Solid-state battery and recycling method of the solid-state battery

Abstract

To obtain a solid-state battery capable of improving recyclability.SOLUTION: A solid-state battery 10 is formed by laminating two or more battery units 14 in which a positive electrode current collector 20, a positive electrode active material layer 42, a solid electrolyte layer 44, a negative electrode active material layer 46, a negative electrode current collector 30, a negative electrode active material layer 46, the solid electrolyte layer 44, the positive electrode active material layer 42, and the positive electrode current collector 20 are laminated in this order. The two or more laminated battery units 14 have bonding portions 50 that bond the positive electrode current collectors 20 facing each other in a laminated direction D between adjacent battery units 14, and a peeling strength of the bonding portions 50 is less than the peeling strength in the battery unit 14.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a solid-state battery and a method for recycling a solid-state battery. [Background technology]

[0002] Solid-state batteries in which the electrolytic solution in liquid-based secondary batteries is replaced with a solid electrolyte have been attracting attention (see Patent Document 1).

[0003] Patent Document 1 describes a solid-state battery in which two or more battery units are stacked, each battery unit being formed by stacking a current collector for a first electrode, an active material layer for the first electrode, a solid electrolyte layer, an active material layer for a second electrode, a current collector for the second electrode, an active material layer for the second electrode, a solid electrolyte layer, and an active material layer for the first electrode in this order. In this solid-state battery, the first current collectors of adjacent battery units that face each other in the stacking direction are bonded together by an adhesive. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2017-204377 Summary of the Invention [Problem to be solved by the invention]

[0005] In recent years, growing environmental awareness has led to a demand for recyclability in secondary batteries. In solid-state batteries consisting of two or more stacked battery units, as in Patent Document 1, it is conceivable to enhance recyclability by enabling replacement of some battery units whose performance has deteriorated. In this case, it is desirable to separate the battery units bonded together by an adhesive in a reusable state. However, if the first current collector arranged in the outermost layer is damaged or if each layer within the battery unit is destroyed due to stress during separation, it becomes difficult to recycle and reuse the battery.

[0006] In consideration of the above, an object of the present invention is to provide a solid-state battery that can be improved in recyclability. [Means for solving the problem]

[0007] The solid-state battery according to the present invention as set forth in claim 1 is a solid-state battery in which two or more stacked battery units are formed, each stacked in the following order: a first current collector, a first active material layer, a solid electrolyte layer, a second active material layer, a second current collector, a second active material layer, a solid electrolyte layer, a first active material layer, and a first current collector; the two or more stacked battery units have adhesive parts that bond the first current collectors that face each other in the stacking direction between adjacent battery units, and the peel strength of the adhesive parts is less than the peel strength within the battery unit.

[0008] The solid state battery according to the present invention as set forth in claim 1 is formed by stacking two or more battery units. Each battery unit is formed by stacking a first current collector, a first active material layer, a solid electrolyte layer, a second active material layer, a second current collector, a second active material layer, a solid electrolyte layer, a first active material layer, and a first current collector in this order, with the first current collector being disposed as the outermost layer.

[0009] Here, the two or more stacked battery units have adhesive joints that bond the first current collectors facing each other in the stacking direction between adjacent battery units, and the peel strength of the adhesive joints is less than the peel strength within the battery unit. This prevents damage to the first current collectors arranged in the outermost layers or destruction of each layer inside the battery unit due to stress when separating adjacent battery units from the adhesive joints. As a result, the bonded battery units can be separated in a reusable state, improving recyclability.

[0010] The peel strength within the battery unit referred to here is the absolute value of the fracture stress when stress is applied to the outermost first current collector so as to peel the first current collector from the first active material layer, resulting in fracture of at least a portion of the first current collector, the first active material layer, the solid electrolyte layer, the second active material layer, and the second current collector constituting each layer of the battery unit. Therefore, the peel strength within the battery unit can also be referred to as the "fracture strength of the battery unit."

[0011] A solid state battery according to a second aspect of the present invention has the configuration according to the first aspect, wherein the peel strength of the adhesive portion is 20% or more and 73% or less of the peel strength within the battery unit.

[0012] In the solid-state battery described in claim 2, the peel strength of the adhesive portion is set to 20% or more and 73% or less of the peel strength within the battery unit. By setting the peel strength of the adhesive portion to 20% or more of the peel strength within the battery unit, handling during manufacturing is improved. Furthermore, by setting the peel strength of the adhesive portion to 73% or more of the peel strength within the battery unit, recyclability of practical batteries can be stably ensured.

[0013] The solid-state battery described in claim 3 has the configuration described in claim 1 or claim 2, wherein the peel strength of the adhesive is equal to or greater than the peel strength at which peeling does not occur between the battery units when two or more stacked battery units are transported at an acceleration of 1 [G].

[0014] In the solid-state battery according to claim 3, even when two or more stacked battery units are transported at an acceleration of 1 G during manufacturing, separation between the battery units does not occur, which makes it easier to handle the stack obtained by stacking two or more battery units during the manufacturing process.

[0015] A solid state battery described in claim 4 has the configuration described in any one of claims 1 and 2, wherein the adhesive portion contains an ethylene-vinyl acetate copolymer resin.

[0016] In the solid-state battery described in claim 4, the adhesive containing ethylene-vinyl acetate copolymer resin enables low-temperature sealing at temperatures below the degradation temperature of the battery material, and water can be used as a solvent, making it possible to reduce emissions of VOCs (volatile organic compounds), thereby improving the environmental performance of the solid-state battery.

[0017] The method for recycling a solid state battery according to claim 5 is the method for recycling a solid state battery according to any one of claims 1 to 4, and includes the steps of peeling the first current collector from the adhesive portion to separate the two or more stacked battery units into individual units, and measuring the voltages of the separated battery units and replacing any battery unit whose voltage is determined to be abnormal.

[0018] In the method for recycling a solid-state battery according to the present invention as set forth in claim 5, bonded battery units can be separated in a reusable state, and therefore, the solid-state battery can be regenerated by replacing some of the two or more stacked battery units whose battery performance has deteriorated. [Effects of the Invention]

[0019] As described above, the solid-state battery and the method for recycling the solid-state battery according to the present invention can improve recyclability. [Brief explanation of the drawings]

[0020] [Figure 1] 1A and 1B are schematic views of a solid-state battery according to an embodiment, in which FIG. 1A is a plan view of an electrode assembly seen from the stacking direction, and FIG. 1B is a side view of the electrode assembly seen from the second width direction. [Figure 2] FIG. 2 is a partially enlarged cross-sectional view showing the electrode body cut along line 2-2 in FIG. 1(B). [Figure 3]1A and 1B are conceptual diagrams for explaining a method for recycling a solid-state battery according to an embodiment, in which (A) shows a process for separating a terminal member from an electrode body, (B) shows a process for individually separating a battery unit from an electrode body, and (C) shows a process for replacing a battery unit. [Figure 4] (A) is a plan view showing the bonded state of measurement sample 20A and measurement sample 20B used to evaluate the peel strength of the adhesive joint, and (B) is a graph showing the relationship between the film thickness of the adhesive joint and the concentration of EVA in the solvent. [Figure 5] The graph shows the relationship between the percentage of the peel strength of the joint relative to the peel strength within the battery unit and the joining temperature of the joint. DETAILED DESCRIPTION OF THE INVENTION

[0021] Hereinafter, one embodiment of a solid-state battery according to the present invention and a method for recycling the solid-state battery will be described with reference to Figures 1 to 5. The solid-state battery according to the present invention includes so-called all-solid-state batteries that use a solid electrolyte as an electrolyte.

[0022] Furthermore, unless otherwise specified in the specification, each element is not limited to one, and may be present in plural. Furthermore, in the drawings, substantially identical elements are denoted by the same reference numerals, and redundant explanations in the specification will be omitted. In the numerical ranges described in stages in the specification, the upper or lower limit value described in one numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. Furthermore, in the numerical ranges described in the specification, the upper or lower limit value of the numerical range may be replaced with a value shown in the examples.

[0023] Each component may contain multiple types of the corresponding substance. When referring to the amount of each component in a composition, if there are multiple substances corresponding to each component in the composition, the amount refers to the total amount of those multiple substances present in the composition, unless otherwise specified. The term "process" includes not only independent processes but also processes that cannot be clearly distinguished from other processes as long as the intended effect of the process is achieved.

[0024] The solid state battery according to the present invention is formed by stacking two or more battery units, each of which is formed by stacking a first current collector, a first active material layer, a solid electrolyte layer, a second active material layer, a second current collector, a second active material layer, a solid electrolyte layer, a first active material layer, and a first current collector in this order.

[0025] The first current collector and the second current collector can be the positive or negative electrode of the solid-state battery, and the first current collector and the second current collector are in a counter-electrode relationship. That is, when the first current collector is the positive electrode, the second current collector is the negative electrode. Conversely, when the first current collector is the negative electrode, the second current collector is the positive electrode.

[0026] Therefore, the solid state battery according to the present invention may have a configuration in which two or more battery units are stacked, each battery unit being formed by stacking a positive electrode current collector (first current collector), a positive electrode active material layer (first active material layer), a solid electrolyte layer, a negative electrode active material layer (second active material layer), a negative electrode current collector (second current collector), a negative electrode active material layer, a solid electrolyte layer, a positive electrode active material layer, and a positive electrode current collector in this order.

[0027] Furthermore, the solid state battery according to the present invention may have a configuration in which two or more battery units are stacked, each battery unit being formed by stacking a negative electrode current collector (first current collector), a negative electrode active material layer (first active material layer), a solid electrolyte layer, a positive electrode active material layer (second active material layer), a positive electrode current collector (second current collector), a positive electrode active material layer, a solid electrolyte layer, a negative electrode active material layer, and a negative electrode current collector in this order.

[0028] Hereinafter, an embodiment will be described in which the first current collector is a positive electrode and the second current collector is a negative electrode. For convenience of explanation, arrow W1 shown as appropriate in each drawing indicates a first width direction in a plan view of the solid state battery 10, arrow W2 indicates a second width direction perpendicular to the first width direction W1 in a plan view of the solid state battery 10, and arrow D indicates the stacking direction (thickness direction) of the solid state battery 10.

[0029] [Main components of solid-state batteries] 1(A) and 1(B) schematically show a solid-state battery 10 according to an embodiment, where FIG. 1(A) is a plan view of the electrode body as seen from the stacking direction D, and FIG. 1(B) is a side view of the electrode body as seen from the second width direction W2.

[0030] (electrode body) 1(A) and 1(B), a solid-state battery 10 includes an electrode assembly 12 having a positive electrode and a negative electrode. The electrode assembly 12 is housed inside an exterior member (not shown) such as a box-shaped case or a laminate sheet.

[0031] The electrode assembly 12 is formed by stacking two or more battery units 14. In the electrode assembly 12, adjacent battery units 14 are bonded to each other via adhesive parts 50.

[0032] The number of stacked battery units 14 may be two or more. For example, in the solid state battery 10 of this embodiment, the number of battery units 14 may be 60 or more and 80 or less.

[0033] (battery unit) The battery unit 14 includes a pair of positive electrode current collectors 20 arranged on the outermost layers of the battery unit 14, one negative electrode current collector 30 arranged between the pair of positive electrode current collectors 20, and a composite material 40 arranged between each positive electrode current collector 20 and the negative electrode current collector 30. Each composite material 40 has a positive electrode active material layer 42 on one side of the stacking direction D, with a solid electrolyte layer 44 at the center, and a negative electrode active material layer 46 on the other side of the stacking direction D. The positive electrode active material layer 42 is arranged between the positive electrode current collector 20 and the solid electrolyte layer 44. The negative electrode active material layer 46 is arranged between the negative electrode current collector 30 and the solid electrolyte layer 44.

[0034] Therefore, as shown in FIG. 2, the battery unit 14 is formed by stacking a positive electrode current collector 20, a positive electrode active material layer 42, a solid electrolyte layer 44, a negative electrode active material layer 46, a negative electrode current collector 30, a negative electrode active material layer 46, a solid electrolyte layer 44, a positive electrode active material layer 42, and a positive electrode current collector 20 in this order.

[0035] (Positive electrode current collector) The positive electrode current collector 20 collects current from the positive electrode. The positive electrode current collector 20 is disposed on the opposite side of the positive electrode active material layer 42 from the solid electrolyte layer 44. The positive electrode current collector 20 may be made of, for example, stainless steel, aluminum, copper, nickel, iron, titanium, or carbon, with aluminum alloy foil or aluminum foil being preferred. Aluminum alloy foil and aluminum foil may be manufactured using powder. The positive electrode current collector 20 may be, for example, in the form of a foil or a mesh.

[0036] The positive electrode current collector 20 has a current collecting portion 22 provided so as to protrude in one direction in the first width direction W1 from a region overlapping with the composite material 40. The current collecting portion 22 is electrically connected to the positive electrode side terminal member 16 (see FIG. 3(A)) via a current collecting tab (not shown). However, the current collecting portion 22 may also be electrically connected to the terminal member 16 without via a current collecting tab.

[0037] Furthermore, the current collecting portion 22 has a predetermined excess length so that the portion separated from the terminal member 16 can be reused in a recycling process of the solid-state battery 10, which will be described later. For this reason, the current collecting portion 22 may be folded in an accordion-like manner so as to form a plurality of inflection points 22A in a state in which the electrode body 12 is housed inside the exterior member (see FIG. 3(A)).

[0038] (Cathode active material layer) The positive electrode active material layer 42 contains a positive electrode active material. The positive electrode active material layer 42 may contain at least one of a positive electrode solid electrolyte, a conductive additive, and a binder, as necessary.

[0039] The positive electrode active material preferably contains a lithium composite oxide. The lithium composite oxide may contain at least one element selected from the group consisting of F, Cl, N, S, Br, and I. The lithium composite oxide may have a crystal structure belonging to at least one space group selected from the space groups R-3m, Immm, and P63-mmc (also referred to as P63mc or P6 / mmc). The lithium composite oxide may have an O2-type structure in which the transition metal, oxygen, and lithium are primarily arranged. Examples of conductive additives include carbon materials, metal materials, and conductive polymer materials. Examples of carbon materials include carbon black (e.g., acetylene black, furnace black, ketjen black, etc.), fibrous carbon (e.g., vapor-grown carbon fiber, carbon nanotube, carbon nanofiber, etc.), graphite, and carbon fluoride. Examples of metallic materials include metal powder (e.g., aluminum powder, etc.), conductive whiskers (e.g., zinc oxide, potassium titanate, etc.), and conductive metal oxides (e.g., titanium oxide, etc.). Examples of conductive polymer materials include polyaniline, polypyrrole, and polythiophene. One type of conductive additive may be used alone, or two or more types may be mixed and used. The positive electrode solid electrolyte preferably contains at least one solid electrolyte species selected from the group consisting of sulfide solid electrolytes, oxide solid electrolytes, and halide solid electrolytes. Specific examples of the sulfide solid electrolyte, oxide solid electrolyte, and halide solid electrolyte include those described below. Examples of binders include vinyl halide resins, rubbers, and polyolefin resins. Examples of other components include oxide solid electrolytes, halide solid electrolytes, thickeners, surfactants, dispersants, wetting agents, antifoaming agents, and solvents.

[0040] (Negative electrode current collector) The negative electrode current collector 30 collects current from the negative electrode. The negative electrode current collector 30 is disposed on the opposite side of the negative electrode active material layer 46 from the solid electrolyte layer 44. The negative electrode current collector 30 may be made of, for example, stainless steel, aluminum, copper, nickel, iron, titanium, or carbon, with copper being preferred. The negative electrode current collector 30 may be in the form of, for example, a foil or a mesh.

[0041] The negative electrode current collector 30 has a current collecting portion 32 provided so as to protrude from the region overlapping with the composite material 40 to the other side in the first width direction W1. The current collecting portion 32 is electrically connected to the negative electrode side terminal member 16 (see FIG. 3(A)) via a current collecting tab (not shown). However, the current collecting portion 32 may also be electrically connected to the terminal member 16 without via a current collecting tab.

[0042] Furthermore, like the positive electrode side current collecting portion 22, the current collecting portion 32 may be folded in an accordion-like manner to form multiple inflection points 32A when the electrode body 12 is housed inside the exterior member (see Figure 3(A)).

[0043] (Negative electrode active material layer) The negative electrode active material layer 46 contains a negative electrode active material. The negative electrode active material layer 46 may contain at least one of a negative electrode solid electrolyte, a conductive additive, and a binder, as necessary. Examples of negative electrode active materials include Li-based active materials such as metallic lithium, carbon-based active materials such as graphite, oxide-based active materials such as lithium titanate, and Si-based active materials such as elemental Si. The conductive additive, negative electrode solid electrolyte, and binder used in the negative electrode active material layer may be the same as those exemplified as the conductive additive contained in the positive electrode active material layer, the solid electrolyte contained in the solid electrolyte layer, and the binder.

[0044] (Solid electrolyte layer) The solid electrolyte layer 44 includes a solid electrolyte. The solid electrolyte preferably includes one selected from the group consisting of a sulfide solid electrolyte, an oxide solid electrolyte, and a halide solid electrolyte. The solid electrolyte may include an electrolytic solution in an amount of less than 10 mass % based on the total amount of the electrolyte. The solid electrolyte may also be a composite solid electrolyte including an inorganic solid electrolyte and a polymer electrolyte.

[0045] The sulfide solid electrolyte preferably contains sulfur (S) as a main anion element, and further contains, for example, Li and an element A. The element A is at least one selected from the group consisting of P, As, Sb, Si, Ge, Sn, B, Al, Ga, and In. The oxide solid electrolyte contains oxygen (O) as a main component of an anion element, and may also contain, for example, Li and a Q element (Q represents at least one of Nb, B, Al, Si, P, Ti, Zr, Mo, W, and S). As the halide solid electrolyte, a solid electrolyte containing Li, M, and X (M represents at least one of Ti, Al, and Y, and X represents F, Cl, or Br) is suitable.

[0046] The solid electrolyte layer 44 may or may not contain a binder. Examples of binders that can be contained in the solid electrolyte layer 44 include halogenated vinyl resins, rubbers, and polyolefin resins. Examples of halogenated vinyl resins include polyvinylidene fluoride (PVdF) and copolymers of polyvinylidene fluoride and hexafluoropropylene (PVdF-HFP). Examples of polyolefin resins include butadiene rubber (BR), acrylate butadiene rubber (ABR), styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber (NBR), and butyl rubber (isobutylene-isoprene rubber). Examples of polyolefin resins include polyethylene and polypropylene. The binder may be a diene-based rubber containing a double bond in the main chain, such as a butadiene-based rubber in which butadiene accounts for 30 mol % or more of the total.

[0047] (Adhesive part) 2, in the electrode body 12, two adjacent battery units 14 are bonded together via an adhesive portion 50. More specifically, in the electrode body 12, between two adjacent battery units 14, the positive electrode current collectors 20 arranged in the outermost layers of each battery unit 14 face each other in the stacking direction D. Therefore, the adhesive portion 50 bonds the positive electrode current collectors 20 arranged to face each other in the stacking direction D between the adjacent battery units 14.

[0048] The adhesive portion 50 preferably contains, for example, a thermoplastic resin. The thermoplastic resin is more preferably a resin whose melting point or softening point is equal to or lower than the degradation temperature of the battery material, and for example, a polyolefin resin can be used.

[0049] Examples of polyolefin resins that can be used include low-density polyethylene (LDPE) and ethylene-vinyl acetate copolymer (EVA), with ethylene-vinyl acetate copolymer (EVA) being more preferable. The use of ethylene-vinyl acetate copolymer (EVA) enables low-temperature sealing at temperatures below the degradation temperature of the battery material. Furthermore, since ethylene-vinyl acetate copolymer (EVA) can use water as a solvent, it is possible to reduce VOC (volatile organic compounds) emissions, improving environmental performance.

[0050] The adhesive portion 50 can be applied to the surface of the positive electrode current collector 20, and then multiple battery units 14 are stacked together. The resulting stack can be pressurized, preferably under heat, to fix two adjacent battery units 14 together.

[0051] The adhesive portion 50 may be applied to the entire surface of the positive electrode current collector 20 and interposed in the form of a layer between two adjacent battery units 14, or may be applied to only a portion of the surface of the positive electrode current collector 20.

[0052] The thickness of the adhesive part 50 is preferably as thin as possible so as not to unnecessarily increase the thickness of the solid state battery 10 in the stacking direction D, and can be set to 5% or less of the thickness of the electrode body 12 in the stacking direction D. As an example, the thickness can be set in the range of 0.3 μm to 2 μm, and 0.5 μm to 1 μm is more preferable.

[0053] Furthermore, the greater the peel strength of the adhesive portion 50, the better, in order to handle the electrode body 12 without it collapsing due to acceleration during transportation in the manufacturing method of the solid state battery 10 described below, and it is more preferable to set the peel strength to be equal to or greater than the peel strength at which peeling does not occur between the battery units 14 due to acceleration during transportation.

[0054] Furthermore, the smaller the peel strength of the adhesive portion 50, the better, in order to release the adhesion between adjacent battery units 14 without destroying the battery units 14 in the recycling method of the solid state battery 10 described below, and it is more preferable that the peel strength be set to be less than the peel strength within the battery unit 14.

[0055] The peel strength within the battery unit 14 referred to here is the absolute value of the fracture stress at which at least a portion of the positive electrode current collector 20, the positive electrode active material layer 42, the solid electrolyte layer 44, the negative electrode active material layer 46, and the negative electrode current collector 30 constituting the layers of the battery unit 14 are fractured when stress is applied to the outermost positive electrode current collector 20 so as to peel the positive electrode current collector 20 from the positive electrode active material layer 42 (composite material 40). Therefore, the peel strength within the battery unit 14 can also be referred to as the "fracture strength of the battery unit." The fracture referred to here also includes, for example, breaking of the outermost positive electrode current collector 20, cracks occurring in at least a portion of each layer of the composite material 40, and chipping of a portion of the composite material 40 due to adhesion of a portion of the composite material 40 to the positive electrode current collector 20 when stress is applied so as to peel the positive electrode current collector 20 from the composite material 40.

[0056] In the solid state battery 10 of this embodiment, the peel strength within the battery unit 14 is set to 0.4 [N / cm], for example.

[0057] Furthermore, in the solid-state battery 10 of this embodiment, when the electrode body 12 is configured as a stack of 60 battery units 14, the stress generated in the adhesive portion 50 of the electrode body 12 when the electrode body 12 is transported at an acceleration of 1 G is 0.08 N / cm. In other words, when the magnitude of the stress during transportation is expressed as a percentage of the peel strength within the battery unit 14, it is 20% of the peel strength within the battery unit 14 (0.4 N / cm).

[0058] From the above, when considering recyclability, the peel strength of the adhesive joint 50 can be set to less than 100% of the peel strength within the battery unit 14. As will be explained later in "Evaluation of Peel Strength of Joints," it is more preferable to set it to a range of 72% or less. Furthermore, when considering handleability during manufacturing, it is more preferable to set it to a range of 20% or more but less than 72% of the peel strength within the battery unit 14.

[0059] The peel strength of the adhesive portion 50 may be set to a value that allows the adhesion between the battery units 14 to be released due to expansion and contraction caused by charging or discharging of the solid state battery 10.

[0060] Furthermore, the adhesive part 50 is not limited to the above-described configuration in which it is applied to the surface of the positive electrode current collector 20. The adhesive part 50 may be configured, for example, as a double-sided tape having adhesive layers on both sides of a sheet-like substrate.

[0061] [Solid-state battery manufacturing method] The method for manufacturing the solid state battery 10 includes, for example, the following first to third steps.

[0062] (1st step) The first step is a step of obtaining a battery unit 14 by stacking a positive electrode current collector 20, a positive electrode active material layer 42, a solid electrolyte layer 44, a negative electrode active material layer 46, a negative electrode current collector 30, a negative electrode active material layer 46, a solid electrolyte layer 44, a positive electrode active material layer 42, and a positive electrode current collector 20 in this order.

[0063] The first step may be performed by sequentially applying onto the positive electrode current collector 20 a slurry containing the material that constitutes the positive electrode active material layer 42, a slurry containing the material that constitutes the solid electrolyte layer 44, and a slurry containing the material that constitutes the negative electrode active material layer 46, or by separately preparing the positive electrode active material layer 42, the solid electrolyte layer 44, and the negative electrode active material layer 46 and stacking them on the positive electrode current collector 20.

[0064] (2nd process) The second step is a step of stacking two or more battery units 14 obtained in the first step to obtain the electrode body 12. In this second step, two battery units 14 adjacent to each other in the stacking direction are bonded together via an adhesive part 50.

[0065] Specifically, in the second step, adhesive portions 50 are placed at predetermined locations on the positive electrode current collectors 20 that form the upper surfaces of the battery units 14. Next, two or more battery units 14, each with an adhesive portion 50 placed on the upper positive electrode current collectors 20, are stacked to obtain the electrode assembly 12. In this embodiment, as an example, 60 battery units 14 are stacked to form the electrode assembly 12. Thereafter, the stack is preferably pressurized under heat.

[0066] The method of pressing the laminate can be, for example, mechanical pressing, gas pressing, etc. The pressure when pressing the laminate can be, for example, 1 MPa, and the heating temperature can be set in the range of, for example, 20°C to 100°C.

[0067] (3rd step) The third step is a step of housing the electrode body 12 obtained in the second step in an exterior member to obtain a solid state battery 10. In this third step, the current collecting portions 22, 32 of the electrode body 12 may be made to meander in the stacking direction D, bent so as to form multiple inflection points, and joined to the terminal member 16. This is then covered with an exterior member such as a laminate film to obtain a solid state battery 10.

[0068] In the third step, the electrode body 12 is transported to the work position for each step, that is, the step of welding the terminal member 16 to the electrode body 12 and the step of covering the electrode body 12 with an exterior member. The method for transporting the electrode body 12 is, for example, to transport it in a lifted state by sucking the upper surface of the electrode body 12 with a suction-type robot arm or the like. The acceleration during transportation can be, for example, 1 [G].

[0069] In this embodiment, the peel strength of the adhesive portion 50 is set to be equal to or greater than the peel strength at which peeling does not occur between the battery units 14 when the electrode body 12 is transported using a robot arm at an acceleration of 1 G. This allows the electrode body 12 as a stack formed by stacking two or more battery units 14 to be transported using a robot arm.

[0070] [Solid-state battery recycling methods] 3(A) to 3(C), an example of a method for recycling the solid state battery 10 will be described below. The method for recycling the solid state battery 10 includes, for example, the following first to fourth steps.

[0071] (1st step) 3(A), the first step is a step of releasing the connection between the current collecting parts 22, 32 of the electrode body 12 and the terminal member 16, and separating the terminal member 16 from the electrode body 12. In the first step, for example, the welded portion of the current collecting part 22 to the terminal member 16 is cut off to separate the terminal member 16 from the electrode body 12.

[0072] (2nd process) As shown in FIG. 3(B), the second step is a step of separating individual battery units 14 from the electrode assembly 12. Specifically, in the electrode assembly 12, adjacent battery units 14 in the stacking direction D are joined together via adhesive joints 50. Therefore, in the second step, stress is applied to each battery unit 14 so as to pull it away from the electrode assembly 12, thereby peeling the positive electrode current collector 20 (first current collector) of each battery unit 14 from the adhesive joint 50 and separating the two or more stacked battery units 14 individually. If damage occurs to any of the positive electrode current collector 20, the negative electrode current collector 30, and the composite material 40, the battery unit 14 will not be usable as a recycled product due to a decrease in battery performance.

[0073] In this embodiment, the peel strength of the adhesive joint 50 is set to be less than the peel strength within the battery unit 14. This prevents the battery units 14 from being destroyed by stress when adjacent battery units 14 are separated from each other at the adhesive joint 50, and allows each battery unit 14 to be separated in a reusable state.

[0074] (3rd step) As shown in FIG. 3(C), the third step is to measure the voltage of the separated battery unit 14, and replace the battery unit 14 whose voltage is determined to be abnormal with a battery unit 14 whose voltage is determined to be normal.

[0075] (4th step) The fourth step is a step of regenerating the solid-state battery 10 in the same manner as the steps in the above-described method of manufacturing the solid-state battery 10. In the step of welding the terminal member 16 to the electrode body 12, the remaining excess length of the current collecting parts 22, 32 of the electrode body 12 can be used as a welding allowance.

[0076] [Evaluation of peel strength of adhesive joints]

[0077] In the solid state battery 10 described above, the peel strength of the adhesive portion 50 that bonds the positive electrode current collectors 20 that face each other in the stacking direction D between adjacent battery units 14 was evaluated.

[0078] (Method for measuring peel strength) 4(A), a measurement sample 20A having dimensions of 20 mm in length and 20 mm in width and a measurement sample 20B having dimensions of 15 mm in length and 60 mm in width, both cut out from a positive electrode current collector 20, were joined via an adhesive joint 50, and the peel strength of the adhesive joint 50 was measured. In this example, the positive electrode current collector 20 was made of aluminum (Al) foil. The adhesive portion 50 is made of a solvent that is a 1:1 mixture of water and isopropyl alcohol (IPA), mixed with a predetermined concentration of ethylene-vinyl acetate copolymer resin (hereinafter simply referred to as EVA) as a thermoplastic resin.

[0079] The concentration of EVA in the solvent was determined based on the graph shown in Fig. 4(B) taking into consideration the film thickness of the adhesive portion 50 when applied to the surface of the positive electrode current collector 20. The graph shown in Fig. 4(B) shows the relationship between the film thickness of the adhesive portion 50 and the concentration of EVA in the solvent, with the vertical axis representing the film thickness of the adhesive portion 50 and the horizontal axis representing the mass percent concentration of EVA in the solvent. The film thickness shown in the graph was measured after the adhesive portion 50 was applied to the surface of the positive electrode current collector 20 (aluminum foil) and dried for 30 minutes in an 80°C environment.

[0080] As described above, the thickness of the adhesive portion 50 in the solid-state battery 10 is preferably as thin as possible so as not to unnecessarily increase the thickness of the solid-state battery 10 in the stacking direction D, and can be set in the range of 0.3 μm to 2 μm, more preferably 0.5 μm to 1 μm. Therefore, the peel strength was measured for the adhesive portion 50 in the following <Example 1> and <Example 2>.

[0081] Example 1 The concentration of EVA in the solvent is set to 1 wt %, and the film thickness is approximately 0.5 μm. <Example 2> The concentration of EVA in the solvent is set to 2 wt %, and the film thickness is approximately 1 μm.

[0082] The peel strength is measured according to the following steps (1) to (6). (1) The surfaces of the measurement sample 20A and the measurement sample 20B are wiped with ethanol to remove oils and grease from the surfaces. (2) The adhesive portion 50 is applied to one surface of the measurement sample 20A. (3) One surface of the measurement sample 20A is dried in an environment of 80°C for 30 minutes. In this process, the measurement sample 20A whose deviation from the reference film thickness (0.5 μm or 1 μm) was less than a predetermined value was used as an acceptable product in the following process. (4) The measurement sample 20A is dried for 10 hours in a glove box in an environment of 40°C. (5) As shown in Fig. 4(A), the measurement sample 20B is placed on one surface (top surface) of the measurement sample 20A coated with the adhesive portion 50, and they are bonded in a glove box. Specifically, the measurement sample 20B is bonded by applying pressure under heat for 2 minutes using a uniaxial press from above. The pressure applied is 1 MPa. Three sets of samples were produced by joining measurement sample 20A and measurement sample 20B using adhesive 50 of <Example 1>, with the heating temperature during pressing set to 40[°C], 50[°C], 70[°C], and 80[°C]. Three sets of samples were produced by joining measurement sample 20A and measurement sample 20B using adhesive 50 of <Example 2>, with the heating temperature during pressing set to 25[°C], 50[°C], and 80[°C]. (6) The underside of the measurement sample 20A is fixed to a stage with double-sided tape or the like, and the longitudinal end 20B1 of the measurement sample 20B is pinched, and a 90° peel test (peel test) is performed to measure the peel strength.

[0083] (Recyclability evaluation) In the graph shown in Fig. 5, the vertical axis represents the ratio of the peel strength of the adhesive joint 50 to the peel strength within the battery unit 14 (the breaking strength of the battery unit 14), and the horizontal axis represents the joining temperature (heating temperature when pressure is applied) of the adhesive joint 50. Fig. 5 shows the relationship between the joining temperature and the ratio, expressed as a percentage, of the peel strength of the adhesive joint 50 to the peel strength within the battery unit 14, based on the results of measuring the peel strength of the adhesive joint 50 performed in the above steps (1) to (6).

[0084] As described above, in consideration of the recyclability of the solid-state battery 10, the peel strength of the adhesive portion 50 can be set to a range that is less than the peel strength within the battery unit 14. That is, in the graph shown in Fig. 5, a measurement sample in which the peel strength of the adhesive portion 50 is less than 100% of the peel strength within the battery unit 14 can be determined to be acceptable.

[0085] In Example 1, measurement samples that could be judged as passing were obtained at all bonding temperatures (40°C, 50°C, 70°C, 80°C). In Example 2, measurement samples that could be judged as passing were obtained when the bonding temperature was set to 25°C.

[0086] 5, recyclability can be stably ensured when the peel strength of the adhesive 50 is 73% or less of the peel strength within the battery unit 14. Therefore, it is more preferable for a practical battery that the peel strength of the adhesive 50 is set to a range of 73% or less of the peel strength within the battery unit 14.

[0087] (Evaluation of handling during manufacturing) As described above, in consideration of the handling properties during manufacturing of the solid state battery 10, in the graph shown in FIG. 5, the peel strength of the adhesive portion 50 can be set in the range of 20% or more of the peel strength within the battery unit 14.

[0088] In Example 1, measurement samples that could be judged as passing were obtained when the bonding temperature was set to 60°C, 70°C, and 80°C. In Example 2, no measurement samples that could be judged as passing were obtained, but it is expected that measurement samples that could be judged as passing will be obtained by adjusting the bonding temperature between 25°C and 50°C.

[0089] (Evaluation of robustness against temperature changes during charging and discharging) The temperature of the solid-state battery 10 according to this embodiment may rise to a maximum of approximately 60°C to 80°C during charging or discharging. Therefore, it is preferable that the peel strength of the adhesive portion 50 is highly robust against such temperature changes of the solid-state battery 10.

[0090] In <Example 1>, in the measurement sample in which the bonding temperature was set to 60[°C] to 80[°C], the peel strength of the adhesive joint 50 was less than 100[%] of the peel strength within the battery unit 14, and it can be judged as passing in terms of robustness. In Example 2, in the measurement sample in which the bonding temperature was set to 50°C, the peel strength of the adhesive 50 exceeded 100% of the peel strength in the battery unit 14 in some cases. Furthermore, although not shown in the graph of Fig. 5, in the measurement sample in which the bonding temperature was set to 80°C, the peel strength of the adhesive 50 exceeded 300% of the peel strength in the battery unit 14. Therefore, in Example 2, the peel strength of the adhesive 50 may change due to a temperature rise during use of the solid-state battery 10, which may impair subsequent recyclability.

[0091] From the above, it is preferable that the concentration of EVA in the solvent of the adhesive 50 is set to less than 2 [wt %], and more preferably to 1 [wt %], in terms of robustness against temperature changes in the solid-state battery 10. Furthermore, when the concentration of EVA in the solvent is set to less than 2 [wt %], the film thickness of the adhesive 50 becomes less than 1 [μm], which is also preferable in that the thickness of the solid-state battery 10 in the stacking direction D is suppressed. [Explanation of symbols]

[0092] 10 solid-state battery, 14 battery unit, 20 positive electrode current collector (first current collector), 42 positive electrode active material layer (first active material layer), 44 solid electrolyte layer, 46 negative electrode active material layer (second active material layer), 30 negative electrode current collector (second current collector), 50 adhesive portion, D stacking direction

Claims

1. A solid-state battery including two or more stacked battery units, each of which includes a first current collector, a first active material layer, a solid electrolyte layer, a second active material layer, a second current collector, a second active material layer, a solid electrolyte layer, a first active material layer, and a first current collector stacked in this order, The two or more stacked battery units have adhesive portions that bond first current collectors that face each other in the stacking direction between adjacent battery units, and the peel strength of the adhesive portions is less than the peel strength within the battery unit. solid state battery.

2. The peel strength of the adhesive portion is set to 20% or more and 73% or less of the peel strength within the battery unit. The solid-state battery according to claim 1 .

3. The peel strength of the adhesive joint is equal to or greater than the peel strength at which peeling does not occur between the battery units when the two or more stacked battery units are transported at an acceleration of 1 [G]. The solid-state battery according to claim 1 or 2.

4. The adhesive portion is configured to contain an ethylene-vinyl acetate copolymer resin. The solid-state battery according to claim 1 or 2.

5. The method for recycling the solid-state battery according to claim 1, peeling the first current collector from the adhesive portion to separate the two or more stacked battery units into individual units; measuring the voltage of the separated battery unit and replacing the battery unit whose voltage is determined to be abnormal; How to recycle solid-state batteries.

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