Case for secondary battery and secondary battery including same

Abstract

To provide a secondary battery case capable of improving heat resistance to laser welding and the like while suppressing leakage of an electrolytic solution to the exterior and infiltration of moisture to the interior.SOLUTION: A secondary battery case comprises: a case main body 10; a collector terminal 2 provided so as to penetrate through the case main body; a first sealing member 31 that seals between the case main body and the collector terminal; and a second sealing member 32 provided at an inner side of the case main body from the first sealing member and in contact with a lateral face 2a of the collector terminal and a part of an inner surface of the case main body. The first sealing member contains fluorine-based rubber as a main component. The second sealing member contains ethylene-α olefin-based copolymer rubber as a main component.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to a case for a secondary battery and a secondary battery including the same. [Background technology]

[0002] Japanese Patent Application Laid-Open No. 2010-92658 (Patent Document 1) discloses that an ethylene-α-olefin copolymer rubber (such as ethylene-propylene-diene rubber (EPDM)), which has high resistance to electrolyte, is used as a seal material for sealing the electrolyte of a secondary battery. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2010-92658 A Summary of the Invention [Problem to be solved by the invention]

[0004] Ethylene-α-olefin copolymer rubber has low heat resistance, so when laser welding or the like is performed near the sealed portion, it may deteriorate due to the effects of heat (e.g., about 200°C) during welding, resulting in a decrease in sealing performance. When sealing performance decreases, problems occur in that the electrolyte inside the secondary battery leaks to the outside, and moisture from the outside easily penetrates into the secondary battery.

[0005] An object of the present disclosure is to provide a case for a secondary battery that has improved heat resistance against laser welding and the like while suppressing leakage of electrolyte to the outside and intrusion of moisture into the inside. [Means for solving the problem]

[0006] (1) A case for a secondary battery according to the present disclosure, The case body and A current collecting terminal provided so as to penetrate the case body; a first seal member that seals between the case body and the current collecting terminal; The housing further includes a second seal member that is provided closer to the inside of the case body than the first seal member and that contacts a side surface of the current collecting terminal and a part of the inner surface of the case body. The first seal member contains a fluorine-based rubber as a main component. The second seal member contains an ethylene-α-olefin copolymer rubber as a main component.

[0007] For example, during laser welding between a bus bar and a current collecting terminal, the heat of the laser welding is conducted downward from the upper side of the current collecting terminal 2, so that the upper side of the current collecting terminal (the outside of the case) becomes hot, but the lower side (the inside of the case) is relatively cold. In the case for a secondary battery according to the present disclosure, the first seal member is exposed to higher temperatures than the second seal member, but since the first seal member has excellent heat resistance, it is unlikely to deteriorate due to the heat of laser welding. On the other hand, the second seal member has low heat resistance, but since it is separated from the upper side of the current collecting terminal 2, it is unlikely to be exposed to high temperatures and is unlikely to deteriorate. Therefore, the case for a secondary battery according to the present disclosure has improved heat resistance against laser welding and the like.

[0008] In addition, the second seal member disposed on the inside of the case is likely to come into contact with the electrolyte, but is unlikely to swell in response to the electrolyte. Therefore, the electrolyte is unlikely to permeate the second seal member. On the other hand, the first seal member is unlikely to be directly exposed to the electrolyte due to the presence of the second seal member. With this configuration, the case for a secondary battery according to the present disclosure can suppress leakage of the electrolyte to the outside and intrusion of moisture into the inside.

[0009] (2) The secondary battery according to the present disclosure is The case described in (1) and The battery includes an electrode body and an electrolyte contained in the case. The electrode body is connected to the current collecting terminal.

[0010] The secondary battery according to the present disclosure has an improved product life (durability over time) by adopting the above-mentioned secondary battery case which has improved heat resistance against laser welding and the like while suppressing leakage of electrolyte to the outside and intrusion of moisture into the inside. Effect of the Invention

[0011] According to the present disclosure, it is possible to provide a case for a secondary battery that has improved heat resistance against laser welding and the like while suppressing leakage of electrolyte to the outside and intrusion of moisture into the inside. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a perspective view illustrating a secondary battery case according to an embodiment of the present disclosure. [Diagram 2] FIG. 2 is a cross-sectional view taken along line II-II in FIG. [Diagram 3] 1 is a cross-sectional view for explaining an effect of a case for a secondary battery according to an embodiment of the present disclosure. [Figure 4] 5 is a schematic graph for explaining the effect of a case for a secondary battery according to an embodiment of the present disclosure. [Diagram 5] 11 is another schematic graph for explaining the effect of the case for a secondary battery according to the embodiment of the present disclosure. [Figure 6] 1 is a perspective view illustrating an example of a configuration of a secondary battery according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present disclosure will now be described with reference to the accompanying drawings, in which the same or corresponding components are designated by the same reference numerals.

[0014] <Case for secondary batteries> 1 and 2, a case 1 for a secondary battery of this embodiment includes a case body 10, a current collecting terminal 2, a first sealing member 31, and a second sealing member 32. As shown in FIG.

[0015] [Case body] The case body 10 may be made of, for example, an aluminum (Al) alloy. At least one of the inner and outer surfaces of the case body 10 may be covered with an insulator (such as an insulating sheet). The case body 10 may be, for example, a pouch made of an Al laminate film.

[0016] [Collection terminal] The current collecting terminals 2 are provided so as to penetrate the case body 10. The current collecting terminals 2 are metal members connected to the electrodes (positive and negative electrodes) housed inside the case 1.

[0017] [First seal member] The first seal member 31 is a member for sealing between the case body 10 and the current collecting terminal 2. The first seal member 31, together with the second seal member 32 described below, seals (liquid-tightly) between the case body 10 and the current collecting terminal 2, thereby preventing the electrolyte (such as scattered electrolyte) inside the secondary battery from leaking to the outside and also preventing external moisture from entering the inside of the secondary battery.

[0018] In this way, in order to sufficiently prevent leakage of the electrolyte to the outside and intrusion of moisture into the inside, the first seal member 31 contacts (liquid-tight) with the side surface 2a of the current collecting terminal 2 and the case body 10 as shown in Fig. 3. The first seal member 31 is, for example, an O-ring-shaped member having a cross-sectional shape as shown in Fig. 2. By adjusting the inner and outer diameters of the O-ring according to the diameter of the current collecting terminal 2 and the size of the opening of the case body 10, the first seal member 31 can contact (liquid-tight) with the side surface 2a of the current collecting terminal 2 and the case body 10.

[0019] As shown in FIG. 2, it is preferable that the surface of the current collecting terminal 2, including the side exposed to the outside of the case body 10 and the surface in contact with the outer surface of the case body 10 (the portion where the first sealing member 31 is not present), be covered with an insulator 33.

[0020] The first seal member 31 contains fluororubber as a main component. In this specification, the term "main component" refers to the component that has the largest mass ratio of the main component to all components. The mass ratio of the main component to all components is preferably 70 mass% or more, more preferably 80 mass% or more, and even more preferably 90 mass% or more.

[0021] The fluororubber is not particularly limited as long as it is a rubber containing fluorine, and examples thereof include fluororubbers such as vinylidene fluoride rubber (FKM), tetrafluoroethylene-propylene rubber (FEPM), and tetrafluoroethylene-purple vinyl ether rubber (FFKM), and copolymers thereof.

[0022] Fluorine-based rubber has excellent heat resistance. That is, due to the presence of fluorine atoms, fluorine-based rubber is not easily deteriorated even by heat (for example, 200° C.) that it receives during laser welding or the like.

[0023] Fluorine-based rubber has excellent resistance to copper damage. Copper damage is a polymer degradation phenomenon in which contact with copper accelerates a reaction that decomposes the polymer. Since fluororubber does not have a -ROOH group, which is a hydroperoxide, such a decomposition reaction is unlikely to occur. Therefore, the first seal member 31 has the advantage that copper damage is unlikely to occur even if the current collecting terminal 2 is made of copper.

[0024] [Second sealing member] The second seal member 32 is provided on the inner side of the case body 10 (lower side in FIG. 2) than the first seal member 31. The second seal member 32 contacts the side surface 2a of the current collecting terminal 2 and a part of the inner surface of the case body 10. This makes it possible to prevent the electrolyte from entering the first seal member 31, and to prevent the electrolyte from permeating the first seal member 31 and leaking to the outside due to swelling of the first seal member 31 caused by the electrolyte.

[0025] The second seal member 32 is, for example, an O-ring-shaped member having a cross-sectional shape as shown in Fig. 2. By adjusting the inner diameter of the O-ring to match the diameter of the current collecting terminal 2, the second seal member 32 can be in (liquid-tight) contact with the side surface 2a of the current collecting terminal 2. In addition, by making the outer diameter of the O-ring larger than the size of the opening of the case body 10, the second seal member 32 can be in contact with a part of the inner surface of the case body 10, and the electrolyte can be prevented from entering the first seal member 31 side.

[0026] 1, the second seal member 32 is also in contact with the surface of the first seal member 31 on the inner side of the case body 10 (the lower side in FIG. 2). The first seal member 31 and the second seal member 32 may be separate members, but it is preferable that the first seal member 31 and the second seal member 32 are joined to form an integrated seal member. In this case, the second seal member 32 is less likely to separate from the inner surface of the case body 10.

[0027] The second seal member 32 contains ethylene-α-olefin copolymer rubber as a main component. The ethylene-α-olefin copolymer rubber is not particularly limited as long as it is a copolymer rubber containing ethylene and α-olefin as unit monomers (containing structural units derived from ethylene and α-olefin), and examples thereof include ethylene-propylene-diene rubber (EPDM) and ethylene-propylene rubber (EPM).

[0028] Ethylene-α-olefin copolymer rubber has excellent electrolyte resistance. The electrolyte permeates through the rubber bulk as the rubber swells. The ethylene-α-olefin copolymer rubber has low compatibility with the electrolyte (for example, a mixed solvent of EC / EMC / DMC) described below, so swelling does not occur easily. Therefore, the electrolyte does not easily permeate through the second seal member 32.

[0029] 2, at least a portion of the inner surface of the case body 10 where the second seal member 32 is not present is preferably covered with an insulator 34. Furthermore, although not shown, the outer surface of the case body 10 may be covered with an insulator.

[0030] 3 is a cross-sectional view for explaining the effect of a case for a secondary battery according to an embodiment of the present disclosure. For example, in a battery pack, the positive and negative terminals of adjacent cells are electrically connected by a metal bus bar. As shown in FIG. 3, the bus bar 4 is electrically connected to a current collector terminal 2 (positive or negative terminal) by, for example, laser welding.

[0031] During this laser welding, the heat of the laser welding is conducted downward from the upper side of the current collecting terminal 2. As a result, the upper side of the current collecting terminal (the outer side of the case) becomes hot, but the lower side (the inner side of the case) is relatively cold. In the case for a secondary battery according to the present disclosure, the first seal member is exposed to higher temperatures than the second seal member, but since the first seal member has excellent heat resistance, it is unlikely to deteriorate due to the heat of laser welding. On the other hand, the second seal member has low heat resistance, but since it is separated from the upper side of the current collecting terminal 2, it is unlikely to be exposed to high temperatures and is unlikely to deteriorate. As a result, the case for a secondary battery according to the present disclosure has improved heat resistance against laser welding and the like.

[0032] In addition, the second seal member disposed on the inside of the case is likely to come into contact with the electrolyte, but is unlikely to swell in response to the electrolyte. Therefore, the electrolyte is unlikely to permeate the second seal member. On the other hand, the first seal member is unlikely to be directly exposed to the electrolyte due to the presence of the second seal member. With this configuration, the case for a secondary battery according to the present disclosure can suppress leakage of the electrolyte to the outside and intrusion of moisture into the inside.

[0033] In addition, in the case where heat is generated by the conduction of a large amount of current through the current collecting terminal 2, there is a possibility that the second seal member 32 may also be exposed to high temperatures. However, even if a part of the second seal member 32 (near the current collecting terminal 2) is deteriorated due to such high temperatures, the first seal member 31 is unlikely to be immediately exposed to the electrolyte, and therefore, due to the presence of the first seal member 31, the seal between the case body 10 and the current collecting terminal 2 is maintained, and it is considered that the effect of suppressing leakage of the electrolyte and intrusion of moisture is maintained for a sufficient period of time.

[0034] As described above, in the case of this embodiment, by using a combination of the first seal member 31 and the second seal member 32 as a seal between the case body 10 and the current collecting terminal 2, it is possible to provide a case for a secondary battery that has improved heat resistance against laser welding, etc. while suppressing leakage of electrolyte to the outside and intrusion of moisture into the inside. Furthermore, by employing such a case, it is possible to improve the product life (durability over time) of the secondary battery.

[0035] In addition, in a secondary battery using the case of the present disclosure, as shown in FIG. 4, for example, the amount of electrolyte permeation (amount of leakage to the outside of the battery) is reduced compared to a secondary battery of the conventional technology such as that disclosed in Patent Document 1.

[0036] Furthermore, in a secondary battery using the case of the present disclosure, as shown in FIG. 5, for example, the ratio of the amount of moisture (amount of moisture in the electrolyte) that penetrates into the battery is reduced compared to a secondary battery of the conventional technology such as that disclosed in Patent Document 1.

[0037] <Secondary battery> The secondary battery of this embodiment includes the above-mentioned case, and an electrode assembly and an electrolyte contained in the case. The electrode assembly is connected to a current collecting terminal.

[0038] In the following, a lithium ion secondary battery will be described as an example of the secondary battery according to the embodiment, but the secondary battery according to the embodiment is not limited thereto. Note that the secondary battery according to the embodiment (lithium ion secondary battery) will be referred to as a cell 5.

[0039] Fig. 6 is a perspective view that illustrates a schematic example of a configuration of a secondary battery (cell 5) according to an embodiment of the present disclosure. For ease of understanding, Fig. 6 illustrates a see-through view of the inside of cell 5.

[0040] The secondary battery (cell 5) shown in Fig. 6 is a sealed rectangular battery. However, the shape of the cell 5 (secondary battery) according to this embodiment is not limited to a rectangular shape, and may be, for example, a cylindrical shape. The cell 5 includes an electrode assembly 6, an electrolyte 7, and a case 1. The electrode assembly 6 and the electrolyte 7 are housed in the case 1.

[0041] The electrode assembly 6 shown in Fig. 6 is a laminated type (stack type) electrode assembly 6. That is, the electrode assembly 6 is formed by, for example, laminating positive electrodes and negative electrodes alternately with a separator sandwiched between them.

[0042] The electrolyte 7 is poured into the case 1 and impregnates the electrode assembly 6 (positive electrode, negative electrode, and separator). In FIG. 6, the liquid level of the electrolyte 7 is indicated by a dashed line.

[0043] The case 1 (case body 10) has, for example, a flat rectangular parallelepiped outer shape. The case body 10 can be composed of, for example, a container 10a having an opening at the top end, and a lid 10b having current collector terminals 2 (positive electrode terminal 21 and negative electrode terminal 22) to be joined to the electrode body 6. For example, the case 1 can be produced by housing the electrode body 6 in the container 10a having an opening at the top end, and then joining the container 10a and the lid 10b by laser welding. The lid 10b may further be provided with a liquid injection port for injecting the electrolyte 7, a gas exhaust valve, a current interrupt device (CID), and the like.

[0044] Although the laminated electrode body 6 will be described in detail below as an example, the electrode body 6 is not limited to this and may be, for example, a wound electrode body.

[0045] (positive electrode) The positive electrode constituting the electrode body 6 is a strip-shaped sheet. The positive electrode includes a positive electrode current collector and a positive electrode composite layer. The positive electrode current collector is electrically connected to a positive electrode terminal 21. In this manner, the electrode body 6 is connected to a current collector terminal 2. The positive electrode current collector may be, for example, an aluminum (Al) foil, an Al alloy foil, or the like.

[0046] In this example, the positive electrode mixture layer is formed on both the front and back surfaces of the positive electrode current collector. However, the positive electrode mixture layer may be formed only on the front surface (either one surface) of the positive electrode current collector. The positive electrode mixture layer includes a positive electrode active material, a conductive material, a binder, and a flame retardant.

[0047] The positive electrode active material is, for example, LiCoO2, LiNiO2, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2(NCM), LiNi 0.8 Co 0.15 Al 0.05 O2(NCA), LiMnO2, LiMn2O4, LiFePO4. Two or more positive electrode active materials can be combined. may be used interchangeably.

[0048] The conductive material can be, for example, acetylene black (AB), furnace black, vapor grown carbon fiber (VGCF), graphite.

[0049] The binder can be, for example, polyvinylidene fluoride (PVdF), styrene butadiene rubber (SBR), polytetrafluoroethylene (PTFE).

[0050] The flame retardant is not particularly limited as long as it is a flame retardant containing phosphorus (P) or sulfur (S) and has a thermal decomposition temperature of 80° C. or more and 210° C. or less. The flame retardant may be, for example, guanidine sulfamate, guanidine phosphate, guanylurea phosphate, diammonium phosphate, ammonium polyphosphate, ammonium sulfamate, melamine cyanurate, bisphenol A bis(diphenyl phosphate), resorcinol bis(diphenyl phosphate), triisopropylphenyl phosphate, triphenyl phosphate, trimethyl phosphate, triethyl phosphate, tricresyl phosphate, tris(chloroisopropyl)phosphate, (C4H9)3PO, (HO-C3H6)3PO, phosphazene compounds, diphosphorus pentoxide, polyphosphoric acid, melamine, etc. These flame retardants may be used alone or in combination of two or more kinds.

[0051] (Negative electrode) The negative electrode constituting the electrode body 6 is a strip-shaped sheet. The negative electrode includes a negative electrode current collector and a negative electrode mixture layer. The negative electrode current collector is electrically connected to the negative electrode terminal 22. In this manner, the electrode body 6 is connected to the current collector terminal 2. The negative electrode current collector may be, for example, a copper (Cu) foil.

[0052] In this example, the negative electrode mixture layer is formed on both the front and back surfaces of the negative electrode current collector. However, the negative electrode mixture layer may be formed only on the front surface (either one surface) of the negative electrode current collector. The negative electrode mixture layer includes a negative electrode active material and a binder (negative electrode active material and binder are not shown).

[0053] The negative electrode active material is a graphite-based material. Specifically, the negative electrode active material may be amorphous-coated graphite (graphite particles having surfaces coated with amorphous carbon), graphite, graphitizable carbon, or non-graphitizable carbon.

[0054] The binder can be, for example, carboxymethyl cellulose (CMC), styrene butadiene rubber (SBR).

[0055] (Separator) The separator constituting the electrode assembly 6 is a strip-shaped film. The separator is disposed between the positive electrode and the negative electrode, and electrically insulates the positive electrode and the negative electrode. The separator is made of a porous material, such as polyethylene (PE) or polypropylene (PP).

[0056] The separator may have a single layer structure. The separator may be formed, for example, only from a porous film made of polyethylene (PE). On the other hand, the separator may have a multi-layer structure. For example, the separator may have a three-layer structure consisting of a first porous film made of polypropylene (PP), a porous film made of polyethylene (PE), and a second porous film made of polypropylene (PP).

[0057] (electrolyte) The electrolyte 7 contains at least a lithium (Li) salt and a solvent. The Li salt is dissolved in the solvent. The supporting electrolyte is LiPF6, LiBF4, Li[N(FSO2)2], Li[N(CF3SO2)2], for example. One type of Li salt may be used alone, or two or more types of Li salts may be used in combination.

[0058] The solvent is aprotic. The solvent may be, for example, a mixture of cyclic and linear carbonates.

[0059] The cyclic carbonate may be, for example, ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), fluoroethylene carbonate (FEC), etc. One type of cyclic carbonate may be used alone. Two or more types of cyclic carbonates may be used in combination.

[0060] The chain carbonate may be, for example, dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), etc. One type of chain carbonate may be used alone. Two or more types of chain carbonates may be used in combination.

[0061] The solvent may include, for example, lactones, cyclic ethers, linear ethers, carboxylic acid esters, etc. The lactones may be, for example, γ-butyrolactone (GBL), δ-valerolactone, etc. The cyclic ethers may be, for example, tetrahydrofuran (THF), 1,3-dioxolane, 1,4-dioxane, etc. The linear ethers may be, for example, 1,2-dimethoxyethane (DME), etc. The carboxylic acid esters may be, for example, methyl formate (MF), methyl acetate (MA), methyl propionate (MP), etc.

[0062] The electrolyte 7 may further contain various functional additives in addition to the Li salt and the solvent. Examples of the functional additives include a gas generating agent (overcharge additive) and a SEI (Solid Electrolyte Interface) film forming agent. Examples of the gas generating agent include cyclohexyl The SEI film former can be, for example, vinylene carbonate (VC), vinyl ethylene carbonate (VEC), Li[B(C2O4)2], LiPO2F2, propane sultone (PS), ethylene sulfite (ES).

[0063] It should be noted that the embodiments disclosed herein are illustrative in all respects and should not be considered as limiting. The scope of the present disclosure is indicated by the claims, not by the description of the above embodiments, and further includes all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0064] 1 case, 10 case body, 10a container, 10b lid, 11 insulator, 2 current collecting terminal, 2a side, 21 positive electrode terminal, 22 negative electrode terminal, 31 first sealing member, 32 second sealing member, 33, 34 insulators, 4 bus bar, 5 cell (secondary battery), 6 electrode body, 7 electrolyte.

Claims

1. The case body and A current collecting terminal provided so as to penetrate the case body; a first seal member that seals between the case body and the current collecting terminal; a second seal member provided on an inner side of the case body relative to the first seal member and in contact with a side surface of the current collecting terminal and a part of an inner surface of the case body, The first seal member contains a fluorine-based rubber as a main component, The second sealing member is a case for a secondary battery, the main component of which is an ethylene-α-olefin copolymer rubber.

2. A case according to claim 1; An electrode assembly and an electrolyte solution are contained in the case, The electrode body is connected to the current collecting terminal.

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