Solid electrolyte membrane, lithium ion secondary battery and lithium ion secondary battery module

Abstract

To provide a solid electrolyte membrane capable of suppressing battery short circuit occurrence.SOLUTION: Provided is a solid electrolyte membrane that comprises a solid electrolyte and a binder. The membrane has a first diffusion completion time of 20 seconds or longer, as measured by a method 1. In the method 1, a test piece measuring 2 cm in height and 2 cm in width is cut from the membrane. Next, under conditions of 25°C temperature, -70°C dew point, and atmospheric pressure, 20 μL of butyl butyrate is dropped from a position 1 cm vertically above the center of the test piece. The time required for the butyl butyrate to diffuse across the entire surface of the test piece is measured and defined as the first diffusion completion time.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a solid electrolyte membrane, a lithium ion secondary battery, and a lithium ion secondary battery module. [Background technology]

[0002] Lithium ion secondary batteries are known as batteries with high energy density.

[0003] Patent Document 1 describes a method for producing a positive electrode-solid electrolyte composite for an all-solid-state energy storage element, which aims to enable bonding at a relatively low temperature to suppress the generation of a high-resistance reaction layer at the interface, and to maximize the bonding area by increasing the adhesion between the plate-shaped positive electrode and the plate-shaped solid electrolyte at the interface, and includes the steps of: laminating a plate-shaped positive electrode made of a ceramic sintered body containing a positive electrode active material and a plate-shaped solid electrolyte made of a ceramic sintered body having ion conductivity to obtain a laminate; and simultaneously applying heat and pressure to the laminate to integrate the positive electrode and the solid electrolyte by a solid-phase reaction. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-243111 Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention provides a solid electrolyte membrane that can suppress the occurrence of short circuits in a battery. [Means for solving the problem]

[0006] The present inventors have found that, in a solid electrolyte membrane containing a solid electrolyte and a binder, there is a correlation between the density of the solid electrolyte membrane and the occurrence of a short circuit in a battery. As a result of further intensive research based on the above findings, the present inventors have found that the occurrence of a short circuit in a battery can be suppressed by setting the time measured for the solid electrolyte membrane by a predetermined method within a predetermined range, and have completed the present invention.

[0007] That is, according to the present invention, there are provided the following solid electrolyte membrane, lithium ion secondary battery, and lithium ion secondary battery module.

[0008] [1] A solid electrolyte membrane comprising a solid electrolyte and a binder, A solid electrolyte membrane having a first diffusion completion time of 20 seconds or longer as measured by the following method 1. (Method 1) A test piece measuring 2 cm (length) × 2 cm (width) was cut from the solid electrolyte membrane. Next, under conditions of a temperature of 25°C, a dew point temperature of −70°C, and atmospheric pressure, 20 μL of butyl butyrate was dropped from a position 1 cm away from the surface of the test piece in a vertical direction toward the center of the test piece. The time from the drop until the butyl butyrate was diffused over the entire surface was measured, and this time was designated as the first diffusion completion time. [2] The solid electrolyte membrane according to [1], wherein the first diffusion completion time is 100 seconds or more. [3] The solid electrolyte membrane according to [1] or [2], wherein the second diffusion completion time measured by the following method 2 is 1 second or longer. (Method 2) A test piece measuring 2 cm (length) × 2 cm (width) is cut out from the solid electrolyte membrane. Then, under the conditions of temperature: 25°C, dew point temperature: -70°C, and pressure: atmospheric pressure, 20 μL of butyl butyrate is dropped from a position 1 cm away from the surface of the test piece in the vertical direction toward the center of the test piece. After dropping, the area where the butyl butyrate has spread is 2 cm. 2 The time required for this to occur is measured, and this time is designated as the second diffusion completion time. [4] The solid electrolyte membrane according to [3], wherein the second diffusion completion time is 10 seconds or less. [5] The solid electrolyte membrane according to any one of [1] to [4], wherein the solid electrolyte contains a sulfide-based solid electrolyte. [6] The solid electrolyte membrane according to any one of [1] to [5], wherein the content of the solid electrolyte in the solid electrolyte membrane is 70 mass % or more and less than 100 mass % when the entire solid electrolyte membrane is taken as 100 mass %. [7] The solid electrolyte membrane according to any one of [1] to [6], wherein the binder comprises one or more binders selected from the group consisting of fluorine-based binders and rubber-based binders. [8] The solid electrolyte membrane according to any one of [1] to [7], wherein the content of the binder in the solid electrolyte membrane is more than 0 mass % and 30 mass % or less, when the entire solid electrolyte membrane is taken as 100 mass %. [9] The solid electrolyte membrane according to any one of [1] to [8], wherein the porosity of the solid electrolyte membrane is 15.0% or less.

[10] A positive electrode and a solid electrolyte layer comprising the solid electrolyte membrane according to any one of [1] to [9]; a negative electrode; A lithium-ion secondary battery comprising the above in this order.

[11]

[10] A lithium ion secondary battery module including the lithium ion secondary battery according to

[10] . [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a solid electrolyte membrane that can suppress the occurrence of short circuits in a battery. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a cross-sectional view schematically illustrating an example of a lithium-ion secondary battery according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the drawings are schematic diagrams and do not correspond to actual dimensional proportions. In this specification, "A to B" indicating a numerical range means A or more and B or less unless otherwise specified.

[0012] (solid electrolyte membrane) The solid electrolyte membrane according to this embodiment includes a solid electrolyte and a binder. The solid electrolyte membrane according to this embodiment has a first diffusion completion time of 20 seconds or more as measured by the following method 1. (Method 1) A 2 cm (length) x 2 cm (width) test piece was cut out from the solid electrolyte membrane. Next, under the conditions of temperature: 25°C, dew point temperature: -70°C, and pressure: atmospheric pressure, 20 μL of butyl butyrate was dropped from a position 1 cm away from the surface of the test piece in a vertical direction toward the center of the test piece. The time from the drop until the butyl butyrate was diffused over the entire surface was measured, and this time was defined as the first diffusion completion time.

[0013] In Method 1, if the diffusion of butyl butyrate is not completed over the entire surface of the test piece even after the first specified time has elapsed, the first diffusion completion time can be evaluated as exceeding the first specified time. The first specified time may be, for example, 3600 seconds, 1800 seconds, 1200 seconds, 600 seconds, or 300 seconds.

[0014] The solid electrolyte membrane according to this embodiment has a first diffusion completion time of 20 seconds or more, preferably 40 seconds or more, more preferably 60 seconds or more, even more preferably 80 seconds or more, even more preferably 100 seconds or more, even more preferably 150 seconds or more, and even more preferably 200 seconds or more. By setting the first diffusion completion time within the above range, the occurrence of a short circuit in the battery can be further suppressed. The upper limit of the first diffusion completion time is not particularly limited, but may be, for example, 3600 seconds or less, 1800 seconds or less, 1200 seconds or less, 600 seconds or less, or 300 seconds or less. Furthermore, from the viewpoint of further suppressing the occurrence of a short circuit in the battery, the first diffusion completion time is preferably 40 seconds or more and 3600 seconds or less, more preferably 60 seconds or more and 1800 seconds or less, even more preferably 80 seconds or more and 1200 seconds or less, even more preferably 100 seconds or more and 600 seconds or less, even more preferably 150 seconds or more and 300 seconds or less, and even more preferably 200 seconds or more and 300 seconds or less.

[0015] The present inventors have found that, in a solid electrolyte membrane containing a solid electrolyte and a binder, there is a correlation between the density of the solid electrolyte membrane and the occurrence of a short circuit in a battery. As a result of further intensive research based on the above findings, the present inventors have found that the occurrence of a short circuit in a battery can be suppressed by setting the first diffusion completion time of the solid electrolyte membrane within a predetermined range.

[0016] In this embodiment, for example, the first diffusion completion time can be set within the above range by controlling the following manufacturing conditions. (A) Types and blending ratios of solid electrolytes and binders contained in the solid electrolyte membrane (B) Preparation conditions of the slurry for forming the solid electrolyte membrane (use of solvent, type and blending ratio of the solvent used, stirring speed) (C) Drying conditions of the slurry (temperature, time, atmosphere) (D) Pressing conditions for solid electrolyte membrane

[0017] The solid electrolyte membrane according to this embodiment preferably has a second diffusion completion time of 1 second or more as measured by the following method 2. By setting the second diffusion completion time within the above range, the occurrence of a short circuit in the battery can be further suppressed. (Method 2) A test piece measuring 2 cm (length) x 2 cm (width) is cut out from the solid electrolyte membrane. Then, under the conditions of temperature: 25°C, dew point temperature: -70°C, and pressure: atmospheric pressure, 20 μL of butyl butyrate is dropped from a position 1 cm away from the surface of the test piece in a vertical direction toward the center of the test piece. After dropping, the area where the butyl butyrate has spread is 2 cm. 2 The time required for this to occur is measured, and this time is designated as the second diffusion completion time.

[0018] In Method 2, the area in which butyl butyrate has diffused is 2 cm2 even after the second specified time has elapsed. 2 If the second diffusion completion time is not equal to or greater than the second specified time, the second specified time may be, for example, 360 seconds, 180 seconds, 120 seconds, 60 seconds, or 30 seconds or less.

[0019] The upper limit of the second diffusion completion time is not particularly limited, but may be, for example, 360 seconds or less, 180 seconds or less, 120 seconds or less, 60 seconds or less, 30 seconds or less, 10 seconds or less, or 5 seconds or less. Furthermore, from the viewpoint of further suppressing the occurrence of a short circuit in the battery, the second diffusion completion time is preferably 1 second or more and 180 seconds or less, more preferably 1 second or more and 120 seconds or less, even more preferably 1 second or more and 60 seconds or less, even more preferably 1 second or more and 30 seconds or less, even more preferably 1 second or more and 10 seconds or less, and even more preferably 1 second or more and 5 seconds or less.

[0020] In this embodiment, for example, the second diffusion completion time can be set within the above range by controlling the following manufacturing conditions. (A) Types and blending ratios of solid electrolytes and binders contained in the solid electrolyte membrane (B) Preparation conditions of the slurry for forming the solid electrolyte membrane (use of solvent, type and blending ratio of the solvent used, stirring speed) (C) Drying conditions of the slurry (temperature, time, atmosphere) (D) Pressing conditions for solid electrolyte membrane

[0021] Next, each component contained in the solid electrolyte membrane according to this embodiment will be described.

[0022] (solid electrolyte) The solid electrolyte membrane according to the present embodiment includes a solid electrolyte. The solid electrolyte according to the present embodiment preferably includes one or more solid electrolytes selected from the group consisting of sulfide-based solid electrolytes, oxide-based solid electrolytes, and polymer-based solid electrolytes, and more preferably includes a sulfide-based solid electrolyte.

[0023] Examples of sulfide-based solid electrolytes include Li2S-P2S5 materials, Li2S-SiS2 materials, Li2S-GeS2 materials, Li2S-Al2S3 materials, Li2S-SiS2-Li3PO4 materials, Li2S-P2S5-GeS2 materials, Li2S-Li2O-P2S5-SiS2 materials, Li2S-GeS2-P2S5-SiS2 materials, Li2S-SnS2-P2S5-SiS2 materials, Li2S-P2S5-Li3N materials, and Li2S 2+X -P4S3 material, Li2S-P2S5-P4S3 material, LiPO4-Li2S-SiS material, Li3PS4, Li3PO4-Li2S-Si2S material, Li3PO4-Li2S-SiS2 material, LiI-L i2S-B2S3 material, LiI-Li2S-SiS2 material, LiI-Li2S-P2S5 material, LiI-Li2S-P2O5 material, LiI-Li3PO4-P2S5Li2S-P2S5-LiCl material, Li 7-x PS 6-x Cl x (where 0≦x≦2), Li 7-x PS 6-x Br x (where 0≦x≦2), Li 7-x PS 6-x I x (where 0≦x≦2), Li 10 GeP2S 12 , and Li 3.25 Ge 0.25 P 0.75 S4, more preferably Li 7-x PS 6-x Cl x (where 0≦x≦2), Li 7-x PS 6-x Br x (where 0≦x≦2) and Li 7-x PS 6-x I x(where 0≦x≦2), more preferably it contains one or two or more selected from the group consisting of Li6PS5Cl, Li6PS5Br and Li6PS5I, even more preferably it contains one or two or more selected from the group consisting of Li6PS5Cl and Li6PS5Br, and even more preferably it contains Li6PS5Cl.

[0024] Examples of oxide-based solid electrolytes include NASICON-type solid electrolyte materials such as LiTi2(PO4)3, LiZr2(PO4)3, and LiGe2(PO4)3; 0.5+x Li 0.5-3x ) Perovskite-type solid electrolyte materials such as TiO3; one or more selected from the group consisting of Li2O-P2O5 materials, Li2O-P2O5-Li3N materials, etc.

[0025] The polymer-based solid electrolyte includes one or more selected from the group consisting of polyether-based electrolyte materials such as polyethylene oxide, polypropylene oxide, ethylene oxide-propylene copolymer, and dimethylsiloxane-ethylene oxide copolymer; gel polymer electrolyte materials such as polyacrylonitrile, polyvinylidene fluoride, and vinylidene fluoride-hexafluoropropylene polymer; and polymer solid electrolyte materials using hyperbranched polymers.

[0026] The content of the solid electrolyte in the solid electrolyte membrane according to this embodiment, when the entire solid electrolyte membrane is taken as 100 mass%, is preferably 70 mass% or more and less than 100 mass%, more preferably 85 mass% or more and 99.5 mass% or less, even more preferably 90 mass% or more and 99.2 mass% or less, even more preferably 93.0 mass% or more and 99.0 mass% or less, even more preferably 94.0 mass% or more and 98.5 mass% or less, and even more preferably 94.0 mass% or more and 97.0 mass% or less. By setting the content of the solid electrolyte in the solid electrolyte membrane within the above range, the occurrence of a short circuit in the battery can be further suppressed.

[0027] The average particle diameter d of the solid electrolyte according to this embodiment in the volume-based particle size distribution measured by the laser diffraction scattering particle size distribution measurement method 50 is preferably 0.01 μm or more and 30.0 μm or less, more preferably 0.1 μm or more and 20.0 μm or less, even more preferably 0.5 μm or more and 15.0 μm or less, even more preferably 1.0 μm or more and 10.0 μm or less, even more preferably 2.0 μm or more and 9.0 μm or less, even more preferably 2.5 μm or more and 8.0 μm or less, and even more preferably 3.0 μm or more and 7.0 μm or less. 50 By setting the range above, the occurrence of short circuits in the battery can be further suppressed.

[0028] The specific surface area of ​​the solid electrolyte according to this embodiment, as measured by nitrogen adsorption BET, is preferably 0.1 m 2 / g or more 20.0m 2 / g or less, more preferably 0.5m 2 / g or more 17.5m 2 / g or less, more preferably 1.0m 2 / g or more 15.0m 2 By setting the specific surface area of ​​the solid electrolyte, as measured by the nitrogen adsorption BET method, within the above range, the occurrence of short circuits in the battery can be further suppressed.

[0029] (binder) The solid electrolyte membrane according to this embodiment contains a binder, which preferably contains one or more binders selected from the group consisting of fluorine-based binders and rubber-based binders.

[0030] The fluorine-based binder preferably contains a constituent unit derived from vinylidene fluoride (VdF). More preferably, the fluorine-based binder contains a constituent unit derived from vinylidene fluoride (VdF) and one or more constituent units selected from the group consisting of a constituent unit derived from hexafluoropropylene (HFP), a constituent unit derived from trifluoropropylene (TFP), a constituent unit derived from tetrafluoroethylene (TFE), a constituent unit derived from 2,3,3,3-tetrafluoropropylene, a constituent unit derived from 1,3,3,3-tetrafluoropropylene, and a constituent unit derived from perfluoroalkyl vinyl ether (PAVE). This can further suppress the occurrence of short circuits in the battery. Furthermore, the fluorine-based binder more preferably contains one or more selected from the group consisting of a copolymer of vinylidene fluoride (VdF) and hexafluoropropylene (HFP) and a copolymer of vinylidene fluoride (VdF) and trifluoropropylene (TFP), and more preferably contains a copolymer of vinylidene fluoride (VdF) and hexafluoropropylene (HFP), which can further suppress the occurrence of short circuits in the battery.

[0031] The mass average molecular weight (Mw) of the fluorine-based binder is preferably 10,000 or more and 10,000,000 or less, more preferably 30,000 or more and 5,000,000 or less, even more preferably 50,000 or more and 1,000,000 or less, even more preferably 80,000 or more and 800,000 or less, and even more preferably 100,000 or more and 500,000 or less. By setting the mass average molecular weight (Mw) of the fluorine-based binder within the above range, the occurrence of short circuits in the battery can be further suppressed.

[0032] When the fluorine-based binder contains a constituent unit derived from vinylidene fluoride (VdF), the content of the constituent unit derived from vinylidene fluoride (VdF) in the fluorine-based binder is preferably 20 mol% to 100 mol%, more preferably 20 mol% to 99 mol%, even more preferably 30 mol% to 95 mol%, even more preferably 40 mol% to 90 mol%, even more preferably 60 mol% to 85 mol%, and even more preferably 70 mol% to 85 mol%. By setting the content of the constituent unit derived from vinylidene fluoride (VdF) in the fluorine-based binder within the above range, the occurrence of short circuits in the battery can be further suppressed.

[0033] The rubber-based binder preferably contains one or more selected from the group consisting of styrene-butadiene rubber, acrylate-butadiene rubber, butadiene rubber, and butylene rubber, and more preferably contains styrene-butadiene rubber, which can further suppress the occurrence of short circuits in the battery.

[0034] The content of the binder in the solid electrolyte membrane according to this embodiment, when the entire solid electrolyte membrane is taken as 100 mass%, is preferably more than 0 mass% and not more than 30 mass%, more preferably 0.5 mass% to 15 mass%, even more preferably 0.8 mass% to 10 mass%, even more preferably 1.0 mass% to 7.0 mass%, even more preferably 1.5 mass% to 6.0 mass%, and even more preferably 3.0 mass% to 6.0 mass%. By setting the binder content in the solid electrolyte membrane within the above range, the occurrence of short circuits in the battery can be further suppressed.

[0035] The amount of binder contained in the solid electrolyte membrane is preferably more than 0 part by mass and not more than 20 parts by mass, more preferably 0.5 parts by mass or more and not more than 15 parts by mass, even more preferably 1 part by mass or more and not more than 10 parts by mass, and even more preferably 2 parts by mass or more and not more than 8 parts by mass, relative to 100 parts by mass of the solid electrolyte contained in the solid electrolyte membrane. This can further suppress the occurrence of short circuits in the battery.

[0036] The thickness of the solid electrolyte membrane according to this embodiment may be, for example, 1 μm or more and 500 μm or less, 5 μm or more and 300 μm or less, 10 μm or more and 200 μm or less, or 50 μm or more and 150 μm or less.

[0037] (Physical properties of solid electrolyte membranes) The porosity of the solid electrolyte membrane according to this embodiment is preferably 15.0% or less, more preferably 13.0% or less, even more preferably 10.0% or less, even more preferably 8.0% or less, and even more preferably 6.0% or less. By setting the porosity of the solid electrolyte membrane within the above range, the occurrence of short circuits in the battery can be further suppressed. The lower limit of the porosity of the solid electrolyte membrane is not particularly limited, but may be, for example, 0% or more, 0.5% or more, 1.0% or more, or 2.0% or more.

[0038] The porosity of the solid electrolyte membrane according to this embodiment is calculated by the following method. First, a total of five test pieces measuring 2 cm (length) x 2 cm (width) are cut out from the solid electrolyte membrane. Next, the surface of each test piece (the surface perpendicular to the membrane thickness direction of the test piece) is observed using a scanning electron microscope (SEM). Next, the SEM image in the observation area is binarized to separate the solid and void areas. Next, smoothing is performed over a width of 25 μm before and after the target point (the center point of the observation area). Smoothing is performed by fitting a cubic approximation equation using the least squares method and using the value at the target point of this cubic approximation equation. The average value of the five test pieces is used as the porosity.

[0039] (Method of manufacturing solid electrolyte membrane) The solid electrolyte membrane according to this embodiment can be manufactured by, for example, the following method. That is, the method for manufacturing the solid electrolyte membrane according to this embodiment includes, for example, the steps of: (A) mixing a solid electrolyte with a binder; (B) applying the mixture obtained in step (A) to a support; (C) drying the mixture applied to the support to obtain a solid electrolyte membrane precursor; (D) compressing the obtained solid electrolyte membrane precursor; and (E) peeling off the support to obtain a solid electrolyte membrane. In order to prevent moisture from being adsorbed by the solid electrolyte, it is preferable to manufacture the solid electrolyte membrane in a low-moisture environment under dew point control. Each step will be described in more detail below.

[0040] (Process (A)) In step (A), the solid electrolyte and the binder are mixed. Mixing can be performed using, for example, a mixer. The stirring speed of the mixer is preferably 500 rpm to 3500 rpm, more preferably 1000 rpm to 3000 rpm, and even more preferably 1500 rpm to 2500 rpm. Mixing is preferably performed while adding the solvent dropwise. This allows for a more uniform mixture to be obtained. The solvent preferably includes one or more solvents selected from the group consisting of acetonitrile, xylene, dimethoxyethane, dimethyl carbonate, triethylamine, and other tertiary amine solvents, heptane, hexane, tetrahydrofuran, toluene, N-methylpyrrolidone, as well as ether solvents, thiol solvents, and butyl butyrate, and all of these solvents are preferably dehydrated. When adding the solvent dropwise, the solids concentration of the mixture obtained in step (A) is preferably 40% to 80% by mass, more preferably 45% to 75% by mass, and even more preferably 50% to 70% by mass.

[0041] (Process (B)) In step (B), the mixture obtained in step (A) is applied to a support. The support is preferably a release film. This makes it easy to peel off the support in step (E), which will be described later.

[0042] (Process (C)) In step (C), the mixture applied to the support in step (B) is dried to obtain a solid electrolyte membrane precursor. For example, the mixture is dried for 30 minutes on a hot plate at 80°C under an argon atmosphere, and then dried in a vacuum dryer at 100°C. Drying is preferably performed under an inert gas atmosphere (e.g., argon or helium) or under vacuum. This can prevent moisture from being adsorbed onto the solid electrolyte.

[0043] (Process (D)) In step (D), the obtained solid electrolyte membrane precursor is compressed. Compression can be performed using, for example, a vacuum laminator. Specifically, the obtained solid electrolyte membrane precursor is vacuum-sealed using the vacuum laminator and held at room temperature (25°C) under a pressure of 300 MPa for 1 minute. Next, the solid electrolyte membrane precursor is removed from the vacuum laminator and compressed by cold isostatic pressing (CIP).

[0044] (Process (E)) In step (E), the support is peeled off to obtain a solid electrolyte membrane.

[0045] (Lithium-ion battery) The solid electrolyte membrane according to this embodiment is suitable for use in a lithium ion secondary battery. A lithium ion secondary battery 100 according to this embodiment will be described below with reference to FIG.

[0046] Fig. 1 is a cross-sectional view schematically showing an example of a lithium-ion secondary battery according to this embodiment. As shown in Fig. 1, the lithium-ion secondary battery 100 according to this embodiment includes a positive electrode 10, a solid electrolyte layer 30 including a solid electrolyte film, and a negative electrode 20, in this order. The lithium-ion secondary battery 100 also preferably includes an outer casing 40. The outer casing 40 houses the positive electrode active material layer 11, the negative electrode active material layer 21, and the solid electrolyte layer 30.

[0047] The positive electrode 10 preferably includes a positive electrode active material layer 11, a positive electrode current collector 13, and a positive electrode terminal 15. The positive electrode active material layer 11 preferably includes a positive electrode active material, a solid electrolyte, and a binder. As shown in FIG. 1 , one end of the positive electrode terminal 15 is disposed in contact with the positive electrode current collector 13, and the other end of the positive electrode terminal 15 is disposed so as to be drawn out of the exterior body 40.

[0048] The negative electrode 20 preferably includes a negative electrode active material layer 21, a negative electrode current collector 23, and a negative electrode terminal 25. The negative electrode active material layer 21 preferably includes a negative electrode active material, a solid electrolyte, and a binder. As shown in FIG. 1 , one end of the negative electrode terminal 25 is disposed in contact with the negative electrode current collector 23, and the other end of the negative electrode terminal 25 is disposed so as to be drawn out of the exterior body 40.

[0049] (Method of manufacturing lithium-ion secondary batteries) The method for manufacturing the lithium ion secondary battery 100 is not particularly limited, and any known method can be applied. For example, the lithium ion secondary battery 100 can be manufactured by the following method.

[0050] First, the preparation of the negative electrode will be described. The negative electrode can be prepared by a known method. Regardless of the method used to prepare the negative electrode, it is preferable to prepare it in a low-moisture environment under dew point control in order to suppress adsorption of moisture into the solid electrolyte.

[0051] When using a negative electrode in which a negative electrode active material layer is formed on a negative electrode current collector, a slurry in which a negative electrode active material, a solid electrolyte, and a binder are dispersed in a dehydrated organic solvent is applied to part or all of the surface of a negative electrode current collector such as copper foil, followed by drying to obtain a negative electrode precursor sheet. The obtained negative electrode precursor sheet can be compressed using a press molding method such as a roll press, a uniaxial press, a rubber press, or an isostatic press (CIP, WIP) to obtain a negative electrode sheet. The organic solvent preferably includes one or more solvents selected from the group consisting of tertiary amine solvents such as acetonitrile, xylene, dimethoxyethane, dimethyl carbonate, and triethylamine, as well as heptane, hexane, tetrahydrofuran, toluene, and N-methylpyrrolidone, as well as ether solvents, thiol solvents, and butyl butyrate, all of which are preferably dehydrated.

[0052] The negative electrode can be obtained by placing a metallic lithium layer (negative electrode active material layer) such as lithium foil on part or all of a negative electrode current collector such as stainless steel foil, and then adhering them together by rolling or other processing.

[0053] Next, the obtained negative electrode and the solid electrolyte membrane according to this embodiment are laminated to obtain a negative electrode-solid electrolyte layer laminate.

[0054] Next, the fabrication of the positive electrode will be described. Regardless of the method used to fabricate the positive electrode, it is preferable to fabricate the positive electrode in a low moisture environment under dew point control in order to suppress moisture adsorption.

[0055] The positive electrode of this embodiment can be produced, for example, by dissolving or dispersing the components constituting the positive electrode active material layer in a solvent to produce a positive electrode slurry, applying the positive electrode slurry to at least one surface of a positive electrode current collector, drying, and rolling. Alternatively, the positive electrode of this embodiment can be produced, for example, by applying the positive electrode slurry to a support, drying it, peeling it from the support, and laminating the resulting film on the positive electrode current collector. The solvent preferably includes one or more solvents selected from the group consisting of tertiary amine solvents such as acetonitrile, xylene, dimethoxyethane, dimethyl carbonate, and triethylamine, heptane, hexane, tetrahydrofuran, toluene, N-methylpyrrolidone, ether solvents, thiol solvents, and butyl butyrate, and each of these solvents is preferably dehydrated.

[0056] A positive electrode is laminated on the negative electrode-solid electrolyte layer laminate to obtain an electrode laminate precursor. When a sulfide-based solid electrolyte is used as the solid electrolyte, the ionic conductivity of the solid electrolyte may decrease due to exposure to moisture. Therefore, after obtaining the electrode laminate precursor, it is preferable to compress the electrode laminate precursor using a vacuum laminator, roll press, uniaxial press, rubber press, isostatic pressing (CIP, WIP), or other method to obtain an electrode laminate.

[0057] The resulting electrode laminate is preferably quickly sealed in an exterior housing. One end of a rectangular metal plate serving as a negative electrode terminal is attached to the negative electrode current collector, and one end of a rectangular metal terminal serving as a positive electrode terminal is attached to the positive electrode current collector, and then the electrode laminate is housed in an aluminum exterior housing. A resin layer such as polyolefin is preferably formed on at least the surface of the inner surface of the exterior housing facing the electrode laminate. The resin layer is heated to melt the resin and solidify it again, and the electrode laminate is sealed in the aluminum exterior housing. At this time, the other end of the positive electrode terminal and the other end of the negative electrode terminal are positioned so as to extend outside the exterior housing. A layer of resin of the same type or a different type from the resin used in the resin layer on the interior surface of the exterior housing can be provided in the areas where the positive electrode terminal and the negative electrode terminal contact the resin layer on the interior surface of the exterior housing.

[0058] (Lithium-ion secondary battery module) The lithium ion secondary battery module of this embodiment includes the lithium ion secondary battery of this embodiment. Since the lithium ion secondary battery of this embodiment can suppress the occurrence of a short circuit in the battery, the lithium ion secondary battery module of this embodiment can suppress the occurrence of a short circuit in the battery.

[0059] The lithium-ion secondary battery module of this embodiment preferably includes two or more lithium-ion secondary batteries of this embodiment connected in series or parallel. The battery module of this embodiment more preferably includes a housing capable of accommodating two or more lithium-ion secondary batteries of this embodiment connected in series or parallel. The battery module of this embodiment further preferably includes one or more components selected from the group consisting of a protection circuit that protects the lithium-ion secondary batteries from overcurrent, a balancing circuit that equalizes the voltage between the electrodes of the lithium-ion secondary batteries, a controller that controls the lithium-ion secondary batteries, a cooler that can cool the lithium-ion secondary batteries, and a heater that can heat the lithium-ion secondary batteries.

[0060] The lithium-ion secondary battery module of this embodiment can be used in a battery system including a plurality of electrically connected battery modules and a battery control system. Examples of battery systems include battery packs, stationary storage battery systems, automotive power storage battery systems, automotive auxiliary storage battery systems, and emergency power storage battery systems.

[0061] Although the embodiments of the present invention have been described above, these are merely examples of the present invention, and various other configurations may be adopted. Furthermore, the present invention is not limited to the above-described embodiments, and modifications and improvements within the scope of achieving the object of the present invention are included in the present invention. [Example]

[0062] The present embodiment will be described in detail below with reference to examples and comparative examples, but the present embodiment is not limited to the descriptions of these examples.

[0063] (1) Raw materials The materials used in the preparation of the solid electrolyte membrane and the lithium ion secondary battery are listed below. (solid electrolyte) ·Li6PS5Cl (average particle size d 50 :6μm) ·Li6PS5Br (average particle size d 50 :4μm)

[0064] (binder) SBR: Styrene-butadiene rubber PVDF-HFP: Vinylidene fluoride-hexafluoropropylene copolymer

[0065] (positive electrode) ·Cathode active material: LiNi 0.8 Co 0.1 Mn 0.1 O2(average particle diameter d 50 : 5 μm), content in positive electrode active material layer: 76 mass% ·Solid electrolyte: Li6PS5Cl (average particle size d 50 : 6.5 μm), content in positive electrode active material layer: 19.5 mass% Conductive additive: CB (carbon black), content in positive electrode active material layer: 1.5% by mass Binder: SBR (styrene-butadiene rubber), content in positive electrode active material layer: 3% by mass

[0066] The average particle diameter d of the solid electrolyte and the positive electrode active material 50 was measured using a laser diffraction / scattering particle size distribution analyzer (MT3000, manufactured by Microtrac), and the value at which the cumulative volume in the volume-based particle size distribution measured by the laser diffraction / scattering particle size distribution measurement method was 50% was used.

[0067] (2) Preparation of solid electrolyte membrane For Examples 1 and 2 and Comparative Example 1, the solid electrolytes and binders shown in Table 1 were used to prepare solid electrolyte membranes. First, the solid electrolyte and binder were mixed at a mass ratio of 95.0:5.0 (solid electrolyte:binder). Next, a solvent (butyl butyrate, Tokyo Chemical Industry Co., Ltd., purity 99.9%) was added dropwise while mixing at 2000 rpm using a mixer (Thinky Corporation, product name: AR-100) to obtain a mixture with a solid content of 62% by mass. The mixture was then coated onto a release film, dried on a hot plate at 80°C for 30 minutes under an argon atmosphere, and then dried in a vacuum dryer at 100°C to obtain a solid electrolyte membrane precursor. The obtained solid electrolyte membrane precursor was then vacuum sealed using a vacuum laminator and held at room temperature (25°C) under a pressure of 300 MPa for 1 minute. The solid electrolyte membrane precursor was then removed from the vacuum laminator and compressed by cold isostatic pressing (CIP). The release film was then peeled off to obtain a solid electrolyte membrane with a thickness of 100 μm after pressing.

[0068] For Examples 1 and 2 and Comparative Example 1, the porosity of the solid electrolyte membrane was calculated by the following method. First, a total of five test pieces measuring 2 cm (length) x 2 cm (width) were cut out from the solid electrolyte membrane. Next, the surface of each test piece (the surface perpendicular to the membrane thickness direction of the test piece) was observed using a scanning electron microscope (SEM). Next, the shading of the SEM image in the observation area was binarized to separate the solid and void areas. Next, smoothing was performed over a width of 25 μm before and after the target point (the center point of the observation area). Smoothing was performed by fitting a cubic approximation equation using the least squares method and using the value at the target point of this cubic approximation equation. The average value of the five test pieces was used as the porosity. The results are shown in Table 1.

[0069] (3) Measurement of the first diffusion completion time and the second diffusion completion time A total of five test pieces measuring 2 cm (length) x 2 cm (width) were cut out from the solid electrolyte membrane. Next, under the conditions of temperature: 25°C, dew point temperature: -70°C, and pressure: atmospheric pressure, 20 μL of butyl butyrate (manufactured by Tokyo Chemical Industry Co., Ltd., purity 99.9%) was dropped from a position 1 cm away from the surface of the test piece in the vertical direction toward the center of the test piece. The time from the drop until the butyl butyrate was diffused over the entire surface was measured, and this time was defined as the first diffusion completion time. In addition, when the area over which the butyl butyrate was diffused after the drop was 2 cm, 2 The time until the diffusion reached or exceeded half the surface area of ​​the test piece was measured, and this time was designated the second diffusion completion time. For each solid electrolyte membrane, the first diffusion completion time and the second diffusion completion time were measured for five test pieces, and their average values ​​were used as the first diffusion completion time and the second diffusion completion time of the solid electrolyte membrane. During the measurement, the surface of the test piece was photographed every second for one minute after the butyl butyrate was added, and then every 10 seconds after one minute had elapsed. The photographed images were analyzed using image analysis software (ImageJ) to measure the first diffusion completion time and the second diffusion completion time. The results are shown in Table 1.

[0070] (4) Fabrication of lithium-ion secondary batteries A film (manufactured by Honjo Metals Co., Ltd.) was prepared as a negative electrode, in which a negative electrode active material layer (metallic lithium foil, 20 μm thick) was formed on a negative electrode current collector (stainless steel foil, 10 μm thick). Next, the negative electrode and a solid electrolyte membrane were laminated to obtain a laminate (I). At this time, the negative electrode active material layer and the solid electrolyte layer were laminated so as to be in contact with each other. Next, the positive electrode active material, solid electrolyte, conductive additive, and binder were dispersed in butyl butyrate to obtain a slurry, which was then applied to a positive electrode current collector (aluminum foil, 10 μm thick) and dried to form a positive electrode active material layer, thereby obtaining a positive electrode. Next, the obtained positive electrode was cut into a size of 20 mm × 20 mm, and the positive electrode and the laminate (I) were laminated so that the positive electrode active material layer was in contact with the solid electrolyte layer of the laminate (I), thereby obtaining an electrode laminate precursor. The number of laminated layers of the positive electrode and the laminate (I) was one each. The resulting electrode laminate precursor was then vacuum-sealed using a vacuum laminator and held at room temperature (25°C) under a pressure of 300 MPa for 1 minute. The electrode laminate precursor was then removed from the vacuum laminator and compressed by cold isostatic pressing (CIP) to obtain an electrode laminate with a positive electrode active material layer porosity of 5%. Next, one end of the positive electrode terminal was attached to the positive electrode current collector, and one end of the negative electrode terminal was attached to the negative electrode current collector, and then the electrode stack was housed in an aluminum exterior body (manufactured by Dai Nippon Printing Co., Ltd.) to obtain a lithium ion secondary battery. At this time, the other end of the positive electrode terminal and the other end of the negative electrode terminal were arranged so as to be drawn out of the exterior body.

[0071] (5) Evaluation of battery characteristics The lithium ion secondary battery was charged by a constant current-constant voltage method under the following conditions. Rate: 0.1C Cut: 0.01C Temperature: 45℃ Confining pressure: 3MPa The results are shown in Table 1. It was found that in Comparative Example 1, dendrites were formed during charging, causing a short circuit.

[0072] [Table 1] [Explanation of symbols]

[0073] 10 positive electrode 11 Cathode active material layer 13 Positive electrode current collector 15 Positive terminal 20 negative electrode 21 Negative electrode active material layer 23 Negative electrode current collector 25 Negative terminal 30 Solid electrolyte layer 40 Exterior body 100 Lithium-ion secondary battery

Claims

1. A solid electrolyte membrane comprising a solid electrolyte and a binder, A solid electrolyte membrane having a first diffusion completion time of 20 seconds or more as measured by the following method 1. (Method 1) A test piece measuring 2 cm (length) x 2 cm (width) was cut from the solid electrolyte membrane. Next, under conditions of a temperature of 25°C, a dew point temperature of -70°C, and atmospheric pressure, 20 μL of butyl butyrate was dropped from a position 1 cm away from the surface of the test piece in a vertical direction toward the center of the test piece. The time from the drop until the butyl butyrate was diffused over the entire surface was measured, and this time was designated as the first diffusion completion time.

2. The solid electrolyte membrane according to claim 1 , wherein the first diffusion completion time is 100 seconds or more.

3. 3. The solid electrolyte membrane according to claim 1, wherein the second diffusion completion time measured by the following method 2 is 1 second or longer. (Method 2) A test piece measuring 2 cm (length) × 2 cm (width) is cut out from the solid electrolyte membrane, and 20 μL of butyl butyrate is dropped from a position 1 cm away from the surface of the test piece in the vertical direction toward the center of the test piece under the conditions of a temperature of 25° C., a dew point temperature of −70° C., and atmospheric pressure. After dripping, the area where the butyl butyrate spread is 2 cm ２ The time required for this to occur is measured, and this time is designated as the second diffusion completion time.

4. The solid electrolyte membrane according to claim 3 , wherein the second diffusion completion time is 10 seconds or less.

5. 5. The solid electrolyte membrane according to claim 1, wherein the solid electrolyte comprises a sulfide-based solid electrolyte.

6. 6. The solid electrolyte membrane according to claim 1, wherein a content of the solid electrolyte in the solid electrolyte membrane is 70 mass% or more and less than 100 mass%, when the entire solid electrolyte membrane is taken as 100 mass%.

7. 7. The solid electrolyte membrane according to claim 1, wherein the binder comprises one or more binders selected from the group consisting of fluorine-based binders and rubber-based binders.

8. 8. The solid electrolyte membrane according to claim 1, wherein a content of the binder in the solid electrolyte membrane is more than 0 mass% and 30 mass% or less, when the entire solid electrolyte membrane is taken as 100 mass%.

9. 9. The solid electrolyte membrane according to claim 1, wherein the porosity of the solid electrolyte membrane is 15.0% or less.

10. A positive electrode and A solid electrolyte layer comprising the solid electrolyte membrane according to any one of claims 1 to 9; a negative electrode; A lithium-ion secondary battery comprising the above in this order.

11. A lithium ion secondary battery module comprising the lithium ion secondary battery according to claim 10.

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