Solid electrolyte sheet

Abstract

The solid electrolyte sheet contains a solid electrolyte and a binder. The solid electrolyte sheet has a thickness of 90 [mu] m or less. The content of the binder in the solid electrolyte sheet is greater than 1 mass%. The solid electrolyte includes a crystal phase having an argyrodite-type crystal structure. The solid electrolyte sheet does not contain a porous support. The solid electrolyte sheet has a self-supporting property. The content of the binder is preferably 20% by mass or less. The tensile strength of the solid electrolyte sheet is also suitably 2.0 N / mm2 or more.

Description

Technical Field

[0001] This invention relates to solid electrolyte sheets. Background Technology

[0002] In recent years, secondary batteries have attracted attention as a countermeasure to prevent global warming by reducing CO2. Among them, solid-state batteries are expected to be practical due to their combination of safety and high energy density. In the manufacture of solid-state batteries, solid electrolyte sheets, which mainly contain powdered solid electrolytes, are sometimes used as one of the components constituting the solid-state battery. For example, Patent Document 1 describes a solid electrolyte sheet in which powdered solid electrolytes are supported by a support formed of nonwoven fabric, the binder content is less than 0.5% by mass, and the thickness is less than 100 μm.

[0003] However, when a solid electrolyte sheet has a support, the support sometimes hinders the close contact between the solid electrolyte particles, making it difficult to improve conductivity. Furthermore, current concentration in specific areas within the solid electrolyte sheet can sometimes contribute to battery degradation. Therefore, solid electrolyte sheets without a support have also been proposed. For example, Non-Patent Literature 1 describes a method where a slurry containing powder of a solid electrolyte with the composition Li6PS5Cl, dispersed together with a binder in a solvent, is coated onto a polytetrafluoroethylene film. The resulting coating is then dried and compacted at 300 MPa to produce a solid electrolyte sheet with a thickness of 90 μm to 120 μm.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2018-129307

[0007] Non-patent literature

[0008] Non-patent literature 1: J. Energy Storage, 66 (2023) 107480 Summary of the Invention

[0009] However, solid electrolyte sheets without a support tend to be thicker to ensure their self-support. If the thickness of the solid electrolyte sheet increases, its resistance increases, resulting in a decrease in conductivity.

[0010] Therefore, the objective of this invention is to provide a solid electrolyte sheet in which the decrease in conductivity is suppressed.

[0011] The present invention provides a solid electrolyte sheet comprising a solid electrolyte and a binder, wherein the thickness of the solid electrolyte sheet is less than 90 μm, the content of the binder is greater than 1% by mass, the solid electrolyte comprises a crystal phase having a sulforaphite-germanium type crystal structure, and the solid electrolyte sheet does not contain a porous support and has self-supporting properties. Detailed Implementation

[0012] This invention relates to solid electrolyte sheets. The solid electrolyte sheet of this invention comprises a sheet-like component containing a solid electrolyte. In this specification, a sheet refers to a component having a first main surface and a second main surface located on its opposite side, wherein the distance between the two main surfaces, i.e., the thickness, is extremely small (e.g., less than 1 / 100th of the thickness relative to the longitudinal and transverse dimensions of the main surface).

[0013] One characteristic of the solid electrolyte sheet of the present invention is that it is self-supporting even though it does not contain a porous support. In this specification, self-supporting refers to the rigidity of the solid electrolyte sheet; having self-supporting means that even without using a support that is a different component from the solid electrolyte sheet, the solid electrolyte sheet itself can maintain its shape. For example, if a test piece is prepared by cutting the solid electrolyte sheet of the present invention into a 1cm × 1cm square, and the test piece is held by adjacent corners (e.g., within a 3mm × 3mm rectangular area) and suspended, and the test piece does not break due to its own weight, then the solid electrolyte sheet can be said to have self-supporting properties.

[0014] Materials known in this art can be listed as porous supports. Examples include woven and nonwoven fabrics made of natural or synthetic fibers, porous membranes made of synthetic resins, and glass fiber cloth.

[0015] To enable the solid electrolyte sheet of the present invention to possess self-supporting properties, one of its characteristics lies in its composition. Specifically, the solid electrolyte sheet of the present invention is suitable to comprise a solid electrolyte and a binder, wherein the binder content relative to the solid electrolyte sheet is preferably greater than 1% by mass. By including the binder at such a content, the solid electrolyte sheet of the present invention can maintain its own shape even without containing a porous support. The binder content can, for example, be 2% by mass or more, 3% by mass or more, 4% by mass or more, or 5% by mass or more.

[0016] On the other hand, from the viewpoint of maintaining the conductivity of the solid electrolyte sheet at a high level, the content of binder in the solid electrolyte sheet of the present invention is preferably set to 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less.

[0017] As a binder contained in the solid electrolyte sheet of the present invention, it is suitable to use a substance that has the function of binding the particles of the solid electrolyte together without affecting the reduction of the conductivity of the solid electrolyte sheet. Examples of binders include polymeric compounds obtained using at least one selected from isobutylene, styrene, butadiene, ethylene, propylene, methyl methacrylate, acrylonitrile, vinylidene chloride, and vinylidene fluoride as polymerizable monomers. Some or all of the hydrogen contained in these polymerizable monomers may optionally be fluorinated.

[0018] Specific examples of adhesives include polyisobutylene, styrene-butadiene rubber, styrene-butadiene-styrene rubber, styrene-ethylene-butadiene-styrene rubber, polymethyl methacrylate, poly(acrylonitrile-butadiene), hydrogenated poly(acrylonitrile-butadiene), and polyvinylidene fluoride.

[0019] These various adhesives can be used alone or in combination of two or more.

[0020] In addition, in these various adhesives, some or all of the hydrogen contained therein may optionally be fluorinated.

[0021] In particular, using a fluorinated polymer as a binder provides sufficient self-support to the solid electrolyte sheet even in small quantities and maintains a high level of conductivity, making it preferable. It is especially preferred to use a polymer containing fluorine atoms in its main chain as a binder. Examples of such binders include polyvinylidene fluoride (PVDF) and copolymers of PVDF with fluorinated or unfluorinated polyolefins.

[0022] From the viewpoint of achieving good battery energy density, it is ideal that the solid electrolyte sheet of the present invention has a small thickness while possessing self-supporting properties. From this viewpoint, the thickness of the solid electrolyte sheet of the present invention is preferably, for example, 90 μm or less, more preferably 70 μm or less, and even more preferably 50 μm or less.

[0023] Furthermore, from the viewpoint of maintaining self-support, the thickness of the solid electrolyte sheet of the present invention is preferably 5 μm or more, preferably 10 μm or more, more preferably 20 μm or more, and even more preferably 30 μm or more.

[0024] The thickness of the solid electrolyte sheet can be determined by microscopic observation of its cross-section. Alternatively, a thickness gauge can be used. When using either method, the thickness is measured at at least 10 different locations, and the arithmetic mean of these measurements is taken as the thickness of the solid electrolyte sheet.

[0025] From the viewpoint of maintaining a high level of conductivity of the solid electrolyte sheet, the content of solid electrolyte in the solid electrolyte sheet of the present invention is preferably 80% by mass or more, more preferably 85% by mass or more, and even more preferably 90% by mass or more.

[0026] Furthermore, from the viewpoint of adding a binder to improve self-support, the content of solid electrolyte in the solid electrolyte sheet of the present invention is preferably less than 97% by mass, more preferably 95% by mass or less, and even more preferably 93% by mass or less.

[0027] The density of the solid electrolyte sheet of the present invention can be, for example, 1.0 g / cm³. 3 The above can be 1.3 g / cm³ 3 The above can also be 1.5 g / cm³. 3 above.

[0028] Furthermore, the density of the solid electrolyte sheet of the present invention can be, for example, 2.0 g / cm³. 3 The following can be 1.9 g / cm³ 3 The following can also be 1.8 g / cm³ 3 the following.

[0029] By giving the solid electrolyte sheet of the present invention such a density, it is possible to perform a compression process on the solid electrolyte sheet in a subsequent process, such as in the manufacturing process of a solid-state battery. This is advantageous from the viewpoint of manufacturing high-performance solid-state batteries.

[0030] From the viewpoint of improving self-support, the basis weight of the solid electrolyte sheet of the present invention is preferably, for example, 30 g / m³. 2 The above, preferably 35g / m 2 The above is further preferred to be 40g / m 2 That's all. Furthermore, from the viewpoint of maintaining a high conductivity level for the solid electrolyte sheet, the basis weight of the solid electrolyte sheet of the present invention is preferably, for example, 70 g / m³. 2 The preferred value is 65g / m 2 The following is a further preferred value: 60g / m 2 the following.

[0031] In this specification, basis weight refers to the mass per unit area of ​​a solid electrolyte sheet. Therefore, for two solid electrolyte sheets formed of the same material and having the same thickness but different densities (apparent densities), the solid electrolyte sheet with the higher density will have a higher basis weight.

[0032] The basis weight of the solid electrolyte sheet can be controlled by adjusting the coating thickness in the manufacturing method of the solid electrolyte sheet described later.

[0033] The solid electrolyte sheet of the present invention, possessing sufficient self-support, has strength adequate to withstand use. In this invention, even without a support structure, the strength of the solid electrolyte sheet can be ensured to be within a specified range. Specifically, the tensile strength of the solid electrolyte sheet of the present invention is preferably, for example, 2.0 N / mm². 2 The above is preferred, with 4.0 N / mm being more ideal. 2 The above is further preferred to be 5.0 N / mm. 2 The above is further optimized to 5.5 N / mm. 2 That's all. On the other hand, the tensile strength of the solid electrolyte sheet can be 20.0 N / mm². 2 The following can also be 15.0 N / mm 2 The tensile strength referred to here is the breaking strength obtained by first preparing a dumbbell-shaped test piece (No. 6) from the solid electrolyte sheet of the present invention, and then conducting a tensile test on the test piece at a tensile speed of 20 mm / min.

[0034] To set the strength of the solid electrolyte sheet to the above value, it is possible to appropriately control, for example, the type and content of the binder in the solid electrolyte sheet, the compression conditions during the manufacture of the solid electrolyte sheet, and the particle size of the solid electrolyte particles.

[0035] The solid electrolyte contained in the solid electrolyte sheet of the present invention may, for example, be in particulate form. From the viewpoint of improving the self-supporting properties of the solid electrolyte sheet, when the solid electrolyte is in particulate form, the particle size is defined as the volumetric cumulative particle size D at a cumulative volume of 50% capacity, based on a laser diffraction scattering particle size distribution method. 50 This indicates that, for example, it is preferably 20 μm or less, more preferably 10 μm or less, more preferably 7 μm or less, and even more preferably 5 μm or less. On the other hand, D 50 For example, it can be 0.1μm or larger, 0.3μm or larger, or 0.5μm or larger.

[0036] The solid electrolyte contained in the solid electrolyte sheet of the present invention is preferably a material with lithium-ion conductivity. Examples of such solid electrolytes include inorganic solid electrolytes such as sulfide solid electrolytes, oxide solid electrolytes, nitride solid electrolytes, and halide solid electrolytes, as well as organic polymer electrolytes such as polymer electrolytes. From the viewpoint of making the effects of the present invention more significant, the solid electrolyte is preferably a sulfide solid electrolyte.

[0037] Sulfide solid electrolytes can use previously known substances without particular restrictions. For example, sulfide solid electrolytes can contain Li and S and have lithium-ion conductivity.

[0038] Sulfide solid electrolytes can be any of crystalline materials, glass ceramics, or glass. Examples of such sulfide solid electrolytes include Li₂S-P₂S₅, Li₂S-P₂S₅-LiX (where "X" represents one or more halogen elements), Li₂S-P₂S₅-P₂O₅, Li₂S-Li₃PO₄-P₂S₅, Li₃PS₄, Li₄P₂S₆, and Li₂S₅. 10 GeP2S 12 Li 3.25 Ge 0.25 P 0.75 S4, Li7P3S 11 Li 3.25 P 0.95 S4, Li a PS b X c ("X" represents one or more halogen elements, "a" represents a number of 3.0 or higher and 9.0 or lower, "b" represents a number of 3.5 or higher and 6.0 or lower, and "c" represents a number of 0.1 or higher and 3.0 or lower.) Examples of such compounds include sulfide solid electrolytes described in International Publication No. 2013 / 099834 and International Publication No. 2015 / 001818.

[0039] In particular, from the viewpoint of maintaining a higher level of conductivity of the solid electrolyte sheet, the solid electrolyte preferably contains a crystal phase with a sulfogermanium ore-type crystal structure.

[0040] The argyrogermanite-type crystal structure refers to the crystal structure of compounds derived from minerals with the chemical formula Ag8GeS6. Whether a solid electrolyte possesses a argyrogermanite-type crystal phase can be confirmed using X-ray diffraction (hereinafter also referred to as "XRD"). For example, in the diffraction pattern obtained using CuKα1 XRD, the argyrogermanite-type crystal phase exhibits characteristic diffraction peaks at positions of 2θ = 25.5° ± 1.0°, 30.0° ± 1.0°, and 30.9° ± 1.0°. In addition to the aforementioned diffraction peaks, depending on the elements constituting the solid electrolyte, characteristic diffraction peaks sometimes also appear at 2θ = 15.3°±1.0°, 18.0°±1.0°, 44.3°±1.0°, 47.2°±1.0°, 51.7°±1.0°, 58.3°±1.0°, 60.7°±1.0°, 61.5°±1.0°, 70.4°±1.0°, and 72.6°±1.0°. For the identification of diffraction peaks originating from argillite-type crystal structures, data such as PDF number 00-034-0688 are used.

[0041] The Young's modulus of the solid electrolyte is preferably 30 GPa or less. This is because during the pressing process in the manufacture of the solid electrolyte sheet, the solid electrolyte particles are easily crushed, making the solid electrolyte sheet denser and thus improving its self-supporting properties. From the viewpoint of making this advantage even more significant, the Young's modulus of the solid electrolyte is preferably 28 GPa or less, more preferably 25 GPa or less.

[0042] In addition, the Young's modulus of solid electrolytes can be above 1 GPa, above 5 GPa, or above 10 GPa.

[0043] The Young's modulus of a solid electrolyte can be controlled by adjusting the composition of the solid electrolyte and the conditions during its manufacture (e.g., calcination temperature and / or calcination atmosphere).

[0044] The Young's modulus of a solid electrolyte can be determined, for example, by the method described in the applicant's earlier application WO2019 / 9228.

[0045] The solid electrolyte used in this invention preferably contains at least lithium (Li), phosphorus (P), and sulfur (S), and more preferably at least lithium (Li), phosphorus (P), sulfur (S), and halogen (X). In this case, from the viewpoint of improving lithium-ion conductivity, the solid electrolyte preferably has the following composition (I): Li a PS b X c (X represents at least one of the elements fluorine (F), chlorine (Cl), bromine (Br), and iodine (I).)

[0046] In composition formula (I), 'a', representing the molar ratio of Li, is preferably 3.0 or more, more preferably 4.0 or more, and particularly preferably 5.0 or more. On the other hand, 'a' is preferably 6.5 or less, more preferably 5.9 or less, and particularly preferably 5.6 or less. By setting 'a' to this range, the cubic argyroclase-germanium sulfide crystal structure near room temperature (25°C) becomes more stable, thereby enabling the sufficient introduction of lithium-ion holes into the structure, and as a result, effectively improving lithium-ion conductivity.

[0047] In composition (I), b is preferably 3.5 or more, more preferably 4.0 or more, and particularly preferably 4.2 or more. On the other hand, b is preferably 5.5 or less, more preferably 4.9 or less, and particularly preferably 4.7 or less. By keeping b within the above range, the sulfide-germanium ore-type crystal structure near room temperature (25°C) becomes more stable, and lithium-ion conductivity is effectively improved.

[0048] In composition (I), c is preferably 0.1 or more, more preferably 1.1 or more, and particularly preferably 1.4 or more. On the other hand, c is preferably 2.5 or less, more preferably 2.0 or less, and particularly preferably 1.8 or less.

[0049] In addition, solid electrolytes can be composed of formula (II): Li 7-d PS 6-d X d The composition shown in formula (II) is the stoichiometric composition of the silver-germanium sulfide crystalline phase. In formula (II), X has the same meaning as in formula (I).

[0050] In composition (II), d is preferably 0.4 or more, more preferably 0.8 or more, and particularly preferably 1.2 or more. On the other hand, d is preferably 2.2 or less, more preferably 2.0 or less, and particularly preferably 1.8 or less.

[0051] In addition, solid electrolytes can be composed of formula (III): Li 7-d-2e PS 6-d-e X d The sulfide-germanium ore type crystal phase having the composition represented by formula (III) is generated, for example, by reacting the sulfide-germanium ore type crystal phase having the composition represented by formula (II) with P2S5 (phosphorus pentasulfide).

[0052] In composition formula (III), e is a value representing the deviation of the Li2S composition from the stoichiometric composition shown in composition formula (II). e is preferably -0.9 or more, more preferably -0.6 or more, and particularly preferably -0.3 or more. On the other hand, e is preferably (-d+2) or less, more preferably (-d+1.6) or less, and particularly preferably (-d+1.0) or less.

[0053] In solid electrolytes, the atomic ratio of element X to element P, X / P, is preferably greater than 1.0, more preferably 1.1 or more, even more preferably 1.2 or more, and still more preferably 1.4 or more. On the other hand, the atomic ratio X / P is preferably 2.5 or less, more preferably 2.3 or less, and even more preferably 2.2 or less. By having the atomic ratio X / P within the above range, lithium-ion conductivity is further improved. The atomic ratio X / P can be determined, for example, by high-frequency inductively coupled plasma atomic emission spectrometry (ICP emission spectrometry) or SEM-EDS analysis.

[0054] In particular, when element X includes at least Cl and Br, the atomic ratio of Cl and Br combined to P (Cl+Br) / P is preferably greater than 1.0, more preferably 1.1 or more, further preferably 1.2 or more, and even more preferably 1.4 or more. On the other hand, the atomic ratio (Cl+Br) / P is preferably 2.5 or less, more preferably 2.3 or less, and even more preferably 2.0 or less. By keeping the atomic ratio (Cl+Br) / P within the aforementioned range, lithium-ion conductivity is further improved, which is therefore preferable. The atomic ratio (Cl+Br) / P can be determined, for example, by high-frequency inductively coupled plasma atomic emission spectrometry (ICP emission spectrometry) or elemental analysis using an EDS-equipped scanning electron microscope (SEM-EDS).

[0055] Regarding the solid electrolyte used in this invention, among the above-described compositions (I) to (III), it is particularly preferred to be composed of composition (IV): Li 7-d PS 6-d Cl d1 Br d2 express.

[0056] In the aforementioned composition (IV), the total molar ratio d (=d1+d2) of Cl and Br is preferably greater than 1.0, more preferably 1.2 or more, and particularly preferably 1.4 or more. On the other hand, the total molar ratio d is preferably less than 2.5, more preferably less than 2.0, particularly preferably 1.8 or less, and even more preferably 1.7 or less. By keeping the total molar ratio d within the aforementioned range, the formation of heterogeneous phases can be adequately controlled, and the decrease in lithium-ion conductivity can be effectively suppressed.

[0057] In the aforementioned compositional formula (IV), the molar ratio of Br to Cl (d2 / d1) is preferably 0.1, more preferably 0.3 or more, and particularly preferably 0.5 or more. On the other hand, the aforementioned molar ratio is preferably 10 or less, more preferably 5 or less, and particularly preferably 3 or less. By keeping the above molar ratio within the aforementioned range, lithium-ion conductivity can be further improved.

[0058] In the aforementioned compositional formula (IV), d1, representing the molar ratio of Cl, is preferably 0.3 or more, more preferably 0.4 or more, and particularly preferably 0.6 or more. On the other hand, d1 is preferably 1.5 or less, more preferably 1.2 or less, and particularly preferably 1.0 or less. By setting d1 to the aforementioned lower limit or above, lithium-ion conductivity can be further improved. On the other hand, by setting d1 to the aforementioned upper limit or below, a solid electrolyte can be easily obtained.

[0059] In the aforementioned compositional formula (IV), d2, representing the molar ratio of Br, is preferably 0.3 or more, more preferably 0.4 or more, and particularly preferably 0.6 or more. On the other hand, d2 is preferably 1.5 or less, more preferably 1.2 or less, and particularly preferably 1.0 or less. By setting d2 to the aforementioned lower limit or above, a solid electrolyte is readily obtained. On the other hand, by setting d2 to the aforementioned upper limit or below, lithium-ion conductivity can be further improved.

[0060] When the solid electrolyte used in this invention is any of the aforementioned compositional formulas (I), (II), (III) and (IV), the lithium-ion conductivity is further improved if element X contains element Br, which is therefore preferred.

[0061] The solid electrolyte sheet of the present invention may consist only of a solid electrolyte and a binder, or it may contain other components in addition to the solid electrolyte and the binder. Examples of such other components include, for instance, dispersants.

[0062] The content of other components in the solid electrolyte tablets of the present invention is expressed as the total amount of all other components, for example, it may be less than 7.0% by mass, less than 3.0% by mass, or less than 1.0% by mass.

[0063] Next, a suitable manufacturing method for the solid electrolyte sheet of the present invention will be described.

[0064] The solid electrolyte sheet of the present invention is suitably manufactured by a method comprising the following steps (a) to (e).

[0065] (a) The process of preparing a slurry containing a solid electrolyte, a binder and a volatile liquid medium;

[0066] (b) The process of applying the aforementioned slurry onto a substrate sheet to form a coating film;

[0067] (c) The process of removing the aforementioned volatile liquid medium from the aforementioned coating;

[0068] (d) The process of pressing the aforementioned coating to obtain a solid electrolyte sheet; and

[0069] (e) The process of peeling the aforementioned solid electrolyte sheet from the aforementioned substrate sheet.

[0070] The following is a description of each process.

[0071] In step (a), the aforementioned solid electrolyte particles and binder are mixed with a volatile liquid medium to prepare a slurry. Examples of volatile liquid media include nonpolar solvents such as heptane, methylcyclohexane, and toluene; aprotic polar solvents such as methyl isobutyl ketone and cyclohexanone; and mixtures thereof.

[0072] Methods for mixing solid electrolyte particles, binders, and volatile liquid media include, for example, ultrasonic homogenizers, oscillators, thin-film rotary mixers, dissolvers, homogenizers, kneaders, roller mills, sand mills, grinders, ball mills, vibratory mills, and high-speed impeller mills.

[0073] From the viewpoint of smoothly forming a coating film from the slurry, the proportion of volatile liquid medium contained in the slurry is preferably 20% by mass or more, more preferably 40% by mass or more, and even more preferably 50% by mass or more. Furthermore, from the viewpoint of efficiently removing volatile liquid medium from the coating film formed from the slurry, the proportion of volatile liquid medium contained in the slurry is preferably 90% by mass or less, more preferably 80% by mass or less, and even more preferably 70% by mass or less.

[0074] In step (b), the aforementioned slurry is applied to a substrate sheet to form a coating film. Examples of slurry application methods include blade coating, die coating, gravure coating, spray coating, electrostatic coating, and bar coating. By adjusting the amount of slurry applied, the thickness of the final solid electrolyte sheet can be adjusted.

[0075] The substrate sheet to which the aforementioned slurry is applied can be, for example, a film, cloth, or foil made of resin, metal, or glass.

[0076] When the substrate sheet is made of resin, for example, the resin can be acrylic resin, polyester resin, cellulose derivative resin, polyvinyl acetal resin, polyvinyl butyral resin, vinyl chloride-vinyl acetate copolymer, chlorinated polyolefin, and copolymers of the resin groups thereof.

[0077] When the substrate sheet is made of metal, for example, copper, stainless steel, aluminum, nickel, silver, gold, chromium, cobalt, tin, zinc and brass, as well as their alloys, can be used.

[0078] In step (c), the volatile liquid medium is removed by the coating film. Examples of methods for removing the volatile liquid medium include warm air drying, hot air drying, infrared drying, reduced pressure drying, and induction heating drying. Regarding the degree of removal, the content of the volatile liquid medium in the removed coating film can be, for example, less than 10% by mass, less than 7% by mass, or less than 5% by mass.

[0079] In step (d), the coating film after the removal of the volatile liquid medium is pressed. This yields the target solid electrolyte sheet. For example, a uniaxial press can be used to press the coating film along its thickness direction. Alternatively, the coating film can be pressed isotropically throughout using CIP (cold isostatic pressing).

[0080] When using any method, from the viewpoint of obtaining a solid electrolyte sheet with high self-support, the pressing pressure is preferably 200 MPa or more, more preferably 400 MPa or more, and even more preferably 600 MPa or more. There is no particular upper limit to the pressing pressure; if a high pressure of around 1500 MPa is applied, a solid electrolyte sheet with sufficiently high self-support can be easily obtained.

[0081] Pressing can be performed under heating. This further improves the self-supporting properties of the solid electrolyte sheet. From this perspective, the heating temperature can be, for example, above 0°C, above 10°C, or above 20°C. Furthermore, from the viewpoint of suppressing binder degradation, the heating temperature can be, for example, below 200°C, below 100°C, or below 50°C.

[0082] After obtaining the target solid electrolyte sheet, the solid electrolyte sheet is peeled off from the substrate sheet. The peeled solid electrolyte sheet has sufficient self-support and can therefore be processed separately.

[0083] A positive electrode, formed by a positive electrode layer on a current collector, and a negative electrode, formed by a negative electrode layer on a current collector, are respectively disposed on each surface of the solid electrolyte sheet obtained in this way. After these three are pressed together, they are hermetically sealed into a battery can, thereby obtaining a solid-state battery.

[0084] The positive electrode layer contains a positive electrode active material. Examples of positive electrode active materials include oxides containing lithium transition metals. Specifically, examples include lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), and LiNi... 1 / 3 Co 1 / 3 Mn 1 / Layered active materials such as rock salt (3O2); lithium manganese oxide (LiMn2O4), Li(Ni) 0.5 Mn 1.5 O4, Li 1+x Mn 2-x-y M y O4 (where M is one or more selected from the group consisting of Al, Mg, Co, Fe, Ni, and Zn) and other spinel-type active materials; lithium titanate (Li x TiO y LiFePO4, LiMnPO4, LiCoPO4, LiNiPO4 and other olivine-type active substances, etc.

[0085] On the other hand, the negative electrode layer contains a negative electrode active material. Examples of negative electrode active materials include graphite and silicon, which are capable of absorbing and storing lithium.

[0086] Regarding the above-described embodiments, the present invention discloses the following solid electrolyte sheet.

[0087] [1]

[0088] A solid electrolyte sheet comprising a solid electrolyte and a binder, wherein the thickness of the solid electrolyte sheet is less than 90 μm, the binder content is greater than 1% by mass, the solid electrolyte comprises a crystal phase having a sulforaphite-germanium type crystal structure, and the solid electrolyte sheet does not contain a porous support and has self-supporting properties.

[0089] [2]

[0090] According to the solid electrolyte sheet described in [1], the binder content is less than 20% by mass.

[0091] [3]

[0092] The solid electrolyte sheet according to [1] or [2] has a tensile strength of 2.0 N / mm. 2 above.

[0093] [4]

[0094] The solid electrolyte sheet according to any one of [1] to [3] has a density of 1.0 g / cm³. 3 Above and 2.0 g / cm 3 the following.

[0095] [5]

[0096] The solid electrolyte sheet according to any one of [1] to [4], wherein the Young's modulus of the solid electrolyte is less than 30 GPa.

[0097] [6]

[0098] According to any one of [1] to [5], the solid electrolyte sheet, wherein the cumulative particle size D of the solid electrolyte when the cumulative volume is 50% based on the laser diffraction scattering particle size distribution determination method is... 50 It is between 0.1μm and 20μm.

[0099] [7]

[0100] The solid electrolyte sheet according to any one of [1] to [6], wherein the binder is a fluorinated polymer compound.

[0101] Example

[0102] The present invention will now be described in more detail through experimental examples. However, the scope of the present invention is not limited to these embodiments. Unless otherwise specified, "%" refers to "mass %".

[0103] [Example 1]

[0104] As a solid electrolyte, a solution with the formula Li is prepared. 5.4 PS 4.4 Cl 0.8 Br 0.8 This refers to a powder containing a lithium-ion conductive sulfide with a crystalline phase having a sulfide-germanium-sulfide type crystal structure. The particle size D of this powder is... 50 It is 3.4μm.

[0105] As a binder, a fluorinated polymer compound obtained by polymerization using at least vinylidene fluoride as a polymerizable monomer is used.

[0106] The solid electrolyte and binder are used in such a manner that the solid electrolyte accounts for 95% and the binder accounts for 5% of their total mass.

[0107] Butyl butyrate was used as the volatile liquid medium. A slurry was obtained by mixing butyl butyrate with a solid electrolyte and a binder. The proportion of the volatile liquid medium in the slurry was 47%.

[0108] The slurry was applied to a 38 μm thick polyethylene terephthalate (PET) substrate using a doctor blade with a 70 μm gap to form a coating. The coating was then vacuum dried at 120 °C.

[0109] The coating was pressed using a CIP (manufactured by Kobe Steel Corporation) at a pressure of 700 MPa. The pressed coating was then peeled off from the substrate sheet to obtain a solid electrolyte sheet.

[0110] [Example 2]

[0111] The solid electrolyte and binder were used in such a manner that the solid electrolyte comprised 93% and the binder 7% of their total mass. Otherwise, a solid electrolyte sheet was obtained in the same manner as in Example 1.

[0112] [Example 3]

[0113] The solid electrolyte and binder were used in such a manner that the solid electrolyte comprised 90% and the binder 10% of their total mass. Otherwise, a solid electrolyte sheet was obtained in the same manner as in Example 1.

[0114] [Example 4]

[0115] The solid electrolyte and binder were used in a manner that, relative to their combined mass, the solid electrolyte comprised 80% and the binder comprised 20%. Otherwise, a solid electrolyte sheet was obtained in the same manner as in Example 1.

[0116] [Comparative Example 1]

[0117] The solid electrolyte and binder were used in such a manner that the solid electrolyte comprised 99% and the binder 1% of their total mass. Otherwise, a solid electrolyte sheet was obtained in the same manner as in Example 1.

[0118] [Comparative Example 2]

[0119] This comparative example is an example of manufacturing a solid electrolyte sheet containing a porous support.

[0120] The solid electrolyte and binder were used in such a manner that the solid electrolyte comprised 99% and the binder 1% of their total mass. Otherwise, the slurry was obtained in the same manner as in Example 1.

[0121] Using the obtained slurry, a coating film was formed on the substrate sheet in the same manner as in Example 1, and then the coating film was dried.

[0122] A laminate was obtained by sandwiching a 21 μm thick support made of nonwoven fabric between a pair of the aforementioned coatings. After pressing the laminate using the same method as in Example 1, the substrate sheet was peeled off to obtain a solid electrolyte sheet.

[0123] [Comparative Example 3]

[0124] This comparative example is also an example of manufacturing a solid electrolyte sheet containing a porous support.

[0125] The solid electrolyte and binder were used in such a manner that the solid electrolyte comprised 95% and the binder comprised 5% of their total mass. Otherwise, a solid electrolyte sheet was obtained in the same manner as in Comparative Example 2.

[0126] [Comparative Example 4]

[0127] This comparative example is also an example of manufacturing a solid electrolyte sheet containing a porous support.

[0128] The solid electrolyte and binder were used in a manner that, relative to their combined mass, the solid electrolyte comprised 80% and the binder comprised 20%. Otherwise, a solid electrolyte sheet was obtained in the same manner as in Comparative Example 2.

[0129] 〔evaluate〕

[0130] For the solid electrolyte sheets obtained in the examples and comparative examples, the thickness, tensile strength, and density were determined using the methods described above. The ionic conductivity was then determined using the methods described below, and the self-supporting properties were also evaluated. The results are shown in Table 1 below. Tensile strength was measured using a small benchtop tensile testing machine (Shimadzu EZ-SX5000N).

[0131] [Determination of ionic conductivity]

[0132] For the solid electrolyte sheets obtained in the examples and comparative examples, the lithium-ion conductivity was determined using a Biologic VSP-300 high-performance electrochemical measurement system. The measurement conditions were set as follows: temperature 25°C, frequency 100MHz~7MHz, and amplitude 100mV using AC impedance spectroscopy.

[0133] [Evaluation of self-support]

[0134] The self-supporting properties of the solid electrolyte sheets obtained in the examples and comparative examples are evaluated by assessing whether the solid electrolyte sheet possesses sufficient strength for handling and / or movement when held and lifted with tweezers. Specifically, the evaluation is conducted as follows.

[0135] ○: No cracks and / or fractures have occurred to the extent that would render the product unusable as a solid electrolyte sheet.

[0136] ×: Cracks and / or fractures have occurred to a degree that renders the product unusable as a solid electrolyte sheet.

[0137] [Table 1]

[0138]

[0139] As shown in Table 1, the solid electrolyte sheet obtained in the examples, although it does not have a support, has high self-support and high ion conductivity.

[0140] In contrast, the solid electrolyte sheet of Comparative Example 1 lacked sufficient self-support due to its low binder content. Therefore, its ionic conductivity could not be measured.

[0141] Although the solid electrolyte sheets of Comparative Examples 2 and 3 have sufficient self-support due to the presence of a support, their ionic conductivity is reduced due to the presence of the support.

[0142] Industrial availability

[0143] According to the present invention, a solid electrolyte sheet is provided that still has self-supporting properties despite not having a support and that suppresses the increase in thickness.

Claims

1. A solid electrolyte sheet comprising a solid electrolyte and a binder, The thickness of the solid electrolyte sheet is less than 90 μm. The adhesive contains more than 1% by mass. The solid electrolyte contains a crystalline phase with a sulforaphite-germanium type crystal structure. The solid electrolyte sheet does not contain a porous support and has self-supporting properties.

2. The solid electrolyte sheet according to claim 1, wherein, The content of the adhesive is less than 20% by mass.

3. The solid electrolyte sheet according to claim 1 or 2, wherein the tensile strength is 2.0 N / mm. 2 above.

4. The solid electrolyte sheet according to claim 1 or 2, wherein the density is 1.0 g / cm³. 3 Above and 2.0 g / cm 3 the following.

5. The solid electrolyte sheet according to claim 1 or 2, wherein, The Young's modulus of the solid electrolyte is below 30 GPa.

6. The solid electrolyte sheet according to claim 1 or 2, wherein, The volumetric cumulative particle size D of the solid electrolyte at a cumulative volume of 50% capacity was determined using laser diffraction scattering particle size distribution method. 50 It is between 0.1μm and 20μm.

7. The solid electrolyte sheet according to claim 1 or 2, wherein, The adhesive is a fluorine-containing polymer compound.

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