Laminated film

Abstract

The present disclosure addresses the problem of providing a laminated film that is used as an exterior body of a solid-state battery and that is capable of achieving preferable heat dissipation. One embodiment for solving the problem is a laminated film used as an exterior body of a solid-state battery. The laminated film has at least a metal layer and an inner resin layer, and the metal layer has the thickness at least twice the thickness of the inner resin layer.

Description

Laminate film

[0001] The present invention relates to a laminate film.

[0002] In recent years, research and development into secondary batteries that contribute to energy efficiency has been conducted to ensure that more people have access to affordable, reliable, sustainable and advanced energy.

[0003] Examples of the exterior body that houses the secondary battery include a laminate film having at least a metal layer and a resin layer (for example, Patent Document 1).

[0004] Japanese Patent Application Laid-Open No. 2022-126645

[0005] Known secondary batteries include solid-state batteries such as lithium metal batteries and lithium ion secondary batteries, which have a solid electrolyte layer disposed between a positive electrode layer and a negative electrode layer. Solid-state batteries have a wider operating temperature range than secondary batteries that use an electrolyte solution. Therefore, when a laminate film is used as an exterior body for a solid-state battery, it is preferable that the exterior body itself has high heat dissipation properties.

[0006] The present invention has been made in view of the above, and an object of the present invention is to provide a laminate film to be used as an exterior body of a solid state battery, which laminate film has favorable heat dissipation properties.

[0007] (1) A laminate film used as an exterior body of a solid-state battery, the laminate film having at least a metal layer and an inner resin layer, the metal layer being at least twice as thick as the inner resin layer.

[0008] According to the invention (1), a laminate film that can obtain favorable heat dissipation properties can be provided.

[0009] (2) The laminate film according to (1), wherein the metal layer has a thickness 2.5 times or more that of the inner resin layer.

[0010] According to the invention of (2), a laminate film that can obtain more preferable heat dissipation properties can be provided.

[0011] (3) A laminate film used as an exterior body of a solid-state battery, the laminate film having at least a metal layer, an inner resin layer, and an outer resin layer, wherein the thickness of the metal layer is 65% or more of the total thickness of the laminate film.

[0012] According to the invention of (3), a laminate film can be provided that can provide more preferable heat dissipation properties.

[0013] (4) The laminate film according to (3), wherein the thickness of the metal layer is 70% or more of the total thickness of the laminate film.

[0014] According to the invention of (4), a laminate film can be provided that can provide more preferable heat dissipation properties.

[0015] (5) The laminate film according to any one of (1) to (4), wherein the laminate film includes a housing portion that houses an electrode stack and a peripheral portion around the housing portion, the sealing portion is disposed in the peripheral portion, the sealing portion is disposed in an approximate center portion in the stacking direction of the electrode stack, and the sealing portion has a folded portion and has a first region extending to one side in the stacking direction of the electrode stack and a second region extending from an end portion on the one side of the first region to the other side opposite to the one side.

[0016] According to the fifth aspect of the present invention, the portion on the folded-back side is folded back to form multiple regions, which reduces the unevenness of the contact surface between the storage battery and the heat transfer member. This makes it difficult for gaps to form between the secondary battery and the heat transfer member, and makes it easier for the storage battery and the heat transfer member to come into closer contact with each other, allowing the heat of the secondary battery to be efficiently transferred to the cooling / heating element.

[0017] (6) The laminate film according to (5), further comprising a third region extending from the other end of the second region to the folded portion on the one side.

[0018] According to the sixth aspect of the present invention, the height of the folded-back portion is stabilized, and irregularities on the contact surface between the storage battery and the heat transfer member can be further reduced.

[0019] 1 is a schematic diagram showing the configuration of a solid state battery including a laminate film according to an embodiment of the present invention; 2 is a graph showing the relationship between the metal layer thickness and the cell temperature according to an example of the present invention; 3 is a graph showing the relationship between the inner resin layer thickness and the cell temperature according to an example of the present invention; 4 is a graph showing the results of a tensile strength and T-peel test of a laminate film according to an example of the present invention;

[0020] As shown in FIG. 1 , the laminate film 20 according to this embodiment is used as an exterior body for a solid-state battery 1. The solid-state battery 1 includes an electrode stack 10 and a laminate film 20. A plurality of solid-state batteries 1 are modularized for use. A buffer material 3 is disposed at the end of the solid-state battery 1. The solid-state battery 1 is placed on a bind bar V. A water jacket 4 serving as a cooling device is disposed below the bind bar V. The buffer material 3, the bind bar V, and the water jacket 4 are examples of components of a battery module including a plurality of solid-state batteries 1. FIG. 1 is a diagram that schematically illustrates the solid-state battery 1 and some of the components of the battery module, and does not faithfully depict the shape and size of each component. In other words, the shape and size of each component are not limited to the configuration shown in FIG. 1 and can be changed within a range that does not impair the effects of the present invention.

[0021] (Electrode Stack) The electrode stack 10 is a power-generating element of the solid-state battery 1. The electrode stack 10 has a structure in which positive electrode layers and negative electrode layers are alternately stacked with a solid electrolyte layer interposed therebetween. The number of stacked layers is not particularly limited. The solid-state battery 1 having the electrode stack 10 is not particularly limited, but may be a lithium-ion solid-state secondary battery or a lithium metal solid-state secondary battery. The operating temperature range of the solid-state battery 1 is not particularly limited, but may be, for example, -40°C to 100°C. Since the upper limit of the operating temperature range of the solid-state battery 1 is higher than that of secondary batteries using an electrolyte solution, it is important to improve heat dissipation when the temperature of the solid-state battery 1 rises. In particular, when the size of the solid-state battery 1 is large, temperature differences are likely to occur within the solid-state battery 1, making it even more important to improve heat dissipation. The size of the solid-state battery 1 is not particularly limited, but may be, for example, 4 x 50 x 50 mm or more, or 15 x 100 x 500 mm or more.

[0022] The negative electrode layer has a negative electrode active material layer and a negative electrode current collector layer. The negative electrode active material layer is not particularly limited and can be made of a material that can be used as a negative electrode active material in a solid-state battery. The negative electrode active material layer can be made of a silicon-based active material such as lithium metal, lithium alloy, Si, or Si alloy, or lithium titanate (Li ４ Ti ５ O １２ ), lithium transition metal oxides such as TiO ２ , Nb ２ O ３ and W.O. ３ The negative electrode active material layer may contain, in addition to the negative electrode active material, materials that can be used as materials for solid-state batteries, such as a solid electrolyte, a conductive additive, and a binder. The negative electrode current collector layer is not particularly limited, and may be made of copper, nickel, stainless steel, or the like.

[0023] The solid electrolyte layer is disposed between the anode layer and the cathode layer. The solid electrolyte material constituting the solid electrolyte layer is not particularly limited, and may be any material that can be used as an electrolyte in a solid-state battery. Examples include inorganic solid electrolytes such as sulfide solid electrolyte materials, oxide solid electrolyte materials, halide solid electrolytes, and lithium-containing salts, and polymer solid electrolytes such as polyethylene oxide.

[0024] The positive electrode layer has a positive electrode active material layer and a positive electrode current collector layer. The positive electrode active material layer is not particularly limited and can be made of a material that can be used as a positive electrode active material in a solid-state battery. Examples of positive electrode active materials that make up the positive electrode active material layer include LiCoO ２ , LiNiO ２ , LiCo ｘ Ni ｙ Mn ｚ O ２ (x+y+z=1), LiVO ２ , LiCrO ２ Layered positive electrode active material particles such as LiMn ２ O ４ , Li(Ni ０．２５ Mn ０．７５ ) ２ O４ , LiCoMnO ４ , Li ２ NiMn ３ O ８ Spinel-type positive electrode active materials such as LiCoPO ４ , LiMnPO ４ , LiFePO ４ Olivine-type positive electrode active materials such as solid solution oxides (Li ２ MnO ３ -LiMO ２ (M=Co, Ni, etc.), conductive polymers such as polyaniline and polypyrrole, Li ２ S, CuS, Li-Cu-S compound, TiS ２ , FeS, MoS ２ Examples of the cathode active material include sulfides such as Li-Mo-S compounds, and mixtures of sulfur and carbon. The cathode active material may be one of the above materials, or may be composed of two or more of the above materials. In addition to the cathode active material, the cathode layer may contain materials such as a solid electrolyte, a conductive additive, and a binder that can be used as materials for solid-state batteries. The cathode current collector layer is not particularly limited, but may be composed of, for example, aluminum, stainless steel, conductive carbon (graphite, carbon nanotubes, etc.), etc.

[0025] The electrode stack 10 may have any layer other than those described above. For example, an intermediate layer may be provided between the negative electrode layer and the solid electrolyte layer. The intermediate layer has the function of suppressing the formation of dendrites and stabilizing the interface between the negative electrode layer and the solid electrolyte layer. The intermediate layer is made of a metal such as tin, amorphous carbon, or the like.

[0026] (Laminate Film) As shown in Fig. 1 , the laminate film 20 has at least an inner resin layer 21 and a metal layer 22. In this embodiment, the laminate film 20 further has outer resin layers 23 and 24. Fig. 1 schematically shows the layer structure of the laminate film 20 in direction D. Direction D is the direction along the surface on which the electrode stack 10 is placed. The layer structure of the laminate film 20 below the electrode stack 10 in Fig. 1 is omitted and simply indicated collectively by the reference numeral 20, but the layer structure in this portion is also the same as the layer structure in direction D.

[0027] The inner resin layer 21 is a layer of the laminate film 20 that is disposed on the innermost side, that is, the electrode stack 10 side. The inner resin layer 21 is made of, for example, a heat-sealable resin. For example, the electrode stack 10 can be sealed by forming the laminate film 20 into a bag or a tube shape to enclose the electrode stack 10, and then heat-sealing the inner resin layers 21 together. Examples of resins that can be used to form the inner resin layer 21 include polypropylene, low-density polyethylene, high-density polyethylene, polystyrene, polyvinyl chloride, AS resin, and ABS resin.

[0028] The thickness of the inner resin layer 21 is not particularly limited, but is preferably, for example, 35 μm or less. From the viewpoint of ensuring sealing strength and insulating properties, it is more preferably 23 μm or more. By reducing the thickness of the inner resin layer 21 within a range that provides preferable insulating properties and sealing properties as an exterior body of the solid-state battery 1, the energy density of the solid-state battery 1 can be improved.

[0029] The outer resin layers 23 and 24 are disposed on the outermost side of the laminate film 20. In this embodiment, the outer resin layers are described as two layers, namely, the outer resin layers 23 and 24. However, the number of outer resin layers is not particularly limited and may be one. Having a single outer resin layer reduces the number of adhesive layers (described later), thereby improving the energy density of the solid-state battery 1. The resin constituting the outer resin layers 23 and 24 is not particularly limited as long as it has heat resistance sufficient to prevent melting and chipping during heat sealing. Examples of such resins include polyethylene terephthalate, polyvinyl chloride, polyvinyl alcohol, polyvinylidene chloride, polyamide, polybutylene terephthalate, and polyphenylene sulfide. It is preferable that the outer resin layer be composed of polyethylene terephthalate.

[0030] The laminate film 20 may be provided with an adhesive layer to enhance adhesion between the outer resin layers 23 and 24, or between the outer resin layer 23 and the metal layer 22, which are arranged on the metal layer 22 side. In this embodiment, an adhesive layer a1 is provided between the metal layer 22 and the outer resin layer 23, and an adhesive layer a2 is provided between the outer resin layer 23 and the outer resin layer 24. The adhesive layers a1 and a2 are not particularly limited, and may include adhesive layers made of any laminating adhesive or the like. Note that an adhesive layer (not shown) may also be provided between the inner resin layer 21 and the metal layer 22.

[0031] The metal layer 22 is disposed on the outer side of the solid-state battery 1 relative to the inner resin layer 21. Examples of metals constituting the metal layer 22 include aluminum (Al) and stainless steel (SUS). Aluminum (Al) is preferred. In this embodiment, the metal layer 22 is disposed between the inner resin layer 21 and the outer resin layer 23. The laminate film 20 according to this embodiment has a thicker metal layer 22 than conventional laminate films, thereby achieving favorable heat dissipation properties. That is, heat is more easily dissipated from the electrode stack 10 to the outside via the metal layer 22. As shown in FIG. 1 , heat generated from the electrode stack 10 is dissipated to the outside (cooling device) via the transfer path R1. Alternatively, heat generated from the electrode stack 10 is dissipated to the outside (cooling device) via the transfer paths R21 and R22. The transfer paths R1, R21, and R22 in FIG. 1 schematically illustrate the directions of heat transfer. Since the thickness of the metal layer 22 is greater than that of conventional metal layers, the heat generated from the electrode stack 10 is more likely to be dissipated to the outside, particularly via the transfer paths R21 and R22.

[0032] The thickness of the metal layer 22 is at least twice as thick as the thickness of the inner resin layer 21. Preferably, the thickness of the metal layer 22 is at least 2.5 times as thick as the thickness of the inner resin layer 21. Furthermore, the thickness of the metal layer is preferably at least 65%, and more preferably at least 70%, of the total thickness of the laminate film 20 including the outer resin layer. This allows the laminate film 20 to achieve favorable heat dissipation properties. The absolute value of the thickness of the metal layer 22 is not particularly limited, but is preferably at least 80 μm.

[0033] The total thickness of the laminate film 20 including the above layers is preferably 120 μm or less. This allows the volume of the laminate film 20 to be reduced, thereby improving the energy density of the solid-state battery 1 or a battery module including a plurality of solid-state batteries 1. Alternatively, the thickness of the buffer material 3 can be increased to improve the absorption of cell expansion, thereby improving the strength of the battery module.

[0034] The laminate film according to the above embodiment includes, for example, a housing portion that houses the electrode stack and a peripheral portion around the housing portion. A sealing portion is disposed in the peripheral portion. The sealing portion is formed by bonding the laminate films together by adhesion, welding, or the like.

[0035] The sealing portion preferably has a folded portion, a first region extending to one side in the stacking direction of the electrode stack, a second region extending from one end of the first region to the other side opposite to the one side, and a third region extending to one side from the other end of the second region to the folded portion.

[0036] According to the above configuration, the portion of the peripheral edge closer to the folded portion than the side surface of the housing adjacent to the folded portion is folded along the side surface, so that the exterior body tends to be flat at this folded portion. Therefore, when this portion comes into contact with the heat transfer member, the contact area can be increased. Therefore, heat from the secondary battery can be efficiently transferred to the outside, such as a cooling / heating element.

[0037] Furthermore, according to the above configuration, the portion on the folded-back side is folded back to form multiple regions, which facilitates reducing unevenness on the contact surface between the secondary battery and the heat transfer member. This reduces the likelihood of gaps or the like occurring between the secondary battery and the heat transfer member, making it easier for the secondary battery and the heat transfer member to come into closer contact, thereby enabling efficient transfer of heat from the secondary battery to an external device such as a cooling / heating element. Furthermore, by further including the third region, the height of the portion on the folded-back side is stabilized, further reducing unevenness on the contact surface between the secondary battery and the heat transfer member.

[0038] Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and appropriate modifications can be made within the scope that does not impair the effects of the present invention.

[0039] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the contents of the following examples.

[0040] [Relationship between Metal Layer Thickness and Solid-State Battery Cell Temperature] The laminate film 20 was configured as follows: PP (polypropylene) with a thickness of 80 μm was used as the inner resin layer 21, Al (aluminum) was used as the metal layer 22, PA (polyamide) with a thickness of 15 μm was used as the outer resin layer 23, and PET (polyethylene terephthalate) with a thickness of 12 μm was used as the outer resin layer 24. Adhesive layers were provided between the metal layer 22 and the outer resin layer 23, and between the outer resin layer 23 and the outer resin layer 24. The reference numerals of each component correspond to those in FIG. 1, and the same applies below.

[0041] The laminate film 20 was fabricated with the metal layer 22 having a thickness of 40 μm, 60 μm, or 80 μm. A heater (50 × 50 × 4 mm) simulating the electrode laminate 10 was housed in the laminate film 20 and sealed. The heater temperature was kept constant at a heat output of 3 W, and the temperature at the temperature measuring point M in Figure 1 was measured. The relationship between the thickness of the metal layer 22 and the measured temperature is shown in the graph of Figure 2.

[0042] The vertical axis of the graph in Figure 2 represents the temperature difference from a predetermined temperature T, expressed as the temperature (°C) at the temperature measurement point M. The horizontal axis of the graph in Figure 2 represents the thickness (µm) of Al (aluminum) as the metal layer 22. As shown in Figure 2, by increasing the thickness of Al (aluminum) as the metal layer 22, the temperature at the temperature measurement point M decreases, and it is clear that this result makes it easier for heat generated from the electrode stack 10 to dissipate to the outside. In addition, when a similar test was performed with a heater size of 16.2 mm x 106 mm x 520 mm, the temperature at the temperature measurement point M decreased by approximately 3.65°C by increasing the thickness of Al (aluminum) from 40 µm to 80 µm.

[0043] [Relationship between Thickness of Inner Resin Layer and Temperature of Solid-State Battery Cell] The laminate film 20 was constructed as follows. PP (polypropylene) was used as the inner resin layer 21, and Al (aluminum) with a thickness of 80 μm was used as the metal layer 22. The above-described laminate film 20 was fabricated with the inner resin layer 21 having a thickness of 80 μm, 35 μm, or 23 μm. The other configurations were the same as those shown in FIG. 2. A heater similar to that shown in FIG. 2 was housed and sealed in the above-described laminate film 20, and the temperature at the temperature measurement point M in FIG. 1 was measured under the same conditions as those shown in FIG. 2. The relationship between the thickness of the inner resin layer 21 and the measured temperature is shown in the graph of FIG. 3.

[0044] The vertical axis of the graph in Fig. 3 represents the temperature (°C) at the temperature measurement point M, which is the temperature difference from a predetermined temperature T1. The horizontal axis of the graph in Fig. 3 represents the thickness (µm) of PP (polypropylene) as the inner resin layer 21. As shown in Fig. 3, by reducing the thickness of PP (polypropylene) as the inner resin layer 21, the temperature at the temperature measurement point M is reduced, and it is clear that this results in the heat generated from the electrode stack 10 being more easily dissipated to the outside.

[0045] [Insulation Test] The laminate film 20 was constructed as follows: the inner resin layer 21 was made of PP (polypropylene) with a thickness of 23 μm, the metal layer 22 was made of Al (aluminum) with a thickness of 80 μm, and the outer resin layer was made of PET (polyethylene terephthalate) with a thickness of 6 μm (the outer resin layer was considered to be one layer). An adhesive layer was provided between the metal layer 22 and the outer resin layer. The insulation resistance value of the laminate film 20 was measured when 1000 V was applied. Measurements were performed on the surface of the outer resin layer and the surface of the inner resin layer 21, with N=2. The insulation resistance values ​​of the outer resin layer surface were 12.7 GΩ and 73.4 GΩ, and the insulation resistance values ​​of the inner resin layer 21 surface were 25.0 GΩ and 45.5 GΩ. The evaluation standard was 100 MΩ or more, confirming that the laminate film 20 provided satisfactory insulation properties.

[0046] [Sealability Test (Tensile Strength / T-Peel Test)] Tensile and T-peel tests were conducted using the laminate film 20 used in the insulation test. The tensile strength of a single laminate film was measured, and two laminate films were partially overlapped and bonded together to measure the T-peel strength of the bonded joint. The tensile strength measurement test and the T-peel test (seal strength measurement) were both conducted under the following conditions: sample size: 15 mm x 10 cm, tensile speed: 100 mm / min, number of tests: 3. The tests were also conducted under several different temperature conditions. The results are shown in the graph in Figure 4.

[0047] The vertical axis of the graph in Figure 4 represents the tensile strength of the laminate film alone and the T-peel strength of the adhesive joint (both units are N / 15 mm). The horizontal axis of the graph in Figure 4 represents the temperature (°C) during measurement. As shown in Figure 4, the test results were above the criterion (0.3 MPa) under all conditions, confirming that the laminate film 20 provides favorable sealing properties and strength.

[0048] REFERENCE SIGNS LIST 1 solid-state battery 20 laminate film 21 inner resin layer 22 metal layer 23, 24 outer resin layer

Claims

1. A laminate film used as an exterior body of a solid-state battery, the laminate film having at least a metal layer and an inner resin layer, the metal layer being at least twice as thick as the inner resin layer.

2. The laminate film according to claim 1, wherein the metal layer is 2.5 times or more thicker than the inner resin layer.

3. A laminate film used as an exterior body for a solid-state battery, the laminate film having at least a metal layer, an inner resin layer, and an outer resin layer, wherein the thickness of the metal layer is 65% or more of the total thickness of the laminate film.

4. The laminate film according to claim 3, wherein the thickness of the metal layer is 70% or more of the total thickness of the laminate film.

5. A laminate film according to claim 1, wherein the laminate film includes a housing portion that houses an electrode stack and a peripheral portion around the housing portion, wherein the sealing portion is located on the peripheral portion, and wherein the sealing portion is located approximately in the center of the stacking direction of the electrode stack, and wherein the sealing portion has a folded portion and has a first region that extends to one side of the stacking direction of the electrode stack, and a second region that extends from the end of the one side of the first region to the other side opposite the one side.

6. The laminate film according to claim 5, further comprising a third region extending from the other end of the second region to the folded portion on the one side.

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