Composite for secondary batteries, composite sheet for secondary batteries and method of manufacturing the same, and solid secondary battery

Abstract

The present disclosure provides a composite for a secondary battery containing a sulfide-based electrolyte having good properties, a sheet of the composite for a secondary battery containing the composite for a secondary battery, and a solid secondary battery using the sheet of the composite for a secondary battery. The composite for a secondary battery is characterized in that it contains a sulfide-based solid electrolyte and a binder, wherein the binder is a fibrillary resin. The binder is suitable for having a fibrous structure with a fibrillary diameter (median value) of 100 nm or less.

Description

Technology Field

[0001] The present disclosure relates to a composite for a secondary battery, a composite sheet for a secondary battery, a method for manufacturing the same, and a solid secondary battery. Background Technology

[0002] In lithium-ion secondary batteries, a solid secondary battery sheet is generally produced by coating and drying a slurry obtained by mixing an electrode active material and a conductive aid with a binder and a solvent.

[0003] Meanwhile, fibrillable resins such as polytetrafluoroethylene resin are used, and by fibrillating them, they are also used as binders.

[0004] Patent Document 1 discloses a method for producing an electrode that fibrillates polytetrafluoroethylene by treating a mixture comprising an active material and a polytetrafluoroethylene mixed binder material with a high shear using a jet mill.

[0005] Patent Document 2 discloses the production of a solid electrolyte layer, a positive electrode, or a negative electrode using an inorganic sulfide having a specific composition in which a crystalline phase and a glass phase coexist as a binder.

[0006] Patent document 3 discloses a solid electrolyte-containing sheet having a thickness of t㎛, comprising a fiber having an average diameter d of 0.1 to 2㎛ and an average length L of 0.2 to 50㎜ prepared by field spinning, microfluidizer spinning, or wet spinning, and a solid electrolyte-containing layer having a thickness of t㎛ including the fiber and an inorganic solid electrolyte, wherein L and t satisfy the relationship 100×t≤L≤2500×t.

[0007] Patent document 4 discloses a method of mixing sulfur-based solid ion conductor inorganic particles with a tetrafluoroethylene (TFE) polymer, forming a paste, and then manufacturing a film by calendering or extrusion. Prior art literature

[0008] Japanese Patent Publication No. 2017-517862, International Publication No. 2018-096957, International Publication No. 2019-208347, International Publication No. 2021-043493 The problem to be solved

[0009] The present disclosure aims to provide a composite for a secondary battery containing a sulfide-based solid electrolyte having good properties, a sheet of the composite for a secondary battery containing the composite, and a solid secondary battery using the sheet of the composite for a secondary battery.

[0010] In addition, the present disclosure aims to provide a composite for a secondary battery containing a sulfide-based solid electrolyte that has high productivity and can be handled without using a support when forming a composite sheet for a secondary battery, and a composite sheet for a secondary battery containing said composite. means of solving the problem

[0011] The present disclosure is a composite for a secondary battery containing a sulfide-based solid electrolyte and a binder, and

[0012] The binder is a composite material for a secondary battery characterized by being a fibril-like resin.

[0013] The above fibril resin preferably has a fibrous structure with a fibril diameter (median value) of 100 nm or less.

[0014] It is preferable that the above fibril resin is a polytetrafluoroethylene resin.

[0015] It is preferable that the average particle size of the above sulfide-based solid electrolyte be 0.1㎛ or more and 20㎛ or less.

[0016] It is preferable that the above sulfide-based solid electrolyte is represented by the following formula (A).

[0017]

[0018] (where 0.6≤a≤0.86, 0≤b≤0.333, 0≤c≤0.3, 0.05≤b+c≤0.4, X1 Silver is Ge, Sn, Ti, or Si, X 2 represents Cl, Br, or I, provided that neither b nor c is 0.

[0019] The above-mentioned composite for secondary batteries is preferably for lithium-ion solid secondary batteries.

[0020] The above-mentioned composite for a secondary battery is a composite for a secondary battery obtained using a raw material composition containing a sulfide-based solid electrolyte and a binder, and

[0021] It is preferable that the binder in the above raw material composition is a powdered fibril resin.

[0022] It is preferable that the above raw material composition substantially does not contain a liquid medium.

[0023] The above-mentioned powdered fibril resin preferably has a moisture content of 500 ppm or less.

[0024] It is preferable that the above-mentioned powdered fibril resin is a powdered polytetrafluoroethylene resin.

[0025] The above powdered polytetrafluoroethylene resin preferably has a standard specific gravity of 2.12 to 2.20.

[0026] The above powdered polytetrafluoroethylene resin preferably contains 50 mass% or more of polytetrafluoroethylene resin having a secondary particle size of 450 μm or more.

[0027] The present disclosure is also a composite sheet for a secondary battery comprising the above-mentioned composite for a secondary battery.

[0028] The present disclosure describes a process (1) of applying shear force while mixing a raw material composition comprising a sulfide-based solid electrolyte and a binder.

[0029] A process (2) for forming a composite material for a secondary battery obtained by the above process (1) into a bulk form and

[0030] A process (3) of rolling the bulk composite for secondary batteries obtained by the above process (2) into a sheet.

[0031] The method for manufacturing a composite sheet for a secondary battery having a binder is also a method for manufacturing a composite sheet for a secondary battery characterized in that the binder is a powdered fibril resin.

[0032] The present disclosure is also a solid secondary battery having the composite sheet for the secondary battery. Effects of the invention

[0033] In the present disclosure, when forming a composite sheet for a secondary battery containing a sulfide-based solid electrolyte, a solvent is not used, and a powdered binder with low moisture content is used, thereby enabling the manufacture of a battery with minimal degradation of the sulfide-based solid electrolyte.

[0034] In addition, the present disclosure can provide a composite for a secondary battery containing a sulfide-based electrolyte that has high productivity and can be handled without using a support when used as a composite sheet for a secondary battery, and a composite sheet for a secondary battery containing said composite. Specific details for implementing the invention

[0035] The present disclosure will be described in detail below.

[0036] The present disclosure provides a composite for a secondary battery that can be suitably used in a sulfide-based solid secondary battery, and a composite sheet containing the same.

[0037] In the composite for secondary batteries and the composite sheet containing the same disclosed in the present disclosure, a fibrillary resin such as polytetrafluoroethylene resin (PTFE) is used as a binder. In conventional composites for solid secondary batteries, a method of producing a composite for solid secondary batteries was generally used by using a solvent-soluble resin such as a copolymer of vinylidene fluoride and hexafluoropropylene as a binder and by coating and drying a slurry containing the same.

[0038] Meanwhile, it is known that, for example, when shear stress is applied to PTFE in a particulate state, it easily fibrillates. By utilizing this fibrillating property, PTFE can be used as a binder. That is, the fibrillated PTFE binds the powder components by interlocking with other powder components, and thereby can act as a binder when molding the powder components.

[0039] The present disclosure was completed by discovering that, in obtaining a composite for a secondary battery containing a sulfide-based solid electrolyte, a fibrillary resin can be used as a binder to obtain a composite for a secondary battery having good properties and a composite sheet containing the same without using a solvent.

[0040] In addition, with the goal of commercializing solid-state secondary batteries, considerations are being made for the industrial production of solid-state secondary batteries, along with improvements in battery performance such as battery voltage. In order to improve handling characteristics and manufacturing efficiency of solid-state secondary batteries when examining the performance of secondary battery composites and composite sheets containing them, it is desired that the secondary battery composite sheets constituting the solid-state secondary battery be handled without using a support. Furthermore, from the perspective of manufacturability, these secondary battery composite sheets are desired to withstand winding with large curvature when wound into a roll. For this reason, improvement in flexibility is also desired.

[0041] As described above, by using a fibrillary resin as a binder, the present disclosure enables the manufacture of a composite sheet for a secondary battery without using a solvent, and thus enables the manufacture of a composite sheet for a secondary battery without using a support. Furthermore, the composite sheet for a secondary battery according to the present disclosure can be made to have good flexibility and strength that is easy to handle by using a sulfide-based solid electrolyte.

[0042] The composite for secondary batteries disclosed herein is obtained by using a raw material composition containing a sulfide-based solid electrolyte and a binder, and the binder is preferably a powdered fibrillic resin. Since a powdered binder is used as a raw material rather than a binder-containing dispersion, the moisture originating from the raw material in the composite for secondary batteries is low, and problems caused by the mixing of moisture are not caused. This provides the advantage of improving battery performance. Furthermore, it is possible to produce a battery with excellent ion conductivity.

[0043] In addition, it is preferable that the above raw material composition substantially does not contain a liquid medium. As such, the composite for secondary batteries disclosed herein has the advantage of not using a solvent in its manufacture. That is, conventional methods for forming composites for secondary batteries generally involved preparing a slurry in which a powder component of the composite for secondary batteries is dispersed using a solvent in which a binder is dissolved, and then preparing a composite sheet for secondary batteries by coating and drying the slurry. In this case, a solvent that dissolves the binder is used. However, the solvents capable of dissolving binder resins that have been generally used in the past are limited to specific solvents such as butyl butyrate. Since these react with sulfide-based solid electrolytes and degrade the performance of the sulfide-based solid electrolytes, they cause a decrease in battery performance. Furthermore, in low-polarity solvents such as heptane, not only are the binder resins that dissolve very limited, but handling is cumbersome due to their low flash points.

[0044] In the above view, the composite for secondary batteries of the present disclosure preferably has a liquid medium content of 1 mass% or less. In addition, the raw material composition also preferably has a liquid medium content of 1 mass% or less.

[0045] The composite for a secondary battery of the present disclosure is a composite for a secondary battery containing a sulfide-based electrolyte, and has a binder having a fibrous structure as a component. In the present disclosure, it is important that the binder exists in a fibrillated state. The objective of the present disclosure is achieved by the presence of such a fibrillated binder in the composite for the secondary battery, and by the action of binding the powders of the components constituting the composite for the secondary battery together.

[0046] That is, the present disclosure was completed by discovering that a composite for a secondary battery having good properties and a composite sheet containing the same can be obtained by using a fibril resin as a binder and making the binder in the composite for a secondary battery have a fiber structure.

[0047] In addition, it is preferable that the binder in the composite for secondary batteries has a fibrous structure with a fibril diameter (median value) of 100 nm or less. By having a binder with a fine fibril diameter in the composite for secondary batteries, it exerts an effect of further binding the powders of the components constituting the composite for secondary batteries together.

[0048] In the present disclosure, by performing fine fibrillation processing so that the binder has a fibrous structure with a fibrill diameter (median value) of 100 nm or less, the fibrillated binder can be used as a binder for a secondary battery composite, thereby reducing the degradation of the oxide-based solid electrolyte and enabling good performance.

[0049] The above fibril diameter (median value) is a value measured by the following method.

[0050] (1) Using a scanning electron microscope (S-4800 model, manufactured by Hitachi Seisakusho Co., Ltd.), a magnified photograph (7000x) of the composite sheet for secondary batteries is taken and an image is obtained.

[0051] (2) Divide the image into three equal parts by drawing two lines horizontally at equal intervals.

[0052] (3) For all fibrillated binders on the straight line above, the diameter of each fibrillated binder is measured at three locations, and the average value is taken as the diameter of the fibrillated binder. The three locations to be measured are the intersection point between the fibrillated binder and the straight line, and locations offset by 0.5 μm upward and downward from each intersection point (excluding primary particles of the non-fiberized binder).

[0053] (4) The above operation of (3) is performed on all fibrillated binders located on the straight line below.

[0054] (5) Move 1 mm to the right of the screen starting from the first image and take another picture to measure the diameter of the fibrillated binder according to (3) and (4). Repeat this process, and stop when the number of measurements exceeds 80.

[0055] (6) The median value of the diameters of all fibrillated binders measured above was taken as the size of the fibrillation diameter.

[0056] The above fibril diameter (median) is preferably 100 nm or less, more preferably 85 nm or less, and even more preferably 70 nm or less. Additionally, if fibrillation is performed excessively, flexibility tends to be lost. Although the lower limit is not specifically limited, from the perspective of strength, it is preferably 15 nm or more, more preferably 20 nm or more, and particularly preferably 31 nm or more.

[0057] The method for obtaining a binder having the above fibril diameter (median value) is not particularly limited, but for example,

[0058] A process of applying shear force while mixing a raw material composition containing a sulfide-based solid electrolyte and a binder powder (1)

[0059] A process (2) for forming a composite material for a secondary battery obtained by the above process (1) into a bulk form and

[0060] A method can be performed by rolling the bulk composite for secondary batteries obtained by the above process (2) into a sheet by process (3).

[0061] In this method, for example, in process (1), by making the mixing conditions of the raw material composition 3000 rpm or less, the fibrillation of the binder can be carried out while maintaining flexibility, and by controlling the applied shear stress, the fibrill diameter (median value) of the binder can be made 100 nm or less.

[0062] In addition, it is also desirable to have a process (4) in which, after process (3), a greater load is applied to the obtained rolled sheet to roll it into a thinner sheet. It is also desirable to repeat process (4).

[0063] In addition, the fibril diameter can be adjusted by having a process (5) in which, after process (3) or process (4), the obtained rolled sheet is crushed, then formed back into a bulk form, and rolled into a sheet form. It is preferable to repeat process (5) at least once and no more than 12 times.

[0064] That is, by applying shear force, the binder powder is fibrillated, and by intertwining with powder components such as sulfide-based solid electrolytes, a composite material for secondary batteries can be manufactured. Furthermore, the manufacturing method described above will be described later.

[0065] Furthermore, the term "binding agent powder" refers to a solid state as a powder, rather than a dispersed state mixed with a liquid medium. By utilizing such a state and using a binding agent in a state where no liquid medium is present, the objective of the present disclosure can be suitably achieved.

[0066] The powdered fibril resin used as a raw material for manufacturing the composite for secondary batteries of the present disclosure preferably has a moisture content of 500 ppm or less.

[0067] It is desirable that the moisture content is 500 ppm or less, as this reduces the deterioration of the sulfide-based solid electrolyte.

[0068] It is more preferable that the above moisture content be 300 ppm or less.

[0069] In the present disclosure, the fibrillable resin is a resin that easily fibrillates when shear stress is applied. By using such a fibrillable resin as a binder, the fibrillated resin intertwines with other powder components, thereby binding the powder components and acting as a binder when molding the powder components. Examples of fibrillable resins include liquid crystal polymer (LCP), cellulose, acrylic resin, ultra-high molecular weight polyethylene, PTFE, etc., and among these, PTFE is suitable in terms of chemical stability, thermal stability, and processability.

[0070] In the present disclosure, the PTFE is not particularly limited and may be a homopolymer or a copolymer capable of fibrillation.

[0071] In the case of copolymers, fluorine atom-containing monomers that serve as comonomers include chlorotrifluoroethylene, hexafluoropropylene, fluoroalkylethylene, perfluoroalkylethylene, fluoroalkyl-fluorovinyl ether, etc.

[0072] It is preferable that the PTFE in powder form has a standard specific gravity of 2.12 to 2.20. Having a standard specific gravity within this range offers an advantage in that it allows for the production of composite sheets with high strength. It is more preferable that the lower limit of the standard specific gravity be 2.13 or higher. It is more preferable that the upper limit of the standard specific gravity be 2.19 or lower, and even more preferable that it be 2.18 or lower.

[0073] Standard Specific Gravity [SSG] is determined by preparing a sample in accordance with ASTM D-4895-89 and measuring the specific gravity of the obtained sample by the water displacement method.

[0074] The above powdered PTFE preferably contains 50 mass% or more of a polytetrafluoroethylene resin having a secondary particle size of 450 μm or more, and more preferably contains 80 mass% or more. Since the PTFE having a secondary particle size of 450 μm or more is within this range, it has the advantage of being able to produce a composite sheet with high strength.

[0075] By using PTFE with a secondary particle size of 450㎛ or more, a composite sheet with lower resistance and high toughness can be obtained.

[0076] The lower limit of the average secondary particle size of the above powdered PTFE is more preferably 450 μm, and even more preferably 500 μm. The upper limit of the above secondary particle size is more preferably 700 μm or less, and even more preferably 600 μm or less. The secondary particle size can be determined, for example, by a sieve classification method.

[0077] The above powdered PTFE preferably has an average primary particle size of 150 nm or more, in order to obtain a composite sheet with higher strength and excellent homogeneity. More preferably, it is 180 nm or more, even more preferably 210 nm or more, and particularly preferably 220 nm or more.

[0078] The larger the average primary particle size of PTFE, the more the increase in extrusion pressure is suppressed and the moldability is excellent when extrusion molding is performed using the powder. The upper limit is not specifically limited, but 500 nm is acceptable. From the perspective of productivity in the polymerization process, the upper limit is preferably 350 nm.

[0079] The above average primary particle size can be determined by using an aqueous dispersion of PTFE obtained by polymerization, adjusting the polymer concentration to 0.22 mass%, creating a calibration curve for the average primary particle size determined by measuring the transmittance of 550 nm of projected light per unit length of the aqueous dispersion and the positive diameter in a transmission electron microscope image, measuring the transmittance for the aqueous dispersion to be measured, and determining the value based on the calibration curve.

[0080] The PTFE used in the present disclosure may have a core-shell structure. Examples of PTFE having a core-shell structure include polytetrafluoroethylene comprising a high molecular weight polytetrafluoroethylene core and a shell of lower molecular weight polytetrafluoroethylene or modified polytetrafluoroethylene within the particles. Examples of such modified polytetrafluoroethylene include the polytetrafluoroethylene described in Japanese Patent Publication No. 2005-527652.

[0081] PTFE in powder form satisfying each of the parameters described above can be obtained by conventional manufacturing methods. For example, it may be manufactured according to the manufacturing methods described in International Publication No. 2015-080291 or International Publication No. 2012-086710, etc.

[0082] In the present disclosure, the lower limit of the content of the binder in the composite for solid secondary batteries is preferably 0.2 mass% or more, and more preferably 0.3 mass% or more. It is even more preferable to exceed 0.5 mass%. The upper limit of the content of the binder in the composite for solid secondary batteries is preferably 10 mass% or less, more preferably 7 mass% or less, particularly preferably 6 mass% or less, more preferably 4 mass% or less, even more preferably 1.7 mass% or less, and most preferably 1.0 mass% or less. If the binder is within the above range, it is possible to form a self-standing sheet with excellent handling properties while suppressing an increase in electrode resistance.

[0083] The solid electrolyte used in the composite for solid secondary batteries of the present disclosure is a sulfide-based solid electrolyte. Using a sulfide-based solid electrolyte has the advantage of flexibility.

[0084] As a sulfide-based solid electrolyte, for example, a lithium ion-conducting inorganic solid electrolyte that satisfies the composition represented by the following formula (1) can be cited.

[0085]

[0086] In the formula, M represents an element selected from B, Zn, Sn, Si, Cu, Ga, Sb, Al, Ti, and Ge. A represents an element selected from I, Br, Cl, and F. a1 to e1 represent the compositional ratio of each element, and a1:b1:c1:d1:e1 satisfies 1 to 12:0 to 5:1:2 to 12:0 to 10. a1 is preferably 1 to 9, and more preferably 1.5 to 7.5. b1 is preferably 0 to 3, and more preferably 0 to 1. d1 is preferably 2.5 to 10, and more preferably 3.0 to 8.5. e1 is preferably 0 to 5, and more preferably 0 to 3.

[0087] In the present disclosure, the sulfide-based solid electrolyte preferably contains lithium. The lithium-containing sulfide-based solid electrolyte is used in solid-state batteries that use lithium ions as carriers and is particularly preferred in that it is an electrochemical device having high energy density.

[0088] The compositional ratio of each element can be controlled by adjusting the amount of raw material compounds used when manufacturing a sulfide-based inorganic solid electrolyte, as follows.

[0089] Sulfide-based inorganic solid electrolytes may be amorphous (glass), crystallized (glass ceramic), or only partially crystallized. For example, Li-PS-based glass containing Li, P, and S, or Li-PS-based glass ceramics containing Li, P, and S may be used.

[0090] Sulfide-based inorganic solid electrolytes can be prepared by the reaction of at least two raw materials selected from, for example, lithium sulfide (Li2S), phosphorus sulfide (e.g., phosphorus pentasulfide (P2S5)), elemental phosphorus, elemental sulfur, sodium sulfide, hydrogen sulfide, lithium halide (e.g., LiI, LiBr, LiCl), and sulfides of the element represented by M (e.g., SiS2, SnS, GeS2).

[0091] As a specific example of a sulfide-based inorganic solid electrolyte, an example of a combination of raw materials is shown below. For example, Li2S-P2S5-LiCl, Li2S-P2S5-H2S, Li2S-P2S5-H2S-LiCl, Li2S-LiI-P2S5, Li2S-LiI-Li2O-P2S5, Li2S-LiBr-P2S5, Li2S-Li2O-P2S5, Li2S-Li3PO4-P2S5, Li2S-P2S5-P2O5, Li2S-P2S5-SiS2, Li2S-P2S5-SiS2-LiCl, Li2S-P2S5-SnS, Li2S-P2S5-Al2S3, Li2S-GeS2, Li2S-GeS2-ZnS, Li2S-Ga2S3, Li2S-GeS2-Ga2S3, Li2S-GeS2-P2S5, Li2S-GeS2-Sb2S5, Li2S-GeS2-Al2S3, Li2S-SiS2, Li2S-Al2S3, Li2S-SiS2-Al2S3, Li2S-SiS2-P2S5, Li2S-SiS2-P2S5-LiI, Li2S-SiS2-LiI, Li2S-SiS2-Li4SiO4, Li2S-SiS2-Li3PO4, Li 10 GeP2S 12 Examples include the above. However, the mixing ratio of each ingredient is irrelevant.

[0092] In particular, it is preferable that the sulfide-based solid electrolyte be a sulfide-based solid electrolyte that satisfies the composition represented by the following formula (A).

[0093]

[0094] (where 0.6≤a≤0.86, 0≤b≤0.333, 0≤c≤0.3, 0.05≤b+c≤0.4, X 1 Silver is Ge, Sn, Ti, or Si, X 2 represents Cl, Br, or I, provided that neither b nor c is 0.

[0095] It is advantageous in that it is a sulfide-based solid electrolyte satisfying the composition represented by the above formula (A), thereby enabling stable high ionic conductivity.

[0096] As an example of a sulfide-based solid electrolyte represented by the above formula (A), specifically, 0.714Li2S-0.143SnS2-0.143P2S5(Li 10 SnP2S 12 (LSPS)), 0.625Li2S-0.25LiCl-0.125P2S5(Li6PS5Cl(LPSCl)), 0.715Li2S-0.143GeS2-0.142P2S5(Li 10 GeP2S 12 Any of the selected from (LGPS), etc., or a mixture of two or more types may be used.

[0097] The average particle size of the sulfide-based solid electrolyte is preferably 0.1 μm or more and 20 μm or less. As a lower limit, it is more preferable to be 0.2 μm or more, and even more preferable to be 0.3 μm or more. As an upper limit, it is more preferable to be 18 μm or less, and even more preferable to be 15 μm or less.

[0098] If the average particle size of the sulfide-based solid electrolyte is less than 0.1㎛, handling of the powder may become difficult. On the other hand, if the average particle size of the sulfide-based solid electrolyte exceeds 20㎛, press formability may deteriorate.

[0099] In addition, the average particle size of the sulfide-based solid electrolyte particles is measured in the following procedure.

[0100] A 1 mass% dispersion of sulfide-based solid electrolyte particles is diluted in a 20 ml sample bottle using water (or heptane in the case of substances unstable in water). The diluted dispersion sample is irradiated with 1 kHz ultrasound for 10 minutes and used for testing immediately thereafter. Using this dispersion sample, data is introduced 50 times using a laser diffraction / scattering particle size distribution measuring device LA-920 (manufactured by HORIBA) at a temperature of 25°C with a measuring quartz cell to obtain the volume-averaged particle size. For other detailed conditions, refer to the description in JIS Z8828:2013 “Particle Size Analysis - Dynamic Light Scattering Method” as necessary. Five samples are prepared per level, and the average value is adopted.

[0101] The method for adjusting the average particle size of the sulfide solid electrolyte is not particularly limited, but is performed as follows, for example. A known grinder or classifier is used. For example, a mortar, sand mill, ball mill, jet mill, or sieve is suitably used. Depending on the properties of the solid electrolyte, a solvent such as water or ethanol may be added during grinding. To achieve the desired particle size, it is desirable to perform classification. Classification is not particularly limited and can be performed using a sieve, an air classifier, etc.

[0102] When considering the reduction of interfacial resistance and the maintenance of the reduced interfacial resistance when used in a solid secondary battery, the content of the solid component in the sulfide-based solid electrolyte composite for secondary batteries is preferably 5 mass% or more, more preferably 9 mass% or more, and particularly preferably 12 mass% or more, in the case of the electrode, based on 100 mass% of the solid component. As for the upper limit, from the perspective of battery capacity, it is preferably 60 mass% or less, more preferably 50 mass% or less, and particularly preferably 40 mass% or less.

[0103] In addition, regarding the solid electrolyte layer disposed between the positive electrode and the negative electrode, it is preferable that it be 50 mass% or more, more preferable that it be 60 mass% or more, and particularly preferable that it be 70 mass% or more. In the same regard, as for the upper limit, it is preferable that it be 99.9 mass% or less, more preferable that it be 99.8 mass% or less, and particularly preferable that it be 99.7 mass% or less.

[0104] The above sulfide-based solid electrolyte may be used as a single type or in combination of two or more types.

[0105] In addition, in this specification, solid content (solid component) refers to a component that does not volatilize or evaporate and disappear when a drying treatment is performed at 170°C for 6 hours under a nitrogen atmosphere.

[0106] The composite for secondary batteries of the present disclosure is particularly suitable for lithium-ion solid secondary batteries.

[0107] The composite for secondary batteries disclosed in the present disclosure is typically used in a sheet form when used in solid-state secondary batteries.

[0108] The composite sheet for a secondary battery disclosed in this disclosure may be used as a positive electrode sheet or as a negative electrode sheet. Additionally, it may be used as a solid electrolyte layer sheet.

[0109] Among these, when used as an electrode sheet, it further contains active material particles. The active material particles may be a positive electrode active material or a negative electrode active material. The composite sheet for a secondary battery disclosed herein is more suitably used as a positive electrode sheet using a positive electrode active material. Furthermore, when used as an electrode sheet, it may contain a conductivity aid if necessary.

[0110] The following describes electrode active materials, conductivity aids, etc.

[0111] (Electrode active material)

[0112] When the composite sheet for a secondary battery disclosed in this disclosure is used as a positive electrode sheet, a positive electrode active material is incorporated into the composite sheet for the secondary battery. The positive electrode active material may be a positive electrode active material known as a positive electrode active material for a solid-state battery. In particular, it is preferable to use a positive electrode active material capable of absorbing and releasing lithium ions.

[0113] The above positive electrode active material is not particularly limited as long as it is capable of electrochemically absorbing and releasing alkali metal ions, but, for example, a material containing an alkali metal and at least one transition metal is preferred. Specific examples include alkali metal-containing transition metal composite oxides, alkali metal-containing transition metal phosphate compounds, conductive polymers, etc.

[0114] Among these, as a positive electrode active material, an alkali metal-containing transition metal composite oxide that generates particularly high voltage is preferred. Examples of the alkali metal ions include lithium ions, sodium ions, potassium ions, etc. In a preferred embodiment, the alkali metal ion may be a lithium ion. That is, in this embodiment, the alkali metal ion secondary battery is a lithium ion secondary battery.

[0115] As the above alkali metal-containing transition metal complex oxide, for example

[0116] Formula: M a Mn 2-b M 1 b O4

[0117] (wherein M is at least one metal selected from the group consisting of Li, Na, and K; 0.9≤a; 0≤b≤1.5; M 1 Alkali metal-manganese spinel composite oxide represented by at least one metal selected from the group consisting of Fe, Co, Ni, Cu, Zn, Al, Sn, Cr, V, Ti, Mg, Ca, Sr, B, Ga, In, Si, and Ge,

[0118] Formula: MNi 1-c M 2 c O2

[0119] (wherein M is at least one metal selected from the group consisting of Li, Na, and K; 0≤c≤0.5; M 2 is an alkali metal-nickel complex oxide represented by at least one metal selected from the group consisting of Fe, Co, Mn, Cu, Zn, Al, Sn, Cr, V, Ti, Mg, Ca, Sr, B, Ga, In, Si, and Ge, or

[0120] Formula: MCo 1-d M 3 d O2

[0121] (wherein M is at least one metal selected from the group consisting of Li, Na, and K; 0≤d≤0.5; M 3 (at least one metal selected from the group consisting of Fe, Ni, Mn, Cu, Zn, Al, Sn, Cr, V, Ti, Mg, Ca, Sr, B, Ga, In, Si, and Ge)

[0122] Examples include alkali metal-cobalt complex oxides represented by . In the above, M is preferably one metal selected from the group consisting of Li, Na, and K, more preferably Li or Na, and even more preferably Li.

[0123] Among them, MCoO2, MMnO2, MNiO2, MMn2O4, and MNi are capable of providing high-energy density and high-output secondary batteries. 0.8 Co 0.15 Al 0.05 O2 or MNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, etc. is preferred, and it is preferred to be a compound represented by the following general formula (3).

[0124]

[0125] (In the formula, M is at least one metal selected from the group consisting of Li, Na, and K, and M 5 represents at least one selected from the group consisting of Fe, Cu, Zn, Al, Sn, Cr, V, Ti, Mg, Ca, Sr, B, Ga, In, Si, and Ge, and (h+i+j+k)=1.0, 0≤h≤1.0, 0≤i≤1.0, 0≤j≤1.5, 0≤k≤0.2)

[0126] As the above alkali metal-containing transition metal phosphate compound, for example, the following formula (4)

[0127]

[0128] (In the formula, M is at least one metal selected from the group consisting of Li, Na, and K, and M 4 represents at least one selected from the group consisting of V, Ti, Cr, Mn, Fe, Co, Ni, and Cu, and may be an example of a compound represented by 0.5≤e≤3, 1≤f≤2, and 1≤g≤3. In the above, M is preferably one metal selected from the group consisting of Li, Na, and K, more preferably Li or Na, and even more preferably Li.

[0129] As the transition metal of the lithium-containing transition metal phosphate compound, V, Ti, Cr, Mn, Fe, Co, Ni, Cu, etc. are preferred. Specific examples include iron phosphates such as LiFePO4, Li3Fe2(PO4)3, LiFeP2O7, cobalt phosphates such as LiCoPO4, and those in which some of the transition metal atoms that form the main component of these lithium transition metal phosphate compounds are substituted with other elements such as Al, Ti, V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, Nb, Si, etc.

[0130] As for the above lithium-containing transition metal phosphate compound, it is preferable to have an olivine-type structure.

[0131] Other positive electrode active materials include MFePO4 and MNi 0.8 Co 0.2 O2, M 1.2 Fe 0.4 Mn 0.4 O2, MNi 0.5 Mn 1.5 Examples include O2, MV3O6, M2MnO3 (wherein M is at least one metal selected from the group consisting of Li, Na, and K). In particular, M2MnO3, MNi 0.5 Mn 1.5 Positive electrode active materials such as O2 are desirable in that their crystal structure does not collapse when the secondary battery is operated at a voltage exceeding 4.4V or 4.6V or higher. Therefore, an electrochemical device such as a secondary battery using a positive electrode material including the positive electrode active material exemplified above is desirable in that, even when stored at high temperatures, the remaining capacity is unlikely to decrease and the resistance increase rate is unlikely to change, and the battery performance is not degraded even when operated at high voltage.

[0132] Other positive electrode active materials include M2MnO3 and MM 6 O2(wherein M is at least one metal selected from the group consisting of Li, Na, and K, and M 6 Solid solution materials of transition metals such as silver, Co, Ni, Mn, and Fe can also be cited.

[0133] As the above solid solution material, for example, the general formula Mx[Mn (1-y) M 7 y ]O z It is an alkali metal manganese oxide represented by . Here, M in the formula is at least one metal selected from the group consisting of Li, Na, and K, and M 7It consists of at least one metallic element other than silver, M, and Mn, and includes one or more elements selected from the group consisting of, for example, Co, Ni, Fe, Ti, Mo, W, Cr, Zr, and Sn. In addition, the values ​​of x, y, and z in the formula are 1 <x<2, 0≤y<1, 1.5<z<3의 범위이다. 그 중에서도, Li 1.2 Mn 0.5 Co 0.14 Ni 0.14 Manganese-containing solid solution materials that incorporate LiNiO2 or LiCoO2 based on Li2MnO3, such as O2, are desirable in that they can provide alkali metal ion secondary batteries with high energy density.

[0134] In addition, it is desirable to include lithium phosphate in the positive electrode active material as this improves continuous charging characteristics. Although there are no restrictions on the use of lithium phosphate, it is preferable to use a mixture of the above-mentioned positive electrode active material and lithium phosphate. The amount of lithium phosphate used is preferably 0.1 mass% or more, more preferably 0.3 mass% or more, and even more preferably 0.5 mass% or more with respect to the total of the above-mentioned positive electrode active material and lithium phosphate, and is preferably 10 mass% or less, more preferably 8 mass% or less, and even more preferably 5 mass% or less.

[0135] Examples of the above conductive polymers include p-doped conductive polymers and n-doped conductive polymers. Examples of conductive polymers include polyacetylene-based, polyphenylene-based, heterocyclic polymers, ionic polymers, ladder and network polymers, etc.

[0136] In addition, a material having a different composition may be attached to the surface of the above positive electrode active material. Examples of surface-attached materials include oxides such as aluminum oxide, silicon oxide, titanium oxide, zirconium oxide, magnesium oxide, calcium oxide, boron oxide, antimony oxide, and bismuth oxide; sulfates such as lithium sulfate, sodium sulfate, potassium sulfate, magnesium sulfate, calcium sulfate, and aluminum sulfate; carbonates such as lithium carbonate, calcium carbonate, and magnesium carbonate; and carbon.

[0137] These surface-attaching materials can be attached to the surface of a positive electrode active material by methods such as dissolving or suspending them in a solvent and impregnating them into the corresponding positive electrode active material, or adding them and then drying; by dissolving or suspending a surface-attaching material precursor in a solvent and adding it to the corresponding positive electrode active material, followed by a reaction through heating, etc.; or by adding it to a positive electrode active material precursor and simultaneously calcining it. In addition, when carbon is attached, a method of mechanically attaching carbonaceous material in the form of, for example, activated carbon, later may also be utilized.

[0138] As for the amount of the surface-attached material, in terms of mass relative to the positive electrode active material, it is used in a lower limit preferably at least 0.1 ppm, more preferably at least 1 ppm, and even more preferably at least 10 ppm, and in an upper limit preferably at least 20%, more preferably at least 10%, and even more preferably at least 5%. By means of the surface-attached material, the oxidation reaction of the solid electrolyte on the surface of the positive electrode active material can be suppressed, thereby improving battery life. If the amount of attachment is excessively small, the effect is not sufficiently manifested, and if it is excessively large, resistance may increase in order to hinder the entry and exit of lithium ions.

[0139] Examples of particle shapes of the positive electrode active material include conventionally used bulk, polyhedral, spherical, elliptical, plate-like, needle-like, and columnar shapes. Additionally, primary particles may aggregate to form secondary particles.

[0140] The tap density of the positive electrode active material is preferably 0.5 g / cm³ or higher, more preferably 0.8 g / cm³ or higher, and even more preferably 1.0 g / cm³ or higher. If the tap density of the positive electrode active material falls below the above lower limit, the amount of dispersion medium required during the formation of the positive electrode active material layer increases, along with the required amount of conductive material or binder, and the filling rate of the positive electrode active material in the positive electrode active material layer is restricted, which may result in a limitation of the battery capacity. By using a composite oxide powder with a high tap density, a high-density positive electrode active material layer can be formed. Generally, a higher tap density is preferable, and there is no specific upper limit; however, if it is excessively high, the diffusion of lithium ions using the solid electrolyte as a medium within the positive electrode active material layer becomes rate-limited, and load characteristics may easily deteriorate; therefore, the upper limit is preferably 4.0 g / cm³ or lower, more preferably 3.7 g / cm³ or lower, and even more preferably 3.5 g / cm³ or lower.

[0141] In addition, in the present disclosure, the tap density is determined as the powder packing density (tap density) g / cm³ when 5 to 10 g of positive electrode active material powder is placed in a 10 ml glass graduated cylinder and tapped 200 times with a stroke of about 20 mm.

[0142] The particle median diameter d50 of the positive electrode active material (the secondary particle diameter in cases where primary particles aggregate to form secondary particles) is preferably 0.3 μm or more, more preferably 0.5 μm or more, even more preferably 0.8 μm or more, and most preferably 1.0 μm or more, and is also preferably 30 μm or less, more preferably 27 μm or less, even more preferably 25 μm or less, and most preferably 22 μm or less. If it falls below the lower limit, it may not be possible to obtain a high-tap density product, and if it exceeds the upper limit, it may cause a decrease in battery performance because lithium diffusion within the particles takes time, or problems such as streaks may occur when manufacturing the positive electrode of the battery, that is, when slurrying the active material with a conductive material or binder with a solvent and applying it as a thin film. Here, by mixing two or more types of the positive electrode active materials having different median diameters d50, the chargeability during the manufacturing of the positive electrode can be further improved.

[0143] In addition, in the present disclosure, the median diameter d50 is measured by a known laser diffraction / scattering particle size distribution measuring device. When using HORIBA LA-920 as the particle size distribution meter, a 0.1 mass% aqueous sodium hexametaphosphate solution is used as the dispersion medium during measurement, and the measurement is performed by setting the refractive index to 1.24 after 5 minutes of ultrasonic dispersion.

[0144] In cases where primary particles aggregate to form secondary particles, the average primary particle size of the positive electrode active material is preferably 0.05 μm or more, more preferably 0.1 μm or more, and even more preferably 0.2 μm or more, and the upper limit is preferably 5 μm or less, more preferably 4 μm or less, even more preferably 3 μm or less, and most preferably 2 μm or less. If the upper limit is exceeded, it is difficult to form spherical secondary particles, and the powder packing properties are adversely affected, or the specific surface area is significantly reduced, which increases the likelihood of battery performance, such as output characteristics, deteriorating. Conversely, if the lower limit is lowered, problems such as reduced reversibility of charge and discharge may occur because crystals are not developed properly.

[0145] In addition, in the present disclosure, the average primary particle size of the positive electrode active material is measured by observation using a scanning electron microscope (SEM). Specifically, in a photograph at a magnification of 10,000 times, the longest value of the intercept by the left and right boundary lines of the primary particles with respect to a straight line in the horizontal direction is obtained for any 50 primary particles, and the average value is taken.

[0146] The BET specific surface area of ​​the positive electrode active material is preferably 0.1 m² / g or more, more preferably 0.2 m² / g or more, and even more preferably 0.3 m² / g or more, and the upper limit is preferably 50 m² / g or less, more preferably 40 m² / g or less, and even more preferably 30 m² / g or less. If the BET specific surface area is smaller than this range, battery performance is likely to degrade, and if it is larger, it becomes difficult to increase the tap density, which may cause problems with coating properties when forming the positive electrode active material layer.

[0147] In addition, in the present disclosure, the BET specific surface area is defined as a value measured by the nitrogen adsorption BET 1-point method by the gas flow method, using a surface area meter (e.g., an automatic surface area measuring device manufactured by Okura Riken), pre-drying the sample at 150°C for 30 minutes under nitrogen flow, and then using a nitrogen-helium mixed gas that is accurately adjusted so that the relative pressure of nitrogen with respect to atmospheric pressure is 0.3.

[0148] When the secondary battery of the present disclosure is used as a large lithium-ion secondary battery for hybrid vehicles or distributed power sources, high output is required, so it is preferable that the particles of the positive electrode active material consist mainly of secondary particles.

[0149] It is preferable that the particles of the positive electrode active material contain 0.5 to 7.0 volume% of fine particles having an average particle size of secondary particles of 40 μm or less and an average primary particle size of 1 μm or less. By including fine particles with an average primary particle size of 1 μm or less, the contact area with the solid electrolyte is increased, and the diffusion of lithium ions between the sheet for the all-solid-state secondary battery and the solid electrolyte can be accelerated, thereby improving the output performance of the battery.

[0150] As a method for manufacturing positive electrode active materials, general methods for manufacturing inorganic compounds are used. In particular, various methods are considered to produce spherical or elliptical active materials; examples include a method in which a transition metal raw material is dissolved or ground and dispersed in a solvent such as water, a spherical precursor is prepared and recovered by adjusting the pH while stirring, and then dried as necessary, followed by the addition of a Li source such as LiOH, Li2CO3, or LiNO3 and calcination at a high temperature to obtain the active material.

[0151] For the manufacture of the positive electrode, the above-described positive electrode active material may be used alone, or two or more materials of different compositions may be used in combination or in any ratio. In this case, a preferred combination is LiCoO2 and LiNi 0.33 Co 0.33 Mn 0.33 Examples include combinations of ternary systems such as O2, combinations of LiCoO2 and LiMn2O4 or in which part of this Mn is substituted with other transition metals, or combinations of LiFePO4 and LiCoO2 or in which part of this Co is substituted with other transition metals.

[0152] The content of the positive electrode active material is preferably 40 mass% or more, more preferably 50 mass% or more, and particularly preferably 60 mass% or more. In addition, the upper limit is preferably 94.8 mass% or less, more preferably 90.5 mass% or less, and particularly preferably 87.5 mass% or less. If the content of the positive electrode active material in the positive electrode composite is low, the electrical capacitance may become insufficient. Conversely, if the content is excessively high, the electron-ion conductivity or strength of the positive electrode may be insufficient.

[0153] The above negative electrode active material is not particularly limited and includes, for example, carbonaceous materials such as lithium metal, artificial graphite, graphite carbon fiber, resin calcined carbon, pyrolytic vapor-grown carbon, coke, mesocarbon micro beads (MCMB), furfuryl alcohol resin calcined carbon, polyacene, pitch-based carbon fiber, vapor-grown carbon fiber, natural graphite, and non-graphitizable carbon, silicon-containing compounds such as silicon and silicon alloys, and Li4Ti5O 12 Examples include any of the above, or a mixture of two or more types. Among these, a carbonaceous material containing at least a part of it, or a silicon-containing compound can be particularly suitablely used.

[0154] The content of the above negative electrode active material is preferably 40 mass% or more, more preferably 50 mass% or more, and particularly preferably 60 mass% or more. In addition, the upper limit is preferably 94.8 mass% or less, more preferably 90.5 mass% or less, and particularly preferably 87.5 mass% or less. If the content of the negative electrode active material in the negative electrode composite is low, the electrical capacitance may become insufficient. Conversely, if the content is too high, the electron-ion conductivity or strength of the negative electrode may be insufficient.

[0155] (Challenge Supplement)

[0156] As the above-mentioned conductive aid, known conductive materials may be used at will. Specific examples include metal materials such as copper and nickel, graphite such as natural graphite and artificial graphite, carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black, and carbon materials such as needle coke, carbon nanotubes, fullerene, and amorphous carbon such as VGCF. In addition, one of these may be used alone, or two or more may be used in any combination and ratio.

[0157] When a conductivity aid is used, the conductivity aid is used in the electrode active material layer in an amount of typically 0.01 mass% or more, preferably 0.1 mass% or more, more preferably 0.5 mass% or more, and typically 50 mass% or less, preferably 30 mass% or less, more preferably 15 mass% or less. If the content is lower than this range, the conductivity may become insufficient. Conversely, if the content is higher than this range, the battery capacity may decrease.

[0158] (Other ingredients)

[0159] The composite sheet for secondary batteries may further include a thermoplastic resin.

[0160] Examples of thermoplastic resins include vinylidene fluoride, polypropylene, polyethylene, polystyrene, polyethylene terephthalate, polyethylene oxide, etc. One type may be used alone, or two or more types may be used in any combination and ratio.

[0161] The ratio of thermoplastic resin to the electrode active material is typically 0.01 mass% or more, preferably 0.05 mass% or more, more preferably 0.10 mass% or more, and is also typically 3.0 mass% or less, preferably 2.5 mass% or less, more preferably 2.0 mass% or less. By adding thermoplastic resin, the mechanical strength of the electrode can be improved. If this range is exceeded, the proportion of active material in the composite decreases, and problems such as a decrease in battery capacity or an increase in resistance between active materials may occur.

[0162] In the composite sheet for a secondary battery of the present disclosure, the content of the binder is, as a ratio of the binder in the composite sheet for a secondary battery, typically 0.2 mass% or more, preferably 0.3 mass% or more, more preferably 0.5 mass% or more, and typically 10 mass% or less, preferably 6.0 mass% or less, more preferably 4 mass% or less, even more preferably 1.7 mass% or less, and most preferably 1.0 mass% or less. If the ratio of the binder is excessively low, the active material cannot be sufficiently retained and supported within the composite sheet for a secondary battery, resulting in insufficient mechanical strength of the composite sheet for a secondary battery and potentially deteriorating battery performance such as cycle characteristics. On the other hand, if it is too high, it may lead to a decrease in battery capacity or conductivity.

[0163] (Manufacturing method)

[0164] The method for manufacturing a composite sheet for a secondary battery according to the present disclosure preferably involves using a raw material composition obtained by mixing each of the components described above and forming it into a sheet. In the sheet formation process, in order to omit the drying process, it is preferable to reduce or completely eliminate the use of a liquid medium and to apply shear stress to the powdered raw material composition without preparing a slurry. Additionally, to reduce the load on the equipment, a small amount of solvent may be added as a lubricant. The solvent is preferably an organic solvent, and regarding the amount of solvent contained, it is preferable to have 10 mass% or less relative to the raw material composition, more preferable to have 5 mass% or less, and even more preferable to have 3 mass% or less.

[0165] Although the manufacturing method of the composite sheet for secondary batteries disclosed in this disclosure is not limited, an example of a specific manufacturing method is provided below.

[0166] The composite sheet for secondary batteries of the present disclosure is,

[0167] A process of applying shear force while mixing a raw material composition containing an oxide-based solid electrolyte and a binder (1)

[0168] A process (2) for forming a composite material for a secondary battery obtained by the above process (1) into a bulk form and

[0169] A process (3) of rolling the bulk composite for secondary batteries obtained by the above process (2) into a sheet.

[0170] It can be obtained by a method for manufacturing a composite sheet for a secondary battery having.

[0171] In the step of applying shear force while mixing the raw material composition in the above process (1), the resulting composite for secondary batteries exists in a state without a fixed shape, consisting only of oxide-based solid electrolytes, binders, etc., simply mixed together. Specific mixing methods include mixing using a W-type mixer, V-type mixer, drum-type mixer, ribbon mixer, conical screw-type mixer, uniaxial mixer, twin-axial mixer, mixer, stirring mixer, planetary mixer, Henschel mixer, high-speed mixer, etc.

[0172] In the above process (1), the mixing conditions can be set by appropriately adjusting the rotational speed and mixing time. For example, it is suitable to set the rotational speed to 15,000 rpm or less. Preferably, it is 10 rpm or more, more preferably 1,000 rpm or more, and even more preferably 3,000 rpm or more; further preferably, it is in the range of 12,000 rpm or less, more preferably 11,000 rpm or less, and even more preferably 10,000 rpm. If the speed falls below the above range, mixing takes time and affects productivity. In addition, if the speed exceeds the range, excessive fibrillation may occur, and there is a risk that the composite sheet will have reduced strength.

[0173] In the above process (1), it is preferable to perform it at 30°C or higher, and more preferable at 60°C or higher.

[0174] In addition, it is preferable to include a process (A) for mixing the raw material composition and dispersing the binder prior to the above process (1). In the above process (A), it is preferable to mix with the smallest possible shear force.

[0175] In the above process (A), the mixing conditions can be set by appropriately setting the rotational speed and mixing time. For example, it is suitable to set the rotational speed to 500 rpm or less. Preferably, it is 20 rpm or more, more preferably 30 rpm or more, even more preferably 40 rpm or more, and also preferably 400 rpm or less, more preferably 300 rpm or less, and even more preferably 200 rpm.

[0176] In the above process (A), it is preferable to perform the mixing at a temperature of 19°C or lower.

[0177] By adopting this temperature range, processing into the desired sheet can be performed in a shorter time.

[0178] PTFE has two transition temperatures at approximately 19°C and 30°C. Below 19°C, PTFE can be easily mixed while maintaining its shape. However, above 19°C, the structure of the PTFE particles loosens, making it more sensitive to mechanical shear. At temperatures exceeding 30°C, a higher degree of fibrillation occurs.

[0179] As described above, the raw material composition preferably does not substantially contain a liquid medium and is preferably in the form of a powder. In the raw material composition in the form of a powder, the content of the liquid medium is preferably 1 mass% or less.

[0180] For this reason, when using PTFE resin as a fibrillary resin, it is preferable to carry out the above process (A) at a temperature of 19°C or lower, preferably from 0°C to 19°C.

[0181] That is, in such a process (A), it is desirable to mix and homogenize without causing fibrillation. And, it is desirable to cause fibrillation through subsequent processes (1) to (5).

[0182] In the above process (2), forming into a bulk form means forming the composite material for the secondary battery into a single mass.

[0183] Specific methods for forming in bulk include extrusion molding and press molding.

[0184] In addition, the term "bulk form" does not require a specific shape, but simply needs to be in a state of being in a single mass, and includes forms such as rod-shaped, sheet-shaped, spherical, and cube-shaped forms. The size of the mass is preferably such that the diameter of its cross-section or at least one side is 10,000 μm or more. More preferably, it is 20,000 μm or more.

[0185] Specific rolling methods in the above process (3) include rolling using a roll press, a flat plate press, a calender roll, etc.

[0186] In addition, after process (3), it is also desirable to have process (4) of applying a greater load to the obtained rolled sheet and rolling it into a thinner sheet. It is also desirable to repeat process (4). In this way, the flexibility is improved by rolling the rolled sheet little by little in stages rather than making it thin all at once.

[0187] As for the number of steps (4), it is preferable to have 2 or more and 10 or fewer, and more preferable to have 3 or more and 9 or fewer.

[0188] Specific rolling methods include, for example, a method of processing into a thinner sheet by rotating two or more rolls and passing a rolled sheet between them.

[0189] In addition, from the perspective of adjusting the fibril diameter, it is also desirable to have a process (5) in which, after process (3) or process (4), the rolled sheet is crushed, then formed back into a bulk form, and rolled into a sheet form. It is also desirable to repeat process (5). As for the number of times process (5) is performed, it is desirable to perform it 1 to 12 times, and more desirable to perform it 2 to 11 times.

[0190] In process (5), specific methods for crushing and forming the rolled sheet into a bulk form include folding the rolled sheet, forming it into a rod or thin film sheet, or chipping it. In the present disclosure, "crushing" means changing the shape of the rolled sheet obtained in process (3) or process (4) into a different shape in order to roll it into a sheet in the next process, and simply folding the rolled sheet is included.

[0191] In addition, after process (5), process (4) may be performed, or it may be performed repeatedly.

[0192] In addition, uniaxial stretching or biaxial stretching may be performed in processes (2) to (3), (4), and (5).

[0193] In addition, the fibril diameter (median value) can be adjusted according to the degree of crushing in process (5).

[0194] Processes (2) to (5) are preferably carried out at 30°C or higher, and more preferably at 60°C or higher.

[0195] In the above process (3), (4) or (5), the rolling rate is preferably 10% or more, more preferably 20% or more, and also preferably 80% or less, more preferably 65% ​​or less, and more preferably 50% or less. If it is below the above range, the number of rolling passes increases and time is required, which affects productivity. Also, if it is above the above range, excessive fibrillation occurs, and there is a risk that the composite sheet will have reduced strength and flexibility.

[0196] Furthermore, the rolling ratio referred to herein indicates the ratio of the thickness reduction after processing to the thickness of the sample before rolling. The sample before rolling may be a bulk composite or a sheet composite. The thickness of the sample refers to the thickness in the direction in which the load is applied during rolling.

[0197] As described above, PTFE powder undergoes fibrillation by applying shear force. However, in order to have a fibrous structure with a median fibrillation diameter of 100 nm or less, excessive shear stress can cause fibrillation to be excessively promoted, which may impair flexibility. Additionally, weak shear stress may result in insufficient strength. Therefore, by appropriately applying shear stress to PTFE during mixing or rolling to promote fibrillation, and by rolling the composite to extend it into a sheet, the fibrous structure with a median fibrillation diameter of 100 nm or less can be achieved.

[0198] As described above, the composite sheet for a secondary battery of the present disclosure may be either a positive electrode sheet or a negative electrode sheet. In addition, it may be a sheet for a solid electrolyte layer.

[0199] In the case of using a composite sheet for a positive electrode or a sheet for a negative electrode, in the manufacture of the composite sheet for the secondary battery, the positive electrode active material or the negative electrode active material can be mixed together with the solid electrolyte and the binder.

[0200] The positive and negative poles are explained below.

[0201] (Straight play)

[0202] In the present disclosure, the positive electrode is preferably composed of a current collector and a positive electrode sheet.

[0203] As materials for the current collector for the positive electrode, metal materials such as aluminum, titanium, tantalum, stainless steel, nickel, or their alloys; and carbon materials such as carbon cloth or carbon paper may be used. Among these, metal materials, particularly aluminum or its alloys, are preferred.

[0204] As for the shape of the entire current collector, for metal materials, examples include metal foil, metal cylinder, metal coil, metal plate, expanded metal, punched metal, foamed metal, etc., and for carbon materials, examples include carbon plate, carbon thin film, carbon cylinder, etc. Among these, metal foil is preferred. In addition, the metal foil may be appropriately formed into a mesh shape.

[0205] The thickness of the metal foil is arbitrary, but is typically 1 μm or more, preferably 3 μm or more, more preferably 5 μm or more, and also typically 1 mm or less, preferably 100 μm or less, more preferably 50 μm or less. If the metal foil is thinner than this range, it may lack the strength required as a current collector. Conversely, if the metal foil is thicker than this range, handling properties may be compromised.

[0206] In addition, it is desirable to have a conductive aid applied to the surface of the current collector, in order to reduce the electrical contact resistance between the current collector and the positive electrode composite sheet. Examples of conductive aids include carbon and precious metals such as gold, platinum, and silver.

[0207] The positive electrode can be manufactured using conventional methods. For example, methods such as laminating the positive electrode sheet and the current collector with an adhesive interposed therebetween and drying can be used.

[0208] The density of the positive electrode sheet is preferably 2.0 g / cm³ or higher, more preferably 2.1 g / cm³ or higher, and even more preferably 2.3 g / cm³ or higher, and is also preferably 4.0 g / cm³ or lower, more preferably 3.9 g / cm³ or lower, and even more preferably 3.8 g / cm³ or lower. If it exceeds this range, the conductivity between active materials decreases and the battery resistance increases, which may result in a failure to obtain high output. If it falls below this range, the content of hard and brittle active materials is low, which may result in a battery with low capacity.

[0209] The thickness of the positive electrode is not particularly limited, but from the perspective of high capacity and high power, the thickness of the composite sheet after subtracting the thickness of the current collector is preferably 10 μm or more, more preferably 20 μm or more, as a lower limit with respect to one side of the current collector, and also preferably 500 μm or less, more preferably 450 μm or less.

[0210] In addition, a material with a different composition may be attached to the surface of the above positive electrode. Examples of surface-attached materials include oxides such as aluminum oxide, silicon oxide, titanium oxide, zirconium oxide, magnesium oxide, calcium oxide, boron oxide, antimony oxide, and bismuth oxide; sulfates such as lithium sulfate, sodium sulfate, potassium sulfate, magnesium sulfate, calcium sulfate, and aluminum sulfate; carbonates such as lithium carbonate, calcium carbonate, and magnesium carbonate; and carbon.

[0211] (Polar)

[0212] In the present disclosure, the negative electrode is preferably composed of a current collector and a negative electrode sheet.

[0213] As materials for the current collector for the negative electrode, metal materials such as copper, nickel, titanium, tantalum, stainless steel, or their alloys; and carbon materials such as carbon cloth or carbon paper may be used. Among these, metal materials, particularly copper, nickel, or their alloys, are preferred.

[0214] Examples of shapes for the current collector include metal foil, metal cylinder, metal coil, metal plate, expanded metal, punched metal, foamed metal, etc. for metal materials, and carbon plate, carbon thin film, carbon cylinder, etc. Among these, a metal foil is preferred. Additionally, the metal foil may be formed into a mesh shape as appropriate. The thickness of the metal foil is arbitrary, but is typically 1 μm or more, preferably 3 μm or more, more preferably 5 μm or more, and typically 1 mm or less, preferably 100 μm or less, more preferably 50 μm or less. If the metal foil is thinner than this range, it may lack the strength required as a current collector. Conversely, if the metal foil is thicker than this range, handling properties may be compromised.

[0215] The negative electrode can be manufactured using conventional methods. For example, methods such as laminating the negative electrode sheet and the current collector with an adhesive interposed therebetween and drying them may be used.

[0216] The density of the negative electrode sheet is preferably 1.3 g / cm³ or higher, more preferably 1.4 g / cm³ or higher, and even more preferably 1.5 g / cm³ or higher, and is also preferably 2.0 g / cm³ or lower, more preferably 1.9 g / cm³ or lower, and even more preferably 1.8 g / cm³ or lower. If it exceeds this range, the permeability of the solid electrolyte to the vicinity of the interface between the current collector and the active material decreases, and in particular, charge / discharge characteristics at high current densities deteriorate, which may result in failure to obtain high output. Furthermore, if it falls below this range, the conductivity between the active materials decreases, increasing battery resistance, which may result in failure to obtain high output.

[0217] The thickness of the negative electrode is not particularly limited, but from the perspective of high capacity and high power, the thickness of the composite sheet after subtracting the thickness of the metal foil of the current collector is preferably 10 μm or more, more preferably 20 μm or more, and also preferably 500 μm or less, more preferably 450 μm or less, as a lower limit with respect to one side of the current collector.

[0218] (Solid-state secondary battery)

[0219] The present disclosure is also a solid secondary battery using the composite sheet for the secondary battery described above.

[0220] As for the solid secondary battery, it may be an all-solid secondary battery, or a hybrid solid secondary battery combining a gel-type polymer electrolyte and a solid electrolyte.

[0221] In addition, it is preferable that the solid secondary battery be a lithium-ion battery.

[0222] The solid secondary battery of the present disclosure is a solid secondary battery comprising a positive electrode, a negative electrode, and a solid electrolyte layer interposed between said positive electrode and said negative electrode, wherein the positive electrode, negative electrode, and solid electrolyte layer contain a positive electrode sheet, a negative electrode sheet, or a solid electrolyte layer sheet, which is a composite sheet for a secondary battery of the present disclosure described above. Furthermore, the solid secondary battery of the present disclosure may use a material other than the composite sheet for a secondary battery of the present disclosure in a part of the positive electrode, negative electrode, and solid electrolyte layer.

[0223] The stacked structure of the solid secondary battery of the present disclosure comprises a positive electrode having a positive electrode sheet and a positive electrode current collector, a negative electrode having a negative electrode sheet and a negative electrode current collector, and a sulfide-based solid electrolyte layer fitted and supported on the positive electrode and the negative electrode.

[0224] Hereinafter, a separator and a battery case used in a solid-state secondary battery according to the present disclosure will be described in detail.

[0225] (Separator)

[0226] The solid secondary battery of the present disclosure may be provided with a separator between the positive electrode and the negative electrode. Examples of the separator include a porous membrane such as polyethylene or polypropylene; and a nonwoven fabric such as a nonwoven fabric made of a resin such as polypropylene or a glass fiber nonwoven fabric.

[0227] (Battery Design)

[0228] The solid secondary battery of the present disclosure may further comprise a battery case. The shape of the battery case used in the present disclosure is not particularly limited as long as it is capable of accommodating the positive electrode, negative electrode, and electrolyte layer for a sulfide-based solid battery described above, but specifically, cylindrical, prismatic, coin, laminated types may be provided.

[0229] The method for manufacturing a solid secondary battery of the present disclosure may, for example, first stack the positive electrode, the solid electrolyte layer sheet, and the negative electrode in sequence and press them to form a solid secondary battery.

[0230] By using the composite sheet for secondary batteries disclosed in the present disclosure, it is possible to manufacture a solid secondary battery in a state with low moisture content in the system, and it is suitable for producing a solid secondary battery having good performance.

[0231] Examples

[0232] The present disclosure will be described in detail below based on examples.

[0233] In the following examples, unless otherwise specifically stated, “parts” and “%” represent “parts by mass” and “mass%”, respectively.

[0234] [Production Example 1]

[0235] At the point when 367 g of TFE (35.6 mass% relative to the total polymerization amount of 1032 g of TFE) was consumed from the start of polymerization, an aqueous solution of 12.0 mg of hydroquinone dissolved in 20 ml of water as a radical scavenger was injected into the TFE (concentration of 4.0 ppm relative to the aqueous medium). Polymerization continued thereafter, and when the polymerization amount of TFE reached 1000 g from the start of polymerization, the supply of TFE was stopped, the gas in the system was immediately released to atmospheric pressure, and the polymerization reaction was terminated to obtain a polytetrafluoroethylene aqueous dispersion (solid content 31.2 mass%). The obtained polytetrafluoroethylene aqueous dispersion was diluted to a solid content concentration of 15% and solidified by quietly stirring in the presence of nitric acid in a vessel equipped with a stirrer. The solidified polytetrafluoroethylene was separated and dried at 160°C for 18 hours to obtain powdered PTFE-1.

[0236] [Production Example 2]

[0237] Powdered PTFE-2 was prepared by referring to Example 3 of International Publication No. 2015-080291.

[0238] [Production Example 3]

[0239] Powdered PTFE-3 was prepared by referring to Example 1 of International Publication No. 2012 / 086710.

[0240] [Production Example 4]

[0241] Powdered PTFE-4 was prepared by referring to Adjustment Example 1 of International Patent No. 2012-063622.

[0242] The physical properties of the manufactured PTFE are shown in Table 1.

[0243]

[0244] (Example 1)

[0245] Sulfide-based solid electrolyte Li 10 SnP2S 12(LSPS, 0.714Li2S-0.143SnS2-0.143P2S5) (average particle size: 7㎛) and powdered PTFE-1 were weighed and mixed using a high-speed mixer (500 rpm, 1 minute). Stirring was performed after cooling the container to 10°C. Afterward, the mixture was stirred using a high-speed mixer (10,000 rpm, 3 minutes) to obtain a mixture. Stirring was performed after heating the container to 60°C.

[0246] The solid content was set so that the mass ratio of solid electrolyte to binder was 98.5:1.5.

[0247] In addition, powdered PTFE-1 was dried in a vacuum dryer at 50°C for 1 hour. Powdered PTFE was previously sieved using a stainless steel sieve with a mesh size of 500 μm, and the residue remaining on the sieve was used.

[0248] The obtained mixture was formed into a bulk form and rolled into a sheet. Rolling was performed by heating to 80°C.

[0249] After that, the previously obtained rolled sheet was crushed by folding it into two pieces, formed back into a bulk form, and then rolled into a sheet using a metal roll on a flat plate to promote fibrillation, a process that was repeated four times. After that, by rolling further, a sheet-like solid electrolyte layer with a thickness of 500 μm was obtained. In addition, the sheet-like solid electrolyte layer was cut, fed into a press machine, and rolled.

[0250] In addition, the thickness was adjusted by repeatedly applying a load of 5 kN. The gap was adjusted so that the final thickness of the solid electrolyte layer was 120 μm. Furthermore, the above operation was performed inside an Ar glow box (dew point approximately -80°C).

[0251] (Example 2)

[0252] Sulfide-based solid electrolyte Li 10 SnP2S 12(LSPS) and powdered PTFE-2 were weighed, and sheet molding was performed in the same procedure as in Example 1. The composition ratio was adjusted to the mass ratio listed in Table 2.

[0253] (Example 3)

[0254] Sulfide-based solid electrolyte Li 10 SnP2S 12 (LSPS) and powdered PTFE-3 were weighed, and sheet molding was performed in the same procedure as in Example 1. The composition ratio was adjusted to the mass ratio listed in Table 2.

[0255] (Example 4)

[0256] Sulfide-based solid electrolyte Li 10 SnP2S 12 (LSPS) and powdered PTFE-4 were weighed, and sheet molding was performed in the same procedure as in Example 1. The composition ratio was adjusted to the mass ratio listed in Table 2.

[0257] (Example 5)

[0258] A sulfide-based solid electrolyte Li6PS5Cl (LPSCl, 0.625Li2S-0.25LiCl-0.125P2S5) (average particle size: 8 μm) and powdered PTFE-1 were weighed, and sheet molding was performed in the same procedure as in Example 1. The composition ratio was adjusted to the mass ratios listed in Table 2.

[0259] (Example 6)

[0260] Positive electrode active material LiNi 0.8 Mn 0.1 Co 0.1 O2, sulfide-based solid electrolyte LPSCl (average particle size: 8 μm), and powdered PTFE-1 were weighed, and sheet molding was performed in the same procedure as in Example 1. The composition ratio was adjusted to the mass ratio listed in Table 3.

[0261] (Example 7)

[0262] Positive electrode active material LiNi 0.8 Co 0.15 Al 0.05O2, sulfide-based solid electrolyte LPSCl (average particle size: 8 μm), and powdered PTFE-1 were weighed, and sheet molding was performed in the same procedure as in Example 1. The composition ratio was adjusted to the mass ratio listed in Table 3.

[0263] (Example 8)

[0264] Sulfide-based solid electrolyte Li 10 GeP2S 12 (LGPS, manufactured by Ampcera, average particle size: 18 μm) and powdered PTFE-2 were weighed, and sheet molding was performed in the same procedure as in Example 1. The composition ratio was adjusted to the mass ratio listed in Table 3.

[0265] Each test was conducted using the following methods.

[0266] [Measurement of moisture content]

[0267] Powdered PTFE was dried in a vacuum dryer at 50°C for 1 hour. The moisture content of the PTFE after vacuum drying was measured using a Karl Fischer moisture meter (ADP-511 / MKC-510N, manufactured by Kyoto Denshi Kogyo Co., Ltd.) equipped with a boat-type moisture vaporizer. The moisture was heated to 210°C in the moisture vaporizer to measure the vaporized moisture. Nitrogen gas was flowed as a carrier gas at a flow rate of 200 mL / min, and the measurement time was set to 30 minutes. Additionally, ChemAqua was used as the Karl Fischer reagent. The sample weight was 1.5 g.

[0268] [Median Fibril Diameter of PTFE]

[0269] (1) An image is obtained by taking a magnified photograph (7000x) of the sheet-like solid electrolyte layer using a scanning electron microscope (S-4800 type, manufactured by Hitachi Seisakusho).

[0270] (2) Divide the image into three equal parts by drawing two lines horizontally at equal intervals.

[0271] (3) For all PTFE fibers on the straight line above, the diameter of each PTFE fiber is measured at three locations, and the average value is taken as the diameter of the PTFE fiber. The three measurement locations are selected as the intersection point between the PTFE fiber and the straight line, and locations offset by 0.5 μm upward and downward from the intersection point (excluding primary PTFE particles that have undergone microfiberization).

[0272] (4) The above operation (3) is performed on all PTFE fibers in the straight line below.

[0273] (5) Move 1 mm to the right of the screen starting from the first image and take another picture, and measure the diameter of the PTFE fibers according to (3) and (4) above. Repeat this process until the number of measured fibers exceeds 80, at which point the process ends.

[0274] (6) The median value of the diameters of all PTFE fibers measured above was taken as the size of the fibril diameter.

[0275] [Ion Conductivity Measurement]

[0276] Conductivity was measured by the following method.

[0277] After fabricating a gold electrode on the surface of the prepared solid electrolyte sheet by sputtering, it was punched to a diameter of Φ10 mm. It was inserted into a stainless steel current collector, sealed, and used as a measuring cell. After leaving this cell in a constant temperature bath at 80°C for 12 hours, AC impedance measurements were performed using an impedance analyzer (Solartron Model 1260) in a frequency range of 0.1 Hz to 8 Hz, and the ionic conductivity was determined.

[0278] [Flexibility Assessment]

[0279] The prepared solid electrolyte sheet was cut into a length of 2 cm and a width of 6 cm to serve as a test specimen. After being wound onto a 4 mm diameter rod, the test specimen was visually inspected and evaluated according to the following criteria. It was evaluated as ○ if no defects or cracks were found, and × if cracks were found.

[0280] [Intensity Measurement]

[0281] Measurements were taken using a digital force gauge (Imada ZTS-20N) on a rectangular electrode composite test specimen 4 mm wide under a condition of 100 mm / min. The spacing between rods was set to 30 mm. Displacement was applied until fracture, and the maximum stress measured was taken as the strength of each sample. The test was performed five times, and the average value was used as the evaluation result.

[0282] The test results are shown in Tables 2 and 3.

[0283]

[0284]

[0285] From the results of Tables 2 and 3, the sheet-like solid electrolyte layer of the example had excellent physical properties.

[0286] Next, a gold electrode was fabricated on the surface of the positive electrode composite sheet prepared in Example 8 by sputtering, and then the solid electrolyte sheet prepared in Example 2, the Li foil, and the insulating sheet were overlapped and integrated by uniaxial molding for 3 minutes under a load of 60 kN, and a half cell was fabricated by punching to a diameter of 10 mm. The fabricated half cell was placed in a flat cell and left in a bath at 25°C for 12 hours. Charging and discharging were performed at 0.1 C (0.05 C cut).

[0287] As a result of performing 8 cycles of charge and discharge, the capacity retention rate at the 8th cycle was 98.4% when the 3rd cycle was set to 100%. Industrial applicability

[0288] The composite for secondary batteries and the composite sheet for secondary batteries containing the same of the present disclosure can be used in the manufacture of solid secondary batteries.

Claims

Claim 1 A composite for a secondary battery containing a sulfide-based solid electrolyte and a binder, wherein the fibril resin that serves as the binder is a fibril resin having a fibrous structure with a fibril diameter (median value) of 70 nm or less, the content of the binder is 0.3 mass% or more and 1.5 mass% or less in the composite for the secondary battery, and the average particle size of the sulfide solid electrolyte is 0.1 μm or more and 20 μm or less. Claim 2 A composite for a secondary battery according to claim 1, wherein the fibril resin is polytetrafluoroethylene resin. Claim 3 A composite for a secondary battery according to claim 1 or 2, wherein the sulfide solid electrolyte is represented by the following formula (A). (where 0.6≤a≤0.86, 0≤b≤0.333, 0≤c≤0.3, 0.05≤b+c≤0.4, X 1 Silver is Ge, Sn, Ti, or Si, X 2 represents Cl, Br, or I, provided that neither b nor c is 0. Claim 4 A composite for a secondary battery, wherein, in paragraph 1 or 2, it is for a lithium-ion solid secondary battery. Claim 5 A secondary battery composite according to claim 1, wherein the secondary battery composite is obtained using a raw material composition containing a sulfide-based solid electrolyte and a binder, and the binder in the raw material composition is a powdered fibril-like resin. Claim 6 In paragraph 5, the raw material composition is a composite for a secondary battery that substantially does not contain a liquid medium. Claim 7 In claim 5 or 6, the powdered fibril resin is a composite for secondary batteries having a moisture content of 500 ppm or less. Claim 8 A composite for a secondary battery according to claim 5 or 6, wherein the powdered fibril resin is a powdered polytetrafluoroethylene resin. Claim 9 In claim 8, the powdered polytetrafluoroethylene resin is a composite for secondary batteries having a standard specific gravity of 2.12 to 2.

20. Claim 10 In claim 8, the powdered polytetrafluoroethylene resin comprises 50 mass% or more of a polytetrafluoroethylene resin having a secondary particle size of 450 μm or more, for use in a secondary battery composite. Claim 11 A composite sheet for a secondary battery comprising the composite for a secondary battery described in paragraph 1 or 2. Claim 12 A method for manufacturing a composite sheet for a secondary battery, comprising a process (1) of applying shear force while mixing a raw material composition including a sulfide-based solid electrolyte and a binder, a process (2) of forming the composite for a secondary battery obtained by the process (1) into a bulk form, and a process (3) of rolling the bulk composite for a secondary battery obtained by the process (2) into a sheet form, wherein the binder is a powdered fibril resin, and the content of the binder in the manufactured composite sheet for a secondary battery is 0.3 mass% or more and 1.5 mass% or less of the composite for a secondary battery, and the fibril resin has a fibrous structure with a fibril diameter (median value) of 70 nm or less, and the average particle size of the sulfide solid electrolyte is 0.1 μm or more and 20 μm or less. Claim 13 A solid secondary battery having a composite sheet for a secondary battery as described in Clause 11. Claim 14 delete Claim 15 delete

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