Positive electrode active material, positive electrode, lithium-ion battery, and method for producing positive electrode active material

Abstract

This positive electrode active material has a composition represented by LixNiaCobMncM1dM2eM3fO2. M1 to M3 each include at least one element selected from the following element group. M1, M2, and M3 include a total of three or more elements. 0.1≤x≤1.5, 0.5≤a≤1.0, 0≤b≤0.5, 0≤c≤0.5, a+b+c=1.0, 0.0005≤d≤0.05, 0.0005≤e≤0.05, and 0.0005≤f≤0.05 are satisfied. M1 represents Ba, Pr, La, Y, Sr, Ce, Se, Hf, Rh, Zr, or Sn. M2 represents W, Re, Sb, Sn, Ta, Os, Ir, Mo, Nb, Tc, Ru, Ga, Ag, Pd, Ge, As, Zr, In, Pt, Al, or Ti. M3 represents B, Mg, Si, P, Ca, Sc, Ti, V, Cr, Fe, Ga, Ge, Y, Zr, Nb, Mo, Ru, Rh, Al, Hf, Ta, W, Re, Os, Ir, La, Ce, Pr, or Nd. M1 and M3 are different from each other.

Description

Positive electrode active material, positive electrode, lithium ion battery, and method for producing positive electrode active material

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

[0002] BACKGROUND ART Conventionally, various additive elements have been added to positive electrode active materials used in batteries in order to improve the resistance characteristics and the like of the batteries.

[0003] Patent Document 1 discloses a method for manufacturing a positive electrode active material, and a positive electrode and a secondary battery including the positive electrode active material. The positive electrode active material includes a nickel-cobalt-manganese-based lithium transition metal oxide containing 60 mol% or more of nickel relative to the total moles of metals excluding lithium. The nickel-cobalt-manganese-based lithium transition metal oxide is doped with a doping element M1 (the doping element M1 is a metal element including Al) and a doping element M2 (the doping element M2 is one or more metal elements selected from the group consisting of Mg, La, Ti, Zn, B, W, Ni, Co, Fe, Cr, V, Ru, Cu, Cd, Ag, Y, Sc, Ga, In, As, Sb, Pt, Au, and Si). The nickel-cobalt-manganese-based lithium transition metal oxide includes 100 to 10,000 ppm of the doping element M1. The doping elements M1 and M2 are contained in a weight ratio of 50:50 to 99:1.

[0004] Patent Document 2 discloses a method for manufacturing a positive electrode active material. The manufacturing method includes a first step and a second step. In the first step, a transition metal precursor having a nickel content of 70 atm % or more and a lithium source material are mixed and primarily fired to form a pre-fired product. In the second step, the pre-fired product is secondary fired to form a lithium transition metal composite oxide. The primary firing is performed so that the pre-fired product has a spinel phase ratio of 7 to 16%.

[0005] In Non-Patent Document 1, W doping and perovskite La ４ NiLiO ８ LiNi coating ０．８５ Co０．０５ Mn ０．１０ O ２ discloses a positive electrode active material powder (particle size: about 2.01 μm).

[0006] Patent Document 1: Japanese Translation of PCT Publication No. 2022-513681 Patent Document 2: Japanese Patent Publication No. 2023-536251

[0007] Non-patent document 1: Journal of Materials Chemistry A, “Perovskite-coated small-size single-crystalline W-doped Ni-rich cathodes with greatly enhanced power density for Li-ion batteries”, 2024, Vol.12, Issue.36, p.24542-24548

[0008] In a battery containing elements represented by M1 and M2, after repeated charging and discharging (hereinafter also referred to as "charging and discharging"), the elements represented by M1 and M2 may fall out of the layered crystal structure (e.g., a layered rock-salt crystal structure), causing Ni mixing (i.e., cation mixing), and increasing the resistance of the battery. Therefore, it is desired to suppress the increase in battery resistance even after repeated charging and discharging.

[0009] The present disclosure has been made in consideration of the above circumstances, and aims to provide a positive electrode active material that, when used in a battery, can suppress an increase in the resistance of the battery after repeated charging and discharging, a positive electrode including the positive electrode active material, a lithium-ion battery including the positive electrode, and a method for producing the positive electrode active material.

[0010] The means for solving the above problems include the following aspects: <1> Li ｘ Ni ａ Co ｂ Mn ｃ M1 ｄ M2 ｅ M3 ｆ O ２a positive electrode active material having a composition represented by the formula: wherein M1, M2, and M3 each contain at least one element selected from the group of elements shown below, and M1, M2, and M3 contain three or more elements in total; (In the composition, 0.1≦x≦1.5, 0.5≦a≦1.0, 0≦b≦0.5, 0≦c≦0.5, a+b+c=1.0, 0.0005≦d≦0.050, 0.0005≦e≦0.050, and 0.0005≦f≦0.050 are satisfied, M1 represents at least one element selected from the group of elements consisting of Ba, Pr, La, Y, Sr, Ce, Se, Hf, Rh, Zr, and Sn, and M2 represents W, Re, Sb, Sn, Ta, Os, Ir, M <2> The positive electrode active material according to <1>, wherein M1 represents at least one element selected from the group consisting of O, Nb, Tc, Ru, Ga, Ag, Pd, Ge, As, Zr, In, Pt, Al, and Ti, and M3 represents at least one element selected from the group consisting of B, Mg, Si, P, Ca, Sc, Ti, V, Cr, Fe, Ga, Ge, Y, Zr, Nb, Mo, Ru, Rh, Al, Hf, Ta, W, Re, Os, Ir, La, Ce, Pr, and Nd, and M1 and M3 are different. <2> The positive electrode active material according to <1>, wherein an ionic radius of the element included in M3 is smaller than the ionic radius of the element included in M1 and larger than the ionic radius of the element included in M2. <3> The positive electrode active material according to <1> or <2>, wherein the combination of M1 and M2 is at least one combination selected from the group consisting of Ba—W, Pr—W, La—W, Y—W, Sr—W, Ce—W, Pr—Re, Ba—Re, Sr—Sb, Se—W, Y—Re, Hf—W, Sr—Re, Rh—W, Zr—W, Sr—Sn, Y—Ta, Pr—Ta, Y—Sb, Sr—Os, Sr—Ta, Ce—Re, La—Re, Ba—Ta, Sr—Ir, Sn—W, Sr—Mo, Sr—Nb, Ba—Ti, Ba—Zr, and Ba—Al; and wherein M3 includes at least one element selected from the group consisting of B, Zr, Mg, Al, and Sc. <4> The positive electrode active material according to <3>, wherein the combination of M1 and M2 is at least one combination selected from the group consisting of Ba—W, Pr—W, La—W, Hf—W, Sr—Nb, and Pr—Ta.<5> The cathode active material according to any one of <1> to <4>, wherein M1 includes at least one element selected from the group consisting of Pr, La, and Sr, M2 includes at least one element selected from the group consisting of W and Nb, and M3 includes at least one element selected from the group consisting of B, Zr, Mg, Al, and Sc. <6> The cathode active material according to any one of <1> to <5>, wherein the combination of M1, M2, and M3 is at least one combination selected from the group consisting of Ba-W-B, Pr-W-B, La-W-B, La-W-Zr, La-W-Mg, La-W-Al, La-W-Sc, Hf-W-B, Hf-W-Zr, Hf-W-Mg, Hf-W-Al, Hf-W-Sc, Sr-Nb-Al, and Pr-Ta-Mg. <7> The cathode active material according to any one of <1> to <6>, having a layered crystal structure including a lithium layer containing Li and a transition metal layer containing at least one selected from the group consisting of Ni, Co, and Mn, wherein the lithium layer further contains M3, and the transition metal layer further contains M1 and M2. <8> A cathode comprising the cathode active material according to any one of <1> to <7>. <9> A lithium ion battery having the cathode according to <8>. <10> A method for producing the cathode active material according to any one of <1> to <7>, comprising: a step of mixing a raw material containing Ni, a raw material containing Co, a raw material containing Mn, a raw material containing Li, a raw material containing an element represented by M1, and a raw material containing an element represented by M2 to obtain a first mixture; a first firing step of heating the first mixture in an oxygen atmosphere at a temperature increase rate A of 1°C / min to 10°C / min to a maximum temperature X-100°C, and then heating the first mixture from the maximum temperature X-100°C to the maximum temperature X at a temperature increase rate B of 0.1°C / min to 5°C / min that is slower than the temperature increase rate A; a step of mixing a raw material containing an element represented by M3 with the first mixture obtained after the first firing step to obtain a second mixture; and a second firing step of firing the second mixture in an oxygen atmosphere at a maximum temperature that is lower than the maximum temperature X.

[0011] The present disclosure provides a positive electrode active material that, when used in a battery, can suppress an increase in the resistance of the battery after repeated charging and discharging; a positive electrode including the positive electrode active material; a lithium-ion battery including the positive electrode; and a method for producing the positive electrode active material.

[0012] Hereinafter, an embodiment that is an example of the present disclosure will be described. These descriptions and examples are intended to illustrate the embodiments and do not limit the scope of the invention. In the numerical ranges described in stages in this specification, the upper or lower limit value described in one numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. In the numerical ranges described in this specification, the upper or lower limit value of that numerical range may be replaced with the value shown in the examples.

[0013] Each component may contain multiple corresponding substances. When referring to the amount of each component in a composition, if multiple substances corresponding to each component are present in the composition, the total amount of those multiple substances present in the composition is meant unless otherwise specified. 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.

[0014] <Positive Electrode Active Material> The positive electrode active material according to the embodiment of the present disclosure is Li ｘ Ni ａ Co ｂ Mn ｃ M1 ｄ M2 ｅ M3 ｆ O ２The M1, M2, and M3 each contain at least one element selected from the group of elements shown below. The M1, M2, and M3 contain a total of three or more elements. (In the composition, 0.1≦x≦1.5, 0.5≦a≦1.0, 0≦b≦0.5, 0≦c≦0.5, a+b+c=1.0, 0.0005≦d≦0.050, 0.0005≦e≦0.050, and 0.0005≦f≦0.050 are satisfied, and the M1 represents at least one element selected from the group of elements consisting of Ba, Pr, La, Y, Sr, Ce, Se, Hf, Rh, Zr, and Sn, and the M2 represents W, Re, Sb, Sn, Ta, Os, Ir, M M1 represents at least one element selected from the group consisting of O, Nb, Tc, Ru, Ga, Ag, Pd, Ge, As, Zr, In, Pt, Al, and Ti, and M3 represents at least one element selected from the group consisting of B, Mg, Si, P, Ca, Sc, Ti, V, Cr, Fe, Ga, Ge, Y, Zr, Nb, Mo, Ru, Rh, Al, Hf, Ta, W, Re, Os, Ir, La, Ce, Pr, and Nd, and M1 and M3 are different.

[0015] When used in a battery, the positive electrode active material according to an embodiment of the present disclosure can suppress an increase in the resistance of the battery after repeated charge and discharge. The reason for this effect is presumed to be as follows.

[0016] Conventionally, additive elements (so-called doping elements) have been added to positive electrode active materials for purposes such as improving the resistance characteristics of batteries. The positive electrode active material has a layered crystal structure (e.g., a layered rock-salt crystal structure). The layered crystal structure includes a lithium layer (hereinafter also referred to as a "Li layer") containing Li and a transition metal layer (hereinafter also referred to as a "TM layer") containing transition metals such as Ni, Co, and Mn. Certain doping elements are difficult to incorporate into the layered crystal structure of the positive electrode active material. As a result, conventional positive electrode active materials have the characteristic of having a small structural stabilization effect.

[0017] In response to this, a method of incorporating two doping elements, M1 and M2, into the positive electrode active material is considered. Since the ionic radius of the element represented by M1 (hereinafter referred to as the "M1 element") is large, it is difficult for the element to enter the layered crystal structure of the positive electrode active material. In contrast, by combining the M1 element with an element represented by M2 (hereinafter referred to as the "M2 element"), the M1 element is easily incorporated into the layered crystal structure. As a result, by combining the doping elements M1 and M2, the doping elements can be present in large amounts in the layered crystal structure of the positive electrode active material, greatly improving the structural stabilization effect. The improved structural stabilization effect suppresses Ni mixing (cation mixing) into the Li layer during charging and discharging in a lithium-ion battery, suppressing the inhibition of Li ion migration during charging and discharging, and suppressing an increase in battery resistance. However, repeated charge and discharge in a battery can cause the M1 and M2 elements to fall out of the layered crystal structure, resulting in Ni mixing (cation mixing). As a result, the battery resistance increases after repeated charge and discharge. In addition, M1 and M2 may not be located in the targeted portion (specifically, the Li layer or the TM layer). If M1 and M2 are not located in the targeted portion, malfunctions are likely to occur. For example, unreacted M1 and M2 inhibit the entry and exit of Li into the layered crystal structure during the battery reaction, increasing the battery resistance. Furthermore, when a battery contains an electrolyte, unreacted M1 and M2 react with the electrolyte (e.g., decomposition reaction of the electrolyte, etc.), resulting in a decrease in the battery capacity.

[0018] In contrast, in the positive electrode active material according to an embodiment of the present disclosure, in addition to the M1 element and the M2 element, an element represented by M3 (hereinafter referred to as the "M3 element") is used in combination. The M3 element has a high valence, and therefore exerts an electrostatic repulsion effect. In addition, since the ionic radius of the M3 element is relatively large (for example, the ionic radius of the M3 element is smaller than the ionic radius of the M1 element but larger than the ionic radius of the M2 element), the M3 element also exerts a steric repulsion effect. In particular, when the Li layer further contains the M3 and the TM layer further contains the M1 and M2, the M3 element supports the M1 element and the M2 element, and the M1 element is prevented from falling out of the layered crystal structure (for example, mixing of the M1 element and the M2 element into the Li layer). This suppresses the occurrence of Ni mixing (cation mixing), and suppresses an increase in the resistance of the battery even after repeated charge and discharge.

[0019] The positive electrode active material according to the embodiment of the present disclosure can reduce the initial battery resistance when used in a battery. The reason for this effect is presumed to be as follows.

[0020] By including the M3 element in the positive electrode active material, the M3 element in the Li layer does not move during charge and discharge and functions as a pillar. The M3 element keeps the M1 and M2 elements within the TM layer. As a result, expansion and contraction of the layered crystal structure during Li desorption is suppressed, and the movement of Li is not hindered. This reduces the initial battery resistance.

[0021] Next, the positive electrode active material according to an embodiment of the present disclosure will be described in detail.

[0022] (Composition) The positive electrode active material according to the embodiment of the present disclosure comprises Li ｘ Ni ａ Co ｂ Mn ｃ M1 ｄ M2 ｅ M3 ｆ O ２(In the composition, 0.1≦x≦1.5, 0.5≦a≦1.0, 0≦b≦0.5, 0≦c≦0.5, a+b+c=1.0, 0.0005≦d≦0.050, 0.0005≦e≦0.050, and 0.0005≦f≦0.050 are satisfied. M1 represents at least one element selected from the group consisting of Ba, Pr, La, Y, Sr, Ce, Se, Hf, Rh, Zr, and Sn, and M2 represents at least one element selected from the group consisting of W, Re, Sb, Sn, Ta, and the like.) , Os, Ir, Mo, Nb, Tc, Ru, Ga, Ag, Pd, Ge, As, Zr, In, Pt, Al, and Ti, and M3 represents at least one element selected from the group of elements consisting of B, Mg, Si, P, Ca, Sc, Ti, V, Cr, Fe, Ga, Ge, Y, Zr, Nb, Mo, Ru, Rh, Al, Hf, Ta, W, Re, Os, Ir, La, Ce, Pr, and Nd.

[0023] In the composition of the positive electrode active material, from the viewpoint of the resistance characteristics of the battery, the Li ratio x is 0.1 to 1.5, preferably 0.3 to 1.4, more preferably 0.5 to 1.2, particularly preferably 0.9 to 1.2, and even more preferably 1.0 to 1.2. From the viewpoint of the resistance characteristics of the battery, the Ni ratio a is 0.5 to 1.0, preferably 0.6 to 0.9, and more preferably 0.7 to 0.8. When the Ni ratio a is increased, the ratio a is preferably 0.6 to 1.0 (i.e., 0.6≦a≦1.0), more preferably 0.7 to 1.0 (i.e., 0.7≦a≦1.0), and particularly preferably 0.7 to 0.9 (i.e., 0.7≦a≦0.9). From the viewpoint of the resistance characteristics of the battery, the Co ratio b is 0 to 0.5, preferably 0 to 0.4, more preferably 0.1 to 0.3, and particularly preferably 0.1 to 0.2. From the viewpoint of the resistance characteristics of the battery, the Mn ratio c is 0 to 0.5, preferably 0 to 0.4, more preferably 0.1 to 0.3, and particularly preferably 0.1 to 0.2. The sum of the ratios of Ni, Co, and Mn (a+b+c) is 1.0.

[0024] The ratio d of the M1 element is 0.0005 or more and 0.050 or less, preferably 0.001 or more and 0.040 or less, and more preferably 0.003 or more and 0.030 or less, from the viewpoint of the resistance characteristics of the battery (particularly, the suppression of an increase in the resistance of the battery after repeated charge and discharge, and the reduction of the initial battery resistance), etc. The ratio e of the M2 element is 0.0005 or more and 0.050 or less, preferably 0.001 or more and 0.040 or less, and more preferably 0.003 or more and 0.030 or less, from the viewpoint of the resistance characteristics of the battery (particularly, the suppression of an increase in the resistance of the battery after repeated charge and discharge, and the reduction of the initial battery resistance), etc. From the viewpoint of the resistance characteristics of the battery (particularly, suppression of an increase in the resistance of the battery after repeated charge and discharge, and reduction of the initial battery resistance), the ratio f of the M3 element is 0.0005 or more and 0.050 or less, preferably 0.001 or more and 0.040 or less, and more preferably 0.003 or more and 0.030 or less.

[0025] It is preferable that the ratio d of the M1 element is 0.0005 or more and less than 0.010, the ratio e of the M2 element is 0.0005 or more and less than 0.010, and the ratio f of the M3 element is 0.0005 or more and less than 0.010. This results in better resistance characteristics in the battery (especially suppression of increase in battery resistance after repeated charge and discharge, and reduction in initial battery resistance). Each element has a limit amount that can be dissolved in the particles. When the ratio d of the M1 element, the ratio e of the M2 element, and the ratio f of the M3 element are each less than 0.010, it is unlikely that troublesome by-products will be generated, and the effect of improving the resistance characteristics of the battery will be improved.

[0026] The positive electrode active material contains an M1 element, an M2 element, and an M3 element as additive elements. M1 represents at least one element selected from the group consisting of Ba, Pr, La, Y, Sr, Ce, Se, Hf, Rh, Zr, and Sn. M2 represents at least one element selected from the group consisting of W, Re, Sb, Sn, Ta, Os, Ir, Mo, Nb, Tc, Ru, Ga, Ag, Pd, Ge, As, Zr, In, Pt, Al, and Ti. M3 represents at least one element selected from the group consisting of B, Mg, Si, P, Ca, Sc, Ti, V, Cr, Fe, Ga, Ge, Y, Zr, Nb, Mo, Ru, Rh, Al, Hf, Ta, W, Re, Os, Ir, La, Ce, Pr, and Nd. In the positive electrode active material, the M1 element, the M2 element, and the M3 element each contain at least one element selected from the group of elements shown above. The M1, the M2, and the M3 contain a total of three or more different elements. The M1 element and the M3 element are different. When the positive electrode active material contains the M1 element, the M2 element, and the M3 element listed above as additive elements, an increase in the resistance of the battery after repeated charge and discharge when the positive electrode active material is used in a battery is suppressed, and the initial battery resistance is reduced.

[0027] From the viewpoint of suppressing an increase in the resistance of the battery after repeated charge and discharge and reducing the initial battery resistance, the combinations of the M1 element and the M2 element are Ba—W, Pr—W, La—W, Y—W, Sr—W, Ce—W, Pr—Re, Ba—Re, Sr—Sb, Se—W, Y—Re, Hf—W, Sr—Re, Rh—W, Zr—W, Sr—Sn, Y—Ta, Pr—Ta, Y—Sb, Sr Preferably, the combination of the M1 element and the M2 element is at least one selected from the group consisting of: —Os, Sr—Ta, Ce—Re, La—Re, Ba—Ta, Sr—Ir, Sn—W, Sr—Mo, Sr—Nb, Ba—Ti, Ba—Zr, and Ba—Al (the left side of the - in the above combination notation (e.g., Ba—W, etc.) indicates the M1 element, and the right side of the - in the above combination notation indicates the M2 element). Furthermore, from the viewpoint of suppressing an increase in battery resistance after repeated charge and discharge and reducing the initial battery resistance, the combination of the M1 element and the M2 element is more preferably at least one selected from the group consisting of Ba—W, Pr—W, La—W, Hf—W, Sr—Nb, and Pr—Ta.

[0028] From the viewpoint of suppressing an increase in the resistance of the battery after repeated charge and discharge and reducing the initial battery resistance, it is preferable that the M3 element to be combined with the combination of the M1 element and the M2 element is at least one element selected from the group consisting of B, Zr, Mg, Al, and Sc.

[0029] From the viewpoint of suppressing an increase in the resistance of the battery after repeated charge and discharge and reducing the initial battery resistance, it is preferable that the M1 element, the M2 element, and the M3 element each contain at least one element selected from the following group of elements: It is preferable that the M1 element contains at least one element selected from the group of elements consisting of Pr, La, and Sr, the M2 element contains at least one element selected from the group of elements consisting of W and Nb, and the M3 element contains at least one element selected from the group of elements consisting of B, Zr, Mg, Al, and Sc.

[0030] Furthermore, from the viewpoint of suppressing an increase in battery resistance after repeated charge and discharge and reducing initial battery resistance, the combination of the M1 element, the M2 element, and the M3 element is preferably at least one combination selected from the group consisting of Ba-W-B, Pr-W-B, La-W-B, La-W-Zr, La-W-Mg, La-W-Al, La-W-Sc, Hf-W-B, Hf-W-Zr, Hf-W-Mg, Hf-W-Al, Hf-W-Sc, Sr-Nb-Al, and Pr-Ta-Mg (the element on the left side of the notation of the above combination (e.g., Ba-W-B, etc.) represents the M1 element, the element in the middle of the notation of the above combination represents the M2 element, and the element on the right side of the notation of the above combination represents the M3 element).

[0031] From the viewpoints of raw material costs and ease of element diffusion during firing, the combination of the M1 element, the M2 element, and the M3 element is preferably Pr-W-B, Pr-W-Zr, La-W-B, La-W-Zr, Sr-Nb-B, or La-W-Zr.

[0032] The positive electrode active material has a layered crystal structure (e.g., a layered rock-salt crystal structure) having a lithium layer containing Li (i.e., a Li layer) and a transition metal layer containing at least one selected from the group consisting of Ni, Co, and Mn (i.e., a TM layer), and it is preferable that the lithium layer further contains M3, and the transition metal layer further contains M1 and M2. The layered crystal structure may be a layered crystal structure in which Li layers and TM layers are alternately arranged. The term "transition metal" refers to an element in groups 3A to 7A, 8, and 1B in the periodic table.

[0033] The fact that the Li layer contains M3 and the TM layer contains M1 and M2 can be confirmed by using a transmission electron microscope (TEM)-energy dispersive X-ray spectroscopy (EDX). TEM-EDX can identify each atom and pinpoint the elemental position.

[0034] (Ionic Radius of Element) The ionic radius of the M3 element is preferably smaller than that of the M1 element and larger than that of the M2 element. When the ionic radius of the M3 element is smaller than that of the M1 element and larger than that of the M2 element, the steric repulsion effect of the M3 element is more effectively exerted, and an increase in the resistance of the battery after repeated charge and discharge is more easily suppressed.

[0035] The ionic radius of each element is taken from the ionic radius table compiled by Shannon, which is described in RD Schannon, Acta Crystallogr. A32, 751 (1976).

[0036] The ionic radius of Ba may be 1.35 Å to 1.61 Å (e.g., 1.53 Å, 1.35 Å, 1.38 Å, 1.42 Å, 1.47 Å, 1.52 Å, 1.57 Å, and 1.61 Å, etc.). The ionic radius of Pr may be 0.85 Å to 1.179 Å (e.g., 0.99 Å, 1.126 Å, 1.179 Å, 0.85 Å, and 0.96 Å, etc.). The ionic radius of La may be 1.032 Å to 1.39 Å (e.g., 1.39 Å, 1.032 Å, 1.10 Å, 1.160 Å, 1.216 Å, 1.27 Å, and 1.36 Å, etc.). The ionic radius of Y may be 0.900 Å to 1.075 Å (e.g., 0.900 Å, 0.96 Å, 1.019 Å, 1.075 Å, etc.). The ionic radius of Sr may be 1.18 Å to 1.44 Å (e.g., 1.18 Å, 1.21 Å, 1.26 Å, 1.31 Å, 1.36 Å, 1.44 Å, etc.). The ionic radius of Ce may be 0.87 Å to 1.34 Å (e.g., 1.27 Å, 1.01 Å, 1.07 Å, 1.143 Å, 1.196 Å, 1.25 Å, 1.34 Å, 0.87 Å, 0.97 Å, 1.07 Å, 1.14 Å, etc.). The ionic radius of Se may be 0.28 Å to 2.32 Å (e.g., 1.98 Å, 2.32 Å, 0.66 Å, 0.50 Å, 0.28 Å, and 0.42 Å, etc.). The ionic radius of Hf may be 0.58 Å to 0.83 Å (e.g., 0.58 Å, 0.71 Å, 0.76 Å, and 0.83 Å, etc.). The ionic radius of Rh may be 0.55 Å to 0.665 Å (e.g., 0.665 Å, 0.60 Å, and 0.55 Å, etc.). The ionic radius of Zr may be 0.59 Å to 1.09 Å (e.g., 1.09 Å, 0.59 Å, 0.66 Å, 0.72 Å, 0.78 Å, 0.84 Å, and 0.89 Å, etc.). The ionic radius of Sn may be 0.55 Å to 3.70 Å (e.g., 2.94 Å, 3.70 Å, 0.93 Å, 0.55 Å, 0.62 Å, 0.690 Å, 0.75 Å, 0.81 Å, etc.). The ionic radius of W may be 0.42 Å to 0.66 Å (e.g., 0.66 Å, 0.62 Å, 0.42 Å, 0.51 Å, 0.60 Å, etc.). The ionic radius of Re may be 0.38 Å to 0.63 Å (e.g., 0.63 Å, 0.58 Å, 0.55 Å, 0.38 Å, 0.53 Å, etc.).The ionic radius of Sb may be 0.60 Å to 2.45 Å (e.g., 2.45 Å, 0.76 Å, 0.80 Å, 0.76 Å, and 0.60 Å, etc.). The ionic radius of Ta may be 0.64 Å to 0.74 Å (e.g., 0.72 Å, 0.68 Å, 0.64 Å, 0.69 Å, and 0.74 Å, etc.). The ionic radius of Os may be 0.39 Å to 0.630 Å (e.g., 0.630 Å, 0.575 Å, 0.49 Å, 0.545 Å, 0.525 Å, and 0.39 Å, etc.). The ionic radius of Ir may be 0.57 Å to 0.68 Å (e.g., 0.68 Å, 0.625 Å, and 0.57 Å, etc.). The ionic radius of Mo may be 0.41 Å to 0.93 Å (e.g., 0.93 Å, 0.69 Å, 0.650 Å, 0.46 Å, 0.61 Å, 0.41 Å, 0.50 Å, 0.59 Å, and 0.73 Å, etc.). The ionic radius of Nb may be 0.48 Å to 1.00 Å (e.g., 1.00 Å, 0.72 Å, 0.68 Å, 0.79 Å, 0.48 Å, 0.64 Å, 0.69 Å, and 0.74 Å, etc.). The ionic radius of Tc may be 0.37 Å to 0.645 Å (e.g., 0.645 Å, 0.60 Å, 0.37 Å, and 0.56 Å, etc.). The ionic radius of Ru may be 0.36 Å to 0.68 Å (e.g., 0.68 Å, 0.620 Å, 0.565 Å, 0.38 Å, and 0.36 Å, etc.). The ionic radius of Ga may be 0.47 Å to 0.81 Å (e.g., 0.81 Å, 0.47 Å, 0.55 Å, and 0.620 Å, etc.). The ionic radius of Ag may be 0.67 Å to 1.28 Å (e.g., 0.67 Å, ​​1.00 Å, 1.09 Å, 1.15 Å, 1.22 Å, 1.28 Å, 0.94 Å, and 0.75 Å, etc.). The ionic radius of Pd may be 0.59 Å to 0.86 Å (e.g., 0.59 Å, 0.64 Å, 0.86 Å, 0.76 Å, and 0.615 Å, etc.). The ionic radius of Ge may be 0.390 Å to 2.72 Å (e.g., 2.72 Å, 0.73 Å, 0.390 Å, and 0.530 Å, etc.). The ionic radius of As may be 0.335 Å to 2.22 Å (e.g., 2.22 Å, 0.58 Å, 0.335 Å, and 0.46 Å, etc.). The ionic radius of In may be 0.62 Å to 0.92 Å (e.g., 0.62 Å, 0.800 Å, and 0.92 Å, etc.).The ionic radius of Pt may be 0.57 Å to 0.80 Å (e.g., 0.60 Å, 0.80 Å, 0.625 Å, and 0.57 Å, etc.). The ionic radius of Al may be 0.39 Å to 0.535 Å (e.g., 0.39 Å, 0.48 Å, and 0.535 Å, etc.). The ionic radius of Ti may be 0.42 Å to 0.96 Å (e.g., 0.96 Å, 0.86 Å, 0.670 Å, 0.42 Å, 0.51 Å, 0.605 Å, and 0.74 Å, etc.). The ionic radius of B may be 0.01 Å to 0.35 Å (e.g., 0.35 Å, 0.01 Å, 0.11 Å, and 0.27 Å, etc.). The ionic radius of Mg may be 0.57 Å to 0.89 Å (e.g., 0.82 Å, 0.57 Å, 0.66 Å, 0.720 Å, and 0.89 Å, etc.). The ionic radius of Si may be 0.26 Å to 4.00 Å (e.g., 2.71 Å, 3.84 Å, 0.65 Å, 0.26 Å, and 0.400 Å, etc.). The ionic radius of P may be 0.17 Å to 2.12 Å (e.g., 2.12 Å, 0.44 Å, 0.17 Å, 0.29 Å, and 0.38 Å, etc.). The ionic radius of Ca may be 1.00 Å to 1.34 Å (e.g., 1.18 Å, 1.00 Å, 1.06 Å, 1.12 Å, 1.18 Å, 1.23 Å, and 1.34 Å, etc.). The ionic radius of Sc may be 0.745 Å to 0.870 Å (e.g., 0.745 Å and 0.870 Å, etc.). The ionic radius of V may be 0.355 Å to 0.79 Å (e.g., 0.79 Å, 0.640 Å, 0.53 Å, 0.58 Å, 0.72 Å, 0.355 Å, 0.46 Å, and 0.54 Å, etc.). The ionic radius of Cr may be 0.26 Å to 0.81 Å (e.g., 0.81 Å, 0.73 Å, 0.80 Å, 0.615 Å, 0.41 Å, 0.55 Å, 0.345 Å, 0.49 Å, 0.57 Å, 0.26 Å, and 0.44 Å, etc.). The ionic radius of Fe may be 0.25 Å to 0.92 Å (e.g., 0.63 Å, 0.61 Å, 0.780 Å, 0.92 Å, 0.49 Å, 0.58 Å, 0.55 Å, 0.645 Å, 0.78 Å, 0.585 Å, and 0.25 Å, etc.). The ionic radius of Nd may be 0.983 Å to 1.35 Å (e.g., 1.29 Å, 1.35 Å, 0.983 Å, 1.109 Å, 1.163 Å, and 1.27 Å, etc.).

[0037] (Method for Producing 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.

[0038] The cathode active material according to the embodiment of the present disclosure can be produced, for example, by a step of obtaining a mixture and a step of calcining the mixture. The mixture is obtained by mixing raw materials containing Ni, Co, and Mn, a raw material containing Li, a raw material containing an element represented by M1, a raw material containing an element represented by M2, and a raw material containing an element represented by M3.

[0039] A method for producing a positive electrode active material according to an embodiment of the present disclosure preferably includes: a step of mixing a raw material containing Ni, a raw material containing Co, a raw material containing Mn, a raw material containing Li, a raw material containing an element represented by M1, and a raw material containing an element represented by M2 to obtain a first mixture; a first firing step of heating the first mixture in an oxygen atmosphere at a temperature rise rate A of 1°C / min or more and 10°C / min or less to a maximum temperature X-100°C, and then heating it from the maximum temperature X-100°C to the maximum temperature X at a temperature rise rate B of 0.1°C / min or more and 5°C / min that is slower than the temperature rise rate A to obtain a second mixture; and a second firing step of firing the second mixture in an oxygen atmosphere at a maximum temperature that is lower than the maximum temperature X.

[0040] In a positive electrode active material, an M1 element with a large ionic radius has a characteristic that it is difficult to enter the TM layer in the layered crystal structure. However, by using a combination of an M1 element and an M2 element and performing firing under the conditions of the first firing step, the M1 element is incorporated into the TM layer and the added element in the TM layer is diffused. Therefore, it is possible to make the M1 element and the M2 element present in large amounts in the layered crystal structure of the positive electrode active material. By adding a raw material containing an M3 element after the first firing step and performing firing under the conditions of the second firing step, the M3 element is incorporated into the Li layer. This results in a positive electrode active material that, when used in a battery, can suppress an increase in battery resistance after repeated charge and discharge.

[0041] A method for producing a positive electrode active material according to an embodiment of the present disclosure preferably includes the following steps (1) to (7): (1) preparing a solution in which raw materials containing Ni, Co, and Mn are dissolved (raw material dissolution); (2) adding the solution to an alkaline solution to precipitate hydroxides (crystallization); (3) collecting a precipitate from the alkaline solution; (4) mixing the precipitate with a raw material containing Li, a raw material containing an element represented by M1, and a raw material containing an element represented by M2 to obtain a first mixture (first mixing); (5) a first firing step of firing the first mixture; (6) mixing the first mixture after the first firing step with a raw material containing the element represented by M2 to obtain a second mixture (second mixing); and (7) a second firing step of firing the second mixture.

[0042] Each step will be described in detail below.

[0043] (1) Step of preparing a solution containing raw materials containing Ni, Co, and Mn. A solution containing a raw material containing Ni, a raw material containing Co, and a raw material containing Mn is prepared. For example, the solution can be prepared by dissolving the raw material containing Ni, the raw material containing Co, and the raw material containing Mn in a solvent such as water. The concentration of the solution is preferably within a range of, for example, 10% by mass to 40% by mass. The ratio of Ni / Co / Mn is preferably 1.0 / 0.8-1.2 / 0.8-1.2 (atm %) with respect to Ni:1.0.

[0044] NiSO is a raw material containing Ni. ４ Examples of raw materials containing Co include CoSO ４ Examples of raw materials containing Mn include sulfates such as MnSO ４ and the like sulfates.

[0045] (2) Step of adding the solution to an alkaline solution to precipitate hydroxides. Next, the solution is added to an alkaline solution to precipitate hydroxides. As a result, particles containing hydroxides containing Ni, Co, and Mn are crystallized and obtained as precipitates. In this step, for example, the alkaline solution in which the hydroxides have precipitated is controlled to a constant pH (e.g., pH 10 to 12) while the solution and NH ３By adding dropwise, hydroxides of the transition metals are precipitated.

[0046] (3) Step of collecting precipitate from alkaline solution Next, the precipitate is collected from the alkaline solution. Examples of methods for collecting the precipitate particles include filtration and washing with water. First, the precipitate (particles) are removed by filtration and washed with water, and the washed solution is further filtered to remove the precipitate (particles). The precipitate (particles) after washing with water may be further dried.

[0047] (4) A step of mixing the precipitate with a raw material containing Li, a raw material containing an element represented by M1 (M1 element), and a raw material containing an element represented by M2 (M2 element) to obtain a first mixture. Next, the collected precipitate (particles) is mixed with the raw material containing Li, the raw material containing M1 element, and the raw material containing M2 element to obtain a first mixture. For example, the collected precipitate particles can be mixed with the raw material containing Li, the raw material containing M1 element, and the raw material containing M2 element in a mortar.

[0048] The raw material containing Li is Li ２ CO ３ The raw material containing M1 (i.e., at least one element selected from the group consisting of Ba, Pr, La, Y, Sr, Ce, Se, Hf, Rh, Zr, and Sn) may be an oxide of each element (e.g., BaO, Pr, ２ O ３ , La ２ O ３ As a raw material containing M2 (that is, at least one element selected from the group consisting of W, Re, Sb, Sn, Ta, Os, Ir, Mo, Nb, Tc, Ru, Ga, Ag, Pd, Ge, As, Zr, In, Pt, Al, and Ti), oxides of each element (for example, W ２ O ３ , MoO ３ , and NbO).

[0049] (5) First firing step of firing the first mixture: Next, the first mixture of the collected precipitate (particles), the raw material containing Li, the raw material containing the M1 element, and the raw material containing the M2 element is fired. For example, the first mixture can be fired in a firing furnace (e.g., a muffle furnace).

[0050] As the temperature rise conditions during firing, it is preferable to raise the temperature at a temperature rise rate A of 1 ° C. / min to 10 ° C. / min to the maximum temperature X-100 ° C., and then raise the temperature from the maximum temperature X-100 ° C. to the maximum temperature X at a temperature rise rate B of 0.1 ° C. / min to 5 ° C. / min, which is slower than the temperature rise rate A. By adjusting the temperature rise conditions as described above, it is possible to make the M1 element and the M2 element exist in a larger amount in the layered crystal structure of the positive electrode active material. The temperature rise rate A to the maximum temperature X-100 ° C. is 1 ° C. / min to 10 ° C. / min, and is preferably 3 ° C. / min to 6 ° C. / min. The temperature rise rate B from the maximum temperature X-100 ° C. to the maximum temperature X is 0.1 ° C. / min to 5 ° C. / min, which is slower than the temperature rise rate A, and is preferably 0.5 ° C. / min to 2 ° C. / min. The time required for raising the temperature from the maximum temperature X-100° C. to the maximum temperature X° C. is preferably 20 minutes or more and 1000 minutes or less, and more preferably 50 minutes or more and 200 minutes or less.

[0051] As for the firing conditions, the maximum temperature X is preferably 500° C. to 1500° C., and more preferably 800° C. to 1200° C. The firing is carried out in an oxygen atmosphere, and the heating time after the maximum temperature X is reached can be 5 hours or more and 20 hours or less.

[0052] In order to make the resulting mixture have a predetermined particle size, the fired first mixture may be crushed. Examples of the crushing method include crushing using a crusher (e.g., a jet mill).

[0053] (6) A step of mixing the first mixture after the first firing step with a raw material containing an element represented by M3 (M3 element) to obtain a second mixture. Next, the first mixture after the first firing step is mixed with a raw material containing the M3 element to obtain a second mixture. For example, mixing can be performed in a mortar.

[0054] The raw material containing M3 (i.e., at least one element selected from the group consisting of B, Mg, Si, P, Ca, Sc, Ti, V, Cr, Fe, Ga, Ge, Y, Zr, Nb, Mo, Ru, Rh, Al, Hf, Ta, W, Re, Os, Ir, La, Ce, Pr, and Nd) may be an oxide of each element (e.g., B ２ O ３ , and ZrO).

[0055] (7) Second Firing Step of Firing the Second Mixture Next, the second mixture containing the raw material containing the M3 element is fired. For example, the second mixture can be fired in a firing furnace (such as a muffle furnace).

[0056] As for the firing conditions during firing, firing is preferably performed at a maximum temperature that is lower than the maximum temperature X in the first firing step (for example, a temperature that is 50° C. or more and 150° C. or less than the maximum temperature X). The firing is performed in an oxygen atmosphere, and the heating time after the maximum temperature is reached can be 1 hour or more and 5 hours or less.

[0057] In order to make the resulting mixture have a predetermined particle size, the fired second mixture may be crushed. Examples of the crushing method include crushing using a crusher (e.g., a jet mill).

[0058] By going through these steps, the positive electrode active material according to the embodiment of the present disclosure can be obtained.

[0059] <Lithium-ion battery> A lithium-ion battery according to an embodiment of the present disclosure includes a positive electrode active material according to an embodiment of the present disclosure. The lithium-ion battery includes, for example, a negative electrode, a positive electrode, a separator, and an electrolyte. The lithium-ion battery according to an embodiment of the present disclosure may be a solid-state battery including a solid electrolyte or a liquid battery including a liquid electrolyte. The lithium-ion battery may also be a bipolar battery including a positive electrode active material layer and a negative electrode active material layer on both sides of a current collector that functions as a positive electrode current collector and a negative electrode current collector.

[0060] (Positive Electrode) The positive electrode includes, for example, a positive electrode current collector and a positive electrode active material layer fixed on the positive electrode current collector. The positive electrode active material layer includes the positive electrode active material according to an embodiment of the present disclosure as the positive electrode active material. Details of the positive electrode active material have already been described, so they will not be discussed here. The positive electrode active material layer may include a conductive material in addition to the positive electrode active material, and may further include other components (e.g., binders, various additives, etc.). Examples of conductive materials include non-graphitizable carbon, graphitizable carbon such as acetylene black or carbon black, and graphite. Examples of binders include vinyl halide resins such as polyvinylidene fluoride (PVdF).

[0061] The positive electrode current collector is preferably a conductive member made of a metal with good conductivity (e.g., aluminum). A current collector that functions as both a positive electrode current collector and a negative electrode current collector (i.e., a bipolar battery) may also be used.

[0062] (Negative Electrode) The negative electrode includes, for example, a negative electrode current collector and a negative electrode active material layer fixed on the negative electrode current collector. The negative electrode current collector is preferably a conductive material made of a metal with good conductivity (e.g., copper). A current collector that functions as both a positive electrode current collector and a negative electrode current collector (i.e., a bipolar battery) may also be used. The negative electrode active material layer contains a negative electrode active material. Examples of negative electrode active materials include graphite-based carbons such as natural graphite, artificial graphite, and amorphous-coated graphite. The proportion of graphite in the graphite-based carbon may be approximately 50% by mass or more, preferably 80% by mass or more. The negative electrode active material layer may be composed solely of the negative electrode active material, or may contain components other than the negative electrode active material (e.g., thickeners, binders, etc.) as needed. Examples of thickeners include celluloses such as carboxymethyl cellulose (CMC). Examples of binders include rubbers such as styrene butadiene copolymer (SBR) and vinyl halide resins such as polyvinylidene fluoride (PVdF).

[0063] (Separator) The separator is an electrically insulating porous film. The separator electrically isolates the positive electrode and the negative electrode. The separator may have a thickness of, for example, 5 μm to 30 μm. The separator may be composed of, for example, a porous polyethylene (PE) film or a porous polypropylene (PP) film. The separator may have a multilayer structure. For example, the separator may be composed of a porous PP film, a porous PE film, and a porous PP film laminated in this order. The separator may have a heat-resistant layer on its surface. The heat-resistant layer contains a heat-resistant material. Examples of heat-resistant materials include metal oxide particles such as alumina, and high-melting-point resins such as polyimide.

[0064] (Electrolyte) The battery according to the embodiment of the present disclosure may be a liquid-based battery further containing an electrolyte, and a non-aqueous electrolyte is particularly preferred.

[0065] The non-aqueous electrolyte solution contains a solvent (non-aqueous solvent) and an electrolyte. Examples of the solvent (non-aqueous solvent) include ethyl carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), propylene carbonate (PC), fluoroethylene carbonate (FEC), 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).

[0066] The electrolyte in the electrolyte solution may be, for example, a Li salt. Examples of the Li salt include lithium bis(fluorosulfonyl)imide (LiFSI) and LiPF ６ (lithium hexafluorophosphate), lithium tetrafluoroborate (LiBF ４ ), and Li[N(CF ３ SO ２ ) ２ The amount of the electrolyte may be, for example, 1.0 mol / L to 2.0 mol / L, and preferably 1.0 mol / L to 1.5 mol / L.

[0067] The electrolytic solution may contain various additives (e.g., thickeners, film-forming agents, gas generating agents, etc.) in addition to the solvent and electrolyte. The electrolyte is typically a non-aqueous electrolytic solution that is liquid at room temperature (e.g., 25±10°C). The electrolytic solution typically remains liquid in the environment in which the battery is used (e.g., a temperature environment of −20 to +60°C).

[0068] (Applications) Applications of the battery include, for example, power sources for hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and electric vehicles (BEVs).

[0069] The present disclosure will be described below based on examples, but the present disclosure is not limited to these examples in any way.

[0070] Example 1 Synthesis of Positive Electrode Active Material The positive electrode active material was synthesized by the following method. ｘ Ni ａ Co ｂ Mn ｃ M1 ｄ M2 ｅ M3 ｆ O ２ The ratios of x, a, b, c, d, e, and f are shown in Table 1. The elements shown in Table 1 were used as the element represented by M1, the element represented by M2, and the element represented by M3.

[0071] ・Raw material solution NiSO ４ , CoSO ４ , and MnSO ４ The Ni / Co / Mn ratio was 80 / 10 / 10 (atm %), and the concentration of the aqueous solution was 30 mass %.

[0072] NH in the crystallization reaction vessel ３ A certain amount of aqueous solution was added, 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, the raw material solution and NH ３ was added dropwise to precipitate the transition metal hydroxide.

[0073] Washing with water, filtration, and drying: The precipitated transition metal hydroxide was filtered out, and ion-exchanged water was added and stirred with a spoon to disperse it, followed by washing 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.

[0074] A mixture of a Li raw material, an M1 raw material, and an M2 raw material, a dried transition metal hydroxide, and Li as a Li raw material. ２ CO ３ and LiOH, and Pr as M1 raw material ２ O ３ and W as M2 raw material ２ O ３ and were mixed in a mortar.

[0075] - First calcination and crushing A mixture of transition metal hydroxide, Li raw material, M1 raw material, and M2 raw material was calcined in a calcination furnace (muffle furnace). The calcination conditions were: maximum temperature (X) 800 ° C, temperature rise rate to maximum temperature (X) -100 ° C. 5 ° C. / min, temperature rise rate from maximum temperature (X) -100 ° C. to maximum temperature (X) 1 ° C. / min, heating time after reaching the maximum temperature was 10 hours, and the calcination atmosphere was an oxygen atmosphere. Next, the calcined mixture was crushed to a predetermined particle size by pulverizing it with a pulverizer (jet mill) to obtain particles.

[0076] Mixing of M3 raw materials Then, the particles obtained in the first firing and crushing step and B as M3 raw materials ２ O ３ were mixed in a mortar.

[0077] Second Calcination and Crushing: A mixture of the particles obtained in the first calcination and crushing step and the M3 raw material was calcined in a calcination furnace (muffle furnace). The calcination conditions included a maximum temperature of 700°C, a heating time of 3 hours after reaching the maximum temperature, and an oxygen atmosphere. The calcined mixture was then crushed to a predetermined particle size by pulverizing it with a pulverizer (jet mill). Thus, the positive electrode active material of Example 1 was obtained. The above-described TEM-EDX analysis revealed that in the layered crystal structure of the positive electrode active material of Example 1, the TM layer contained M1 and M2, and the Li layer contained M3.

[0078] Examples 2 to 8 The M1 raw material in Example 1 was replaced with Pr ２ O ３ From La ２ O ３ (Examples 3 to 6), and SrO (Examples 7 to 8), and the M2 raw material was changed to W ２ O ３ The M3 raw material was changed to NbO (Examples 7-8), and the M4 raw material was changed to B ２ O ３ The positive electrode active materials of each Example were obtained in the same manner as in Example 1, except that the TM layer contained M1 and M2, and the Li layer contained M3, in the layered crystal structure of the positive electrode active materials of Examples 2 to 8.

[0079] Comparative Example 1 A positive electrode active material of Comparative Example 1 was obtained in the same manner as in Example 1, except that the M1 raw material, M2 raw material, and M3 raw material in Example 1 were not added, the second firing and crushing step was not performed, and only the first firing and crushing step was performed, and the firing conditions were such that the heating rate (°C / min) to the maximum temperature (X) - 100°C and the heating rate (°C / min) from the maximum temperature (X) - 100°C to the maximum temperature (X) were both 5°C / min (that is, the same heating rate was used for both).

[0080] Comparative Examples 2 and 3: The M1 raw material in Example 1 was replaced with Pr ２ O ３ From ZrO (Comparative Example 2), and La ２ O ３ (Comparative Example 3), and the M2 raw material was changed to W ２ O ３ From Al ２ O ３ (Comparative Example 2), and W ２ O ３The positive electrode active materials of Comparative Examples 2 and 3 were obtained in the same manner as in Example 1, except that the M3 raw material was not added, the ratios of M1 and M2 (d and e) were adjusted to the ratios shown in Table 1, the second firing and crushing steps were not performed, and only the first firing and crushing steps were performed, and the firing conditions were the same as in Comparative Example 1 (that is, the heating rate (°C / min) to the maximum temperature (X) - 100°C, and the heating rate (°C / min) from the maximum temperature (X) - 100°C to the maximum temperature (X) were both 5°C / min).

[0081] Comparative Examples 4 to 9: The M1 raw material in Example 1 was replaced with Pr ２ O ３ From the above, BaO (Comparative Example 4), La ２ O ３ (Comparative Example 6), and SrO (Comparative Examples 7 to 9), and the M2 raw material was changed to W ２ O ３ From MoO ３ The positive electrode active materials of Comparative Examples 4 to 9 were obtained in the same manner as in Example 1, except that the M3 raw material was changed to NbO (Comparative Example 8), and NbO (Comparative Example 9), the M3 raw material was not added, the second firing and crushing step was not performed, and only the first firing and crushing step was performed, and the firing conditions were the same as in Example 1 (that is, the maximum temperature (X) was 800°C, the heating rate to the maximum temperature (X) -100°C was 5°C / min, the heating rate from the maximum temperature (X) -100°C to the maximum temperature (X) was 1°C / min, and the heating time after reaching the maximum temperature was 10 hours, and firing was performed in an oxygen atmosphere).

[0082] Comparative Example 10: The M3 raw material in Example 1 was replaced with B ２ O ３ From SO ３ A positive electrode active material of Comparative Example 10 was obtained in the same manner as in Example 1, except that the above-mentioned conditions were changed.

[0083] Comparative Example 11: The M1 raw material and the M2 raw material in Example 1 were not added, and the M3 raw material was added to B ２ O ３ A positive electrode active material of Comparative Example 11 was obtained in the same manner as in Example 1, except that ZrO was changed from

[0084] Comparative Example 12 A positive electrode active material of Comparative Example 12 was obtained in the same manner as in Example 1, except that the synthesis method in Example 1 was changed from the synthesis method in which the first firing and crushing step and the second firing and crushing step were performed under the same conditions as in Example 1 to a synthesis method in which the first firing and crushing step was performed under the same conditions as in Comparative Example 1 (but the second firing and crushing step was not performed).

[0085] [Cell Fabrication] Cells were fabricated using the positive electrode active materials obtained in each Example and Comparative Example. Cell configuration: wound cylindrical 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: LiPF ６ (1M), solvent = ethylene carbonate (EC) / dimethyl carbonate (DMC) / ethyl methyl carbonate (EMC), solvent volume ratio (EC / DMC / EMC) = 3 / 4 / 3 (volume %)

[0086] - 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.

[0087] [Initial Resistance Ratio] The initial battery resistance of the cells obtained in each Example and Comparative Example was measured. Table 2 shows the ratio of the battery resistance of the cells in each Example and Comparative Example, where the battery resistance of Comparative Example 1 is set to "1".

[0088] [Ni-mixing / After 100 Cycles and 150 Cycles] The cells obtained in each Example and Comparative Example were subjected to 100 and 150 charge-discharge cycles under the following test conditions, and the Ni-mixing of the positive electrode active material layer thereafter was calculated using the following method. Synchrotron XRD (X-ray diffraction) diffraction was performed on the positive electrode active material, and Rietveld analysis (FullProf) was performed on the XRD diffraction data. Next, the Ni-mixing amount was arbitrarily input to calculate the Chi2 value, and the Ni-mixing with the lowest Chi2 value was designated as the "Ni-mixing" for each positive electrode active material. Ni-mixing indicates the ratio of the number of moles of Ni in the Li layer to the total number of moles of Ni. Test conditions: The test was performed at 60°C, at a 2C rate, with one cycle consisting of charge and discharge from 0% to 100% SOC.

[0089] [Resistance Increase Rate / After 100 Cycles and After 150 Cycles] The cells obtained in each Example and Comparative Example were subjected to 100 and 150 charge / discharge cycles under the following test conditions, and the battery resistance was measured before and after the cycles. Table 2 shows the results of the percentage of battery resistance after 100 cycles and 150 cycles (resistance increase rate (%)), assuming the battery resistance before the cycles to be "100%." ​​It can be said that the closer the resistance increase rate is to 100%, the better the battery characteristics are. Test conditions: The test was conducted at 60°C, at a 2C rate, with charge / discharge from 0% to 100% SOC being one cycle.

[0090] "Synthesis method 1" in Table 1 refers to a synthesis method in which the first firing and crushing step is performed under the same conditions as Comparative Example 1 (but the second firing and crushing step is not performed). "Synthesis method 2" refers to a synthesis method in which the first firing and crushing step is performed under the same conditions as Comparative Example 4 (but the second firing and crushing step is not performed). "Synthesis method 3" refers to a synthesis method in which the first firing and crushing step and the second firing and crushing step are performed under the same conditions as Example 1.

[0091]

[0092]

[0093] As shown in Tables 1 and 2, it can be seen that the positive electrode active materials of the examples containing elements defined in the present disclosure as the elements M1, M2, and M3 can suppress an increase in battery resistance after repeated charge and discharge and can also reduce the initial battery resistance, compared to the positive electrode active materials of the comparative examples which do not contain elements defined in the present disclosure as the elements M1, M2, and M3.

[0094] The disclosures of Japanese Patent Application No. 2024-122654, filed on July 29, 2024, and Japanese Patent Application No. 2025-050692, filed on March 25, 2025, are incorporated herein by reference in their entirety. All documents, patent applications, and technical standards described herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard was specifically and individually indicated to be incorporated by reference.

Claims

1. Li ｘ Ni ａ Co ｂ Mn ｃ M1 ｄ M2 ｅ M3 ｆ O ２ a positive electrode active material having a composition represented by the formula: wherein M1, M2, and M3 each contain at least one element selected from the group of elements shown below, and M1, M2, and M3 contain three or more elements in total; (In the composition, 0.1≦x≦1.5, 0.5≦a≦1.0, 0≦b≦0.5, 0≦c≦0.5, a+b+c=1.0, 0.0005≦d≦0.050, 0.0005≦e≦0.050, and 0.0005≦f≦0.050 are satisfied, M1 represents at least one element selected from the group of elements consisting of Ba, Pr, La, Y, Sr, Ce, Se, Hf, Rh, Zr, and Sn, and M2 represents W, Re, Sb, Sn, Ta, Os, Ir, M M1 represents at least one element selected from the group consisting of O, Nb, Tc, Ru, Ga, Ag, Pd, Ge, As, Zr, In, Pt, Al, and Ti, and M3 represents at least one element selected from the group consisting of B, Mg, Si, P, Ca, Sc, Ti, V, Cr, Fe, Ga, Ge, Y, Zr, Nb, Mo, Ru, Rh, Al, Hf, Ta, W, Re, Os, Ir, La, Ce, Pr, and Nd, and M1 and M3 are different.

2. The positive electrode active material according to claim 1, wherein the ionic radius of the element contained in M3 is smaller than the ionic radius of the element contained in M1 and larger than the ionic radius of the element contained in M2.

3. The positive electrode active material according to claim 1, wherein the combination of M1 and M2 is at least one combination selected from the group consisting of Ba—W, Pr—W, La—W, Y—W, Sr—W, Ce—W, Pr—Re, Ba—Re, Sr—Sb, Se—W, Y—Re, Hf—W, Sr—Re, Rh—W, Zr—W, Sr—Sn, Y—Ta, Pr—Ta, Y—Sb, Sr—Os, Sr—Ta, Ce—Re, La—Re, Ba—Ta, Sr—Ir, Sn—W, Sr—Mo, Sr—Nb, Ba—Ti, Ba—Zr, and Ba—Al; and M3 includes at least one element selected from the group consisting of B, Zr, Mg, Al, and Sc.

4. The positive electrode active material according to claim 3, wherein the combination of M1 and M2 is at least one combination selected from the group consisting of Ba—W, Pr—W, La—W, Hf—W, Sr—Nb, and Pr—Ta.

5. The positive electrode active material according to claim 1, wherein M1 contains at least one element selected from the group of elements consisting of Pr, La, and Sr, M2 contains at least one element selected from the group of elements consisting of W and Nb, and M3 contains at least one element selected from the group of elements consisting of B, Zr, Mg, Al, and Sc.

6. The positive electrode active material according to claim 1, wherein the combination of M1, M2, and M3 is at least one combination selected from the group consisting of Ba-W-B, Pr-W-B, La-W-B, La-W-Zr, La-W-Mg, La-W-Al, La-W-Sc, Hf-W-B, Hf-W-Zr, Hf-W-Mg, Hf-W-Al, Hf-W-Sc, Sr-Nb-Al, and Pr-Ta-Mg.

7. The positive electrode active material according to claim 1, having a layered crystal structure having a lithium layer containing Li and a transition metal layer containing at least one selected from the group consisting of Ni, Co, and Mn, wherein the lithium layer further contains M3, and the transition metal layer further contains M1 and M2.

8. A positive electrode comprising the positive electrode active material according to any one of claims 1 to 7.

9. A lithium ion battery having the positive electrode of claim 8.

10. A method for producing the cathode active material according to claim 1, comprising the steps of: mixing raw materials containing Ni, Co, and Mn, a raw material containing Li, a raw material containing an element represented by M1, and a raw material containing an element represented by M2 to obtain a first mixture; a first firing step of heating the mixture in an oxygen atmosphere to a maximum temperature X-100°C at a heating rate A of 1°C / min to 10°C / min, and then heating the mixture from the maximum temperature X-100°C to the maximum temperature X at a heating rate B of 0.1°C / min to 5°C / min which is slower than the heating rate A, thereby firing the first mixture; a step of mixing a raw material containing an element represented by M3 with the first mixture after the first firing step to obtain a second mixture; and a second firing step of firing the second mixture in an oxygen atmosphere at a maximum temperature lower than the maximum temperature X.

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