Positive electrode active material, battery, and method of manufacturing positive electrode active material

Abstract

To provide a positive electrode active material that can improve the cycling characteristic when used in a battery.SOLUTION: A positive electrode active material has a composition represented by LixNiaCobMncMdO2. When an inner region, which extends 70% of a radius from a center of a particle of the positive electrode active material, in a TEM-EDX image of a cross-section of the particle of the positive electrode active material is sectioned into square regions of 10 nm, a proportion of regions at which a concentration of an element represented by M is greater than or equal to 10 mass% is greater than or equal to 1.0% with respect to all regions. In the composition, 0.1≤x≤1.5, 0.5≤a≤1.0, 0≤b≤0.3, 0≤c≤0.3, a+b+c=1.0 and 0.0005≤d≤0.05 are satisfied, and M represents at least one element selected from the group consisting of Ta, Al, Ba, Pr, La, Y, Sr, Ce, Se, Hf, Rh and Zr.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a positive electrode active material, a battery, and a method for manufacturing a positive electrode active material.

Background Art

[0002] Conventionally, various additive elements have been added to the positive electrode active material used in a battery for the purpose of improving the resistance characteristics and the like of the battery.

[0003] For example, Patent Document 1 discloses a transition metal composite hydroxide particle containing nickel (Ni), manganese (Mn), cobalt (Co), and element A (A) in a molar ratio of Ni:Mn:Co:A = x:y:z:t (x + y + z = 1, 0.3 ≤ x ≤ 0.95, 0.05 ≤ y ≤ 0.55, 0 ≤ z ≤ 0.4, 0 < t ≤ 0.1, and the element A is at least one element selected from Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, La, Hf, Ta, and W), having a central portion containing primary particles and an outer shell portion disposed outside the central portion and having primary particles more densely arranged than the central portion, and the proportion (th) of the element A in the central portion being smaller than the proportion (ts) of the element A in the outer shell portion.

[0004] Further, Patent Document 2 discloses a compound represented by the general formula (Li 1+x (Co (1-a-b-m) Ni a Al b M m ) 1-x O 2-(f / 2) F f) The surface of the lithium-containing composite oxide represented by is modified with a surface modification compound containing at least one element selected from the group consisting of elements of Group S1 and Group S2, Group S1 is a group consisting of Al, Zr, Ti, Mg, Zn, Nb, Mo, Ta, W, and rare earths, Group S2 is a group consisting of F, P, and S, M is at least one element selected from the group consisting of transition metals other than Co and Ni, Sn, Ge, Na, K, B, C, Si, P, S, Zn, Ga, Bi, Group 2 elements, and rare earths, -0.05 ≦ x ≦ 0.05, 0 < a ≦ 0.25, 0 < b ≦ 0.05, 0 ≦ m ≦ 0.04, 0 ≦ f ≦ 0.05, and a surface-modified lithium-containing composite oxide for a positive electrode of a lithium-ion secondary battery is disclosed.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] In a battery having a conventionally used positive electrode active material, the battery resistance may increase after repeating charge and discharge cycles, and it is desired that the increase in battery resistance be suppressed even after charge and discharge cycles, that is, the cycle characteristics be improved.

[0007] The present disclosure has been made in view of the above circumstances, and an object thereof is to provide a positive electrode active material capable of improving cycle characteristics when used in a battery, a battery including the positive electrode active material, and a method for manufacturing the positive electrode active material.

Means for Solving the Problems

[0008] Means for solving the above problems include the following aspects. <1> Li x Ni a Co b Mn c M d A positive electrode active material having a composition represented by O2, A positive electrode active material in which, in a TEM-EDX image of a cross section of a particle of the positive electrode active material, when an internal region that is 70% of the radius from the center of the particle is divided into 10 nm square regions, the proportion of the region in which the concentration of the element represented by M is 10 mass % or more is 1.0% or more of the entire region. (In the above composition, 0.1≦x≦1.5, 0.5≦a≦1.0, 0≦b≦0.3, 0≦c≦0.3, a+b+c=1.0, 0.0005≦d≦0.05, and M represents at least one element selected from the group consisting of Ta, Al, Ba, Pr, La, Y, Sr, Ce, Se, Hf, Rh, and Zr.) <2> The element represented by M is at least one element selected from the group consisting of Ta, Al, Ba, Pr, and La. <1> The positive electrode active material according to claim 1, <3> The element represented by M is La. <2> The positive electrode active material according to claim 1, <4> The ratio of the region in which the concentration of the element represented by M is 10 mass% or more is 3.0% or more with respect to the entire region. <1> ~ <3> 13. The positive electrode active material according to claim 12 . <5> <1> ~ <4> 13. A battery comprising the positive electrode active material according to claim 12. <6> A step of preparing a solution A in which a raw material containing an element represented by M is dissolved; A step of preparing a solution B in which raw materials each containing Ni, Co, and Mn are dissolved; adding said solution A to an alkaline solution to precipitate hydroxides; adding solution B to the alkaline solution in which the hydroxide has been precipitated to cause precipitation; collecting a precipitate from the alkaline solution; mixing the precipitate with a raw material containing Li to obtain a mixture; calcining the mixture; and The method for producing a positive electrode active material comprising the steps of: (Note that M represents at least one element selected from the group consisting of Ta, Al, Ba, Pr, La, Y, Sr, Ce, Se, Hf, Rh, and Zr.) Effect of the Invention

[0009] According to the present disclosure, there are provided a positive electrode active material capable of improving cycle characteristics when used in a battery, a battery including the positive electrode active material, and a method for producing the positive electrode active material. [Brief description of the drawings]

[0010] [Figure 1] FIG. 2 is a schematic cross-sectional view for explaining a method for measuring an uneven distribution rate of M element in a positive electrode active material according to an embodiment of the present disclosure. [Diagram 2] FIG. 2 is a schematic cross-sectional view for explaining a method for measuring an uneven distribution rate of M element in a positive electrode active material according to an embodiment of the present disclosure. [Diagram 3] 1 is a schematic cross-sectional view for explaining a method for producing a positive electrode active material according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, an embodiment that is an example of the present disclosure will be described. These descriptions and examples are merely illustrative of the embodiment, and do not limit the scope of the invention. In the present specification, the upper or lower limit of one numerical range may be replaced with the upper or lower limit of another numerical range. In addition, in the present specification, the upper or lower limit of the numerical range may be replaced with a value shown in the examples.

[0012] Each component may contain multiple types of the corresponding substance. When referring to the amount of each component in a composition, if there are multiple substances corresponding to each component in the composition, unless otherwise specified, it means the total amount of those multiple substances present in the composition. The term "process" includes not only independent processes, but also processes that cannot be clearly distinguished from other processes as long as the intended effect of the process is achieved.

[0013] <Cathode active material> The positive electrode active material according to the embodiment of the present disclosure is Li x Ni a Co b Mn c M d It has a composition represented by O2. In a TEM-EDX (Transmission Electron Microscope-Energy Dispersive X-ray Spectroscopy) image of a cross section of a particle of the positive electrode active material, when an internal region that is 70% of the radius from the center of the particle is divided into regions of 10 nm square, the proportion of the region in which the concentration of an element represented by M is 10 mass% or more (hereinafter also simply referred to as the "M element uneven distribution rate") is 1.0% or more with respect to the entire region. (In the above composition, 0.1≦x≦1.0, 0.5≦a≦1.0, 0≦b≦0.3, 0≦c≦0.3, a+b+c=1.0, 0.0005≦d≦0.05, and M represents at least one element selected from the group consisting of Ta, Al, Ba, Pr, La, Y, Sr, Ce, Se, Hf, Rh, and Zr.)

[0014] Conventionally, an additive element (i.e., an element represented by M above, hereinafter also referred to as "M element") has been added to a positive electrode active material for the purpose of improving the resistance characteristics of a battery, etc. Note that, conventionally, this additive element (M element) was unevenly distributed on the surface of particles of the positive electrode active material (for example, forming a coating layer on the surface). In batteries using such conventional positive electrode active materials, the battery resistance may increase after repeated charge-discharge cycles. Therefore, it is desired to suppress the increase in battery resistance even after repeated charge-discharge cycles, that is, to improve cycle characteristics.

[0015] The positive electrode active material according to the embodiment of the present disclosure has an M element uneven distribution rate of 1.0% or more, that is, the additive element (M element) is sufficiently dispersed and present in the inner region of the particles of the positive electrode active material. The presence of a sufficient amount of M element in the inner region greatly improves the stabilization effect of the layered structure, and as a result, Ni mixing (cation mixing) into the Li layer during charging and discharging in the battery is suppressed, and the inhibition of the movement of Li ions during charging and discharging is suppressed. This makes it possible to improve the cycle characteristics of a battery using the positive electrode active material.

[0016] Next, the positive electrode active material according to an embodiment of the present disclosure will be described in detail.

[0017] (composition) The positive electrode active material according to the embodiment of the present disclosure is Li x Ni a Co b Mn c M d It has a composition represented by O2. (In the above composition, 0.1≦x≦1.5, 0.5≦a≦1.0, 0≦b≦0.3, 0≦c≦0.3, a+b+c=1.0, 0.0005≦d≦0.05, and M represents at least one element selected from the group consisting of Ta, Al, Ba, Pr, La, Y, Sr, Ce, Se, Hf, Rh, and Zr.)

[0018] In the composition of the positive electrode active material, from the viewpoint of the resistance characteristics of the battery, the Li ratio x is from 0.1 to 1.5, preferably from 0.3 to 1.4, and more preferably from 0.5 to 1.2. The ratio a of Ni is 0.5 or more and 1.0 or less, preferably 0.6 or more and 0.9 or less, and more preferably 0.7 or more and 0.8 or less. The ratio b of Co is 0 or more and 0.3 or less, preferably 0 or more and 0.2 or less, and more preferably 0.1 or more and 0.2 or less. The ratio c of Mn is 0 or more and 0.3 or less, preferably 0 or more and 0.2 or less, and more preferably 0.1 or more and 0.2 or less. The total ratio of Ni, Co and Mn (a+b+c) is 1.0.

[0019] The positive electrode active material contains at least one element selected from the group consisting of Ta, Al, Ba, Pr, La, Y, Sr, Ce, Se, Hf, Rh, and Zr as an additive element (M element). By containing the above-listed elements as additive elements, it is possible to improve the cycle characteristics of the battery, that is, the degree of suppression of an increase in battery resistance after repeated charge and discharge cycles. From the viewpoint of further improving cycle characteristics, the positive electrode active material preferably contains, as an additive element (M element), at least one element selected from the group consisting of Ta, Al, Ba, Pr, and La, and more preferably contains La.

[0020] In the composition of the positive electrode active material, the ratio d of M is 0.0005 or more and 0.05 or less, preferably 0.001 or more and 0.04 or less, and more preferably 0.005 or more and 0.02 or less.

[0021] (M element distribution rate) In the positive electrode active material according to an embodiment of the present disclosure, when an internal region that is 70% of the radius from the center of the particle is divided into 10 nm square regions in a TEM-EDX image of a cross section of a particle of the positive electrode active material, the proportion of the regions where the concentration of an element represented by M is 10 mass % or more (M element uneven distribution rate) is 1.0% or more with respect to the entire region. An M element uneven distribution rate of 1.0% or more means that the additive element (M element) is sufficiently dispersed and present even in the inner region of the particles of the positive electrode active material, thereby enabling the cycle characteristics of a battery using the positive electrode active material to be improved.

[0022] From the viewpoint of further improving the cycle characteristics of the battery, the M element uneven distribution rate is preferably 3.0% or more, and more preferably 4.0% or more. On the other hand, the upper limit of the M element uneven distribution rate is not particularly limited, but from the viewpoint of suppressing the amount of the added element (M element), it is preferably 15.0% or less, and more preferably 10.0% or less.

[0023] [Measurement of uneven distribution of M element] A method for measuring the uneven distribution rate of the M element in the particles of the positive electrode active material will be described. First, a TEM-EDX image of a cross section of a particle of a positive electrode active material is taken. Here, a schematic diagram of the cross section image is shown in FIG. 1. A positive electrode active material particle 2 shown in FIG. 1 contains a particle 4B of an M element inside. In the cross section image of this positive electrode active material particle 2, an internal region that is 70% of the radius from the center (i.e., a region excluding a surface layer region that is 30% of the radius from the surface, the inner region surrounded by a dotted line in FIG. 1) is observed. This internal region is divided into regions of 10 nm square as shown in FIG. 2, and the concentration of the M element is measured for each region. However, in the 10 nm square region present at the edge of the internal region (the inner region surrounded by the dotted line in FIG. 1), there is a region that is not filled with the positive electrode active material particles 2. Therefore, of the 10 nm square regions, the regions that are not completely filled with the positive electrode active material particles 2 are excluded from the measurement, and only the regions that are entirely filled with the positive electrode active material particles 2 are measured. Then, the percentage of the regions having an M element concentration of 10 mass % or more among all the regions divided into 10 nm squares (excluding regions not filled with positive electrode active material particles 2) is calculated. This percentage is calculated by the following formula. The ratio = number of regions in which the concentration of M element is 10 mass % or more / number of all regions divided into 10 nm squares in the internal region (excluding regions not filled with positive electrode active material particles) x 100 This ratio is calculated for the cross-sectional images of 10 particles of the positive electrode active material, and the arithmetic average value is taken as the M element uneven distribution ratio.

[0024] <Method of manufacturing positive electrode active material> Next, a method for producing a positive electrode active material according to an embodiment of the present disclosure will be described. The positive electrode active material according to the embodiment of the present disclosure described above can be produced by the method for producing a positive electrode active material according to an embodiment of the present disclosure described below.

[0025] The method for producing a positive electrode active material according to an embodiment of the present disclosure includes the following steps (1) to (7). (1) A step of preparing a solution A in which a raw material containing an element represented by M is dissolved (Note that M represents at least one element selected from the group consisting of Ta, Al, Ba, Pr, La, Y, Sr, Ce, Se, Hf, Rh, and Zr.) (2) A step of preparing a solution B in which raw materials each containing Ni, Co, and Mn are dissolved. (3) Adding solution A to an alkaline solution to precipitate hydroxide (4) A process of adding solution B to the alkaline solution in which the hydroxide has precipitated to cause precipitation (5) A process for collecting the precipitate from the alkaline solution. (6) A step of mixing the precipitate with a raw material containing Li to obtain a mixture. (7) Firing the mixture

[0026] (1) A step of preparing a solution A in which a raw material containing an element represented by M is dissolved First, solution A is prepared by dissolving a raw material containing an additive element (M element, i.e., at least one element selected from the group consisting of Ta, Al, Ba, Pr, La, Y, Sr, Ce, Se, Hf, Rh, and Zr). For example, a raw material containing element M can be dissolved in a solvent such as water to prepare solution A. The concentration of solution A is preferably in the range of, for example, 5 to 30 mass %.

[0027] Examples of raw materials containing M elements include sulfates such as Ta(SO4)2 as raw materials containing Ta, sulfates such as Al2(SO4)3 as raw materials containing Al, sulfates such as BaSO4 as raw materials containing Ba, sulfates such as Pr2(SO4)3 as raw materials containing Pr, and sulfates such as La2(SO4)3 as raw materials containing La. Also, commonly used raw materials can be used as raw materials containing other M elements, and examples thereof include sulfates containing each M element.

[0028] (2) A step of preparing a solution B in which raw materials each containing Ni, Co, and Mn are dissolved. A solution B is prepared by dissolving a raw material containing Ni, a raw material containing Co, and a raw material containing Mn. For example, solution B can be prepared by dissolving a raw material containing Ni, a raw material containing Co, and a raw material containing Mn in a solvent such as water. The concentration of solution B is preferably in the range of, for example, 10 to 40 mass %. The ratio of Ni / Co / Mn is preferably 1.0 / 0.8-1.2 / 0.8-1.2 (atm %) with respect to Ni1.

[0029] Examples of raw materials containing Ni include sulfates such as NiSO4, raw materials containing Co include sulfates such as CoSO4, and raw materials containing Mn include sulfates such as MnSO4.

[0030] (3) Adding solution A to an alkaline solution to precipitate hydroxide Next, solution A (a solution in which a raw material containing the M element is dissolved) is added to the alkaline solution to precipitate hydroxides.

[0031] Here, a method for producing a positive electrode active material according to an embodiment of the present disclosure will be described with reference to Fig. 3. By adding solution A to an alkaline solution to precipitate hydroxide, nuclei 4A of the additive (element M) can be formed as shown in (a) of Fig. 3.

[0032] In this step, for example, an aqueous NH3 solution is substituted with nitrogen, the pH is adjusted to alkaline, and while controlling the pH at a constant value (for example, pH 10 to 12), solution A is added dropwise to precipitate hydroxide (i.e., additive nuclei 4A in FIG. 3).

[0033] (4) A process of adding solution B to the alkaline solution in which the hydroxide has precipitated to cause precipitation Next, solution B is added to the alkaline solution in which the hydroxide (core 4A of the additive) has precipitated to obtain a precipitate. By further adding solution B to the alkaline solution in which the hydroxide has precipitated, particles 20 in which hydroxide 2 containing Ni, Co, and Mn is generated are crystallized around core 4A of the additive (M element) as shown in (b) of FIG. 3, and the particles 20 are obtained as a precipitate.

[0034] In this step, for example, the alkaline solution in which the hydroxide has been precipitated is further controlled to a constant pH (for example, pH 10 to 12) while solution B and NH3 are added dropwise, whereby the hydroxide of the transition metal is precipitated.

[0035] (5) A process for collecting the precipitate from the alkaline solution. The precipitate is then collected from the alkaline solution. Examples of methods for collecting the precipitate particles include filtration and washing with water. First, the precipitate (particles) is taken out by filtration, washed with water, and the washed liquid is further filtered to take out the precipitate (particles). The precipitate (particles) after washing with water may be further dried.

[0036] (6) A step of mixing the precipitate with a raw material containing Li to obtain a mixture. 3(c), the collected precipitate (i.e., particles 20 in which hydroxides 2 containing Ni, Co, and Mn are generated around cores 4A of the additive) is mixed with a raw material 6 containing Li. For example, the collected precipitate particles and the raw material containing Li can be mixed in a mortar. Examples of raw materials containing Li include Li2CO3 and LiOH.

[0037] (7) Firing the mixture Next, the mixture of the collected precipitate (i.e., particles 20) and the Li-containing raw material 6 is fired. For example, the mixture can be fired in a firing furnace (such as a muffle furnace). The firing conditions can be, for example, a temperature of 800°C to 1100°C in an oxygen atmosphere for a time of 5 hours to 20 hours.

[0038] In addition, after the above-mentioned calcination (hereinafter referred to as "first calcination"), it is preferable to carry out calcination at a lower temperature (hereinafter referred to as "second calcination"). For example, the particles that have been subjected to the first calcination are crushed, and a reducing agent (e.g., ascurbic acid) is mixed with the crushed particles, and the mixture is calcined in a calcination furnace (e.g., muffle furnace) at a temperature lower than that of the first calcination. Conditions for the second calcination can be, for example, a temperature of 400°C to 600°C in an oxygen atmosphere for a time of 5 hours to 20 hours.

[0039] By passing through the step of firing the mixture, the additive 4B diffuses inside the collected precipitate (i.e., particles 20 in which hydroxide 2 containing Ni, Co, and Mn is formed around a core 4A of the additive), and the additive element (M element) is sufficiently dispersed and present even in the inner region of the particle of the positive electrode active material, as shown in (d) of FIG. 3. As a result, the uneven distribution rate of M element in the positive electrode active material can be controlled within the above-mentioned range.

[0040] <Battery> The battery according to the embodiment of the present disclosure includes the positive electrode active material according to the embodiment of the present disclosure. The battery includes, for example, a negative electrode, a positive electrode, a separator, and an electrolyte. The battery according to the embodiment of the present disclosure is preferably a liquid battery including a liquid electrolyte. Alternatively, the battery may be a solid battery including a solid electrolyte.

[0041] (electrolyte) The battery according to the embodiment of the present disclosure is preferably a liquid battery having an electrolyte. ·solvent The electrolytic solution contains a solvent (non-aqueous solvent) and an electrolyte. Examples of the solvent (non-aqueous solvent) include N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium bis(fluorosulfonyl)imide (DEME), 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EMI), and 1-ethyl-2,3-dimethylimidazolium bis(fluorosulfonyl)imide (DEMI-FSI).

[0042] ·Electrolyte The electrolyte in the electrolytic solution may be, for example, a Li salt, such as lithium bis(fluorosulfonyl)imide (LiFSI), LiPF6 (lithium hexafluorophosphate), lithium tetrafluoroborate (LiBF4), or Li[N(CF3SO2)2]. The amount of the electrolyte may be, for example, 1.0 to 2.0 mol / L, and is preferably 1.0 to 1.5 mol / L.

[0043] The electrolytic solution may contain various additives, such as a thickener, a film-forming agent, a gas generating agent, etc., in addition to the solvent and the electrolyte. The electrolyte is typically a non-aqueous electrolytic solution that is liquid at room temperature (e.g., 25±10°C). The electrolytic solution is typically liquid in the environment in which the battery is used (e.g., a temperature environment of -20 to +60°C).

[0044] (positive electrode) The positive electrode active material includes a positive electrode active material according to an embodiment of the present disclosure, the details of which have already been described and will not be repeated here.

[0045] Examples of the conductive material include carbon materials. The electrolyte may be a solid electrolyte or a liquid electrolyte. The solid electrolyte may be an organic solid electrolyte such as a gel electrolyte, or an inorganic solid electrolyte such as an oxide solid electrolyte or a sulfide solid electrolyte. The liquid electrolyte (electrolytic solution) contains, for example, a supporting salt such as LiPF6 and a solvent such as a carbonate-based solvent. Examples of the binder include a rubber-based binder and a fluoride-based binder.

[0046] In addition, the positive electrode preferably contains a solid electrolyte selected from the group of solid electrolytes consisting of sulfide solid electrolytes, oxide solid electrolytes, and halide solid electrolytes in addition to the positive electrode active material, and a mode in which at least a part of the surface of the positive electrode active material is coated with a sulfide solid electrolyte, an oxide solid electrolyte, or a halide solid electrolyte is more preferable. As the halide solid electrolyte that coats at least a part of the surface of the positive electrode active material, Li 6-(4-x)b (Ti 1-x Al x ) b F6 (0 < x < 1, 0 < b ≤ 1.5) [LTAF electrolyte] is preferable.

[0047] The positive electrode current collector conducts electricity for the positive electrode active material layer. Examples of the positive electrode current collector include stainless steel, aluminum, nickel, iron, titanium, carbon, etc., and an aluminum alloy foil or an aluminum foil is preferable. The aluminum alloy foil and the aluminum foil may be manufactured using powder. The shape of the positive electrode current collector is, for example, foil-shaped or mesh-shaped.

[0048] (Negative electrode) The negative electrode active material layer contains at least a negative electrode active material. The negative electrode active material layer may further contain at least one of a conductive material, an electrolyte, and a binder. Examples of the negative electrode active material include metal active materials such as Li and Si, carbon active materials such as graphite, and oxide active materials such as Li4Ti5O 12 etc. The shape of the negative electrode current collector is, for example, foil-shaped or mesh-shaped. The conductive material, the electrolyte, and the binder are the same as those described above.

[0049] The electrolyte layer is disposed between the positive electrode active material layer and the negative electrode active material layer and contains at least an electrolyte. The electrolyte may be a solid electrolyte or a liquid electrolyte. As the electrolyte layer, a solid electrolyte layer is preferable. The electrolyte layer may have a separator.

[0050] The negative electrode current collector conducts current collection for the negative electrode active material layer. Examples of materials for the negative electrode current collector include metals such as copper, SUS, and nickel. Examples of the shape of the negative electrode current collector include foil shape and mesh shape.

[0051] (Solid-state battery) As described above, the battery according to the embodiment of the present disclosure is preferably a liquid battery having a liquid electrolyte. On the other hand, the battery according to the embodiment of the present disclosure may also be a solid-state battery having a solid electrolyte. Therefore, the solid-state battery will be described below.

[0052] ·Solid electrolyte The solid-state battery preferably includes at least one solid electrolyte species selected from the group of solid electrolytes consisting of sulfide solid electrolytes, oxide solid electrolytes, and halide solid electrolytes as the solid electrolyte.

[0053] As the sulfide solid electrolyte, it is preferable to contain sulfur (S) as the main component of the anion element, and further preferably contain, for example, Li element, A element, and S element. The A element is at least one selected from the group consisting of P, As, Sb, Si, Ge, Sn, B, Al, Ga, and In. The sulfide solid electrolyte may further contain at least one of O and halogen elements. Examples of the halogen element (X) include F, Cl, Br, I, etc. The composition of the sulfide solid electrolyte is not particularly limited, and examples include xLi2S·(100-x)P2S5 (70≦x≦80), yLiI·zLiBr·(100-y-z)(xLi2S·(1-x)P2S5) (0.7≦x≦0.8, 0≦y≦30, 0≦z≦30). The sulfide solid electrolyte may have a composition represented by the following general formula (1). Li 4-x Ge 1-x P x S4(0<x<1) ··· Formula (1) In formula (1), at least a part of Ge may be substituted with at least one selected from the group consisting of Sb, Si, Sn, B, Al, Ga, In, Ti, Zr, V and Nb. At least a part of P may be substituted with at least one selected from the group consisting of Sb, Si, Sn, B, Al, Ga, In, Ti, Zr, V and Nb. At least a part of Li may be substituted with at least one selected from the group consisting of Na, K, Mg, Ca and Zn. At least a part of S may be substituted with a halogen. The halogen is at least one of F, Cl, Br and I.

[0054] The oxide solid electrolyte preferably contains oxygen (O) as a main component of an anion element, and may contain, for example, Li, Q element (Q represents at least one of Nb, B, Al, Si, P, Ti, Zr, Mo, W, and S), and O. Examples of the oxide solid electrolyte include garnet-type solid electrolytes, perovskite-type solid electrolytes, Nasicon-type solid electrolytes, Li-PO-based solid electrolytes, and Li-BO-based solid electrolytes. Examples of the garnet-type solid electrolyte include Li7La3Zr2O 12 , Li 7-x La3(Zr 2-x Nb x )O 12 (0≦x≦2), Li5La3Nb2O 12 Examples of the perovskite-type solid electrolyte include (Li,La)TiO3, (Li,La)NbO3, (Li,Sr)(Ta,Zr)O3, etc. Examples of the Nasicon-type solid electrolyte include Li(Al,Ti)(PO4)3, Li(Al,Ga)(PO4)3, etc. Examples of the Li-PO-based solid electrolyte include Li3PO4 and LIPON (a compound in which part of O in Li3PO4 is replaced with N), and examples of the Li-BO-based solid electrolyte include Li3BO3 and a compound in which part of O in Li3BO3 is replaced with C, etc.

[0055] As the halide solid electrolyte, a solid electrolyte containing Li, M and X (M represents at least one of Ti, Al and Y, and X represents F, Cl or Br) is suitable. 6-3zY z X6 (where X represents Cl or Br, and z satisfies 0 < z < 2), Li 6-(4-x)b (Ti 1-x Al x ) b F6 (0 < x < 1, 0 < b ≤ 1.5) is preferred. Li 6-3z Y z Among X6, Li3YX6 (where X represents Cl or Br) is more preferred in terms of excellent lithium ion conductivity, and further Li3YCl6 is preferred. Also, Li 6-(4-x)b (Ti 1-x Al x ) b F6 (0 < x < 1, 0 < b ≤ 1.5) is preferably included together with a solid electrolyte such as a sulfide solid electrolyte, for example, from the viewpoint of suppressing oxidative decomposition of the sulfide solid electrolyte.

[0056] · Solid battery structure The structure of the solid battery has a laminated structure of a positive electrode / solid electrolyte layer / negative electrode. The solid battery includes a so-called all-solid battery using a solid electrolyte as an electrolyte, and the solid electrolyte may contain an electrolytic solution of less than 10% by mass with respect to the total amount of the electrolyte. Note that the solid electrolyte may be a composite solid electrolyte including an inorganic solid electrolyte and a polymer electrolyte.

[0057] The positive electrode has a positive electrode active material layer and a current collector, and the negative electrode has a negative electrode active material layer and a current collector. The solid electrolyte layer may have a single-layer structure or a multi-layer structure of two or more layers. The solid battery may have, for example, a cross-sectional structure, and the solid electrolyte layer may have a two-layer structure. The solid battery has a negative electrode including a negative electrode current collector and a negative electrode active material layer, a solid electrolyte layer, and a positive electrode including a positive electrode current collector and a positive electrode active material layer. The negative electrode active material layer includes a negative electrode active material, a conductive auxiliary agent, and a binder. The positive electrode active material layer includes a coated positive electrode active material, a conductive auxiliary agent, and a binder, and the coated positive electrode active material has the surface of the positive electrode active material coated with an LTAF electrolyte or a LiNbO3 electrolyte. The solid-state battery may be configured by sealing the end faces (side faces) of the laminated structure of the positive electrode / solid electrolyte layer / negative electrode with resin. The electrode current collector may have a buffer layer, an elastic layer, or a PTC (Positive Temperature Coefficient) thermistor layer disposed on the surface.

[0058] (battery) The laminated battery in the present disclosure is typically a lithium-ion secondary battery. Examples of uses of the battery include power sources for vehicles such as hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), electric vehicles (BEVs), gasoline-powered vehicles, and diesel-powered vehicles. In particular, the battery is preferably used as a driving power source for hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), or electric vehicles (BEVs). The battery in the present disclosure may also be used as a power source for moving objects other than vehicles (e.g., railways, ships, and aircraft), and may also be used as a power source for electrical appliances such as information processing devices.

[0059] The present disclosure is not limited to the above-described embodiments. The above-described embodiments are merely examples, and anything that has substantially the same configuration as the technical idea described in the claims of the present disclosure and exhibits similar effects is included in the technical scope of the present disclosure. EXAMPLES

[0060] The present disclosure will be described below based on examples, but the present disclosure is not limited to these examples in any way.

[0061] <Example 1> (Synthesis of positive electrode active material) Li x Ni a Co b Mn c M d A positive electrode active material having a composition represented by O2, in which x, a, b, c, and d are in the ratios shown in Table 1, and the element represented by M is an element shown in Table 1, was synthesized by the method of the present disclosure.

[0062] ·Raw material 1 solution Al2(SO4)3 was dissolved in ion-exchanged water to obtain a solution of raw material 1. The concentration of the aqueous solution was adjusted to the range of 5 to 30 mass %. ·Raw material 2 solution NiSO4, CoSO4, and MnSO4 were dissolved in ion-exchanged water to obtain a solution of raw material 2. The ratio of Ni / Co / Mn was 1 / 1 / 1 (atm %), and the concentration of the aqueous solution was 30 mass %.

[0063] Crystallization A certain amount of NH3 aqueous solution was placed in a reaction vessel, and the atmosphere was replaced with nitrogen while stirring with a stirrer. NaOH was added to the reaction vessel to make the pH alkaline. Next, while controlling the pH inside the reaction vessel at a constant value (pH 10-12), the solution of raw material 1 was added dropwise to precipitate hydroxides. Furthermore, while controlling the pH inside the reaction vessel at a constant value (pH 10-12), the solution of raw material 2 and NH3 were added dropwise to precipitate transition metal hydroxides.

[0064] Washing, filtering, drying The precipitated transition metal hydroxide was removed by filtration, and ion-exchanged water was added thereto, and the mixture was stirred with a spoon to disperse the hydroxide, and then washed with water. The washed liquid was then filtered to remove the transition metal hydroxide. The filtered transition metal hydroxide was then dried at 120° C. for 16 hours to evaporate the water.

[0065] Lithium raw material mixing The dried transition metal hydroxide was mixed with Li2CO3 and LiOH as Li raw materials in a mortar.

[0066] Firing 1 A mixture of the transition metal hydroxide and the Li raw material was calcined in a calcination furnace (muffle furnace) at 800 to 1100° C. in an oxygen atmosphere for 10 hours. Firing 2 The particles obtained in Firing 1 were crushed, and the crushed particles were mixed with ascurbic acid (reducing agent) and baked in a baking furnace (muffle furnace) at 400 to 600° C. in an oxygen atmosphere for 10 hours. In this way, the positive electrode active material of Example 1 was obtained.

[0067] <Examples 2 to 4> The positive electrode active materials of each Example were obtained in the same manner as in Example 1, except that the additive used in the raw material 1 solution in Example 1 was changed from Al2(SO4)3 to BaSO4 (Example 2), Pr2(SO4)3 (Example 3), and La2(SO4)3 (Example 4).

[0068] <Comparative Example 1> (Synthesis of positive electrode active material) Li x Ni a Co b Mn c A positive electrode active material having a composition represented by O2, in which x, a, b, and c are in the ratios shown in Table 1, was synthesized.

[0069] ·Raw material 2 solution NiSO4, CoSO4, and MnSO4 were dissolved in ion-exchanged water to obtain a solution of raw material 2. The ratio of Ni / Co / Mn was 1 / 1 / 1 (atm %), and the concentration of the aqueous solution was 30 mass %.

[0070] Crystallization A certain amount of NH3 aqueous solution was placed in a reaction vessel, and the atmosphere was replaced with nitrogen while stirring with a stirrer. NaOH was added to the reaction vessel to make the pH alkaline. Next, while controlling the pH inside the reaction vessel at a constant value (pH 10 to 12), the raw material 2 solution and NH3 were dropped to precipitate transition metal hydroxides.

[0071] Washing, filtering, drying The precipitated transition metal hydroxide was removed by filtration, and ion-exchanged water was added thereto, and the mixture was stirred with a spoon to disperse the hydroxide, and then washed with water. The washed liquid was then filtered to remove the transition metal hydroxide. The filtered transition metal hydroxide was then dried at 120° C. for 16 hours to evaporate the water.

[0072] Lithium raw material mixing The dried transition metal hydroxide was mixed with Li2CO3 and LiOH as Li raw materials in a mortar.

[0073] Firing 1 A mixture of the transition metal hydroxide and the Li raw material was calcined in a calcination furnace (muffle furnace) at 800 to 1100° C. in an oxygen atmosphere for 10 hours. Firing 2 The particles obtained in Firing 1 were crushed, and the crushed particles were mixed with ascurbic acid (reducing agent) and fired in a firing furnace (muffle furnace) at 400 to 600° C. in an oxygen atmosphere for 10 hours. In this way, a positive electrode active material of Comparative Example 1 was obtained.

[0074] <Comparative Example 2> (Synthesis of positive electrode active material) Li x Ni a Co b Mn c M d A positive electrode active material having a composition represented by O2, in which x, a, b, c, and d are in the ratios shown in Table 1, and in which the element represented by M is an element shown in Table 1, was synthesized by a conventional method.

[0075] ·Raw material 2 solution NiSO4, CoSO4, and MnSO4 were dissolved in ion-exchanged water to obtain a solution of raw material 2. The ratio of Ni / Co / Mn was 1 / 1 / 1 (atm %), and the concentration of the aqueous solution was 30 mass %.

[0076] Crystallization A certain amount of NH3 aqueous solution was placed in a reaction vessel, and the atmosphere was replaced with nitrogen while stirring with a stirrer. NaOH was added to the reaction vessel to make the pH alkaline. Next, while controlling the pH inside the reaction vessel at a constant value (pH 10 to 12), the raw material 2 solution and NH3 were dropped to precipitate transition metal hydroxides.

[0077] Washing, filtering, drying The precipitated transition metal hydroxide was removed by filtration, and ion-exchanged water was added thereto, and the mixture was stirred with a spoon to disperse the hydroxide, and then washed with water. The washed liquid was then filtered to remove the transition metal hydroxide. The filtered transition metal hydroxide was then dried at 120° C. for 16 hours to evaporate the water.

[0078] Mixing of Li raw material and additive elements The dried transition metal hydroxide, Li2CO3 and LiOH as Li raw materials, and Ta(SO4)2 as a compound containing an additive element (M element = Ta) were mixed in a mortar.

[0079] Firing 1 A mixture of the transition metal hydroxide and the Li raw material was calcined in a calcination furnace (muffle furnace) at 800 to 1100° C. in an oxygen atmosphere for 10 hours. Firing 2 The particles obtained in Firing 1 were crushed, and the crushed particles and ascurbic acid (reducing agent) were mixed and fired in a firing furnace (muffle furnace) at 400 to 600° C. in an oxygen atmosphere for 10 hours. In this way, a positive electrode active material of Comparative Example 2 was obtained.

[0080] [Measurement of uneven distribution of M element] Cross-sectional TEM-EDX images were taken for the particles of the positive electrode active material obtained in Examples 1 to 4 and Comparative Example 2. A schematic diagram of the cross-sectional image is shown in FIG. 1. The positive electrode active material particle 2 shown in FIG. 1 contains a particle 4B of the M element inside. In the cross-sectional image of this positive electrode active material particle 2, the internal region that is 70% of the radius from the center (i.e., the region excluding the surface layer region that is 30% of the radius from the surface, the inner region surrounded by the dotted line in FIG. 1) is observed. This internal region was divided into regions of 10 nm square as shown in FIG. 2, and the concentration of the M element was measured for each region. However, in the 10 nm square region present at the edge of the inner region, there is a region that is not filled with the positive electrode active material particles 2. Therefore, only the region that is entirely filled with the positive electrode active material particles 2 among the 10 nm square regions was measured. Then, the percentage of the regions having an M element concentration of 10 mass % or more among all the regions divided into 10 nm squares (excluding regions not filled with positive electrode active material particles 2) was calculated. This percentage was calculated by the following formula. The ratio = number of regions in which the concentration of M element is 10 mass % or more / number of all regions divided into 10 nm squares in the internal region (excluding regions not filled with positive electrode active material particles) x 100 This calculation of the ratio was performed for the cross-sectional images of 10 particles of the positive electrode active material, and the arithmetic average value was taken as the uneven distribution ratio of element M. The results are shown in Table 1.

[0081] [Cell Preparation] A cell was fabricated using the positive electrode active material obtained in each of the Examples and Comparative Examples. Cell configuration Wound cylinder Positive electrode composition: Positive electrode active material / acetylene black (conductive material) / polyvinylidene fluoride = 88 / 10 / 2 (mass%) Negative electrode composition: natural graphite / styrene butadiene rubber (SBR) / carboxymethyl cellulose (CMC) Electrolyte composition: electrolyte = LiPF6 (1M), solvent = ethylene carbonate (EC) / dimethyl carbonate (DMC) / ethyl methyl carbonate (EMC) = 3 / 4 / 3 (volume%)

[0082] Preparation of electrodes A positive electrode and a negative electrode were applied onto a current collector using a film applicator with a film thickness adjustment function (All Good Co., Ltd.), and the applied film was dried in a dryer at 80°C for 5 minutes to prepare a cell.

[0083] [Measurement of resistance increase rate after cycling] The battery resistance of the cells obtained in each of the Examples and Comparative Examples was measured before and after cycling under the following test conditions. The results of the ratio of the battery resistance after cycling (resistance increase rate (%)) when the battery resistance before cycling is set to "100%" are shown in Table 1. It can be said that the closer the resistance increase rate is to 100%, the better the battery characteristics are. Test conditions: Charge and discharge 300 cycles between SOC 0% and 100% at 60°C and 2C rate.

[0084] [Table 1]

[0085] As shown in Table 1, in Examples 1 to 4 in which the uneven distribution rate of the M element is 1.0% or more, the resistance increase rate after cycling can be reduced compared to Comparative Example 2 in which the uneven distribution rate of the M element is less than 1.0% and Comparative Example 1 which does not contain the additive element (M element). [Explanation of symbols]

[0086] 2 Positive electrode active material particles 4A Nuclei of M elements 4B M element particles 20 particles

Claims

1. Li ｘ Ni ａ Co ｂ Mn ｃ M ｄ O ２ A positive electrode active material having a composition represented by the formula: A positive electrode active material in which, in a TEM-EDX image of a cross section of a particle of the positive electrode active material, an internal region that is 70% of the radius from the center of the particle is divided into 10 nm square regions, the proportion of the region in which the concentration of the element represented by M is 10 mass % or more is 1.0% or more of the entire region. (In the above composition, 0.1≦x≦1.5, 0.5≦a≦1.0, 0≦b≦0.3, 0≦c≦0.3, a+b+c=1.0, 0.0005≦d≦0.05, and M represents at least one element selected from the group consisting of Ta, Al, Ba, Pr, La, Y, Sr, Ce, Se, Hf, Rh, and Zr.)

2. 2. The positive electrode active material according to claim 1, wherein the element represented by M is at least one element selected from the group consisting of Ta, Al, Ba, Pr, and La.

3. The positive electrode active material according to claim 2 , wherein the element represented by M is La.

4. 2 . The positive electrode active material according to claim 1 , wherein a ratio of the region in which the concentration of the element represented by M is 10 mass % or more is 3.0 mass % or more with respect to the entire region.

5. A battery comprising the positive electrode active material according to any one of claims 1 to 4.

6. A step of preparing a solution A in which a raw material containing an element represented by M is dissolved; A step of preparing a solution B in which raw materials each containing Ni, Co, and Mn are dissolved; adding said solution A to an alkaline solution to precipitate hydroxides; adding solution B to the alkaline solution in which the hydroxide has been precipitated to cause precipitation; collecting a precipitate from the alkaline solution; A step of mixing the precipitate with a raw material containing Li to obtain a mixture; calcining the mixture; The method for producing a positive electrode active material comprising the steps of: (Note that M represents at least one element selected from the group consisting of Ta, Al, Ba, Pr, La, Y, Sr, Ce, Se, Hf, Rh, and Zr.)

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