Composite positive electrode active material

Abstract

A composite positive electrode active material is provided that can reduce the rate of increase in resistance that accompanies charging and discharging of a battery. [Solution] A composite positive electrode active material, the composite positive electrode active material comprising a positive electrode active material, compound A containing La, Ni, and O, and compound B containing Li, W, and O, the positive electrode active material being crystalline primary particles containing Li, a transition metal, and O, the positive electrode active material being a single-crystal active material constituted by the primary particles, compound B being present in the form of a film on at least a portion of the surface of the primary particles, and compound A being present independently as isolated particles.

Description

[Technical Field]

[0001] The present disclosure relates to composite positive electrode active materials. [Background technology]

[0002] Various techniques have been proposed regarding positive electrode active materials as disclosed in Patent Documents 1 and 2. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 2022-542774 [Patent Document 2] Special Publication No. 2024-511223 Summary of the Invention [Problem to be solved by the invention]

[0004] Conventionally, various positive electrode active materials have been proposed in order to obtain a positive electrode having high battery characteristics such as high cycle characteristics and high output characteristics. Conventional positive electrode active materials have room for improvement in terms of the rate of increase in resistance that accompanies charging and discharging of a battery when used in the battery.

[0005] The present disclosure has been made in view of the above circumstances, and has as its main object to provide a composite positive electrode active material that can reduce the rate of increase in resistance that accompanies charging and discharging of a battery. [Means for solving the problem]

[0006] That is, the present disclosure includes the following aspects. <1> A composite positive electrode active material, The composite positive electrode active material includes a positive electrode active material, a compound A including La, Ni, and O, and a compound B including Li, W, and O, the positive electrode active material is a crystalline primary particle containing Li, a transition metal, and O, the positive electrode active material is a single-crystal active material composed of the primary particles, the compound B is present in the form of a film on at least a part of the surface of the primary particles, The compound A is a composite positive electrode active material that exists independently as isolated particles.

[0007] <2> the composite positive electrode active material contains 0.005 mol or more and 2,000 mol or less of La per 1 mol of Ni, Co, and Mn contained in the positive electrode active material in total; <1> The composite positive electrode active material according to claim 1.

[0008] <3> the composite positive electrode active material contains 0.010 mol or more and 1.000 mol or less of W per 1 mol of Ni, Co, and Mn contained in the positive electrode active material in total; <1> or <2> The composite positive electrode active material according to claim 1.

[0009] <4> the particle size of the primary particles of the positive electrode active material is 0.5 μm or more; <1> ~ <3> 10. The composite positive electrode active material according to claim 9, wherein the positive electrode active material is a composite positive electrode active material.

[0010] <5> the average particle size of the isolated particles of the compound A is 0.1 μm or more and 20 μm or less; <1> ~ <4> 10. The composite positive electrode active material according to claim 9, wherein the positive electrode active material is a composite positive electrode active material.

[0011] <6> The compound A is La4LiNiO8, <1> ~ <5> 10. The composite positive electrode active material according to claim 9, wherein the positive electrode active material is a composite positive electrode active material.

[0012] <7> The compound B is at least one of Li2WO4 and Li6WO6. <1> ~ <6> 10. The composite positive electrode active material according to claim 9, wherein the positive electrode active material is a composite positive electrode active material.

[0013] <8> <1> ~ <7> 10. A positive electrode layer comprising the composite positive electrode active material according to any one of claims 1 to 9.

[0014] <9> <1> ~ <7> A battery comprising a positive electrode layer containing the composite positive electrode active material according to any one of the above items.

[0015] <10> <1> ~ <7> A method for producing the composite positive electrode active material according to any one of the above, a first-stage calcination step of calcining a first mixture of a transition metal hydroxide, which is a precursor of the positive electrode active material, and a lithium compound at 800°C to 1000°C to obtain the positive electrode active material; a second-stage firing step of firing a second mixture of the positive electrode active material and a W source that is a raw material of compound B at 500°C to 700°C to obtain a fired body that includes the positive electrode active material and compound B that is present in the form of a film on at least a portion of the surface of the primary particles of the positive electrode active material; a third-stage firing step of firing a third mixture of the fired body and a La source, which is a raw material of Compound A, at 800°C to 1100°C to obtain the composite positive electrode active material. [Effects of the Invention]

[0016] According to the present disclosure, it is possible to provide a composite positive electrode active material that can reduce the rate of increase in resistance that accompanies charging and discharging of a battery. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is an image diagram showing an example structure of the composite positive electrode active material of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, embodiments of the present disclosure will be described. It should be noted that matters other than those specifically mentioned in this specification that are necessary for implementing the present disclosure (for example, the general configuration and manufacturing process of a composite positive electrode active material that does not characterize the present disclosure) can be understood as design matters for those skilled in the art based on conventional technology in the relevant field. The present disclosure can be implemented based on the contents disclosed in this specification and common general technical knowledge in the relevant field. Furthermore, the dimensional relationships (length, width, thickness, etc.) in the drawings do not reflect the actual dimensional relationships. Elements described in the "singular" may also include the plural unless otherwise specified. For example, a particle may refer to a plurality of particles (particles). In the present disclosure, an example of a method for calculating the average particle size is as follows. First, for a given particle, the particle size is calculated when the particle is considered to be spherical in a transmission electron microscope (hereinafter referred to as TEM) image or a scanning electron microscope (hereinafter referred to as SEM) image taken at an appropriate magnification (for example, 50,000 to 1,000,000 times). This calculation of particle size from TEM or SEM observation is performed on 2 to 300 particles of the same type, and the average of these particles is taken as the average particle size.

[0019] 1. Composite positive electrode active material In the present disclosure, there is provided a composite positive electrode active material, The composite positive electrode active material includes a positive electrode active material, a compound A including La, Ni, and O, and a compound B including Li, W, and O, the positive electrode active material is a crystalline primary particle containing Li, a transition metal, and O, the positive electrode active material is a single-crystal active material composed of the primary particles, the compound B is present in the form of a film on at least a part of the surface of the primary particles, The compound A provides a composite positive electrode active material that exists independently as isolated particles.

[0020] In conventional sintered cathode active materials containing Li, Ni, Co, and Mn, structural changes occur due to oxygen elimination from Ni during sintering, and the single-crystal particles produced by sintering undergo chloride ionization, increasing reaction resistance when used in batteries. As the particle size of the single-crystal particles decreases, the contact area with the conductive material contained in the positive electrode layer decreases, reducing electronic conductivity. It is conceivable to add compound A containing La, which has excellent electronic conductivity, to the positive electrode active material to improve electronic conductivity, and to add compound B containing W, which has excellent Li conductivity, to the positive electrode active material to reduce reaction resistance. However, when an La source and a W source are mixed together with a transition metal hydroxide, which is a precursor of the positive electrode active material, and then calcined, a layer containing a mixture of compound A containing La and compound B containing W is formed on the surface of the resulting positive electrode active material, making it difficult to obtain the effects of improving Li conductivity and electronic conductivity. In the present disclosure, a composite positive electrode active material having the configuration of the present disclosure is obtained by producing a positive electrode active material, then firing a mixture of the positive electrode active material and a W source at a medium temperature of 500° C. to 700° C. to attach W-containing compound B to the surfaces of primary particles of the positive electrode active material, adding a La source thereto, and firing at a high temperature of 800° C. to 1000° C. According to the present disclosure, a composite positive electrode active material having an excellent balance between the Li conductivity improving effect of W-containing compound B and the electronic conductivity improving effect of La-containing compound A can be obtained.

[0021] Fig. 1 is a conceptual diagram showing an example of the structure of the composite positive electrode active material of the present disclosure. As shown in Fig. 1, the composite positive electrode active material 100 of the present disclosure has a film-like coating layer of compound B20 on the surfaces of multiple primary particles 10 of the positive electrode active material, and compound A30 exists independently as isolated particles on the surfaces of compound B20.

[0022] The composite positive electrode active material includes a positive electrode active material, a compound A, and a compound B. The composite positive electrode active material is for use in a battery, the details of which will be described later. The composite positive electrode active material may be in the form of particles. The particles of the composite positive electrode active material may be secondary particles. The average particle size of the particles of the composite positive electrode active material may be, for example, 0.5 μm or more, or may be, for example, 30 μm or less.

[0023] The positive electrode active material is a lithium transition metal composite oxide containing Li, a transition metal (TM), and O. The lithium transition metal composite oxide may contain one type of transition metal, two types of transition metals, three types of transition metals, or four or more types of transition metals. Examples of transition metals include Ti, V, Cr, Mn, Fe, Co, Ni, Zr, and Nb. The lithium transition metal composite oxide may contain at least Ni as a transition metal, and may further contain, for example, Co, Mn, and the like as transition metals. Lithium transition metal composite oxides contain not only Li and transition metals but also other metals other than Li and transition metals. 1 Other metals M (including metalloids) may be contained. 1 Examples of the elements include Al, Si, Ga, Ge, In, and Sn. The lithium transition metal composite oxide may contain Li, Ni, Co, Mn and O, or may contain Li, Ni, Co, Al and O. The total proportion of Ni, Co, and Mn contained in the lithium transition metal composite oxide relative to the total of 1 mol of all metals contained in the lithium transition metal composite oxide excluding Li is, for example, 0.80 mol or more, or alternatively 0.90 mol or more, or even 0.95 mol or more. Note that the "total of Ni, Co, and Mn" also includes cases where the proportion of one or both of Ni, Co, and Mn is 0. The lithium transition metal composite oxide may have a composition represented by the general formula LixNiaCobMncOy (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). In the general formula, the Li composition ratio "x" may satisfy the relationship "0.1≦x≦1.5". The Li composition ratio "x" may be, for example, 0.4 or more, 0.6 or more, 0.8 or more, 1.0 or more, or 1.05 or more. The Li composition ratio "x" may be, for example, 1.4 or less, or 1.2 or less. In the above general formula, the O composition ratio "y" may satisfy the relationship "1.5≦y≦2.1". The O composition ratio "y" may be, for example, 1.6 or more, 1.7 or more, 1.8 or more, or 1.9 or more. The O composition ratio "y" may be, for example, 2.0 or less. In the above general formula, the Ni composition ratio "a", the Co composition ratio "b", and the Mn composition ratio "c" satisfy the relationship "a+b+c=1.0". In the above general formula, the Ni composition ratio "a" may satisfy the relationship "0.5≦a≦1.0". The Ni composition ratio "a" may be, for example, 0.6 or more, 0.7 or more, 0.8 or more, or 0.85 or more. The Ni composition ratio "a" may be, for example, 0.9 or less. In the above general formula, the Co composition ratio "b" may satisfy the relationship "0≦b≦0.3". The Co composition ratio "b" may be, for example, 0.01 or more, 0.02 or more, 0.03 or more, 0.04 or more, 0.05 or more, 0.06 or more, 0.07 or more, or 0.075 or more. The Co composition ratio "b" may be, for example, 0.25 or less, 0.20 or less, 0.15 or less, 0.10 or less, 0.09 or less, or 0.08 or less. In the above general formula, the Mn composition ratio "c" may satisfy the relationship "0≦c≦0.3". The Mn composition ratio "c" may be, for example, 0.01 or more, 0.02 or more, 0.03 or more, 0.04 or more, 0.05 or more, 0.06 or more, 0.07 or more, or 0.075 or more. The Mn composition ratio "c" may be, for example, 0.25 or less, 0.20 or less, 0.15 or less, 0.10 or less, 0.09 or less, or 0.08 or less. An arbitrary dopant may be added to the lithium transition metal composite oxide. The dopant refers to an element other than Li, Ni, Co, Mn, and O. The dopant may include, for example, at least one selected from the group consisting of Zr, Mo, Mg, Ca, Na, Fe, Cr, Zn, Si, Sn, Al, and Ag. The composition ratio of the dopant may be, for example, 0.005 or more, 0.01 or more, 0.02 or more, 0.03 or more, or 0.04 or more. The composition ratio of the dopant may be, for example, 0.05 or less, 0.04 or less, 0.03 or less, 0.02 or less, or 0.01 or less.

[0024] The positive electrode active material is a crystalline primary particle. The positive electrode active material is a single-crystal active material composed of the above primary particles. The single-crystal active material is not a polycrystalline active material (an active material in which many primary particles are tightly packed together). In other words, the single-crystal active material may be a single-crystal particle. The single-crystal active material has the advantage of being less susceptible to deterioration over time than a polycrystalline active material. In SEM images, the single-crystalline active material appears as a single, independent particle (primary particle) without any apparent aggregation. In SEM images, the single-crystalline active material appears to have no grain boundaries. The magnification of the SEM image may be, for example, 10,000 to 30,000 times. The positive electrode active material may have a layered rock salt structure or a crystal structure belonging to the space group R-3m. The particle size of the primary particles of the positive electrode active material may be 0.5 μm or more, 0.6 μm or more, 0.8 μm or more, or 1.0 μm or more. If the particle size of the primary particles is too small, the particles may not grow sufficiently, making it difficult to produce a single crystal. On the other hand, the particle size of the primary particles may be, for example, 10 μm or less, or 5 μm or less. The particle size of the primary particles can be determined, for example, as the longest diameter in a TEM image or SEM image. Furthermore, for example, when primary particles (positive electrode active material) are contained in the positive electrode layer, the particle size of the primary particles may be determined from the longest diameter of the primary particles in an SEM cross-sectional image of the positive electrode layer. The "particle size of the primary particles" referred to here does not mean the average particle size. In other words, when multiple primary particles are contained in the positive electrode active material, the "particle size of the primary particles" refers to the "particle size of each primary particle." The primary particles of the lithium transition metal composite oxide as the positive electrode active material may not contain La and W, or may contain La and W in an amount of less than 0.005 mol.

[0025] Compound A contains La, Ni, and O. Compound A may be composed of only La, Ni, and O, or may further contain other elements. Examples of other elements include Li. That is, compound A may or may not contain Li. An example of the composition of compound A is La. a Ni b O c (0.8≦a≦1.2, 0.8≦b≦1.2, 2.8≦c≦3.2). For example, LaNiO3 is a typical perovskite composition and has good electronic conductivity. Another example of the composition of compound A is La a Li b Ni c O d (3.5≦a≦4.5, 0.5≦b≦1.5, 0.5≦c≦0.8, 7.5≦d≦8.5). Compound A may be, for example, La4LiNiO8, which is known to have good electronic conductivity and is thought to have a crystalline phase similar to perovskite. Compound A may have a crystalline phase of perovskite or a crystalline phase similar to perovskite. Compound A may have a crystalline phase of at least one of LaNiO3 and La4LiNiO8. This is because good electronic conductivity can be obtained. The crystalline phase may include a crystalline phase in which some of the constituent atoms (e.g., some O atoms) are missing, or a crystalline phase in which some of the constituent atoms (e.g., some La atoms) are present in excess. Compound A exists independently as an isolated particle, or compound A may exist on the surface of compound B. An isolated particle appears to be an independent particle in an SEM image. The isolated particle may be a primary particle or a secondary particle. In a cross-sectional image of compound A, when the length of compound A in the normal direction to the surface of compound A is L1 and the length of compound A in the direction perpendicular to the normal direction is L2, the ratio of L2 to L1 (L2 / L1) may be 3.0 or less. The cross-sectional image of compound A is, for example, an SEM cross-sectional image. The average particle size of the isolated particles of compound A may be 0.1 μm or more and 20 μm or less. The ratio of La contained in compound A in the composite positive electrode active material to 1 mol of the total of metals other than Li contained in the positive electrode active material may be, for example, 0.005 mol or more and 2,000 mol or less. Furthermore, the ratio of La contained in compound A in the composite positive electrode active material to 1 mol of the total of Ni, Co, and Mn contained in the positive electrode active material may be, for example, 0.005 mol or more and 2,000 mol or less. If the amount of La contained in the composite positive electrode active material is too small, the electronic conductivity will not improve, and if the amount of La contained in the composite positive electrode active material is too large, Li conduction will be inhibited. The volume ratio of the isolated particles of Compound A contained in the composite positive electrode active material may be 0.005% by volume to 75% by volume.

[0026] Compound B contains Li, W, and O. Compound B may consist of only Li, W, and O, or may further contain other elements. An example of the composition of compound B is Li a W b Oc (5.5≦a≦6.5, 0.5≦b≦1.5, 5.5≦c≦6.5). Compound B having the above composition is typically Li6WO6. Other examples of the composition of compound B include Li a W b O c (1.5≦a≦2.5, 0.5≦b≦1.5, 3.5≦c≦4.5) Compound B having the above composition is typically Li2WO4. Compound B may be at least one of Li2WO4 and Li6WO6. The compound B may be present in the form of a film on at least a portion of the surface of the primary particles of the positive electrode active material, and may be present in the form of a film on the entire surface of the primary particles of the positive electrode active material. In a cross-sectional image of the composite positive electrode active material, when the length of the compound B in the normal direction to the surface of the composite positive electrode active material is L3 and the length of the compound B in the direction perpendicular to the normal direction is L4, the film-like compound B may have a ratio (L4 / L3) of L4 to L3 that is greater than 3.0. The cross-sectional image of the composite positive electrode active material is, for example, a TEM cross-sectional image. That is, the composite positive electrode active material may have a coating layer made of compound B on at least a portion of the surface of the primary particle of the positive electrode active material, may cover 50% or more of the surface area of ​​the primary particle of the positive electrode active material, or may have a coating layer on the entire surface of the primary particle of the positive electrode active material. The coverage rate with the coating layer made of compound B can be determined, for example, by TEM observation. The coating layer made of Compound B can be confirmed by, for example, performing composition analysis (element analysis) on a TEM image obtained by observation using a TEM using energy dispersive X-ray spectrometry (EDX). The composition analysis can be performed using known methods, such as TEM-EDX, SEM-EDX, X-ray photoelectron spectroscopy (XPS), etc. The thickness of the coating layer made of compound B is not particularly limited, but may be, for example, 0.5 nm to 20 nm, or 1 nm to 15 nm. Here, the thickness of the coating layer made of compound B is determined as the average value of thicknesses measured at at least five locations in observation of primary particles of the positive electrode active material by TEM. Compound B may be crystalline or amorphous. "A compound is crystalline" means that a peak derived from the target compound is observed by X-ray diffraction using CuKα radiation. On the other hand, "a compound is amorphous" means that a peak derived from the target compound is not observed by X-ray diffraction using CuKα radiation. Note that when the target compound is amorphous, a halo pattern may be observed instead of a peak.

[0027] The proportion of W contained in compound B in the composite positive electrode active material may be, for example, 0.010 mol or more and 1.000 mol or less relative to 1 mol of the total of metals other than Li contained in the positive electrode active material. Furthermore, the proportion of W contained in compound B in the composite positive electrode active material may be, for example, 0.010 mol or more and 1.000 mol or less relative to 1 mol of the total of Ni, Co, and Mn contained in the positive electrode active material. If the amount of W contained in the composite positive electrode active material is too small, the Li conductivity will not improve, and if the amount of W contained in the composite positive electrode active material is too large, the electron conduction will be inhibited. The volume ratio of the film-like compound B contained in the composite positive electrode active material may be 0.010% by volume to 50% by volume.

[0028] 2. Manufacturing method of composite positive electrode active material In the present disclosure, there is provided a method for producing the above-described composite positive electrode active material, a first-stage calcination step of calcining a first mixture of a transition metal hydroxide, which is a precursor of the positive electrode active material, and a lithium compound at 800°C to 1000°C to obtain the positive electrode active material; a second-stage firing step of firing a second mixture of the positive electrode active material and a W source that is a raw material of compound B at 500°C to 700°C to obtain a fired body that includes the positive electrode active material and compound B that is present in the form of a film on at least a portion of the surface of the primary particles of the positive electrode active material; and a third firing step of firing a third mixture of the fired body and a La source, which is a raw material of Compound A, at 800°C to 1100°C to obtain the composite positive electrode active material.

[0029] The method for producing a composite positive electrode active material of the present disclosure includes (1) a first-stage firing step, (2) a second-stage firing step, and (3) a third-stage firing step.

[0030] (1) First stage baking process The first-stage calcination step is a step of calcining a first mixture of a transition metal hydroxide, which is a precursor of the positive electrode active material, and a lithium compound at 800° C. to 1000° C. to obtain the positive electrode active material.

[0031] The method for producing the precursor of the positive electrode active material of the present disclosure is not particularly limited, and examples thereof include the following methods. First, a raw material aqueous solution of a transition metal hydroxide is prepared. Examples of methods for producing the raw material aqueous solution include dissolving a water-soluble transition metal compound in water. Examples of transition metal compounds include metal salts such as sulfates and nitrates. Examples of Ni sources include NiSO4 and Ni(NO3)2. Examples of Co sources include CoSO4, Co(NO3)2, and Co(NO3)3. Examples of Mn sources include MnSO4 and Mn(NO3)2. The composition of the raw material aqueous solution is appropriately adjusted according to the desired positive electrode active material. Next, a certain amount of NH3 aqueous solution is placed in a reaction vessel, and the atmosphere is replaced with nitrogen while stirring with a stirrer or the like to create a non-oxidizing atmosphere. The flow rate of nitrogen gas used for nitrogen replacement is not particularly limited, but can be, for example, 2 to 6 L / min. Next, an aqueous sodium hydroxide solution is added to the reaction vessel, and while maintaining the pH at an alkaline level (e.g., pH 11.3 to 12.0), the raw material aqueous solution and the NH3 aqueous solution are added dropwise to the reaction vessel over 5 to 15 hours. The reaction temperature is not particularly limited and can be, for example, 50°C or higher and 65°C or lower. After the reaction is completed, the mixture is calcined, for example, at 120° C. to 220° C. for 4 to 10 hours under a pressure of 0.2 to 1.0 MPa. After the calcination is completed, the mixture is washed with water and filtered to remove the transition metal hydroxide, which is then dried at 110° C. for 10 to 12 hours.

[0032] In the present disclosure, the transition metal hydroxide contains a transition metal. The transition metal hydroxide may be a nickel-cobalt-manganese composite hydroxide containing nickel (Ni), cobalt (Co), and manganese (Mn). In the nickel-cobalt-manganese composite hydroxide, the ratio (molar ratio) of each metal species to the total amount of nickel, cobalt, and manganese is the same as the composition ratio represented by the above general formula in the positive electrode active material.

[0033] Examples of the lithium compound (Li source) include at least one selected from lithium carbonate, lithium nitrate, lithium acetate, lithium hydroxide, lithium oxide, and lithium chloride. The lithium compound may be lithium hydroxide. The molar ratio of Li in the Li source to TM contained in the transition metal hydroxide may be, for example, 0.4 or more, 0.6 or more, 0.8 or more, 1.0 or more, or 1.05 or more, or may be 1.4 or less, or 1.2 or less. The ratio of the lithium compound and precursor in the mixture is set so that the ratio (molar ratio) of lithium and each of the other metal species to the total amount of lithium and the metal species contained in the precursor in the target positive electrode active material is typically equal to the ratio (molar ratio) of lithium and each of the other metal species in the first mixture. The mixing method is not particularly limited, and any known method can be used. The first mixture may contain a molten salt. The molten salt functions as a flux, thereby enabling the primary particles to grow sufficiently. The molten salt may contain Li. An example of the molten salt is lithium hydroxide. The molar ratio of Li contained in the molten salt to TM contained in the transition metal hydroxide (Li / TM) is, for example, 0.01 or more, or may be 0.05 or more, or 0.10 or more, or may be 0.15 or more. On the other hand, Li / TM is, for example, 0.60 or less, or may be 0.50 or less, or may be 0.40 or less, or may be 0.30 or less. The first mixture may contain lithium hydroxide as a Li source and a molten salt. The molar ratio (Li' / TM) of Li contained in the Li source and the molten salt to TM contained in the transition metal hydroxide is, for example, 1.01 or more, or may be 1.05 or more, or 1.10 or more, or 1.15 or more. On the other hand, Li' / TM is, for example, 1.60 or less, or may be 1.50 or less, or 1.40 or less, or 1.30 or less.

[0034] The first mixture can be calcined for 8 to 15 hours at 800 to 1000° C. to obtain a positive electrode active material that is a lithium transition metal composite oxide. For the calcination, a known calcination furnace such as a muffle furnace can be used. The firing temperature in the first firing step may be 850°C or higher, 900°C or higher, or 950°C or higher. The firing time in the first firing step may be 9 hours or more, or 10 hours or more. The firing time in the first firing step may be 13 hours or less, or 11 hours or less. The positive electrode active material obtained by firing the precursor of the present disclosure is usually a single-crystal active material composed of primary particles.

[0035] (2) Second firing process The second-stage firing step is a step of firing a second mixture of the positive electrode active material and a W source that is a raw material of compound B at 500°C to 700°C to obtain a fired body that includes the positive electrode active material and compound B that is present in the form of a film on at least a part of the surface of the primary particles of the positive electrode active material. Examples of the raw material (W source) of compound B include H2WO4, etc. The amount of W source added is appropriately adjusted according to the desired composite positive electrode active material. In the second-stage firing step, the second mixture is fired at 500°C to 700°C, thereby suppressing compound B from becoming isolated particles, and compound B can be preferentially formed into a film on the surfaces of the primary particles of the positive electrode active material over compound A. The firing temperature in the second firing step may be 550°C or higher, 600°C or higher, or 650°C or higher. The firing time in the second firing step may be 1 hour or more, 9 hours or more, or 10 hours or more, while the firing time in the second firing step may be 15 hours or less, 13 hours or less, or 11 hours or less.

[0036] (3) Third firing process The third firing step is a step of firing a third mixture of the fired body and a La source, which is a raw material of Compound A, at 800° C. to 1100° C. to obtain the composite positive electrode active material. Examples of the raw material (La source) for compound A include La(OH)3, LaSO4, and La(NO3)3. The amount of the La source added is adjusted appropriately according to the desired composite positive electrode active material. In the third firing step, the third mixture is fired at 800°C to 1100°C, thereby accelerating the formation of compound A into isolated particles. The firing temperature in the third firing step may be 850°C or higher, 900°C or higher, 950°C or higher, 1000°C or higher, or 1050°C or higher. The firing time in the third firing step may be 1 hour or more, 9 hours or more, or 10 hours or more, while the firing time in the third firing step may be 15 hours or less, 13 hours or less, or 11 hours or less.

[0037] 3.Battery The composite positive electrode active material provided by the present disclosure can be used, for example, as a positive electrode active material constituting the positive electrode of a battery (such as a lithium ion battery). That is, the present disclosure can provide a battery in which a positive electrode, an electrolyte layer, and a negative electrode are laminated in this order, and the positive electrode contains the composite positive electrode active material of the present disclosure. According to the present disclosure, by using the above-described composite positive electrode active material in a battery, the rate of increase in resistance that accompanies charging and discharging of the battery can be reduced. The battery will be described below.

[0038] [Positive electrode] The positive electrode has a positive electrode layer and, if necessary, further has a positive electrode current collector. The positive electrode layer is a layer containing at least the composite positive electrode active material of the present disclosure as the positive electrode active material. The positive electrode layer may be disposed on one surface of the positive electrode current collector, or may be disposed on both surfaces of the positive electrode current collector. The positive electrode may have a multilayer structure in which two or more positive electrode layers are formed on at least one surface of the positive electrode current collector. When two or more positive electrode layers are formed, the types of positive electrode active materials contained in each positive electrode layer may be the same or different.

[0039] The positive electrode layer may contain only the composite positive electrode active material of the present disclosure as the positive electrode active material, or may further contain other active materials. The positive electrode layer may also contain at least one of an electrolyte, a conductive material, and a binder, as needed. The mixing ratio (mass ratio) of the composite positive electrode active material to the other active materials may be, for example, "composite positive electrode active material / other active materials = 9.5 / 0.5 to 0.5 / 9.5," "composite positive electrode active material / other active materials = 9 / 1 to 1 / 9," "composite positive electrode active material / other active materials = 8 / 2 to 2 / 8," "composite positive electrode active material / other active materials = 7 / 3 to 3 / 7," or "composite positive electrode active material / other active materials = 6 / 4 to 4 / 6." The other active materials may be polycrystalline active materials (polycrystalline particles) composed of secondary particles of the lithium transition metal composite oxides described above. Furthermore, the other active materials may be, for example, lithium iron phosphate (olivine structure), lithium manganese phosphate (olivine structure), lithium manganese iron phosphate (olivine structure), LiMnO2 (rock salt structure), Li(NiMn)2O4 (spinel structure), and LiCoO2 (layered structure). The proportion of the positive electrode active material in the positive electrode layer is, for example, 20% by mass or more, or may be 30% by mass or more, or 40% by mass or more. If the proportion of the positive electrode active material is too low, sufficient energy density may not be obtained. On the other hand, the proportion of the positive electrode active material in the positive electrode layer is, for example, 95% by mass or less, or may be 70% by mass or less, or may be 60% by mass or less. If the proportion of the positive electrode active material is too high, the ionic conductivity and electronic conductivity of the positive electrode layer may relatively decrease.

[0040] Examples of the electrolyte include solid electrolytes, which may be inorganic solid electrolytes such as sulfide solid electrolytes, halide solid electrolytes, oxide solid electrolytes, and complex hydride solid electrolytes, or organic solid electrolytes such as gel electrolytes.

[0041] The sulfide solid electrolyte is an electrolyte containing the element S. The sulfide solid electrolyte usually contains at least the elements Li and S. The sulfide solid electrolyte may further contain an element M (M is at least one of P, As, Sb, Si, Ge, Sn, B, Al, Ga, and In). The sulfide solid electrolyte may also contain a halogen element such as F, Cl, Br, or I.

[0042] The sulfide solid electrolyte may be a glass-based (amorphous) sulfide solid electrolyte, a glass-ceramic sulfide solid electrolyte, or a crystalline sulfide solid electrolyte. The sulfide solid electrolyte may have a crystalline phase. Examples of the crystalline phase include, for example, a Thio-LISICON type crystalline phase, an argyrodite type crystalline phase, and an LGPS type crystalline phase.

[0043] The composition of the sulfide solid electrolyte is not particularly limited, and examples thereof include, for example, xLi2S·(1-x)P2S5 (0.5≦x<1), and yLiI·zLiBr·(100-y-z)(xLi2S·(1-x)P2S5) (0.5≦x<1, 0≦y≦30, 0≦z≦30). In these compositions, x may satisfy 0.7≦x≦0.8. Further, as other examples of the composition of the sulfide solid electrolyte, there is 7-x PS 6-x X x and the like. X is at least one of F, Cl, Br, and I, and x satisfies 0≦x<2. Further, as other examples of the composition of the sulfide solid electrolyte, there is Li 4-x Me 1-x P x S4 (0<x<1). Me is at least one of Al, Zn, In, Ge, Si, Sn, Sb, Ga, and Bi. Examples of the sulfide solid electrolyte include LiI-LiBr-Li2S-P2S5, LiI-Li2S-P2S5, LiI-Li2S-P2O5, and LiI-Li3PO4-P2S5, and the like.

[0044] Examples of the oxide solid electrolyte include substances having a garnet-type crystal structure having, for example, a Li element, a La element, an A element (A is at least one of Zr, Nb, Ta, and Al), and an O element. Examples of the oxide solid electrolyte include, for example, Li2O-B2O3-P2O, Li2O-SiO2, Li2O-B2O3, Li 1.3 Al 0.3 Ti 0.7 (PO4)3, Li5La3Ta2O 12 Li7La3Zr2O 12 Li6BaLa2Ta2O12 , Li 3.6 Si 0.6 P 0.4 O4, Li4SiO4, Li3PO4, and Li 3+x PO 4-x N x (1≦x≦3) etc. may also be used.

[0045] The halide solid electrolyte may be, for example, a solid electrolyte containing Li, D, and X (D represents at least one of Ti, Al, and Y, and X represents F, Cl, or Br).

[0046] The gel electrolyte may include an electrolyte solution and a polymer material. The polymer material may form a polymer matrix. The polymer material may include at least one selected from the group consisting of polyvinylidene fluoride (PVdF), poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), polyacrylonitrile (PAN), PVdF-PAN, polyethylene oxide (PEO), polyethylene glycol (PEG), and derivatives thereof.

[0047] The solid electrolyte may be in the form of particles from the viewpoint of ease of handling. The average particle size of the solid electrolyte particles is not particularly limited and may be from 1 nm to 100 μm.

[0048] The proportion of the solid electrolyte in the positive electrode layer may be, for example, 1% by mass or more. If the proportion of the solid electrolyte is too low, the ion conduction paths in the positive electrode layer may be insufficient. On the other hand, the proportion of the solid electrolyte in the positive electrode layer may be, for example, 60% by mass or less. If the proportion of the solid electrolyte is too high, the proportion of the positive electrode active material may be relatively low, which may result in a low energy density.

[0049] The positive electrode layer may contain a conductive material. The addition of a conductive material improves the electronic conductivity of the positive electrode layer. Examples of conductive materials include carbon-based conductive materials, metal particles, and conductive polymers. Examples of carbon-based conductive materials include particulate materials such as acetylene black (AB) and ketjen black (KB), and fibrous materials such as vapor-grown carbon fiber (VGCF), carbon nanotubes (CNT), and carbon nanofibers (CNF). The proportion of the conductive material in the positive electrode layer may be, for example, 0.1% by mass or more. If the proportion of the conductive material is too low, the electron conduction path in the positive electrode layer may be insufficient. On the other hand, the proportion of the conductive material in the positive electrode layer may be, for example, 5% by mass or less. If the proportion of the conductive material is too high, the proportion of the positive electrode active material may be relatively low, which may result in a low energy density.

[0050] The positive electrode layer may contain a binder, such as styrene-butadiene rubber (SBR), polyimide (PI), polyacrylic acid (PAA), acrylonitrile-butadiene rubber (NBR), butadiene rubber (BR), polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), styrene-isoprene-styrene block copolymer (SIS), and ethylene-propylene-diene copolymer (EPDM). The proportion of the binder in the positive electrode layer may be, for example, 0.5% by mass or more. If the proportion of the binder is too low, it may be difficult to sufficiently reduce the increase in resistance due to charging and discharging. On the other hand, the proportion of the binder in the positive electrode layer may be, for example, 15% by mass or less. If the proportion of the binder is too high, the proportion of the positive electrode active material may be relatively low, which may result in a low energy density.

[0051] The thickness of the positive electrode layer is, for example, 0.1 μm or more and 1000 μm or less, or may be 1 μm or more and 500 μm or less, or may be 30 μm or more and 100 μm or less.

[0052] The method for producing the positive electrode layer is not particularly limited, but examples thereof include a method in which the composite positive electrode active material, the conductive material, and a solvent are mixed to obtain a positive electrode slurry, and the positive electrode slurry is applied to a positive electrode current collector and dried to form the positive electrode layer. When forming the positive electrode layer, a pressing process may be performed to press the positive electrode layer in the thickness direction. Examples of pressing processes include a roller press and a flat plate press. Examples of the solvent include N-methylpyrrolidone (NMP), tetralin, diisobutyl ketone, butyl butyrate, mesitylene, heptane, dibutyl ether, decane, dodecane, isodecane, and toluene, and the solvent may contain two or more of these components.

[0053] Examples of materials for the positive electrode current collector include SUS, Cr, Au, Pt, Zn, aluminum, copper, nickel, iron, titanium, and carbon. The thickness of the positive electrode current collector is, for example, 0.1 μm or more and 100 μm or less. The shape of the positive electrode current collector may be foil, plate, or the like. The planar shape of the positive electrode current collector is not particularly limited, and examples include a circle, an ellipse, a rectangle, and any polygonal shape. The positive electrode current collector may have a buffer layer, an elastic layer, or a PTC (Positive Temperature Coefficient) thermistor layer disposed on its surface.

[0054] [Negative electrode] The negative electrode has a negative electrode layer and, if necessary, further has a negative electrode current collector. The negative electrode layer is a layer containing at least a negative electrode active material. The negative electrode layer may also contain at least one of an electrolyte, a conductive material, and a binder, as necessary. The negative electrode layer may have a larger area than the positive electrode layer. The negative electrode active material may be, for example, in the form of particles or a sheet. The average particle size of the particles of the negative electrode active material may be, for example, 1 μm or more. The average particle size of the particles of the negative electrode active material may be, for example, 30 μm or less. The negative electrode active material may include, for example, at least one selected from the group consisting of a carbon-based active material, a Li-based active material, a Si-based active material, a Si—C composite material, and lithium titanate. The carbon-based active material may contain, for example, at least one selected from the group consisting of graphite, soft carbon, and hard carbon. "Graphite" is a general term for natural graphite and artificial graphite. Graphite may be a mixture of natural graphite and artificial graphite. The mixing ratio (mass ratio) of natural graphite to artificial graphite may be, for example, "natural graphite / artificial graphite = 1 / 9 to 9 / 1" or "natural graphite / artificial graphite = 3 / 7 to 7 / 3." Examples of Li-based active materials include Li, Li silicate, and Li alloys. Examples of the Si-based active material include Si, SiO, and Si alloys. The Si-C composite material refers to a composite material of a carbon-based active material (such as graphite) and a Si-based active material (such as Si). For example, Si fine particles may be dispersed in carbon particles. For example, Si fine particles may be dispersed in graphite particles. For example, Li silicate particles may be coated with a carbon material (such as amorphous carbon). The electrolyte, conductive material, and binder used in the negative electrode layer may be the same as those described above for the positive electrode layer.

[0055] Examples of materials for the negative electrode current collector include SUS, aluminum, copper, nickel, iron, titanium, and carbon. The thickness of the negative electrode current collector varies depending on the shape, but may be, for example, within a range of 1 μm to 50 μm. The shape of the negative electrode current collector may be a foil, a plate, or the like. The shape of the negative electrode current collector in plan view is not particularly limited, but examples include a circle, an ellipse, a rectangle, and any polygonal shape. The negative electrode current collector may have a buffer layer, an elastic layer, or a PTC thermistor layer disposed on its surface.

[0056] [Electrolyte layer] The electrolyte layer is a layer formed between the positive electrode layer and the negative electrode layer, and contains at least an electrolyte. The electrolyte may be a solid electrolyte or a liquid electrolyte (electrolytic solution). The electrolyte layer may include a solid electrolyte, an electrolytic solution, and the like. Examples of the solid electrolyte include those similar to those described above for the positive electrode layer. The electrolyte may be an aqueous electrolyte, a non-aqueous electrolyte, or the like, and may be used alone or in combination of two or more.

[0057] The solvent of the aqueous electrolyte solution contains water as a main component. That is, based on the total amount (100 mol%) of the solvent (liquid component) constituting the electrolyte solution, water may account for 50 mol% or more, particularly 70 mol% or more, and even 90 mol% or more. Meanwhile, there is no particular upper limit to the proportion of water in the solvent.

[0058] The solvent contains water as a main component, but may contain a solvent other than water. Examples of the solvent other than water include one or more selected from ethers, carbonates, nitriles, alcohols, ketones, amines, amides, sulfur compounds, and hydrocarbons. The solvent other than water may be 50 mol% or less, particularly 30 mol% or less, and even 10 mol% or less, based on the total amount (100 mol%) of the solvents (liquid components) constituting the electrolytic solution.

[0059] The aqueous electrolyte used in the present disclosure includes an electrolyte. Conventionally known electrolytes can be used for aqueous electrolytes. Examples of the electrolyte include lithium salts, nitrates, acetates, and sulfates of imide acid compounds. Specific examples of the electrolyte include lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(pentafluoroethanesulfonyl)imide (LiBETI), lithium bis(nonafluorobutanesulfonyl)imide, lithium nonafluoro-N-[(trifluoromethane)sulfonyl]butanesulfonylamide, lithium N,N-hexafluoro-1,3-disulfonylimide, CHClCOOLi, LiPF, LiBF, LiSO, and LiNO.

[0060] The concentration of the electrolyte in the aqueous electrolyte solution can be appropriately set according to the desired battery characteristics, as long as it does not exceed the saturated concentration of the electrolyte in the solvent, because if a solid electrolyte remains in the aqueous electrolyte solution, the solid may inhibit the battery reaction. For example, when LiTFSI is used as the electrolyte, the aqueous electrolyte solution may contain 1 mol or more, particularly 5 mol or more, or even 7.5 mol or more of LiTFSI per kg of water. The upper limit is not particularly limited, and may be, for example, 25 mol or less.

[0061] The non-aqueous electrolyte solution generally contains a lithium salt and a non-aqueous solvent. Examples of lithium salts include inorganic lithium salts such as LiPF6, LiBF4, LiClO4, and LiAsF6; and organic lithium salts such as LiCF3SO3, LiN(SO2CF3)2(Li-TFSI), LiN(SO2C2F5)2, and LiC(SO2CF3)3. Examples of non-aqueous solvents include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), γ-butyrolactone, sulfolane, acetonitrile (AcN), dimethoxymethane, 1,2-dimethoxyethane (DME), 1,3-dimethoxypropane, diethyl ether, tetraethylene glycol dimethyl ether (TEGDME), tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide (DMSO), and mixtures thereof. From the viewpoint of ensuring a high dielectric constant and a low viscosity, the solvent may be a mixture of a cyclic carbonate compound having a high dielectric constant and a high viscosity, such as EC, PC, or BC, and a chain carbonate compound having a low dielectric constant and a low viscosity, such as DMC, DEC, or EMC, or a mixture of EC and DEC. The concentration of the lithium salt in the non-aqueous electrolyte may be, for example, 0.3 to 5M.

[0062] The non-aqueous electrolyte may contain an ionic liquid, such as at least one selected from the group consisting of sulfonium salts, ammonium salts, pyridinium salts, piperidinium salts, pyrrolidinium salts, morpholinium salts, phosphonium salts, imidazolium salts, and derivatives thereof.

[0063] The electrolyte layer may be impregnated with the above-mentioned electrolytic solution and may include a separator that prevents contact between the positive electrode layer and the negative electrode layer. The separator material is not particularly limited as long as it is a porous film, and examples thereof include resins such as polyethylene (PE), polypropylene (PP), polyester, polyvinyl alcohol, cellulose, and polyamide, among which polyethylene and polypropylene are preferred. The separator may have a single-layer structure or a multi-layer structure. Examples of multi-layer separators include a two-layer structure of PE / PP, or a three-layer structure of PP / PE / PP or PE / PP / PE. The separator may be a nonwoven fabric such as a resin nonwoven fabric or a glass fiber nonwoven fabric.

[0064] [Solid electrolyte layer] The electrolyte layer may be a solid electrolyte layer made of a solid. When the electrolyte layer is a solid electrolyte layer, the solid electrolyte layer contains a solid electrolyte and, if necessary, a binder and the like. Examples of the solid electrolyte include those similar to those described above for the positive electrode layer. The solid electrolyte may be used alone or in combination of two or more. When two or more solid electrolytes are used, the two or more solid electrolytes may be mixed, or two or more solid electrolyte layers may be formed to form a multilayer structure. The proportion of the solid electrolyte in the solid electrolyte layer is not particularly limited, but is, for example, 50% by mass or more, and may be in the range of 60% by mass to 100% by mass, 70% by mass to 100% by mass, or even 100% by mass. The solid electrolyte layer may contain less than 1% by mass of electrolytic solution relative to the total amount of the solid electrolyte layer. Examples of the binder include the binders that can be contained in the positive electrode layer described above. The content of the binder in the solid electrolyte layer may be 0% by mass to 10% by mass with respect to the total amount of the solid electrolyte layer.

[0065] The thickness of the electrolyte layer is, for example, 0.1 μm or more and 1000 μm or less, or may be 0.1 μm or more and 500 μm or less, or may be 0.1 μm or more and 100 μm or less.

[0066] The battery of the present disclosure may further include a restraining jig that applies a restraining pressure to the positive electrode layer, the electrolyte layer, and the negative electrode layer in the thickness direction. In particular, when the electrolyte layer is a solid electrolyte layer, the restraining pressure may be applied to form good ion conduction paths and electron conduction paths. The restraining pressure may be, for example, 0.1 MPa or more, 1 MPa or more, or 5 MPa or more. Meanwhile, the restraining pressure may be, for example, 100 MPa or less, 50 MPa or less, or 20 MPa or less.

[0067] [battery] The type of battery in the present disclosure is not particularly limited, but is typically a lithium-ion battery. Furthermore, the battery in the present disclosure may be a liquid battery whose electrolyte layer contains an electrolytic solution, or a solid battery whose electrolyte layer contains a solid electrolyte. The solid battery may be a semi-solid battery or an all-solid-state battery. In the present disclosure, a semi-solid battery is a battery whose electrolyte layer contains a solid component such as an inorganic solid electrolyte and a liquid component (e.g., a solvent and an electrolytic solution). In the present disclosure, an all-solid-state battery is a battery whose electrolyte layer contains only a solid component such as an inorganic solid electrolyte. Furthermore, the battery in the present disclosure may be a primary battery or a secondary battery, but a secondary battery is particularly preferred. This is because it can be repeatedly charged and discharged and is useful, for example, as an on-board battery. The shape of the battery is not particularly limited, and may be, for example, a coin type, a cylindrical type, a square type, a sheet type, a button type, a flat type, or a laminate type. In the case of a battery stack in which a plurality of batteries are stacked, the battery stack may be of a monopolar type or a bipolar type.

[0068] Examples of uses of the battery include power sources for vehicles such as hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), electric vehicles (BEVs), gasoline-powered vehicles, and diesel-powered vehicles. In particular, the battery may be used as a driving power source for hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), or electric vehicles (BEVs). The battery may also be used as a power source for mobile objects other than vehicles (for example, trains, ships, and aircraft), and as a power source for electrical appliances such as information processing devices.

[0069] The present disclosure is not limited to the above-described embodiments. The above-described embodiments are merely examples, and any configuration that is substantially identical to the technical idea described in the claims of the present disclosure and that provides similar effects is included within the technical scope of the present disclosure. [Example]

[0070] Example 1 [Synthesis of precursors (transition metal hydroxides) for positive electrode active materials] NiSO4, CoSO4, and MnSO4 were dissolved in ion-exchanged water to prepare a raw material aqueous solution. The molar ratio of Ni, Co, and Mn in the raw material aqueous solution was Ni:Co:Mn=85:7.5:7.5. The concentration of the raw material aqueous solution (the ratio of all raw materials to the raw material aqueous solution) was 0.2 mol%. <Hydrothermal synthesis (crystallization)> A certain amount of NH3 aqueous solution was placed in a reaction vessel, and the atmosphere inside the reaction vessel was replaced with nitrogen while stirring with a stirrer. NaOH aqueous solution was added to the reaction vessel to maintain the pH alkaline (pH = 12). While controlling the temperature at a constant level, the raw material aqueous solution and NH3 aqueous solution were added dropwise to precipitate transition metal hydroxides. The reaction temperature was 60°C, and the reaction time was 10 hours. <Pre-firing> After the precipitation reaction was completed, the transition metal hydroxide was dehydrated and calcined under the following temperature and pressure conditions. Temperature: 120℃~220℃ Time: 4h~10h Pressure: 0.2MPa to 1.0MPa <Filtration> After calcination, the transition metal hydroxide was dispersed in ion-exchanged water and washed with water. Then, the washed transition metal hydroxide was filtered to obtain the transition metal hydroxide. <Drying> The transition metal hydroxide was dried at 110 °C for 12 h to evaporate the moisture.

[0071] [Synthesis of Cathode Active Material] <Mixing of Li Raw Materials> The dried transition metal hydroxide and LiOH as a lithium compound as a lithium source were mixed in an agate mortar to obtain a mixture. The mixture was mixed so that the molar ratio of the lithium compound to the total of Ni, Co, and Mn (NCM) contained in the transition metal hydroxide (Li / NCM ratio) was 1.05. <First-stage Calcination> The obtained mixture was calcined in a calcination furnace at 900 °C for 10 h in an oxygen atmosphere to synthesize a cathode active material (Li 1.05 Ni 0.85 Co 0.075 Mn 0.075 O2).

[0072] [Preparation of Composite Cathode Active Material] <Second-stage Calcination> The obtained cathode active material and H2WO4 as a W source previously classified with a 40-μm sieve were mixed in an agate mortar, and the obtained mixture was calcined in a calcination furnace at 600 °C for 10 h in an oxygen atmosphere to obtain a second-stage calcined product. The W source was mixed with the cathode active material so that the molar ratio of W to the total of Ni, Co, and Mn (NCM) 1 mol contained in the cathode active material (W / NCM ratio) was 0.01.

[0073] <Third-stage Calcination> The obtained second-stage calcined product and La(OH)3 as a La source previously classified with a 40-μm sieve were mixed in an agate mortar, and the obtained mixture was calcined in a calcination furnace at 1000 °C for 10 h in an oxygen atmosphere to obtain a third-stage calcined product. The La source was mixed with the positive electrode active material so that the molar ratio of La to 1 mol of the total of Ni, Co, and Mn (NCM) contained in the positive electrode active material (La / NCM ratio) was 0.01.

[0074] <Washing and filtration> The third-stage fired product was crushed in an agate mortar to a particle size of 0.2 mm or less to obtain a crushed product, which was then dispersed in 500 mL of pure water and stirred vigorously for 1 minute to obtain a slurry. Thereafter, the slurry was filtered using a Buchner funnel and filter paper, the obtained filtrate was rinsed with 500 mL of pure water, and the obtained cake was vacuum dried at 90°C to obtain a dried product.

[0075] <Crushing> The dried product was crushed to a predetermined particle size in an agate mortar to obtain particles of a composite positive electrode active material.

[0076] Example 2 A composite positive electrode active material was produced in the same manner as in Example 1, except that in the above <third-stage firing>, the La source was mixed with the positive electrode active material so that the molar ratio of La to 1 mol of the total of Ni, Co, and Mn (NCM) contained in the positive electrode active material (La / NCM ratio) was 0.005, and the resulting mixture was fired in a firing furnace at 850°C for 10 hours in an oxygen atmosphere to obtain a third-stage fired product.

[0077] Example 3 A composite positive electrode active material was prepared in the same manner as in Example 1, except that in the above <third-stage firing>, the obtained mixture was fired in a firing furnace at 850°C in an oxygen atmosphere for 10 hours to obtain a third-stage fired product.

[0078] Example 4 A composite positive electrode active material was produced in the same manner as in Example 1, except that in the above <third-stage firing>, the La source was mixed with the positive electrode active material so that the molar ratio of La to 1 mol of the total of Ni, Co, and Mn (NCM) contained in the positive electrode active material (La / NCM ratio) was 1.0, and the resulting mixture was fired in a firing furnace at 850°C for 10 hours in an oxygen atmosphere to obtain a third-stage fired product.

[0079] Example 5 A composite positive electrode active material was produced in the same manner as in Example 1, except that in the above <third-stage firing>, the La source was mixed with the positive electrode active material so that the molar ratio of La to 1 mol of the total of Ni, Co, and Mn (NCM) contained in the positive electrode active material (La / NCM ratio) was 2.0, and the resulting mixture was fired in a firing furnace at 850°C for 10 hours in an oxygen atmosphere to obtain a third-stage fired product.

[0080] Example 6 In the second firing step, a W source is mixed with the positive electrode active material so that the molar ratio of W to 1 mol of the total of Ni, Co, and Mn (NCM) contained in the positive electrode active material (W / NCM ratio) is 0.5; A composite positive electrode active material was produced in the same manner as in Example 1, except that in the above <third-stage firing>, the La source was mixed with the positive electrode active material so that the molar ratio of La to 1 mol of the total of Ni, Co, and Mn (NCM) contained in the positive electrode active material (La / NCM ratio) was 1.0, and the resulting mixture was fired in a firing furnace at 850°C for 10 hours in an oxygen atmosphere to obtain a third-stage fired product.

[0081] Example 7 In the second firing step, a W source is mixed with the positive electrode active material so that the molar ratio of W to 1 mol of the total of Ni, Co, and Mn (NCM) contained in the positive electrode active material (W / NCM ratio) is 1.0; A composite positive electrode active material was produced in the same manner as in Example 1, except that in the above <third-stage firing>, the La source was mixed with the positive electrode active material so that the molar ratio of La to 1 mol of the total of Ni, Co, and Mn (NCM) contained in the positive electrode active material (La / NCM ratio) was 1.0, and the resulting mixture was fired in a firing furnace at 850°C for 10 hours in an oxygen atmosphere to obtain a third-stage fired product.

[0082] (Comparative Example 1) A composite positive electrode active material was prepared in the same manner as in Example 1, except that in the above [Preparation of composite positive electrode active material], the <second-stage calcination> and <third-stage calcination> were not performed, and in the <first-stage calcination> of [Synthesis of positive electrode active material], a mixture of a transition metal hydroxide and a lithium compound was mixed with a W source so that the molar ratio of W to 1 mol of the total of Ni, Co, and Mn (NCM) contained in the transition metal hydroxide (W / NCM ratio) was 0.01, and the mixture was calcined in a calcination furnace at 1000°C in an oxygen atmosphere for 10 hours to obtain a calcined product.

[0083] (Comparative Example 2) A composite positive electrode active material was produced in the same manner as in Example 1, except that in the above [Preparation of composite positive electrode active material], the <second-stage calcination> and the <third-stage calcination> were not performed, and in the <first-stage calcination> of [Synthesis of positive electrode active material], a mixture of a transition metal hydroxide and a lithium compound was mixed with a W source so that the molar ratio of W to 1 mol of the total of Ni, Co, and Mn contained in the transition metal hydroxide (NCM) (W / NCM ratio) was 0.01, and a La source was mixed with the mixture so that the molar ratio of La to 1 mol of the total of Ni, Co, and Mn contained in the transition metal hydroxide (NCM) (La / NCM ratio) was 0.01, and the mixture was calcined in a calcination furnace at 1000°C in an oxygen atmosphere for 10 hours to obtain a calcined product.

[0084] (Comparative Example 3) A composite positive electrode active material was produced in the same manner as in Example 1, except that in the above [Preparation of composite positive electrode active material], the <second-stage calcination> and the <third-stage calcination> were not performed, and in the <first-stage calcination> of [Synthesis of positive electrode active material], a mixture of a transition metal hydroxide and a lithium compound was mixed with a W source so that the molar ratio of W to 1 mol of the total of Ni, Co, and Mn contained in the transition metal hydroxide (NCM) (W / NCM ratio) was 0.01, and a La source was mixed with the mixture so that the molar ratio of La to 1 mol of the total of Ni, Co, and Mn contained in the transition metal hydroxide (NCM) (La / NCM ratio) was 0.005, and the mixture was calcined in a calcination furnace at 850°C in an oxygen atmosphere for 10 hours to obtain a calcined product.

[0085] Comparative Example 4 A composite positive electrode active material was produced in the same manner as in Example 1, except that in the above [Preparation of composite positive electrode active material], the <second-stage calcination> and the <third-stage calcination> were not performed, and in the <first-stage calcination> of [Synthesis of positive electrode active material], a mixture of a transition metal hydroxide and a lithium compound was mixed with a W source so that the molar ratio of W to 1 mol of the total of Ni, Co, and Mn contained in the transition metal hydroxide (NCM) (W / NCM ratio) was 0.01, and a La source was mixed with the mixture so that the molar ratio of La to 1 mol of the total of Ni, Co, and Mn contained in the transition metal hydroxide (NCM) (La / NCM ratio) was 0.01, and the mixture was calcined in a calcination furnace at 850°C in an oxygen atmosphere for 10 hours to obtain a calcined product.

[0086] [SEM-EDX analysis] The resulting composite positive electrode active materials of Examples 1 to 7 and Comparative Examples 1 to 4 were subjected to cross-sectional observation and elemental analysis by SEM-EDX, and the following results were obtained. The results are shown in Table 2. It was confirmed that the positive electrode active materials contained in the composite positive electrode active materials of Examples 1 to 7 and Comparative Examples 1 to 4 contained Ni, Co, and Mn. Furthermore, in Examples 1 to 7 and Comparative Examples 2 to 4, compound A containing La, Ni, and O was confirmed from the mapping images. Furthermore, in Examples 1 to 7 and Comparative Examples 3 and 4, a particulate compound was confirmed, and it was confirmed from the mapping images that the particulate compound was Compound A containing La, Ni, and O. It was confirmed that Compound A contained in the composite positive electrode active materials of Examples 1 to 7 and Comparative Examples 3 and 4 existed independently as isolated particles. It is presumed that the independent existence of Compound A as isolated particles makes it easier to obtain the effect of improving electronic conductivity by Compound A. It was confirmed that compound A contained in the composite positive electrode active material of Comparative Example 2 was present in the form of a film on the surfaces of the primary particles of the positive electrode active material. It is presumed that compound B was converted into isolated particles by firing at a high temperature of 1000°C, and that the isolated particles of compound B caused compound A to form a film on the surfaces of the primary particles of the positive electrode active material. It is presumed that when compound A forms a film on the surfaces of the primary particles of the positive electrode active material, it becomes difficult to ensure contact between compound B and the primary particles of the positive electrode active material, thereby reducing the Li-conducting effect of compound B. Cross-sectional image analysis by SEM-EDX confirmed that the average particle size of isolated particles of Compound A in Examples 1 to 7 was 0.1 μm. Cross-sectional image analysis by SEM-EDX confirmed that the average particle size of isolated particles of Compound A in Comparative Examples 3 and 4 was 5 μm. Cross-sectional image analysis by SEM-EDX also confirmed that the particle size of primary particles of the positive electrode active material contained in the composite positive electrode active materials in Examples 1 to 7 and Comparative Examples 1 to 4 was 0.5 μm.

[0087] [TEM-EDX analysis] The composite positive electrode active materials of Examples 1 to 7 and Comparative Examples 1 to 4 were subjected to cross-sectional image analysis and elemental analysis by TEM-EDX, and the following results were obtained. The results are shown in Table 2. In the composite positive electrode active materials of Examples 1 to 7 and Comparative Examples 1 to 4, compound B containing Li, W, and O was confirmed from the mapping images. Compound B contained in the composite positive electrode active materials of Examples 1 to 7 was confirmed to exist in the form of a film, based on the presence of W-enriched regions on the surfaces of the primary particles of the positive electrode active material by TEM-EDX. It is presumed that the W source was fired at 600°C, which did not promote sintering of compound B, resulting in the formation of a film on the surfaces of the primary particles of the positive electrode active material. It is presumed that when compound B forms a film on the surfaces of the primary particles, contact with the primary particles of the positive electrode active material is secured, improving the Li conductivity effect of compound B. Mapping images confirmed that compound B contained in the composite positive electrode active materials of Comparative Examples 1 to 4 existed independently as isolated particles. It is presumed that the single-stage firing at a high temperature of 850°C or higher promoted sintering of compound B, causing compound B to become isolated particles. It is presumed that when compound B becomes isolated particles, it becomes difficult to secure contact points with the primary particles of the positive electrode active material, reducing the Li-conducting effect of compound B. Cross-sectional image analysis by TEM-EDX confirmed that Compound B contained in the composite positive electrode active materials of Examples 1 to 7 and Comparative Examples 1 to 4 was Li6WO6.

[0088] [XRD measurement] The XRD patterns of the composite positive electrode active materials of Examples 1 to 7 and Comparative Examples 1 to 4 were obtained at Rigaku Smart-Lab. The measurement samples were placed on glass sample plates and measured under the following measurement conditions. 2θ measurement range: 10°~120° X-ray: Cu-Kα (λ=1.5418Å) Scan speed: 2.0° / min ·Temperature: Room temperature As a result of XRD measurement, it was confirmed that the positive electrode active materials contained in the composite positive electrode active materials of Examples 1 to 7 and Comparative Examples 1 to 4 all have a layered rock salt type crystalline phase belonging to the space group R-3m. The compounds were identified using Rigaku Smart-Lab Studio II based on the diffraction data obtained by XRD measurement. Peaks derived from the LaNiO-based crystalline phase (La4LiNiO8) were confirmed in the composite positive electrode active materials of Examples 1 to 7 and Comparative Examples 2 to 4. A peak derived from the LiWO-based crystalline phase (Li6WO6) was observed in the composite positive electrode active materials of Comparative Examples 1 to 4. On the other hand, no peak derived from the LiWO-based crystalline phase was observed in the composite positive electrode active materials of Examples 1 to 7. Therefore, it is presumed that Compound B present on the surface of the composite positive electrode active materials of Examples 1 to 7 is amorphous.

[0089] [Cell (small laminate cell) fabrication] Using each of the composite positive electrode active materials of Examples 1 to 7 and Comparative Examples 1 to 4, small laminate cells of Examples 1 to 7 and Comparative Examples 1 to 4 were fabricated. Specifically, a cathode composite paste containing a composite cathode active material and acetylene black, a conductive material, was first applied to the surface of a metal foil cathode current collector using a film applicator with a film thickness adjustment function (manufactured by Allgrid Co., Ltd.) and then dried in a dryer at 80°C for 5 minutes to produce a cathode with a cathode layer on the cathode current collector. On the other hand, a negative electrode composite paste containing natural graphite as the negative electrode active material was applied to the surface of a metal foil as the negative electrode current collector using a film applicator with a film thickness adjustment function (manufactured by Allgrid Co., Ltd.) and then dried in a dryer at 80°C for 5 minutes to produce a negative electrode having a negative electrode layer on the negative electrode current collector. A 1M LiPF6 solution containing LiPF6 as an electrolyte and ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) as a solvent in a ratio of EC / DMC / EMC = 3 / 4 / 3 vol% was prepared as an electrolyte. The positive electrode, separator and negative electrode were stacked together, and the separator was impregnated with the electrolytic solution, to prepare small laminate cells of Examples 1 to 7 and Comparative Examples 1 to 4.

[0090] Cell Evaluation The IV resistance of each of the produced small laminate cells was measured before and after 100 cycles of cycling test. The cycling test was carried out for 100 cycles under the following conditions. <Cycle conditions> Voltage range: 3.0V-4.3V C rate: 0.3C Mode: CC charge / discharge ·Temperature 50℃ [Measurement of IV resistance] In the voltage range of 3.0V to 4.3V, the upper limit voltage of 4.3V was set to SOC 100%, and the voltage was adjusted so that SOC was 50%. The voltage drop (V) was measured when discharging for 10 seconds at 0°C under the conditions of C rates of 0.1C, 0.3C, 0.5C, 0.7C, and 1.0C. The relationship between the voltage drop (V) and the current value was plotted, and the slope of the linearly approximated line was taken as the IV resistance. [Calculation of IV resistance increase rate after 100 cycles] The above measurements were carried out before and after the 100-cycle cycle test, and the amount of change before and after the cycle test was calculated and treated as the resistance increase rate. IV resistance increase rate after 100 cycles (%) = (IV resistance after cycle test) / (IV resistance before cycle test) × 100 In the present disclosure, the IV resistance increase rate was calculated by standardizing it based on Comparative Example 1. The results are shown in Table 2.

[0091] [Table 1]

[0092] [Table 2]

[0093] Based on the results shown in Tables 1 and 2, the following comparative considerations were made. (Comparison between Comparative Example 1 and Comparative Example 2) As shown in Table 2, the battery using the composite positive electrode active material of Comparative Example 2 had a smaller resistance increase rate after 100 cycles than the battery using the composite positive electrode active material of Comparative Example 1. This shows that the inclusion of a predetermined amount of compound A in the composite positive electrode active material can reduce the resistance increase rate associated with the charge and discharge of the battery. (Comparison between Example 1 and Comparative Example 2) It can be seen that the battery using the composite positive electrode active material of Example 1 has a smaller resistance increase rate after 100 cycles than the battery using the composite positive electrode active material of Comparative Example 2. Therefore, it can be seen that when the La / NCM ratio in the composite positive electrode active material is 0.01, the presence of compound A as isolated particles can reduce the resistance increase rate associated with charge and discharge of the battery. (Comparison between Example 2 and Comparative Example 3) It can be seen that the battery using the composite positive electrode active material of Example 2 had a smaller resistance increase rate after 100 cycles than the battery using the composite positive electrode active material of Comparative Example 3. Therefore, it can be seen that when the La / NCM ratio in the composite positive electrode active material is 0.005, the presence of compound B in the coating on the surfaces of the primary particles of the positive electrode active material can reduce the resistance increase rate associated with charge and discharge of the battery. (Comparison between Example 3 and Comparative Example 4) It can be seen that the battery using the composite positive electrode active material of Example 3 has a smaller resistance increase rate after 100 cycles than the battery using the composite positive electrode active material of Comparative Example 4. Therefore, it can be seen that when Compound A is obtained at a firing temperature of 850°C and the La / NCM ratio in the composite positive electrode active material is 0.01, the resistance increase rate associated with the charge and discharge of the battery can be reduced. (Comparison of Example 4 and Example 3) It can be seen that the battery using the composite positive electrode active material of Example 4, in which the La / NCM ratio in the composite positive electrode active material was 1.000, had a smaller resistance increase rate after 100 cycles compared to the battery using the composite positive electrode active material of Example 3, in which the La / NCM ratio in the composite positive electrode active material was 0.01. Therefore, it can be seen that when Compound A is obtained by setting the firing temperature to 850°C, the resistance increase rate during battery charge and discharge can be reduced more effectively when the La / NCM ratio in the composite positive electrode active material is 1.000 than when it is 0.01. (Comparison of Example 5 and Example 2) The battery using the composite positive electrode active material of Example 5, in which the La / NCM ratio in the composite positive electrode active material was 2.000, exhibited a higher resistance increase rate after 100 cycles compared to the battery using the composite positive electrode active material of Example 2, in which the La / NCM ratio in the composite positive electrode active material was 0.005. Therefore, when Compound A was obtained by setting the firing temperature to 850°C, it was found that the resistance increase rate associated with battery charge and discharge can be reduced more effectively when the La / NCM ratio in the composite positive electrode active material was 0.005 than when it was 2.000. It is presumed that lithium conduction was inhibited in Example 5 because the amount of La contained in the composite positive electrode active material was greater than in Example 2. (Comparison of Example 6, Example 7 and Example 4) The battery using the composite cathode active material of Example 6, in which the W / NCM ratio of the composite cathode active material was 0.500, exhibited a higher resistance increase rate after 100 cycles than the battery using the composite cathode active material of Example 4, in which the W / NCM ratio of the composite cathode active material was 0.010, and the battery using the composite cathode active material of Example 7, in which the W / NCM ratio of the composite cathode active material was 1.000. Therefore, when Compound A was obtained by setting the firing temperature to 850°C and the La / NCM ratio of the composite cathode active material was 1.000, it was found that a W / NCM ratio of 0.010 in the composite cathode active material can reduce the resistance increase rate associated with battery charge and discharge compared to a W / NCM ratio of 1.000 in the composite cathode active material, and that a W / NCM ratio of 0.500 in the composite cathode active material can reduce the resistance increase rate associated with battery charge and discharge compared to a W / NCM ratio of 0.010 in the composite cathode active material. In Example 7, the amount of W contained in the composite positive electrode active material was greater than in Examples 4 and 6, and it is presumed that this inhibited electron conduction. [Explanation of symbols]

[0094] 10... Primary particles of positive electrode active material 20...Compound B 30...Compound A 100 Composite positive electrode active material

Claims

1. A composite positive electrode active material, The composite positive electrode active material includes a positive electrode active material, a compound A including La, Ni, and O, and a compound B including Li, W, and O, the positive electrode active material is a crystalline primary particle containing Li, a transition metal, and O, the positive electrode active material is a single-crystal active material composed of the primary particles, the compound B is present in the form of a film on at least a part of the surface of the primary particle, The compound A is a composite positive electrode active material that exists independently as an isolated particle.

2. 2. The composite positive electrode active material according to claim 1, wherein the composite positive electrode active material contains 0.005 mol to 2.000 mol of La per 1 mol of Ni, Co, and Mn contained in the positive electrode active material in total.

3. 2. The composite positive electrode active material according to claim 1, wherein the composite positive electrode active material contains 0.010 mol or more and 1.000 mol or less of W per 1 mol of Ni, Co, and Mn contained in the positive electrode active material in total.

4. The composite positive electrode active material of claim 1 , wherein the primary particles of the positive electrode active material have a particle size of 0.5 μm or more.

5. 2. The composite positive electrode active material according to claim 1, wherein the average particle size of the isolated particles of compound A is 0.1 μm or more and 20 μm or less.

6. The compound A is La ４ LiNiO ８ 2. The composite positive electrode active material of claim 1 , wherein:

7. The compound B is Li ２ WO ４ , and Li ６ WO ６ The composite positive electrode active material of claim 1 , wherein the composite positive electrode active material is at least one of the following:

8. A positive electrode layer comprising the composite positive electrode active material of claim 1 .

9. A battery comprising a positive electrode layer comprising the composite positive electrode active material of claim 1.

10. A method for producing the composite positive electrode active material according to claim 1, a first-stage calcination step of calcining a first mixture of a transition metal hydroxide, which is a precursor of the positive electrode active material, and a lithium compound at 800°C to 1000°C to obtain the positive electrode active material; a second-stage firing step of firing a second mixture of the positive electrode active material and a W source that is a raw material of the compound B at 500°C to 700°C to obtain a fired body that includes the positive electrode active material and the compound B that is present in the form of a coating on at least a portion of the surface of the primary particles of the positive electrode active material; a third-stage firing step of firing a third mixture of the fired body and a La source that is a raw material of the compound A at 800°C to 1100°C to obtain the composite positive electrode active material.

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