Coating active material, electrode composite material, battery, and method for manufacturing the coating active material

Abstract

To provide a coated active material capable of suppressing a resistance increase due to moisture and a resistance increase due to a high resistance layer.SOLUTION: In the present disclosure, there is provided a coated active material including an electrode active material and a coating layer that covers the electrode active material and contains a coating material including a B element, a P element, and an O element. In the coated active material, a moisture amount X generated in a temperature range of 120°C or more and 180°C or less is 10.0 ppm or less, and a coverage of the coating layer with respect to the electrode active material is larger than 67%.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This disclosure relates to a coating active material, an electrode composite material, a battery, and a method for manufacturing a coating active material. [Background technology]

[0002] In recent years, battery development has been thriving. For example, in the automotive industry, development is progressing on batteries used in electric vehicles (BEVs), plug-in hybrid vehicles (PHEVs), and hybrid electric vehicles (HEVs). It is also known that the surface of the electrode active material used in batteries is coated with a phosphorus-based coating solution.

[0003] For example, Patent Document 1 discloses composite particles comprising positive electrode active material particles and a coating film containing a phosphorus compound that covers at least a portion of the surface of the positive electrode active material particles. Furthermore, Patent Document 1 discloses the production of composite particles by mixing positive electrode active material particles with an aqueous coating liquid (aqueous coating liquid) containing phosphorus and drying the mixture. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2023-136753 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] In coating methods using a phosphorus-containing aqueous coating solution, moisture may remain in the coating layer even after thorough drying. This residual moisture can degrade the electrode active material or the electrolyte surrounding the electrode active material, potentially leading to an increase in resistance.

[0006] Therefore, the inventor of the present application considered coating the electrode active material with a coating material by a dry method. By using the dry method, the moisture content of the coating layer can be reduced. On the other hand, the inventor of the present application found a new problem that it is difficult to increase the coating rate of the coating layer with respect to the electrode active material in the case of the dry method. When the coating rate of the coating layer with respect to the electrode active material is low, a high-resistance layer may be generated by the reaction of the electrode active material and the electrolyte, causing an increase in resistance.

[0007] The present disclosure has been made in view of the above circumstances, and the main object thereof is to provide a coated active material capable of suppressing an increase in resistance due to moisture and an increase in resistance due to a high-resistance layer.

Means for Solving the Problems

[0008] [1] A coated active material having an electrode active material and a coating layer that coats the electrode active material and contains a coating material having B element, P element and O element, wherein the amount of moisture X generated in the temperature range of 120°C or higher and 180°C or lower is 10.0 ppm or less, and the coating rate of the coating layer with respect to the electrode active material is greater than 67%, the coated active material.

[0009] [2] The coated active material according to [1], wherein the amount of moisture X is 8.0 ppm or less.

[0010] [3] The coated active material according to [1] or [2], wherein the amount of moisture Y generated in the temperature range of 180°C or higher and 300°C or lower is 350 ppm or less.

[0011] [4] The coated active material according to any one of [1] to [3], wherein the coating rate is 75% or more.

[0012] [5] The coated active material according to any one of [1] to [4], wherein the coating material further has Li element.

[0013] [6] The above electrode active material comprises Li element, M element (where M is a metal other than Li), and O element. The above M contains at least Ni, The coating active material according to any one of [1] to [5], wherein the molar ratio of Ni to M (Ni / M) is 50% or more.

[0014] [7] The coating active material described in [6], wherein the above Ni / M ratio is 80% or more.

[0015] [8] The BET specific surface area is 0.50 m². 2 / g or more, 1.20m 2 A coated active material described in any of [1] to [7], which is less than / g.

[0016] [9] An electrode composite comprising a coating active material according to any one of [1] to [8], and at least one of a conductive material and a binder.

[0017]

[10] The electrode mixture described in [9], wherein the electrode mixture contains a solid electrolyte.

[0018]

[11] The electrode composite material according to

[10] , wherein the solid electrolyte is a sulfide solid electrolyte.

[0019]

[12] A battery having a positive electrode layer, a negative electrode layer, and an electrolyte layer disposed between the positive electrode layer and the negative electrode layer, A battery in which the positive electrode layer or the negative electrode layer contains the electrode composite material described in any of [9] to

[11] .

[0020]

[13] The battery according to

[12] , wherein the positive electrode layer contains the electrode composite material.

[0021]

[14] The battery according to

[12] or

[13] , wherein the electrolyte layer contains a solid electrolyte.

[0022]

[15] A method for producing a coated active material, comprising producing a coated active material according to any one of [1] to [8], Preparation steps for preparing the above-mentioned electrode active material and the above-mentioned coating material, The process includes a coating layer formation step in which the electrode active material is coated with the coating material by a dry method to form the coating layer, Particle size D of the above coating material 90 A method for producing a coated active material, wherein the particle size is 2 μm or less. [Effects of the Invention]

[0023] The coating active material in this disclosure has the effect of suppressing the increase in resistance due to moisture and the increase in resistance due to the high-resistance layer. [Brief explanation of the drawing]

[0024] [Figure 1] This is a schematic cross-sectional view illustrating an example of a coated active material in this disclosure. [Figure 2] This is a schematic cross-sectional view illustrating a battery in this disclosure. [Figure 3] This is a flowchart illustrating the method for producing the coated active material in this disclosure. [Figure 4] This graph shows the resistance of the batteries prepared in Examples 1-4 and Comparative Examples 1-7. [Modes for carrying out the invention]

[0025] The coating active material, electrode composite material, battery, and method for manufacturing the coating active material as described herein will be explained in detail below.

[0026] A. Coated active material Figure 1 is a schematic cross-sectional view illustrating a coated active material in this disclosure. The coated active material 10 shown in Figure 1 comprises an electrode active material 1 and a coating layer 2 that covers the electrode active material 1 and includes a coating material having elements B, P, and O. In the coated active material 10, the amount of moisture X generated in the temperature range of 120°C to 180°C is usually 10.0 ppm or less. Also, the coverage rate of the coating layer 2 over the electrode active material 1 is usually greater than 67%.

[0027] According to this disclosure, the coating active material has a low moisture content X and a high coverage rate of the coating layer, thus suppressing the increase in resistance due to moisture and the increase in resistance due to the high-resistance layer. As mentioned above, Patent Document 1 discloses the production of composite particles by mixing positive electrode active material particles with an aqueous coating solution containing phosphorus and drying them. In coating methods using an aqueous coating solution containing phosphorus, moisture may remain in the coating layer even after sufficient drying, and this residual moisture may degrade the electrode active material or the electrolyte present around the electrode active material, potentially causing an increase in resistance.

[0028] Therefore, the inventors of the present invention considered coating the electrode active material with a coating material using a dry method. When using the dry method, there is no need to use a solvent such as water, so the amount of moisture in the coating layer can be reduced. On the other hand, the inventors of the present invention discovered a new problem: when using the dry method, it is difficult to increase the coverage rate of the coating layer over the electrode active material. If the coverage rate of the coating layer over the electrode active material is low, a high-resistance layer may be formed by a reaction between the electrode active material and the electrolyte, which may cause an increase in resistance.

[0029] The inventors of this invention conducted extensive research to solve the above-mentioned new problem and discovered that the reason why it is difficult to increase the coverage rate is that phosphorus-containing coating materials are hard, and when coating the electrode active material with the coating material, the surface of the electrode active material is significantly damaged by the coating material. Therefore, they found that by using a fine coating material to suppress damage to the surface of the electrode active material, the coverage rate of the coating material could be greatly improved. As a result, it was possible to obtain a coated active material with a low moisture content and a high coverage rate of the coating layer, thereby making it possible to simultaneously suppress the increase in resistance due to moisture and the increase in resistance due to the high-resistance layer. Furthermore, since the coating material contains element P, the chemical stability of the coating layer is improved. Moreover, since the coating material contains element B in addition to element P, it is possible to improve the ionic conductivity of the coating layer while improving the chemical stability of the coating layer.

[0030] 1.Coating layer The coating layer in this disclosure is a layer that coats the electrode active material. The coating layer also includes a coating material having elements B, P, and O. The coating material may further contain the element Li. Preferably, the coating material has a PO4 structure.

[0031] In the coating material, the molar ratio of element B to element P (B / P) is not particularly limited, but may be, for example, 0.5 or more and 2.0 or less, 0.8 or more and 1.25 or less, or 0.9 or more and 1.11 or less. Furthermore, if the coating material also contains element Li, the molar ratio of element Li to the sum of elements P and B (Li / (P+B)) is not particularly limited, but may be, for example, 0.3 or more and 1.2 or less, or 0.5 or more and 1.0 or less.

[0032] The coverage rate of the coating layer over the electrode active material is usually greater than 67%, and may be 75% or more, or even 80% or more. If the coverage rate is too low, it is difficult to sufficiently suppress the increase in resistance due to the high-resistance layer. On the other hand, the coverage rate may be 100%, or less than 100%. In this disclosure, the coverage rate is determined by calculating the elemental ratio from the intensity ratio of each major element based on X-ray photoelectron spectroscopy (XPS) measurements, and is determined as the ratio of the elements contained in the coating layer to the total of the elements contained in the electrode active material and the elements contained in the coating layer.

[0033] The thickness of the coating layer is not particularly limited, but for example, it may be between 1 nm and 100 nm, between 5 nm and 50 nm, or between 10 nm and 30 nm. The thickness of the coating layer can be determined, for example, as the average thickness of multiple samples (e.g., 100 or more samples) observed by a scanning electron microscope (SEM) or a transmission electron microscope (TEM).

[0034] 2. Electrode active material The electrode active material in this disclosure is not particularly limited, but it is preferably composed of Li, M, and O. M is a metal other than Li (including metalloids). M may be a transition metal, or a metal (including metalloids) belonging to groups 13 to 16 of the periodic table. M may be one metal or two or more metals. In particular, M is preferably at least one of Ni, Co, Mn, Al, V, and Fe.

[0035] In particular, M preferably contains at least Ni. Electrode active materials containing Ni are susceptible to degradation by moisture, but the coating active material in this disclosure has a low moisture content, thus suppressing the degradation of Ni-containing electrode active materials. The molar ratio of Ni to M (Ni / M) is not particularly limited, but may be, for example, 30% or more, 50% or more, 60% or more, 70% or more, or 80% or more. On the other hand, Ni / M may be 100% or less than 100%.

[0036] In addition to Li element, M element and O element, the electrode active material may contain a non-metallic element such as P element. Also, the crystal structure of the electrode active material is not particularly limited, and examples thereof include a rock salt layered structure, a spinel structure, and an olivine structure.

[0037] As an example of the composition of the electrode active material, LiNi x Co y Al z O2 (0.5 ≤ x, 0 ≤ y, 0 ≤ z, x + y + z = 1) can be mentioned. x may be 0.6 or more, may be 0.7 or more, or may be 0.8 or more. y may be 0, or may be greater than 0. Also, y is, for example, 0.3 or less. z may be 0, or may be greater than 0. Also, z is, for example, 0.1 or less.

[0038] As another example of the composition of the electrode active material, LiNi a Co b Mn c O2 (0.5 ≤ a, 0 ≤ b, 0 ≤ c, a + b + c = 1) can be mentioned. a may be 0.6 or more, may be 0.7 or more, or may be 0.8 or more. b may be 0, or may be greater than 0. Also, b is, for example, 0.3 or less. c may be 0, or may be greater than 0. Also, c is, for example, 0.3 or less.

[0039] The shape of the electrode active material is usually particulate. The particle diameter D of the electrode active material 50 is, for example, 100 nm or more, may be 1 μm or more, or may be 5 μm or more. On the other hand, the particle diameter D of the electrode active material 50 is, for example, 50 μm or less, or may be 20 μm or less. In the present disclosure, the particle diameter D 50 corresponds to the particle diameter corresponding to 50 volume% cumulative measured by a laser diffraction particle size distribution measuring device.

[0040] 3. Coating active material In this disclosure, the moisture content X generated in the coating active material in the temperature range of 120°C to 180°C is typically 10.0 ppm or less. The moisture content X may be 9.0 ppm or less, or 8.0 ppm or less. A low moisture content X suppresses the increase in resistance due to moisture. Furthermore, the moisture content Y generated in the coating active material in the temperature range of 180°C to 300°C is, for example, 350 ppm or less, or 320 ppm or less. A low moisture content Y suppresses the increase in resistance due to moisture. The methods for measuring the moisture content X and moisture content Y are as described in the examples below.

[0041] The BET specific surface area of ​​the coating active material is not particularly limited, but for example, 0.50 m² 2 It is 0.70m or more 2 It may be 1 / g or more. On the other hand, the BET specific surface area of ​​the coating active material is, for example, 1.20 m². 2 Less than / g, 1.00m 2 It may be less than / g.

[0042] The coating active material in this disclosure is typically used in batteries. The electrode active material in the coating active material may be a positive electrode active material or a negative electrode active material, but the former is preferred. An example of a method for manufacturing the coating active material is the method described in "D. Method for Manufacturing the Coating Active Material" below.

[0043] B. Electrode composite material The electrode composite material in this disclosure contains the above-described coating active material and at least one of a conductive material and a binder.

[0044] According to this disclosure, by using the above-mentioned coating active material, an electrode composite material is obtained that can suppress the increase in resistance due to moisture and the increase in resistance due to the high-resistance layer.

[0045] The electrode mixture contains a coating active material and at least one of a conductive material and a binder. The coating active material is the same as described in "A. Coating Active Material" above. The electrode active material in the coating active material may be a positive electrode active material or a negative electrode active material, but the former is preferred. That is, the electrode mixture may be a positive electrode mixture or a negative electrode mixture, but the former is preferred.

[0046] The proportion of coating active material in the electrode mixture is, for example, 20% by weight or more, but may also be 30% by weight or more, or 40% by weight or more. If the proportion of coating active material is too low, a sufficient energy density may not be obtained. On the other hand, the proportion of coating active material is, for example, 80% by weight or less, but may also be 70% by weight or less, or 60% by weight or less. If the proportion of coating active material is too high, the ionic conductivity and electronic conductivity of the electrode mixture may relatively decrease.

[0047] The electrode composite material contains at least one of a conductive material and a binder. Examples of conductive materials include carbon materials, metal particles, and conductive polymers. Examples of carbon materials include particulate carbon materials such as acetylene black (AB) and Ketjenblack (KB), and fibrous carbon materials such as carbon fibers, carbon nanotubes (CNTs), and carbon nanofibers (CNFs). Examples of binders include rubber-based binders and fluoride-based binders.

[0048] The electrode mixture may further contain a solid electrolyte. The solid electrolyte may be an organic solid electrolyte such as a gel electrolyte, or an inorganic solid electrolyte such as a sulfide solid electrolyte or an oxide solid electrolyte. Among these, a sulfide solid electrolyte is preferred because it has high ionic conductivity.

[0049] Sulfide solid electrolytes usually contain at least Li element and S element. The sulfide solid electrolyte preferably further contains a Me element (Me is at least one of P, As, Sb, Si, Ge, Sn, B, Al, Ga, In). Also, the sulfide solid electrolyte may contain halogen elements such as F, Cl, Br, I.

[0050] The sulfide solid electrolyte may be a glass-based (amorphous) sulfide solid electrolyte, a glass-ceramics-based 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, Thio-LISICON type crystalline phase, argyrodite type crystalline phase, LGPS type crystalline phase.

[0051] The composition of the sulfide solid electrolyte is not particularly limited, and examples include, for example, xLi2S·(1 - x)P2S5 (0.5 ≤ x < 1), yLiI·zLiBr·(100 - y - z)(xLi2S·(1 - x)P2S5) (0.5 ≤ x < 1, 0 ≤ y ≤ 30, 0 ≤ z ≤ 30). In these compositions, x preferably satisfies 0.7 ≤ x ≤ 0.8. Also, as other examples of the composition of the sulfide solid electrolyte, Li 7-x-2y PS <00000​​​​​​​​​​​​​​Figure 2 is a schematic cross-sectional view illustrating a battery in this disclosure. The battery 20 shown in Figure 2 includes a positive electrode layer 11, a negative electrode layer 12, an electrolyte layer 13 disposed between the positive electrode layer 11 and the negative electrode layer 12, a positive electrode current collector 14 for collecting current from the positive electrode layer 11, and a negative electrode current collector 15 for collecting current from the negative electrode layer 12. In this disclosure, the positive electrode layer 11 or the negative electrode layer 12 contains the electrode mixture described in "B. Electrode Mixture" above.

[0053] According to this disclosure, by using the electrode mixture described above, a battery is obtained that suppresses the increase in resistance due to moisture and the increase in resistance due to the high-resistance layer. As described above, the electrode mixture may be a positive electrode mixture or a negative electrode mixture, but the former is preferred. The details of the battery will be described below in the case where the electrode mixture is a positive electrode mixture.

[0054] 1. Positive electrode layer The positive electrode layer in this disclosure contains the electrode mixture (positive electrode mixture) described above. The electrode mixture is the same as described in "B. Electrode Mixture" above, so its description is omitted here. The positive electrode layer may also contain an electrolyte as needed. The electrolyte is the same as described in "3. Electrolyte Layer". The thickness of the positive electrode layer is, for example, 0.1 μm or more and 1000 μm or less, and may be 0.1 μm or more and 500 μm or less, or 0.1 μm or more and 100 μm or less. As a method for forming the positive electrode layer, for example, a method of coating the electrode mixture (positive electrode mixture) onto a positive electrode current collector can be mentioned.

[0055] 2. Negative electrode layer The negative electrode layer is a layer containing at least a negative electrode active material. The negative electrode layer may also optionally contain at least one of an electrolyte, a conductive material, and a binder.

[0056] Examples of negative electrode active materials include metallic active materials such as Li and Sn, Si-based active materials, carbon active materials such as graphite, and Li4Ti5O 12 Examples of oxide-active materials include the following.

[0057] The negative electrode active material is preferably a Si-based active material because it allows for higher battery capacity. A Si-based active material is an active material whose main component is Si. The Si-based active material may be pure Si, a Si alloy, or a Si oxide. Furthermore, the Si-based active material may have a diamond-type crystalline phase, a clathrate I-type crystalline phase, or a clathrate II-type crystalline phase. In the clathrate I-type or II-type crystalline phase, multiple Si elements form polyhedra (cages) containing pentagons or hexagons. Since these polyhedra have spaces inside that can encapsulate Li ions, volume changes due to charging and discharging can be suppressed.

[0058] The shape of the negative electrode active material can be particulate, for example. The particle size D of the negative electrode active material. 50 The particle size D of the negative electrode active material is not particularly limited, but for example it may be 10 nm or more, and may also be 100 nm or more. 50 For example, it may be 50 μm or less, or 20 μm or less.

[0059] The electrolyte used in the negative electrode layer is the same as described in "3. Electrolyte Layer". The conductive material and binder used in the negative electrode layer are the same as described in "B. Electrode Mixture" above, so they are omitted here. The thickness of the negative electrode layer is, for example, 0.1 μm or more and 1000 μm or less, and may be 0.1 μm or more and 500 μm or less, or 0.1 μm or more and 100 μm or less.

[0060] 3. 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 (electrolyte solution).

[0061] The solid electrolyte is the same as described in "B. Electrode Mixture" above, so it will not be described here. On the other hand, the electrolyte preferably contains a supporting salt and a solvent. Examples of supporting salts (lithium salts) for lithium-ion conductive electrolytes include inorganic lithium salts such as LiPF6, LiBF4, LiClO4, and LiAsF6, and organic lithium salts such as LiCF3SO3, LiN(CF3SO2)2, LiN(C2F5SO2)2, LiN(FSO2)2, and LiC(CF3SO2)3. Examples of solvents used in the electrolyte include cyclic esters (cyclic carbonates) such as ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC), and linear esters (linear carbonates) such as dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC). The electrolyte preferably contains two or more solvents.

[0062] The thickness of the electrolyte layer is, for example, 0.1 μm or more and 1000 μm or less, and may be 0.1 μm or more and 500 μm or less, or 0.1 μm or more and 100 μm or less.

[0063] 4. Other configurations The battery in this disclosure preferably has a positive electrode current collector for collecting current from the positive electrode layer and a negative electrode current collector for collecting current from the negative electrode layer. Examples of materials for the positive electrode current collector include SUS, aluminum, nickel, iron, titanium, and carbon. On the other hand, examples of materials for the negative electrode current collector include SUS, copper, nickel, and carbon.

[0064] The battery in this disclosure may further include a restraining jig that applies restraining pressure along the thickness direction to the positive electrode layer, electrolyte layer, and negative electrode layer. In particular, when the electrolyte layer is a solid electrolyte layer, it is preferable to apply restraining pressure in order 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. On the other hand, the restraining pressure may be, for example, 100 MPa or less, 50 MPa or less, or 20 MPa or less.

[0065] 5.Battery The type of battery described herein is not particularly limited, but is typically a lithium-ion battery. The battery described herein may be a liquid battery containing an electrolyte as the electrolyte layer, or a solid battery having a solid electrolyte layer. The solid battery may be a semi-solid battery or a fully solid battery. The battery described herein may be a primary battery or a secondary battery, but a secondary battery is preferred because it can be repeatedly charged and discharged, making it useful, for example, as an in-vehicle battery.

[0066] Applications of batteries include, for example, powering vehicles such as hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), battery electric vehicles (BEVs), gasoline cars, and diesel cars. In particular, they are preferred for use as a power source for hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), or battery electric vehicles (BEVs). Batteries may also be used as a power source for other mobile devices (e.g., trains, ships, aircraft), or as a power source for electrical products such as information processing devices.

[0067] D. Method for producing coated active material Figure 3 is a flowchart illustrating a method for producing a coated active material in this disclosure. In the manufacturing method shown in Figure 3, the electrode active material and coating material are prepared (preparation step). Next, the electrode active material is coated with the coating material by a dry method to form a coating layer (coating layer formation step). In this disclosure, the coating conditions are adjusted so that the coated active material described in "A. Coated Active Material" above is obtained. In particular, particle size D 90 A coating material with a thickness of 2 μm or less is used.

[0068] According to this disclosure, by using a fine coating material, it is possible to obtain a coating active material that can suppress the increase in resistance due to moisture and the increase in resistance due to a high-resistance layer.

[0069] 1. Preparation process The preparation step in this disclosure is the step of preparing the electrode active material and the coating material. The electrode active material and coating material are the same as those described in "A. Coating Active Material" above.

[0070] The shape of the coating material in the preparation process is usually particulate. The particle size D of the coating material. 90 The particle size D of the coating material is usually 2 μm or less, but may be 1 μm or less, or 0.8 μm or less. By using a fine coating material, damage to the surface of the electrode active material by the coating material can be suppressed when the electrode active material is coated with the coating material. As a result, the coverage rate of the coating layer can be improved. On the other hand, the particle size D of the coating material 90 The particle size D is not particularly limited, but for example, it is 0.2 μm or larger. 90 This corresponds to the particle size that represents 90% of the cumulative volume from the small particle side, as measured by a laser diffraction particle size distribution analyzer.

[0071] Particle size D of coating material 50 For example, the particle size D of the coating material may be 1 μm or less, 0.6 μm or less, or 0.4 μm or less. 50 The particle size D of the electrode active material is not particularly limited, but for example, it is 0.1 μm or larger. 50 Particle size D of the coating material 50The ratio is not particularly limited, but for example, it may be 1% or more and 25% or less, or 5% or more and 15% or less.

[0072] The method for producing the coating material is not particularly limited, but examples include a synthesis step of synthesizing a coarse-grained material for the coating material and a micronization step of micronizing the coarse-grained material. The synthesis step is, for example, a step of dissolving a solute containing a B source and a P source in a solvent to produce a coating solution, and then drying the coating solution.

[0073] The B source is not particularly limited as long as it is an element or compound containing the element B, but an example is boric acid (H3BO3). The P source is not particularly limited as long as it is an element or compound containing the element P, but an example is orthophosphoric acid (H3PO4) or metaphosphoric acid (HPO3). Furthermore, it is preferable that the coating solution contains an O source. An example of an O source is the element O contained in the B source or P source mentioned above. Furthermore, the above solute may also contain a Li source. An example of a Li source is lithium hydroxide (LiOH), but an example is lithium phosphorus (LiOH). Furthermore, an example of a solvent is water.

[0074] A specific example of a method for preparing a coating solution is to first prepare a first aqueous solution by dissolving orthophosphoric acid (H3PO4) or metaphosphoric acid (HPO3) in water, then prepare a second aqueous solution by dissolving boric acid (H3BO3) in the first aqueous solution, and finally prepare a coating solution by dissolving lithium hydroxide monohydrate (LiOH·H2O) in the second aqueous solution. A coarse-grained material can be obtained by drying the coating solution. The method for drying the coating solution is not particularly limited, but examples include spray drying, electric furnaces, vacuum drying ovens, and spray pyrolysis apparatuses.

[0075] The micronization process is a process of micronizing the coarse material described above. By micronizing the coarse material, the particle size D 90A coating material with a particle size of 2 μm or less can be obtained. Methods for micronizing the coarse-grained material include, for example, mechanical milling such as a bead mill or ball mill. Mechanical milling may be performed dry or wet. When performed wet, it is preferable to use a solvent other than water. The conditions for mechanical milling are not particularly limited, and the particle size D 90 The material is adjusted as appropriate so that a coating material with a particle size of 2 μm or less is obtained.

[0076] 2.Coating layer formation process The coating layer formation step in this disclosure is a step of forming the coating layer by coating the electrode active material with the coating material using a dry method.

[0077] As a dry method, for example, a method is to apply a shearing treatment to a mixture containing electrode active material and coating material. The above mixture basically does not contain water, but may contain a small amount of water whose effect can be ignored. The shearing treatment is, for example, a process of rotating a chopper placed in a container. Another example of shearing treatment is a method of applying compressive shear energy to the mixture present between the blade and the wall of the container by rotating a blade placed in the container. Furthermore, the conditions for the shearing treatment are not particularly limited and are adjusted as appropriate so that the coating active material described in "A. Coating Active Material" above is obtained.

[0078] 3.Coated active material The coating active material obtained through each of the above processes is the same as that described in "A. Coating Material" above.

[0079] This disclosure is not limited to the embodiments described above. The embodiments described above are illustrative, and any configuration that is substantially identical to the technical idea described in the claims of this disclosure and achieves similar effects is included within the technical scope of this disclosure. [Examples]

[0080] [Comparative Example 1] (Preparation of coating solution) Metaphosphoric acid (manufactured by Fujifilm Wako Pure Chemical Industries) and deionized water were mixed in a ratio of metaphosphoric acid:deionized water = 4.52:191.8 (by weight) to obtain an aqueous solution. Boric acid (manufactured by Nacalai Tesque) was added to the obtained aqueous solution and dissolved so that the molar ratio of element B to element P (B / P) was 1.0. Furthermore, lithium hydroxide monohydrate (manufactured by Fujifilm Wako Pure Chemical Industries) was added and dissolved so that the molar ratio of element Li to the sum of elements P and B (Li / (P+B)) was 0.9. This obtained a coating solution.

[0081] (Preparation of coated active material) The resulting coating solution contains active material particles (LiNi 0.81 Co 0.15 Al 0.04 O2, particle size D 50 A slurry was prepared by dispersing particles (4.5 μm). The solid content concentration of the slurry was 69% by weight. Next, a coating layer was formed on the surface of the active material particles by drying the slurry using a spray drying device manufactured by BUCHI Corporation (product name: Mini Spray Dryer B-290). The air supply temperature of the spray drying device was 200°C, and the air supply volume was 0.45 m³. 3 The value was / min. Next, the active material particles with the coated layer were heat-treated in an atmospheric environment to obtain coated active material. The heat treatment temperature was 200°C and the heat treatment time was 5 hours.

[0082] [Comparative Example 2] (Preparation of coating material A) A coating solution was obtained in the same manner as in Comparative Example 1. The obtained coating solution was dried using a spray drying device manufactured by BUCHI Corporation (product name: Mini Spray Dryer B-290) to obtain a powder. The air supply temperature of the spray drying device was 200°C, and the air supply volume was 0.45 m³. 3 The initial rate was / min. Subsequently, an additional heat treatment was performed under an atmospheric environment. The heat treatment temperature was 200°C, and the heat treatment time was 5 hours. This yielded powdered coating material A.

[0083] (Preparation of coated active material) 1000g of the same active material particles as in Comparative Example 1 and 31.0g of coating material A were placed in a mixing and stirring machine Balance Gran BG-2L (manufactured by Freund Turbo). Next, the mixture was stirred for 1 hour at a chopper rotation speed of 1500 rpm to form a coating layer on the surface of the active material particles, thereby obtaining coated active material.

[0084] [Comparative Example 3] The coated active material was obtained in the same manner as in Comparative Example 2, except that when forming a coating layer on the surface of the active material particles, stirring treatments were performed for 1 hour each at chopper rotation speeds of 1500 rpm and 2000 rpm.

[0085] [Comparative Example 4] The coated active material was obtained in the same manner as in Comparative Example 2, except that when forming a coating layer on the surface of the active material particles, stirring treatment was performed for 1 hour each at chopper rotation speeds of 1500 rpm, 2000 rpm, and 2500 rpm.

[0086] [Comparative Example 5] The coated active material was obtained in the same manner as in Comparative Example 2, except that when forming a coating layer on the surface of the active material particles, stirring treatment was performed for 1 hour each at chopper rotation speeds of 1500 rpm, 2000 rpm, 2500 rpm, and 3000 rpm.

[0087] [Comparative Example 6] The coated active material was obtained in the same manner as in Comparative Example 2, except that when forming a coating layer on the surface of the active material particles, stirring treatment was performed for 1 hour each at chopper rotation speeds of 1500 rpm, 2000 rpm, 2500 rpm, 3000 rpm, and 3600 rpm.

[0088] [Comparative Example 7] (Preparation of coating material B) Coating material A was obtained in the same manner as in Comparative Example 2. Coating material A was dispersed in ethanol to obtain a dispersion with a solid content concentration of 20% by weight. A wet bead mill grinding device, Labstar Mini MGF015 (manufactured by Ashizawa Fine Tech), was prepared, and the obtained dispersion was placed in the grinding chamber together with zirconia balls (Φ0.1 mm) and ground for 90 minutes. The bead peripheral speed was 14 m / s and the circulation flow rate was 0.3 L / min. Next, the material was air-dried in an atmospheric environment for 24 hours to evaporate the ethanol. Furthermore, it was vacuum-dried at 100°C for 8 hours. This obtained coating material B.

[0089] (Preparation of coated active material) 1000g of the same active material particles as in Comparative Example 1 and 31.0g of coating material B were placed in a mixing and stirring machine Balance Gran BG-2L (manufactured by Freund Turbo). Next, the mixture was stirred for 1 hour at a chopper rotation speed of 1500 rpm to form a coating layer on the surface of the active material particles, thereby obtaining coated active material.

[0090] [Example 1] The coated active material was obtained in the same manner as in Comparative Example 7, except that when forming a coating layer on the surface of the active material particles, stirring treatments were performed for 1 hour each at chopper rotation speeds of 1500 rpm and 2000 rpm.

[0091] [Example 2] The coated active material was obtained in the same manner as in Comparative Example 7, except that when forming a coating layer on the surface of the active material particles, stirring treatment was performed for 1 hour each at chopper rotation speeds of 1500 rpm, 2000 rpm, and 2500 rpm.

[0092] [Example 3] The coated active material was obtained in the same manner as in Comparative Example 7, except that when forming a coating layer on the surface of the active material particles, stirring treatment was performed for 1 hour each at chopper rotation speeds of 1500 rpm, 2000 rpm, 2500 rpm, and 3000 rpm.

[0093] [Example 4] The coated active material was obtained in the same manner as in Comparative Example 7, except that when forming a coating layer on the surface of the active material particles, stirring treatment was performed for 1 hour each at chopper rotation speeds of 1500 rpm, 2000 rpm, 2500 rpm, 3000 rpm, and 3600 rpm. The coating conditions for Examples 1 to 4 and Comparative Examples 1 to 7 are shown in Table 1.

[0094] [Table 1]

[0095] [evaluation] (Particle size distribution measurement) The particle size distribution of coating material A and coating material B was measured using a laser diffraction particle size distribution analyzer. As a result, coating material A had a particle size of D 50 The particle size D is 2.3 μm. 90 The particle size was 4.3 μm. On the other hand, the particle size of coating material B was D 50 The particle size D is 0.34 μm. 90 The size was 0.75 μm.

[0096] (Measurement of coverage) The coverage of the coating active materials obtained in Examples 1-4 and Comparative Examples 1-7 was measured by X-ray photoelectron spectroscopy (XPS). Specifically, surface elemental analysis of the coating active materials was performed using an X-ray photoelectron spectrometer (ULVAC-PHI, PHI X-tool). The pass energy was set to 224 eV, and narrow-scan analysis was performed. Subsequently, the elemental ratios were calculated from the intensity values ​​of the detected C1s, O1s, P2p, Ni2p3, Co2p3, Al2p, and B1s using analysis software (MultiPak, ULVAC-PHI), and the value of (P+B) / (P+B+Ni+Co+Al) [%] was determined as the coverage. The results are shown in Table 2.

[0097] (Measurement of BET specific surface area) The BET specific surface area of ​​the coated active materials obtained in Examples 1-4 and Comparative Examples 1-7 was measured by the BET method. Specifically, the N2 adsorbed BET specific surface area was measured using a BELSORPmaxII manufactured by Microtrac. 5.0 g of the sample was weighed into a measuring tube under a nitrogen atmosphere, connected to the measuring device, and vacuum degassed at room temperature for 8 hours. Subsequently, measurements were taken at at least 10 points between relative pressures P / P0 = 0.250 and 0.995, and the BET specific surface area was calculated. The results are shown in Table 2.

[0098] (Measurement of moisture content) The moisture content of the coating active materials obtained in Examples 1-4 and Comparative Examples 1 and 7 was measured using the Karl Fischer method. Specifically, the trace moisture content in the samples was measured using the MKC-710 series from Kyoto Electronics Manufacturing Co., Ltd. 1.0 g of the coating active material was placed in a sample container under a nitrogen atmosphere and then set in the apparatus. After a blank measurement at 120°C, the temperature was maintained at 120°C, and moisture was detected until the minimum electrolytic amount was 0.1 μg or less. Then, the temperature was raised to 180°C and the same procedure was performed, and moisture was detected until the minimum electrolytic amount was 0.1 μg or less. Next, the temperature was raised to 300°C, and the same procedure was repeated to measure the amount of moisture generated in each temperature range, and this was converted to moisture content (in ppm) by dividing by the sample weight. The results are shown in Table 2.

[0099] (Resistance measurement) The coating active materials obtained in Examples 1-4 and Comparative Examples 1-7 were used as positive electrode active materials to fabricate batteries, and their resistance was measured.

[0100] First, a positive electrode slurry was prepared by mixing positive electrode active material (coating active material), sulfide solid electrolyte (10LiI-15LiBr-75Li3PS4), conductive material (VGCF), binder (SBR), and dispersion medium (heptane). The mixing ratio of positive electrode active material to sulfide solid electrolyte was positive electrode active material:sulfide solid electrolyte = 6:4 (volume ratio). The amount of conductive material and binder added was 3 parts by weight per 100 parts by weight of positive electrode active material, respectively. The positive electrode slurry was thoroughly stirred using an ultrasonic homogenizer, and the slurry was coated onto the surface of the positive electrode current collector (Al foil) to form a coating film. The coating film was dried on a hot plate at 100°C for 30 minutes. This obtained a positive electrode base material. A disc-shaped positive electrode was cut from the positive electrode base material. The area of ​​the positive electrode was 1 cm². 2 That was the case.

[0101] Next, the negative electrode and solid electrolyte layer were prepared. The negative electrode active material was graphite. The same type of sulfide solid electrolyte was used between the positive electrode, solid electrolyte layer, and negative electrode. A laminate was formed by stacking the positive electrode, solid electrolyte layer, and negative electrode in this order within a cylindrical jig. A power generation element was formed by pressing the laminate. A battery (all-solid-state battery) was obtained by connecting terminals to the power generation element. After adjusting the open-circuit voltage (OCV) of the obtained all-solid-state battery to 2.03V, constant current discharge was performed, and the battery resistance was measured by dividing the voltage drop over 5 seconds by the amount of current. The discharge current rate was 2.5C. The resistance of each example and the battery of each example were evaluated relative to the reference resistance (1.0) of the battery of Comparative Example 1. The results are shown in Table 2 and Figure 4.

[0102] [Table 2]

[0103] As shown in Table 2, in Comparative Example 1, a wet method was used, and it was confirmed that the moisture content was relatively high even after drying. In contrast, in Examples 1 to 4, a dry method was used, and it was confirmed that the moisture content was low. Also, as shown in Table 2 and Figure 4, comparing Example 1 and Comparative Example 1, the coverage rate of Example 1 (84%) was lower than that of Comparative Example 1 (96%), creating a situation where resistance increase due to a high-resistance layer was likely to occur. However, the moisture content of Example 1 was lower than that of Comparative Example 1, which suppressed the resistance increase due to moisture, and as a result, the resistance became similar. Furthermore, in Examples 2 to 4, the resistance was lower than that of Example 1. Examples 1 to 4 did not use organic solvents, which was advantageous from the viewpoint of cost reduction and reduction of environmental impact.

[0104] On the other hand, as shown in Table 2, comparing Comparative Examples 2-6 with Examples 1-4, it was confirmed that using the atomized coating material B significantly improved the coverage rate. Also, as shown in Table 2 and Figure 4, in Comparative Examples 2-6, the moisture content was low because a dry method was used, but it is presumed that the low coverage rate resulted in an increase in resistance due to the high-resistance layer. On the other hand, in Comparative Example 7, although the moisture content was low because a dry method was used and atomized coating material B was used, the coating treatment was not sufficiently performed, resulting in a low coverage rate. Therefore, it is presumed that an increase in resistance occurred due to the high-resistance layer. In contrast, in Examples 1-4, the moisture content was low because a dry method was used and the coating treatment was sufficiently performed using atomized coating material B, which allowed for a high coverage rate. As a result, it is considered that the increase in resistance due to moisture and the increase in resistance due to the high-resistance layer were suppressed.

[0105] Furthermore, regarding the BET specific surface area, as shown in Table 2, the BET specific surface area of ​​the coated active material was almost the same in Comparative Examples 2 to 6 using coating material A. This supports the idea that the coating rate does not improve with agitation. On the other hand, in Comparative Example 7 and Examples 1 to 4 using coating material B, the coating rate improved as the agitation time increased, and the value decreased to a BET specific surface area equivalent to that of Comparative Example 1 (wet method). This indicates that the coating rate improved with agitation as coating material B spread on the surface of the active material. [Explanation of symbols]

[0106] 1...electrode active material 2...Covering layer 10...Coated active material 11 ... Positive electrode layer 12 ... Negative electrode layer 13...electrolyte layer 14...Positive electrode current collector 15...Negative electrode current collector 20...battery

Claims

1. A coated active material comprising an electrode active material and a coating layer that covers the electrode active material and includes a particulate coating material having elements B, P, and O, The amount of moisture X generated in the temperature range of 120°C to 180°C is 10.0 ppm or less. A coated active material wherein the coverage rate of the coating layer over the electrode active material is greater than 67%.

2. The coating active material according to claim 1, wherein the moisture content X is 8.0 ppm or less.

3. The coating active material according to claim 1, wherein the amount of moisture Y generated in the temperature range of 180°C to 300°C is 350 ppm or less.

4. The coating active material according to claim 1, wherein the coating rate is 75% or more.

5. The coating active material according to claim 1, wherein the coating material further comprises an element Li.

6. The electrode active material comprises Li element, M element (where M is a metal other than Li), and O element. The aforementioned M contains at least Ni, The coating active material according to claim 1, wherein the molar ratio of Ni to M (Ni / M) is 50% or more.

7. The coating active material according to claim 6, wherein the Ni / M ratio is 80% or more.

8. The BET specific surface area is 0.50 m². ２ / g or more, 1.20m ２ The coated active material according to claim 1, wherein the amount is less than / g.

9. An electrode composite comprising a coating active material according to any one of claims 1 to 8, and at least one of a conductive material and a binder.

10. The electrode mixture according to claim 9, wherein the electrode mixture contains a solid electrolyte.

11. The electrode composite material according to claim 10, wherein the solid electrolyte is a sulfide solid electrolyte.

12. A battery having a positive electrode layer, a negative electrode layer, and an electrolyte layer disposed between the positive electrode layer and the negative electrode layer, A battery comprising the positive electrode layer or the negative electrode layer containing the electrode composite material described in claim 9.

13. The battery according to claim 12, wherein the positive electrode layer contains the electrode composite material.

14. The battery according to claim 12, wherein the electrolyte layer contains a solid electrolyte.

15. A method for producing a coated active material according to any one of claims 1 to 8, Preparation steps for preparing the electrode active material and the coating material, The process includes a coating layer formation step in which the electrode active material is coated with the coating material by a dry method to form the coating layer, Particle size D of the coating material ９０ A method for producing a coated active material, wherein the particle size is 2 μm or less.

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