Elastic sheet for all-solid-state secondary battery and all-solid-state secondary battery module

Abstract

Provided is an elastic sheet that has sufficient flame retardancy and is capable of repeatedly absorbing volume changes caused by expansion and contraction of an all-solid-state secondary battery. The elastic sheet for an all-solid-state secondary battery buffers volume changes caused by expansion and contraction of the all-solid-state secondary battery and is composed of a closed-cell foam formed of a fluorine-based elastomer, wherein the porosity of the foam is 40% or more and 70% or less.

Description

Elastic sheets for all-solid-state secondary batteries and all-solid-state secondary battery modules

[0001] The present invention relates to an elastic sheet for an all-solid-state secondary battery and an all-solid-state secondary battery module having the elastic sheet for an all-solid-state secondary battery.

[0002] All-solid-state secondary batteries, because they do not contain organic electrolytes, offer relatively high safety. To further enhance the safety of all-solid-state secondary batteries, countermeasures are being considered to address external risk factors, such as moisture intrusion from the outside environment due to cracks, which can trigger an exothermic reaction with lithium within the battery. One such countermeasure involves placing a flame-retardant resin layer around the all-solid-state secondary battery.

[0003] Additionally, all-solid-state secondary batteries expand and contract in volume due to charging and discharging or temperature changes. Therefore, to prevent damage to restraint members due to such expansion and contraction, for example, the placement of a resin layer between all-solid-state secondary batteries is being considered.

[0004] In this way, conventional examples of placing a resin layer between all-solid-state secondary batteries are disclosed in patent documents. A resin layer is placed within an all-solid-state secondary battery module comprising multiple all-solid-state secondary batteries, and a filler is added to this resin layer to impart flame retardancy.

[0005] However, due to the addition of fillers, the resin layers described in the aforementioned patent documents lose their elasticity. Therefore, using a resin layer to impart flame retardancy poses the problem of not being able to repeatedly absorb volume changes due to expansion and contraction of the all-solid-state secondary battery.

[0006] The problem to be solved by the present invention is to provide an elastic sheet within an all-solid-state secondary battery, thereby ensuring sufficient flame retardancy and at the same time being able to repeatedly absorb and cushion volume changes due to expansion and contraction of the all-solid-state secondary battery.

[0007] The elastic sheet and the all-solid-state secondary battery module having the elastic sheet according to the present invention are as follows.

[0008] According to one embodiment of the present invention, an elastic sheet for an all-solid-state secondary battery is provided that buffers volume changes due to expansion and contraction of the all-solid-state secondary battery. The elastic sheet for the all-solid-state secondary battery is composed of an independent foam formed of a fluorine-based elastomer, and the porosity of the foam may be 40% or more and 70% or less.

[0009] When the entire fluorine-based elastomer is 100 mass%, the content of fluorine element contained in the elastic sheet for the all-solid-state secondary battery may be 60 mass% or more and 80 mass% or less.

[0010] When an external pressure of 0.1 MPa is applied to the above-mentioned elastic sheet for a solid-state secondary battery, the deformation may be 10% or less.

[0011] The stress retention rate of the above-mentioned elastic sheet for a solid-state secondary battery may be 80% or more.

[0012] The thickness of the above-mentioned elastic sheet for the all-solid-state secondary battery may be 10㎛ or more and 1000㎛ or less.

[0013] The flame retardancy UL94 evaluation of the above-mentioned elastic sheet for all-solid-state secondary batteries may be V-0.

[0014] When the above-mentioned elastic sheet for a solid-state secondary battery is brought into contact with metallic lithium for 4 days, there may be no change in the infrared absorption spectrum before and after the contact.

[0015] The mass change rate before and after the above-mentioned elastic sheet for the all-solid-state secondary battery is brought into contact with a sulfide-based solid electrolyte for 30 days may be less than 1%.

[0016] The above-mentioned elastic sheet for an all-solid-state secondary battery may have electrical insulation properties.

[0017] According to one embodiment of the present invention, an all-solid-state secondary battery module may be provided. The all-solid-state secondary battery module may include the aforementioned elastic sheet for an all-solid-state secondary battery, an all-solid-state secondary battery, and a case housing them therein.

[0018] According to the present invention, an all-solid-state secondary battery can have sufficient flame retardancy. By placing an elastic sheet between multiple all-solid-state secondary batteries, fire occurrence within the all-solid-state secondary battery module can be suppressed, thereby improving safety. The elastic sheet according to the present invention can repeatedly absorb volume changes due to expansion and contraction of the all-solid-state secondary battery.

[0019] As a result, the unevenness of pressure within the all-solid-state secondary battery module is sufficiently suppressed and current concentration in a part of the all-solid-state secondary battery is prevented, thereby maintaining the cycle characteristics of the all-solid-state secondary battery module for a longer period of time than before.

[0020] FIG. 1 is a schematic diagram showing a schematic configuration of an all-solid-state secondary battery module according to one embodiment of the present invention.

[0021] Figure 2 is a cross-sectional schematic diagram showing a schematic configuration of an all-solid-state secondary battery module according to one embodiment of the present invention.

[0022] FIG. 3 is a cross-sectional schematic diagram showing the structure of an all-solid-state secondary battery and an elastic sheet provided in an all-solid-state secondary battery module according to one embodiment of the present invention.

[0023] Figure 4 is a cross-sectional schematic diagram showing the structure of an all-solid-state secondary battery according to one embodiment of the present invention.

[0024] Hereinafter, the best embodiments of the present invention will be described in detail with reference to the attached drawings. In this specification and drawings, components with substantially the same functions and configurations are assigned the same reference numerals, and redundant descriptions are omitted. Furthermore, components in the drawings are appropriately enlarged or reduced for convenience of explanation, and the sizes and proportions of components may differ from the actual figures.

[0025] <1. Configuration of an all-solid-state secondary battery module according to one embodiment>

[0026] As illustrated in FIGS. 1 and 2, an all-solid-state secondary battery module (100) according to one embodiment comprises a case (C), one or more all-solid-state secondary batteries (A) accommodated within the case (C), and one or more elastic sheets (B).

[0027] Below, each component is explained.

[0028] <1-1. Case>

[0029] As illustrated in FIGS. 1 and 2, the case (C) accommodates a plurality (e.g., 13) of all-solid-state secondary batteries (A) and a plurality (here, 14) of elastic sheets (B) by stacking them therein.

[0030] The case (C) may have, for example, a rectangular parallelepiped shape and may be formed of a metal such as aluminum or an aluminum laminate film. The case (C) may have, for example, three sets of facing surfaces having different areas, and the facing surface having the smallest area may be a bottom surface (S). A plurality of all-solid-state secondary batteries (A) and a plurality of elastic sheets (B) may be laminated in a height direction perpendicular to the bottom surface (S). The case (C) accommodates the all-solid-state secondary batteries (A) and the elastic sheets (B) so that no gap is formed inside the case in the height direction. When the case (C) is formed of a soft material such as an aluminum laminate film, the all-solid-state secondary batteries (A) and the plurality of elastic sheets (B) may be accommodated and then sealed under pressure so that no gap is formed inside the case.

[0031] <1-2. All-solid-state secondary batteries>

[0032] An all-solid-state secondary battery (A) according to one embodiment may include a positive electrode layer (10), a negative electrode layer (20), and a solid electrolyte layer (30). For example, as illustrated in FIG. 3, the all-solid-state secondary battery (A) may include a positive electrode layer (10), a solid electrolyte layer (30) laminated on both sides of the positive electrode layer (10) with the positive electrode layer (10) interposed therebetween, and a negative electrode layer (20) laminated on the opposite side of the all-solid-state secondary battery (A) and the positive electrode layer (10). Meanwhile, the lamination direction of each layer constituting the all-solid-state secondary battery (A) is the same as the direction in which the all-solid-state secondary battery (A) and the elastic sheet (B) are laminated.

[0033] (1-2-1. Bipolar layer)

[0034] As illustrated in FIG. 3, the positive electrode layer (10) may include a positive electrode current collector (11) and a positive electrode active material layer (12).

[0035] The positive electrode current collector (11) may be composed of, for example, stainless steel, titanium, nickel, aluminum, or an alloy thereof. The positive electrode current collector (11) may have a plate shape or a foil shape. The thickness of the positive electrode current collector (11) may be, for example, 1 μm or more and 50 μm or less, more preferably 5 μm or more and 30 μm or less.

[0036] As illustrated in Fig. 3, a positive electrode active material layer (12) may be provided on both sides of a positive electrode current collector (11). The positive electrode active material layer (12) may contain at least a positive electrode active material and a solid electrolyte.

[0037] The solid electrolyte contained in the positive electrode active material layer (12) may be the same as the solid electrolyte contained in the solid electrolyte layer (30). However, it is not limited thereto. Details of the solid electrolyte are described in the solid electrolyte layer (30) section described later.

[0038] The cathode active material can reversibly absorb and desorb lithium ions.

[0039] The cathode active material may be, for example, in powder or granular form, and may be formed of a lithium salt such as lithium cobalt oxide (LCO), lithium nickel oxide, lithium nickel cobalt oxide, lithium nickel cobalt aluminum oxide (NCA), lithium nickel cobalt manganese oxide (NCM), lithium manganate, or lithium iron phosphate. Furthermore, the cathode active material may be formed of nickel sulfide, copper sulfide, sulfur, iron oxide, or vanadium oxide. These cathode active materials may be used alone, or may be formed by combining two or more thereof.

[0040] It is preferable that the cathode active material be formed to contain a lithium salt of a transition metal oxide having a layered rock salt structure. Here, 'layered' means a thin sheet-like shape. In addition, the 'rock salt structure' means a sodium chloride structure, which is one of the crystal structures, and specifically, it means a structure in which face-centered cubic lattices formed by cations and anions respectively are arranged to be offset from each other by half of the ridge of the unit cell.

[0041] Lithium salts of transition metal oxides having this layered rock salt structure are, for example, LiNi x Co y Al z O2(NCA) or LiNi x Co y Mn z O2(NCM) (but, 0 <x <1, 0 <y <1, 0 <z <1, 그리고 x+y+z=1)과 같은 삼원계 전이 금속산화물의 리튬염을 함유할 수 있다.

[0042] When the positive electrode active material contains a lithium salt of a ternary transition metal oxide having the layered rock salt structure, the energy density of the all-solid-state secondary battery (A) can be improved.

[0043] The positive electrode active material may be covered by a coating layer. The coating layer of the present embodiment may be any known coating layer for the positive electrode active material of the all-solid-state secondary battery (A). Examples of the coating layer may be, for example, LiNBO3, Li2WO4, or Li2-ZrO2.

[0044] Furthermore, when the positive electrode active material is formed of a lithium salt of a ternary transition metal oxide such as NCA or NCM and the positive electrode active material contains nickel, the capacity density of the all-solid-state secondary battery (A) can be increased.

[0045] Here, the positive electrode active material may have a particle shape, such as, for example, a true spherical shape or an elliptical spherical shape. In addition, the particle size of the positive electrode active material is not particularly limited, and may be within a range applicable to positive electrode active materials of conventional all-solid-state secondary batteries. Meanwhile, the content of the positive electrode active material in the positive electrode layer (10) is not particularly limited, and may be within a range applicable to positive electrode layers of conventional all-solid-state secondary batteries.

[0046] In addition, in addition to the above-described positive electrode active material and solid electrolyte, additives such as a conductive additive, a binder, a filler, a dispersant, or an ion conductive additive may be appropriately blended into the positive electrode active material layer (12).

[0047] The conductive additive that can be mixed into the positive electrode active material layer (12) may be, for example, graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanotube, graphene, or metal powder. In addition, the binder that can be mixed into the positive electrode active material layer (12) may be, for example, styrene-butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, a copolymer of vinylidene fluoride and 2,3,3,3-tetrafluoropropylene, polyethylene, or a denaturation thereof. Moreover, fillers, dispersants, and ion conductive agents that can be mixed into the positive electrode active material layer (12) can be known materials that can be generally used in the electrode of an all-solid-state secondary battery (A).

[0048] The thickness of a completed battery using a positive electrode active material layer (12) is not particularly limited, but is preferably 20 µm or more and 1000 µm or less, more preferably 50 µm or more and 500 µm or less, and particularly preferably 100 µm or more and 300 µm or less.

[0049] (1-2-2. Cathode layer)

[0050] The negative electrode layer (20) may include, for example, a positive electrode current collector (21) in a plate shape or foil shape, as shown in FIG. 3, and a negative electrode active material layer (22) formed on the negative electrode current collector (21).

[0051] In this embodiment, the negative electrode collector (21) can constitute the outermost layer of the all-solid-state secondary battery (A).

[0052] The negative electrode current collector (21) does not react with lithium. That is, it is preferable that the negative electrode current collector (21) be composed of a material that does not contain any alloy or compound. The material constituting the negative electrode current collector (21) may be, for example, copper, titanium, iron, cobalt, or nickel, in addition to stainless steel. The negative electrode current collector (21) may be composed of any one of these metals, or may be composed of an alloy of two or more metals or a cladding material.

[0053] The thickness of the negative electrode current collector (21) is, for example, 1 µm or more and 50 µm or less, more preferably 5 µm or more and 30 µm or less.

[0054] The negative electrode active material layer (22) may include, for example, at least one of a negative electrode active material that forms an alloy with lithium and a negative electrode active material that forms a compound with lithium. In addition, by containing such a negative electrode active material, the negative electrode active material layer (22) may be configured to deposit metallic lithium on the surface of one or both sides of the negative electrode active material layer (22), as described below.

[0055] The negative active material may be, for example, graphite, amorphous carbon, gold, platinum, palladium, silicon, silver, aluminum, bismuth, tin, antimony, or zinc.

[0056] Here, the amorphous carbon may be, for example, carbon black such as acetylene black, furnace black, and ketjen black, or graphene.

[0057] The shape of the negative active material may be granular, but is not particularly limited thereto, and may be a uniform layer, such as a plating layer, for example.

[0058] Lithium ions or lithium may be completely absorbed into the interior of the anode active material, or into the interior of the anode active material or the plating layer. Alternatively, lithium ions or lithium may pass through the gaps between the anode active materials to form a metal layer mainly composed of lithium between the anode active material layer (22) and the anode current collector (21), and some of the lithium may form an alloy with the metal element in the anode active material and exist in the anode active material layer (22).

[0059] When the negative active material layer (22) is amorphous carbon, the specific surface area measured by the nitrogen gas adsorption method is 10 m 2 / g or more and 100m 2 / g or less is preferable.

[0060] The negative electrode active material layer (22) may contain one or two or more of these negative electrode active materials. For example, the negative electrode active material may have only amorphous carbon. Alternatively, the negative electrode active material may include one or more selected from the group consisting of gold, platinum, palladium, silicon, silver, aluminum, bismuth, tin, antimony, and zinc. Furthermore, the negative electrode active material may include a mixture of one or more selected from the group consisting of gold, platinum, palladium, silicon, silver, aluminum, bismuth, tin, antimony, and zinc and amorphous carbon.

[0061] The mixing ratio (mass ratio) of the mixture of amorphous carbon and the aforementioned metal, such as gold, is preferably about 1:2 to 4:1. By composing the negative active material with such a material, the characteristics of the all-solid-state secondary battery (A) can be further improved.

[0062] When at least one selected from the group consisting of gold, platinum, palladium, silicon, silver, aluminum, bismuth, tin, antimony, and zinc is used together with amorphous carbon as the negative active material, the particle size of the negative active material is preferably 4 μm or less. In this case, the characteristics of the all-solid-state secondary battery (A) can be further improved.

[0063] In addition, when a material capable of forming an alloy with lithium (for example, at least one selected from the group consisting of gold, platinum, palladium, silicon, silver, aluminum, bismuth, tin, antimony, and zinc) is used as the negative electrode active material, the negative electrode active material layer (22) may be a layer made of such a metal. For example, this metal layer may be a plating layer.

[0064] If necessary, the negative electrode active material layer (22) may additionally contain a binder. The binder may be, for example, styrene butadiene rubber, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene oxide, carboxymethylcellulose, or an alkali metal salt, an ammonium salt, or a modified product thereof. The binder may be composed of one type or two or more types thereof. By containing such a binder in the negative electrode active material layer (22), the detachment of the negative electrode active material can be suppressed, especially when the negative electrode active material is in a granular form. The content of the binder contained in the negative electrode active material layer (22) is, for example, 0.3 mass% or more and 20.0 mass% or less, preferably 1.0 mass% or more and 15.0 mass% or less, and more preferably 3.0 mass% or more and 15.0 mass% or less, with respect to the total mass of the negative electrode active material layer (22).

[0065] In addition, the negative electrode active material layer (22) may further include a solid electrolyte, a negative electrode layer conductive agent, and additives contained in a conventional all-solid-state secondary battery (A).

[0066] The negative electrode layer conductive agent and solid electrolyte may be the same compound as the conductive agent and solid electrolyte contained in the positive electrode active material layer (12). Therefore, a description of their composition is omitted.

[0067] The thickness of the negative electrode active material layer (22) in a state completed as a battery is not particularly limited, but when the negative electrode active material is granular, it is, for example, 1 µm or more and 1000 µm or less. Lithium ions or lithium can pass through the gap between the negative electrode active materials to form a metal layer mainly composed of lithium between the negative electrode active material layer (22) and the negative electrode current collector (21). When a portion of the lithium forms an alloy with a metal element in the negative electrode active material and exists in the negative electrode active material layer (22), the thickness of the negative electrode active material layer (22) in a state completed as a battery is preferably 2 µm or more and 20 µm or less. By making it with such a thickness, the resistance value of the negative electrode active material layer (22) can be sufficiently reduced, and the characteristics of the all-solid-state secondary battery (A) can be improved.

[0068] (1-2-3. Solid electrolyte layer)

[0069] As shown in FIG. 3, the solid electrolyte layer (30) is formed between, for example, the anode layer (10) and the cathode layer (20) and includes a solid electrolyte.

[0070] The thickness of the solid electrolyte layer (30) in a completed battery state is preferably 5 µm or more and 100 µm or less, more preferably 8 µm or more and 80 µm or less, and even more preferably 10 µm or more and 50 µm or less.

[0071] The solid electrolyte may be, for example, in powder form and composed of a sulfide-based solid electrolyte material. The sulfide-based solid electrolyte material may be, for example, Li2S-P2S5, Li2S-P2S5-LiX (wherein X is a halogen element, for example, I, Br, Cl), Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-Z. m S n (m, n are defined numbers, Z is any one of Ge, Zn or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, or Li2S-SiS2-Li p MO q (p, q are integers, M can be any one of P, Si, Ge, B, Al, Ga or In). Here, the sulfide-based solid electrolyte material can be manufactured by performing a treatment such as a melting quenching method or mechanical milling on the starting raw material (e.g., Li2S, P2S5, etc.). In addition, an additional heat treatment can be provided after performing such treatment. The solid electrolyte can be amorphous, crystalline, or a mixed state thereof.

[0072] Among these, Li6PS5Cl, a solid electrolyte material with an argyrodite-type crystal structure (argyrodite system), is easy to control in particle size and can be highly packed by miniaturization, thereby forming a good interface with the positive electrode active material. In addition, Li6PS5Cl has a wide electric potential window, excellent withstand voltage characteristics, an established mass production process, and is an attractive material in terms of price.

[0073] In addition to the above, the solid electrolyte material is Li6PS5Br of the argyrodite system.x Cl 1-x , or it can be Li2S-P2S5-LiX (X=Br or I) of glass ceramic system.

[0074] The solid electrolyte layer (30) may further contain a binder. The binder contained in the solid electrolyte layer (30) may be, for example, styrene butadiene rubber (SBR), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), a copolymer of vinylidene fluoride and hexafluoropropylene, a copolymer of vinylidene fluoride and 2,3,3,3-tetrafluoropropylene, polyethylene (PE), polyacrylic acid (PAA), a copolymer of acrylic acid ester, or a modified product thereof. The binder contained in the solid electrolyte layer (30) may be the same type as the binder in the positive electrode active material layer (12) and the negative electrode active material layer (22), but is not limited thereto and may be a different type.

[0075] (1-2-4. Power supply unit)

[0076] As illustrated in FIGS. 1 and 2, the positive electrode current collector (11) includes a positive electrode current collecting part (111) protruding on one side thereof and is connected to external wiring through the positive electrode current collecting part (111). Similarly, the negative electrode current collector (21) includes a negative electrode current collecting part (211) protruding on the other side thereof and is connected to external wiring through the negative electrode current collecting part (211).

[0077] Moreover, the one side / the other side in this specification refers to, for example, a direction facing outward along the surface from the outer rim of the positive electrode current collector, and more specifically, a direction perpendicular to the stacking direction of each layer constituting the all-solid-state secondary battery (A).

[0078] <1-3. Elastic sheet>

[0079] The elastic sheet (B) according to the present embodiment may have a rectangular shape in plan view, which may be a film shape, a sheet shape, or a plate shape. The elastic sheet (B) is arranged so that the thickness direction is aligned with the stacking direction of the all-solid-state secondary battery (A), so that it can absorb volume changes due to expansion and contraction of the all-solid-state secondary battery (A).

[0080] The elastic sheet (B) according to the present embodiment is provided between neighboring solid-state secondary batteries (A), and between the solid-state secondary batteries (A) and the case (C) at both ends in the stacking direction, for example, as shown in FIG. 1 or FIG. 2.

[0081] As described above, lithium metal may be precipitated on the negative electrode when the all-solid-state secondary battery (A) according to the present embodiment is charged. In this case, precipitation and elution of lithium metal may occur during charging and discharging, and a relatively large volume change may occur in the stacking direction.

[0082] The elastic sheet (B) according to the present embodiment, arranged as described above, contracts in response to the expansion of the all-solid-state secondary battery (A) when charging the all-solid-state secondary battery (A), and when discharging the all-solid-state secondary battery (A), the elastic sheet (B) itself can uniformly restore the all-solid-state secondary battery (A) to its original volume by the compressive force (elasticity) of the elastic sheet (B). Therefore, a charge / discharge reaction can occur uniformly throughout each of the all-solid-state secondary batteries (A) within the case (C).

[0083] For the function as described above, the elastic sheet (B) is preferably provided so that the area of ​​each elastic sheet (B) is equal to or larger than the area of ​​each solid-state secondary battery (A) when viewed in the stacking direction of the solid-state secondary battery (A) (i.e., from a planar perspective), so as to cover the portion excluding the positive electrode collector (111) and the negative electrode collector (211) of the solid-state secondary battery (A).

[0084] In addition, it is preferable that the thickness of each elastic sheet (B) be set so that the total value thereof is greater than the total value of the thickness change amount due to charging and discharging in the stacking direction of the all-solid-state secondary battery (A).

[0085] Since the elastic sheet (B) is a subsidiary material included in the all-solid-state secondary battery module (100) but does not contribute to energy accumulation as a battery, it is preferable that the thickness of the elastic sheet (B) be small in order to increase the energy density per volume of the all-solid-state secondary battery module (100) as much as possible. The thickness of the elastic sheet (B) is preferably 10 ㎛ or more and 1000 ㎛ or less, more preferably 50 ㎛ or more and 80 ㎛ or less, and still more preferably 100 ㎛ or more and 600 ㎛ or less.

[0086] The thickness of the elastic sheet (B) can be measured, for example, by applying a pressure of approximately 15 kPa to the elastic sheet (B) by using a pressure thickness measuring device: J type PG-01 (measuring element diameter 5 mm) from TECLOCK, and attaching a 5.6 g stainless steel weight to the upper part of the measuring element diameter at room temperature.

[0087] The hardness of the elastic sheet (B) of type A measured by durometer A is preferably in the range of 5 or more and 70 or less, more preferably in the range of 10 or more and 60 or less, and even more preferably in the range of 20 or more and 50 or less. In addition, the hardness of the elastic sheet (B) of type C measured by durometer C is preferably in the range of 10 or more and 80 or less, more preferably in the range of 20 or more and 75 or less, and even more preferably in the range of 30 or more and 70 or less.

[0088] As described above, since the all-solid-state secondary battery (A) has a property of repeating expansion and contraction due to charge and discharge, the elastic sheet (B) can repeatedly absorb the volume change due to such expansion and contraction. From this point of view, it is preferable that the stress retention rate of the elastic sheet (B) is 80% or more and 100% or less. The stress retention rate is calculated from the rate of change in pressure at the time of the first release and at the time of release after a predetermined number of times when compression and release are repeated at a constant thickness ((pressure at release after a predetermined number of times / pressure at first release) × 100).

[0089] According to the present embodiment, since the all-solid-state secondary battery (A) is sealed in a vacuum state inside the case (C) during the manufacture of the all-solid-state secondary battery module (100), it is necessary to lower the pressure inside the case. Since the elastic sheet (B) is a porous, independently bubbled type, when the pressure is lowered, a pressure difference occurs between the inside of the bubble and the outside of the elastic sheet (B), causing deformation (volume change) in the elastic sheet (B), which may make it difficult to precisely stack the all-solid-state secondary battery (A) and the elastic sheet (B). When a pressure of 0.1 MPa is applied to the elastic sheet (B), if the deformation (volume change rate) of the elastic sheet (B) is 10% or less, it is preferable to reduce the deformation (volume change rate) due to the pressure difference between the inside of the bubble and the outside of the elastic sheet (B) when the pressure is lowered. Meanwhile, since the deformation of the elastic sheet (B) according to the present embodiment occurs due to the difference in pressure between the external pressure and the pressure within the independent bubble, the deformation (volume change due to shrinkage) when a pressure of 0.1 MPa is applied and the deformation (volume change due to expansion) when the pressure of 0.1 MPa is lowered may be the same.

[0090] In order to sufficiently suppress fire in the all-solid-state secondary battery module (100), it is preferable that the elastic sheet (B) be flame retardant. Flame retardancy can be evaluated by a vertical combustion test according to the UL94 standard, and it is preferable that it be determined as V-0.

[0091] In order to prevent the properties of the elastic sheet (B) from changing during the operation of the all-solid-state secondary battery (A), it is preferable that the elastic sheet (B) does not react with the components constituting the all-solid-state secondary battery (A). When the all-solid-state secondary battery (A) according to the present embodiment is charged, lithium metal may be precipitated on the negative electrode. In this case, since the elastic sheet may come into contact with the lithium metal, it is preferable that the elastic sheet has low reactivity when in contact with the lithium metal. The reactivity when the elastic sheet (B) comes into contact with the lithium metal can be judged by the change in the infrared absorption spectrum on the surface of the elastic sheet (B) when the elastic sheet (B) and the lithium metal are in contact for 4 days (such as the appearance of a new peak of a size that can be visually confirmed), and it is preferable that there is no change therein. In addition, since the sulfide-based solid electrolyte is generally a highly reactive material, it is preferable that the reactivity between the elastic sheet (B) and the sulfide-based solid electrolyte is low. The reactivity of the elastic sheet (B) and the sulfide-based solid electrolyte can be determined by the mass change rate before and after contact with Li6PS5Cl for 30 days. It is preferable that this mass change rate be zero or less than 1%.

[0092] In order to suppress the risk of internal short circuit due to electrical conduction between the anode layer (10) and the cathode layer (20) by interposing the elastic sheet (B), it is preferable that the elastic sheet (B) have electrical insulation properties.

[0093] Specifically, the elastic sheet (B) according to the present embodiment can be formed as an independent foam made of a fluorinated elastomer. The independent foam type can reduce the size and distribution of the bubble sizes so that the bubbles do not connect with each other, and can make the microscopic physical properties of the elastic sheet (B) uniform. The independent foam type can provide a stress retention rate within a favorable numerical range to achieve the purpose of the present embodiment.

[0094] The porosity of the elastic sheet (B) is preferably 40% or more and 70% or less, more preferably 41% or more and 69% or less, and even more preferably 42% or more and 68% or less.

[0095] Fluorine-based elastomers contain fluorine elements, and when the entire elastomer is 100 mass%, the fluorine element content is preferably 60 mass% or more and 80 mass% or less, and more preferably 65 mass% or more and 75 mass% or less. Such fluorine elastomers may be, for example, fluoroelastomers (FKM) or perfluoroelastomers (FFKM). The fluorine element content is measured using a theoretical value calculated from the molecular structural formula of the elastomer, but can also be measured by an analysis method such as combustion ion chromatography.

[0096] Such elastic sheets (B) can be formed by heating a composition in which a foaming agent or crosslinking agent is mixed with a fluorinated elastomer, thereby crosslinking and foaming. The fluorinated elastomer can be, for example, the IL series from Daikin Industries, Ltd., the foaming agent can be, for example, the azodicarbonamide-based foaming agent Uniform series from Otsuka Chemical Co., Ltd., and the crosslinking agent can be, for example, the organic peroxide Perhexa series from NOF Corporation.

[0097] <2. Effects of this Example>

[0098] Since the vertical combustion test evaluation of the UL94 standard of the elastic sheet (B) according to the present embodiment is V-0, the elastic sheet (B) can provide sufficient flame retardancy to ensure the safety of the all-solid-state secondary battery module (100). Since the stress retention rate of the elastic sheet (B) according to the present embodiment is 80% or more, the elastic sheet (B) can repeatedly absorb volume changes due to expansion and contraction of the all-solid-state secondary battery (A).

[0099] When an external pressure of 0.1 MPa is applied to the elastic sheet (B) according to the present embodiment, the deformation (change in the thickness direction) is 10% or less, so that the deformation due to the pressure reduction during the manufacture of the all-solid-state secondary battery module (100) is sufficiently small, and the all-solid-state secondary battery (A) and the elastic sheet (B) can be precisely laminated. As a result, the volume change of the all-solid-state secondary battery (A) can be uniformly buffered. Meanwhile, the ability to precisely laminate means that during the process of laminating the all-solid-state secondary battery (A) and the elastic sheet (B), deformation occurs in the elastic sheet (B) that has been decompressively dried in advance, thereby partially reducing the thickness, or deformation occurs in the elastic sheet (B) during decompressing when encapsulating it in an exterior body, thereby partially increasing the thickness, and thus deviating from the direction perpendicular to the lamination direction of the elastic sheet (B) (plane direction) can be suppressed.

[0100] Since it is difficult for the properties of the elastic sheet (B) to change due to a reaction with lithium metal or a solid electrolyte, it is possible to maintain the function of the elastic sheet (B) for a long period of time, thereby maintaining the cycle characteristics of the all-solid-state secondary battery module (100) for a long time.

[0101] Since the elastic sheet (B) according to the present embodiment is formed using a fluorine-based elastomer, it can exhibit sufficiently high flame retardancy even without separately adding a filler or the like as a flame retardant material. As a result, since there is no effect on stress retention rate or the like due to adding a large amount of filler or the like, even when the thickness of the elastic sheet (B) is reduced, it can have the desired elasticity (hardness or stress retention rate) as described above.

[0102] <3. Other embodiments according to the present invention>

[0103] The all-solid-state secondary battery according to the present invention is not limited to the above-described one.

[0104] For example, the elastic sheet according to the above-described embodiment is provided between adjacent all-solid-state secondary batteries and between the all-solid-state secondary batteries and the case at both ends in the stacking direction, but is not limited thereto. The elastic sheet may be provided so that groups of all-solid-state secondary batteries, each of which is composed of a plurality of all-solid-state secondary batteries, are interposed vertically along the stacking direction. In this case, an insulating layer, such as an insulating film, may be provided at a location where an elastic sheet is not arranged between the all-solid-state secondary batteries.

[0105] Additionally, according to the above-described embodiment, the all-solid-state secondary battery and the elastic sheet are accommodated to be stacked from the bottom surface (the surface with the smallest area) of the case of the all-solid-state secondary battery module, but this is not limited thereto. According to another embodiment, the all-solid-state secondary battery and the elastic sheet may be accommodated to be stacked from another surface (the surface that is not the smallest area) of the case.

[0106] For example, as illustrated in FIG. 4, an insulating material that suppresses short circuits between the positive electrode layer and the negative electrode layer can be additionally provided by covering the positive electrode layer or the negative electrode layer in a direction perpendicular to the stacking direction (circumferential direction) around the positive electrode layer or the negative electrode layer of the all-solid-state secondary battery.

[0107] According to the above-described embodiment, an all-solid-state secondary battery having a sandwich structure in which cells are laminated on both ends of a positive electrode collector has been described, but this is not limited thereto. For example, a solid electrolyte and a negative electrode layer may be laminated on only one end of the positive electrode collector.

[0108] Furthermore, although the above-described embodiment described an all-solid-state secondary battery in which a lithium metal layer is deposited on the negative electrode layer, the lithium metal layer may not be deposited on the negative electrode layer. For example, when using a material capable of reversibly absorbing and releasing more lithium ions, such as silicon, the volume of the negative electrode active material changes several times. According to this example, the sum of the thicknesses of the positive electrode layer, the solid electrolyte layer, and the negative electrode layer of each battery unit becomes larger in a fully charged state than in a discharged state.

[0109] In addition, the elastic sheet according to the present invention is not limited to an all-solid-state secondary battery having an all-solid-state lithium ion secondary battery, and can be widely applied to, for example, an all-solid-state secondary battery having a volume change during charging and discharging.

[0110] (Example)

[0111] Below, the present invention will be described with more specific examples, but the present invention is not limited thereto.

[0112] According to the present example, porous sheets formed from various resins as described in Table 1 were evaluated. Meanwhile, the porous sheets used in Examples 1 and 2 and Comparative Examples 1 to 3 were of the independent bubble type. The porous sheet used in Comparative Example 4 was a porous extended sheet that did not contain independent bubbles and was made of a resin that was made porous by extension rather than foaming.

[0113] <Evaluation of porosity>

[0114] The porosity of the porous sheet was calculated as follows.

[0115] First, the mass per volume of the porous sheet was measured and the apparent density was calculated.

[0116] The porosity was calculated from the apparent density and the true density of the resin constituting the porous sheet. The results are shown in Table 1.

[0117] <Flame retardancy evaluation>

[0118] The flame retardancy of the porous sheets was evaluated according to the UL94 50W (20mm) vertical burning test of the UL94 standard; protocols V-0, V-1, and V-2. The results are shown in Table 1. The thickness of the porous sheets used in the test is shown in Table 1, and the test was performed at least five times for each porous sheet.

[0119] <Deformation Evaluation>

[0120] The porous sheets described in Table 1 were cut to the same thickness and volume, and the deformation in the thickness direction when a pressure of 0.1 MPa was applied to these porous sheets was measured. The deformation was defined as a percentage of the thickness before the pressure was applied. The results are shown in Table 1.

[0121] <Stress retention rate evaluation>

[0122] The porous sheet (0.5 mm thick) described in Table 1 was initially subjected to a pressure of 2 MPa, and the pressure was applied until the thickness of the porous sheet was compressed by 50 μm from the initial state, and then the pressure was reduced until the thickness of the porous sheet was expanded by 50 μm from the initial state. This operation was repeated 10 cycles, with one cycle being the pressure retention ratio of the porous sheet divided by the pressure at the first expansion. The results are shown in Table 1.

[0123] <Evaluation of Reaction with Solid Electrolyte>

[0124] A sheet (solid electrolyte sheet) formed of Li6PS5Cl, a sulfide-based solid electrolyte cut to a larger area than the porous sheet, was mounted on a SUS foil, and the porous sheets listed in Table 1 were laminated onto the solid electrolyte sheet so that their entire cross-sections were in direct contact. This laminate was vacuum packed and allowed to stand at 60°C for 30 days. After 30 days, the vacuum pack was opened, the surface of the porous sheet was washed with ethanol, and the solid electrolyte attached to the surface of the porous sheet was removed. After the porous sheet was sufficiently dried, the change in mass of the porous sheet before and after contact with the solid electrolyte was measured, and the change rate (%) in mass of the porous sheet before and after the test was obtained. As a result of the test, the mass change rates of the porous sheets of Example 1, Comparative Example 2, and Comparative Example 4 were less than 1%. The same results can be estimated for Comparative Examples 1, 3 and Example 2 because the composition of the porous sheet is similar.

[0125] <Evaluation of Reaction with Metallic Lithium>

[0126] A metal lithium foil cut to a larger area than the porous sheet was placed on a SUS foil, and the porous sheets listed in Table 1 were laminated so that their entire cross-sections were in direct contact with the lithium metal foil. A SUS foil was further laminated on the porous sheet. This laminate was vacuum packed and allowed to stand at 45°C for 4 days. After 4 days, the vacuum pack was opened, and the visual appearance change and infrared absorption spectrum of the porous sheet surface that had been in contact with the lithium metal foil were compared with those of the porous sheet that had not been in contact with the lithium metal foil.

[0127] Infrared absorption spectra were measured using a Thero Scientific FT-IR Nicolet iS5 (iD7 ATR accessory). Infrared absorption spectra were measured at room temperature (dew point ~ 40°C) in the wave number range of 4000 to 650 cm. -1 The spectrum was measured using the ATR method with an accumulation count of 16 in the range of . After correction using the spectrum measured without placing the sample as the background, the infrared absorption spectrum of the porous sheet that was in contact with the lithium metal foil was compared with the infrared absorption spectrum of the porous sheet that was not in contact with the lithium metal foil to evaluate the presence or absence of changes in the height and position of the peaks.

[0128] As a result of the test, the porous sheets of Comparative Examples 2 and 3 showed no change in appearance and no change in the infrared absorption spectrum. Since the porous sheets of Examples 1 and 2 and Comparative Example 1 have similar compositions to those of Comparative Examples 2 and 3, it can be assumed that the results are the same. On the other hand, Comparative Example 4 showed a clear change in appearance and a change in the infrared absorption spectrum.

[0129] Example, ComparisonPreliminaryComparative Example 1Comparative Example 2Comparative Example 3Comparative Example 4Example 1Example 2Fluorine polymerFKMFKMFEPMPTFEFKMFKMPorosity (%)877883734367Fluorine content (w / w%)64~7164~7154~587664~7164~71UL94(Thickness)V-0V-0FailV-0V-0V-0(0.3mm)(0.3mm)(0.5mm)(0.5mm)(0.3mm)(0.3mm)Strain when 0.1MPa pressure is applied(%)51.930.145.5<53.58.4Stress retention rate(%)Unable to measure due to reaching the device measurement limit6220(Not restorable)9187HardnessA type6227-4822C type153613-638

[0130] As shown in Table 1, it can be seen that the independent foam-type porous sheets formed from the elastomers shown in Examples 1 and 2 have sufficient flame retardancy and elasticity (appropriate hardness and stress retention).

Claims

1. In an elastic sheet for an all-solid-state secondary battery that buffers volume changes due to expansion and contraction of the all-solid-state secondary battery, It is composed of an independent foam-type foam formed from a fluorine-based elastomer, An elastic sheet for an all-solid-state secondary battery, wherein the porosity of the foam is 40% or more and 70% or less.

2. In claim 1, An elastic sheet for an all-solid-state secondary battery, wherein the content of fluorine element is 60 mass% or more and 80 mass% or less, when the entire fluorine-based elastomer is 100 mass%.

3. In claim 1, An elastic sheet for an all-solid-state secondary battery having a deformation of 10% or less when an external pressure of 0.1 MPa is applied.

4. In claim 1, Elastic sheet for all-solid-state secondary batteries with a stress retention rate of 80% or more.

5. In claim 1, An elastic sheet for an all-solid-state secondary battery having a thickness of 10㎛ or more and 1000㎛ or less.

6. In claim 1, Elastic sheet for all-solid-state secondary batteries with a flame retardancy rating of V-0 by UL94.

7. In claim 1, An elastic sheet for an all-solid-state secondary battery that shows no change in the infrared absorption spectrum before and after contact with metallic lithium for 4 days.

8. In claim 1, An elastic sheet for an all-solid-state secondary battery having a mass change rate of less than 1% before and after 30 days of contact with a sulfide-based solid electrolyte.

9. In claim 1, Elastic sheet for electrically insulating all-solid-state secondary batteries.

10. An all-solid-state secondary battery module comprising an elastic sheet for an all-solid-state secondary battery, an all-solid-state secondary battery, and a case accommodating them therein, as described in any one of claims 1 to 9.

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