Thin film for solid-state batteries

Abstract

The present disclosure aims to provide a thin film for solid-state batteries that has a low residual solvent content, is less likely to adversely affect the performance of the solid-state battery, and can be manufactured by a roll-to-roll continuous coating method. [Solution] A thin film 100 for a solid-state battery is provided, comprising solid electrolyte particles 110 and crystalline fluororesins 120 and 130 that bind the solid electrolyte particles 110 to each other, wherein at least a portion of the crystalline fluororesins 130 is fibrous, and the content of volatile components measured by gas analysis means is 10 ppm by mass or less.

Description

[Technical Field]

[0001] This disclosure relates to thin films for solid-state batteries. [Background technology]

[0002] Solid-state batteries are secondary batteries that contain a solid electrolyte, and they are attracting attention because they have higher performance in terms of charging performance and other aspects compared to liquid-system batteries that use only a liquid electrolyte. As a method for forming the positive electrode active material layer, solid electrolyte layer, or negative electrode active material layer (hereinafter, these three layers will be referred to as thin films for solid-state batteries) contained in such solid-state batteries, a generally known method is the slurry deposition method, in which a slurry is generated by incorporating a solvent into each component, and then the slurry is coated and dried.

[0003] However, slurry deposition methods involve a drying process, resulting in high energy consumption and significant equipment costs. In contrast, solvent-free deposition methods (dry deposition methods) have been proposed.

[0004] For example, Patent Document 1 discloses a positive electrode for a secondary battery having a positive electrode active material layer containing at least a positive electrode active material and a solid electrolyte, wherein the amount of oil absorbed, which is specified as the amount of linseed oil absorbed within and between the primary particles of the positive electrode active material particles, is 35 to 50 ml per 100 g, the average particle size of the solid electrolyte particles is 1.5 to 2.5 μm, and the positive electrode active material layer is formed by mixing the positive electrode active material particles and the solid electrolyte particles in a solvent-free environment and press-molding the mixture. Patent Document 1 states that, according to the disclosure in Patent Document 1, it is possible to provide a positive electrode for a secondary battery with a high capacity retention rate, a method for manufacturing a positive electrode for a secondary battery, and an all-solid-state secondary battery equipped with the positive electrode. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2014-143133 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] The Disclosers have found that the presence of a large amount of residual solvent in a thin film for solid-state batteries can degrade the performance of the solid-state battery. In contrast, as described in Patent Document 1, if a thin film for solid-state batteries is fabricated by a dry deposition method, the residual solvent in the solid-state battery thin film can be reduced.

[0007] However, in order to perform battery film deposition efficiently and at low cost, it is necessary to manufacture the thin film for solid-state batteries using a continuous roll-to-roll coating method, similar to conventional methods. Dry film deposition using a batch-type pressure molding method, as described in Patent Document 1, has the problem that the flexibility of the thin film for solid-state batteries is low, making the continuous roll-to-roll coating method unsuitable.

[0008] Therefore, the present disclosure aims to provide a thin film for solid-state batteries that has a low residual solvent content, is less likely to adversely affect the performance of the solid-state battery, and can be manufactured by a continuous roll-to-roll coating method. [Means for solving the problem]

[0009] This disclosure aims to achieve the above objectives by the following means: <Aspect 1> The material comprises solid electrolyte particles and a crystalline fluororesin that binds the solid electrolyte particles together. At least a portion of the above-mentioned crystalline fluororesin is fibrous, and A thin film for solid-state batteries, wherein the content of volatile components, as measured by gas analysis, is 10 ppm by mass or less. <Aspect 2> The thin film for a solid battery according to Embodiment 1, wherein the content of the above-mentioned volatile component is 1 ppm by mass or less. <Aspect 3> A thin film for a solid-state battery according to embodiment 1 or 2, wherein the particle size of the solid electrolyte particles is 1.0 μm or less. <Aspect 4> The thin film for a solid battery according to any one of Aspects 1 to 3, wherein the content of the crystalline fluororesin is 1.0% by mass or less. <Aspect 5> The thin film for a solid battery according to any one of Aspects 1 to 4, wherein the content of the crystalline fluororesin is 0.6% by mass or more. <Aspect 6> The thin film for a solid battery according to any one of Aspects 1 to 5, wherein the solid electrolyte particles are sulfide solid electrolyte particles. <Aspect 7> The thin film for a solid battery according to any one of Aspects 1 to 6, wherein the crystalline fluororesin is polytetrafluoroethylene, a perfluoroalkyl compound, a polyfluoroalkyl compound, or a combination thereof. <Aspect 8> The thin film for a solid battery according to any one of Aspects 1 to 7, which is a positive electrode active material layer further containing a positive electrode active material. <Aspect 9> The thin film for a solid battery according to any one of Aspects 1 to 7, which is a solid electrolyte layer. <Aspect 10> The thin film for a solid battery according to any one of Aspects 1 to 7, which is a negative electrode active material layer further containing a negative electrode active material. <Aspect 11> Having a positive electrode active material layer, a solid electrolyte layer, and a negative electrode active material layer in this order, and At least one layer selected from the positive electrode active material layer, the solid electrolyte layer, and the negative electrode active material layer is the thin film for a solid battery according to any one of Aspects 1 to 7. Solid battery.

Advantages of the Invention

[0010] According to the present disclosure, it is possible to provide a thin film for a solid battery that is less likely to adversely affect the performance of the solid battery due to a low content of residual solvent and can be manufactured by a roll-to-roll continuous coating method.

Brief Description of the Drawings

[0011] [Figure 1]Figure 1 is a schematic cross-sectional view illustrating the thin film for solid-state batteries of the present disclosure. [Figure 2] Figure 2 is a schematic cross-sectional view illustrating the solid-state battery of this disclosure. [Modes for carrying out the invention]

[0012] 《Thin film for solid-state batteries》 The thin film for solid-state batteries disclosed herein is The material comprises solid electrolyte particles and a crystalline fluororesin that binds the solid electrolyte particles together. At least a portion of the above-mentioned crystalline fluororesin is fibrous, and The content of volatile components, as measured by gas analysis methods, is 10 ppm by mass or less.

[0013] According to this disclosure, it is possible to provide a thin film for solid-state batteries that has a low residual solvent content, is less likely to adversely affect the performance of the solid-state battery, and can be manufactured by a roll-to-roll continuous coating method.

[0014] The performance of solid-state batteries may deteriorate if a large amount of residual solvent, i.e., volatile components, remains in the thin film used for solid-state batteries. Although not limited to theory, this is thought to be because some of the particles contained in the thin film, such as solid electrolyte particles, are coated by the decomposition products of the volatile components.

[0015] In contrast, the Disclosers have found that when the content of volatile components in the thin film for solid-state batteries is 10 ppm by mass or less, the performance degradation of the solid-state battery can be suppressed, and desirable physical properties for the solid-state battery can be obtained.

[0016] Furthermore, the presence of a crystalline fluororesin as a binder in the thin film for solid-state batteries allows for high flexibility after film formation. While not limited to theory, it is believed that applying shear force to the crystalline fluororesin causes it to fibrousize, promoting the bonding of solid electrolyte particles and thus improving flexibility.

[0017] Specifically, as shown in Figure 1, for example, the thin film 100 for solid-state batteries of this disclosure includes solid electrolyte particles 110, crystalline fluororesin particles 120, and crystalline fluororesin fibers 130 formed by the fibrousization of a portion of the crystalline fluororesin particles 120. The solid electrolyte particles 110 are bound together by the crystalline fluororesin particles 120, and further bound together by the crystalline fluororesin fibers 130. Therefore, the thin film 100 for solid-state batteries has high flexibility.

[0018] The following describes each component of the present invention.

[0019] In this disclosure, "thin film for solid-state battery" means the positive electrode material layer, solid electrolyte layer, or negative electrode active material layer included in a solid-state battery. The thin film for solid-state battery of this disclosure may be applied to one of these layers or to two or more layers.

[0020] In this disclosure, “solid-state battery” means a battery that uses at least solid electrolyte particles as the electrolyte, and therefore a solid-state battery may use a combination of solid electrolyte particles and a liquid electrolyte as the electrolyte. Furthermore, in this disclosure, “solid-state battery” may be an all-solid-state battery, i.e., a battery that uses only solid electrolyte particles as the electrolyte.

[0021] The material includes solid electrolyte particles and a crystalline fluororesin that binds the solid electrolyte particles together. The crystalline fluororesin functions as a binder, and the binding of the solid electrolyte particles to each other via the crystalline fluororesin allows the thin film for the solid battery to have high flexibility.

[0022] The content of crystalline fluororesin is not particularly limited, but may be 1.0% by mass or less, 0.9% by mass or less, or 0.8% by mass or less relative to the thin film for solid-state batteries. Factors that adversely affect the battery performance of solid-state batteries include the presence of additives that hinder contact between solid electrolyte particles and reduce lithium ion conductivity. Therefore, if a large amount of crystalline fluororesin is included in the thin film for solid-state batteries to increase its flexibility, the ionic conductivity will decrease.

[0023] The content of crystalline fluororesin is not particularly limited, but it is preferable that it be 0.6% by mass or 0.7% by mass or more relative to the thin film for the solid battery, from the viewpoint of ensuring the flexibility of the thin film for the solid battery.

[0024] The content of solid electrolyte particles is not particularly limited and may be determined appropriately according to the application, performance, etc., of the thin film for solid-state batteries. For example, the content of solid electrolyte particles may be 1% by mass or more, 5% by mass or more, 10% by mass or more, 15% by mass or more, or 20% by mass or more relative to the thin film for solid-state batteries, and may be 90% by mass or less, 80% by mass or less, 70% by mass or less, 60% by mass or less, or 50% by mass or less.

[0025] The solid electrolyte particles and the particles other than the solid electrolyte particles contained in the thin film for the solid-state battery may be bonded together by a crystalline fluororesin, and the particles other than the solid electrolyte particles contained in the thin film for the solid-state battery may be bonded together by a crystalline fluororesin. Examples of particles other than the solid electrolyte particles contained in the thin film for the solid-state battery include positive electrode active material, negative electrode active material, and conductive additives.

[0026] The volatile component content of the thin film for solid-state batteries of this disclosure, as measured by gas analysis means, is 10 ppm by mass or less. From the viewpoint of preventing a decrease in battery performance, a low amount of volatile components is preferable. The above content may be 8 ppm by mass or less, 6 ppm by mass or less, 4 ppm by mass or less, 2 ppm by mass or less, or 1 ppm by mass or less. Alternatively, the above content may be 1 ppb by mass or more, 10 ppb by mass or more, or 100 ppb by mass or more. Here, if there are multiple types of volatile components, the above content refers to the content of each volatile component.

[0027] The content of volatile components was measured by gas analysis. This gas analysis was performed using a temperature-dependent desorption mass spectrometry (TPD-MS) method, which incorporates a heating device into a mass spectrometer (GC / MS-QP2010, manufactured by Shimadzu Corporation). Qualitative and quantitative analysis of the target solvent was then conducted. Helium was used as the carrier gas and heated to 250°C at a rate of 10°C / min using the heating device.

[0028] In this specification, "volatile components" refers to solvents used in the manufacturing process of solid-state battery thin films that remain in the solid-state battery thin films. Examples of solvents include alcohols such as methanol, ethanol, propanol, and butanol; aliphatic hydrocarbons such as hexane and heptane; ketones such as acetone, methyl ethyl ketone, and 2-pentanone; and esters such as ethyl acetate and butyl acetate.

[0029] The flexibility of the thin film for solid-state batteries is not particularly limited and may be appropriately determined depending on the required performance of the solid-state battery. The flexibility can be determined, for example, in a cylindrical mandrel test, by winding a laminate having the thin film for solid-state batteries around a cylinder, and the diameter of the cylinder at which cracks begin to appear in the electrode active material layer may be 45 mm or less, 40 mm or less, 35 mm or less, 30 mm or less, 25 mm or less, or 20 mm or less, and may also be 5 mm or more, 10 mm or more, or 15 mm or more.

[0030] The shape of the thin film for solid-state batteries is not particularly limited, but may be, for example, a sheet with a substantially flat surface. The thickness of the thin film for solid-state batteries is not particularly limited, but may be, for example, 0.1 μm or more, 1 μm or more, or 10 μm or more, or 2 mm or less, 1 mm or less, or 500 μm or less.

[0031] The method for forming a thin film for solid-state batteries is not particularly limited, but from the viewpoint of reducing the content of volatile components in the thin film for solid-state batteries, it is preferable to form it by a dry film formation method that does not require volatile components.

[0032] <Solid electrolyte particles> The particle size of the solid electrolyte particles may be 1.0 μm or less. A smaller particle size can improve the flexibility of the thin film for solid-state batteries. This is not limited to theory, but it is thought that a smaller particle size of the solid electrolyte particles allows the solid electrolyte particles to efficiently apply shear force to the crystalline fluororesin when the solid electrolyte particles are kneaded with the crystalline fluororesin, thereby increasing the amount of crystalline fluororesin that becomes fibrous. The particle size of the solid electrolyte particles may be 0.9 μm or less, 0.8 μm or less, 0.7 μm or less, or 0.5 μm or less, and may be 0.1 μm or more, 0.2 μm or more, or 0.3 μm or more.

[0033] Here, the particle size of the solid electrolyte particles is the particle size (median diameter) at 50% of the integrated value in the volume-based particle size distribution determined by laser diffraction and scattering.

[0034] The solid electrolyte particles are not particularly limited, but may be sulfide solid electrolyte particles. Alternatively, the solid electrolyte particles may be oxide solid electrolyte particles, polymer electrolyte particles, etc.

[0035] Examples of sulfide solid electrolyte particles include, but are not limited to, sulfide-based amorphous solid electrolyte particles, sulfide-based crystalline solid electrolyte particles, or argyrodite-type solid electrolyte particles. Specific examples of sulfide solid electrolyte particles include the Li2S-P2S5 system (Li7P3S 11, such as Li3PS4, Li8P2S9, etc., Li2S - SiS2, LiI - Li2S - SiS2, LiI - Li2S - P2S5, LiI - LiBr - Li2S - P2S5, Li2S - P2S5 - GeS2 (Li 13 GeP3S 16 , Li 10 GeP2S 12 , etc., LiI - Li2S - P2O5, LiI - Li3PO4 - P2S5, Li 7-x PS 6-x Cl x , etc.; or combinations thereof can be mentioned, but not limited thereto.

[0036] Examples of oxide solid electrolyte particles include Li7La3Zr2O 12 , Li 7-x La3Zr 1-x Nb x O 12 , Li 7-3x La3Zr2Al x O 12 , Li 3x La 2 / 3-x TiO3, Li 1+x Al x Ti 2-x (PO4)3, Li 1+x Al x Ge 2-x (PO4)3, Li3PO4, or Li 3+x PO 4-x N x (LiPON), etc.; or combinations thereof can be mentioned, but not limited thereto.

[0037] The sulfide solid electrolyte particles and oxide solid electrolyte particles may be glass or crystallized glass (glass ceramics).

[0038] Examples of polymer electrolyte particles include polyethylene oxide (PEO), polypropylene oxide (PPO), and copolymers thereof, etc., but not limited thereto.

[0039] 〈Crystalline fluororesin〉 Crystalline fluororesins are fibrous in some respects. This fibrous structure enhances the bonding between solid electrolyte particles, resulting in high flexibility.

[0040] The crystalline fluororesin is not particularly limited and may be, for example, polytetrafluoroethylene (PTFE), perfluoroalkyl compounds, or polyfluoroalkyl compounds. The crystalline fluororesin material may be used alone or in combination of two or more types.

[0041] The perfluoroalkyl compound may be, for example, perfluorooctanesulfonic acid (PFOS), perfluorooctanoic acid (PFOA), perfluorohexanesulfonic acid (PFHxS), etc.

[0042] The polyfluoroalkyl compound may be, for example, polyfluoroalkyl vinyl ether (PFA), polyfluoroalkyl acrylate (PFAA), etc.

[0043] The crystalline fluororesin may contain particulate matter. The particle size of the crystalline fluororesin is not particularly limited and may be 0.5 μm or less, 0.4 μm or less, 0.3 μm or less, 0.2 μm or less, or 0.1 μm or less, or 0.01 μm or more, 0.03 μm or more, or 0.05 μm or more. Here, the particle size of the crystalline fluororesin is the particle size (median diameter) at 50% of the cumulative value in the volume-based particle size distribution determined by laser diffraction-scattering method.

[0044] The method for producing fibrous crystalline fluororesin is not particularly limited, but for example, by kneading particulate crystalline fluororesin together with solid electrolyte particles while applying shear force, a portion of the crystalline fluororesin becomes fibrous.

[0045] <Cathode active material layer> The thin film for solid-state batteries may further contain a positive electrode active material layer. In this case, the positive electrode active material layer may contain at least a positive electrode active material, solid electrolyte particles, and a crystalline fluororesin, and may optionally contain a conductive additive. For solid electrolyte particles, refer to the above description of solid electrolyte particles, and for crystalline fluororesins, refer to the above description of crystalline fluororesins. The positive electrode active material layer may also contain various other additives.

[0046] The respective content amounts of the positive electrode active material, solid electrolyte particles, and conductive additives in the positive electrode active material layer can be appropriately determined according to the desired battery performance. For example, if the total amount of the positive electrode active material layer (total solid content) is 100% by mass, the content of the positive electrode active material may be 40% by mass or more, 50% by mass or more, 60% by mass or more, 100% by mass or less, or 90% by mass or less.

[0047] (Cathode active material) The material of the positive electrode active material is not particularly limited as long as it is capable of intercalating and releasing lithium ions. Examples of positive electrode active materials include lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMn2O4), and nickel-cobalt-manganese oxide (NCM:LiCO2). 1 / 3 Ni 1 / 3 Mn 1 / 3 O2), lithium nickel-cobalt aluminum oxide (LiNi 0.8 (CoAl) 0.2 O2), Li 1+x Mn 2-x-y M y This may include, but is not limited to, heteroatom-substituted Li-Mn spinel with a composition represented by O4 (where M is one or more metallic elements selected from Al, Mg, Co, Fe, Ni, and Zn).

[0048] The positive electrode active material is not particularly limited, but may have a coating layer. The coating layer is a layer containing a material that has lithium ion conductivity, low reactivity with the positive electrode active material and solid electrolyte particles, and can maintain a coating layer form that does not flow even when in contact with the active material and solid electrolyte particles. Specific examples of materials constituting the coating layer include LiNbO3 and Li4Ti5O3. 12 Examples include Li3PO4, but are not limited to these.

[0049] The shape of the positive electrode active material is not particularly limited, as long as it is a shape common for positive electrode active materials in batteries. The positive electrode active material may be, for example, particulate. The positive electrode active material may be primary particles or secondary particles formed by the aggregation of multiple primary particles. The particle size of the positive electrode active material may be, for example, 1 nm or more, 5 nm or more, or 10 nm or more, or 500 μm or less, 100 μm or less, 50 μm or less, or 30 μm or less. Note that the particle size of the positive electrode active material is the particle size (median diameter) at 50% of the cumulative value in the volume-based particle size distribution determined by laser diffraction-scattering method.

[0050] (Conductive additive) The conductive additive is not particularly limited. Examples of conductive additives include, but are not limited to, vapor-grown carbon fibers (VGCF), acetylene black (AB), Ketjenblack (KB), carbon nanotubes (CNT), and carbon nanofibers (CNF). The conductive additive may be particulate or fibrous, and its size is not particularly limited. The conductive additive is not particularly limited, but one type may be used alone, or two or more types may be used in combination.

[0051] <Solid electrolyte layer> The thin film for the solid-state battery may be a solid electrolyte layer. In this case, the solid electrolyte layer includes at least solid electrolyte particles and a crystalline fluororesin, and may optionally include a conductive additive. For solid electrolyte particles, refer to the description of solid electrolyte particles above, and for conductive additives, refer to the description of conductive additives above. The solid electrolyte layer may also contain various other additives.

[0052] <Negative electrode active material layer> The thin film for the solid-state battery may further contain a negative electrode active material layer. In this case, the negative electrode active material layer may contain at least a negative electrode active material, solid electrolyte particles, and a crystalline fluororesin, and may optionally contain a conductive additive. For solid electrolyte particles, refer to the above description of solid electrolyte particles; for crystalline fluororesins, refer to the above description of crystalline fluororesins; and for conductive additives, refer to the above description of conductive additives. The negative electrode active material layer may also contain various other additives.

[0053] The respective content amounts of the negative electrode active material, solid electrolyte particles, and conductive additives in the negative electrode active material layer can be appropriately determined according to the desired battery performance. For example, if the total amount of the negative electrode active material layer (total solid content) is 100% by mass, the content of the negative electrode active material may be 40% by mass or more, 50% by mass or more, or 60% by mass or more, or it may be 100% by mass or less, or 90% by mass or less.

[0054] (Negative electrode active material) As the negative electrode active material, various materials can be used whose potential for intercalating and releasing lithium ions (charge / discharge potential) is lower than that of the positive electrode active material described above. The material of the negative electrode active material is not particularly limited and may be metallic lithium, or any material capable of intercalating and releasing metallic ions such as lithium ions. Examples of materials capable of intercalating and releasing metallic ions such as lithium ions include alloy-based negative electrode active materials, carbon materials, or lithium titanate (Li4Ti5O4). 12 Examples include, but are not limited to, those listed above.

[0055] The alloy-based anode active material is not particularly limited and includes, for example, Si alloy-based anode active materials or Sn alloy-based anode active materials. Si alloy-based anode active materials include silicon, silicon oxide, silicon carbide, silicon nitride, or solid solutions thereof. Si alloy-based anode active materials may also contain metallic elements other than silicon, such as Fe, Co, Sb, Bi, Pb, Ni, Cu, Zn, Ge, In, Sn, Ti, etc. Sn alloy-based anode active materials include tin, tin oxide, tin nitride, or solid solutions thereof. Sn alloy-based anode active materials may also contain metallic elements other than tin, such as Fe, Co, Sb, Bi, Pb, Ni, Cu, Zn, Ge, In, Ti, Si, etc.

[0056] The carbon material is not particularly limited and examples include hard carbon, soft carbon, and graphite.

[0057] The shape of the negative electrode active material is not particularly limited, but any shape common for negative electrode active materials in batteries is acceptable. The negative electrode active material may be in the form of parts or sheets, for example.

[0058] 《Solid-state battery》 The solid-state battery described herein is It has a positive electrode active material layer, a solid electrolyte layer, and a negative electrode active material layer in this order, and At least one layer selected from the above positive electrode active material layer, the above solid electrolyte layer, and the above negative electrode active material layer is the thin film for the solid-state battery of this disclosure.

[0059] According to this disclosure, it is possible to provide a solid-state battery that includes a thin film for solid-state batteries, which has a low residual solvent content that is less likely to adversely affect the performance of the solid-state battery and can be manufactured by a roll-to-roll continuous coating method.

[0060] The solid-state battery of this disclosure comprises at least a positive electrode active material layer, a solid electrolyte layer, and a negative electrode active material layer in this order, and may further optionally include a positive electrode current collector layer, a negative electrode current collector layer, and a liquid electrolyte.

[0061] Specifically, for example, as shown in Figure 1, the solid-state battery 200 has a positive electrode active material layer 210, a solid electrolyte layer 220, and a negative electrode active material layer 230 in that order.

[0062] At least one layer selected from a positive electrode active material layer, a solid electrolyte layer, and a negative electrode active material layer is the thin film for a solid-state battery of this disclosure. Two or more of these layers may be the thin film for a solid-state battery of this disclosure. For the positive electrode active material layer, refer to the description of the positive electrode active material layer above; for the solid electrolyte layer, refer to the description of the solid electrolyte layer above; and for the negative electrode active material layer, refer to the description of the negative electrode active material layer above.

[0063] <Positive electrode current collector layer> The material used for the positive electrode current collector layer is not particularly limited, but any material commonly used for positive electrode current collectors in solid-state batteries can be appropriately adopted. Examples of materials used for the positive electrode current collector layer include, but are not limited to, Cu, Ni, Cr, Au, Pt, Ag, Al, Fe, Ti, Zn, Co, and stainless steel. The positive electrode current collector layer may also have some kind of coating layer on its surface for purposes such as adjusting resistance. Furthermore, the positive electrode current collector layer may be a metal foil or a substrate on which the above metals are plated or vapor-deposited.

[0064] The shape of the positive electrode current collector layer is not particularly limited, but examples include foil-like, plate-like, or mesh-like shapes. Among these, the foil-like shape is preferred. The thickness of the positive electrode current collector layer is not particularly limited, but may be 0.1 μm or more, 1 μm or more, 1 mm or less, or 100 μm or less.

[0065] <Negative electrode current collector layer> The material used for the negative electrode current collector layer is not particularly limited, but a material commonly used for the negative electrode current collector of a solid-state battery can be appropriately adopted. Examples of materials used for the negative electrode current collector layer include, but are not limited to, Cu, Ni, Cr, Au, Pt, Ag, Al, Fe, Ti, Zn, Co, stainless steel, or carbon sheets. The negative electrode current collector layer may have some kind of coating layer on its surface for purposes such as adjusting resistance.

[0066] The shape of the negative electrode current collector layer is not particularly limited, but examples include foil-like, plate-like, or mesh-like shapes. Of these, the foil-like shape is preferred. The thickness of the negative electrode current collector layer is not particularly limited, but may be 0.1 μm or more, 1 μm or more, 1 mm or less, or 100 μm or less.

[0067] <Liquid electrolyte> The liquid electrolyte is not particularly limited, but it preferably contains a supporting salt and a solvent.

[0068] The supporting salt (lithium salt) for the lithium-ion conductive electrolyte is not particularly limited, but examples include inorganic lithium salts and organic lithium salts. Examples of inorganic lithium salts include, but are not limited to, LiPF6, LiBF4, LiClO4, and LiAsF6. Examples of organic lithium salts include, but are not limited to, LiCF3SO3, LiN(CF3SO2)2, LiN(C2F5SO2)2, LiN(FSO2)2, and LiC(CF3SO2)3.

[0069] The solvent used in the electrolyte is not particularly limited, but examples include cyclic carbonates and linear carbonates. Examples of cyclic carbonates include, but are not limited to, ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC). Examples of linear carbonates include, but are not limited to, dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC). The electrolyte is not particularly limited, but may be used alone or in combination of two or more types. [Examples]

[0070] The present disclosure will be specifically illustrated by examples and comparative examples, but will not be limited thereto.

[0071] Fabrication of thin films for solid-state batteries <Examples 1-4> As shown in Table 1, solid electrolyte particles of the Li2S-P2S5 system and PTFE, a crystalline fluororesin used as a binder, were kneaded under shear force. The resulting mixture was pressed into a plate shape using a dry deposition method to obtain the solid-state battery thin films of Examples 1 to 4.

[0072] <Comparative Example 1> As shown in Table 1, a slurry was obtained by mixing a Li2S-P2S5 system as solid electrolyte particles and PVDF as a binder in a solvent. The slurry was coated using a blade method with an applicator and dried to obtain the thin film for solid-state batteries of Comparative Example 1.

[0073] <Measurement of volatile component content> The amount of volatile components contained in the thin films for solid-state batteries of Examples 1-4 and Comparative Example 1 was measured by performing qualitative and quantitative analysis of the target solvent using temperature-dependent desorption mass spectrometry (TPD-MS) with a heating device incorporated into a mass spectrometer (GC / MS-QP2010, Shimadzu Corporation). Helium was used as the carrier gas, and the samples were heated to 250°C at a rate of 10°C / min using the heating device. The measurement results are shown in Table 1.

[0074] "evaluation" <Presence or absence of degradation of solid electrolyte particles> The presence or absence of degradation of solid electrolyte particles was confirmed by ion conductivity measurement and elemental analysis. The evaluation criteria were as follows. A: No degradation of the solid electrolyte particles was detected through ion conductivity measurement and elemental analysis. B: Degradation of solid electrolyte particles was confirmed by ion conductivity measurement and elemental analysis.

[0075] <Flexibility of thin films for solid-state batteries> In a cylindrical mandrel test, laminates containing the solid-state battery thin films of Examples 1-4 and Comparative Example 1 were wrapped around cylinders with diameters of 40 mm and 50 mm, and their flexibility was evaluated. The evaluation criteria were as follows. A: When wrapped around a 40mm diameter cylinder, the thin film for solid-state batteries was not damaged and possessed sufficient flexibility. B: When wrapped around a cylinder with a diameter of 50 mm, the thin film for the solid-state battery was not damaged and possessed sufficient flexibility. C: When wrapped around a cylinder with a diameter of 50 mm, the thin film for the solid-state battery was damaged and did not have sufficient flexibility.

[0076] The results of each evaluation are shown in Table 1.

[0077] [Table 1]

[0078] From Examples 1-4 and Comparative Example 1 in Table 1, it can be seen that when the amount of volatile components in the thin film for solid-state batteries is small, no degradation of the solid electrolyte is observed, and the thin film for solid-state batteries does not adversely affect the performance of the solid-state battery.

[0079] Examples 1 and 2 in Table 1 show that a smaller particle size of the solid electrolyte increases the amount of fibrous crystalline fluororesin, resulting in a solid electrolyte layer with high flexibility. Therefore, it can be seen that a smaller particle size of the solid electrolyte is a more preferable condition. [Explanation of symbols]

[0080] 100 Thin film for solid-state batteries 110 Solid electrolyte particles 120 Crystalline fluororesin particles 130 Crystalline fluoropolymer resin fibers 200 solid state battery 210 Cathode active material layer 220 Solid electrolyte layer 230 Negative electrode active material layer

Claims

1. The material comprises solid electrolyte particles and a crystalline fluororesin that binds the solid electrolyte particles together. At least a portion of the crystalline fluororesin is fibrous, and A thin film for solid-state batteries, wherein the content of volatile components, as measured by gas analysis, is 10 ppm by mass or less.

2. The thin film for a solid battery according to claim 1, wherein the content of the volatile component is 1 ppm by mass or less.

3. The thin film for a solid-state battery according to claim 1, wherein the particle size of the solid electrolyte particles is 1.0 μm or less.

4. The thin film for a solid-state battery according to claim 1, wherein the content of the crystalline fluororesin is 1.0% by mass or less.

5. The thin film for a solid-state battery according to claim 1, wherein the content of the crystalline fluororesin is 0.6% by mass or more.

6. The thin film for a solid-state battery according to any one of claims 1 to 5, wherein the solid electrolyte particles are sulfide solid electrolyte particles.

7. The thin film for a solid-state battery according to any one of claims 1 to 5, wherein the crystalline fluorine-based resin is polytetrafluoroethylene, a perfluoroalkyl compound, a polyfluoroalkyl compound, or a combination thereof.

8. Furthermore, the thin film for a solid battery according to any one of claims 1 to 5, wherein the positive electrode active material layer contains a positive electrode active material.

9. A thin film for a solid-state battery according to any one of claims 1 to 5, which is a solid electrolyte layer.

10. Furthermore, the thin film for a solid battery according to any one of claims 1 to 5, wherein the negative electrode active material layer contains a negative electrode active material.

11. It has a positive electrode active material layer, a solid electrolyte layer, and a negative electrode active material layer in this order, and At least one layer selected from the positive electrode active material layer, the solid electrolyte layer, and the negative electrode active material layer is a thin film for a solid-state battery according to any one of claims 1 to 5. solid state battery.

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