JP6040392B2 - Composite oxide, composite transition metal compound, method for producing composite oxide, positive electrode active material for non-aqueous electrolyte secondary battery, and non-aqueous electrolyte secondary battery - Google Patents

Description

  The present invention relates to a composite oxide used as a positive electrode active material for a non-aqueous electrolyte secondary battery, a composite transition metal compound as a precursor thereof, a method for producing the composite oxide, and a positive electrode active material for a non-aqueous electrolyte secondary battery And a non-aqueous electrolyte secondary battery.

  As a non-aqueous electrolyte secondary battery, a lithium ion secondary battery has been used in mobile devices such as mobile phones. In recent years, interest in the global environment has increased, and lithium ion secondary batteries are expected to be used for EV (Electric Vehicle) or PHEV (Plug-in Hybrid Electric Vehicle) applications.

Li [Ni _1-x M _x ] O ₂ is used as a positive electrode active material of a lithium ion secondary battery, and for example, there is a material in which particles of a positive electrode active material have a concentration gradient (Non-patent Document 1). 2). In the particles of the positive electrode active material, the core is made of Li [Ni _0.8 Co _0.1 Mn _0.1 ] O ₂ and the shell is Li [Ni _0.46 Co _0.23 Mn _0.31 ] O ₂ or It consists of Li [Ni _0.5 Mn _0.5 ] O ₂ . A concentration gradient is formed by forming a core and a shell at the stage of a composite hydroxide of Ni, Co, and Mn before adding Li salt and firing. In the positive electrode active material, the capacity is ensured by increasing the concentration of Ni in the core, and the safety such as thermal stability is enhanced by decreasing the concentration of Ni in the shell.

  However, merely having a concentration gradient as described above does not necessarily make the cycle life sufficient at a practical level even if the positive electrode active material can have a high capacity and high safety, and improvement of the cycle life is desired. ing.

Nature Materials / VOL8 / APRIL 2009 / www.naturematerials, PP320-324 Electrochemical and Solid-state Letters, 9 (3) A1761-A174 (2006)

  The present invention has been made in view of the above background, and provides a composite oxide that can be used as a positive electrode active material, can be made to have high capacity and safety, and can improve cycle life. For the purpose.

  Another object of the present invention is to provide a method for producing the composite oxide, a positive electrode active material for a non-aqueous electrolyte secondary battery, and a non-aqueous electrolyte secondary battery.

  According to the present invention, [1] to [9] composite oxide, [10] to [14] composite oxide production method, [15] a non-aqueous electrolyte secondary battery positive electrode active material, and [16] A non-aqueous electrolyte secondary battery is provided.

[1] The following formula (1):
Li _x MeO _{2 + 0.5 (x-1)} (1)
(In the formula, Me is a transition metal containing Ni and at least one metal selected from other transition metals, and x represents a number greater than 1.00 and not greater than 1.25.)
A particulate composite oxide represented by:
A composite oxide in which the atomic ratio of Ni to Me (A = Ni / Me × 100) is 60 mol% or more and 90 mol% or less in the whole particle, and the value of the atomic ratio is smaller in the peripheral portion than in the central portion .

[2] A core having an atomic ratio (B) of Ni to Me of 70 mol% or more and 100 mol% or less at the center, and a shell having an atomic ratio of Ni to Me smaller than that at the periphery of the core; The atomic ratio (B0) of Ni to Me in the whole particle including the shell is 60 mol% or more and 90% or less, and the atomic ratio (B1) of Ni to Me in the center of the core and the peripheral portion of the shell The precursor of the composite transition metal compound having a difference (B1-B2) between Ni and Me in the atomic ratio (B2) of 10 mol% to 80 mol%, and the Li compound, the atomic ratio of Li to Me is 1 The composite oxide according to the above [1], which is produced by firing a mixture obtained by mixing at a ratio of greater than 0.000 to 1.25 or less.

[3] The ratio of the volume of the core and the volume of the shell [(core volume) :( shell volume)] in the precursor is 50:50 to 90:10, according to the above [2] Complex oxide.

[4] The composite oxide according to any one of [1] to [3], wherein x is a number of 1.03 to 1.20.

[5] The composite oxide according to any one of [1] to [3], wherein x is a number from 1.05 to 1.18.

[6] x is the following relational expression (2):
x = (0.005y + 1.06) ± 0.06 (2)
(In the relational expression, y is a value obtained by subtracting the atomic ratio (B0) of Ni to Me in the whole particle including the core and the shell from the atomic ratio (B1) of Ni to the center of the core.) Is shown.)
The composite oxide according to any one of [2] or [3] above,

[7] The composite oxide according to any one of [1] to [6], wherein the difference in atomic ratio of Ni to Me in the central part of the particle and the peripheral part of the particle is 20 mol% or more and 70 mol% or less.

[8] The above-mentioned [1] to [1], wherein the cation mixing rate is 2.8% to 4.4% and the S value is 1.36 to 1.50 by structural analysis by the Rietveld method. 7].

[9] The following formula (1):
Li _x MeO _{2 + 0.5 (x-1)} (1)
(In the formula, Me is a transition metal containing Ni and at least one metal selected from other transition metals, and x represents a number greater than 1.00 and not greater than 1.25.)
A particulate composite oxide represented by:
The atomic ratio of Ni to Me (A = Ni / Me × 100) is 60 mol% or more and 90 mol% or less in the whole particle, and the value of the atomic ratio is smaller in the peripheral portion than in the central portion,
A composite oxide having a cation mixing rate of 2.0% to 6.0% and an S value of 1.30 to 1.60 by structural analysis by a Rietveld method.

[10] A method for producing the composite oxide according to any one of [1] to [8] above,
A core having an atomic ratio (B) of Ni to Me of 70 mol% or more and 100 mol% or less at the center, and a shell having an atomic ratio of Ni to Me smaller than that at the periphery of the core; The atomic ratio (B0) of Ni to Me in the whole of the included particles is 60 mol% or more and 90% or less. The atomic ratio (B1) of Ni to Me in the center of the core and the Me of Ni in the periphery of the shell A step (I) of obtaining a precursor of a composite metal compound having a difference (B1-B2) from the atomic ratio (B2) to 10 mol% to 80 mol%;
A step of firing the mixture obtained by mixing the precursor obtained in the step (I) and the Li compound at a ratio such that the atomic ratio of Ni to Me is greater than 1.00 and 1.25 or less (II And a method for producing a composite oxide.
[11] The composite oxide according to [10], wherein the atomic ratio of Li to Ni when mixing the precursor of the metal compound and the Li compound is 1.03 or more and 1.20 or less. Manufacturing method.

[12] The composite oxide according to [10], wherein the atomic ratio of Li to Ni when mixing the precursor of the metal compound and the Li compound is 1.05 or more and 1.18 or less. Manufacturing method.

[13] In the step (II), the atomic ratio (x) of Li to Me in the precursor and the Li compound obtained in the step (I) is the following relational expression (2):
x = (0.005y + 1.06) ± 0.06 (2)
(In the relational expression, y is a value obtained by subtracting the atomic ratio (B0) of Ni to Me in the whole particle including the core and the shell from the atomic ratio (B1) of Ni to the center of the core.) Show.)
The method for producing a composite oxide according to the above [10], wherein the mixture obtained by mixing so as to satisfy the condition is fired.

[14] With respect to the composite oxide obtained after firing, the cation mixing ratio is 2.0% to 6.0% and the S value is 1.30 to 1. The method for producing a composite oxide according to any one of [10] to [13], which is 60 or less.

[15] A positive electrode active material for a non-aqueous electrolyte secondary battery obtained from the composite oxide according to any one of [1] to [9].

[16] A non-aqueous electrolyte secondary battery having a positive electrode, a separator, and a negative electrode mainly composed of the positive electrode active material for the non-aqueous electrolyte secondary battery according to [15].

  In the composite oxide according to the present invention, the atomic ratio of Ni to Me (A = Ni / Me × 100) is 60 mol% or more and 90 mol% or less in the whole particle, and the value of the atomic ratio is a peripheral portion rather than a central portion. Therefore, it is useful as a highly safe positive electrode active material having excellent capacity characteristics and being thermally stable. And since x in Formula (1) is larger than 1.00, cycle life can be improved. In addition, by making x into 1.25 or less, the increase in residual Li can be suppressed and an electrical resistance can be made comparatively low.

It is a graph which shows the result of having measured the distribution of the pore about the nickel cobalt manganese complex oxide particle of an Example and a comparative example. (A)-(D) are the SEM enlarged images of the nickel cobalt manganese composite oxide particle of an Example and a comparative example. It is a figure which shows the measurement result of DSC of an Example and a comparative example. It is a graph which compares the capacity | capacitance degradation at the time of changing the atomic ratio of Li / Me about the positive electrode active material of an Example. It is a graph which compares the capacity | capacitance degradation at the time of changing the atomic ratio of Li / Me about the positive electrode active material of another Example. It is a chart which shows the relationship between the atomic ratio of Li / Me and a diffraction peak. (A)-(C) are the conceptual perspective views explaining the premise of the structural analysis by the Rietveld method. (A)-(C) are the charts which show the result of having analyzed cross-sectional structure about the complex oxide of the specific Example and the comparative example.

  Hereinafter, the present invention will be described in detail by dividing into 1) a composite oxide, 2) a positive electrode active material for a non-aqueous electrolyte secondary battery, and 3) a non-aqueous electrolyte secondary battery.

1) Composite oxide The composite oxide of the present invention is obtained by subjecting a composite transition metal compound comprising the transition metal Me and a Li compound to a solid phase reaction or a solid-liquid phase reaction.

The composite oxide of the present invention has the following formula (1):
Li _x MeO _{2 + 0.5 (x-1)} (1)
(In the formula, Me is a transition metal containing Ni and at least one metal selected from other transition metals, and x represents a number greater than 1.00 and not greater than 1.25.)
It is a compound shown by these.
In the formula (1), the transition metal Me includes at least one metal selected from Ni and other transition metals. As the other transition metal, for example, Co or Mn is used. Various transition metals such as Al, Mg, Fe, Ti, Zr, Cu, Cr, Zn, V, and Mo can be included. In the case of a combination of Ni, Co, and Mn, the composite oxide is a lithium-nickel cobalt manganese composite oxide. In addition, even if it is components other than a transition metal, another element can also be added in the range which does not degrade the characteristic as a positive electrode active material.

  X in the above formula (1) is a number greater than 1.00 and less than or equal to 1.25 in order to reduce the electrical resistance while improving the cycle life. x is preferably 1.03 or more and more preferably 1.05 or more from the viewpoint of further improving the cycle life. On the other hand, x is preferably 1.20 or less from the viewpoint of reducing the Li compound remaining as Li carbonate or the like and lowering the electrical resistance or preventing gelation when the positive electrode active material is made into a paste. The following is preferred.

  In the composite oxide particles, the atomic ratio of Ni to Me (A = Ni / Me × 100) is not uniform, and the atomic ratio (A1) at the center of the particle is 70 mol% or more and 100 mol% or less. As a result of the Ni concentration gradient, the composite oxide particles are composed of a core having a high Ni concentration and a shell having a low Ni concentration. The difference (A1-A2) between the atomic ratio (A1) of Ni to Me in the central part of the particle or core and the atomic ratio (A2) of Ni to Me in the peripheral part of the particle or shell is, for example, 10 mol% to 70 mol% It becomes.

  The composite oxide particles are obtained by firing a mixture obtained by mixing a precursor composed of a composite transition metal compound and an Li compound in a ratio such that the atomic ratio of Li to Me is greater than 1.00 and 1.25 or less. Manufactured by. The precursor as described above has a core in which the atomic ratio (B) of Ni to Me is 70 mol% or more and 100 mol% or less in the center, and a shell in which the atomic ratio of Ni to Me is smaller in the periphery than the core. In addition, the atomic ratio (B0) of Ni to Me in the whole particle including the core and the shell is 60 mol% or more and 90% or less, and the atomic ratio (B1) of Ni to Me in the central portion of the core and the peripheral portion of the shell The difference (B1-B2) from the atomic ratio (B2) of Ni to Me is 10 mol% or more and 80 mol% or less. In the above, the central part of the core means a central region having a radius of about 1/5 from the center of the precursor particle toward the surface, and the peripheral part of the shell means from the surface of the precursor particle. The outermost edge region having a radius of about 1/50 to 1/100 toward the center is meant.

  In the precursor, the ratio of the core volume to the shell volume [(core volume) :( shell volume)] is 50:50 to 90:10. That is, the volume ratio of the core can be adjusted in the range of 50 to 90 with 100 as the whole particle. As a result, the volume ratio of the shell is adjusted in the range of 50 to 10 with 100 as the entire particle. In the precursor particles, the core is a spherical or substantially spherical body that forms the center, and the shell is a spherical shell that forms the outer edge including the surface. In the present invention, the composition may change continuously from the core to the shell, but the composition may change stepwise from the core to the shell. Further, the composition is preferably uniform in the core, but the core itself can be composed of a central portion and one or more peripheral portions. The shell need not have a uniform composition along the radial direction, and the shell may include a gradation layer in which the atomic ratio of Ni to Me gradually decreases in the radial direction.

  The above is the explanation of the precursor particles made of the composite transition metal compound, but the composite oxide particles obtained by mixing and firing the precursor particles and the Li compound also have the same core and shell. It has a structure. That is, the precursor particles have a core having a high Ni concentration and a shell having a low Ni concentration, and the atomic ratio of Ni and Me is the same as that of the target composite oxide. However, the distribution of Ni or the like in the composite oxide particles obtained by firing is somewhat different from the distribution of Ni or the like in the precursor particles due to the influence of heat or the like during firing, and is generally somewhat uniform. It has become.

With respect to the composite oxide particles obtained by firing, a rough state of the core-shell structure can be estimated or confirmed by structural analysis using the Rietveld method. As a structural model of the composite oxide used for the Rietveld analysis, a particle having no shell, that is, a crystal in which Ni and a transition metal Me such as Mn, Co, and other transition metals Me have a single structure is assumed. Specifically, the composite oxide has a layered rock salt structure, Li is present at the 3a site (0, 0, 0) in the space group R-3m, and the 3b site (0, 0, 1/2) is present. A transition metal is present and oxygen is present at the 6c site (0, 0, z). Furthermore, it is assumed that cation mixing in which Li ions at the 3a site are replaced with Ni ions at the 3b site exists with a certain probability. The cation mixing rate, which is the probability of cation mixing, is considered for the entire 3a site where transition metals such as Ni are present. That is, if the composite oxide is LiNiO ₂ , the cation mixing rate of 100% means that the Li at the 3a site and the Ni at the 3b site are all substituted. Further, if the composite oxide has a composition such as LiNi _0.8 Co _0.1 Mn _0.1 O ₂ , since Ni is only 80%, the cation mixing rate is 80% at the maximum. By performing Rietveld analysis on the premise of the above structural model, the cation mixing rate most suitable for the result of X-ray diffraction measurement performed on the actually obtained composite oxide particles and the S value indicating the degree of fitting Can be obtained. At this time, the S value is minimized by performing the fitting by the least square method so that the X-ray diffraction pattern simulated by the above structural model is most suitable for the measured X-ray diffraction pattern of the obtained complex oxide. A combination of a cation mixing rate and an S value can be obtained, and such a combination is used as a characteristic value or a structural evaluation value of the actually obtained composite oxide particles. As a practical tendency, the higher the cation mixing rate, the clearer the core / shell structure and the thicker the shell. The reason is not necessarily clear, but the following can be considered. For an X-ray diffraction pattern with a core-shell structure, the simulation is trying to fit a single structure model, so the fitting is not so good and there is a tendency to improve this poorness by cation mixing. In other words, when the above Rietveld analysis is performed, it is not possible to clearly distinguish between an apparent phenomenon and an actual phenomenon, but if there is a core-shell structure as a phenomenological theory, there are many cation mixing, and if there is no such structure There tends to be less cation mixing. The S value indicates the degree of deviation from the single structure. The larger the S value is, the more clearly the core / shell structure is, and it is indirectly recognized that the shell is thick. In the composite oxide particles of the present invention, it is desirable that a clear shell is present from the viewpoint of thermal stability. However, if the shell is too thick, electrochemical characteristics such as capacity density tend to deteriorate. For these reasons, it is considered that the cation mixing rate is desirably 2.0% or more and 6.0% or less, and the S value is desirably 1.30 or more and 1.60 or less.

  A method for producing the composite oxide will be described. First, a composite transition metal compound (for example, nickel cobalt manganese composite transition metal hydroxide) as a precursor is dried, classified, and mixed with a lithium salt. As the lithium salt, any one of lithium carbonate, lithium nitrate, lithium acetate, lithium hydroxide, lithium hydroxide hydrate, lithium oxide, or a mixture of two or more can be used. The lithium salt and the composite transition metal compound (for example, nickel cobalt manganese composite transition metal hydroxide) are used in such a ratio that the atomic ratio x of Li / Me becomes a target value. Next, a composite oxide (eg, lithium-nickel cobalt manganese composite oxide) is obtained by firing a mixture of a composite transition metal compound (eg, nickel cobalt manganese composite transition metal hydroxide) and a lithium salt. In addition, dry air, oxygen atmosphere, etc. are used for baking according to a desired composition, and if necessary, a plurality of heating steps are performed. The firing temperature is 600 to 950 ° C.

In the production of the composite oxide, the atomic ratio (x) of Li to Me for the precursor and the Li compound is expressed by the following relational expression (2):
x = (0.005y + 1.06) ± 0.06 (2)
(In the relational expression, y is a value obtained by subtracting the atomic ratio (B0) of Ni to Me in the whole particle including the core and the shell from the atomic ratio (B1) of Ni to the center of the core.) Show.)
The resulting mixture is fired or the like. Here, the atomic ratio (x) of Li to Me is equal to the atomic ratio (x) of Li to Me in the composite oxide after firing. The appropriate value of the atomic ratio x tends to change depending on the volume ratio of the core and the shell. For example, when the volume ratio of the core and the shell is 50:50, x = 1.10 to 1.25 is preferable. When the volume ratio is 80:20, x = 1.03 to 1.18 is preferable.

  The composite transition metal compound (precursor) for obtaining the composite oxide is, for example, a transition metal composite hydroxide containing a transition metal such as nickel. The transition metal contained in the transition metal composite hydroxide as the precursor is the same as the composite oxide. In other words, when the target composite oxide is nickel cobalt manganese composite oxide, the precursor composite transition metal compound is nickel cobalt manganese hydroxide, oxyhydroxide, oxide, carbonate Etc.

  A method for producing the composite transition metal compound (precursor) will be described. A composite transition metal compound is obtained by reacting multiple types of metal salts in the gas phase, liquid phase or solid phase and crystallizing them, and forms a core and a shell having different atomic ratios of Ni and Me. In view of the above, it is relatively easy to form a crystal by growing a crystal by reacting the metal salt in a solution containing a plurality of types of metal salts. When the composite transition metal compound is nickel cobalt manganese composite hydroxide, for example, a coprecipitation method is used in which sulfate, nitrate, etc. of nickel cobalt manganese are reacted in a pH adjusted aqueous solution and crystallized.

In using the coprecipitation method in the present invention, as a reaction system, (a) a continuous system in which a liquid is continuously supplied to a reaction tank and overflowed crystals are continuously taken out, and (b) a continuous system is used. Both the batch type in which the liquid is supplied to the reaction tank and the crystals are extracted after the reaction for a predetermined time is used according to the purpose. In producing the composite transition metal compound which is a precursor of the composite oxide according to the present invention, the core crystal once taken out may be applied to the shell process after removing impurities as necessary. It is possible to carry out the reaction continuously in one step without interrupting the reaction between the core and the shell.
In order to narrow the particle size distribution of the precursor, it is generally desirable to align the residence time distribution of each particle in the manufacturing process, and batch reaction is suitable, but fine particles are removed by classification using a continuous method. May be. When it is desired to widen the particle size distribution of the precursor, it is generally desirable to widen the residence time distribution of each particle in the production process to some extent, and batch reaction (which can be handled by controlling the conditions) and continuous reaction are suitable. It is also possible to control the distribution by mixing fine particles and coarse particles produced by the above method.
The core can be used as it is when the composite transition metal compound (precursor) is produced as fine particles, but may be crushed into fine particles when the produced composite transition metal compound is in a lump shape. it can. The shell can be obtained not only by the liquid phase reaction as described above but also by growing a crystal on the surface of the core by a gas phase reaction. However, when the composite transition metal compound is nickel cobalt manganese composite hydroxide, the composition is controlled. However, the coprecipitation method is preferable because it is easy.

2) Positive electrode active material for non-aqueous electrolyte secondary battery and method for producing the same A positive electrode active material for non-aqueous electrolyte secondary battery is composed of the above-described composite oxide (for example, lithium-nickel cobalt manganese composite oxide). The composite oxide as the positive electrode active material is used as a powder, and the powder shape is not particularly limited but is preferably approximately spherical. The powder of the positive electrode active material may be any of primary particles of a composite oxide having a crystal structure, secondary particles formed by aggregating a plurality of such primary particles, and a mixture thereof.

A method for producing the positive electrode active material will be described. A composite oxide (for example, lithium-nickel cobalt manganese composite oxide) obtained by firing is classified, for example, after pulverization, and used as a positive electrode active material applicable to a non-aqueous electrolyte secondary battery. Such a positive electrode active material has a spherical shape or a shape close to a spherical shape, and preferably has an average particle size in the range of 3 μm to 30 μm, more preferably in the range of 3 μm to 20 μm. The powder of the positive electrode active material has a specific surface area (BET) of 0.1 to 2.0 m ² / g, more preferably 0.1 to 1.0 m ² / g.

3) Nonaqueous electrolyte secondary battery The nonaqueous electrolyte secondary battery of the present invention is not particularly limited as long as it uses the positive electrode active material described above. The structure of the nonaqueous electrolyte secondary battery can be of various known types. In addition, various characteristics and performance of the obtained nonaqueous electrolyte secondary battery (lithium ion battery) can be determined based on a generally known evaluation method and measuring apparatus.

  Hereinafter, an example of the structure of the nonaqueous electrolyte secondary battery will be described separately for the positive electrode, the negative electrode, the nonaqueous electrolyte, and the like.

(Positive electrode)
The positive electrode of the nonaqueous electrolyte battery of the present invention is prepared by mixing a positive electrode active material described above, that is, a composite oxide (for example, lithium-nickel cobalt manganese composite oxide), a conductive agent, a binder, and the like in a solvent. The obtained slurry can be applied to a positive electrode current collector and further dried.

  The conductive agent is added to bring out good battery performance. Examples of the conductive agent include natural graphite; artificial graphite; carbon black such as acetylene black; amorphous carbon such as needle coke;

  The binder is not particularly limited as long as it has resistance to a nonaqueous electrolyte and has adhesiveness. For example, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polytetrafluoroethylene, fluorinated polyvinylidene fluoride, ethylene-propylene-butadiene terpolymer, styrene-butadiene rubber, acrylonitrile-butadiene rubber, carboxy Methyl cellulose, fluororubber, polyvinyl acetate, polymethyl methacrylate, polyethylene, nitrocellulose, or derivatives thereof can be used alone or in combination.

  The solvent used when mixing the lithium-nickel cobalt manganese composite oxide and the binder is not particularly limited as long as the solvent dissolves or disperses the binder. For example, N-methyl-2-pyrrolidone, N, N-dimethylformamide, N, N-dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, N, N-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran, etc. Water or an aqueous solution such as an aqueous solution to which a dispersant, a thickener, or the like is added can be used.

  Examples of the current collector used for the positive electrode include aluminum, titanium, stainless steel, nickel, calcined carbon, and a conductive polymer. Examples of the shape include a sheet shape, a foam shape, a sintered porous shape, and an expanded lattice shape.

(Negative electrode)
The negative electrode of the nonaqueous electrolyte battery can be produced by mixing a negative electrode material, a conductive agent, a binder, and the like in a solvent, applying the resulting slurry to a negative electrode current collector, and further drying.

  The negative electrode material may be any material as long as it can occlude and release lithium ions. For example, lithium metal, lithium alloy (lithium metal-containing alloys such as lithium-aluminum, lithium-lead, lithium-tin, lithium-aluminum-tin, lithium-gallium, and wood alloy), and lithium composite oxide (titanate) Lithium, etc.), silicon, silicon oxide, tin oxide, carbon materials (eg, graphite, hard carbon, low-temperature calcined carbon, amorphous carbon, etc.). Among these, graphite has an operating potential very close to that of metallic lithium, and therefore, when a lithium salt is employed as an electrolyte salt described later, it exhibits a high discharge voltage and a small irreversible capacity, and therefore is preferable as a negative electrode material.

  As the conductive agent and binder for the negative electrode, the same conductive agent and binder as those for the positive electrode can be used. Examples of the current collector used for the negative electrode include copper, nickel, iron, stainless steel, titanium, aluminum, calcined carbon, and conductive polymer. Examples of the shape include a sheet shape, a foam shape, a sintered porous shape, and an expanded lattice shape.

(Non-aqueous electrolyte)
The nonaqueous electrolyte is an electrolyte salt containing a nonaqueous solvent.
Examples of the electrolyte salt include lithium hexafluorophosphate (LiPF ₆ ), lithium perchlorate (LiClO ₄ ), lithium tetrafluoroborate (LiBF ₄ ), lithium hexafluoroarsenide (LiAsF ₆ ), and trifluoromethane. Examples thereof include lithium salts such as lithium sulfonate (LiCF ₃ SO ₃ ), lithium bistrifluoromethylsulfonylimide (LiN (CF ₃ SO ₂ ) ₂ ), and borate (for example, LiBOB).

  Examples of the organic solvent used in the non-aqueous electrolyte include cyclic carbonates such as ethylene carbonate, propylene carbonate, and vinylene carbonate; chain carbonates such as dimethyl carbonate, methyl ethyl carbonate, and diethyl carbonate; tetrahydrofuran, 2-methyltetrahydrofuran, and the like. Cyclic ethers; chain ethers such as dimethoxyethane; lactones such as γ-butyrolactone; nitriles such as acetonitrile; sultones such as sulfolane, 1,3-propane sultone, 1,3-propene sultone; it can. These organic solvents can be used alone or in the form of a mixture of two or more. Moreover, a room temperature molten salt containing lithium ions can be used as the non-aqueous electrolyte.

(separator)
As the separator, a microporous polymer film, a synthetic resin nonwoven fabric, or the like can be used. Examples of the material include nylon, cellulose acetate, nitrocellulose, polysulfone, polyacrylonitrile, polyvinylidene fluoride, and polyolefin (for example, polypropylene, polyethylene, polybutene, etc.). A microporous film in which polyethylene and polypropylene are laminated can also be used.

  A solid electrolyte can also be used as the nonaqueous electrolyte. Examples of the solid electrolyte include Li—P—O—N composed of Li, P, O, and N in addition to Li 2 S and P 2 S 5.

  Hereinafter, specific examples of the present invention will be described. However, the present invention is not limited to these examples.

(1) Example 1
(Production of composite transition metal compounds)
As the composite transition metal compound, a fine particle nickel cobalt manganese composite hydroxide was prepared by a coprecipitation method. The nickel-cobalt-manganese composite hydroxide particles in Example 1 are spherical as a whole, the core on the center side where the composition ratio of Ni is high, and the composition ratio of Ni gradually decreases toward the surface direction of the particles. And a peripheral shell. Here, the volume (or mass) of the core and the shell volume (or mass) were made equal.

  A specific production process will be described. Regarding the continuous type, 4.5 L of water was put into a cylindrical reaction tank having a volume of 15 L equipped with a stirrer and an overflow pipe. Further, ammonium sulfate powder was added so that the ammonium ion concentration in the tank was 10 g / L. Next, a 32% aqueous sodium hydroxide solution was added until the pH reached 11.6, the temperature of the aqueous solution was maintained at 50 ° C. with an electric heater, and the solution in the reaction vessel was stirred at a constant rate. Further, nitrogen gas having a purity of 99% or more was continuously supplied to the reaction tank at a flow rate of 2.0 L / min. On the other hand, regarding the batch system, 4 L of water was put into a cylindrical reaction vessel having a volume of 10 L, and the other operations were performed in the same manner as the continuous system.

  Next, as a first step, a nickel (II) sulfate aqueous solution, a cobalt sulfate (II) aqueous solution and a manganese (II) sulfate aqueous solution are mixed so that Ni: Co: Mn = 80: 10: 10 (molar ratio). The mixture was diluted with water so that the total concentration of nickel, cobalt, and manganese in the mixed solution was 1.7 mol / L, and a mixed aqueous solution of nickel sulfate-cobalt sulfate-manganese sulfate was prepared and held in the supply container. The mixed aqueous solution in the supply container was continuously supplied from the upper part of the reaction tank to the liquid level in the tank (the surface of the solution being stirred) at a constant rate of 2 ml / min. In synchronization with this, a 6 mol / L ammonium sulfate aqueous solution was continuously supplied as a complexing agent from the inlet at the top of the reaction tank to the liquid level in the reaction tank at a constant rate of 0.3 ml / min. Furthermore, the reaction solution temperature is kept at 50 ° C., and a 32% sodium hydroxide aqueous solution is intermittently added so that the reaction solution is kept at pH 11.6, and a core of uniform composition of the composite transition metal hydroxide particles is formed. Formed. In addition, the mixed aqueous solution of the same concentration was added when the mixed aqueous solution in the supply container decreased.

  Next, as a second step, composite transition metal hydroxide particles were grown while gradually decreasing the nickel sulfate concentration in the nickel sulfate-cobalt sulfate-manganese sulfate mixed aqueous solution supplied to the reaction vessel. Specifically, the amount of nickel sulfate added to the supply container is changed to cobalt sulfate and sulfuric acid so that Ni: Co: Mn = 80: 10: 10 (molar ratio) to 33:33:33 (molar ratio). By making the relative reduction with respect to manganese, for example, 0, the relative proportion of nickel sulfate in the reaction solution stored in the reaction vessel can be gradually reduced at a constant rate. The reaction solution temperature, the supply method of the ammonium sulfate aqueous solution as the complexing agent, the supply method of the sodium hydroxide aqueous solution for pH adjustment, and the like were the same as in the core formation of the composite transition metal hydroxide particles in the first step. Thus, a shell in which the Ni concentration gradually decreases is formed around the core having a uniform composition, and the formation of the composite transition metal hydroxide particles is completed.

  Then, the composite transition metal hydroxide particles in the reaction vessel are collected, filtered after washing with water, dried with a warm air at 110 ° C. for 12 hours in a shelf-type hot air dryer, and composite transition metal hydroxide, that is, nickel. A dry powder of cobalt manganese composite hydroxide was obtained. The obtained nickel cobalt manganese composite hydroxide particles had an average particle size (APS) of 8 μm. In the nickel-cobalt-manganese composite hydroxide, the ratio of the particle core volume to the shell volume was 50:50. In the core of nickel cobalt manganese composite hydroxide particles, the atomic ratio of Ni to Me is approximately uniform 80 mol%, and in the shell, the atomic ratio of Ni to Me gradually decreases toward the outside. The outermost edge was 33.3 mol%, and the average atomic ratio (B0) of the entire particle was 60 mol%. That is, the difference (B1-B2) between the atomic ratio (B1) of Ni to Me in the center of the core and the atomic ratio (B2) of Ni to Me in the peripheral part of the shell is 46.7 mol%.

(Preparation of positive electrode active material)
The obtained nickel cobalt manganese composite hydroxide (composite transition metal compound) and lithium hydroxide are mixed so that the atomic ratio of Li / Me (total of Ni, Co, and Mn) is 1.11 and used for firing. In an atmosphere filled with alumina sheath and using an electric furnace, dry air was continuously supplied into the electric furnace at a flow rate of 3 L / min, the temperature was raised to 700 ° C. at a temperature rising rate of 100 ° C./hour, and 700 ° C. For 10 hours. Then, it stood to cool to room temperature. About the obtained baked product, it heated up to 800 degreeC with the temperature increase rate of 200 degreeC / hour after crushing, and hold | maintained at 800 degreeC for 10 hours. The obtained lithium-nickel cobalt manganese composite oxide (composite oxide) had an average particle size of 8 μm. In the core of the lithium-nickel cobalt manganese composite oxide particle, the atomic ratio of Ni to Me is approximately uniform 80 mol%, and in the shell, the atomic ratio of Ni to Me gradually increases toward the outside. It decreases to 43 mol% at the outermost edge. That is, the difference (A1−A2) between the atomic ratio (A1) of Ni to Me in the central portion of the core and the atomic ratio (A2) of Ni to Me in the peripheral portion of the shell is 37 mol%.

(Evaluation of positive electrode active material)
Weight of 90: 5: 5 of lithium-nickel cobalt manganese composite oxide as a positive electrode active material obtained by the above method, acetylene black as a conductive agent, and polyvinylidene fluoride resin (hereinafter referred to as PVDF) as a binder. The mixture was mixed at a ratio, N-methyl-2-pyrrolidone was added, and the mixture was kneaded and dispersed to prepare a slurry. The slurry was applied to an aluminum foil, dried at 60 ° C. for 6 hours, and dried at 120 ° C. for 12 hours. The electrode after drying was roll-pressed and punched into a disc shape so as to have an area of 2 cm ² as a positive electrode. As a method for producing the evaluation cell, a negative electrode plate was prepared by attaching lithium metal to a stainless steel plate. A solution obtained by adding hexafluorophosphoric acid to a solution in which ethylene carbonate and dimethyl carbonate were mixed at a volume ratio of 3: 7 so as to have a concentration of 1 mol / L was used as an electrolytic solution. A polypropylene separator was used as a separator, and a positive electrode plate, a separator, and a negative electrode plate were sandwiched between stainless plates and sealed with an exterior material to prepare a bipolar evaluation cell.

  The charge rate was 0.2C and the discharge rate was 0.2C for the bipolar evaluation cell, and the battery was charged at a constant current / constant voltage to 4.3V and then discharged at a constant current to 3.0V. The initial charge capacity of Example 1 obtained as a result was 186.8 mAh / g, the initial discharge capacity was 173.8 mAh / g, and the charge / discharge efficiency was 93.0%. In addition, the 3C capacity maintenance rate, that is, the capacity maintenance rate when discharged in 20 minutes, was relatively high at 88.2%, and could withstand fast discharge. In addition, the cycle deterioration rate, that is, when the charge / discharge cycle of 50 cycles is performed at a constant rate, the decrease in the discharge capacity maintenance rate for each cycle is 0.068% / cy, which is relatively low. It could endure repeated.

  About Example 1, 2 positive electrode active materials of Example 1 were produced as a modification. In the case of Example 1-2, nickel cobalt manganese composite hydroxide and lithium hydroxide are mixed and fired so that the atomic ratio of Li / Me is 1.09. As a result, the initial charge capacity of the positive electrode active material of Example 2 obtained as a result was 185.7 mAh / g, the initial discharge capacity was 170.8 mAh / g, and the charge / discharge efficiency was 92.0%. there were. The 3C capacity retention rate was 87.2%, and the cycle degradation rate was 0.098% / cy.

  For Example 1, the positive electrode active material 3 of Example 1 was produced as another modification. In the case of Example 1-3, nickel cobalt manganese composite hydroxide and lithium hydroxide are mixed and fired so that the atomic ratio of Li / Me is 1.04. As a result, the initial charge capacity of the positive electrode active material of Example 4 obtained in Example 1 was 181.6 mAh / g, the initial discharge capacity was 165.0 mAh / g, and the charge / discharge efficiency was 90.9%. there were. The 3C capacity retention rate was 85.8%, and the cycle deterioration rate was 0.15% / cy.

(2) Example 2
Example 2 changes Example 1 regarding the atomic ratio of Li / Me, The manufacturing process of the nickel cobalt manganese composite hydroxide which is a composite transition metal compound (precursor) is the same as that of Example 1. is there. That is, in the nickel cobalt manganese composite hydroxide particles, the volume ratio of the core to the shell was 50:50. In the core of nickel cobalt manganese composite hydroxide particles, the atomic ratio of Ni to Me is approximately uniform 80 mol%, and in the shell, the atomic ratio of Ni to Me gradually decreases toward the outside. And the average atomic ratio (B0) of the whole particle | grains was 60 mol%. The difference (B1-B2) between the atomic ratio (B1) of Ni to Me in the center of the core and the atomic ratio (B2) of Ni to Me in the peripheral part of the shell is 46.7 mol%.

  In preparing the positive electrode active material, other conditions were matched except that nickel cobalt manganese composite hydroxide and lithium hydroxide were adjusted so that the atomic ratio of Li / Me was 1.16. That is, the atomic ratio of Ni to Me in the core of nickel cobalt manganese composite oxide particles is substantially uniform 80 mol%, and in the shell, the atomic ratio of Ni to Me gradually decreases toward the outside. . The difference (A1-A2) between the atomic ratio (A1) of Ni to Me in the center of the core and the atomic ratio (A2) of Ni to Me in the peripheral part of the shell is 35 mol%.

  The evaluation method for evaluating the positive electrode active material was also the same as in Example 1. As a result, the initial charge capacity of the positive electrode active material of Example 2 obtained was 192.1 mAh / g, the initial discharge capacity was 179 mAh / g, and the charge / discharge efficiency was 93.2%. Further, the maintenance rate of the 3C capacity was relatively high at 89.2%, and the cycle deterioration rate was relatively low at 0.031% / cy.

(3) Example 3
Example 3 changes Example 1 regarding the atomic ratio of Li / Me, and the manufacturing process of the nickel cobalt manganese composite hydroxide which is a composite transition metal compound is the same as that of Example 1. FIG. That is, in the particles of nickel cobalt manganese composite hydroxide, the volume ratio of the core to the shell was 50:50. In the core of the nickel cobalt manganese composite hydroxide particles as the precursor, the atomic ratio of Ni to Me is approximately uniform 80 mol%, and in the shell, the atomic ratio of Ni to Me is directed outward. The average atomic ratio (B0) of the entire particle was 60 mol%. The difference (B1-B2) between the atomic ratio (B1) of Ni to Me in the center of the core and the atomic ratio (B2) of Ni to Me in the peripheral part of the shell is 46.7 mol%.

  In preparing the positive electrode active material, other conditions were matched except that the nickel cobalt manganese composite hydroxide and lithium hydroxide were adjusted so that the atomic ratio of Li / Me was 1.21. That is, the atomic ratio of Ni to Me in the core of nickel cobalt manganese composite oxide particles is substantially uniform 80 mol%, and in the shell, the atomic ratio of Ni to Me gradually decreases toward the outside. . The difference (A1-A2) between the atomic ratio (A1) of Ni to Me in the center of the core and the atomic ratio (A2) of Ni to Me in the peripheral part of the shell is 34 mol%.

  The evaluation method for evaluating the positive electrode active material was also the same as in Example 1. The initial charge capacity of the positive electrode active material of Example 3 obtained as a result was 191.2 mAh / g, the initial discharge capacity was 177.1 mAh / g, and the charge / discharge efficiency was 92.6%. . Further, the maintenance rate of the 3C capacity was relatively high at 87.9%, and the cycle deterioration rate was relatively low at 0.022% / cy.

(4) Example 4
Example 4 is a modification of Example 1 regarding not only the Li / Me atomic ratio but also the volume ratio or mass ratio of the core and shell, and the production of nickel cobalt manganese composite hydroxide, which is a composite transition metal compound The process was the same as in Example 1. However, in order to make the core relatively large, the first step was lengthened and the second step was shortened. In the nickel cobalt manganese composite hydroxide particles of this example, the volume ratio of the core to the shell was 80:20. Further, in the core of the nickel cobalt manganese composite hydroxide particles that are the precursors of this example, the atomic ratio of Ni to Me is approximately uniform 80 mol%, and in the shell, the atomic ratio of Ni to Me is It gradually decreased toward the outside, and the average atomic ratio (B0) of the entire particle was 72 mol%. The difference (B1-B2) between the atomic ratio (B1) of Ni to Me in the center of the core and the atomic ratio (B2) of Ni to Me in the peripheral part of the shell is 46.7 mol%.

  Further, in the production of the positive electrode active material, other conditions were the same as those in Example 1 except that the nickel cobalt manganese composite hydroxide and lithium hydroxide were adjusted so that the atomic ratio of Li / Me was 1.07. Matched with the case. That is, the atomic ratio of Ni to Me in the core of nickel cobalt manganese composite oxide particles is substantially uniform 80 mol%, and in the shell, the atomic ratio of Ni to Me gradually decreases toward the outside. . The difference (A1-A2) between the atomic ratio (A1) of Ni to Me in the center of the core and the atomic ratio (A2) of Ni to Me in the peripheral part of the shell is 18 mol%.

  The evaluation method for evaluating the positive electrode active material was the same as in Example 1. As a result, the initial charge capacity of the positive electrode active material of Example 4 obtained was 212.5 mAh / g, the initial discharge capacity was 188.7 mAh / g, and the charge / discharge efficiency was 88.8%. . Further, the maintenance rate of the 3C capacity was relatively high at 86.7%, and the cycle deterioration rate was relatively low at 0.014% / cy.

  For Example 4, as a modification, the positive electrode active material of Example 2 was produced. In the case of Example 4-2, nickel cobalt manganese composite hydroxide and lithium hydroxide are mixed and fired so that the atomic ratio of Li / Me is 1.03. As a result, the initial charge capacity of the positive electrode active material of Example 4 2 obtained was 211.8 mAh / g, the initial discharge capacity was 185.6 mAh / g, and the charge / discharge efficiency was 87.6%. there were. In addition, the maintenance ratio of the 3C capacity was 83.9%. The cycle deterioration rate was relatively low at 0.023% / cy.

(5) Example 5
Example 5 changes Example 4 regarding the atomic ratio of Li / Me, The manufacturing process of the nickel cobalt manganese composite hydroxide which is a composite transition metal compound is the same as that of Example 1 or 4. In the nickel cobalt manganese composite hydroxide particles of this example, the volume ratio of the core to the shell was 80:20. Further, in the particles of nickel cobalt manganese composite hydroxide which is the precursor of this example, the atomic ratio of Ni to Me is approximately uniform 80 mol%, and in the shell, the atomic ratio of Ni to Me is outside. The average atomic ratio (B0) of the entire particles was 72 mol%. The difference (B1-B2) between the atomic ratio (B1) of Ni to Me in the center of the core and the atomic ratio (B2) of Ni to Me in the peripheral part of the shell is 46.7 mol%.

  In addition, in preparing the positive electrode active material, other conditions were the same as in Example 1 except that the nickel / cobalt / manganese composite hydroxide and lithium hydroxide were adjusted so that the atomic ratio of Li / Me was 1.11. Matched with the case. That is, the atomic ratio of Ni to Me in the core of nickel cobalt manganese composite oxide particles is substantially uniform 80 mol%, and in the shell, the atomic ratio of Ni to Me gradually decreases toward the outside. . The difference (A1-A2) between the atomic ratio (A1) of Ni to Me in the center of the core and the atomic ratio (A2) of Ni to Me in the peripheral part of the shell is 22 mol%.

The evaluation method for evaluating the positive electrode active material was the same as in Example 1. As a result, the initial charge capacity of Example 5 obtained was 208.3 mAh / g, the initial discharge capacity was 173.8 mAh / g, and the charge / discharge efficiency was 83.4%. Further, the maintenance rate of the 3C capacity was relatively high at 87.1%, and the cycle deterioration rate was relatively low at 0.012% / cy.
(6) Example 6
Example 6 changes Example 4 regarding the atomic ratio of Li / Me, and the manufacturing process of the nickel cobalt manganese composite hydroxide which is a composite transition metal compound is the same as that of Example 1 or 4. In the nickel cobalt manganese composite hydroxide particles of this example, the volume ratio of the core to the shell was 80:20. Further, in the particles of nickel cobalt manganese composite hydroxide which is the precursor of this example, the atomic ratio of Ni to Me is approximately uniform 80 mol%, and in the shell, the atomic ratio of Ni to Me is outside. The average atomic ratio (B0) of the entire particles was 72 mol%. The difference (B1-B2) between the atomic ratio (B1) of Ni to Me in the center of the core and the atomic ratio (B2) of Ni to Me in the peripheral part of the shell is 46.7 mol%.

  In addition, in preparing the positive electrode active material, other conditions were the same as in Example 1 except that the nickel / cobalt / manganese composite hydroxide and lithium hydroxide were adjusted so that the atomic ratio of Li / Me was 1.15. Matched with the case. That is, the atomic ratio of Ni to Me in the core of nickel cobalt manganese composite oxide particles is substantially uniform 80 mol%, and in the shell, the atomic ratio of Ni to Me gradually decreases toward the outside. . The difference (A1−A2) between the atomic ratio (A1) of Ni to Me in the center of the core and the atomic ratio (A2) of Ni to Me in the peripheral part of the shell is 28 mol%.

  The evaluation method for evaluating the positive electrode active material was the same as in Example 1. As a result, the initial charge capacity of the positive electrode active material of Example 6 obtained was 208 mAh / g, the initial discharge capacity was 173.6 mAh / g, and the charge / discharge efficiency was 83.5%. Further, the maintenance rate of the 3C capacity was relatively high at 87.4%, and the cycle deterioration rate was relatively low at 0.020% / cy.

(7) Example 7
In the seventh embodiment, the Ni concentration distribution in the shell is made substantially uniform without being inclined, but other conditions are the same as those in the fourth embodiment. In the nickel cobalt manganese composite hydroxide particles of this example, the volume ratio of the core to the shell was 80:20. Further, in the core of the nickel cobalt manganese composite hydroxide particles that are the precursors of this example, the atomic ratio of Ni to Me is approximately uniform 80 mol%, and in the shell, the atomic ratio of Ni to Me is The average atomic ratio (B0) of the entire particle was 71 mol%. The difference (B1-B2) between the atomic ratio (B1) of Ni to Me in the center of the core and the atomic ratio (B2) of Ni to Me in the peripheral part of the shell is 46.7 mol%.

  In preparing the positive electrode active material, the nickel cobalt manganese composite hydroxide and lithium hydroxide were adjusted so that the atomic ratio of Li / Me was 1.03, and other conditions were the same as in Example 4. I let you. In other words, the atomic ratio of Ni to Me in the core of the nickel cobalt manganese composite oxide particles is approximately uniform 80 mol%, and the atomic ratio of Ni to Me is approximately uniform in the shell surface. 6 mol%. The difference (A1-A2) between the atomic ratio (A1) of Ni to Me in the center of the core and the atomic ratio (A2) of Ni to Me in the peripheral part of the shell is 14.4 mol%.

  The evaluation method for evaluating the positive electrode active material was the same as in Example 4. As a result, the initial charge capacity of the positive electrode active material of Example 7 obtained was 209 mAh / g, the initial discharge capacity was 184 mAh / g, and the charge / discharge efficiency was 88.0%. Moreover, the maintenance rate of 3C capacity | capacitance was 84.2%, and the cycle degradation rate was 0.038% / cy.

(8) Example 8
In Example 8, the Ni concentration distribution in the shell is made substantially uniform without inclining, but other conditions are the same as those in Example 4. In the nickel cobalt manganese composite hydroxide particles of this example, the volume ratio of the core to the shell was 80:20. In the core of the nickel cobalt manganese composite hydroxide particle that is the precursor of this example, the atomic ratio of Ni to Me is substantially uniform 80 mol%, and in the shell, the atomic ratio of Ni to Me is The average atomic ratio (B0) of the entire particle was 73.0 mol%. The difference (B1-B2) between the atomic ratio (B1) of Ni to Me in the center of the core and the atomic ratio (B2) of Ni to Me in the peripheral part of the shell is 35 mol%.

  In preparing the positive electrode active material, the nickel cobalt manganese composite hydroxide and lithium hydroxide were adjusted so that the atomic ratio of Li / Me was 1.07, and other conditions were the same as in Example 4. I let you. That is, the atomic ratio of Ni to Me in the core of the particles of the nickel cobalt manganese composite oxide is substantially uniform 80 mol%, and the atomic ratio of Ni to Me is substantially uniform on the shell surface. 1 mol%. The difference (A1-A2) between the atomic ratio (A1) of Ni to Me in the center of the core and the atomic ratio (A2) of Ni to Me in the peripheral part of the shell is 20.9 mol%.

  The evaluation method for evaluating the positive electrode active material was the same as in Example 4. The initial charge capacity of the positive electrode active material of Example 8 obtained as a result was 210.3 mAh / g, the initial discharge capacity was 188.8 mAh / g, and the charge / discharge efficiency was 89.8%. . Further, the maintenance rate of the 3C capacity was 84.6%, and the cycle deterioration rate was 0.022% / cy.

  For Example 8, as a modification, the positive electrode active material of Example 2 was produced. In the case of Example 8-2, nickel cobalt manganese composite hydroxide and lithium hydroxide are mixed and fired so that the atomic ratio of Li / Me is 1.03. As a result, the initial charge capacity of the positive electrode active material of Example 8 2 obtained was 203.7 mAh / g, the initial discharge capacity was 183.2 mAh / g, and the charge / discharge efficiency was 89.9%. there were. In addition, the maintenance ratio of the 3C capacity was 84.1%. The cycle deterioration rate was 0.08% / cy.

(9) Example 9
In Example 9, Example 8 was changed with respect to the volume ratio or mass ratio of the core and shell, and the production process of the nickel-cobalt-manganese composite hydroxide, which is a composite transition metal compound, was the same as Example 1. It was. However, in order to make the core relatively large, the first step was lengthened and the second step was shortened. In the particles of nickel cobalt manganese composite hydroxide, which is the precursor of this example, the volume ratio of the core to the shell was 90:10. Further, in the core of the nickel cobalt manganese composite hydroxide particles of this example, the atomic ratio of Ni to Me is approximately uniform 80 mol%, and in the shell, the atomic ratio of Ni to Me is approximately uniform. 45 mol%, and the average atomic ratio (B0) of the whole particle was 77 mol%. The difference (B1-B2) between the atomic ratio (B1) of Ni to Me in the center of the core and the atomic ratio (B2) of Ni to Me in the peripheral part of the shell is 35 mol%.

  In preparing the positive electrode active material, nickel cobalt manganese composite hydroxide and lithium hydroxide were adjusted so that the atomic ratio of Li / Me was 1.07, and other conditions were the same as in Example 8. I let you. That is, the atomic ratio of Ni to Me in the core of the nickel cobalt manganese composite oxide particles is substantially uniform 80 mol%, and the atomic ratio of Ni to Me in the shell is substantially uniform 64.8 mol%. Met. The difference (A1-A2) between the atomic ratio (A1) of Ni to Me in the center of the core and the atomic ratio (A2) of Ni to Me in the peripheral part of the shell is 15.2 mol%.

  The evaluation method for evaluating the positive electrode active material was the same as in Example 8. As a result, the initial charge capacity of the positive electrode active material of Example 9 obtained was 219 mAh / g, the initial discharge capacity was 195 mAh / g, and the charge / discharge efficiency was 89.0%. Moreover, the maintenance rate of 3C capacity | capacitance was 87.1%, and the cycle deterioration rate was 0.029% / cy.

(8) Comparative Example 1
In Comparative Example 1, the shell is not provided and only the core is used. Other conditions are the same as those in Example 4. In the particles of nickel cobalt manganese composite hydroxide which is the precursor of this comparative example, the composition ratio of the transition metal is Ni: Co: Mn = 80: 10: 10 (molar ratio) as in the cores of Examples 1-7. )Met.

  In preparing the positive electrode active material, the nickel cobalt manganese composite hydroxide and lithium hydroxide were adjusted so that the atomic ratio of Li / Me was 1.11, and other conditions were the same as in Example 4. I let you. Further, in the particles of the nickel cobalt manganese composite oxide, the composition ratio of the transition metal was Ni: Co: Mn = 80: 10: 10 (molar ratio) as in the cores of Examples 1 to 7.

  The evaluation method for evaluating the positive electrode active material was the same as in Example 4. The initial discharge capacity of the positive electrode active material of Comparative Example 1 obtained as a result was 178.4 mAh / g. Moreover, the maintenance rate of 3C capacity | capacitance was 80.1%, and the cycle deterioration rate was 0.2% / cy.

(9) Comparative Example 2
In Comparative Example 2, the shell is not provided and only the core is provided. In the particles of the nickel cobalt manganese composite hydroxide that is the precursor of this Comparative Example, the composition ratio of the transition metal is the same as that in Examples 1 to 7 above. Unlike the core, Ni: Co: Mn = 70: 20: 10 (molar ratio). Other conditions are the same as those in Comparative Example 1 and Example 4.

  In preparing the positive electrode active material, nickel cobalt manganese composite hydroxide and lithium hydroxide were adjusted so that the atomic ratio of Li / Me was 1.11, and other conditions were also set in Comparative Example 1 and Example 4. The case was matched.

  The evaluation method for evaluating the positive electrode active material was the same as in Comparative Example 1 and Example 4. The initial discharge capacity of the positive electrode active material of Comparative Example 2 obtained as a result was 169 mAh / g. Moreover, the maintenance rate of 3C capacity | capacitance was 79.6%, and the cycle deterioration rate was 0.19% / cy.

(10) Comparative Example 3
Comparative Example 3 is the same as Comparative Example 2 except that a core is not provided, and the nickel-cobalt-manganese composite hydroxide particles, which are precursors of this comparative example, have a transition metal composition ratio of Ni : Co: Mn = 70: 20: 10 (molar ratio). Other conditions are the same as those in Comparative Example 1 and Example 4 as in Comparative Example 2.

  In preparing the positive electrode active material, nickel cobalt manganese composite hydroxide and lithium hydroxide were adjusted so that the atomic ratio of Li / Me was 0.95, and other conditions were the same as in Comparative Example 2. The results were the same as those in Example 1 and Example 4.

  The evaluation method for evaluating the positive electrode active material was the same as in Comparative Example 1 and Example 4 as in Comparative Example 2. The initial discharge capacity of the positive electrode active material of Comparative Example 3 obtained as a result was 170.6 mAh / g. The 3C capacity retention rate was 81.2%, and the cycle degradation rate was 0.33% / cy.

(11) Comparative Example 4
Comparative Example 4 is the same as Comparative Example 2 except that the shell is not provided, and the core of the nickel cobalt manganese composite hydroxide, which is the precursor of this Comparative Example, has a transition metal composition ratio of Ni. : Co: Mn = 70: 20: 10 (molar ratio). Other conditions are the same as those in Comparative Example 1 and Example 4 as in Comparative Example 2.

  In preparing the positive electrode active material, the nickel cobalt manganese composite hydroxide and lithium hydroxide were adjusted so that the Li / Me atomic ratio was 1.28, and other conditions were compared in the same manner as in Comparative Example 2. The results were the same as those in Example 1 and Example 4.

  In the case of Comparative Example 4, a large amount of unreacted lithium hydroxide remained, the positive electrode active material gelled, and the electrochemical characteristics could not be measured.

(12) Comparative Example 5
Comparative Example 5 is provided with a core and a shell in the same manner as in Example 1. The production process of nickel cobalt manganese composite hydroxide, which is a composite transition metal compound (precursor), is the same as in Example 1. . That is, in the nickel cobalt manganese composite hydroxide particles, the volume ratio of the core to the shell was 50:50. In the core of nickel cobalt manganese composite hydroxide particles, the atomic ratio of Ni to Me is approximately uniform 80 mol%, and in the shell, the atomic ratio of Ni to Me gradually decreases toward the outside. And it was 33.3 mol% in the outermost surface, and the average atomic ratio (B0) of the whole particle | grains was 60 mol%. The difference (B1-B2) between the atomic ratio (B1) of Ni to Me in the center of the core and the atomic ratio (B2) of Ni to Me in the peripheral part of the shell is 46.7 mol%.

  In preparing the positive electrode active material, other conditions were matched except that nickel cobalt manganese composite hydroxide and lithium hydroxide were adjusted so that the atomic ratio of Li / Me was 1.00. That is, the atomic ratio of Ni to Me in the core of the nickel cobalt manganese composite oxide particles is substantially uniform 80 mol%, and in the shell, the atomic ratio of Ni to Me gradually decreases toward the outside. It was. The difference (A1−A2) between the atomic ratio (A1) of Ni to Me in the center of the core and the atomic ratio (A2) of Ni to Me in the peripheral part of the shell is 38 mol%.

  The evaluation method for evaluating the positive electrode active material was also the same as in Example 1. The resulting initial charge capacity of the positive electrode active material of Example 2 was 178.1 mAh / g, the initial discharge capacity was 159.2 mAh / g, and the charge / discharge efficiency was 89.4%. . Further, the maintenance rate of the 3C capacity was relatively low at 83.9%, and the cycle deterioration rate was relatively low at 0.21% / cy.

Table 1 below summarizes the structural features and performance features of Examples 1-9 and Comparative Examples 1-5.
[Table 1]

  Hereinafter, various evaluations performed on the nickel-cobalt-manganese composite oxide (positive electrode active material) and the bipolar evaluation cell (nonaqueous electrolyte secondary battery) obtained therefrom using Examples will be described.

  FIG. 1 shows the pore distribution of the nickel cobalt manganese composite oxide particles of Example 1, the nickel cobalt manganese composite oxide particles of Example 7, and the nickel cobalt manganese composite oxide particles of Comparative Example 1. The horizontal axis indicates the pore diameter, and the vertical axis indicates the pore volume. As is apparent from the graph, the nickel-cobalt-manganese composite oxide particles (positive electrode active material particles) of Example 1 have a peak corresponding to pores with a diameter of several nm, but the pores with diameters larger than that. Does not have a corresponding peak. In addition, the peak which exists in 5 micrometers or more is estimated as the space | gap between particle | grains. The nickel cobalt manganese composite oxide particles (positive electrode active material particles) of Example 7 have a peak corresponding to pores having a diameter of 1 μm. The positive electrode active material particles of Example 7 have a large Ni composition difference of 46.7 mol% at the core-shell interface, and it is considered that pores are relatively easily formed due to the difference in shrinkage behavior during firing. The nickel cobalt manganese composite oxide particles (positive electrode active material particles) of Comparative Example 1 have a gentle peak corresponding to pores having a diameter of several μm. From comparison with Comparative Example 1, it can be seen that the positive electrode active material particles of Examples 1 and 7 have few pores having a diameter of several μm.

  2 (A) to 2 (E) show the nickel cobalt manganese composite oxide particles of Example 1, the nickel cobalt manganese composite oxide particles of Example 4, and the nickel cobalt manganese composite oxide particles of Example 7. It is the enlarged image which observed the nickel cobalt manganese complex oxide particle of the comparative example 1 with SEM. FIG. 2A shows nickel cobalt manganese composite oxide particles (positive electrode active material particles) of Example 1. The positive electrode active material particles are aggregates of fine primary particles. FIG. 2B shows nickel cobalt manganese composite oxide particles (positive electrode active material particles) of Example 4. 2 (C) and 2 (D) show nickel cobalt manganese composite oxide particles (positive electrode active material particles) of Examples 7 and 8. FIG. FIG. 2E shows nickel cobalt manganese composite oxide particles (positive electrode active material particles) of Comparative Example 1. In any of the positive electrode active material particles described above, no significant pores are found.

FIG. 3 shows the positive electrode active material of Example 1, the positive electrode active material of Example 4, the positive electrode active material of Example 7, the positive electrode active material of Example 8, and the positive electrode active material of Comparative Example 1 with respect to DSC. The horizontal axis indicates the temperature [° C.] and the vertical axis indicates the heat flow [w / g]. The DSC measurement for the active material was performed by charging and discharging for 3 cycles in a voltage range of 3.0 V to 4.3 V at 0.05 C using Li metal as the counter electrode, and charging to 4.3 V in the final cycle. Thereafter, the charged active material was taken out under an inert atmosphere. As a specific method of measurement, the temperature of a container packed with a sample was raised at 10 ° C./min, and the heat generation behavior when applying heat from room temperature to 400 ° C. was confirmed. The calorific value was obtained by calculating the peak area of the profile obtained thereafter.
As is apparent from the chart, the thermal stability of the positive electrode active materials of Examples 1, 4, and 8 is considered to be relatively high. In particular, the positive electrode active material of Example 1 is considered to have high thermal stability and is considered to be superior to Example 4 and the like. Although the thermal stability of the positive electrode active material of Example 7 is not so high, an improvement is seen when compared with the positive electrode active material of Comparative Example 1.

  FIG. 4 is a graph comparing capacity deterioration when the Li / Me atomic ratio is changed in the lithium-nickel cobalt manganese composite oxide (positive electrode active material). The horizontal axis represents the charge / discharge cycle, and the vertical axis represents the decrease [%] in the discharge capacity. In the case of the positive electrode active material of Example 1, the Li / Me atomic ratio x = 1.11 and the cycle deterioration rate was 0.068% / cy. The atomic ratio x of Me = 1.09, the cycle deterioration rate was 0.098% / cy, and in the case of the positive electrode active material of Example 1, the Li / Me atomic ratio x = 1.04, The cycle deterioration rate is 0.150% / cy. That is, it can be seen that the cycle deterioration rate improves as the atomic ratio x increases when the Li / Me atomic ratio x is 1.0 or more. That is, regarding the cycle deterioration rate, that is, the cycle life, when the core / shell volume ratio is 50:50, the atomic ratio x is preferably 1.09 or more, and more preferably 1.11 or more.

  FIG. 5 is another graph comparing capacity deterioration when the atomic ratio of Li / Me in the nickel cobalt manganese composite oxide (positive electrode active material) is changed. In the case of the positive electrode active material of Example 4, the Li / Me atomic ratio x = 1.07, the cycle deterioration rate was 0.014% / cy, and in the case of the positive electrode active material of Example 4, the Li / Me The atomic ratio x of Me = 1.03, and the cycle deterioration rate is 0.022% / cy. That is, it can be seen that the cycle deterioration rate improves as the atomic ratio x increases when the Li / Me atomic ratio x is 1.0 or more. That is, regarding the cycle deterioration rate, that is, the cycle life, when the core / shell volume ratio is 80:20, the atomic ratio x is preferably 1.07 or more.

Table 2 below is a sample of the positive electrode active material prepared based on Example 4 so that the Li / Me atomic ratio is 1.03, 1.07, 1.11 and 1.15 (Example 4). 2, 4, 4, 3, 4, 4) shows the results of measurement of residual LiOH, residual Li carbonate and the like. As is apparent from Table 2, the residual Li increases as the Li / Me atomic ratio increases. Moreover, the particle size of the positive electrode active material powder tends to increase as the atomic ratio of Li / Me increases. Furthermore, it can be seen that when the atomic ratio of Li / Me is 1.15 or more, the specific surface area (BET) starts to increase.
[Table 2]

  FIG. 6 shows the analysis result by X-ray diffraction, and shows the diffraction peak of each sample. As is clear from the figure, the peak position moves to the right as the atomic ratio of Li / Me increases. However, when the atomic ratio of Li / Me exceeds 1.11, the movement of the peak position is hardly observed. Until the atomic ratio of Li / Me reaches 1.11, it is thought that the lattice spacing is changed by the incorporation of Li atoms into the crystal structure of the nickel cobalt manganese composite oxide particles. When the atomic ratio exceeds 1.11, it is considered that Li atoms do not enter the crystal structure of the particles.

Hereinafter, the result of structural analysis using the Rietveld method for the composite oxide (positive electrode active material) will be described.
FIGS. 7A to 7C are conceptual diagrams illustrating the structure of the complex oxide that is a precondition in the Rietveld analysis performed as the embodiment.

The composite oxide particles 11 shown in FIG. 7A are the Li _x MeO ₂ +0.5 _(x−1) (1) already described.
(In the formula, Me is a transition metal containing Ni and at least one metal selected from other transition metals, and x represents a number greater than 1.00 and not greater than 1.25.)
And has a core 21 and a shell 22. Here, Me specifically includes Ni, Co, and Mn. That is, the composite oxide is a lithium-nickel cobalt manganese composite oxide.
In the core 21, the atomic ratio of Ni to Me (A = Ni / Me × 100) is the above-described value A1 and is uniform. In the shell 22, the atomic ratio of Ni to Me is a value A (r) set according to the radial position r, and in this case, the value is equal to a value A1 from the innermost p value A1 to the outermost value A21 in the shell 22. It shall be reduced in the same way. That is, the composite oxide particles 11 shown in FIG. 7A have a core-shell structure, and have a tilted shell type in which the Ni composition ratio gradually decreases in the shell 22. The composite oxide particles 11 correspond to Examples 1 to 6, Comparative Example 5, and the like.

The composite oxide particles 12 shown in FIG. 7B are also described as Li _x MeO ₂ +0.5 _(x−1) (1).
(In the formula, Me is a transition metal containing Ni and at least one metal selected from other transition metals, and x represents a number greater than 1.00 and not greater than 1.25.)
And has a core 21 and a shell 22. Here, Me specifically includes Ni, Co, and Mn. That is, the composite oxide is a lithium-nickel cobalt manganese composite oxide.
In the core 21, the atomic ratio of Ni to Me (A = Ni / Me × 100) is the above-described value A1 and is uniform. In the shell 22, the atomic ratio of Ni to Me is a value Ar (r) set according to the radial position r, and in this case, it is assumed to be a substantially uniform value A22 within the shell 22. That is, the composite oxide particles 12 shown in FIG. 7B have a core-shell structure in which the composition is switched stepwise, and the single shell type in which the composition ratio of Ni in the shell 22 is substantially uniform. It has become. The composite oxide particles 12 correspond to Examples 7 to 9 above.

The composite oxide particles 13 shown in FIG. 7C are also described as Li _x MeO ₂ +0.5 _(x−1) (1).
(In the formula, Me is a transition metal containing Ni and at least one metal selected from other transition metals, and x represents a number greater than 1.00 and not greater than 1.25.)
However, it has a uniform composition without a clear core or shell. Here, Me specifically includes Ni, Co, and Mn. That is, the composite oxide is a lithium-nickel cobalt manganese composite oxide. The composite oxide particles 13 correspond to Comparative Examples 1 to 4 described above.

  In the structural analysis of the present application using the Rietveld method, a single structural model is adopted for simplicity. That is, an X-ray diffraction pattern simulation is performed on the premise of the composite oxide particles 13 shown in FIG. At this time, as a crystal structure of the composite oxide, lithium ions exist in the 3a site (0, 0, 0) of the space group R-3m, and Ni, Co, and 3b sites (0, 0, 1/2) exist. It was assumed that Mn exists in a distribution corresponding to the composition ratio and oxygen exists in the 6c site (0, 0, z). As is clear from this premise, the composite oxide particles 13 shown in FIG. 7C have a high degree of fitting for the simulation of the X-ray diffraction pattern, and the composite shown in FIGS. 7A and 7B. The oxide particles 11 and 12 tend to have a low fitting degree in the simulation of the diffraction pattern.

  Further, in the composite oxide particles 11 to 13 shown in FIGS. 7A to 7C, cation mixing is assumed to occur with a random distribution at a predetermined probability. Here, cation mixing means an ion exchange phenomenon in which nickel ions and lithium ions are interchanged, and is considered to be caused by the fact that the ion radius of nickel is close to the ion radius of lithium. It is considered that this cation mixing is more likely to occur as the shell 22 is present and the density of the nickel ions is lower, that is, as the shell 22 is thicker and clearly present.

Based on the above assumptions, structural analysis using the Rietveld method is performed. Pre-mixed composite oxide particles (Examples 1 to 9, Comparative Examples 1 to 5 and the like) are packed in a glass cell in advance, and X-ray diffraction measurement is performed. RINT-2000 manufactured by Rigaku Corporation was used as the powder X-ray diffractometer. Measurement was performed using a CuKα radiation source (tube voltage 40 kV, tube current 40 mA), with a diffraction angle 2θ = 10 ° -70 °, a step width 0.03 °, a measurement time of 1.0 sec / °, and a divergence of each slit. The measurement was performed at 00 °, scattering of 1.00 °, and light reception of 0.3 mm. The obtained powder X-ray data is measured X-ray diffraction data used in the Rietveld method. Next, by performing Rietveld analysis to fit the measured X-ray diffraction data on the premise of the structure of the composite oxide particles 13 shown in FIG. 7C and the occurrence of a certain amount (variable) of cation mixing, The structure of the produced composite oxide particles is evaluated. Rietveld analysis uses the analysis program Rietan-FP (see F. Izumi and K. Mamma, Solid State Phenom., 130, 15-20 (2007)), and the profile function uses Toraya's divided pseudo-Voigt function. I did it. Such structural evaluation can include a cation mixing rate indicating the degree of cation mixing and an S value indicating the degree of fitting in the structure analysis. These cation mixing rate and S value are the values of the core and shell. It can be seen that the expression of the structure is quantified. The cation mixing rate is specifically the proportion of the portion of all lithium sites that is replaced with nickel sites. Further, the S value is specifically expressed by the following formula S = Rwp / Re
It is represented by Here, the value Rwp is a measure representing how much the XRD pattern based on the structural model assumed in Rietveld analysis matches the measured XRD pattern (the above powder X-ray data), and the value Re is the measured XRD. It means the value of Rwp that becomes the minimum when the pattern matches the XRD pattern of the structural model.

Of the structure evaluation using Rietveld analysis, the cation mixing rate, which is the first judgment value, will be specifically described. In the composite oxide particles 11 and 12 having a cation mixing rate of 2.0% to 6.0%, the low nickel shell 22 is considered to have an appropriate thickness. In other words, the presence of the low nickel shell 22 having an appropriate thickness can suppress the thermal instability corresponding to ΔH (change in enthalpy due to melting and phase transition) in DSC. When the cation mixing rate is 2.0% or less, the effect of the shell 22 is not sufficiently exerted. When the cation mixing rate is 6.0% or more, the shell 22 becomes thick and ΔH decreases, but as a result, It is thought that electrochemical properties such as capacity density deteriorate due to lack of nickel.
The cation mixing rate is preferably 2.0% or more and 5.0% or less. In this case, it becomes more advantageous with respect to electrochemical properties. The cation mixing rate is more preferably 2.0% to 4.5%. This is further advantageous with regard to electrochemical properties.

Of the structural evaluation using the Rietveld analysis, the S value that is the second judgment value will be specifically described. In the composite oxide particles 11 and 12 having an S value of 1.30 or more and 1.60 or less, it is considered that the presence of the low nickel shell 22 is moderate. That is, when the S value representing the degree of fitting is 1.30 or more, the obtained composite oxide has a structure like the composite oxide particles 11 and 12 shown in FIGS. 7 (A) and 7 (B). In other words, this is an indirect support for the existence of the shell 22 that can improve the thermal characteristics. On the other hand, when the S value is 1.60 or less, the obtained composite oxide has a structure that is not far from the structure such as the composite oxide particle 13 shown in FIG. This is an indirect support for not being too thick to degrade the electrochemical properties.
The S value is preferably 1.32 or more and 1.55 or less. In this case, a core-shell structure in which the balance between electrochemical characteristics and thermal stability is achieved is advantageous. The cation mixing rate is more preferably 1.35 or more and 1.50 or less. In this case, a core / shell structure in which electrochemical properties and thermal stability are balanced is further advantageous.

  Referring to Table 1 again, corresponding to Examples 1 to 9, Comparative Examples 1 to 5, etc., the S value and the cation mixing rate are appended to the bottom column. In Examples 1-9, it turns out that the cation mixing rate is 2.0% or more and 6.0% or less. Moreover, in Examples 1-9, it turns out that S value is 1.30 or more and 1.60 or less except 3 and 9 of Example 1. On the other hand, in Comparative Examples 1 to 5, except for Comparative Example 3, there is no cation mixing rate of 2.0% to 6.0%. Of Comparative Examples 1 to 5, in Comparative Example 5, the S value is not 1.30 or more and 1.60 or less.

  For example, Example 8 has a cation mixing rate of 3.3% and an S value of 1.40, and Example 8-2 has a cation mixing rate of 4.4% and an S value of 1.42. 3 of Example 1 has a cation mixing rate of 5.2% and an S value of 1.56. Comparative Example 2 has a cation mixing rate of 1.7% and an S value of 1.33, and Comparative Example 5 has a cation mixing rate of 6.1% and an S value of 1.61. Among the examples, 3 of Example 1 is excellent from the viewpoint of ΔH, but the cycle deterioration rate is large. Further, Comparative Example 2 has high ΔH and low thermal stability, and Comparative Example 5 has a large cycle deterioration rate.

For reference, a composite oxide (Comparative Example 6) having the same process as that of the composite oxide of Example 4 in which the sintering time is excessively long and the core-shell structure is substantially eliminated is produced. Also for this, evaluation such as measurement of an X-ray diffraction pattern was performed. In the case of Comparative Example 6, the cation mixing rate was 1.7%, and the S value was 1.33. In Comparative Example 6, since the shell 22 does not substantially exist, ΔH = 1345 J / g and the effect of reducing ΔH does not occur.
Further, a composite oxide corresponding to the core composition of Example 8 and a composite oxide corresponding to the shell composition of Example 8 were produced separately, and these composite oxides were compared with the core-shell ratio of Example 8. An X-ray diffraction pattern was measured for a composite oxide (Comparative Example 7) mixed at a similar ratio of 80:20. In this case, the cation mixing rate is 2.5% and the S value is 1.34. However, since the shell 22 does not exist, ΔH = 1131 J / g and the effect of reducing ΔH does not occur.

  8 (A) to 8 (C) show the results of composition analysis of the particle cross section of the composite oxide having a core-shell structure by energy dispersive X-ray analysis (EDX). 8A shows the particle cross section of Example 8, FIG. 8B shows the particle cross section of Example 8, and FIG. 8C shows the particle cross section of Comparative Example 6. FIG. It can be seen that the composite oxide particles of Example 8 have a thin but sufficient shell 22 and the composite oxide particles of Example 8 two have a thicker distinct shell 22. It can be seen that the composite oxide particles of Comparative Example 6 have a gentle cross-sectional composition distribution and no substantial shell 22.

Claims (13)

The following formula (1):
Li _x MeO _{2 + 0.5 (x-1)} (1)
(In the formula, Me is a transition metal containing Ni and at least one metal selected from other transition metals, and x is a number from 1.05 to 1.25.)
A particulate composite oxide represented by:
A composite oxide in which the atomic ratio of Ni to Me (A = Ni / Me × 100) is 60 mol% or more and 90 mol% or less in the whole particle, and the value of the atomic ratio is smaller in the peripheral portion than in the central portion . The following formula (1):
Li _x MeO _{2 + 0.5 (x-1)} (1)
[In the formula, Me is a transition metal containing Ni and at least one metal selected from other transition metals, and x is a number from 1.05 to 1.25, and
The following relational expression (2):
x = (0.005y + 1.06) ± 0.06 (2)
(In the relational expression, y is a value obtained by subtracting the atomic ratio (B0) of Ni to Me in the whole particle including the core and the shell from the atomic ratio (B1) of Ni to the center of the core.) ). ]
A particulate composite oxide represented by:
A composite oxide in which the atomic ratio of Ni to Me (A = Ni / Me × 100) is 60 mol% or more and 90 mol% or less in the whole particle, and the value of the atomic ratio is smaller in the peripheral portion than in the central portion . The composite oxide according to claim 1 or 2 , wherein a difference in atomic ratio of Ni to Me in the central part of the particle and the peripheral part of the particle is 20 mol% or more and 70 mol% or less. By structure analysis by the Rietveld method, it is the cation mixing ratio is 6.0% or more and 2.0% or less, and, S value is 1.30 or more 1.60 or less, any of claims 1 to 3 one The composite oxide according to item. The following formula (1):
Li _x MeO _{2 + 0.5 (x-1)} (1)
(In the formula, Me is a transition metal containing Ni and at least one metal selected from other transition metals, and x is a number from 1.05 to 1.25.)
A particulate composite oxide represented by:
The atomic ratio of Ni to Me (A = Ni / Me × 100) is 60 mol% or more and 90 mol% or less in the whole particle, and the value of the atomic ratio is smaller in the peripheral portion than in the central portion,
A composite oxide having a cation mixing rate of 2.0% to 6.0% and an S value of 1.30 to 1.60 by structural analysis by a Rietveld method. The following formula (1):
Li _x MeO _{2 + 0.5 (x-1)}     (1)
[In the formula, Me is a transition metal containing Ni and at least one metal selected from other transition metals, x is a number of 1.05 or more and 1.25 or less, and
The following relational expression (2):
x = (0.005y + 1.06) ± 0.06 (2)
(In the relational expression, y is a value obtained by subtracting the atomic ratio (B0) of Ni to Me in the whole particle including the core and the shell from the atomic ratio (B1) of Ni to the center of the core.) ). ]
A particulate composite oxide represented by:
The atomic ratio of Ni to Me (A = Ni / Me × 100) is 60 mol% or more and 90 mol% or less in the whole particle, and the value of the atomic ratio is smaller in the peripheral portion than in the central portion,
A composite oxide having a cation mixing rate of 2.0% to 6.0% and an S value of 1.30 to 1.60 by structural analysis by a Rietveld method. The composite oxide according to claim 1, wherein Me is a transition metal composed of Ni, Co, and Mn. It is a manufacturing method of the complex oxide according to any one of claims 1 to 7 ,
A core having an atomic ratio (B) of Ni to Me of 70 mol% or more and 100 mol% or less at the center, and a shell having an atomic ratio of Ni to Me smaller than that at the periphery of the core; The atomic ratio (B0) of Ni to Me in the whole of the included particles is 60 mol% or more and 90% or less. The atomic ratio (B1) of Ni to Me in the center of the core and the Me of Ni in the periphery of the shell The step (I) of obtaining a precursor comprising a composite metal compound having a difference (B1-B2) from the atomic ratio (B2) to 10 mol% to 80 mol%;
A step of firing the mixture obtained by mixing the precursor obtained in the step (I) and the Li compound at a ratio such that the atomic ratio of Li to Me is 1.05 or more and 1.25 or less; A method for producing a composite oxide, comprising: A method for producing the composite oxide according to any one of claims 2 to 7,
A core having an atomic ratio (B) of Ni to Me of 70 mol% or more and 100 mol% or less at the center, and a shell having an atomic ratio of Ni to Me smaller than that at the periphery of the core; The atomic ratio (B0) of Ni to Me in the whole of the included particles is 60 mol% or more and 90% or less. The atomic ratio (B1) of Ni to Me in the center of the core and the Me of Ni in the periphery of the shell The step (I) of obtaining a precursor comprising a composite metal compound having a difference (B1-B2) from the atomic ratio (B2) to 10 mol% to 80 mol%;
A ratio in which the atomic ratio (x) of Li to Me is 1.05 or more and 1.25 or less in the precursor and Li compound obtained in the step (I); and
The following relational expression (2):
x = (0.005y + 1.06) ± 0.06 (2)
(In the relational expression, y is a value obtained by subtracting the atomic ratio (B0) of Ni to Me in the whole particle including the core and the shell from the atomic ratio (B1) of Ni to the center of the core.) Show.)
And a step (II) of firing a mixture obtained by mixing so as to satisfy the requirements. The composite oxidation according to claim 8 or 9, wherein, in the precursor, a ratio of the volume of the core to the volume of the shell [(core volume) :( shell volume)] is 50:50 to 90:10. Manufacturing method. With respect to the composite oxide obtained after firing, the cation mixing rate is 2.0% or more and 6.0% or less and the S value is 1.30 or more and 1.60 or less by structural analysis by the Rietveld method. The manufacturing method of the complex oxide as described in any one of Claims 8-10 which exists. Positive electrode active material for the composite obtained from the oxide, a non-aqueous electrolyte secondary battery according to any one of claims 1-7. The nonaqueous electrolyte secondary battery which has a positive electrode which has as a main component the positive electrode active material for nonaqueous electrolyte secondary batteries of Claim 12 , a separator, and a negative electrode.

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