WO2021177291A1 - Secondary battery electrode additive - Google Patents

Secondary battery electrode additive Download PDF

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Publication number
WO2021177291A1
WO2021177291A1 PCT/JP2021/007915 JP2021007915W WO2021177291A1 WO 2021177291 A1 WO2021177291 A1 WO 2021177291A1 JP 2021007915 W JP2021007915 W JP 2021007915W WO 2021177291 A1 WO2021177291 A1 WO 2021177291A1
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Prior art keywords
electrode
carbon
secondary battery
additive
carbon material
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PCT/JP2021/007915
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French (fr)
Japanese (ja)
Inventor
偉 毛
克之 福谷
暁明 夏
Original Assignee
国立大学法人 東京大学
日本水素株式会社
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Application filed by 国立大学法人 東京大学, 日本水素株式会社 filed Critical 国立大学法人 東京大学
Priority to CN202180018868.2A priority Critical patent/CN115210913A/en
Priority to JP2022504389A priority patent/JPWO2021177291A1/ja
Publication of WO2021177291A1 publication Critical patent/WO2021177291A1/en

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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B32/00—Carbon; Compounds thereof
    • C01B32/05—Preparation or purification of carbon not covered by groups C01B32/15, C01B32/20, C01B32/25, C01B32/30
    • 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
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • 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
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • 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
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present invention relates to an additive for an electrode of a secondary battery, and more specifically, an additive for an electrode for suppressing a decrease in conductivity of a secondary battery under low temperature operation.
  • Lithium-ion batteries which are secondary batteries, are expected to be used as large storage batteries for electric vehicles and electric power storage, in addition to small portable devices such as mobile phones and laptop computers.
  • high levels of battery capacity and charge / discharge cycle characteristics have been required. Therefore, improvements are being made to various battery components such as negative electrode materials, positive electrode materials, separators, and non-aqueous electrolytes (Patent Document 1 and the like).
  • the present inventors have used a particulate carbon material having specific properties as an electrode additive (particularly, a positive electrode additive) at ⁇ 20 ° C. It has been found that a decrease in conductivity of a secondary battery such as a lithium ion battery can be suppressed and good charge / discharge characteristics can be obtained in an extremely low temperature usage environment below the above, and the present invention has been completed. Further, they have also found that by further adding carbon nanomaterials such as carbon nanotubes (CNT) and graphene in addition to the above carbon materials, it is possible to more efficiently suppress a decrease in conductivity in a low temperature environment.
  • CNT carbon nanotubes
  • the present invention is an additive for an electrode for suppressing a decrease in conductivity of a secondary battery under low temperature operation in one embodiment, and has an average particle size of 20 to 50 nm; 750 to 800 m. It has a specific surface area in the range of 2 / g; is characterized by containing a particulate carbon material having an oxygen atom to carbon atom ratio (O / C) of 0.025 to 0.035 in the surface functional group.
  • O / C oxygen atom to carbon atom ratio
  • Additives for electrodes ⁇ 2> The electrode additive according to ⁇ 1> above, wherein the carbon material is surface-modified carbon black; ⁇ 3> Additive for electrode according to ⁇ 1> or ⁇ 2> above, further comprising carbon nanotube (CNT), graphene, or a combination thereof; and ⁇ 4> Weight ratio of carbon material to carbon nanotube to graphene.
  • the electrode additive according to ⁇ 3> above which is in the range of 80 to 90% by weight: 0 to 10% by weight: 0 to 10% by weight.
  • the present invention comprises a ⁇ 5> current collector and an active material layer formed on the current collector, and the active material layer is any one of the above ⁇ 1> to ⁇ 4>.
  • An electrode for a secondary battery which comprises the electrode additive according to the above; ⁇ 6> The electrode for a secondary battery according to ⁇ 5> above, which is a positive electrode; ⁇ 7> The electrode for a secondary battery according to claim 6, wherein the active material in the active material layer is a lithium-containing transition metal oxide; ⁇ 8> The secondary battery according to claim 8, wherein the secondary battery includes the electrode for the secondary battery according to any one of ⁇ 5> to ⁇ 7>above; and ⁇ 9> a lithium ion battery. ..
  • the present invention is a method for producing an additive for an electrode for suppressing a decrease in conductivity under low temperature operation of a ⁇ 10> secondary battery, in which a particulate carbon material is heated at 400 to 700 ° C.
  • the production method comprising a step, a step of treating the heated carbon material in an acidic aqueous solution, and a step of drying the obtained carbon material to obtain a surface-modified carbon material; ⁇ 11>
  • ⁇ 12> The production method according to ⁇ 10> or ⁇ 11> above, wherein the acidic aqueous solution is a nitric acid aqueous solution;
  • the present invention it is possible to suppress a decrease in conductivity of a secondary battery such as a lithium ion battery even in an extremely low temperature usage environment of less than ⁇ 20 ° C., and to obtain good charge / discharge characteristics close to normal temperature operation. Can be done. This makes it possible to solve charge / discharge defects when using power battery products (unmanned aerial vehicles, electric vehicles, robots, balance vehicles, etc.) in cold regions.
  • the electrode additive of the present invention since the electrode additive of the present invention has good dispersion, the conductivity, rate and cycle can be increased by a very small amount (for example, 1% or less) as compared with the conventional conductive agent. It also has the advantage that the properties can be improved.
  • FIG. 1 is a graph showing the particle size and pore size distribution of the electrode additive of the present invention.
  • FIG. 2 is an XPS chart of the electrode additive of the present invention.
  • FIG. 3 is an electron microscope image of the surface of the electrode containing the additive for the electrode of the present invention.
  • FIG. 4 is a graph showing a discharge curve when the temperature environment is changed in the range of 0 ° C. to ⁇ 35 ° C.
  • FIG. 5 is a graph showing a discharge curve when the temperature environment is changed to ⁇ 40 ° C.
  • FIG. 6 is a graph showing a discharge curve when the temperature environment is changed to ⁇ 50 ° C.
  • FIG. 7 is a graph showing charge / discharge curves at different rates.
  • FIG. 8 is a graph showing a charge / discharge cycle when LiFePO 4 is used as the active material.
  • FIG. 9 is a graph showing a charge / discharge cycle when a ternary system [Li (Ni—Mn—Co) O 2] is used as the active material.
  • FIG. 10 is a graph showing a charge / discharge cycle when LiMn 2 O 4 is used as the active material.
  • the additive for electrodes of the present invention is for suppressing a decrease in conductivity under low temperature operation of a secondary battery, and contains a particulate carbon material satisfying the following 1) to 3). It is characterized by that. 1) Have an average particle size of 20-50 nm; 2) Have a specific surface area in the range of 750 to 800 m 2 / g; 3) The ratio (O / C) of oxygen atom to carbon atom in the surface functional group is 0.025 to 0.035.
  • the surface-modified carbon material having conductivity has an appropriate balance between hydrophobicity and hydrophilicity, and the surface oxidation of the carbon material and the improvement of dispersibility by the high-speed vibration pulverization method are performed. It was found that the mixture was uniformly dispersed on the surface of the electrode and crosslinked with the active electrode material to form a three-dimensional network having a multi-branched structure. As a result, it is possible to suppress a decrease in the conductivity of the secondary battery even in an extremely low temperature usage environment, and it is possible to obtain good charge / discharge characteristics close to those during normal temperature operation. At the same time, such an effect can be obtained with a very small amount of addition (for example, 1% or less) as compared with the conventional conductive agent.
  • a very small amount of addition for example, 1% or less
  • carbon-based materials having various degrees of graphitization can be used, from graphitized materials to amorphous materials.
  • carbon black natural graphite, artificial graphite, hard carbon, soft carbon, Ketjen black, acetylene black, activated carbon and the like can be mentioned.
  • a carbon material having a small degree of graphitization is preferable, and carbon black is particularly preferable.
  • these carbon materials are preferably surface-modified so as to satisfy the above 1) to 3).
  • the carbon material is appropriately mixed with particles such as metal particles and metal oxide particles in any combination. Is also good. Further, a plurality of materials may be mixed in each particle. For example, carbonaceous particles having a structure in which the surface of graphite is coated with a carbon-based material having a low degree of graphitization can be used.
  • the average particle size of the carbon material used in the present invention can be 20 to 50 nm, preferably 25 to 45 nm. Thereby, the dispersibility in the solvent used at the time of manufacturing the electrode and the uniformity on the surface of the electrode can be made appropriate.
  • the average particle size can be measured by a known method using a commercially available laser diffraction / scattering type particle size distribution measuring device or the like.
  • the specific surface area of the carbon material used in the present invention is in the range of 750 to 800 m 2 / g, preferably in the range of 760 to 780 m 2 / g. If the specific surface area is less than this range, the fast charging characteristics may be inferior, and if it exceeds the range, the initial irreversible capacity may become too large.
  • the specific surface area can be measured by using a known method and apparatus such as a nitrogen gas adsorption and flow method.
  • the carbon material used in the present invention has an oxygen atom to carbon atom ratio (O / C atom ratio) in the surface functional group in the range of 0.025 to 0.035, preferably 0.027 to 0.033.
  • the portion corresponding to the oxygen atom (O) is mainly derived from the OH group on the particle surface of the carbon material, and by setting the O / C atom ratio within such a range, it is hydrophobic and hydrophilic. It has an appropriate balance of, and can be dispersed in an organic solvent used as a solvent used when producing an electrode, or in a hydrophilic solvent such as water. In addition, it can be uniformly distributed on the electrode surface.
  • the O / C atomic ratio can be measured using X-ray photoelectron spectroscopy (XPS). For example, from the oxygen atom concentration obtained based on the peak area of the O1s spectrum (525 to 545 eV) in the XPS analysis and the carbon atom concentration obtained based on the peak area of the C1s spectrum (280 to 300 eV) in the XPS analysis. The O / C atomic ratio can be determined.
  • XPS X-ray photoelectron spectroscopy
  • the electrode additive of the present invention may further contain another carbon nanomaterial in addition to the above carbon material.
  • carbon nanomaterials include carbon nanotubes (CNTs), carbon nanofibers (CNFs), graphene, carbon nanohorns (CNH), fullerenes, or combinations thereof, or chemicals thereof. It may be a substance modified to. Preferably, it is carbon nanotube (CNT), graphene, or a combination thereof.
  • the method for producing these carbon nanomaterials is not particularly limited, and they can be produced by a conventionally known method, or commercially available ones can be used as they are.
  • Carbon nanotubes are generally materials having a tubular structure having a diameter of about several nm, in which one sheet-shaped graphite (graphene sheet) having a six-membered ring arrangement structure of carbon is wound in a cylindrical shape.
  • the "carbon nanotube” includes a single-walled carbon nanotube composed of one sheet of graphite and a multi-walled carbon nanotube (inside the carbon nanotube) in which a plurality of the tubular sheets are laminated in the direction perpendicular to the axis.
  • multi-walled carbon nanotubes containing one or more small-diameter carbon nanotubes carbon nanohorns having a conical and closed end of single-walled carbon nanotubes, carbon nanotubes containing fullerene inside, and the like are also included. These carbon nanotubes can be used alone or in combination of two or more.
  • the average diameter of the carbon nanotubes can be selected from, for example, 0.5 nm to 1 ⁇ m, preferably 1 to 100 nm, and in the case of single-walled carbon nanotubes. For example, it is about 0.5 to 10 nm, preferably about 1 to 5 nm, and in the case of multi-walled carbon nanotubes, it is, for example, about 5 to 300 nm, preferably about 10 to 100 nm.
  • the average length of carbon nanotubes is, for example, in the range of 1 to 1000 ⁇ m, preferably 5 to 500 ⁇ m.
  • the ratio with the carbon material can be appropriately adjusted from the viewpoint of desired conductivity and dispersibility.
  • the weight ratio of carbon material: carbon nanomaterial can be in the range of 80-90% by weight: 10-20% by weight.
  • the weight ratio of the carbon material, carbon nanotubes, and graphene in the electrode additive is 80 to 90% by weight: 0 to 10% by weight: 0. It is preferably in the range of ⁇ 10% by weight.
  • the electrode additive of the present invention can be used in either a powder form or a dispersion liquid form dispersed in a solvent.
  • the solvent in the case of the dispersion liquid can be an organic solvent, water, or a mixed solvent thereof.
  • carbon nanomaterials and carbon nanomaterials, if any
  • a dispersant such as a surfactant may be added to the dispersion liquid.
  • the present invention also relates to the method for manufacturing the additive for electrode, and the manufacturing method includes the following steps.
  • Step (a) is a step of firing the carbon material at a heating temperature of 400 to 700 ° C., preferably 500 to 650 ° C.
  • the step is preferably carried out in an atmosphere of an inert gas such as argon for 2 to 3 hours.
  • an inert gas such as argon
  • the carbon material used as a raw material carbon-based materials having various degrees of graphitization can be used as described above, and carbon black is preferable.
  • the method for producing the carbon material itself as a raw material is not particularly limited, and it can be produced by a conventionally known method, or a commercially available material can be used as it is.
  • Step (b) is a step of appropriately cooling the carbon material obtained in step (a) and then treating it in an acidic aqueous solution.
  • an acidic aqueous solution an aqueous solution of a strong acid such as nitric acid can be typically used.
  • the step (c) is a step of separating the carbon material from the acidic aqueous solution of the step (b) and drying it to obtain the target surface-modified carbon material.
  • a separation means known in the art such as filtration can be used.
  • the production method of the present invention can further include a step of mixing the surface-modified carbon material and any carbon nanomaterial after the above (c).
  • the types of such carbon nanomaterials are as exemplified above, but it is preferable to use carbon nanotubes (CNT), graphene, or a combination thereof.
  • the electrode additive containing the obtained surface-modified carbon material is in either a powder form or a dispersion liquid form dispersed in a solvent. Can also be used.
  • the present invention comprises a current collector and an active material layer formed on the current collector, wherein the active material layer is the above-mentioned electrode addition. It also relates to electrodes for secondary batteries, which are characterized by containing an agent. Preferably, the electrode is a positive electrode (anode).
  • the active material material in the active material layer a known material can be used depending on the type of the secondary battery.
  • the secondary battery is a lithium ion battery
  • an active material capable of storing and releasing lithium ions can be used.
  • the positive electrode active material contains lithium containing one or more transition metals such as lithium cobalt oxide (LiCoO 2 ), lithium manganate (LiMn 2 O 4 ), and lithium nickel oxide (LiNiO 2).
  • Lithium-containing polyanionic compounds containing one or more transition metals such as transition metal oxides, transition metal sulfides, metal oxides, lithium iron oxide (LiFePO 4 ) and lithium iron pyrophosphate (Li 2 FeP 2 O 7).
  • the active material is a lithium-containing transition metal oxide.
  • examples of the negative electrode active material include carbonaceous materials such as natural graphite (graphite), highly oriented pyrolytic graphite (HOPG), and amorphous carbon. Can be mentioned. These negative electrode active materials may be used alone or in combination of two or more.
  • the electrode can contain a binder, if necessary.
  • a binder for example, a fluororesin such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), or ethylene tetrafluoroethylene (ETFE), polyethylene, polypropylene, or the like can be used.
  • PVDF polyvinylidene fluoride
  • PTFE polytetrafluoroethylene
  • ETFE ethylene tetrafluoroethylene
  • polyethylene polypropylene, or the like
  • the electrode can be prepared by pulverizing and mixing the electrode additive of the present invention and the electrode active material material.
  • crushing / mixing is not particularly limited, but can be performed by using a crusher such as a vibration mill, a jet mill, or a ball mill.
  • a method of supporting the mixture on the current collector there is a method of pressure molding, or a method of pasting with an organic solvent, coating on the electrode current collector, drying and pressing to fix the mixture.
  • a slurry consisting of an electrode active material, an electrode additive, a binder, and an organic solvent is prepared.
  • the electrode active material can be coated with the electrode additive of the present invention.
  • a method of performing such coating a method of immersing the powder of the electrode active material in a liquid containing the electrode additive and then heat-treating the powder to deposit the electrode active material on the powder surface of the active material can be mentioned. Be done.
  • the present invention also relates to a secondary battery comprising electrodes for the secondary battery.
  • the secondary battery is preferably a non-aqueous secondary battery, more preferably a lithium ion battery.
  • the configuration of the secondary battery of the present invention is the same as that of a conventionally known lithium ion secondary battery, and usually includes a positive electrode and a negative electrode capable of storing and releasing lithium ions, a separator, and an electrolytic solution.
  • the positive electrode contains the additive for the electrode of the present invention.
  • the low temperature electrolyte is not particularly limited as long as it uses a lithium salt as an electrolyte.
  • electrolytes include, for example, those selected from LiPF 6 , LiBF 4 , LiClO 4 , LiNO 3 , LiCl, Li 2 SO 4 and Li 2 S and any combination thereof.
  • solvent in the electrolytic solution examples include propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate, 4-trifluoromethyl-1,3-dioxolan-2- Carbonates such as on, 1,2-di (methoxycarbonyloxy) ethane; 1,2-dimethoxyethane, 1,3-dimethoxypropane, pentafluoropropylmethyl ether, 2,2,3,3-tetrafluoropropyldifluoro Ethers such as methyl ether, tetrahydrofuran and 2-methyltetraxyl; esters such as methyl formate, methyl acetate and ⁇ -butyrolactone; nitriles such as acetonitrile and butyronitrile; N, N-dimethylformamide, N, N-dimethylacetamide and the like. Amides of be able to. One of these
  • a solid electrolyte can be used instead of the electrolytic solution.
  • the solid electrolyte include polymer electrolytes such as polyethylene oxide-based polymer compounds and polymer compounds containing at least one polyorganosiloxane chain or polyoxyalkylene chain. It can also be used in the form of a non-aqueous gel electrolyte obtained by adding a polymer to the above electrolytic solution and gelling it.
  • the electrolytic solution may contain other components as necessary for the purpose of improving its function.
  • Other components include, for example, conventionally known overcharge inhibitors, dehydrating agents, deoxidizers, and property improving aids for improving capacity retention properties and cycle properties after high temperature storage.
  • the separator used in the secondary battery of the present invention is not particularly limited as long as it has a function of electrically separating the positive electrode layer and the negative electrode layer, but for example, polyethylene (PE) and polypropylene (PP). ), Porous sheets made of resins such as polyester, cellulose and polyamide, and porous insulating materials such as non-woven fabrics such as non-woven fabrics and glass fiber non-woven fabrics.
  • PE polyethylene
  • PP polypropylene
  • the shape of the secondary battery of the present invention is not particularly limited as long as it can store the positive electrode, the negative electrode, and the electrolytic solution, and examples thereof include a cylindrical type, a coin type, a flat plate type, and a laminated type. can.
  • Example 1 An additive containing only surface-modified carbon (Example 1) and an additive containing CNT and graphene in addition to the surface-modified carbon (Example 2) were obtained.
  • FIG. 1 shows a graph of particle size / pore size distribution. As a result, it was found that the additive of Example 1 had an average particle size of 35.6 nm, a specific surface area of 780 m 2 / g, and a primary particle size of 35.4 nm.
  • FIG. 2 shows an XPS chart obtained with the additive of Example 1.
  • Electrodes 1 Using the additive obtained in the above, a positive electrode was prepared by the following procedure. Active material (Li (Ni-Mn-Co) O 2 ) 94 wt.%, Conductive material (MEC380) 1 wt.%, Binder (PolyVinylidene DiFluoride (PVDF)) 5 wt. The paste kneaded with% was uniformly applied to the current collector (positive electrode: Al foil, negative electrode: Cu foil) by a doctor blade. Then, it was vacuum dried to remove the solvent.
  • Active material Li (Ni-Mn-Co) O 2
  • Conductive material MEC380
  • Binder PolyVinylidene DiFluoride (PVDF)
  • FIG. 3 An electron microscope image of the prepared electrode surface is shown in FIG. According to FIG. 3, it was found that the additive component of the present invention was uniformly dispersed on the electrode surface, and the electrode was completely covered. Further, it was found that the additive component of the present invention was strongly connected to the active material in the electrode and had a high degree of contact, and as a result, a three-dimensional network having a multi-branched structure was formed by cross-linking with each other.
  • Fig. 4 shows the discharge curve when the temperature environment is changed from 0 ° C to -35 ° C. As a result, it was confirmed that it operates normally even in a low temperature environment of ⁇ 35 ° C.
  • FIGS. 5 and 6 the discharge curves when the temperature environment is lowered to ⁇ 40 ° C. and ⁇ 50 ° C. are shown in FIGS. 5 and 6, respectively.
  • charging / discharging occupies 85% or more of the rated capacity at ⁇ 40 ° C. and 70% or more at ⁇ 50 ° C., and the lithium ion battery is normal even in an environment of ⁇ 50 ° C. by using the electrode containing the additive of the present invention. It was confirmed that it can be operated.

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Abstract

[Problem] To provide: a secondary battery that can maintain good battery characteristics even when used in an extremely low-temperature environment; and particularly, an electrode material for the secondary battery. [Solution] Provided is an electrode additive for suppressing a decrease in conductivity in low-temperature operation of a secondary battery, the additive being characterized by the inclusion of a particulate carbon material with an average particle diameter of 20–50 nm, a specific surface area in the range 750–800 m2/g, and a ratio (O/C) of oxygen atoms to carbon atoms in a surface functional group that is 0.025–0.035.

Description

二次電池電極用添加剤Additives for secondary battery electrodes
　本発明は、二次電池の電極用添加剤、より詳細には、二次電池の低温作動下における導電性低下を抑制するための電極用添加剤に関する。 The present invention relates to an additive for an electrode of a secondary battery, and more specifically, an additive for an electrode for suppressing a decrease in conductivity of a secondary battery under low temperature operation.
　二次電池であるリチウムイオン電池は、携帯電話やノートパソコンなどの小型携帯機器用途に加えて、電気自動車や電力蓄電用途などの大型蓄電池としての用途も期待されている。一方で、リチウムイオン電池の用途が広範囲になるにつれて、電池容量、充放電サイクル特性（寿命特性）において高い水準が要求されてきている。そのため、負極材料、正極材料、セパレータ、非水電解液といった各種電池構成部材の改善が進められている（特許文献１等）。 Lithium-ion batteries, which are secondary batteries, are expected to be used as large storage batteries for electric vehicles and electric power storage, in addition to small portable devices such as mobile phones and laptop computers. On the other hand, as the applications of lithium-ion batteries have become widespread, high levels of battery capacity and charge / discharge cycle characteristics (life characteristics) have been required. Therefore, improvements are being made to various battery components such as negative electrode materials, positive electrode materials, separators, and non-aqueous electrolytes (Patent Document 1 and the like).
　正極材料についても、その充放電プロセスは、活物質自体の導電率によって十分には程遠いものとなっているため、電極の良好な充放電性能を確保するために、一定量の導電剤（カーボンブラック、グラファイト、カーボンナノチューブ、グラフェンなど）が添加されている。 Since the charge / discharge process of the positive electrode material is far from sufficient due to the conductivity of the active material itself, a certain amount of conductive agent (carbon black) is used to ensure good charge / discharge performance of the electrode. , Graphite, carbon nanotubes, graphene, etc.) are added.
　しかしながら、－２０℃を下回るような極低温環境下では、リチウムイオン電池正極材料の導電材の活量が低下し、導電性が低下することで、リチウムイオン電池の容量の低下、内部抵抗の上昇、放電効率の低下といった一連の結果が生じるという問題があった。 これに対し、現状では予熱を充電するという使用時の対応がなされているが、バッテリーの使用時間が短縮され、設計コストが増加するため、根本的な対策とはなっていなかった。 However, in an extremely low temperature environment below -20 ° C, the activity of the conductive material of the positive electrode material of the lithium ion battery decreases, and the conductivity decreases, so that the capacity of the lithium ion battery decreases and the internal resistance increases. There is a problem that a series of results such as a decrease in discharge efficiency occur. On the other hand, at present, measures are taken at the time of use to charge the preheat, but it has not been a fundamental measure because the battery usage time is shortened and the design cost is increased.
特開２０１４－２４１３０２号公報Japanese Unexamined Patent Publication No. 2014-241302
　そこで、本発明は、極低温の使用環境下においても良好な電池特性を維持可能な二次電池、特に、そのための電極材料を提供することを課題とするものである。 Therefore, it is an object of the present invention to provide a secondary battery capable of maintaining good battery characteristics even in an extremely low temperature usage environment, particularly an electrode material for that purpose.
　本発明者らは、上記課題を解決するべく鋭意検討を行った結果、特定の性質を有する粒子状のカーボン材料を電極用添加剤（特に、正極用添加剤）として用いることで、－２０℃を下回るような極低温の使用環境下におけるリチウムイオン電池等の二次電池の導電性の低下を抑制でき、良好な充放電特性が得られることを見出し、本発明を完成するに至った。また、上記カーボン材料に加えて、カーボンナノチューブ（ＣＮＴ）やグラフェンのようなカーボンナノ材料をさらに添加することで、低温環境下における導電性の低下をさらに効率的に抑制できることを併せて見出した。 As a result of diligent studies to solve the above problems, the present inventors have used a particulate carbon material having specific properties as an electrode additive (particularly, a positive electrode additive) at −20 ° C. It has been found that a decrease in conductivity of a secondary battery such as a lithium ion battery can be suppressed and good charge / discharge characteristics can be obtained in an extremely low temperature usage environment below the above, and the present invention has been completed. Further, they have also found that by further adding carbon nanomaterials such as carbon nanotubes (CNT) and graphene in addition to the above carbon materials, it is possible to more efficiently suppress a decrease in conductivity in a low temperature environment.
　すなわち、本発明は、一態様において
＜１＞二次電池の低温作動下における導電性低下を抑制するための電極用添加剤であって、２０～５０ｎｍの平均粒径を有し；７５０～８００ｍ２／ｇの範囲の比表面積を有し；表面官能基における酸素原子と炭素原子の比（Ｏ／Ｃ）が０．０２５～０．０３５である粒子状のカーボン材料を含むことを特徴とする、電極用添加剤；
＜２＞前記カーボン材料が、表面改質カーボンブラックである、上記＜１＞に記載の電極用添加剤；
＜３＞カーボンナノチューブ（ＣＮＴ）、グラフェン、又はこれらの組み合わせをさらに含む、上記＜１＞又は＜２＞に記載の電極用添加剤；及び
＜４＞前記カーボン材料とカーボンナノチューブとグラフェンの重量比が、８０～９０重量％：０～１０重量％：０～１０重量％の範囲である、上記＜３＞に記載の電極用添加剤
に関する。 That is, the present invention is an additive for an electrode for suppressing a decrease in conductivity of a secondary battery under low temperature operation in one embodiment, and has an average particle size of 20 to 50 nm; 750 to 800 m. It has a specific surface area in the range of 2 / g; is characterized by containing a particulate carbon material having an oxygen atom to carbon atom ratio (O / C) of 0.025 to 0.035 in the surface functional group. , Additives for electrodes;
<2> The electrode additive according to <1> above, wherein the carbon material is surface-modified carbon black;
<3> Additive for electrode according to <1> or <2> above, further comprising carbon nanotube (CNT), graphene, or a combination thereof; and <4> Weight ratio of carbon material to carbon nanotube to graphene. However, the electrode additive according to <3> above, which is in the range of 80 to 90% by weight: 0 to 10% by weight: 0 to 10% by weight.
　本発明は、別の態様において
＜５＞集電体と、前記集電体上に形成された活物質層とを備え、前記活物質層が、上記＜１＞～＜４＞のいずれか１に記載の電極用添加剤を含有することを特徴とする、二次電池用電極；
＜６＞正極である、上記＜５＞に記載の二次電池用電極；
＜７＞前記活物質層における活物質が、リチウム含有遷移金属酸化物である、請求項６に記載の二次電池用電極；
＜８＞上記＜５＞～＜７＞のいずれか１に記載の二次電池用電極を備える、二次電池；及び
＜９＞リチウムイオン電池である、請求項８に記載の二次電池
に関する。 In another aspect, the present invention comprises a <5> current collector and an active material layer formed on the current collector, and the active material layer is any one of the above <1> to <4>. An electrode for a secondary battery, which comprises the electrode additive according to the above;
<6> The electrode for a secondary battery according to <5> above, which is a positive electrode;
<7> The electrode for a secondary battery according to claim 6, wherein the active material in the active material layer is a lithium-containing transition metal oxide;
<8> The secondary battery according to claim 8, wherein the secondary battery includes the electrode for the secondary battery according to any one of <5> to <7>above; and <9> a lithium ion battery. ..
　本発明は、さらなる態様において
＜１０＞二次電池の低温作動下における導電性低下を抑制するための電極用添加剤の製造方法であって、粒子状のカーボン材料を４００～７００℃で加熱する工程、加熱後のカーボン材料を酸性水溶液中で処理する工程、及び得られたカーボン材料を乾燥させて、表面改質カーボン材料を得る工程を含む、該製造方法；
＜１１＞前記カーボン材料が、カーボンブラックである、上記＜１０＞に記載の製造方法；
＜１２＞前記酸性水溶液が、硝酸水溶液である、上記＜１０＞又は＜１１＞に記載の製造方法；及び
＜１３＞前記表面改質カーボン材料を、カーボンナノチューブ（ＣＮＴ）、グラフェン、又はこれらの組み合わせと混合する工程をさらに含む、上記＜１０＞～＜１２＞のいずれか１に記載の製造方法
に関する。 In a further aspect, the present invention is a method for producing an additive for an electrode for suppressing a decrease in conductivity under low temperature operation of a <10> secondary battery, in which a particulate carbon material is heated at 400 to 700 ° C. The production method comprising a step, a step of treating the heated carbon material in an acidic aqueous solution, and a step of drying the obtained carbon material to obtain a surface-modified carbon material;
<11> The production method according to <10> above, wherein the carbon material is carbon black;
<12> The production method according to <10> or <11> above, wherein the acidic aqueous solution is a nitric acid aqueous solution; The production method according to any one of <10> to <12> above, further comprising a step of mixing with the combination.
　本発明によれば、－２０℃を下回るような極低温の使用環境下においてもリチウムイオン電池等の二次電池の導電性の低下を抑制でき、常温作動時に近い良好な充放電特性を得ることができる。これにより、寒冷地域でのパワーバッテリー製品（無人航空機、電気自動車、ロボット、天秤車など）の使用時における充放電欠陥を解決することができる。また、本発明の電極用添加剤は、良好な分散を有しているため、従来の導電剤と比較して、非常に少ない添加量（例えば、１％以下）によって、導電率、レート及びサイクル特性を改善することができるという利点も有する。 According to the present invention, it is possible to suppress a decrease in conductivity of a secondary battery such as a lithium ion battery even in an extremely low temperature usage environment of less than −20 ° C., and to obtain good charge / discharge characteristics close to normal temperature operation. Can be done. This makes it possible to solve charge / discharge defects when using power battery products (unmanned aerial vehicles, electric vehicles, robots, balance vehicles, etc.) in cold regions. In addition, since the electrode additive of the present invention has good dispersion, the conductivity, rate and cycle can be increased by a very small amount (for example, 1% or less) as compared with the conventional conductive agent. It also has the advantage that the properties can be improved.
図１は、本発明の電極用添加剤の粒径・空孔径分布を示すグラフである。FIG. 1 is a graph showing the particle size and pore size distribution of the electrode additive of the present invention. 図２は、本発明の電極用添加剤のＸＰＳチャートである。FIG. 2 is an XPS chart of the electrode additive of the present invention. 図３は、本発明の電極用添加剤を含有する電極表面の電子顕微鏡イメージ画像である。FIG. 3 is an electron microscope image of the surface of the electrode containing the additive for the electrode of the present invention. 図４は、温度環境を０℃～－３５℃の範囲で変化させた場合の放電曲線を示すグラフである。FIG. 4 is a graph showing a discharge curve when the temperature environment is changed in the range of 0 ° C. to −35 ° C. 図５は、温度環境を－４０℃に変化させた場合の放電曲線を示すグラフである。FIG. 5 is a graph showing a discharge curve when the temperature environment is changed to −40 ° C. 図６は、温度環境を－５０℃に変化させた場合の放電曲線を示すグラフである。FIG. 6 is a graph showing a discharge curve when the temperature environment is changed to −50 ° C. 図７は、異なるレートにおける充放電曲線を示すグラフである。FIG. 7 is a graph showing charge / discharge curves at different rates. 図８は、活物質としてＬｉＦｅＰＯ４を用いた場合の充放電サイクルを示グラフである。FIG. 8 is a graph showing a charge / discharge cycle when LiFePO 4 is used as the active material. 図９は、活物質として３元系［Ｌｉ（Ｎｉ－Ｍｎ－Ｃｏ）Ｏ２］を用いた場合の充放電サイクルを示グラフである。FIG. 9 is a graph showing a charge / discharge cycle when a ternary system [Li (Ni—Mn—Co) O 2] is used as the active material. 図１０は、活物質としてＬｉＭｎ２Ｏ４を用いた場合の充放電サイクルを示グラフである。FIG. 10 is a graph showing a charge / discharge cycle when LiMn 2 O 4 is used as the active material.
　以下、本発明の実施形態について説明する。本発明の範囲はこれらの説明に拘束されることはなく、以下の例示以外についても、本発明の趣旨を損なわない範囲で適宜変更し実施することができる。 Hereinafter, embodiments of the present invention will be described. The scope of the present invention is not limited to these explanations, and other than the following examples, the scope of the present invention can be appropriately modified and implemented as long as the gist of the present invention is not impaired.
１．電極用添加剤
　本発明の電極用添加剤は、二次電池の低温作動下における導電性低下を抑制するためのものであって、以下の１）～３）を満たす粒子状のカーボン材料を含むことを特徴とする。
　１）２０～５０ｎｍの平均粒径を有すること；
　２）７５０～８００ｍ２／ｇの範囲の比表面積を有すること；
　３）表面官能基における酸素原子と炭素原子の比（Ｏ／Ｃ）が０．０２５～０．０３５であること。 1. 1. Additives for Electrodes The additive for electrodes of the present invention is for suppressing a decrease in conductivity under low temperature operation of a secondary battery, and contains a particulate carbon material satisfying the following 1) to 3). It is characterized by that.
1) Have an average particle size of 20-50 nm;
2) Have a specific surface area in the range of 750 to 800 m 2 / g;
3) The ratio (O / C) of oxygen atom to carbon atom in the surface functional group is 0.025 to 0.035.
　これら１）～３）を満たすことにより、導電性を有する表面改質カーボン材料が、疎水性と親水性の適度なバランスを有し、カーボン材料の表面酸化と高速振動粉砕法による分散性向上について、電極表面に均一に分散するとともに、電極活物質と架橋して多分岐構造の３次元ネットワークを形成することが見いだされた。これにより、極低温の使用環境下においても二次電池の導電性の低下を抑制でき、常温作動時に近い良好な充放電特性を得ることができる。同時に、従来の導電剤と比較して、非常に少ない添加量（例えば、１％以下）によって、かかる効果を得ることができる。 By satisfying these 1) to 3), the surface-modified carbon material having conductivity has an appropriate balance between hydrophobicity and hydrophilicity, and the surface oxidation of the carbon material and the improvement of dispersibility by the high-speed vibration pulverization method are performed. It was found that the mixture was uniformly dispersed on the surface of the electrode and crosslinked with the active electrode material to form a three-dimensional network having a multi-branched structure. As a result, it is possible to suppress a decrease in the conductivity of the secondary battery even in an extremely low temperature usage environment, and it is possible to obtain good charge / discharge characteristics close to those during normal temperature operation. At the same time, such an effect can be obtained with a very small amount of addition (for example, 1% or less) as compared with the conventional conductive agent.
　本発明において用いられるカーボン材料は、黒鉛化されたものから非晶質のものにいたるまで種々の黒鉛化度の炭素系材料を用いることができる。例えば、カーボンブラック、天然黒鉛、人工黒鉛、ハードカーボン、ソフトカーボン、ケッチェンブラック、アセチレンブラック、活性炭などが挙げられる。また、黒鉛化度の小さいカーボン材料が良く、中でも、カーボンブラックであることが好ましい。これらのカーボン材料は、後述のように、上記１）～３）を満たすように表面改質処理されたものであることが好ましい。 As the carbon material used in the present invention, carbon-based materials having various degrees of graphitization can be used, from graphitized materials to amorphous materials. For example, carbon black, natural graphite, artificial graphite, hard carbon, soft carbon, Ketjen black, acetylene black, activated carbon and the like can be mentioned. Further, a carbon material having a small degree of graphitization is preferable, and carbon black is particularly preferable. As will be described later, these carbon materials are preferably surface-modified so as to satisfy the above 1) to 3).
　また、カーボン材料としては、本発明で規定する上記１）～３）を満たすものである限り、カーボン材料に金属粒子、及び金属酸化物粒子等の粒子を任意の組み合わせで適宜混合して用いても良い。また、個々の粒子中に複数の材料が混在するものであってもよい。例えば、黒鉛の表面を黒鉛化度の小さい炭素系材料で被覆した構造の炭素質粒子とすることもできる。 Further, as the carbon material, as long as it satisfies the above 1) to 3) specified in the present invention, the carbon material is appropriately mixed with particles such as metal particles and metal oxide particles in any combination. Is also good. Further, a plurality of materials may be mixed in each particle. For example, carbonaceous particles having a structure in which the surface of graphite is coated with a carbon-based material having a low degree of graphitization can be used.
　上述のように、本発明において用いられるカーボン材料の平均粒径は、２０～５０ｎｍであり、好ましくは、２５～４５ｎｍであることができる。これにより、電極作製時に用いる溶媒中への分散性や電極表面における均一性を適切なものをすることができる。なお、平均粒径は、市販のレーザー回折／散乱式粒度分布測定装置などを用いて、公知の手法により測定することができる。 As described above, the average particle size of the carbon material used in the present invention can be 20 to 50 nm, preferably 25 to 45 nm. Thereby, the dispersibility in the solvent used at the time of manufacturing the electrode and the uniformity on the surface of the electrode can be made appropriate. The average particle size can be measured by a known method using a commercially available laser diffraction / scattering type particle size distribution measuring device or the like.
　本発明において用いられるカーボン材料の比表面積は、７５０～８００ｍ２／ｇの範囲であり、好ましくは７６０～７８０ｍ２／ｇの範囲である。かかる比表面積が当該範囲未満であると高速充電特性が劣る可能性があり、また、当該範囲を超えると初期不可逆容量が大きくなり過ぎる可能性がある。なお、比表面積は、窒素ガス吸着流通法などの公知の手法及び装置を用いて測定することができる。 The specific surface area of the carbon material used in the present invention is in the range of 750 to 800 m 2 / g, preferably in the range of 760 to 780 m 2 / g. If the specific surface area is less than this range, the fast charging characteristics may be inferior, and if it exceeds the range, the initial irreversible capacity may become too large. The specific surface area can be measured by using a known method and apparatus such as a nitrogen gas adsorption and flow method.
　また、本発明において用いられるカーボン材料は、表面官能基における酸素原子と炭素原子の比（Ｏ／Ｃ原子比）が０．０２５～０．０３５、好ましくは、０．０２７～０．０３３の範囲である。ここで、酸素原子（Ｏ）に相当する部分は、カーボン材料の粒子表面上におけるＯＨ基に主として由来するものであり、Ｏ／Ｃ原子比をかかる範囲内とすることで、疎水性と親水性の適度なバランスを有し、電極作製時に用いる溶媒として用いられる有機溶媒中にも、或いは水等の親水性溶媒中にも分散させることができる。加えて、電極表面にも均一に分布することができる。 Further, the carbon material used in the present invention has an oxygen atom to carbon atom ratio (O / C atom ratio) in the surface functional group in the range of 0.025 to 0.035, preferably 0.027 to 0.033. Is. Here, the portion corresponding to the oxygen atom (O) is mainly derived from the OH group on the particle surface of the carbon material, and by setting the O / C atom ratio within such a range, it is hydrophobic and hydrophilic. It has an appropriate balance of, and can be dispersed in an organic solvent used as a solvent used when producing an electrode, or in a hydrophilic solvent such as water. In addition, it can be uniformly distributed on the electrode surface.
　かかるＯ／Ｃ原子比は、Ｘ線光電子分光法（ＸＰＳ）を用いて測定することができる。例えば、ＸＰＳ分析におけるＯ１ｓのスペクトル（５２５～５４５ｅＶ）のピーク面積に基づいて求めた酸素原子濃度と、ＸＰＳ分析におけるＣ１ｓのスペクトル（２８０～３００ｅＶ）のピーク面積に基づいて求めた炭素原子濃度から、Ｏ／Ｃ原子比を求めることができる。 The O / C atomic ratio can be measured using X-ray photoelectron spectroscopy (XPS). For example, from the oxygen atom concentration obtained based on the peak area of the O1s spectrum (525 to 545 eV) in the XPS analysis and the carbon atom concentration obtained based on the peak area of the C1s spectrum (280 to 300 eV) in the XPS analysis. The O / C atomic ratio can be determined.
　好ましい態様において、本発明の電極用添加剤は、上記カーボン材料に加えて、これとは別のカーボンナノ材料をさらに含むことができる。かかるカーボンナノ材料を含有することにより、低温環境下における導電性の低下をさらに効率的に抑制できる。そのようなカーボンナノ材料としては、例えば、カーボンナノチューブ（ＣＮＴ）、カーボンナノファイバー（ＣＮＦ）、グラフェン、カーボンナノホーン（ＣＮＨ）、フラーレン、又はそれらの組み合わせを挙げることができ、或いは、これらを化学的に修飾した物質であってもよい。好ましくは、カーボンナノチューブ（ＣＮＴ）、グラフェン、又はこれらの組み合わせである。これらカーボンナノ材料の製造方法は特に制限されず、従来から公知の方法によって製造することができ、また、市販のものをそのまま用いることもできる。 In a preferred embodiment, the electrode additive of the present invention may further contain another carbon nanomaterial in addition to the above carbon material. By containing such carbon nanomaterials, it is possible to more efficiently suppress a decrease in conductivity in a low temperature environment. Examples of such carbon nanomaterials include carbon nanotubes (CNTs), carbon nanofibers (CNFs), graphene, carbon nanohorns (CNH), fullerenes, or combinations thereof, or chemicals thereof. It may be a substance modified to. Preferably, it is carbon nanotube (CNT), graphene, or a combination thereof. The method for producing these carbon nanomaterials is not particularly limited, and they can be produced by a conventionally known method, or commercially available ones can be used as they are.
　カーボンナノチューブは、一般に、炭素の六員環配列構造を有する１枚のシート状グラファイト（グラフェンシート）が円筒状に巻かれた直径数ｎｍ程度のチューブ状構造を有する材料である。本明細書において「カーボンナノチューブ」には、１枚のシート状グラファイトで構成された単層カーボンナノチューブの他、前記筒状のシートが軸直角方向に複数積層した多層カーボンナノチューブ（カーボンナノチューブの内部にさらに径の小さいカーボンナノチューブを１個以上内包する多層カーボンナノチューブ）、単層カーボンナノチューブの端部が円錐状で閉じた形状のカーボンナノホーン、内部にフラーレンを内包するカーボンナノチューブなども包含される。これらのカーボンナノチューブは、単独で又は二種以上組み合わせて使用できる。 Carbon nanotubes are generally materials having a tubular structure having a diameter of about several nm, in which one sheet-shaped graphite (graphene sheet) having a six-membered ring arrangement structure of carbon is wound in a cylindrical shape. In the present specification, the "carbon nanotube" includes a single-walled carbon nanotube composed of one sheet of graphite and a multi-walled carbon nanotube (inside the carbon nanotube) in which a plurality of the tubular sheets are laminated in the direction perpendicular to the axis. Further, multi-walled carbon nanotubes containing one or more small-diameter carbon nanotubes), carbon nanohorns having a conical and closed end of single-walled carbon nanotubes, carbon nanotubes containing fullerene inside, and the like are also included. These carbon nanotubes can be used alone or in combination of two or more.
　カーボンナノチューブの平均径（軸方向に対して直交する方向の直径又は横断面径）は、例えば、０．５ｎｍ～１μｍ、好ましくは１～１００ｎｍの範囲から選択でき、単層カーボンナノチューブの場合には、例えば、０．５～１０ｎｍ、好ましくは１～５ｎｍ程度であり、多層カーボンナノチューブの場合は、例えば、５～３００ｎｍ、好ましくは１０～１００ｎｍ程度である。カーボンナノチューブの平均長は、例えば、１～１０００μｍ、好ましくは５～５００μｍの範囲である。 The average diameter of the carbon nanotubes (diameter in the direction orthogonal to the axial direction or cross-sectional diameter) can be selected from, for example, 0.5 nm to 1 μm, preferably 1 to 100 nm, and in the case of single-walled carbon nanotubes. For example, it is about 0.5 to 10 nm, preferably about 1 to 5 nm, and in the case of multi-walled carbon nanotubes, it is, for example, about 5 to 300 nm, preferably about 10 to 100 nm. The average length of carbon nanotubes is, for example, in the range of 1 to 1000 μm, preferably 5 to 500 μm.
　カーボンナノ材料を用いる場合、カーボン材料との比率は、所望の導電性や分散性の観点から適宜調整することができる。好ましくは、カーボン材料：カーボンナノ材料の重量比が、８０～９０重量％：１０～２０重量％の範囲であることができる。カーボンナノ材料として複数成分を用いる場合も同様である。例えば、カーボンナノ材料としてカーボンナノチューブ（ＣＮＴ）とグラフェンを用いる場合には、電極用添加剤中におけるカーボン材料とカーボンナノチューブとグラフェンの重量比は、８０～９０重量％：０～１０重量％：０～１０重量％の範囲であることが好ましい。 When carbon nanomaterials are used, the ratio with the carbon material can be appropriately adjusted from the viewpoint of desired conductivity and dispersibility. Preferably, the weight ratio of carbon material: carbon nanomaterial can be in the range of 80-90% by weight: 10-20% by weight. The same applies when a plurality of components are used as the carbon nanomaterial. For example, when carbon nanotubes (CNT) and graphene are used as carbon nanomaterials, the weight ratio of the carbon material, carbon nanotubes, and graphene in the electrode additive is 80 to 90% by weight: 0 to 10% by weight: 0. It is preferably in the range of ~ 10% by weight.
　本発明の電極用添加剤は、粉末の形態、又は溶媒中に分散させた分散液形態のいずれの形態でも用いることができる。分散液の場合の溶媒としては、有機溶媒、水、又はこれらの混合溶媒であることができる。典型的には、分散液の場合には、カーボンナノ材料（及び、存在する場合はカーボンナノ材料）を１～２０重量％、好ましくは、５～１０重量％の範囲で含有することができる。なお、分散液には、必要に応じて、界面活性剤などの分散剤を添加してもよい。 The electrode additive of the present invention can be used in either a powder form or a dispersion liquid form dispersed in a solvent. The solvent in the case of the dispersion liquid can be an organic solvent, water, or a mixed solvent thereof. Typically, in the case of a dispersion, carbon nanomaterials (and carbon nanomaterials, if any) can be contained in the range of 1-20% by weight, preferably 5-10% by weight. If necessary, a dispersant such as a surfactant may be added to the dispersion liquid.
２．電極用添加剤の製造方法
　本発明は、上記電極用添加剤の製造方法にも関し、当該製造方法を以下の工程を含む。
（ａ）粒子状のカーボン材料を４００～７００℃で加熱する工程；
（ｂ）加熱後のカーボン材料を酸性水溶液中で処理する工程；及び
（ｃ）得られたカーボン材料を乾燥させて、表面改質カーボン材料を得る工程。 2. Method for Producing Additive for Electrode The present invention also relates to the method for manufacturing the additive for electrode, and the manufacturing method includes the following steps.
(A) Step of heating particulate carbon material at 400-700 ° C;
(B) A step of treating the heated carbon material in an acidic aqueous solution; and (c) a step of drying the obtained carbon material to obtain a surface-modified carbon material.
　工程（ａ）～（ｃ）を行うことにより、上述の（１）～（３）の物性を満たす表面改質カーボン材料を得ることができる。 By performing the steps (a) to (c), a surface-modified carbon material satisfying the above-mentioned physical properties of (1) to (3) can be obtained.
　工程（ａ）は、４００～７００℃、好ましくは、５００～６５０℃の加熱温度で、カーボン材料を焼成する工程である。当該工程は、アルゴン等の不活性ガス雰囲気下で、２～３時間行うことが好ましい。原料となるカーボン材料としては、上述のように種々の黒鉛化度の炭素系材料を用いることができ、好ましくは、カーボンブラックである。原料となるカーボン材料自体の製造方法は特に制限されず、従来から公知の方法によって製造することができ、また、市販のものをそのまま用いることもできる。 Step (a) is a step of firing the carbon material at a heating temperature of 400 to 700 ° C., preferably 500 to 650 ° C. The step is preferably carried out in an atmosphere of an inert gas such as argon for 2 to 3 hours. As the carbon material used as a raw material, carbon-based materials having various degrees of graphitization can be used as described above, and carbon black is preferable. The method for producing the carbon material itself as a raw material is not particularly limited, and it can be produced by a conventionally known method, or a commercially available material can be used as it is.
　工程（ｂ）は、工程（ａ）で得られたカーボン材料を適宜冷却後、酸性水溶液中で処理する工程である。これにより、表面にＯＨ基等を生じさせ、カーボン材料に適度の親水性を付与することができる。酸性水溶液としては、典型的には、硝酸などの強酸の水溶液を用いることができる。 Step (b) is a step of appropriately cooling the carbon material obtained in step (a) and then treating it in an acidic aqueous solution. As a result, OH groups and the like can be generated on the surface, and appropriate hydrophilicity can be imparted to the carbon material. As the acidic aqueous solution, an aqueous solution of a strong acid such as nitric acid can be typically used.
　工程（ｃ）は、工程（ｂ）の酸性水溶液からカーボン材料を分離して、乾燥することにより目的物である表面改質カーボン材料を得る工程である。酸性水溶液からのカーボン材料の分離は、ろ過など当該技術分野で公知の分離手段を用いることができる。 The step (c) is a step of separating the carbon material from the acidic aqueous solution of the step (b) and drying it to obtain the target surface-modified carbon material. For the separation of the carbon material from the acidic aqueous solution, a separation means known in the art such as filtration can be used.
　好ましい態様において、本発明の製造方法は、上記（ｃ）の後に、表面改質カーボン材料と任意のカーボンナノ材料を混合する工程をさらに含むことができる。かかるカーボンナノ材料の種類は、上記で例示したとおりであるが、カーボンナノチューブ（ＣＮＴ）、グラフェン、又はこれらの組み合わせを用いることが好ましい。 In a preferred embodiment, the production method of the present invention can further include a step of mixing the surface-modified carbon material and any carbon nanomaterial after the above (c). The types of such carbon nanomaterials are as exemplified above, but it is preferable to use carbon nanotubes (CNT), graphene, or a combination thereof.
　得られた表面改質カーボン材料（及び、存在する場合はカーボンナノ材料）を含む電極用添加剤は、上述のように、粉末の形態、又は溶媒中に分散させた分散液形態のいずれの形態でも用いることができる。 As described above, the electrode additive containing the obtained surface-modified carbon material (and carbon nanomaterial if present) is in either a powder form or a dispersion liquid form dispersed in a solvent. Can also be used.
３．二次電池用電極及び二次電池
　別の態様において、本発明は、集電体と、前記集電体上に形成された活物質層とを備え、前記活物質層が、上述の電極用添加剤を含有することを特徴とする、二次電池用電極にも関する。好ましくは、当該電極は、正極（アノード）である。 3. 3. Secondary Battery Electrode and Secondary Battery In another embodiment, the present invention comprises a current collector and an active material layer formed on the current collector, wherein the active material layer is the above-mentioned electrode addition. It also relates to electrodes for secondary batteries, which are characterized by containing an agent. Preferably, the electrode is a positive electrode (anode).
　集電体としては、当該技術分野において公知のものを用いることができ、例えば、銅、ニッケル、アルミニウム、ステンレススチール等を主体とする棒状体、板状体、箔状体、網状体等を使用することができる。 As the current collector, those known in the art can be used, and for example, a rod-shaped body, a plate-shaped body, a foil-shaped body, a net-like body, etc. mainly made of copper, nickel, aluminum, stainless steel, etc. are used. can do.
　活物質層における活物質材料は、二次電池の種類に応じて公知の材料を用いることができる。例えば、二次電池がリチウムイオン電池の場合には、リチウムイオンを吸蔵・放出できる活物質を用いることができる。リチウムイオン電池の場合の正極活物質材料としては、コバルト酸リチウム（ＬｉＣｏＯ２）、マンガン酸リチウム（ＬｉＭｎ２Ｏ４）、ニッケル酸リチウム（ＬｉＮｉＯ２）等の１種類以上の遷移金属を含むリチウム含有遷移金属酸化物、遷移金属硫化物、金属酸化物、リン酸鉄リチウム（ＬｉＦｅＰＯ４）やピロリン酸鉄リチウム（Ｌｉ２ＦｅＰ２Ｏ７）などの１種類以上の遷移金属を含むリチウム含有ポリアニオン系化合物などが挙げられる。好ましくは、活物質材料は、リチウム含有遷移金属酸化物である。 As the active material material in the active material layer, a known material can be used depending on the type of the secondary battery. For example, when the secondary battery is a lithium ion battery, an active material capable of storing and releasing lithium ions can be used. In the case of a lithium ion battery, the positive electrode active material contains lithium containing one or more transition metals such as lithium cobalt oxide (LiCoO 2 ), lithium manganate (LiMn 2 O 4 ), and lithium nickel oxide (LiNiO 2). Lithium-containing polyanionic compounds containing one or more transition metals such as transition metal oxides, transition metal sulfides, metal oxides, lithium iron oxide (LiFePO 4 ) and lithium iron pyrophosphate (Li 2 FeP 2 O 7). And so on. Preferably, the active material is a lithium-containing transition metal oxide.
　また、二次電池がリチウムイオン電池の場合の負極活物質材料としては、例えば、天然グラファイト（黒鉛）、高配向性グラファイト（Ｈｉｇｈｌｙ Ｏｒｉｅｎｔｅｄ Ｐｙｒｏｌｙｔｉｃ Ｇｒａｐｈｉｔｅ；ＨＯＰＧ）、非晶質炭素等の炭素質材料が挙げられる。これら負極活物質は、１種を単独で用いてもよく、２種以上を併用してもよい。 When the secondary battery is a lithium ion battery, examples of the negative electrode active material include carbonaceous materials such as natural graphite (graphite), highly oriented pyrolytic graphite (HOPG), and amorphous carbon. Can be mentioned. These negative electrode active materials may be used alone or in combination of two or more.
　上記電極は、必要に応じて、結着剤（バインダ）を含有することができる。結着剤としては、例えば、ポリフッ化ビニリデン（ＰＶＤＦ）、ポリテトラフルオロエチレン（ＰＴＦＥ）、エチレンテトラフルオロエチレン（ＥＴＦＥ）等のフッ素系樹脂、或いは、ポリエチレン、ポリプロピレンなどを用いることができる。 The electrode can contain a binder, if necessary. As the binder, for example, a fluororesin such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), or ethylene tetrafluoroethylene (ETFE), polyethylene, polypropylene, or the like can be used.
　典型的には、本発明の電極用添加剤と電極活物質材料とを粉砕・混合することによって電極を調製することができる。かかる粉砕・混合は、特に限定されるものではないが、振動ミル、ジェットミル、ボールミル等の粉砕機を用いて行うことが可能である。かかる混合物を集電体に担持させる方法としては、加圧成型する方法、または有機溶媒などを用いてペースト化し、電極集電体上に塗工し、乾燥後プレスするなどして固着する方法が挙げられる。ペースト化する場合、電極活物質、電極用添加剤、結着剤、有機溶媒からなるスラリーを作製する。 Typically, the electrode can be prepared by pulverizing and mixing the electrode additive of the present invention and the electrode active material material. Such crushing / mixing is not particularly limited, but can be performed by using a crusher such as a vibration mill, a jet mill, or a ball mill. As a method of supporting the mixture on the current collector, there is a method of pressure molding, or a method of pasting with an organic solvent, coating on the electrode current collector, drying and pressing to fix the mixture. Can be mentioned. When making a paste, a slurry consisting of an electrode active material, an electrode additive, a binder, and an organic solvent is prepared.
　また、好ましい態様では、本発明の電極用添加剤によって電極活物質材料を被覆することもできる。かかる被覆を行う方法としては、電極用添加剤を含む液体中に電極活物質材料の粉体を浸し、その後熱処理することで当該活物質の粉体表面に電極用添加剤を析出させる手法が挙げられる。 Further, in a preferred embodiment, the electrode active material can be coated with the electrode additive of the present invention. As a method of performing such coating, a method of immersing the powder of the electrode active material in a liquid containing the electrode additive and then heat-treating the powder to deposit the electrode active material on the powder surface of the active material can be mentioned. Be done.
４．二次電池
　更なる態様において、本発明は、二次電池用電極を備える、二次電池にも関する。当該二次電池は、好ましくは、非水系二次電池、より好ましくはリチウムイオン電池である。 4. Secondary Battery In a further aspect, the present invention also relates to a secondary battery comprising electrodes for the secondary battery. The secondary battery is preferably a non-aqueous secondary battery, more preferably a lithium ion battery.
　本発明の二次電池の構成は、従来公知のリチウムイオン二次電池と同様であり、通常、リチウムイオンを吸蔵・放出可能な正極及び負極、セパレータ、電解液を備える。電極については、既に述べたとおりであるが、好ましくは、正極は本発明の電極用添加剤を含有する。 The configuration of the secondary battery of the present invention is the same as that of a conventionally known lithium ion secondary battery, and usually includes a positive electrode and a negative electrode capable of storing and releasing lithium ions, a separator, and an electrolytic solution. As for the electrode, as described above, preferably, the positive electrode contains the additive for the electrode of the present invention.
　リチウムイオン二次電池の場合、低温電解液は、リチウム塩を電解質とするものであれば特に限定されない。そのような電解質は、例えば、ＬｉＰＦ６、ＬｉＢＦ４、ＬｉＣｌＯ４、ＬｉＮＯ３、ＬｉＣｌ、Ｌｉ２ＳＯ４及びＬｉ２Ｓ等及びこれらの任意の組み合わせから選択されるものが挙げられる。 In the case of a lithium ion secondary battery, the low temperature electrolyte is not particularly limited as long as it uses a lithium salt as an electrolyte. Such electrolytes include, for example, those selected from LiPF 6 , LiBF 4 , LiClO 4 , LiNO 3 , LiCl, Li 2 SO 4 and Li 2 S and any combination thereof.
　電解液における溶媒としては、例えばプロピレンカーボネート（ＰＣ）、エチレンカーボネート（ＥＣ）、ジメチルカーボネート（ＤＭＣ）、ジエチルカーボネート（ＤＥＣ）、エチルメチルカーボネート、４－トリフルオロメチル－１，３－ジオキソラン－２－オン、１，２－ジ（メトキシカルボニルオキシ）エタンなどのカーボネート類；１，２－ジメトキシエタン、１，３－ジメトキシプロパン、ペンタフルオロプロピルメチルエーテル、２，２，３，３－テトラフルオロプロピルジフルオロメチルエーテル、テトラヒドロフラン、２－メチルテトラヒドロフランなどのエーテル類；ギ酸メチル、酢酸メチル、γ－ブチロラクトンなどのエステル類；アセトニトリル、ブチロニトリルなどのニトリル類；Ｎ，Ｎ－ジメチルホルムアミド、Ｎ，Ｎ－ジメチルアセトアミドなどのアミド類；３－メチル－２－オキサゾリドンなどのカーバメート類；スルホラン、ジメチルスルホキシド、１，３－プロパンサルトンなどの含硫黄化合物、あるいは上記の有機溶媒にさらにフッ素置換基を導入したものを用いることができる。これらのうち１種を単独で用いてもよく、２種以上を組み合わせて用いてもよい。ただし、これらに限定されるものではない。 Examples of the solvent in the electrolytic solution include propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate, 4-trifluoromethyl-1,3-dioxolan-2- Carbonates such as on, 1,2-di (methoxycarbonyloxy) ethane; 1,2-dimethoxyethane, 1,3-dimethoxypropane, pentafluoropropylmethyl ether, 2,2,3,3-tetrafluoropropyldifluoro Ethers such as methyl ether, tetrahydrofuran and 2-methyltetraxyl; esters such as methyl formate, methyl acetate and γ-butyrolactone; nitriles such as acetonitrile and butyronitrile; N, N-dimethylformamide, N, N-dimethylacetamide and the like. Amides of be able to. One of these may be used alone, or two or more thereof may be used in combination. However, it is not limited to these.
　また、電解液の代わりに、固体電解質を用いることもできる。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もしくはポリオキシアルキレン鎖の少なくとも１種以上を含む高分子化合物などの高分子電解質が挙げられる。また、上記電解液にポリマーを添加してゲル化させた非水ゲル電解質の形態で用いることもできる。 Also, a solid electrolyte can be used instead of the electrolytic solution. Examples of the solid electrolyte include polymer electrolytes such as polyethylene oxide-based polymer compounds and polymer compounds containing at least one polyorganosiloxane chain or polyoxyalkylene chain. It can also be used in the form of a non-aqueous gel electrolyte obtained by adding a polymer to the above electrolytic solution and gelling it.
　また、電解液には、その機能の向上等の目的で、必要に応じて他の成分を含むこともできる。他の成分としては、例えば、従来公知の過充電防止剤、脱水剤、脱酸剤、高温保存後の容量維持特性およびサイクル特性を改善するための特性改善助剤が挙げられる。 Further, the electrolytic solution may contain other components as necessary for the purpose of improving its function. Other components include, for example, conventionally known overcharge inhibitors, dehydrating agents, deoxidizers, and property improving aids for improving capacity retention properties and cycle properties after high temperature storage.
　本発明の二次電池において用いられるセパレータとしては、正極層と負極層とを電気的に分離する機能を有するものであれば特に限定されるものではないが、例えばポリエチレン（ＰＥ）、ポリプロピレン（ＰＰ）、ポリエステル、セルロース、ポリアミド等の樹脂からなる多孔質シートや、不織布、ガラス繊維不織布等の不織布等の多孔質絶縁材料等を挙げることができる。 The separator used in the secondary battery of the present invention is not particularly limited as long as it has a function of electrically separating the positive electrode layer and the negative electrode layer, but for example, polyethylene (PE) and polypropylene (PP). ), Porous sheets made of resins such as polyester, cellulose and polyamide, and porous insulating materials such as non-woven fabrics such as non-woven fabrics and glass fiber non-woven fabrics.
　本発明の二次電池の形状は、正極、負極、及び電解液を収納することができれば特に限定されるものではないが、例えば、円筒型、コイン型、平板型、ラミネート型等を挙げることができる。 The shape of the secondary battery of the present invention is not particularly limited as long as it can store the positive electrode, the negative electrode, and the electrolytic solution, and examples thereof include a cylindrical type, a coin type, a flat plate type, and a laminated type. can.
　以下、実施例により本発明をさらに詳細に説明するが、本発明はこれらによって限定されるものではない。 Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto.
１．電極用添加剤の調製
　以下の手順により、本発明の電極用添加剤（ＭＥＣ３８０）を調製した。カーボンブラックを５ｍｌ／ｍｉｎの空気気流中において５５０℃で３０分間加熱し、加熱後のカーボン材料を強酸（H2SO4/HNO3＝75 ml/25 ml，H2SO4:18 mol/L, HNO3:15.6 mol/L,25 ℃，30min）中で処理した。孔径0.2μm程度の耐酸性濾紙にてカーボン材料を濾過・回収し、その後アセトンにて洗浄した。さらに、得られたカーボン材料を乾燥（50 ℃，6h）させて、表面改質カーボン材料を得た。表面改質カーボンのみを含む添加剤（実施例１）と、表面改質カーボンに加えてＣＮＴ及びグラフェンを含油する添加剤（実施例２）を得た。 1. 1. Preparation of Electrode Additive The electrode additive (MEC380) of the present invention was prepared by the following procedure. Carbon black is heated at 550 ° C. for 30 minutes in an air stream of 5 ml / min, and the heated carbon material is subjected to strong acid (H 2 SO 4 / HNO 3 = 75 ml / 25 ml, H 2 SO 4 : 18 mol / L). , HNO 3 : 15.6 mol / L, 25 ° C, 30 min). The carbon material was filtered and recovered with an acid-resistant filter paper having a pore size of about 0.2 μm, and then washed with acetone. Further, the obtained carbon material was dried (50 ° C, 6 hours) to obtain a surface-modified carbon material. An additive containing only surface-modified carbon (Example 1) and an additive containing CNT and graphene in addition to the surface-modified carbon (Example 2) were obtained.
２．電極添加剤の物性測定
　上記で得られた電極用添加剤について、粒径分布及びＸＰＳ分析の測定を行った。図１に、粒径・空孔径分布のグラフを示す。その結果、実施例１の添加剤は、平均粒径３５．６ｎｍ、比表面積７８０ｍ２／ｇ、一次粒子径３５．４ｎｍであることが分かった。 2. Measurement of Physical Properties of Electrode Additives The particle size distribution and XPS analysis of the electrode additives obtained above were measured. FIG. 1 shows a graph of particle size / pore size distribution. As a result, it was found that the additive of Example 1 had an average particle size of 35.6 nm, a specific surface area of 780 m 2 / g, and a primary particle size of 35.4 nm.
　図２に、実施例１の添加剤のついて得られたＸＰＳチャートを示す。ＸＰＳのようにスペクトル(波形)を採取する測定方法でのＯとＣの定量分析は、スペクトル中に現れたピークの強度を基に計算を行うが、これはその元素の濃度比例その元素から生じる光電子の数 ＝ ピーク強度という関係があることを利用したものである。その結果、Ｏ１ｓのスペクトル（５２５～５４５ｅＶ）のピーク面積と、Ｃ１ｓのスペクトル（２８０～３００ｅＶ）のピーク面積から、粒子表面上における酸素原子と炭素原子の比（Ｏ／Ｃ）が、３．１／９６．９（＝０．０３２）であることが分かった。 FIG. 2 shows an XPS chart obtained with the additive of Example 1. Quantitative analysis of O and C in a measurement method that collects spectra (waveforms) such as XPS is calculated based on the intensity of peaks appearing in the spectrum, which is proportional to the concentration of the element and arises from the element. This is based on the relationship that the number of photoelectrons = peak intensity. As a result, the ratio of oxygen atoms to carbon atoms (O / C) on the particle surface is 3.1 from the peak area of the O1s spectrum (525 to 545 eV) and the peak area of the C1s spectrum (280 to 300 eV). It was found to be / 96.9 (= 0.032).
３．電極の作製
　上記１．で得た添加剤を用いて、以下の手順により正極を作製した。活物質（Ｌｉ（Ｎｉ－Ｍｎ－Ｃｏ）Ｏ２）94wt.%、導電材（MEC380）1 wt.%、バインダー（Ｎ－メチルピロリドンに溶解したポリフッ化ビニリデン: PolyVinylidene DiFluoride（PVDF））5 wt.%を混練したペーストをドクタ ーブレードにより均一に集電体（正極： Ａｌ箔、負極：Ｃｕ箔）に塗布した。その後、 真空乾燥して溶剤を除去した。 3. 3. Preparation of electrodes 1. Using the additive obtained in the above, a positive electrode was prepared by the following procedure. Active material (Li (Ni-Mn-Co) O 2 ) 94 wt.%, Conductive material (MEC380) 1 wt.%, Binder (PolyVinylidene DiFluoride (PVDF)) 5 wt. The paste kneaded with% was uniformly applied to the current collector (positive electrode: Al foil, negative electrode: Cu foil) by a doctor blade. Then, it was vacuum dried to remove the solvent.
　作製した電極表面の電子顕微鏡画像を図３に示す。図３によれば、本発明の添加剤成分が電極表面で均一に分散しており、電極が完全に被覆されていることが分かった。また、本発明の添加剤成分は、電極中の活物質と強く繋がり、接触度が高く、その結果、互いの架橋により、多分岐構造の３次元ネットワークが形成していることが分かった。 An electron microscope image of the prepared electrode surface is shown in FIG. According to FIG. 3, it was found that the additive component of the present invention was uniformly dispersed on the electrode surface, and the electrode was completely covered. Further, it was found that the additive component of the present invention was strongly connected to the active material in the electrode and had a high degree of contact, and as a result, a three-dimensional network having a multi-branched structure was formed by cross-linking with each other.
４．充放電効率の測定
　上記３．で得られた電極を用いて、充放電特性を測定した。測定は、正極材（Ａｌ）および負極材（Ｃｕ）からなるフルセルを用いて行った。０．５ｍＡ／ｃｍ２の電流値で１時間充電を行い、容量０．５ｍＡｈ／ｃｍ２相当のリチウムを負電極上に析出させた後、電圧が２．４Ｖに達するまで同電流値で放電を行った。 4. Measurement of charge / discharge efficiency 3. The charge / discharge characteristics were measured using the electrodes obtained in. The measurement was performed using a full cell composed of a positive electrode material (Al) and a negative electrode material (Cu). The battery is charged at a current value of 0.5 mA / cm 2 for 1 hour, lithium having a capacity of 0.5 mAh / cm 2 is deposited on a negative electrode, and then discharged at the same current value until the voltage reaches 2.4 V. rice field.
　温度環境を０℃～－３５℃まで変化させた場合の放電曲線を図４に示す。その結果、－３５℃の低温環境下でも正常に動作することが確認された。 Fig. 4 shows the discharge curve when the temperature environment is changed from 0 ° C to -35 ° C. As a result, it was confirmed that it operates normally even in a low temperature environment of −35 ° C.
　さらに、温度環境を－４０℃、－５０℃まで低下させた場合の放電曲線をそれぞれ図５及び図６に示す。その結果、充放電は－４０℃で定格容量の８５％以上、－５０℃でも７０％以上を占め、本発明の添加剤を含む電極を用いることによりリチウムイオン電池を－５０℃の環境でも正常に動作させることができることが確認された。 Further, the discharge curves when the temperature environment is lowered to −40 ° C. and −50 ° C. are shown in FIGS. 5 and 6, respectively. As a result, charging / discharging occupies 85% or more of the rated capacity at −40 ° C. and 70% or more at −50 ° C., and the lithium ion battery is normal even in an environment of −50 ° C. by using the electrode containing the additive of the present invention. It was confirmed that it can be operated.
　－５０℃の条件で得られた放電容量を以下の表に示す。
Figure JPOXMLDOC01-appb-T000001
 The discharge capacity obtained under the condition of -50 ° C is shown in the table below.
Figure JPOXMLDOC01-appb-T000001
　異なるレートにおいても正常な充放電特性が得られることも併せて確認した（図７）。 It was also confirmed that normal charge / discharge characteristics can be obtained even at different rates (Fig. 7).
５．サイクル特性の測定
　上記４．と同様の条件で、種々の活物質を用いた電極を用いて、２５℃におけるサイクル特性を測定した。 5. Measurement of cycle characteristics Above 4. Under the same conditions as above, the cycle characteristics at 25 ° C. were measured using electrodes using various active materials.
　活物質として、ＬｉＦｅＰＯ４、３元系［Ｌｉ（Ｎｉ－Ｍｎ－Ｃｏ）Ｏ２］、及びＬｉＭｎ２Ｏ４を用いた場合の結果を、それぞれ図８～１０に示す。その結果、５０００以上のサイクルの後でも、それぞれ、７７％、８０％、５６％の容量を維持していた。 The results when LiFePO 4 , the ternary system [Li (Ni—Mn—Co) O 2 ], and LiMn 2 O 4 are used as the active material are shown in FIGS. 8 to 10, respectively. As a result, even after 5000 or more cycles, the capacities were maintained at 77%, 80%, and 56%, respectively.

Claims (13)

  1. 　二次電池の低温作動下における導電性低下を抑制するための電極用添加剤であって、
    　２０～５０ｎｍの平均粒径を有し；７５０～８００ｍ２／ｇの範囲の比表面積を有し；表面官能基における酸素原子と炭素原子の比（Ｏ／Ｃ）が０．０２５～０．０３５である粒子状のカーボン材料を含むことを特徴とする、電極用添加剤。     An electrode additive for suppressing a decrease in conductivity under low temperature operation of a secondary battery.
    It has an average particle size of 20 to 50 nm; a specific surface area in the range of 750 to 800 m 2 / g; an oxygen atom to carbon atom ratio (O / C) in the surface functional group is 0.025 to 0.035. An additive for an electrode, which comprises a particulate carbon material.
  2. 　前記カーボン材料が、表面改質カーボンブラックである、請求項１に記載の電極用添加剤。 The electrode additive according to claim 1, wherein the carbon material is surface-modified carbon black.
  3. 　カーボンナノチューブ（ＣＮＴ）、グラフェン、又はこれらの組み合わせをさらに含む、請求項１又は２に記載の電極用添加剤。 The electrode additive according to claim 1 or 2, further comprising carbon nanotubes (CNT), graphene, or a combination thereof.
  4. 　前記カーボン材料とカーボンナノチューブとグラフェンの重量比が、８０～９０重量％：０～１０重量％：０～１０重量％の範囲である、請求項３に記載の電極用添加剤。 The electrode additive according to claim 3, wherein the weight ratio of the carbon material, carbon nanotubes, and graphene is in the range of 80 to 90% by weight: 0 to 10% by weight: 0 to 10% by weight.
  5. 　集電体と、前記集電体上に形成された活物質層とを備え、前記活物質層が、請求項１～４のいずれか１に記載の電極用添加剤を含有することを特徴とする、二次電池用電極。 It is characterized by comprising a current collector and an active material layer formed on the current collector, and the active material layer contains the additive for an electrode according to any one of claims 1 to 4. Electrodes for secondary batteries.
  6. 　正極である、請求項５に記載の二次電池用電極。 The secondary battery electrode according to claim 5, which is a positive electrode.
  7. 　前記活物質層における活物質が、リチウム含有遷移金属酸化物である、請求項６に記載の二次電池用電極。 The electrode for a secondary battery according to claim 6, wherein the active material in the active material layer is a lithium-containing transition metal oxide.
  8. 　請求項５～７のいずれか１に記載の二次電池用電極を備える、二次電池。 A secondary battery comprising the electrode for the secondary battery according to any one of claims 5 to 7.
  9. 　リチウムイオン電池である、請求項８に記載の二次電池。 The secondary battery according to claim 8, which is a lithium ion battery.
  10. 　二次電池の低温作動下における導電性低下を抑制するための電極用添加剤の製造方法であって、
    　粒子状のカーボン材料を４００～７００℃で加熱する工程、
    　加熱後のカーボン材料を酸性水溶液中で処理する工程、及び
    　得られたカーボン材料を乾燥させて、表面改質カーボン材料を得る工程
    を含む、該製造方法。     A method for manufacturing an electrode additive for suppressing a decrease in conductivity under low temperature operation of a secondary battery.
    The process of heating particulate carbon material at 400-700 ° C,
    The production method comprising a step of treating the heated carbon material in an acidic aqueous solution and a step of drying the obtained carbon material to obtain a surface-modified carbon material.
  11. 　前記カーボン材料が、カーボンブラックである、請求項１０に記載の製造方法。 The manufacturing method according to claim 10, wherein the carbon material is carbon black.
  12. 　前記酸性水溶液が、硝酸水溶液である、請求項１０又は１１に記載の製造方法。 The production method according to claim 10 or 11, wherein the acidic aqueous solution is a nitric acid aqueous solution.
  13. 　前記表面改質カーボン材料を、カーボンナノチューブ（ＣＮＴ）、グラフェン、又はこれらの組み合わせと混合する工程をさらに含む、請求項１０～１２のいずれか１に記載の製造方法。 The production method according to any one of claims 10 to 12, further comprising a step of mixing the surface-modified carbon material with carbon nanotubes (CNT), graphene, or a combination thereof.
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JP2011195761A (en) * 2010-03-23 2011-10-06 Mitsubishi Chemicals Corp Flame-retardant polyolefin resin composition
JP2016096125A (en) * 2014-05-19 2016-05-26 日本ケミコン株式会社 Electrode, method for producing the electrode, electricity storage device provided with the electrode, and conductive carbon mixture for electricity storage device electrode
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