WO2012124256A1 - Positive electrode active material for nonaqueous electrolyte secondary batteries, positive electrode using same, and method for producing positive electrode active material - Google Patents

Positive electrode active material for nonaqueous electrolyte secondary batteries, positive electrode using same, and method for producing positive electrode active material Download PDF

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Publication number
WO2012124256A1
WO2012124256A1 PCT/JP2012/000978 JP2012000978W WO2012124256A1 WO 2012124256 A1 WO2012124256 A1 WO 2012124256A1 JP 2012000978 W JP2012000978 W JP 2012000978W WO 2012124256 A1 WO2012124256 A1 WO 2012124256A1
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positive electrode
active material
electrode active
electrolyte secondary
phosphorus
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PCT/JP2012/000978
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French (fr)
Japanese (ja)
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純一 菅谷
宇賀治　正弥
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パナソニック株式会社
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    • 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
    • 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
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
    • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
    • 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 a positive electrode active material for a non-aqueous electrolyte secondary battery, a positive electrode using the same, and a method for producing the positive electrode active material, and more particularly to an improvement of a lithium nickel cobalt composite oxide as a positive electrode active material.
  • Non-aqueous electrolyte secondary batteries such as lithium-ion batteries have high electromotive force and high energy density, and therefore demand is increasing as a main power source for mobile communication devices and portable electronic devices.
  • Nonaqueous electrolyte secondary batteries are also expected as a drive power source for electric vehicles.
  • lithium composite oxide containing cobalt as a main component As a positive electrode active material.
  • a lithium composite oxide containing cobalt as a main component has a high raw material cost. Therefore, a lithium nickel cobalt composite oxide in which a part of cobalt is replaced with nickel has attracted attention.
  • Patent Document 1 proposes to improve charge and discharge efficiency by including phosphorus as a covering element on the particle surface of the lithium composite oxide. Also in Patent Document 2, phosphorus, magnesium and the like are added to the lithium composite oxide.
  • the additive element is distributed on the surface of the positive electrode active material particles as in Patent Document 1. It is advantageous. However, since the positive electrode active material occludes and releases lithium during charge and discharge, the crystal structure is likely to deteriorate when charge and discharge are repeated. When the crystal structure deteriorates, the positive electrode active material particles may be cracked or chipped. Therefore, if the additive element is unevenly distributed on the particle surface, when the positive electrode active material particles are cracked or chipped, the internal positive electrode active material is exposed and the effect of the additive element is reduced.
  • lithium nickel cobalt composite oxide has a high capacity, but has a lower crystal structure stability than other lithium-containing composite oxides such as lithium cobalt composite oxide. . Therefore, cracks and chips of the positive electrode active material particles are likely to become conspicuous with repeated charge / discharge. If cracks and chips are excessive, many gaps are formed between the particles, and the current collecting property may be lowered. Further, when the internal positive electrode active material is exposed due to cracks or chips, a high-resistance film is formed on the exposed surface, and the resistance in the positive electrode active material layer increases. As a result, the capacity maintenance rate in the charge / discharge cycle may decrease.
  • An object of the present invention is to provide a positive electrode active material capable of suppressing a decrease in capacity retention rate in a charge / discharge cycle of a nonaqueous electrolyte secondary battery.
  • One aspect of the present invention includes particles of a composite oxide containing lithium, phosphorus, nickel, and cobalt (that is, lithium nickel cobalt composite oxide containing phosphorus), and the average radius of the composite oxide particles is r
  • the ratio C Ps / C Pc between the concentration C Ps of phosphorus contained in the region within 0.3r from the surface of the particle and the concentration C Pc of phosphorus contained in the region within 0.3r from the center of the particle is 1
  • the present invention relates to a positive electrode active material for a non-aqueous electrolyte secondary battery, which is / 1 to 5/1.
  • Another aspect of the present invention includes a positive electrode current collector and a positive electrode active material layer attached to a surface of the positive electrode current collector, and the positive electrode active material layer includes the positive electrode active material and the binder.
  • the present invention relates to a positive electrode for an electrolyte secondary battery.
  • Still another aspect of the present invention provides: Preparing a first raw material containing nickel and cobalt; An oxide containing a first raw material and a second raw material containing phosphorus, calcined at a temperature exceeding 750 ° C., containing nickel and cobalt, and containing phosphorus at a predetermined concentration in the surface layer and inside And a step of mixing the oxide particles and a third raw material containing lithium, firing these at a temperature of 800 ° C. or lower, and composite oxidation containing lithium, phosphorus, nickel, and cobalt.
  • the average radius of the composite oxide particles is r
  • the ratio C Ps / C Pc with C Pc is 1 / 1-5 / 1, a method for producing a positive active material for a nonaqueous electrolyte secondary battery.
  • phosphorus is distributed not only on the surface layer of the particles of the lithium nickel cobalt composite oxide but also in the interior at a predetermined concentration, so that the non-aqueous electrolyte secondary containing this composite oxide particle as a positive electrode active material A decrease in capacity maintenance rate in the charge / discharge cycle of the battery is suppressed.
  • FIG. 1 is a longitudinal sectional view of a cylindrical lithium ion battery of Example 1.
  • the positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention includes composite oxide particles containing lithium, phosphorus, nickel, and cobalt.
  • the average radius of the composite oxide particles is r
  • the ratio C Ps / C Pc to the concentration C Pc is 1/1 to 5/1 .
  • the complex oxide particles When the complex oxide particles are repeatedly charged and discharged, the crystal structure is deteriorated, which may cause cracking or chipping.
  • the composite oxide particles lithium-containing composite oxides containing nickel have particularly low crystal structure stability. Therefore, cracks and chips are likely to be prominent.
  • the positive electrode active material layer may be cracked or chipped when formed by rolling. In particular, when the active material density in the positive electrode active material layer is high, cracking and chipping during rolling tend to be prominent. Furthermore, when the density of the positive electrode active material layer is high (for example, when having an active material density of 3.6 g / cm 3 or more), a large stress is applied to the composite oxide particles even during the charge / discharge cycle. Cracks and chips are particularly prominent.
  • the composite oxide particles contain phosphorus in a predetermined ratio not only on the surface layer but also inside. Therefore, the composite oxide particles have a stable crystal structure not only on the surface layer but also inside. Therefore, the composite oxide particles are less likely to be cracked or chipped, and even if cracked or chipped, further deterioration of the crystal structure can be suppressed. Thereby, since the fall of electroconductivity can be suppressed and the increase in resistance in a positive electrode active material layer can be suppressed, even if charging / discharging is repeated as a result, it is thought that the fall of charging / discharging characteristics can be prevented.
  • Phosphorus may be distributed at substantially uniform intervals in the composite oxide particles.
  • the distribution of phosphorus in the surface layer and the distribution of phosphorus in the inside may be substantially the same. Further, as long as the composite oxide particles contain phosphorus at a predetermined content, the phosphorus content may decrease from the surface layer to the inside.
  • the distribution of phosphorus in the composite oxide particles can be evaluated based on the ratio C Ps / C Pc between the concentration of phosphorus in the surface layer of the particles and the concentration of phosphorus in the particles.
  • the ratio C Ps / C Pc is, for example, 1.1 / 1 to 4/1, 1.2 / 1 to 3/1, 1.2 / 1 to 2.5 / 1, or 1.2 / 1 to 2. 2/1 may be used.
  • the concentration of phosphorus in the region within 0.3r from the particle surface and within 0.3r from the center can be measured, for example, by the following method. First, composite oxide particles are formed into a pellet, and a region from the surface of the pellet to a depth of 0.3 r is sputtered to determine the composition of elements contained in the region. Thereafter, sputtering is continued, and the composition of elements contained in the region from the depth of 0.7r to the depth of 1r from the surface of the pellet is determined. From the composition thus obtained, the phosphorus concentration can be calculated.
  • the elemental composition can be determined by Auger spectroscopic analysis (AES), X-ray microanalysis (EPMA), secondary ion mass spectrometry (SIMS), time-of-flight mass spectrometry (TOF-SIMS), or the like.
  • AES Auger spectroscopic analysis
  • EPMA X-ray microanalysis
  • SIMS secondary ion mass spectrometry
  • TOF-SIMS time-of-flight mass spectrometry
  • the content of phosphorus in the composite oxide is, for example, more than 1 atomic%, preferably 1.2 atomic% or more, more preferably 1.3 atomic% or more with respect to the total amount of elements excluding lithium and oxygen. is there.
  • phosphorus is distributed even inside the composite oxide particles. Therefore, when the phosphorus content is in the above range, the crystal structure of the composite oxide can be effectively stabilized over the entire particle. Therefore, it is advantageous in obtaining the effect of adding phosphorus effectively.
  • the phosphorus content is 1 atomic% or less, the effect of stabilizing the crystal structure of the composite oxide becomes poor by distributing phosphorus up to the inside of the composite oxide particles.
  • the upper limit of the content is, for example, 5 atomic% or less, preferably 4 atomic% or less, and more preferably 3 atomic% or less. These upper and lower limits can be combined as appropriate.
  • the content of nickel in the composite oxide is, for example, 60 to 90 atomic%, preferably 65 to 85 atomic%, based on the total amount of elements excluding lithium and oxygen.
  • the content of nickel is large, it becomes difficult to stabilize the crystal structure. Therefore, when the nickel content is in such a range, the effect of adding phosphorus is remarkably obtained. Further, when the nickel content is in the above range, a high battery capacity can be secured more effectively.
  • the cobalt content in the composite oxide is, for example, 5 to 30 atomic%, preferably 10 to 25 atomic%, based on the total amount of elements excluding lithium and oxygen.
  • the cobalt content is in such a range, it is more advantageous in terms of stabilization of the crystal structure, and a high battery capacity can be secured more effectively. Moreover, it is advantageous also in terms of cost.
  • the composite oxide may further contain an element M other than lithium, phosphorus, nickel, cobalt, and oxygen.
  • the element M include alkaline earth metal elements, transition metal elements other than nickel and cobalt, rare earth elements, Group 13 elements and Group 14 elements of the periodic table.
  • Specific examples of the element M include Mg, Ca, Y, Ti, Zr, Nb, Mn, Al, In, Sn, and W.
  • the composite oxide may include one of these elements M, or may include two or more. Among the elements M, at least one selected from the group consisting of Mg, Al, Ti and Zr is particularly preferable.
  • the characteristics such as conductivity can be further improved, the crystal structure can be further stabilized, or the interface resistance of the complex oxide particles can be reduced. Can do. Note that when the interfacial resistance of the composite oxide particles decreases, the reactivity between the composite oxide and lithium ions increases.
  • Mg and Al are relatively easy to co-precipitate with nickel and cobalt in an aqueous solution. Therefore, when producing a composite oxide using the first raw material obtained by coprecipitation, Mg and Al can be dispersed more uniformly or at even intervals in the composite oxide, This is advantageous in that it can be contained in the composite oxide particles at a predetermined concentration. In addition, when Mg or Al is used, the crystal structure of the composite oxide can be further stabilized. High conductivity can be obtained with a complex oxide containing Mg. When Ti or Zr is used, the interface resistance of the composite oxide can be lowered.
  • the composite oxide contains at least one selected from the first element group consisting of Mg and Al as the element M.
  • the complex oxide contains at least one selected from the second element group consisting of Ti and Zr as the element M.
  • the composite oxide may include at least one selected from the first element group and at least one selected from the second element group.
  • the element M may be included in a part of the complex oxide particles, for example, the surface layer or the inside. Further, the element M may be distributed at a predetermined ratio between the surface layer and the inside of the composite oxide particle, as in the case of phosphorus. This ratio can be evaluated as in the case of phosphorus. Specifically, the concentration C Ms of the element M contained in the surface layer of the composite oxide particle (region within 0.3r from the surface of the particle) and the inside of the particle (region within 0.3r from the center of the particle) The ratio C Ms / C Mc of the concentration C Mc of the element M to be selected can be selected from the same range as the phosphorus ratio C Ps / C Pc . Even in the case where the element M is in such a distribution state, the effect of adding the element M can be obtained more effectively even when cracks or chipping of the composite oxide particles occur as in the case of phosphorus.
  • Mg and Al are likely to be distributed more uniformly or more evenly in the obtained composite oxide particles as in the case of phosphorus, and predetermined inside the composite oxide particles. It can be made to contain in the density
  • the ratio M Ms / C Mc (also referred to as the ratio C Ms2 / C Mc2 ) of the element M with respect to the second element group, for example, 5. 5/1 or more, preferably 7/1 or more.
  • C Ms2 is the concentration of the second element group contained in the surface layer (region within 0.3 r from the surface of the particle) of the composite oxide particle
  • C Mc2 is the inside of the particle (from the center of the particle). This is the concentration of the second element group included in the region within 0.3r.
  • the concentration C Mc2 may be zero.
  • the content of the element M in the composite oxide is, for example, 0.1 to 10 atomic%, preferably 1 to 10 atomic%, more preferably 2 to 8 atomic%, with respect to the total amount of elements excluding lithium and oxygen It is. In such a range, the addition effect can be more effectively obtained according to the type of the element M while maintaining the capacity of the battery using the composite oxide as the positive electrode active material at a high level.
  • the content of the first element group in the element M is, for example, 0.1 to 10 atomic%, preferably 1 to 10 atomic%, and more preferably 1.5 to the total amount of elements excluding lithium and oxygen. ⁇ 6 atomic%.
  • the capacity of the battery using the composite oxide as the positive electrode active material can be maintained at a high level.
  • the conductivity can be improved more effectively, and the decrease in capacity maintenance rate during the charge / discharge cycle can be prevented. Since the first element group can be distributed to the inside of the composite oxide particles by coprecipitation, it can be contained in a relatively large amount.
  • the content of the second element group is, for example, 0.1 to 1 atom%, preferably 0.2 to 0.7 atom%, based on the total amount of elements excluding lithium and oxygen. Since the second element group is likely to be distributed in a relatively large amount on the surface layer, the content is likely to be smaller than that of the first element group. In such a range, the interface resistance of the composite oxide can be more effectively lowered while maintaining the capacity of the battery using the composite oxide as the positive electrode active material at a high level.
  • the complex oxide has a layered structure (such as a layered rock salt structure) in which an oxygen layer and a metal layer (such as a lithium layer and another metal layer) are stacked when focusing on hexagonal crystals of oxygen. It preferably has a crystal structure.
  • a crystal structure is advantageous in that lithium can be inserted and extracted smoothly and the capacity of the battery can be increased.
  • the average particle size of the composite oxide particles is, for example, 5 to 50 ⁇ m, preferably 10 to 40 ⁇ m, and more preferably 15 to 30 ⁇ m.
  • the positive electrode active material may be a mixture of a plurality of composite oxide particles having different average particle sizes. That is, the positive electrode active material may have a plurality of peaks in the volume-based particle size distribution. In this case, the average particle diameter of the entire composite oxide particle can be selected from the above average particle diameter range.
  • the number of peaks in the volume-based particle size distribution may be 2 to 4, but is not particularly limited.
  • the positive electrode active material may include a large particle group having a large average particle diameter and a small particle group having a small average particle diameter.
  • the large particle group may have a peak in the volume-based particle size distribution, for example, larger than 16 ⁇ m and 50 ⁇ m or less, preferably between 17 and 30 ⁇ m.
  • the small particle group may have a peak in the volume-based particle size distribution, for example, between 1 and 16 ⁇ m, preferably between 2 and 12 ⁇ m.
  • the mixing ratio of the large particle group and the small particle group is not particularly limited, but is, for example, 60:40 to 95: 5, preferably 70:30 to 90:10.
  • the average particle size of the composite oxide particles may be adjusted by a method such as pulverization or classification. Moreover, you may adjust the average particle diameter of composite oxide particle
  • the volume particle size distribution of the composite oxide particles can be measured by, for example, a commercially available laser diffraction particle size distribution measuring device.
  • the positive electrode active material containing the composite oxide as described above can be produced through the following steps (1) to (3). (1) preparing a first raw material containing nickel and cobalt; (2) Mixing the first raw material and the second raw material containing phosphorus, pre-baking them at a temperature exceeding 750 ° C., containing nickel and cobalt, and adding phosphorus at a predetermined concentration in the surface layer and inside A step of obtaining oxide particles containing, and (3) mixing the oxide particles obtained in step (2) with a third raw material containing lithium, and subjecting them to a main firing at a temperature of 800 ° C. or lower. And obtaining a composite oxide particle containing lithium, phosphorus, nickel and cobalt.
  • the composite oxide includes the element M described above, the element M may be added at any stage of the steps (1) to (3).
  • Examples of the first raw material include various compounds containing nickel and cobalt, such as oxides, hydroxides, and salts (inorganic acid salts such as carbonates and sulfates; organic acid salts such as acetates). Of these, hydroxides, particularly composite hydroxides containing nickel and cobalt are preferred.
  • the composite hydroxide can be obtained by a coprecipitation method, and the coprecipitation method is particularly advantageous because nickel and cobalt can be uniformly dispersed in the composite hydroxide.
  • the first raw material may further contain one or more elements M described above.
  • the first raw material a commercial product may be prepared, or may be synthesized by a known method according to the type of the first raw material. From the viewpoint of the dispersibility of phosphorus and lithium in the finally obtained composite oxide particles, it is preferable that nickel and cobalt form a solid solution.
  • the first raw material is a hydroxide
  • the first raw material containing the solid solution can be synthesized by a coprecipitation method.
  • the first raw material contains the metal element M
  • a solid solution containing the element M may be formed together with nickel and cobalt by coprecipitation.
  • the element M capable of forming a solid solution by coprecipitation include at least one selected from the first element group consisting of Mg and Al.
  • an aqueous solution containing raw material salts such as nickel salt and cobalt salt is prepared, and the composite hydroxide is precipitated in a reducing atmosphere.
  • the composite hydroxide can be obtained by adding an alkali to an aqueous solution containing a raw material salt.
  • a nickel salt, a cobalt salt, and a salt containing the element M are used as the raw material salt.
  • Each salt is mixed at a ratio such that each element has a predetermined atomic ratio.
  • the raw material salt for example, inorganic acid salts such as sulfate, hydrochloride, phosphate and nitrate are used. Of these, sulfate is often used.
  • an inorganic alkali such as an alkali metal hydroxide such as potassium hydroxide or sodium hydroxide can be used.
  • the coprecipitation may be performed under an inert gas atmosphere or a reducing gas atmosphere.
  • a commercially available product or a synthesized product may be purified, pulverized and / or classified, if necessary, for the step (2).
  • the average particle diameter of the first raw material is, for example, 1 to 40 ⁇ m, preferably 3 to 25 ⁇ m. In such a range, in the step (2), phosphorus can be more effectively distributed even inside the oxide particles.
  • the average particle diameter means the median diameter (D50) in the volume particle size distribution of the first raw material particles.
  • the volume particle size distribution can be measured by, for example, a commercially available laser diffraction type particle size distribution measuring apparatus.
  • oxide particles containing phosphorus, nickel and cobalt are obtained by temporarily firing a mixture of the first raw material and the second raw material containing phosphorus.
  • the second raw material include phosphorus-containing compounds, for example, phosphoric acids (monophosphoric acids such as orthophosphoric acid, phosphorous acid, and hypophosphorous acid; polyphosphoric acids such as pyrophosphoric acid and metaphosphoric acid), phosphates (the above-mentioned phosphorus Examples thereof include salts of acids and metals, phosphorus oxides (such as diphosphorus pentoxide), and the like.
  • phosphoric acids such as orthophosphoric acid and polyphosphoric acid, and salts of these phosphoric acids and metals are preferable.
  • These 2nd raw materials can be used individually by 1 type or in combination of 2 or more types.
  • the second raw material may contain the element M in addition to phosphorus.
  • the first raw material does not contain the element M, it is advantageous to contain the element M in the second raw material.
  • the second raw material contains the element M, it is advantageous to use a salt of phosphoric acid and the element M as the second raw material.
  • the element M contained in the second raw material is preferably at least one selected from the group consisting of Mg, Al, Ti and Zr. Examples of such second raw material include at least one selected from the group consisting of magnesium phosphate, aluminum phosphate, titanium phosphate, and zirconium phosphate.
  • the second raw material preferably contains at least one selected from the first element group consisting of Mg and Al among the elements M.
  • a specific example of magnesium phosphate is selected from the group consisting of first magnesium phosphate, second magnesium phosphate, third magnesium phosphate, magnesium pyrophosphate and magnesium metaphosphate.
  • the aluminum phosphate include at least one selected from the group consisting of a first aluminum phosphate, a second aluminum phosphate, a third aluminum phosphate, and an aluminum metaphosphate.
  • the second raw material may include at least one selected from the second element group made of Ti and Zr. Since Ti and Zr are difficult to coprecipitate with nickel and cobalt in an aqueous solution, when the first raw material is obtained by coprecipitation, it is advantageous to include the second element group in the second raw material.
  • the first raw material and the second raw material are mixed at a ratio such that nickel, cobalt, phosphorus, and the element M added if necessary have a predetermined atomic ratio, and are subjected to provisional firing.
  • the temperature for pre-baking is not particularly limited as long as the temperature exceeds 750 ° C., preferably 850 ° C., more preferably 900 ° C. or more. Pre-baking at such a temperature is advantageous in that phosphorus can be distributed at a predetermined concentration to the inside of the oxide particles.
  • the upper limit of the calcination temperature is, for example, 1200 ° C., preferably 1100 ° C., and more preferably 1050 ° C. from the viewpoint of suppressing the substitution reaction between nickel and lithium. These lower limit and upper limit values can be combined as appropriate.
  • the phosphorus distribution state in the oxide particles specifically, the concentration of phosphorus in the surface layer and inside and the ratio thereof can be adjusted so that the ratio C Ps / C Pc in the composite oxide particles is within a predetermined range. .
  • Pre-baking is normally performed in an atmosphere containing oxygen gas.
  • the oxygen gas concentration in the pre-baking atmosphere is, for example, 18 to 30 mol%.
  • Pre-baking is often performed in air.
  • the oxygen partial pressure in the pre-baking atmosphere is, for example, 18 to 30 kPa.
  • the temporary firing time is, for example, 5 to 48 hours, although it depends on the firing temperature.
  • step (3) composite oxide particles are obtained by subjecting the mixture of the oxide particles obtained in step (2) and the third raw material containing lithium to main firing.
  • the third raw material include lithium-containing compounds such as oxides, hydroxides, and salts (inorganic acid salts such as carbonates and sulfates; organic acid salts such as acetates).
  • lithium hydroxide is preferred from the viewpoint of reactivity.
  • a compound containing the element M may be used in combination with the third raw material.
  • the compound containing the element M include oxides, hydroxides, nitrides, sulfides, salts (such as inorganic acid salts), and the like.
  • the firing temperature is 800 ° C. or lower, preferably 770 ° C. or lower, more preferably 750 ° C. or lower.
  • the lower limit of the main firing temperature is, for example, 600 ° C., preferably 650 ° C. By performing the main firing at such a temperature, lithium can be effectively dispersed in the composite oxide particles while suppressing volatilization of the third raw material. These upper limit and lower limit values can be appropriately selected and combined.
  • the temperature of this baking is lower than the temperature of temporary baking.
  • the main firing is usually performed in an atmosphere containing oxygen gas such as in the air.
  • the oxygen gas concentration, oxygen partial pressure, and firing time in the main firing atmosphere can be appropriately selected from the same ranges as in the case of temporary firing.
  • the positive electrode of the present invention includes a positive electrode current collector and a positive electrode active material layer attached to the surface of the positive electrode current collector.
  • the positive electrode active material layer includes the positive electrode active material and the binder.
  • As the positive electrode current collector a foil or a sheet formed of aluminum, stainless steel, nickel, titanium, carbon, conductive resin, or the like can be used.
  • the positive electrode current collector may be nonporous or porous.
  • the shape of the positive electrode current collector may be a belt shape, a coin shape, or the like depending on the shape of the nonaqueous electrolyte secondary battery.
  • the thickness of the positive electrode current collector is, for example, 5 to 50 ⁇ m.
  • Binders include olefin resins such as polyethylene and polypropylene; fluorine resins such as polytetrafluoroethylene, polyvinylidene fluoride (PVDF), tetrafluoroethylene-hexafluoropropylene copolymer; styrene butadiene rubber (SBR), and modified SBR. And rubber-like resin.
  • binders can be used singly or in combination of two or more.
  • the ratio of the binder is, for example, 0.1 to 15 parts by weight, preferably 0.2 to 10 parts by weight with respect to 100 parts by weight of the positive electrode active material.
  • the density of the positive electrode active material in the positive electrode active material layer is, for example, 3 g / cm 3 or more, preferably 3.5 g / cm 3 or more, and more preferably 3.6 g / cm 3 or more.
  • the present invention is effective even when the positive electrode active material density is high because the increase in resistance can be suppressed even when the positive electrode active material particles are cracked or chipped.
  • the upper limit of the density of the positive electrode active material for example, 4g / cm 3, preferably 3.8 g / cm 3. These lower and upper limit values can be appropriately selected and combined.
  • the positive electrode active material layer may further contain a conductive agent.
  • the conductive agent include conductive carbon materials and metal materials.
  • the conductive agent may be in the form of particles, flakes, fibers, or the like.
  • the conductive carbon material include graphite such as natural graphite and artificial graphite; carbon black and the like.
  • a conductive agent can be used individually by 1 type or in combination of 2 or more types. Of the conductive agents, conductive carbon materials are preferred.
  • the proportion of the conductive agent is, for example, 0.1 to 1.5 parts by weight, preferably 0.2 to 1.2 parts by weight, with respect to 100 parts by weight of the positive electrode active material.
  • the positive electrode active material of the present invention has high conductivity.
  • the composite oxide as the positive electrode active material contains Mg as the element M
  • the effect of Mg is further enhanced by the phosphorus being distributed at a predetermined concentration to the inside of the composite oxide particles. Therefore, at least the amount of the conductive agent used can ensure high conductivity.
  • the positive electrode can be produced by attaching a positive electrode mixture containing a positive electrode active material and a binder to the surface of the positive electrode current collector to form a positive electrode active material layer.
  • the positive electrode mixture may further contain a conductive agent and / or other additives.
  • the positive electrode mixture can be usually prepared by dispersing a positive electrode active material, a binder, and, if necessary, a conductive agent and / or an additive in a dispersion medium. In the positive electrode mixture, the binder and additives may be dissolved in the dispersion medium.
  • the positive electrode can be produced by applying a positive electrode mixture to the surface of the positive electrode current collector, drying it, and then rolling it with a pair of rollers or the like.
  • the positive electrode active material layer may be formed on one surface of the positive electrode current collector, or may be formed on both surfaces.
  • the thickness of the positive electrode is, for example, 50 to 230 ⁇ m, preferably 80 to 200 ⁇ m.
  • additives include thickeners and known additives used for positive electrode mixtures.
  • thickener include ethylene-vinyl alcohol copolymers, cellulose derivatives (carboxymethyl cellulose, methyl cellulose, etc.) and the like.
  • dispersion medium examples include water, alcohols such as ethanol, ethers such as tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), or a mixed solvent thereof.
  • a positive electrode is useful for a nonaqueous electrolyte secondary battery such as a lithium ion battery.
  • the non-aqueous electrolyte secondary battery has the positive electrode, the negative electrode, a separator that isolates them, and a non-aqueous electrolyte.
  • the negative electrode has a negative electrode current collector and a negative electrode active material layer attached to the surface. Examples of the negative electrode current collector include copper foil and copper alloy foil.
  • the negative electrode current collector may be nonporous or porous. The shape and thickness of the negative electrode current collector are the same as those of the positive electrode current collector.
  • the negative electrode active material layer may be formed of a negative electrode active material, and may contain a conductive agent, a binder, a thickener, and the like in addition to the negative electrode active material.
  • a negative electrode active material various materials capable of reversibly occluding and releasing lithium ions, for example, materials having a graphite-type crystal structure; silicon; silicon-containing compounds such as silicon oxide; Sn, Al, Zn and / or Mg
  • Examples of the lithium alloy include: Examples of the material having a graphite-type crystal structure include carbon materials such as natural graphite, spherical or fibrous artificial graphite, non-graphitizable carbon, and graphitizable carbon. These negative electrode active materials can be used individually by 1 type or in combination of 2 or more types.
  • binder conductive agent, thickener, and dispersion medium
  • those exemplified for the positive electrode can be used.
  • the ratio of the binder and the conductive agent to 100 parts by weight of the negative electrode active material can be selected from the same range as the range exemplified for the positive electrode with respect to 100 parts by weight of the positive electrode active material.
  • the negative electrode active material layer can be formed by the same method as the positive electrode active material layer. Depending on the type of the negative electrode active material, the negative electrode active material layer may be formed by depositing the negative electrode active material on the surface of the current collector by a vapor phase method such as vacuum deposition or sputtering. The negative electrode active material layer may be formed on one surface of the negative electrode current collector, or may be formed on both surfaces.
  • the thickness of the negative electrode is, for example, 100 to 250 ⁇ m, preferably 110 to 210 ⁇ m.
  • the separator As the separator, a resin-made microporous film, nonwoven fabric or woven fabric can be used.
  • the resin constituting the separator include polyolefins such as polyethylene and polypropylene; polyamides; polyamideimides; polyimides and the like.
  • the microporous film may be a single layer film or a multilayer film. The thickness of the separator is, for example, 5 to 50 ⁇ m.
  • Non-aqueous electrolyte includes a non-aqueous solvent and a lithium salt dissolved in the non-aqueous solvent.
  • Non-aqueous solvents include cyclic carbonates such as propylene carbonate and ethylene carbonate (EC); chain carbonates such as diethyl carbonate, ethyl methyl carbonate (EMC) and dimethyl carbonate; cyclic esters such as ⁇ -butyrolactone and ⁇ -valerolactone Examples thereof include carboxylic acid esters.
  • EC propylene carbonate and ethylene carbonate
  • EMC ethyl methyl carbonate
  • Examples thereof include carboxylic acid esters.
  • lithium salt examples include LiPF 6 , LiBF 4 , LiClO 4 , LiAsF 6 , LiCF 3 SO 3 , LiN (SO 2 CF 3 ) 2 , LiN (SO 2 C 2 F 5 ) 2 , LiC (SO 2 CF 3 3 ).
  • a lithium salt can be used individually by 1 type or in combination of 2 or more types.
  • the concentration of the lithium salt in the nonaqueous electrolyte is, for example, 0.5 to 1.8M.
  • a known additive such as a vinylene carbonate compound such as vinylene carbonate may be added to the non-aqueous electrolyte.
  • a nonaqueous electrolyte secondary battery can be usually produced by housing a positive electrode, a negative electrode, and a separator separating them together with a nonaqueous electrolyte in a battery case.
  • a battery case material steel plates, aluminum, aluminum alloys (alloys containing a trace amount of metals such as manganese and copper, etc.) and the like can be used.
  • the shape of the nonaqueous electrolyte secondary battery may be a cylindrical shape, a square shape, a coin shape, or the like.
  • the electrode group may be formed by winding, laminating or spell-folding the positive electrode, the negative electrode, and the separator that separates them prior to housing in the battery case.
  • the shape of the electrode group may be a cylindrical shape or a flat shape having an oval end surface perpendicular to the winding axis, depending on the shape of the battery or battery case.
  • Example 1 (1) Synthesis of positive electrode active material (i) Synthesis of composite hydroxide (first raw material) containing nickel and cobalt (first step) 3.2 kg of a mixture of nickel sulfate and cobalt sulfate mixed so that the atomic ratio of Ni atoms to Co atoms was 80:20 was dissolved in 10 L of water to obtain a raw material solution. 400 g of sodium hydroxide was added to the raw material solution to form a precipitate. The precipitate was sufficiently washed with water and dried to obtain a coprecipitated composite hydroxide (Ni 0.80 Co 0.20 (OH) 2 ) (first raw material).
  • the peaks in the volume-based particle size distribution of the coprecipitated composite hydroxide were 20 ⁇ m and 5 ⁇ m.
  • the coprecipitated composite hydroxide is a mixed particle containing a large particle group having an average particle diameter of 20 ⁇ m and a small particle group having an average particle diameter of 5 ⁇ m at a weight ratio of 8: 2 from the peak intensity ratio.
  • the particle size was 17 ⁇ m.
  • a positive electrode was produced using the lithium-containing composite oxide particles obtained in (1) above as the positive electrode active material. Specifically, 1 kg of the positive electrode active material is kneaded with a double arm type together with an NMP solution of PVDF (manufactured by Kureha Co., Ltd., PVDF # 7208, solid content 8 wt%) 0.2 kg, acetylene black 10 g, and an appropriate amount of NMP. The mixture was stirred in a machine to prepare a positive electrode mixture paste. This paste was applied to both sides of an aluminum foil having a thickness of 20 ⁇ m, dried, and rolled to a total thickness of 160 ⁇ m. Thereafter, the obtained electrode plate was slit to a width that could be inserted into a cylindrical battery case of 18650 to obtain a positive electrode. The density of the positive electrode active material in the positive electrode active material layer was 3.6 g / cm 3 .
  • the positive electrode 5 and the negative electrode 6 were wound in a state of being separated by a separator 7 to produce a spiral electrode group 4.
  • a positive electrode lead 5a and a negative electrode lead 6a made of nickel were attached to the positive electrode 5 and the negative electrode 6, respectively.
  • An upper insulating plate 8 a is disposed on the upper surface of the electrode group 4, and a lower insulating plate 8 b is disposed on the lower surface, and inserted into the battery case 1.
  • the electrode group 4 was held in the battery case 1 by forming an inwardly protruding step 9 above the upper insulating plate 8 a and on the upper side surface of the battery case 1.
  • 5 g of nonaqueous electrolyte was injected into the battery case 1.
  • the sealing plate 2 provided with the insulating gasket 3 around it was electrically connected to the positive electrode lead 5 a, and then the opening of the battery case 1 was sealed with the sealing plate 2.
  • a cylindrical 18650 lithium secondary battery was completed.
  • Example 2 Instead of a mixture of nickel sulfate and cobalt sulfate, it is obtained by mixing nickel sulfate, cobalt sulfate, and aluminum sulfate so that the atomic ratio of Ni atoms, Co atoms, and Al atoms is 80: 17: 3.
  • a coprecipitated composite hydroxide (first raw material) was obtained in the same manner as in Example 1 except that the obtained mixture was used.
  • the coprecipitated composite hydroxide was a mixed particle containing a large particle group having an average particle diameter of 20 ⁇ m and a small particle group having an average particle diameter of 5 ⁇ m at a weight ratio of 8: 2, and the overall average particle diameter was 17 ⁇ m.
  • Example 2 In the same manner as in Example 1, except that the obtained coprecipitated composite hydroxide was used instead of the first raw material of Example 1, and orthophosphoric acid was used as the second raw material instead of the first magnesium phosphate.
  • An active material was synthesized.
  • a positive electrode was prepared in the same manner as in Example 1 except that the synthesized positive electrode active material was used, and a lithium ion battery was produced using this positive electrode.
  • the C Ps / C Pc value of the phosphorus element and the C Ms / C Mc value of the Al element were calculated in the same manner as in the case of the phosphorus element in Example 1.
  • Example 3 A positive electrode active material was synthesized in the same manner as in Example 2 except that magnesium sulfate was used instead of aluminum sulfate. A positive electrode was prepared in the same manner as in Example 1 except that the synthesized positive electrode active material was used, and a lithium ion battery was produced using this positive electrode.
  • the C Ps / C Pc value of the phosphorus element and the C Ms / C Mc value of the Mg element were calculated in the same manner as in the case of the phosphorus element in Example 1.
  • Example 4 A positive electrode active material was synthesized in the same manner as in Example 1 except that titanium phosphate was used instead of the first magnesium phosphate (second raw material). A positive electrode was prepared in the same manner as in Example 1 except that the synthesized positive electrode active material was used, and a lithium ion battery was produced using this positive electrode. The C Ps / C Pc value of the phosphorus element and the C Ms / C Mc value of the Ti element were calculated in the same manner as in the case of the phosphorus element in Example 1.
  • Example 5 A positive electrode active material was synthesized in the same manner as in Example 1 except that zirconium phosphate was used instead of the first magnesium phosphate (second raw material). A positive electrode was prepared in the same manner as in Example 1 except that the synthesized positive electrode active material was used, and a lithium ion battery was produced using this positive electrode.
  • the C Ps / C Pc value of the phosphorus element and the C Ms / C Mc value of the Zr element were calculated in the same manner as in the case of the phosphorus element in Example 1.
  • Example 6 A positive electrode active material was synthesized in the same manner as in Example 1 except that orthophosphoric acid was used in place of the first magnesium phosphate (second raw material). A positive electrode was prepared in the same manner as in Example 1 except that the synthesized positive electrode active material was used, and a lithium ion battery was produced using this positive electrode. The C Ps / C Pc value of the phosphorus element was calculated in the same manner as in the case of the phosphorus element of Example 1.
  • Example 7 A positive electrode active material was synthesized in the same manner as in Example 6 except that the temperature of the preliminary firing (second step) in Example 6 was changed from 1000 ° C. to 800 ° C. A positive electrode was prepared in the same manner as in Example 1 except that the synthesized positive electrode active material was used, and a lithium ion battery was produced using this positive electrode. The C Ps / C Pc value of the phosphorus element was calculated in the same manner as in the case of the phosphorus element of Example 1.
  • Example 8 Instead of aluminum sulfate, magnesium sulfate is used, and the raw materials are mixed so that the atomic ratio of Ni atoms, Co atoms, and Mg atoms is 80: 17: 2.5.
  • the first raw material was synthesized.
  • the first raw material was mixed particles containing a large particle group having an average particle diameter of 20 ⁇ m and a small particle group having an average particle diameter of 5 ⁇ m in a weight ratio of 8: 2, and the overall average particle diameter was 17 ⁇ m.
  • the obtained first raw material was used in place of the first raw material of Example 1. Instead of the aqueous solution of the first magnesium phosphate, an aqueous solution containing orthophosphoric acid and titanium phosphate at concentrations of 5 wt% and 10 wt%, respectively, was used. Except for these, a positive electrode active material was synthesized in the same manner as in Example 1. A positive electrode was prepared in the same manner as in Example 1 except that the synthesized positive electrode active material was used, and a lithium ion battery was produced using this positive electrode. The C Ps / C Pc value of the phosphorus element and the C Ms / C Mc value of the Mg element and Ti element were calculated in the same manner as in the case of the phosphorus element of Example 1.
  • Example 9 A positive electrode active material was synthesized in the same manner as in Example 8 except that aluminum sulfate was used instead of magnesium sulfate. A positive electrode was prepared in the same manner as in Example 1 except that the synthesized positive electrode active material was used, and a lithium ion battery was produced using this positive electrode.
  • the C Ps / C Pc value of the phosphorus element and the C Ms / C Mc value of the Al element and Ti element were calculated in the same manner as in the case of the phosphorus element in Example 1.
  • Example 10 A positive electrode active material was synthesized in the same manner as in Example 8 except that zirconium phosphate was used instead of titanium phosphate. A positive electrode was prepared in the same manner as in Example 1 except that the synthesized positive electrode active material was used, and a lithium ion battery was produced using this positive electrode. The C Ps / C Pc value of phosphorus element and the C Ms / C Mc value of Mg element and Zr element were calculated in the same manner as in the case of the phosphorus element of Example 1.
  • Example 11 A positive electrode active material was synthesized in the same manner as in Example 9 except that zirconium phosphate was used in place of titanium phosphate. A positive electrode was prepared in the same manner as in Example 1 except that the synthesized positive electrode active material was used, and a lithium ion battery was produced using this positive electrode. The C Ps / C Pc value of phosphorus element and the C Ms / C Mc value of Al element and Zr element were calculated in the same manner as in the case of the phosphorus element of Example 1.
  • Examples 12 to 16 A positive electrode active material was synthesized in the same manner as in Example 2 except that the concentration of the aqueous solution of orthophosphoric acid was changed. A positive electrode was prepared in the same manner as in Example 1 except that the synthesized positive electrode active material was used, and a lithium ion battery was produced using this positive electrode. The concentrations of orthophosphoric acid in the aqueous solution were 20% by weight (Example 12), 15% by weight (Example 13), 8% by weight (Example 14), 5% by weight (Example 15) and 4% by weight, respectively. (Example 16). The C Ps / C Pc value of the phosphorus element and the C Ms / C Mc value of the Al element were calculated in the same manner as in the case of the phosphorus element in Example 1.
  • Examples 17 to 20 A positive electrode active material was synthesized in the same manner as in Example 2 except that the atomic ratio of Ni atoms, Co atoms, and Al atoms was changed. A positive electrode was prepared in the same manner as in Example 1 except that the synthesized positive electrode active material was used, and a lithium ion battery was produced using this positive electrode. Ni: Co: Al (atomic ratio) was 84: 13: 3 (Example 17), 69: 28: 3 (Example 18), 62: 35: 3 (Example 19) and 50:47: respectively. 3 (Example 20). The C Ps / C Pc value of the phosphorus element and the C Ms / C Mc value of the Al element were calculated in the same manner as in the case of the phosphorus element in Example 1.
  • a positive electrode active material was synthesized in the same manner as in Example 1 except that the firing temperature in the preliminary firing (second step) was changed from 1000 ° C. to 700 ° C.
  • a positive electrode was prepared in the same manner as in Example 1 except that the synthesized positive electrode active material was used, and a lithium ion battery was produced using this positive electrode.
  • the phosphorus element concentration distribution of the lithium-containing composite oxide particles was analyzed by EPMA in the same manner as in Example 1. As a result, it was confirmed that the phosphorus element was unevenly distributed in the particle surface layer.
  • the C Ps / C Pc value of the phosphorus element and the C Ms / C Mc value of the Al element were calculated in the same manner as in the case of the phosphorus element in Example 1.
  • a positive electrode active material was synthesized in the same manner as in Example 2 except that the firing temperature in the preliminary firing (second step) was changed from 1000 ° C. to 700 ° C.
  • a positive electrode was prepared in the same manner as in Example 1 except that the synthesized positive electrode active material was used, and a lithium ion battery was produced using this positive electrode.
  • the concentration distribution of phosphorus element in the lithium-containing composite oxide particles was analyzed by EPMA. As a result, it was confirmed that the phosphorus element was unevenly distributed in the particle surface layer.
  • the C Ps / C Pc value of the phosphorus element and the C Ms / C Mc value of the Al element were calculated in the same manner as in the case of the phosphorus element in Example 1.
  • the battery of Example 1 showed a high capacity retention rate even after 500 cycles of charge / discharge compared to Comparative Example 1. This is because phosphorus is added to the inside of the positive electrode active material in the positive electrode active material of Example 1. For this reason, particle breakage of the positive electrode active material occurs during the charge / discharge cycle, the reaction between the new surface of the positive electrode active material and the electrolyte is stabilized by phosphorus inside the positive electrode active material, and an increase in resistance in the positive electrode active material layer is suppressed. It is thought that there is. On the other hand, the reason why the capacity retention ratio decreased in Comparative Example 1 is considered to be that the resistance in the positive electrode active material layer increased due to repeated charge and discharge. In Comparative Example 2, the same result as in Comparative Example 1 was obtained. Even when the positive electrode active material contains phosphorus, as in Comparative Examples 1 and 2, when phosphorus is unevenly distributed on the particle surface of the positive electrode active material, a sufficient capacity retention rate could not be obtained.
  • the positive electrode active material layer was analyzed for the concentration distribution of the phosphorus element in the lithium-containing composite oxide particles by EPMA as in Example 1. As a result, it was confirmed that the phosphorus element was distributed even inside the particles. Therefore, even in the batteries of Examples 2 to 20 using such lithium-containing composite oxide particles as the positive electrode active material, as shown in Table 1, a high capacity retention ratio was obtained even after 500 cycles of charge and discharge. It is thought that it was done.
  • the present invention can be applied to non-aqueous electrolyte secondary batteries used for various purposes.
  • Specific examples of uses of the non-aqueous electrolyte secondary battery include a portable information terminal, a portable electronic device, a small electric power storage device for home use, a motorcycle, an electric vehicle, and a hybrid electric vehicle.

Abstract

The purpose of the present invention is to provide a positive electrode active material which is capable of suppressing decrease in the capacity retention rate in charge and discharge cycles of a nonaqueous electrolyte secondary battery. This positive electrode active material for nonaqueous electrolyte secondary batteries comprises particles of a complex oxide that contains lithium, phosphorus, nickel and cobalt, and when the average radius of the complex oxide particles is represented by r, the ratio of the concentration (CPs) of the phosphorous contained in regions within 0.3r from the surfaces of the particles relative to the concentration (CPc) of the phosphorous contained in regions within 0.3r from the centers of the particles, namely the concentration ratio CPs/CPc is from 1/1 to 5/1. The complex oxide may additionally contain at least one element M that is selected from the group consisting of Mg, Al, Ti and Zr.

Description

非水電解質二次電池用正極活物質およびそれを用いた正極、並びに正極活物質の製造方法Positive electrode active material for non-aqueous electrolyte secondary battery, positive electrode using the same, and method for producing positive electrode active material
　本発明は、非水電解質二次電池用正極活物質およびそれを用いた正極、並びに正極活物質の製造方法に関し、より詳細には、正極活物質としてのリチウムニッケルコバルト複合酸化物の改良に関する。 The present invention relates to a positive electrode active material for a non-aqueous electrolyte secondary battery, a positive electrode using the same, and a method for producing the positive electrode active material, and more particularly to an improvement of a lithium nickel cobalt composite oxide as a positive electrode active material.
　リチウムイオン電池などの非水電解質二次電池は、起電力が高く、高エネルギー密度であるため、移動体通信機器および携帯電子機器の主電源として需要が拡大している。また、非水電解質二次電池は、電気自動車の駆動電源としても期待されている。 Non-aqueous electrolyte secondary batteries such as lithium-ion batteries have high electromotive force and high energy density, and therefore demand is increasing as a main power source for mobile communication devices and portable electronic devices. Nonaqueous electrolyte secondary batteries are also expected as a drive power source for electric vehicles.
　現在、市販されているリチウムイオン電池の大半は、正極活物質として、コバルトを主成分とするリチウム複合酸化物を含む。しかし、コバルトを主成分とするリチウム複合酸化物は、原料コストが高い。そのため、コバルトの一部をニッケルで置き換えたリチウムニッケルコバルト複合酸化物が注目されている。 Currently, most of the commercially available lithium ion batteries include a lithium composite oxide containing cobalt as a main component as a positive electrode active material. However, a lithium composite oxide containing cobalt as a main component has a high raw material cost. Therefore, a lithium nickel cobalt composite oxide in which a part of cobalt is replaced with nickel has attracted attention.
　また、リチウム複合酸化物に、Ｍｇなどのアルカリ土類金属元素、遷移金属元素、典型金属元素、および／または半金属元素などを添加することにより、電池特性などを向上させることも検討されている。例えば、特許文献１では、リチウム複合酸化物の粒子表面に、被覆元素としてリンを含有させることにより、充放電効率を改善することを提案している。特許文献２でも、リチウム複合酸化物に、リン、マグネシウムなどを添加している。 In addition, it has been studied to improve battery characteristics by adding alkaline earth metal elements such as Mg, transition metal elements, typical metal elements, and / or metalloid elements to lithium composite oxides. . For example, Patent Document 1 proposes to improve charge and discharge efficiency by including phosphorus as a covering element on the particle surface of the lithium composite oxide. Also in Patent Document 2, phosphorus, magnesium and the like are added to the lithium composite oxide.
国際公開２００６／１２３５７２号パンフレットInternational Publication No. 2006/123572 Pamphlet 特開平１１－４０１５４号公報Japanese Patent Laid-Open No. 11-40154
　正極活物質に、リンやマグネシウムなどの元素を添加する場合、添加元素による効果を効率よく得るためには、特許文献１のように、添加元素を、正極活物質粒子の表面に分布させるのが有利である。しかし、正極活物質は、充放電時にリチウムを吸蔵および放出するため、充放電を繰り返すと、結晶構造が劣化しやすい。結晶構造が劣化すると、正極活物質粒子がひび割れたり、欠けたりする場合がある。そのため、添加元素が粒子表面に偏在していると、正極活物質粒子が、ひび割れたり、欠けたりした場合に、内部の正極活物質が露出し、添加元素による効果が低減する。 When an element such as phosphorus or magnesium is added to the positive electrode active material, in order to efficiently obtain the effect of the added element, the additive element is distributed on the surface of the positive electrode active material particles as in Patent Document 1. It is advantageous. However, since the positive electrode active material occludes and releases lithium during charge and discharge, the crystal structure is likely to deteriorate when charge and discharge are repeated. When the crystal structure deteriorates, the positive electrode active material particles may be cracked or chipped. Therefore, if the additive element is unevenly distributed on the particle surface, when the positive electrode active material particles are cracked or chipped, the internal positive electrode active material is exposed and the effect of the additive element is reduced.
　正極活物質の中でも、特に、リチウムニッケルコバルト複合酸化物は、高容量であるが、リチウムコバルト複合酸化物などの他のリチウム含有複合酸化物に比べて、結晶構造の安定性が低い面がある。そのため、充放電の繰り返しに伴う、正極活物質粒子のひび割れや欠けが顕著になりやすい。ひび割れや欠けが過度になると、粒子間に多くの隙間が形成され、集電性が低下する場合がある。また、ひび割れや欠けにより、内部の正極活物質が露出すると、露出面に高抵抗性の被膜が形成され、正極活物質層における抵抗が増加する。その結果、充放電サイクルにおける容量維持率が低下する場合がある。 Among the positive electrode active materials, in particular, lithium nickel cobalt composite oxide has a high capacity, but has a lower crystal structure stability than other lithium-containing composite oxides such as lithium cobalt composite oxide. . Therefore, cracks and chips of the positive electrode active material particles are likely to become conspicuous with repeated charge / discharge. If cracks and chips are excessive, many gaps are formed between the particles, and the current collecting property may be lowered. Further, when the internal positive electrode active material is exposed due to cracks or chips, a high-resistance film is formed on the exposed surface, and the resistance in the positive electrode active material layer increases. As a result, the capacity maintenance rate in the charge / discharge cycle may decrease.
　本発明の目的は、非水電解質二次電池の充放電サイクルにおいて、容量維持率の低下を抑制できる正極活物質を提供することにある。 An object of the present invention is to provide a positive electrode active material capable of suppressing a decrease in capacity retention rate in a charge / discharge cycle of a nonaqueous electrolyte secondary battery.
　本発明の一局面は、リチウム、リン、ニッケルおよびコバルトを含む複合酸化物（すなわち、リンを含むリチウムニッケルコバルト複合酸化物）の粒子を含み、複合酸化物の粒子の平均半径をｒとするとき、粒子の表面から０．３ｒ以内の領域に含まれるリンの濃度ＣPsと、粒子の中心から０．３ｒ以内の領域に含まれるリンの濃度ＣPcとの比率ＣPs／ＣPcが、１／１～５／１である、非水電解質二次電池用正極活物質に関する。 One aspect of the present invention includes particles of a composite oxide containing lithium, phosphorus, nickel, and cobalt (that is, lithium nickel cobalt composite oxide containing phosphorus), and the average radius of the composite oxide particles is r The ratio C Ps / C Pc between the concentration C Ps of phosphorus contained in the region within 0.3r from the surface of the particle and the concentration C Pc of phosphorus contained in the region within 0.3r from the center of the particle is 1 The present invention relates to a positive electrode active material for a non-aqueous electrolyte secondary battery, which is / 1 to 5/1.
　本発明の他の一局面は、正極集電体および正極集電体の表面に付着した正極活物質層を含み、正極活物質層が、上記の正極活物質および結着剤を含む、非水電解質二次電池用正極に関する。 Another aspect of the present invention includes a positive electrode current collector and a positive electrode active material layer attached to a surface of the positive electrode current collector, and the positive electrode active material layer includes the positive electrode active material and the binder. The present invention relates to a positive electrode for an electrolyte secondary battery.
　本発明のさらに他の一局面は、
　ニッケルおよびコバルトを含む第１原料を準備する工程、
　第１原料と、リンを含む第２原料と、を混合し、これらを、７５０℃を超える温度で仮焼成し、ニッケルおよびコバルトを含むとともに、表層および内部に所定の濃度でリンを含む酸化物の粒子を得る工程、並びに
　前記酸化物の粒子と、リチウムを含む第３原料と、を混合し、これらを、８００℃以下の温度で本焼成し、リチウム、リン、ニッケルおよびコバルトを含む複合酸化物の粒子を得る工程、を有し、
　複合酸化物の粒子の平均半径をｒとするとき、粒子の表面から０．３ｒ以内の領域に含まれるリンの濃度ＣPsと、粒子の中心から０．３ｒ以内の領域に含まれるリンの濃度ＣPcとの比率ＣPs／ＣPcが、１／１～５／１である、非水電解質二次電池用正極活物質の製造方法に関する。 Still another aspect of the present invention provides:
Preparing a first raw material containing nickel and cobalt;
An oxide containing a first raw material and a second raw material containing phosphorus, calcined at a temperature exceeding 750 ° C., containing nickel and cobalt, and containing phosphorus at a predetermined concentration in the surface layer and inside And a step of mixing the oxide particles and a third raw material containing lithium, firing these at a temperature of 800 ° C. or lower, and composite oxidation containing lithium, phosphorus, nickel, and cobalt. Obtaining particles of the object,
When the average radius of the composite oxide particles is r, the phosphorus concentration C Ps contained in the region within 0.3r from the particle surface and the phosphorus concentration contained in the region within 0.3r from the particle center. the ratio C Ps / C Pc with C Pc is 1 / 1-5 / 1, a method for producing a positive active material for a nonaqueous electrolyte secondary battery.
　本発明によれば、リチウムニッケルコバルト複合酸化物の粒子の表層だけでなく、内部にも所定の濃度でリンを分布させることから、この複合酸化物粒子を正極活物質として含む非水電解質二次電池の充放電サイクルにおける容量維持率の低下が抑制される。 According to the present invention, phosphorus is distributed not only on the surface layer of the particles of the lithium nickel cobalt composite oxide but also in the interior at a predetermined concentration, so that the non-aqueous electrolyte secondary containing this composite oxide particle as a positive electrode active material A decrease in capacity maintenance rate in the charge / discharge cycle of the battery is suppressed.
　本発明の新規な特徴を添付の請求の範囲に記述するが、本発明は、構成および内容の両方に関し、本発明の他の目的および特徴と併せ、図面を照合した以下の詳細な説明によりさらによく理解されるであろう。 While the novel features of the invention are set forth in the appended claims, the invention will be further described by reference to the following detailed description, taken in conjunction with the other objects and features of the invention, both in terms of construction and content. It will be well understood.
実施例１の円筒型リチウムイオン電池の縦断面図である。1 is a longitudinal sectional view of a cylindrical lithium ion battery of Example 1. FIG.
［正極活物質］
　本発明の非水電解質二次電池用正極活物質は、リチウム、リン、ニッケルおよびコバルトを含む複合酸化物の粒子を含む。そして、複合酸化物の粒子の平均半径をｒとするとき、粒子の表面から０．３ｒ以内の領域に含まれるリンの濃度ＣPsと、粒子の中心から０．３ｒ以内の領域に含まれるリンの濃度ＣPcとの比率ＣPs／ＣPcが、１／１～５／１である。 [Positive electrode active material]
The positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention includes composite oxide particles containing lithium, phosphorus, nickel, and cobalt. When the average radius of the composite oxide particles is r, the phosphorus concentration C Ps contained in the region within 0.3r from the particle surface and the phosphorus contained in the region within 0.3r from the particle center. The ratio C Ps / C Pc to the concentration C Pc is 1/1 to 5/1 .
　このような正極活物質では、充放電の繰り返しにより、複合酸化物粒子がひび割れを起こしたり、欠けたりしても、容量維持率の低下を抑制できる。そのメカニズムは定かではないが、リンには、ニッケルを含む複合酸化物の結晶構造を安定化させる作用があると考えられる。このような作用を有するリンが、粒子の表層だけでなく、内部にも所定の比率で分布するので、安定な結晶構造が、複合酸化物粒子の表層だけでなく、内部にも形成されるものと考えられる。 In such a positive electrode active material, even if the composite oxide particles are cracked or chipped by repeated charge and discharge, a decrease in capacity retention rate can be suppressed. Although the mechanism is not clear, it is considered that phosphorus has an effect of stabilizing the crystal structure of the composite oxide containing nickel. Phosphorus having such an action is distributed not only in the surface layer of the particle but also in the inside at a predetermined ratio, so that a stable crystal structure is formed not only in the surface layer of the composite oxide particle but also inside. it is conceivable that.
　複合酸化物粒子は、充放電を繰り返すと、結晶構造が劣化し、ひび割れを起こしたり、欠けたりする場合がある。複合酸化物粒子の中でも、ニッケルを含むリチウム含有複合酸化物は、特に、結晶構造の安定性が低い。そのため、ひび割れや欠けが顕著になりやすい。また、正極活物質層は、圧延により形成するときにも、正極活物質粒子が、ひび割れたり、欠けたりする場合がある。特に、正極活物質層における活物質密度が高い場合には、圧延時のひび割れや欠けが顕著になりやすい。さらに、正極活物質層の密度が高い場合（例えば、３．６ｇ／ｃｍ3以上の活物質密度を有する場合）には、充放電サイクル中にも、複合酸化物粒子に大きな応力がかかるため、ひび割れや欠けが特に顕著になりやすい。 When the complex oxide particles are repeatedly charged and discharged, the crystal structure is deteriorated, which may cause cracking or chipping. Among the composite oxide particles, lithium-containing composite oxides containing nickel have particularly low crystal structure stability. Therefore, cracks and chips are likely to be prominent. Also, the positive electrode active material layer may be cracked or chipped when formed by rolling. In particular, when the active material density in the positive electrode active material layer is high, cracking and chipping during rolling tend to be prominent. Furthermore, when the density of the positive electrode active material layer is high (for example, when having an active material density of 3.6 g / cm 3 or more), a large stress is applied to the composite oxide particles even during the charge / discharge cycle. Cracks and chips are particularly prominent.
　リンが、複合酸化物粒子の表層にしか含まれていない場合、複合酸化物粒子がひび割れたり欠けたりすると、リンを含まない、結晶構造が不安定な複合酸化物が、表面に露出する。そのため、充放電サイクル中に、結晶構造が劣化しやすい。 When phosphorus is contained only in the surface layer of the composite oxide particles, if the composite oxide particles are cracked or chipped, the composite oxide containing no phosphorus and having an unstable crystal structure is exposed on the surface. Therefore, the crystal structure tends to deteriorate during the charge / discharge cycle.
　本発明では、複合酸化物粒子が、表層だけでなく、内部にも所定の比率でリンを含む。よって、複合酸化物粒子は、表層だけでなく、内部にも、安定な結晶構造を有している。そのため、複合酸化物粒子が、ひび割れや欠けを生じにくくなるとともに、仮にひび割れや欠けを生じても、結晶構造のさらなる劣化を抑制できる。これにより、導電性の低下を抑制でき、正極活物質層における抵抗の増加を抑制できるため、結果として、充放電を繰り返しても、充放電特性の低下を防止できると考えられる。 In the present invention, the composite oxide particles contain phosphorus in a predetermined ratio not only on the surface layer but also inside. Therefore, the composite oxide particles have a stable crystal structure not only on the surface layer but also inside. Therefore, the composite oxide particles are less likely to be cracked or chipped, and even if cracked or chipped, further deterioration of the crystal structure can be suppressed. Thereby, since the fall of electroconductivity can be suppressed and the increase in resistance in a positive electrode active material layer can be suppressed, even if charging / discharging is repeated as a result, it is thought that the fall of charging / discharging characteristics can be prevented.
　リンは、複合酸化物粒子において、実質的に均等な間隔で分布していてもよい。複合酸化物粒子において、表層におけるリンの分布と、内部におけるリンの分布とが、実質的に同程度であってもよい。また、複合酸化物粒子が、内部に所定の含有量でリンを含有している限り、リンの含有量が、表層から内部にかけて、減少していてもよい。 Phosphorus may be distributed at substantially uniform intervals in the composite oxide particles. In the composite oxide particles, the distribution of phosphorus in the surface layer and the distribution of phosphorus in the inside may be substantially the same. Further, as long as the composite oxide particles contain phosphorus at a predetermined content, the phosphorus content may decrease from the surface layer to the inside.
　複合酸化物粒子におけるリンの分布は、上記のように、粒子の表層におけるリンの濃度と、粒子の内部におけるリンの濃度との比率ＣPs／ＣPcに基づいて、評価することができる。比率ＣPs／ＣPcは、例えば、１．１／１～４／１、１．２／１～３／１、１．２／１～２．５／１、または１．２／１～２．２／１であってもよい。 As described above, the distribution of phosphorus in the composite oxide particles can be evaluated based on the ratio C Ps / C Pc between the concentration of phosphorus in the surface layer of the particles and the concentration of phosphorus in the particles. The ratio C Ps / C Pc is, for example, 1.1 / 1 to 4/1, 1.2 / 1 to 3/1, 1.2 / 1 to 2.5 / 1, or 1.2 / 1 to 2. 2/1 may be used.
　粒子の表面から０．３ｒ以内および中心から０．３ｒ以内の領域におけるリンの濃度は、例えば、以下の方法により測定できる。まず、複合酸化物粒子をペレット状に成形し、ペレットの表面から０．３ｒまでの深さまでの領域をスパッタリングして、その領域に含まれる元素の組成を決定する。その後、スパッタリングを続け、ペレットの表面から０．７ｒの深さから１ｒの深さまでの領域に含まれる元素の組成を決定する。こうして得られた組成から、リンの濃度を算出することができる。元素の組成は、オージェ分光分析（ＡＥＳ）、Ｘ線マイクロ分析（ＥＰＭＡ）、二次イオン質量分析（ＳＩＭＳ）、飛行時間型質量分析（ＴＯＦ－ＳＩＭＳ）などにより決定できる。ＡＥＳやＥＰＭＡを用いる場合、まず、複合酸化物粒子の中心を通る断面を、集束イオンビーム（ＦＩＢ）で切り出し、断面における元素マッピングを行うことにより元素の組成を決定できる。 The concentration of phosphorus in the region within 0.3r from the particle surface and within 0.3r from the center can be measured, for example, by the following method. First, composite oxide particles are formed into a pellet, and a region from the surface of the pellet to a depth of 0.3 r is sputtered to determine the composition of elements contained in the region. Thereafter, sputtering is continued, and the composition of elements contained in the region from the depth of 0.7r to the depth of 1r from the surface of the pellet is determined. From the composition thus obtained, the phosphorus concentration can be calculated. The elemental composition can be determined by Auger spectroscopic analysis (AES), X-ray microanalysis (EPMA), secondary ion mass spectrometry (SIMS), time-of-flight mass spectrometry (TOF-SIMS), or the like. When using AES or EPMA, first, a cross section passing through the center of the composite oxide particle is cut out with a focused ion beam (FIB), and elemental composition in the cross section can be determined.
　複合酸化物におけるリンの含有量は、リチウムと酸素を除いた元素の合計量に対し、例えば、１原子％より多く、好ましくは１．２原子％以上、さらに好ましくは１．３原子％以上である。本発明では、複合酸化物粒子の内部にまでリンが分布している。そのため、リンの含有量が上記の範囲である場合、粒子全体において、複合酸化物の結晶構造を効果的に安定化できる。よって、リンの添加効果を有効に得る上で、有利である。リンの含有量が１原子％以下の場合、リンを複合酸化物粒子の内部にまでに分布させることにより、複合酸化物の結晶構造を安定化する効果が乏しくなる。さらに、高い電池容量を確保する観点などから、含有量の上限は、例えば、５原子％以下、好ましくは４原子％以下、さらに好ましくは３原子％以下である。これらの上限および下限の値は、適宜組み合わせることができる。 The content of phosphorus in the composite oxide is, for example, more than 1 atomic%, preferably 1.2 atomic% or more, more preferably 1.3 atomic% or more with respect to the total amount of elements excluding lithium and oxygen. is there. In the present invention, phosphorus is distributed even inside the composite oxide particles. Therefore, when the phosphorus content is in the above range, the crystal structure of the composite oxide can be effectively stabilized over the entire particle. Therefore, it is advantageous in obtaining the effect of adding phosphorus effectively. When the phosphorus content is 1 atomic% or less, the effect of stabilizing the crystal structure of the composite oxide becomes poor by distributing phosphorus up to the inside of the composite oxide particles. Furthermore, from the viewpoint of securing a high battery capacity, the upper limit of the content is, for example, 5 atomic% or less, preferably 4 atomic% or less, and more preferably 3 atomic% or less. These upper and lower limits can be combined as appropriate.
　複合酸化物におけるニッケルの含有量は、リチウムと酸素を除いた元素の合計量に対し、例えば、６０～９０原子％であり、好ましくは６５～８５原子％である。ニッケルの含有量が多い場合、結晶構造を安定化するのが難しくなる。そのため、ニッケルの含有量がこのような範囲である場合、リンの添加効果が顕著に得られる。また、ニッケルの含有量が上記の範囲である場合、より有効に、高い電池容量を確保できる。 The content of nickel in the composite oxide is, for example, 60 to 90 atomic%, preferably 65 to 85 atomic%, based on the total amount of elements excluding lithium and oxygen. When the content of nickel is large, it becomes difficult to stabilize the crystal structure. Therefore, when the nickel content is in such a range, the effect of adding phosphorus is remarkably obtained. Further, when the nickel content is in the above range, a high battery capacity can be secured more effectively.
　複合酸化物におけるコバルトの含有量は、リチウムと酸素を除いた元素の合計量に対し、例えば、５～３０原子％、好ましくは１０～２５原子％である。コバルトの含有量が、このような範囲である場合、結晶構造の安定化の点で、より有利であり、かつ、高い電池容量をより有効に確保できる。また、コスト面でも有利である。 The cobalt content in the composite oxide is, for example, 5 to 30 atomic%, preferably 10 to 25 atomic%, based on the total amount of elements excluding lithium and oxygen. When the cobalt content is in such a range, it is more advantageous in terms of stabilization of the crystal structure, and a high battery capacity can be secured more effectively. Moreover, it is advantageous also in terms of cost.
　複合酸化物は、さらに、リチウム、リン、ニッケル、コバルトおよび酸素以外の元素Ｍを含有してもよい。元素Ｍとしては、例えば、アルカリ土類金属元素、ニッケルおよびコバルト以外の遷移金属元素、希土類元素、周期表第１３族元素および第１４族元素などが例示できる。元素Ｍとしては、具体的には、Ｍｇ、Ｃａ、Ｙ、Ｔｉ、Ｚｒ、Ｎｂ、Ｍｎ、Ａｌ、Ｉｎ、Ｓｎ、Ｗなどが例示できる。複合酸化物は、これらの元素Ｍのうち１種を含んでもよく、２種以上を含んでもよい。元素Ｍのうち、特に、Ｍｇ、Ａｌ、ＴｉおよびＺｒよりなる群から選択される少なくとも１種が好ましい。これらの元素を含む複合酸化物では、元素の種類に応じて、導電性などの特性をさらに向上させたり、結晶構造をさらに安定化させたり、または複合酸化物粒子の界面抵抗を下げたりすることができる。なお、複合酸化物粒子の界面抵抗が下がると、複合酸化物とリチウムイオンとの反応性が高くなる。 The composite oxide may further contain an element M other than lithium, phosphorus, nickel, cobalt, and oxygen. Examples of the element M include alkaline earth metal elements, transition metal elements other than nickel and cobalt, rare earth elements, Group 13 elements and Group 14 elements of the periodic table. Specific examples of the element M include Mg, Ca, Y, Ti, Zr, Nb, Mn, Al, In, Sn, and W. The composite oxide may include one of these elements M, or may include two or more. Among the elements M, at least one selected from the group consisting of Mg, Al, Ti and Zr is particularly preferable. In complex oxides containing these elements, depending on the type of element, the characteristics such as conductivity can be further improved, the crystal structure can be further stabilized, or the interface resistance of the complex oxide particles can be reduced. Can do. Note that when the interfacial resistance of the composite oxide particles decreases, the reactivity between the composite oxide and lithium ions increases.
　ＭｇやＡｌは、水溶液中で、ニッケルおよびコバルトとともに共沈させることが比較的容易である。そのため、共沈により得られる第１原料を用いて複合酸化物を製造する場合には、複合酸化物中に、ＭｇやＡｌを、より均一にまたはより均等な間隔で分散させることができるとともに、複合酸化物粒子の内部に所定の濃度で含有させることができる点で、有利である。また、ＭｇやＡｌを用いると、複合酸化物の結晶構造をさらに安定化させることができる。Ｍｇを含む複合酸化物では、高い導電性が得られる。
　ＴｉやＺｒを用いる場合、複合酸化物の界面抵抗を下げることができる。 Mg and Al are relatively easy to co-precipitate with nickel and cobalt in an aqueous solution. Therefore, when producing a composite oxide using the first raw material obtained by coprecipitation, Mg and Al can be dispersed more uniformly or at even intervals in the composite oxide, This is advantageous in that it can be contained in the composite oxide particles at a predetermined concentration. In addition, when Mg or Al is used, the crystal structure of the composite oxide can be further stabilized. High conductivity can be obtained with a complex oxide containing Mg.
When Ti or Zr is used, the interface resistance of the composite oxide can be lowered.
　本発明の好ましい一形態において、複合酸化物は、元素Ｍとして、ＭｇおよびＡｌよりなる第１元素群から選択される少なくとも１種を含んでいる。また、本発明の好ましい他の形態では、複合酸化物は、元素Ｍとして、ＴｉおよびＺｒよりなる第２元素群から選択される少なくとも１種を含んでいる。また、複合酸化物は、第１元素群から選択される少なくとも１種と、第２元素群から選択される少なくとも１種とを含んでもよい。第１元素群と第２元素群とを組み合わせると、より効果的に、結晶構造を安定化できるとともに、導電性および／またはリチウムイオンとの反応性を向上したりできる。その結果、充放電サイクル中の容量維持率の低下を防止することができる。 In a preferred embodiment of the present invention, the composite oxide contains at least one selected from the first element group consisting of Mg and Al as the element M. In another preferable embodiment of the present invention, the complex oxide contains at least one selected from the second element group consisting of Ti and Zr as the element M. The composite oxide may include at least one selected from the first element group and at least one selected from the second element group. When the first element group and the second element group are combined, the crystal structure can be more effectively stabilized and the conductivity and / or the reactivity with lithium ions can be improved. As a result, it is possible to prevent a decrease in capacity retention rate during the charge / discharge cycle.
　元素Ｍは、複合酸化物粒子中の一部の領域、例えば、表層または内部に含まれていてもよい。また、元素Ｍは、リンの場合と同様に、複合酸化物粒子の表層と内部とにおいて、所定の比率で分布していてもよい。この比率は、リンの場合と同様に評価できる。具体的には、複合酸化物粒子の表層（粒子の表面から０．３ｒ以内の領域）に含まれる元素Ｍの濃度ＣMsと、粒子内部（粒子の中心から０．３ｒ以内の領域）に含まれる元素Ｍの濃度ＣMcの比率ＣMs／ＣMcは、上記リンの比率ＣPs／ＣPcと同様の範囲から選択できる。元素Ｍがこのような分布状態である場合にも、リンの場合と同様に、複合酸化物粒子のひび割れや欠けが生じても、元素Ｍの添加効果をより有効に得ることができる。 The element M may be included in a part of the complex oxide particles, for example, the surface layer or the inside. Further, the element M may be distributed at a predetermined ratio between the surface layer and the inside of the composite oxide particle, as in the case of phosphorus. This ratio can be evaluated as in the case of phosphorus. Specifically, the concentration C Ms of the element M contained in the surface layer of the composite oxide particle (region within 0.3r from the surface of the particle) and the inside of the particle (region within 0.3r from the center of the particle) The ratio C Ms / C Mc of the concentration C Mc of the element M to be selected can be selected from the same range as the phosphorus ratio C Ps / C Pc . Even in the case where the element M is in such a distribution state, the effect of adding the element M can be obtained more effectively even when cracks or chipping of the composite oxide particles occur as in the case of phosphorus.
　ＭｇおよびＡｌは、ニッケルおよびコバルトと共沈させる場合、得られる複合酸化物粒子において、リンと同様に、より均一またはより均等な間隔で分布させやすく、また、複合酸化物粒子の内部にまで所定の濃度で含有させることができる。この場合、リンの場合と同様に、結晶構造をより効果的に安定化することができる。 When co-precipitated with nickel and cobalt, Mg and Al are likely to be distributed more uniformly or more evenly in the obtained composite oxide particles as in the case of phosphorus, and predetermined inside the composite oxide particles. It can be made to contain in the density | concentration. In this case, as in the case of phosphorus, the crystal structure can be stabilized more effectively.
　ＴｉおよびＺｒは、複合酸化物粒子において、表層に多く分布しやすい。この場合、より有効に、複合酸化物の界面抵抗を下げることができる。これらの２元素群の元素が、複合酸化物粒子の表層に分布する場合、第２元素群についての元素Ｍの比率ＣMs／ＣMc（比率ＣMs2／ＣMc2ともいう）、例えば、５．５／１以上、好ましくは７／１以上である。ここで、ＣMs2は、複合酸化物粒子の表層（粒子の表面から０．３ｒ以内の領域）に含まれる、第２元素群の濃度であり、ＣMc2は、粒子の内部（粒子の中心から０．３ｒ以内の領域）に含まれる第２元素群の濃度である。濃度ＣMc2は０であってもよい。 Ti and Zr are easily distributed in the surface layer in the composite oxide particles. In this case, the interface resistance of the composite oxide can be reduced more effectively. When the elements of these two element groups are distributed on the surface layer of the composite oxide particle, the ratio M Ms / C Mc (also referred to as the ratio C Ms2 / C Mc2 ) of the element M with respect to the second element group, for example, 5. 5/1 or more, preferably 7/1 or more. Here, C Ms2 is the concentration of the second element group contained in the surface layer (region within 0.3 r from the surface of the particle) of the composite oxide particle, and C Mc2 is the inside of the particle (from the center of the particle). This is the concentration of the second element group included in the region within 0.3r. The concentration C Mc2 may be zero.
　複合酸化物における元素Ｍの含有量は、リチウムと酸素を除いた元素の合計量に対し、例えば、０．１～１０原子％、好ましくは１～１０原子％、さらに好ましくは２～８原子％である。このような範囲では、複合酸化物を正極活物質として用いた電池の容量を高いレベルで維持しながらも、より効果的に、元素Ｍの種類に応じて、その添加効果を得ることができる。 The content of the element M in the composite oxide is, for example, 0.1 to 10 atomic%, preferably 1 to 10 atomic%, more preferably 2 to 8 atomic%, with respect to the total amount of elements excluding lithium and oxygen It is. In such a range, the addition effect can be more effectively obtained according to the type of the element M while maintaining the capacity of the battery using the composite oxide as the positive electrode active material at a high level.
　元素Ｍのうち第１元素群の含有量は、リチウムと酸素を除いた元素の合計量に対し、例えば、０．１～１０原子％、好ましくは１～１０原子％、さらに好ましくは１．５～６原子％である。このような範囲では、複合酸化物を正極活物質として用いた電池の容量を高いレベルで維持できる。また、より効果的に、導電性を向上したり、充放電サイクル中の容量維持率の低下を防止したりできる。第１元素群は、共沈により、複合酸化物粒子の内部にまで分布させることができるため、比較的多く含有させることができる。 The content of the first element group in the element M is, for example, 0.1 to 10 atomic%, preferably 1 to 10 atomic%, and more preferably 1.5 to the total amount of elements excluding lithium and oxygen. ~ 6 atomic%. In such a range, the capacity of the battery using the composite oxide as the positive electrode active material can be maintained at a high level. In addition, the conductivity can be improved more effectively, and the decrease in capacity maintenance rate during the charge / discharge cycle can be prevented. Since the first element group can be distributed to the inside of the composite oxide particles by coprecipitation, it can be contained in a relatively large amount.
　第２元素群の含有量は、リチウムと酸素を除いた元素の合計量に対し、例えば、０．１～１原子％、好ましくは０．２～０．７原子％である。第２元素群は、表層に比較的多く分布しやすいため、含有量は第１元素群に比較すると少なくなりやすい。このような範囲では、複合酸化物を正極活物質として用いた電池の容量を高いレベルで維持しながらも、より効果的に、複合酸化物の界面抵抗を下げることができる。 The content of the second element group is, for example, 0.1 to 1 atom%, preferably 0.2 to 0.7 atom%, based on the total amount of elements excluding lithium and oxygen. Since the second element group is likely to be distributed in a relatively large amount on the surface layer, the content is likely to be smaller than that of the first element group. In such a range, the interface resistance of the composite oxide can be more effectively lowered while maintaining the capacity of the battery using the composite oxide as the positive electrode active material at a high level.
　複合酸化物は、例えば、酸素の六方晶に着目したときに、酸素の層と、金属の層（リチウムの層および他の金属の層など）とが積層した層状構造（層状岩塩構造など）の結晶構造を有するのが好ましい。このような結晶構造を有する場合、リチウムの吸蔵および放出がスムーズに行われやすく、電池を高容量化する点から有利である。 For example, the complex oxide has a layered structure (such as a layered rock salt structure) in which an oxygen layer and a metal layer (such as a lithium layer and another metal layer) are stacked when focusing on hexagonal crystals of oxygen. It preferably has a crystal structure. Such a crystal structure is advantageous in that lithium can be inserted and extracted smoothly and the capacity of the battery can be increased.
　複合酸化物粒子の平均粒径は、例えば、５～５０μｍ、好ましくは１０～４０μｍ、さらに好ましくは１５～３０μｍである。
　正極活物質は、互いに異なる平均粒径を有する複数の複合酸化物粒子群の混合物であってもよい。つまり、正極活物質は、体積基準の粒度分布において複数のピークを有してもよい。この場合、複合酸化物粒子全体の平均粒径は、上記の平均粒径の範囲から選択できる。 The average particle size of the composite oxide particles is, for example, 5 to 50 μm, preferably 10 to 40 μm, and more preferably 15 to 30 μm.
The positive electrode active material may be a mixture of a plurality of composite oxide particles having different average particle sizes. That is, the positive electrode active material may have a plurality of peaks in the volume-based particle size distribution. In this case, the average particle diameter of the entire composite oxide particle can be selected from the above average particle diameter range.
　正極活物質について、体積基準の粒度分布におけるピークの個数は、２～４個であってもよいが、特に制限されない。正極活物質は、平均粒径の大きな大粒子群と、平均粒径の小さな小粒子群とを含んでもよい。大粒子群は、体積基準の粒度分布において、例えば、１６μｍより大きく、５０μｍ以下、好ましくは１７～３０μｍの間にピークを有してもよい。小粒子群は、体積基準の粒度分布において、例えば、１～１６μｍ、好ましくは２～１２μｍの間にピークを有してもよい。平均粒径の異なる複数の粒子群を併用することにより、正極合剤層の密度をより大きくすることができる。大粒子群と、小粒子群との混合比は、特に制限されないが、例えば、６０：４０～９５：５、好ましくは７０：３０～９０：１０である。 Regarding the positive electrode active material, the number of peaks in the volume-based particle size distribution may be 2 to 4, but is not particularly limited. The positive electrode active material may include a large particle group having a large average particle diameter and a small particle group having a small average particle diameter. The large particle group may have a peak in the volume-based particle size distribution, for example, larger than 16 μm and 50 μm or less, preferably between 17 and 30 μm. The small particle group may have a peak in the volume-based particle size distribution, for example, between 1 and 16 μm, preferably between 2 and 12 μm. By using a plurality of particle groups having different average particle diameters in combination, the density of the positive electrode mixture layer can be further increased. The mixing ratio of the large particle group and the small particle group is not particularly limited, but is, for example, 60:40 to 95: 5, preferably 70:30 to 90:10.
　複合酸化物粒子の平均粒径は、粉砕や分級などの方法により調整してもよい。また、原料（例えば、第１原料など）の平均粒径を調整することにより、複合酸化物粒子の平均粒径を調整してもよい。
　なお、平均粒径とは、複合酸化物粒子の体積粒度分布におけるメディアン径（Ｄ５０）を意味する。複合酸化物粒子の体積粒度分布は、例えば市販のレーザー回折式の粒度分布測定装置により測定することができる。 The average particle size of the composite oxide particles may be adjusted by a method such as pulverization or classification. Moreover, you may adjust the average particle diameter of composite oxide particle | grains by adjusting the average particle diameter of raw materials (for example, 1st raw material etc.).
In addition, an average particle diameter means the median diameter (D50) in the volume particle size distribution of complex oxide particle. The volume particle size distribution of the composite oxide particles can be measured by, for example, a commercially available laser diffraction particle size distribution measuring device.
［正極活物質の製造方法］
　上記のような複合酸化物を含む正極活物質は、下記の工程（１）～（３）を経ることにより製造できる。
（１）ニッケルおよびコバルトを含む第１原料を準備する工程、
（２）第１原料と、リンを含む第２原料と、を混合し、これらを、７５０℃を超える温度で仮焼成し、ニッケルおよびコバルトを含むとともに、表層および内部に所定の濃度でリンを含む酸化物の粒子を得る工程、並びに
（３）工程（２）で得られた酸化物の粒子と、リチウムを含む第３原料と、を混合し、これらを、８００℃以下の温度で本焼成し、リチウム、リン、ニッケルおよびコバルトを含む複合酸化物の粒子を得る工程。
　複合酸化物が、既述の元素Ｍを含む場合、元素Ｍは、工程（１）～（３）のいずれの段階で添加してもよい。 [Method for producing positive electrode active material]
The positive electrode active material containing the composite oxide as described above can be produced through the following steps (1) to (3).
(1) preparing a first raw material containing nickel and cobalt;
(2) Mixing the first raw material and the second raw material containing phosphorus, pre-baking them at a temperature exceeding 750 ° C., containing nickel and cobalt, and adding phosphorus at a predetermined concentration in the surface layer and inside A step of obtaining oxide particles containing, and (3) mixing the oxide particles obtained in step (2) with a third raw material containing lithium, and subjecting them to a main firing at a temperature of 800 ° C. or lower. And obtaining a composite oxide particle containing lithium, phosphorus, nickel and cobalt.
When the composite oxide includes the element M described above, the element M may be added at any stage of the steps (1) to (3).
　（工程（１））
　第１原料としては、ニッケルおよびコバルトを含む各種化合物、例えば、酸化物、水酸化物、塩（炭酸塩、硫酸塩などの無機酸塩；酢酸塩などの有機酸塩など）などが挙げられる。これらのうち、水酸化物、特に、ニッケルおよびコバルトを含む複合水酸化物が好ましい。複合水酸化物は、共沈法により得ることが可能であり、共沈法では、ニッケルおよびコバルトを、複合水酸化物中に均一に分散させることができるため、特に有利である。第１原料は、さらに、既述の元素Ｍを１種または２種以上含有してもよい。 (Process (1))
Examples of the first raw material include various compounds containing nickel and cobalt, such as oxides, hydroxides, and salts (inorganic acid salts such as carbonates and sulfates; organic acid salts such as acetates). Of these, hydroxides, particularly composite hydroxides containing nickel and cobalt are preferred. The composite hydroxide can be obtained by a coprecipitation method, and the coprecipitation method is particularly advantageous because nickel and cobalt can be uniformly dispersed in the composite hydroxide. The first raw material may further contain one or more elements M described above.
　第１原料としては、市販品を準備してもよく、第１原料の種類に応じて、公知の方法により合成してもよい。最終的に得られる複合酸化物粒子中のリンおよびリチウムの分散性の観点から、ニッケルとコバルトとは、固溶体を形成しているのが好ましい。固溶体を含む第１原料は、例えば、第１原料が水酸化物である場合、共沈法により合成できる。第１原料が、金属元素Ｍを含む場合には、共沈により、ニッケルおよびコバルトとともに、元素Ｍを含む固溶体を形成してもよい。共沈により固溶体を形成可能な元素Ｍとしては、例えば、ＭｇおよびＡｌよりなる第１元素群から選択される少なくとも１種が挙げられる。 As the first raw material, a commercial product may be prepared, or may be synthesized by a known method according to the type of the first raw material. From the viewpoint of the dispersibility of phosphorus and lithium in the finally obtained composite oxide particles, it is preferable that nickel and cobalt form a solid solution. For example, when the first raw material is a hydroxide, the first raw material containing the solid solution can be synthesized by a coprecipitation method. When the first raw material contains the metal element M, a solid solution containing the element M may be formed together with nickel and cobalt by coprecipitation. Examples of the element M capable of forming a solid solution by coprecipitation include at least one selected from the first element group consisting of Mg and Al.
　共沈法では、ニッケル塩およびコバルト塩などの原料塩を含む水溶液を調製し、還元性雰囲気下で複合水酸化物を沈殿させる。具体的には、複合水酸化物は、原料塩を含む水溶液に、アルカリを添加することにより得ることができる。共沈により第１原料に元素Ｍを含有させる場合、原料塩としては、ニッケル塩、コバルト塩および元素Ｍを含む塩を用いる。各塩は、各元素が所定の原子比となるような割合で混合される。 In the coprecipitation method, an aqueous solution containing raw material salts such as nickel salt and cobalt salt is prepared, and the composite hydroxide is precipitated in a reducing atmosphere. Specifically, the composite hydroxide can be obtained by adding an alkali to an aqueous solution containing a raw material salt. When the element M is contained in the first raw material by coprecipitation, a nickel salt, a cobalt salt, and a salt containing the element M are used as the raw material salt. Each salt is mixed at a ratio such that each element has a predetermined atomic ratio.
　原料塩としては、例えば、硫酸塩、塩酸塩、リン酸塩、硝酸塩などの無機酸塩が使用される。中でも、硫酸塩を用いる場合が多い。アルカリとしては、例えば、水酸化カリウム、水酸化ナトリウムなどのアルカリ金属水酸化物などの無機アルカリが使用できる。原料塩を含む水溶液にアルカリを添加することにより、水溶液のｐＨは、例えば、７～１４に調整される。共沈は、不活性ガス雰囲気下または還元性ガス雰囲気下などで行ってもよい。
　第１原料は、市販品または合成品を、必要により、精製したり、粉砕および／または分級したりしたものを、工程（２）に供してもよい。 As the raw material salt, for example, inorganic acid salts such as sulfate, hydrochloride, phosphate and nitrate are used. Of these, sulfate is often used. As the alkali, for example, an inorganic alkali such as an alkali metal hydroxide such as potassium hydroxide or sodium hydroxide can be used. By adding an alkali to the aqueous solution containing the raw material salt, the pH of the aqueous solution is adjusted to 7 to 14, for example. The coprecipitation may be performed under an inert gas atmosphere or a reducing gas atmosphere.
As the first raw material, a commercially available product or a synthesized product may be purified, pulverized and / or classified, if necessary, for the step (2).
　第１原料の平均粒径は、例えば、１～４０μｍ、好ましくは３～２５μｍである。このような範囲では、工程（２）において、酸化物粒子の内部にまで、より有効にリンを分布させることができる。なお、平均粒径とは、第１原料の粒子の体積粒度分布におけるメディアン径（Ｄ５０）を意味する。体積粒度分布は、例えば市販のレーザー回折式の粒度分布測定装置により測定することができる。 The average particle diameter of the first raw material is, for example, 1 to 40 μm, preferably 3 to 25 μm. In such a range, in the step (2), phosphorus can be more effectively distributed even inside the oxide particles. The average particle diameter means the median diameter (D50) in the volume particle size distribution of the first raw material particles. The volume particle size distribution can be measured by, for example, a commercially available laser diffraction type particle size distribution measuring apparatus.
　（工程（２））
　工程（２）では、第１原料と、リンを含む第２原料との混合物を、仮焼成することにより、リン、ニッケルおよびコバルトを含む酸化物粒子を得る。
　第２原料としては、リンを含む化合物、例えば、リン酸類（オルトリン酸、亜リン酸、次亜リン酸などのモノリン酸類；ピロリン酸、メタリン酸などのポリリン酸類など）、リン酸塩類（前記リン酸類と金属との塩など）、リン酸化物（五酸化二リンなど）などが例示できる。これらの中でも、オルトリン酸やポリリン酸などのリン酸類、これらのリン酸類と金属との塩が好ましい。これらの第２原料は、１種を単独でまたは２種以上を組み合わせて使用できる。 (Process (2))
In the step (2), oxide particles containing phosphorus, nickel and cobalt are obtained by temporarily firing a mixture of the first raw material and the second raw material containing phosphorus.
Examples of the second raw material include phosphorus-containing compounds, for example, phosphoric acids (monophosphoric acids such as orthophosphoric acid, phosphorous acid, and hypophosphorous acid; polyphosphoric acids such as pyrophosphoric acid and metaphosphoric acid), phosphates (the above-mentioned phosphorus Examples thereof include salts of acids and metals, phosphorus oxides (such as diphosphorus pentoxide), and the like. Among these, phosphoric acids such as orthophosphoric acid and polyphosphoric acid, and salts of these phosphoric acids and metals are preferable. These 2nd raw materials can be used individually by 1 type or in combination of 2 or more types.
　第２原料は、リンに加え、元素Ｍを含んでもよい。第１原料が元素Ｍを含有しない場合、第２原料に元素Ｍを含有させるのが有利である。
　第２原料が元素Ｍを含む場合には、リン酸と元素Ｍとの塩を第２原料として用いるのが有利である。第２原料に含まれる元素Ｍとしては、Ｍｇ、Ａｌ、ＴｉおよびＺｒよりなる群から選択される少なくとも１種が好ましい。このような第２原料としては、例えば、リン酸マグネシウム、リン酸アルミニウム、リン酸チタンおよびリン酸ジルコニウムよりなる群から選択される少なくとも１種が例示できる。 The second raw material may contain the element M in addition to phosphorus. When the first raw material does not contain the element M, it is advantageous to contain the element M in the second raw material.
When the second raw material contains the element M, it is advantageous to use a salt of phosphoric acid and the element M as the second raw material. The element M contained in the second raw material is preferably at least one selected from the group consisting of Mg, Al, Ti and Zr. Examples of such second raw material include at least one selected from the group consisting of magnesium phosphate, aluminum phosphate, titanium phosphate, and zirconium phosphate.
　第２原料は、元素Ｍの中でも、特に、ＭｇおよびＡｌよりなる第１元素群から選択される少なくとも１種を含むのが好ましい。このような第２原料のうち、リン酸マグネシウムの具体例としては、第１リン酸マグネシウム、第２リン酸マグネシウム、第３リン酸マグネシウム、ピロリン酸マグネシウムおよびメタリン酸マグネシウムよりなる群から選択される少なくとも１種などが挙げられる。また、リン酸アルミニウムの具体例としては、第１リン酸アルミニウム、第２リン酸アルミニウム、第３リン酸アルミニウムおよびメタリン酸アルミニウムよりなる群から選択される少なくとも１種などが挙げられる。 The second raw material preferably contains at least one selected from the first element group consisting of Mg and Al among the elements M. Among such second raw materials, a specific example of magnesium phosphate is selected from the group consisting of first magnesium phosphate, second magnesium phosphate, third magnesium phosphate, magnesium pyrophosphate and magnesium metaphosphate. There are at least one kind. Specific examples of the aluminum phosphate include at least one selected from the group consisting of a first aluminum phosphate, a second aluminum phosphate, a third aluminum phosphate, and an aluminum metaphosphate.
　なお、第１原料が、第１元素群から選択される少なくとも１種を含む場合には、第２原料は、ＴｉおよびＺｒよりなる第２元素群から選択される少なくとも１種を含んでもよい。ＴｉやＺｒは、水溶液中で、ニッケルおよびコバルトとともに共沈しにくいため、第１原料を共沈により得る場合には、第２元素群を第２原料に含有させるのが有利である。 When the first raw material includes at least one selected from the first element group, the second raw material may include at least one selected from the second element group made of Ti and Zr. Since Ti and Zr are difficult to coprecipitate with nickel and cobalt in an aqueous solution, when the first raw material is obtained by coprecipitation, it is advantageous to include the second element group in the second raw material.
　第１原料と第２原料とは、ニッケルと、コバルトと、リンと、必要により添加される元素Ｍとが所定の原子比となるような割合で混合され、仮焼成に供される。 The first raw material and the second raw material are mixed at a ratio such that nickel, cobalt, phosphorus, and the element M added if necessary have a predetermined atomic ratio, and are subjected to provisional firing.
　仮焼成の温度は、７５０℃を超える温度であれば特に制限されず、好ましくは８５０℃、さらに好ましくは９００℃以上である。このような温度で仮焼成を行うと、リンを酸化物粒子の内部にまで所定の濃度で分布させることができる点で有利である。仮焼成温度の上限は、ニッケルとリチウムとの置換反応を抑制する観点などから、例えば、１２００℃、好ましくは１１００℃、さらに好ましくは１０５０℃である。これらの下限および上限の値は、適宜組み合わせることができる。 The temperature for pre-baking is not particularly limited as long as the temperature exceeds 750 ° C., preferably 850 ° C., more preferably 900 ° C. or more. Pre-baking at such a temperature is advantageous in that phosphorus can be distributed at a predetermined concentration to the inside of the oxide particles. The upper limit of the calcination temperature is, for example, 1200 ° C., preferably 1100 ° C., and more preferably 1050 ° C. from the viewpoint of suppressing the substitution reaction between nickel and lithium. These lower limit and upper limit values can be combined as appropriate.
　なお、酸化物粒子におけるリンの分布状態、具体的には、表層および内部におけるリンの濃度およびこれらの比率は、複合酸化物粒子における比率ＣPs／ＣPcが所定の範囲となるように調整できる。 The phosphorus distribution state in the oxide particles, specifically, the concentration of phosphorus in the surface layer and inside and the ratio thereof can be adjusted so that the ratio C Ps / C Pc in the composite oxide particles is within a predetermined range. .
　仮焼成は、通常、酸素ガスを含む雰囲気下で行われる。仮焼成雰囲気の酸素ガス濃度は、例えば、１８～３０モル％である。仮焼成は、空気中で行われる場合が多い。
　コストおよび反応性などの観点から、仮焼成雰囲気の酸素分圧は、例えば、１８～３０ｋＰａである。
　仮焼成時間は、焼成温度にも依存するが、例えば５～４８時間である。 Pre-baking is normally performed in an atmosphere containing oxygen gas. The oxygen gas concentration in the pre-baking atmosphere is, for example, 18 to 30 mol%. Pre-baking is often performed in air.
From the viewpoint of cost and reactivity, the oxygen partial pressure in the pre-baking atmosphere is, for example, 18 to 30 kPa.
The temporary firing time is, for example, 5 to 48 hours, although it depends on the firing temperature.
　（工程（３））
　工程（３）では、工程（２）で得られた酸化物粒子と、リチウムを含む第３原料との混合物を、本焼成することにより、複合酸化物粒子を得る。
　第３原料としては、リチウムを含む化合物、例えば、酸化物、水酸化物、塩（炭酸塩、硫酸塩などの無機酸塩；酢酸塩などの有機酸塩など）などが例示できる。これらのうち、反応性などの点から、水酸化リチウムが好ましい。 (Process (3))
In step (3), composite oxide particles are obtained by subjecting the mixture of the oxide particles obtained in step (2) and the third raw material containing lithium to main firing.
Examples of the third raw material include lithium-containing compounds such as oxides, hydroxides, and salts (inorganic acid salts such as carbonates and sulfates; organic acid salts such as acetates). Of these, lithium hydroxide is preferred from the viewpoint of reactivity.
　また、必要により、第３原料とともに、元素Ｍを含む化合物を併用してもよい。元素Ｍを含む化合物としては、酸化物、水酸化物、窒化物、硫化物、塩（無機酸塩など）などが例示できる。 If necessary, a compound containing the element M may be used in combination with the third raw material. Examples of the compound containing the element M include oxides, hydroxides, nitrides, sulfides, salts (such as inorganic acid salts), and the like.
　本焼成の温度は、８００℃以下、好ましくは７７０℃以下、さらに好ましくは７５０℃以下である。本焼成温度の下限は、例えば、６００℃、好ましくは６５０℃である。このような温度で本焼成を行うことにより、第３原料の揮発などを抑制しながら、複合酸化物粒子中にリチウムを効果的に分散することができる。これらの上限および下限の値は、適宜選択して組み合わせることができる。また、本焼成の温度は、仮焼成の温度より低いのが好ましい。
　本焼成は、通常、空気中などの酸素ガスを含む雰囲気下で行われる。本焼成雰囲気の酸素ガス濃度および酸素分圧、焼成時間は、仮焼成の場合と同様の範囲から適宜選択できる。 The firing temperature is 800 ° C. or lower, preferably 770 ° C. or lower, more preferably 750 ° C. or lower. The lower limit of the main firing temperature is, for example, 600 ° C., preferably 650 ° C. By performing the main firing at such a temperature, lithium can be effectively dispersed in the composite oxide particles while suppressing volatilization of the third raw material. These upper limit and lower limit values can be appropriately selected and combined. Moreover, it is preferable that the temperature of this baking is lower than the temperature of temporary baking.
The main firing is usually performed in an atmosphere containing oxygen gas such as in the air. The oxygen gas concentration, oxygen partial pressure, and firing time in the main firing atmosphere can be appropriately selected from the same ranges as in the case of temporary firing.
［正極］
　本発明の正極は、正極集電体および正極集電体の表面に付着した正極活物質層を含む。正極活物質層は、上記の正極活物質および結着剤を含む。
　正極集電体としては、アルミニウム、ステンレス鋼、ニッケル、チタン、炭素、導電性樹脂などで形成された箔もしくはシートを用いることができる。正極集電体は、無孔性であってもよく、多孔性であってもよい。正極集電体の形状は、非水電解質二次電池の形状などに応じて、帯状、コイン状などであってもよい。正極集電体の厚みは、例えば、５～５０μｍである。 [Positive electrode]
The positive electrode of the present invention includes a positive electrode current collector and a positive electrode active material layer attached to the surface of the positive electrode current collector. The positive electrode active material layer includes the positive electrode active material and the binder.
As the positive electrode current collector, a foil or a sheet formed of aluminum, stainless steel, nickel, titanium, carbon, conductive resin, or the like can be used. The positive electrode current collector may be nonporous or porous. The shape of the positive electrode current collector may be a belt shape, a coin shape, or the like depending on the shape of the nonaqueous electrolyte secondary battery. The thickness of the positive electrode current collector is, for example, 5 to 50 μm.
　結着剤としては、ポリエチレン、ポリプロピレンなどのオレフィン樹脂；ポリテトラフルオロエチレン、ポリフッ化ビニリデン（ＰＶＤＦ）、テトラフルオロエチレン－ヘキサフルオロプロピレン共重合体などのフッ素樹脂；スチレンブタジエンゴム（ＳＢＲ）、変性ＳＢＲなどのゴム状樹脂などが挙げられる。これらの結着剤は、１種を単独でまたは２種以上を組み合わせて使用できる。
　結着剤の割合は、正極活物質１００重量部に対して、例えば、０．１～１５重量部、好ましくは０．２～１０重量部である。 Binders include olefin resins such as polyethylene and polypropylene; fluorine resins such as polytetrafluoroethylene, polyvinylidene fluoride (PVDF), tetrafluoroethylene-hexafluoropropylene copolymer; styrene butadiene rubber (SBR), and modified SBR. And rubber-like resin. These binders can be used singly or in combination of two or more.
The ratio of the binder is, for example, 0.1 to 15 parts by weight, preferably 0.2 to 10 parts by weight with respect to 100 parts by weight of the positive electrode active material.
　正極活物質層における正極活物質の密度は、例えば、３ｇ／ｃｍ3以上、好ましくは３．５ｇ／ｃｍ3以上、さらに好ましくは３．６ｇ／ｃｍ3以上である。本発明は、正極活物質粒子がひび割れや欠けを生じたりする場合にも、抵抗の増加を抑制できるため、正極活物質密度が大きい場合にも有効である。正極活物質の密度の上限は、例えば、４ｇ／ｃｍ3、好ましくは３．８ｇ／ｃｍ3である。これらの下限および上限の値は、適宜選択して組み合わせることができる。 The density of the positive electrode active material in the positive electrode active material layer is, for example, 3 g / cm 3 or more, preferably 3.5 g / cm 3 or more, and more preferably 3.6 g / cm 3 or more. The present invention is effective even when the positive electrode active material density is high because the increase in resistance can be suppressed even when the positive electrode active material particles are cracked or chipped. The upper limit of the density of the positive electrode active material, for example, 4g / cm 3, preferably 3.8 g / cm 3. These lower and upper limit values can be appropriately selected and combined.
　正極活物質層は、さらに導電剤を含んでもよい。導電剤としては、導電性炭素材料、金属材料などが例示できる。導電剤の形態は、粒子、フレーク、または繊維などであってもよい。導電性炭素材料としては、天然黒鉛、人造黒鉛などの黒鉛；カーボンブラックなどが例示できる。導電剤は、１種を単独でまたは２種以上を組み合わせて使用できる。導電剤のうち、導電性炭素材料が好ましい。
　導電剤の割合は、正極活物質１００重量部に対して、例えば、０．１～１．５重量部、好ましくは０．２～１．２重量部である。本発明の正極活物質は、導電性が高い。特に、正極活物質としての複合酸化物が、元素ＭとしてＭｇを含む場合、リンが複合酸化物粒子の内部にまで所定の濃度で分布することにより、Ｍｇの効果がさらに高められる。そのため、導電剤の使用量が少なくとも、高い導電性を確保できる。 The positive electrode active material layer may further contain a conductive agent. Examples of the conductive agent include conductive carbon materials and metal materials. The conductive agent may be in the form of particles, flakes, fibers, or the like. Examples of the conductive carbon material include graphite such as natural graphite and artificial graphite; carbon black and the like. A conductive agent can be used individually by 1 type or in combination of 2 or more types. Of the conductive agents, conductive carbon materials are preferred.
The proportion of the conductive agent is, for example, 0.1 to 1.5 parts by weight, preferably 0.2 to 1.2 parts by weight, with respect to 100 parts by weight of the positive electrode active material. The positive electrode active material of the present invention has high conductivity. In particular, when the composite oxide as the positive electrode active material contains Mg as the element M, the effect of Mg is further enhanced by the phosphorus being distributed at a predetermined concentration to the inside of the composite oxide particles. Therefore, at least the amount of the conductive agent used can ensure high conductivity.
　正極は、正極集電体の表面に、正極活物質および結着剤を含む正極合剤を付着させて正極活物質層を形成することにより作製できる。正極合剤は、さらに導電剤および／または他の添加剤を含んでいてもよい。正極合剤は、通常、正極活物質と、結着剤と、必要により導電剤および／または添加剤とを、分散媒に分散させることにより調製できる。なお、正極合剤において、結着剤や添加剤は、分散媒中に溶解していてもよい。正極は、具体的には、正極集電体の表面に正極合剤を塗布し、乾燥させ、次いで、一対のローラなどで圧延することにより作製できる。正極活物質層は、正極集電体の一方の表面に形成してもよく、両方の表面に形成してもよい。
　正極の厚みは、例えば、５０～２３０μｍ、好ましくは８０～２００μｍである。 The positive electrode can be produced by attaching a positive electrode mixture containing a positive electrode active material and a binder to the surface of the positive electrode current collector to form a positive electrode active material layer. The positive electrode mixture may further contain a conductive agent and / or other additives. The positive electrode mixture can be usually prepared by dispersing a positive electrode active material, a binder, and, if necessary, a conductive agent and / or an additive in a dispersion medium. In the positive electrode mixture, the binder and additives may be dissolved in the dispersion medium. Specifically, the positive electrode can be produced by applying a positive electrode mixture to the surface of the positive electrode current collector, drying it, and then rolling it with a pair of rollers or the like. The positive electrode active material layer may be formed on one surface of the positive electrode current collector, or may be formed on both surfaces.
The thickness of the positive electrode is, for example, 50 to 230 μm, preferably 80 to 200 μm.
　添加剤としては、増粘剤の他、正極合剤に使用される公知の添加剤が例示できる。増粘剤としては、エチレン－ビニルアルコール共重合体、セルロース誘導体（カルボキシメチルセルロース、メチルセルロースなど）などが例示できる。 Examples of additives include thickeners and known additives used for positive electrode mixtures. Examples of the thickener include ethylene-vinyl alcohol copolymers, cellulose derivatives (carboxymethyl cellulose, methyl cellulose, etc.) and the like.
　分散媒としては、例えば、水、エタノールなどのアルコール、テトラヒドロフランなどのエーテル、Ｎ－メチル－２－ピロリドン（ＮＭＰ）、またはこれらの混合溶媒などが例示できる。
　このような正極は、リチウムイオン電池などの非水電解質二次電池に有用である。 Examples of the dispersion medium include water, alcohols such as ethanol, ethers such as tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), or a mixed solvent thereof.
Such a positive electrode is useful for a nonaqueous electrolyte secondary battery such as a lithium ion battery.
［非水電解質二次電池］
　非水電解質二次電池は、上記の正極と、負極と、これらを隔絶するセパレータと、非水電解質とを有している。
　（負極）
　負極は、負極集電体と、この表面に付着した負極活物質層とを有している。
　負極集電体としては、例えば、銅箔、銅合金箔などが例示できる。負極集電体は、無孔性であってもよく、多孔性であってもよい。負極集電体の形状および厚みは、正極集電体の場合と同様である。 [Nonaqueous electrolyte secondary battery]
The non-aqueous electrolyte secondary battery has the positive electrode, the negative electrode, a separator that isolates them, and a non-aqueous electrolyte.
(Negative electrode)
The negative electrode has a negative electrode current collector and a negative electrode active material layer attached to the surface.
Examples of the negative electrode current collector include copper foil and copper alloy foil. The negative electrode current collector may be nonporous or porous. The shape and thickness of the negative electrode current collector are the same as those of the positive electrode current collector.
　負極活物質層は、負極活物質で形成してもよく、負極活物質の他、導電剤、結着剤、増粘剤などを含有してもよい。負極活物質としては、リチウムイオンを可逆的に吸蔵および放出し得る各種材料、例えば、黒鉛型結晶構造を有する材料；ケイ素；ケイ素酸化物などのケイ素含有化合物；Ｓｎ、Ａｌ、Ｚｎおよび／またはＭｇなどを含むリチウム合金などが例示できる。黒鉛型結晶構造を有する材料としては、例えば、天然黒鉛や球状または繊維状の人造黒鉛、難黒鉛化性炭素、易黒鉛化性炭素などの炭素材料が例示できる。これらの負極活物質は、１種を単独でまたは２種以上を組み合わせて使用できる。 The negative electrode active material layer may be formed of a negative electrode active material, and may contain a conductive agent, a binder, a thickener, and the like in addition to the negative electrode active material. As the negative electrode active material, various materials capable of reversibly occluding and releasing lithium ions, for example, materials having a graphite-type crystal structure; silicon; silicon-containing compounds such as silicon oxide; Sn, Al, Zn and / or Mg Examples of the lithium alloy include: Examples of the material having a graphite-type crystal structure include carbon materials such as natural graphite, spherical or fibrous artificial graphite, non-graphitizable carbon, and graphitizable carbon. These negative electrode active materials can be used individually by 1 type or in combination of 2 or more types.
　結着剤、導電剤、増粘剤および分散媒としては、それぞれ、正極について例示したものなどが使用できる。負極活物質１００重量部に対する結着剤および導電剤の割合は、正極について正極活物質１００重量部に対する割合として例示した範囲と同様の範囲から選択できる。 As the binder, conductive agent, thickener, and dispersion medium, those exemplified for the positive electrode can be used. The ratio of the binder and the conductive agent to 100 parts by weight of the negative electrode active material can be selected from the same range as the range exemplified for the positive electrode with respect to 100 parts by weight of the positive electrode active material.
　負極活物質層は、正極活物質層と同様の方法により形成することができる。また、負極活物質の種類によっては、真空蒸着法、スパッタリング法などの気相法により負極活物質を集電体表面に堆積させることにより負極活物質層を形成してもよい。
　負極活物質層は、負極集電体の一方の表面に形成してもよく、両方の表面に形成してもよい。
　負極の厚みは、例えば、１００～２５０μｍ、好ましくは１１０～２１０μｍである。 The negative electrode active material layer can be formed by the same method as the positive electrode active material layer. Depending on the type of the negative electrode active material, the negative electrode active material layer may be formed by depositing the negative electrode active material on the surface of the current collector by a vapor phase method such as vacuum deposition or sputtering.
The negative electrode active material layer may be formed on one surface of the negative electrode current collector, or may be formed on both surfaces.
The thickness of the negative electrode is, for example, 100 to 250 μm, preferably 110 to 210 μm.
　（セパレータ）
　セパレータとしては、樹脂製の、微多孔フィルム、不織布または織布などが使用できる。セパレータを構成する樹脂としては、例えば、ポリエチレン、ポリプロピレンなどのポリオレフィン；ポリアミド；ポリアミドイミド；ポリイミドなどが例示できる。微多孔フィルムは、単層フィルムであってもよく、多層フィルムであってもよい。
　セパレータの厚みは、例えば、５～５０μｍである。 (Separator)
As the separator, a resin-made microporous film, nonwoven fabric or woven fabric can be used. Examples of the resin constituting the separator include polyolefins such as polyethylene and polypropylene; polyamides; polyamideimides; polyimides and the like. The microporous film may be a single layer film or a multilayer film.
The thickness of the separator is, for example, 5 to 50 μm.
　（非水電解質）
　非水電解質は、非水溶媒と、非水溶媒に溶解したリチウム塩とを含む。
　非水溶媒としては、プロピレンカーボネート、エチレンカーボネート（ＥＣ）などの環状炭酸エステル；ジエチルカーボネート、エチルメチルカーボネート（ＥＭＣ）、ジメチルカーボネートなどの鎖状炭酸エステル；γ－ブチロラクトン、γ－バレロラクトンなどの環状カルボン酸エステルなどが例示できる。これらの非水溶媒は、１種を単独でまたは２種以上を組み合わせて使用できる。 (Non-aqueous electrolyte)
The non-aqueous electrolyte includes a non-aqueous solvent and a lithium salt dissolved in the non-aqueous solvent.
Non-aqueous solvents include cyclic carbonates such as propylene carbonate and ethylene carbonate (EC); chain carbonates such as diethyl carbonate, ethyl methyl carbonate (EMC) and dimethyl carbonate; cyclic esters such as γ-butyrolactone and γ-valerolactone Examples thereof include carboxylic acid esters. These non-aqueous solvents can be used alone or in combination of two or more.
　リチウム塩としては、例えば、ＬｉＰＦ6、ＬｉＢＦ4、ＬｉＣｌＯ4、ＬｉＡｓＦ6、ＬｉＣＦ3ＳＯ3、ＬｉＮ（ＳＯ2ＣＦ3）2、ＬｉＮ（ＳＯ2Ｃ2Ｆ5）2、ＬｉＣ（ＳＯ2ＣＦ3）3などが挙げられる。リチウム塩は、１種を単独でまたは２種以上を組み合わせて使用できる。
　非水電解質中のリチウム塩の濃度は、例えば、０．５～１．８Ｍである。 Examples of the lithium salt include LiPF 6 , LiBF 4 , LiClO 4 , LiAsF 6 , LiCF 3 SO 3 , LiN (SO 2 CF 3 ) 2 , LiN (SO 2 C 2 F 5 ) 2 , LiC (SO 2 CF 3 3 ). A lithium salt can be used individually by 1 type or in combination of 2 or more types.
The concentration of the lithium salt in the nonaqueous electrolyte is, for example, 0.5 to 1.8M.
　非水電解質には、公知の添加剤、例えば、ビニレンカーボネートなどのビニレンカーボネート化合物などを添加してもよい。 A known additive such as a vinylene carbonate compound such as vinylene carbonate may be added to the non-aqueous electrolyte.
　非水電解質二次電池は、通常、正極、負極およびこれらを隔離するセパレータを、非水電解質とともに、電池ケースに収容することにより作製できる。
　電池ケース材料としては、鋼鈑、アルミニウム、アルミニウム合金（マンガン、銅等などの金属を微量含有する合金など）などが使用できる。 A nonaqueous electrolyte secondary battery can be usually produced by housing a positive electrode, a negative electrode, and a separator separating them together with a nonaqueous electrolyte in a battery case.
As the battery case material, steel plates, aluminum, aluminum alloys (alloys containing a trace amount of metals such as manganese and copper, etc.) and the like can be used.
　非水電解質二次電池の形状は、円筒型、角型、コイン型などであってもよい。円筒型または角型の電池では、電池ケースへの収容に先だって、正極と、負極と、これらを隔離するセパレータとを、捲回、積層またはつづら折りにして電極群を形成してもよい。電極群の形状は、電池または電池ケースの形状に応じて、円筒状、捲回軸に垂直な端面が長円形である扁平形状であってもよい。 The shape of the nonaqueous electrolyte secondary battery may be a cylindrical shape, a square shape, a coin shape, or the like. In the case of a cylindrical or prismatic battery, the electrode group may be formed by winding, laminating or spell-folding the positive electrode, the negative electrode, and the separator that separates them prior to housing in the battery case. The shape of the electrode group may be a cylindrical shape or a flat shape having an oval end surface perpendicular to the winding axis, depending on the shape of the battery or battery case.
　以下に、本発明を実施例および比較例に基づいて具体的に説明するが、本発明は以下の実施例に限定されるものではない。 Hereinafter, the present invention will be specifically described based on Examples and Comparative Examples, but the present invention is not limited to the following Examples.
《実施例１》
（１）正極活物質の合成
（i）ニッケルおよびコバルトを含む複合水酸化物（第１原料）の合成（第１工程）
　Ｎｉ原子とＣｏ原子との原子比が８０：２０になるように混合した硫酸ニッケルと硫酸コバルトとの混合物３．２ｋｇを、１０Ｌの水に溶解させて、原料溶液を得た。原料溶液に、水酸化ナトリウムを４００ｇ加えて、沈殿を生成させた。沈殿を十分に水洗し、乾燥させ、共沈複合水酸化物（Ｎｉ0.80Ｃｏ0.20（ＯＨ）2）（第１原料）を得た。この共沈複合水酸化物の体積基準の粒度分布におけるピークは、２０μｍおよび５μｍであった。共沈複合水酸化物は、ピーク強度比から、平均粒径２０μｍの大粒子群と、平均粒径５μｍの小粒子群とを、８：２の重量比で含む混合粒子であり、全体の平均粒径は１７μｍであった。 Example 1
(1) Synthesis of positive electrode active material (i) Synthesis of composite hydroxide (first raw material) containing nickel and cobalt (first step)
3.2 kg of a mixture of nickel sulfate and cobalt sulfate mixed so that the atomic ratio of Ni atoms to Co atoms was 80:20 was dissolved in 10 L of water to obtain a raw material solution. 400 g of sodium hydroxide was added to the raw material solution to form a precipitate. The precipitate was sufficiently washed with water and dried to obtain a coprecipitated composite hydroxide (Ni 0.80 Co 0.20 (OH) 2 ) (first raw material). The peaks in the volume-based particle size distribution of the coprecipitated composite hydroxide were 20 μm and 5 μm. The coprecipitated composite hydroxide is a mixed particle containing a large particle group having an average particle diameter of 20 μm and a small particle group having an average particle diameter of 5 μm at a weight ratio of 8: 2 from the peak intensity ratio. The particle size was 17 μm.
（ii）仮焼成（第２工程）
　１０重量％濃度で第１リン酸マグネシウム（第２原料）を含む水溶液３Ｌに、上記第１工程（i）で得られた共沈複合水酸化物３ｋｇを分散させ、２５℃で３時間撹拌した。分散混合物から水分を除去し、得られた固形分を、真空下、８０℃で５時間乾燥させた。乾燥物を、空気中（酸素含有率２１モル％、酸素分圧２０ｋＰａ）、１０００℃の温度で１２時間焼成することにより、リン元素およびマグネシウム元素が拡散した複合酸化物粒子を得た。 (Ii) Temporary firing (second step)
In 3 L of an aqueous solution containing the first magnesium phosphate (second raw material) at a concentration of 10% by weight, 3 kg of the coprecipitated composite hydroxide obtained in the first step (i) was dispersed and stirred at 25 ° C. for 3 hours. . Water was removed from the dispersion mixture and the resulting solid was dried under vacuum at 80 ° C. for 5 hours. The dried product was fired in air (oxygen content 21 mol%, oxygen partial pressure 20 kPa) at a temperature of 1000 ° C. for 12 hours to obtain composite oxide particles in which phosphorus element and magnesium element were diffused.
（iii）本焼成（第３工程）
　上記第２工程で得られた複合酸化物粒子３ｋｇと、所定量の水酸化リチウムとを混合し、空気中（酸素含有率２１モル％、酸素分圧２０ｋＰａ）で、７５０℃の温度で１２時間焼成することにより、リチウム含有複合酸化物粒子を得た。得られたリチウム含有複合酸化物の組成は、ＬｉＮｉ0.78Ｃｏ0.195Ｐ0.02Ｍｇ0.005Ｏ2であり、平均粒径は１５μｍであった。このリチウム含有複合酸化物は、平均粒径１８μｍの大粒子群と、平均粒径４μｍの小粒子群とを、重量比８：２で含む混合粒子であった。 (Iii) Main firing (third step)
3 kg of the composite oxide particles obtained in the second step and a predetermined amount of lithium hydroxide are mixed and in the air (oxygen content 21 mol%, oxygen partial pressure 20 kPa) at a temperature of 750 ° C. for 12 hours. By firing, lithium-containing composite oxide particles were obtained. The composition of the obtained lithium-containing composite oxide was LiNi 0.78 Co 0.195 P 0.02 Mg 0.005 O 2 , and the average particle size was 15 μm. This lithium-containing composite oxide was a mixed particle containing a large particle group having an average particle diameter of 18 μm and a small particle group having an average particle diameter of 4 μm at a weight ratio of 8: 2.
（２）正極の作製
　正極活物質として、上記（１）で得られたリチウム含有複合酸化物粒子を用いて正極を作製した。
　具体的には、正極活物質１ｋｇを、ＰＶＤＦのＮＭＰ溶液（（株）クレハ製、ＰＶＤＦ＃７２０８、固形分８重量％）０．２ｋｇ、アセチレンブラック１０ｇ、および適量のＮＭＰとともに双腕式練合機にて攪拌し、正極合剤ペーストを調製した。このペーストを厚さ２０μｍのアルミニウム箔の両面に塗布し、乾燥し、総厚が１６０μｍとなるように圧延した。その後、得られた極板を円筒型１８６５０の電池ケースに挿入可能な幅にスリットし、正極を得た。正極活物質層における正極活物質の密度は、３．６ｇ／ｃｍ3であった。 (2) Production of positive electrode A positive electrode was produced using the lithium-containing composite oxide particles obtained in (1) above as the positive electrode active material.
Specifically, 1 kg of the positive electrode active material is kneaded with a double arm type together with an NMP solution of PVDF (manufactured by Kureha Co., Ltd., PVDF # 7208, solid content 8 wt%) 0.2 kg, acetylene black 10 g, and an appropriate amount of NMP. The mixture was stirred in a machine to prepare a positive electrode mixture paste. This paste was applied to both sides of an aluminum foil having a thickness of 20 μm, dried, and rolled to a total thickness of 160 μm. Thereafter, the obtained electrode plate was slit to a width that could be inserted into a cylindrical battery case of 18650 to obtain a positive electrode. The density of the positive electrode active material in the positive electrode active material layer was 3.6 g / cm 3 .
　リチウム含有複合酸化物粒子のリン元素およびマグネシウム元素（元素Ｍ）の濃度分布をＥＰＭＡで分析した。具体的には、次の方法で、元素の濃度分布を分析した。カーボンテープ上に分散させた活物質粒子を０．３ｒ（ｒ（平均粒径）＝１４μｍ）の深さまで、公知の方法によりＦＩＢで削った。ＥＰＭＡを用いて、切削面における粒子断面の元素マッピングを、公知の方法により行い、これにより、複合酸化物粒子の元素の組成を決定した。 The concentration distribution of phosphorus element and magnesium element (element M) in the lithium-containing composite oxide particles was analyzed by EPMA. Specifically, the element concentration distribution was analyzed by the following method. The active material particles dispersed on the carbon tape were shaved with FIB to a depth of 0.3r (r (average particle diameter) = 14 μm) by a known method. Using EPMA, elemental mapping of the cross section of the particle on the cutting surface was performed by a known method, thereby determining the elemental composition of the composite oxide particle.
　その結果、リン元素は、粒子内部にまで分布していることが確認された。リン元素について、ＣPs／ＣPcは２．５／１であった。マグネシウム元素について、ＣMs／ＣMcは３／１であった。
　リン元素のＣPs／ＣPc値およびマグネシウム元素のＣMs／ＣMc値を、正極活物質中に含まれる各元素の含有量とともに、表１に示す。 As a result, it was confirmed that the phosphorus element was distributed even inside the particles. For phosphorus element, C Ps / C Pc was 2.5 / 1. For the magnesium element, C Ms / C Mc was 3/1.
Table 1 shows the C Ps / C Pc value of the phosphorus element and the C Ms / C Mc value of the magnesium element, together with the content of each element contained in the positive electrode active material.
（３）負極の作製
　人造黒鉛３ｋｇを、変性ＳＢＲの分散液（日本ゼオン（株）製、ＢＭ－４００Ｂ、固形分４０重量％）２００ｇ、ＣＭＣ５０ｇ、および適量の水とともに双腕式練合機にて撹拌し、負極合剤ペーストを調製した。このペーストを厚さ１２μｍの銅箔の両面に塗布し、乾燥し、総厚が１６０μｍとなるように圧延した。その後、得られた極板を円筒型１８６５０の電池ケースに挿入可能な幅にスリットし、負極を得た。 (3) Preparation of negative electrode 3 kg of artificial graphite was added to a double-arm kneader together with 200 g of modified SBR dispersion (manufactured by Nippon Zeon Co., Ltd., BM-400B, solid content 40 wt%), CMC 50 g, and an appropriate amount of water. And stirred to prepare a negative electrode mixture paste. This paste was applied to both sides of a 12 μm thick copper foil, dried, and rolled to a total thickness of 160 μm. Then, the obtained electrode plate was slit to a width that can be inserted into a cylindrical 18650 battery case to obtain a negative electrode.
（４）電池の組立
　上記（２）および（３）で作製した正極および負極を用い、セパレータとして、ポリエチレンとポリプロピレンとの複合フィルム（セルガード（株）製の２３００、厚さ２５μｍ）を用いて、図１に示すリチウムイオン電池を作製した。 (4) Battery assembly Using the positive and negative electrodes produced in (2) and (3) above, as a separator, using a composite film of polyethylene and polypropylene (2300 made by Celgard, thickness 25 μm), The lithium ion battery shown in FIG. 1 was produced.
　具体的には、図１のように、正極５と負極６とを、セパレータ７で隔絶した状態で捲回し、渦巻状の電極群４を作製した。正極５および負極６には、それぞれニッケル製の正極リード５ａおよび負極リード６ａを取り付けた。この電極群４の上面に上部絶縁板８ａ、下面に下部絶縁板８ｂを配して、電池ケース１内に挿入した。上部絶縁板８ａの上方で、かつ電池ケース１の上部側面に、内側に突出した段部９を形成することにより、電極群４を電池ケース１内に保持した。次いで、５ｇの非水電解質を電池ケース１内に注液した。周囲に絶縁ガスケット３を配した封口板２と、正極リード５ａとを導通させ、次いで、電池ケース１の開口部を封口板２で封口した。こうして、円筒型１８６５０のリチウム二次電池を完成させた。 Specifically, as shown in FIG. 1, the positive electrode 5 and the negative electrode 6 were wound in a state of being separated by a separator 7 to produce a spiral electrode group 4. A positive electrode lead 5a and a negative electrode lead 6a made of nickel were attached to the positive electrode 5 and the negative electrode 6, respectively. An upper insulating plate 8 a is disposed on the upper surface of the electrode group 4, and a lower insulating plate 8 b is disposed on the lower surface, and inserted into the battery case 1. The electrode group 4 was held in the battery case 1 by forming an inwardly protruding step 9 above the upper insulating plate 8 a and on the upper side surface of the battery case 1. Subsequently, 5 g of nonaqueous electrolyte was injected into the battery case 1. The sealing plate 2 provided with the insulating gasket 3 around it was electrically connected to the positive electrode lead 5 a, and then the opening of the battery case 1 was sealed with the sealing plate 2. Thus, a cylindrical 18650 lithium secondary battery was completed.
　非水電解質は、ＥＣおよびＭＥＣの混合溶媒（ＥＣ：ＭＥＣ（体積比）＝１０：３０）に、ビニレンカーボネート２重量％、およびＬｉＰＦ6１．５ｍｏｌ／Ｌを溶解させることにより調製した。 The non-aqueous electrolyte was prepared by dissolving 2% by weight of vinylene carbonate and 1.5 mol / L of LiPF 6 in a mixed solvent of EC and MEC (EC: MEC (volume ratio) = 10: 30).
《実施例２》
　硫酸ニッケルと硫酸コバルトとの混合物に代えて、Ｎｉ原子とＣｏ原子とＡｌ原子との原子比が８０：１７：３になるように、硫酸ニッケルと硫酸コバルトと硫酸アルミニウムとを混合することにより得られた混合物を用いる以外は、実施例１と同様にして、共沈複合水酸化物（第１原料）を得た。共沈複合水酸化物は、平均粒径２０μｍの大粒子群と平均粒径５μｍの小粒子群とを重量比８：２で含む混合粒子であり、全体の平均粒径は１７μｍであった。 Example 2
Instead of a mixture of nickel sulfate and cobalt sulfate, it is obtained by mixing nickel sulfate, cobalt sulfate, and aluminum sulfate so that the atomic ratio of Ni atoms, Co atoms, and Al atoms is 80: 17: 3. A coprecipitated composite hydroxide (first raw material) was obtained in the same manner as in Example 1 except that the obtained mixture was used. The coprecipitated composite hydroxide was a mixed particle containing a large particle group having an average particle diameter of 20 μm and a small particle group having an average particle diameter of 5 μm at a weight ratio of 8: 2, and the overall average particle diameter was 17 μm.
　得られた共沈複合水酸化物を実施例１の第１原料に代えて用いるとともに、第１リン酸マグネシウムに代えてオルトリン酸を第２原料として用いる以外は、実施例１と同様に、正極活物質を合成した。合成した正極活物質を用いる以外は、実施例１と同様にして、正極を準備し、この正極を用いてリチウムイオン電池を作製した。
　リン元素のＣPs／ＣPc値およびＡｌ元素のＣMs／ＣMc値は、実施例１のリン元素の場合と同様にして算出した。 In the same manner as in Example 1, except that the obtained coprecipitated composite hydroxide was used instead of the first raw material of Example 1, and orthophosphoric acid was used as the second raw material instead of the first magnesium phosphate. An active material was synthesized. A positive electrode was prepared in the same manner as in Example 1 except that the synthesized positive electrode active material was used, and a lithium ion battery was produced using this positive electrode.
The C Ps / C Pc value of the phosphorus element and the C Ms / C Mc value of the Al element were calculated in the same manner as in the case of the phosphorus element in Example 1.
《実施例３》
　硫酸アルミニウムに代えて、硫酸マグネシウムを用いる以外は、実施例２と同様にして、正極活物質を合成した。合成した正極活物質を用いる以外は、実施例１と同様にして、正極を準備し、この正極を用いてリチウムイオン電池を作製した。リン元素のＣPs／ＣPc値およびＭｇ元素のＣMs／ＣMc値は、実施例１のリン元素の場合と同様にして算出した。 Example 3
A positive electrode active material was synthesized in the same manner as in Example 2 except that magnesium sulfate was used instead of aluminum sulfate. A positive electrode was prepared in the same manner as in Example 1 except that the synthesized positive electrode active material was used, and a lithium ion battery was produced using this positive electrode. The C Ps / C Pc value of the phosphorus element and the C Ms / C Mc value of the Mg element were calculated in the same manner as in the case of the phosphorus element in Example 1.
《実施例４》
　第１リン酸マグネシウム（第２原料）に代えて、リン酸チタニウムを用いる以外は、実施例１と同様にして、正極活物質を合成した。合成した正極活物質を用いる以外は、実施例１と同様にして、正極を準備し、この正極を用いてリチウムイオン電池を作製した。リン元素のＣPs／ＣPc値およびＴｉ元素のＣMs／ＣMc値は、実施例１のリン元素の場合と同様にして算出した。 Example 4
A positive electrode active material was synthesized in the same manner as in Example 1 except that titanium phosphate was used instead of the first magnesium phosphate (second raw material). A positive electrode was prepared in the same manner as in Example 1 except that the synthesized positive electrode active material was used, and a lithium ion battery was produced using this positive electrode. The C Ps / C Pc value of the phosphorus element and the C Ms / C Mc value of the Ti element were calculated in the same manner as in the case of the phosphorus element in Example 1.
《実施例５》
　第１リン酸マグネシウム（第２原料）に代えて、リン酸ジルコニウムを用いる以外は、実施例１と同様にして、正極活物質を合成した。合成した正極活物質を用いる以外は、実施例１と同様にして、正極を準備し、この正極を用いてリチウムイオン電池を作製した。リン元素のＣPs／ＣPc値およびＺｒ元素のＣMs／ＣMc値は、実施例１のリン元素の場合と同様にして算出した。 Example 5
A positive electrode active material was synthesized in the same manner as in Example 1 except that zirconium phosphate was used instead of the first magnesium phosphate (second raw material). A positive electrode was prepared in the same manner as in Example 1 except that the synthesized positive electrode active material was used, and a lithium ion battery was produced using this positive electrode. The C Ps / C Pc value of the phosphorus element and the C Ms / C Mc value of the Zr element were calculated in the same manner as in the case of the phosphorus element in Example 1.
《実施例６》
　第１リン酸マグネシウム（第２原料）に代えて、オルトリン酸を用いる以外は、実施例１と同様にして、正極活物質を合成した。合成した正極活物質を用いる以外は、実施例１と同様にして、正極を準備し、この正極を用いてリチウムイオン電池を作製した。リン元素のＣPs／ＣPc値は、実施例１のリン元素の場合と同様にして算出した。 Example 6
A positive electrode active material was synthesized in the same manner as in Example 1 except that orthophosphoric acid was used in place of the first magnesium phosphate (second raw material). A positive electrode was prepared in the same manner as in Example 1 except that the synthesized positive electrode active material was used, and a lithium ion battery was produced using this positive electrode. The C Ps / C Pc value of the phosphorus element was calculated in the same manner as in the case of the phosphorus element of Example 1.
《実施例７》
　実施例６の仮焼成（第２工程）の温度を、１０００℃から８００℃に変更する以外は、実施例６と同様にして、正極活物質を合成した。合成した正極活物質を用いる以外は、実施例１と同様にして、正極を準備し、この正極を用いてリチウムイオン電池を作製した。リン元素のＣPs／ＣPc値は、実施例１のリン元素の場合と同様にして算出した。 Example 7
A positive electrode active material was synthesized in the same manner as in Example 6 except that the temperature of the preliminary firing (second step) in Example 6 was changed from 1000 ° C. to 800 ° C. A positive electrode was prepared in the same manner as in Example 1 except that the synthesized positive electrode active material was used, and a lithium ion battery was produced using this positive electrode. The C Ps / C Pc value of the phosphorus element was calculated in the same manner as in the case of the phosphorus element of Example 1.
《実施例８》
　硫酸アルミニウムに代えて、硫酸マグネシウムを用いるとともに、Ｎｉ原子とＣｏ原子とＭｇ原子との原子比が８０：１７：２．５になるように原料を混合する以外は、実施例２と同様にして、第１原料を合成した。第１原料は、平均粒径２０μｍの大粒子群と平均粒径５μｍの小粒子群とを重量比８：２で含む混合粒子であり、全体の平均粒径は１７μｍであった。 Example 8
Instead of aluminum sulfate, magnesium sulfate is used, and the raw materials are mixed so that the atomic ratio of Ni atoms, Co atoms, and Mg atoms is 80: 17: 2.5. The first raw material was synthesized. The first raw material was mixed particles containing a large particle group having an average particle diameter of 20 μm and a small particle group having an average particle diameter of 5 μm in a weight ratio of 8: 2, and the overall average particle diameter was 17 μm.
　得られた第１原料を実施例１の第１原料に代えて用いた。第１リン酸マグネシウムの水溶液に代えて、オルトリン酸およびリン酸チタニウムをそれぞれ５重量％および１０重量％の濃度で含む水溶液を用いた。これら以外は、実施例１と同様にして、正極活物質を合成した。合成した正極活物質を用いる以外は、実施例１と同様にして、正極を準備し、この正極を用いてリチウムイオン電池を作製した。
　リン元素のＣPs／ＣPc値、Ｍｇ元素およびＴｉ元素のＣMs／ＣMc値は、実施例１のリン元素の場合と同様にして算出した。 The obtained first raw material was used in place of the first raw material of Example 1. Instead of the aqueous solution of the first magnesium phosphate, an aqueous solution containing orthophosphoric acid and titanium phosphate at concentrations of 5 wt% and 10 wt%, respectively, was used. Except for these, a positive electrode active material was synthesized in the same manner as in Example 1. A positive electrode was prepared in the same manner as in Example 1 except that the synthesized positive electrode active material was used, and a lithium ion battery was produced using this positive electrode.
The C Ps / C Pc value of the phosphorus element and the C Ms / C Mc value of the Mg element and Ti element were calculated in the same manner as in the case of the phosphorus element of Example 1.
《実施例９》
　硫酸マグネシウムに代えて、硫酸アルミニウムを用いる以外は、実施例８と同様にして、正極活物質を合成した。合成した正極活物質を用いる以外は、実施例１と同様にして、正極を準備し、この正極を用いてリチウムイオン電池を作製した。
　リン元素のＣPs／ＣPc値、Ａｌ元素およびＴｉ元素のＣMs／ＣMc値は、実施例１のリン元素の場合と同様にして算出した。 Example 9
A positive electrode active material was synthesized in the same manner as in Example 8 except that aluminum sulfate was used instead of magnesium sulfate. A positive electrode was prepared in the same manner as in Example 1 except that the synthesized positive electrode active material was used, and a lithium ion battery was produced using this positive electrode.
The C Ps / C Pc value of the phosphorus element and the C Ms / C Mc value of the Al element and Ti element were calculated in the same manner as in the case of the phosphorus element in Example 1.
《実施例１０》
　リン酸チタニウムに代えて、リン酸ジルコニウムを用いる以外は、実施例８と同様に、正極活物質を合成した。合成した正極活物質を用いる以外は、実施例１と同様にして、正極を準備し、この正極を用いてリチウムイオン電池を作製した。
　リン元素のＣPs／ＣPc値、Ｍｇ元素およびＺｒ元素のＣMs／ＣMc値は、実施例１のリン元素の場合と同様にして算出した。 Example 10
A positive electrode active material was synthesized in the same manner as in Example 8 except that zirconium phosphate was used instead of titanium phosphate. A positive electrode was prepared in the same manner as in Example 1 except that the synthesized positive electrode active material was used, and a lithium ion battery was produced using this positive electrode.
The C Ps / C Pc value of phosphorus element and the C Ms / C Mc value of Mg element and Zr element were calculated in the same manner as in the case of the phosphorus element of Example 1.
《実施例１１》
　リン酸チタニウムに代えて、リン酸ジルコニウムを用いる以外は、実施例９と同様に、正極活物質を合成した。合成した正極活物質を用いる以外は、実施例１と同様にして、正極を準備し、この正極を用いてリチウムイオン電池を作製した。
　リン元素のＣPs／ＣPc値、Ａｌ元素およびＺｒ元素のＣMs／ＣMc値は、実施例１のリン元素の場合と同様にして算出した。 Example 11
A positive electrode active material was synthesized in the same manner as in Example 9 except that zirconium phosphate was used in place of titanium phosphate. A positive electrode was prepared in the same manner as in Example 1 except that the synthesized positive electrode active material was used, and a lithium ion battery was produced using this positive electrode.
The C Ps / C Pc value of phosphorus element and the C Ms / C Mc value of Al element and Zr element were calculated in the same manner as in the case of the phosphorus element of Example 1.
《実施例１２～１６》
　オルトリン酸の水溶液の濃度を変更する以外は、実施例２と同様にして、正極活物質を合成した。合成した正極活物質を用いる以外は、実施例１と同様にして、正極を準備し、この正極を用いてリチウムイオン電池を作製した。水溶液中のオルトリン酸の濃度は、それぞれ、２０重量％（実施例１２）、１５重量％（実施例１３）、８重量％（実施例１４）、５重量％（実施例１５）および４重量％（実施例１６）であった。
　リン元素のＣPs／ＣPc値およびＡｌ元素のＣMs／ＣMc値は、実施例１のリン元素の場合と同様にして算出した。 << Examples 12 to 16 >>
A positive electrode active material was synthesized in the same manner as in Example 2 except that the concentration of the aqueous solution of orthophosphoric acid was changed. A positive electrode was prepared in the same manner as in Example 1 except that the synthesized positive electrode active material was used, and a lithium ion battery was produced using this positive electrode. The concentrations of orthophosphoric acid in the aqueous solution were 20% by weight (Example 12), 15% by weight (Example 13), 8% by weight (Example 14), 5% by weight (Example 15) and 4% by weight, respectively. (Example 16).
The C Ps / C Pc value of the phosphorus element and the C Ms / C Mc value of the Al element were calculated in the same manner as in the case of the phosphorus element in Example 1.
《実施例１７～２０》
　Ｎｉ原子とＣｏ原子とＡｌ原子との原子比を変更する以外は、実施例２と同様にして正極活物質を合成した。合成した正極活物質を用いる以外は、実施例１と同様にして、正極を準備し、この正極を用いてリチウムイオン電池を作製した。
　Ｎｉ：Ｃｏ：Ａｌ（原子比）は、それぞれ、８４：１３：３（実施例１７）、６９：２８：３（実施例１８）、６２：３５：３（実施例１９）および５０：４７：３（実施例２０）であった。
　リン元素のＣPs／ＣPc値およびＡｌ元素のＣMs／ＣMc値は、実施例１のリン元素の場合と同様にして算出した。 << Examples 17 to 20 >>
A positive electrode active material was synthesized in the same manner as in Example 2 except that the atomic ratio of Ni atoms, Co atoms, and Al atoms was changed. A positive electrode was prepared in the same manner as in Example 1 except that the synthesized positive electrode active material was used, and a lithium ion battery was produced using this positive electrode.
Ni: Co: Al (atomic ratio) was 84: 13: 3 (Example 17), 69: 28: 3 (Example 18), 62: 35: 3 (Example 19) and 50:47: respectively. 3 (Example 20).
The C Ps / C Pc value of the phosphorus element and the C Ms / C Mc value of the Al element were calculated in the same manner as in the case of the phosphorus element in Example 1.
《比較例１》
　仮焼成（第２工程）の焼成温度を１０００℃から７００℃に変更する以外は、実施例１と同様にして、正極活物質を合成した。合成した正極活物質を用いる以外は、実施例１と同様にして、正極を準備し、この正極を用いてリチウムイオン電池を作製した。
　正極活物質層について、リチウム含有複合酸化物粒子のリン元素の濃度分布を、実施例１と同様に、ＥＰＭＡで分析した。その結果、リン元素は、粒子表層に偏在していることが確認された。
　リン元素のＣPs／ＣPc値およびＡｌ元素のＣMs／ＣMc値は、実施例１のリン元素の場合と同様にして算出した。 << Comparative Example 1 >>
A positive electrode active material was synthesized in the same manner as in Example 1 except that the firing temperature in the preliminary firing (second step) was changed from 1000 ° C. to 700 ° C. A positive electrode was prepared in the same manner as in Example 1 except that the synthesized positive electrode active material was used, and a lithium ion battery was produced using this positive electrode.
For the positive electrode active material layer, the phosphorus element concentration distribution of the lithium-containing composite oxide particles was analyzed by EPMA in the same manner as in Example 1. As a result, it was confirmed that the phosphorus element was unevenly distributed in the particle surface layer.
The C Ps / C Pc value of the phosphorus element and the C Ms / C Mc value of the Al element were calculated in the same manner as in the case of the phosphorus element in Example 1.
《比較例２》
　仮焼成（第２工程）の焼成温度を１０００℃から７００℃に変更する以外は、実施例２と同様にして、正極活物質を合成した。合成した正極活物質を用いる以外は、実施例１と同様にして、正極を準備し、この正極を用いてリチウムイオン電池を作製した。
　正極活物質層について、リチウム含有複合酸化物粒子のリン元素の濃度分布をＥＰＭＡで分析した。その結果、リン元素は、粒子表層に偏在していることが確認された。
　リン元素のＣPs／ＣPc値およびＡｌ元素のＣMs／ＣMc値は、実施例１のリン元素の場合と同様にして算出した。 << Comparative Example 2 >>
A positive electrode active material was synthesized in the same manner as in Example 2 except that the firing temperature in the preliminary firing (second step) was changed from 1000 ° C. to 700 ° C. A positive electrode was prepared in the same manner as in Example 1 except that the synthesized positive electrode active material was used, and a lithium ion battery was produced using this positive electrode.
With respect to the positive electrode active material layer, the concentration distribution of phosphorus element in the lithium-containing composite oxide particles was analyzed by EPMA. As a result, it was confirmed that the phosphorus element was unevenly distributed in the particle surface layer.
The C Ps / C Pc value of the phosphorus element and the C Ms / C Mc value of the Al element were calculated in the same manner as in the case of the phosphorus element in Example 1.
［評価］
（放電特性）
　各電池について２度の慣らし充放電を行い、その後、４０℃環境下で２日間保存した。その後、各電池について、以下のサイクル試験を行った。ただし、電池の設計容量を１ＣｍＡｈとする。１サイクル目の放電容量に対する５００サイクル目の放電容量の割合を、容量維持率として表１に示す。 [Evaluation]
(Discharge characteristics)
Each battery was conditioned and discharged twice and then stored for 2 days in a 40 ° C. environment. Thereafter, the following cycle tests were performed for each battery. However, the design capacity of the battery is 1 CmAh. The ratio of the discharge capacity at the 500th cycle to the discharge capacity at the first cycle is shown in Table 1 as the capacity retention rate.
　（１）定電流充電（４５℃）：０．７ＣｍＡ（終止電圧４．２Ｖ）
　（２）定電圧充電（４５℃）：４．２Ｖ（終止電流０．０５ＣｍＡ）
　（３）充電レスト（４５℃）：３０分
　（４）定電流放電（４５℃）：１ＣｍＡ（終止電圧３Ｖ）
　（５）放電レスト（４５℃）：３０分 (1) Constant current charging (45 ° C.): 0.7 CmA (end voltage 4.2 V)
(2) Constant voltage charging (45 ° C.): 4.2 V (end current 0.05 CmA)
(3) Charging rest (45 ° C): 30 minutes (4) Constant current discharge (45 ° C): 1 CmA (end voltage 3 V)
(5) Discharge rest (45 ° C): 30 minutes
Figure JPOXMLDOC01-appb-T000001
 表１中、*は、仮焼成温度を示す。
Figure JPOXMLDOC01-appb-T000001
 In Table 1, * indicates a temporary firing temperature.
　表１より、実施例１の電池は、比較例１に比べて、充放電を５００サイクル繰り返した後も、高い容量維持率を示した。これは、実施例１の正極活物質が、正極活物質の内部までリンが添加されているためである。そのため、充放電サイクル時に正極活物質の粒子割れが起こって、正極活物質の新生面と電解液との反応を正極活物質内部のリンが安定化させ、正極活物質層における抵抗増加を抑制していると考えられる。一方、比較例１で容量維持率が低下したのは、充放電を繰り返すことにより、正極活物質層における抵抗が大きくなったためと考えられる。比較例２でも、比較例１と同様の結果が得られた。正極活物質がリンを含む場合でも、比較例１および２のように、正極活物質の粒子表面にリンが偏在している場合には、十分な容量維持率が得られなかった。 From Table 1, the battery of Example 1 showed a high capacity retention rate even after 500 cycles of charge / discharge compared to Comparative Example 1. This is because phosphorus is added to the inside of the positive electrode active material in the positive electrode active material of Example 1. For this reason, particle breakage of the positive electrode active material occurs during the charge / discharge cycle, the reaction between the new surface of the positive electrode active material and the electrolyte is stabilized by phosphorus inside the positive electrode active material, and an increase in resistance in the positive electrode active material layer is suppressed. It is thought that there is. On the other hand, the reason why the capacity retention ratio decreased in Comparative Example 1 is considered to be that the resistance in the positive electrode active material layer increased due to repeated charge and discharge. In Comparative Example 2, the same result as in Comparative Example 1 was obtained. Even when the positive electrode active material contains phosphorus, as in Comparative Examples 1 and 2, when phosphorus is unevenly distributed on the particle surface of the positive electrode active material, a sufficient capacity retention rate could not be obtained.
　実施例２～２０についても、正極活物質層について、リチウム含有複合酸化物粒子のリン元素の濃度分布を、実施例１と同様に、ＥＰＭＡで分析した。その結果、リン元素は、粒子内部にまで分布していることが確認された。そのため、このようなリチウム含有複合酸化物粒子を正極活物質として用いた実施例２～２０の電池でも、表１に示すように、充放電を５００サイクル繰り返した後も、高い容量維持率が得られたと考えられる。 In Examples 2 to 20, the positive electrode active material layer was analyzed for the concentration distribution of the phosphorus element in the lithium-containing composite oxide particles by EPMA as in Example 1. As a result, it was confirmed that the phosphorus element was distributed even inside the particles. Therefore, even in the batteries of Examples 2 to 20 using such lithium-containing composite oxide particles as the positive electrode active material, as shown in Table 1, a high capacity retention ratio was obtained even after 500 cycles of charge and discharge. It is thought that it was done.
　本発明を現時点での好ましい実施態様に関して説明したが、そのような開示を限定的に解釈してはならない。種々の変形および改変は、上記開示を読むことによって本発明に属する技術分野における当業者には間違いなく明らかになるであろう。したがって、添付の請求の範囲は、本発明の真の精神および範囲から逸脱することなく、すべての変形および改変を包含する、と解釈されるべきものである。 Although the present invention has been described in terms of the presently preferred embodiments, such disclosure should not be construed as limiting. Various changes and modifications will no doubt become apparent to those skilled in the art to which the present invention pertains after reading the above disclosure. Accordingly, the appended claims should be construed to include all variations and modifications without departing from the true spirit and scope of this invention.
　本発明は、様々な用途に用いられる非水電解質二次電池に適用できる。非水電解質二次電池の用途の具体例としては、携帯情報端末、携帯電子機器、家庭用小型電力貯蔵装置、自動二輪車、電気自動車、ハイブリッド電気自動車などが例示できる。 The present invention can be applied to non-aqueous electrolyte secondary batteries used for various purposes. Specific examples of uses of the non-aqueous electrolyte secondary battery include a portable information terminal, a portable electronic device, a small electric power storage device for home use, a motorcycle, an electric vehicle, and a hybrid electric vehicle.
　１　電池ケース
　２　封口板
　３　絶縁ガスケット
　４　電極群
　５　正極
　５ａ　正極リード
　６　負極
　６ａ　負極リード
　７　セパレータ
　８ａ　上部絶縁板
　８ｂ　下部絶縁板
　９　段部 DESCRIPTION OF SYMBOLS 1 Battery case 2 Sealing plate 3 Insulating gasket 4 Electrode group 5 Positive electrode 5a Positive electrode lead 6 Negative electrode 6a Negative electrode lead 7 Separator 8a Upper insulating plate 8b Lower insulating plate 9 Step part

Claims (18)

  1. 　リチウム、リン、ニッケルおよびコバルトを含む複合酸化物の粒子を含み、
    　前記複合酸化物の粒子の平均半径をｒとするとき、粒子の表面から０．３ｒ以内の領域に含まれるリンの濃度ＣPsと、粒子の中心から０．３ｒ以内の領域に含まれるリンの濃度ＣPcとの比率ＣPs／ＣPcが、１／１～５／１である、非水電解質二次電池用正極活物質。     Including composite oxide particles comprising lithium, phosphorus, nickel and cobalt;
    When the average radius of the composite oxide particles is r, the concentration C Ps of phosphorus contained in the region within 0.3r from the surface of the particle and the concentration of phosphorus contained in the region within 0.3r from the center of the particle. A positive electrode active material for a non-aqueous electrolyte secondary battery, wherein a ratio C Ps / C Pc to a concentration C Pc is 1/1 to 5/1.
  2. 　前記複合酸化物が、さらに元素Ｍを含み、
    　前記元素Ｍは、Ｍｇ、Ａｌ、ＴｉおよびＺｒよりなる群から選択される少なくとも１種である、請求項１記載の非水電解質二次電池用正極活物質。     The composite oxide further includes an element M;
    2. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the element M is at least one selected from the group consisting of Mg, Al, Ti, and Zr.
  3. 　前記複合酸化物が、前記元素Ｍとして、
    　ＭｇおよびＡｌよりなる第１元素群から選択される少なくとも１種と、
    　ＴｉおよびＺｒよりなる第２元素群から選択される少なくとも１種と、を含む、請求項２記載の非水電解質二次電池用正極活物質。     The complex oxide is the element M,
    At least one selected from the first element group consisting of Mg and Al;
    The positive electrode active material for a nonaqueous electrolyte secondary battery according to claim 2, comprising at least one selected from the second element group consisting of Ti and Zr.
  4. 　前記複合酸化物におけるリンの含有量が、リチウムと酸素を除いた元素の合計量に対し、１原子％より多い、請求項１～３のいずれか１項に記載の非水電解質二次電池用正極活物質。 The nonaqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein a content of phosphorus in the composite oxide is greater than 1 atomic% with respect to a total amount of elements excluding lithium and oxygen. Positive electrode active material.
  5. 　前記複合酸化物におけるニッケルの含有量が、リチウムと酸素を除いた元素の合計量に対し、６０～９０原子％であり、
    　前記複合酸化物におけるコバルトの含有量が、リチウムと酸素を除いた元素の合計量に対し、５～３０原子％である、請求項１～４のいずれか１項に記載の非水電解質二次電池用正極活物質。     The content of nickel in the composite oxide is 60 to 90 atomic% with respect to the total amount of elements excluding lithium and oxygen;
    The nonaqueous electrolyte secondary according to any one of claims 1 to 4, wherein a content of cobalt in the composite oxide is 5 to 30 atomic% with respect to a total amount of elements excluding lithium and oxygen. Positive electrode active material for batteries.
  6. 　前記複合酸化物における前記元素Ｍの含有量が、リチウムと酸素を除いた元素の合計量に対し、１～１０原子％である、請求項２記載の非水電解質二次電池用正極活物質。 The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 2, wherein the content of the element M in the composite oxide is 1 to 10 atomic% with respect to the total amount of elements excluding lithium and oxygen.
  7. 　前記元素Ｍのうち、
    　前記第１元素群の含有量が、リチウムと酸素を除いた元素の合計量に対し、１～１０原子％であり、
    　前記第２元素群の含有量が、リチウムと酸素を除いた元素の合計量に対し、０．１～１原子％である、請求項３記載の非水電解質二次電池用正極活物質。     Among the elements M,
    The content of the first element group is 1 to 10 atomic% with respect to the total amount of elements excluding lithium and oxygen,
    The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 3, wherein the content of the second element group is 0.1 to 1 atomic% with respect to the total amount of elements excluding lithium and oxygen.
  8. 　体積基準の粒度分布において複数のピークを有する、請求項１～７のいずれか１項に記載の非水電解質二次電池用正極活物質。 The positive electrode active material for a nonaqueous electrolyte secondary battery according to any one of claims 1 to 7, which has a plurality of peaks in a volume-based particle size distribution.
  9. 　正極集電体および前記正極集電体の表面に付着した正極活物質層を含み、
    　前記正極活物質層が、請求項１～８のいずれか１項に記載の正極活物質および結着剤を含む、非水電解質二次電池用正極。     A positive electrode current collector and a positive electrode active material layer attached to a surface of the positive electrode current collector;
    A positive electrode for a non-aqueous electrolyte secondary battery, wherein the positive electrode active material layer includes the positive electrode active material according to any one of claims 1 to 8 and a binder.
  10. 　前記正極活物質層における前記正極活物質の密度が、３．６ｇ／ｃｍ3以上である、請求項９記載の非水電解質二次電池用正極。 The positive electrode for a non-aqueous electrolyte secondary battery according to claim 9, wherein a density of the positive electrode active material in the positive electrode active material layer is 3.6 g / cm 3 or more.
  11. 　前記正極活物質層が、さらに導電性炭素材料を含み、
    　前記正極活物質１００重量部あたりの前記導電性炭素材料の量が、０．１～１．５重量部である、請求項９または１０に記載の非水電解質二次電池用正極。     The positive electrode active material layer further includes a conductive carbon material,
    The positive electrode for a nonaqueous electrolyte secondary battery according to claim 9 or 10, wherein an amount of the conductive carbon material per 100 parts by weight of the positive electrode active material is 0.1 to 1.5 parts by weight.
  12. 　ニッケルおよびコバルトを含む第１原料を準備する工程、
    　前記第１原料と、リンを含む第２原料と、を混合し、これらを、７５０℃を超える温度で仮焼成し、ニッケルおよびコバルトを含むとともに、表層および内部に所定の濃度でリンを含む酸化物の粒子を得る工程、並びに
    　前記酸化物の粒子と、リチウムを含む第３原料と、を混合し、これらを、８００℃以下の温度で本焼成し、リチウム、リン、ニッケルおよびコバルトを含む複合酸化物の粒子を得る工程、を有し、
    　前記複合酸化物の粒子の平均半径をｒとするとき、粒子の表面から０．３ｒ以内の領域に含まれるリンの濃度ＣPsと、粒子の中心から０．３ｒ以内の領域に含まれるリンの濃度ＣPcとの比率ＣPs／ＣPcが、１／１～５／１である、非水電解質二次電池用正極活物質の製造方法。     Preparing a first raw material containing nickel and cobalt;
    The first raw material and a second raw material containing phosphorus are mixed, and these are pre-fired at a temperature exceeding 750 ° C., and include nickel and cobalt, and an oxidation containing phosphorus at a predetermined concentration in the surface layer and inside. A step of obtaining particles of the product, and a mixture of the oxide particles and a third raw material containing lithium, firing these at a temperature of 800 ° C. or less, and containing lithium, phosphorus, nickel and cobalt Obtaining oxide particles,
    When the average radius of the composite oxide particles is r, the concentration C Ps of phosphorus contained in the region within 0.3r from the surface of the particle and the concentration of phosphorus contained in the region within 0.3r from the center of the particle. A method for producing a positive electrode active material for a nonaqueous electrolyte secondary battery, wherein the ratio C Ps / C Pc to the concentration C Pc is 1/1 to 5/1 .
  13. 　前記本焼成の温度が７５０℃以下である、請求項１２記載の非水電解質二次電池用正極活物質の製造方法。 The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 12, wherein the temperature of the main baking is 750 ° C or lower.
  14. 　前記仮焼成の温度が９００℃以上である、請求項１２または１３記載の非水電解質二次電池用正極活物質の製造方法。 The manufacturing method of the positive electrode active material for nonaqueous electrolyte secondary batteries of Claim 12 or 13 whose temperature of the said temporary baking is 900 degreeC or more.
  15. 　前記第１原料が、ニッケルおよびコバルトを含む複合水酸化物である、請求項１２～１４のいずれか１項に記載の非水電解質二次電池用正極活物質の製造方法。 The method for producing a positive electrode active material for a nonaqueous electrolyte secondary battery according to any one of claims 12 to 14, wherein the first raw material is a composite hydroxide containing nickel and cobalt.
  16. 　前記複合水酸化物が、さらに、ＭｇおよびＡｌよりなる群から選択される少なくとも１種を含む、請求項１５記載の非水電解質二次電池用正極活物質の製造方法。 The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 15, wherein the composite hydroxide further contains at least one selected from the group consisting of Mg and Al.
  17. 　前記第２原料が、リン酸マグネシウム、リン酸アルミニウム、リン酸チタンおよびリン酸ジルコニウムよりなる群から選択される少なくとも１種である、請求項１２～１６のいずれか１項に記載の非水電解質二次電池用正極活物質の製造方法。 The nonaqueous electrolyte according to any one of claims 12 to 16, wherein the second raw material is at least one selected from the group consisting of magnesium phosphate, aluminum phosphate, titanium phosphate, and zirconium phosphate. A method for producing a positive electrode active material for a secondary battery.
  18. 　前記第３原料が、水酸化リチウムである、請求項１２～１７のいずれか１項に記載の非水電解質二次電池用正極活物質の製造方法。 The method for producing a positive electrode active material for a nonaqueous electrolyte secondary battery according to any one of claims 12 to 17, wherein the third raw material is lithium hydroxide.
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