Coated positive electrode active material, positive electrode material, battery, and method for manufacturing a coated positive electrode active material

Abstract

A coated positive electrode active substance 130 comprises: a positive electrode active substance 110; a first coating layer 111 coating at least a portion of a surface of the positive electrode active substance110; and a second coating layer 112 coating at least a portion of a surface of a base active substance 120 comprising the first coating layer 111 and the positive electrode active substance 110. The first coating layer 111 comprises an oxide solid electrolyte. The second coating layer 112 comprises Li, Ti, and M. M is at least one element selected from the group consisting of Ca, Mg, Al, Y, and Zr.

Description

[Technical Field]

[0001] This disclosure relates to coated cathode active material, cathode material, battery, and method for manufacturing coated cathode active material. [Background technology]

[0002] Patent Document 1 discloses a positive electrode material comprising a positive electrode active material and a halide solid electrolyte. Patent Document 1 discloses a solid electrolyte as a halide solid electrolyte comprising lithium, yttrium, and at least one selected from the group consisting of chlorine, bromine, and iodine.

[0003] Patent Document 2 discloses a positive electrode material comprising a positive electrode active material whose surface is coated with a coating material, and a solid electrolyte. Patent Document 2 discloses a halogen solid electrolyte as the coating material, comprising lithium, yttrium, and chlorine and / or bromine. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] International Publication No. 2019 / 135322 [Patent Document 2] International Publication No. 2019 / 146236 [Overview of the project]

[0005] This disclosure provides a coated positive electrode active material that can reduce the output resistance of a battery.

[0006] In one aspect of this disclosure, the coated positive electrode active material is Positive electrode active material and, A first coating layer covering at least a portion of the surface of the positive electrode active material, A second coating layer covering at least a portion of the surface of the first coating layer and the base active material including the positive electrode active material, Equipped with, The first coating layer contains an oxide solid electrolyte. The second coating layer contains Li, Ti, M, and F. M is at least one element selected from the group consisting of Ca, Mg, Al, Y, and Zr.

[0007] According to the present disclosure, the output resistance of the battery can be reduced.

Brief Description of the Drawings

[0008] [Figure 1] FIG. 1 is a cross-sectional view showing a schematic configuration of a positive electrode material in Embodiment 1. [Figure 2] FIG. 2 is a cross-sectional view showing a schematic configuration of a battery in Embodiment 2.

Modes for Carrying Out the Invention

[0009] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0010] The following descriptions are all illustrative of comprehensive or specific examples. The numerical values, compositions, shapes, thicknesses, electrical characteristics, structures of secondary batteries, electrode materials, etc. shown below are examples and are not intended to limit the present disclosure. In addition, components not described in the independent claims indicating the most general concept are arbitrary components.

[0011] (Findings on which the present disclosure is based) Patent Document 1 describes a positive electrode material including a positive electrode active material and a halide solid electrolyte containing lithium and at least one selected from the group consisting of yttrium and chlorine, bromine, and iodine.

[0012] On the other hand, the inventors, through diligent research, have found that in batteries using a halide solid electrolyte as the positive electrode material, the halide solid electrolyte undergoes oxidative decomposition during charging. The products of this oxidative decomposition function as a resistive layer, increasing the internal resistance of the battery during charging. It is presumed that this increase in the internal resistance of the battery during charging is due to the oxidation reaction of at least one element selected from the group consisting of chlorine, bromine, and iodine contained in the halide solid electrolyte.

[0013] Patent Document 2 describes a battery using a positive electrode material in which at least a portion of the surface of the positive electrode active material is coated with a halogen solid electrolyte containing lithium, yttrium, chlorine, and / or bromine. Similar to Patent Document 1, the battery described in Patent Document 2 also has a problem with the oxidation resistance of the halogen solid electrolyte containing chlorine and / or bromine.

[0014] Here, the inventors have discovered that batteries using a positive electrode material in which at least a portion of the surface of the positive electrode active material is coated with a fluorine-containing halide solid electrolyte exhibit excellent oxidation resistance. A positive electrode material coated with a halide solid electrolyte can suppress the increase in the internal resistance of the battery during charging. The details of the mechanism are not clear, but it is presumed to be as follows: Fluorine has the highest electronegativity among halogen elements. Therefore, fluorine strongly bonds with cations. Consequently, when fluorine is contained in the halide solid electrolyte, the oxidation reaction of fluorine, i.e., the side reaction in which electrons are extracted from fluorine, is less likely to proceed. As a result, a resistance layer due to oxidative decomposition is less likely to be formed.

[0015] On the other hand, the inventors investigated the output resistance of a battery using a positive electrode material in which at least a portion of the surface of the positive electrode active material is coated with a fluorine-containing halide solid electrolyte. As a result, they discovered a problem of high output resistance during discharge. Although the details of the mechanism are not clear, it is presumed to be as follows: At the contact interface between the positive electrode active material and the fluorine-containing halide solid electrolyte, some of the oxygen ions in the positive electrode active material and some of the fluorine ions in the halide solid electrolyte undergo anionic substitution. This creates a resistive layer at the interface between the positive electrode active material and the halide solid electrolyte. This resistive layer increases the output resistance of the battery.

[0016] The inventors, through diligent research to reduce the output resistance of batteries, have discovered a positive electrode material that can suppress the formation of a resistive layer at the interface between the positive electrode active material and the fluorine-containing halide solid electrolyte. By using such a positive electrode material, the output resistance of batteries can be reduced.

[0017] (Summary of one aspect of this disclosure) The coated positive electrode active material according to the first aspect of this disclosure is Positive electrode active material and, A first coating layer covering at least a portion of the surface of the positive electrode active material, A second coating layer covering at least a portion of the surface of the first coating layer and the base active material including the positive electrode active material, Equipped with, The first coating layer contains an oxide solid electrolyte, The second coating layer comprises Li, Ti, M, and F. M is at least one element selected from the group consisting of Ca, Mg, Al, Y, and Zr.

[0018] The coated positive electrode active material according to the first embodiment can reduce the output resistance of the battery.

[0019] In a second aspect of this disclosure, for example, in the coated positive electrode active material according to the first aspect, the volume ratio of the second coating layer to the positive electrode active material may be 0.1% or more and 5% or less.

[0020] The coated positive electrode active material according to the second embodiment can further reduce the output resistance of the battery.

[0021] In a third aspect of this disclosure, for example, in the coated positive electrode active material according to the first or second aspect, M may be Al.

[0022] The coated positive electrode active material according to the third embodiment can further reduce the output resistance of the battery.

[0023] In a fourth aspect of this disclosure, for example, in the coated positive electrode active material according to the third aspect, the material constituting the second coating layer may be represented by the following composition formula (1): Li α Ti β Al γ F6...Formula (1) Here, α, β, and γ satisfy α + 4β + 3γ = 6 and γ > 0.

[0024] The coated positive electrode active material according to the fourth embodiment can further reduce the output resistance of the battery.

[0025] In a fifth aspect of this disclosure, for example, in the coated positive electrode active material according to the fourth aspect, γ may satisfy 0.5 ≤ γ < 1.

[0026] The coated positive electrode active material according to the fifth embodiment can further reduce the output resistance of the battery.

[0027] In a sixth aspect of this disclosure, for example, in the coated positive electrode active material according to the fourth aspect, α, β, and γ may satisfy 2.5 ≤ α ≤ 2.9, 0.1 ≤ β ≤ 0.5, and 0.5 ≤ γ ≤ 0.9.

[0028] The coated positive electrode active material according to the sixth embodiment can further reduce the output resistance of the battery.

[0029] In a seventh aspect of this disclosure, for example, in a coated cathode active material according to any one of the first to sixth aspects, the oxide solid electrolyte may include at least one selected from the group consisting of lithium niobate, lithium titanate, lithium aluminate, lithium silicate, lithium borate, lithium zirconate, and lithium tungstate.

[0030] The coated positive electrode active material according to the seventh embodiment can further reduce the output resistance of the battery.

[0031] In the eighth aspect of this disclosure, for example, in the coated cathode active material according to any one of the first to seventh aspects, the oxide solid electrolyte may contain lithium niobate.

[0032] The coated positive electrode active material according to the eighth embodiment can further reduce the output resistance of the battery.

[0033] In the ninth aspect of this disclosure, for example, in a coated cathode active material according to any one of the first to eighth aspects, the average thickness of the first coating layer may be 1 nm or more and 50 nm or less.

[0034] The coated positive electrode active material according to the ninth embodiment can further reduce the output resistance of the battery.

[0035] In the tenth aspect of this disclosure, for example, in the coated positive electrode active material according to any one of the first to ninth aspects, the positive electrode active material may contain lithium nickel-cobalt-aluminate.

[0036] The coated positive electrode active material according to the tenth embodiment can increase the energy density of the battery.

[0037] The cathode material relating to the 11th aspect of this disclosure is A coated positive electrode active material relating to any one of the first to tenth embodiments, and It further contains a first solid electrolyte.

[0038] The cathode material according to the 11th embodiment can achieve high ionic conductivity in the cathode material.

[0039] In a twelfth aspect of this disclosure, for example, in the cathode material according to the eleventh aspect, the first solid electrolyte may include a halide solid electrolyte.

[0040] The positive electrode material according to the 12th embodiment can improve the output characteristics of the battery.

[0041] In a thirteenth aspect of this disclosure, for example, in a cathode material according to the eleventh or twelfth aspect, the first solid electrolyte may include a sulfide solid electrolyte.

[0042] The positive electrode material according to the 13th embodiment can further improve the output characteristics of the battery.

[0043] The battery relating to the 14th aspect of this disclosure is A positive electrode containing a positive electrode material according to any one of the 11th to 13th embodiments, Negative electrode, and An electrolyte layer provided between the positive electrode and the negative electrode, It is equipped with.

[0044] The battery according to the 14th embodiment can reduce the output resistance of the battery.

[0045] In a 15th aspect of this disclosure, for example, in a battery according to a 14th aspect, the electrolyte layer may include a second solid electrolyte, the second solid electrolyte may include a solid electrolyte having the same composition as the solid electrolyte contained in the first solid electrolyte.

[0046] The battery according to the 15th embodiment can improve the output characteristics of the battery.

[0047] In a sixteenth aspect of this disclosure, for example, in a battery according to a fourteenth aspect, the electrolyte layer may include a second solid electrolyte, the second solid electrolyte may include a halogen solid electrolyte having a different composition from the solid electrolyte contained in the first solid electrolyte.

[0048] The battery according to the 16th embodiment can improve the output characteristics of the battery.

[0049] In a 17th aspect of this disclosure, for example, in a battery according to a 14th aspect, the electrolyte layer may include a second solid electrolyte, and the second solid electrolyte may include a sulfide solid electrolyte.

[0050] The battery according to the 17th embodiment can improve the output characteristics of the battery.

[0051] A method for producing a coated positive electrode active material according to the 18th aspect of this disclosure is: A method for manufacturing a coated positive electrode active material according to the first embodiment, The aforementioned manufacturing method The method includes treating a mixture comprising the positive electrode active material, whose surface at least a portion is covered by the first coating layer, and the material constituting the second coating layer, by a dry particle compounding method. The dry particle compounding method includes applying mechanical energy such as impact, compression, and shear to the mixture.

[0052] According to the manufacturing method of the 18th embodiment, a positive electrode material that can improve the output characteristics of a battery can be manufactured.

[0053] In a 19th aspect of this disclosure, for example, in the method for manufacturing a coated positive electrode active material according to the 18th aspect, the ratio Da / Dc of the average particle size Da of the positive electrode active material whose surface is at least partially covered by the first coating layer to the average particle size Dc of the material constituting the second coating layer may be 2 or more.

[0054] According to the manufacturing method of the 19th embodiment, a positive electrode material can be manufactured that can further reduce the output resistance of the battery.

[0055] In the 20th aspect of this disclosure, for example, in the method for manufacturing a cathode material according to the 19th aspect, the ratio Da / Dc may be 5 or more.

[0056] According to the manufacturing method of the 20th embodiment, a positive electrode material can be manufactured that can further reduce the output resistance of the battery.

[0057] (Embodiment 1) [Coated cathode active material] The coated positive electrode active material 130 in Embodiment 1 comprises a positive electrode active material 110, a first coating layer 111, and a second coating layer 112. The first coating layer 111 covers at least a portion of the surface of the positive electrode active material 110. Here, the positive electrode active material 110 whose surface is at least partially covered by the first coating layer 111 is defined as the base active material 120. The second coating layer 112 covers at least a portion of the surface of the base active material 120, which includes the first coating layer 111 and the positive electrode active material 110. The first coating layer 111 contains an oxide solid electrolyte. The second coating layer 112 contains lithium (i.e., Li), titanium (i.e., Ti), M, and fluorine (i.e., F). M is at least one element selected from the group consisting of Ca, Mg, Al, Y, and Zr. M may also be aluminum (i.e., Al).

[0058] The first coating layer 111 is in direct contact with the positive electrode active material 110. The second coating layer 112 may be in direct contact with the first coating layer 111, or it may be in direct contact with the positive electrode active material 110.

[0059] Hereinafter, the material constituting the first coating layer 111 will be referred to as the "first coating material." The material constituting the second coating layer 112 will be referred to as the "second coating material." The coated positive electrode active material 130 in Embodiment 1 includes the positive electrode active material 110, the first coating material, and the second coating material. The second coating material is present on at least a portion of the surface of the base active material 120 to form the second coating layer 112.

[0060] The coating of the positive electrode active material 110 by the first coating layer 111 and the second coating layer 112 suppresses the formation of an oxide film due to the oxidative decomposition of other solid electrolytes (for example, the first solid electrolyte 100 described later) during battery charging. Therefore, with the above configuration, the coated positive electrode active material 130 in Embodiment 1 can reduce the output resistance of the battery.

[0061] (Second coating layer 112) In Embodiment 1, the second coating material may consist of Li, Ti, Al, and F. "Consisting of Li, Ti, Al, and F" means that, excluding unavoidable impurities, no materials other than Li, Ti, Al, and F are intentionally added.

[0062] In Embodiment 1, the second coating material may be represented by the following composition formula (1).

[0063] Li α Ti β Al γ F6...Formula (1)

[0064] Here, α, β, and γ satisfy α + 4β + 3γ = 6 and γ > 0.

[0065] With the above configuration, the ionic conductivity of the second coating material can be improved. Therefore, the positive electrode material containing the second coating material represented by composition formula (1) can further reduce the output resistance of the battery.

[0066] The second coating material does not need to contain sulfur.

[0067] In empirical formula (1), γ may satisfy the condition 0.5 ≤ γ < 1.

[0068] With the above configuration, the ionic conductivity of the second coating material can be further improved. Therefore, the output resistance of the battery can be further reduced.

[0069] In compositional formula (1), α, β, and γ may satisfy 2.5 ≤ α ≤ 2.9, 0.1 ≤ β ≤ 0.5, and 0.5 ≤ γ ≤ 0.9.

[0070] With the above configuration, the ionic conductivity of the second coating material can be further improved. Therefore, the output resistance of the battery can be further reduced.

[0071] In empirical formula (1), α, β, and γ may satisfy α=2.7, β=0.3, and γ=0.7.

[0072] With the above configuration, the ionic conductivity of the second coating material can be further improved. Therefore, the output resistance of the battery can be further reduced.

[0073] In this disclosure, the second coating material is not limited to one that strictly satisfies composition formula (1), but also includes materials that contain trace amounts of impurities other than the constituent elements shown in composition formula (1). For example, in the second coating material, the amount of impurities other than the constituent elements shown in composition formula may be 10% by mass or less.

[0074] In the coated positive electrode active material 130 of Embodiment 1, the volume ratio of the second coating layer 112 to the positive electrode active material 110 may be 0.1% or more and 5% or less. In other words, the ratio V2 / V1 of the volume of the second coating layer 112 to the volume V1 of the positive electrode active material 110 may be in the range of 0.001 or more and 0.05 or less. If the volume ratio of the second coating layer 112 to the positive electrode active material 110 is 0.1% or more, the surface of the base active material 120 can be sufficiently covered with the second coating material, so that the formation of a resistive layer between the positive electrode active material 110 and / or the first coating layer 111 and the second coating layer 112 can be effectively suppressed. If the volume ratio of the second coating layer 112 to the positive electrode active material 110 is 5% or less, it is possible to avoid the surface of the base active material 120 being over-covered by the second coating material. As a result, the electron conduction paths between the particles of the positive electrode active material 110 are appropriately ensured. Note that the volume V1 of the positive electrode active material 110 refers to the total volume of the positive electrode active material 110 within the particle group of the coated positive electrode active material 130. The volume V2 of the second coating layer 112 refers to the total volume of the second coating layer 112 within the particle group of the coated positive electrode active material 130.

[0075] With the above configuration, the output resistance of the battery can be further reduced.

[0076] In the coated positive electrode active material 130 of Embodiment 1, the volume ratio of the second coating layer 112 to the positive electrode active material 110 may be 0.1% to 4%, or 0.1% to 3%. When the volume ratio of the second coating layer 112 to the positive electrode active material 110 is within this range, the output resistance of the battery can be further reduced.

[0077] The volume ratio of the first coating layer 111 or the second coating layer 112 to the positive electrode active material 110 can be determined, for example, by obtaining the volume ratio for 20 arbitrarily selected cross-sectional SEM images of the coated positive electrode active material 130 obtained by a scanning electron microscope (SEM), and then calculating the average value of these ratios. When the volume of the positive electrode active material 110 is defined as V1 and the volume of the base active material 120 is defined as V2, the ratio of the volume of the first coating layer 111 (V2-V1) to the volume of the positive electrode active material 110 (V1) is calculated as (V2-V1) / V1. When the volume of the coated positive electrode active material 130 is defined as V3, the ratio of the volume of the second coating layer 112 (V3-V2) to the volume of the positive electrode active material 110 (V1) is calculated as (V3-V2) / V1.

[0078] The volume V1 of the positive electrode active material 110 can be calculated by the following method: The area of ​​the positive electrode active material 110 is calculated from the outline of the positive electrode active material 110 extracted from the cross-sectional SEM image. The radius (equivalent diameter) r1 of a circle having an area equivalent to this area is calculated. Assuming that the positive electrode active material 110 is a perfect sphere with an equivalent diameter r1, the volume V1 of the positive electrode active material 110 can be calculated from the equivalent diameter r1. The volume of the first coating layer 111 can be calculated as the value obtained by subtracting the volume V1 of the positive electrode active material 110 from the volume V2 of the base active material 120 (V2-V1). The volume V2 of the base active material 120 can be calculated by the following method: The average thickness of the first coating layer 111 is added to the equivalent diameter r1 of the positive electrode active material 110 calculated from the cross-sectional SEM image, and this is considered to be the equivalent diameter r2 of the base active material 120. Assuming that the base active material 120 is a perfect sphere with an equivalent diameter r2, the volume V2 of the base active material 120 can be calculated from the equivalent diameter r2. The volume of the second coating layer 112 can be calculated as the value obtained by subtracting the volume V2 of the base active material 120 from the volume V3 of the coated positive electrode active material 130 (V3-V2). The volume V3 of the coated positive electrode active material 130 can be calculated by the following method: Add the average thickness of the first coating layer 111 and the second coating layer 112 to the equivalent diameter r1 of the positive electrode active material 110 calculated from the cross-sectional SEM image, and consider this to be the equivalent diameter r3 of the coated positive electrode active material 130. Assuming that the coated positive electrode active material 130 is a perfect sphere with an equivalent diameter r3, the volume V3 of the coated positive electrode active material 130 can be calculated from the equivalent diameter r3.

[0079] The method for measuring the average thickness of the first coating layer 111 or the second coating layer 112 is not particularly limited. The average thickness of the coating layer can be determined, for example, by measuring the thickness of the coating layer at 20 arbitrarily selected points from the cross-sectional SEM image of the coated positive electrode active material 130 and calculating the average value from these measured values.

[0080] The average thickness of the second coating layer 112 may be 1 nm or more and 50 nm or less, or may be 5 nm or more and 30 nm or less. When the average thickness of the second coating layer 112 is 1 nm or more, the surface of the base active material 120 can be sufficiently coated with the second coating material, so that the generation of a resistance layer between the positive electrode active material 110 and / or the first coating layer 111 and the second coating layer 112 can be efficiently suppressed. When the average thickness of the second coating layer 112 is 50 nm or less, it is possible to avoid overcoating the surface of the base active material 120 with the second coating material. As a result, an appropriate conduction path for electrons between the particles of the positive electrode active material 110 is ensured.

[0081] According to the above configuration, the output resistance of the battery can be further reduced.

[0082] <Manufacturing method of the second coating material> The second coating material in Embodiment 1 can be manufactured, for example, by the following method.

[0083] Prepare raw material powder so as to have a mixing ratio of the desired composition. For example, when preparing Li 2.7 Al 0.7 Ti 0.3 F6, prepare LiF, AlF3 and TiF4 in a molar ratio of 2.7:0.7:0.3. Also, by adjusting the raw materials, mixing ratio and synthesis process, the values of "α", "β" and "γ" in the above composition formula (1) can be adjusted. [[ID=二十九]]

[0084] [[ID=三十]] After thoroughly mixing the raw material powders, the powders are mixed, pulverized, and reacted using a mechanochemical milling method. Alternatively, after thoroughly mixing the raw material powders, they may be fired in a vacuum or inert atmosphere. The firing conditions are, for example, firing at a temperature in the range of 100°C to 800°C for at least one hour. This yields a second coating material having the composition described above.

[0085] Furthermore, the composition of the crystalline phase (crystal structure) in the second coating material can be determined by adjusting the reaction method and reaction conditions of the raw material powders.

[0086] (First coating layer 111) In Embodiment 1, the first coating material may consist of an oxide solid electrolyte. "Consists of an oxide solid electrolyte" means that, excluding unavoidable impurities, no materials other than the oxide solid electrolyte are intentionally added.

[0087] In Embodiment 1, the oxide solid electrolyte includes at least one selected from the group consisting of lithium niobate, lithium titanate, lithium aluminate, lithium silicate, lithium borate, lithium zirconate, and lithium tungstate.

[0088] With the above configuration, the formation of a resistive layer between the positive electrode active material 110 and the first coating layer 111 can be further suppressed. This makes it possible to further reduce the output resistance of the battery.

[0089] Oxide solid electrolytes, advantageously, include lithium niobate.

[0090] With the above configuration, the output resistance of the battery can be further reduced.

[0091] The oxide solid electrolyte may be at least one selected from the group consisting of lithium niobate, lithium titanate, lithium aluminate, lithium silicate, lithium borate, lithium zirconate, and lithium tungstate. Furthermore, the oxide solid electrolyte may be lithium niobate. That is, the oxide solid electrolyte may consist of lithium niobate. "Consisting of lithium niobate" means that, excluding unavoidable impurities, no materials other than lithium niobate have been intentionally added.

[0092] With the above configuration, the output resistance of the battery can be further reduced.

[0093] The volume ratio of the first coating layer 111 to the positive electrode active material 110 may be between 0.1% and 5%. If the volume ratio of the first coating layer 111 to the positive electrode active material 110 is 0.1% or more, the surface of the positive electrode active material 110 can be sufficiently covered by the first coating material, thereby effectively suppressing the formation of a resistive layer between the positive electrode active material 110 and the first coating layer 111. If the volume ratio of the first coating layer 111 to the positive electrode active material 110 is 5% or less, it is possible to avoid over-covering the surface of the positive electrode active material 110 with the first coating layer material. As a result, the electron conduction paths between the particles of the positive electrode active material 110 are appropriately ensured.

[0094] With the above configuration, the output resistance of the battery can be further reduced.

[0095] The average thickness of the first coating layer 111 may be 1 nm or more and 50 nm or less, or 5 nm or more and 30 nm or less. If the average thickness of the first coating layer 111 is 1 nm or more, the surface of the positive electrode active material 110 can be sufficiently covered by the first coating material, so the formation of a resistive layer between the positive electrode active material 110 and the first coating layer 111 can be efficiently suppressed. If the average thickness of the first coating layer 111 is 50 nm or less, it is possible to avoid the surface of the positive electrode active material 110 being over-covered by the first coating layer material. As a result, the electron conduction paths between the particles of the positive electrode active material 110 are appropriately ensured.

[0096] With the above configuration, the output resistance of the battery can be further reduced.

[0097] The same method described for the second coating layer 112 can be applied to measure the thickness of the first coating layer 111.

[0098] (Cathode active material 110) The positive electrode active material 110 is a material having the property of intercalating and releasing metal ions (e.g., lithium ions). Examples of positive electrode active materials 110 include lithium-containing transition metal oxides, transition metal fluorides, polyanionic materials, fluorinated polyanionic materials, transition metal sulfides, transition metal oxysulfides, or transition metal oxynitrides. Examples of lithium-containing transition metal oxides include Li(Ni,Co,Al)O2, Li(Ni,Co,Mn)O2, or LiCoO2. When a lithium-containing transition metal oxide is used as the positive electrode active material 110, the manufacturing cost of the positive electrode can be reduced and the average discharge voltage can be increased.

[0099] The shape of the positive electrode active material 110 is, for example, particulate.

[0100] The positive electrode active material 110 may contain lithium nickel-cobalt aluminate.

[0101] With the above configuration, the energy density of the battery can be increased.

[0102] The positive electrode active material 110 may also be Li(Ni,Co,Al)O2.

[0103] <Method for producing basic active material 120> The positive electrode active material 110, i.e., the basic active material 120, whose surface is covered with at least a portion of the first coating layer 111, can be manufactured, for example, by the following method.

[0104] Methods for coating at least a portion of the surface of the positive electrode active material 110 with an oxide solid electrolyte as the first coating material include a liquid-phase coating method and a gas-phase coating method.

[0105] For example, in the liquid-phase coating method, a precursor solution of the oxide solid electrolyte is applied to the surface of the positive electrode active material 110. For example, when coating with LiNbO3 as the oxide solid electrolyte, the precursor solution may be a mixture of a solvent, lithium alkoxide, and niobalkoxide. An example of lithium alkoxide is lithium ethoxide. An example of niobalkoxide is niobethoxide. The solvent is, for example, an alcohol such as ethanol. The amounts of lithium alkoxide and niobalkoxide are adjusted to achieve the desired oxide solid electrolyte composition. The precursor solution may be acidic or alkaline.

[0106] The method for applying the precursor solution to the surface of the positive electrode active material 110 is not particularly limited. For example, the precursor solution can be applied to the surface of the positive electrode active material 110 using a rolling fluid coating apparatus. With the rolling fluid coating apparatus, the precursor solution can be sprayed onto the positive electrode active material 110 while rolling and fluidizing it, thereby coating the surface of the positive electrode active material 110. This forms a precursor film on the surface of the positive electrode active material 110. Subsequently, the positive electrode active material 110 coated with the precursor film is heat-treated. The heat treatment promotes gelation of the precursor film, and an oxide solid electrolyte is coated on at least a portion of the surface of the positive electrode active material 110, forming the base active material 120.

[0107] Examples of vapor deposition methods include pulsed laser deposition, vacuum deposition, sputtering, thermochemical vapor deposition, and plasma chemical vapor deposition. For example, in pulsed laser deposition, a high-energy pulsed laser (e.g., KrF excimer laser, wavelength: 248 nm) is irradiated onto an oxide solid electrolyte target, and the sublimated oxide solid electrolyte is deposited onto the surface of the positive electrode active material. When LiNbO3 is used as the oxide solid electrolyte, high-density sintered LiNbO3 is used as the target.

[0108] The average thickness of the oxide solid electrolyte coating formed on the surface of the positive electrode active material 110 can be determined, for example, by measuring the thickness of the oxide solid electrolyte coating on 20 arbitrarily selected basic active materials 120 from cross-sectional SEM images of the basic active material 120, and calculating the average value from these measurements.

[0109] <Method for manufacturing coated positive electrode active material 130> The coated positive electrode active material 130 can be manufactured, for example, by the following method.

[0110] The coated positive electrode active material 130 can be produced by processing a mixture containing the basic active material 120 and the second coating material by a dry particle compounding method. As a dry particle compounding method, a method may be used in which the basic active material 120 and the second coating material are mixed in an appropriate ratio, and mechanical energy such as impact, compression, and shear is applied to the mixture and stirred.

[0111] The equipment that can be used in the manufacturing process of the coated positive electrode active material 130 is not particularly limited, as long as it can impart mechanical energy such as impact, compression, or shear to the mixture. However, preferred equipment includes a ball mill, a compression-shear type processing device (particle compounding device) such as "Mechanofusion" (manufactured by Hosokawa Micron Corporation), or "Nobilta" (manufactured by Hosokawa Micron Corporation). Among these, "Mechanofusion" and "Nobilta" are more preferred, with "Nobilta" being even more preferred.

[0112] "Mechanofusion" is a particle compounding device that uses a dry mechanical compounding technology that applies strong mechanical energy to multiple different material particles. In mechanofusion, the powder raw material fed between a rotating container and a press head is subjected to mechanical energy such as compression, shearing, and friction, which causes the particles to compound.

[0113] "Nobilta" is a particle compounding device that uses dry mechanical compounding technology, an advanced particle compounding technology, to compound nanoparticles as raw materials. This technology produces composite particles by applying mechanical energy such as impact, compression, and shear to multiple raw material powders.

[0114] "Nobilta" is a device that produces composite particles of positive electrode active material and coating material by applying impact, compression, and shear forces to the mixture through a rotor that rotates at high speed in a horizontal cylindrical mixing container, with a predetermined gap between the rotor and the inner wall of the mixing container, and by repeatedly forcing the raw material particles through the gap. The rotor's rotation speed, processing time, and the amount of material to be charged can be adjusted as appropriate.

[0115] In the manufacturing process of the coated positive electrode active material 130, the ratio Da / Dc of the average particle size Da of the base active material 120 to the average particle size Dc of the second coating material may be 2 or more. With this configuration, the second coating material can be densely coated onto the surface of the base active material 120, and the formation of a resistive layer at the interface between the positive electrode active material 110 and the coating layer can be effectively suppressed. This makes it possible to further reduce the output resistance of the battery.

[0116] The average particle sizes of the positive electrode active material 110, the base active material 120, and the coated positive electrode active material 130 can be measured, for example, using SEM images. Specifically, for each active material, the average particle size can be determined by calculating the average of the equivalent circle diameters of 50 arbitrarily selected active material particles using SEM images.

[0117] In the manufacturing process of the coated positive electrode active material 130, the ratio Da / Dc may be 5 or greater. With this configuration, the second coating material can be more densely coated onto the surface of the base active material 120, and the formation of the battery's resistance layer can be suppressed more efficiently. As a result, the output resistance of the battery can be further reduced.

[0118] [Positive electrode material] Figure 1 is a cross-sectional view showing the schematic configuration of the positive electrode material 1000 in Embodiment 1.

[0119] The positive electrode material 1000 in Embodiment 1 includes the coated positive electrode active material 130 and the first solid electrolyte 100 of Embodiment 1. The shape of the first solid electrolyte 100 is, for example, particulate. The first solid electrolyte 100 enables high ionic conductivity in the positive electrode material 1000.

[0120] (1st solid electrolyte 100) The first solid electrolyte 100 contains a solid electrolyte with high ionic conductivity. The first solid electrolyte 100 may also contain a halide solid electrolyte. Halide solid electrolytes have high ionic conductivity and excellent high potential stability. Furthermore, since halide solid electrolytes have low electronic conductivity and high oxidation resistance, they are less susceptible to oxidative decomposition upon contact with the coated positive electrode active material 130. Therefore, by including a halide solid electrolyte in the first solid electrolyte 100, the output characteristics of the battery can be improved.

[0121] Examples of halide solid electrolytes that can be used include Li3(Ca,Y,Gd)X6, Li2MgX4, Li2FeX4, Li(Al,Ga,In)X4, Li3(Al,Ga,In)X6, and LiI. In these halide solid electrolytes, element X is at least one selected from the group consisting of Cl, Br, and I. In this disclosure, when an element in a formula is represented as "(Al,Ga,In)", this notation indicates at least one element selected from the group of elements in parentheses. That is, "(Al,Ga,In)" is synonymous with "at least one selected from the group consisting of Al, Ga, and In". The same applies to other elements.

[0122] The halide solid electrolyte does not need to contain sulfur.

[0123] The first solid electrolyte 100 may contain a sulfide solid electrolyte. Such a configuration can improve the output characteristics of the battery.

[0124] Examples of sulfide solid electrolytes include Li2S-P2S5, Li2S-SiS2, Li2S-B2S3, Li2S-GeS2, Li 3.25 Ge 0.25 P 0.75 S4, Li 10 GeP2S 12 These can be used. These include LiX, Li2O, and MO q Li p MO q The following may be added. Here, element X in "LiX" is at least one element selected from the group consisting of F, Cl, Br, and I. q " and "Li p MO q In ", element M is at least one element selected from the group consisting of P, Si, Ge, B, Al, Ga, In, Fe, and Zn. q " and "Li p MO q In this example, p and q are independent natural numbers.

[0125] The first solid electrolyte 100 may be a sulfide solid electrolyte. That is, the first solid electrolyte 100 may consist of a sulfide solid electrolyte. "Consists of a sulfide solid electrolyte" means that, excluding unavoidable impurities, no materials other than the sulfide solid electrolyte have been intentionally added. For example, the sulfide solid electrolyte may contain lithium sulfide and phosphorus sulfide. For example, the sulfide solid electrolyte may be Li2S-P2S5.

[0126] The shape of the first solid electrolyte 100 is not particularly limited and may be, for example, needle-shaped, spherical, ellipsoidal, etc. For example, the shape of the first solid electrolyte 100 may be particles.

[0127] If the shape of the first solid electrolyte 100 is particulate (for example, spherical), the average particle size may be 100 μm or less. If the average particle size is greater than 100 μm, there is a possibility that the coated positive electrode active material 130 and the first solid electrolyte 100 will not be able to form a good dispersion state in the positive electrode material 1000. As a result, the charge-discharge characteristics will deteriorate. The average particle size of the first solid electrolyte 100 may be 10 μm or less. By having the average particle size of the first solid electrolyte 100 within the above range, the coated positive electrode active material 130 and the first solid electrolyte 100 can form a good dispersion state in the positive electrode material 1000.

[0128] The average particle size of the first solid electrolyte 100 may be smaller than the average particle size of the coated positive electrode active material 130. With this configuration, the coated positive electrode active material 130 and the first solid electrolyte 100 can form a better dispersion state in the electrode.

[0129] The average particle size of the coated positive electrode active material 130 may be 0.1 μm or more and 100 μm or less. When the average particle size of the coated positive electrode active material 130 is 0.1 μm or more, the coated positive electrode active material 130 and the first solid electrolyte 100 can form a good dispersion state in the positive electrode material 1000. As a result, the charge and discharge characteristics of the battery are improved. Furthermore, when the average particle size of the coated positive electrode active material 130 is 100 μm or less, the lithium diffusion rate within the positive electrode active material is improved. Therefore, the battery can operate at high power.

[0130] The average particle size of the coated positive electrode active material 130 may be larger than the average particle size of the first solid electrolyte 100. Even with this configuration, a good dispersion state of the coated positive electrode active material 130 and the first solid electrolyte 100 can be formed in the electrode.

[0131] In the positive electrode material 1000, the first solid electrolyte 100 and the coated positive electrode active material 130 may be in contact with each other, as shown in Figure 1.

[0132] In the coated positive electrode active material 130, the first coating layer 111 may uniformly coat the positive electrode active material 110. In other words, the base active material 120 may be formed by the entire surface of the positive electrode active material 110 being covered by the first coating layer 111. The first coating layer 111 suppresses direct contact between the positive electrode active material 110 and the first solid electrolyte 100, thereby suppressing the formation of an oxide film due to oxidative decomposition of the first solid electrolyte 100. Therefore, with this configuration, the output resistance of the battery is further reduced.

[0133] In the coated positive electrode active material 130, the first coating layer 111 may cover only a portion of the surface of the positive electrode active material 110. In other words, the base active material 120 may be formed by the first coating layer 111 covering a portion of the surface of the positive electrode active material 110.

[0134] In the coated positive electrode active material 130, the second coating layer 112 may uniformly coat the base active material 120. In other words, the coated positive electrode active material 130 may be formed by the entire surface of the base active material 120 being covered by the second coating layer 112. The second coating layer 112 suppresses direct contact between the base active material 120 and the first solid electrolyte 100, thereby suppressing the formation of an oxide film due to oxidative decomposition of the first solid electrolyte 100. Therefore, with this configuration, the output resistance of the battery is further reduced.

[0135] In the coated positive electrode active material 130, the second coating layer 112 may cover only a portion of the surface of the base active material 120. In other words, the coated positive electrode active material 130 may be formed by the second coating layer 112 covering a portion of the surface of the base active material 120.

[0136] The positive electrode material 1000 may include a plurality of first solid electrolytes 100 and a plurality of coated positive electrode active materials 130.

[0137] The content of the first solid electrolyte 100 relative to the positive electrode material 1000 and the content of the coated positive electrode active material 130 relative to the positive electrode material 1000 may be the same or different.

[0138] <Method for manufacturing positive electrode material 1000> A positive electrode material 1000 is obtained by mixing the coated positive electrode active material 130 and the first solid electrolyte 100. The method of mixing the coated positive electrode active material 130 and the first solid electrolyte 100 is not particularly limited. For example, the coated positive electrode active material 130 and the first solid electrolyte 100 may be mixed using an instrument such as a mortar and pestle, or they may be mixed using a mixing device such as a ball mill. The mixing ratio of the coated positive electrode active material 130 and the first solid electrolyte 100 is not particularly limited.

[0139] (Embodiment 2) Embodiment 2 will be described below. Descriptions that overlap with Embodiment 1 will be omitted as appropriate.

[0140] Figure 2 is a cross-sectional view showing the schematic configuration of the battery 2000 in Embodiment 2.

[0141] The battery 2000 in Embodiment 2 comprises a positive electrode 201, an electrolyte layer 202, and a negative electrode 203. The electrolyte layer 202 is positioned between the positive electrode 201 and the negative electrode 203.

[0142] The positive electrode 201 includes the positive electrode material 1000 in Embodiment 1. That is, the positive electrode 201 includes a coated positive electrode active material 130 and a first solid electrolyte 100. The positive electrode 201 includes a material having the property of intercalating and releasing metal ions (e.g., lithium ions).

[0143] With the above configuration, the charge and discharge efficiency of the battery 2000 can be improved.

[0144] The volume ratio "v1:100-v1" of the positive electrode active material 110 contained in the positive electrode 201 to the total volume of the first coating material, second coating material, and first solid electrolyte 100 may satisfy the condition 30≦v1≦95. Here, v1 represents the volume fraction of the positive electrode active material 110 when the total volume of the positive electrode active material 110, first coating material, second coating material, and first solid electrolyte 100 contained in the positive electrode 201 is set to 100. If 30≦v1 is satisfied, it is easier to ensure a sufficient energy density for the battery 2000. If v1≦95 is satisfied, it becomes easier to operate the battery 2000 at high power.

[0145] The thickness of the positive electrode 201 may be 10 μm or more and 500 μm or less. If the thickness of the positive electrode 201 is 10 μm or more, the energy density of the battery 2000 is sufficiently ensured. If the thickness of the positive electrode 201 is 500 μm or less, high-power operation becomes possible.

[0146] The electrolyte layer 202 is a layer containing an electrolyte. This electrolyte is, for example, a solid electrolyte. The solid electrolyte contained in the electrolyte layer 202 is called the second solid electrolyte. That is, the electrolyte layer 202 may contain a second solid electrolyte layer.

[0147] As the second solid electrolyte, a halogenated solid electrolyte, a sulfide solid electrolyte, an oxide solid electrolyte, a polymer solid electrolyte, or a complex hydride solid electrolyte may be used.

[0148] The second solid electrolyte may contain a solid electrolyte having the same composition as the solid electrolyte contained in the first solid electrolyte 100.

[0149] If the second solid electrolyte includes a halide solid electrolyte, the second solid electrolyte may include a halide solid electrolyte having the same composition as the halide solid electrolyte included in the first solid electrolyte 100 in Embodiment 1. That is, the electrolyte layer 202 may include a halide solid electrolyte having the same composition as the halide solid electrolyte included in the first solid electrolyte 100 in Embodiment 1 described above. With such a configuration, the output characteristics of the battery can be further improved.

[0150] The second solid electrolyte may contain a solid electrolyte having a different composition from the solid electrolyte contained in the first solid electrolyte 100.

[0151] If the second solid electrolyte includes a halide solid electrolyte, the second solid electrolyte may include a halide solid electrolyte having a different composition from the halide solid electrolyte included in the first solid electrolyte 100 in Embodiment 1. That is, the electrolyte layer 202 may include a halide solid electrolyte having a different composition from the halide solid electrolyte included in the first solid electrolyte 100 in Embodiment 1. With such a configuration, the output characteristics of the battery can be further improved.

[0152] The second solid electrolyte may contain a sulfide solid electrolyte. The second solid electrolyte may contain a sulfide solid electrolyte having the same composition as the sulfide solid electrolyte contained in the first solid electrolyte 100 in Embodiment 1. That is, the electrolyte layer 202 may contain a sulfide solid electrolyte having the same composition as the sulfide solid electrolyte contained in the first solid electrolyte 100 in Embodiment 1.

[0153] With the above configuration, since the electrolyte layer 202 contains a sulfide solid electrolyte with excellent reduction stability, a low-potential negative electrode material such as graphite or metallic lithium can be used for the negative electrode 203. This makes it possible to improve the energy density of the battery. Furthermore, if the electrolyte layer 202 contains a sulfide solid electrolyte having the same composition as the sulfide solid electrolyte contained in the first solid electrolyte 100 in Embodiment 1, the output characteristics of the battery can be further improved.

[0154] The second solid electrolyte may contain an oxide solid electrolyte. Examples of oxide solid electrolytes include NASICON-type solid electrolyte materials represented by LiTi2(PO4)3 and its elemental substitutions, (LaLi)TiO3-based perovskite-type solid electrolyte materials, and Li 14 ZnGe4O 16 , LISICON-type solid electrolyte materials such as Li4SiO4, LiGeO4 and their elemental substitutions, Li7La3Zr2O 12 Garnet-type solid electrolyte materials, such as those represented by elemental substitutions thereof, Li-BO compounds such as Li3PO4 and its N-substituted counterparts, LiBO2 and Li3BO3, with Li2SO4, Li2CO3, etc. added as a base, as well as glass ceramics, can be used.

[0155] The second solid electrolyte may contain a polymer solid electrolyte. For example, a compound of a polymer and a lithium salt can be used as the polymer solid electrolyte. The polymer compound may have an ethylene oxide structure. Polymer compounds having an ethylene oxide structure can contain a large amount of lithium salt. Therefore, the ionic conductivity can be further increased. Examples of lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiSO3CF3, LiN(SO2F)2, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiN(SO2CF3)(SO2C4F9), and LiC(SO2CF3)3. A single lithium salt may be used, or two or more may be used in combination.

[0156] The second solid electrolyte may contain a complex hydride solid electrolyte. Examples of complex hydride solid electrolytes that can be used include LiBH4-LiI and LiBH4-P2S5.

[0157] The electrolyte layer 202 may contain the above-mentioned second solid electrolyte as its main component. That is, the electrolyte layer 202 may contain the second solid electrolyte in a mass ratio of 50% or more (i.e., 50% by mass or more) of the total electrolyte layer 202.

[0158] With the above configuration, the output characteristics of the battery can be further improved.

[0159] The electrolyte layer 202 may contain a second solid electrolyte in an amount of 70% or more by mass relative to the total electrolyte layer 202 (i.e., 70% by mass or more).

[0160] With the above configuration, the output characteristics of the battery can be further improved.

[0161] The electrolyte layer 202 mainly contains a second solid electrolyte, but may also contain unavoidable impurities, or starting materials, by-products, and decomposition products used in the synthesis of the second solid electrolyte.

[0162] The electrolyte layer 202 may contain a second solid electrolyte in a mass ratio of 100% (i.e., 100% by mass) of the total electrolyte layer 202, excluding impurities that are unavoidable to be present. In other words, the electrolyte layer 202 may consist of a second solid electrolyte.

[0163] With the above configuration, the output characteristics of the battery can be further improved.

[0164] The electrolyte layer 202 may contain two or more of the materials listed as solid electrolyte materials as a second solid electrolyte. For example, the electrolyte layer 202 may contain a halide solid electrolyte and a sulfide solid electrolyte as a second solid electrolyte.

[0165] The thickness of the electrolyte layer 202 may be 1 μm or more and 300 μm or less. When the thickness of the electrolyte layer 202 is 1 μm or more, the possibility of a short circuit between the positive electrode 201 and the negative electrode 203 is reduced. Also, when the thickness of the electrolyte layer 202 is 300 μm or less, high-power operation becomes easier. In other words, if the thickness of the electrolyte layer 202 is appropriately adjusted, sufficient safety of the battery can be ensured, and the battery can be operated at high power.

[0166] The negative electrode 203 includes a material having the property of intercalating and releasing metal ions (e.g., lithium ions). The negative electrode 203 includes, for example, a negative electrode active material (e.g., negative electrode active material particles).

[0167] The negative electrode active material can be a metallic material, a carbon material, an oxide, a nitride, a tin compound, or a silicon compound. The metallic material may be a pure metal or an alloy. Examples of metallic materials include lithium metal or lithium alloys. Examples of carbon materials include natural graphite, coke, carbon in the process of graphitization, carbon fibers, spheroidal carbon, artificial graphite, or amorphous carbon. From the viewpoint of capacity density, silicon, tin, silicon compounds, or tin compounds can be suitably used.

[0168] The negative electrode 203 may contain a third solid electrolyte. Such a configuration improves the lithium-ion conductivity inside the negative electrode 203, enabling high-power operation. As the third solid electrolyte included in the negative electrode 203, the materials listed as examples of the second solid electrolyte in the electrolyte layer 202 can be used.

[0169] The average particle size of the negative electrode active material may be larger than the average particle size of the third solid electrolyte contained in the negative electrode 203. This allows for the formation of a good dispersion state between the negative electrode active material and the third solid electrolyte.

[0170] The volume ratio "v2:100-v2" of the negative electrode active material and the third solid electrolyte contained in the negative electrode 203 may satisfy the condition 30 ≤ v2 ≤ 95. Here, v2 represents the volume ratio of the negative electrode active material when the total volume of the negative electrode active material and the third solid electrolyte contained in the negative electrode 203 is set to 100. When 30 ≤ v2 is satisfied, it is easier to ensure a sufficient energy density of the battery. When v2 ≤ 95 is satisfied, it becomes easier to operate the battery at high power.

[0171] The thickness of the negative electrode 203 may be 10 μm or more and 500 μm or less. When the thickness of the negative electrode 203 is 10 μm or more, it becomes easier to ensure sufficient energy density of the battery. When the thickness of the negative electrode 203 is 500 μm or less, it becomes easier to operate the battery at high power.

[0172] At least one selected from the group consisting of a positive electrode 201, an electrolyte layer 202, and a negative electrode 203 may contain a binder for the purpose of improving the adhesion between particles. The binder is used to improve the bonding properties of the materials constituting the electrode. Examples of binders include polyvinylidene fluoride, polytetrafluoroethylene, polyethylene, polypropylene, aramid resin, polyamide, polyimide, polyamideimide, polyacrylonitrile, polyacrylic acid, polymethyl polyacrylate, polyethyl polyacrylate, polyhexyl polyacrylate, polymethacrylic acid, polymethyl polymethacrylate, polyethyl polymethacrylate, polyhexyl polymethacrylate, polyvinyl acetate, polyvinylpyrrolidone, polyether, polyethersulfone, hexafluoropolypropylene, styrene-butadiene rubber, carboxymethylcellulose, and the like. Furthermore, a copolymer of two or more materials selected from tetrafluoroethylene, hexafluoroethylene, hexafluoropropylene, perfluoroalkyl vinyl ether, vinylidene fluoride, chlorotrifluoroethylene, ethylene, propylene, pentafluoropropylene, fluoromethyl vinyl ether, acrylic acid, and hexadiene may be used as a binder. Alternatively, two or more materials selected from these may be mixed and used as a binder.

[0173] At least one of the positive electrode 201 and the negative electrode 203 may contain a conductive additive for the purpose of enhancing electronic conductivity. Examples of conductive additives include graphites such as natural or artificial graphite, carbon blacks such as acetylene black and Ketjenblack, conductive fibers such as carbon fibers or metal fibers, metal powders such as carbon fluoride and aluminum, conductive whiskers such as zinc oxide or potassium titanate, conductive metal oxides such as titanium oxide, and conductive polymer compounds such as polyaniline, polypyrrole, and polythiophene. Using a carbon conductive additive can help reduce costs.

[0174] The battery in Embodiment 2 can be configured as a battery of various shapes, such as coin-type, cylindrical, prismatic, sheet-type, button-type, flat-type, or stacked-type.

[0175] The battery in Embodiment 2 can be manufactured, for example, by the following method: Prepare the positive electrode material 1000, the material for forming the electrolyte layer 202, and the material for forming the negative electrode 203, respectively, as in Embodiment 1. A laminate is fabricated in which the positive electrode 201, the electrolyte layer 202, and the negative electrode 203 are arranged in this order, using a known method. [Examples]

[0176] Details of this disclosure will be explained below with reference to examples, comparative examples, and reference examples.

[0177] Examples 1 to 3 [Preparation of the second coating material] In a glove box with an argon atmosphere, dew point below -60°C and oxygen level below 5 vol ppm, the raw material powders LiF, AlF3, and TiF4 were weighed in a molar ratio of LiF:AlF3:TiF4 = 2.7:0.7:0.3. These raw material powders were mixed in an agate mortar to obtain a mixture. Next, the obtained mixture was milled using a planetary ball mill (Fritsch, P-7 type) for 12 hours at 500 rpm. As a result, Li 2.7 Al0.7 Ti 0.3 A powder of the compound represented by the compositional formula F6 (hereinafter referred to as LTAF) was obtained. The powder of the compound was mixed with an appropriate amount of solvent, and the mixture was milled using a planetary ball mill (Fritsch, P-7 type) for 20 minutes at 200 rpm. After that, the solvent was removed and the resulting product was dried. This yielded LTAF powder with an average particle size of 0.5 μm as the second coating material. The average particle size was obtained by calculating the average value of the equivalent circle diameter of 50 arbitrarily selected particles from the LTAF powder observed at a magnification of 5000x using a scanning electron microscope (Keyence, 3D Real Surface View Microscope, VE-8800).

[0178] [Cathode active material] As the positive electrode active material, Li(Ni,Co,Al)O2 (hereinafter referred to as NCA) with an average particle size of 5 μm was used.

[0179] [Preparation of the first coating material (oxide solid electrolyte)] Lithium niobate (hereinafter referred to as LiNbO3) was used as the first coating material (oxide solid electrolyte). Coated NCA was prepared by coating the surface of NCA with LiNbO3 as the basic active material. The coated NCA was prepared by the following procedure.

[0180] First, a coating solution was prepared by dissolving lithium ethoxide and niobium pentaethoxide in ethanol in a glove box under an argon atmosphere with a dew point of -60°C or lower and an oxygen level of 5 vol ppm or lower.

[0181] A rolling fluid granulation coating apparatus was used to coat the surface of NCA. The prepared coating solution was applied to the surface of NCA using the rolling fluid granulation coating apparatus. At this time, the coating solution was applied so that the average thickness of LiNbO3 was 15 nm. The treated powder was placed in an alumina crucible and removed under an air atmosphere. The treated powder was then heat-treated at 220°C for 1 hour under an air atmosphere.

[0182] By re-grinding the heat-treated powder in an agate mortar, coated NCA was obtained as the basic active material, by coating the surface of NCA with LiNbO3.

[0183] The average thickness of the LiNbO3 coating layer (first coating layer) in coated NCA was measured by cross-sectional SEM. The average thickness was 14 nm.

[0184] [Fabrication of coated cathode active material] The coating of the coated NCA with the second coating material was performed using a particle compounding apparatus (Nobilta, NOB-MINI, manufactured by Hosokawa Micron Corporation). 49 g of coated NCA and 0.31 g (Example 1), 0.63 g (Example 2), and 0.95 g (Example 3) of LTAF powder were placed in the NOB-MINI container. The coated NCA and LTAF powder were compounded at a rotation speed of 6000 rpm, an operating time of 60 minutes, and a power value of 550 W to 740 W to produce coated cathode active materials.

[0185] The volume ratio of the LiNbO3 coating layer (first coating layer) to the positive electrode active material and the volume ratio of the LTAF coating layer (second coating layer) to the positive electrode active material were calculated from cross-sectional SEM in Examples 1 to 3. In all Examples 1 to 3, the volume ratio of the first coating layer to the positive electrode active material was 1.7%. In Examples 1 to 3, the volume ratio of the second coating layer to the positive electrode active material was 1.2%, 2.0%, and 2.5%, respectively.

[0186] [Manufacturing of secondary batteries] The following steps were performed using the coated positive electrode active materials of Examples 1 to 3 described above.

[0187] In a glove box with an argon atmosphere, dew point below -60°C and oxygen level below 5 vol ppm, one of the coated positive electrode active materials from Examples 1 to 3 and the first solid electrolyte, Li2S-P2S5, were weighed so that the total volume ratio of the positive electrode active material, the first coating material, the second coating material, and the first solid electrolyte was 75:25. Furthermore, a conductive additive (VGCF-H, manufactured by Showa Denko Corporation) was weighed so that it was 1.5% by mass relative to the mass of the positive electrode active material. These were mixed in an agate mortar to prepare the positive electrode materials of Examples 1 to 3. "VGCF" is a registered trademark of Showa Denko Corporation.

[0188] In this invention, an electrolyte layer was obtained by placing 60 mg of Li2S-P2S5, a second solid electrolyte, inside an insulating outer casing and pressurizing it at a pressure of 80 MPa. Next, a positive electrode layer was obtained by placing 15.6 mg of any of the positive electrode materials from Examples 1 to 3 (in terms of positive electrode active material equivalent) inside and pressurizing it at a pressure of 720 MPa. Then, a layer of metallic Li (200 μm thick) was placed on top of the electrolyte layer on the counter electrode side. This was then pressurized at a pressure of 80 MPa to obtain the negative electrode layer. Next, stainless steel current collectors were placed above and below the laminate, and current collector leads were attached to the current collectors. Finally, a secondary battery was fabricated by using an insulating ferrule to isolate and seal the inside of the insulating outer casing from the outside air. The inner diameter of the insulating outer casing used in this invention was 9.5 mm, and the projected area of ​​the electrodes was 0.71 cm². 2 That was the case.

[0189] (Evaluation of output resistance) The output resistance was evaluated using the secondary batteries of Examples 1 to 3 under the following conditions.

[0190] The secondary batteries of Examples 1 to 3 were placed in a constant temperature bath at 25°C. Constant current charging was performed at a current value of 319 μA, which corresponds to a rate of 0.1 C (10-hour rate) relative to the theoretical capacity of the battery, and the voltage was set to 4.3 V (Li / Li + Charging was terminated at the reference voltage. Next, constant voltage charging was performed at 4.3V, and charging was terminated when the current value, which corresponds to a 0.01C rate, fell below 31.9μA. After a 20-minute rest, constant current discharge was performed at a current value of 319μA, which corresponds to a 0.1C rate, and the voltage was 3.62V (Li / Li+ Discharge was terminated at the reference voltage. Next, constant voltage discharge was performed at 3.62V, and the discharge was terminated when the current value, which corresponds to a 0.01C rate, fell below 31.9μA. After a 10-minute pause, the output resistance was calculated from the voltage drop by discharging at 4.63mA for 10 seconds, which corresponds to a 1.45C rate, using Ohm's law (R=ΔV / 0.00463). Next, constant current discharge was performed at a current value of 319μA, which corresponds to a 0.1C rate, and the voltage was 2.5V (Li / Li + Discharge was terminated at the reference voltage. Finally, constant voltage discharge was performed at 2.5V, and the discharge was terminated when the current value, which corresponds to a 0.01C rate, was 31.9μA or less. The output resistances of the secondary batteries in Examples 1 to 3 were obtained. These results are shown in Table 1 below.

[0191] Examples 4 to 6 The coated positive electrode active material and secondary battery were fabricated using the same procedure as in Examples 1 to 3, except that the coating solution was applied so that the average thickness of the LiNbO3 was 20 nm. In Examples 4 to 6, the average thickness of the LiNbO3 coating layer (first coating layer), as measured by cross-sectional SEM, was 22 nm. In Examples 4 to 6, the volume ratio of the first coating layer to the positive electrode active material, calculated from cross-sectional SEM, was 2.6% in all cases. In Examples 4 to 6, the volume ratio of the LTAF coating layer (second coating layer) to the positive electrode active material, calculated from cross-sectional SEM, was 1.1%, 2.0%, and 2.5%, respectively.

[0192] Example 7 49 g of coated NCA and 1.46 g of LTAF powder were placed in a NOB-MINI container, and coated positive electrode active material and secondary batteries were prepared using the same procedure as in Examples 4 to 6. In Example 7, the average thickness of the LiNbO3 coating layer (first coating layer), measured by cross-sectional SEM, was 22 nm. In Example 7, the volume ratio of the first coating layer to the positive electrode active material, calculated from cross-sectional SEM, was 2.6%. In Example 7, the volume ratio of the LTAF coating layer (second coating layer) to the positive electrode active material, calculated from cross-sectional SEM, was 4.3%.

[0193] ≪Comparative Example 1≫ In Comparative Example 1, NCA without a coating layer (first coating layer and second coating layer) was used as the positive electrode active material. In a glove box with an argon atmosphere, dew point below -60°C and oxygen value below 5 vol ppm, the positive electrode active material of Comparative Example 1 and the first solid electrolyte, Li2S-P2S5, were weighed so that the volume ratio of the positive electrode active material to the first solid electrolyte was 75:25. Furthermore, a conductive additive (VGCF-H, manufactured by Showa Denko Corporation) was weighed so that it was 1.5% by mass relative to the mass of the positive electrode active material. These were mixed in an agate mortar to prepare the positive electrode material of Comparative Example 1. After that, a secondary battery was prepared using the same procedure as in Examples 1 to 3.

[0194] ≪Reference Examples 1 to 4≫ In the NOB-MINI container, 49 g of NCA without a LiNbO3 coating layer and 0.31 g (Reference Example 1), 0.63 g (Reference Example 2), 0.95 g (Reference Example 3), and 1.46 g (Reference Example 4) of LTAF powder were placed. The NCA and LTAF were combined and processed at a rotation speed of 6000 rpm, an operating time of 60 minutes, and a power value of 550 W to 740 W to produce a positive electrode active material coated only with LTAF. A secondary battery was fabricated using the same procedure as in Examples 1 to 3. In Reference Examples 1 to 4, the volume ratio of the LTAF layer (second coating layer) to the positive electrode active material, calculated from cross-sectional SEM, was 1.2%, 2.0%, 2.6%, and 4.4%, respectively.

[0195] The output resistance was evaluated using the secondary batteries of Examples 4 to 7, Comparative Example 1, and Reference Examples 1 to 4, under the same conditions as in Examples 1 to 3. The results are shown in Table 1 below.

[0196] [Table 1]

[0197] ≪Consideration≫ The positive electrode active material in Examples 1 to 7 is the same as that in Comparative Example 1. However, Examples 1 to 7, which have a coating layer, had a significantly lower output resistance than Comparative Example 1, which does not have a coating layer. Examples 1, 4, and Reference Example 1 have the same volume ratio of the second coating layer. However, Examples 1 and 4, which have the first coating layer, had a lower output resistance than Reference Example 1, which does not have the first coating layer. Examples 2, 5, and Reference Example 2 have the same volume ratio of the second coating layer. However, Examples 2 and 5, which have the first coating layer, had a lower output resistance than Reference Example 2, which does not have the first coating layer. Examples 3, 6, and Reference Example 3 have the same volume ratio of the second coating layer. However, Examples 3 and 6, which have the first coating layer, had a lower output resistance than Reference Example 3, which does not have the first coating layer. Also, Examples 4 to 7 have the same average thickness of the first coating layer. However, in Examples 4 to 6, where the volume ratio of the second coating layer was 4% or less, the output resistance was reduced more than in Example 7, where the volume ratio of the second coating layer was greater than 4%.

[0198] From the results of Examples 1 to 7, Comparative Example 1, and Reference Examples 1 to 4 shown in Table 1, the following was confirmed: When a coated positive electrode active material having a coating layer is used, the output resistance of the battery is significantly reduced compared to when a positive electrode active material without a coating layer is used. Furthermore, in a coated positive electrode active material having a first coating layer and a second coating layer, if the volume ratio of the second coating layer to the positive electrode active material is 0.1% or more and 5% or less, the output resistance of the battery is reduced. If the volume ratio of the second coating layer to the positive electrode active material is less than 0.1%, the surface of the first coating layer made of oxide solid electrolyte cannot be sufficiently covered by the second coating material. Therefore, it is not possible to efficiently suppress the formation of a resistive layer between the first and second coating layers. If the volume ratio of the second coating layer to the positive electrode active material is 5% or less, it is possible to avoid the surface of the base active material being over-covered by the second coating material. As a result, the electron conduction paths between the particles of the positive electrode active material are appropriately secured. The output resistance of the battery is further reduced when the volume ratio of the second coating layer to the positive electrode active material is 0.1% to 4%, and even more specifically, 0.1% to 3%. Furthermore, the output resistance of the battery is reduced when the average thickness of the first coating layer is 1 nm or more and 30 nm or less. [Industrial applicability]

[0199] The battery described herein can be used, for example, as an all-solid-state lithium secondary battery. [Explanation of Symbols]

[0200] 1000 Cathode Materials 100 1st solid electrolyte 110 Cathode active material 111 First coating layer 112 Second coating layer 120 Basic active materials 130 Coated positive electrode active material 2000 batteries 201 Positive electrode 202 Electrolyte layer 203 Negative electrode

Claims

1. Positive electrode active material and, A first coating layer covering at least a portion of the surface of the positive electrode active material, A second coating layer covering at least a portion of the surface of the first coating layer and the base active material including the positive electrode active material, Equipped with, The first coating layer contains an oxide solid electrolyte, The second coating layer comprises a compound containing Li, Ti, M, and F. M is at least one element selected from the group consisting of Ca, Mg, Al, Y, and Zr. Coated positive electrode active material.

2. The volume ratio of the second coating layer to the positive electrode active material is 0.1% or more and 5% or less. The coated positive electrode active material according to claim 1.

3. M is Al. The coated positive electrode active material according to claim 1 or 2.

4. The material constituting the second coating layer is represented by the following compositional formula (1): Li α Ti β Al γ F 6 ... Formula (1) Herein, α, β, and γ satisfy α + 4β + 3γ = 6 and γ > 0, the coated positive electrode active material according to claim 3.

5. The above γ satisfies 0.5 ≤ γ < 1. The coated positive electrode active material according to claim 4.

6. The above α, β, and γ satisfy 2.5 ≤ α ≤ 2.9, 0.1 ≤ β ≤ 0.5, and 0.5 ≤ γ ≤ 0.

9. The coated positive electrode active material according to claim 4.

7. The oxide solid electrolyte includes at least one selected from the group consisting of lithium niobate, lithium titanate, lithium aluminate, lithium silicate, lithium borate, lithium zirconate, and lithium tungstate. The coated positive electrode active material according to any one of claims 1 to 6.

8. The oxide solid electrolyte includes lithium niobate. The coated positive electrode active material according to any one of claims 1 to 7.

9. The average thickness of the first coating layer is 1 nm or more and 50 nm or less. The coated positive electrode active material according to any one of claims 1 to 8.

10. The positive electrode active material includes lithium nickel-cobalt aluminum oxide. The coated positive electrode active material according to any one of claims 1 to 9.

11. A coated positive electrode active material according to any one of claims 1 to 10, and a first solid electrolyte; A positive electrode material that includes [this material].

12. The first solid electrolyte includes a halogenated solid electrolyte. The positive electrode material according to claim 11.

13. The first solid electrolyte includes a sulfide solid electrolyte. The positive electrode material according to claim 11 or 12.

14. A positive electrode comprising the positive electrode material according to any one of claims 11 to 13, Negative electrode, and An electrolyte layer provided between the positive electrode and the negative electrode, A battery equipped with a battery.

15. The electrolyte layer includes a second solid electrolyte, The second solid electrolyte includes a solid electrolyte having the same composition as the solid electrolyte contained in the first solid electrolyte. The battery according to claim 14.

16. The electrolyte layer includes a second solid electrolyte, The second solid electrolyte includes a halogenated solid electrolyte having a different composition from the solid electrolyte contained in the first solid electrolyte. The battery according to claim 14.

17. The electrolyte layer includes a second solid electrolyte, The second solid electrolyte comprises a sulfide solid electrolyte. The battery according to claim 14.

18. A method for producing a coated positive electrode active material according to claim 1, The aforementioned manufacturing method The method includes treating a mixture comprising the positive electrode active material, whose surface at least a portion is covered by the first coating layer, and the material constituting the second coating layer, by a dry particle compounding method. The dry particle compounding method includes applying mechanical energy of impact, compression, and shear to the mixture. A method for manufacturing coated positive electrode active material.

19. The ratio Da / Dc of the average particle size Da of the positive electrode active material whose surface is at least partially covered by the first coating layer to the average particle size Dc of the material constituting the second coating layer is 2 or more. A method for producing a coated positive electrode active material according to claim 18.

20. The ratio Da / Dc is 5 or more. A method for producing a coated positive electrode active material according to claim 19.

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