WO2024195636A1 - 全固体二次電池用正極および全固体二次電池 - Google Patents

全固体二次電池用正極および全固体二次電池 Download PDF

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WO2024195636A1
WO2024195636A1 PCT/JP2024/009611 JP2024009611W WO2024195636A1 WO 2024195636 A1 WO2024195636 A1 WO 2024195636A1 JP 2024009611 W JP2024009611 W JP 2024009611W WO 2024195636 A1 WO2024195636 A1 WO 2024195636A1
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positive electrode
solid
state secondary
active material
secondary battery
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French (fr)
Japanese (ja)
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健太郎 冨田
一揮 古川
春樹 上剃
昂一 末松
賢 渡邉
憲剛 島ノ江
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Maxell Ltd
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Maxell Ltd
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Priority to JP2025508344A priority Critical patent/JPWO2024195636A1/ja
Priority to EP24774775.1A priority patent/EP4682970A1/en
Priority to KR1020257029226A priority patent/KR20250144424A/ko
Priority to CN202480017715.XA priority patent/CN120883383A/zh
Publication of WO2024195636A1 publication Critical patent/WO2024195636A1/ja
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    • 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
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • 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
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/058—Construction or manufacture
    • H01M10/0585—Construction or manufacture of accumulators having only flat construction elements, i.e. flat positive electrodes, flat negative electrodes and flat separators
    • 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
    • H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
    • H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
    • 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
    • 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
    • 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

  • the present invention relates to an all-solid-state secondary battery that has high capacity and excellent heat resistance, and a positive electrode for constituting the all-solid-state secondary battery.
  • lithium secondary batteries particularly lithium ion secondary batteries, that can meet this demand use lithium-containing composite oxides such as lithium cobalt oxide ( LiCoO2 ) and lithium nickel oxide ( LiNiO2 ) as the positive electrode active material, graphite or the like as the negative electrode active material, and an organic electrolyte solution containing an organic solvent and a lithium salt as the non-aqueous electrolyte.
  • lithium-containing composite oxides such as lithium cobalt oxide ( LiCoO2 ) and lithium nickel oxide ( LiNiO2 ) as the positive electrode active material, graphite or the like as the negative electrode active material, and an organic electrolyte solution containing an organic solvent and a lithium salt as the non-aqueous electrolyte.
  • lithium-ion secondary batteries With the further development of devices that use lithium-ion secondary batteries, there is a demand for lithium-ion secondary batteries with longer life, higher capacity, and higher energy density, as well as a high demand for the reliability of lithium-ion secondary batteries with longer life, higher capacity, and higher energy density.
  • the organic electrolyte used in lithium-ion secondary batteries contains organic solvents, which are flammable substances, and so there is a possibility that the organic electrolyte may generate abnormal heat if an abnormality such as a short circuit occurs in the battery. Furthermore, with the recent trend toward higher energy density in lithium-ion secondary batteries and an increasing amount of organic solvent in the organic electrolyte, there is a demand for even greater reliability in lithium-ion secondary batteries.
  • All-solid-state lithium secondary batteries that do not use organic solvents (all-solid-state secondary batteries) are also being considered.
  • All-solid-state lithium secondary batteries use a molded solid electrolyte that does not use organic solvents instead of the conventional organic solvent-based electrolyte, and are highly reliable with no risk of abnormal heat generation from the solid electrolyte.
  • all-solid-state secondary batteries are also highly reliable and environmentally resistant, and have a long lifespan, making them promising maintenance-free batteries that can contribute to social development while also continuing to contribute to safety and security.
  • Providing all-solid-state secondary batteries to society can contribute to the achievement of Goal 3 (Ensure healthy lives and promote well-being for all at all ages), Goal 7 (Ensure access to affordable, reliable, sustainable and modern energy for all), Goal 11 (Make cities and human settlements inclusive, safe, resilient and sustainable), and Goal 12 (Ensure sustainable consumption and production patterns) out of the 17 Sustainable Development Goals (SDGs) established by the United Nations.
  • SDGs Sustainable Development Goals
  • Non-Patent Documents 1 to 3 As the solid electrolyte for all-solid-state secondary batteries, sulfide-based solid electrolytes with excellent ionic conductivity are often used. However, attempts have also been made to use compositions containing Li 3 PO 4 , Li 3 BO 3 , Li 2 SO 4 and the like as the solid electrolyte (Non-Patent Documents 1 to 3).
  • a molded body of a positive electrode mixture containing a solid electrolyte and a conductive additive together with a positive electrode active material, or a layer (positive electrode mixture layer) made of the positive electrode mixture is generally formed on a current collector.
  • the solid electrolyte may oxidize to form a resistance layer, which may reduce the ionic conductivity in the positive electrode. This type of problem is particularly likely to occur when a sulfide-based solid electrolyte is used as the solid electrolyte contained in the positive electrode mixture.
  • the use of a solid electrolyte instead of an organic solvent electrolyte is expected to improve the heat resistance of all-solid-state secondary batteries, and there is a demand for applications in which the batteries are placed in high-temperature environments.
  • the inventors have found that the resistance of the positive electrode is likely to increase due to the generation of a resistance layer caused by the deterioration of the sulfide-based solid electrolyte in the positive electrode, which causes a decrease in the battery characteristics.
  • the present invention was made in consideration of the above circumstances, and its purpose is to provide an all-solid-state secondary battery that has a high capacity and excellent heat resistance, and a positive electrode for constituting the all-solid-state secondary battery.
  • the positive electrode for an all-solid-state secondary battery of the present invention contains a positive electrode active material and a sulfide-based solid electrolyte, and is characterized in that at least a portion of the surface of the positive electrode active material is coated with a coating layer having a composition that includes a compound containing a P-O bond and a compound containing a B-O bond.
  • the all-solid-state secondary battery of the present invention is characterized in that it has at least one laminate in which a positive electrode and a negative electrode face each other via a solid electrolyte layer, and that the positive electrode is the positive electrode for the all-solid-state secondary battery of the present invention.
  • the present invention provides an all-solid-state secondary battery that has high capacity and excellent heat resistance, and a positive electrode for constituting the all-solid-state secondary battery.
  • FIG. 1 is a cross-sectional view illustrating an example of an all-solid-state secondary battery of the present invention.
  • FIG. 2 is a plan view illustrating another example of the all-solid-state secondary battery of the present invention.
  • 3 is a cross-sectional view taken along line II in FIG. 2.
  • the positive electrode for an all-solid-state secondary battery of the present invention (hereinafter, may be simply referred to as "positive electrode”) contains a positive electrode active material and a sulfide-based solid electrolyte, and at least a portion of the surface of the positive electrode active material is coated with a coating layer having a composition containing a compound containing a P-O bond and a compound containing a B-O bond.
  • LiNbO 3 and Al 2 O 3 used as materials for the coating layer of the positive electrode active material of the all-solid-state secondary battery are oxides consisting of only O 2- anions, so that a side reaction occurs in which electrons are pulled out from O 2- at a voltage of 4.1 V or more.
  • highly reactive oxygen radicals are generated, which react with S 2- and PS 4 3- , which are components of the sulfide-based solid electrolyte, forming a resistance layer that hinders ion conduction at the interface between the positive electrode active material and the sulfide-based solid electrolyte.
  • the formation of such a resistance layer is likely to occur, particularly when the all-solid-state secondary battery is placed in a high-temperature environment. Therefore, when the all-solid-state secondary battery is used in a high-temperature environment, the formation of the resistance layer proceeds by charging the all-solid-state secondary battery, increasing the internal resistance and deteriorating the battery characteristics.
  • a positive electrode having a positive electrode active material and a sulfide-based solid electrolyte at least a portion of the surface of the positive electrode active material is coated with a coating layer having a composition that includes a compound containing a P-O bond and a compound containing a B-O bond.
  • the coating layer having the composition unlike the coating layer composed of LiNbO 3 or Al 2 O 3 , the above-mentioned side reaction generating oxygen radicals is unlikely to occur. Therefore, even when the all-solid-state secondary battery having the positive electrode for the all-solid-state secondary battery of the present invention (the all-solid-state secondary battery of the present invention) is placed in a high-temperature environment of, for example, about 160° C., the formation of a resistance layer at the interface between the positive electrode active material and the sulfide-based solid electrolyte is suppressed, and an increase in internal resistance is suppressed.
  • a compound having a P-O bond has a very low Li ion conductivity
  • Li 3 PO 4 has a Li ion conductivity of the order of 10 ⁇ 8 S/cm
  • the composition in which a compound containing a P-O bond and a compound containing a B-O bond coexist has a high Li ion conductivity of the order of 10 ⁇ 6 to 10 ⁇ 5 S/cm.
  • Li ions can be smoothly transferred between the positive electrode active materials and between the positive electrode active material and the sulfide-based solid electrolyte, and therefore an increase in the initial resistance of the positive electrode for an all-solid-state secondary battery and in the initial internal resistance of the all-solid-state secondary battery is suppressed.
  • Positive electrodes include those consisting only of a compact of a positive electrode mixture containing a positive electrode active material and a sulfide-based solid electrolyte (such as pellets), and those having a structure in which a layer (positive electrode mixture layer) consisting of a compact of a positive electrode mixture is formed on a current collector.
  • the positive electrode active material can be any positive electrode active material used in conventionally known non-aqueous electrolyte secondary batteries, that is, any active material capable of absorbing and releasing Li ions, but it is preferable for it to satisfy any of the following general formulas (1) to (4).
  • M1 is at least one element selected from the group consisting of Al, Mg, Ti, V, Cr, Zr, Fe, Ni, Cu, Zn, Ga, Ge, Nb, Mo, Sn, Sb, and Ba, and 0 ⁇ x ⁇ 0.5.
  • M2 is at least one element selected from the group consisting of Co, Mg, Al, B, Ti, V, Cr, Fe, Cu, Zn, Zr, Mo, Sn, Ca, Sr, and W, and 0 ⁇ a ⁇ 1, 0 ⁇ b ⁇ 1, and 0 ⁇ a+b ⁇ 1.
  • M3 is at least one selected from the group consisting of Al, Mg, Ti, Zr, Fe, Co, Cu, Zn, Ga, Ge, Nb, Mo, Sn, Sb and Ba. and 0 ⁇ c ⁇ 0.5.
  • M4 is Li, B, Mg, Ca, Sr, Ba, Ti, V, Cr, Fe, Co, Ni, Cu, Al, Sn, Sb, In, Nb, Mo, W , Y, Ru, and Rh
  • X is at least one element selected from the group consisting of F, Cl, Br, and S, and 0 ⁇ d ⁇ 1 .2, 0 ⁇ e ⁇ 0.5.
  • impurities such as sodium sulfate that are generated during the synthesis of the positive electrode active material may adhere to the surface of the positive electrode active material as long as the effect of the present invention is not impaired.
  • the average particle diameter of the positive electrode active material is preferably 0.1 ⁇ m or more, more preferably 0.5 ⁇ m or more, and preferably 25 ⁇ m or less, more preferably 10 ⁇ m or less, from the viewpoint of reducing side reactions that cause deterioration of the battery capacity and increasing the density of the positive electrode.
  • the positive electrode active material may be either primary particles or secondary particles formed by agglomeration of primary particles. When a positive electrode active material with an average particle diameter in the above range is used, a large interface with the sulfide-based solid electrolyte contained in the positive electrode can be obtained, and the load characteristics of an all-solid-state secondary battery using this positive electrode are further improved.
  • the average particle diameter of the positive electrode active material and the solid electrolyte described later in this specification means the 50% diameter value ( D50 ) in the volume-based integrated fraction when the integrated volume is determined from particles with small particle sizes using a particle size distribution measurement device (such as a Microtrack particle size distribution measurement device "HRA9320” manufactured by Nikkiso Co., Ltd.).
  • At least a portion of the surface of the positive electrode active material is coated with a coating layer having a composition that includes a compound containing a P-O bond and a compound containing a B-O bond.
  • compounds containing a P-O bond include Li3PO4 , Li4P2O7 , LiTi2 ( PO4 ) 3 , LiLa( PO3 ) 4 , LiCs ( PO3 ) 2 , and P2O5 .
  • compounds containing a B- O bond include Li3BO3, Li2B4O7 , LiBO2 , Li2B2O4 , B2O3 , and LiBa( B3O5 ) 3 .
  • the composition constituting the coating layer preferably further contains a compound containing an S-O bond.
  • the effect of lowering the initial resistance of the positive electrode and the effect of increasing the heat resistance of the positive electrode are further improved.
  • Specific examples of compounds containing an S—O bond include Li 2 SO 4 and Li 2 S 2 O 7 .
  • the coating layer may contain inorganic particles in addition to the composition.
  • inorganic particles it becomes easier to increase the coverage of the positive electrode active material surface with the coating layer, and the effect of forming the coating layer is further improved.
  • inorganic particles contained in the coating layer include Al2O3 , BaTiO3, Li4Ti5O12 , Li4GeO4 , ZrO2 , Li2ZrO3 , LiNbO3 , LiTaO3 , WO3 , LiWO2 , MoO3 , and Li2MoO4 .
  • oxide particles such as Al2O3
  • the formation of a resistance layer at the interface between the positive electrode active material and the sulfide-based solid electrolyte proceeds when the battery in a charged state is placed in a high-temperature environment, as described above.
  • the coating layer is composed of a composition containing such oxide particles as well as a compound containing a P—O bond and a compound containing a B—O bond, it has been found that the formation of a resistance layer at the interface between the positive electrode active material and the sulfide-based solid electrolyte is suppressed even when the charged battery is placed in a high-temperature environment, although the reason is not clear.
  • the relationship between the content of P (phosphorus) derived from the compound containing a P-O bond and the content of B (boron) derived from the compound containing a B-O bond is preferably P ⁇ B in element ratio.
  • the composition contains a compound containing a P-O bond and a compound containing a B-O bond such that such a relationship is satisfied, the Li ion conductivity of the composition is further improved, and the initial resistance of the positive electrode can be further reduced.
  • the content of the compound containing a P-O bond and the content of the compound containing a B-O bond are preferably as follows, from the viewpoint of ensuring the effect of increasing the capacity of the all-solid-state secondary battery and improving its heat resistance.
  • the content of the compound containing a P-O bond is preferably 40 mol% or more, more preferably 45 mol% or more, preferably 95 mol% or less, and more preferably 80 mol% or less, when the total of the P element, the B element, and the S element is taken as 100 mol%.
  • the content of the compound containing a B-O bond is preferably 5 mol% or more, more preferably 10 mol% or more, preferably 50 mol% or less, and more preferably 40 mol% or less, when the total of the P element, the B element, and the S element is taken as 100 mol%.
  • the content of the S element in the composition is preferably 1 mol % or more, and more preferably 3 mol % or more, when the total of the P element, the B element, and the S element is taken as 100 mol %, from the viewpoint of better ensuring the above-mentioned effect by using the compound containing an S-O bond. Furthermore, if the amount of the compound containing an S-O bond in the composition constituting the coating layer is too large, the amount of the compound containing a P-O bond and the compound containing a B-O bond will decrease, and there is a risk that the effects due to these will be reduced.
  • the content of the compound containing an S-O bond in the composition constituting the coating layer is preferably 40 mol % or less, and more preferably 35 mol % or less, when the total of the P element, the B element, and the S element is taken as 100 mol %.
  • the content of the composition in the coating layer is preferably 10% by mass or more, and more preferably 20% by mass or more, from the viewpoint of better ensuring the effect. Note that since the coating layer may be composed of only the composition, the upper limit of the content of the composition in the coating layer is 100% by mass.
  • the content of the inorganic particles in the coating layer is preferably 3% by mass or more, and more preferably 5% by mass or more, from the viewpoint of ensuring good effects due to its use.
  • the upper limit of the content of the inorganic particles in the coating layer is desirably set within a range in which the content of the composition in the coating layer satisfies the above-mentioned preferable lower limit.
  • the component analysis of the coating layer and the composition is carried out according to the following procedure.
  • the cut surface of the electrode is smoothed by ion milling, and elemental analysis is carried out by observation with a field emission electron microanalyzer (FE-EPMA) or by observation with an Auger electron microscope.
  • FE-EPMA field emission electron microanalyzer
  • the electrode surface is processed with an FIB to prepare a cross section of the electrode, and elemental analysis may be carried out using an energy dispersive X-ray spectrometer (EDX) or an electron energy loss spectrometer (EELS) with a scanning transmission electron microscope (STEM).
  • EDX energy dispersive X-ray spectrometer
  • EELS electron energy loss spectrometer
  • STEM scanning transmission electron microscope
  • the average thickness of the coating layer is preferably 1 nm or more, and more preferably 5 nm or more.
  • the average thickness of the coating layer is preferably 100 nm or less, and more preferably 30 nm or less.
  • the average thickness of the coating layer can be measured by performing various element mappings in addition to the component analysis of the coating layer and the composition. Specifically, the region containing P, B and O in the interval between the region containing transition metal elements as constituent elements of the positive electrode active material and the region containing S as a constituent element of the solid electrolyte, or F, Cl, Br or I if the solid electrolyte contains a halogen element, is regarded as the coating layer, and the thickness can be evaluated by obtaining the arithmetic average.
  • the boundary of the above region is the point where the intensity of the signal attributable to the transition metal elements as constituent elements of the positive electrode active material and S, F, Cl, Br or I as constituent elements of the solid electrolyte is half that of the average intensity in the bulk.
  • the coverage of the coating layer on the surface of the positive electrode active material is preferably 50% or more, more preferably 70% or more, and particularly preferably 100%, from the viewpoint of better ensuring the effect of the coating layer.
  • the coverage rate of the coating layer is calculated by dividing the length of the boundary line where the coating layer and the positive electrode active material particle contact each other by the perimeter of the cross section of the positive electrode active material particle for five or more particles of each positive electrode active material sample used in the thickness measurement described above, and then averaging the results.
  • a method can be used in which an aqueous solution containing the components of the composition (e.g., a compound containing a P-O bond, a compound containing a B-O bond, etc.) is prepared, the positive electrode active material is immersed in this aqueous solution, or the aqueous solution is sprayed onto the surface of the positive electrode active material to adhere the aqueous solution to the surface of the positive electrode active material, and then the aqueous solution is dried to remove the water.
  • the components of the composition e.g., a compound containing a P-O bond, a compound containing a B-O bond, etc.
  • a method can be adopted in which inorganic particles are attached to the surface of the positive electrode active material by wet or dry methods, and then an aqueous solution containing the composition is used to attach the aqueous solution in the same manner as described above, followed by drying.
  • an aqueous solution containing the composition is used to attach the aqueous solution in the same manner as described above, followed by drying.
  • the content of the positive electrode active material in the positive electrode mixture is preferably 40 to 90 mass %.
  • Examples of sulfide-based solid electrolytes for the positive electrode include particles of Li 2 S-P 2 S 5 , Li 2 S-SiS 2 , Li 2 S - P 2 S 5 -GeS 2 , and Li 2 S - B 2 S 3 - based glass .
  • thio - LISICON -type electrolytes which have been attracting attention in recent years for their high Li ion conductivity , are also available .
  • argyrodite-type sulfide-based solid electrolytes are preferred, as they have particularly high Li-ion conductivity and high chemical stability.
  • the positive electrode may contain, in addition to the sulfide-based solid electrolyte, a solid electrolyte other than the sulfide-based solid electrolyte (such as a hydride-based solid electrolyte, a halide-based solid electrolyte, or an oxide-based solid electrolyte).
  • a solid electrolyte other than the sulfide-based solid electrolyte such as a hydride-based solid electrolyte, a halide-based solid electrolyte, or an oxide-based solid electrolyte.
  • Examples of hydride-based solid electrolytes include LiBH 4 , solid solutions of LiBH 4 and the following alkali metal compounds (for example, those in which the molar ratio of LiBH 4 to the alkali metal compound is 1:1 to 20:1), etc.
  • Examples of the alkali metal compounds in the solid solutions include at least one selected from the group consisting of lithium halides (LiI, LiBr, LiF, LiCl, etc.), rubidium halides (RbI, RbBr, RbF, RbCl, etc.), cesium halides (CsI, CsBr, CsF, CsCl, etc.), lithium amide, rubidium amide, and cesium amide.
  • lithium halides LiI, LiBr, LiF, LiCl, etc.
  • rubidium halides RbI, RbBr, RbF, RbCl, etc.
  • cesium halides CsI, CsBr, CsF, Cs
  • Other known solid electrolytes that can be used include those described in, for example, WO 2020/070958 and WO 2020/070955.
  • the average particle size of the solid electrolyte is preferably 0.1 ⁇ m or more, and more preferably 0.2 ⁇ m or more, from the viewpoint of reducing grain boundary resistance, while it is preferably 10 ⁇ m or less, and more preferably 5 ⁇ m or less, from the viewpoint of forming a sufficient contact interface between the positive electrode active material and the solid electrolyte.
  • the content of the solid electrolyte in the positive electrode mixture is preferably 5 to 60 mass%.
  • a solid electrolyte other than a sulfide-based solid electrolyte it is preferable that the proportion of the sulfide-based solid electrolyte is 50 mass% or more when the total amount of the solid electrolyte in the positive electrode mixture is taken as 100 mass%.
  • the positive electrode can contain a conductive additive.
  • conductive additives include carbon materials such as graphite (natural graphite, artificial graphite), graphene, carbon black, carbon nanofibers, and carbon nanotubes.
  • the content of the conductive additive in the positive electrode mixture is preferably 1 to 10 mass%.
  • a positive electrode having a molded body of a positive electrode mixture since it contains a sulfide-based solid electrolyte, the molded body of the positive electrode mixture can ensure good moldability even if it does not contain a binder. Therefore, the positive electrode does not need to contain a binder, but it can also contain a fluororesin such as polyvinylidene fluoride (PVDF) as a binder.
  • PVDF polyvinylidene fluoride
  • the binder content in the positive electrode mixture is preferably 5% by mass or less, more preferably 3% by mass or less, and even more preferably 0% by mass (i.e., no binder is contained).
  • the current collector can be made of a metal foil such as aluminum, nickel, or stainless steel, punched metal, mesh, expanded metal, foamed metal, carbon sheet, etc.
  • the positive electrode can be formed, for example, by compressing a positive electrode mixture prepared by mixing a positive electrode active material and a sulfide-based solid electrolyte, etc., into a molded body by pressure molding or the like.
  • a positive electrode having a current collector it can be manufactured by bonding the molded body of the positive electrode mixture formed by the method described above to the current collector by pressing it together.
  • the positive electrode mixture may be mixed with a solvent to prepare a positive electrode mixture-containing composition, which may then be applied to a substrate such as a current collector or a solid electrolyte layer that faces the positive electrode, dried, and then pressed to form a positive electrode mixture compact, thereby producing a positive electrode.
  • a substrate such as a current collector or a solid electrolyte layer that faces the positive electrode, dried, and then pressed to form a positive electrode mixture compact, thereby producing a positive electrode.
  • a solvent for the positive electrode mixture-containing composition that does not easily deteriorate the solid electrolyte.
  • non-polar aprotic solvents such as hydrocarbon solvents such as hexane, heptane, octane, nonane, decane, decalin, toluene, xylene, methanestyrene, and tetralin.
  • ultra-dehydrated solvents with a water content of 0.001 mass% (10 ppm) or less.
  • fluorine-based solvents such as “Vertrel (registered trademark)” manufactured by Mitsui DuPont Fluorochemicals, “Zeorolla (registered trademark)” manufactured by Nippon Zeon Co., Ltd., and “Novec (registered trademark)” manufactured by Sumitomo 3M Co., Ltd., as well as non-aqueous organic solvents such as dichloromethane, diethyl ether, and anisole can also be used.
  • the thickness of the positive electrode mixture compact (in the case of a positive electrode having a current collector, the thickness of the positive electrode mixture compact per one side of the current collector; the same applies below) is usually 100 ⁇ m or more, but from the viewpoint of increasing the capacity of the all-solid-state secondary battery, it is preferably 200 ⁇ m or more. In addition, the thickness of the positive electrode mixture compact is usually 3000 ⁇ m or less.
  • the thickness of the positive electrode mixture layer is preferably 10 to 1000 ⁇ m.
  • the Raman spectrum thereof has two peaks in the region of 900 to 950 cm ⁇ 1 , that is, a peak derived from a compound containing a P—O bond and a peak derived from a compound containing a B—O bond.
  • the Raman spectrum of the positive electrode can be obtained by observing the polished surface of the electrode using a confocal laser Raman microscope (RAMANTouch, Nanophoton) and an airtight cell (LIBcell, Nanophoton).
  • the polished surface of the electrode can be prepared by peeling off the current collector from the positive electrode in a glove box in an Ar gas environment with a dew point of -60°C or less, or by polishing it with a coarse polishing film, and finally polishing it with a polishing film with a grit of 4000 or more.
  • the sample obtained is sealed so that the polished surface of the sample faces the quartz window plate of the airtight cell, and observation is performed using an excitation laser with a wavelength of 532 nm and an objective lens with a magnification of 50 times or more (with a glass correction ring).
  • an excitation laser with a wavelength of 532 nm and an objective lens with a magnification of 50 times or more (with a glass correction ring).
  • it is more preferable to obtain a Raman microscope image of the sample examine the position of the aggregates of the positive electrode active material from the position where the peak attributed to the positive electrode active material was obtained, and point-observe the coating layer in the space between the particles.
  • the positive electrode described above has the coating layer on the surface of the positive electrode active material, its XPS (X-ray photoelectron spectroscopy) spectrum has peaks at 134 ⁇ 1 eV and 191.5 ⁇ 1 eV (peaks derived from compounds containing P-O bonds and peaks derived from compounds containing B-O bonds).
  • XPS X-ray photoelectron spectroscopy
  • the XPS spectrum of the positive electrode can be obtained as follows.
  • the polished surface of the positive electrode is prepared in the same manner as in the measurement of the Raman spectrum, and the battery is fixed to the sample stage with insulating double-sided tape with the polished surface facing up.
  • a conductive metal clip is attached to the sample stage, and the tip of the clip is pressed against the polished surface by the elastic force of the clip to balance the Fermi level between the polished surface and the spectrometer.
  • charging neutralization such as low-energy electron beam irradiation or low-energy ion beam irradiation may be performed for measurement.
  • the bond energy of the obtained XPS spectrum is corrected by setting the peak position of the peak attributable to the hydrocarbon adsorbed on the sample surface in the C1s spectrum to 284.8 eV.
  • the bond energy may be corrected by performing Au sputtering treatment on the polished surface of the sample and setting the peak position of Au4f to 83.95 eV.
  • the all-solid-state secondary battery of the present invention is a battery having at least one laminate in which a positive electrode and a negative electrode face each other via a solid electrolyte layer, and the positive electrode is the positive electrode for the all-solid-state secondary battery of the present invention.
  • the configuration other than the positive electrode various configurations adopted in conventionally known all-solid-state secondary batteries can be applied.
  • FIG. 1 A cross-sectional view showing a schematic example of an all-solid-state secondary battery of the present invention is shown in FIG. 1.
  • the all-solid-state battery 1 shown in FIG. 1 has a positive electrode 10, a negative electrode 20, and a solid electrolyte layer 30 interposed between the positive electrode 10 and the negative electrode 20 enclosed within an exterior body formed of an exterior can 40, a sealing can 50, and a resin gasket 60 interposed between them, and the positive electrode 10 is the positive electrode for the all-solid-state secondary battery of the present invention.
  • the sealing can 50 fits into the opening of the exterior can 40 via a gasket 60, and the open end of the exterior can 40 is tightened inward, causing the gasket 60 to come into contact with the sealing can 50, sealing the opening of the exterior can 40 and creating an airtight structure inside the element.
  • the outer can and the sealing can can be made of stainless steel or the like.
  • the gasket can be made of polypropylene, nylon, or other materials.
  • a heat-resistant resin with a melting point of over 240°C can be used.
  • heat-resistant resins include fluororesins (such as tetrafluoroethylene-perfluoroalkoxyethylene copolymer (PFA)), polyphenylene ether (PPE), polysulfone (PSF), polyarylate (PAR), polyethersulfone (PES), polyphenylene sulfide (PPS), and polyetheretherketone (PEEK).
  • PFA tetrafluoroethylene-perfluoroalkoxyethylene copolymer
  • PPE polyphenylene ether
  • PSF polysulfone
  • PAR polyarylate
  • PES polyethersulfone
  • PPS polyphenylene sulfide
  • PEEK polyetheretherketone
  • FIGS. 2 and 3 are diagrams showing schematic diagrams of other examples of the all-solid-state secondary battery of the present invention.
  • FIG. 2 is a plan view of the all-solid-state secondary battery
  • FIG. 3 is a cross-sectional view taken along line I-I in FIG. 2.
  • the all-solid-state secondary battery 100 shown in Figures 2 and 3 contains an electrode body 200 consisting of a positive electrode for the all-solid-state secondary battery of the present invention, a solid electrolyte layer, and a negative electrode, inside a laminate film exterior body 500 made of two sheets of metal laminate film, and the laminate film exterior body 500 is sealed at its outer periphery by heat fusing the upper and lower metal laminate films.
  • the layers constituting the laminate film exterior body 500 and the positive electrode, solid electrolyte layer, and negative electrode constituting the electrode body are not shown separately.
  • the positive electrode of the electrode body 200 is connected to the positive electrode external terminal 300 within the battery 100, and although not shown, the negative electrode of the electrode body 200 is also connected to the negative electrode external terminal 400 within the battery 100.
  • One end of the positive electrode external terminal 300 and the negative electrode external terminal 400 is extended to the outside of the laminate film exterior body 500 so that they can be connected to external devices, etc.
  • the negative electrode of the all-solid-state secondary battery has, for example, a molded body of a negative electrode mixture containing a negative electrode active material, a lithium sheet, or a lithium alloy sheet.
  • the negative electrode is a molded product of a negative electrode mixture containing a negative electrode active material
  • examples of the negative electrode include a molded product (such as a pellet) made by molding the negative electrode mixture, and a structure in which a layer (negative electrode mixture layer) made of a molded product of the negative electrode mixture is formed on a current collector.
  • the negative electrode active material may be, for example, one or a mixture of two or more carbonaceous materials capable of absorbing and releasing lithium, such as graphite, pyrolytic carbons, cokes, glassy carbons, fired bodies of organic polymer compounds, mesocarbon microbeads (MCMB), and carbon fibers.
  • carbonaceous materials capable of absorbing and releasing lithium
  • simple substances, compounds and alloys thereof containing elements such as Si, Sn, Ge, Bi, Sb, and In
  • compounds capable of charging and discharging at a low voltage close to that of lithium metal such as lithium-containing nitrides or lithium-containing oxides; lithium metal; and lithium/aluminum alloys may also be used as the negative electrode active material.
  • one or a mixture of two or more of metal oxides such as Li 4 Ti 5 O 12 , TiO 2 , NbO 2.5- ⁇ ( 0 ⁇ 0.5), MoO 3- ⁇ (0 ⁇ 1), WO 3- ⁇ (0 ⁇ 1), TiNb 2 O 7 , and metal sulfides such as WS 2 and MoS 2 can be used as the negative electrode active material.
  • metal oxides such as Li 4 Ti 5 O 12 , TiO 2 , NbO 2.5- ⁇ ( 0 ⁇ 0.5), MoO 3- ⁇ (0 ⁇ 1), WO 3- ⁇ (0 ⁇ 1), TiNb 2 O 7 , and metal sulfides such as WS 2 and MoS 2 can be used as the negative electrode active material.
  • the content of the negative electrode active material in the negative electrode mixture is preferably 50 to 95 mass %.
  • the negative electrode mixture may contain a solid electrolyte.
  • the solid electrolyte contained in the negative electrode mixture may be one or more of the sulfide-based solid electrolytes, hydride-based solid electrolytes, and oxide-based solid electrolytes previously exemplified as the solid electrolytes that may be contained in the positive electrode mixture.
  • the solid electrolyte content in the negative electrode mixture is preferably 4 to 70 mass %.
  • the negative electrode mixture may contain a conductive additive.
  • a conductive additive include carbon materials such as graphite (natural graphite, artificial graphite), graphene, carbon black, vapor-grown carbon fiber, carbon nanofiber, and carbon nanotubes.
  • the content of the conductive additive in the negative electrode mixture is preferably 1 to 10 mass %.
  • the negative electrode mixture may or may not contain a binder.
  • Specific examples include the same binders as those exemplified above as those that may be contained in the positive electrode mixture. Note that, for example, in the case where the negative electrode mixture contains a sulfide-based solid electrolyte, if good moldability can be ensured in forming a compact of the negative electrode mixture without using a binder, the negative electrode mixture may not contain a binder.
  • the negative electrode mixture requires a binder, its content is preferably 15% by mass or less, and more preferably 0.5% by mass or more. On the other hand, if good moldability can be obtained without the binder in the negative electrode mixture, its content is preferably 0.5% by mass or less, more preferably 0.3% by mass or less, and even more preferably 0% by mass (i.e., no binder is included).
  • the current collector can be made of copper or nickel foil, punched metal, mesh, expanded metal, foamed metal; carbon sheet; etc.
  • the negative electrode mixture compact can be formed, for example, by compressing the negative electrode mixture prepared by mixing the negative electrode active material, conductive additive, solid electrolyte, and optionally added binder, by pressure molding or the like.
  • a negative electrode having a current collector it can be manufactured by bonding the negative electrode mixture formed by the method described above to the current collector by pressing it together.
  • the negative electrode mixture may be mixed with a solvent to prepare a composition containing the negative electrode mixture, which may then be applied to a substrate such as a current collector or a solid electrolyte layer that faces the negative electrode, dried, and then pressed to form a molded body of the negative electrode mixture.
  • a solvent such as a current collector or a solid electrolyte layer that faces the negative electrode, dried, and then pressed to form a molded body of the negative electrode mixture.
  • the solvent used in the positive electrode mixture-containing composition it is desirable to select a solvent that is unlikely to deteriorate the solid electrolyte, and it is preferable to use the various solvents listed above as examples of solvents for the positive electrode mixture-containing composition, and it is particularly preferable to use an ultra-dehydrated solvent with a moisture content of 0.001% by mass (10 ppm) or less.
  • the thickness of the negative electrode mixture compact (in the case of an electrode having a current collector, the thickness of the negative electrode mixture compact per one side of the current collector; the same applies below) is usually 100 ⁇ m or more, but from the viewpoint of increasing the capacity of the all-solid-state secondary battery, it is preferably 200 ⁇ m or more. In addition, the thickness of the negative electrode mixture compact is usually 3000 ⁇ m or less.
  • the thickness of the negative electrode mixture layer is preferably 10 to 1000 ⁇ m.
  • Solid electrolyte layer For the solid electrolyte layer in the all-solid-state secondary battery, one or more of the sulfide-based solid electrolyte, hydride-based solid electrolyte, and oxide-based solid electrolyte exemplified above as the solid electrolyte that can be contained in the positive electrode mixture can be used.
  • the solid electrolytes in order to improve the battery characteristics, it is more preferable to use a sulfide-based solid electrolyte, and it is even more preferable to use an argyrodite-type sulfide-based solid electrolyte.
  • the solid electrolyte layer can be formed by a method of compressing the solid electrolyte by pressure molding or the like; a method of dispersing the solid electrolyte in a solvent to prepare a composition for forming the solid electrolyte layer, applying it to the substrate, positive electrode, or negative electrode, drying it, and, if necessary, performing pressure molding such as pressing.
  • the solid electrolyte layer may also have a porous body such as a resin nonwoven fabric as a support.
  • the solvent used in the positive electrode mixture-containing composition it is desirable to select a solvent that is unlikely to deteriorate the solid electrolyte for use in the composition for forming the solid electrolyte layer. It is preferable to use the various solvents listed above as examples of solvents for the positive electrode mixture-containing composition, and it is particularly preferable to use an ultra-dehydrated solvent with a moisture content of 0.001% by mass (10 ppm) or less.
  • the thickness of the solid electrolyte layer is preferably 10 to 500 ⁇ m.
  • the positive electrode and the negative electrode can be used in a battery in the form of a laminated electrode body in which the positive electrode and the negative electrode are laminated with a solid electrolyte layer interposed therebetween, or in the form of a wound electrode body in which this laminated electrode body is wound.
  • the electrode body When forming the electrode body, it is preferable to pressure mold the positive electrode, negative electrode, and solid electrolyte layer in a stacked state in order to increase the mechanical strength of the electrode body.
  • the form of the all-solid-state secondary battery may be one having an exterior body composed of an exterior can, a sealing can, and a gasket as shown in FIG. 1, that is, one generally called a coin-type battery or a button-type battery, or one having an exterior body composed of a resin film or a metal-resin laminate film as shown in FIGS. 2 and 3, or one having an exterior body having a metallic, bottomed, tubular (cylindrical or rectangular) exterior can and a sealing structure that seals the opening of the can.
  • This precursor was heated from room temperature to 1000 ° C at 11 ° C / min, baked at 1000 ° C for 1 hour, cooled from 1000 ° C to 850 ° C at 1.7 ° C / min, baked at 850 ° C for 12 hours, cooled from 850 ° C to 550 ° C at 3.0 ° C / min, baked at 550 ° C for 12 hours, cooled from 550 ° C to 200 ° C at 3.0 ° C / min, naturally cooled from 200 ° C to room temperature, and then crushed using a mortar to obtain particles of a spinel type positive electrode active material (LiNi 0.5 Mn 1.5 O 4 ).
  • a citric acid aqueous solution with a concentration of 7.5% by mass was prepared. 4.32 g of the citric acid aqueous solution was mixed with 122.4 mg of Li 3 PO 4 , 31.2 mg of Li 3 BO 3 , and 155.0 mg of Al 2 O 3 nanoparticles, and ultrasonically treated for 1 minute, and then stirred until the solution became colorless and transparent. The pH of the aqueous solution was adjusted to 7 using 10% by mass of ammonia water, and 0.25 g of ethanol was added to prepare a coating liquid.
  • the results of STEM-EELS analysis of the sample piece showed that, when the total content of the composition containing Li 3 PO 4 and Li 3 BO 3 was taken as 100 mol%, Li 3 PO 4 was 70 mol%, Li 3 BO 3 was 30 mol% (the relationship between the content of P derived from Li 3 PO 4 and the content of B derived from Li 3 BO 3 was P ⁇ B in element ratio), and the content of each component in the total amount of the coating layer was Li 3 PO 4 and Li 3 BO 3 : composition containing Li 3 PO 4 and Li 3 BO 3: 50 mass%, Al 2 O 3 particles: 50 mass%.
  • the average thickness of the coating layer was 17 nm, and the coverage of the coating layer on the surface of the positive electrode active material was 88%.
  • the cathode active material the surface of which was coated with the coating layer as described above, vapor-grown carbon fiber (conductive assistant), and Li 6 PS 5 Cl (sulfide-based solid electrolyte) were mixed to prepare a cathode mixture.
  • the mixture ratio of the cathode material, conductive assistant, and sulfide-based solid electrolyte was 75:3:22 by mass.
  • 56 mg of this cathode mixture was put into a powder molding die having a diameter of 7.5 mm, and molded at a pressure of 6000 kgf/cm 2 using a press machine to produce a cylindrical cathode mixture compact.
  • the obtained positive electrode had two peaks in the region of 900 to 950 cm ⁇ 1 in the Raman spectrum, and peaks at 134 ⁇ 1 eV and 191.5 ⁇ 1 eV in the XPS spectrum.
  • Lithium titanate Li 4 Ti 5 O 12 , negative electrode active material
  • graphene conductive assistant
  • the laminated electrode body was placed on top of the graphite sheet with the negative electrode facing the graphite sheet side, and another sheet of the graphite sheet was placed on top of that, and a stainless steel outer can was then placed over it, after which the open end of the outer can was crimped inward to seal, thereby producing a flat all-solid-state secondary battery with a diameter of approximately 9 mm in which the graphite sheet was placed between the inner bottom surface of the sealing can and the laminated body, and between the inner bottom surface of the outer can and the laminated electrode body, respectively.
  • Example 2 Particles of a spinel-type positive electrode active material having a coating layer on the surface were obtained in the same manner as in Example 1, except that the Al 2 O 3 nanoparticles were omitted from the composition of the coating liquid.
  • the results of STEM-EELS analysis of a sample piece showed that, when the total content of Li3PO4 and Li3BO3 in the composition containing these was taken as 100 mol%, Li3PO4 : 70 mol% and Li3BO3: 30 mol% (the relationship between the content of P derived from Li3PO4 and the content of B derived from Li3BO3 was P ⁇ B in element ratio ) .
  • the average thickness of the coating layer was 10 nm, and the coverage of the coating layer on the surface of the positive electrode active material was 75%.
  • a flat all-solid-state secondary battery was fabricated in the same manner as in Example 1, except that the positive electrode active material with the surface coated with a coating layer was used.
  • Example 3 The same procedure as in Example 1 was repeated except that Al2O3 nanoparticles were removed from the composition of the coating solution, and the heat treatment conditions were changed to increase the temperature from room temperature to 350°C at 1°C/min, bake at 350°C for 5 hours, and decrease the temperature from 350°C to 200°C at 0.8°C/min, to obtain spinel-type positive electrode active material particles having a coating layer on the surface.
  • the results of STEM-EELS analysis of the sample piece showed that, when the total content of Li3PO4 and Li3BO3 in the composition containing these was taken as 100 mol%, Li3PO4 : 70 mol% and Li3BO3: 30 mol% (the relationship between the content of P derived from Li3PO4 and the content of B derived from Li3BO3 was P ⁇ B in element ratio ) .
  • the average thickness of the coating layer was 11 nm, and the coverage of the coating layer on the surface of the positive electrode active material was 76%.
  • a flat all-solid-state secondary battery was fabricated in the same manner as in Example 1, except that the positive electrode active material with the surface coated with a coating layer was used.
  • Example 4 Particles of a spinel-type positive electrode active material having a coating layer on the surface were obtained in the same manner as in Example 1, except that Al 2 O 3 nanoparticles were removed from the composition of the coating solution and the lithium salt was changed to 96.2 mg of Li 3 PO 4, 27.0 mg of Li 3 BO 3 , and 37.1 mg of Li 2 SO 4.H 2 O.
  • the results of STEM-EELS analysis of a sample piece showed that, when the total content of Li 3 PO 4 , Li 3 BO 3 and Li 2 SO 4 in the composition was taken as 100 mol %, Li 3 PO 4 : 55 mol %, Li 3 BO 3 : 26 mol %, Li 2 SO 4 : 19 mol % (the relationship between the content of P derived from Li 3 PO 4 and the content of B derived from Li 3 BO 3 was P ⁇ B in element ratio).
  • the average thickness of the coating layer was 10 nm, and the coverage of the coating layer on the surface of the positive electrode active material was 75%.
  • a flat all-solid-state secondary battery was then fabricated in the same manner as in Example 1, except that the positive electrode active material with the surface coated with a coating layer was used.
  • Example 5 Particles of spinel-type positive electrode active material having a coating layer on the surface were obtained in the same manner as in Example 1, except that Al2O3 nanoparticles were removed from the composition of the coating solution, the amount of citric acid aqueous solution was changed to 23.8 g , and the lithium salt was changed to 385.8 mg of Li3PO4 , 229.3 mg of Li3BO3 , and 215.3 mg of Li2SO4.H2O.
  • the results of STEM-EELS analysis of a sample piece showed that, when the total content of Li 3 PO 4 , Li 3 BO 3 and Li 2 SO 4 in the composition was taken as 100 mol %, Li 3 PO 4 : 40 mol %, Li 3 BO 3 : 40 mol %, Li 2 SO 4 : 20 mol % (the relationship between the content of P derived from Li 3 PO 4 and the content of B derived from Li 3 BO 3 was P ⁇ B in element ratio).
  • the average thickness of the coating layer was 55 nm, and the coverage of the coating layer on the surface of the positive electrode active material was 80%.
  • a flat all-solid-state secondary battery was fabricated in the same manner as in Example 1, except that the positive electrode active material with the surface coated with a coating layer was used.
  • Example 1 A flat all-solid-state secondary battery was produced in the same manner as in Example 1, except that the same LiNi 0.5 Mn 1.5 O 4 as used in Example 1 was used as the positive electrode active material without providing a coating layer.
  • Comparative Example 2 5 g of LiNi0.5Mn1.5O4 and 0.155 g of Al2O3 nanoparticles were mixed in an agate mortar for 40 minutes, and the mixture was subjected to the same heat treatment as in Example 1, and then crushed in the agate mortar for 10 minutes to obtain a positive electrode active material.
  • a flat all-solid-state secondary battery was produced in the same manner as in Example 1, except that LiNi 0.5 Mn 1.5 O 4 whose surface was coated with Al 2 O 3 nanoparticles as described above was used as the positive electrode active material.
  • a flat all-solid-state secondary battery was produced in the same manner as in Example 1, except that LiNi 0.5 Mn 1.5 O 4 having a surface coated with Li 3 PO 4 as described above was used as the positive electrode active material.
  • the voltage measured after the open circuit voltage measurement was subtracted from the voltage measured one second after the initial discharge was started to obtain the voltage, and the direct current resistance (DCR) was calculated from this value.
  • DCR direct current resistance
  • the all-solid-state secondary battery of the present invention can be used in the same applications as conventionally known secondary batteries, but as described above, because of its excellent heat resistance, it can be preferably used in applications where it is exposed to high temperatures.
  • the positive electrode for the all-solid-state secondary battery of the present invention can constitute the all-solid-state secondary battery of the present invention.
  • Reference Signs List 1 100 All-solid-state secondary battery 10 Positive electrode 20 Negative electrode 30 Solid electrolyte layer 40 Outer can 50 Sealing can 60 Gasket 200 Electrode body 300 Positive electrode external terminal 400 Negative electrode external terminal 500 Laminate film outer case

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