Coated cathode active material, cathode material, battery, and method for producing coated cathode active material

Abstract

A coated positive electrode active substance 100 according to the present disclosure comprises a positive electrode active substance 101 and a coating layer 102 that coats at least a part of a surface of the positive electrode active substance 101. The coating layer 102 contains Li, Zr and F. A material that constitutes the coating layer 102 may be represented by, for example, compositional formula (1): LiαZrβFγ. In compositional formula (1), α, β and γ satisfy the relationships 0 < α < 8, 0 < β ≤ 1.1 and 0 < γ ≤ 8. A positive electrode material 1000 of the present disclosure includes the coated positive electrode active substance 100 and a first solid electrolyte 103. A battery of the present disclosure comprises a positive electrode, which contains the positive electrode material 1000, a negative electrode, and an electrolyte layer provided between the positive electrode and the negative electrode.

Description

[Technical Field]

[0001] The present disclosure relates to a coated cathode active material, a cathode material, a battery, and a method for producing the coated cathode active material. [Background technology]

[0002] Patent Document 1 discloses a positive electrode material including a positive electrode active material whose surface is coated with a coating material and a halide solid electrolyte. Patent Document 1 discloses a solid electrolyte including yttrium and chlorine and / or bromine as the halide solid electrolyte.

[0003] Patent Document 2 discloses an all-solid-state lithium battery containing a positive electrode active material whose surface is coated with a lithium ion conductive oxide that has substantially no electronic conductivity. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2019 / 135322 [Patent Document 2] Patent No. 4982866 Summary of the Invention [Problem to be solved by the invention]

[0005] The present disclosure provides a positive electrode active material that can suppress the formation of a high-resistance layer between the positive electrode active material and the solid electrolyte. [Means for solving the problem]

[0006] The coated positive electrode active material of the present disclosure is a positive electrode active material, and a coating layer that covers at least a portion of the surface of the positive electrode active material; Equipped with where: The coating layer contains Li, Zr and F. [Effects of the Invention]

[0007] The present disclosure provides a positive electrode active material that can suppress the formation of a high-resistance layer between the positive electrode active material and the solid electrolyte. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a cross-sectional view showing a schematic configuration of a positive electrode material according to the first embodiment. [Figure 2] FIG. 2 is a cross-sectional view showing a schematic configuration of a battery according to the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

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

[0010] The following descriptions are all comprehensive or provide specific examples. The numerical values, compositions, shapes, film thicknesses, electrical properties, secondary battery structures, electrode materials, etc. shown below are merely examples and are not intended to limit the present disclosure. In addition, any components not described in an independent claim showing a top concept are optional components.

[0011] (Findings that formed the basis of this disclosure) As a result of intensive research by the present inventors, the present inventors have found that in a battery using a positive electrode material including a positive electrode active material and a halide solid electrolyte containing chlorine or bromine, there is a problem in that the halide solid electrolyte undergoes oxidative decomposition during charging, resulting in the formation of a high-resistance layer between the positive electrode active material and the solid electrolyte.

[0012] Specifically, when a material containing chlorine or bromine as an anion constituting the solid electrolyte is used as a positive electrode active material with an average potential vs. Li of 3.7 V or higher, the solid electrolyte may undergo oxidative decomposition through an oxidation reaction during charging, and the oxidative decomposition product may function as a high-resistance layer. Here, the oxidation reaction refers to not only the normal charging reaction in which lithium and electrons are extracted from the positive electrode active material in the positive electrode material, but also a side reaction in which electrons are extracted from the solid electrolyte containing anions in contact with the positive electrode active material. This oxidation reaction forms an oxidative decomposition layer with poor lithium ion conductivity between the positive electrode active material and the solid electrolyte, and it is thought that this oxidative decomposition layer functions as a large interfacial resistance in the electrode reaction at the positive electrode.

[0013] Patent Document 1 discloses a cathode material including a cathode active material and a halide solid electrolyte containing chlorine or bromine. In the cathode active material disclosed in Patent Document 1, the surface of the cathode active material is coated with a coating material, such as an oxide solid electrolyte, such as lithium niobate, to suppress the formation of the oxidative decomposition layer. Patent Document 1 discloses that by interposing a coating material between the cathode active material and the halide solid electrolyte, the oxidative decomposition reaction between the cathode active material and the halide solid electrolyte is suppressed, thereby suppressing the formation of the oxidative decomposition layer. However, even when the cathode active material is coated with a coating material, such as an oxide solid electrolyte, it is difficult to sufficiently suppress the oxidative decomposition reaction between the chlorine or bromine-containing halide solid electrolyte and the cathode active material. Therefore, even with the cathode material disclosed in Patent Document 1, the formation of the oxidative decomposition layer between the cathode active material and the solid electrolyte cannot be sufficiently suppressed.

[0014] Furthermore, Patent Document 2 discloses that a high-resistance layer is formed upon contact between a sulfide solid electrolyte and a positive electrode active material that exhibits an oxidation-reduction reaction at a potential of 3 V or higher, and that the formation of the high-resistance layer can be suppressed by coating the surface of the positive electrode active material with a lithium ion conductive oxide that does not have electronic conductivity. However, even when the surface of the positive electrode active material is coated with a lithium ion conductive oxide that does not have electronic conductivity, it is difficult to sufficiently suppress the formation of a high-resistance layer between the positive electrode active material and the solid electrolyte. Therefore, positive electrode materials using a sulfide solid electrolyte also have the problem of the formation of a high-resistance layer between the positive electrode active material and the solid electrolyte, similar to positive electrode materials using a halide solid electrolyte containing chlorine or bromine.

[0015] In order to suppress the oxidative decomposition of the solid electrolyte and to suppress the formation of a high-resistance layer between the positive electrode active material and the solid electrolyte, it is necessary to select a solid electrolyte with excellent oxidation resistance. On the other hand, in order to improve the output characteristics of the battery, it is necessary to select a solid electrolyte with high ionic conductivity. In a battery made of a single solid electrolyte, it has been difficult to simultaneously suppress the formation of a high-resistance layer and improve the output characteristics of the battery.

[0016] The present inventors have conducted extensive research to find a way to prevent the formation of a high-resistance layer between a positive electrode active material and a solid electrolyte. As a result, they have found that when a coating layer covering at least a portion of the surface of a positive electrode active material contains lithium (i.e., Li), zirconium (i.e., Zr), and fluorine (i.e., F), the oxidation reaction of the solid electrolyte is suppressed, and the formation of a high-resistance layer between the positive electrode active material and the solid electrolyte can be sufficiently prevented. Although the details of this mechanism are not clear, it is thought that when the coating layer contains fluorine, which has a high electronegativity, as an anion, it strongly bonds with cations made of metal elements or metalloid elements, making it difficult for the oxidation reaction of fluorine, i.e., a side reaction in which electrons are extracted from fluorine, to proceed.

[0017] Furthermore, the present inventors have found that a material containing lithium and zirconium as cations and fluorine as an anion has higher ionic conductivity than a solid electrolyte such as lithium fluoride (i.e., LiF) composed only of lithium and fluorine. Therefore, a battery using a positive electrode active material in which a coating layer containing lithium, zirconium, and fluorine is provided on the surface of the positive electrode active material can have even better output characteristics.

[0018] Furthermore, for example, in the case of a battery using a material with high ionic conductivity but poor oxidation resistance as the solid electrolyte, the surface of the positive electrode active material can be coated with the above-mentioned material containing lithium, zirconium, and fluorine, which has excellent oxidation resistance, thereby preventing direct contact between the positive electrode active material and the solid electrolyte. Furthermore, materials containing lithium, zirconium, and fluorine have high electronic resistance, which prevents direct electron transfer between the positive electrode active material and the solid electrolyte. This configuration prevents the formation of a high-resistance layer between the positive electrode active material and the solid electrolyte, enabling the use of a solid electrolyte with high ionic conductivity but poor oxidation resistance as the positive electrode material, thereby improving the output characteristics of the battery.

[0019] (Summary of one aspect of the present disclosure) The coated positive electrode active material according to the first aspect of the present disclosure is a positive electrode active material, and a coating layer that covers at least a portion of the surface of the positive electrode active material; Equipped with where: The coating layer contains Li, Zr and F.

[0020] The coated positive electrode active material according to the first aspect can prevent a high-resistance layer from being formed between the positive electrode active material and the solid electrolyte.

[0021] In a second aspect of the present disclosure, for example, in the coated positive electrode active material according to the first aspect, the material constituting the coating layer may be represented by the following composition formula (1): Li α Zr β Fγ ...Equation (1) Here, α, β, and γ satisfy 0<α<8, 0<β≦1.1, and 0<γ≦8.

[0022] The coated positive electrode active material according to the second aspect can improve the output characteristics of a battery.

[0023] In the third embodiment of the present disclosure, for example, in the coated positive electrode active material according to the second embodiment, the α, β, and γ may satisfy 0.35≦α≦4, 1≦β≦1.1, and 4.75≦γ≦8.

[0024] The coated positive electrode active material according to the third aspect can further improve the output characteristics of the battery.

[0025] In the fourth embodiment of the present disclosure, for example, in the coated positive electrode active material according to the third embodiment, the α, β, and γ may satisfy 3.6≦α≦4, 1≦β≦1.1, and γ=8.

[0026] The coated positive electrode active material according to the fourth aspect can further improve the output characteristics of the battery.

[0027] In the fifth embodiment of the present disclosure, for example, in the coated positive electrode active material according to the third embodiment, the α, β, and γ may satisfy 1.6≦α≦2, 1≦β≦1.1, and γ=6.

[0028] The coated positive electrode active material according to the fifth aspect can further improve the output characteristics of the battery.

[0029] In a sixth aspect of the present disclosure, for example, in the coated positive electrode active material according to any one of the first to fifth aspects, the ratio of the mass of the coating layer to the mass of the positive electrode active material may be in the range of 3 / 100 or more and 15 / 100 or less.

[0030] The coated positive electrode active material according to the sixth embodiment can effectively prevent a high-resistance layer from being formed between the positive electrode active material and the solid electrolyte.

[0031] In a seventh aspect of the present disclosure, for example, in the coated positive electrode active material according to the sixth aspect, the ratio of the mass of the coating layer to the mass of the positive electrode active material may be in the range of 7 / 100 or more and 10 / 100 or less.

[0032] The coated positive electrode active material according to the seventh embodiment can more effectively prevent a high-resistance layer from being formed between the positive electrode active material and the solid electrolyte.

[0033] In an eighth aspect of the present disclosure, for example, in the coated positive electrode active material according to any one of the first to seventh aspects, the coating layer may have an average thickness of 1 nm or more and 300 nm or less.

[0034] The coated positive electrode active material according to the eighth embodiment can effectively prevent a high-resistance layer from being formed between the positive electrode active material and the solid electrolyte.

[0035] In a ninth aspect of the present disclosure, for example, in the coated positive electrode active material according to the eighth aspect, the coating layer may have an average thickness of 2 nm or more and 200 nm or less.

[0036] The coated positive electrode active material according to the ninth embodiment can effectively prevent a high-resistance layer from being formed between the positive electrode active material and the solid electrolyte.

[0037] In a tenth aspect of the present 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-manganese oxide.

[0038] The coated positive electrode active material according to the tenth embodiment can increase the energy density of the battery.

[0039] The positive electrode material according to the eleventh aspect of the present disclosure comprises: A coated positive electrode active material according to any one of the first to tenth aspects, and A first solid electrolyte is included.

[0040] The positive electrode material according to the eleventh aspect can prevent a high-resistance layer from being formed between the positive electrode active material and the first solid electrolyte.

[0041] In a twelfth aspect of the present disclosure, for example, in the positive electrode material according to the eleventh aspect, the first solid electrolyte may include a halide solid electrolyte.

[0042] The positive electrode material according to the twelfth aspect can improve the output characteristics of a battery.

[0043] In a thirteenth aspect of the present disclosure, for example, in the positive electrode material according to the eleventh or twelfth aspect, the first solid electrolyte may include a sulfide solid electrolyte.

[0044] The positive electrode material according to the thirteenth aspect can improve the output characteristics of a battery.

[0045] A battery according to a fourteenth aspect of the present disclosure comprises: a positive electrode comprising the positive electrode material according to any one of the eleventh to thirteenth aspects; a negative electrode, and an electrolyte layer provided between the positive electrode and the negative electrode; Equipped with.

[0046] The battery according to the fourteenth aspect can prevent a high-resistance layer from being formed between the positive electrode active material and the first solid electrolyte.

[0047] In a fifteenth aspect of the present disclosure, for example, in the battery according to the fourteenth aspect, the electrolyte layer may include a second solid electrolyte, and the second solid electrolyte may include a solid electrolyte having the same composition as the solid electrolyte included in the first solid electrolyte.

[0048] The battery according to the fifteenth aspect can improve the output characteristics.

[0049] In a sixteenth aspect of the present disclosure, for example, in the battery according to the fourteenth aspect, the electrolyte layer may include a second solid electrolyte, and the second solid electrolyte may include a halide solid electrolyte having a different composition from the solid electrolyte included in the first solid electrolyte.

[0050] The battery according to the sixteenth aspect can improve the output characteristics.

[0051] In a seventeenth aspect of the present disclosure, for example, in the battery according to the fourteenth aspect, the electrolyte layer may include a second solid electrolyte, and the second solid electrolyte may include a sulfide solid electrolyte.

[0052] The battery according to the seventeenth aspect can improve the output characteristics.

[0053] A method for producing a coated positive electrode active material according to an eighteenth aspect of the present disclosure includes: A method for producing a coated positive electrode active material according to a first embodiment, The manufacturing method comprises: treating the positive electrode active material and a material constituting the coating layer by a dry particle compositing method; The dry particle composite method involves applying mechanical energy of impact, compression, and shear to the positive electrode active material and the material that constitutes the coating layer.

[0054] According to the production method of the eighteenth aspect, it is possible to produce a coated positive electrode active material that can prevent a high-resistance layer from being formed between the positive electrode active material and the solid electrolyte.

[0055] In a nineteenth aspect of the present disclosure, for example, in the manufacturing method according to the eighteenth aspect, a ratio Da / Dc of an average particle diameter Da of the positive electrode active material to an average particle diameter Dc of the material of the coating layer may be 2 or more.

[0056] According to the production method of the nineteenth aspect, it is possible to produce a coated positive electrode active material that can effectively prevent a high-resistance layer from being formed between the positive electrode active material and the solid electrolyte.

[0057] In a twentieth aspect of the present disclosure, for example, in the manufacturing method according to the nineteenth aspect, a ratio Da / Dc of an average particle diameter Da of the positive electrode active material to an average particle diameter Dc of the material of the coating layer may be 5 or more.

[0058] According to the production method of the twentieth aspect, it is possible to produce a coated positive electrode active material that can more effectively prevent a high-resistance layer from being formed between the positive electrode active material and the solid electrolyte.

[0059] (Embodiment 1) (Coated positive electrode active material) The coated positive electrode active material in the first embodiment includes a positive electrode active material and a coating layer that coats at least a portion of the surface of the positive electrode active material. The coating layer includes lithium (i.e., Li), zirconium (i.e., Zr), and fluorine (i.e., F). That is, the coating layer is composed of a material that includes Li, Zr, and F. Hereinafter, the material that composes the coating layer will be referred to as the "coating material." In other words, the coated positive electrode active material in the first embodiment includes a positive electrode active material and a coating material, and the coating material is located on at least a portion of the surface of the positive electrode active material to form the coating layer.

[0060] According to the above configuration, the coated positive electrode active material in the first embodiment can prevent a high-resistance layer from being formed between the positive electrode active material and the solid electrolyte.

[0061] The coating material in the first embodiment may be represented by the following composition formula (1). Li α Zr β F γ ...Equation (1) Here, α, β, and γ satisfy 0<α<8, 0<β≦1.1, and 0<γ≦8.

[0062] When the coating material is represented by composition formula (1), the ionic conductivity of the coating material is further improved, thereby enabling the coated positive electrode active material of embodiment 1 to improve the output characteristics of the battery.

[0063] In the compositional formula (1), 0.35 ≦ α ≦ 4, 1 ≦ β ≦ 1.1, and 4.75 ≦ γ ≦ 8 may be satisfied.

[0064] According to the above configuration, the ionic conductivity of the coating material can be further improved. Thereby, the coated positive electrode active material in Embodiment 1 can further improve the output characteristics of the battery.

[0065] In the compositional formula (1), 3.6 ≦ α ≦ 4, 1 ≦ β ≦ 1.1, and γ = 8 may be satisfied.

[0066] According to the above configuration, the ionic conductivity of the coating material can be further improved. Thereby, the coated positive electrode active material in Embodiment 1 can further improve the output characteristics of the battery.

[0067] Also, in the compositional formula (1), 1.6 ≦ α ≦ 2, 1 ≦ β ≦ 1.1, and γ = 6 may be satisfied.

[0068] According to the above configuration, the ionic conductivity of the coating material can be further improved. Thereby, the coated positive electrode active material in Embodiment 1 can further improve the output characteristics of the battery.

[0069] Note that the coating material may be a material represented by the following compositional formula (A1). Li 8-4d Zr d F8 ··· Formula (A1) Here, in the compositional formula (A1), d satisfies 0 < d < 1.

[0070] According to the above configuration, the ionic conductivity of the coating material can be further improved. Thereby, the coated positive electrode active material in Embodiment 1 can further improve the output characteristics of the battery.

[0071] Note that the coating material may be a material represented by the following compositional formula (A2). Li4ZrF8 ··· Formula (A2)

[0072] According to the above configuration, the ionic conductivity of the coating material can be further improved. Thereby, the coated positive electrode active material in Embodiment 1 can further improve the output characteristics of the battery.

[0073] The coating material may be a material represented by the following compositional formula (A3). Li 4-4δ Zr 1+δ F8 ··· Formula (A3) Here, in the compositional formula (A3), 0 < δ ≦ 0.1 is satisfied.

[0074] According to the above configuration, the ionic conductivity of the coating material can be further improved. Thereby, the coated positive electrode active material in Embodiment 1 can further improve the output characteristics of the battery.

[0075] The coating material may be a material represented by the following compositional formula (B1). Li 6-4d Zr d F6 ··· Formula (B1) Here, in the compositional formula (B1), 0 < d < 1 is satisfied.

[0076] According to the above configuration, the ionic conductivity of the coating material can be further improved. Thereby, the coated positive electrode active material in Embodiment 1 can further improve the output characteristics of the battery.

[0077] The coating material may be a material represented by the following compositional formula (B2). Li2ZrF6 ··· Formula (B2)

[0078] According to the above configuration, the ionic conductivity of the coating material can be further improved. Thereby, the coated positive electrode active material in Embodiment 1 can further improve the output characteristics of the battery.

[0079] The coating material may be a material represented by the following compositional formula (B3). Li2-4δ Zr 1+δ F6...Formula (B3) Here, in the composition formula (B3), 0<δ≦0.1 is satisfied.

[0080] According to the above configuration, the ionic conductivity of the coating material can be further improved, and the coated positive electrode active material according to the first embodiment can thereby further improve the output characteristics of the battery.

[0081] The "coating material" in this disclosure is not limited to materials that strictly satisfy the above composition formula, but also includes materials that contain trace amounts of impurities other than the constituent elements represented by the composition formula. For example, the impurities contained in the coating material other than the constituent elements represented by the composition formula may be 10 mass% or less. Note that the coating material does not have to contain sulfur.

[0082] The mass ratio of the coating layer to the mass of the positive electrode active material may be in the range of 3 / 100 or more and 15 / 100 or less. If the mass ratio of the coating layer is 3 / 100 or more, the proportion of the coating material covering the surface of the positive electrode active material is sufficiently high, so that the coating layer can effectively suppress the formation of a high-resistance layer. Furthermore, if the mass ratio of the coating layer is 15 / 100 or less, the coating material covering the surface of the positive electrode active material does not inhibit electron exchange between the positive electrode active materials, so that the output characteristics of the battery can be improved.

[0083] According to the above configuration, the coated positive electrode active material in the first embodiment can effectively prevent a high-resistance layer from being formed between the coated positive electrode active material and the solid electrolyte.

[0084] The mass ratio of the coating layer to the mass of the positive electrode active material may be in the range of 7 / 100 or more and 10 / 100 or less. If the mass ratio of the coating layer is 7 / 100 or more, the proportion of the coating material covering the surface of the positive electrode active material is sufficiently high, so that the coating layer can effectively suppress the formation of a high-resistance layer. Furthermore, if the mass ratio of the coating layer is 10 / 100 or less, the coating material covering the surface of the positive electrode active material does not inhibit electron exchange between the positive electrode active materials, so that the output characteristics of the battery can be improved.

[0085] According to the above configuration, the coated positive electrode active material in the first embodiment can effectively prevent a high-resistance layer from being formed between the coated positive electrode active material and the solid electrolyte.

[0086] The average thickness of the coating layer may be, for example, in the range of 1 nm or more and 300 nm or less. When the average thickness of the coating layer is 1 nm or more, the proportion of the coating material covering the surface of the positive electrode active material is sufficiently high, so that the coating layer can effectively suppress the formation of a high-resistance layer. When the average thickness of the coating layer is 300 nm or less, the coating material covering the surface of the positive electrode active material does not inhibit electron exchange between the positive electrode active material, so that the output characteristics of the battery can be improved. The average thickness of the coating layer can be determined, for example, by measuring the thickness of the coating layer at any 16 points on a cross-sectional SEM image of the coated positive electrode active material obtained using a scanning electron microscope (SEM) and calculating the average value from these measurements. The average film thickness of the coating layer may be in the range of 2 nm or more and 200 nm or less.

[0087] According to the above configuration, the coated positive electrode active material in the first embodiment can effectively prevent a high-resistance layer from being formed between the coated positive electrode active material and the solid electrolyte.

[0088] (Method of manufacturing coating material) The coating material in the first embodiment can be produced, for example, by the following method.

[0089] Prepare raw material powders with the desired composition ratio. For example, to produce Li4ZrF8, prepare LiF and ZrF4 in a 4:1 molar ratio. In addition, the above-mentioned values ​​"α", "β", "γ", "d", and "δ" can be adjusted by adjusting the raw materials, composition ratio, and synthesis process.

[0090] After thoroughly mixing the raw material powders, the raw material powders are mixed, pulverized, and reacted using a mechanochemical milling method. Alternatively, after thoroughly mixing the raw material powders, the mixed powder may be fired in a vacuum or in an inert atmosphere. The firing conditions may be, for example, within a range of 100°C or higher and 650°C or lower, for one hour or longer. This results in a coating material having the composition described above.

[0091] The constitution of the crystalline phase (crystalline structure) in the coating material can be determined by adjusting the reaction method and reaction conditions of the raw material powders.

[0092] (Cathode active material) The positive electrode active material is, for example, a material that has the property of absorbing and releasing metal ions (e.g., lithium ions). Examples of the positive electrode active material include lithium-containing transition metal oxides, transition metal fluorides, polyanion materials, fluorinated polyanion materials, transition metal sulfides, transition metal oxysulfides, and transition metal oxynitrides. Examples of lithium-containing transition metal oxides include Li(Ni,Co,Al)O2, Li(Ni,Co,Mn)O2, and LiCoO2. When a lithium-containing transition metal oxide is used as the positive electrode active material, the manufacturing cost of the positive electrode can be reduced and the average discharge voltage can be increased.

[0093] To increase the energy density of the battery, the positive electrode active material may be lithium nickel-cobalt-manganese oxide, for example, Li(Ni,Co,Mn)O2.

[0094] In the first embodiment, the positive electrode active material may be a positive electrode active material having a coating containing, for example, lithium metal oxide provided on its surface. That is, a coating made of, for example, lithium metal oxide may be provided between the positive electrode active material and the coating layer. For example, LiNbO3 (lithium niobate) may be used as the lithium metal oxide. By providing a coating containing a lithium metal oxide such as LiNbO3 on the surface of the positive electrode active material, side reactions between the positive electrode active material and the coating layer during charging are suppressed. Therefore, according to this configuration, the coated positive electrode active material in the first embodiment can effectively suppress the formation of a high-resistance layer on the surface of the positive electrode active material.

[0095] (Method of manufacturing coated positive electrode active material) The method for producing the coated positive electrode active material in the first embodiment includes, for example, processing the positive electrode active material and the material constituting the coating layer (i.e., the coating material) by a dry particle compositing method. The dry particle compositing method includes applying mechanical energy of impact, compression, and shear to the positive electrode active material and the coating material. The positive electrode active material and the coating material are mixed at an appropriate blending ratio.

[0096] The apparatus that can be used in the method for producing a coated positive electrode active material is not particularly limited as long as it is an apparatus that can impart mechanical energy such as impact, compression, and shear to the mixture, but examples include a ball mill, and a compression shear processing apparatus (particle composite apparatus) such as "Mechanofusion" (manufactured by Hosokawa Micron Corporation) or "Nobilta" (manufactured by Hosokawa Micron Corporation). Among these, "Mechanofusion" and "Nobilta" are more preferred, and "Nobilta" is even more preferred.

[0097] "Mechanofusion" is a particle compounding device that uses dry mechanical compounding technology by applying strong mechanical energy to particles of multiple different materials. In mechanofusion, powder raw materials are fed between a rotating container and a press head, and mechanical energy such as compression, shear, and friction is applied to them, causing the particles to compound.

[0098] "Nobilta" is a particle compounding device that uses dry mechanical compounding technology, an advanced form of particle compounding technology, to compound nanoparticles as raw materials. Nobilta produces composite particles by applying mechanical energy of impact, compression, and shear to multiple raw material powders.

[0099] Nobilta uses a rotor that rotates at high speed in a horizontal cylindrical mixing vessel, positioned with a specified gap between it and the inner wall of the vessel. This process of forcing the raw material powder through the gap is repeated multiple times, applying impact, compression, and shear forces to the mixture, producing composite particles of positive electrode active material and coating material. Conditions such as rotor rotation speed, processing time, and feed amounts can be adjusted as needed.

[0100] The ratio Da / Dc of the average particle size Da of the positive electrode active material to the average particle size Dc of the coating material used in the method for producing a coated positive electrode active material may be 2 or greater. When the ratio Da / Dc is 2 or greater, the surface of the positive electrode active material is more likely to be densely coated with the coating material, making it possible to produce a coated positive electrode active material that can effectively suppress an oxidation reaction between the positive electrode active material and the solid electrolyte. Therefore, the method for producing a coated positive electrode active material in embodiment 1 makes it possible to produce a coated positive electrode active material that can efficiently suppress the formation of a high-resistance layer between the positive electrode active material and the solid electrolyte.

[0101] The ratio Da / Dc of the average particle size Da of the positive electrode active material to the average particle size Dc of the coating material used in the method for producing a coated positive electrode active material may be 5 or greater. When the ratio Da / Dc is 5 or greater, the surface of the positive electrode active material is more likely to be more densely coated with the coating material, making it possible to produce a coated positive electrode active material that can more effectively suppress the oxidation reaction between the positive electrode active material and the solid electrolyte. Therefore, when the ratio Da / Dc is 5 or greater, the method for producing a coated positive electrode active material in embodiment 1 can produce a coated positive electrode active material that can efficiently suppress the formation of a high-resistance layer between the positive electrode active material and the solid electrolyte.

[0102] The average particle size of the positive electrode active material and the coating material can be measured, for example, using SEM images. Specifically, the average particle size of the positive electrode active material and the coating material can be determined by calculating the average circle-equivalent diameters of 50 randomly selected particles of the positive electrode active material and 50 randomly selected particles of the coating material using SEM images.

[0103] (cathode material) FIG. 1 is a cross-sectional view showing a schematic configuration of a positive electrode material according to the first embodiment.

[0104] The cathode material 1000 according to the first embodiment includes the coated cathode active material 100 according to the first embodiment described above, and a first solid electrolyte 103. The coated cathode active material 100 includes a cathode active material 101 and a coating layer 102 that coats at least a portion of the surface of the cathode active material 101.

[0105] The first solid electrolyte 103 includes, for example, a solid electrolyte with high ionic conductivity.

[0106] The first solid electrolyte 103 may include a halide solid electrolyte. 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 solid electrolytes, the element X is at least one element selected from the group consisting of Cl, Br, and I. In this disclosure, when an element in a formula is expressed as "(Al,Ga,In)," this notation indicates at least one element selected from the group of elements in parentheses. In other words, "(Al,Ga,In)" is synonymous with "at least one element selected from the group consisting of Al, Ga, and In." The same applies to other elements.

[0107] The first solid electrolyte 103 may include a sulfide solid electrolyte. Examples of sulfide solid electrolytes include Li2S-P2S5, Li2S-SiS2, Li2S-B2S3, Li2S-GeS2, and Li 3.25 Ge 0.25 P 0.75S4, Li 10 GeP2S 12 , etc., can be used. In addition to these, LiX, LiO, MO q , and / or Li p MO q The element X in "LiX" is one or more elements selected from the group consisting of F, Cl, Br, and I. q " and "Li p MO q " element M is one or more elements selected from the group consisting of P, Si, Ge, B, Al, Ga, In, Fe, and Zn. q " and "Li p MO q " p and q in this expression are independent natural numbers.

[0108] The first solid electrolyte 103 may be a sulfide solid electrolyte. For example, the sulfide solid electrolyte may contain lithium sulfide and phosphorus sulfide. For example, the sulfide solid electrolyte may be Li2S-P2S5.

[0109] The shape of first solid electrolyte 103 is not particularly limited and may be, for example, needle-like, spherical, oval-spherical, etc. For example, first solid electrolyte 103 may have the shape of particles.

[0110] For example, when the first solid electrolyte 103 is particulate (e.g., spherical), the median diameter of the first solid electrolyte 103 may be 100 μm or less. When the median diameter of the first solid electrolyte 103 is 100 μm or less, the coated cathode active material 100 and the first solid electrolyte 103 can be well dispersed in the cathode material 1000. This improves the charge / discharge characteristics of a battery using the cathode material 1000.

[0111] The median diameter of the first solid electrolyte 103 may be 10 μm or less. With this configuration, in the positive electrode material 1000, the coated positive electrode active material 100 and the first solid electrolyte 103 can be in a better dispersed state.

[0112] The median diameter of first solid electrolyte 103 may be smaller than the median diameter of coated cathode active material 100. This configuration allows coated cathode active material 100 and first solid electrolyte 103 to form a better dispersed state in cathode material 1000.

[0113] The median diameter of the coated positive electrode active material 100 may be 0.1 μm or more and 100 μm or less.

[0114] When the median diameter of the coated cathode active material 100 is 0.1 μm or more, the coated cathode active material 100 and the first solid electrolyte 103 can be well dispersed in the cathode material 1000. As a result, the charge / discharge characteristics of a battery using the cathode material 1000 are improved. Furthermore, when the median diameter of the coated cathode active material 100 is 100 μm or less, the lithium diffusion rate within the coated cathode active material 100 is improved. As a result, a battery using the cathode material 1000 can operate at high power.

[0115] The median diameter means the particle size when the cumulative volume in the volume-based particle size distribution is equal to 50%. The volume-based particle size distribution is measured, for example, by a laser diffraction measuring device or an image analyzer.

[0116] In the positive electrode material 1000 according to the first embodiment, the first solid electrolyte 103 and the coating layer 102 may be in contact with each other, as shown in Fig. 1. In this case, the coating layer 102 and the positive electrode active material 101 are in contact with each other.

[0117] Moreover, the positive electrode material 1000 in the first embodiment may include a plurality of first solid electrolytes 103 and a plurality of coated positive electrode active materials 100 .

[0118] In addition, in the cathode material 1000 of the first embodiment, the content of the first solid electrolyte 103 and the content of the coated cathode active material 100 may be the same as or different from each other.

[0119] (Embodiment 2) The following describes the second embodiment. Explanations that overlap with the first embodiment will be omitted where appropriate.

[0120] FIG. 2 is a cross-sectional view showing a schematic configuration of a battery according to the second embodiment.

[0121] The battery 2000 in the second embodiment includes a positive electrode 201 containing the positive electrode material 1000 described in the first embodiment above, an electrolyte layer 202, and a negative electrode 203.

[0122] The positive electrode 201 includes a material having the property of absorbing and releasing metal ions (for example, lithium ions). The positive electrode 201 includes a coated positive electrode active material 100 and a first solid electrolyte 103.

[0123] When the volume ratio of the positive electrode active material 101 contained in the positive electrode 201 to the total volume of the coating layer 102 and the first solid electrolyte 103 is "v1:100-v1," 30≦v1≦95 may be satisfied. Here, v1 represents the volume fraction of the positive electrode active material 101 when the total volume of the positive electrode active material 101, the coating layer 102, and the first solid electrolyte 103 contained in the positive electrode 201 is taken as 100. When 30≦v1 is satisfied, it is easy to ensure a sufficient energy density of the battery 2000. When v1≦95 is satisfied, it is easier for the battery 2000 to operate at high output.

[0124] The thickness of the positive electrode 201 may be 10 μm or more and 500 μm or less. When the thickness of the positive electrode 201 is 10 μm or more, a sufficient energy density of the battery 2000 can be ensured. When the thickness of the positive electrode 201 is 500 μm or less, high-power operation of the battery 2000 can be achieved.

[0125] The electrolyte layer 202 is disposed between the positive electrode 201 and the negative electrode 203 .

[0126] The electrolyte layer 202 is a layer containing an electrolyte material. The electrolyte material may contain, for example, a second solid electrolyte material. That is, the electrolyte layer 202 may be a solid electrolyte layer.

[0127] The second solid electrolyte included in the electrolyte layer 202 may be a halide solid electrolyte, a sulfide solid electrolyte, an oxide solid electrolyte, a polymer solid electrolyte, or a complex hydride solid electrolyte.

[0128] The second solid electrolyte may include a solid electrolyte having the same composition as the solid electrolyte included in the first solid electrolyte.

[0129] For example, when 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 in embodiment 1. That is, electrolyte layer 202 may include a halide solid electrolyte having the same composition as the halide solid electrolyte included in the first solid electrolyte in embodiment 1 described above.

[0130] According to the above configuration, the output characteristics of the battery 2000 can be further improved.

[0131] Furthermore, the second solid electrolyte contained in electrolyte layer 202 may contain a halide solid electrolyte having a composition different from that of the halide solid electrolyte contained in the first solid electrolyte in embodiment 1. That is, electrolyte layer 202 may contain a halide solid electrolyte having a composition different from that of the halide solid electrolyte contained in the first solid electrolyte in embodiment 1 described above.

[0132] According to the above configuration, the output characteristics of the battery 2000 can be further improved.

[0133] The second solid electrolyte included in electrolyte layer 202 may include a sulfide solid electrolyte. The second solid electrolyte may include a sulfide solid electrolyte having the same composition as the sulfide solid electrolyte included in the first solid electrolyte of embodiment 1. That is, electrolyte layer 202 may include a sulfide solid electrolyte having the same composition as the sulfide solid electrolyte included in the first solid electrolyte of embodiment 1 described above.

[0134] According to the above configuration, since the electrolyte layer 202 contains a sulfide solid electrolyte having excellent reduction stability, a low-potential negative electrode material such as graphite or metallic lithium can be used for the negative electrode 203. This can improve the energy density of the battery 2000. Furthermore, according to the configuration in which the electrolyte layer 202 contains the same sulfide solid electrolyte as the sulfide solid electrolyte contained in the first solid electrolyte in the first embodiment, the output characteristics of the battery 2000 can be further improved.

[0135] The second solid electrolyte contained in the electrolyte layer 202 may include an oxide solid electrolyte. Examples of the oxide solid electrolyte contained in the electrolyte layer 202 include NASICON-type solid electrolyte materials such as LiTi2(PO4)3 and its element substitution products, (LaLi)TiO3-based perovskite-type solid electrolyte materials, and Li 14 ZnGeO 16 LISICON-type solid electrolyte materials, such as Li4SiO4, LiGeO4 and their elemental substitution products, Li7La3Zr2O 12 Garnet-type solid electrolyte materials, such as those typified by element substitution products thereof, Li3PO4 and its N-substituted products, glasses based on Li-BO compounds such as LiBO2 and Li3BO3 and to which Li2SO4, Li2CO3, etc. are added, and glass ceramics can be used.

[0136] The second solid electrolyte contained in the electrolyte layer 202 may include a polymer solid electrolyte. The polymer solid electrolyte contained in the electrolyte layer 202 may be, for example, a compound of a polymer compound and a lithium salt. The polymer compound may have an ethylene oxide structure. A polymer compound having an ethylene oxide structure can contain a large amount of lithium salt. This can further increase ionic conductivity. Examples of the lithium salt that may be used include LiPF6, LiBF4, LiSbF6, LiAsF6, LiSO3CF3, LiN(SO2F)2, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiN(SO2CF3)(SO2C4F9), and LiC(SO2CF3)3. One type of lithium salt may be used alone, or two or more types may be used in combination.

[0137] The second solid electrolyte included in the electrolyte layer 202 may include a complex hydride solid electrolyte. Examples of the complex hydride solid electrolyte included in the electrolyte layer 202 include LiBH—LiI and LiBH—P—S.

[0138] The electrolyte layer 202 may contain the second solid electrolyte as a main component, i.e., the electrolyte layer 202 may contain the second solid electrolyte in a mass ratio of 50% or more (i.e., 50 mass% or more) relative to the entire electrolyte layer 202.

[0139] According to the above configuration, the output characteristics of the battery 2000 can be further improved.

[0140] Furthermore, the electrolyte layer 202 may contain the second solid electrolyte in a mass ratio relative to the entire electrolyte layer 202 of 70% or more (ie, 70 mass % or more).

[0141] According to the above configuration, the output characteristics of the battery 2000 can be further improved.

[0142] The electrolyte layer 202 contains the second solid electrolyte as a main component, and may further contain unavoidable impurities, or starting materials, by-products, and decomposition products used in synthesizing the second solid electrolyte.

[0143] Furthermore, the electrolyte layer 202 may contain the second solid electrolyte in a mass ratio of 100% (ie, 100% by weight) relative to the entire electrolyte layer 202, excluding unavoidable impurities, for example.

[0144] According to the above configuration, the output characteristics of the battery 2000 can be further improved.

[0145] As described above, the electrolyte layer 202 may be composed of only the second solid electrolyte.

[0146] The electrolyte layer may contain two or more of the materials listed as solid electrolyte materials. For example, the electrolyte layer may contain a halide solid electrolyte and a sulfide solid electrolyte.

[0147] 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 short-circuiting between the positive electrode 201 and the negative electrode 203 is reduced. Furthermore, when the thickness of the electrolyte layer 202 is 300 μm or less, high-power operation is facilitated. In other words, if the thickness of the electrolyte layer 202 is appropriately adjusted, sufficient safety of the battery 2000 can be ensured, and the battery 2000 can be operated at high power.

[0148] The negative electrode 203 includes a material having the property of absorbing and releasing metal ions (for example, lithium ions) and includes, for example, a negative electrode active material (for example, negative electrode active material particles).

[0149] The negative electrode active material may be a metal material, a carbon material, an oxide, a nitride, a tin compound, or a silicon compound. The metal material may be a simple metal. Alternatively, the metal material may be an alloy. Examples of the metal material include lithium metal or a lithium alloy. Examples of the carbon material include natural graphite, coke, partially graphitized carbon, carbon fiber, spherical carbon, artificial graphite, and amorphous carbon. From the viewpoint of capacity density, silicon, tin, a silicon compound, or a tin compound can be preferably used.

[0150] The negative electrode 203 may contain a third solid electrolyte. This configuration improves the lithium ion conductivity inside the negative electrode, enabling high-power operation. The third solid electrolyte contained in the negative electrode 203 can be any of the materials listed as examples of the second solid electrolyte of the electrolyte layer 202.

[0151] The median diameter of the negative electrode active material particles may be larger than the median diameter of the third solid electrolyte contained in the negative electrode 203. This allows the negative electrode active material and the third solid electrolyte to be well dispersed.

[0152] The volume ratio "v2:100-v2" of the negative electrode active material to the third solid electrolyte contained in the negative electrode 203 may satisfy 30≦v2≦95. Here, v2 indicates 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 taken as 100. When 30≦v2 is satisfied, it is easy to ensure a sufficient energy density of the battery 2000. When v2≦95 is satisfied, it is easier for the battery 2000 to operate at high output.

[0153] 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 is easy to ensure a sufficient energy density of the battery 2000. When the thickness of the negative electrode 203 is 500 μm or less, it is easier for the battery 2000 to operate at high power.

[0154] At least one selected from the group consisting of the positive electrode 201, the electrolyte layer 202, and the negative electrode 203 may contain a binder to improve adhesion between particles. The binder is used to improve the binding of the materials constituting the electrode. Examples of binders include polyvinylidene fluoride, polytetrafluoroethylene, polyethylene, polypropylene, aramid resin, polyamide, polyimide, polyamideimide, polyacrylonitrile, polyacrylic acid, polymethyl ester of acrylic acid, polyethyl ester of acrylic acid, polyhexyl ester of acrylic acid, polymethacrylic acid, polymethyl ester of methacrylic acid, polyethyl ester of methacrylic acid, polyhexyl ester of methacrylic acid, polyvinyl acetate, polyvinylpyrrolidone, polyether, polyethersulfone, hexafluoropolypropylene, styrene-butadiene rubber, and carboxymethyl cellulose. The binder may be 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. Alternatively, a mixture of two or more materials selected from these may be used as the binder.

[0155] At least one of the positive electrode 201 and the negative electrode 203 may contain a conductive additive to enhance electronic conductivity. Examples of conductive additives that can be used include graphites such as natural graphite or artificial graphite, carbon blacks such as acetylene black or ketjen black, conductive fibers such as carbon fiber or metal fiber, metal powders such as carbon fluoride or 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, or polythiophene. Using a carbon conductive additive can reduce costs.

[0156] The battery 2000 in the second embodiment can be configured as a battery of various shapes, such as a coin type, a cylindrical type, a square type, a sheet type, a button type, a flat type, or a laminated type.

[0157] The battery 2000 in the second embodiment may be manufactured, for example, by preparing the positive electrode material, the material for forming the electrolyte layer, and the material for forming the negative electrode in the first embodiment, and by using a known method to fabricate a laminate in which the positive electrode, the electrolyte layer, and the negative electrode are arranged in this order. [Example]

[0158] The present disclosure will now be described in more detail using examples.

[0159] Examples 1a to 1f [Preparation of coating material] In a glove box with an argon atmosphere and a dew point of -60°C or less and an oxygen concentration of 5 ppm or less, raw material powders of LiF and ZrF were weighed out to a molar ratio of LiF:ZrF = 4:1. These raw material powders were mixed in an agate mortar to obtain a mixture. Next, a planetary ball mill (Fritsch, Model P-7) was used to mill the mixture at 600 rpm for 12 hours to obtain a compound represented by the formula Li4ZrF8 (hereinafter referred to as LZF). The compound LZF was then pulverized in the agate mortar to obtain a powder coating material with an average particle size of 5 μm. The average particle size of the coating material was the median diameter, and was obtained by calculating the average circle-equivalent diameter of 50 randomly selected particles of the coating material observed at 5000x magnification using a scanning electron microscope (Keyence, 3D Real Surface View Microscope, VE-8800).

[0160] [Cathode active material] As the positive electrode active material, Li(Ni,Co,Mn)O2 (hereinafter referred to as NCM) with an average particle size of 5 μm was used.

[0161] [Preparation of coated positive electrode active material] Coating of the positive electrode active material with the coating material was performed using a particle compositer (Nobilta, NOB-MINI, manufactured by Hosokawa Micron Corporation). 50 g of NCM and 1.5 g (Example 1a), 2.0 g (Example 1b), 2.5 g (Example 1c), 3.5 g (Example 1d), 5.0 g (Example 1e), or 7.5 g (Example 1f) of LZF powder were placed in the NOB-MINI container. The coated positive electrode active materials of Examples 1a to 1f were prepared by composite processing of the NCM and LZF at a rotation speed of 5,000 to 6,000 rpm, an operating time of 15 minutes, and a power of 640 W.

[0162] [Battery construction] The following steps were carried out using the coated positive electrode active materials of Examples 1a to 1f described above.

[0163] In a glove box with an argon atmosphere having a dew point of -60°C or less and an oxygen level of 5 ppm or less, the coated positive electrode active material of any one of Examples 1a to 1f and the first solid electrolyte Li2S-P2S5 were weighed out so that the volume ratio of the positive electrode active material to the coating layer and the first solid electrolyte was 60:40. These were mixed in an agate mortar to produce the positive electrode materials of Examples 1a to 1f.

[0164] 80 mg of Li2S-P2S5 was added as a second solid electrolyte to the insulating outer cylinder, and the mixture was press-molded at a pressure of 80 MPa to obtain an electrolyte layer. Next, 14 mg of any of the positive electrode materials from Examples 1a to 1f, equivalent to the positive electrode active material, was added, and the mixture was press-molded at a pressure of 720 MPa to obtain a positive electrode layer. Next, metal In (200 μm thick), metal Li (300 μm thick), and metal In (200 μm thick) were stacked in this order on the electrolyte layer on the counter electrode side. This was press-molded at a pressure of 80 MPa to obtain a negative electrode layer. Next, stainless steel current collectors were placed above and below the stack, and current collecting leads were attached to the current collectors. Finally, an insulating ferrule was used to isolate the interior of the insulating outer cylinder from the ambient atmosphere and seal it, thereby producing a battery. The inner diameter of the insulating outer cylinder used in this example was 9.5 mm, and the projected area of ​​the electrode was 0.71 cm2. 2 It was.

[0165] [Battery evaluation] Using the batteries of Examples 1a to 1f described above, battery evaluation was carried out under the following conditions.

[0166] The batteries of Examples 1a to 1f were placed in a thermostatic chamber at 25°C.

[0167] The battery was charged at a constant current of 140 μA, corresponding to a 0.05 C rate (20-hour rate) relative to the theoretical capacity of the battery, and the charge was terminated at a voltage of 3.68 V (corresponding to 4.3 V in terms of the Li / Li+ reference voltage). Next, the battery was charged at a constant voltage of 3.68 V, and the charge was terminated when the current reached 28 μA or less, corresponding to a 0.01 C rate. After charging, the interfacial resistance between the coated positive electrode active material and the first solid electrolyte was determined by impedance measurement using an AC impedance method. The impedance measurement conditions were a voltage amplitude of 5 mV, a measurement frequency of 1 MHz to 0.1 Hz, and 25°C. The results are shown in Table 1. The battery was then stored in an open-circuit state for 3 days. Next, the battery was discharged at a current of 140 μA, corresponding to a 0.05 C rate, and the discharge was terminated at a voltage of 1.88 V (corresponding to 2.5 V in terms of the Li / Li+ reference voltage).

[0168] As a result, the discharge capacity and capacity efficiency of Examples 1a to 1f were obtained. Capacity efficiency is the ratio of discharge capacity to charge capacity. The results are shown in Table 1 below.

[0169] Example 1g A coated positive electrode active material and a battery were produced in the same manner as in Example 1e, except that LZF having an average particle size of 0.8 μm was used instead of LZF having an average particle size of 5 μm.

[0170] (Comparative Example 1) A battery was fabricated in the same manner as in Examples 1a to 1g, except that a positive electrode active material without a coating layer was used as the positive electrode material.

[0171] Battery evaluation was carried out under the same conditions as in Examples 1a to 1g using the batteries of Example 1g and Comparative Example 1. The results are shown in Table 1 below.

[0172] [Table 1]

[0173] As can be seen from Table 1, the batteries of Examples 1a to 1g exhibited higher discharge capacities and capacity efficiencies than the battery of Comparative Example 1. Furthermore, the batteries of Examples 1d to 1g exhibited particularly higher discharge capacities and capacity efficiencies than the battery of Comparative Example 1. Furthermore, the batteries of Examples 1a to 1f exhibited lower interfacial resistance than the battery of Comparative Example 1. Furthermore, Example 1g exhibited an even higher discharge capacity than Example 1e. Furthermore, Example 1g exhibited an even lower interfacial resistance than Example 1e. When the ratio (Da / Dc) of the median diameter Da of the positive electrode active material used in the coating step to the median diameter Dc of the coating material is 5 or greater, the coating layer is densely formed on the surface of the positive electrode active material, thereby reducing the contact resistance of lithium ions between the surface of the positive electrode active material and the coating layer. This effectively suppresses the oxidation reaction between the positive electrode active material and the first solid electrolyte, and more efficiently suppresses the formation of a high-resistance layer between the positive electrode active material and the first solid electrolyte.

[0174] Example 2 In a glove box with an argon atmosphere having a dew point of -60°C or less and an oxygen level of 5 ppm or less, raw material powders of LiF and ZrF4 were weighed out so that the molar ratio of LiF:ZrF4 was 2:1. These raw material powders were mixed in an agate mortar to obtain a mixture. A compound represented by the formula Li2ZrF6 was obtained using the same procedure as in Examples 1a to 1f. The compound was pulverized in the agate mortar to obtain a powder coating material with an average particle size of 5 μm. A coated positive electrode active material and a battery were fabricated using the same procedure as in Example 1c.

[0175] (Comparative Example 2) A coated positive electrode active material and a battery were produced in the same manner as in Example 1c, except that LiF was used as the coating material instead of LZF.

[0176] Battery evaluation was carried out under the same conditions as in Examples 1a to 1g using the batteries of Example 2 and Comparative Example 2. The results are shown in Table 2 below.

[0177] [Table 2]

[0178] As can be seen from Table 2, the battery of Example 2 exhibited higher discharge capacity and capacity efficiency than the battery of Comparative Example 2. Furthermore, the battery of Example 2 exhibited lower interfacial resistance than the battery of Comparative Example 2. A comparison of the batteries of Examples 1a to 1f and Example 2 with the battery of Comparative Example 2 reveals that the formation of a high-resistance layer between the positive electrode active material and the solid electrolyte can be efficiently suppressed by using a coating material containing lithium, zirconium, and fluorine. Furthermore, when the coating material is represented by composition formula (1) and α, β, and γ satisfy the ranges 0.35≦α≦4, 1≦β≦1.1, and 4.75≦γ≦8, the formation of a high-resistance layer between the positive electrode active material and the solid electrolyte can be more efficiently suppressed.

[0179] Example 3 A battery was fabricated in the same manner as in Example 1g, except that Li3YBr2Cl4 was used as the first solid electrolyte of the positive electrode material, and 2 mass % of a conductive additive (VGCF-H, manufactured by Showa Denko K.K.) was further added to the positive electrode active material.

[0180] (Comparative Example 3) A battery was fabricated in the same manner as in Comparative Example 1, except that Li3YBr2Cl4 was used as the first solid electrolyte of the positive electrode material, and 2 wt % of a conductive additive (VGCF-H) was further added to the positive electrode active material.

[0181] Battery evaluation was carried out under the same conditions as in Example 1g using the batteries of Example 3 and Comparative Example 3. The results are shown in Table 3 below.

[0182] As can be seen from Table 3, even when a halide solid electrolyte is used as the first solid electrolyte of the positive electrode material, the battery of Example 3 is able to suppress the formation of a high-resistance layer between the positive electrode active material and the solid electrolyte compared to the battery of Comparative Example 3.

[0183] [Table 3]

[0184] Example 4 The positive electrode active material is LiNi with an average particle size of 4 μm. 0.5 Mn 1.5 A coated positive electrode active material and a battery were produced using the same procedure as in Example 1g, except that O4 was used, Li3YBr2Cl4 was used as the first solid electrolyte, and 2 mass% of a conductive additive (VGCF-H) was added to the positive electrode active material.

[0185] Comparative Example 4 The positive electrode active material is LiNi with an average particle size of 4 μm. 0.5 Mn 1.5 A battery was fabricated in the same manner as in Comparative Example 1, except that O4 was used, Li3YBr2Cl4 was used as the first solid electrolyte, and 2 mass % of a conductive additive (VGCF-H) was added to the positive electrode active material.

[0186] Using the batteries of Example 4 and Comparative Example 4 described above, battery evaluation was carried out under the following conditions.

[0187] The batteries of Example 4 and Comparative Example 4 were placed in a thermostatic chamber at 25°C.

[0188] The battery was charged at a constant current of 96 μA, which corresponds to a 0.05 C rate (20-hour rate) relative to the theoretical capacity of the battery, and the charge was terminated at a voltage of 4.38 V (equivalent to 5.0 V in terms of the Li / Li+ reference voltage). Next, the battery was charged at a constant voltage of 4.38 V, and the charge was terminated when the current reached 19.2 μA or less, which corresponds to a 0.01 C rate. After charging, the interfacial resistance between the coated positive electrode active material and the first solid electrolyte was determined by impedance measurement using the AC impedance method. The impedance measurement conditions were a voltage amplitude of 5 mV, a measurement frequency of 1 MHz to 0.1 Hz, and 25°C. The results are shown in Table 4. Next, the battery was discharged at a current of 96 μA, which corresponds to a 0.05 C rate, and the voltage reached 2.38 V (Li / Li+). + The discharge was terminated at a voltage of 2.38V (equivalent to 3.0V at the reference voltage). Next, the battery was discharged at a current of 19.2μA, also at a 0.01C rate, and the discharge was terminated at a voltage of 2.38V.

[0189] As a result, the discharge capacity and capacity efficiency of the batteries of Example 4 and Comparative Example 4 were obtained. The results are shown in Table 4 below.

[0190] From Table 4, the positive electrode active material is LiNi, which is a 5V class positive electrode active material. 0.5 Mn 1.5 Using O4, Li / Li + Even when charged at a reference voltage of 5 V, the battery of Example 4 was able to suppress the formation of a high-resistance layer between the positive electrode active material and the solid electrolyte more effectively than the battery of Comparative Example 4, and exhibited higher discharge capacity and capacity efficiency.

[0191] [Table 4] [Industrial Applicability]

[0192] The battery of the present disclosure is used, for example, in an all-solid-state lithium-ion secondary battery.

Claims

1. Positive electrode, a negative electrode, and an electrolyte layer provided between the positive electrode and the negative electrode; Equipped with the positive electrode includes a positive electrode material including a coated positive electrode active material and a first solid electrolyte; The coated positive electrode active material is a positive electrode active material, and a coating layer that covers at least a portion of the surface of the positive electrode active material; Equipped with The material constituting the coating layer is represented by the following composition formula (1): Li α Zr β F γ ... Formula (1) wherein α, β, and γ satisfy 3.6≦α≦4, 1≦β≦1.1, and γ=8; the electrolyte layer includes a second solid electrolyte; the second solid electrolyte includes a halide solid electrolyte having a different composition from the solid electrolyte included in the first solid electrolyte; battery.

2. a ratio of the mass of the coating layer to the mass of the positive electrode active material is in the range of 3 / 100 or more and 15 / 100 or less; The battery of claim 1 .

3. a ratio of the mass of the coating layer to the mass of the positive electrode active material is in the range of 7 / 100 or more and 10 / 100 or less; The battery of claim 2.

4. The average thickness of the coating layer is 1 nm or more and 300 nm or less. The battery according to any one of claims 1 to 3.

5. The average thickness of the coating layer is 2 nm or more and 200 nm or less. The battery of claim 4.

6. The positive electrode active material includes lithium nickel-cobalt-manganese oxide. The battery of any one of claims 1 to 5.

7. The first solid electrolyte includes a halide solid electrolyte. The battery of any one of claims 1 to 6.

8. The first solid electrolyte includes a sulfide solid electrolyte. The battery of any one of claims 1 to 7.

9. A method for producing a coated positive electrode active material, comprising: The coated positive electrode active material includes a positive electrode active material and a coating layer that coats at least a portion of a surface of the positive electrode active material, The material constituting the coating layer is represented by the following composition formula (1): Li α Zr β F γ ...Formula (1) wherein α, β, and γ satisfy 3.6≦α≦4, 1≦β≦1.1, and γ=8; The manufacturing method comprises: treating the positive electrode active material and a material constituting the coating layer by a dry particle compositing method; the dry particle composite method includes applying mechanical energy of impact, compression, and shear to the positive electrode active material and the material constituting the coating layer; A method for producing a coated positive electrode active material.

10. a ratio Da / Dc of the average particle diameter Da of the positive electrode active material to the average particle diameter Dc of the material of the coating layer is 2 or more; The method for producing the coated positive electrode active material according to claim 9 .

11. a ratio Da / Dc of the average particle diameter Da of the positive electrode active material to the average particle diameter Dc of the material of the coating layer is 5 or more; The method for producing the coated positive electrode active material according to claim 10 .

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