌｉ２ＦｅＳ２から成り、Ｒｉｅｔｖｅｌｄ解析から求めた硫化リチウム（Ｌｉ２Ｓ）の存在比は８７モル％、Ｌｉ２ＦｅＳ２の存在比は１３モル％であった。また、硫化リチウムの（１１１）面に基づく回折ピークの半値幅から算出される結晶子サイズは１０６ｎｍであった。 The X-ray diffraction pattern of the obtained sample was composed of crystalline lithium sulfide (Li 2 S) and crystalline Li 2 FeS 2 , and the abundance ratio of lithium sulfide (Li 2 S) obtained by Rietveld analysis was 87 mol %, and the abundance ratio of Li 2 FeS 2 was 13 mol %. In addition, the crystallite size calculated from the half width of the diffraction peak based on the (111) plane of lithium sulfide was 106 nm.
　得られた複合体粉末を実施例３と同様にして全固体電池に組み上げて充放電試験を行った。初回（１サイクル目）放電曲線は図５に示す通りで、初回放電容量は、放電電流密度が低電流密度（０．１３ｍＡ／ｃｍ２）において約１５０ｍＡｈ／ｇの低い放電容量しか得られず、電流密度０．２５ｍＡ／ｃｍ２においては約１４０ｍＡｈ／ｇ、０．６４ｍＡ／ｃｍ２においては約１３０ｍＡｈ／ｇ、高電流密度（１．３ｍＡ／ｃｍ２）においては約１２０ｍＡｈ／ｇといずれも低い放電容量しか得られず、Ｌｉ１０ＦｅＳ６にＬｉ２ＦｅＳ２を混合するのみでは容量及びレート特性の双方に優れた電極材料が得られないことが分かった。 The obtained composite powder was assembled into an all-solid-state battery in the same manner as in Example 3, and a charge/discharge test was performed. The initial (first cycle) discharge curve is shown in Fig. 5, and the initial discharge capacity was only a low discharge capacity of about 150 mAh/g at a low discharge current density (0.13 mA/ cm2 ), about 140 mAh/g at a current density of 0.25 mA/ cm2 , about 130 mAh/g at a current density of 0.64 mA/ cm2 , and about 120 mAh/ g at a high current density (1.3 mA/ cm2 ). It was found that an electrode material excellent in both capacity and rate characteristics cannot be obtained by simply mixing Li10FeS6 with Li2FeS2 .
　実施例４
　市販の硫化リチウム（Ｌｉ２Ｓ）（（株）高純度化学研究所製、型番：ＬＩＩ０６ＰＢ）と硫化鉄（ＦｅＳ）（Ａｌｆａ　Ａｅｓａｒ製、型番：１４０２４）を、モル比がＬｉ２Ｓ：ＦｅＳ＝５：１となるよう、アルゴンガス雰囲気のグローブボックス内（露点－８０℃）で秤量し、乳鉢で充分に混合後、室温（２５℃）で、Ｍｏ６Ｓ８（ＭｏＳ２、Ｍｏ、ＣｕＳをモル比３：３：２で混合した粉をアルゴンガス雰囲気下、１０００℃で熱処理することによりＣｕ２Ｍｏ６Ｓ８を合成し、これを５ｍｏｌ／ＬのＨＣｌに１時間浸漬してＣｕを溶出させることによりＭｏ６Ｓ８を作製）を、硫化リチウムと硫化鉄との反応物：Ｍｏ６Ｓ８＝８：２（質量比）となるように乳鉢で混合し、アルゴンガス雰囲気下でジルコニア製ポットに入れ、フリッチュ・ジャパン株式会社（株）製の遊星ボールミル（型式Ｐ－７）を用い、メカニカルミリング法により、４００ｒｐｍで４０時間処理した。 Example 4
Commercially available lithium sulfide (Li 2 S) (manufactured by Kojundo Chemical Laboratory Co., Ltd., model number: LII06PB) and iron sulfide (FeS) (manufactured by Alfa Aesar, model number: 14024) were weighed out in a glove box (dew point -80°C) in an argon gas atmosphere so that the molar ratio was Li 2 S:FeS = 5:1, and then mixed thoroughly in a mortar. The mixture was then quenched at room temperature (25°C) to produce Mo 6 S 8 (Cu 2 Mo 6 S 8 was synthesized by heat treating a powder of MoS 2 , Mo, and CuS mixed in a molar ratio of 3:3:2 at 1000°C under an argon gas atmosphere, and this was then immersed in 5 mol/L HCl for 1 hour to dissolve Cu to produce Mo 6 S 8 ), which was then used to prepare a reaction product of lithium sulfide and iron sulfide: Mo 6 S 8. The mixture was mixed in a mortar so that the ratio of the powder to the powder was 8:2 (mass ratio), placed in a zirconia pot under an argon gas atmosphere, and processed by mechanical milling at 400 rpm for 40 hours using a planetary ball mill (model P-7) manufactured by Fritsch Japan Co., Ltd.
　得られた試料の各元素の比率（原子％）は、Ｌｉ５５％、Ｆｅ５％、Ｓ３７％、Ｍｏ３％であった。なお、得られた試料には、炭素やハロゲンは含まれていなかった。また、得られた試料の電気伝導度を測定するために粉末を３００ＭＰａで圧粉成型し、電圧印加で電流値を測定することにより測定したところ、３．５×１０－４Ｓ／ｃｍであり、メカニカルミリング処理を施さない比較例４の電気伝導度である１０－８Ｓ／ｃｍ未満（測定不能）と比較して劇的に向上していた。 The ratios (atomic %) of each element in the obtained sample were Li 55%, Fe 5%, S 37%, and Mo 3%. The obtained sample did not contain carbon or halogen. In order to measure the electrical conductivity of the obtained sample, the powder was compressed at 300 MPa and the current value was measured by applying a voltage, which was 3.5×10 −4 S/cm, which was dramatically improved compared to the electrical conductivity of Comparative Example 4, which was not subjected to mechanical milling, which was less than 10 −8 S/cm (immeasurable).
　得られた試料のＸ線回折パターンは、図６に示す通り、主相として低結晶性硫化リチウム（Ｌｉ２Ｓ）由来のピークが認められ、それ以外に硫化鉄（ＦｅＳ）由来のピークが認められなかった。つまり、Ｒｉｅｔｖｅｌｄ解析により見積もられた硫化リチウム（Ｌｉ２Ｓ）の存在比は１００モル％であった。また、硫化リチウムの（１１１）面に基づく回折ピークの半値幅から算出される結晶子サイズは１７ｎｍであった。 As shown in Fig. 6, the X-ray diffraction pattern of the obtained sample showed a peak derived from low-crystalline lithium sulfide (Li 2 S) as the main phase, and no peak derived from iron sulfide (FeS) was observed. In other words, the abundance ratio of lithium sulfide (Li 2 S) estimated by Rietveld analysis was 100 mol%. In addition, the crystallite size calculated from the half-width of the diffraction peak based on the (111) plane of lithium sulfide was 17 nm.
　得られた鉄含有多硫化リチウムを正極活物質に用い、負極にインジウム金属、電解質にアルジロダイト型硫化物系固体電解質を用いて全固体リチウムイオン二次電池を組み上げ、充放電試験を行った。 The obtained iron-containing lithium polysulfide was used as the positive electrode active material, indium metal was used as the negative electrode, and an argyrodite-type sulfide-based solid electrolyte was used as the electrolyte to assemble an all-solid-state lithium-ion secondary battery, and charge/discharge tests were conducted.
　正極については、上記した鉄含有多硫化リチウムと、アルジロダイト型硫化物系固体電解質と、アセチレンブラックとを、質量比４：５：１で混合して正極合材として用い、正極合材／アルジロダイト型硫化物系固体電解質／リチウムインジウム箔を加圧成型することにより直径１０ｍｍのペレット電池を作製した。これを、３．０Ｖから１．０Ｖまでの範囲内での定電流測定で充電開始により充放電試験を行った。なお、電流密度は、充電においては０．１３ｍＡ／ｃｍ２とし、放電においては０．１３～１．３ｍＡ／ｃｍ２とした。 For the positive electrode, the above-mentioned iron-containing lithium polysulfide, argyrodite-type sulfide-based solid electrolyte, and acetylene black were mixed in a mass ratio of 4:5:1 to form a positive electrode composite, and a pellet battery with a diameter of 10 mm was produced by pressure molding the positive electrode composite/argyrodite-type sulfide-based solid electrolyte/lithium indium foil. A charge/discharge test was performed by starting charging with constant current measurement in the range of 3.0 V to 1.0 V. The current density was 0.13 mA/ cm2 for charging and 0.13 to 1.3 mA/ cm2 for discharging.
　初回（１サイクル目）放電曲線は図７に示すとおり、初回放電容量は、放電電流密度が低電流密度（０．１３ｍＡ／ｃｍ２）の場合で５２０ｍＡｈ／ｇ、０．２５ｍＡ／ｃｍ２の場合で５００ｍＡｈ／ｇ、０．６４ｍＡ／ｃｍ２の場合で４８０ｍＡｈ／ｇ、高電流密度（１．３ｍＡ／ｃｍ２）の場合で４２０ｍＡｈ／ｇであった。つまり、高電流密度（１．３ｍＡ／ｃｍ２）における初回放電容量は、低電流密度（０．１３ｍＡ／ｃｍ２）における初回放電容量の８１％という高い値を示し、容量及びレート特性に優れた正極活物質が得られたことが理解できる。 As shown in Fig. 7, the initial discharge capacity was 520 mAh/g when the discharge current density was low (0.13 mA/ cm2 ), 500 mAh/g when it was 0.25 mA/ cm2 , 480 mAh/g when it was 0.64 mA/ cm2 , and 420 mAh/g when it was high current density (1.3 mA/ cm2 ). In other words, the initial discharge capacity at high current density (1.3 mA/ cm2 ) was as high as 81% of the initial discharge capacity at low current density (0.13 mA/ cm2 ), and it can be understood that a positive electrode active material excellent in capacity and rate characteristics was obtained.
　比較例４
　硫化リチウムと硫化鉄との反応物とＭｏ６Ｓ８とのメカニカルミリング時間を０時間とする（硫化リチウムと硫化鉄との反応物とＭｏ６Ｓ８とを混合するが、メカニカルミリング処理を行わない）こと以外は実施例４と全く同様にして試料を作製した。 Comparative Example 4
A sample was prepared in exactly the same manner as in Example 4, except that the mechanical milling time of the reaction product of lithium sulfide and iron sulfide with Mo6S8 was set to 0 hours (the reaction product of lithium sulfide and iron sulfide was mixed with Mo6S8 , but mechanical milling was not performed).
　得られた試料の各元素の比率（原子％）は、実施例４と同様、Ｌｉ５５％、Ｆｅ５％、Ｓ３７％、Ｍｏ３％であった。なお、得られた試料には、炭素やハロゲンは含まれていなかった。また、得られた試料の電気伝導度を測定するために粉末を３００ＭＰａで圧粉成型し、電圧印加で電流値を測定することにより測定したところ、１０－８Ｓ／ｃｍ未満（測定不能）と実施例４と比較して劇的に低い値であった。 The ratios (atomic %) of the elements in the obtained sample were Li 55%, Fe 5%, S 37%, and Mo 3%, similar to those in Example 4. The obtained sample did not contain carbon or halogens. In order to measure the electrical conductivity of the obtained sample, the powder was compacted at 300 MPa and the current value was measured by applying a voltage, resulting in a value of less than 10 −8 S/cm (immeasurable), which was dramatically lower than that in Example 4.
　得られた試料のＸ線回折パターンは、図６に示す通り、結晶性硫化リチウム（Ｌｉ２Ｓ）、結晶性Ｍｏ６Ｓ８及び結晶性硫化鉄（ＦｅＳ）から成り、Ｒｉｅｔｖｅｌｄ解析から求めた硫化リチウム（Ｌｉ２Ｓ）の存在比は８２モル％、Ｍｏ６Ｓ８の存在比は２モル％、硫化鉄（ＦｅＳ）の存在比は１６モル％であった。また、硫化リチウムの（１１１）面に基づく回折ピークの半値幅から算出される結晶子サイズは８０ｎｍであった。 The X-ray diffraction pattern of the obtained sample was composed of crystalline lithium sulfide (Li 2 S), crystalline Mo 6 S 8 , and crystalline iron sulfide (FeS) as shown in Fig. 6, and the abundance ratio of lithium sulfide (Li 2 S) was 82 mol%, the abundance ratio of Mo 6 S 8 was 2 mol%, and the abundance ratio of iron sulfide (FeS) was 16 mol% as determined by Rietveld analysis. In addition, the crystallite size calculated from the half-width of the diffraction peak based on the (111) plane of lithium sulfide was 80 nm.
　得られた複合体粉末を実施例４と同様にして全固体電池に組み上げて充放電試験を行った。初回（１サイクル目）放電曲線は図７に示す通りで、初回放電容量は、放電電流密度が低電流密度（０．１３ｍＡ／ｃｍ２）において約１１０ｍＡｈ／ｇの低い放電容量しか得られず、電流密度０．２５ｍＡ／ｃｍ２においては約１００ｍＡｈ／ｇ、０．６４ｍＡ／ｃｍ２においては約９０ｍＡｈ／ｇ、高電流密度（１．３ｍＡ／ｃｍ２）においては約７０ｍＡｈ／ｇといずれも低い放電容量しか得られなかった。 The obtained composite powder was assembled into an all-solid-state battery in the same manner as in Example 4, and a charge/discharge test was performed. The initial (first cycle) discharge curve is shown in Fig. 7, and the initial discharge capacity was only a low discharge capacity of about 110 mAh/g at a low discharge current density (0.13 mA/ cm2 ), about 100 mAh/g at a current density of 0.25 mA/ cm2 , about 90 mAh/g at a current density of 0.64 mA/ cm2 , and about 70 mAh/g at a high current density (1.3 mA/ cm2 ).
　実施例５
　市販の硫化リチウム（Ｌｉ２Ｓ）（（株）高純度化学研究所製、型番：ＬＩＩ０６ＰＢ）と硫化鉄（ＦｅＳ）（Ａｌｆａ　Ａｅｓａｒ製、型番：１４０２４）をモル比がＬｉ２Ｓ：ＦｅＳ＝５：１となるよう、アルゴンガス雰囲気のグローブボックス内（露点－８０℃）で秤量し、乳鉢で充分に混合後、室温（２５℃）で、ＭｏＳ２（（株）高純度化学研究所製、型番：ＭＯＩ０６ＰＢ）を、硫化リチウムと硫化鉄との反応物：ＭｏＳ２＝８：２（質量比）となるように乳鉢で混合し、アルゴンガス雰囲気下でジルコニア製ポットに入れ、フリッチュ・ジャパン株式会社（株）製の遊星ボールミル（型式Ｐ－７）を用い、メカニカルミリング法により、４００ｒｐｍで２０時間行うことにより試料を作製した。 Example 5
Commercially available lithium sulfide (Li 2 S) (manufactured by Kojundo Chemical Laboratory Co., Ltd., model number: LII06PB) and iron sulfide (FeS) (manufactured by Alfa Aesar, model number: 14024) were weighed in a glove box (dew point -80°C) in an argon gas atmosphere so that the molar ratio was Li 2 S:FeS = 5:1, and mixed thoroughly in a mortar. Then, MoS 2 (manufactured by Kojundo Chemical Laboratory Co., Ltd., model number: MOI06PB) was mixed in a mortar at room temperature (25°C) so that the reactant of lithium sulfide and iron sulfide:MoS 2 = 8:2 (mass ratio), and the mixture was placed in a zirconia pot under an argon gas atmosphere and subjected to mechanical milling at 400 rpm for 20 hours using a planetary ball mill (model P-7) manufactured by Fritsch Japan Co., Ltd., to prepare a sample.
　得られた試料の各元素の比率（原子％）は、Ｌｉ５４％、Ｆｅ５％、Ｓ３８％、Ｍｏ３％であった。なお、得られた試料には、炭素やハロゲンは含まれていなかった。また、得られた試料の電気伝導度を測定するために粉末を３００ＭＰａで圧粉成型し、電圧印加で電流値を測定することにより測定したところ、３．４×１０－３Ｓ／ｃｍであり、メカニカルミリング処理を施さない比較例５の電気伝導度である１０－８Ｓ／ｃｍ未満（測定不能）と比較して劇的に向上していた。 The ratios (atomic %) of each element in the obtained sample were Li 54%, Fe 5%, S 38%, and Mo 3%. The obtained sample did not contain carbon or halogen. In order to measure the electrical conductivity of the obtained sample, the powder was compressed at 300 MPa and the current value was measured by applying a voltage, which was 3.4 × 10 -3 S/cm, which was dramatically improved compared to the electrical conductivity of Comparative Example 5, which was not subjected to mechanical milling, which was less than 10 -8 S/cm (immeasurable).
　得られた試料のＸ線回折パターンは、図８に示す通り、低結晶性硫化リチウム（Ｌｉ２Ｓ）及び硫化鉄（ＦｅＳ）から成り、Ｒｉｅｔｖｅｌｄ解析により見積もられた硫化リチウム（Ｌｉ２Ｓ）の存在比は９１モル％、ＭｏＳ２の存在比は０モル％、硫化鉄（ＦｅＳ）の存在比は９モル％であった。また、硫化リチウムの（１１１）面に基づく回折ピークの半値幅から算出される結晶子サイズは１９ｎｍであった。 The X-ray diffraction pattern of the obtained sample was composed of low-crystalline lithium sulfide (Li 2 S) and iron sulfide (FeS) as shown in Fig. 8, and the abundance ratio of lithium sulfide (Li 2 S) estimated by Rietveld analysis was 91 mol%, the abundance ratio of MoS 2 was 0 mol%, and the abundance ratio of iron sulfide (FeS) was 9 mol%. In addition, the crystallite size calculated from the half-width of the diffraction peak based on the (111) plane of lithium sulfide was 19 nm.
　得られた鉄含有多硫化リチウムを正極活物質に用い、負極にインジウム金属、電解質にアルジロダイト型硫化物系固体電解質を用いて全固体リチウムイオン二次電池を組み上げ、充放電試験を行った。 The obtained iron-containing lithium polysulfide was used as the positive electrode active material, indium metal was used as the negative electrode, and an argyrodite-type sulfide-based solid electrolyte was used as the electrolyte to assemble an all-solid-state lithium-ion secondary battery, and charge/discharge tests were conducted.
　正極については、上記した鉄含有多硫化リチウムと、アルジロダイト型硫化物系固体電解質と、アセチレンブラックとを、質量比４：５：１で混合して正極合材として用い、正極合材／アルジロダイト型硫化物系固体電解質／リチウムインジウム箔を加圧成型することにより直径１０ｍｍのペレット電池を作製した。これを、３．０Ｖから１．０Ｖまでの範囲内での定電流測定で充電開始により充放電試験を行った。なお、電流密度は、充電においては０．１３ｍＡ／ｃｍ２とし、放電においては０．１３～１．３ｍＡ／ｃｍ２とした。 For the positive electrode, the above-mentioned iron-containing lithium polysulfide, argyrodite-type sulfide-based solid electrolyte, and acetylene black were mixed in a mass ratio of 4:5:1 to form a positive electrode composite, and a pellet battery with a diameter of 10 mm was produced by pressure molding the positive electrode composite/argyrodite-type sulfide-based solid electrolyte/lithium indium foil. A charge/discharge test was performed by starting charging with constant current measurement in the range of 3.0 V to 1.0 V. The current density was 0.13 mA/ cm2 for charging and 0.13 to 1.3 mA/ cm2 for discharging.
　初回（１サイクル目）放電曲線は図９に示す通りで、初回放電容量は、放電電流密度が低電流密度（０．１３ｍＡ／ｃｍ２）において約６６０ｍＡｈ／ｇ、０．２５ｍＡ／ｃｍ２において約６２０ｍＡｈ／ｇ、０．６４ｍＡ／ｃｍ２において約６００ｍＡｈ／ｇ、高電流密度（１．３ｍＡ／ｃｍ２）において約５６０ｍＡｈ／ｇの放電容量が得られた。すなわち、高電流密度（１．３ｍＡ／ｃｍ２）での放電容量は低電流密度（０．１３ｍＡ／ｃｍ２）での約８６％もの高い値を示し、レート特性に優れた電極材料が得られた。 The initial (first cycle) discharge curve is shown in Figure 9, and the initial discharge capacity was about 660 mAh/g at a low discharge current density (0.13 mA/ cm2 ), about 620 mAh/g at 0.25 mA/ cm2 , about 600 mAh/g at 0.64 mA/ cm2 , and about 560 mAh/g at a high current density (1.3 mA/ cm2 ). That is, the discharge capacity at a high current density (1.3 mA/ cm2 ) was as high as about 86% of that at a low current density (0.13 mA/ cm2 ), and an electrode material with excellent rate characteristics was obtained.
　比較例５
　硫化リチウムと硫化鉄との反応物とＭｏＳ２とのメカニカルミリング処理時間を０時間とする（硫化リチウムと硫化鉄との反応物とＭｏＳ２とを混合するが、メカニカルミリング処理を行わない）こと以外は実施例５と全く同様にして試料を作製した。 Comparative Example 5
A sample was prepared in the same manner as in Example 5 except that the mechanical milling treatment time of the reaction product of lithium sulfide and iron sulfide with MoS2 was 0 hours (the reaction product of lithium sulfide and iron sulfide was mixed with MoS2 , but the mechanical milling treatment was not performed).
　得られた試料の各元素の比率（原子％）は、実施例５と同様、Ｌｉ５４％、Ｆｅ５％、Ｓ３８％、Ｍｏ３％であった。なお、得られた試料には、炭素やハロゲンは含まれていなかった。また、得られた試料の電気伝導度を測定するために粉末を３００ＭＰａで圧粉成型し、電圧印加で電流値を測定することにより測定したところ、１０－８Ｓ／ｃｍ未満（測定不能）と実施例５と比較して劇的に低い値であった。 The ratios (atomic %) of the elements in the obtained sample were Li 54%, Fe 5%, S 38%, and Mo 3%, similar to those in Example 5. The obtained sample did not contain carbon or halogens. In order to measure the electrical conductivity of the obtained sample, the powder was compressed at 300 MPa and the current value was measured by applying a voltage, resulting in a value of less than 10 −8 S/cm (impossible to measure), which was dramatically lower than that of Example 5.
　得られた試料のＸ線回折パターンは、図８に示す通り、結晶性硫化リチウム（Ｌｉ２Ｓ）、硫化鉄（ＦｅＳ）及びＭｏＳ２から成り、Ｒｉｅｔｖｅｌｄ解析から求めた硫化リチウム（Ｌｉ２Ｓ）の存在比は７７モル％、Ｍｏ６Ｓ８の存在比は８モル％、硫化鉄（ＦｅＳ）の存在比は１５モル％であった。また、硫化リチウムの（１１１）面に基づく回折ピークの半値幅から算出される結晶子サイズは８４ｎｍであった。 The X-ray diffraction pattern of the obtained sample was composed of crystalline lithium sulfide (Li 2 S), iron sulfide (FeS) and MoS 2 , and the abundance ratio of lithium sulfide (Li 2 S) was 77 mol%, the abundance ratio of Mo 6 S 8 was 8 mol%, and the abundance ratio of iron sulfide (FeS) was 15 mol%, as determined by Rietveld analysis, as shown in Figure 8. The crystallite size calculated from the half-width of the diffraction peak based on the (111) plane of lithium sulfide was 84 nm.
　得られた複合体粉末を実施例５と同様にして全固体電池に組み上げて充放電試験を行った。結果は図９に示す通りで、初回放電容量は、放電電流密度が低電流密度（０．１３ｍＡ／ｃｍ２）において約３ｍＡｈ／ｇの低い放電容量しか得られず、電流密度０．２５ｍＡ／ｃｍ２においても約３ｍＡｈ／ｇ、０．６４ｍＡ／ｃｍ２においても約２ｍＡｈ／ｇ、高電流密度（１．３ｍＡ／ｃｍ２）においても約２ｍＡｈ／ｇといずれも低い放電容量しか得られず、ＭｏＳ２を混合するのみでは容量及びレート特性の双方に優れた電極材料が得られないことが分かった。 The obtained composite powder was assembled into an all-solid-state battery in the same manner as in Example 5, and a charge/discharge test was performed. The results are shown in Fig. 9, and the initial discharge capacity was only low at about 3 mAh/g at a low discharge current density (0.13 mA/ cm2 ), about 3 mAh/g at a current density of 0.25 mA/ cm2 , about 2 mAh/g at a current density of 0.64 mA/ cm2 , and about 2 mAh/g at a high current density (1.3 mA/ cm2 ). It was found that an electrode material excellent in both capacity and rate characteristics cannot be obtained by simply mixing MoS2 .
　実施例６
　市販の硫化リチウム（Ｌｉ２Ｓ）（（株）高純度化学研究所製、型番：ＬＩＩ０６ＰＢ）と硫化鉄（ＦｅＳ）（Ａｌｆａ　Ａｅｓａｒ製、型番：１４０２４）をモル比がＬｉ２Ｓ：ＦｅＳ＝５：１で秤量し、乳鉢で充分に混合後、室温（２５℃）で、ＣｕＳ（（株）富士フイルム和光純薬製、型番：０３４－０４４６２）を、硫化リチウムと硫化鉄との反応物：ＣｕＳ＝８：２（質量比）となるように乳鉢で混合し、アルゴンガス雰囲気下でジルコニア製ポットに入れ、フリッチュ・ジャパン株式会社（株）製の遊星ボールミル（型式Ｐ－７）を用い、メカニカルミリング法により、４００ｒｐｍで４０時間行うことにより試料を作製した。 Example 6
Commercially available lithium sulfide (Li 2 S) (manufactured by Kojundo Chemical Laboratory Co., Ltd., model number: LII06PB) and iron sulfide (FeS) (manufactured by Alfa Aesar, model number: 14024) were weighed out in a molar ratio of Li 2 S:FeS = 5:1, thoroughly mixed in a mortar, and then CuS (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., model number: 034-04462) was mixed in a mortar at room temperature (25 ° C.) so that the reaction product of lithium sulfide and iron sulfide:CuS = 8:2 (mass ratio), and the mixture was placed in a zirconia pot under an argon gas atmosphere and subjected to mechanical milling at 400 rpm for 40 hours using a planetary ball mill (model P-7) manufactured by Fritsch Japan Co., Ltd. to prepare a sample.
　得られた試料の各元素の比率（原子％）は、Ｌｉ５４％、Ｆｅ５％、Ｓ３７％、Ｃｕ４％であった。なお、得られた試料には、炭素やハロゲンは含まれていなかった。また、得られた試料の電気伝導度を測定するために粉末を３００ＭＰａで圧粉成型し、電圧印加で電流値を測定することにより測定したところ、１．６×１０－６Ｓ／ｃｍであり、メカニカルミリング処理を施さない比較例６の電気伝導度である１０－８Ｓ／ｃｍ未満（測定不能）と比較して劇的に向上していた。 The ratios (atomic %) of each element in the obtained sample were Li 54%, Fe 5%, S 37%, and Cu 4%. The obtained sample did not contain carbon or halogen. In order to measure the electrical conductivity of the obtained sample, the powder was compacted at 300 MPa and the current value was measured by applying a voltage, which was 1.6×10 −6 S/cm, which was dramatically improved compared to the electrical conductivity of Comparative Example 6, which was not subjected to mechanical milling, which was less than 10 −8 S/cm (immeasurable).
　得られた試料のＸ線回折パターンは、図１０に示す通り、低結晶性硫化リチウム（Ｌｉ２Ｓ）から成り、Ｒｉｅｔｖｅｌｄ解析から求めた硫化リチウム（Ｌｉ２Ｓ）の存在比は１００モル％であった。また、硫化リチウムの（１１１）面に基づく回折ピークの半値幅から算出される結晶子サイズは２３ｎｍであった。 The X-ray diffraction pattern of the obtained sample was composed of low-crystalline lithium sulfide (Li 2 S), and the abundance ratio of lithium sulfide (Li 2 S) obtained by Rietveld analysis was 100 mol % as shown in Fig. 10. The crystallite size calculated from the half-width of the diffraction peak based on the (111) plane of lithium sulfide was 23 nm.
　得られた鉄含有多硫化リチウムを正極活物質に用い、負極にインジウム金属、電解質にアルジロダイト型硫化物系固体電解質を用いて全固体リチウムイオン二次電池を組み上げ、充放電試験を行った。 The obtained iron-containing lithium polysulfide was used as the positive electrode active material, indium metal was used as the negative electrode, and an argyrodite-type sulfide-based solid electrolyte was used as the electrolyte to assemble an all-solid-state lithium-ion secondary battery, and charge/discharge tests were conducted.
　正極については、上記した鉄含有多硫化リチウムと、アルジロダイト型硫化物系固体電解質と、アセチレンブラックとを、質量比４：５：１で混合して正極合材として用い、正極合材／アルジロダイト型硫化物系固体電解質／リチウムインジウム箔を加圧成型することにより直径１０ｍｍのペレット電池を作製した。これを、３．０Ｖから１．０Ｖまでの範囲内での定電流測定で充電開始により充放電試験を行った。なお、電流密度は、充電においては０．１３ｍＡ／ｃｍ２とし、放電においては０．１３～１．３ｍＡ／ｃｍ２とした。 For the positive electrode, the above-mentioned iron-containing lithium polysulfide, argyrodite-type sulfide-based solid electrolyte, and acetylene black were mixed in a mass ratio of 4:5:1 to form a positive electrode composite, and a pellet battery with a diameter of 10 mm was produced by pressure molding the positive electrode composite/argyrodite-type sulfide-based solid electrolyte/lithium indium foil. A charge/discharge test was performed by starting charging with constant current measurement in the range of 3.0 V to 1.0 V. The current density was 0.13 mA/ cm2 for charging and 0.13 to 1.3 mA/ cm2 for discharging.
　初回（１サイクル目）放電曲線は図１１に示す通りで、初回放電容量は、放電電流密度が低電流密度（０．１３ｍＡ／ｃｍ２）において約５５０ｍＡｈ／ｇ、０．２５ｍＡ／ｃｍ２において約４９０ｍＡｈ／ｇ、０．６４ｍＡ／ｃｍ２において約４５０ｍＡｈ／ｇ、１．３ｍＡ／ｃｍ２において約３８０ｍＡｈ／ｇの放電容量が得られた。すなわち、高電流密度（１．３ｍＡ／ｃｍ２）での放電容量は低電流密度（０．１３ｍＡ／ｃｍ２）での約７０％もの高い値を示し、レート特性に優れた電極材料が得られた。 The initial (first cycle) discharge curve is shown in Figure 11, and the initial discharge capacity was about 550 mAh/g at a low discharge current density (0.13 mA/ cm2 ), about 490 mAh/g at 0.25 mA/ cm2 , about 450 mAh/g at 0.64 mA/ cm2 , and about 380 mAh/g at 1.3 mA/ cm2 . That is, the discharge capacity at a high current density (1.3 mA/ cm2 ) was as high as about 70% of that at a low current density (0.13 mA/ cm2 ), and an electrode material with excellent rate characteristics was obtained.
　比較例６
　硫化リチウムと硫化鉄との反応物とＣｕＳとのメカニカルミリング処理時間を０時間（硫化リチウムと硫化鉄との反応物とＣｕＳとを混合するが、メカニカルミリング処理を行わない）とする以外は実施例６と全く同様にして試料を作製した。 Comparative Example 6
A sample was prepared in the same manner as in Example 6, except that the mechanical milling treatment time of the reaction product of lithium sulfide and iron sulfide and CuS was 0 hours (the reaction product of lithium sulfide and iron sulfide and CuS were mixed, but the mechanical milling treatment was not performed).
　得られた試料の各元素の比率（原子％）は、実施例６と同様、Ｌｉ５４％、Ｆｅ５％、Ｓ３７％、Ｃｕ４％であった。なお、得られた試料には、炭素やハロゲンは含まれていなかった。また、得られた試料の電気伝導度を測定するために粉末を３００ＭＰａで圧粉成型し、電圧印加で電流値を測定することにより測定したところ、１０－８Ｓ／ｃｍ未満（測定不能）と実施例６と比較して劇的に低い値であった。 The ratios (atomic %) of the elements in the obtained sample were Li 54%, Fe 5%, S 37%, and Cu 4%, similar to Example 6. The obtained sample did not contain carbon or halogens. In order to measure the electrical conductivity of the obtained sample, the powder was compressed at 300 MPa and the current value was measured by applying a voltage, resulting in a value of less than 10 −8 S/cm (impossible to measure), which was dramatically lower than that of Example 6.
　得られた試料のＸ線回折パターンは、図１０に示す通り、結晶性硫化リチウム（Ｌｉ２Ｓ）、硫化鉄（ＦｅＳ）及びＣｕＳから成り、Ｒｉｅｔｖｅｌｄ解析から求めた硫化リチウム（Ｌｉ２Ｓ）の存在比は７３モル％、ＣｕＳの存在比は１２モル％、硫化鉄（ＦｅＳ）の存在比は１５モル％であった。また、硫化リチウムの（１１１）面に基づく回折ピークの半値幅から算出される結晶子サイズは８６ｎｍであった。 The X-ray diffraction pattern of the obtained sample was composed of crystalline lithium sulfide (Li 2 S), iron sulfide (FeS) and CuS, and the abundance ratio of lithium sulfide (Li 2 S) was 73 mol %, the abundance ratio of CuS was 12 mol %, and the abundance ratio of iron sulfide (FeS) was 15 mol % as determined by Rietveld analysis, as shown in Figure 10. The crystallite size calculated from the half-width of the diffraction peak based on the (111) plane of lithium sulfide was 86 nm.
　得られた複合体粉末を実施例６と同様にして全固体電池に組み上げて充放電試験を行った。結果は図１１に示す通りで、初回放電容量は、放電電流密度が低電流密度（０．１３ｍＡ／ｃｍ２）において約７ｍＡｈ／ｇの低い放電容量しか得られず、電流密度０．２５ｍＡ／ｃｍ２においても約４ｍＡｈ／ｇ、０．６４ｍＡ／ｃｍ２においても約３ｍＡｈ／ｇ、１．３ｍＡ／ｃｍ２においても約３ｍＡｈ／ｇといずれも低い放電容量しか得られなかった。すなわち、硫化リチウムと硫化鉄との反応物にＣｕＳを混合するのみでは、容量にもレート特性にも優れた電極材料が得られないことが分かった。 The obtained composite powder was assembled into an all-solid-state battery in the same manner as in Example 6, and a charge/discharge test was performed. The results are shown in FIG. 11. The initial discharge capacity was only about 7 mAh/g at a low discharge current density (0.13 mA/cm 2 ), and was about 4 mAh/g at a current density of 0.25 mA/cm 2 , about 3 mAh/g at 0.64 mA/cm 2 , and about 3 mAh/g at 1.3 mA/cm 2 . In other words, it was found that an electrode material excellent in both capacity and rate characteristics cannot be obtained by simply mixing CuS with the reaction product of lithium sulfide and iron sulfide.
１　通電焼結装置
２　試料
３　ダイ（導電性容器）
４、５　通電用パンチ
６，７　パンチ電極
８　水冷真空チャンバー
９　冷却水路
１０、１６　水冷却機構
１１　焼結用電源
１２　制御装置
１３　加圧機構
１４　位置計測機構
１５　雰囲気制御機構
１７　温度計測装置 1 Electric current sintering device 2 Sample 3 Die (conductive container)
4, 5: Current-carrying punch 6, 7: Punch electrode 8: Water-cooled vacuum chamber 9: Cooling water passage 10, 16: Water cooling mechanism 11: Sintering power source 12: Control device 13: Pressurizing mechanism 14: Position measuring mechanism 15: Atmosphere control mechanism 17: Temperature measuring device

Claims (14)

  1. リチウム、鉄及び硫黄を構成元素として含む鉄含有多硫化リチウムであって、
    硫化リチウム（Ｌｉ２Ｓ）を主相として含み、
    粉末Ｘ線回折によって得られたＬｉ２Ｓの（１１１）面に基づく回折ピークの半価幅から算出される結晶子サイズが５０ｎｍ以下であり、且つ、
    前記鉄含有多硫化リチウムの総量を１００原子％として、Ｌｉ含有量が５０～７０原子％、Ｆｅ含有量が２～１２原子％、Ｓ含有量が２０～４０原子％、Ｃ含有量が０～５原子％、ハロゲン含有量が０～０．８原子％である、鉄含有多硫化リチウム。     An iron-containing lithium polysulfide containing lithium, iron, and sulfur as constituent elements,
    Contains lithium sulfide (Li 2 S) as a main phase;
    The crystallite size calculated from the half-width of the diffraction peak based on the (111) plane of Li 2 S obtained by powder X-ray diffraction is 50 nm or less, and
    The iron-containing lithium polysulfide has a Li content of 50 to 70 atomic %, an Fe content of 2 to 12 atomic %, an S content of 20 to 40 atomic %, a C content of 0 to 5 atomic %, and a halogen content of 0 to 0.8 atomic %, relative to 100 atomic % of the total amount of the iron-containing lithium polysulfide.
  2. 前記鉄含有多硫化リチウムを基準として、Ｒｉｅｔｖｅｌｄ解析により見積もられた硫化リチウム（Ｌｉ２Ｓ）の存在比が７０モル％以上である、請求項１に記載の鉄含有多硫化リチウム。 2. The iron-containing lithium polysulfide according to claim 1, wherein the abundance ratio of lithium sulfide (Li 2 S) is 70 mol % or more based on the iron-containing lithium polysulfide as estimated by Rietveld analysis.
  3. さらに、硫化鉄（ＦｅＳ）相を有する、請求項１に記載の鉄含有多硫化リチウム。 The iron-containing lithium polysulfide of claim 1, further comprising an iron sulfide (FeS) phase.
  4. ２５℃における電気伝導度が１０－３～１０－６Ｓ／ｃｍである、請求項１に記載の鉄含有多硫化リチウム。 2. The iron-containing lithium polysulfide according to claim 1, which has an electrical conductivity at 25° C. of 10 −3 to 10 −6 S/cm.
  5. リチウムイオン二次電池用である、請求項１に記載の鉄含有多硫化リチウム。 The iron-containing lithium polysulfide according to claim 1, which is for use in a lithium-ion secondary battery.
  6. リチウムイオン二次電池の正極活物質用である、請求項５に記載の鉄含有多硫化リチウム。 The iron-containing lithium polysulfide according to claim 5, which is used as a positive electrode active material for a lithium ion secondary battery.
  7. 請求項１～６のいずれか１項に記載の鉄含有多硫化リチウムの製造方法であって、
    （３）リチウム含有化合物、鉄含有化合物及び硫黄含有化合物を含む混合物；前記混合物の加熱処理物；又は前記混合物の加熱生成物のメカニカルミリング処理物と、電気伝導度が１０－３Ｓ／ｃｍ以上である金属硫化物とを、メカニカルミリング処理する工程
    を備える、製造方法。     A method for producing the iron-containing lithium polysulfide according to any one of claims 1 to 6, comprising the steps of:
    (3) A production method comprising a step of mechanically milling a mixture containing a lithium-containing compound, an iron-containing compound, and a sulfur-containing compound; a heat-treated product of the mixture; or a mechanically milled product of the heat-treated product of the mixture, and a metal sulfide having an electrical conductivity of 10 −3 S/cm or more.
  8. 前記工程（３）の前に、さらに、
    （２）リチウム含有化合物、鉄含有化合物及び硫黄含有化合物を含む混合物；又は前記混合物の加熱処理物を、メカニカルミリング処理する工程
    を備える、請求項７に記載の製造方法。     Before the step (3),
    (2) The method according to claim 7, further comprising a step of subjecting a mixture containing a lithium-containing compound, an iron-containing compound, and a sulfur-containing compound, or a heat-treated product of the mixture, to mechanical milling.
  9. 前記工程（２）の前に、さらに、
    （１）リチウム含有化合物、鉄含有化合物及び硫黄含有化合物を含む混合物を加熱する工程
    を備える、請求項８に記載の製造方法。     Before the step (2),
    The method of claim 8, comprising the step of: (1) heating a mixture containing a lithium-containing compound, an iron-containing compound, and a sulfur-containing compound.
  10. 前記工程（１）が、前記混合物に対して、直流パルス電流を通電して該混合物を加熱反応させる工程である、請求項９に記載の製造方法。 The method according to claim 9, wherein step (1) is a step of passing a direct current pulse current through the mixture to heat and react the mixture.
  11. 前記工程（１）～（３）を、非酸化性雰囲気下において行う、請求項９に記載の製造方法。 The manufacturing method according to claim 9, wherein steps (1) to (3) are carried out in a non-oxidizing atmosphere.
  12. 請求項１～６のいずれか１項に記載の鉄含有多硫化リチウムを含むリチウムイオン二次電池用正極活物質。 A positive electrode active material for a lithium ion secondary battery comprising the iron-containing lithium polysulfide according to any one of claims 1 to 6.
  13. 請求項１２に記載のリチウムイオン二次電池用正極活物質を構成要素とするリチウムイオン二次電池。 A lithium ion secondary battery comprising the positive electrode active material for lithium ion secondary batteries according to claim 12 as a component.
  14. 請求項１３に記載のリチウムイオン二次電池用正極活物質と、リチウムイオン伝導性固体電解質とを、構成要素として含む、全固体リチウムイオン二次電池。 An all-solid-state lithium ion secondary battery comprising, as components, the positive electrode active material for a lithium ion secondary battery according to claim 13 and a lithium ion conductive solid electrolyte.
PCT/JP2023/039491 2022-11-04 2023-11-01 Iron-containing lithium polysulfide WO2024096075A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
JP2022177465 2022-11-04
JP2022-177465 2022-11-04

Publications (1)

Publication Number Publication Date
WO2024096075A1 true WO2024096075A1 (en) 2024-05-10

Family

ID=90930632

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/JP2023/039491 WO2024096075A1 (en) 2022-11-04 2023-11-01 Iron-containing lithium polysulfide

Country Status (1)

Country Link
WO (1) WO2024096075A1 (en)

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2010084808A1 (en) * 2009-01-22 2010-07-29 独立行政法人産業技術総合研究所 Process for production of iron sulfide/lithium composite
WO2015037598A1 (en) * 2013-09-13 2015-03-19 独立行政法人産業技術総合研究所 Lithium sulfide-iron-carbon composite body
WO2016080443A1 (en) * 2014-11-18 2016-05-26 国立研究開発法人産業技術総合研究所 Lithium-iron-phosphorus-sulfur-carbon composite body and method for producing same
WO2019039582A1 (en) * 2017-08-25 2019-02-28 国立研究開発法人産業技術総合研究所 Lithium metal sulfide and method for producing same
WO2019130863A1 (en) * 2017-12-25 2019-07-04 国立研究開発法人産業技術総合研究所 Halogen-containing composite body and method for producing same

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2010084808A1 (en) * 2009-01-22 2010-07-29 独立行政法人産業技術総合研究所 Process for production of iron sulfide/lithium composite
WO2015037598A1 (en) * 2013-09-13 2015-03-19 独立行政法人産業技術総合研究所 Lithium sulfide-iron-carbon composite body
WO2016080443A1 (en) * 2014-11-18 2016-05-26 国立研究開発法人産業技術総合研究所 Lithium-iron-phosphorus-sulfur-carbon composite body and method for producing same
WO2019039582A1 (en) * 2017-08-25 2019-02-28 国立研究開発法人産業技術総合研究所 Lithium metal sulfide and method for producing same
WO2019130863A1 (en) * 2017-12-25 2019-07-04 国立研究開発法人産業技術総合研究所 Halogen-containing composite body and method for producing same

Similar Documents

Publication Publication Date Title
JP6501272B2 (en) Lithium-iron-phosphorus-sulfur-carbon complex and method for producing the same
JP6485232B2 (en) Method for producing positive electrode active material
JP6150233B2 (en) Lithium sulfide-iron-carbon composite
Yu et al. Reaction mechanism and enhancement of cyclability of SiO anodes by surface etching with NaOH for Li-ion batteries
WO2017221554A1 (en) Method for producing positive electrode active material for lithium ion secondary batteries, positive electrode active material for lithium ion secondary batteries, and lithium ion secondary battery
Shi et al. Core–shell structured Li [(Ni0. 8Co0. 1Mn0. 1) 0.7 (Ni0. 45Co0. 1Mn0. 45) 0.3] O2 cathode material for high-energy lithium ion batteries
JP5177183B2 (en) Method for producing negative electrode active material for non-aqueous secondary battery
Liu et al. Synthesis and electrochemical properties of Li 2 MnSiO 4/C nanoparticles via polyol process
JPWO2009028326A1 (en) Method for producing metal sulfide
KR20170044060A (en) Positive electrode active material for sodium ion secondary batteries and method for producing same
JP6014821B2 (en) Lithium manganese composite oxide and carbon composite thereof
TW201616707A (en) Si-based alloy negative electrode material for electricity storage devices and electrode using same
JP7145519B2 (en) Halogen-containing composite and method for producing the same
Kosova et al. From ‘core–shell’to composite mixed cathode materials for rechargeable lithium batteries by mechanochemical process
WO2012160738A1 (en) Positive electrode active material for nonaqueous electrolyte secondary battery, nonaqueous electrolyte secondary battery, vehicle, and method for manufacturing positive electrode active material for nonaqueous electrolyte secondary battery
US8480932B2 (en) Composite of metal sulfide and metal oxide and process for producing the composite
JP2021147314A (en) Transition metal composite hydroxide particle, manufacturing method of transition metal composite hydroxide particle, positive electrode active material for lithium ion secondary battery, and lithium ion secondary battery
WO2024096075A1 (en) Iron-containing lithium polysulfide
WO2023167132A1 (en) Lithium sulfide-iron-carbon composite
WO2019031601A1 (en) Si-BASED NEGATIVE ELECTRODE ACTIVE MATERIAL
Woo et al. Electrochemical characteristics of rancieite-type manganese oxide by mechanochemical synthesis
JP2013040096A (en) Method for manufacturing composite of metal sulfide and metal oxide
Woo-Hyun et al. A study on the Active Material FeS 2 in Battery Fabricated by Mechanical Alloying
Applestone Synthesis and characterization of nanocomposite alloy anodes for lithium-ion batteries
Nwokeke Development of nanoparticulate forms of tin-based alloy materials for high energy density anodes in lithium-ion batteries