Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M10/00—Secondary cells; Manufacture thereof
  • H01M10/05—Accumulators with non-aqueous electrolyte
  • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
  • H01M10/0561—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of inorganic materials only
  • H01M10/0562—Solid materials
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
  • H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/36—Selection of substances as active materials, active masses, active liquids
  • H01M4/362—Composites
  • H01M4/366—Composites as layered products
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/36—Selection of substances as active materials, active masses, active liquids
  • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
  • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
  • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
  • H01M4/624—Electric conductive fillers
  • H01M4/625—Carbon or graphite
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M10/00—Secondary cells; Manufacture thereof
  • H01M10/05—Accumulators with non-aqueous electrolyte
  • H01M10/052—Li-accumulators
  • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M2004/021—Physical characteristics, e.g. porosity, surface area
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
  • H01M2004/028—Positive electrodes
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M2300/00—Electrolytes
  • H01M2300/0017—Non-aqueous electrolytes
  • H01M2300/0065—Solid electrolytes
  • H01M2300/0068—Solid electrolytes inorganic
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M2300/00—Electrolytes
  • H01M2300/0017—Non-aqueous electrolytes
  • H01M2300/0065—Solid electrolytes
  • H01M2300/0068—Solid electrolytes inorganic
  • H01M2300/008—Halides
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
  • Y02E60/10—Energy storage using batteries

Definitions

• This disclosure relates to positive electrode materials, positive electrodes, and batteries.
• Patent Document 1 discloses a positive electrode material including a positive electrode active material and a first solid electrolyte material that covers at least a portion of the surface of the positive electrode active material.
• the first solid electrolyte material includes Li, Ti, M1, and F, where M1 is at least one element selected from the group consisting of Ca, Mg, Al, Y, and Zr.
• Patent Document 1 discloses that the positive electrode material further includes a second electrolyte material that is a material different from the first solid electrolyte material.
• the purpose of this disclosure is to provide a positive electrode material that can reduce the initial resistance of a battery and suppress the increase in battery resistance when the battery is repeatedly charged and discharged.
• the positive electrode material of the present disclosure is A positive electrode active material; a coating material including a first conductive material and a first solid electrolyte, the coating material coating at least a portion of a surface of the positive electrode active material; a second conductive material which is a fibrous carbon material; A second solid electrolyte; Equipped with The first solid electrolyte comprises Li, Ti, M, and F;
• the M is at least one selected from the group consisting of Ca, Mg, Al, Y, and Zr;
• the second conductive material has an average fiber diameter of 0.4 nm to 50 nm.
• This disclosure provides a positive electrode material that can reduce the initial resistance of a battery and suppress the increase in battery resistance when the battery is repeatedly charged and discharged.
• FIG. 1 is a cross-sectional view showing a schematic configuration of a positive electrode material according to the first embodiment.
• FIG. 2 is a cross-sectional view showing a schematic configuration of a positive electrode in accordance with the second embodiment.
• FIG. 3 is a cross-sectional view showing a schematic configuration of a battery according to the third embodiment.
• FIG. 4 is a cross-sectional view showing a schematic configuration of a battery according to a modified example.
• FIG. 5 is a secondary electron image of particles of the basic active material of Example 1 taken with a scanning electron microscope (SEM).
• FIG. 6 is a backscattered electron image of the particles of the basic active material of Example 1 taken by SEM in the same observation region as in FIG. FIG.
• FIG. 7 is a cross-sectional secondary electron image of the positive electrode active material layer of Example 3 taken by an SEM.
• FIG. 8 is an element mapping image showing the distribution of Ni obtained by a SEM-energy dispersive X-ray analyzer (EDS) in the same observation region as in FIG.
• FIG. 9 is an element mapping image showing the distribution of Nb obtained by SEM-EDS in the same observation region as in FIG.
• FIG. 10 is an element mapping image showing the distribution of C obtained by SEM-EDS in the same observation region as in FIG.
• FIG. 11 is an element mapping image showing the distribution of F obtained by SEM-EDS in the same observation region as in FIG.
• FIG. 12 is an element mapping image showing the distribution of S obtained by SEM-EDS in the same observation region as in FIG.
• FIG. 13 is a cross-sectional backscattered electron image of the positive electrode active material layer of Example 3 taken by an SEM.
• FIG. 14 is an enlarged view of area A in FIG.
• Batteries using a positive electrode material including a positive electrode active material and a solid electrolyte that covers at least a part of the surface of the positive electrode active material tend to have a relatively high initial resistance.
• a second electrolyte material is added as a material for increasing the ease of movement of Li ions to improve the ion conductivity in the positive electrode, thereby reducing the initial resistance of the battery and suppressing the increase in the internal resistance of the battery during charging.
• batteries using the positive electrode material disclosed in Patent Document 1 may tend to have an increase in resistance when repeatedly charged and discharged.
• the inventors conducted extensive research to develop a positive electrode material that can reduce the initial resistance of a battery and suppress the increase in the battery resistance when the battery is repeatedly charged and discharged. As a result, they came up with the positive electrode material disclosed herein.
• FIG. 1 is a cross-sectional view showing a schematic configuration of a positive electrode material 100 according to the first embodiment.
• the positive electrode material 100 includes a positive electrode active material 11, a coating material 14, a second conductive material 15, and a second solid electrolyte 16.
• the coating material 14 includes a first conductive material 12 and a first solid electrolyte 13.
• the coating material 14 coats at least a part of the surface 11s of the positive electrode active material 11.
• the first solid electrolyte 13 includes Li, Ti, M, and F, where M is at least one selected from the group consisting of Ca, Mg, Al, Y, and Zr.
• the second conductive material 15 is a fibrous carbon material and has an average fiber diameter of 0.4 nm or more and 50 nm or less. According to the positive electrode material 100 in the first embodiment, the initial resistance of the battery can be reduced, and an increase in the resistance of the battery during repeated charging and discharging can be suppressed.
• the conductive material serves to ensure electronic conductivity and uniformity of the electrochemical reaction throughout the positive electrode active material layer.
• the conductive material narrows the ion conduction path in the positive electrode active material layer, and as a result, uniformity of the electrochemical reaction may not be ensured.
• the inventors have found that by using a fibrous carbon material having an average fiber diameter of 0.4 nm or more and 50 nm or less as the conductive material, the electronic conductivity of the positive electrode active material layer can be ensured even if the content of the conductive material is small.
• a positive electrode active material layer is formed using a positive electrode material including a positive electrode active material whose surface is coated with a first solid electrolyte, a fibrous carbon material, and a second solid electrolyte, the fibrous carbon material does not easily penetrate into the first solid electrolyte. This can result in insufficient contact between the positive electrode active material and the fibrous carbon material. Insufficient contact between the positive electrode active material and the fibrous carbon material can result in the uniformity of the electrochemical reaction in the positive electrode active material layer not being ensured.
• the inventors further studied ways to ensure uniformity of the electrochemical reaction in the positive electrode active material layer, and came up with the idea of including a conductive material in the coating material that coats the positive electrode active material.
• a conductive material in the coating material that coats the positive electrode active material.
• an electronic conduction path can be formed between the positive electrode active material 11 and the second conductive material 15 via the first conductive material 12, and between the positive electrode active material 11 and the positive electrode active material 11 via the first conductive material 12. This makes it easier to ensure uniformity of the electrochemical reaction throughout the positive electrode active material layer. As a result, the initial resistance of the battery can be reduced.
• the positive electrode material 100 of the first embodiment even if the content of the second conductive material 15 is small, the electronic conductivity of the positive electrode active material layer is ensured, so the contact area between the second conductive material 15 and the second solid electrolyte 16 can be reduced. As a result, the resistance of the battery is less likely to increase even when the battery is repeatedly charged and discharged.
• the potential of the cathode active material 11 and the potential of the second conductive material 15 are likely to rise during charging of the battery.
• the high potential cathode active material 11 or the high potential second conductive material 15 comes into contact with the first solid electrolyte 13, which has a narrow potential window on the high potential side, i.e., has low oxidation resistance, the first solid electrolyte 13 is decomposed.
• an oxidative decomposition layer is formed in the cathode active material layer.
• the oxidative decomposition layer functions as a resistance layer and can increase the internal resistance of the battery during charging.
• the first solid electrolyte 13 contains Li, Ti, M, and F, and M is at least one selected from the group consisting of Ca, Mg, Al, Y, and Zr. Therefore, the first solid electrolyte 13 is not easily decomposed even under high potential and has high oxidation resistance. As a result, the battery resistance is less likely to increase even after repeated charging and discharging.
• the average fiber diameter of the second conductive material 15 can be determined, for example, by SEM observation of a cross section of a positive electrode active material layer made using the positive electrode material 100.
• the first conductive material 12 may be in direct contact with the surface 11s of the positive electrode active material 11.
• the first solid electrolyte 13 may be in direct contact with the first conductive material 12, or may be in direct contact with the surface 11s of the positive electrode active material 11. That is, the surface 11s of the positive electrode active material 11 that is not covered with the first conductive material 12 and a part of the first conductive material 12 may be covered with the first solid electrolyte 13. Note that a part of the first conductive material 12 may not be covered with the first solid electrolyte 13 due to, for example, the flow of the first solid electrolyte 13 that covered the first conductive material 12 when the positive electrode active material layer is pressed.
• the first conductive material 12 covers at least a part of the surface 11s of the positive electrode active material 11.
• the positive electrode active material 11 with at least a part of the surface 11s covered by the first conductive material 12 is defined as the basic active material 10.
• the first solid electrolyte 13 covers at least a part of the surface of the basic active material 10 including the first conductive material 12 and the positive electrode active material 11. According to the above configuration, at least a part of the first conductive material 12 is covered by the first solid electrolyte 13.
• the second solid electrolyte 16 is not easily decomposed even if the potential of the positive electrode active material 11 and the potential of the first conductive material 12 increase during charging of the battery. As a result, the increase in the resistance of the battery when charging and discharging is repeated is further suppressed.
• the positive electrode active material 11 having at least a portion of its surface 11s coated with the coating material 14 is defined as a composite active material 20.
• the positive electrode material 100 comprises a composite active material 20, a second conductive material 15, and a second solid electrolyte 16.
• the second conductive material 15 and the second solid electrolyte 16 are located between particles of the composite active material 20 including the positive electrode active material 11 and the coating material 14.
• Examples of the positive electrode active material 11 include lithium-containing transition metal oxides, lithium-containing transition metal phosphates, transition metal fluorides, polyanion materials, fluorinated polyanion materials, transition metal sulfides, transition metal oxysulfides, and transition metal oxynitrides.
• the manufacturing cost of the battery can be reduced and the average discharge voltage can be increased.
• the lithium-containing transition metal oxides include lithium cobalt oxide, lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganese oxide, and lithium nickel manganese oxide.
• Examples of the lithium-containing transition metal phosphates include lithium iron phosphate, lithium vanadium phosphate, lithium cobalt phosphate, and lithium nickel phosphate. At least one selected from these positive electrode active materials can be used.
• the particles of the positive electrode active material 11 may be primary particles or secondary particles.
• the positive electrode active material 11 has a median diameter of, for example, 0.1 ⁇ m or more and 100 ⁇ m or less.
• the median diameter means the particle size (d50) 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.
• the positive electrode active material 11 may have a particle shape having multiple recesses on the surface 11s.
• the first conductive material 12 may be disposed in the multiple recesses of the positive electrode active material 11.
• the average spacing between the multiple recesses may be 500 nm or less, and the average height between the multiple recesses may be 500 nm or less.
• the first conductive material 12 is a particulate material. With the above configuration, the first conductive material 12 is easily attached to the surface 11s of the positive electrode active material 11. As a result, the initial resistance of the battery is further reduced, and an increase in the resistance of the battery during repeated charging and discharging is further suppressed.
• the shape of the first conductive material 12 may be, for example, spherical, elliptical, or the like.
• the shape of the first conductive material 12 may be spherical.
• Examples of the first conductive material 12 that can be used include graphites such as natural graphite or artificial graphite, carbon blacks such as acetylene black and ketjen black, and conductive polymer compounds such as polyaniline, polypyrrole, and polythiophene.
• the first conductive material 12 may contain carbon black. With the above configuration, the electronic conductivity in the positive electrode active material layer may be improved.
• the first conductive material 12 may be carbon black.
• acetylene black can be used as carbon black.
• the first conductive material 12 contains acetylene black, the electronic conductivity in the positive electrode active material layer can be improved.
• the first conductive material 12 may have a median diameter of 100 nm or less. With the above configuration, the first conductive material 12 is more likely to adhere to the surface 11s of the positive electrode active material 11. Therefore, in the positive electrode active material layer, an electronic conduction path is more likely to be formed by connecting the first conductive material 12 and the second conductive material 15. As a result, the electronic conductivity in the positive electrode active material layer can be improved.
• the lower limit of the median diameter of the first conductive material 12 is not particularly limited.
• the lower limit of the median diameter of the first conductive material 12 may be, for example, 10 nm.
• the second conductive material 15 is a fibrous carbon material. According to the above configuration, the first conductive material 12 and the second conductive material 15 contained in the coating material 14 that coats at least a part of the surface 11s of the positive electrode active material 11 are easily connected to each other. As a result, the initial resistance of the battery is further reduced, and an increase in the resistance of the battery when the battery is repeatedly charged and discharged is further suppressed.
• the second conductive material 15 may be vapor-grown carbon fiber, carbon nanotubes, carbon nanofibers, etc.
• the second conductive material 15 may contain any one of these materials, or may contain two or more of these materials.
• the second conductive material 15 may be made of any one of these materials, or may be made of two or more of these materials.
• the second conductive material 15 may contain carbon nanotubes.
• a second conductive material 15 that is a carbon nanotube and a second conductive material 15 other than a carbon nanotube may be present between the multiple composite active materials 20.
• the second conductive material 15 may be a carbon nanotube.
• the second conductive material 15 has an average fiber diameter of 0.4 nm or more and 50 nm or less. With the above configuration, the second conductive material 15 is likely to form an electronic conduction path in the positive electrode active material layer. As a result, the electronic conductivity in the positive electrode active material layer can be improved.
• the lower limit of the average fiber diameter of the second conductive material 15 may be 0.8 nm or 1.2 nm.
• the upper limit of the average fiber diameter of the second conductive material 15 may be 10 nm, 5 nm, or 2 nm.
• the second conductive material 15 may have an average length of 5 ⁇ m or more. With the above configuration, the second conductive material 15 is more likely to form an electronic conduction path in the positive electrode active material layer. As a result, the electronic conductivity in the positive electrode active material layer can be further improved.
• the upper limit of the average length of the second conductive material 15 is not particularly limited.
• the upper limit of the average length of the second conductive material 15 may be, for example, 20 ⁇ m.
• the average length of the second conductive material 15 can be determined using the same method as that for determining the average fiber diameter of the second conductive material 15 described above.
• the ratio M 2 /M 1 of the mass M 2 of the second conductive material 15 to the sum M 1 of the mass of the positive electrode active material 11 and the mass of the second conductive material 15 may be 0.005% or more and 0.02% or less. If the content of the second conductive material 15 in the positive electrode active material layer is too large, the contact area between the second conductive material 15 and the second solid electrolyte 16 increases, and the second solid electrolyte 16 is easily decomposed when the battery is charged. If the ratio M 2 /M 1 is 0.02% or less, the decomposition of the second solid electrolyte 16 is suppressed when the battery is charged.
• the content of the second conductive material 15 is too large, the ion conduction path in the positive electrode active material layer is narrowed by the second conductive material 15, and as a result, the uniformity of the electrochemical reaction may not be ensured. If the ratio M 2 /M 1 is 0.02% or less, the uniformity of the electrochemical reaction is easily ensured.
• the ratio M 2 /M 1 can be determined, for example, from the charge ratio.
• First solid electrolyte 13 contains Li, Ti, M, and F.
• M is at least one selected from the group consisting of Ca, Mg, Al, Y, and Zr. With the above configuration, first solid electrolyte 13 has high oxidation resistance and is not easily decomposed under high potential.
• the first solid electrolyte 13 may be composed of Li, Ti, M, and F. "Composed of Li, Ti, M, and F" means that, except for unavoidable impurities, no materials other than Li, Ti, M, and F are intentionally added.
• M may contain Al.
• the first solid electrolyte 13 may include, for example, a solid electrolyte represented by the following composition formula (1):
• ⁇ , ⁇ , ⁇ , and ⁇ are each independently a value greater than 0.
• the solid electrolyte represented by formula (1) has a higher ionic conductivity than a solid electrolyte consisting only of Li and a halogen element. Therefore, when the solid electrolyte represented by formula (1) is used in a battery, the charge and discharge efficiency of the battery can be improved.
• M in composition formula (1) may be Al.
• the first solid electrolyte 13 may include a solid electrolyte represented by the following composition formula (2):
• M2 is at least one selected from the group consisting of Zr, Ni, Fe, and Cr
• m is the valence of M2, and 0.1 ⁇ x ⁇ 0.9, 0 ⁇ y ⁇ 0.1, 0 ⁇ z ⁇ 0.1, and 0.8 ⁇ b ⁇ 1.2 are satisfied.
• m is the total value of the product of the composition ratio of each element and the valence of the element.
• M2 contains the element Me1 and the element Me2
• the composition ratio of the element Me1 is a1 and the valence is m1
• the composition ratio of the element Me2 is a2 and the valence of the element Me2 is m2
• m is expressed as m1a1+m2a2.
• the solid electrolyte 13 may consist essentially of Li, Ti, Al, and F.
• the halide solid electrolyte consists essentially of Li, Ti, Al, and F
• the molar ratio (i.e., molar fraction) of the total amount of substance of Li, Ti, Al, and F to the total amount of substance of all elements constituting the halide solid electrolyte is 90% or more.
• the molar ratio (i.e., molar fraction) may be 95% or more.
• the solid electrolyte 13 may consist only of Li, Ti, Al, and F.
• the ratio of the amount of Li to the sum of the amounts of Ti and Al may be 1.12 or more and 5.07 or less.
• the first solid electrolyte 13 may include a solid electrolyte represented by the following composition formula (3): In composition formula (3), 0 ⁇ x ⁇ 1 and 0 ⁇ b ⁇ 1.5 are satisfied.
• Solid electrolytes with this composition have high ionic conductivity.
• composition formula (3) In order to increase the ionic conductivity of the first solid electrolyte 13, 0.1 ⁇ x ⁇ 0.9 may be satisfied in composition formula (3).
• composition formula (3) 0.1 ⁇ x ⁇ 0.7 may be satisfied.
• the upper and lower limits of the range of x in composition formula (3) can be defined by any combination selected from the numerical values of 0.1, 0.3, 0.4, 0.5, 0.6, 0.67, 0.7, 0.8, and 0.9.
• composition formula (3) can be defined by any combination selected from the numerical values of 0.8, 0.9, 0.94, 1.0, 1.06, 1.1, and 1.2.
• the solid electrolyte may be crystalline or amorphous.
• the shape of the first solid electrolyte 13 is not particularly limited, and may be, for example, needle-like, spherical, or elliptical.
• the shape of the first solid electrolyte 13 may be particulate.
• the first solid electrolyte 13 has a particulate shape (e.g., spherical shape)
• the first solid electrolyte 13 has an average particle size of, for example, 10 nm or more and 100 nm or less. With this configuration, it becomes relatively easy to uniformly coat the coating material containing the first solid electrolyte 13.
• the average particle size of the first solid electrolyte 13 can be measured, for example, using an SEM image. Specifically, the average particle size can be obtained by calculating the average circle equivalent diameter of 20 arbitrarily selected particles of the first solid electrolyte 13 using the SEM image. The average particle size of other materials, such as the second solid electrolyte 16 described below, can also be obtained using the same method.
• the second solid electrolyte 16 includes a solid electrolyte having high ion conductivity.
• the second solid electrolyte 16 may include a plurality of solid electrolytes having different chemical compositions.
• a solid electrolyte having a different chemical composition from the first solid electrolyte 13 and a solid electrolyte having the same chemical composition as the first solid electrolyte 13 may be present as the second solid electrolyte 16 between the plurality of composite active materials 20.
• the second solid electrolyte 16 may contain a halide solid electrolyte.
• a halide solid electrolyte has high ionic conductivity and excellent high potential stability. Furthermore, since a halide solid electrolyte has low electronic conductivity and high oxidation resistance, it is not easily oxidized and decomposed by contact with the composite active material 20. Therefore, by having the second solid electrolyte 16 contain a halide solid electrolyte, the output characteristics of the battery can be improved.
• halide solid electrolyte examples include Li3 (Ca,Y,Gd) X6 , Li2MgX4 , Li2FeX4 , Li(Al,Ga,In) X4 , Li3 (Al,Ga,In) X6 , and LiI.
• the element X is at least one selected from the group consisting of Cl, Br, and I.
• the halide solid electrolyte may not contain sulfur. In this case, it is possible to avoid the generation of sulfur-containing gases such as hydrogen sulfide gas from the solid electrolyte.
• a sulfur-free solid electrolyte means a solid electrolyte represented by a composition formula that does not contain elemental sulfur. Therefore, a solid electrolyte that contains a very small amount of sulfur, for example a solid electrolyte with a sulfur content of 0.1 mass% or less, belongs to the category of solid electrolytes that do not contain sulfur.
• the halide solid electrolyte may further contain oxygen as an anion other than the halogen element.
• the second solid electrolyte 16 may contain a sulfide solid electrolyte. Compared to solid electrolytes such as oxide solid electrolytes and halide solid electrolytes, sulfide solid electrolytes have a narrow potential window and are easily decomposed under high potentials. However, with the above configuration, the contact area between the positive electrode active material 11 and the first conductive material 12 and the second solid electrolyte 16 is reduced, making it difficult for an oxidative decomposition layer to form in the positive electrode active material layer. As a result, the initial resistance of the battery can be reduced.
• Li2S - P2S5 Li2S - SiS2 , Li2S - B2S3 , Li2S - GeS2 , Li3.25Ge0.25P0.75S4, and Li10GeP2S12.
• LiX, Li2O , MOq , and LipMOq may be added to these.
• the element X in “LiX” is at least one element selected from the group consisting of F, Cl , Br, and I.
• the element M in “ MOq " and " LipMOq " is at least one element selected from the group consisting of P, Si , Ge, B, Al, Ga, In, Fe, and Zn .
• MO q " and " Lip MO q ", p and q are each independent natural numbers.
• the second solid electrolyte 16 may be a sulfide solid electrolyte. That is, the second solid electrolyte 16 may be made of a sulfide solid electrolyte. "Made of a sulfide solid electrolyte" means that, except for inevitable impurities, no materials other than the sulfide solid electrolyte are intentionally added.
• the sulfide solid electrolyte may contain lithium sulfide and phosphorus sulfide.
• the sulfide solid electrolyte may be Li2S - P2S5 .
• the shape of the second solid electrolyte 16 is not particularly limited, and may be, for example, needle-like, spherical, or elliptical.
• the shape of the second solid electrolyte 16 may be particulate.
• the average particle size of the second solid electrolyte 16 may be 100 ⁇ m or less. If the average particle size is greater than 100 ⁇ m, the composite active material 20 and the second solid electrolyte 16 may not form a good dispersion state in the positive electrode material 100. This results in a deterioration in charge/discharge characteristics.
• the average particle size of the second solid electrolyte 16 may be 10 ⁇ m or less. When the average particle size of the second solid electrolyte 16 is within the above range, the composite active material 20 and the second solid electrolyte 16 can form a good dispersion state in the positive electrode material 100.
• the average particle size of the second solid electrolyte 16 may be smaller than the average particle size of the composite active material 20. With this configuration, the composite active material 20 and the second solid electrolyte 16 can be better dispersed in the electrode.
• the average particle size of the composite active material 20 may be 0.1 ⁇ m or more and 100 ⁇ m or less.
• the composite active material 20 and the second solid electrolyte 16 can form a good dispersion state in the positive electrode material 100.
• the charge and discharge characteristics of the battery are improved.
• the average particle size of the composite active material 20 is 100 ⁇ m or less, the lithium diffusion rate in the positive electrode active material 11 is improved. This enables the battery to operate at high power.
• the average particle size of the composite active material 20 may be larger than the average particle size of the second solid electrolyte 16. Even with this configuration, a good dispersion state of the composite active material 20 and the second solid electrolyte 16 can be formed in the electrode.
• the covering material 14 may further include a material such as an oxide material or an oxide solid electrolyte as an underlayer material.
• a first layer including the underlayer material and a second layer including the first conductive material 12 and the first solid electrolyte 13 may be formed by the covering material 14.
• the underlayer material may be a material including Nb.
• the underlayer material typically includes lithium niobate (LiNbO 3 ). With this configuration, the charge and discharge efficiency of the battery can be improved.
• As the oxide solid electrolyte that is the underlayer material it is also possible to use an oxide solid electrolyte to be described later.
• the second solid electrolyte 16 and the composite active material 20 may be in contact with each other, as shown in FIG. 1.
• the positive electrode material 100 may include a plurality of composite active materials 20, a plurality of second conductive materials 15, and a plurality of second solid electrolytes 16.
• the shape of the positive electrode material 100 is not particularly limited.
• the positive electrode material 100 may be in the form of a powder or a slurry.
• the positive electrode material 100 may also be in the form of a compressed powder obtained by pressing the positive electrode material 100.
• the positive electrode material 100 can be produced, for example, by the following method.
• the surface of the particles of the positive electrode active material 11 is coated with the first conductive material 12 to prepare the basic active material 10.
• the surface of the particles of the basic active material 10 is coated with the first solid electrolyte 13 to prepare the composite active material 20.
• the method of coating the first conductive material 12 and the first solid electrolyte 13 is not particularly limited. For example, by mixing the particles of the positive electrode active material 11 and the particles of the first conductive material 12, the particles of the basic active material 10 in which the surfaces of the particles of the positive electrode active material 11 are coated with the first conductive material 12 are obtained. By mixing the particles of the basic active material 10 and the particles of the first solid electrolyte 13, the particles of the composite active material 20 in which the surfaces of the particles of the basic active material 10 are coated with the first solid electrolyte 13 are obtained.
• the positive electrode material 100 is obtained by mixing the particles of the composite active material 20, the particles of the second conductive material 15, and the particles of the second solid electrolyte 16.
• (Embodiment 2) 2 is a cross-sectional view showing a schematic configuration of a positive electrode 200 in the second embodiment.
• the positive electrode 200 includes a positive electrode current collector 21 and a positive electrode active material layer 22 supported by the positive electrode current collector 21.
• the positive electrode active material layer 22 includes the positive electrode material 100 of the first embodiment. That is, the positive electrode active material layer 22 includes a composite active material 20, a second conductive material 15, and a second solid electrolyte 16. According to the positive electrode 200 in the second embodiment, the initial resistance of the battery can be reduced, and an increase in the resistance of the battery when the battery is repeatedly charged and discharged can be suppressed.
• the volume ratio "v1:100-v1" of the positive electrode active material 11 to the total of the first conductive material 12, the first solid electrolyte 13, the second conductive material 15, and the second solid electrolyte 16 may satisfy 30 ⁇ v1 ⁇ 95.
• v1 indicates the volume fraction of the positive electrode active material 11 when the total volume of the positive electrode active material 11 contained in the positive electrode active material layer 22, the first conductive material 12, the first solid electrolyte 13, the second conductive material 15, and the second solid electrolyte 16 is taken as 100.
• 30 ⁇ v1 it is easy to ensure a sufficient energy density of the battery.
• v1 ⁇ 95 it becomes easier for the battery to operate at high output.
• the material of the positive electrode collector 21 is not limited to a specific material, and materials that are generally used in batteries can be used. Examples of materials for the positive electrode collector 21 include aluminum, aluminum alloys, stainless steel, carbon, and conductive resins.
• the shape of the positive electrode collector 21 is also not limited to a specific shape. Examples of the shape include foil, film, and sheet. The surface of the positive electrode collector 21 may be uneven.
• the battery in the third embodiment includes the positive electrode and the negative electrode in the second embodiment.
• the battery in the third embodiment may be a solid-state battery or a liquid battery.
• a "solid-state battery” refers to a battery using a solid electrolyte as an electrolyte.
• a solid-state battery is typically an all-solid-state battery that does not contain an electrolyte.
• a "liquid battery” refers to a battery using an electrolyte.
• the battery in the third embodiment can reduce the initial resistance and can suppress an increase in resistance when the battery is repeatedly charged and discharged.
• FIG. 3 is a cross-sectional view showing a schematic configuration of a battery 300 in embodiment 3.
• the battery 300 may include the positive electrode 200, electrolyte layer 201, and negative electrode 202 of embodiment 2.
• the electrolyte layer 201 is disposed between the positive electrode 200 and the negative electrode 202.
• the electrolyte layer 201 is a layer including an electrolyte.
• the electrolyte is, for example, a solid electrolyte.
• the solid electrolyte included in the electrolyte layer 201 is called a third solid electrolyte. That is, the electrolyte layer 201 may include the third solid electrolyte.
• the third solid electrolyte may be a halide solid electrolyte, a sulfide solid electrolyte, an oxide solid electrolyte, a polymer solid electrolyte, or a complex hydride solid electrolyte.
• a material that is unlikely to decompose at the potential of the negative electrode active material used may be selected and used as the third solid electrolyte.
• the third solid electrolyte may include a solid electrolyte having the same composition as the solid electrolyte included in the first solid electrolyte 13.
• the third solid electrolyte may include a solid electrolyte having the same composition as the solid electrolyte included in the second solid electrolyte 16.
• the third solid electrolyte may include a solid electrolyte having a different composition from the solid electrolyte included in the first solid electrolyte 13.
• the third solid electrolyte may include a halide solid electrolyte having the same composition as the halide solid electrolyte included in the second solid electrolyte 16.
• the electrolyte layer 201 may include a halide solid electrolyte having the same composition as the halide solid electrolyte included in the second solid electrolyte 16.
• the third solid electrolyte may include a solid electrolyte having a different composition than the solid electrolyte included in the second solid electrolyte 16.
• the third solid electrolyte may include a halide solid electrolyte having a different composition from the halide solid electrolyte included in the second solid electrolyte 16. That is, the electrolyte layer 201 may include a halide solid electrolyte having a different composition from the halide solid electrolyte included in the second solid electrolyte 16.
• the third solid electrolyte may include a sulfide solid electrolyte.
• the third solid electrolyte may include a sulfide solid electrolyte having the same composition as the sulfide solid electrolyte included in the second solid electrolyte 16.
• the electrolyte layer 201 may include a sulfide solid electrolyte having the same composition as the sulfide solid electrolyte included in the second solid electrolyte 16.
• the above configuration can improve the energy density of the battery 300. Furthermore, when the electrolyte layer 201 contains a sulfide solid electrolyte having the same composition as the sulfide solid electrolyte contained in the first solid electrolyte 13, the initial resistance of the battery 300 can be further reduced.
• the third solid electrolyte may include an oxide solid electrolyte.
• oxide solid electrolyte examples include NASICON-type solid electrolyte materials represented by LiTi 2 (PO 4 ) 3 and its elemental substitution products, (LaLi) TiO 3 -based perovskite-type solid electrolyte materials, LISICON-type solid electrolyte materials represented by Li 14 ZnGe 4 O 16 , Li 4 SiO 4 , LiGeO 4 and its elemental substitution products, garnet-type solid electrolyte materials represented by Li 7 La 3 Zr 2 O 12 and its elemental substitution products, Li 3 PO 4 and its N-substitution products, glasses based on Li-B-O compounds such as LiBO 2 and Li 3 BO 3 and to which Li 2 SO 4 , Li 2 CO 3 , etc. are added, and glass ceramics.
• Li-B-O compounds such as LiBO 2 and Li 3 BO 3 and to which Li 2 SO 4 , Li 2 CO 3 , etc. are added, and glass ceramics.
• the third solid electrolyte may include a polymer solid electrolyte.
• a polymer solid electrolyte for example, a compound of a polymer compound and a lithium salt may be used.
• the polymer compound may have an ethylene oxide structure.
• the polymer compound having an ethylene oxide structure may contain a large amount of lithium salt. Therefore, the ion conductivity can be further increased.
• LiPF 6 , LiBF 4 , LiSbF 6 , LiAsF 6 , LiSO 3 CF 3 , LiN (SO 2 F) 2 , LiN (SO 2 CF 3 ) 2 , LiN (SO 2 C 2 F 5 ) 2 , LiN (SO 2 CF 3 ) (SO 2 C 4 F 9 ), LiC (SO 2 CF 3 ) 3 , etc. may be used.
• the lithium salt may be used alone or in combination of two or more.
• the third solid electrolyte may include a complex hydride solid electrolyte, such as LiBH 4 --LiI or LiBH 4 --P 2 S 5 .
• the negative electrode 202 includes a negative electrode current collector 23 and a negative electrode active material layer 24 supported by the negative electrode current collector 23.
• the negative electrode active material layer 24 includes a material having a property of absorbing and releasing metal ions (e.g., lithium ions).
• the negative electrode active material layer 24 includes, for example, a negative electrode active material (e.g., negative electrode active material particles).
• a metal material, a carbon material, an oxide, a nitride, a tin compound, a silicon compound, or the like can be used as the negative electrode active material.
• the metal material may be a single metal.
• the metal material may be an alloy.
• metal materials include lithium metal and lithium alloys.
• Examples of carbon materials include natural graphite, spherical carbon, artificial graphite, and amorphous carbon. From the viewpoint of capacity density, silicon, tin, silicon compounds, and tin compounds can be preferably used.
• the negative electrode active material layer 24 may contain a solid electrolyte.
• the solid electrolyte contained in the negative electrode active material layer 24 is called a fourth solid electrolyte. That is, the negative electrode active material layer 24 may contain a fourth solid electrolyte. With such a configuration, the lithium ion conductivity inside the negative electrode active material layer 24 is improved, and the battery 300 can operate at high output.
• a material that does not decompose at the potential of the negative electrode active material used can be selected from the materials given as examples of the third solid electrolyte of the electrolyte layer 201.
• the average particle size of the negative electrode active material may be larger than the average particle size of the fourth solid electrolyte contained in the negative electrode active material layer 24. This allows a good dispersion state to be formed between the negative electrode active material and the fourth solid electrolyte.
• the volume ratio "v2:100-v2" of the negative electrode active material contained in the negative electrode active material layer 24 to the fourth solid electrolyte may be 30 ⁇ v2 ⁇ 95.
• v2 indicates the volume ratio of the negative electrode active material when the total volume of the negative electrode active material and the fourth solid electrolyte contained in the negative electrode active material layer 24 is taken as 100.
• the material of the negative electrode current collector 23 is not limited to a specific material, and materials that are generally used in batteries can be used. Examples of materials for the negative electrode current collector 23 include copper, copper alloys, aluminum, aluminum alloys, stainless steel, nickel, and conductive resins.
• the shape of the negative electrode current collector 23 is also not limited to a specific shape. Examples of the shape include foil, film, and sheet. The surface of the negative electrode current collector 23 may be uneven.
• At least one selected from the group consisting of the positive electrode active material layer 22, the electrolyte layer 201, and the negative electrode active material layer 24 may contain a binder for the purpose of improving adhesion between particles.
• the binder is used to improve the binding property of the materials that constitute the electrode.
• the negative electrode active material layer 24 may contain a conductive material for the purpose of increasing electronic conductivity.
• a conductive material for the purpose of increasing electronic conductivity.
• the conductive material include graphites such as natural graphite or artificial graphite, carbon blacks such as acetylene black and ketjen black, carbon fibers, and conductive polymer compounds such as polyaniline, polypyrrole, and polythiophene. When a carbon-based conductive material is used, costs can be reduced.
• FIG. 4 is a cross-sectional view showing a schematic configuration of a battery 400 according to a modified example.
• the battery 400 shown in Fig. 4 includes the positive electrode 200, the separator 301, and the negative electrode 202 of the second embodiment.
• the battery 400 has the same configuration as the battery 300 described above, except that the battery 400 includes the separator 301 instead of the electrolyte layer 201.
• the separator 301 is disposed between the positive electrode 200 and the negative electrode 202, and prevents direct contact between the positive electrode 200 and the negative electrode 202.
• the separator 301 ensures sufficient safety of the battery 400.
• Separator 301 has lithium ion conductivity. There are no particular limitations on the material of separator 301 as long as it allows lithium ions to pass through.
• the material of the separator 301 may be a porous material.
• the separator 301 may have a membrane shape.
• examples of the porous membrane include a woven fabric, a nonwoven fabric, a porous membrane made of a polyolefin resin, and a porous membrane made of glass paper obtained by weaving glass fibers into a nonwoven fabric.
• Separator 301 may be impregnated with an electrolyte.
• battery 400 can achieve both charge/discharge efficiency and discharge capacity.
• the electrolyte may contain at least one selected from the group consisting of cyclic ethers, glymes, and sulfolane.
• the electrolyte may contain an ether.
• the ether include cyclic ethers and glycol ethers.
• the glycol ether may be a glyme represented by the composition formula CH3 ( OCH2CH2 ) nOCH3 . In the composition formula, n is an integer of 1 or more.
• the electrolyte may contain a mixture of a cyclic ether and a glyme , or a cyclic ether as a solvent.
• Cyclic ethers include tetrahydrofuran (THF), 2-methyltetrahydrofuran (2MeTHF), 2,5-dimethyltetrahydrofuran, 1,3-dioxolane (1,3DO), 4-methyl-1,3-dioxolane (4Me1,3DO), etc. One or a mixture of two or more selected from these can be used.
• Glymes include monoglyme (1,2-dimethoxyethane), diglyme (diethylene glycol dimethyl ether), triglyme (triethylene glycol dimethyl ether), tetraglyme (tetraethylene glycol dimethyl ether), pentaethylene glycol dimethyl ether, polyethylene glycol dimethyl ether, etc.
• the glyme may be a mixture of tetraglyme and pentaethylene glycol dimethyl ether.
• sulfolanes is 3-methylsulfolanes.
• the electrolyte may contain an electrolyte salt.
• the electrolyte salt include lithium salts such as LiPF6 , LiBF4 , LiSbF6 , LiAsF6, LiSO3CF3, LiN(SO2CF3)2 , LiN ( SO2C2F5 ) 2 , LiN(SO2CF3)( SO2C4F9 ) , LiC(SO2CF3)3 , LiClO4 , and lithium bis( oxalate )borate.
• the electrolyte may contain lithium dissolved therein .
• Battery 300 and battery 400 can be configured as batteries of various shapes, such as coin type, cylindrical type, square type, sheet type, button type, flat type, and laminated type.
• a positive electrode active material comprising Li, Ti, M, and F;
• the M is at least one selected from the group consisting of Ca, Mg, Al, Y, and Zr;
• the second conductive material has an average fiber diameter of 0.4 nm or more and 50 nm or less.
• the positive electrode material of Technology 1 can reduce the initial resistance of the battery and suppress the increase in resistance of the battery when it is repeatedly charged and discharged.
• the positive electrode active material layer includes the positive electrode material according to any one of techniques 1 to 9. Positive electrode.
• the positive electrode of Technology 10 can reduce the initial resistance of the battery and suppress the increase in the battery resistance when the battery is repeatedly charged and discharged.
• the battery of Technology 11 can reduce the initial resistance and suppress the increase in resistance when repeatedly charged and discharged.
• the battery of Technology 12 can reduce the initial resistance and suppress the increase in resistance when repeatedly charged and discharged.
• LiI-LiBr- Li2S - P2S5 type glass ceramic particles (average particle size: 1.0 ⁇ m, density: 2.2 g/ cm3 ) were used.
• the average particle size of the second solid electrolyte was calculated by the same method as that of the first solid electrolyte.
• Secondary electron images have the property that the surface shape of the sample (e.g., unevenness) is easily reflected in the image contrast.
• Backscattered electron images have the property that the composition of the sample is easily reflected in the image contrast.
• materials with high atomic numbers and high density are observed brightly.
• particles with diameters of about 10 nm to 50 nm were particles of acetylene black, which is the first conductive material 12.
• the area where the surface of the positive electrode active material 11 was covered with the first conductive material 12 was observed to be darker in color than the area where the surface of the positive electrode active material 11 was not covered with the first conductive material 12.
• the positive electrode active material 11 has multiple recesses on its surface, and the first conductive material 12 is disposed in the multiple recesses.
• the positive electrode slurries of Examples 1 to 5 were prepared by changing the content of CNT, which is the second conductive material.
• the content (volume %) of the second solid electrolyte, the content (mass %) of the second conductive material, and the contents (mass %) of the first binder and the second binder in the positive electrode slurries of Examples 1 to 5 are shown in Table 1.
• the content of the second solid electrolyte shown in Table 1 is the ratio of the volume of the second solid electrolyte to the total volume of the positive electrode active material and the second solid electrolyte (100 x second solid electrolyte/(positive electrode active material + second solid electrolyte)).
• the content of the second solid electrolyte was calculated using the density of the positive electrode active material and the density of the second solid electrolyte.
• the mass of the second binder was adjusted so that the sum of the mass of the first binder and the mass of the second binder was in the ratio shown in Table 1.
• first binder As the first binder, in the same manner as in Examples 1 to 4, a solution was prepared by dissolving a styrene-ethylene/butylene-styrene block copolymer (N504, manufactured by Asahi Kasei Corporation) in a dispersion medium.
• a styrene-ethylene/butylene-styrene block copolymer N504, manufactured by Asahi Kasei Corporation
• VGCF-H the same CNT and vapor grown carbon fiber (VGCF-H, manufactured by Showa Denko KK, average fiber diameter: 150 nm, average length: 6 ⁇ m) (hereinafter referred to as VGCF) as in Examples 1 to 4 were used.
• LiI-LiBr-Li 2 S-P 2 S 5 type glass ceramic particles (average particle size: 1.0 ⁇ m, density: 2.2 g/cm 3 ) were used as the second solid electrolyte.
• Positive electrode slurries of Comparative Examples 1 to 3 were prepared by changing the type and content of the second conductive material.
• the content (volume %) of the second solid electrolyte, the content (mass %) of the second conductive material, and the contents (mass %) of the first binder and the second binder in the positive electrode slurries of Comparative Examples 1 to 3 are shown in Table 2.
• particles of acetylene black (Li-435, manufactured by Denka Co., Ltd., average particle size: 23 nm) (hereinafter referred to as AB) and the same VGCF as in Comparative Example 3 were used.
• LiI-LiBr-Li 2 S-P 2 S 5 type glass ceramic particles (average particle size: 1.0 ⁇ m, density: 2.2 g/cm 3 ) were used as the second solid electrolyte.
• Positive electrode slurries of Comparative Examples 4 to 7 were prepared by changing the type and content of the second conductive material.
• the content (volume %) of the second solid electrolyte, the content (mass %) of the second conductive material, and the content (mass %) of the second binder in the positive electrode slurries of Comparative Examples 4 to 7 are shown in Table 3.
• the content of the second binder shown in Table 3 is the ratio of the mass of the second binder to the total mass of the positive electrode active material and the second binder (100 x second binder/(positive electrode active material + second binder)).
• the positive electrode slurries of Examples 1 to 4 and Comparative Examples 1 to 7 were applied onto a current collector foil and dried at 100° C. to obtain a positive electrode.
• the positive electrode was composed of a current collector foil and a positive electrode active material layer formed on the current collector foil. The thickness of the positive electrode active material layer was adjusted so that the discharge capacity was 2 mAh/cm 2 in the measurement of the initial battery capacity described later.
• the two punched positive electrodes were stacked with the positive electrode active material layers facing each other, and roll pressed at 2 ton/cm to produce a positive electrode molded body.
• After measuring the thickness of the positive electrode active material layer of the positive electrode molded body it was housed in an exterior body made of a laminate sheet and restrained at 0.5 MPa. In this way, test pieces of the positive electrodes of Examples 1 to 4 and Comparative Examples 1 to 7 were obtained.
• LiI-LiBr- Li2S - P2S5 -based glass ceramic particles (average particle size: 1.0 ⁇ m, density: 2.2 g/ cm3 ) were used, similarly to the second solid electrolyte used in the positive electrode materials of Examples 1 to 5.
• the average particle size of the solid electrolyte was calculated by the same method as that for the first solid electrolyte of Examples 1 to 4.
• a solution was prepared by dissolving a butadiene rubber-based binder in a dispersion medium, similar to the second binder used in the positive electrode materials of Examples 1 to 4.
• the content of the butadiene rubber-based binder was 5 mass% relative to the total mass of the solution.
• the conductive material used was VGCF, the same as the second conductive material used in the positive electrode materials of Comparative Examples 3, 6, and 7.
• the negative electrode active material, solid electrolyte, binder solution, and conductive material were weighed out so that the mass ratio of negative electrode active material: solid electrolyte: binder solution: conductive material was 73.8:24.8:0.6:0.8.
• a dispersion medium was added to these and mixed to prepare a negative electrode slurry.
• the negative electrode slurry was applied onto a current collector foil as a negative electrode current collector and dried at 100°C to obtain a negative electrode.
• the negative electrode consisted of a current collector foil and a negative electrode active material layer formed on the current collector foil. The thickness of the negative electrode active material layer was adjusted so that the capacity per unit area of the negative electrode was 1.15 times the capacity per unit area of the positive electrode.
• Capacity per unit area of negative electrode refers to the capacity per unit area of the negative electrode when the specific capacity of the negative electrode active material is 175 mAh/g.
• Capacity per unit area of positive electrode refers to the initial charge capacity in the initial battery capacity measurement described below.
• LiI-LiBr- Li2S - P2S5 - based glass ceramic particles (average particle size: 2.5 ⁇ m, density: 2.2 g/ cm3 ) were used as the solid electrolyte.
• the average particle size of the solid electrolyte was calculated by the same method as for the first solid electrolyte in Examples 1 to 5.
• the average particle size of the solid electrolyte used in the electrolyte layer was different from the average particle size of the second solid electrolyte used in the positive electrode material in the Examples and Comparative Examples, and the average particle size of the solid electrolyte used in the negative electrode.
• a solution was prepared by dissolving a butadiene rubber-based binder in a dispersion medium, similar to the second binder used in the positive electrode materials of Examples 1 to 4.
• the content of the butadiene rubber-based binder was 5 mass% relative to the total mass of the solution.
• the solid electrolyte and butadiene rubber binder were weighed out so that the mass ratio of solid electrolyte to butadiene rubber binder was 99.6:0.4.
• a dispersion medium was added to these and mixed to prepare a solid electrolyte slurry.
• the evaluation cell was charged at a constant current of 1/3 C rate until the voltage of the evaluation cell reached 2.7 V, and then constant voltage charging was performed, and was terminated when the charging current reached the equivalent of 0.01 C.
• the charging rate was calculated from the design capacity of the evaluation cell (capacity per unit area of the positive electrode was 2 mAh/ cm2 ).
• the evaluation cell was discharged at a constant current of 1/3C until the voltage of the evaluation cell reached 1.5V, and then discharged at a constant voltage, terminating when the discharge current reached the equivalent of 0.01C.
• the evaluation cell was discharged at a constant current rate of 1/3C until the voltage reached 1.5V, after which it was discharged at a constant voltage, which was terminated when the discharge current reached the equivalent of 0.01C.
• the evaluation cell was charged at a constant current rate of 5C until the voltage of the evaluation cell reached 2.7V, then it was charged at a constant voltage, and charging was terminated when the charging current reached the equivalent of 1/3C.
• the current was discharged at a constant rate of 1C until the voltage of the evaluation cell reached 1.8V.
• the evaluation cell was placed in a thermostatic chamber at 25°C and charged at a constant current of 1/3 rate until the voltage of the evaluation cell reached 2.2V, and then charged at a constant voltage, which was terminated when the charging current reached the equivalent of 0.01C.
• the evaluation cell was left to stand for 1 minute, and then discharged for 10 seconds at a current of 24C rate.
• the value obtained by dividing the voltage drop of the evaluation cell immediately before the start of discharge and 0.1 seconds after the start of discharge by the current value was taken as the resistance R2 after the cycle test.
• the values ( R2 / R1 ) obtained by dividing the resistance R2 after the cycle test by the initial resistance R1 are shown in Tables 4 to 7.
• the content of the second conductive material shown in Tables 4 to 7 is the ratio of the mass of the second conductive material to the total mass of the positive electrode active material and the second conductive material (100 x second conductive material/(positive electrode active material + second conductive material)).
• the electronic conductivity of the positive electrode active material layer of Examples 1 and 2 was equivalent to that of the positive electrode active material layer of Comparative Examples 1 and 4 to 7.
• the initial resistance R 1 of the evaluation cells of Comparative Examples 1 and 4 to 7 was greater than the initial resistance R 1 of the evaluation cells of Examples 1 and 2, being 9.5 ⁇ cm 2 or more. It is presumed that the initial resistance R 1 of the evaluation cell of Comparative Example 1 was greater than the initial resistance R 1 of the evaluation cells of Examples 1 and 2 because the positive electrode material of Comparative Example 1 did not contain the second conductive material, and therefore the uniformity of the electrochemical reaction of the positive electrode active material layer was not ensured.
• the reason why the initial resistance R 1 of the evaluation cells of Comparative Examples 4 to 7 was larger than the initial resistance R 1 of the evaluation cells of Examples 1 and 2 is presumably because the second conductive material contained in the positive electrode materials of Comparative Examples 4 to 7 was not a fibrous carbon material, or because the average diameter or average fiber diameter of the second conductive material was large and the content was high, causing the second conductive material to narrow the ion conduction path in the positive electrode active material layer, and as a result, uniformity of the electrochemical reaction was not ensured.
• the content of the second conductive material in the positive electrode material of Example 3 was the same as the content of the second conductive material in the positive electrode material of Comparative Example 2.
• the electronic conductivity of the positive electrode active material layer of Comparative Example 2 was smaller than that of the positive electrode active material layer of Example 3. This is presumed to be because the positive electrode material of Comparative Example 2 did not contain the first conductive material, and therefore the uniformity of the electrochemical reaction of the positive electrode active material layer was not ensured.
• both the initial resistances R 1 and R 2 /R 1 of the evaluation cell of Comparative Example 2 were larger than the initial resistances R 1 and R 2 /R 1 of the evaluation cell of Example 3.
• the positive electrode materials of Examples 1 to 4 had different contents of the second conductive material. As shown in Table 7, in the evaluation cells of Examples 1 to 4, the initial resistance R 1 was reduced and the increase in resistance when charging and discharging was repeated was suppressed. In addition, as can be seen from the comparison of the electronic conductivity of the positive electrode active material layer of Examples 1 to 4, in the evaluation cells of Examples 1 to 3 in which the content of the second conductive material was 0.005% or more and 0.02% or less, R 2 /R 1 was 1.5 or less, and the increase in resistance when charging and discharging was further suppressed.
• the present disclosure provides a positive electrode material that can reduce the initial resistance of a battery and suppress the increase in battery resistance when the battery is repeatedly charged and discharged.
• the positive electrode material disclosed herein is used, for example, in batteries (e.g., all-solid-state lithium-ion secondary batteries).

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