Method for producing solid electrolyte membrane and method for producing lithium ion secondary battery

Abstract

To provide a method for producing a solid electrolyte membrane capable of suppressing battery short circuit occurrence.SOLUTION: Provided is a method for producing a solid electrolyte membrane, comprising the following steps: forming the solid electrolyte membrane from a mixture containing a solid electrolyte and a binder; measuring a first diffusion completion time using the following method 1; and selecting the solid electrolyte membrane whose first diffusion completion time is 20 seconds or longer. In the method 1, a test piece measuring 2 cm in height and 2 cm in width is cut from the solid electrolyte 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 method for producing a solid electrolyte membrane and a method for producing a lithium ion secondary battery. [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 method for producing 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 methods for producing a solid electrolyte membrane and a lithium ion secondary battery.

[0008] [1] forming a solid electrolyte membrane from a mixture containing a solid electrolyte and a binder; a measuring step of measuring a first diffusion completion time for the solid electrolyte membrane by the following method 1; a selection step of selecting the solid electrolyte membrane having the first diffusion completion time of 20 seconds or more; A method for manufacturing a solid electrolyte membrane, comprising: (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 method for producing a solid electrolyte membrane according to [1], wherein in the selection step, the solid electrolyte membranes having the first diffusion completion time of 100 seconds or more are selected. [3] the measuring step includes a step of measuring a second diffusion completion time for the solid electrolyte membrane by the following method 2, the selection step includes a step of selecting the solid electrolyte membrane having the second diffusion completion time of 1 second or more. [1] or [2], a method for producing a solid electrolyte membrane. (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 method for producing a solid electrolyte membrane according to [3], wherein in the selection step, the solid electrolyte membrane having the second diffusion completion time of 10 seconds or less is selected. [5] The method for producing a solid electrolyte membrane according to any one of [1] to [4], wherein the solid electrolyte contains a sulfide-based solid electrolyte. [6] The method for producing a solid electrolyte membrane according to any one of [1] to [5], 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] The method for producing a solid electrolyte membrane according to any one of [1] to [6], wherein the binder contains one or more binders selected from the group consisting of fluorine-based binders and rubber-based binders. [8] The method for producing a 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 method for producing a 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] The method for producing a solid electrolyte membrane according to any one of [1] to [9], wherein the step of forming the solid electrolyte membrane includes a step of applying the mixture to a support to form the solid electrolyte membrane.

[11] A method for producing a lithium ion secondary battery, comprising the step of producing a lithium ion secondary battery using a solid electrolyte layer including a solid electrolyte membrane produced by the method for producing a solid electrolyte membrane according to any one of [1] to

[10] , a positive electrode, and a negative electrode. [Effects of the Invention]

[0009] According to the present invention, a method for producing a solid electrolyte membrane that can suppress the occurrence of short circuits in a battery can be provided. [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] The method for producing a solid electrolyte membrane according to this embodiment includes a step of forming a solid electrolyte membrane from a mixture containing a solid electrolyte and a binder, a measuring step of measuring the first diffusion completion time of the solid electrolyte membrane by the following method 1, and a sorting step of sorting out solid electrolyte membranes having a first diffusion completion time of 20 seconds or more. (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] That is, the selection process according to this embodiment is a process of selecting solid electrolyte membranes whose first diffusion completion time is equal to or longer than a first specified time, and the first specified time is 20 seconds. Note that 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.

[0014] The present inventors have found that, for 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. Based on this finding, the present inventors have conducted further intensive research and 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. In the selection process according to this embodiment, by selecting solid electrolyte membranes whose first diffusion completion time is equal to or longer than a first specified time, a solid electrolyte membrane capable of suppressing the occurrence of a short circuit in a battery can be produced.

[0015] In this embodiment, the first specified time is determined taking into consideration both the ability to produce a solid electrolyte membrane that can further suppress the occurrence of short circuits in the battery and the ability to shorten the time required for the selection step. Specifically, the first specified time is preferably 20 seconds or more and 3600 seconds or less, more preferably 20 seconds or more and 1800 seconds or less, even more preferably 20 seconds or more and 1200 seconds or less, even more preferably 20 seconds or more and 600 seconds or less, and even more preferably 20 seconds or more and 300 seconds or less. The first specified time may be, for example, 20 seconds, 40 seconds, 60 seconds, 80 seconds, 100 seconds, 150 seconds, 200 seconds, or 300 seconds. For example, when the first specified time is 100 seconds, the method for producing a solid electrolyte membrane according to this embodiment selects solid electrolyte membranes having a first diffusion completion time of 100 seconds or more in the selection step.

[0016] In the method for producing a solid electrolyte membrane according to the present embodiment, the measuring step preferably includes a step of measuring a second diffusion completion time of the solid electrolyte membrane by the following method 2, and the sorting step preferably includes a step of sorting a solid electrolyte membrane having a second diffusion completion time equal to or longer than a second specified time. (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.

[0017] Furthermore, even after the second specified time has elapsed, the area in which butyl butyrate has spread is 2cm 2 If the second diffusion completion time is not equal to or greater than the second specified time, it can be evaluated that the second diffusion completion time exceeds the second specified time.

[0018] In this embodiment, the second specified time is determined taking into consideration both the possibility of producing a solid electrolyte membrane that can further suppress the occurrence of short circuits in the battery and the possibility of shortening the time required for the selection step. Specifically, the second specified time is preferably 1 second or more and 360 seconds or less, more preferably 1 second or more and 180 seconds or less, even more preferably 1 second or more and 120 seconds or less, even more preferably 1 second or more and 60 seconds or less, and even more preferably 1 second or more and 30 seconds or less. The second specified time may be, for example, 1 second, 5 seconds, 10 seconds, or 30 seconds. For example, when the second specified time is 1 second, the selection step according to this embodiment includes a step of selecting solid electrolyte membranes having a second diffusion completion time of 1 second or more.

[0019] In the selection step according to this embodiment, a solid electrolyte membrane having a second diffusion completion time of 30 seconds or less is preferably selected, more preferably a solid electrolyte membrane having a second diffusion completion time of 10 seconds or less is selected, and even more preferably a solid electrolyte membrane having a second diffusion completion time of 5 seconds or less is selected, thereby enabling the production of a solid electrolyte membrane that can further suppress the occurrence of short circuits in batteries.

[0020] The method for manufacturing a solid electrolyte membrane according to this embodiment includes a step of forming a solid electrolyte membrane from a mixture containing a solid electrolyte and a binder. The step of forming the solid electrolyte membrane will be described below.

[0021] The step of forming the solid electrolyte membrane preferably includes a step of applying the mixture to a support to form the solid electrolyte membrane. More specifically, the step of forming the solid electrolyte membrane preferably includes a step (A) of mixing the solid electrolyte and the binder, and a step (B) of applying the mixture obtained in the step (A) to the support.

[0022] Furthermore, the step of forming a solid electrolyte membrane preferably includes a step (C) of drying the mixture applied to the support in the step (B) to obtain a solid electrolyte membrane precursor, and a step (D) of compressing the obtained solid electrolyte membrane precursor.

[0023] (Process (A)) In step (A), the solid electrolyte and the binder are mixed. Mixing is preferably performed using 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, and N-methylpyrrolidone, as well as ether solvents, thiol solvents, and butyl butyrate, and more preferably includes butyl butyrate. It is preferable that all solvents have been 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.

[0024] (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.

[0025] (Process (C)) In step (C), the mixture applied to the support in step (B) is dried to obtain a solid electrolyte membrane precursor. More specifically, step (C) preferably includes drying the mixture on a hot plate at 80°C for 30 minutes in an argon atmosphere, followed by drying in a vacuum dryer at 100°C. The drying is preferably carried out in an inert gas atmosphere (e.g., argon or helium) or under vacuum. This can prevent moisture from being adsorbed onto the solid electrolyte.

[0026] (Process (D)) In step (D), the obtained solid electrolyte membrane precursor is compressed. Compression is preferably performed using a vacuum laminator. More specifically, step (D) preferably includes the steps of vacuum-sealing the obtained solid electrolyte membrane precursor using the vacuum laminator and holding it at room temperature (25°C) under a pressure of 300 MPa for 1 minute, and removing the solid electrolyte membrane precursor from the vacuum laminator and compressing it by cold isostatic pressing (CIP).

[0027] Furthermore, the step of forming the solid electrolyte membrane is preferably carried out in a low moisture environment under dew point control in order to prevent moisture from being adsorbed onto the solid electrolyte.

[0028] As described above, in the process of forming the solid electrolyte membrane, for example, by controlling the following manufacturing conditions, the first diffusion completion time and the second diffusion completion time can be set within a predetermined range. (A) Types and blending ratios of solid electrolyte and binder 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

[0029] Furthermore, the method for producing a solid electrolyte membrane according to this embodiment preferably includes a step (E) of peeling off the support to obtain the solid electrolyte membrane.

[0030] (solid electrolyte membrane) Next, each component contained in the solid electrolyte membrane produced by the production method according to this embodiment will be described.

[0031] (solid electrolyte) The solid electrolyte according to this embodiment preferably includes one or more selected from the group consisting of a sulfide-based solid electrolyte, an oxide-based solid electrolyte, and a polymer-based solid electrolyte, and more preferably includes a sulfide-based solid electrolyte.

[0032] 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 0.75S4, 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] (binder) The binder preferably contains one or more selected from the group consisting of fluorine-based binders and rubber-based binders.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] (Physical properties of solid electrolyte membranes) Next, the physical properties of the solid electrolyte membrane produced by the production method according to this embodiment will be described.

[0047] 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.

[0048] 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.

[0049] (Lithium-ion battery) The solid electrolyte membrane manufactured by the manufacturing method 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 now be described with reference to FIG.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] (Method of manufacturing lithium-ion secondary batteries) The method for manufacturing a lithium ion secondary battery according to this embodiment includes a step of manufacturing a lithium ion secondary battery using a solid electrolyte layer including a solid electrolyte membrane manufactured by the method for manufacturing a solid electrolyte membrane according to this embodiment, a positive electrode, and a negative electrode. An example of the method for manufacturing a lithium ion secondary battery according to this embodiment will be specifically described below.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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 then 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.

[0062] 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]

[0063] 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.

[0064] (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)

[0065] (binder) SBR: Styrene-butadiene rubber PVDF-HFP: Vinylidene fluoride-hexafluoropropylene copolymer

[0066] (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

[0067] The average particle diameter d of the solid electrolyte and the positive electrode active material 50was 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.

[0068] (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.

[0069] 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.

[0070] (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.

[0071] (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.

[0072] (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.

[0073] [Table 1] [Explanation of symbols]

[0074] 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. forming a solid electrolyte membrane from a mixture containing a solid electrolyte and a binder; a measuring step of measuring a first diffusion completion time for the solid electrolyte membrane by the following method 1; a selection step of selecting the solid electrolyte membrane having the first diffusion completion time of 20 seconds or more; A method for manufacturing a solid electrolyte membrane, comprising: (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. 2. The method for producing a solid electrolyte membrane according to claim 1, wherein in the selection step, the solid electrolyte membranes having the first diffusion completion time of 100 seconds or more are selected.

3. the measuring step includes a step of measuring a second diffusion completion time for the solid electrolyte membrane by the following method 2, the selecting step includes a step of selecting the solid electrolyte membrane having the second diffusion completion time of 1 second or more. The method for producing the solid electrolyte membrane according to claim 1 or 2. (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 method for producing a solid electrolyte membrane according to claim 3 , wherein in the selection step, the solid electrolyte membranes having the second diffusion completion time of 10 seconds or less are selected.

5. The method for producing a solid electrolyte membrane according to any one of claims 1 to 4, wherein the solid electrolyte includes a sulfide-based solid electrolyte.

6. 6. The method for producing a 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 method for producing a 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 method for producing a 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. The method for producing a solid electrolyte membrane according to any one of claims 1 to 8, wherein the porosity of the solid electrolyte membrane is 15.0% or less.

10. 10. The method for producing a solid electrolyte membrane according to claim 1, wherein the step of forming the solid electrolyte membrane comprises a step of applying the mixture to a support to form the solid electrolyte membrane.

11. A method for producing a lithium ion secondary battery, comprising the step of producing a lithium ion secondary battery using a solid electrolyte layer including the solid electrolyte membrane produced by the method for producing a solid electrolyte membrane according to any one of claims 1 to 10, a positive electrode, and a negative electrode.

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