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

Abstract

To suppress increase in battery resistance after repetition of charge and discharge.SOLUTION: A positive electrode active material represented by LixNiaCobMncM1dM2eM3fO2 and containing, as M1 to M3, one or more elements from the following element group, that is, three or more elements in total. 0.1 ≤ a ≤ 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, 0.0005 ≤ f ≤ 0.05, M1 represents Ba, Pr, La, Y, Sr, Ce, Se, Hf, Rh, Zr, and Sn, M2 represents W, Re, Sb, Sn, Ta, Os, Ir, Mo, Nb, Tc, Ru, Ga, Ag, Pd, Ge, As, Zr, In, Pt, Al, and Ti, and 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, and Nd, the M1 and the M3 are different.SELECTED DRAWING: None

Description

[Technical Field]

[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. [Background technology]

[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 producing 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 producing a positive electrode active material. The 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 raw 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 La4NiLiO8 coating are introduced into LiNi 0.85 Co 0.05 Mn 0.10 A positive electrode active material powder of O2 (particle size: approximately 2.01 μm) is disclosed. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Special Publication No. 2022-513681 [Patent Document 2] Special Publication No. 2023-536251 [Non-patent literature]

[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 Summary of the Invention [Problem to be solved by the invention]

[0008] In batteries containing elements represented by M1 and M2, after repeated charge and discharge, 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 (cation mixing) and increasing the battery resistance. Therefore, there is a need to suppress the increase in battery resistance even after repeated charge and discharge.

[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. [Means for solving the problem]

[0010] 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 O2, The positive electrode active material contains at least one element selected from the group of elements shown below as M1, M2, and M3, totaling 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, 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 W, Re, Sb, Sn, Ta, 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, and M1 and M3 are different. <2> The element contained as M3 has an ionic radius smaller than that of M1 and larger than that of M2. <1> The positive electrode active material according to claim 1. <3> the combination of M1 and M2 is at least one combination selected from the group consisting of Ba—W, Pr—W, La—W, YW, 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; The M3 includes at least one element selected from the group consisting of B, Zr, Mg, Al, and Sc. <1> or <2> The positive electrode active material according to claim 1. <4> 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. <3> The positive electrode active material according to claim 1. <5> M1 contains at least one element selected from the group consisting of Pr, La, and Sr, The M2 includes at least one element selected from the group consisting of W and Nb, The M3 includes at least one element selected from the group consisting of B, Zr, Mg, Al, and Sc. <1> ~ <4> 10. The positive electrode active material according to claim 1, <6> the combination of M1, M2, and M3 is at least one combination selected from the group consisting of Ba-WB, Pr-WB, La-WB, La-W-Zr, La-W-Mg, La-W-Al, La-W-Sc, Hf-WB, Hf-W-Zr, Hf-W-Mg, Hf-W-Al, Hf-W-Sc, Sr-Nb-Al, and Pr-Ta-Mg; <1> ~ <5> 10. The positive electrode active material according to claim 1, <7> 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; the lithium layer further comprises M3, the transition metal layer further comprises the M1 and the M2; <1> ~ <6> 10. The positive electrode active material according to claim 1, <8> <1> ~ <7> 10. A positive electrode comprising the positive electrode active material according to claim 1. <9> <8> A lithium ion battery having the positive electrode according to claim 1. <10> <1> ~ <7> A method for producing a positive electrode active material according to any one of claims 1 to 4, 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 firing the first mixture by 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 that is slower than the heating rate A; 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; a second firing step of firing the second mixture in an oxygen atmosphere at a maximum temperature lower than the maximum temperature X. [Effects of the Invention]

[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. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, an embodiment of the present disclosure will be described. These descriptions and examples are intended to illustrate the embodiment and are not intended to limit the scope of the invention. In the present specification, the upper or lower limit of one numerical range may be replaced by the upper or lower limit of another numerical range. In the present specification, the upper or lower limit of a numerical range may be replaced by a value shown in the examples.

[0013] Each component may contain multiple types of the corresponding substance. When referring to the amount of each component in a composition, if there are multiple substances corresponding to each component in the composition, the amount refers to the total amount of those multiple substances present in the composition, 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] <Cathode active material> The positive electrode active material according to the embodiment of the present disclosure is Li x Ni a Co b Mn c M1 d M2 e M3 f It has a composition represented by O2. The M1, M2, and M3 each contain at least one element selected from the following element group, totaling 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, 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 W, Re, Sb, Sn, Ta, 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, and M1 and M3 are different.

[0015] When the positive electrode active material according to the embodiment of the present disclosure is used in a battery, an increase in the resistance of the battery after repeated charge and discharge can be suppressed. 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 the purpose of improving the resistance characteristics of batteries. The positive electrode active material has a layered crystal structure (e.g., a layered rock-salt crystal structure) having a lithium layer containing Li (hereinafter also referred to as a "Li layer") and a transition metal layer containing transition metals such as Ni, Co, and Mn (hereinafter also referred to as a "TM layer"). However, certain doping elements have difficulty entering the layered crystal structure of the positive electrode active material, and conventional positive electrode active materials have the characteristic of having little structural stabilization effect.

[0017] In response to this problem, a method of incorporating two doping elements, M1 and M2, is considered. While elements represented by M1 (hereinafter referred to as "M1 elements") have a large ionic radius and therefore are difficult to incorporate into the layered crystal structure of a positive electrode active material, combining an M1 element with an element represented by M2 (hereinafter referred to as "M2 elements") makes it easier for the M1 element to be incorporated into the layered crystal structure. This allows the doping elements, M1 and M2, to be present in large amounts in the layered crystal structure of the positive electrode active material, significantly 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, thereby suppressing the inhibition of Li ion migration during charging and discharging, and thus suppressing an increase in battery resistance. However, repeated charge-discharge cycles of 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-discharge cycles. In addition, M1 and M2 may not be located in the intended location (specifically, the Li layer or TM layer). Failure to locate M1 and M2 in the intended location can easily lead to defects. For example, unreacted M1 and M2 can inhibit the entry and exit of Li into the layered crystal structure during the battery reaction, increasing the battery resistance. Furthermore, if the battery contains an electrolyte, unreacted M1 and M2 can react with the electrolyte (e.g., decomposition of the electrolyte), resulting in a decrease in battery capacity.

[0018] In contrast, in the positive electrode active material according to an embodiment of the present disclosure, in addition to the M1 and M2 elements, an element represented by M3 (hereinafter referred to as the "M3 element") is used in combination. The M3 element exerts electrostatic repulsion due to its high valence, and also exerts steric repulsion due to its relatively large ionic radius (e.g., smaller than that of the M1 element but larger than that of the M2 element). In particular, when the Li layer further contains the M3 element and the TM layer further contains the M1 and M2 elements, the M3 element supports the M1 and M2 elements, preventing the M1 element from falling out of the layered crystal structure (e.g., mixing of the M1 and M2 elements into the Li layer). This prevents Ni mixing (cation mixing) from occurring, and thus prevents an increase in battery resistance even after repeated charge / discharge cycles.

[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] The inclusion of the M3 element prevents the M3 element in the Li layer from moving and functions as a pillar during charge and discharge. 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, preventing the movement of Li from being impeded. 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 is Li x Ni a Co b Mn c M1 d M2 e M3 f It has a composition represented by O2. (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, 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 W, Re, Sb, Sn, Ta, O 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.

[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 or more and 1.5 or less, preferably 0.3 or more and 1.4 or less, more preferably 0.5 or more and 1.2 or less, particularly preferably 0.9 or more and 1.2 or less, and even more preferably 1.0 or more and 1.2 or less, From the viewpoint of the resistance characteristics of the battery, the ratio a of Ni is 0.5 to 1.0, preferably 0.6 to 0.9, and more preferably 0.7 to 0.8. When the ratio a of Ni is increased, the ratio a is preferably 0.6 to 1.0 (0.6≦a≦1.0), more preferably 0.7 to 1.0 (0.7≦a≦1.0), and particularly preferably 0.7 to 0.9 (0.7≦a≦0.9). From the viewpoint of resistance characteristics in 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 resistance characteristics in the battery, the ratio c of Mn 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 proportions of Ni, Co and Mn (a+b+c) is 1.0.

[0024] 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 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, suppression of an increase in the resistance of the battery after repeated charge and discharge, and reduction of the initial battery resistance), 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, 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 (particularly suppression of increase in battery resistance after repeated charge / discharge and reduction of 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 thought that the generation of troublesome by-products is less likely, and the effect of improving the resistance characteristics of the battery is 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. The positive electrode active material contains at least one element M1, one element M2, and one element M3 from the above-described element group, for 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, M2 element, and 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 the battery is suppressed, and the initial battery resistance is reduced.

[0027] From the viewpoints of suppressing an increase in battery resistance after repeated charge / discharge and reducing the initial battery resistance, the combination of the M1 element and the M2 element is preferably at least one combination selected from the group consisting of Ba—W, Pr—W, La—W, YW, 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 (the left side of the - indicates the M1 element, and the right side of the - indicates the M2 element). Furthermore, from the viewpoint of suppressing an increase in battery resistance after repeated charge / discharge and reducing the initial battery resistance, it is more preferable that the combination of the M1 element and the M2 element be at least one combination 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 battery resistance after repeated charge / 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 battery resistance after repeated charge and discharge and reducing the initial battery resistance, it is preferable that the M1 element, M2 element, and 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 / discharge cycles and reducing the initial battery resistance, it is preferable that the combination of the M1 element, the M2 element, and the M3 element be at least one combination selected from the group consisting of Ba-WB, Pr-WB, La-WB, La-W-Zr, La-W-Mg, La-W-Al, La-W-Sc, Hf-WB, Hf-W-Zr, Hf-W-Mg, Hf-W-Al, Hf-W-Sc, Sr-Nb-Al, and Pr-Ta-Mg (the element on the left represents the M1 element, the element in the middle represents the M2 element, and the element on the right 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-WB, Pr-W-Zr, La-WB, 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 of the periodic table.

[0033] The fact that the Li layer contains M3 and the TM layer contains M1 and M2 can be confirmed using transmission electron microscope (TEM)-energy dispersive X-ray spectroscopy (EDX), which can identify individual atoms and pinpoint the element locations.

[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, 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, 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, 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, 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, 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, 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, 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, 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, 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, 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, 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, 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, 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, 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, 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, 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, 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, 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, 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, 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, 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, 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, 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, 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, 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, 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, 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, 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, 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, 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, 1.27 Å, etc.).

[0037] (Method of manufacturing positive electrode active material) Next, a method for producing a positive electrode active material according to an embodiment of the present disclosure will be described.

[0038] The positive electrode active material according to the embodiment of the present disclosure can be produced, for example, through a step of mixing raw materials each 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 to obtain a mixture, and a firing step of firing the mixture.

[0039] A method for producing a positive electrode active material according to an embodiment of the present disclosure preferably includes the steps 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 heating rate A of 1°C / min to 10°C / min 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 heating rate B of 0.1°C / min to 5°C / min which is slower than the heating rate A; 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.

[0040] In positive electrode active materials, the M1 element, which has a large ionic radius, has difficulty entering the TM layer in the layered crystal structure. However, by using a combination of M1 and M2 elements and performing firing under the conditions of the first firing step, the M1 element is incorporated into the TM layer and the added elements in the TM layer are diffused. This allows the M1 and M2 elements to be present in large amounts in the layered crystal structure of the positive electrode active material. By adding a raw material containing the 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] The 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) A step of 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 hydroxide (crystallization) (3) collecting the precipitate from the alkaline solution (4) A step of 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) A step of mixing the first mixture after the first firing step with a raw material containing an element represented by M2 to obtain a second mixture (second mixing). (7) A second firing step of firing the second mixture

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

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

[0044] Examples of raw materials containing Ni include sulfates such as NiSO4, Co include sulfates such as CoSO4, and Mn include sulfates such as MnSO4.

[0045] (2) Adding the solution to an alkaline solution to precipitate hydroxide Next, the solution is added to an alkaline solution to precipitate the hydroxides. This causes the generated particles of hydroxides containing Ni, Co, and Mn to crystallize, and these particles are obtained as a precipitate. In this process, 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 NH3 are added dropwise, thereby precipitating the transition metal hydroxides.

[0046] (3) A step of collecting the precipitate from the alkaline solution The precipitate is then collected from the alkaline solution. Examples of methods for collecting the precipitate particles include filtration and washing with water. First, the precipitate (particles) are removed by filtration and washed with water, and the washed liquid is then filtered to remove the precipitate (particles). The washed precipitate (particles) 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) are mixed with a raw material containing Li, a raw material containing the M1 element, and a raw material containing the M2 element to obtain a first mixture. For example, the collected precipitate particles, the raw material containing Li, the raw material containing the M1 element, and the raw material containing the M2 element can be mixed in a mortar.

[0048] Examples of raw materials containing Li include Li2CO3 and LiOH. Examples of raw materials 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) include oxides of each element (e.g., BaO, Pr2O3, La2O3, and SrO). Examples of raw materials containing M2 (i.e., 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) include oxides of each element (e.g., W2O3, MoO3, and NbO).

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

[0050] The heating conditions during firing are preferably such that the temperature is increased at a heating rate A of 1°C / min to 10°C / min up to the maximum temperature X-100°C, and then increased 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 that is slower than heating rate A. Adjusting the heating conditions as described above allows the M1 element and M2 element to be present in larger amounts in the layered crystal structure of the positive electrode active material. The temperature rise rate A up to the maximum temperature X-100°C is 1°C / min or more and 10°C / min or less, and preferably 3°C / min or more and 6°C / min or less. The temperature rise rate B from the maximum temperature X-100°C to the maximum temperature X is 0.1°C / min or more and 5°C / min, and is slower than the temperature rise rate A, and is preferably 0.5°C / min or more and 2°C / min or less. The time required for raising the temperature from the maximum temperature to be reached (X-100°C) to the maximum temperature to be reached (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, for example, by crushing with a crusher (for example, 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, which can be mixed in a mortar, for example.

[0054] Examples of raw materials 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) include oxides of each element (e.g., BO and ZrO).

[0055] (7) A second firing step of firing the second mixture Next, the second mixture containing the raw material containing the M3 element is fired, for example, in a firing furnace (such as a muffle furnace).

[0056] As for the firing conditions, 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 lower 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 second mixture after firing may be crushed. Examples of the crushing method include crushing with a crusher (for example, 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 the embodiment of the present disclosure may be a solid-state battery having a solid electrolyte, a liquid battery having a liquid electrolyte, or a bipolar battery having 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 onto the positive electrode current collector. The positive electrode active material layer contains 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, and therefore will not be repeated here. The positive electrode active material layer may contain a conductive material in addition to the positive electrode active material, and may further contain other components (e.g., binders, various additives, etc.). Examples of conductive materials include non-graphitizable carbon, graphitizable carbon such as acetylene black and 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). It may also be a current collector that functions as both a positive electrode current collector and a negative electrode current collector (i.e., a bipolar battery).

[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 member 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 the negative electrode active material include graphite-based carbons such as natural graphite, artificial graphite, and amorphous-coated graphite. The proportion of graphite in the graphite-based carbon is approximately 50% by mass or more, preferably 80% by mass or more. The negative electrode active material layer may be composed of only the negative electrode active material, or may contain components other than the negative electrode active material (e.g., thickeners, binders, etc.) as necessary. 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 to 30 μm. The separator may be made of, for example, a porous polyethylene (PE) film, a porous polypropylene (PP) film, or the like. The separator may have a multilayer structure. For example, the separator may be made by laminating a porous PP film, a porous PE film, and a porous PP film 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 the heat-resistant material 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 comprising an electrolyte, with a non-aqueous electrolyte being particularly preferred.

[0065] ·solvent The non-aqueous electrolytic solution contains a solvent (non-aqueous solvent) and an electrolyte. Examples of solvents (nonaqueous solvents) 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] ·Electrolyte The electrolyte in the electrolytic solution may be, for example, a Li salt, such as lithium bis(fluorosulfonyl)imide (LiFSI), LiPF6 (lithium hexafluorophosphate), lithium tetrafluoroborate (LiBF4), or Li[N(CF3SO2)2]. The amount of electrolyte may be, for example, 1.0 to 2.0 mol / L, and is preferably 1.0 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] (Application) Examples of applications of batteries include power sources for hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and battery electric vehicles (BEVs). [Example]

[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) Lix Ni a Co b Mn c M1 d M2 e M3 f A positive electrode active material having a composition represented by O2, in which x, a, b, c, d, e, and f are in the ratios shown in Table 1, and using the elements shown in Table 1 as the element represented by M1, the element represented by M2, and the element represented by M3, was synthesized by the method shown below.

[0071] ·Raw material solution NiSO4, CoSO4, and MnSO4 were dissolved in ion-exchanged water to obtain a raw material solution. The ratio of Ni / Co / Mn was 80 / 10 / 10 (atm %), and the concentration of the aqueous solution was 30 mass %.

[0072] Crystallization A certain amount of NH3 aqueous solution was placed in a reaction vessel, and the atmosphere was replaced with nitrogen while stirring with a stirrer. NaOH was added to the reaction vessel to make the pH alkaline. Next, the raw material solution and NH3 were added dropwise while maintaining a constant pH (pH 10-12) in the reaction vessel, causing the transition metal hydroxide to precipitate.

[0073] Washing, filtering, drying The precipitated transition metal hydroxide was filtered off, dispersed in ion-exchanged water by stirring with a spoon, and washed with water. The washed liquid was then filtered to remove the transition metal hydroxide. The filtered transition metal hydroxide was then dried at 120° C. for 16 hours to evaporate the water.

[0074] Mixture of Li, M1 and M2 raw materials The dried transition metal hydroxide, Li2CO3 and LiOH as Li raw materials, Pr2O3 as M1 raw material, and W2O3 as M2 raw material were mixed in a mortar.

[0075] First firing and crushing A mixture of transition metal hydroxide, Li raw material, M1 raw material, and M2 raw material was fired in a firing furnace (muffle furnace) under the following firing conditions: maximum temperature (X) was 800°C, the heating rate was 5°C / min to the maximum temperature (X) -100°C, the heating rate was 1°C / min from the maximum temperature (X) -100°C to the maximum temperature (X), and the heating time after reaching the maximum temperature was 10 hours. The firing was performed in an oxygen atmosphere. Next, the fired mixture was pulverized in a pulverizer (jet mill) to obtain particles having a predetermined particle size.

[0076] M3 raw material mixing Next, the particles obtained in the first firing and crushing step were mixed with B2O3 as the M3 raw material in a mortar.

[0077] Second firing and crushing The 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) under the conditions of a maximum temperature of 700°C, a heating time of 3 hours after reaching the maximum temperature, and calcination in an oxygen atmosphere. Next, the fired mixture was pulverized in a pulverizer (jet mill) to a predetermined particle size. This resulted in the production of the positive electrode active material of Example 1. The above-mentioned TEM-EDX 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 positive electrode active materials of each Example were obtained in the same manner as in Example 1, except that the M1 raw material in Example 1 was changed from Pr2O3 to La2O3 (Examples 3 to 6) and SrO (Examples 7 to 8), the M2 raw material was changed from W2O3 to NbO (Examples 7 to 8), the M3 raw material was changed from B2O3 to ZrO (Examples 2, 6, and 8), and the ratios of M1, M2, and M3 (d, e, and f) were adjusted to the ratios shown in Table 1. The above-mentioned TEM-EDX revealed that in the layered crystal structures of the positive electrode active materials of Examples 2 to 8, the TM layer contained M1 and M2, and the Li layer contained M3.

[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 (i.e., the same heating rate was used for both).

[0080] <Comparative Examples 2 and 3> The positive electrode active materials of Comparative Examples 2 and 3 were obtained in the same manner as in Example 1, except that the M1 raw material in Example 1 was changed from Pr2O3 to ZrO (Comparative Example 2) and La2O3 (Comparative Example 3), the M2 raw material was changed from W2O3 to Al2O3 (Comparative Example 2) and W2O3 (Comparative Example 3), 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 under the same firing conditions as in Comparative Example 1 (i.e., 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 positive electrode active materials of Comparative Examples 4 to 9 were obtained in the same manner as in Example 1, except that the M1 raw material in Example 1 was changed from PrO to BaO (Comparative Example 4), LaO (Comparative Example 6), and SrO (Comparative Examples 7 to 9), the M2 raw material was changed from WO to MoO (Comparative Example 8), and NbO (Comparative Example 9), the M3 raw material was not added, and only the first firing and crushing step was performed without performing the second firing and crushing step, and the firing conditions were the same as in Example 1 (i.e., 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> A positive electrode active material of Comparative Example 10 was obtained in the same manner as in Example 1, except that the M3 raw material in Example 1 was changed from B2O3 to SO3.

[0083] <Comparative Example 11> A positive electrode active material of Comparative Example 11 was obtained in the same manner as in Example 1, except that the M1 raw materials and M2 raw materials in Example 1 were not added and the M3 raw material was changed from B2O3 to ZrO.

[0084] <Comparative Example 12> The 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 a 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 (the second firing and crushing step was not performed).

[0085] [Cell preparation] Cells were fabricated using the positive electrode active materials obtained in each of the examples and comparative examples. Cell configuration Wound cylinder Positive electrode composition: Positive electrode active material / acetylene black (conductive material) / polyvinylidene fluoride = 88 / 10 / 2 (mass%) Negative electrode composition: natural graphite / styrene butadiene rubber (SBR) / carboxymethyl cellulose (CMC) Electrolyte composition: electrolyte = LiPF6 (1M), solvent = ethylene carbonate (EC) / dimethyl carbonate (DMC) / ethyl methyl carbonate (EMC) = 3 / 4 / 3 (volume%)

[0086] Electrode preparation A positive electrode and a negative electrode were applied to 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 was measured for the cells obtained in each example and comparative example. Table 1 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 and 150 cycles] The cells obtained in each of the Examples and Comparative Examples were subjected to 100 and 150 charge / discharge cycles under the test conditions below, and the Ni-mixing of the positive electrode active material layer thereafter was calculated by the following method. The positive electrode active material was subjected to synchrotron XRD (X-ray diffraction) diffraction, and Rietveld analysis (Fullprof) was performed on the XRD diffraction data. Next, the amount of Ni-mixing was input arbitrarily 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: Charging and discharging was performed at 60°C and a 2C rate between 0% and 100% SOC as one cycle.

[0089] [Resistance increase rate / 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 battery resistance was measured before and after each cycle. The results of the percentage increase in resistance (%) of the battery resistance after 100 and 150 cycles, with the battery resistance before each cycle being taken as "100%," are shown in Table 1. The closer the resistance increase rate is to 100%, the better the battery characteristics are. Test conditions: Charging and discharging was performed at 60°C and a 2C rate between 0% and 100% SOC as 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] [Table 1]

[0092] As shown in Table 1, 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 not containing elements defined in the present disclosure as the elements M1, M2, and M3.

Claims

1. Li ｘ Ni ａ Co ｂ Mn ｃ M1 ｄ M2 ｅ M3 ｆ O ２ It has a composition represented by The positive electrode active material contains at least one element selected from the group of elements shown below as M1, M2, and M3, totaling 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, 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 W, Re, Sb, Sn, Ta, 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, and M1 and M3 are different.

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

3. 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; The positive electrode active material according to claim 1 , wherein M3 contains at least one element selected from the group consisting of B, Zr, Mg, Al, and Sc.

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

6. 2. 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. 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; The lithium layer further comprises M3, The positive electrode active material according to claim 1 , wherein the transition metal layer further comprises the M1 and the 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 comprising the positive electrode of claim 8.

10. A method for producing the positive electrode active material according to claim 1, comprising: a step of mixing raw materials each 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 firing the first mixture by heating the mixture in an oxygen atmosphere to a maximum temperature X-100°C at a heating rate A of 1°C / min or more and 10°C / min or less, 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 or more and 5°C / min that is slower than the heating rate A; 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; 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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