Positive electrode active material, battery, and method for 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 in 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[[ID=2I]] (1-a-b-m) , (Co (1-a-b-m) Ni a Al b M m )[[ID=ZI]] 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-discharge cycles, and it is desired to suppress the increase in battery resistance even after charge-discharge cycles, that is, to improve cycle characteristics.

[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, wherein Regarding the TEM-EDX image of the cross-section of the particles of the positive electrode active material, when the internal region having a radius of 70% from the center of the particles is divided into regions of 10 nm square, the ratio of the region where the concentration of the element represented by M is 10% by mass or more is 1.0% or more with respect to the total region. Positive electrode active material. (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, 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 positive electrode active material according to <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 <2>, wherein the element represented by M is La. <4> The positive electrode active material according to any one of <1> to <3>, wherein the ratio of the region where the concentration of the element represented by M is 10% by mass or more is 3.0% or more with respect to the total region. <5> A battery having the positive electrode active material according to any one of <1> to <4>. <6> A step of preparing a solution A in which a raw material containing an element represented by M is dissolved; <00001!9>A step of preparing a solution B in which raw materials containing Ni, Co, and Mn are respectively dissolved; A step of adding the solution A to an alkaline solution to precipitate a hydroxide; A step of adding the solution B to the alkaline solution in which the hydroxide has precipitated to precipitate; A step of collecting a precipitate from the alkaline solution; A step of mixing the aforementioned precipitate with a raw material containing Li to obtain a mixture, A step of firing the mixture, A method for producing a positive electrode active material having the following characteristics. (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.) [Effects of the Invention]

[0009] This disclosure provides a positive electrode active material that can improve cycle characteristics when used in a battery, a battery equipped with the positive electrode active material, and a method for manufacturing the positive electrode active material. [Brief explanation of the drawing]

[0010] [Figure 1] This is a schematic cross-sectional view illustrating a method for measuring the M element segregation rate in a positive electrode active material according to an embodiment of the present disclosure. [Figure 2] This is a schematic cross-sectional view illustrating a method for measuring the M element segregation rate in a positive electrode active material according to an embodiment of the present disclosure. [Figure 3] This is a schematic cross-sectional view illustrating a method for manufacturing a cathode active material according to the embodiments of this disclosure. [Modes for carrying out the invention]

[0011] The following describes an example of an embodiment of this disclosure. These descriptions and examples are illustrative and do not limit the scope of the invention. In numerical ranges described stepwise within this specification, the upper or lower limit of one numerical range may be replaced with the upper or lower limit of another numerical range described stepwise. Furthermore, in numerical ranges described within this specification, the upper or lower limit of that range may be replaced with the values ​​shown in the examples.

[0012] Each component may contain multiple types of the relevant 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 refers to the total amount of those multiple substances present in the composition. The term "process" includes not only independent processes, but also any process that cannot be clearly distinguished from other processes, as long as its intended function is achieved.

[0013] <Cathode active material> The cathode active material according to the embodiments of this disclosure is Li x Ni a Co b Mn c M d It has a composition represented by O2. Furthermore, in the TEM-EDX (Transmission Electron Microscope - Energy Dispersive X-ray Spectroscopy) image of the cross-section of the positive electrode active material particles, when the internal region, which is 70% of the radius from the center of the particle, is divided into 10 nm square regions, the proportion of regions where the concentration of the element represented by M is 10 mass% or more (hereinafter also simply referred to as the "M element segregation rate") is 1.0% or more of the total 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, and 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, additive elements (i.e., elements represented by M, hereinafter also referred to as "M elements") have been added to the positive electrode active material for purposes such as improving the resistance characteristics of batteries. In the past, these additive elements (M elements) were unevenly distributed on the surface of the particles of the positive electrode active material (for example, by forming a coating layer on the surface). Furthermore, in batteries using these conventional positive electrode active materials, the battery resistance sometimes increased after repeated charge-discharge cycles. Therefore, it is desirable to suppress the increase in battery resistance even after repeated charge-discharge cycles, in other words, to improve the cycle characteristics.

[0015] The positive electrode active material according to the embodiment of this disclosure has an M element segregation rate of 1.0% or more, meaning that the added element (M element) is sufficiently dispersed in the internal region of the particles of the positive electrode active material. The presence of a sufficient amount of M element in the internal 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 Li ion movement 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 the embodiment of this disclosure will be described in detail.

[0017] (composition) The cathode active material according to the embodiments of this 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, and 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 resistance characteristics in the battery, the ratio x of Li is preferably 0.1 to 1.5, preferably 0.3 to 1.4, and more preferably 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 between 0 and 0.3, preferably between 0 and 0.2, and more preferably between 0.1 and 0.2. The sum of the ratios 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). Including the elements listed above as additive elements can improve the cycle characteristics of the battery, that is, the degree to which the increase in battery resistance after repeated charge-discharge cycles is suppressed. Furthermore, from the viewpoint of further improving the cycle characteristics, the positive electrode active material preferably contains at least one element selected from the group consisting of Ta, Al, Ba, Pr, and La as an additive element (M element), and more preferably contains La.

[0020] In the composition of the positive electrode active material, the ratio d of M is preferably 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 embodiment of the positive electrode active material of the present disclosure, when the TEM-EDX image of the cross-section of the particles of the positive electrode active material is divided into a 10 nm square region within the internal region which is 70% of the radius from the center of the particle, the proportion of the region in which the concentration of the element represented by M is 10 mass% or more (M element segregation rate) is 1.0% or more of the total region. A M element segregation rate of 1.0% or higher means that the added element (M element) is sufficiently dispersed in the internal region of the positive electrode active material particles, thereby improving the cycle characteristics of batteries using this positive electrode active material.

[0022] Furthermore, from the viewpoint of further improving the cycle characteristics of the battery, the M element segregation rate is preferably 3.0% or higher, and more preferably 4.0% or higher. On the other hand, there is no particular upper limit to the M element segregation rate, but from the viewpoint of suppressing the amount of additive element (M element) added, it is preferably 15.0% or lower, and more preferably 10.0% or lower.

[0023] [Measurement of the M element distribution ratio] This document describes a method for measuring the M element segregation rate in particles of the positive electrode active material. First, a TEM-EDX image of the cross-section of the positive electrode active material particles is taken. A schematic diagram of the cross-sectional image is shown in Figure 1. The positive electrode active material particle 2 shown in Figure 1 contains particle 4B of element M inside. In the cross-sectional image of this positive electrode active material particle 2, the internal region at 70% of the radius from the center (i.e., the region excluding the surface region at 30% of the radius from the surface, the inner region enclosed by the dotted line in Figure 1) is to be observed. This internal region is divided into 10 nm square regions as shown in Figure 2, and the concentration of element M is measured in each region. However, in the 10nm square regions located at the edges of the internal region (the inner region enclosed by the dotted line in Figure 1), there are areas that are not filled with positive electrode active material particles 2. Therefore, within the 10nm square regions, the areas not completely filled with positive electrode active material particles 2 are excluded from the study, and only the regions that are entirely filled with positive electrode active material particles 2 are included in the measurement. Then, the percentage of regions where the concentration of element M is 10% by mass or more is calculated from all regions divided into 10 nm squares (excluding regions not filled with positive electrode active material particles 2). This percentage is calculated using the following formula. The above ratio = Number of regions where the concentration of element M is 10% by mass or more / Number of all regions within the internal region that are divided into 10 nm squares (excluding regions not filled with positive electrode active material particles) × 100 This ratio is calculated for cross-sectional images of 10 positive electrode active material particles, and the arithmetic mean is defined as the M element eclecticity.

[0024] <Method for manufacturing positive electrode active material> Next, a method for manufacturing the positive electrode active material according to the embodiments of this disclosure will be described. The positive electrode active material according to the embodiments of this disclosure can be manufactured by the method for manufacturing the positive electrode active material according to the embodiments of this disclosure described below.

[0025] A method for producing a positive electrode active material according to the embodiment of this disclosure comprises the following steps (1) to (7). (1) A step of preparing a solution A by dissolving a raw material containing the element represented by M. (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 solution B by dissolving raw materials containing Ni, Co, and Mn, respectively. (3) Adding solution A to the alkaline solution and allowing the hydroxide to precipitate. (4) Adding solution B to the alkaline solution in which hydroxide has precipitated to allow precipitation. (5) Steps to collect precipitate from alkaline solution (6) A step of mixing the precipitate with a Li-containing raw material to obtain a mixture. (7) The process of baking the mixture.

[0026] (1) A step of preparing a solution A by dissolving a raw material containing the element represented by M. First, prepare solution A by dissolving a raw material containing an additive element (element M, 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, solution A can be prepared by dissolving a raw material containing element M in a solvent such as water. The concentration of solution A is preferably in the range of 5 to 30% by mass.

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

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

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

[0030] (3) Adding solution A to the alkaline solution and allowing the hydroxide to precipitate. Next, solution A (a solution containing raw materials with element M dissolved in it) is added to the alkaline solution to precipitate the hydroxide.

[0031] Here, a method for producing a positive electrode active material according to an embodiment of this disclosure will be described using Figure 3. By adding solution A to an alkaline solution and precipitating hydroxide, a nucleus 4A of the additive (element M) can be formed, as shown in Figure 3(a).

[0032] In this process, for example, by purging an NH3 aqueous solution with nitrogen and adjusting the pH to be alkaline, and while controlling the pH to a constant level (e.g., pH 10-12), solution A can be added dropwise to precipitate the hydroxide (i.e., the additive nucleus 4A in Figure 3).

[0033] (4) Adding solution B to the alkaline solution in which hydroxide has precipitated to allow precipitation. Next, solution B is added to the alkaline solution in which the hydroxide (nucleus 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, as shown in Figure 3(b), particles 20 in which hydroxide 2 containing Ni, Co, and Mn is formed around the nucleus 4A of the additive (element M) crystallizes, and these particles 20 are obtained as a precipitate.

[0034] In this process, for example, by adding solution B and NH3 dropwise to an alkaline solution in which hydroxide has precipitated, while controlling the pH to a constant level (e.g., pH 10-12), the hydroxide of the transition metal precipitates.

[0035] (5) Steps to collect precipitate from alkaline solution Next, the precipitate is collected from the alkaline solution. Methods for collecting precipitate particles include, for example, filtration and washing. One method involves first removing the precipitate (particles) by filtration and washing with water, and then filtering the washed liquid to remove the precipitate (particles). The precipitate (particles) after washing may be further dried.

[0036] (6) A step of mixing the precipitate with a Li-containing raw material to obtain a mixture. Next, as shown in (c) in Figure 3, the collected precipitate (i.e., particles 20 in which hydroxide 2 containing Ni, Co, and Mn has formed around the additive nucleus 4A) is mixed with the Li-containing raw material 6. For example, the collected precipitate particles and the Li-containing raw material can be mixed in a mortar. Examples of raw materials containing lithium include Li2CO3 and LiOH.

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

[0038] Furthermore, it is preferable to perform a lower-temperature firing (hereinafter referred to as "second firing") after the above-mentioned firing (hereinafter referred to as "first firing"). For example, the particles that have undergone the first firing can be crushed, a reducing agent (e.g., ascurbic acid) can be mixed with the crushed particles, and the mixture can be fired in a firing furnace (such as a muffle furnace) at a lower temperature than that of the first firing. The conditions for the second firing can be, for example, a temperature of 400°C to 600°C, under an oxygen atmosphere, and for a time of 5 to 20 hours.

[0039] Through the calcination process of the mixture, as shown in Figure 3(d), the additive 4B diffuses within the collected precipitate (i.e., particles 20 in which hydroxide 2 containing Ni, Co, and Mn is formed around the additive nucleus 4A), resulting in a state where the additive element (M element) is sufficiently dispersed in the internal region of the positive electrode active material particles. As a result, the M element segregation rate in the positive electrode active material can be controlled within the aforementioned range.

[0040] <Battery> A battery according to an embodiment of this disclosure has a positive electrode active material according to an embodiment of this disclosure. The battery has, for example, a negative electrode, a positive electrode, a separator, and an electrolyte. A battery according to an embodiment of this disclosure is preferably a liquid battery having a liquid electrolyte. Alternatively, it may be a solid battery having a solid electrolyte.

[0041] (electrolyte) The battery according to the embodiment of this disclosure is preferably a liquid battery having an electrolyte. ·solvent The electrolyte solution contains a solvent (non-aqueous solvent) and an electrolyte. Examples of solvents (non-aqueous solvents) 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 Examples of electrolytes in electrolyte solutions include lithium salts. Examples of lithium salts include lithium bis(fluorosulfonyl)imide (LiFSI), LiPF6 (lithium hexafluoride phosphate), lithium tetrafluoroborate (LiBF4), and Li[N(CF3SO2)2]. The amount of electrolyte may be, for example, 1.0 to 2.0 ml / L, and preferably 1.0 to 1.5 ml / L.

[0043] The electrolyte may contain various additives in addition to the solvent and electrolyte, such as thickeners, film-forming agents, and gas-generating agents. The electrolyte is typically a non-aqueous electrolyte that is liquid at room temperature (e.g., 25±10°C). The electrolyte is typically liquid under the battery's operating environment (e.g., a temperature environment of -20 to +60°C).

[0044] (positive electrode) The positive electrode active material is the positive electrode active material according to the embodiment of this disclosure. Details have already been explained and are therefore omitted here.

[0045] Examples of conductive materials 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 (electrolyte solution) may contain, for example, a supporting salt such as LiPF6 and a solvent such as a carbonate-based solvent. Examples of binders include rubber-based binders and fluoride-based binders.

[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 current collection 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 Li4Ti 12 O and the like. 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. The electrolyte layer is preferably a solid electrolyte layer. 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, but 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 portion 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. Also, at least a portion 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. A portion of Li may be substituted with at least one selected from the group consisting of Na, K, Mg, Ca, and Zn. A portion 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 the main component of the anionic element, and may also contain, for example, Li, the element Q (where Q represents at least one of Nb, B, Al, Si, P, Ti, Zr, Mo, W, and S), and O. Examples of oxide solid electrolytes include garnet-type solid electrolytes, perovskite-type solid electrolytes, NASICON-type solid electrolytes, Li-PO-based solid electrolytes, and Li-BO-based solid electrolytes. An example of a garnet-type solid electrolyte is Li7La3Zr2O 12 Li 7-x La3(Zr 2-x Nb x )O 12 (0≦x≦2), Li5La3Nb2O 12 Examples include the following. Perovskite-type solid electrolytes include (Li,La)TiO3, (Li,La)NbO3, and (Li,Sr)(Ta,Zr)O3. Nasicone-type solid electrolytes include the following: Li(Al,Ti)(PO4)3 and Li(Al,Ga)(PO4)3. Li-PO-based solid electrolytes include Li3PO4 and LIPON (a compound in which some of the O in Li3PO4 is replaced with N), and Li-BO-based solid electrolytes include Li3BO3 and a compound in which some of the O in Li3BO3 is replaced with C.

[0055] As a halide solid electrolyte, a solid electrolyte containing Li, M, and X (where M represents at least one of Ti, Al, and Y, and X represents F, Cl, or Br) is preferred. Specifically, Li 6-3zY z X6 (where X represents Cl or Br, and 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 and Li3YCl6 is even more preferred in terms of excellent lithium ion conductivity. 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 from the viewpoint of, for example, suppressing the 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 so-called all-solid batteries that use a solid electrolyte as the electrolyte, and the solid electrolyte may contain less than 10% by mass of an electrolytic solution 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 multilayer 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 assistant, and a binder. The positive electrode active material layer includes a coated positive electrode active material, a conductive assistant, 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. Furthermore, the solid-state battery may be constructed by sealing the laminated end faces (sides) of the positive electrode / solid electrolyte layer / negative electrode laminated structure with resin. The current collector of the electrode may have a buffer layer, an elastic layer, or a PTC (Positive Temperature Coefficient) thermistor layer arranged on its surface.

[0058] (battery) The laminated battery in this disclosure is typically a lithium-ion secondary battery. Applications of the battery include, for example, powering vehicles such as hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), battery electric vehicles (BEVs), gasoline cars, and diesel cars. It is particularly preferable for the battery to be used as a power source for hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), or electric vehicles (BEVs). Furthermore, the battery in this disclosure may be used as a power source for mobile devices other than vehicles (e.g., railways, ships, aircraft), or as a power source for electrical products such as information processing devices.

[0059] This disclosure is not limited to the embodiments described above. The embodiments described above are illustrative, and any configuration that is substantially identical to the technical idea described in the claims of this disclosure and achieves similar effects is included within the technical scope of this disclosure. [Examples]

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

[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 in which the element represented by M is one of the elements listed in Table 1, was synthesized by the method of this disclosure.

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

[0063] • Crystallization A fixed amount of NH3 aqueous solution was added to the reaction vessel, and the mixture was purged with nitrogen while stirring with a stirrer. NaOH was added to the reaction vessel to make the pH alkaline. Next, while maintaining a constant pH (pH 10-12) in the reaction vessel, the solution of starting material 1 was added dropwise to precipitate the hydroxide. Furthermore, while maintaining a constant pH (pH 10-12) in the reaction vessel, the solution of starting material 2 and NH3 were added dropwise to precipitate the transition metal hydroxide.

[0064] • Wash, filter, dry The precipitated transition metal hydroxide was removed by filtration, deionized water was added, and the mixture was dispersed by stirring with a spoon, then washed with water. Next, the rinsed solution was filtered to extract the transition metal hydroxide. Next, the filtered transition metal hydroxide was dried at 120°C for 16 hours to evaporate the water.

[0065] • Mixing of Li raw materials Dried transition metal hydroxides were mixed with Li2CO3 and LiOH as Li raw materials in a mortar.

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

[0067] <Examples 2-4> The cathode active materials for each example were obtained in the same manner as in Example 1, except that the additive used in the raw material 1 solution of 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 was synthesized having a composition represented by O2, where x, a, b, and c are in the ratios shown in Table 1.

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

[0070] • Crystallization A fixed amount of NH3 aqueous solution was added to the reaction vessel, and the mixture was purged with nitrogen while stirring with a stirrer. NaOH was added to the reaction vessel to make the pH alkaline. Then, while controlling the pH of the reaction vessel to a constant level (pH 10-12), the two starting material solutions and NH3 were added dropwise to precipitate the transition metal hydroxide.

[0071] • Wash, filter, dry The precipitated transition metal hydroxide was removed by filtration, deionized water was added, and the mixture was dispersed by stirring with a spoon, then washed with water. Next, the rinsed solution was filtered to extract the transition metal hydroxide. Next, the filtered transition metal hydroxide was dried at 120°C for 16 hours to evaporate the water.

[0072] • Mixing of Li raw materials Dried transition metal hydroxides were mixed with Li2CO3 and LiOH as Li raw materials in a mortar.

[0073] Firing 1 A mixture of transition metal hydroxide and Li raw material was calcined in a muffle furnace at 800-1100°C in an oxygen atmosphere for 10 hours. Firing 2 The particles obtained in calcination 1 were crushed, and the crushed particles were mixed with ascurbic acid (reducing agent). The mixture was then calcined in a calcination furnace (muffle furnace) at 400-600°C in an oxygen atmosphere for 10 hours. In this way, the 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 one of the elements listed in Table 1, was synthesized by a conventional method.

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

[0076] • Crystallization A fixed amount of NH3 aqueous solution was added to the reaction vessel, and the mixture was purged with nitrogen while stirring with a stirrer. NaOH was added to the reaction vessel to make the pH alkaline. Then, while controlling the pH of the reaction vessel to a constant level (pH 10-12), the two starting material solutions and NH3 were added dropwise to precipitate the transition metal hydroxide.

[0077] • Wash, filter, dry The precipitated transition metal hydroxide was removed by filtration, deionized water was added, and the mixture was dispersed by stirring with a spoon, then washed with water. Next, the rinsed solution was filtered to extract the transition metal hydroxide. Next, the filtered transition metal hydroxide was dried at 120°C for 16 hours to evaporate the water.

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

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

[0080] [Measurement of the M element distribution ratio] Cross-sectional TEM-EDX images were taken of the positive electrode active material particles obtained in Examples 1-4 and Comparative Example 2. A schematic diagram of the cross-sectional image is shown in Figure 1. The positive electrode active material particle 2 shown in Figure 1 contains particles 4B of element M inside. In the cross-sectional image of this positive electrode active material particle 2, the internal region at 70% of the radius from the center (i.e., the region excluding the surface region at 30% of the radius from the surface, the inner region enclosed by the dotted line in Figure 1) was selected for observation. This internal region was divided into 10 nm square regions as shown in Figure 2, and the concentration of element M was measured in each region. However, in the 10nm square regions located at the edges of the internal area, there are areas that are not filled with positive electrode active material particles 2. Therefore, only the regions within the 10nm square areas that are completely filled with positive electrode active material particles 2 were included in the measurement. Then, the percentage of all regions (excluding regions not filled with positive electrode active material particles 2) divided into 10 nm squares, where the concentration of element M is 10 mass% or more, was calculated. This percentage is calculated using the following formula. The above ratio = Number of regions where the concentration of element M is 10% by mass or more / Number of all regions within the internal region that are divided into 10 nm squares (excluding regions not filled with positive electrode active material particles) × 100 This ratio was calculated for cross-sectional images of 10 positive electrode active material particles, and the arithmetic mean was defined as the M element segregation rate. The results are shown in Table 1.

[0081] [Cell creation] Cells were fabricated using the positive electrode active materials obtained in each example and comparative example. • Cell configuration Winding 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) / Carboxymethylcellulose (CMC) Electrolyte composition: Electrolyte = LiPF6 (1M), Solvent = Ethylene carbonate (EC) / Dimethyl carbonate (DMC) / Ethyl methyl carbonate (EMC) = 3 / 4 / 3 (volume %)

[0082] • Electrode fabrication A cell was fabricated by coating the positive and negative electrodes onto the current collector using a film applicator with film thickness adjustment function (Allgood Co., Ltd.), and then drying them in a dryer at 80°C for 5 minutes.

[0083] [Measurement of resistance increase rate after cycle] For each example and comparative example, the battery resistance was measured before and after cycling under the following test conditions. Table 1 shows the percentage increase in resistance after cycling, with the battery resistance before cycling set to "100%". A resistance increase closer to 100% indicates better battery characteristics. Test conditions: Charge and discharge were performed 300 times between 0% and 100% SOC at 60°C and a 2C rate.

[0084] [Table 1]

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

[0086] 2 Positive electrode active material particles 4A The nucleus of element M 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, A positive electrode active material in which, in a TEM-EDX image of a cross-section of a particle, when the internal region, which is 70% of the radius from the center of the particle, is divided into a 10 nm square region, 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 total 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, Y, Sr, Ce, Se, Hf, Rh, and Zr.)

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, and Pr.

3. The positive electrode active material according to claim 1, wherein the proportion of the region in which the concentration of the element represented by M is 10% by mass or more is 3.0% or more of the total region.

4. A battery having the positive electrode active material according to any one of claims 1 to 3.

5. A step of preparing a solution A by dissolving a raw material containing an element represented by M, The process involves preparing solution B by dissolving raw materials containing Ni, Co, and Mn, respectively. The process involves adding solution A to an alkaline solution to precipitate the hydroxide, The steps include adding solution B to the alkaline solution in which the hydroxide has precipitated and allowing it to precipitate, A step of collecting a precipitate from the aforementioned alkaline solution, A step of mixing the aforementioned precipitate with a raw material containing Li to obtain a mixture, A step of firing the mixture, A method for producing a positive electrode active material having the following characteristics. (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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