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

Abstract

To provide a positive electrode active material that can realize low battery resistance when used in a battery.SOLUTION: In a positive electrode active material with a composition represented by LixNiaCobMncM1dM2eO2, the TM interlayer distance (D) is 2.02 Å or more and 2.30 Å or less. (In the composition, 0.1≤x≤1.5, 0.5≤a≤1.0, 0≤b≤0.3, 0≤c≤0.3, a+b+c=1.0, 0.0005≤d≤0.050, and 0.0005≤e≤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 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.)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] For example, Patent Document 1 discloses a nickel-cobalt-manganese lithium transition metal oxide containing 60 mol % or more of nickel relative to the total moles of metals excluding lithium, and the nickel-cobalt-manganese lithium transition metal oxide contains a doping element M1 (the doping element M1 is a metal element containing Al) and a doping element M2 (the doping element M2 is 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) and the nickel-cobalt-manganese-based lithium transition metal oxide contains 100 to 10,000 ppm of doping element M1, and the doping elements M1 and M2 are contained in a weight ratio of 50:50 to 99:1. Also disclosed are a positive electrode active material, a method for producing the positive electrode active material, and a positive electrode and a secondary battery including the positive electrode active material.

[0004] Patent Document 2 also discloses a positive electrode active material for a lithium secondary battery, which contains nickel-based lithium metal oxide particles doped with Zr and Al, and which is composed of a core portion having a region with a constant molar content of nickel and a shell portion that surrounds the outer surface of the core portion and has a concentration gradient in which the molar content of nickel gradually decreases in a direction from the boundary surface with the core portion to the outermost shell. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Special Publication No. 2022-513681 [Patent Document 2] Patent Publication No. 2021-177491 Summary of the Invention [Problem to be solved by the invention]

[0006] In conventional positive electrode active materials, additive elements have been added to the positive electrode active material for the purpose of improving the resistance characteristics of the battery. However, certain ignition elements have difficulty entering the crystalline structure of the positive electrode active material, and therefore, it has been difficult for them to contribute to improving the resistance characteristics. Therefore, further improvement is required from the viewpoint of reducing the battery resistance when this positive electrode active material is used in a lithium-ion battery.

[0007] The present disclosure has been made in view of the above circumstances, and aims to provide a positive electrode active material that can achieve low battery resistance when used in a battery, 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]

[0008] Means for solving the above problems include the following aspects. <1> Li x Ni a Co b Mn c M1 d M2 e O2, A positive electrode active material having a TM interlayer distance (D) of 2.02 Å or more and 2.30 Å or less. (In the composition, 0.1≦x≦1.5, 0.5≦a≦1.0, 0≦b≦0.3, 0≦c≦0.3, a+b+c=1.0, 0.0005≦d≦0.050, and 0.0005≦e≦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 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.) <2> the combination of the M1 element and the M2 element is at least one combination selected from the group consisting of Ba—W, Pr—W, La—W, Hf—W, Sr—Nb, Pr—Ta, YW, Sr—W, Ce—W, Pr—Re, Ba—Re, Sr—Sb, Se—W, Y—Re, Sr—Re, Rh—W, Zr—W, Sr—Sn, Y—Ta, Y—Sb, Sr—Os, Sr—Ta, Ce—Re, La—Re, Ba—Ta, Sr—Ir, Sn—W, Sr—Mo, Ba—Ti, Ba—Zr, and Ba—Al; <1> The positive electrode active material according to claim 1. <3> The combination of the M1 element and the M2 element is at least one combination selected from the group consisting of La—W, Pr—W, and Sr—Nb. <1> The positive electrode active material according to claim 1. <4> a is 0.7≦a≦1.0; <1> ~ <3> The positive electrode active material according to any one of claims 1 to 10. <5> The M1 element is Sr; <1> ~ <4> The positive electrode active material according to any one of claims 1 to 10. <6> The M1 element is at least one element selected from the group consisting of La and Ce. <1> ~ <4> The positive electrode active material according to any one of claims 1 to 10. <7> The M2 element is W. <1> ~ <6> The positive electrode active material according to any one of claims 1 to 10. <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> a step 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 mixture; a firing step of heating the mixture in an oxygen atmosphere at a temperature rise rate A of 1°C / min to 10°C / min to a maximum temperature X-100°C, and then heating the mixture 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 that is slower than the temperature rise rate A; The method for producing a positive electrode active material comprising the steps of: (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, Os, Ir, Mo, Nb, Tc, Ru, Ga, Ag, Pd, Ge, As, Zr, In, Pt, Al, and Ti.) [Effects of the Invention]

[0009] The present disclosure provides a positive electrode active material that can achieve low battery resistance when used in a battery, 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

[0010] 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 with the upper or lower limit of another numerical range. In addition, in the present specification, the upper or lower limit of a numerical range may be replaced with a value shown in the examples.

[0011] 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.

[0012] <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 It has a composition represented by O2. The TM interlayer distance (D) is 2.02 Å or more and 2.30 Å or less. (In the composition, 0.1≦x≦1.5, 0.5≦a≦1.0, 0≦b≦0.3, 0≦c≦0.3, a+b+c=1.0, 0.0005≦d≦0.050, and 0.0005≦e≦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 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.)

[0013] In the past, additive elements (so-called doping elements) have been added to positive electrode active materials for purposes such as improving the resistance characteristics of batteries. In the positive electrode active material, a crystalline structure is formed, which includes a Li layer containing Li and a TM layer containing transition metals such as Ni, Co, and Mn. However, certain doping elements have difficulty entering the crystalline structure of the positive electrode active material, and thus have a characteristic of having a small structural stabilization effect. Therefore, further improvements are required in terms of reducing the battery resistance when this positive electrode active material is used in lithium-ion batteries.

[0014] In contrast, the cathode active material according to an embodiment of the present disclosure contains two doping elements, M1 and M2. By combining the doping elements M1 and M2, the doping elements can be present in large amounts in the crystal structure of the cathode active material, significantly improving the structural stabilization effect. This is thought to be because the elements represented by M1 (M1 elements) have a large ionic radius and are therefore difficult to incorporate into the crystal structure of the cathode active material, whereas by combining them with the elements represented by M2 (M2 elements), they are more easily incorporated into the crystal structure. As a result, the TM interlayer distance (D) in the crystal structure of the cathode active material falls within the aforementioned range, i.e., the interlayer distance is increased. Furthermore, by improving the structural stabilization effect, Ni mixing (cation mixing) into the Li layer during charging and discharging in a lithium-ion battery is suppressed, and the inhibition of Li ion movement during charging and discharging is suppressed, thereby suppressing an increase in battery resistance.

[0015] Next, the positive electrode active material according to an embodiment of the present disclosure will be described in detail.

[0016] (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 It has a composition represented by O2. (In the composition, 0.1≦x≦1.5, 0.5≦a≦1.0, 0≦b≦0.3, 0≦c≦0.3, a+b+c=1.0, 0.0005≦d≦0.050, and 0.0005≦e≦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 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.)

[0017] In the composition of the particles of compound A, from the viewpoint of resistance characteristics in a battery, the Li ratio x is 0.1 to 1.5, preferably 0.3 to 1.4, and more preferably 0.5 to 1.2. 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. The ratio a of Ni can be increased, in which case the ratio a is preferably 0.6 to 1.0 (0.6≦a≦1.0), and more preferably 0.7 to 1.0 (0.7≦a≦1.0). From the viewpoint of the resistance characteristics of the battery, the ratio b of Co is 0 or more and 0.3 or less, preferably 0 or more and 0.2 or less, and more preferably 0.1 or more and 0.2 or less. From the viewpoint of the resistance characteristics of the battery, the ratio c of Mn is 0 or more and 0.3 or less, preferably 0 or more and 0.2 or less, and more preferably 0.1 or more and 0.2 or less. The total ratio of Ni, Co and Mn (a+b+c) is 1.0.

[0018] From the viewpoint of resistance characteristics in the battery, the ratio d of the M1 element is 0.0005 or more and 0.05 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 resistance characteristics in a battery, the ratio e of the M2 element is 0.0005 or more and 0.05 or less, preferably 0.001 or more and 0.040 or less, and more preferably 0.003 or more and 0.030 or less.

[0019] The positive electrode active material contains an M1 element and an M2 element as additive elements, where 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, Os, Ir, Mo, Nb, Tc, Ru, Ga, Ag, Pd, Ge, As, Zr, In, Pt, Al, and Ti. When the positive electrode active material contains the M1 element and M2 element listed above as additive elements, the battery resistance can be reduced when the positive electrode active material is used in a battery.

[0020] From the viewpoint of reducing the 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, Hf—W, Sr—Nb, Pr—Ta, YW, Sr—W, Ce—W, Pr—Re, Ba—Re, Sr—Sb, Se—W, Y—Re, Sr—Re, Rh—W, Zr—W, Sr—Sn, Y—Ta, Y—Sb, Sr—Os, Sr—Ta, Ce—Re, La—Re, Ba—Ta, Sr—Ir, Sn—W, Sr—Mo, Ba—Ti, Ba—Zr, and Ba—Al. Furthermore, from the viewpoint of reducing the battery resistance, it is more preferable that the combination of the M1 element and the M2 element is at least one combination selected from the group consisting of La—W, Pr—W, and Sr—Nb.

[0021] As the M1 element, for example, Sr is preferable. From the viewpoint of the resistance characteristics of the battery, it is also preferable that the M1 element is at least one element selected from the group consisting of La and Ce. As the M2 element, W is preferable, for example.

[0022] (TM interlayer distance (D)) The positive electrode active material according to an embodiment of the present disclosure has a TM interlayer distance (D) of 2.02 Å or more and 2.30 Å or less. The positive electrode active material forms a crystalline structure with a Li layer containing Li and a TM layer containing transition metals such as Ni, Co, and Mn. The TM interlayer distance (D) within the above range indicates that the TM layer is sufficiently large, i.e., that a large amount of M1 elements with a large ionic radius are incorporated into the TM layer. This improves the structural stabilization effect of the positive electrode active material and suppresses an increase in battery resistance. If the TM interlayer distance (D) is less than 2.02 Å, the battery resistance will be high, whereas it is difficult to form a TM layer with a large interlayer distance (D) exceeding 2.30 Å. From the viewpoint of resistance characteristics in a battery, the TM interlayer distance (D) is preferably 2.04 Å or more and 2.21 Å or less, and more preferably 2.06 Å or more and 2.19 Å or less.

[0023] Here, we will explain how to measure the TM interlayer distance (D). First, synchrotron radiation XRD (X-ray diffraction) diffraction is performed on the positive electrode active material, and Rietveld analysis (Fullprof) is performed on the XRD diffraction data. Fullprof is an application for performing Rietveld analysis of XRD diffraction data, and can calculate the lattice constant and atomic coordinates of the material. The c-axis length (C h ) and the z-coordinate of oxygen (Z oxy The Chi2 value is a convergence index obtained by fitting XRD diffraction data using the least squares method, and the Chi2 value is smallest when the discrepancy between the XRD diffraction data and the profile fitting is smallest. Then, the TM interlayer distance (D) is calculated based on the following formula: Formula: D=2[(1 / 3)-Z oxy ]C h

[0024] The positive electrode active material has a crystal structure including a Li layer containing Li element and a TM layer. The interlayer distance between the Li layers is not particularly limited, but is, for example, 2.2 Å to 2.8 Å, and preferably about 2.5 Å.

[0025] <Method of manufacturing positive electrode active material> Next, a method for producing a positive electrode active material according to an embodiment of the present disclosure will be described. The positive electrode active material according to the embodiment of the present disclosure described above can be produced by the method for producing a positive electrode active material according to an embodiment of the present disclosure shown below.

[0026] A method for producing a positive electrode active material according to an embodiment of the present disclosure includes 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 mixture, and a firing step of heating the mixture in an oxygen atmosphere at a heating 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 heating rate B of 0.1°C / min or more and 5°C / min that is slower than the heating rate A, and firing the mixture. (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, Os, Ir, Mo, Nb, Tc, Ru, Ga, Ag, Pd, Ge, As, Zr, In, Pt, Al, and Ti.)

[0027] In a positive electrode active material, the M1 element, which has a large ionic radius, has difficulty entering the TM layer in the crystal structure. However, in a method for producing a positive electrode active material according to an embodiment of the present disclosure, a combination of the M1 element and the M2 element is used, and the firing temperature is gradually increased as the maximum temperature X approaches. Specifically, the rate of temperature increase from the maximum temperature X-100°C to the maximum temperature X is slowed. This allows the M1 element to be incorporated into the TM layer near X-100°C, and the additive element in the TM layer to diffuse near the maximum temperature X°C. This allows the M1 element and the M2 element to be present in large amounts in the crystal structure of the positive electrode active material, thereby increasing the TM interlayer distance (D) within the aforementioned range, i.e., the interlayer distance.

[0028] The method for producing a positive electrode active material according to an embodiment of the present disclosure preferably includes the following steps (1) to (5). (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 mixture (mixing). (5) A step of firing the mixture (firing) Each step will be described in detail below.

[0029] (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.

[0030] Examples of raw materials containing Ni include sulfates such as NiSO4, raw materials containing Co include sulfates such as CoSO4, and raw materials containing Mn include sulfates such as MnSO4.

[0031] (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.

[0032] (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 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 precipitate (particles) after washing may be further dried.

[0033] (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 mixture. Next, the collected precipitate (particles) are mixed 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 mixture. For example, the collected precipitate particles, the raw material containing Li, the raw material containing an element represented by M1, and the raw material containing an element represented by M2 can be mixed in a mortar.

[0034] 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).

[0035] (5) A step of firing the mixture Next, a mixture of the collected precipitate (particles), a raw material containing Li, a raw material containing an element represented by M1, and a raw material containing an element represented by M2 is fired. For example, the first mixture can be fired in a firing furnace (such as a muffle furnace).

[0036] The heating conditions during firing are as follows: 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 large amounts in the crystal structure of the positive electrode active material, and the TM interlayer distance (D) can be within the aforementioned range, i.e., the interlayer distance can be increased. The rate of temperature rise 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.

[0037] 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.

[0038] In order to make the positive electrode active material have a predetermined particle size, the mixture after firing may be crushed, for example, by crushing with a crusher (for example, a jet mill).

[0039] By going through these steps, the positive electrode active material according to the embodiment of the present disclosure can be obtained.

[0040] <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.

[0041] (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 such as a binder, various additives, etc. Examples of the conductive material include non-graphitizable carbon, graphitizable carbon such as acetylene black or carbon black, and graphite. Examples of the binder include vinyl halide resins such as polyvinylidene fluoride (PVdF).

[0042] The positive electrode current collector is preferably a conductive member made of a metal with good conductivity (e.g., aluminum). Note that the positive electrode current collector 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).

[0043] (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). Note that the negative electrode current collector 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). The negative electrode active material layer contains a negative electrode active material. Examples of the negative electrode active material include graphite-based carbon such as natural graphite, artificial graphite, and amorphous-coated graphite. The graphite-based carbon has a graphite content of 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, such as a thickener or binder, 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).

[0044] (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.

[0045] (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.

[0046] ·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).

[0047] ·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.

[0048] In addition to the solvent and electrolyte, the electrolytic solution may contain various additives such as a thickener, a film-forming agent, a gas generating agent, etc. 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).

[0049] (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]

[0050] The present disclosure will be described below based on examples, but the present disclosure is not limited to these examples in any way.

[0051] Example 1 (Synthesis of positive electrode active material) Lix Ni a Co b Mn c M1 d M2 e A positive electrode active material having a composition represented by O2, in which x, a, b, c, d, and e are in the ratios shown in Table 1, and in which the elements represented by M1 and M2 are those shown in Table 1, was synthesized by the method shown below.

[0052] ·Raw material solution NiSO4, CoSO4, and MnSO4 were dissolved in ion-exchanged water to obtain a raw material solution. The Ni / Co / Mn ratio was 1 / 1 / 1 (atm %), and the concentration of the aqueous solution was 30 mass %.

[0053] 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.

[0054] 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.

[0055] Mixture of Li, M1 and M2 raw materials The dried transition metal hydroxide, Li2CO3 and LiOH as Li raw materials, BaO as M1 raw material, and W2O3 as M2 raw material were mixed in a mortar.

[0056] · Calcination and crushing A mixture of a transition metal hydroxide, a Li raw material, an M1 raw material, and an 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 (°C / min) from the maximum temperature (X) to -100°C, and the heating rate (°C / min) from the maximum temperature (X) to -100°C were as shown in Table 2, 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 a predetermined particle size. In this way, the positive electrode active material of Example 1 was obtained.

[0057] <Examples 2 to 6> 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 BaO to Pr2O3 (Example 2), La2O3 (Example 3), and SrO (Examples 4 to 6), and the M2 raw material was changed from W2O3 to W2O3 (Examples 2 to 4), MoO3 (Example 5), and NbO (Example 6).

[0058] <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 and the M2 raw material in Example 1 were not added, 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 the same as those in Table 2 (i.e., the heating rates were the same for both).

[0059] <Comparative Examples 2 and 4> The positive electrode active materials of Comparative Examples 2 and 4 were obtained in the same manner as in Example 1, except that the M1 raw material in Example 1 was changed from BaO to ZrO (Comparative Example 2) and La2O3 (Comparative Example 4), the M2 raw material was changed from W2O3 to Al2O3 (Comparative Example 2) and W2O3 (Comparative Example 4), and the firing conditions were changed 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 the same as those in Table 2 (i.e., the same heating rate was used for both).

[0060] <Comparative Example 3> The positive electrode active material of Comparative Example 3 was obtained in the same manner as in Example 1, except that the M1 raw material and the M2 raw material in Example 1 were changed to four types of raw materials: Al2O3, MgO, TiO2, and La2O3, and the firing conditions, namely, 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 set to the conditions shown in Table 2 (i.e., the same heating rate was used for all).

[0061] [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%)

[0062] 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.

[0063] [TM interlayer distance (D)] The TM interlayer distance (D) of the positive electrode active material layers obtained in each of the Examples and Comparative Examples was determined by the method described above. The results are shown in Table 1.

[0064] [Ni-mixing] The Ni-mixing of the positive electrode active material layer obtained in each of the examples and comparative examples was calculated by the following method. First, 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 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.

[0065] [Measurement of resistance increase rate after cycling] The battery resistance of the cells obtained in each example and comparative example was measured before and after cycling under the following test conditions. The results of the percentage of the battery resistance after cycling (resistance increase rate (%)) when the battery resistance before cycling is set to "100%" are shown in Table 1. It can be said that the closer the resistance increase rate is to 100%, the better the battery characteristics are. Test conditions: 300 cycles of charge and discharge between SOC 0% and 100% at 60°C and 2C rate.

[0066] [Table 1]

[0067] [Table 2]

[0068] As shown in Table 1, it can be seen that the positive electrode active materials of the examples containing both the X1 element and X2 and having a TM interlayer distance (D) within the above-mentioned range can achieve lower battery resistance than the positive electrode active materials of the comparative examples having a TM interlayer distance (D) outside the above-mentioned range.

Claims

1. Li ｘ Ni ａ Co ｂ Mn ｃ M1 ｄ M2 ｅ O ２ It has a composition represented by A positive electrode active material having a TM interlayer distance (D) of 2.02 Å or more and 2.30 Å or less. (In the composition, 0.1≦x≦1.5, 0.5≦a≦1.0, 0≦b≦0.3, 0≦c≦0.3, a+b+c=1.0, 0.0005≦d≦0.050, and 0.0005≦e≦0.050; M1 represents at least one element selected from the group consisting of Ba, Pr, La, Y, Sr, Ce, Se, Hf, Rh, 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, In, Pt, and Ti; M1 and M2 are different elements; and the ionic radius of M1 is larger than the ionic radius of M2.)

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

3. 2. The positive electrode active material according to claim 1, wherein the combination of the M1 element and the M2 element is at least one combination selected from the group consisting of La—W, Pr—W, and Sr—Nb.

4. 2. The positive electrode active material according to claim 1, wherein a satisfies the condition 0.7≦a≦1.

0.

5. The positive electrode active material according to claim 1 , wherein the M1 element is Sr.

6. The positive electrode active material according to claim 1 , wherein the M1 element is at least one element selected from the group consisting of La and Ce.

7. The positive electrode active material according to claim 1 , wherein the M2 element is W.

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 step 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 mixture; a firing step of heating the mixture in an oxygen atmosphere at a temperature rise rate A of 1°C / min to 10°C / min to a maximum temperature of X-100°C, and then heating the mixture from the maximum temperature of X-100°C to the maximum temperature of 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; and a TM interlayer distance (D) of 2.02 Å or more and 2.30 Å or less. (M1 represents at least one element selected from the group consisting of Ba, Pr, La, Y, Sr, Ce, Se, Hf, Rh, 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, In, Pt, and Ti, M1 and M2 are different elements, and the ionic radius of M1 is larger than the ionic radius of M2.)

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