Negative electrode for all-solid-state secondary battery, method for producing same, and all-solid-state secondary battery

Abstract

Provided are: a negative electrode for an all-solid-state secondary battery, which has a low resistance value; a method for producing the negative electrode; and an all-solid-state secondary battery. The present invention relates to targets 12, 3, 7, 11 of sustainable development targets (SDGs). This negative electrode for an all-solid-state secondary battery is characterized by comprising a molded body of a negative electrode mixture containing a solid electrolyte and a negative electrode material containing a negative electrode active material, the negative electrode material containing, as the negative electrode active material, a carbon material having, on the surface thereof, a layer containing an oxide having lithium ion conductivity. The carbon material contains hard carbon, the oxide contains a lithium titanium oxide, the amount of the oxide is 1 part by mass or more with respect to 100 parts by mass of the carbon material, a sulfide-based solid electrolyte is contained as the solid electrolyte, and the thickness of a molded article of the negative electrode mixture is 200 [mu] m or more and 3000 [mu] m or less.

Description

[0001] This application is a divisional application of Chinese patent application No. 202180038233.9, filed on May 21, 2021, entitled “Negative electrode for all-solid-state secondary battery, method of manufacturing the same and all-solid-state secondary battery”. Technical Field

[0002] This invention relates to a negative electrode for an all-solid-state secondary battery with low resistance, a method for manufacturing the same, and an all-solid-state secondary battery using the aforementioned negative electrode. Background Technology

[0003] In recent years, with the development of handheld electronic devices such as mobile phones and laptop computers, and the practical application of electric vehicles, there is a need for small, lightweight, high-capacity, and high-energy-density rechargeable batteries.

[0004] Currently, in lithium secondary batteries that can meet this requirement, especially lithium-ion secondary batteries, lithium-containing composite oxides such as lithium cobalt oxide (LiCoO2) and lithium nickel oxide (LiNiO2) are used as positive electrode active materials, while graphite is used as negative electrode active material. As a non-aqueous electrolyte, an organic electrolyte containing organic solvents and lithium salts is used.

[0005] Furthermore, with the further development of applicable devices for lithium-ion secondary batteries, there is a demand for lithium-ion secondary batteries to have longer lifespans, higher capacity, and higher energy density.

[0006] For example, regarding the high capacity of lithium-ion secondary batteries with organic electrolytes (non-aqueous electrolyte secondary batteries), in Patent Document 1, in order to reduce the irreversible capacity of the negative electrode, a technique was proposed to coat the surface of a carbon material as the negative electrode active material with a solid electrolyte that has lithium-ion conductivity.

[0007] In addition, lithium-ion secondary batteries are required to have long lifespan, high capacity, high energy density, and improved reliability.

[0008] However, the organic electrolytes used in lithium-ion secondary batteries contain organic solvents, which are flammable substances. Therefore, in the event of an abnormal situation such as a short circuit, the organic electrolyte may generate abnormal heat. Furthermore, with the increasing energy density of lithium-ion secondary batteries and the growing trend of increasing organic solvent content in organic electrolytes in recent years, the reliability of lithium-ion secondary batteries is becoming increasingly critical.

[0009] Under the aforementioned circumstances, all-solid-state lithium-ion batteries that do not use organic solvents (all-solid-state secondary batteries) have attracted attention. All-solid-state secondary batteries use a molded form of a solid electrolyte that does not use organic solvents to replace the conventional organic solvent-based electrolyte, eliminating concerns about abnormal heat generation from the solid electrolyte and providing high safety.

[0010] Furthermore, all-solid-state rechargeable batteries not only possess high safety but also high reliability and environmental resistance, along with a long lifespan. Therefore, they are anticipated as a reliable and maintenance-free battery that contributes to social development while ensuring continued safety. Providing society with all-solid-state rechargeable batteries can help achieve the United Nations Sustainable Development Goals (SDGs), specifically Goal 12 (ensuring sustainable production and consumption), Goal 3 (ensuring healthy lives and promoting well-being for all people of all ages), Goal 7 (ensuring access to affordable, reliable, and sustainable modern energy for all), and Goal 11 (enabling inclusive, safe, resilient, and sustainable cities and human habitation).

[0011] In addition, various improvements have been attempted in all-solid-state secondary batteries. For example, Patent Document 2 proposes using coated negative electrode active material in all-solid-state secondary batteries. This coated negative electrode active material suppresses heat generation and reduces resistance by coating the structural defects of a graphite-structured negative electrode active material with lithium niobate particles with an average particle size of less than 1.5 nm.

[0012] Existing technical documents

[0013] Patent documents

[0014] Patent Document 1: International Publication No. 2017 / 169616

[0015] Patent Document 2: Japanese Patent Application Publication No. 2017-54615 Summary of the Invention

[0016] The problem that the invention aims to solve

[0017] Furthermore, the applications of all-solid-state secondary batteries are rapidly expanding, including applications requiring high-current discharge. Therefore, there is a need to improve load characteristics to handle such situations. Additionally, the typical charging method for all-solid-state secondary batteries involves constant-current charging until the battery voltage reaches a specified value, followed by constant-voltage charging until the current decreases to a specified value. However, to improve the fast-charging characteristics of all-solid-state secondary batteries, a large charging capacity during constant-current charging is preferred. Thus, methods to improve the load characteristics and charging capacity (CC capacity) during constant-current charging of all-solid-state secondary batteries include, for example, reducing the resistance of the negative electrode; therefore, there is a need to develop technologies to achieve this.

[0018] In Patent Document 2, as described above, by coating the structural defects of the negative electrode active material with a graphite structure with small-particle lithium niobate, the resistance of the negative electrode active material can be reduced, but the resistance value of the negative electrode cannot be reduced to a degree that sufficiently improves the aforementioned characteristics of the all-solid-state secondary battery.

[0019] The present invention was made in view of the above circumstances, and its object is to provide a negative electrode for an all-solid-state secondary battery with low resistance, a method for manufacturing the same, and an all-solid-state secondary battery using the aforementioned negative electrode.

[0020] Methods for solving problems

[0021] The negative electrode for an all-solid-state secondary battery of the present invention is characterized by having a molded body of a negative electrode mixture, wherein the negative electrode mixture contains a negative electrode material comprising a negative electrode active material and a solid electrolyte, wherein the negative electrode material contains a carbon material having a layer of an oxide having lithium-ion conductivity formed on its surface as a negative electrode active material, wherein the amount of the oxide is 1 part by mass or more relative to 100 parts by mass of the carbon material, and the solid electrolyte contains a sulfide-based solid electrolyte.

[0022] The all-solid-state secondary battery negative electrode of the present invention can be manufactured by the manufacturing method of the present invention, characterized by having the following negative electrode material forming step (A) and a step (B) of forming a molded body of a negative electrode mixture using the negative electrode material obtained by the above negative electrode material forming step (A) and a sulfide-based solid electrolyte.

[0023] Here, in the negative electrode material forming process (A), (1) there is a process (i-1) of attaching an oxide with lithium ion conductivity or a material for forming the oxide to the surface of a carbon material, and a process (i-2) of firing the carbon material that has undergone the above process (i-1) to form a layer containing the oxide on the surface of the carbon material, wherein the amount of the oxide is 1 part by mass or more relative to 100 parts by mass of the carbon material, or (2) there is a process (ii) of mixing the carbon material and the oxide with lithium ion conductivity to form a layer containing the oxide on the surface of the carbon material, wherein the amount of the oxide is 1 part by mass or more relative to 100 parts by mass of the carbon material.

[0024] Furthermore, the all-solid-state secondary battery of the present invention is characterized by having a positive electrode, a negative electrode, and a solid electrolyte layer between the positive electrode and the negative electrode, wherein the negative electrode is the negative electrode for the all-solid-state secondary battery of the present invention.

[0025] Invention Effects

[0026] According to the present invention, it is possible to provide a negative electrode for an all-solid-state secondary battery with low resistance, a method for manufacturing the same, and an all-solid-state secondary battery using the aforementioned negative electrode. Attached Figure Description

[0027] Figure 1 This is a cross-sectional view schematically illustrating an example of the all-solid-state secondary battery of the present invention.

[0028] Figure 2 This is a top view schematically illustrating another example of the all-solid-state secondary battery of the present invention.

[0029] Figure 3 yes Figure 2 Sectional view of line II.

[0030] Symbol Explanation

[0031] 1. 100: All-solid-state secondary battery.

[0032] 10: Positive electrode,

[0033] 20: Negative electrode

[0034] 30: Solid electrolyte layer

[0035] 40: Outer packaging can,

[0036] 50: Sealed jars

[0037] 60: Washer

[0038] 200: Electrode body,

[0039] 300: Positive external terminal,

[0040] 400: External negative terminal

[0041] 500: Laminated outer casing. Detailed Implementation

[0042] <Negative electrode for all-solid-state secondary batteries>

[0043] The all-solid-state secondary battery negative electrode of the present invention has a molded body of a negative electrode mixture containing a negative electrode material including a negative electrode active material and a solid electrolyte. Furthermore, the negative electrode material is a material on which a layer containing an oxide having lithium-ion conductivity is formed on the surface of a carbon material serving as the negative electrode active material, and the solid electrolyte is a sulfide-based solid electrolyte.

[0044] Carbon materials used as negative electrode active materials are usually hydrophobic and have low affinity for sulfide-based solid electrolytes. Therefore, it is difficult to form a good interface between them in the negative electrode (the molded body of the negative electrode compound), making it difficult to reduce the resistance value of the negative electrode.

[0045] Therefore, in this invention, a carbon material with a layer containing an oxide having lithium-ion conductivity formed on its surface is used as the negative electrode material. This negative electrode material exhibits high affinity for sulfide-based solid electrolytes, enabling the formation of a good interface. Consequently, the negative electrode for the all-solid-state secondary battery of this invention has low resistance and high lithium-ion acceptability, thus improving the C / C capacity of the all-solid-state secondary battery using it (i.e., the all-solid-state secondary battery of this invention), and also enhancing its load characteristics.

[0046] Examples of negative electrodes for all-solid-state secondary batteries include molded bodies (granules, etc.) formed by molding a negative electrode compound, and negative electrodes with a structure in which a layer (negative electrode compound layer) composed of the molded body of the negative electrode compound is formed on a current collector.

[0047] Examples of carbon materials that constitute the negative electrode material include graphite (natural graphite, and artificial graphite obtained by graphitizing easily graphitizable carbons such as thermally decomposable carbon, mesophase carbon microspheres, and carbon fibers at temperatures above 2800℃), easily graphitizable carbon (soft carbon), difficult-to-graphitizable carbon (hard carbon), thermally decomposable carbon, coke, glassy carbon, sintered organic polymer compounds, mesophase carbon microspheres, carbon fibers, and activated carbon. One or more of these materials can be used.

[0048] The oxides constituting the layers formed on the surface of the negative electrode material have lithium-ion conductivity; examples include lithium niobium oxide (LiNbO3, etc.) and lithium titanium oxide (Li4Ti5O3, etc.). 12 Examples of lithium electrolytes include lithium phosphorus oxides (Li3PO4, etc.), lithium boron oxides (Li3BO3, etc.), lithium tungsten oxides (Li4WO5, etc.), and lithium aluminum oxides (LiAlO2, etc.). It should be noted that Li3PO4 is an oxide-based solid electrolyte, but other oxide-based solid electrolytes, such as Li7La3Zr2O... 12 LiTi(PO4)3, LiGe(PO4)3, LiLaTiO3, etc. can also be used as constituent materials of the layers formed on the surface of the negative electrode material.

[0049] From the viewpoint of effectively ensuring a reduction in the resistance value of the negative electrode for all-solid-state secondary batteries, the amount of lithium-ion conductive oxide in the negative electrode material is at least 1 part by mass relative to 100 parts by mass of carbon material, preferably at least 1.5 parts by mass. However, if the amount of the aforementioned oxide is too large, the capacity of the negative electrode active material may decrease, or the conductivity in the molded negative electrode compound may decrease. Therefore, the amount of lithium-ion conductive oxide in the negative electrode material is preferably 20 parts by mass or less relative to 100 parts by mass of carbon material, more preferably 10 parts by mass or less.

[0050] From the perspective of further increasing the CC capacity of the all-solid-state secondary battery and improving its load characteristics, the oxide contained in the aforementioned layer formed on the surface of the negative electrode material is preferably amorphous. The amorphous nature of the oxide can be confirmed, for example, by the absence of peaks indicating crystallinity or the presence of broad peaks during X-ray diffraction (XRD).

[0051] The negative electrode additive in the negative electrode of an all-solid-state secondary battery may contain other negative electrode active materials commonly used in lithium-ion secondary batteries, along with the aforementioned negative electrode material. When other negative electrode active materials are used in combination with the aforementioned negative electrode material in the negative electrode active material, it is preferable that the proportion of the aforementioned negative electrode material in the total negative electrode active material is 60% by mass or more. It should be noted that the negative electrode additive in the negative electrode of an all-solid-state secondary battery may also omit negative electrode active materials other than the aforementioned negative electrode material; therefore, the preferred upper limit for the proportion of the aforementioned negative electrode material in the total negative electrode active material is 100% by mass.

[0052] The content of all negative electrode active substances, including the aforementioned negative electrode materials, in the negative electrode mixture is preferably 30-70% by mass.

[0053] Sulfide-based solid electrolytes used as negative electrodes in all-solid-state secondary batteries include, for example, Li₂S-P₂S₅, Li₂S-SiS₂, Li₂S-P₂S₅-GeS₂, and Li₂S-B₂S₃ glass particles. Additionally, LGPS-based materials (Li₂S₅, Li₂S₅, Li₂S₅, Li₂S₅, which have gained attention in recent years for their high lithium-ion conductivity) can also be used. 10 GeP2S 12 Substances of the argyrodite (Li6PS5Cl, etc.) series (Li6PS5Cl, etc.) 7-x+y PS 6-x Cl x+y (Where 0.05≤y≤0.9, -3.0x+1.8≤y≤-3.0x+5.7) represents the substance, Li 7-a PS 6-a Cl b Br c (where a = b + c, 0 < a ≤ 1.8, 0.1 ≤ b / c ≤ 10.0 represent substances, etc.). Among them, from the perspective of high lithium-ion conductivity, sulfide-based solid electrolytes containing lithium and phosphorus are preferred, and sulfide-silver-germanium mineral-based materials with high lithium-ion conductivity and high chemical stability are even more preferred.

[0054] From the viewpoint of reducing grain boundary resistance, the average particle size of the sulfide-based solid electrolyte is preferably 0.1 μm or more, more preferably 0.2 μm or more. On the other hand, from the viewpoint of forming a sufficient contact interface between the negative electrode material and the solid electrolyte, it is preferably 10 μm or less, more preferably 5 μm or less.

[0055] The average particle size of the solid electrolyte and the positive electrode active material mentioned later in this specification refers to the value of 50% of the diameter in the cumulative fraction of the volume reference when calculating the integral volume starting from the smallest particle size using a particle size distribution measuring device (such as the Microtrac particle size distribution measuring device "HRA9320" manufactured by Nikko Co., Ltd.). 50 ).

[0056] In the negative electrode of an all-solid-state secondary battery, other solid electrolytes (hydride-based solid electrolytes, oxide-based solid electrolytes, etc.) can also be used together with sulfide-based solid electrolytes. However, the proportion of solid electrolytes other than sulfide-based solid electrolytes in the total amount of solid electrolyte particles in the negative electrode of an all-solid-state battery is preferably 30% by mass or less. It should be noted that the solid electrolyte in the negative electrode of an all-solid-state secondary battery can be entirely sulfide-based solid electrolytes; therefore, the lower limit of the proportion of solid electrolytes other than sulfide-based solid electrolytes in the total amount of solid electrolyte is 0% by mass.

[0057] Examples of hydride-based solid electrolytes include LiBH4 and solid solutions of LiBH4 with alkali metal compounds (e.g., solid solutions with a molar ratio of LiBH4 to an alkali metal compound of 1:1 to 20:1). Examples of alkali metal compounds in these 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 amides, rubidium amides, and cesium amides.

[0058] Examples of oxide-based solid electrolytes include Li7La3Zr2O. 12 , LiTi(PO4)3, LiGe(PO4)3, LiLaTiO3, etc.

[0059] The average particle size of solid electrolytes other than sulfide-based solid electrolytes is preferably the same as that of sulfide-based solid electrolytes.

[0060] The content of solid electrolyte in the negative electrode mixture is preferably 4 to 70% by mass.

[0061] The negative electrode mixture may also contain conductive additives such as carbon black and graphene, as needed. When the negative electrode mixture contains conductive additives, their content is preferably 1-10% by mass.

[0062] The negative electrode binder may or may not contain a resin-based binder. Examples of resin-based binders include fluoropolymers such as polyvinylidene fluoride (PVDF). Since the resin-based binder also functions as a resistive component in the negative electrode binder, its amount is desirable to be as low as possible. Therefore, it is preferable that the negative electrode binder does not contain a resin-based binder, or if it does contain a resin-based binder, its content is preferably set to 0.5% by mass or less. More preferably, the content of the resin-based binder in the negative electrode binder is 0.3% by mass or less, and even more preferably 0% by mass (i.e., no resin-based binder).

[0063] When a current collector is used as the negative electrode in an all-solid-state secondary battery, copper or nickel foil, perforated metal, mesh, expanded alloy, foamed metal, carbon sheet, etc. can be used as the current collector.

[0064] The negative electrode for an all-solid-state secondary battery can be manufactured, for example, by a manufacturing method having a negative electrode material forming process (A) and a process (B) of forming a molded body of a negative electrode compound using the negative electrode material obtained in the negative electrode material forming process (A) and a sulfide-based solid electrolyte.

[0065] The negative electrode material forming process (A) includes, for example, a process (i-1) in which an oxide having lithium-ion conductivity or a material for forming the oxide is attached to the surface of a carbon material, and a process (i-2) in which the carbon material having undergone the above process (i-1) is fired to form a layer containing the oxide on the surface of the carbon material.

[0066] In step (i-1), as a method for attaching an oxide with lithium-ion conductivity to the surface of a carbon material, methods such as coating a composition prepared by dissolving or dispersing the oxide in a solvent onto the surface of the carbon material, or dry mixing the carbon material and the oxide, can be used. Alternatively, in step (i-1), as a method for attaching a material used to form the oxide to the surface of a carbon material, methods such as coating a composition prepared by dissolving or dispersing the material in a solvent onto the surface of the carbon material can be used.

[0067] As solvents in compositions containing the aforementioned oxides or compositions containing materials for forming the aforementioned oxides, alcohols such as methanol and ethanol, and nonpolar, aprotic solvents such as hydrocarbon solvents such as hexane, heptane, octane, nonane, decane, naphthane, toluene, and xylene can be used. It should be noted that when the aforementioned oxides contained in the above composition or the materials used to form the aforementioned oxides are easily reacted with moisture, a dehydrating solvent (super-dehydrating solvent) with a water content of 0.001% by mass (10 ppm) or less is preferably used. On the other hand, when the aforementioned oxides or the materials used to form the aforementioned oxides are difficult to react with moisture, water can also be used as the solvent in the above composition.

[0068] There are no particular limitations on the method of coating the above composition onto the carbon material, and various known coating methods can be used. Furthermore, there are no particular limitations on the method of dry mixing the above oxide and carbon material, and various known mixing methods can be used.

[0069] In step (i-2), the carbon material obtained in step (i-1) is sintered to form a layer containing an oxide with lithium-ion conductivity on the surface of the carbon material. It should be noted that in step (i-1), when a composition containing a material for forming the oxide is coated onto the carbon material, in this step (i-2), the oxide is synthesized by reacting with the material for forming the oxide, and a layer containing the oxide is formed.

[0070] There are no particular restrictions on the firing method in step (i-2), and various known firing methods can be used. The firing temperature in step (i-2) is preferably a temperature that allows the layer to be formed in an amorphous state with the above-mentioned oxide, specifically, preferably 450°C or lower, and more preferably 300°C or higher. The firing time in step (i-2) is preferably 0.5 to 3 hours.

[0071] Alternatively, the negative electrode material forming process (A) can replace the above-mentioned processes (i-1) and (i-2) by having a process (ii) in which carbon material and an oxide with lithium ion conductivity are mixed to form a layer containing the oxide on the surface of the carbon material.

[0072] In step (ii), a negative electrode material is obtained by mixing carbon material and an oxide with lithium-ion conductivity while applying shear, thereby forming a layer containing the oxide with lithium-ion conductivity on the surface of the carbon material. Regarding the method of mixing the carbon material with the oxide, there are no particular limitations as long as a method that can apply shear and mix the two can be used, and various known devices can be employed.

[0073] Next, in process (B), the above-mentioned negative electrode material obtained by process (A) and sulfide-based solid electrolyte are used to form a molded body of negative electrode compound.

[0074] The molded body of the negative electrode compound can be formed, for example, by compressing a negative electrode compound prepared by mixing the aforementioned negative electrode material and a sulfide-based solid electrolyte, as well as conductive additives, binders, etc., as needed, using pressure molding or the like. In the case where the negative electrode for an all-solid-state secondary battery consists only of the molded body of the negative electrode compound, this process (B) can be used to obtain the negative electrode for an all-solid-state secondary battery.

[0075] On the other hand, when the negative electrode for an all-solid-state secondary battery has a current collector, the negative electrode for an all-solid-state secondary battery can be obtained by bonding the molded body of the negative electrode mixture obtained from process (B) to the current collector by pressing or other means.

[0076] From the viewpoint of increasing battery capacity, the thickness of the molded body of the negative electrode compound (in the case of a negative electrode with a current collector, the thickness of the molded body of the positive electrode compound on each side of the current collector, hereinafter the same) is preferably 200 μm or more. It should be noted that the load characteristics of a battery are generally easily improved by making the positive and negative electrodes thinner, but according to the present invention, even when the thickness of the molded body of the negative electrode compound is 200 μm or more, its load characteristics can still be improved. Therefore, in the present invention, the effect becomes more significant when the thickness of the molded body of the negative electrode compound is, for example, 200 μm or more. Furthermore, the thickness of the molded body of the negative electrode compound is typically 3000 μm or less.

[0077] <All-solid-state secondary batteries>

[0078] The all-solid-state secondary battery of the present invention has a positive electrode, a negative electrode and a solid electrolyte layer between the positive electrode and the negative electrode, wherein the negative electrode is the negative electrode of the all-solid-state secondary battery of the present invention.

[0079] A cross-sectional view illustrating an example of the all-solid-state secondary battery of the present invention is shown in the figure. Figure 1 . Figure 1 The all-solid-state secondary battery 1 shown contains a positive electrode 10, a negative electrode 20, and a solid electrolyte layer 30 between the positive electrode 10 and the negative electrode 20, encapsulated in an outer casing formed by an outer casing 40, a sealing casing 50, and a resin gasket 60 between them.

[0080] The sealing can 50 is fitted into the opening of the outer can 40 through the gasket 60. The opening end of the outer can 40 is tightened inward, thereby the gasket 60 abuts against the sealing can 50, and the opening of the outer can 40 is sealed, making the inside of the battery a sealed structure.

[0081] Stainless steel cans can be used for both the outer packaging can and the sealing can. In addition to polypropylene and nylon, the raw materials for the gaskets can also include fluoropolymers such as tetrafluoroethylene-perfluoroalkoxyethylene copolymer (PFA), polyphenylene ether (PEE), polysulfone (PSF), polyarylate (PAR), polyethersulfone (PES), polyphenylene sulfide (PPS), and polyetheretherketone (PEEK), which have melting points exceeding 240°C, depending on the application requirements related to the battery. Furthermore, when the battery is used in applications requiring heat resistance, glass seals can also be used for sealing.

[0082] in addition, Figure 2 and Figure 3 The accompanying drawing shows another example of the all-solid-state secondary battery of the present invention. Figure 2 This is a top view of an all-solid-state secondary battery. Figure 3 yes Figure 2 Sectional view of line II.

[0083] Figure 2 and Figure 3 The all-solid-state secondary battery 100 shown houses an electrode body 200 composed of a positive electrode, a solid electrolyte layer, and the negative electrode of this invention within a laminated membrane outer casing 500 composed of two metal laminated membranes. The outer casing 500 is sealed at its outer periphery by thermally fusing the upper and lower metal laminated membranes. It should be noted that... Figure 3 In order to avoid complicating the accompanying drawings, the layers constituting the laminated membrane outer body 500, the positive electrode, the negative electrode, and the diaphragm constituting the electrode body are not shown separately.

[0084] The positive electrode of the electrode body 200 is connected to the positive electrode external terminal 300 inside the battery 100. Additionally, although not shown, the negative electrode of the electrode body 200 is also connected to the negative electrode external terminal 400 inside the battery 100. Furthermore, the positive electrode external terminal 300 and the negative electrode external terminal 400 are extended to the outside of the laminated film outer casing 500 in a manner that allows connection to external devices or the like.

[0085] (positive electrode)

[0086] The positive electrode of an all-solid-state secondary battery may be a molded body containing a positive electrode compound including a positive electrode active material, a conductive additive, and a solid electrolyte. Examples of positive electrodes include those consisting only of the molded body and those with a structure in which the molded body and a current collector are integrated.

[0087] There are no particular restrictions on the positive electrode active material, as long as it is a previously known positive electrode active material used in lithium-ion secondary batteries, that is, an active material capable of absorbing and releasing Li ions. Specific examples of positive electrode active materials include those made of LiM... x Mn 2-xO4 (where M is at least one element selected from the group consisting of Li, B, Mg, Ca, Sr, Ba, Ti, V, Cr, Fe, Co, Ni, Cu, Al, Sn, Sb, In, Nb, Mo, W, Y, Ru, and Rh, 0.01 ≤ x ≤ 0.5) represents a spinel-type lithium-manganese composite oxide, and is composed of Li x Mn (1-y-x) Ni y M z O (2-k) F l (Where M 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, with the following inequalities: 0.8 ≤ x ≤ 1.2, 0 < y < 0.5, 0 ≤ z ≤ 0.5, k + l < 1, -0.1 ≤ k ≤ 0.2, 0 ≤ l ≤ 0.1) represents a layered compound, and is derived from LiCo 1-x M x O2 (where M is at least one element selected from the group consisting of Al, Mg, Ti, Zr, Fe, Ni, Cu, Zn, Ga, Ge, Nb, Mo, Sn, Sb, and Ba, 0 ≤ x ≤ 0.5) represents a lithium-cobalt composite oxide, and LiNi 1-x M x Lithium-nickel composite oxides represented by O2 (where M is at least one element selected from the group consisting of Al, Mg, Ti, Zr, Fe, Co, Cu, Zn, Ga, Ge, Nb, Mo, Sn, Sb, and Ba, 0 ≤ x ≤ 0.5), and LiM 1-x N x PO4 (where M is at least one element selected from the group consisting of Fe, Mn, and Co, and N is at least one element selected from the group consisting of Al, Mg, Ti, Zr, Ni, Cu, Zn, Ga, Ge, Nb, Mo, Sn, Sb, and Ba, 0 ≤ x ≤ 0.5) represents an olivine-type composite oxide, composed of Li4Ti5O 12 The lithium-titanium composite oxides, etc., can be used with only one of them or with two or more of them.

[0088] The average particle size of the positive electrode active material is preferably 1 μm or more, more preferably 2 μm or more, and preferably 10 μm or less, more preferably 8 μm or less. It should be noted that the positive electrode active material can be primary particles or secondary particles formed by the aggregation of primary particles. Using a positive electrode active material with an average particle size within the above-mentioned range allows for a greater interface with the solid electrolyte, thus further improving the battery's load characteristics.

[0089] The positive electrode active material preferably has a reaction inhibition layer on its surface to inhibit the reaction with the solid electrolyte.

[0090] Within the molded body of the positive electrode compound, if the positive electrode active material comes into direct contact with the solid electrolyte, the solid electrolyte will oxidize and form a resistive layer, potentially reducing the ionic conductivity within the molded body. By setting a reaction-inhibiting layer on the surface of the positive electrode active material to suppress the reaction with the solid electrolyte, direct contact between the positive electrode active material and the solid electrolyte can be prevented, thus suppressing the reduction in ionic conductivity within the molded body caused by the oxidation of the solid electrolyte.

[0091] The reaction inhibition layer can be made of any material that has ion conductivity and can inhibit the reaction between the positive electrode active material and the solid electrolyte. Examples of materials that can constitute the reaction inhibition layer include oxides containing Li and at least one element selected from the group consisting of Nb, P, B, Si, Ge, Ti, and Zr. More specifically, examples include Nb-containing oxides such as LiNbO3, Li3PO4, Li3BO3, Li4SiO4, Li4GeO4, LiTiO3, and LiZrO3. The reaction inhibition layer may contain only one of these oxides, or it may contain two or more, and multiple oxides may form a composite compound. Among these oxides, Nb-containing oxides are preferred, and LiNbO3 is more preferred.

[0092] The reaction inhibition layer is preferably present on the surface at a concentration of 0.1 to 1.0 parts by mass relative to 100 parts by mass of the positive electrode active material. If it is within this range, the reaction between the positive electrode active material and the solid electrolyte can be effectively inhibited.

[0093] Methods for forming a reaction-inhibiting layer on the surface of a positive electrode active material include sol-gel method, mechanical fusion method, CVD method, PVD method, etc.

[0094] The content of the positive electrode active substance in the positive electrode mixture is preferably 60-95% by mass.

[0095] Examples of conductive additives used as positive electrodes include graphite (natural graphite and artificial graphite), graphene, carbon black, carbon nanofibers, carbon nanotubes, and other carbon materials. The preferred content of the conductive additive in the positive electrode mixture is 1-10% by mass.

[0096] The solid electrolyte for the positive electrode can be one or more of the various sulfide-based solid electrolytes, hydride-based solid electrolytes, and oxide-based solid electrolytes exemplified above that can be used for the negative electrode. For superior battery performance, a sulfide-based solid electrolyte is preferred.

[0097] The content of solid electrolyte in the positive electrode mixture is preferably 4 to 30% by mass.

[0098] The positive electrode binder may or may not contain a resin-based binder. Examples of resin-based binders include fluoropolymers such as polyvinylidene fluoride (PVDF). However, since the resin-based binder functions as a resistive component in the positive electrode binder, its amount is desirable to be as low as possible. Therefore, it is preferable that the positive electrode binder does not contain a resin-based binder, or if it does contain a resin-based binder, its content is set to 0.5% by mass or less. More preferably, the content of the resin-based binder in the positive electrode binder is 0.3% by mass or less, and even more preferably 0% by mass (i.e., no resin-based binder).

[0099] When a current collector is used at the positive electrode, it can be made of metals such as aluminum or stainless steel foil, perforated metal, mesh, expanded metal, foamed metal, or carbon sheet.

[0100] The positive electrode mixture can be formed, for example, by compressing the positive electrode mixture using pressure molding or the like. The positive electrode mixture is prepared by mixing a positive electrode active material, a conductive additive, a solid electrolyte, and a binder added as needed.

[0101] In the case of a positive electrode having a current collector, it can be manufactured by bonding a molded body of a positive electrode mixture formed using the method described above to the current collector by pressing or other means.

[0102] From the viewpoint of increasing battery capacity, the thickness of the molded positive electrode compound (in the case of a positive electrode with a current collector, the thickness of the molded positive electrode compound on each side of the current collector, hereinafter the same) is preferably 200 μm or more. Furthermore, the thickness of the molded positive electrode compound is typically 2000 μm or less.

[0103] (Solid electrolyte layer)

[0104] In the solid electrolyte layer, one or more of the various sulfide-based solid electrolytes, hydride-based solid electrolytes, and oxide-based solid electrolytes previously exemplified can be used, which are substances that can be used as negative electrodes. Among these, in order to improve battery characteristics, it is preferable to include a sulfide-based solid electrolyte, and more preferably, the positive electrode, the negative electrode, and the solid electrolyte layer all contain a sulfide-based solid electrolyte.

[0105] The solid electrolyte layer can have a porous material such as resin-based nonwoven fabric as a support.

[0106] Solid electrolyte layers can be formed by methods such as: compressing solid electrolytes by means of compression molding, dispersing solid electrolytes in a solvent to form a solid electrolyte layer composition, coating it onto a substrate, a positive electrode, and a negative electrode, drying it, and then pressing it as needed.

[0107] The solvent used in the composition for forming the solid electrolyte layer is preferably a solvent that does not easily degrade the solid electrolyte. In particular, sulfide-based and hydride-based solid electrolytes can undergo chemical reactions due to trace amounts of water; therefore, nonpolar, aprotic solvents, such as hydrocarbon solvents like hexane, heptane, octane, nonane, decane, naphthane, toluene, and xylene, are preferred. In particular, ultra-dehydrating solvents with a water content of 0.001% by mass (10 ppm) or less are more preferred. Additionally, fluorinated solvents such as Vertrel (registered trademark) manufactured by Mitsui-DuPont Fluorochemicals, Zeon Corporation (registered trademark), and Novec (registered trademark) manufactured by Sumitomo 3M, as well as non-aqueous organic solvents such as dichloromethane and diethyl ether, can also be used.

[0108] The thickness of the solid electrolyte layer is preferably 100~300μm.

[0109] (Electrode)

[0110] The positive and negative electrodes can be used in batteries in the form of a stacked electrode body formed by layering solid electrolyte layers, and then the stacked electrode body can be wound into a wound electrode body.

[0111] It should be noted that, from the viewpoint of improving the mechanical strength of the electrode body, it is preferable to perform pressure molding while the positive electrode, negative electrode and solid electrolyte layer are stacked.

[0112] (Battery form)

[0113] In addition to the form of all-solid-state secondary batteries Figure 1 The battery has an outer casing consisting of an outer can, a sealing can, and a gasket (as shown in the diagram). This is the type of battery commonly referred to as a coin-shaped battery or a button-shaped battery. Figure 2 and Figure 3 In addition to the outer packaging body shown, which is composed of a resin film or a metal-resin laminate, it can also have an outer packaging body made of metal with a bottom cylindrical (cylindrical or square) can and a sealing structure that seals its opening.

[0114] Example

[0115] The present invention will now be described in detail based on embodiments. However, the following embodiments do not limit the present invention.

[0116] Example 1

[0117] (Formation of a solid electrolyte layer)

[0118] 80 mg of sulfide-based solid electrolyte (Li6PS5Cl) was placed into a powder molding die with a diameter of 10 mm and pressed to form a solid electrolyte layer.

[0119] (Making the negative electrode)

[0120] A coating-forming composition was prepared by mixing 0.1 mol of lithium and 0.125 mol of tetraisopropoxy titanium in 500 mL of dehydrated ethanol. Next, using a coating apparatus employing a rotating flow layer, the coating-forming composition was coated onto 500 g of graphite at a rate of 2 g per minute for 180 minutes. The resulting powder was then calcined at 400 °C for 30 minutes to obtain a surface formation containing an oxide (Li4Ti5O) with lithium-ion conductivity. 12 The negative electrode material (1) is composed of graphite with a coating. The amount of oxide in the negative electrode material (1) is 1.91 parts by mass relative to 100 parts by mass of graphite. In addition, in the negative electrode material (1), it was confirmed by the above method that the oxide constituting the above coating is amorphous.

[0121] The negative electrode material (1), graphene, and the same sulfide-based solid electrolyte used in the solid electrolyte layer were mixed in a mass ratio of 45:5:50 and thoroughly kneaded to prepare a negative electrode mixture. Next, 15 mg of the negative electrode mixture was added to the solid electrolyte layer within the powder molding die, and pressure molding was performed using a press to form a negative electrode composed of the negative electrode mixture molded body on the solid electrolyte layer.

[0122] (Formation of stacked electrodes)

[0123] As the counter electrode, electrodes are formed by molding Li metal and In metal into cylindrical shapes and then bonding them together. The counter electrode is placed onto the side of the solid electrolyte layer opposite to the negative electrode in the powder molding die, and then pressed using a press to form a laminated electrode body.

[0124] (Assembling the model battery)

[0125] Using the above-described stacked electrode body, fabrication is performed... Figure 2 This is a solid-state battery (model battery) with the same planar structure as the all-solid-state battery shown. On the inner surface of the aluminum laminate that constitutes the outer casing, negative electrode current collector foil (SUS foil) and counter electrode current collector foil (SUS foil) are arranged laterally and bonded at a certain interval. Each of the aforementioned current collector foils is cut into the shape of having a main body portion opposite to the negative electrode side surface or the counter electrode side surface of the aforementioned laminated electrode body, and portions protruding from the main body portion to the outside of the battery that become the negative electrode external terminal 400 and the counter electrode external terminal 300.

[0126] The laminated electrode body is placed on the negative electrode current collector foil of the laminated film outer casing, and the laminated electrode body is wrapped with the laminated film outer casing in such a way that the counter electrode current collector foil is arranged on the counter electrode of the laminated electrode body. The remaining three sides of the laminated film outer casing are sealed by heat fusion under vacuum to obtain a model battery.

[0127] Example 2

[0128] A coating-forming composition was prepared by mixing 0.1 mol of lithium and 0.1 mol of niobium pentoxide in 500 mL of dehydrated ethanol. Next, using a coating apparatus employing a rotating flow layer, the coating-forming composition was coated onto 500 g of graphite at a rate of 2 g per minute for 184 minutes. The resulting powder was calcined at 400 °C to obtain a graphite-based negative electrode material (2) with a coating containing an oxide (LiNbO3) exhibiting lithium-ion conductivity. The amount of oxide in the negative electrode material (2) was 2.55 parts by mass relative to 100 parts by mass of graphite. Furthermore, in the negative electrode material (2), the oxide constituting the coating was confirmed to be amorphous by the above method.

[0129] Except for using negative electrode material (2) instead of negative electrode material (1), the negative electrode is made in the same manner as in Example 1, and except for using the negative electrode, the model battery is made in the same manner as in Example 1.

[0130] Example 3

[0131] The coating composition was applied to graphite at a rate of 2 g per minute for 132 minutes. Otherwise, the negative electrode material (3) was prepared in the same manner as in Example 2. The amount of oxide in the negative electrode material (3) was 1.83 parts by mass relative to 100 parts by mass of graphite. In addition, the oxide constituting the coating in the negative electrode material (3) was confirmed to be amorphous by the above method.

[0132] Except for using negative electrode material (3) instead of negative electrode material (1), the negative electrode is made in the same manner as in Example 1, and except for using the negative electrode, the model battery is made in the same manner as in Example 1.

[0133] Example 4

[0134] The coating composition was applied to graphite at a rate of 2 g per minute for 72 minutes. Otherwise, the negative electrode material (4) was prepared in the same manner as in Example 2. The amount of oxide in the negative electrode material (4) was 1 part by mass relative to 100 parts by mass of graphite. In addition, the oxide constituting the above coating in the negative electrode material (4) was confirmed to be amorphous by the above method.

[0135] Except for using negative electrode material (4) instead of negative electrode material (1), the negative electrode is made in the same manner as in Example 1, and except for using the negative electrode, the model battery is made in the same manner as in Example 1.

[0136] Example 5

[0137] 20g of graphite and 1g of Li3PO4 were thoroughly mixed to obtain a graphite-based negative electrode material (5) with a coating of an oxide (Li3PO4) that has lithium-ion conductivity. The amount of oxide in the negative electrode material (5) was 5 parts by mass relative to 100 parts by mass of graphite.

[0138] Except for using negative electrode material (5) instead of negative electrode material (1), the negative electrode is made in the same manner as in Example 1, and except for using the negative electrode, the model battery is made in the same manner as in Example 1.

[0139] Example 6

[0140] The same coating-forming composition prepared in Example 1 was applied to 300g of hard carbon at a rate of 4g per minute for 190 minutes. The resulting powder was then calcined at 400°C for 30 minutes to obtain a surface formed with an oxide (Li4Ti5O) that is lithium-ion conductive. 12 The negative electrode material (6) is coated with hard carbon. The amount of oxide in the negative electrode material (6) is 6.72 parts by mass relative to 100 parts by mass of hard carbon.

[0141] Except for using negative electrode material (6) instead of negative electrode material (1), the negative electrode is made in the same manner as in Example 1, and except for using the negative electrode, the model battery is made in the same manner as in Example 1.

[0142] Comparative Example 1

[0143] The coating composition was applied to graphite at a rate of 2 g per minute for 36 minutes. Otherwise, the negative electrode material (7) was prepared in the same manner as in Example 2. The amount of oxide in the negative electrode material (7) was 0.5 parts by mass relative to 100 parts by mass of graphite. In addition, the oxide constituting the coating in the negative electrode material (7) was confirmed to be amorphous by the above method.

[0144] Except that the negative electrode material (7) is used instead of the negative electrode material (1), the negative electrode is made in the same manner as in Example 1. Except that the negative electrode is used, the model battery is made in the same manner as in Example 1.

[0145] Comparative Example 2

[0146] Except for using graphite without a coating on its surface instead of the negative electrode material (1), the negative electrode was made in the same manner as in Example 1, and the model battery was made in the same manner as in Example 1 except for using the negative electrode.

[0147] Comparative Example 3

[0148] Except for using hard carbon with no coating on the surface to replace the negative electrode material (6), the negative electrode was made in the same manner as in Example 1, and the model battery was made in the same manner as in Example 1 except for using the negative electrode.

[0149] For the model battery with negative electrodes of the embodiments and comparative examples, the following evaluations were performed.

[0150] <CC Capacity Evaluation>

[0151] For each model battery, pressure was applied at 23°C (1t / cm²). 2 Under the condition of constant current charging at 0.05 C until the voltage reaches 0.62V, constant voltage charging at 0.62V until the current reaches 0.01C, and then discharging at 0.05 C until the voltage reaches 1.88V. This series of steps is repeated twice. The capacity during the second constant current charging and the capacity during the second discharging (initial capacity) are calculated. Then, the capacity of each model battery is evaluated by dividing the capacity during the second constant current charging by the initial capacity, expressed as a percentage.

[0152] <DC Resistance (DCR) Measurement>

[0153] For each model battery after initial capacity measurement, pressure (1t / cm²) was applied at 23℃. 2 Under the same conditions as the initial capacity measurement, constant current charging and constant voltage charging were performed, followed by discharging at a current of 0.1 C until the depth of charge (SOC) reached 50%, and then stopping for 1 hour. For subsequent model batteries, the voltage was measured after a 10-second pulse discharge at a current of 0.1 C. The voltage obtained by subtracting the voltage rise attributable to the solid electrolyte layer and the counter electrode from the voltage difference before and after the pulse discharge was calculated, and the DCR was calculated from this value.

[0154] It can be said that the smaller the DCR of the model battery obtained by this method, the more likely it is to form an all-solid-state secondary battery with low internal resistance, excellent load characteristics, and large CC capacity.

[0155] The evaluation results and the composition of the negative electrode material are shown in Table 1.

[0156] [Table 1]

[0157]

[0158] The model batteries fabricated in Examples 1-6 used negative electrodes composed of a molded body containing a negative electrode material and a sulfide-based solid electrolyte. These negative electrodes exhibited low DCR, and the negative electrode material had a layer on the surface of a carbon material containing an appropriate amount of oxides with lithium-ion conductivity. Therefore, by using these negative electrodes, the load characteristics and CC capacity of the all-solid-state secondary battery can be improved.

[0159] In contrast, the model battery of Comparative Example 1 used a negative electrode material with a low amount of oxide on the surface, and the model batteries of Comparative Examples 2 and 3 used a negative electrode material containing a carbon material without an oxide layer on the surface. The DCR of these model batteries was higher than that of the model batteries of the Examples.

[0160] This invention can also be implemented in ways other than those described above without departing from its spirit. The embodiments disclosed in this application are examples, and the invention is not limited to these embodiments. The scope of the invention is interpreted preferentially to the appended claims compared to the description in the foregoing specification, and all modifications within the scope of the claims are included in the claims.

[0161] Industrial availability

[0162] The all-solid-state secondary battery of the present invention can be used for the same purposes as conventionally known secondary batteries, but because it has a solid electrolyte instead of an organic electrolyte, it has excellent heat resistance and can be preferably used for applications exposed to high temperatures.

Claims

1. A negative electrode for an all-solid-state secondary battery, characterized in that, A molded body having a negative electrode mixture, wherein the negative electrode mixture contains a negative electrode material comprising a negative electrode active substance and a solid electrolyte. The negative electrode material contains a carbon material with a layer of oxides containing lithium-ion conductivity formed on its surface as the negative electrode active material. The carbon material contains hard carbon. The oxide contains lithium titanium oxide. The amount of the oxide is more than 1 part by mass relative to 100 parts by mass of the carbon material. The solid electrolyte contains a sulfide-based solid electrolyte. The thickness of the molded body of the negative electrode compound is more than 200 μm and less than 3000 μm.

2. A method for manufacturing a negative electrode for an all-solid-state secondary battery, wherein the all-solid-state negative electrode has a molded body of a negative electrode mixture with a thickness of 200 μm or more and 3000 μm or less, the negative electrode mixture containing a negative electrode material comprising a negative electrode active substance and a solid electrolyte, the manufacturing method being characterized by having: The following negative electrode material formation process (A), and Step (B) involves forming a molded body of a negative electrode compound using the negative electrode material obtained through the negative electrode material forming step (A) and a sulfide-based solid electrolyte. The negative electrode material forming process (A) includes: The process (i-1) of attaching an oxide with lithium-ion conductivity or a material for forming said oxide to the surface of a carbon material, and In step (i-2), the carbon material that has undergone process (i-1) is fired to form a layer containing the oxide on the surface of the carbon material, wherein the amount of the oxide is 1 part by mass or more relative to 100 parts by mass of the carbon material. Alternatively, the negative electrode material forming process (A) includes: In step (ii), a carbon material is mixed with an oxide that is lithium-ion conductive, and a layer containing the oxide is formed on the surface of the carbon material. The amount of the oxide is 1 part by mass or more relative to 100 parts by mass of the carbon material. The carbon material contains hard carbon. The oxide contains lithium titanium oxide.

3. The method for manufacturing the negative electrode for an all-solid-state secondary battery according to claim 2, wherein, In the process (i-2), firing is carried out at a temperature below 450°C.

4. An all-solid-state secondary battery, characterized in that, The battery has a positive electrode, a negative electrode, and a solid electrolyte layer between the positive electrode and the negative electrode, and the negative electrode is the negative electrode for an all-solid-state secondary battery as described in claim 1.

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