A secondary battery and an electronic device

Abstract

The application provides a secondary battery and an electronic device, which comprises an electrode assembly, an electrolyte, a shell and an adhesive, the adhesive comprises a first adhesive layer and a second adhesive layer which are stacked, the adhesive is arranged between the electrode assembly and the shell, the first adhesive layer adheres to an inner surface of the shell, and the second adhesive layer adheres to an outer surface of the electrode assembly; the first adhesive layer comprises styrene-isoprene-styrene block copolymer and wax; the mass percentage of the styrene-isoprene-styrene block copolymer is 65% to 95% and the mass percentage of the wax is 1% to 5% based on the mass of the first adhesive layer. The secondary battery adhesive in the application reduces the occurrence of the phenomenon of friction and adhesive dropping, thereby improving the safety performance of the secondary battery.

Description

Technical Field

[0001] This application relates to the field of electrochemistry, specifically to a secondary battery and electronic device. Background Technology

[0002] In secondary batteries, due to the gap between the electrode assembly and the casing, the electrode assembly will move relative to the casing, requiring adhesives to be used for insulation protection and fixation of the secondary battery.

[0003] Commonly used adhesives, such as styrene-isoprene-styrene block copolymer (SIS) adhesive tape, are prone to localized detachment during the manufacturing process of secondary batteries due to friction. This results in bumps on the surface of the secondary battery after packaging, leading to poor battery appearance. These bumps become more noticeable with use and affect the safety performance of the secondary battery. Summary of the Invention

[0004] The purpose of this application is to provide a secondary battery and an electronic device to improve the safety performance of the secondary battery. The specific technical solution is as follows:

[0005] The first aspect of this application provides a secondary battery, including an electrode assembly, an electrolyte, a housing, and an adhesive. The adhesive includes a first adhesive layer and a second adhesive layer stacked together, disposed between the electrode assembly and the housing. The first adhesive layer adheres to the inner surface of the housing, and the second adhesive layer adheres to the outer surface of the electrode assembly. The first adhesive layer includes a styrene-isoprene-styrene block copolymer and wax. Based on the mass of the first adhesive layer, the wax content is 1% to 5% by mass. Without being limited to any theory, the inventors of this application have discovered that appropriately adding wax to the first adhesive layer can reduce the surface tack of the first adhesive layer, reducing the occurrence of adhesive detachment due to friction during the secondary battery manufacturing process, thereby improving the safety performance of the secondary battery.

[0006] In some embodiments of this application, the wax includes at least one of microcrystalline wax, paraffin wax, sasol wax, polyethylene wax, or polypropylene wax.

[0007] In some embodiments of this application, the wax content is 2% to 4% by mass, based on the mass of the first adhesive layer.

[0008] In some embodiments of this application, the first adhesive layer further includes a functional resin, wherein the mass percentage of the styrene-isoprene-styrene block copolymer is 65% to 95% based on the mass of the first adhesive layer, and the mass percentage of the functional resin is 10% to 30%; the functional resin includes at least one selected from ethylene-vinyl acetate copolymer, polyurethane elastomer, polyurethane acrylate, polyisobutylene, or polypropylene.

[0009] In some embodiments of this application, the first adhesive layer further includes additives and antioxidants; based on the mass of the first adhesive layer, the additives have a mass percentage content of 1% to 5%, and the antioxidants have a mass percentage content of 1% to 5%.

[0010] In some embodiments of this application, the adhesive further includes a substrate layer located between the first adhesive layer and the second adhesive layer; the substrate layer includes at least one of polyethylene terephthalate, polyimide, or polypropylene.

[0011] In some embodiments of this application, the first adhesive layer further includes a polar resin, including a styrene-ethylene-butene-polyethylene block copolymer and a polyolefin elastomer; based on the mass of the first adhesive layer, the polar resin has a mass percentage content of 5% to 10%, the styrene-ethylene-butene-polyethylene block copolymer (SEBS) has a mass percentage content of 3.5% to 9.5%, and the polyolefin elastomer has a mass percentage content of 0.5% to 1.5%.

[0012] In some embodiments of this application, the casing is a packaging bag.

[0013] In some embodiments of this application, the thickness of the first adhesive layer is 2 μm to 20 μm.

[0014] In some embodiments of this application, the peel strength between the first adhesive layer and the housing is from 10 N / m to 500 N / m.

[0015] A second aspect of this application provides an electronic device that includes a secondary battery as described in any of the foregoing embodiments. The secondary battery provided by this application has good safety performance, thereby providing the electronic device with good safety performance.

[0016] The beneficial effects of this application are:

[0017] This application provides a secondary battery and an electronic device, comprising an electrode assembly, an electrolyte, a housing, and an adhesive component. The adhesive component includes a first adhesive layer and a second adhesive layer stacked together, disposed between the electrode assembly and the housing. The first adhesive layer adheres to the inner surface of the housing, and the second adhesive layer adheres to the outer surface of the electrode assembly. The first adhesive layer comprises a styrene-isoprene-styrene block copolymer and wax. Based on the mass of the first adhesive layer, the wax content is 1% to 5% by mass. The secondary battery provided by this application includes an adhesive component comprising a first adhesive layer and a second adhesive layer stacked together. The first adhesive layer includes wax, which can reduce the surface tack of the first adhesive layer, thereby reducing the occurrence of adhesive detachment due to friction during the secondary battery manufacturing process, further improving the safety performance of the secondary battery, and satisfying the mass production processability requirements of the secondary battery.

[0018] Of course, implementing any product or method of this application does not necessarily require achieving all of the advantages described above at the same time. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other embodiments can be obtained based on these drawings.

[0020] Figure 1 This is a schematic diagram of the structure of the adhesive component in some embodiments of this application;

[0021] Figure 2 This is a schematic diagram of the adhesive component in some other embodiments of this application;

[0022] Figure 3 This is an assembly diagram of a secondary battery in some embodiments of this application.

[0023] Reference numerals: secondary battery 100; casing 10; electrode assembly 20; adhesive 30; first adhesive layer 31; second adhesive layer 32; substrate layer 33. Detailed Implementation

[0024] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0025] It should be noted that, in the specific embodiments of this application, lithium-ion batteries are used as an example of secondary batteries to explain this application, but the secondary batteries in this application are not limited to lithium-ion batteries.

[0026] The first aspect of this application provides a secondary battery, including an electrode assembly, an electrolyte, a housing, and an adhesive, such as... Figure 1As shown, the adhesive 30 includes a first adhesive layer 31 and a second adhesive layer 32 stacked together. The adhesive is disposed between the electrode assembly and the housing. The first adhesive layer adheres to the inner surface of the housing, and the second adhesive layer adheres to the outer surface of the electrode assembly. The first adhesive layer includes styrene-isoprene-styrene block copolymer (SIS) and wax. Based on the mass of the first adhesive layer, the mass percentage of wax is 1% to 5%. For example, the mass percentage of wax can be 1%, 2%, 3%, 4%, 5%, or a range of any two of these values. Without being limited to any theory, in the use of ordinary SIS colloids in secondary batteries, due to the high surface tack of the first adhesive layer and low adhesion to the substrate layer, coupled with dust accumulation on the pull-out surface and high frictional resistance, frictional delamination occurs. Adding wax to the first adhesive layer, when the mass percentage of wax is too high, will reduce the peel strength of the adhesive and worsen its electrochemical stability in the electrolyte. When the mass percentage of wax is too low, it will not achieve the effect of improving the safety performance of the secondary battery. When the amount of wax added is within the scope of this application, the surface tack of the first adhesive layer can be reduced, reducing the occurrence of adhesive peeling due to friction during the preparation of the secondary battery. Furthermore, since the improved adhesive has a smaller swelling rate in the electrolyte, the stability of the secondary battery during use is further guaranteed, thereby improving the safety performance of the secondary battery.

[0027] In some embodiments of this application, the wax includes at least one of microcrystalline wax, paraffin wax, sasol wax, polyethylene wax, or polypropylene wax. Without being limited to any particular theory, adding the aforementioned types of wax to the adhesive components of a secondary battery can reduce the surface tack of the first adhesive layer, decrease the occurrence of friction-induced delamination, and thereby improve the safety performance of the secondary battery.

[0028] In some embodiments of this application, the wax content by mass percentage is 2% to 4% based on the mass of the first adhesive layer. For example, the wax content by mass percentage can be 2%, 2.5%, 3%, 3.5%, 4%, or a range consisting of any two of these values. Controlling the wax content by mass percentage within the above range can reduce the surface tack of the first adhesive layer, reduce the occurrence of friction-induced adhesive failure, and thereby improve the safety performance of the secondary battery.

[0029] In some embodiments of this application, the first adhesive layer further includes a functional resin. Based on the mass of the first adhesive layer, the mass percentage of the styrene-isoprene-styrene block copolymer is 65% to 95%, and the mass percentage of the functional resin is 10% to 30%. The functional resin includes at least one of ethylene-vinyl acetate copolymer, polyurethane elastomer, polyurethane acrylate, polyisobutylene, or polypropylene. For example, the mass percentage of the styrene-isoprene-styrene block copolymer can be 65%, 70%, 75%, 80%, 85%, 90%, 95%, or any combination of two of these values, and the mass percentage of the functional resin can be 10%, 15%, 20%, 25%, 30%, or any combination of two of these values. By controlling the mass percentages of the styrene-isoprene-styrene block copolymer and the functional resin in the first adhesive layer within the above ranges, the morphological deformation of the bonded component can be reduced, the swelling degree of the bonded component immersed in the electrolyte is low, and the electrochemical stability is high, thereby improving the safety performance of the secondary battery.

[0030] In some embodiments of this application, the first adhesive layer further includes additives and antioxidants; based on the mass of the first adhesive layer, the mass percentage of the additives is 1% to 5%, and the mass percentage of the antioxidants is 1% to 5%. For example, the mass percentage of the additives can be 1%, 2%, 3%, 4%, 5%, or any combination of two of these values, and the mass percentage of the antioxidants can be 1%, 2%, 3%, 4%, 5%, or any combination of two of these values. By adding additives within the above range to the first adhesive layer, the heat resistance of the bonded component can be enhanced, the morphological deformation of the bonded component can be reduced, and a shaping effect can be achieved, thereby improving the safety performance of the secondary battery. By adding antioxidants within the above range to the first adhesive layer, oxidation failure of the bonded component in the high-temperature, high-humidity, gas-generating environment of the electrolyte can be prevented, thereby improving the safety performance of the secondary battery. This application does not limit the type of additives, as long as they can achieve the purpose of this application. For example, the additives include at least one of titanium dioxide, talc, silica, or calcium carbonate. This application does not limit the type of antioxidant, as long as it can achieve the purpose of this application. For example, antioxidants include at least one of diphenylamine, triphosphite, or dioctadecyl thiodipropionate.

[0031] In some embodiments of this application, such as Figure 2 As shown, the adhesive component 30 further includes a substrate layer 33, which is located between the first adhesive layer 31 and the second adhesive layer 32. The substrate layer includes at least one of polyethylene terephthalate, polyimide, or polypropylene. Due to the good insulation properties of the substrate layer material, the safety performance of the secondary battery can be further improved, while reducing the deformation of the adhesive component in high-temperature environments.

[0032] In some embodiments of this application, the first adhesive layer further includes a polar resin, comprising a styrene-ethylene-butene-polyethylene block copolymer and a polyolefin elastomer; based on the mass of the first adhesive layer, the mass percentage of the polar resin is 5% to 10%, the mass percentage of the styrene-ethylene-butene-polyethylene block copolymer is 3.5% to 9.5%, and the mass percentage of the polyolefin elastomer is 0.5% to 1.5%. For example, the mass percentage of the polar resin can be 5%, 6%, 7%, 8%, 9%, 10%, or a range consisting of any two of these values; the mass percentage of the styrene-ethylene-butene-polyethylene block copolymer can be 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, or a range consisting of any two of these values; and the mass percentage of the polyolefin elastomer can be 0.5%, 1%, 1.5%, or a range consisting of any two of these values. Polyolefin elastomers (POEs) are thermoplastic elastomers that undergo in-situ polymerization of ethylene and α-olefins using metallocene catalysts. Metallocene catalysts are catalyzed systems consisting of group IVB transition metal complexes (such as Ti, Zr, and Hf) as the main catalyst and alkylaluminoxanes (such as MAO) or organoboronides (such as B(C6F5)3) as co-catalysts. When the adhesive layer includes a substrate layer, adding a polar resin to the first adhesive layer makes the molecular chains of the first adhesive layer more flexible and reduces cohesion. This allows it to quickly develop adhesion at low temperatures, enhancing the adhesion of the first adhesive layer to the substrate layer. Furthermore, it reduces the likelihood of interface damage between the adhesive layer and the electrode assembly under external forces, thereby improving the safety performance of the secondary battery.

[0033] In some embodiments of this application, the casing is a packaging bag, which can improve the safety performance of the secondary battery.

[0034] In some embodiments of this application, the thickness of the first adhesive layer is from 2 μm to 20 μm. For example, the thickness of the first adhesive layer can be 2 μm, 4 μm, 6 μm, 8 μm, 10 μm, 12 μm, 14 μm, 16 μm, 18 μm, 20 μm, or a range of any two of these values. By controlling the thickness of the first adhesive layer within the above range, it is beneficial to reduce the loss of energy density in the secondary battery and improve the safety performance of the secondary battery.

[0035] In some embodiments of this application, the peel strength between the first adhesive layer and the casing is from 10 N / m to 500 N / m. For example, the peel strength between the first adhesive layer and the casing is 10 N / m, 50 N / m, 100 N / m, 150 N / m, 200 N / m, 250 N / m, 300 N / m, 350 N / m, 400 N / m, 450 N / m, 500 N / m, or a range consisting of any two of these values. By controlling the peel strength between the first adhesive layer and the casing within the above range, it is beneficial to reduce the phenomenon of tearing on the electrode surface at the edge of the bonded part, thereby improving the safety performance of the secondary battery. This application does not have any particular limitation on the type of material of the second adhesive layer, as long as it can achieve the purpose of this application. For example, the material of the second adhesive layer includes at least one of polymethyl methacrylate (PMMA, commonly known as acrylic), polypropylene (PP), polyethylene (PE), or polyamide.

[0036] This application does not impose any particular limitation on the preparation method of the adhesive, as long as it can achieve the purpose of this application. For example, this application can be prepared by the following method: mixing styrene-isoprene-styrene block copolymer, wax, polar resin, functional resin, additives, and antioxidants, mixing them evenly, and then coating them onto a substrate layer to form a first adhesive layer, which is then dried at 100°C to 150°C; coating the other side of the substrate layer with the material of the second adhesive layer to form a second adhesive layer, which is then dried at 60°C to 100°C to obtain the adhesive.

[0037] In this application, there is no particular limitation on the weight-average molecular weight of the styrene-ethylene-butene-styrene block copolymer. Those skilled in the art can select it according to actual needs, as long as the purpose of this application is achieved. For example, the weight-average molecular weight of the styrene-ethylene-butene-styrene block copolymer can be from 20,000 to 300,000.

[0038] In some embodiments of this application, the secondary battery includes an electrode assembly, a housing, an adhesive, and an electrolyte, with the electrode assembly and electrolyte housed within the housing. This application does not impose particular limitations on the structure of the electrode assembly, as long as it achieves the purpose of this application. For example, the electrode assembly can be a stacked structure, a wound structure, or a multi-tab structure. The electrode assembly includes a positive electrode, a negative electrode, and a separator, with the separator disposed between the positive and negative electrode. The separator separates the positive and negative electrode to prevent internal short circuits in the secondary battery, while allowing electrolyte ions to pass freely, thus facilitating the electrochemical charge-discharge process.

[0039] This application does not impose any particular limitation on the positive electrode sheet, as long as it achieves the purpose of this application. For example, the positive electrode sheet includes a positive current collector and a positive active material layer. This application does not impose any particular limitation on the positive current collector, as long as it achieves the purpose of this application. For example, the positive current collector may include aluminum foil, aluminum alloy foil, or a composite current collector. The positive active material layer of this application includes a positive active material. This application does not impose any particular limitation on the type of positive active material, as long as it achieves the purpose of this application. For example, the positive active material may include at least one of lithium nickel cobalt manganese oxide (NCM811, NCM622, NCM523, NCM111), lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide (LiCoO2), lithium manganese oxide, lithium manganese iron phosphate, or lithium titanate. In this application, the positive active material may also include non-metallic elements, such as at least one of fluorine, phosphorus, boron, chlorine, silicon, or sulfur, which can further improve the stability of the positive active material. In this application, there are no particular limitations on the thickness of the positive electrode current collector and the positive electrode active material layer, as long as the purpose of this application can be achieved. For example, the thickness of the positive electrode current collector is 5 μm to 20 μm, preferably 6 μm to 18 μm. The thickness of the single-sided positive electrode active material layer is 30 μm to 120 μm. In this application, the positive electrode active material layer can be disposed on one surface or on two surfaces in the thickness direction of the positive electrode current collector. Optionally, the positive electrode active material layer may also include a conductive agent and a binder. This application does not particularly limit the type of binder in the positive electrode active material layer, as long as the purpose of this application can be achieved. For example, the binder may include, but is not limited to, at least one of polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, or polyhexafluoropropylene. This application does not impose any particular limitation on the type of conductive agent in the positive electrode active material layer, as long as it can achieve the purpose of this application. For example, it may include, but is not limited to, at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fibers, flake graphite, Ketjen black, graphene, metallic materials, or conductive polymers. The aforementioned carbon nanotubes may include, but are not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The aforementioned carbon fibers may include, but are not limited to, vapor-grown carbon fibers (VGCF) and / or carbon nanofibers. The aforementioned metallic materials may include, but are not limited to, metal powders and / or metal fibers; specifically, the metal may include, but is not limited to, at least one of copper, nickel, aluminum, or silver. The aforementioned conductive polymers may include, but are not limited to, at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene, or polypyrrole. This application does not impose any particular limitation on the mass ratio of the positive electrode active material, conductive agent, and binder in the positive electrode active material layer; those skilled in the art can select according to actual needs, as long as the purpose of this application can be achieved.

[0040] There is no particular limitation on the negative electrode plate in this application, as long as the object of this application can be achieved. For example, the negative electrode plate includes a negative electrode current collector and a negative electrode active material layer. There is no particular limitation on the negative electrode current collector in this application, as long as the object of this application can be achieved. For example, the negative electrode current collector may include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam or copper foam, etc. The negative electrode active material layer of this application contains a negative electrode active material. There is no particular limitation on the type of the negative electrode active material in this application, as long as the object of this application can be achieved. For example, the negative electrode active material may include natural graphite, artificial graphite, mesocarbon microbeads (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composite, SiO x (0 < x < 2), Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, lithium titanate with spinel structure Li4Ti5O 12 , Li-Al alloy or at least one of metallic lithium. In this application, there is no particular limitation on the thickness of the negative electrode current collector and the negative electrode active material layer, as long as the object of this application can be achieved. For example, the thickness of the negative electrode current collector is 4 μm to 20 μm, and the thickness of the negative electrode active material layer is 30 μm to 130 μm. Optionally, the negative electrode active material layer may further include at least one of a conductive agent, a stabilizer, and a binder. There is no particular limitation on the types of the conductive agent, the stabilizer, and the binder in the negative electrode active material layer of this application, as long as the object of this application can be achieved. There is no particular limitation on the mass ratio of the negative electrode active material, the conductive agent, the stabilizer, and the binder in the negative electrode active material layer of this application, as long as the object of this application can be achieved.

[0041] There is no particular limitation on the separator in this application, as long as the object of this application can be achieved. For example, it may include but is not limited to at least one of polyethylene (PE), polypropylene (PP), polyolefin (PO) membranes mainly composed of polytetrafluoroethylene, polyester membranes (such as polyethylene terephthalate (PET) membranes), cellulose membranes, polyimide membranes (PI), polyamide membranes (PA), spandex, aramid membranes, woven membranes, non-woven membranes (non-woven fabrics), microporous membranes, composite membranes, separator papers, calendared membranes or spun membranes, and preferably PP. The separator of this application may have a porous structure, and there is no particular limitation on the size of the pore diameter, as long as the object of this application can be achieved. For example, the size of the pore diameter may be 0.01 μm to 1 μm. In this application, there is no particular limitation on the thickness of the separator, as long as the object of this application can be achieved. For example, the thickness may be 5 μm to 500 μm.

[0042] For example, the diaphragm may include a substrate layer and a surface treatment layer. The substrate layer may be a nonwoven fabric, membrane, or composite membrane with a porous structure, and the material of the substrate layer may include, but is not limited to, at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide. Optionally, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane may be used. Optionally, a surface treatment layer is provided on at least one surface of the substrate layer, and the surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing polymers and inorganic materials.

[0043] The inorganic layer may include, but is not limited to, inorganic particles and inorganic layer binders. This application does not impose any particular limitation on the inorganic particles, as long as they achieve the purpose of this application. For example, they may include, but are not limited to, at least one of alumina, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. This application does not impose any particular limitation on the inorganic layer binder. For example, it may include, but is not limited to, at least one of polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, or polyhexafluoropropylene. The polymer layer contains a polymer, and the polymer material may include, but is not limited to, at least one of polyamide, polyacrylonitrile, acrylate polymers, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride, or polyvinylidene fluoride and hexafluoropropylene.

[0044] In this application, the secondary battery further includes an electrolyte, which comprises a lithium salt and a non-aqueous solvent. The lithium salt may include at least one of LiPF6, LiBF4, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, Li2SiF6, lithium bis(oxalato)borate (LiBOB), or lithium difluoroborate. This application does not impose any particular limitation on the concentration of the lithium salt in the electrolyte, as long as it achieves the purpose of this application. For example, the concentration of the lithium salt in the electrolyte may be from 0.9 mol / L to 1.5 mol / L. Exemplarily, the concentration of the lithium salt in the electrolyte may be 0.9 mol / L, 1.0 mol / L, 1.1 mol / L, 1.3 mol / L, 1.5 mol / L, or a range consisting of any two of the above values. This application does not impose any particular limitation on non-aqueous solvents, as long as they can achieve the purpose of this application. For example, they may include, but are not limited to, at least one of carbonate compounds, carboxylic acid ester compounds, ether compounds, or other organic solvents. The aforementioned carbonate compounds may include, but are not limited to, at least one of chain carbonate compounds, cyclic carbonate compounds, or fluorinated carbonate compounds. The aforementioned chain carbonate compounds may include, but are not limited to, at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), or methyl ethyl carbonate (MEC). The aforementioned cyclic carbonates may include, but are not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), or vinyl ethylene carbonate (VEC). Fluorocarbonate compounds may include, but are not limited to, at least one of fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, or trifluoromethylethylene carbonate. The aforementioned carboxylic acid ester compounds may include, but are not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolactone, valproic acid lactone, or caprolactone. The aforementioned ether compounds may include, but are not limited to, at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran. The aforementioned other organic solvents may include, but are not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate.

[0045] This application does not impose any particular limitation on the type of secondary battery, which may include any device in which an electrochemical reaction occurs. For example, secondary batteries may include, but are not limited to: lithium metal secondary batteries, lithium-ion secondary batteries (lithium-ion batteries), sodium-ion secondary batteries (sodium-ion batteries), lithium polymer secondary batteries, and lithium-ion polymer secondary batteries.

[0046] This application does not impose any particular limitation on the shape of the secondary battery, as long as it can achieve the purpose of this application. For example, the shape of the secondary battery may include, but is not limited to: square, cylindrical, irregular shape (such as L-shaped, H-shaped, etc.).

[0047] This application does not impose any particular limitation on the preparation method of the secondary battery. Any preparation method known in the art can be used, as long as it can achieve the purpose of this application. For example, the preparation method of the secondary battery includes, but is not limited to, the following steps: stacking the positive electrode, separator, and negative electrode in sequence, and performing operations such as winding and folding as needed to obtain a wound electrode assembly; placing the electrode assembly in a packaging bag; injecting electrolyte into the packaging bag and sealing it to obtain a secondary battery; or, stacking the positive electrode, separator, and negative electrode in sequence, and then fixing the four corners of the entire stacked structure to obtain a stacked electrode assembly; placing the electrode assembly in a packaging bag; injecting electrolyte into the packaging bag and sealing it to obtain a secondary battery.

[0048] A second aspect of this application provides an electronic device that includes a secondary battery as described in any of the foregoing embodiments. Therefore, it offers good safety performance.

[0049] The electronic device described in this application is not particularly limited and can be any electronic device known in the prior art. For example, the electronic device may include, but is not limited to: laptop computers, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, household large-capacity batteries, and lithium-ion capacitors.

[0050] Example

[0051] The embodiments and comparative examples provided below illustrate the implementation of this application in more detail. Various tests and evaluations were conducted according to the methods described below. Furthermore, unless otherwise specified, "parts" and "%" are quality standards.

[0052] Test methods and equipment:

[0053] Peel strength test:

[0054] The peel strength of the lithium-ion battery adhesive was tested according to GB / T 2792-2014 "Test method for peel strength of adhesive tape".

[0055] (1) Adhere the adhesive to the aluminum foil and cut it into strips of 20mm×60mm. The length can be adjusted proportionally according to the actual situation.

[0056] (2) The other side of the above sample and the polypropylene side (25mm×100mm) of the packaging bag were placed under a temperature of 85℃ and a pressure of 1MPa for 40 minutes for hot pressing treatment, and then immersed in an electrolyte (the composition and preparation method are the same as in Example 1-1) at 85℃ for 4 hours. After immersion, the sample was wiped with lint-free paper. Along the length of the sample, the sample was pasted onto the steel plate with double-sided tape (Nitto 5000NS), with a pasting length of not less than 40mm.

[0057] (3) Fix the steel plate in the corresponding position of the high-speed rail tensile testing machine, pull up the other end of the packaging bag that is not adhered to the adhesive, put the sample into the clamp and clamp it, wherein the angle between the pulled sample part and the steel plate in space is 180°, the clamp pulls the sample at a speed of 5±0.2mm / s, and finally the average tensile strength of the stable area is recorded as the peel strength.

[0058] Friction-induced adhesive peeling test:

[0059] The adhesive component of the lithium-ion battery was attached to the electrode assembly, with the other side of the adhesive component facing the conveyor belt (the surfaces of which were respectively covered with polytetrafluoroethylene and mesh release film). Contact friction was performed at a speed of 0.1 m / s, and the adhesive component was observed to see if it had fallen off after 2 hours.

[0060] Pass rate of friction adhesive removal test = Number of friction adhesive removal tests passed / Total number of tests passed.

[0061] Roller test:

[0062] After the lithium-ion battery was left to stand at room temperature for 60 minutes, its voltage and capacity were tested. Before the drop, the battery voltage was measured to be 4.45V and the capacity to be 100%. The battery was placed in a special fixture and dropped 300 times (two drops count as one cycle) at a speed of 4 revolutions / min in a test environment of 20±5℃ using a special roller device.

[0063] Judgment criteria: No fire, no explosion, no cracking, no smoke, no leakage, and voltage drop <50mV.

[0064] Roller test pass rate = Number of rollers that pass the test / Total number of rollers.

[0065] Drop test:

[0066] The lithium-ion batteries were pretreated at 25°C and allowed to stand at room temperature for 60 minutes. After testing their voltage and capacity, the batteries were placed in a special fixture and dropped freely from a height of 1.5m using a specialized drop tester in the following sequence: head-tail-head right corner-tail right corner-head left corner-tail left corner (angle: 45±15°), repeated 6 times. The battery voltage and capacity were measured and recorded after each drop test. The appearance was checked and photographed before and after the test.

[0067] Judgment criteria: No fire, no explosion, no cracking, no smoke, no leakage, and voltage drop <30mV 24 hours after the test.

[0068] Drop test pass rate = Number of drop tests passed / Total number of tests passed.

[0069] Example 1-1

[0070] <Preparation of the positive electrode>

[0071] Lithium cobalt oxide (LiCoO2), a positive electrode active material, nano-conductive carbon black, and polyvinylidene fluoride (PVDF), a binder, were mixed in a weight ratio of 97.5:1.0:1.5. N-methylpyrrolidone (NMP) was added as a solvent to prepare a slurry with a solid content of 75%, and the mixture was stirred evenly. The slurry was uniformly coated onto one surface of a 9 μm thick aluminum foil used as a positive electrode current collector, and dried at 90°C to obtain a positive electrode sheet with a coating thickness of 110 μm. This completes the single-sided coating of the positive electrode sheet. The above steps were then repeated on the other surface of the positive electrode sheet to obtain a double-sided coated positive electrode sheet. After coating, the positive electrode sheet was cut for later use.

[0072] <Preparation of Negative Electrode Sheets>

[0073] Graphite powder (negative electrode active material), conductive carbon black (Super P) (conductive agent), and styrene-butadiene rubber (SBR) (batch) were mixed in a weight ratio of 96:1.5:2.5. Deionized water was then added as a solvent to prepare a slurry with a solid content of 70%, and the mixture was stirred thoroughly. The slurry was uniformly coated onto one surface of a 5 μm thick copper foil used as a negative electrode current collector, and dried at 110°C to obtain a single-sided negative electrode sheet with a coating thickness of 130 μm. This completes the single-sided coating of the negative electrode sheet. The above steps were then repeated on the other surface of the negative electrode sheet to obtain a double-sided negative electrode sheet with a negative electrode active material. After coating, the negative electrode sheet was cut for later use.

[0074] <Preparation of the diaphragm>

[0075] Alumina and polyvinylidene fluoride were mixed at a mass ratio of 90:10 and dissolved in deionized water to form a ceramic slurry with a solid content of 50%. The ceramic slurry was then uniformly coated onto one side of a porous substrate (polyethylene, 7 μm thick, average pore size 0.073 μm, porosity 26%) using a microgravure coating method. After drying, a bilayer structure of ceramic coating and porous substrate was obtained, with the ceramic coating having a thickness of 50 μm.

[0076] Polyvinylidene fluoride (PVDF) and polyacrylate were mixed at a mass ratio of 96:4 and dissolved in deionized water to form a polymer slurry with a solid content of 50%. The polymer slurry was then uniformly coated onto both surfaces of the above-mentioned ceramic coating and porous substrate bilayer structure using a microgravure coating method. After drying, a diaphragm was obtained, wherein the thickness of the single-layer coating formed by the polymer slurry was 2 μm.

[0077] <Preparation of Electrolyte>

[0078] In a dry argon atmosphere, organic solvents ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a mass ratio of 30:50:20 to obtain an organic solution. Then, lithium hexafluorophosphate is added to the organic solvent to dissolve and mix evenly to obtain an electrolyte with a lithium salt concentration of 1.15 mol / L.

[0079] <Preparation of Adhesive Components>

[0080] (1) Polyethylene terephthalate (PET) film is used as the substrate layer of the adhesive, and the substrate layer thickness is 12μm;

[0081] (2) Styrene-isoprene-styrene block copolymer (SIS), microcrystalline wax, polar resin (composed of highly cohesive styrene-ethylene-butene-styrene block copolymer and polyolefin elastomer, with a mass ratio of highly cohesive styrene-ethylene-butene-styrene block copolymer to polyolefin elastomer of 7:3), ethylene-vinyl acetate copolymer, additive titanium dioxide, and antioxidant diphenylamine are mixed in a mass ratio of 75:5:5:10:2.5:2.5. After being mixed evenly, the mixture is coated onto the substrate layer to form the first adhesive layer. The mixture is dried at 120°C. The thickness of the first adhesive layer is 8 μm.

[0082] (3) Polyacrylic acid is coated on the other side of the substrate layer to form a second adhesive layer, which is dried at 80°C. The thickness of the second adhesive layer is 4μm, and the final bonded part is obtained.

[0083] <Preparation of Lithium-ion Batteries>

[0084] The positive and negative electrode sheets prepared above are welded together with tabs, and then stacked sequentially with the prepared separator, so that the separator is positioned between the positive and negative electrodes to provide isolation. The electrodes are then wound to obtain a wound electrode assembly. Figure 3 As shown, an adhesive 30 is attached to the outer surface of the electrode assembly 20, which is then installed in the housing 10. After processes such as top and side sealing, vacuum drying, liquid injection, formation, capacity testing, and evacuation, a secondary battery 100 is manufactured.

[0085] Examples 1-2 to Examples 1-13

[0086] Except for adjusting the preparation parameters according to Table 1, the rest is the same as in Example 1-1.

[0087] Comparative Example 1-1

[0088] Except for the fact that only SIS adhesive is used in the first adhesive layer during the preparation of the adhesive component, the rest is the same as in Example 1-1.

[0089] Comparative Examples 1-2

[0090] Except that the first adhesive layer in the bonding process does not contain wax and the preparation parameters are adjusted according to Table 1, the rest is the same as in Example 1-1.

[0091] Comparative Examples 1-3 to 1-4

[0092] Except for the preparation parameters in Table 1, everything else is the same as in Examples 1-1.

[0093] The relevant preparation parameters and performance tests for each embodiment and comparative example are shown in Table 1.

[0094] Table 1

[0095]

[0096]

[0097] Note: " / " in Table 1 indicates that there is no corresponding preparation parameter.

[0098] As can be seen from Examples 1-1 to 1-13 and Comparative Examples 1-1 to 1-4, the addition of wax can improve the occurrence of friction-induced adhesive failure, further enhancing the safety performance of the secondary battery. In the use of ordinary SIS gel adhesives in lithium-ion batteries, the first adhesive layer contains only SIS, resulting in high surface tack and weak adhesion to the substrate layer. Furthermore, dust accumulation on the pull-out surface leads to high frictional resistance, causing friction-induced adhesive failure. Appropriately adding wax to the first adhesive layer can reduce its surface tack, decreasing the occurrence of friction-induced adhesive failure during secondary battery preparation. This increases the pass rate for friction-induced adhesive failure. Moreover, the roller test pass rate and drop test pass rate of Examples 1-1 to 1-13 are both higher than those of Comparative Example 1-2, further demonstrating that the addition of wax can improve the stability of lithium-ion batteries during use, thereby enhancing their safety performance.

[0099] The mass percentage of wax typically affects the safety performance of lithium-ion batteries. As can be seen from Examples 1-1 to 1-5, when the mass percentage of wax is within the range specified in this application, the surface tack of the first adhesive layer can be reduced, decreasing the occurrence of friction-induced adhesive failure and thus improving the safety performance of the lithium-ion battery. As can be seen from Examples 1-2 to 1-4, when the mass percentage of wax is 2% to 4%, the friction-induced adhesive failure rate of the lithium-ion battery is relatively high. Compared with Example 1-1, the roller test pass rate and drop test pass rate of Examples 1-2 to 1-4 are increased, further improving the safety performance of the lithium-ion battery.

[0100] The mass percentage of polar resin typically affects the safety performance of lithium-ion batteries. As can be seen from Examples 1-1 to 1-9, when the mass percentage of polar resin is within the range of this application, the pass rates for the roller test and drop test are higher, thereby improving the safety performance of the lithium-ion battery.

[0101] The thickness of the first adhesive layer typically affects the safety performance of lithium-ion batteries. As can be seen from Examples 1-6 to 1-9, as the thickness of the first adhesive layer increases, the peel strength between the first adhesive layer and the casing increases accordingly, thereby improving the safety performance of the lithium-ion battery.

[0102] Variations in the mass percentage of additives and antioxidants typically affect the peel strength between the first adhesive layer and the casing, thereby impacting the safety performance of lithium-ion batteries. As seen in Examples 1-3 and 1-11 to 1-13, when the mass percentage of SIS is within the range specified in this application, the peel strength between the first adhesive layer and the casing increases accordingly with increasing SIS mass percentage. However, when the peel strength exceeds 500 N / m, there is a possibility of tearing the aluminum foil, thus reducing the safety performance of the lithium-ion battery.

[0103] Based on the above analysis, it can be seen that adding wax to the first adhesive layer in the secondary battery adhesive can reduce the surface tack of the first adhesive layer, thereby reducing the occurrence of adhesive peeling due to friction during the secondary battery manufacturing process, further improving the safety performance of the secondary battery, and satisfying the mass production processability of the secondary battery.

[0104] It should be noted that, in this document, the terms “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, or article that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, or article.

[0105] The various embodiments in this specification are described in a related manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0106] The above description is merely a preferred embodiment of this application and is not intended to limit the scope of protection of this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application are included within the scope of protection of this application.

Claims

1. A secondary battery, comprising an electrode assembly, an electrolyte, a housing, and an adhesive, wherein the adhesive comprises a first adhesive layer and a second adhesive layer stacked together, the adhesive being disposed between the electrode assembly and the housing, the first adhesive layer being bonded to the inner surface of the housing, and the second adhesive layer being bonded to the outer surface of the electrode assembly; the first adhesive layer comprises a styrene-isoprene-styrene block copolymer and a wax; based on the mass of the first adhesive layer, the wax has a mass percentage content of 1% to 4%, and the styrene-isoprene-styrene block copolymer has a mass percentage content of 65% to 95%.

2. The secondary battery according to claim 1, characterized in that, The wax includes at least one of microcrystalline wax, paraffin wax, sasol wax, polyethylene wax, or polypropylene wax.

3. The secondary battery according to claim 1, characterized in that, Based on the mass of the first adhesive layer, the wax content is 2% to 4% by mass.

4. The secondary battery according to claim 1, characterized in that, The first adhesive layer further includes a functional resin, and the functional resin has a mass percentage content of 10% to 30% based on the mass of the first adhesive layer; the functional resin includes at least one of ethylene-vinyl acetate copolymer, polyurethane elastomer, polyurethane acrylate, polyisobutylene or polybutadiene.

5. The secondary battery according to claim 1, characterized in that, The first adhesive layer also includes additives and antioxidants; Based on the mass of the first adhesive layer, the additive has a mass percentage content of 1% to 5%, and the antioxidant has a mass percentage content of 1% to 5%.

6. The secondary battery according to claim 1, characterized in that, The adhesive further includes a substrate layer located between the first adhesive layer and the second adhesive layer; the substrate layer includes at least one of polyethylene terephthalate, polyimide, or polypropylene.

7. The secondary battery according to claim 6, characterized in that, The first adhesive layer further includes a polar resin, which includes a styrene-ethylene-butene-styrene block copolymer and a polyolefin elastomer; Based on the mass of the first adhesive layer, the polar resin has a mass percentage content of 5% to 10%, the styrene-ethylene-butene-styrene block copolymer has a mass percentage content of 3.5% to 9.5%, and the polyolefin elastomer has a mass percentage content of 0.5% to 1.5%.

8. The secondary battery according to claim 1, characterized in that, The casing is a packaging bag.

9. The secondary battery according to claim 1, characterized in that, The thickness of the first adhesive layer is 2 μm to 20 μm.

10. The secondary battery according to claim 1, characterized in that, The peel strength between the first adhesive layer and the shell is 10 N / m to 500 N / m.

11. An electronic device, characterized in that, Includes the secondary battery as described in any one of claims 1 to 10.

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