All-solid-state battery

Abstract

To provide an all-solid battery which is excellent in flexibility and dendrite resistance and has good heat resistance.SOLUTION: An all-solid battery includes a current collector layer, an electrode mixture layer, and an electrolyte layer, and the electrode mixture layer and the electrolyte layer are layers containing an ion-conductive polymer, and the softening point of the ion-conductive polymer is 80°C or higher.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an all-solid-state battery that has excellent flexibility and dendrite resistance, and also has good heat resistance. [Background technology]

[0002] In recent years, in order to reduce the weight and increase the energy of batteries, there has been active research into metal Li anode batteries, all-solid-state batteries, air batteries, etc., and progress is being made in the design of cathodes, anodes, separators, electrolytes, etc. in preparation for practical application. Of these, all-solid-state batteries do not require flammable electrolytes like conventional secondary batteries, but instead use solid electrolyte membranes capable of ion conduction, and are therefore attracting attention as highly safe secondary batteries that can avoid the risk of fire or explosion.

[0003] Generally, batteries use separators made of porous membranes or nonwoven fabrics with through-holes measuring tens of nanometers to several micrometers in diameter to enable ionic conduction between the positive and negative electrodes while preventing short circuits due to contact between the electrodes. However, the use of porous separators poses the issue of dendrite growth. Solid electrolytes can be used to solve this issue, and are broadly divided into inorganic and organic types. Organic electrolytes can be further divided into polymer gel electrolytes and polymer solid electrolytes (intrinsic polymer electrolytes). Compared to inorganic solid electrolytes, organic solid electrolytes are lighter and more flexible. They do not require complex processes such as vacuum sputtering or high-temperature firing, making them easy to process over large areas and potentially reducing manufacturing costs.

[0004] Inorganic solid electrolytes are composed of anionic lattice sites and metal ions, and many have been reported to have practical ionic conductivity (e.g., Patent Document 1). Among organic electrolytes, the application of polymer gel electrolytes, in which the electrolyte solution is semi-solidified with a polymer, to batteries began with a report by Feuillade et al. in 1975 (Non-Patent Document 1). Since then, various reports have been made (e.g., Patent Document 2), and they have been put to practical use as lithium polymer batteries.

[0005] Research into polymer solid electrolytes began with a paper by Wright published in 1975 (Non-Patent Document 2), and many achievements have been reported to date, primarily focusing on polyether-based electrolytes (for example, Patent Document 3). Furthermore, in recent years, reports have included coating a polymer electrolyte on the negative electrode to improve ionic conductivity (Patent Document 4), improving the shape retention and mechanical strength of polymers (Patent Document 5), and using an ionic liquid to improve ionic conductivity at low temperatures (Patent Document 6). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-13772 [Patent Document 2] Japanese Patent Application Laid-Open No. 2008-159496 [Patent Document 3] Japanese Patent Application Laid-Open No. 2007-103145 [Patent Document 4] Japanese Patent Application Laid-Open No. 2016-167434 [Patent Document 5] Patent No. 6061096 [Patent Document 6] Japanese Patent Application Publication No. 2020-035587 [Non-patent literature]

[0007] [Non-Patent Document 1] G. Feuillade, Ph. Perche, J. Appl. Electrochem., 5, 63 (1975). [Non-patent document 2] PVWright,Br.Polym.J.,7.319(1975). Summary of the Invention [Problem to be solved by the invention]

[0008] However, the polymer electrolyte described in Patent Document 4 is manufactured by applying a polyether-based polymer electrolyte to the negative electrode and then allowing the polymer electrolyte to penetrate into the negative electrode, but the softening point of the polymer film is low, resulting in poor heat resistance. Furthermore, the polymer electrolyte described in Patent Document 5 also has poor thermal properties when the temperature inside the battery reaches high temperatures. The polymer electrolyte described in Patent Document 6 is a mixture of a polyether-based polymer, an ionic liquid, and an inorganic electrolyte, but has issues with the shape retention and flexibility of the polymer film. In view of the above circumstances, the present invention aims to provide an all-solid-state battery that has excellent flexibility, dendrite resistance, and good heat resistance. [Means for solving the problem]

[0009] In order to solve the above problems, the present invention has the following features. (1) An all-solid-state battery having a current collector layer, an electrode mixture layer, and an electrolyte layer, wherein the electrode mixture layer and the electrolyte layer are layers containing an ion-conductive polymer, and the softening point of the ion-conductive polymer is 80°C or higher. (2) The all-solid-state battery according to (1), wherein the electrolyte layer and the electrode mixture layer contain the same ion-conducting polymer. (3) The all-solid-state battery according to (1) or (2), wherein the electrolyte layer is provided on at least one surface layer of the electrode mixture layer, and the surface gloss (60°) of the electrolyte layer is 10 or more and 300 or less. (4) Cell resistance at 25°C is 30 Ω cm 2 The all-solid-state battery according to any one of (1) to (3), which is: (5) The all-solid-state battery according to any one of (1) to (4), wherein the electrolyte layer contains a Li salt in an amount of 5 mass % or more relative to the total mass of the ion-conductive polymer in the electrolyte layer. (6) The all-solid-state battery according to any one of (1) to (5), wherein the electrolyte layer contains 50 μg or more of Li element per 1 g of the ion-conductive polymer in the electrolyte layer. (7) The all-solid-state battery according to any one of (1) to (6), wherein the ion-conductive polymer contains an aromatic polyamide. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide an all-solid-state battery that has excellent flexibility and dendrite resistance, and also has good heat resistance. DETAILED DESCRIPTION OF THE INVENTION

[0011] The present invention will be described in detail below.

[0012] The present invention relates to an all-solid-state battery having a current collector layer, an electrode mixture layer, and an electrolyte layer, wherein the electrode mixture layer and the electrolyte layer are layers containing an ion-conductive polymer, and the softening point of the polymer is 80° C. or higher. To achieve the effects of the present invention, the above characteristics must be satisfied simultaneously.

[0013] The ion-conducting polymer used in the embodiments of the present invention (hereinafter, sometimes referred to as the "ion-conducting polymer of the present invention") is a polymer that enables ion conduction between the positive electrode and the negative electrode when used in an all-solid-state battery. In conventional technology, the electrode mixture layer that becomes the positive electrode or negative electrode of an all-solid-state battery, and the electrolyte layer placed between the positive electrode and the negative electrode, are mainly composed of inorganic materials. In the embodiments of the present invention, the electrode mixture layer and the electrolyte layer contain this ion-conducting polymer, thereby improving the flexibility of each layer and enhancing the handleability and processability during the molding of the all-solid-state battery. Furthermore, cracking and chipping of each layer due to impact during battery use can be prevented, thereby suppressing short circuits and fires due to dendrite formation. Furthermore, the interface between the electrode mixture layer and the electrolyte layer becomes smooth and improves adhesion, thereby reducing the interfacial resistance and improving battery characteristics.

[0014] The softening point of the ion-conductive polymer according to the embodiment of the present invention must be 80° C. or higher. Normally, the electrolyte layer of an all-solid-state battery is a solid membrane, and the risk of ignition at high temperatures is lower than in secondary batteries that use non-aqueous electrolyte solutions. However, in all-solid-state batteries intended for long life and high energy capacity, the softening point of the polymer is set to 80° C. or higher to further increase heat resistance and enhance safety. The softening point of a polymer is the temperature at which the polymer begins to deform when heated, regardless of whether the polymer is a single component or a composite component.

[0015] The polymers that can be used in the embodiments of the present invention are not particularly limited, but examples include polymers having an aromatic ring on the main chain and fluorine-containing polymers such as polyvinylidene fluoride. In particular, polymers having an aromatic ring on the main chain are preferably used, such as aromatic polyamide (aramid), aromatic polyimide, aromatic polyamideimide, aromatic polyetherketone, aromatic polyetheretherketone, aromatic polyarylate, aromatic polysulfone, aromatic polyethersulfone, aromatic polyetherimide, and aromatic polycarbonate. Blends of multiple polymers may also be used. Among these, aromatic polyamides (including aromatic polyamic acids, which are aromatic polyimide precursors), aromatic polyimides, and aromatic polyamideimides are more preferred, as they tend to maintain high strength when thinned, and aromatic polyamides are particularly preferred. That is, the ion-conductive polymer according to the embodiment of the present invention preferably contains an aromatic polyamide.

[0016] The content of the ion-conductive polymer in the electrode mixture layer and the electrolyte layer is not particularly limited, but is preferably 0.05% by mass or more of the entire layer. In particular, from the viewpoints of flexibility and adhesion to the electrode mixture layer, the electrolyte layer preferably contains 5% by mass or more, and even more preferably 10% by mass or more. Furthermore, from the viewpoint of improving ion conductivity by incorporating a lithium salt as described below, the content is preferably 99% by mass or less, and more preferably 95% by mass or less.

[0017] Ion-conductive polymers that can be suitably used in the present invention preferably include polymers having a structure represented by any one of the following chemical formulas (1) to (3). Examples of aromatic polyamides include those having a repeating unit represented by the following chemical formula (1), aromatic polyimides include those having a repeating unit represented by the following chemical formula (2), and aromatic polyamideimides include those having a repeating unit represented by the following chemical formula (3).

[0018] Chemical formula (1):

[0019] [ka]

[0020] Chemical formula (2):

[0021] [ka]

[0022] Chemical formula (3):

[0023] [ka]

[0024] Here, Ar1 and Ar2 in chemical formulas (1) to (3) are groups containing aromatic groups, and each may be a single group or a multi-component copolymer containing multiple groups. Furthermore, the bonds constituting the main chain on the aromatic ring may be either meta-oriented or para-oriented. Furthermore, some of the hydrogen atoms on the aromatic ring may be substituted with any group.

[0025] In the embodiments of the present invention, when an aromatic polyamide, aromatic polyimide, or aromatic polyamideimide is used as the ion-conductive polymer, it is preferable that the main chain or side chain has an ether bond or a thioether bond (in the main chain or on the side chain). The unshared electron pair of the ether bond or the thioether bond accelerates the movement of ions required for battery operation, thereby improving ion conductivity.

[0026] The confirmation of each component and its content of the membrane containing the ion-conductive polymer according to the embodiment of the present invention (hereinafter, sometimes simply referred to as the polymer membrane) is not limited to a specific method, but may be performed by proton nuclear magnetic resonance spectroscopy ( 1 H-NMR and Fourier transform infrared spectroscopy (FT-IR) can be used. If necessary, multiple techniques can be used together to confirm the properties.

[0027] In the all-solid-state battery according to the embodiment of the present invention, the electrolyte layer and the electrode mixture layer preferably contain the same ion-conductive polymer. By containing the same ion-conductive polymer in the electrolyte layer and the electrode mixture layer, the interfacial resistance between the layers can be reduced, and ionic conductivity and cycle characteristics can be dramatically improved, thereby improving the characteristics of the all-solid-state battery. There are no particular restrictions on the method for making the electrolyte layer and the electrode mixture layer contain the same ion-conductive polymer. The electrode mixture layer and the electrolyte layer may be molded separately, or the electrode mixture material and the polymer may be kneaded and applied to the current collector layer, followed by integral molding in which the layers are separated. Alternatively, a liquid of the ion-conductive polymer dissolved in an organic solvent may be applied to the electrode mixture layer and allowed to penetrate.

[0028] The electrolyte layer according to the embodiment of the present invention is provided on at least one surface layer of the electrode mixture layer, and the surface gloss (60°) of the electrolyte layer is preferably 10 or more and 300 or less. It is more preferably 15 or more and 280 or less, and even more preferably 20 or more and 250 or less. If the surface gloss (60°) is 10 or more, inorganic solid electrolytes that may be contained in the electrolyte layer and precipitates generated during molding do not protrude onto the surface. When used as an all-solid-state battery, gaps are less likely to occur at the contact surface with the other electrode mixture layer, making it easier to obtain sufficient ionic conductivity. Furthermore, the low content of ion-conductive polymer in the electrolyte layer prevents the occurrence of continuous voids within the electrolyte layer, thereby preventing short circuits due to dendrite growth when used as an all-solid-state battery. Furthermore, by setting the gloss (60°) to 300 or less, the inorganic solid electrolyte does not become too dense on the surface of the electrolyte layer, resulting in good flexibility. The surface glossiness (60°) of the electrolyte layer is the surface glossiness of the electrolyte layer measured in accordance with JIS Z8741 (1997) at an incident angle and a receiving angle of 60°.

[0029] Examples of how the surface gloss (60°) can be adjusted to fall within the above range include having the ion-conductive polymer content in the electrolyte layer fall within the above range, or isolating and redissolving the ion-conductive polymer using the method described below and removing the precipitate beforehand. By adjusting the surface gloss (60°) to fall within the above range, an all-solid-state battery with excellent ion conductivity, dendrite resistance, and flexibility can be obtained.

[0030] The electrolyte layer according to the present invention preferably contains a Li salt in an amount of 5% by mass or more relative to the total mass of the ion-conductive polymer in the electrolyte layer. The lithium salt is not particularly limited, but from the viewpoints of ionic conductivity, ion migration speed at the interface between each layer, thermal and electrochemical stability, discharge capacity, cycle characteristics, etc., LiPF6, LiAsF6, LiClO4, LiBF4, LiBr, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(pentafluoroethanesulfonyl)imide, etc. are preferred. These lithium salts may be used alone or in combination of two or more.

[0031] The content of the lithium salt is preferably 5% by mass or more, more preferably 7% by mass or more, and even more preferably 10% by mass or more, based on the total mass of the ion-conductive polymer in the electrolyte layer. By setting the content of the lithium salt within the above range, an all-solid-state battery excellent in ionic conductivity, discharge capacity, and cycle characteristics can be obtained. Furthermore, although the upper limit is not particularly specified, it is preferably 95% by mass or less from the viewpoint of the handleability and moldability of the ion-conductive polymer. When two or more types of lithium salts are used, it is preferable to adjust their total amount to be within the above range.

[0032] Furthermore, the electrolyte layer according to the embodiment of the present invention preferably contains 50 μg or more of Li element per 1 g of ion-conductive polymer in the electrolyte layer, more preferably 100 μg or more, and even more preferably 200 μg or more. By setting the lithium element content within the above range, an all-solid-state battery with excellent ionic conductivity, discharge capacity, and cycle characteristics can be obtained. Furthermore, although the upper limit is not particularly specified, it is preferably 100,000 μg or less from the viewpoint of the handleability and moldability of the ion-conductive polymer. To set the lithium element content within the above range, it is preferable that the lithium salt content relative to the ion-conductive polymer be within the above range and that the molding conditions be within the range of the manufacturing method described below. The lithium element content can be evaluated by atomic absorption spectroscopy, which will be described later.

[0033] Furthermore, the electrolyte layer according to the embodiment of the present invention may contain materials such as inorganic solid electrolytes and ionic liquids for the purpose of increasing ion conductivity to improve discharge capacity and cycle characteristics.

[0034] The all-solid-state battery according to the embodiment of the present invention has a cell resistance of 30 Ω·cm at 25°C. 2 It is preferable that the resistance is equal to or less than 25 Ω cm. 2 or less, more preferably 20 Ω·cm 2 By setting the cell resistance within the above range, when used as an all-solid-state battery, high ionic conductivity, excellent output characteristics and cycle characteristics can be obtained, and capacity loss during repeated use can be suppressed. In order to set the cell resistance within the above range, it is preferable to set the structure of the ion-conductive polymer, the amount of lithium salt added, molding conditions, etc. within the ranges of the manufacturing conditions described below.

[0035] Next, a method for manufacturing an all-solid-state battery according to an embodiment of the present invention will be described below. In the all-solid-state battery according to the embodiment of the present invention, a positive electrode current collector layer, an electrode mixture layer containing a positive electrode active material (sometimes referred to as a positive electrode layer), an electrolyte layer, an electrode mixture layer containing a negative electrode active material (sometimes referred to as a negative electrode layer), and a negative electrode current collector layer are laminated in this order or in the reverse order. The ion-conductive polymer of the present invention is contained in the electrolyte layer and the electrode mixture layer, but in the electrode mixture layer, it may be contained in either the positive electrode layer or the negative electrode layer, or in both layers. The all-solid-state battery can be assembled using known battery components.

[0036] The current collector layer in the all-solid-state battery according to the embodiment of the present invention is not particularly limited, but for example, a metal foil made of gold, silver, aluminum, copper, stainless steel, nickel, titanium, an alloy thereof, a carbon-based material, or the like can be used.

[0037] The active material contained in the electrode mixture layer according to the embodiment of the present invention is not particularly specified, but the positive electrode active material may be a known positive electrode active material, such as a lithium metal oxide (such as lithium cobalt oxide or lithium manganese oxide) containing lithium and at least one transition metal selected from manganese, cobalt, nickel, and titanium. The negative electrode active material may be any material capable of absorbing and releasing metal ions, and may be any known negative electrode active material, such as Li, Sn, Si, In, lithium alloy particles (lithium alloy particles of lithium and titanium, magnesium, aluminum, or the like), and carbonaceous materials (carbon, hard carbon, soft carbon, graphite, or the like).

[0038] Furthermore, the electrode mixture layer and the electrolyte layer may contain an inorganic solid electrolyte, a conductive additive, etc., for the purpose of improving ionic conductivity. Although neither is particularly specified, examples of inorganic solid electrolytes include Li2S-P2S5 and Li7P3S 11 Sulfide-based solid electrolytes such as LiI, Li2O-B2O3-P2O5, and Li7La3Zr2O 12Known solid electrolytes, such as oxide-based solid electrolytes such as LLZ, can be used as appropriate. Also, known conductive additives, such as carbon materials, such as carbon black, acetylene black (AB), ketjen black (KB), carbon nanotubes (CNT), carbon nanofibers (CNF), and vapor-grown carbon fibers, and metal materials, can be used as appropriate.

[0039] A method for obtaining a polymer that can be used as an ion-conductive polymer according to an embodiment of the present invention will be described using aromatic polyamides, aromatic polyimides, or polyamic acids, which are precursors thereof, as examples. However, usable polymers and polymerization methods thereof are not limited to these.

[0040] Various methods are available for producing aromatic polyamides. For example, when using low-temperature solution polymerization with acid dichlorides and diamines as raw materials, they are synthesized in aprotic organic polar solvents such as N-methyl-2-pyrrolidone, N,N-dimethylacetamide, dimethylformamide, and dimethyl sulfoxide. In the case of solution polymerization, to obtain a high-molecular-weight polymer, the water content of the solvent used for polymerization is preferably 500 ppm or less (by mass, hereinafter), more preferably 200 ppm or less. Furthermore, a metal salt may be added to promote polymer dissolution. Examples of such metal salts include alkali metal or alkaline earth metal halides that dissolve in aprotic organic polar solvents, such as lithium chloride, lithium bromide, sodium chloride, sodium bromide, potassium chloride, and potassium bromide. Since using equal amounts of both the acid dichloride and diamine may result in the production of an ultrahigh-molecular-weight polymer, it is preferable to adjust the molar ratio of one to the other so that one is 95.0 to 99.95 mol%. Furthermore, the polymerization reaction of aromatic polyamides is exothermic, and if the temperature of the polymerization system rises, side reactions may occur and the degree of polymerization may not increase sufficiently, so it is preferable to cool the temperature of the solution during polymerization to 40° C. or less. Furthermore, when acid dichloride and diamine are used as raw materials, hydrogen chloride is produced as a by-product during the polymerization reaction, and to neutralize this, it is recommended to use an inorganic neutralizing agent such as lithium carbonate, calcium carbonate, or calcium hydroxide, or an organic neutralizing agent such as ethylene oxide, propylene oxide, ammonia, triethylamine, triethanolamine, or diethanolamine.

[0041] On the other hand, when the aromatic polyimide or its precursor polyamic acid that can be used in the present invention is polymerized using, for example, a tetracarboxylic acid anhydride and an aromatic diamine as raw materials, it can be synthesized by solution polymerization in an aprotic organic polar solvent such as N-methyl-2-pyrrolidone, N,N-dimethylacetamide, dimethylformamide, or dimethyl sulfoxide. Since using equal amounts of the tetracarboxylic acid anhydride and aromatic diamine raw materials can produce an ultrahigh molecular weight polymer, it is preferable to adjust the molar ratio so that one is 90.0 to 99.5 mol% of the other. Furthermore, since the polymerization reaction is exothermic and an increase in the temperature of the polymerization system can cause precipitation due to the imidization reaction, it is preferable to keep the solution temperature below 70°C during polymerization. The aromatic polyamic acid synthesized in this way can be imidized to obtain an aromatic polyimide by heat treatment, chemical treatment, or a combination of these methods. Heat treatment generally involves heating the polyamic acid at approximately 100 to 500°C to imidize it. On the other hand, chemical treatments include a method using a tertiary amine such as triethylamine as a catalyst and a dehydrating agent such as an aliphatic acid anhydride or an aromatic acid anhydride, or a method using an imidizing agent such as pyridine.

[0042] Viscosity η of aromatic polyamides and aromatic polyimides or their precursors, polyamic acids inh is preferably 0.5 to 7.0 dl / g. By setting the viscosity within the above range, a polymer excellent in toughness and strength and in ion conductivity can be obtained. The viscosity η can be measured, for example, by the method described below.

[0043] Next, a membrane-forming stock solution (hereinafter referred to as membrane-forming stock solution) used when producing the electrode mixture layer and the electrolyte layer according to the embodiment of the present invention will be described. The polymer solution after polymerization may be used as is as the membrane-forming solution, but if the solution contains a large amount of unnecessary substances such as neutralization salts, it is preferable to isolate the polymer and then redissolve it in an organic solvent such as the above-mentioned aprotic organic polar solvent or sulfuric acid before use. The method for isolating the polymer is not particularly limited, but examples include a method in which the polymer solution after polymerization is poured into a large amount of water to extract the solvent and neutralization salts into the water, and then the precipitated polymer is separated and dried.

[0044] In the manufacturing process of the electrode mixture layer and the electrolyte layer according to the embodiment of the present invention, it is preferable to add an active material, an inorganic solid electrolyte, a conductive aid, a lithium salt, etc. to the ion-conductive polymer. There is no limitation on the timing of adding these materials, and they may be added during the polymer polymerization process, the membrane-forming solution preparation process, or the membrane-forming process. However, it is preferable to add them during the membrane-forming solution preparation process because they can be uniformly dispersed with the polymer. They may also be added in multiple processes, or in multiple batches within the same process.

[0045] The concentration of the ion-conductive polymer in the film-forming solution is preferably 3 to 30% by mass, more preferably 4 to 20% by mass. To improve the strength, heat resistance, and ion permeability of the resulting polymer film, and to reduce the static friction coefficient, inorganic or organic particles may be added to the film-forming solution, provided that the effects of the present invention are not impaired. Examples of inorganic particles include wet and dry silica, colloidal silica, aluminum silicate, titanium oxide, calcium carbonate, calcium phosphate, barium sulfate, alumina, aluminum hydroxide, magnesium hydroxide, magnesium carbonate, zinc carbonate, titanium oxide, zinc oxide (zinc oxide), antimony oxide, cerium oxide, zirconium oxide, tin oxide, lanthanum oxide, magnesium oxide, barium carbonate, zinc carbonate, basic lead carbonate (white lead), barium sulfate, calcium sulfate, lead sulfate, zinc sulfide, mica, titanium mica, talc, clay, kaolin, lithium fluoride, and calcium fluoride. Examples of organic particles include particles obtained by crosslinking a polymer compound with a crosslinking agent. Examples of such crosslinked particles include crosslinked particles of polymethoxysilane-based compounds, crosslinked particles of polystyrene-based compounds, crosslinked particles of acrylic-based compounds, crosslinked particles of polyurethane-based compounds, crosslinked particles of polyester-based compounds, crosslinked particles of fluorine-based compounds, and mixtures thereof.

[0046] The membrane-forming solution obtained by isolating and redissolving the polymer from the polymerized polymer solution as described above can be used to form a membrane by a so-called solution membrane-forming method. Solution membrane-forming methods include dry-wet methods, dry methods, and wet methods. From the viewpoint of protecting the functions of the active material of the electrode mixture layer and the lithium salt of the electrolyte layer, the dry method is preferred. The electrode mixture layer and the electrolyte layer can be produced by stacking the separately molded layers; mixing the active material of the electrode mixture with the membrane-forming solution, applying it to a current collector and drying, and then applying the membrane-forming solution that will become the electrolyte layer on top of it and drying it; mixing the active material of the electrode mixture with the membrane-forming solution, applying it to a current collector, separating the layers, and then drying it to form an integrated structure; or applying an ion-conductive polymer solution dissolved in an organic solvent to the electrode mixture layer and allowing it to penetrate. Any of these methods can be suitably used.

[0047] Here, we will explain a method in which the active material for the electrode mixture layer and a film-forming source solution are mixed, applied to a current collector, and dried, and then the film-forming source solution for the electrolyte layer is applied on top of it, dried, and molded. A film-forming solution containing an ion-conductive polymer, a positive or negative electrode active material, an inorganic solid electrolyte, a conductive additive, and the like is extruded onto a metal foil serving as a current collector using a die or the like to form a film, which is then dried to obtain a positive or negative electrode mixture layer. Drying conditions can be, for example, 50 to 220°C and 120 minutes or less. However, when polyamic acid is used as the ion-conductive polymer and a membrane made of polyamic acid is to be obtained without imidization, the drying temperature is preferably 50 to 150°C. A temperature of 50 to 130°C under reduced pressure is more preferably used. Next, a film-forming solution containing an ion-conductive polymer, a lithium salt, an inorganic solid electrolyte, and the like is applied over the formed electrode mixture layer and further dried to form an electrolyte layer, thereby obtaining a laminate. The drying temperature during electrolyte layer formation is within the same range as for the electrode mixture layer. If necessary, the laminate may be heat-treated at 80 to 500°C, preferably 100 to 300°C, for several seconds to several tens of minutes. However, when polyamic acid is used as the ion-conductive polymer and a membrane made of polyamic acid is to be obtained without imidization, the heat treatment temperature is preferably 80 to 150°C, and more preferably 80 to 130°C under reduced pressure.

[0048] The thickness of the electrolyte layer according to the present invention is not particularly limited, but is preferably 0.05 to 30 μm, more preferably 0.10 to 20 μm, and even more preferably 0.20 to 15 μm. By setting the thickness within the above range, the polymer film has sufficient strength, excellent flexibility and dendrite resistance, and does not increase in resistance due to the film thickness, making it suitable for use. The thickness of the electrolyte layer can be controlled by various conditions, such as the concentration of the membrane-forming solution, the viscosity of the membrane-forming solution, the type and concentration of additives in the membrane-forming solution, the casting thickness of the polymer film, the heat treatment temperature, and the stretching conditions.

[0049] The thickness of the electrode mixture layer according to the embodiment of the present invention is not particularly limited, but is preferably 1 to 1500 μm, more preferably 5 to 1000 μm, and even more preferably 10 to 500 μm. By setting the thickness within the above range, sufficient energy density can be maintained. The thickness of the electrode mixture layer can be controlled by various conditions, such as the concentration of the membrane-forming solution, the viscosity of the membrane-forming solution, the type and concentration of additives in the membrane-forming solution, the casting thickness of the polymer film, the heat treatment temperature, and the stretching conditions.

[0050] An all-solid-state battery can be produced by stacking, on the thus obtained laminate consisting of the current collector layer / electrode mixture layer / electrolyte layer, for example, a separately molded laminate consisting of another electrode mixture layer / another current collector layer.

[0051] When the ion-conductive polymer according to the embodiment of the present invention is used in an electrode mixture layer or an electrolyte layer, excellent properties can be obtained in terms of suppressing short circuits caused by dendrites, etc. Furthermore, effects such as preventing deterioration of the active material contained in the electrode mixture layer and achieving a smaller battery size and higher capacity by reducing the thickness can be expected.

[0052] The all-solid-state battery according to the embodiment of the present invention can be suitably used as a power source for small electronic devices, transportation such as electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs), and large industrial equipment such as industrial cranes. It can also be suitably used as a power storage device for leveling power in solar cells, wind power generation devices, and the like, and for smart grids. Furthermore, it can also be suitably used as a battery for use in special environments such as space. [Example]

[0053] The present invention will be described in more detail below with reference to examples. The physical properties of the examples were measured by the following methods.

[0054] (1) Logarithmic viscosity η inh A polymer is dissolved at a concentration of 0.5 g / dL in N-methylpyrrolidone (NMP) containing 2.5% by mass of lithium bromide (LiBr), and the flow time is measured at 30°C using an Ubbelohde viscometer. The flow time of a blank LiBr 2.5% by mass / NMP solution containing no polymer is also measured in the same manner, and the logarithmic viscosity η is calculated using the following equation: inh This can be determined by calculating (dl / g).

[0055] Logarithmic viscosity η inh (dl / g) = [ln(t / t0)] / 0.5 t0: Blank flow time (seconds) t: Sample flow time (seconds)

[0056] (2) Softening point of ion-conductive polymer (°C) The softening point of the ion-conductive polymer was determined from the inflection point of the storage modulus (E') by dynamic mechanical analysis (DMA) in accordance with ASTM E1640-13. DMA was performed using the following equipment and conditions. The softening points of the ion-conductive polymers used in the electrolyte layers were measured by peeling off the positive electrode layer and the positive electrode current collector layer from the laminates each consisting of a positive electrode current collector layer / positive electrode layer / electrolyte layer obtained in each Example and Comparative Example. The softening points of the ion-conductive polymers used in the positive electrode layers were measured by peeling off the positive electrode current collector layer and the electrolyte layer from the laminates. Apparatus: Viscoelasticity measuring device DMS6100 (Seiko Instruments Inc.) Measurement mode: Tensile mode Measurement frequency: 1Hz Heating rate: 5°C / min Temperature range: 25℃~400℃ Holding time: 2 minutes

[0057] (3) Surface gloss (60°) The gloss (60°) of the electrolyte layer surface was determined in accordance with JIS Z8741 (1997). As a sample, a laminate consisting of a positive electrode current collector layer / positive electrode layer / electrolyte layer obtained in each of the examples and comparative examples was used, and the surface on the electrolyte layer side was measured. Equipment: Suga Testing Instruments Digital Variable Goniophotometer UVG-5D Measurement angle: 60° for both incident and receiving light

[0058] (4) Cell resistance (Ω·cm 2 ) An all-solid-state battery cell was fabricated, and its AC impedance was measured under conditions of a 25°C atmosphere, a voltage amplitude of 10 mV, and a frequency of 10 Hz to 5,000 kHz. The cell resistance (Ω) was calculated from the Cole-Cole plot and normalized by the measurement area. The cell was fabricated in an argon-filled glove box by laminating the negative electrode current collector (copper foil), the negative electrode layer (metallic lithium), and the laminate (electrolyte layer / positive electrode layer / positive electrode current collector layer) obtained in each example and comparative example in that order, and then using a manual press, an all-solid-state battery cell was obtained.

[0059] (5) Li element content (μg / g) The amount of Li element contained per 1 g of polymer was determined using an atomic absorption analyzer. 0.1 g of sample was weighed out, sulfuric acid was added, and the mixture was heated to carbonize, followed by heating to incineration. The incinerated product was thermally decomposed with sulfuric acid and hydrofluoric acid, and dissolved in dilute nitric acid by heating to a constant volume. The Li element content in this solution was measured using atomic absorption spectrometry to determine the content in the sample. For the sample, only the electrolyte layer was peeled off from the laminate consisting of a positive electrode current collector layer / positive electrode layer / electrolyte layer obtained in each example and comparative example, and then measured. Equipment: Atomic absorption spectrometer, Hitachi High-Technologies Z-2300

[0060] (6) Dendrite resistance We evaluated dendrite resistance when metallic Li was used for the anode. In metallic Li anodes, Li ions are deposited on the metal surface during charging and dissolved during discharging. However, Li dendrites are formed when the reaction on the metallic Li surface is uneven, resulting in Li deposition progressing faster in areas with low resistance. When dendrites penetrate the electrolyte layer, fractures are observed in the electrolyte membrane. Therefore, we evaluated dendrite resistance using the following method.

[0061] First, a cell was prepared in the same manner as in (4), and charged for a total of 48 hours using a charge / discharge device (Hokuto Denko Corporation) by constant current charging at 0.05 C up to 4.15 V and constant voltage charging at 4.15 V. After 48 hours of charging, the electrolyte layer was removed from the evaluation cell and its condition was observed, and the dendrite resistance was evaluated according to the following criteria. No electrolyte layer rupture: 〇 Electrolyte layer rupture: ×

[0062] (6) Flexibility Using a mandrel conforming to JIS-K5600-5-1 (1999), the laminates each consisting of a positive electrode current collector layer / positive electrode layer / electrolyte layer obtained in each of the Examples and Comparative Examples were bent and left to stand in an atmosphere at 25° C. The laminates were bent so that the electrolyte layer was on the outside. Sample dimensions: Short side 50mm x Long side 100mm Sample placement: Place the sample so that the folding line (contact point of the cylinder) is 50 mm along the long side. Cylinder dimensions: radius 2 mm Test duration: 72 hours Evaluation criteria: After the test, the surface of the electrolyte layer was observed and evaluated according to the following criteria. ○: No waviness, cracks or breaks were observed, and the product was in good condition. △: Wavy texture was observed, but within the practical range. ×: Cracks or breaks were observed, and it is outside the practical range.

[0063] (Reference Example 1) Polymer solution P-1 4,4'-Diaminodiphenyl ether (Tokyo Chemical Industry Co., Ltd.) as a diamine was dissolved in dehydrated NMP (N-methyl-2-pyrrolidone, Mitsubishi Chemical Corporation) under a nitrogen stream and cooled to below 30°C. To this, 2-chloroterephthaloyl chloride (Nippon Light Metal Co., Ltd.) equivalent to 99 mol% of the total amount of diamine was added over 30 min while maintaining the system at below 30°C under a nitrogen stream. After the entire amount was added, the mixture was stirred for approximately 2 hours to polymerize aromatic polyamide (P-1). The resulting polymerization solution was neutralized with 97 mol% of lithium carbonate (Honjo Chemical Co., Ltd.) and 6 mol% of diethanolamine (Tokyo Chemical Industry Co., Ltd.) based on the total amount of acid chloride to obtain a polymer solution. The viscosity of the resulting polymer, η inh The viscosity was 2.5 dl / g. Next, this polymer solution was poured into purified water in a mass ratio of 10 times or more, the solvent and neutralization salt were extracted into water, and only the precipitated polymer was separated and then dried at 80°C for 10 hours to obtain a polymer powder. Thereafter, the polymer was redissolved in dehydrated NMP (manufactured by Mitsubishi Chemical Corporation) so that the polymer concentration was 8 mass% to obtain polymer solution P-1.

[0064] (Reference Example 2) Polymer solution P-2 A polymer solution P-2 was obtained in the same manner as in Reference Example 1, except that 4,4'-diaminodiphenyl ether was replaced with 1,4-bis(4-aminophenoxy)benzene (manufactured by Tokyo Chemical Industry Co., Ltd.) as the diamine. The viscosity η of the obtained polymer inh was 2.5 dl / g.

[0065] (Reference Example 3) Polymer solution P-3 A polymer solution P-3 was obtained in the same manner as in Reference Example 1, except that 4,4'-thiodianiline (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was used as the diamine instead of 4,4'-diaminodiphenyl ether. The viscosity η of the obtained polymer inh was 1.6 dl / g.

[0066] (Reference Example 4) Polymer solution P-4 A polymer solution P-4 was obtained in the same manner as in Reference Example 1, except that 2-chloroterephthaloyl chloride was replaced with 2-phenoxyterephthaloyl chloride (manufactured by Ihara Nikkei Chemical Industry Co., Ltd.). The viscosity η of the obtained polymer inh was 1.5 dl / g.

[0067] Example 1 The polymer solution P-1 obtained in Reference Example 1 was used as a polymer solution for the electrolyte layer, and was applied to the surface of the positive electrode layer side of a positive electrode sheet (manufactured by Hosen Co., Ltd.) that used lithium cobalt oxide (LiCoO) as the active material and polyvinylidene fluoride (PVDF) as the ion-conductive polymer, 40 μm thick, so that the thickness after drying would be 5 μm. The sheet was then vacuum dried at 120°C for 60 minutes to obtain a laminate consisting of a positive electrode current collector layer / positive electrode layer / electrolyte layer. The evaluation results of the obtained laminate are shown in Table 1. The dendrite resistance and flexibility were good.

[0068] Example 2 The polymer solution P-1 obtained in Reference Example 1 was mixed with a polymer and LiTFSI (lithium bis(trifluoromethanesulfonyl)imide, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) at a mass ratio of 95:5. The mixture was stirred and degassed using a mixer (manufactured by THINKY Corporation, model number: AR-250) to obtain a polymer solution for an electrolyte layer. The resulting polymer solution was applied to the surface of the positive electrode layer side of a 40 μm-thick positive electrode sheet (manufactured by Hosen Co., Ltd.) using lithium cobalt oxide (LiCoO) as the active material and PVDF as the ion-conductive polymer, so that the thickness after drying would be 5 μm. The resulting solution was then vacuum dried at 120°C for 60 minutes to obtain a laminate of a positive electrode current collector layer / positive electrode layer / electrolyte layer. The evaluation results for the resulting laminate are shown in Table 1. The cell resistance, flexibility, and dendrite resistance were good.

[0069] Example 3 Lithium cobalt oxide and carbon black were blended with the polymer solution P-1 obtained in Reference Example 1 so that the ratio of polymer, lithium cobalt oxide, and carbon black was 5:92:3 by mass, and the mixture was stirred and degassed using a mixer (THINKY, model number: AR-250) to obtain a polymer solution for the positive electrode layer. The obtained polymer solution for the positive electrode layer was applied to a 10 μm thick Al foil so that the thickness after drying would be 30 μm, and the foil was vacuum dried at 120°C for 60 minutes to obtain a positive electrode sheet. A laminate of a current collector layer for the electrode, a positive electrode layer, and an electrolyte layer was obtained in the same manner as in Example 2, except that the obtained positive electrode sheet was used. The evaluation results of the above-mentioned evaluations performed using the obtained laminate are shown in Table 1. Cell resistance was improved.

[0070] Examples 4 to 6 A laminate of a positive electrode current collector layer / positive electrode layer / electrolyte layer was obtained in the same manner as in Example 3, except that the ratio of LiTFSI in the electrolyte layer was changed as shown in Table 1. The above evaluations were performed using the obtained laminate, and the results are shown in Table 1. Even when the ratio of polymer to LiTFSI in the electrolyte layer was changed, the cell resistance, flexibility, and dendrite resistance were all good.

[0071] Examples 7 to 9 A laminate was obtained in the same manner as in Example 4, except that the type of polymer solution was changed as shown in Table 1.

[0072] Example 10 The polymer solution for the electrolyte layer contains an oxide-based inorganic solid electrolyte, Li7La3Zr2O 12 A laminate was obtained in the same manner as in Example 3, except that (LLZ) was added as shown in Table 1. A laminate consisting of a positive electrode current collector layer / positive electrode layer / electrolyte layer was obtained. The above evaluations were performed using the obtained laminate, and the results are shown in Table 1. Even when an oxide-based inorganic solid electrolyte was added, the cell resistance, flexibility, and dendrite resistance were all good.

[0073] Example 11 A laminate consisting of a positive electrode current collector layer / positive electrode layer / electrolyte layer was obtained in the same manner as in Example 10, except that the compounding ratio of the polymer, lithium salt, and inorganic solid electrolyte in the polymer solution for the electrolyte layer was changed as shown in Table 1. The above evaluations were performed using the obtained laminate, and the results are shown in Table 1. Although the flexibility was slightly inferior compared to the results of Example 10 due to the large amount of added oxide-based inorganic solid electrolyte, both the cell resistance and dendrite resistance were good.

[0074] (Comparative Example 1) Polyethylene oxide E-45 (PEO) (Meisei Chemical Industry Co., Ltd.) was dissolved in acetonitrile (Tokyo Chemical Industry Co., Ltd.) at 60°C to obtain a 10% by mass solution, which was used for the electrolyte layer polymer. This solution was applied to the surface of the positive electrode layer side of a 40 μm-thick positive electrode sheet (Hosensha) using lithium cobalt oxide (LiCoO2) as the active material and PVDF as the ion-conductive polymer, so that the thickness after drying would be 5 μm. The sheet was then vacuum dried at 80°C for 30 minutes to obtain a positive electrode current collector layer / positive electrode layer / electrolyte layer laminate. The evaluation results of the resulting laminate are shown in Table 1. While the dendrite resistance and flexibility were good, the low softening point of the ion-conductive polymer contained in the electrolyte layer resulted in poor heat resistance, resulting in a failure.

[0075] (Comparative Example 2) The electrolyte layer was made of only the oxide-based inorganic solid electrolyte LLZ. The electrolyte sheet was compression-molded to a thickness of 10 μm. This electrolyte sheet was then placed on the surface of the positive electrode layer of a 40 μm-thick positive electrode sheet (manufactured by Hosen Co., Ltd.) that used lithium cobalt oxide (LiCoO2) as the active material and PVDF as the ion-conductive polymer, and press-molded to obtain a positive electrode current collector layer / positive electrode layer / electrolyte layer laminate. The above evaluations were performed using the resulting laminate, and the results are shown in Table 1. Due to poor dendrite resistance and flexibility, the laminate failed.

[0076] [Table 1]

Claims

1. An all-solid-state battery having a current collector layer, an electrode mixture layer, and an electrolyte layer, wherein the electrolyte layer is provided on at least one surface layer of the electrode mixture layer, the surface gloss (60°) of the electrolyte layer is 10 or more and 300 or less, the electrode mixture layer and the electrolyte layer are layers containing an ion-conductive polymer, and the softening point of the ion-conductive polymer is 80°C or higher.

2. The all-solid-state battery according to claim 1 , wherein the electrolyte layer and the electrode mixture layer contain the same ion-conducting polymer.

3. Cell resistance at 25°C is 30 Ω cm ２ The all-solid-state battery according to claim 1 or 2, wherein:

4. 4. The all-solid-state battery according to claim 1, wherein the electrolyte layer contains a Li salt in an amount of 5 mass % or more relative to the total mass of the ion-conductive polymer in the electrolyte layer.

5. 5. The all-solid-state battery according to claim 1, wherein the electrolyte layer contains 50 μg or more of Li element per 1 g of the ion-conductive polymer in the electrolyte layer.

6. The all-solid-state battery according to any one of claims 1 to 5, wherein the ion-conducting polymer comprises an aromatic polyamide.

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