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

Abstract

The invention relates to a positive electrode active material and a method for producing the positive electrode active material. The positive electrode active material has a composition represented by Li < x > Ni Co Mn < c > O < y >, and the crystallite size in primary particles is 300 nm or more and 1700 nm 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, and 1.5 < = y < = 2.1.

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] So far, in positive electrode active materials for batteries, methods for controlling the crystal grains of particles have been attempted. For example, Japanese Patent Application Laid-Open No. 2023-36570 discloses a method for manufacturing a ternary positive electrode material of large crystal grain aggregates. The manufacturing method includes: a step of preparing a mixed solution of a nickel salt, a cobalt salt, and a manganese salt; a step of 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 it to obtain a precursor A; a step of mixing the washed precursor A with a lithium salt using a ball mill to obtain a precursor B; a step of sintering the precursor B in an atmosphere of air or oxygen, the sintering being heated from 400°C to 800°C at a rate of 5 to 15°C / min, isothermally sintered for 1 to 6 hours, and then further heated from 900°C to 980°C at a rate of 1 to 10°C / min, and isothermally sintered for 8 to 10 hours; a step of cooling to obtain a ternary positive electrode material of large crystal grain aggregates. Summary of the Invention

[0003] For a battery, a performance in which the battery capacity does not decrease even after repeated charge and discharge (i.e., the maintainability of the battery capacity) is required. However, in a battery including a positive electrode containing a positive electrode active material, sometimes the capacity of the battery decreases after repeated charge and discharge. Therefore, a positive electrode active material capable of suppressing a decrease in battery capacity when used in a battery is required.

[0004] The present disclosure has been completed in view of the above actual situation, and an object thereof is to provide a positive electrode active material capable of suppressing a decrease in battery capacity when used in a battery and a method for manufacturing the positive electrode active material.

[0005] Means for solving the above problems include the following aspects.

[0006] <1> A positive electrode active material having a composition represented by Li x Ni a Co b Mn c O y In the composition, the crystal grain size in the primary particle is 300 nm or more and 1700 nm or less, and 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, 1.5 ≤ y ≤ 2.1.

[0007] <2> The positive electrode active material according to <1>, which is a positive electrode active material in which a plurality of primary particles are aggregated to form secondary particles, and the average number of the primary particles constituting one secondary particle is 5 or less.

[0008] <3> The positive electrode active material according to <1> or <2>, wherein the composition further contains at least one element selected from the following group X and the following group Y,

[0009] X: Ba, Pr, La, Y, Sr, Ce, Se, Hf, Rh, Zr, Sn, Mg

[0010] Y: W, Re, Sb, Sn, Ta, Os, Ir, Mo, Nb, Tc, Ru, Ga, Ag, Pd, Ge, As, Zr, In, Pt, Al, Ti.

[0011] <4> The positive electrode active material according to <3>, which contains at least one element selected from the group X and at least one element selected from the group Y, wherein the case where the element selected from the group X is only Zr and the element selected from the group Y is only Zr is excluded, and the case where the element selected from the group X is only Sn and the element selected from the group Y is only Sn is also excluded.

[0012] <5> A method for manufacturing a positive electrode active material, which manufactures a positive electrode active material having a composition represented by Li x Ni a Co b Mn c O y 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, 1.5 ≤ y ≤ 2.1. The manufacturing method includes: a step of mixing raw materials containing Ni, Co, and Mn respectively and a raw material containing Li to obtain a mixture; and a step of performing a staged firing process on the mixture, which successively includes a low-temperature firing treatment at a temperature of 400°C or higher and 600°C or lower, a medium-temperature firing treatment at a temperature of 500°C or higher and 800°C or lower and higher than the temperature in the low-temperature firing treatment, and a high-temperature firing treatment at a temperature of 600°C or higher and 1000°C or lower and higher than the temperature in the medium-temperature firing treatment.

[0013] According to the present disclosure, a positive electrode active material capable of suppressing a decrease in battery capacity when used in a battery and a method for manufacturing the positive electrode active material can be provided. Detailed Description

[0014] Positive electrode active material

[0015] The positive electrode active material according to the embodiment of the present disclosure has a composition represented by Li x Ni a Co b Mn cO y The composition represented. Moreover, the crystallite size in the primary particles of the positive electrode active material is 300 nm or more and 1700 nm or less.

[0016] (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, 1.5 ≤ y ≤ 2.1.)

[0017] The positive electrode active material according to an embodiment of the present disclosure can suppress a decrease in capacity in a battery. The reason for obtaining this effect is presumed as follows.

[0018] As one of the performances required for a battery, suppression of a decrease in battery capacity after repeated charge and discharge (that is, maintainability of battery capacity) can be cited. However, in a battery including a positive electrode containing a positive electrode active material, the battery capacity sometimes decreases after repeated charge and discharge. As one of the main reasons, it is considered that a reaction with the electrolyte occurs in the positive electrode active material, and Li is consumed by the film, resulting in a decrease in battery capacity. Therefore, it is necessary to suppress a decrease in battery capacity accompanying a reaction with the electrolyte in the positive electrode active material.

[0019] The crystallite size in the crystal in the primary particles of the positive electrode active material according to an embodiment of the present disclosure is in the above range. When the crystallite size in the positive electrode active material particles is small (that is, when the crystallite size is less than 300 nm), it means that crystal growth in the positive electrode active material particles has not progressed. Moreover, in a positive electrode active material with a small crystallite size, the reaction area becomes large, and a reaction with the electrolyte occurs in the battery. On the other hand, the crystallite size of the positive electrode active material according to an embodiment of the present disclosure is 300 nm or more, and crystal growth has sufficiently progressed (sufficiently proceeds). Therefore, the reaction area at the positive electrode active material is small, suppressing the reaction with the electrolyte in the battery. As a result, consumption of Li due to the formation of the film is suppressed, and a decrease in the battery capacity is suppressed.

[0020] Next, the positive electrode active material according to an embodiment of the present disclosure will be described in detail.

[0021] Crystallite size

[0022] The crystallite size of the crystal of the positive electrode active material particles (primary particles) is 300 nm or more and 1700 nm or less. By the crystallite size being 300 nm or more, the reaction area at the positive electrode active material is small, suppressing the reaction with the electrolyte in the battery, suppressing consumption of Li due to the formation of the film, and suppressing a decrease in the capacity in the battery. On the other hand, by the crystallite size being 1700 nm or less, the process for increasing the crystallite size can be simplified, specifically, the firing process can be simplified, and manufacturing complexity can be suppressed.

[0023] From the viewpoint of suppressing the decrease in the capacity of the battery, the lower limit value of the crystallite size of the particles (primary particles) of the positive electrode active material is more preferably 500 nm or more, and even more preferably 800 nm or more. On the other hand, from the viewpoint of simplifying the process for increasing the crystallite size, the upper limit value of the crystallite size is more preferably 1500 nm or less, and even more preferably 1000 nm or less.

[0024] There is no particular limitation on the method for controlling the crystallite size of the crystals of the particles (primary particles) of the positive electrode active material. For example, in order to make the crystallite size as high as 300 nm or more, it is preferable to carry out firing in the firing process of manufacturing the positive electrode active material while gradually increasing the temperature from low temperature to high temperature, thereby promoting the growth of crystals. It is more preferable to carry out a stepwise firing process that sequentially includes a low-temperature firing treatment at a temperature of 400 °C or more and 600 °C or less, a medium-temperature firing treatment at a temperature of 500 °C or more and 800 °C or less and higher than the temperature in the low-temperature firing treatment, and a high-temperature firing treatment at a temperature of 600 °C or more and 1000 °C or less and higher than the temperature in the medium-temperature firing treatment.

[0025] Crystallite size calculation method

[0026] Here, the calculation method for the crystallite size of the particles (primary particles) of the positive electrode active material will be described. For the positive electrode active material, a crystallite size measurement is performed using an XRD (X-ray diffraction) measurement device (manufactured by Rigaku Corporation, SmartLab (registered trademark)). Based on the angle (θ) and the full width at half maximum (β) of the peak existing between 17° and 19°, the crystallite size is calculated using the following formula.

[0027] Formula: L = 0.9 × λ / (β cos θ)

[0028] (In the formula, λ represents the wavelength of the X-ray )

[0029] It should be noted that the measurement conditions are as follows.

[0030] Angle: 10° to 120°

[0031] Interval: 0.02° / step

[0032] Speed: 10° / minute

[0033] Composition

[0034] 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 determined by Li x Ni a Co b Mnc The composition represented by O2. In addition, the positive electrode active material may further contain other additive elements.

[0035] (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, 1.5 ≤ y ≤ 2.1.)

[0036] In the composition of the positive electrode active material, from the viewpoint of suppressing the decrease in the capacity of the battery, 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, more preferably 0.5 or more and 1.2 or less. From the viewpoint of suppressing the decrease in the capacity of the battery, 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, more preferably 0.7 or more and 0.8 or less. From the viewpoint of suppressing the decrease in the capacity 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, more preferably 0.1 or more and 0.2 or less. From the viewpoint of suppressing the decrease in the capacity in 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, more preferably 0.1 or more and 0.2 or less. Further, the sum (a + b + c) of the ratios of Ni, Co, and Mn is 1.0.

[0037] The positive electrode active material may further contain other additive elements. In particular, from the viewpoint of suppressing the decrease in the capacity of the battery, it is preferred that the positive electrode active material further contains at least one element selected from the following group X and the following group Y.

[0038] X: Ba, Pr, La, Y, Sr, Ce, Se, Hf, Rh, Zr, Sn, Mg

[0039] Y: W, Re, Sb, Sn, Ta, Os, Ir, Mo, Nb, Tc, Ru, Ga, Ag, Pd, Ge, As, Zr, In, Pt, Al, Ti

[0040] In addition, from the viewpoint of suppressing the decrease in the capacity of the battery, it is preferred that the positive electrode active material contains at least one element selected from the group X and at least one element selected from the group Y. However, it does not include the case where the element selected from the group X is only Zr and the element selected from the group Y is only Zr, and also does not include the case where the element selected from the group X is only Sn and the element selected from the group Y is only Sn.

[0041] The combinations of elements selected from Group X and elements selected from Group Y, which are preferably included in the positive electrode active material, are shown below. From the viewpoint of suppressing a decrease in the capacity of the battery and the like, it is preferred that the positive electrode active material contains one or more of the following combinations of elements. It should be noted that in the combinations shown below, the element described before "-" represents an element selected from Group X, and the element described after "-" represents an element selected from Group Y.

[0042] · Preferred combinations of elements of Group X and elements of Group Y

[0043] 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, Ba-Al

[0044] From the viewpoint of suppressing a decrease in the capacity of the battery and the like, the content ratio (mass%) of the element selected from Group X in the positive electrode active material is 0.0005 or more and 0.05 or less, preferably 0.001 or more and 0.040 or less. More preferably, it is 0.003 or more and 0.030 or less. From the viewpoint of suppressing a decrease in the capacity of the battery and the like, the content ratio (mass%) of the element selected from Group Y in the positive electrode active material is 0.0005 or more and 0.05 or less, preferably 0.001 or more and 0.040 or less. More preferably, it is 0.003 or more and 0.030 or less.

[0045] Secondary particles

[0046] The positive electrode active material according to an embodiment of the present disclosure preferably has a plurality of primary particles aggregated (agglomerated) to form secondary particles. Moreover, from the viewpoint of suppressing a decrease in the capacity of the battery and the like, the average number of primary particles constituting one secondary particle is preferably 5 or less.

[0047] Furthermore, it is possible to confirm that the positive electrode active material forms secondary particles by observing a cross-section of the positive electrode active material layer using a scanning electron microscope (SEM). In addition, in the observation using the microscope, 50 secondary particles are arbitrarily selected as the measurement objects, the number of primary particles constituting each secondary particle is measured, and the arithmetic mean thereof is obtained, thereby calculating the average number of primary particles constituting the secondary particles in the positive electrode active material.

[0048] Method for manufacturing a positive electrode active material

[0049] Next, a method for manufacturing a positive electrode active material according to an embodiment of the present disclosure will be described. Further, the positive electrode active material according to the embodiment of the present disclosure can be manufactured by the method for manufacturing a positive electrode active material according to the embodiment of the present disclosure shown below.

[0050] The method for manufacturing a positive electrode active material according to an embodiment of the present disclosure includes: a step of mixing raw materials respectively containing Ni, Co, and Mn and a raw material containing Li to obtain a mixture; and a step of sequentially performing a low-temperature firing treatment of firing at a temperature of 400 °C or higher and 600 °C or lower, 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 low-temperature firing treatment, and a high-temperature firing treatment of firing at a temperature of 600 °C or higher and 1000 °C or lower and higher than the temperature in the medium-temperature firing treatment. And, a positive electrode active material having a composition represented by Li x Ni a Co b Mn c O y is manufactured.

[0051] (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, 1.5 ≤ y ≤ 2.1).

[0052] In the method for manufacturing a positive electrode active material according to an embodiment of the present disclosure, as described above, there is a stepwise firing step of firing while gradually increasing the temperature from low to high. Therefore, the growth of crystals in the particles of the positive electrode active material can be promoted, and the microcrystalline size can be made up to 300 nm or more. Thus, a positive electrode active material with a small reaction area at the positive electrode active material and capable of suppressing the reaction with the electrolyte in the battery can be obtained. Moreover, by using this positive electrode active material in a battery, the consumption of Li due to the formation of a film can be suppressed, and the reduction of the capacity in the battery can be suppressed.

[0053] Further, 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).

[0054] (1) A step of preparing a solution in which raw materials containing Ni, Co, and Mn are respectively dissolved (raw material dissolution step)

[0055] (2) A step of adding the solution to an alkali solution to precipitate hydroxides (crystallization step)

[0056] (3) A step of extracting the precipitate from the alkali solution

[0057] (4) Process of mixing the precipitate and the raw material containing Li to obtain a mixture (mixing process)

[0058] (5) Process of firing the mixture (firing process)

[0059] Furthermore, when the positive electrode active material contains an additive element, it is preferable to further add a raw material containing the additive element in the (4) mixing process. As the additive element, elements selected from the above group X and elements selected from group Y can be cited.

[0060] The following explains each process in detail.

[0061] (1) Process of preparing solutions in which raw materials containing Ni, Co, and Mn are respectively dissolved

[0062] Prepare solutions in which the raw material containing Ni, the raw material containing Co, and the raw material containing Mn are dissolved. For example, the solutions can be prepared by dissolving the raw material containing Ni, the raw material containing Co, and the raw material containing Mn in a solvent such as water. As the concentration of the solution, for example, a range of 10 to 40 mass% is preferable. As the ratio of Ni / Co / Mn, relative to Ni: 1.0, a ratio of 1.0 / 0.8 to 1.2 / 0.8 to 1.2 (atm%) is preferable.

[0063] As the raw material containing Ni, sulfates such as NiSO4 can be cited. As the raw material containing Co, sulfates such as CoSO4 can be cited. As the raw material containing Mn, sulfates such as MnSO4 can be cited.

[0064] (2) Process of adding the solution to an alkali solution to precipitate hydroxides

[0065] Next, add the solution to the alkali solution to precipitate hydroxides. As a result, particles of hydroxides containing Ni, Co, and Mn are crystallized and the particles are obtained as a precipitate. In this process, for example, while controlling the alkali solution in which the hydroxides are precipitated to a certain pH (for example, pH 10 to 12), the solution and NH3 are dropped in, so that the hydroxides of the transition metals precipitate.

[0066] (3) Process of extracting the precipitate from the alkali solution

[0067] Next, extract (take out) the precipitate from the alkali solution. As a method of extracting the precipitate particles, for example, methods such as filtration and water washing can be cited. The following method can be cited: First, take out the precipitate (particles) by filtration and wash with water, and then filter the washed liquid to take out the precipitate (particles). Furthermore, the washed precipitate (particles) can be further dried.

[0068] (4) Step of mixing the precipitate and the raw material containing Li to obtain a mixture

[0069] Next, the extracted precipitate (particles) and the raw material containing Li are mixed to obtain a mixture. In addition, when the positive electrode active material contains an additive element, it is preferable to further add a raw material containing the additive element. Examples of the additive element include elements selected from the above group X and elements selected from group Y. Examples of the mixing method include the following method: Mixing the particles of the extracted precipitate, the raw material containing Li, and the raw material containing the additive element (for example, a raw material containing elements selected from the above group X and elements selected from group Y) in a mortar.

[0070] Examples of the raw material containing Li include Li2CO3 and LiOH. Examples of the raw material containing an element selected from the above group X (i.e., at least one element selected from Ba, Pr, La, Y, Sr, Ce, Se, Hf, Rh, Zr, Sn, Mg) and an element selected from the above group Y (i.e., at least one element selected from W, Re, Sb, Sn, Ta, Os, Ir, Mo, Nb, Tc, Ru, Ga, Ag, Pd, Ge, As, Zr, In, Pt, Al, Ti) include oxides of each element (for example, BaO, Pr2O3, La2O3, SrO, W2O3, MoO3, and NbO).

[0071] (5) Step of firing the mixture

[0072] Next, the mixture of the extracted precipitate (particles) and the raw material containing Li is fired. For example, a firing furnace (such as a muffle furnace) can be used to fire the mixture.

[0073] In the method for manufacturing a positive electrode active material according to an embodiment of the present disclosure, the firing step is performed through stages of firing processes shown in the following (a) to (c) in sequence.

[0074] (a) Low-temperature firing treatment at a temperature of 400 °C or higher and 600 °C or lower

[0075] (b) Medium-temperature firing treatment at a temperature of 500 °C or higher and 800 °C or lower and higher than the temperature in the low-temperature firing treatment

[0076] (c) High-temperature firing treatment at a temperature of 600 °C or higher and 1000 °C or lower and higher than the temperature in the medium-temperature firing treatment

[0077] By passing through the above-stage firing process, the growth of crystals in the particles of the positive electrode active material can be promoted, and the microcrystal size can be increased to 300 nm or more.

[0078] (a) The temperature in the low-temperature firing treatment is 400 °C or higher and 600 °C or lower. From the viewpoint of suppressing the reduction in the capacity of the battery, etc., it is further preferably 420 °C or higher and 580 °C or lower, and more preferably 450 °C or higher and 550 °C or lower. (a) The heating time at the above temperature in the low-temperature firing treatment is preferably 1 hour or longer and 5 hours or shorter, and more preferably 2 hours or longer and 4 hours or shorter from the viewpoint of suppressing the reduction in the capacity in the battery.

[0079] (b) The temperature in the medium-temperature firing treatment is 500 °C or higher and 800 °C or lower. From the viewpoint of suppressing the reduction in the capacity in the battery, etc., it is further preferably 550 °C or higher and 750 °C or lower, and more preferably 600 °C or higher and 700 °C or lower. (b) The heating time at the above temperature in the medium-temperature firing treatment is preferably 1 hour or longer and 5 hours or shorter, and more preferably 2 hours or longer and 4 hours or shorter from the viewpoint of suppressing the reduction in the capacity in the battery.

[0080] (c) The temperature in the high-temperature firing treatment is 600 °C or higher and 1000 °C or lower. From the viewpoint of suppressing the reduction in the capacity in the battery, etc., it is further 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 high-temperature firing treatment is preferably 1 hour or longer and 5 hours or shorter, and more preferably 2 hours or longer and 4 hours or shorter from the viewpoint of suppressing the reduction in the capacity in the battery.

[0081] The firing is preferably carried out in an oxygen atmosphere. In order to make the positive electrode active material into a specified particle size, the fired mixture can be crushed. As a method of crushing, for example, a method of crushing using a crusher (for example, a jet mill) can be cited.

[0082] By going through these processes, the positive electrode active material according to the embodiment of the present disclosure can be obtained.

[0083] Battery

[0084] The positive electrode active material according to the embodiment of the present disclosure can be used in a battery, and is particularly suitable for a lithium ion battery. The battery has, for example, a negative electrode, a positive electrode, a separator, and an electrolyte.

[0085] The battery according to the embodiment of the present disclosure can be a solid battery having a solid electrolyte or a liquid battery having a liquid electrolyte, and a liquid battery is preferred. In addition, it can 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.

[0086] 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 from the negative electrode. The battery according to an embodiment of the present disclosure may be a liquid-based battery further having an electrolyte. A non-aqueous electrolyte is particularly preferred.

[0087] As uses of the battery, for example, power sources for hybrid electric vehicles (HEV), plug-in hybrid electric vehicles (PHEV), battery electric vehicles (BEV), etc. can be cited.

[0088] Hereinafter, the present disclosure will be described based on examples, but the present disclosure is not limited by any of these examples.

[0089] Example 1

[0090] Synthesis of Positive Electrode Active Material

[0091] Raw Material Dissolution Solution

[0092] 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.

[0093] Crystallization

[0094] A certain amount of aqueous NH3 solution was placed in a reaction vessel, and nitrogen replacement was carried out while stirring with a stirrer. NaOH was added to the reaction vessel to make the pH alkaline. Next, while controlling the pH in the reaction vessel to a certain value (pH 10 to 12), the raw material dissolution solution and NH3 were dropped to precipitate a transition metal hydroxide.

[0095] Washing, Filtration, Drying

[0096] The precipitated transition metal hydroxide was taken out by filtration, ion-exchanged water was added, and it was stirred and dispersed with a spoon and washed with water. Next, the washed liquid was filtered to take out the transition metal hydroxide. Next, the filtered transition metal hydroxide was dried at 120 °C for 16 hours to evaporate the water.

[0097] Mixing of Li Raw Material and Raw Materials of Additive Elements

[0098] The dried transition metal hydroxide, Li2CO3 and LiOH as Li raw materials, MgO as the raw material of additive element 1, and Al2O3 as the raw material of additive element 2 were mixed with a mortar.

[0099] Firing and Crushing

[0100] A mixture of a transition metal hydroxide, a Li raw material, and a raw material of an additive element is fired in a firing furnace (muffle furnace). Further, the firing is carried out in an oxygen atmosphere in a stepwise firing process in which a low-temperature firing treatment at 500 °C, a medium-temperature firing treatment at 700 °C, and a high-temperature firing treatment at 900 °C are each carried out for 3 hours in sequence.

[0101] Next, the fired mixture is pulverized with a pulverizer (jet mill) to be crushed to a specified particle size. Thus, the positive electrode active material of Example 1 was obtained.

[0102] The positive electrode active material of Example 1 contains Li, Ni, Co, Mn, O, Mg, and Al, and its ratio (mass ratio) is the ratio shown in Table 1.

[0103] In addition, a plurality of primary particles of the obtained positive electrode active material aggregate to form secondary particles, and the average number of primary particles constituting one secondary particle is 5 or less.

[0104] Examples 2 to 6

[0105] The raw material of additive element 1 in Example 1 was changed from MgO to La2O3 (Example 2), SrO (Example 3), and Pr2O3 (Example 4), and the raw material of additive element 2 was changed from Al2O3 to W2O3 (Examples 2 and 4), and NbO (Example 3). Except for this, the positive electrode active materials of the respective examples were obtained in the same manner as in Example 1.

[0106] The elements contained in the positive electrode active materials of the respective examples and their ratios (mass ratios) are shown in Table 1. In addition, a plurality of primary particles of the obtained positive electrode active material aggregate to form secondary particles, and the average number of primary particles constituting one secondary particle is 5 or less.

[0107] Comparative Example 1

[0108] The raw materials of additive element 1 and additive element 2 in Example 1 were not added, and the firing conditions were changed to a condition of firing in an oxygen atmosphere at a temperature of 900 °C for 10 hours. Except for this, the positive electrode active material of Comparative Example 1 was obtained in the same manner as in Example 1.

[0109] The elements contained in the positive electrode active material of Comparative Example 1 and their ratios (mass ratios) are shown in Table 1. In addition, a plurality of primary particles of the obtained positive electrode active material aggregate to form secondary particles, and the average number of primary particles constituting one secondary particle is 5 or less.

[0110] Comparative Example 2

[0111] The firing conditions in Example 1 were changed to firing in an oxygen atmosphere at a temperature of 900 °C for 10 hours. Except for this, the positive electrode active material of Comparative Example 2 was obtained in the same manner as in Example 1.

[0112] The elements contained in the positive electrode active material of Comparative Example 2 and their ratios (mass ratios) are shown in Table 1. In addition, a plurality of primary particles of the obtained positive electrode active material aggregated to form secondary particles, and the average number of primary particles constituting one secondary particle was 5 or less.

[0113] Fabrication of battery cell

[0114] Battery cells were fabricated using the positive electrode active materials obtained in each example and each comparative example.

[0115] · Battery cell configuration

[0116] Winding cylinder

[0117] Positive electrode composition: Positive electrode active material / acetylene black (conductive material) / polyvinylidene fluoride = 88 / 10 / 2 (mass%)

[0118] Negative electrode composition: natural graphite / styrene-butadiene rubber (SBR) / carboxymethyl cellulose (CMC)

[0119] Electrolyte composition: electrolyte = LiPF6 (1M), solvent = ethylene carbonate (EC) / dimethyl carbonate (DMC) / ethyl methyl carbonate (EMC) = 3 / 4 / 3 (volume%)

[0120] Fabrication of electrodes

[0121] A film coater (manufactured by Allgood Co., Ltd.) with a film thickness adjustment function was used to coat the positive electrode and the negative electrode on the current collector, and a dryer was used to dry at 80 °C for 5 minutes, thereby fabricating a battery.

[0122] Method for calculating crystallite size

[0123] For the positive electrode active materials obtained in each example and each comparative example, a crystallite size measurement was performed using an XRD (X-ray diffraction) measurement device (manufactured by Rigaku Corporation, SmartLab (registered trademark)). Based on the angle (θ) and the full width at half maximum (β) of the peak existing between 17° and 19°, the crystallite size was calculated using the following formula.

[0124] Formula: L = 0.9 × λ / (β cos θ)

[0125] (In the formula, λ represents the wavelength of the X-ray )

[0126] It should be noted that the measurement conditions are as follows.

[0127] Angle: 10° to 120°

[0128] Interval: 0.02° / step

[0129] Speed: 10° / min

[0130] Measurement of capacity retention rate after cycling

[0131] For the battery cells obtained in each of the examples and comparative examples, the battery capacities before and after cycling were measured under the following test conditions. The results of the ratio of the battery capacity after cycling (capacity retention rate (%)) with the battery capacity before cycling as "100%" are shown in Table 1. It can be said that the closer the capacity retention rate is to 100%, the better the battery characteristics.

[0132] Test conditions: Charge and discharge were carried out for 300 cycles between SOC 0% and 100% at 60°C and a 2C rate.

[0133] Furthermore, "Synthesis method 2" shown in Table 1 means the following synthesis method, which has a stepwise firing process that successively performs a low-temperature firing treatment at a temperature of 400°C or higher and 600°C or lower, a medium-temperature firing treatment at a temperature of 500°C or higher and 800°C or lower and higher than the temperature in the low-temperature firing treatment, and a high-temperature firing treatment at a temperature of 600°C or higher and 1000°C or lower and higher than the temperature in the medium-temperature firing treatment. On the other hand, "Synthesis method 1" means a synthesis method that does not have the above stepwise firing process.

[0134] (Table 1)

[0135]

[0136] As shown in Table 1, it can be seen that the positive electrode active materials of the examples in which the crystal grain size enters a specific range have excellent maintainability of battery capacity compared to the positive electrode active materials of the comparative examples in which the crystal grain size is below the specific range.

Claims

1. A positive electrode active material having a composition represented by Li x Ni a Co b Mn c O y wherein the crystallite size within the primary particles is 300 nm or more and 1700 nm 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, and 1.5 ≤ y ≤ 2.

1.

2. The positive electrode active material according to claim 1 is a positive electrode active material in which a plurality of primary particles are aggregated to form secondary particles, wherein The average number of primary particles constituting one secondary particle is 5 or less.

3. The positive electrode active material according to claim 1, wherein, The composition further contains at least one element selected from the following group X and the following group Y, X: Ba, Pr, La, Y, Sr, Ce, Se, Hf, Rh, Zr, Sn, Mg Y: W, Re, Sb, Sn, Ta, Os, Ir, Mo, Nb, Tc, Ru, Ga, Ag, Pd, Ge, As, Zr, In, Pt, Al, Ti.

4. The positive electrode active material according to claim 3, which contains at least one element selected from the group X and at least one element selected from the group Y, wherein, Excluded are the cases where the element selected from group X is only Zr and the element selected from group Y is only Zr, and also the cases where the element selected from group X is only Sn and the element selected from group Y is only Sn.

5. Method for manufacturing a positive electrode active material, which manufactures a positive electrode active material having a composition represented by Li x Ni a Co b Mn c O y 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, 1.5 ≤ y ≤ 2.1, The manufacturing method has: a step of mixing raw materials containing Ni, Co, and Mn respectively and a raw material containing Li to obtain a mixture; and a staged firing step of sequentially performing a low-temperature firing treatment of firing at a temperature of 400°C or higher and 600°C or lower, 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 low-temperature firing treatment, and a high-temperature firing treatment of firing at a temperature of 600°C or higher and 1000°C or lower and higher than the temperature in the medium-temperature firing treatment on the mixture.

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