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

Abstract

To provide a positive electrode active material that can achieve low battery resistance.SOLUTION: A positive electrode active material contains particles of a compound A having a composition represented by LixNiaCobMncOy, and particles of a compound B having a composition represented by MdOe. In the particles of the compound B, the abundance of an element having an ion radius α of 0.60 Å≤α≤1.38 Å is greater than or equal to 45 mol%. The area ratio X of the particles of the compound B, with respect to a total of the particles of the compound A and the particles of the compound B, is 0.8%≤X≤19.6%. (Where 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, 0.001≤d≤0.2 and 0.002≤e≤0.4 are satisfied, and M represents at least one element selected from the group consisting of Ti, Zr, Ta, Pr, K, La, Ba, Y, Sr, Ce, Se, Hf and Rh.)SELECTED DRAWING: None

Description

Technical Field

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

Background Art

[0002] Conventionally, various additive elements have been added to the positive electrode active material used in a battery for the purpose of improving the resistance characteristics and the like of the battery.

[0003] For example, in Patent Document 1, the surface of a lithium-containing composite oxide represented by the general formula (Li , f , p , 1-x , 1-t , b , z , (1-a-b-m) , x , ,

[0004] , a , 2-(f / 2) , m , , a , 2-p , 1+x , t , y , (Co (1-a-b-m) Ni a Al b M m ) 1-x O 2-(f / 2) F f ) is modified with a surface modification compound containing at least one element selected from the group consisting of elements of Group S1 and Group S2, Group S1 is a group consisting of Al, Zr, Ti, Mg, Zn, Nb, Mo, Ta, W, and rare earths, Group S2 is a group consisting of F, P, and S, M is at least one element selected from the group consisting of transition metals other than Co and Ni, Sn, Ge, Na, K, B, C, Si, P, S, Zn, Ga, Bi, Group 2 elements, and rare earths, and -0.05 ≦ x ≦ 0.05, 0 < a ≦ 0.25, 0 < b ≦ 0.05, 0 ≦ m ≦ 0.04, 0 ≦ f ≦ 0.05, a surface-modified lithium-containing composite oxide for a positive electrode of a lithium-ion secondary battery, is disclosed.

[0004] Further, in Patent Document 2, a secondary particle assembled from at least one primary particle is included, and Chemical Formula 1 (Li a [Ni x Co y Mn<000001十二条>) t M 1-t O 2-p X pA lithium nickel cobalt manganese-based oxide represented by ; and metal oxide particles having an average particle diameter (D50) located inside the secondary particles and having a size in nanometers are included. In Chemical Formula 1, M is any one element selected from the group including Al, Mg, Sn, Ca, Ge, Ga, B, Ti, Mo, Nb, and W, X is any one element selected from the group including F, N, and P, a is 0.8 ≦ a ≦ 1.3, 0.6 ≦ x ≦ 0.95, 0 < y ≦ 0.2, 0 < z ≦ 0.2, x + y + z = 1, 0 ≦ t ≦ 1, 0 ≦ p ≦ 0.1. A positive electrode active material for a lithium secondary battery is disclosed.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] In conventional positive electrode active materials, an additive element (for example, an element represented by M (the "M element")) is added to the positive electrode active material. Conventionally, this additive element (M element) exists in the particles of the positive electrode active material as a Li compound reacted with the Li element, and the M element reacted with the Li element tends to have a high electron resistance. Therefore, there is a demand for a positive electrode active material that can further reduce the battery resistance.

[0007] The present disclosure has been made in view of the above circumstances, and an object thereof is to provide a positive electrode active material that can achieve a low battery resistance when used in a battery, a battery including the positive electrode active material, and a method for manufacturing the positive electrode active material.

Means for Solving the Problems

[0008] The means for solving the above problems include the following embodiments. <1> Li x Ni a Co b Mn c O y Particles of compound A having the composition represented by M d O e A positive electrode active material comprising particles of compound B having a composition represented by, The particles of compound B have an abundance of 45 mol% or more of an element whose ionic radius α is 0.60 Å ≤ α ≤ 1.38 Å. A positive electrode active material in which the area ratio X of the particles of compound B to the total area of ​​the particles of compound B and the particles of compound A is 0.8% ≤ X ≤ 19.6%. (In the composition of compound A, 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; in the composition of compound B, 0.001 ≤ d ≤ 0.2, and 0.002 ≤ e ≤ 0.4; and M represents at least one element selected from the group consisting of Ti, Zr, Ta, Pr, K, La, Ba, Y, Sr, Ce, Se, Hf, and Rh.) <2> The element represented by M is at least one element selected from the group consisting of Ti, Zr, Ta, Pr, K, and La. <1> The positive electrode active material described above. <3> The element represented by M is Ti. <2> The positive electrode active material described above. <4> <1> ~ <3> A battery having a positive electrode active material as described in any one of the items. <5> A step of preparing a solution by dissolving raw materials containing Ni, Co, and Mn, respectively, A step of adding the aforementioned solution to an alkaline solution to precipitate the hydroxide, A step of collecting a precipitate from the aforementioned alkaline solution, A step of mixing the aforementioned precipitate with a raw material containing Li to obtain a first mixture, A first firing step of firing the first mixture, A step of obtaining a second mixture by mixing a raw material containing an element represented by M with the first mixture after firing, A second firing step in which the second mixture is fired, A method for producing a positive electrode active material having the following characteristics. (The above M represents at least one element selected from the group consisting of Ti, Zr, Ta, Pr, K, La, Ba, Y, Sr, Ce, Se, Hf, and Rh.) [Effects of the Invention]

[0009] This disclosure provides a positive electrode active material that can achieve low battery resistance when used in a battery, a battery equipped with the positive electrode active material, and a method for manufacturing the positive electrode active material. [Brief explanation of the drawing]

[0010] [Figure 1] This figure shows a scheme for a method of producing a cathode active material according to an embodiment of this disclosure. [Modes for carrying out the invention]

[0011] The following describes an example of an embodiment of this disclosure. These descriptions and examples are illustrative and do not limit the scope of the invention. In numerical ranges described stepwise within this specification, the upper or lower limit of one numerical range may be replaced with the upper or lower limit of another numerical range described stepwise. Furthermore, in numerical ranges described within this specification, the upper or lower limit of that range may be replaced with the values ​​shown in the examples.

[0012] Each component may contain multiple types of the relevant substance. When referring to the amount of each component in a composition, if there are multiple substances corresponding to each component in the composition, unless otherwise specified, it refers to the total amount of those multiple substances present in the composition. The term "process" includes not only independent processes, but also any process that cannot be clearly distinguished from other processes, as long as its intended function is achieved.

[0013] <Cathode active material> The cathode active material according to the embodiments of this disclosure is Li x Ni a Co b Mn c O y Compound A having the composition represented by M d O e Compound B having the composition represented by , and . The particles of compound B contain an element with an ionic radius α of 0.60 Å ≤ α ≤ 1.38 Å, with an abundance of 45 mol% or more. Furthermore, the area ratio X of compound B particles to the total area of ​​compound B particles is 0.8% ≤ X ≤ 19.6%. (Note that in the composition of compound A, 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. Also, in the composition of compound B, 0.001 ≤ d ≤ 0.2 and 0.002 ≤ e ≤ 0.4, and M represents at least one element selected from the group consisting of Ti, Zr, Ta, Pr, K, La, Ba, Y, Sr, Ce, Se, Hf, and Rh.)

[0014] The ratios of Li (x), Ni (a), Co (b), Mn (c), and O (y) in compound A, and the ratios of M (d) and O (e) in compound B, represent the ratios of the particles of compound A and compound B as a whole. In other words, ratios x, a, b, c, and y represent the ratios of compound A and compound B as a whole, not just within compound A. Similarly, ratios d and e represent the ratios of compound A and compound B as a whole, not just within compound B.

[0015] Conventionally, to improve the resistance characteristics of batteries, additive elements (i.e., elements represented by M, hereinafter also referred to as "M elements") have been added to the positive electrode active material. In the past, these additive elements (M elements) existed within the particles of the positive electrode active material as Li compounds formed by the reaction with Li elements. However, M elements that react with Li elements tend to have high electronic resistance, and further improvements are needed to reduce the battery resistance when this positive electrode active material is used in a battery.

[0016] In contrast, the positive electrode active material according to the embodiment of this disclosure comprises active material particles (i.e., particles of compound A) and an oxide of element M (M d O e It contains two types of particles: particles containing (i.e., particles of compound B) and particles containing (i.e., particles of compound B). Furthermore, in the particles of compound B, the abundance of elements with an ionic radius α of 0.60 Å ≤ α ≤ 1.38 Å is 45 mol% or more. In other words, this means that the elements Ti, Zr, Ta, Pr, K, La, Ba, Y, Sr, Ce, Se, Hf, and Rh are sufficiently present in the particles of compound B. Furthermore, the fact that the area percentage X is in the range of 0.8% ≤ X ≤ 19.6% means that there is a sufficient amount of element M that has not reacted with element Li (i.e., element M contained in the particles of compound B) in the positive electrode active material. As a result, since there is a sufficient amount of M element that has not reacted with the low-electron-resistance Li element between the particles of the positive electrode active material, the battery resistance can be reduced.

[0017] Next, the positive electrode active material according to the embodiment of this disclosure will be described in detail.

[0018] (Particles of compound A) The cathode active material according to the embodiments of this disclosure is Li x Ni a Co b Mn c O y The system contains particles of compound A having the composition represented by [formula]. Note that the particles of compound A contain the positive electrode active material. (In the composition of compound A, 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.)

[0019] In the particle composition of compound A, from the viewpoint of resistance characteristics in a battery, the ratio x of Li is preferably 0.1 to 1.5, preferably 0.3 to 1.4, and more preferably 0.5 to 1.2. 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. 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. The ratio c of Mn is between 0 and 0.3, preferably between 0 and 0.2, and more preferably between 0.1 and 0.2. The sum of the ratios of Ni, Co, and Mn (a+b+c) is 1.0. The ratio y of O is 1.5 or more and 2.1 or less, preferably 1.7 or more and 2.1 or less, and more preferably 1.9 or more and 2.0 or less. As mentioned above, the ratios x, a, b, c, and y in compound A represent the ratio of the particles of compound A to the total number of particles of compound B.

[0020] (Particles of compound B) The positive electrode active material according to the embodiments of this disclosure is M d O e It has particles of compound B having the composition represented by . (In the composition of compound B, 0.001 ≤ d ≤ 0.2 and 0.002 ≤ e ≤ 0.4. M represents at least one element selected from the group consisting of Ti, Zr, Ta, Pr, K, La, Ba, Y, Sr, Ce, Se, Hf, and Rh.)

[0021] Compound B contains at least one element selected from the group consisting of Ti, Zr, Ta, Pr, K, La, Ba, Y, Sr, Ce, Se, Hf, and Rh as an additive element (element M). The inclusion of the elements listed above as oxides in the particles of compound B reduces battery resistance when the positive electrode active material is used in a battery. Furthermore, from the viewpoint of reducing battery resistance, compound B preferably contains at least one element selected from the group consisting of Ti, Zr, Ta, Pr, K, and La as an additive element (element M), and more preferably contains Ti.

[0022] In the particle composition of compound B, from the viewpoint of resistance characteristics in a battery, the ratio d of M is preferably 0.001 or more and 0.2 or less, preferably 0.01 or more and 0.15 or less, and more preferably 0.05 or more and 0.1 or less. The ratio e of O is 0.002 or more and 0.4 or less, preferably 0.01 or more and 0.3 or less, and more preferably 0.03 or more and 0.2 or less. As mentioned above, the ratios d and e in compound B represent the ratio of compound A particles to the total number of compound B particles.

[0023] The particles of compound B contain at least 45 mol% of elements with an ionic radius α of 0.60 Å ≤ α ≤ 1.38 Å (hereinafter also referred to as "specific elements"). Here, the elements with an ionic radius α of 0.60 Å ≤ α ≤ 1.38 Å (specific elements) include the aforementioned additive elements (M elements): Ti, Zr, Ta, Pr, K, La, Ba, Y, Sr, Ce, Se, Hf, and Rh. In other words, the abundance of specific elements in the particles of compound B is an indicator of the abundance of M elements contained in the particles of compound B.

[0024] In the particles of compound B, the proportion of elements (specific elements) with an ionic radius α of 0.60 Å ≤ α ≤ 1.38 Å is 45 mol% or more, and from the viewpoint of resistance characteristics in batteries, it is more preferably 50 mol% to 90 mol%, and more preferably 55 mol% to 87 mol%.

[0025] (Area ratio of particles of compound B: X) In the embodiment of this disclosure, the positive electrode active material has an area ratio X of compound B particles relative to the total area ratio X of compound B particles relative to the total area ratio X of compound B particles relative to compound A particles, where X is 0.8% ≤ X ≤ 19.6%. When the area ratio X is 0.8% or more, there is a sufficient amount of M element that has not reacted with Li element (i.e., M element contained in compound B particles) in the positive electrode active material, which can reduce battery resistance. On the other hand, when the area ratio X is 19.6% or less, there is a sufficient amount of compound A particles (i.e., particles containing the positive electrode active material), which can fully perform its function as a positive electrode. The area ratio X of the particles of compound B is preferably 2.0% ≤ X ≤ 15.0%, and more preferably 4.0% ≤ X ≤ 10.0%, from the viewpoint of resistance characteristics in the battery and the function of the positive electrode.

[0026] [Measurement of the abundance of specific elements and the area ratio X of compound B particles] The relative abundance of elements (specific elements) with an ionic radius α of 0.60 Å ≤ α ≤ 1.38 Å in the particles of compound B, and the area ratio X of the particles of compound B to the total area of ​​the particles of compound A and compound B, are measured by the following method. First, data is acquired for the cathode active material to be measured using a scanning electron microscope (SEM) with 10 particles included, and this is repeated until data for 100 particles is obtained. Next, compositional quantitative analysis is performed using energy-dispersive X-ray fluorescence spectroscopy (EDX), setting a circular analysis region along the outer circumference of each particle and acquiring the data. This quantitative compositional analysis of EDX allows us to determine the relative abundance of elements (specific elements) in the particles of compound B whose ionic radius α is 0.60 Å ≤ α ≤ 1.38 Å. Furthermore, from the data of a circular analysis region set along the outer circumference of each particle, the area percentage of particles (i.e., particles of compound B) in which the abundance of elements with an ionic radius of 0.60 Å to 1.38 Å (specific elements) is 45 mol% or more is calculated.

[0027] <Method for manufacturing positive electrode active material> Next, a method for manufacturing the positive electrode active material according to the embodiments of this disclosure will be described. The positive electrode active material according to the embodiments of this disclosure can be manufactured by the method for manufacturing the positive electrode active material according to the embodiments of this disclosure described below.

[0028] A method for producing a positive electrode active material according to the embodiment of this disclosure comprises the following steps (1) to (7). (1) Step of preparing a solution by dissolving raw materials containing Ni, Co, and Mn respectively (raw material dissolution) (2) Adding the aforementioned solution to an alkaline solution and precipitating the hydroxide (crystallization) (3) Step of collecting precipitate from the alkaline solution (4) A step of mixing the precipitate with a raw material containing Li to obtain a first mixture (addition of Li raw material) (5) A first firing step (first firing) in which the first mixture is fired. (6) A step to obtain a second mixture by mixing a raw material containing the element represented by M into the first mixture after firing (addition of M raw material) (7) A second firing step (second firing) in which the mixture described in the second step is fired. (Note that M represents at least one element selected from the group consisting of Ti, Zr, Ta, Pr, K, La, Ba, Y, Sr, Ce, Se, Hf, and Rh.)

[0029] In the method for producing a positive electrode active material according to the embodiment of this disclosure, a raw material containing Li is added and a first calcination is performed, and then a raw material containing an element represented by M is added and a second calcination is performed. This allows the element M to exist as an oxide (i.e., particles of compound B) without becoming a Li compound, and a positive electrode active material with low resistance can be obtained.

[0030] The following explains each of these processes according to the scheme shown in Figure 1.

[0031] (1) A step of preparing a solution by dissolving raw materials containing Ni, Co, and Mn, respectively. Prepare solutions by dissolving raw materials containing Ni, Co, and Mn (the "raw material dissolution" step shown in Figure 1). For example, a solution can be prepared by dissolving raw materials containing Ni, Co, and Mn in a solvent such as water. The concentration of the solution is preferably in the range of 10 to 40% by mass. The ratio of Ni / Co / Mn is preferably 1.0 / 0.8~1.2 / 0.8~1.2 (atm%) for Ni:1.0.

[0032] Examples of raw materials containing Ni include sulfates such as NiSO4, examples of raw materials containing Co include sulfates such as CoSO4, and examples of raw materials containing Mn include sulfates such as MnSO4.

[0033] (2) Adding the solution to the alkaline solution and allowing the hydroxide to precipitate. Next, the solution is added to an alkaline solution to precipitate the hydroxide (the "crystallization" step shown in Figure 1). As a result, particles containing hydroxides of Ni, Co, and Mn crystallize, and these particles are obtained as a precipitate. In this step, for example, the hydroxides of transition metals are precipitated by adding the solution and NH3 dropwise to the alkaline solution in which the hydroxide has precipitated, while controlling the pH to a constant level (e.g., pH 10-12).

[0034] (3) Steps to collect precipitate from alkaline solution Next, the precipitate is collected from the alkaline solution. Methods for collecting precipitate particles include, for example, filtration and washing. One method involves first removing the precipitate (particles) by filtration and washing with water, and then filtering the washed liquid to remove the precipitate (particles). The precipitate (particles) after washing may be further dried.

[0035] (4) A step of mixing the precipitate with a Li-containing raw material to obtain a first mixture. Next, the collected precipitate (particles) and the Li-containing raw material are mixed to obtain the first mixture (the "Li raw material addition" step shown in Figure 1). For example, the collected precipitate particles and the Li-containing raw material can be mixed in a mortar. Examples of raw materials containing lithium include Li2CO3 and LiOH.

[0036] (5) First firing process of firing the first mixture Next, the first mixture of the collected precipitate (particles) and the Li-containing raw material is calcined (the "first calcination" step shown in Figure 1). For example, the first mixture can be calcined in a calcination furnace (such as a muffle furnace). The calcination conditions can be, for example, a temperature of 800°C to 1100°C, an oxygen atmosphere, and a time of 5 to 20 hours.

[0037] Furthermore, in order to obtain a predetermined particle size from the first mixture, the first mixture may be crushed after the first calcination. Methods of crushing include, for example, crushing using a pulverizer (e.g., a jet mill).

[0038] (6) A step to obtain a second mixture by mixing a raw material containing the element represented by M with the first mixture after firing. Next, the first mixture after the first firing is mixed with a raw material containing the element represented by M to obtain a second mixture (the "addition of M raw material" step shown in Figure 1). For example, the first mixture after the first firing and the raw material containing M can be mixed in a mortar. As a raw material containing M (that is, at least one element selected from the group consisting of Ti, Zr, Ta, Pr, K, La, Ba, Y, Sr, Ce, Se, Hf, and Rh), the oxides of each element (e.g., TiO2, ZrO2, Ta2O5, Pr2O3, La2O3, and K2O) Examples include:

[0039] (7) Second firing process in which the second mixture is fired. Next, a second mixture containing a raw material with an element represented by M is fired (the "second firing" step shown in Figure 1). For example, the second mixture can be fired in a firing furnace (such as a muffle furnace). The firing conditions can be, for example, a temperature of 400°C to 600°C, under an oxygen atmosphere, and for a time of 5 to 20 hours. It is preferable that the firing temperature in the second firing step is lower than the firing temperature in the first firing step.

[0040] Furthermore, in order to obtain a predetermined particle size for the second mixture, the second mixture may be crushed after the second calcination. Methods of crushing include, for example, crushing using a pulverizer (e.g., a jet mill).

[0041] By going through these steps, a positive electrode active material according to the present disclosure can be obtained, which has particles of compound A and particles of compound B.

[0042] <Battery> A battery according to an embodiment of this disclosure has a positive electrode active material according to an embodiment of this disclosure. The battery has, for example, a negative electrode, a positive electrode, a separator, and an electrolyte. The battery according to the embodiments of this disclosure is preferably a liquid battery having a liquid electrolyte, but may also be a solid battery having a solid electrolyte. Alternatively, 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 that functions as both a positive electrode current collector and a negative electrode current collector.

[0043] (positive electrode) The positive electrode comprises, for example, a positive electrode current collector and a positive electrode active material layer fixed on the positive electrode current collector. The positive electrode active material layer has the positive electrode active material according to the embodiment of this disclosure as the positive electrode active material. Details of the positive electrode active material have already been described and are therefore omitted here. The positive electrode active material layer may contain a conductive material in addition to the positive electrode active material, and may also contain other components, such as binders and various additives. Examples of conductive materials include poorly graphitizable carbon, easily graphitizable carbon such as acetylene black and carbon black, and graphite. Examples of binders include vinyl halogenated resins such as polyvinylidene fluoride (PVdF).

[0044] As the positive electrode current collector, a conductive member made of a metal with good conductivity (for example, aluminum) is preferable. Alternatively, a current collector that combines the functions of both a positive and negative electrode current collector (i.e., a bipolar battery) may also be used.

[0045] (Negative electrode) The negative electrode comprises, for example, a negative electrode current collector and a negative electrode active material layer fixed on the negative electrode current collector. A conductive material made of a metal with good conductivity (e.g., copper) is preferred as the negative electrode current collector. Alternatively, a current collector combining the functions of both a positive and negative electrode current collector (i.e., a bipolar battery) may also be used. The negative electrode active material layer contains a negative electrode active material. Examples of negative electrode active materials include graphite-based 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 consist only of the negative electrode active material, or it may contain other components as needed, such as thickeners and binders. Examples of thickeners include celluloses such as carboxymethylcellulose (CMC). Examples of binders include rubbers such as styrene-butadiene copolymer (SBR) and halogenated vinyl resins such as polyvinylidene fluoride (PVdF).

[0046] (Separator) The separator is an electrically insulating porous membrane. 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) membrane, a porous polypropylene (PP) membrane, etc. The separator may have a multilayer structure. For example, the separator may be made by laminating a porous PP membrane, a porous PE membrane, and a porous PP membrane in this order. The separator may have a heat-resistant layer on its surface. The heat-resistant layer contains a heat-resistant material. Examples of heat-resistant materials include metal oxide particles such as alumina and high-melting-point resins such as polyimide.

[0047] (electrolyte) The battery according to the embodiment of this disclosure may further be a liquid-type battery having an electrolyte. A non-aqueous electrolyte is particularly preferred.

[0048] ·solvent Non-aqueous electrolytes contain a solvent (non-aqueous solvent) and an electrolyte. Examples of solvents (non-aqueous 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).

[0049] ·Electrolytes Examples of electrolytes in electrolyte solutions include lithium salts. Examples of lithium salts include lithium bis(fluorosulfonyl)imide (LiFSI), LiPF6 (lithium hexafluoride phosphate), lithium tetrafluoroborate (LiBF4), and Li[N(CF3SO2)2]. The amount of electrolyte may be, for example, 1.0 to 2.0 ml / L, and preferably 1.0 to 1.5 ml / L.

[0050] The electrolyte may contain various additives in addition to the solvent and electrolyte, such as thickeners, film-forming agents, and gas-generating agents. The electrolyte is typically a non-aqueous electrolyte that is liquid at room temperature (e.g., 25±10°C). The electrolyte is typically liquid under the battery's operating environment (e.g., a temperature environment of -20 to +60°C).

[0051] (Application) Applications of batteries include, for example, power sources for hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and battery electric vehicles (BEVs). [Examples]

[0052] The present disclosure will be described below based on examples, but the present disclosure is not limited in any way to these examples.

[0053] <Example 1> (Synthesis of positive electrode active material) Lix Ni a Co b Mn c O y Particles of compound A having the composition represented by and x, a, b, c, and y in the ratios shown in Table 1, and M d O e A positive electrode active material having particles of compound B having the composition represented by , where d and e are in the ratios shown in Table 1, and the element represented by M is one of the elements listed in Table 1, was synthesized by the method shown below.

[0054] ·Raw material solution NiSO4, CoSO4, and MnSO4 were dissolved in deionized water to obtain a raw material solution. The ratio of Ni / Co / Mn was 1 / 1 / 1 (atm%), and the concentration of the aqueous solution was 30% by mass.

[0055] • Crystallization A fixed amount of NH3 aqueous solution was added to the reaction vessel, and the mixture was purged with nitrogen while stirring with a stirrer. NaOH was added to the reaction vessel to make the pH alkaline. Then, while controlling the pH of the reaction vessel to a constant level (pH 10-12), the raw material solution and NH3 were added dropwise to precipitate the transition metal hydroxide.

[0056] • Wash, filter, dry The precipitated transition metal hydroxide was removed by filtration, deionized water was added, and the mixture was dispersed by stirring with a spoon, then washed with water. Next, the rinsed solution was filtered to extract the transition metal hydroxide. Next, the filtered transition metal hydroxide was dried at 120°C for 16 hours to evaporate the water.

[0057] • Mixing of Li raw materials Dried transition metal hydroxides were mixed with Li2CO3 and LiOH as Li raw materials in a mortar.

[0058] • Firing 1 and crushing 1 A mixture of transition metal hydroxide and Li raw material was calcined in a muffle furnace at 800°C in an oxygen atmosphere for 10 hours (calcination 1). Subsequently, the calcined mixture was crushed to a predetermined particle size using a jet mill (crushing 1).

[0059] • Mixing of M raw materials To the crushed mixture, TiO2 was added as the M raw material in a mortar and pestle.

[0060] • 2 calcinations and 2 crushing The crushed mixture and the M raw material (TiO2) were calcined in a muffle furnace at 400°C for 10 hours (calcination 2). Next, the calcined mixture was crushed in a jet mill to a predetermined particle size (crushing 2). Thus, the positive electrode active material of Example 1, containing particles of compound A and particles of compound B, was obtained.

[0061] <Examples 2-4> In Example 1, the positive electrode active material for each example was obtained in the same manner as in Example 1, except that the ratio of element M (Ti) to O in the particles of compound B was adjusted to the ratio shown in Table 2.

[0062] <Examples 5-9> The cathode active materials for each example were obtained in the same manner as in Example 1, except that the M raw material in Example 1 was changed from TiO2 to ZrO2 (Example 5), Ta2O5 (Example 6), Pr2O3 (Example 7), La2O3 (Example 8), and K2O (Example 9).

[0063] <Comparative Example 1> (Synthesis of positive electrode active material) Li x Ni a Co b Mn c O y A positive electrode active material having particles of compound A having the composition represented by [formula], where x, a, b, c, and y are in the ratios shown in Table 1, was synthesized by the method described below.

[0064] Comparative Example 1 was obtained in the same manner as in Example 1, except that the "Mixing of M raw materials" step and the "Castration 2 and crushing 2" step were not performed.

[0065] <Comparative Example 2> (Synthesis of positive electrode active material) Li x Ni a Co b Mn c M d O y A positive electrode active material having particles of compound A having the composition represented by , where x, a, b, c, d, and y are in the ratios shown in Table 1, and the element represented by M is one of the elements listed in Table 1, was synthesized by the method shown below.

[0066] ·Raw material solution NiSO4, CoSO4, and MnSO4 were dissolved in deionized water to obtain a raw material solution. The ratio of Ni / Co / Mn was 1 / 1 / 1 (atm%), and the concentration of the aqueous solution was 30% by mass.

[0067] • Crystallization A fixed amount of NH3 aqueous solution was added to the reaction vessel, and the mixture was purged with nitrogen while stirring with a stirrer. NaOH was added to the reaction vessel to make the pH alkaline. Then, while controlling the pH of the reaction vessel to a constant level (pH 10-12), the raw material solution and NH3 were added dropwise to precipitate the transition metal hydroxide.

[0068] • Wash, filter, dry The precipitated transition metal hydroxide was removed by filtration, deionized water was added, and the mixture was dispersed by stirring with a spoon, then washed with water. Next, the rinsed solution was filtered to extract the transition metal hydroxide. Next, the filtered transition metal hydroxide was dried at 120°C for 16 hours to evaporate the water.

[0069] • Mixing of Li raw material and M raw material Dried transition metal hydroxides, Li2CO3 and LiOH as Li raw materials, and TiO2 as M raw material were mixed in a mortar.

[0070] • Firing 1 and crushing 1 A mixture of transition metal hydroxide and Li raw material was calcined in a muffle furnace at 800°C in an oxygen atmosphere for 10 hours (calcination 1). Subsequently, the calcined mixture was crushed to a predetermined particle size using a jet mill (crushing 1). Thus, a positive electrode active material for Comparative Example 2, containing particles of compound A, was obtained.

[0071] [Measurement of specific element abundance (mol%) and area percentage of compound B particles (area%)] For the positive electrode active materials obtained in Examples 1 to 9, the abundance of elements (specific elements) with an ionic radius α of 0.60 Å ≤ α ≤ 1.38 Å in the particles of compound B, and the area ratio X of particles with an abundance of the specific element of 45 mol% or more (i.e., particles of compound B) relative to the total area of ​​particles of compound A and compound B were measured by the following method.

[0072] First, data for the positive electrode active material was acquired using SEM, with 10 particles included in each sample. This process was repeated until data for 100 particles was obtained. Next, EDX compositional analysis was performed, with a circular analysis region set along the outer circumference of each particle. This EDX compositional analysis was used to determine the abundance of elements (specific elements) in the particles of compound B where the ionic radius α is 0.60 Å ≤ α ≤ 1.38 Å. The results are shown in Table 1. Furthermore, from the data of a circular analysis region set along the outer circumference of each particle, the area percentage of particles (i.e., particles of compound B) in which the abundance of elements with an ionic radius of 0.60 Å to 1.38 Å (specific elements) was 45 mol% or more was calculated.

[0073] [Cell creation] Cells were fabricated using the positive electrode active materials obtained in each example and comparative example. • Cell configuration Winding 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) / Carboxymethylcellulose (CMC) Electrolyte composition: Electrolyte = LiPF6 (1M), Solvent = Ethylene carbonate (EC) / Dimethyl carbonate (DMC) / Ethyl methyl carbonate (EMC) = 3 / 4 / 3 (volume %)

[0074] • Electrode fabrication A cell was fabricated by coating the positive and negative electrodes onto the current collector using a film applicator with film thickness adjustment function (Allgood Co., Ltd.), and then drying them in a dryer at 80°C for 5 minutes.

[0075] [Measurement of resistance increase rate after cycle] The initial battery resistance was measured for the cells obtained in each example and comparative example. Table 1 shows the percentage (%) of the battery resistance of each example and comparative example, with the battery resistance of Comparative Example 1 set to "100%".

[0076] [Table 1]

[0077] As shown in Table 1, in the positive electrode active materials of each example, which contain particles of compound B, an element with an ionic radius α of 0.60 Å ≤ α ≤ 1.38 Å, in an area ratio of 0.8% to 19.6% relative to the total area ratio of compound A particles and compound B particles, it can be seen that the initial battery resistance is reduced compared to the positive electrode active materials of each comparative example that do not contain compound B particles.

Claims

1. Li ｘ Ni ａ Co ｂ Mn ｃ O ｙ Particles of compound A having the composition represented by M ｄ O ｅ A positive electrode active material comprising particles of compound B having a composition represented by, The particles of compound B have an abundance of 45 mol% or more of an element whose ionic radius α is 0.60 Å ≤ α ≤ 1.38 Å. A positive electrode active material in which the area ratio X of the particles of compound B to the total area ratio X of the particles of compound B to the total area ratio X of the particles of compound A is 0.8% ≤ X ≤ 19.6%. (In the composition of compound A, 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; in the composition of compound B, 0.001 ≤ d ≤ 0.2, and 0.002 ≤ e ≤ 0.4; and M represents at least one element selected from the group consisting of Ti, Zr, Ta, Pr, K, La, Ba, Y, Sr, Ce, Se, Hf, and Rh.)

2. The positive electrode active material according to claim 1, wherein the element represented by M is at least one element selected from the group consisting of Ti, Zr, Ta, Pr, K, and La.

3. The positive electrode active material according to claim 2, wherein the element represented by M is Ti.

4. A battery having the positive electrode active material according to any one of claims 1 to 3.

5. A step of preparing a solution by dissolving raw materials containing Ni, Co, and Mn, respectively, A step of adding the aforementioned solution to an alkaline solution to precipitate the hydroxide, A step of collecting a precipitate from the aforementioned alkaline solution, A step of mixing the aforementioned precipitate with a raw material containing Li to obtain a first mixture, A first firing step in which the first mixture is fired, A step of obtaining a second mixture by mixing an oxide containing an element represented by M with the first mixture after firing, A second firing step in which the second mixture is fired at a firing temperature lower than the firing temperature in the first firing step, between 400°C and 600°C, A method for producing a positive electrode active material having the following characteristics. (The above M represents at least one element selected from the group consisting of Ti, Zr, Ta, Pr, K, La, Ba, Y, Sr, Ce, Se, Hf, and Rh.)

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