Positive electrode active material and method for producing positive electrode active material

Abstract

To provide a positive electrode active material which can reduce resistance of a battery when used in the battery.SOLUTION: The positive electrode active material has a composition represented by LixNiaCobMncOy, has a compound A containing La and Ni and a compound B containing Li and W on the surface of primary particles, and contains La and W inside the primary particles. In the composition, 0.1≤x≤1.5, 0.5≤a≤1.0, 0≤b≤0.3, 0≤c≤0.3, a+b+c=1.0 and 1.5≤y≤2.1 are satisfied.SELECTED DRAWING: None

Description

Technical Field

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

Background Art

[0002] Conventionally, methods for controlling the crystallization of particles have been attempted in positive electrode active materials used in batteries. For example, in Patent Document 1, a step of preparing a mixed solution of a nickel salt, a cobalt salt, and a manganese salt, adding a precipitant and a complexing agent to the mixed solution, adjusting the pH of the mixed solution to 10.5 to 12, and precipitating to obtain a precursor A, a step of mixing the washed precursor A and a lithium salt with a ball mill to obtain a precursor B, and sintering the precursor B in an atmosphere of air or oxygen, where the sintering involves heating from 400 to 800 °C at a rate of 5 to 15 °C / min, isothermally sintering for 1 to 6 h, then further heating from 900 to 980 °C at a rate of 1 to 10 °C / min, and isothermally sintering for 8 to 10 h, a step of cooling to obtain a large crystal grain aggregate ternary positive electrode material, a manufacturing method of a large crystal grain aggregate ternary positive electrode material comprising these steps, is disclosed.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Batteries are required to have low resistance, but in a battery provided with a positive electrode containing a positive electrode active material, the resistance may increase due to the positive electrode active material.

[0005] The present disclosure has been made in view of the above circumstances, and an object thereof is to provide a positive electrode active material capable of reducing the resistance of a battery when used in the battery, and a method for manufacturing the positive electrode active material.

Means for Solving the Problems

[0006] Means for solving the above problems include the following aspects. <1> Li x Ni a Co b Mn c O y A positive electrode active material having a composition represented by, having compound A containing La and Ni and compound B containing Li and W on the surface of primary particles, and containing La and W inside the primary particles. (In the above composition, 0.1 ≦ x ≦ 1.5, 0.5 ≦ a ≦ 1.0, 0 ≦ b ≦ 0.3, 0 ≦ c ≦ 0.3, a + b + c = 1.0, 1.5 ≦ y ≦ 2.1.) <2> The positive electrode active material according to <1>, wherein the compound A is a granular compound and the compound B is a layered compound. <3> The positive electrode active material according to <1> or <2>, wherein the compound A contains at least one of La4LiNiO8 and LaNiO3, and the compound B contains Li6WO6. <4> A step of mixing raw materials containing Ni, Co, and Mn respectively, a raw material containing Li, a raw material containing La, and a raw material containing W to obtain a mixture, A step firing process in which the mixture is subjected to a high-temperature firing treatment fired at a temperature of 600°C or higher and 1000°C or lower, a low-temperature firing treatment fired at a temperature of 400°C or higher and 600°C or lower, and a medium-temperature firing treatment fired at a temperature of 500°C or higher and 800°C or lower and lower than the temperature in the high-temperature firing treatment and higher than the temperature in the low-temperature firing treatment, in this order, Li x Ni a Co b Mn c O y A method for producing a positive electrode active material, which produces a positive electrode active material having a composition represented by, having compound A containing La and Ni and compound B containing Li and W on the surface of primary particles, and containing La and W inside the primary particles. (In the above composition, 0.1 ≦ x ≦ 1.5, 0.5 ≦ a ≦ 1.0, 0 ≦ b ≦ 0.3, 0 ≦ c ≦ 0.3, a + b + c = 1.0, 1.5 ≦ y ≦ 2.1.)

Advantages of the Invention

[0007] According to the present disclosure, there are provided a positive electrode active material capable of reducing the resistance of a battery when used in the battery, and a method for producing the positive electrode active material.

Mode for Carrying Out the Invention

[0008] <Positive electrode active material> The positive electrode active material according to an embodiment of the present disclosure contains Li x Ni a Co b Mn c O y and has a composition represented by, and has compound A containing La and Ni, and compound B containing Li and W on the surface of the primary particles, and contains La and W inside the primary particles. (In the above composition, 0.1 ≦ x ≦ 1.5, 0.5 ≦ a ≦ 1.0, 0 ≦ b ≦ 0.3, 0 ≦ c ≦ 0.3, a + b + c = 1.0, 1.5 ≦ y ≦ 2.1.)

[0009] According to the positive electrode active material according to an embodiment of the present disclosure, the resistance in the battery can be reduced. The reason for this effect is speculated as follows.

[0010] One of the performances required for a battery is low resistance. However, in a battery including a positive electrode containing a positive electrode active material, the resistance may increase due to the positive electrode active material. Therefore, it is required to reduce the resistance in the positive electrode active material and thereby reduce the resistance of the battery.

[0011] The positive electrode active material according to an embodiment of the present disclosure has compound A containing La and Ni, and compound B containing Li and W on the surface of the primary particles, and contains La and W inside the primary particles. That is, the positive electrode active material has compound A with high electron conductivity and compound B with high Li conductivity on the surface of the particles, and further contains La and W inside the particles, thereby reducing the resistance on the surface and inside of the particles. By reducing the resistance on the surface and inside of the positive electrode active material particles in this way, when the positive electrode active material is used in a battery, the resistance in the battery can be reduced.

[0012] Next, the cathode active material according to the embodiment of the present disclosure will be described in detail.

[0013] The cathode active material according to the embodiment of the present disclosure contains at least Li, Ni, and O, and may contain Co and Mn. The ratios of these components are Li x Ni a Co b Mn c and has a composition represented by O2. Further, the cathode active material contains La and W as additive elements. And the cathode active material has a compound A containing La and Ni and a compound B containing Li and W on the surface of the particles (primary particles). Further, La and W are contained inside the particles. Note that the cathode active material may further contain other additive elements.

[0014] (Compound A) The cathode active material has a compound A containing La and Ni on the surface of the particles (primary particles). Examples of the compound A containing La and Ni include oxides containing La and Ni, and it is preferable to contain at least one of La4LiNiO8 and LaNiO3. The compound A is preferably a granular compound, that is, it is preferable that the granular compound A adheres to the surface of the particles of the cathode active material.

[0015] (Compound B) The cathode active material has a compound B containing Li and W on the surface of the particles (primary particles). Examples of the compound B containing Li and W include oxides containing Li and W, and it is preferable to contain Li6WO6. The compound B is preferably a layered compound, that is, it is preferable that at least a part of the surface of the particles of the cathode active material is covered with the layered compound B.

[0016] (Inside the particles) The cathode active material contains La and W inside the particles (primary particles).

[0017] Thus, the positive electrode active material has a compound A containing La and Ni, and a compound B containing Li and W on the surface of particles (primary particles), and contains La and W inside the particles. That is, La, Ni with high electron conductivity, and Li, W with high Li conductivity are arranged on the surface of the particles, and La and W are also contained inside the particles, reducing the resistance on the surface and inside of the particles.

[0018] Here, the method for confirming each compound and each element on the particle surface and inside the particles will be described. Regarding the method for confirming the compound A and the compound B on the particle surface, by observing the cross-section of the positive electrode active material layer with a scanning electron microscope (SEM) and an electron probe microanalyzer (EPMA), the presence of the compound A containing La and Ni and the presence of the compound B containing Li and W can be confirmed. In addition, in the present disclosure, the inside of the particle (primary particle) is defined as the range within 50% from the contour of the primary particle in the SEM image of the cross-section of the positive electrode active material layer. And regarding the method for confirming La and W inside the particles, for the inside of the particles (that is, the range within 50% from the contour of the primary particle to the inside), by observing the cross-section of the positive electrode active material layer with a scanning electron microscope (SEM) and an electron probe microanalyzer (EPMA), the presence of La and W can be confirmed.

[0019] The method for controlling the positive electrode active material to dispose a compound A containing La and Ni and a compound B containing Li and W on the surface of particles (primary particles) and to include La and W inside the particles is not particularly limited, but can be controlled, for example, by the following method. In the firing step when manufacturing the positive electrode active material, a method of performing firing at a high temperature and then gradually performing firing at a low temperature and a medium temperature can be mentioned. Specifically, a high-temperature firing treatment of firing at a temperature of 600 °C or higher and 1000 °C or lower, a low-temperature firing treatment of firing at a temperature of 400 °C or higher and 600 °C or lower, and a medium-temperature firing treatment of firing at a temperature of 500 °C or higher and 800 °C or lower and higher than the temperature in the high-temperature firing treatment and lower than the temperature in the low-temperature firing treatment are preferably carried out in this order through a stepwise firing process. By the first high-temperature firing treatment, compound A and compound B are formed on the surface of the particles of the positive electrode active material, and then by the low-temperature firing treatment and the medium-temperature firing treatment, the elements of La and W penetrate into the particles of the positive electrode active material. Thereby, the positive electrode active material according to the embodiment of the present disclosure having the above-described configuration can be obtained.

[0020] (Composition) The positive electrode active material according to the embodiment of the present disclosure contains at least Li, Ni, and O, and may contain Co and Mn. The ratios of these components are Li x Ni a Co b Mn c and has a composition represented by O2. Further, the positive electrode active material contains La and W as additive elements. Note that the positive electrode active material may further contain other additive elements. (In the above composition, 0.1 ≦ x ≦ 1.5, 0.5 ≦ a ≦ 1.0, 0 ≦ b ≦ 0.3, 0 ≦ c ≦ 0.3, a + b + c = 1.0, 1.5 ≦ y ≦ 2.1.)

[0021] In the composition of the positive electrode active material, from the viewpoint of reducing resistance in the battery, etc., the ratio x of Li is 0.1 or more and 1.5 or less, preferably 0.3 or more and 1.4 or less, and more preferably 0.5 or more and 1.2 or less. The ratio a of Ni is 0.5 or more and 1.0 or less, preferably 0.6 or more and 0.9 or less, and more preferably 0.7 or more and 0.8 or less, from the viewpoint of reducing resistance in the battery, etc. 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 reducing resistance in the battery, etc. 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, from the viewpoint of reducing resistance in the battery, etc. Note that the total (a + b + c) of the ratios of Ni, Co, and Mn is 1.0.

[0022] In the positive electrode active material, the content ratio (mass %) of La contained as an additive 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 reducing resistance in the battery, etc. In the positive electrode active material, the content ratio (mass %) of W contained as an additive 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 reducing resistance in the battery, etc. Note that La and W mean the total amount of both the amount contained as compound A and compound B on the surface of the particles of the positive electrode active material and the amount contained in the particles.

[0023] <Method for manufacturing positive electrode active material> Next, the method for manufacturing a positive electrode active material according to an embodiment of the present disclosure will be described. Note that the positive electrode active material according to the embodiment of the present disclosure described above can be manufactured by the method for manufacturing a positive electrode active material according to the embodiment of the present disclosure shown below.

[0024] The method for manufacturing a positive electrode active material according to an embodiment of the present disclosure includes a step of mixing a raw material containing Ni, Co, and Mn respectively, a raw material containing Li, a raw material containing La, and a raw material containing W to obtain a mixture, and subjecting the mixture to a high-temperature firing treatment of firing at a temperature of 600°C or higher and 1000°C or lower, a low-temperature firing treatment of firing at a temperature of 400°C or higher and 600°C or lower, and a medium-temperature firing treatment of firing at a temperature of 500°C or higher and 800°C or lower and lower than the temperature in the high-temperature firing treatment and higher than the temperature in the low-temperature firing treatment, in this order, in a stepwise firing process. And Li x Ni a Co b Mn c O y has a composition represented by, has compound A containing La and Ni, and compound B containing Li and W on the surface of the primary particles, and manufactures a positive electrode active material containing La and W inside the primary particles. (In the above composition, 0.1 ≦ x ≦ 1.5, 0.5 ≦ a ≦ 1.0, 0 ≦ b ≦ 0.3, 0 ≦ c ≦ 0.3, a + b + c = 1.0, 1.5 ≦ y ≦ 2.1.)

[0025] By the first high-temperature firing treatment, compound A and compound B are formed on the surface of the particles of the positive electrode active material, and then by the low-temperature firing treatment and the medium-temperature firing treatment, the elements of La and W penetrate into the particles of the positive electrode active material. Thereby, the positive electrode active material according to the embodiment of the present disclosure having the above-described configuration can be obtained.

[0026] Note that the method for manufacturing a positive electrode active material according to an embodiment of the present disclosure preferably includes the following steps (1) to (5). (1) Step of preparing a solution in which raw materials containing Ni, Co, and Mn respectively are dissolved (raw material dissolution step) (2) Step of adding the solution to an alkaline solution to precipitate a hydroxide (crystallization step) (3) Step of collecting the precipitate from the alkaline solution (4) Step of mixing the precipitate with a raw material containing Li, a raw material containing La, and a raw material containing W to obtain a mixture (mixing step) (5) Step of firing the mixture (firing step) The following describes each step in detail.

[0027] (1) Step of preparing a solution in which raw materials containing Ni, Co, and Mn are each dissolved Prepare a solution in which raw materials containing Ni, raw materials containing Co, and raw materials containing Mn are dissolved. For example, a solution can be prepared by dissolving raw materials containing Ni, raw materials containing Co, and raw materials containing Mn in a solvent such as water. The concentration of the solution is preferably in the range of, for example, 10 to 40% by mass. As the ratio of Ni / Co / Mn, it is preferably in the ratio of 1.0 / 0.8 to 1.2 / 0.8 to 1.2 (atm%) with respect to Ni: 1.0.

[0028] Examples of the raw material containing Ni include sulfates such as NiSO4, examples of the raw material containing Co include sulfates such as CoSO4, and examples of the raw material containing Mn include sulfates such as MnSO4.

[0029] (2) Step of adding the solution to an alkaline solution to precipitate hydroxides Next, add the solution to the alkaline solution to precipitate hydroxides. As a result, particles in which hydroxides containing Ni, Co, and Mn are formed are crystallized, and these particles are obtained as a precipitate. In this step, for example, while controlling the alkaline solution in which hydroxides are precipitated to a certain pH (for example, pH 10 to 12), the solution and NH3 are dropped to precipitate the hydroxides of transition metals.

[0030] (3) Step of collecting the precipitate from the alkaline solution Next, collect the precipitate from the alkaline solution. Examples of the method for collecting the precipitate particles include, for example, filtration and washing with water. First, a method of taking out the precipitate (particles) by filtration, washing with water, and further filtering the washed liquid to take out the precipitate (particles) can be mentioned. Note that the precipitate (particles) after washing with water may be further dried.

[0031] (4) Step of mixing the precipitate with raw materials containing Li, raw materials containing La, and raw materials containing W to obtain a mixture Next, the collected precipitate (particles) is mixed with a raw material containing Li, a raw material containing La, and a raw material containing W to obtain a mixture. When the positive electrode active material further contains other additive elements, a raw material containing the additive elements may be added. As a method of mixing, for example, a method of mixing the particles of the collected precipitate with a raw material containing Li, a raw material containing La, and a raw material containing W in a mortar can be mentioned.

[0032] Examples of the raw material containing Li include Li2CO3 and LiOH. Examples of the raw material containing La include La2O3. Examples of the raw material containing W include W2O3.

[0033] (5) Step of firing the mixture Next, the mixture of the collected precipitate (particles) and the raw material containing Li, the raw material containing La, and the raw material containing W is fired. For example, the mixture can be fired in a firing furnace (such as a muffle furnace).

[0034] In the method for producing a positive electrode active material according to the embodiment of the present disclosure, a step firing process in which the following firing treatments (a) to (c) are performed in this order is performed. (a) High-temperature firing treatment performed at a temperature of 600°C or higher and 1000°C or lower (b) Low-temperature firing treatment performed at a temperature of 400°C or higher and 600°C or lower (c) Medium-temperature firing treatment performed at a temperature of 500°C or higher and 800°C or lower and lower than the temperature in the high-temperature firing treatment and higher than the temperature in the low-temperature firing treatment

[0035] (a) The temperature in the high-temperature firing treatment is 600°C or higher and 1000°C or lower, and from the viewpoint of reducing the resistance in the battery, etc., it is preferably further 550°C or higher and 750°C or lower, and more preferably 600°C or higher and 700°C or lower. The heating time at the above temperature in the (a) high-temperature firing treatment is preferably 1 hour or more and 5 hours or less, and more preferably 2 hours or more and 4 hours or less, from the viewpoint of reducing the resistance in the battery, etc. (b) The temperature in the low-temperature firing process is 400°C or higher and 600°C or lower, and from the perspective of reducing resistance in the battery, etc., it is preferably 420°C or higher and 580°C or lower, and more preferably 450°C or higher and 550°C or lower. (b) The heating time at the above temperature in the low-temperature firing process is preferably 1 hour or more and 5 hours or less, and more preferably 2 hours or more and 4 hours or less, from the perspective of reducing resistance in the battery, etc. (c) The temperature in the medium-temperature firing process is 500°C or higher and 800°C or lower, and from the perspective of reducing resistance in the battery, etc., it is preferably 550°C or higher and 750°C or lower, and more preferably 600°C or higher and 700°C or lower. (c) The heating time at the above temperature in the medium-temperature firing process is preferably 1 hour or more and 5 hours or less, and more preferably 2 hours or more and 4 hours or less, from the perspective of reducing resistance in the battery, etc.

[0036] The firing is preferably performed in an oxygen atmosphere. In order to obtain a positive electrode active material with a predetermined particle size, the fired mixture may be crushed. Examples of the crushing method include crushing using a crusher (for example, a jet mill).

[0037] By going through these steps, the positive electrode active material according to the embodiment of the present disclosure can be obtained.

[0038] <Battery> The positive electrode active material according to the embodiment of the present disclosure can be used in a battery, and is particularly preferably used in a lithium-ion battery. The battery has, for example, a negative electrode, a positive electrode, a separator, and an electrolyte. The battery according to the embodiment of the present disclosure may be a solid battery having a solid electrolyte or a liquid battery having a liquid electrolyte, but a liquid battery is preferred. Further, it may be a bipolar battery having a positive electrode active material layer and a negative electrode active material layer on both sides of a current collector having the functions of a positive electrode current collector and a negative electrode current collector. The positive electrode includes, for example, a positive electrode current collector and a positive electrode active material layer fixed on the positive electrode current collector. The 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 separator is an electrically insulating porous membrane. The separator electrically isolates the positive electrode and the negative electrode. The battery according to the embodiment of the present disclosure may further be a liquid-based battery having an electrolyte. In particular, a non-aqueous electrolyte is preferred. Examples of the use of the battery include power sources for hybrid electric vehicles (HEV), plug-in hybrid electric vehicles (PHEV), battery electric vehicles (BEV), and the like.

Example

[0039] Hereinafter, the present disclosure will be described based on examples, but the present disclosure is not limited to these examples at all.

[0040] <Example 1> (Synthesis of positive electrode active material) ·Raw material dissolution solution NiSO4, CoSO4, and MnSO4 were dissolved in ion-exchanged water to obtain a raw material dissolution solution. The ratio of Ni / Co / Mn was 1 / 1 / 1 (atm%), and the concentration of the aqueous solution was 30% by mass.

[0041] ·Crystallization A certain amount of aqueous NH3 solution was placed in a reaction vessel, and nitrogen substitution was performed while stirring with a stirrer. NaOH was added to the reaction vessel to make the pH alkaline. Then, while controlling the inside of the reaction vessel to a certain pH (pH 10 to 12), the raw material dissolution solution and NH3 were dropped to precipitate a transition metal hydroxide.

[0042] ·Washing, filtration, drying The precipitated transition metal hydroxide was taken out by filtration, deionized water was added, and it was stirred with a spoon for dispersion and then washed with water. Next, the washed solution was filtered to take out the transition metal hydroxide. Then, the filtered transition metal hydroxide was dried at 120 °C for 16 hours to evaporate the moisture.

[0043] ·Mixing of Li raw material and raw materials of additive elements The dried transition metal hydroxide was mixed in a mortar with Li2CO3 and LiOH as Li raw materials and La2O3 and W2O3 as raw materials of additive elements. The amount of La added by La2O3 was adjusted to the ratio at which La4LiNiO8 is formed on the particle surface of the positive electrode active material.

[0044] ·Firing and crushing The mixture of the transition metal hydroxide, Li raw material, and raw materials of additive elements was fired in a firing furnace (muffle furnace). This firing was a stepwise firing process in which high-temperature firing treatment at 900 °C, low-temperature firing treatment at 500 °C, and medium-temperature firing treatment at 700 °C were each carried out for 3 hours in an oxygen atmosphere in this order.

[0045] Next, the fired mixture was crushed with a crusher (jet mill) to be crushed to a predetermined particle size. Thus, the positive electrode active material of Example 1 was obtained.

[0046] The positive electrode active material of Example 1 contained Li, Ni, Co, Mn, O, La, and W, and the ratios (mass ratios) of Li, Ni, Co, Mn, and O were the ratios shown in Table 1. Regarding the obtained positive electrode active material, it was confirmed by the above-mentioned confirmation method that the granular compound A having the composition shown in Table 1 and the layered compound B having the composition shown in Table 1 were present on the surface of the primary particles. Also, regarding the obtained positive electrode active material, it was confirmed by the above-mentioned confirmation method that La and W were present inside the primary particles.

[0047] <Example 2> In Example 1, the positive electrode active materials of the respective examples were obtained in the same manner as in Example 1, except that the amount of La2O3 added as a raw material for the additive element was adjusted to the ratio at which LaNiO3 was formed on the particle surface of the positive electrode active material.

[0048] The positive electrode active material of Example 2 contained Li, Ni, Co, Mn, O, La, and W, and the ratios (mass ratios) of Li, Ni, Co, Mn, and O were the ratios shown in Table 1. Regarding the obtained positive electrode active material, it was confirmed by the above-described confirmation method that the granular compound A having the composition shown in Table 1 and the layered compound B having the composition shown in Table 1 were present on the surface of the primary particles. Further, regarding the obtained positive electrode active material, it was confirmed by the above-described confirmation method that La and W were present inside the primary particles.

[0049] <Comparative Example 1> In Example 1, the positive electrode active material of Comparative Example 1 was obtained in the same manner as in Example 1, except that La2O3 and W2O3 as raw materials for the additive element were not added and the firing conditions were changed to firing for 10 hours in an oxygen atmosphere at a temperature of 900°C.

[0050] The positive electrode active material of Comparative Example 1 contained Li, Ni, Co, Mn, and O, and the ratios (mass ratios) of Li, Ni, Co, Mn, and O were the ratios shown in Table 1. Regarding the obtained positive electrode active material, compound A and compound B were not present on the surface of the primary particles, and La and W were not present inside the primary particles either.

[0051] <Comparative Example 2> In Example 1, the positive electrode active material of Comparative Example 2 was obtained in the same manner as in Example 1, except that only La2O3 as a raw material for the additive element was added and the firing conditions were changed to firing for 10 hours in an oxygen atmosphere at a temperature of 900°C.

[0052] The positive electrode active material of Comparative Example 2 contained Li, Ni, Co, Mn, O, and La, and the ratios (mass ratios) of Li, Ni, Co, Mn, and O were the ratios shown in Table 1. For the obtained positive electrode active material, it was confirmed by the above-described confirmation method that the granular compound A having the composition shown in Table 1 was present on the surface of the primary particles. Also, La and W were not present inside the primary particles.

[0053] <Comparative Example 3> In Example 1, except that only W2O3 as a raw material of the additive element was added and the firing conditions were changed to firing for 10 hours in an oxygen atmosphere at a temperature of 900 °C, the positive electrode active material of Comparative Example 3 was obtained in the same manner as in Example 1.

[0054] The positive electrode active material of Comparative Example 3 contained Li, Ni, Co, Mn, O, and W, and the ratios (mass ratios) of Li, Ni, Co, Mn, and O were the ratios shown in Table 1. For the obtained positive electrode active material, it was confirmed by the above-described confirmation method that the layered compound B having the composition shown in Table 1 was present on the surface of the primary particles. Also, La and W were not present inside the primary particles.

[0055] <Comparative Example 4> In Example 1, except that the firing conditions were changed to firing for 10 hours in an oxygen atmosphere at a temperature of 900 °C, the positive electrode active material of Comparative Example 4 was obtained in the same manner as in Example 1.

[0056] The positive electrode active material of Comparative Example 4 contained Li, Ni, Co, Mn, O, La, and W, and the ratios (mass ratios) of Li, Ni, Co, Mn, and O were the ratios shown in Table 1. For the obtained positive electrode active material, it was confirmed by the above-described confirmation method that the granular compound A having the composition shown in Table 1 and the layered compound B having the composition shown in Table 1 were present on the surface of the primary particles. Also, La and W were not present inside the primary particles.

[0057] <Comparative Example 5> In Example 1, except that only La2O3 as a raw material of the additive element was added, the positive electrode active material of Comparative Example 5 was obtained in the same manner as in Example 1.

[0058] The positive electrode active material of Comparative Example 5 contained Li, Ni, Co, Mn, O, and La, and the ratios (mass ratios) of Li, Ni, Co, Mn, and O were the ratios shown in Table 1. For the obtained positive electrode active material, it was confirmed by the above-described confirmation method that the granular compound A having the composition shown in Table 1 was present on the surface of the primary particles. Further, for the obtained positive electrode active material, it was confirmed by the above-described confirmation method that La was present inside the primary particles.

[0059] <Comparative Example 6> In Example 2, a positive electrode active material of Comparative Example 6 was obtained in the same manner as in Example 2, except that only La2O3 as a raw material of the additive element was added.

[0060] The positive electrode active material of Comparative Example 6 contained Li, Ni, Co, Mn, O, and La, and the ratios (mass ratios) of Li, Ni, Co, Mn, and O were the ratios shown in Table 1. For the obtained positive electrode active material, it was confirmed by the above-described confirmation method that the granular compound A having the composition shown in Table 1 was present on the surface of the primary particles. Further, for the obtained positive electrode active material, it was confirmed by the above-described confirmation method that La was present inside the primary particles.

[0061] <Comparative Example 7> In Example 1, a positive electrode active material of Comparative Example 7 was obtained in the same manner as in Example 1, except that only W2O3 as a raw material of the additive element was added.

[0062] The positive electrode active material of Comparative Example 7 contained Li, Ni, Co, Mn, O, and W, and the ratios (mass ratios) of Li, Ni, Co, Mn, and O were the ratios shown in Table 1. For the obtained positive electrode active material, it was confirmed by the above-described confirmation method that the layered compound B having the composition shown in Table 1 was present on the surface of the primary particles. Further, for the obtained positive electrode active material, it was confirmed by the above-described confirmation method that W was present inside the primary particles.

[0063] [Fabrication of Cells] Cells were fabricated using the positive electrode active materials obtained in each of the examples and each of the 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%)

[0064] · Fabrication of electrodes Using a film applicator with a film thickness adjustment function (All Good Co., Ltd.), the positive and negative electrodes were coated on the current collector and dried at 80 °C for 5 minutes in a dryer to fabricate the cell.

[0065] [Initial resistance] For the cells obtained in each example and comparative example, the initial battery resistance was measured. Table 1 shows the results of the ratios (%) of the battery resistances of each example and comparative example when the battery resistance of Comparative Example 1 was set as "100%".

[0066] The "ratio" of Compound A shown in Table 1 means the ratio of the total amount of La contained in the positive electrode active material, and the "ratio" of Compound B means the ratio of the total amount of W contained in the positive electrode active material.

[0067] Note that the "Synthesis Method 2" shown in Table 1 means a synthesis method having a step firing process in which a high-temperature firing process of firing at a temperature of 600 °C or higher and 1000 °C or lower and at a temperature higher than the temperature in the medium-temperature firing process, a low-temperature firing process of firing at a temperature of 400 °C or higher and 600 °C or lower, and a medium-temperature firing process of firing at a temperature of 500 °C or higher and 800 °C or lower and at a temperature higher than the temperature in the low-temperature firing process are performed in this order. On the other hand, the "Synthesis Method 1" means a synthesis method not having the above step firing process.

[0068]

Table 1

[0069] As shown in Table 1, in the positive electrode active materials of each Example having Compound A containing La and Ni and Compound B containing Li and W on the surface of the primary particles and containing La and W inside the primary particles, it can be seen that the initial resistance of the battery can be reduced compared to the positive electrode active materials of each Comparative Example that do not satisfy these requirements.

Claims

1. Li ｘ Ni ａ Co ｂ Mn ｃ O ｙ A positive electrode active material having a composition represented by, having compound A containing La and Ni and compound B containing Li and W on the surface of primary particles, and containing La and W inside the primary particles. (In the above composition, 0.1 ≤ x ≤ 1.5, 0.5 ≤ a ≤ 1.0, 0 ≤ b ≤ 0.3, 0 ≤ c ≤ 0.3, a + b + c = 1.0, 1.5 ≤ y ≤ 2.1.)

2. The positive electrode active material according to Claim 1, wherein the compound A is a granular compound and the compound B is a layered compound.

3. The compound A is La ４ LiNiO ８ and at least one of LaNiO ３ and the compound B contains Li ６ WO ６ The positive electrode active material according to claim 1, which contains

4. A step of mixing a raw material containing Ni, Co, and Mn respectively, a raw material containing Li, a raw material containing La, and a raw material containing W to obtain a mixture; A step firing process including a high-temperature firing process of firing the mixture at a temperature of 600°C or higher and 1000°C or lower, a low-temperature firing process of firing at a temperature of 400°C or higher and 600°C or lower, and a medium-temperature firing process of firing at a temperature of 500°C or higher and 800°C or lower and lower than the temperature in the high-temperature firing process and higher than the temperature in the low-temperature firing process, in this order. Li ｘ Ni ａ Co ｂ Mn ｃ O ｙ A method for producing a positive electrode active material, which has a composition represented by, has a compound A containing La and Ni and a compound B containing Li and W on the surface of primary particles, and has a positive electrode active material containing La and W inside the primary particles. (In the above composition, 0.1 ≤ x ≤ 1.5, 0.5 ≤ a ≤ 1.0, 0 ≤ b ≤ 0.3, 0 ≤ c ≤ 0.3, a + b + c = 1.0, 1.5 ≤ y ≤ 2.1.)

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