solid-state batteries

Abstract

To provide a solid-state battery with excellent suppression of delamination within the unit electrode stack. [Solution] The solid-state battery 10 according to the present disclosure has a plurality of unit electrode stacks 22, each unit electrode stack 22 comprising at least a first current collector layer 12, a first active material layer 14, a solid electrolyte layer 16, a second active material layer 18, and a second current collector layer 12, and further comprising an adhesive layer 20 between two adjacent unit electrode stacks 22, wherein the product of the area ratio (unit: area %) of the adhesive layer 20 on the surface of the unit electrode stack 22 that the adhesive layer 20 contacts and the thickness (unit: mm) of the unit electrode stack 22 is 12 or less.

Description

Technical Field

[0001] This disclosure relates to a solid-state battery.

Background Art

[0002] As a battery in which a current collector layer and an active material layer in a unit electrode laminate are adhered by an adhesive layer, for example, the one described in Patent Document 1 is known. Patent Document 1 has two or more laminated battery units having a monopolar structure, and the laminated battery unit includes a first current collector layer, a first active material layer, a solid electrolyte layer, a second active material layer, a second current collector layer, a second active material layer, a solid electrolyte layer, a first active material layer, and a first current collector layer laminated in this order, and the first current collector layer and the first active material layer laminated adjacent to each other are adhered to each other by an adhesive. A all-solid-state battery is disclosed.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When adhering unit electrode laminates to each other, stress may occur between layers due to uneven thickness of the active material layer or the like, and delamination between layers may occur.

[0005] This disclosure has been made in view of the above circumstances, and an object thereof is to provide a solid-state battery excellent in suppressing delamination between layers in a unit electrode laminate.

Means for Solving the Problems

[0006] Means for solving the above problems include the following aspects. <1> A solid-state battery having a plurality of unit electrode stacks, each unit electrode stack comprising at least a first current collector layer, a first active material layer, a solid electrolyte layer, a second active material layer, and a second current collector layer, further comprising an adhesive layer between two adjacent unit electrode stacks, wherein the product of the area ratio of the adhesive layer on the surface in contact with the unit electrode stack (unit: area %) and the thickness of the unit electrode stack (unit: mm) is 12 or less. <2> The thickness of the unit electrode stack is 0.15 mm to 1 mm. <1> Solid-state batteries as described above. <3> The adhesive layer is conductive <1> Solid-state batteries as described above. <4> The product of the area ratio of the adhesive layer on the surface in contact with the unit electrode stack and the thickness of the unit electrode stack is 8 or more and 12 or less. <1> Solid-state batteries as described above. [Effects of the Invention]

[0007] According to this disclosure, it is possible to provide a solid-state battery that exhibits excellent suppression of delamination within a unit electrode stack. [Brief explanation of the drawing]

[0008] [Figure 1] This is a schematic partial cross-sectional view of a solid-state battery in one embodiment of the present disclosure. [Modes for carrying out the invention]

[0009] The solid-state battery described herein will be explained in detail below with reference to the drawings. The following figures are schematic representations, and the size and shape of each part have been exaggerated as appropriate for ease of understanding.

[0010] <Solid battery> The solid-state battery according to this disclosure has a plurality of unit electrode stacks, each unit electrode stack comprising at least a first current collector layer, a first active material layer, a solid electrolyte layer, a second active material layer, and a second current collector layer, and further comprising an adhesive layer between two adjacent unit electrode stacks, wherein the product of the area ratio of the adhesive layer on the surface in contact with the unit electrode stack (unit: area %) and the thickness of the unit electrode stack (unit: mm) is 12 or less.

[0011] The solid-state battery relating to this disclosure will be explained below using diagrams.

[0012] Figure 1 is a schematic partial cross-sectional view of a solid-state battery in one embodiment of the present disclosure. The solid-state battery 10 in Figure 1 has multiple unit electrode stacks 22. The unit electrode stack 22 in Figure 1 comprises a first current collector layer 12, a first active material layer 14, a solid electrolyte layer 16, a second active material layer 18, a second current collector layer 12, a second active material layer 18, a solid electrolyte layer 16, a first active material layer 14, and a third current collector layer 12. The configuration of each layer of the unit electrode laminate 22 in this disclosure is not particularly limited, except that it comprises at least a first current collector layer, a first active material layer, a solid electrolyte layer, a second active material layer, and a second current collector layer. It may be a laminate with a configuration as shown in Figure 1, or it may be a laminate comprising a first current collector layer 12, a first active material layer 14, a solid electrolyte layer 16, a second active material layer 18, and a second current collector layer 12. Furthermore, there are no particular restrictions on the number of stacked unit electrode stacks 22 in the solid-state battery 10 according to this disclosure, as long as it is 2 or more, for example, 10 to 100 can be cited. The shape and size of the solid-state battery 10 according to this disclosure can be appropriately selected according to the number of stacks of unit electrode stacks 22 and the desired shape, etc.

[0013] The solid-state battery 10 in Figure 1 further includes an adhesive layer 20 between two adjacent unit electrode stacks 22. By including the adhesive layer, delamination between layers within the unit electrode stack can be suppressed, and in particular, delamination of the active material layer (and even the negative electrode active material layer) can be suppressed. Further, the adhesive layer 20 is preferably a layer that adheres the current collector layers 12 in each of the two unit electrode laminates 22. There is no particular limitation on the material of the adhesive layer 20, and known adhesives, adhesive tapes, adhesive films, etc. can be used. Examples of the material of the adhesive layer 20 may be a binder such as an acrylic resin, polyvinylidene fluoride (PVdF), carboxymethyl cellulose (CMC), butadiene rubber (BR), styrene-butadiene rubber (SBR), or a thermoplastic resin. As the thermoplastic resin, for example, a polyolefin-based resin can be used, and specifically, examples include low-density polyethylene (LDPE), ethylene-vinyl acetate copolymer resin (EVA), polyimide (PI), etc. Also, the adhesive layer 20 is preferably conductive. There is no particular limitation on the conductive material that imparts conductivity to the adhesive layer 20, and known conductive materials such as acetylene black, carbon black, graphite, etc. can be used. The thickness of the adhesive layer 20 is not particularly limited, but is preferably 10 μm to 1 mm, and more preferably 20 μm to 200 μm.

[0014] In the solid battery 10 according to the present disclosure, the value obtained by multiplying the area ratio (unit: area %) of the adhesive layer 20 on the surface where the adhesive layer 20 in the unit electrode laminate 22 contacts by the thickness T (unit: mm) of the unit electrode laminate 22 is 12 or less. From the viewpoint of suppressing interlayer peeling within the unit electrode laminate, it is preferably 5 or more and 12 or less, more preferably 8 or more and 12 or less, and particularly preferably 9 or more and 11 or less.

[0015] From the viewpoint of suppressing interlayer peeling within the unit electrode laminate, the value of the area ratio of the adhesive layer 20 on the surface where the adhesive layer 20 in the unit electrode laminate 22 contacts is preferably 10 area % or more and less than 100 area %, more preferably 30 area % to 85 area %, and particularly preferably 40 area % to 70 area %.

[0016] The thickness T of the unit electrode laminate 22 is preferably 0.10 mm to 2 mm, more preferably 0.15 mm to 1 mm, and particularly preferably 0.15 mm to 0.30 mm from the viewpoint of suppressing delamination between layers in the unit electrode laminate.

[0017] Further, the solid battery 10 according to the present disclosure may have a laminate sheet that covers the laminate of the plurality of unit electrode laminates 22 and a side member (for example, a terminal) and is thermally welded to the side member.

[0018] <Members constituting the battery> The solid battery 10 according to the present disclosure includes at least a first current collector layer 12 and a second current collector layer 12, and may further have a third current collector layer, a fourth current collector layer, and the like. As the current collector layer 12 including the first current collector layer 12, the second current collector layer 12, etc., for example, aluminum foil, copper foil, nickel foil, titanium foil, stainless steel foil, or the like can be used. The thickness of the current collector layer 12 may be, for example, 1 μm to 100 μm.

[0019] Here, the thicknesses of each layer such as the current collector layer 12, the first active material layer 14, the second active material layer 18, etc. are taken as the average values of the measured values at 10 arbitrarily selected locations.

[0020] It is preferable that one of the first active material layer 14 and the second active material layer 18 is a positive electrode active material layer and the other is a negative electrode active material layer. The positive electrode active material layer contains a positive electrode active material capable of occluding and releasing charge carriers such as lithium ions. As the positive electrode active material, those that can be used as the positive electrode active material of a lithium ion secondary battery, such as a lithium composite metal oxide having a layered rock salt structure, a metal oxide having a spinel structure, a polyanion-based compound, etc. may be adopted. Also, two or more positive electrode active materials may be used in combination. In the present embodiment, the positive electrode active material layer contains olivine-type lithium iron phosphate (LiFePO4) as a composite oxide.

[0021] The negative electrode active material layer can be any element, alloy, or compound capable of intercalating and releasing charge carriers such as lithium ions, and is not particularly limited. For example, the negative electrode active material can be Li, or carbon, metal compounds, elements or compounds thereof that can be alloyed with lithium. Examples of carbon include natural graphite, artificial graphite, or hard carbon (difficult-to-graphitize carbon) or soft carbon (easily graphitized carbon). Examples of artificial graphite include highly oriented graphite and mesocarbon microbeads. Examples of elements that can be alloyed with lithium include silicon and tin. In this embodiment, the negative electrode active material layer contains graphite as a carbon-based material.

[0022] Each of the positive electrode active material layer and the negative electrode active material layer may further contain conductive additives, binders, electrolytes (polymer matrix, ion-conducting polymer, electrolyte solution, etc.) to enhance electrical conductivity, electrolyte-supporting salts (lithium salts) to enhance ionic conductivity, etc. The components contained in the positive electrode active material layer and the negative electrode active material layer, or the mixing ratio of said components, and the thickness of the positive electrode active material layer and the negative electrode active material layer are not particularly limited, and conventionally known knowledge regarding lithium-ion secondary batteries may be referred to as appropriate. The thickness of the positive electrode active material layer and the negative electrode active material layer is, for example, 2 μm to 150 μm. Conventionally known methods such as the roll coating method may be used to form the positive electrode active material layer or the negative electrode active material layer on the surface of the current collector layer 12. To improve the thermal stability of the positive electrode active material layer or the negative electrode active material layer, a heat-resistant layer may be provided on the surface (one or both sides) of the current collector layer 12, or on the surface of the positive electrode active material layer or the negative electrode active material layer. The heat-resistant layer may, for example, contain inorganic particles and a binder, and may also contain additives such as thickeners.

[0023] Conductive additives are added to enhance the conductivity of the positive electrode active material layer or the negative electrode active material layer. Examples of conductive additives include acetylene black, carbon black, and graphite.

[0024] Examples of binders include fluororesins such as polyvinylidene fluoride, polytetrafluoroethylene, and fluororubber; thermoplastic resins such as polypropylene and polyethylene; imide resins such as polyimide and polyamideimide; alkoxysilyl group-containing resins; acrylic resins such as poly(meth)acrylic acid; styrene-butadiene rubber (SBR); alginates such as carboxymethylcellulose, sodium alginate, and ammonium alginate; water-soluble cellulose ester crosslinks; and starch-acrylic acid graft polymers. These binders can be used individually or in combination. Examples of solvents include water and N-methyl-2-pyrrolidone (NMP).

[0025] The separator 20 is positioned between the positive electrode active material layer 18 and the negative electrode active material layer 22, separating them to prevent short circuits caused by contact between the two electrodes while allowing charge carriers such as lithium ions to pass through. The separator 20 prevents short circuits between adjacent bipolar electrodes when bipolar electrodes are stacked.

[0026] The solid electrolyte layer 16 may be, for example, a porous sheet or nonwoven fabric containing a polymer that absorbs and retains electrolytes. Examples of materials constituting the solid electrolyte layer 16 include polypropylene, polyethylene, polyolefin, and polyester. The solid electrolyte layer 16 may have a single-layer structure or a multilayer structure. The multilayer structure may include, for example, an adhesive layer, a ceramic layer as a heat-resistant layer, and so on. The solid electrolyte layer 16 may be impregnated with an electrolyte, or the solid electrolyte layer 16 itself may be composed of an electrolyte such as a polymer electrolyte or an inorganic electrolyte.

[0027] Examples of electrolytes to be impregnated into the separator 20 include a liquid electrolyte (electrolyte solution) containing a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent, or a polymer gel electrolyte containing an electrolyte held in a polymer matrix.

[0028] When the solid electrolyte layer 16 is impregnated with an electrolyte solution, known lithium salts such as LiClO4, LiAsF6, LiPF6, LiBF4, LiCF3SO3, LiN(FSO2)2, and LiN(CF3SO2)2 can be used as the electrolyte salt. Furthermore, known solvents such as cyclic carbonates, cyclic esters, linear carbonates, linear esters, and ethers can be used as the non-aqueous solvent. Two or more of these known solvent materials may also be used in combination.

[0029] Examples of side members include current-collecting side members. A current-collecting side member is a side member having a current-collecting section in at least a part of it. The current-collecting section is electrically connected, for example, to a tab in the battery. The current-collecting side member may be entirely a current-collecting section, or only partially a current-collecting section. Examples of materials for the side member include metals such as stainless steel (SUS). The shape of the side member is not particularly limited, but may be, for example, a rectangular parallelepiped.

[0030] The laminate sheet preferably has at least a metal layer, and further has a welding resin layer on the side of the metal layer facing the side member. The laminate sheet may also have a protective layer on the side of the metal layer opposite to the side member. Examples of materials for the welding resin layer include olefin resins such as polypropylene (PP) and polyethylene (PE). Examples of materials for the metal layer include aluminum, aluminum alloys, and stainless steel. Examples of materials for the protective layer include polyethylene terephthalate (PET) and nylon. The thickness of the welded resin layer is, for example, 40 μm to 100 μm. The thickness of the metal layer is, for example, 30 μm to 60 μm. The thickness of the protective layer is, for example, 20 μm to 60 μm. The overall thickness of the laminate sheet is, for example, 70 μm to 220 μm.

[0031] The battery has a resin layer (e.g., a tab film) disposed on the surface of a pair of sides of the side member. The resin layer covers a portion of the surface of the side member and is interposed between the side member and the laminate sheet. Examples of materials for the resin layer include olefin resins such as polypropylene (PP) and polyethylene (PE). The thickness of the resin layer is, for example, 40 μm to 100 μm.

[0032] The solid-state battery according to this disclosure is typically a lithium-ion secondary battery. Applications of the battery include, for example, powering vehicles such as hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), battery electric vehicles (BEVs), gasoline-powered vehicles, and diesel-powered vehicles. It is particularly preferable for use as a power source for hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), or battery electric vehicles (BEVs). Furthermore, the solid-state battery according to this disclosure may be used as a power source for mobile devices other than vehicles (e.g., railways, ships, aircraft), or as a power source for electrical products such as information processing devices.

[0033] This disclosure is not limited to the embodiments described above. The embodiments described above are illustrative, and any configuration that is substantially identical to the technical idea described in the claims of this disclosure and achieves similar effects is included within the technical scope of this disclosure. [Examples]

[0034] The present disclosure will be described in detail below in the form of examples. The following examples do not limit the uses of the present disclosure in any way.

[0035] (Example 1) 1. Formation of the negative electrode active material layer Polyvinylidene fluoride (PVdF), negative electrode active material particles (lithium titanate (LTO) particles), and sulfide solid electrolyte (Li2S-P2S5 glass ceramic) were added to a polypropylene container and stirred for 30 minutes using an ultrasonic dispersion device. Afterward, the mixture was coated onto both sides of an aluminum foil in a 64 mm wide strip.

[0036] 2. Formation of the solid electrolyte layer Heptane, butadiene rubber (BR), and sulfide solid electrolyte (Li2S-P2S5 glass ceramic) were added to a polypropylene container and stirred for 15 minutes using an ultrasonic dispersion device. Afterward, the mixture was coated in a 70mm wide strip onto the center of a 120mm wide piece of aluminum foil.

[0037] 3. Formation of the positive electrode active material layer Using a rolling-flow coating apparatus (manufactured by Pawrec), positive electrode active material particles (Li) are coated in an atmospheric environment. 1.15 Co 1 / 3 Ni 1 / 3 Mn 1 / 3 By coating particles (primarily composed of O2) with lithium niobate and firing them in an atmospheric fire, positive electrode active material particles having a lithium niobate coating layer were obtained. Polyvinylidene fluoride (PVdF), the obtained positive electrode active material particles, sulfide solid electrolyte (Li2S-P2S5 glass ceramic), and vapor-phase carbon fiber (VGCF, manufactured by Showa Denko K.K.) were added to a polypropylene container and stirred for 20 minutes using an ultrasonic dispersion device. After that, the mixture was coated onto the center of an aluminum foil (120 mm wide).

[0038] 4.3-Layer Electrode Fabrication The obtained negative electrode active material layer, solid electrolyte layer, and positive electrode active material layer were cut to a length of 80 mm. The solid electrolyte layer was roll-pressed at 0.4 t / cm onto both sides of the laminate of the negative electrode active material layer / aluminum foil / negative electrode active material layer so that the centers of the coated areas coincided, and the aluminum foil was peeled off to transfer the solid electrolyte layer. Subsequently, the positive electrode active material layer was roll-pressed onto each solid electrolyte layer at 0.4 t / cm, and the aluminum foil was peeled off to transfer the positive electrode active material layer.

[0039] 5. Densification The resulting laminate was densified at 165°C and 5 t / cm, yielding a laminate with a thickness of 150 μm. Next, a polyimide (PI) tape (80 μm thick) slit to a width of 2 mm was attached 23 mm from the edge of the foil. Furthermore, the positive electrode active material layer was cut so that its area was 60 mm wide and 60 mm long.

[0040] 6. Attaching the current collector layer. Acetylene black conductive material and acrylic adhesive were weighed in a volume ratio of 20:80. Then, water was added to prepare a carbon layer composition. Next, this was coated onto one side of aluminum foil at a thickness of 2 μm, dried at 100°C for 1 hour, and a carbon layer-containing aluminum foil was obtained. Subsequently, the material was cut to a width of 57 mm and a length of 57 mm, heated at 140°C and 5 MPa for 2 minutes, and bonded to both sides of the laminate to obtain a unit electrode laminate.

[0041] 7. Cellification A solid-state battery was obtained by alternately stacking unit electrode stacks with adhesive films (adhesive layers) having the bonding area described in Table 1, stacking a total of 20 unit electrode stacks, welding the terminals, and forming a cell.

[0042] <Delamination Evaluation> The fabricated solid-state batteries were stored in a constant temperature bath at 80°C, then disassembled, and evaluated for delamination between layers within the unit electrode stack. The evaluation results are shown in Table 1.

[0043] (Examples 2 and 3, and Comparative Examples 1 and 2) As shown in Table 1, a solid-state battery was fabricated and evaluated in the same manner as in Example 1, except that the area ratio of the adhesive layer on the surface in contact with the adhesive layer and the thickness of the unit electrode stack were changed.

[0044] [Table 1]

[0045] (Example 4) The process from 1. Formation of the negative electrode active material layer to 5. Densification was carried out in the same manner as in Example 1.

[0046] 6. Attaching the current collector layer. Acetylene black conductive material and acrylic adhesive were weighed in a volume ratio of 20:80. Then, water was added to prepare a carbon layer composition. Next, this was coated onto one side of aluminum foil at a thickness of 2 μm, dried at 100°C for 1 hour, and a carbon layer-containing aluminum foil was obtained. Subsequently, the material was cut to a width of 57 mm and a length of 57 mm, heated at 140°C and 5 MPa for 2 minutes, and bonded to both sides of the laminate to obtain a unit electrode laminate.

[0047] 7. Cellification One unit electrode stack was laminated with an adhesive film (adhesive layer) having an adhesive area of ​​80 area, and then another unit electrode stack was laid in a 50mm x 50mm block. The center of the unit electrode stack was heated at 140°C and 5MPa for 2 minutes. Subsequently, another adhesive film (adhesive layer) having an adhesive area of ​​80 area and another unit electrode stack were added and heated again. This process was repeated until a total of 20 unit electrode stacks were stacked, and terminal welding and cell formation were performed to obtain a solid-state battery.

[0048] When the solid-state battery obtained in Example 4 was evaluated in the same manner as in Example 1, no delamination was observed within the unit electrode stack.

[0049] As shown in Table 1 and Example 4, the solid-state batteries of Examples 1 to 4 exhibited excellent suppression of delamination within the unit electrode stack. On the other hand, the solid-state batteries of Comparative Examples 1 and 2 experienced delamination of the negative electrode active material layer within the unit electrode stack. [Explanation of Symbols]

[0050] 10: Solid-state battery, 12: Current collector layer (first current collector layer or second current collector layer), 14: First active material layer, 16: Solid electrolyte layer, 18: Second active material layer, 20: Adhesive layer, 22: Unit electrode stack, T: Thickness of unit electrode stack

Claims

1. It has multiple unit electrode stacks, The unit electrode stack comprises at least a first current collector layer, a first active material layer, a solid electrolyte layer, a second active material layer, and a second current collector layer. An adhesive layer is further provided between two adjacent unit electrode stacks, The product of the area ratio (in area %) of the adhesive layer on the surface in contact with the unit electrode stack and the thickness (in mm) of the unit electrode stack is 12 or less. solid state battery.

2. The solid battery according to claim 1, wherein the thickness of the unit electrode stack is 0.15 mm to 1 mm.

3. The solid battery according to claim 1, wherein the adhesive layer is conductive.

4. The solid battery according to claim 1, wherein the product of the area ratio of the adhesive layer on the surface in contact with the unit electrode stack and the thickness of the unit electrode stack is 8 or more and 12 or less.

Images