Manufacturing method for all-solid-state batteries

Abstract

This invention provides a method for manufacturing all-solid-state batteries that can improve the manufacturing efficiency of all-solid-state batteries. [Solution] A method for manufacturing an all-solid-state battery includes the steps of: S1 creating an electrode body having a positive electrode layer, a solid electrolyte layer, and a negative electrode layer; S2 heating the electrode body at a predetermined heat treatment temperature; S3 measuring the open-circuit voltage (OCV) of the heated electrode body; S4 determining whether the electrode body is good or bad (whether or not it can cause a minor short circuit) based on the OCV value; and S5 assembling an all-solid-state battery by housing the electrode body determined to be good inside a case.

Description

[Technical Field]

[0001] This disclosure relates to a method for manufacturing an all-solid-state battery, particularly an all-solid-state battery comprising a stacked electrode body, in which multiple electrode bodies are stacked, and housed inside a case. [Background technology]

[0002] All-solid-state batteries house electrode bodies, each with a solid electrolyte layer between a positive and negative electrode layer, within a case. Furthermore, for purposes such as increasing capacity, all-solid-state batteries are known that house stacked electrode bodies (multiple electrodes stacked together) within a case.

[0003] International Publication No. 2012 / 020699 (Patent Document 1) discloses a stacked solid-state battery. The stacked solid-state battery comprises at least first and second single cells, each consisting of a positive electrode layer, a solid electrolyte layer, and a negative electrode layer stacked in order, and an internal current collector disposed between the first and second single cells.

[0004] Japanese Patent Publication No. 2019-40759 (Patent Document 2) discloses a method for manufacturing an all-solid-state battery. The method for manufacturing an all-solid-state battery comprises: a first step of assembling an all-solid-state battery including an electrode group comprising a positive electrode, a solid electrolyte layer, and a negative electrode; a second step of heating the all-solid-state battery to a temperature of 80°C or higher in an uncharged state; and a third step of cooling the all-solid-state battery to a temperature of 45°C or lower in an uncharged state after the second step. By heating the all-solid-state battery to a temperature of 80°C or higher, the method for manufacturing an all-solid-state battery brings the solid electrolyte particles into close contact with each other and with the active material particles, thereby reducing contact resistance at the interface between the active material particles and the solid electrolyte particles. As a result, an all-solid-state battery with high output can be obtained using this method. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] International Publication No. 2012 / 020699 [Patent Document 2] Japanese Patent Application Laid-Open No. 2019-40759

SUMMARY OF THE INVENTION

PROBLEMS TO BE SOLVED BY THE INVENTION

[0006] This disclosure aims to provide a method for manufacturing an all-solid-state battery that can improve the manufacturing efficiency of the all-solid-state battery.

MEANS FOR SOLVING THE PROBLEMS

[0007] To solve the above problems, this disclosure is configured as follows. That is, the method for manufacturing an all-solid-state battery according to this disclosure is a method for manufacturing an all-solid-state battery including a case and an electrode body accommodated inside the case, and includes a step of creating an electrode body having a positive electrode layer, a solid electrolyte layer, and a negative electrode layer, a step of heating the electrode body at a predetermined heat treatment temperature, a step of measuring the open circuit voltage of the heated electrode body, a step of determining the quality of the electrode body based on the value of the open circuit voltage (hereinafter sometimes referred to as OCV), and a step of assembling an all-solid-state battery by accommodating the electrode body determined to be a good product inside the case.

EFFECTS OF THE INVENTION

[0008] According to the method for manufacturing an all-solid-state battery according to this disclosure, the manufacturing efficiency of the all-solid-state battery can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] [Figure 1] [[ID=三十二]] [Figure 1] Figure 1 is a flowchart showing the method for manufacturing an all-solid-state battery according to this disclosure. [Figure 2] Figure 2 is a perspective view showing the electrode body according to this disclosure. [Figure 3] Figure 3 is a cross-sectional view of the all-solid-state battery manufactured by the manufacturing method of this disclosure.

MODE FOR CARRYING OUT THE INVENTION

[0010] Conventionally, in all-solid-state batteries, such as the stacked solid-state battery described in Patent Document 1, which contains a stacked electrode body made up of multiple electrode bodies (single cells), if even one of the multiple electrode bodies is defective, for example, if it is an electrode body that can cause a minor short circuit, the entire all-solid-state battery becomes defective, even if the other electrodes are good, for example, not capable of causing a minor short circuit, and the good electrodes are wasted. Furthermore, although it is possible to disassemble the all-solid-state battery, remove the defective electrodes from the stacked electrode body and take out the good electrodes, and then reassemble the all-solid-state battery, it is time-consuming to sort out which electrodes are defective and then reassemble the all-solid-state battery. Therefore, there has been a problem of increased costs and decreased manufacturing efficiency of all-solid-state batteries.

[0011] To avoid such cost increases, the inventors considered determining the quality of the electrodes before assembling the all-solid-state battery, that is, before housing the electrodes inside the case. However, immediately after manufacturing, the electrodes are uncharged and the OCV value is close to 0mV, making it impossible to determine whether or not a micro-short circuit may occur. As a result of diligent research, the inventors found that if the electrodes are heated to a predetermined heat treatment temperature and a predetermined OCV is obtained, the quality of the electrodes, for example, whether or not a micro-short circuit occurs, can be determined based on the OCV value. The present invention was completed by the inventors based on this finding. Patent Document 2 discloses a process of heating an all-solid-state battery to a temperature of 80°C or higher in an uncharged state. However, Patent Document 2 heats the all-solid-state battery after assembly, and does not propose heating the electrodes before assembly of the all-solid-state battery.

[0012] (Composition 1) The method for manufacturing an all-solid-state battery according to this embodiment is a method for manufacturing an all-solid-state battery comprising a case and an electrode body housed inside the case, and includes the steps of: creating an electrode body having a positive electrode layer, a solid electrolyte layer, and a negative electrode layer; heating the electrode body at a predetermined heat treatment temperature; measuring the open-circuit voltage of the heated electrode body; determining whether the electrode body is good or bad based on the value of the open-circuit voltage; and assembling an all-solid-state battery by housing the electrode body determined to be good inside the case.

[0013] This improves the manufacturing efficiency of all-solid-state batteries. Specifically, by pre-assembling the electrode bodies to determine their quality and using only those deemed good, it is possible to eliminate the production of all-solid-state batteries that have minor short circuits.

[0014] (Configuration 2) In the method for manufacturing an all-solid-state battery of configuration 1, the electrode body may be heated to a heat treatment temperature of 60°C or higher during the step of heating the electrode body. This makes it easier to obtain a predetermined OCV of the electrode body.

[0015] (Composition 3) In the method for manufacturing an all-solid-state battery of configuration 1, the electrode body may be heated at a heat treatment temperature of 100°C or higher. This makes it easier to obtain a predetermined OCV of the electrode body in a shorter time, and can further improve the manufacturing efficiency of the all-solid-state battery.

[0016] (Composition 4) A method for manufacturing an all-solid-state battery according to any one of configurations 1 to 3, wherein the electrode body may be in an uncharged state. This allows the OCV to be measured by heating the electrode body in an uncharged state after it has been fabricated.

[0017] (Composition 5) A method for manufacturing an all-solid-state battery according to any one of configurations 1 to 4, wherein in the step of determining the quality of the electrode body, an electrode body with an absolute value of OCV of 5mV or more may be determined to be a good product. By setting 5mV as the threshold value of the absolute value of OCV in determining the quality of the electrode body, the defect rate of the electrode body can be reduced.

[0018] (Composition 6) A method for manufacturing an all-solid-state battery having any one of configurations 1 to 5, wherein the all-solid-state battery includes a plurality of electrode bodies within a case, and the plurality of electrode bodies may be connected in parallel or in series. The method for manufacturing an all-solid-state battery can be particularly useful in all-solid-state batteries that include a stacked electrode body formed by stacking a plurality of electrode bodies.

[0019] The manufacturing method of the all-solid-state battery according to this disclosure will be described in detail below with reference to Figures 1 to 3. In the figures, the same and corresponding components are denoted by the same reference numerals, and the same explanation will not be repeated. In order to make the explanation easier to understand, the components in the drawings referred to below are shown in a simplified or schematic form, and some components are omitted.

[0020] (Electrode preparation process S1) First, the electrode body 1 shown in Figure 2 is created while referring to the flowchart shown in Figure 1. The electrode body 1 has a positive electrode layer 2, a negative electrode layer 3, and a solid electrolyte layer 4 placed between the positive electrode layer 2 and the negative electrode layer 3, and is created by pressure molding the positive electrode layer 2, the negative electrode layer 3, and the solid electrolyte layer 4. The positive electrode layer 2, the negative electrode layer 3, and the solid electrolyte layer 4 are approximately similar circular shapes in a plan view, and are stacked in the order of positive electrode layer 2, solid electrolyte layer 4, and negative electrode layer 3 from top to bottom in the figure. In other words, the electrode body 1 is cylindrical. Note that the electrode body 1 is not limited to a cylindrical shape, and may be changed to various shapes such as a rectangular parallelepiped or polygonal prism depending on the size and shape of the all-solid-state battery.

[0021] When the positive electrode layer 2 is used in a all-solid-state primary battery, as the positive electrode active material, the same materials as those used in the positive electrode active materials of conventionally known non-aqueous electrolyte primary batteries can be used. For example, manganese dioxide, lithium-containing manganese oxides [e.g., LiMn3O6 and composite oxides having the same crystal structure as manganese dioxide (such as β-type, γ-type, or a structure in which β-type and γ-type are mixed), and the content of Li is 3.5% by mass or less, preferably 2% by mass or less, more preferably 1.5% by mass or less, particularly preferably 1% by mass or less, etc.], Li a Ti 5 / 3 Lithium-containing composite oxides such as O4 (4 / 3 ≦ a < 7 / 3); vanadium oxides; niobium oxides; titanium oxides; sulfides such as iron disulfide; graphite fluoride; silver sulfides such as Ag2S; nickel oxides such as NiO2: etc. can be mentioned.

[0022] Also, when the positive electrode layer 2 is used in a all-solid-state secondary battery, as the positive electrode active material, the same materials as those used in the positive electrode active materials of conventionally known non-aqueous electrolyte secondary batteries, that is, the same materials as those capable of occluding and releasing Li (lithium) ions can be used. Specifically, Li 1-x M r Mn 2-r O4 (where M is at least one element selected from the group consisting of Li, Na, K, B, Mg, Ca, Sr, Ba, Ti, V, Cr, Zr, Fe, Co, Ni, Cu, Zn, Al, Sn, Sb, In, Nb, Ta, Mo, W, Y, Ru, and Rh, and 0 ≦ x ≦ 1, 0 ≦ r ≦ 1), spinel-type lithium manganese composite oxides represented by Li r Mn (1-s-t) Ni s M t O (2-u) F v (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, and 0 ≦ r ≦ 1.2, 0 < s < 0.5, 0 ≦ t ≦ 0.5, u + v < 1, -0.1 ≦ u ≦ 0.2, 0 ≦ v ≦ 0.1), layered compounds represented by Li 1-x Co 1-r M rLithium cobalt composite oxide represented as O2 (where M 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, Ba, Mn, Bi, Ca, F, P, Sr, W, Si, Ta, K, S, Er, and Na, with 0 ≤ x ≤ 1 and 0 ≤ r ≤ 0.5), Li 1-x Ni 1-r M r Lithium nickel composite oxide 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, and 0 ≤ x ≤ 1, 0 ≤ r ≤ 0.5), Li 1+s-x M 1-r N r PO4F s (wherein 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, V, and Ba, and 0≦x≦1, 0≦r≦0.5, 0≦s≦1) Li is an olivine-type composite oxide. 2-x M 1-r N r Examples include pyrophosphate compounds represented by P2O7 (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, V, and Ba, with 0≦x≦2 and 0≦r≦0.5). Only one of these may be used, or two or more may be used in combination.

[0023] When used in an all-solid-state primary battery, the negative electrode layer 3 can be made of, for example, metallic lithium, lithium alloys (lithium-aluminum alloy, lithium-indium alloy, etc.) as the negative electrode active material.

[0024] Furthermore, when the negative electrode layer 3 is used in an all-solid-state secondary battery, the negative electrode active material can be any active material that is known to be used in conventional lithium secondary batteries and is capable of intercalating and releasing lithium ions, without any particular limitations. For example, as the negative electrode active material, one or more carbon-based materials capable of intercalating and releasing lithium, such as graphite, pyrolysis carbons, cokes, glassy carbons, calcined organic polymer compounds, mesocarbon microbeads (MCMB), and carbon fibers, can be used. Oxides may also be used as the negative electrode active material, for example, Li x Nb y TiM 6 a O {5y+4 / 2}+δ (However, M 6 This is at least one selected from the group consisting of V, Cr, Mo, Ta, Zr, Mn, Fe, Mg, B, Al, Cu, and Si, and is a composite oxide having a monoclinic crystal structure represented by 0≦x≦49, 0.5≦y<24, -5≦δ≦5, 0≦a≦0.3), titanium dioxide having an anatase structure, lithium titanate having a ramsdelite structure represented by Li2Ti3O7, Li4Ti5O 12 Examples include spinel-type lithium titanium composite oxides represented by [formula], and one or more of these can be used. Elements such as Si, Sn, Ge, Bi, Sb, and In, as well as their compounds and alloys; nitrides or lithium-containing oxides containing transition metals such as Co, Ni, Mn, Fe, Cr, Ti, and W, which can be charged and discharged at low voltages close to lithium metal; or metallic lithium or lithium alloys (such as lithium-aluminum alloys and lithium-indium alloys) can also be used as negative electrode active materials.

[0025] The active material of the electrode material may have a reaction-suppressing layer on its surface to inhibit the reaction between the active material and the solid electrolyte. In particular, when the electrode is a positive electrode, it is preferable that a reaction-suppressing layer is provided on the surface of the active material (positive electrode active material).

[0026] The reaction suppression layer may be composed of a material that has ionic conductivity and can suppress the reaction between the positive electrode active material and the solid electrolyte. Examples of materials that can constitute the reaction suppression layer include oxides containing Li and at least one element selected from the group consisting of Nb, P, B, Si, Ge, Ti, Zr, Ta, and W, more specifically, Nb-containing oxides such as LiNbO3, Li3PO4, Li3BO3, Li4SiO4, Li4GeO4, LiTiO3, LiZrO3, Li2WO4, etc. The reaction suppression layer may contain only one of these oxides, or it may contain two or more, and furthermore, multiple of these oxides may form a composite compound. Among these oxides, it is preferable to use an Nb-containing oxide, and more preferable to use LiNbO3.

[0027] The reaction-inhibiting layer is preferably present on the surface in an amount of 0.1 to 1.0 parts by mass per 100 parts by mass of the active material (matrix particles forming the reaction-inhibiting layer). Within this range, the reaction between the active material and the solid electrolyte can be effectively suppressed.

[0028] Methods for forming a reaction-inhibiting layer on the surface of an active material include the sol-gel method, mechanofusion method, CVD method, PVD method, and ALD method.

[0029] The solid electrolyte layer 4 is positioned between the positive electrode layer 2 and the negative electrode layer 3. The solid electrolyte layer 4 can use one or more of the following as the solid electrolyte: various sulfide-based solid electrolytes (argyrodite-type sulfide-based solid electrolytes and other sulfide-based solid electrolytes), hydride-based solid electrolytes, halide-based solid electrolytes, and oxide-based solid electrolytes. However, to improve battery characteristics, it is preferable to include a sulfide-based solid electrolyte, and more preferably to include an argyrodite-type sulfide-based solid electrolyte.

[0030] Examples of sulfide-based solid electrolytes other than argyrodite-type sulfide-based solid electrolytes include particles such as Li2S-P2S5, Li2S-SiS2, Li2S-P2S5-GeS2, and Li2S-B2S3-based glasses; those of the LGPS type (Li 10 GeP2S 12 etc.); and the like.

[0031] Examples of hydride-based solid electrolytes include, for example, LiBH4, solid solutions of LiBH4 and the following alkali metal compounds (e.g., those having a molar ratio of LiBH4 to the alkali metal compound of 1:1 to 20:1). Examples of the alkali metal compounds in the solid solution include at least one selected from the group consisting of lithium halides (such as LiI, LiBr, LiF, LiCl), rubidium halides (such as RbI, RbBr, RbF, RbCl), cesium halides (such as CsI, CsBr, CsF, CsCl), lithium amide, rubidium amide, and cesium amide.

[0032] Examples of halide-based solid electrolytes include, for example, monoclinic LiAlCl4, defective spinel-type or layered LiInBr4, monoclinic Li 6-3m Y m X6 (where 0 < m < 2 and X = Cl or Br), and the like. In addition, for example, known ones described in International Publication No. 2020 / 070958 and International Publication No. 2020 / 070955 can also be used.

[0033] Examples of oxide-based solid electrolytes include, for example, Li₂O-Al₂O₃-SiO₂-P₂O₅-TiO₂-based glass ceramics, Li₂O-Al₂O₃-SiO₂-P₂O₅-GeO₂-based glass ceramics, garnet-type Li₇La₃Zr₂O 12 , NASICON-type Li 1+O Al 1+O Ti 2-O (PO₄)₃, Li 1+p Al 1+p Ge 2-p (PO₄)₃, perovskite-type Li 3q La 2 / 3-q TiO₃, and the like.

[0034] Furthermore, the average particle diameter Ra of the primary particles of the active material in the electrode material is preferably 1 μm or more, more preferably 3 μm or more, most preferably 4 μm or more, preferably 25 μm or less, more preferably 15 μm or less, and most preferably 10 μm or less.

[0035] Furthermore, the average particle size Rs of the primary particles of the solid electrolyte in the electrode material is preferably 0.2 μm or more, more preferably 0.4 μm or more, preferably 3 μm or less, and more preferably 1.8 μm or less.

[0036] The average particle diameter of the primary particles of the active material contained in the electrode material is determined as follows: Ten particles of the active material whose contours can be confirmed are selected from an image of the cross-section of the molded electrode mixture in electrode body 1, observed at 2000x magnification using a SEM, and the longest diameter of the selected particles is measured using the two-point method. The average value (number mean) of the longest diameters of all measured particles is then taken as the average particle diameter of the primary particles of the active material.

[0037] Furthermore, the average particle size of the primary particles of the solid electrolyte contained in the electrode material is determined using the same method as the average particle size of the primary particles of the active material contained in the electrode material, except that the magnification used for observation with the SEM is changed to 30,000 times.

[0038] The molded electrode mixture of electrode body 1 may contain a conductive additive. Examples of such conductive additives include highly crystalline carbon materials such as graphite (natural graphite, artificial graphite), graphene (single-layer graphene, multi-layer graphene), and carbon nanotubes; and low-crystalline carbon materials such as carbon black. One or more of these can be used.

[0039] The molded body of the electrode mixture of electrode body 1 may or may not contain a resin binder. Examples of resin binders include fluororesins such as polyvinylidene fluoride (PVDF). However, since the resin binder acts as a resistive component in the molded body of the electrode mixture, it is desirable to keep its amount as small as possible. Therefore, it is preferable that the molded body of the electrode mixture does not contain a resin binder, or if it is included, the content in the electrode mixture is 0.5% by mass or less. It is more preferable that the content of the resin binder in the electrode mixture is 0.3% by mass or less, and even more preferable that it is 0% by mass (i.e., does not contain a resin binder).

[0040] When a current collector is used in electrode body 1, the current collector can be metal foil, perforated metal, mesh, expanded metal, foamed metal, carbon sheet, etc. When a metal current collector is used, if the electrode is the positive electrode, aluminum or stainless steel is preferred, and if the electrode is the negative electrode, copper or nickel is preferred.

[0041] A molded electrode mixture can be formed, for example, by compressing an electrode mixture prepared by mixing the aforementioned electrode material and solid electrolyte with conductive additives and binders as needed, using methods such as pressure molding. An electrode consisting solely of a molded electrode mixture can be manufactured by such a method.

[0042] In the case of an electrode body having a current collector, it can be manufactured by bonding a molded electrode mixture to the current collector by pressing or other means.

[0043] Alternatively, an electrode mixture may be mixed with a solvent to prepare an electrode mixture-containing composition, which may be applied to a substrate such as a current collector or a solid electrolyte layer that faces the electrode. After drying, a press treatment may be performed to form a molded body of the electrode mixture.

[0044] For the solvent in the electrode mixture-containing composition, organic solvents such as water or N-methyl-2-pyrrolidone (NMP) can be used. When the electrode mixture-containing composition also contains a solid electrolyte, it is preferable to select a solvent that does not easily degrade the solid electrolyte. In particular, since sulfide-based and hydride-based solid electrolytes undergo chemical reactions with even small amounts of water, it is preferable to use non-polar aprotic solvents such as hydrocarbon solvents like hexane, heptane, octane, nonane, decane, decalin, toluene, xylene, messtyrene, and tetralin. It is even more preferable to use an ultra-dehydrated solvent with a water content of 0.001% by mass (10 ppm) or less. Furthermore, fluorine-based solvents such as "Bartrell®" from Mitsui DuPont Fluorochemicals, "Zeolora®" from Nippon Zeon Corporation, and "Novec®" from Sumitomo 3M, as well as non-aqueous organic solvents such as dichloromethane, diethyl ether, and anisole, can also be used.

[0045] The thickness of the molded electrode mixture (in the case of an electrode with a current collector, the thickness of the molded electrode mixture per side of the current collector; the same applies hereinafter) is usually 50 μm or more, but from the viewpoint of increasing the battery capacity, it is preferable to have a thickness of 200 μm or more. In addition, the thickness of the molded electrode mixture is usually 3000 μm or less.

[0046] In the case of an electrode body manufactured by forming an electrode mixture layer on a current collector using an electrode mixture-containing composition containing a solvent, the thickness of the electrode mixture layer (thickness per side of the current collector) is preferably 50 to 1000 μm.

[0047] (Heat treatment process S2 for the electrode body) Next, the electrode body 1 is heated to a predetermined heat treatment temperature. The electrode body 1 may be heated in an uncharged state. The electrode body 1 may be laminated on its outer surface before heating in order to prevent exposure to the atmosphere. More specifically, the heat treatment step S2 involves placing the electrode body 1 inside a constant temperature bath and heating the electrode body 1. As the constant temperature bath, for example, a forced-air constant temperature incubator "DKM300" manufactured by Yamato Scientific Co., Ltd. can be used.

[0048] The predetermined heat treatment temperature for heating the electrode body 1 can be, for example, 60°C or higher. This makes it easier to obtain a predetermined OCV of the electrode body 1 in the measurement step S3 described later. Preferably, the predetermined heat treatment temperature is 100°C or higher. This makes it possible to obtain a predetermined OCV of the electrode body 1 in a relatively short time. However, if the heat treatment temperature for heating the electrode body 1 is too high, the battery characteristics of the all-solid-state battery including the electrode body 1 may deteriorate. Therefore, from the viewpoint of obtaining good battery characteristics, the heat treatment temperature is preferably 170°C or lower, and more preferably 150°C or lower. In other words, in order to obtain a predetermined OCV and good battery characteristics of the all-solid-state battery, the heat treatment temperature is preferably 60°C to 170°C (or 150°C), and in order to further shorten the heat treatment time required to obtain a predetermined OCV, it is preferable to set it to 100°C to 170°C (or 150°C).

[0049] The heat treatment time for heating the electrode body 1 can be, for example, 2 to 24 hours (h). If the heat treatment temperature is relatively low, the predetermined OCV can be obtained by increasing the heat treatment time, and if the heat treatment temperature is relatively high, the predetermined OCV can be obtained even if the heat treatment time is shortened. However, even if the heat treatment time is further increased, the OCV value of the obtained electrode body 1 will saturate. For example, if the electrode body 1 is heated at a heat treatment temperature of 150°C, the OCV value of the obtained electrode body 1 will saturate in about 2 hours. Therefore, from the viewpoint of obtaining the predetermined OCV and improving the economic efficiency of the heat treatment of the electrode body 1, the heat treatment time for heating the electrode body 1 is preferably 2 to 24 hours, and more preferably 2 to 16 hours, depending on the heat treatment temperature.

[0050] (Measurement process S3) Next, the OCV of electrode 1 is measured. The OCV of electrode 1 may be measured when electrode 1 is uncharged. The OCV of electrode 1 can be measured after the heat treatment process S2 of electrode 1, for example, after waiting for the temperature of electrode 1 to drop to room temperature. More specifically, the OCV of electrode 1 can be measured using, for example, the voltmeter "ACC Milliohm HiTester 3560" manufactured by HIOKI E.E. CORPORATION. OCV is the potential difference between the positive and negative electrodes obtained by subtracting the potential of the negative electrode from the potential of the positive electrode of electrode 1.

[0051] (Judgment step S4) Next, the quality of the electrode body 1 is determined based on the absolute value of the OCV measured in the measurement step S3 described above. More specifically, if the absolute value of the OCV of the electrode body 1 measured in the measurement step S3 is 5mV or more, it is determined that "the electrode body 1 is a good product," and if the absolute value of the OCV is less than 5mV, it is determined that "the electrode body 1 is a defective product." In other words, if the OCV is -5mV or less and if the OCV is 5mV or more, it is determined that it is a "good product," and if the OCV is greater than -5mV and less than 5mV, it is determined that it is a "defective product." That is, in an all-solid-state battery containing an electrode body 1 that has been sufficiently heated in the heat treatment step S2 but whose absolute value of the OCV measured in the measurement step S3 is close to 0mV and has been determined to be a "defective product," a minor short circuit is likely to occur, while in an all-solid-state battery containing an electrode body 1 with an absolute value of OCV of 5mV or more, i.e., an electrode body 1 that has obtained a predetermined OCV, a minor short circuit is unlikely to occur. Thus, by setting a threshold of 5mV as the absolute value of the OCV in determining the quality of electrode body 1, the defect rate of the electrode body can be reduced. While there is no particular upper limit to the absolute value of the OCV of electrode body 1, it may be set to 200mV.

[0052] (Assembly process S5) Finally, as shown in Figure 3, multiple electrode bodies 1 that were determined to be "good products" in the judgment step S4 described above are stacked to create a stacked electrode body 10, and the stacked electrode body 10 is housed in the internal space of the case 20 to assemble the all-solid-state battery 100.

[0053] More specifically, as shown in Figure 3, the case 20 comprises a bottomed cylindrical battery can 21 and a plate-shaped can lid 22 that seals the opening at one end of the battery can 21. The laminated electrode body 10 is inserted through the opening at one end of the battery can 21 and housed in the internal space of the battery can 21. The all-solid-state battery 100 can then be assembled by sealing the opening at one end of the battery can 21. In this embodiment, the can lid 22 has electrode terminals 22a, a main body 22b, an insulating part 22c, and an insulating sheet 22d. Each electrode body 1 has a non-conductive heat-shrinkable tube 11 that covers the outer peripheral side surface, as well as the periphery of the top and bottom surfaces of each electrode body 1. An insulating plate 5 is also provided between each electrode body 1. In each electrode body 1, the positive electrode layer 2 is located on the can lid 22 side, and the negative electrode layer 3 is located on the bottom side of the battery can 21. Each positive electrode layer 2 is connected to the electrode terminals 22a of the can lid 22 via a connection part 2a. Each negative electrode layer 3 is connected to the battery can 21 via a connection part 3a. In Figure 3, the actual all-solid-state battery 100 is equipped with a holding member or insulating material in the internal space of the case 20 to suppress misalignment of the laminated electrode body 10, but these are not shown or explained. Also, in Figure 3, the connection parts 2a and 3a are simplified in order to make the illustration of the laminated electrode body 10 easier to understand.

[0054] In this way, the all-solid-state battery 100 can be manufactured. The method for manufacturing the all-solid-state battery of this disclosure is not limited to the all-solid-state battery 100 shown in Figure 3, but can be applied to various all-solid-state batteries 100. The electrode body 1 housed inside the case 20 may be one or multiple. Each electrode body 1 of the stacked electrode body 10 may be connected in series or in parallel. Furthermore, the case 20 is not particularly limited as long as it is a case 20 that is normally used for all-solid-state batteries 100.

[0055] The manufacturing method for solid-state batteries according to the present disclosure can improve the manufacturing efficiency of solid-state batteries. Specifically, by selecting electrode bodies 1 that may experience minor short circuits before assembling the solid-state battery, and housing only electrode bodies determined to be good inside the case, the production of solid-state batteries with minor short circuits can be eliminated. In particular, in solid-state batteries containing stacked electrode bodies 10, if even one of the multiple electrode bodies 1 is defective, the other good electrode bodies 1 may be wasted, or the cost increases because it is time-consuming to reassemble the solid-state battery. Therefore, in solid-state batteries containing stacked electrode bodies 10, it is preferable to have all of the multiple electrode bodies 1 be good, thereby preventing the aforementioned increase in cost. Accordingly, the manufacturing method for solid-state batteries according to the present disclosure is particularly useful in the manufacturing of solid-state batteries containing stacked electrode bodies 10.

[0056] Furthermore, the electrode body 1 may be covered with a heat-shrinkable resin film called a shrink tube before being housed inside the case. Normally, in the electrode body 1, the positive electrode layer 2 is thicker than the negative electrode layer 3, so the positive electrode layer 2 and the negative electrode layer 3 can be distinguished by appearance. However, when the electrode body 1 is covered with a shrink tube, it becomes difficult to distinguish between the positive electrode layer 2 and the negative electrode layer 3. Also, when the thickness of the positive electrode layer 2 and the negative electrode layer 3 are approximately the same, it becomes difficult to distinguish between the positive electrode layer 2 and the negative electrode layer 3 by appearance. Even in cases where it is difficult to distinguish between the positive electrode layer 2 and the negative electrode layer 3, the positive electrode layer 2 and the negative electrode layer 3 can be distinguished by measuring the OCV of the electrode body 1 using the measurement step S3 described above. This allows the positive electrode layer 2 and the negative electrode layer 3 of the electrode body 1 to be correctly positioned and the electrode body 1 to be housed inside the case.

[0057] Although embodiments have been described above, this disclosure is not limited to the embodiments described above, and various modifications are possible without departing from the spirit of the disclosure. [Examples]

[0058] The electrode bodies for each of Examples 1 to 9 and Comparative Example 1 shown in Table 1 below were prepared as follows.

[0059] First, lithium titanate (Li4Ti5O) with an average particle size of 2 μm. 12 A negative electrode mixture was prepared by mixing a negative electrode active material, a sulfide-based solid electrolyte (Li6PS5Cl) with an average particle size of 0.7 μm, and graphene (conductive additive) in a mass ratio of 50:41:9.

[0060] Furthermore, a positive electrode mixture was prepared by mixing LiCoO2 (positive electrode active material) with an average particle size of 5 μm and a LiNbO3 coating layer formed on its surface, a sulfide-based solid electrolyte (Li6PS5Cl) with an average particle size of 0.7 μm, and graphene in a mass ratio of 65:30.7:4.3.

[0061] Next, a sulfide-based solid electrolyte (Li6PS5Cl) powder with an average particle size of 0.7 μm was placed in a powder molding die and press-molded at a surface pressure of 70 MPa using a press machine to form a preliminary layer of the solid electrolyte. Furthermore, the aforementioned negative electrode mixture was placed on the upper surface of the preliminary layer of the solid electrolyte and press-molded at a surface pressure of 50 MPa to form another preliminary layer of the negative electrode on top of the preliminary layer of the solid electrolyte.

[0062] Furthermore, a circular piece (thickness: 1.2 mm, porosity: 98%) of Sumitomo Electric Industries, Ltd.'s nickel-based foamed metal porous material [nickel-based "Cellmet" (registered trademark)] was placed on the temporary molded layer of the negative electrode layer, and pressure molding was performed at a surface pressure of 300 MPa to form an integrated structure of the temporary molded body of the solid electrolyte layer, the temporary molded layer of the negative electrode layer, and the porous metal substrate (current collector) for the negative electrode.

[0063] Furthermore, after inverting the mold, the above-mentioned positive electrode mixture was placed on the upper surface of the temporary solid electrolyte layer inside the mold (the side opposite to the surface with the temporary negative electrode mixture layer) and molded under a surface pressure of 50 MPa to form a temporary positive electrode layer on top of the temporary solid electrolyte layer.

[0064] Finally, a piece of the same nickel-based foamed porous metal material used for the negative electrode was placed on the provisionally formed positive electrode layer, which was formed on the provisionally formed positive electrode layer on the provisional solid electrolyte layer. Pressure molding was then performed at a surface pressure of 1400 MPa to obtain an electrode body comprising a positive electrode layer (thickness 0.8 mm) with a porous metal substrate acting as a current collector, a solid electrolyte layer (thickness 0.35 mm), and a negative electrode layer (thickness 1.4 mm) with a porous metal substrate acting as a current collector. A nickel alloy positive electrode tab was attached to the porous metal substrate of the positive electrode layer, and a nickel alloy negative electrode tab was attached to the porous metal substrate of the negative electrode layer.

[0065] After heat treatment of each electrode body of Examples 1 to 9 and Comparative Example 1, which were prepared as described above, under the conditions shown in Table 1, the OCV of each electrode body was measured. Subsequently, for each example and comparative example, the eight electrode bodies were connected in parallel, housed inside a case, and assembled into an all-solid-state secondary battery, after which the "1C load characteristics" and "short-circuit failure rate" were evaluated. Note that the manufacturing method of the all-solid-state battery in this disclosure is not limited to the manufacturing method according to this example.

[0066] (1C load characteristics) For each example and comparative example of all-solid-state secondary battery, constant current charging was performed at a current value equivalent to 0.2C until the voltage reached 2.6V. Subsequently, constant voltage charging was performed at a voltage of 2.6V until the current value equivalent to 0.01C, and then constant current discharge was performed at a current value equivalent to 0.1C until the voltage reached 1.0V. The discharge capacity at this time was defined as the 0.1C discharge capacity of each all-solid-state secondary battery. Next, after charging under the same charging conditions, constant current discharge was performed at a current value equivalent to 1C until the voltage reached 1.0V, and the discharge capacity at this time was defined as the 1C discharge capacity. The 1C discharge capacity measured in this way was divided by the 0.1C discharge capacity and expressed as a percentage to obtain the 1C load characteristic value of each all-solid-state secondary battery.

[0067] (Short-circuit failure rate) Twenty all-solid-state secondary batteries were fabricated for each example and comparative example, and the percentage of all-solid-state secondary batteries that experienced internal short circuits was determined as the short-circuit failure rate.

[0068] [Table 1]

[0069] (Examples 1-9) In Examples 1 to 8, a relatively good short-circuit failure rate was obtained when the electrode body was heated at a heat treatment temperature of 60°C or higher. In this case, the OCV value after heat treatment was -5mV or less, and the absolute value of OCV was 5mV or higher. However, in Example 8, when the electrode body was heated at a heat treatment temperature of 180°C for 2 hours, the 1C load characteristic was 45%, and the battery characteristics were slightly reduced. Also, in Example 9, when the electrode body was heated at a heat treatment temperature of 50°C, although the absolute value of OCV was 5mV, the short-circuit failure rate was slightly reduced. From this, it was found that to obtain a better short-circuit failure rate, the heat treatment temperature should be 60°C or higher, and to obtain better battery characteristics, the heat treatment temperature should be 170°C or lower. Comparing Examples 6 and 7, it was found that it is preferable to set the temperature to 150°C or lower.

[0070] Furthermore, in Examples 1-3 and 6-8, setting the heat treatment temperature of the electrode body to 100°C or higher significantly reduced the short-circuit failure rate, and also shortened the heat treatment time. In other words, the higher the heat treatment temperature of the electrode body, the shorter the time required to obtain a sufficient OCV. However, even if the heat treatment time is extended, the OCV value obtained saturates. That is, it becomes difficult to reduce the short-circuit failure rate. Therefore, from the viewpoint of economic efficiency, and also considering the case where heating is performed at a relatively low temperature as in Example 9, it was found that the heat treatment time of the electrode body should be 2 hours or more, 24 hours or less, and preferably 16 hours or less.

[0071] (Comparative Example 1) In Comparative Example 1, since the electrode body was not heat-treated, the OCV became 3mV, and the short-circuit failure rate increased significantly. [Explanation of symbols]

[0072] 1 electrode body, 2 positive electrode layer, 3 negative electrode layer, 4 solid electrolyte layer, 10 stacked electrode body, 20 case, 100 all-solid-state battery

Claims

1. A method for manufacturing an all-solid-state battery, comprising a case and an electrode body housed inside the case, A step of creating the electrode body having a positive electrode layer, a solid electrolyte layer, and a negative electrode layer, A step of heating the electrode body to a predetermined heat treatment temperature, A step of measuring the open-circuit voltage of the heated electrode body, A step of determining whether the electrode body is good or bad based on the value of the open-circuit voltage, A method for manufacturing an all-solid-state battery, comprising the step of assembling an all-solid-state battery by housing the electrode bodies determined to be good products in the above-mentioned determination inside the case.

2. A method for manufacturing an all-solid-state battery according to claim 1, A method for manufacturing an all-solid-state battery, wherein in the step of heating the electrode body, the electrode body is heated to a heat treatment temperature of 60°C or higher.

3. A method for manufacturing an all-solid-state battery according to claim 1, A method for manufacturing an all-solid-state battery, wherein in the step of heating the electrode body, the electrode body is heated to a heat treatment temperature of 100°C or higher.

4. A method for manufacturing an all-solid-state battery according to claim 1, A method for manufacturing an all-solid-state battery, wherein the electrode body is in an uncharged state.

5. A method for manufacturing an all-solid-state battery according to claim 1, A method for manufacturing an all-solid-state battery, comprising the step of determining whether the electrode body is good or bad, wherein the electrode body is determined to be good if the absolute value of the open-circuit voltage is 5 mV or more.

6. A method for manufacturing an all-solid-state battery according to claim 1, The all-solid-state battery includes a plurality of electrode bodies within a case, A method for manufacturing an all-solid-state battery, wherein the plurality of electrode bodies are connected in parallel or in series.

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