Adhesive film, secondary battery and electronic device

Abstract

The invention provides an adhesive film, a secondary battery and an electronic device. The adhesive film comprises a heat absorption layer and electrolyte-resistant layers, the electrolyte-resistant layers are arranged on the two surfaces of the heat absorption layer respectively, the thickness of the adhesive film is H [mu] m, the thickness of the heat absorption layer is H1 [mu] m, the sum of the thicknesses of the two electrolyte-resistant layers is H2 [mu] m, H is larger than or equal to 10 and smaller than or equal to 200, H1 / H is larger than or equal to 50% and smaller than or equal to 80%, H2 / H is larger than or equal to 20% and smaller than or equal to 50%, and the melting point of each electrolyte-resistant layer is larger than or equal to 100 DEG C. The endothermic enthalpy value of the adhesive film in the range of 25 DEG C to 300 DEG C is 220 J / cm < 3 > to 1500 J / cm < 3 >. The secondary battery provided by the invention has good safety performance.

Description

Technical Field

[0001] The present application relates to the field of electrochemical technologies, and particularly to a film, a secondary battery, and an electronic device. Background Art

[0002] Secondary batteries, such as lithium-ion batteries, are widely used in fields such as smart phones, wearable devices, consumer drones, and electric vehicles due to their advantages of high energy density, long cycle life, and no memory effect. With the wide application of lithium-ion batteries in the above fields, the market's requirement for the energy density of lithium-ion batteries is getting higher and higher. However, the continuous increase in energy density will lead to an increase in safety risks such as mechanical abuse and environmental abuse of lithium-ion batteries, and trigger safety problems such as thermal runaway. Therefore, there is an urgent need in the market for a lithium-ion battery with good safety performance. Summary of the Invention

[0003] The purpose of the present application is to provide a film, a secondary battery, and an electronic device to improve the safety performance of the secondary battery. The specific technical solutions are as follows:

[0004] In the first aspect of the present application, a film is provided, which includes an endothermic layer and an electrolyte-resistant layer. The electrolyte-resistant layers are respectively disposed on two surfaces of the endothermic layer. The thickness of the film is H μm, the thickness of the endothermic layer is H1 μm, and the sum of the thicknesses of the two electrolyte-resistant layers is H2 μm, where 10 ≤ H ≤ 200, 50% ≤ H1 / H ≤ 80%, 20% ≤ H2 / H ≤ 50%. The melting point of the electrolyte-resistant layer is greater than or equal to 100 °C, and the endothermic enthalpy value of the film in the range of 25 °C to 300 °C is 220 J / cm 3 to 1500 J / cm 3 . In the film of the present application, the electrolyte-resistant layer can be softened and melted above 100 °C, and the endothermic layer can absorb heat. Therefore, when the film of the present application is applied to a secondary battery, during the thermal abuse of the secondary battery, when the temperature inside the electrode assembly reaches above 100 °C, the electrolyte-resistant layer of the film begins to be softened and melted, and the endothermic layer can absorb more heat, thereby reducing the temperature inside the secondary battery, increasing the critical temperature of thermal runaway, reducing the risk of thermal runaway, and further improving the safety performance of the secondary battery.

[0005] In some embodiments of the present application, the melting point of the electrolyte-resistant layer is 100 °C to 400 °C. The melting point of the electrolyte-resistant layer within the above range is beneficial to improving the safety performance of the secondary battery.

[0006] In some embodiments of the present application, the heat-absorbing layer comprises a first material, and based on the mass of the heat-absorbing layer, the mass percentage of the first material is 30% to 100%. The first material comprises at least one of an organic phase change material or an inorganic phase change material. The organic phase change material comprises at least one of paraffin, polyethylene glycol, fatty acid, fatty alcohol or n-hexadecane. The inorganic phase change material comprises at least one of sodium sulfate decahydrate, magnesium sulfate heptahydrate, calcium nitrate tetrahydrate, sodium nitrate dihydrate, sodium carbonate decahydrate, calcium chloride hexahydrate, magnesium chloride hexahydrate, sodium phosphate dodecahydrate, sodium borate decahydrate, magnesium chloride, sodium chloride, aluminum hydroxide, magnesium hydroxide or a metal alloy. Selecting the above first material and controlling the mass percentage of the first material in the heat-absorbing layer within the above range is beneficial to increasing the heat absorption enthalpy value of the adhesive film so that it can absorb more heat, thereby being beneficial to improving the safety performance of the secondary battery.

[0007] In some embodiments of the present application, the heat-absorbing layer further comprises a second material, and based on the mass of the heat-absorbing layer, the mass percentage of the second material is 0% to 70%. The second material comprises at least one of polyethylene, polypropylene, polyethylene terephthalate, polyimide, polyvinyl chloride, polystyrene, polycarbonate, polyurethane, polyamide, polytetrafluoroethylene, polymethyl methacrylate, polyoxymethylene, polyphenylene sulfide, polyether ether ketone, polyether imide, polyacrylonitrile or polyvinyl alcohol. Selecting the above second material and controlling the mass percentage of the second material in the heat-absorbing layer within the above range is beneficial to improving the processing performance of the adhesive film while having good heat absorption ability, thereby being beneficial to improving the safety performance of the secondary battery.

[0008] In some embodiments of the present application, the electrolyte-resistant layer comprises at least one of polyethylene, polypropylene, polyethylene terephthalate, polyimide, polyvinyl chloride, polystyrene, polycarbonate, polyurethane, polyamide, polytetrafluoroethylene, polymethyl methacrylate, polyoxymethylene, polyphenylene sulfide, polyether ether ketone, polyether imide, polyacrylonitrile or polyvinyl alcohol. The electrolyte-resistant layer material has good electrolyte resistance and mechanical properties and is sensitive to temperature. Preparing it into an adhesive film and applying it to a secondary battery is beneficial to improving the safety performance of the secondary battery.

[0009] In some embodiments of the present application, a bonding layer is provided on the surface of any electrolyte-resistant layer of the adhesive film away from the heat-absorbing layer, and the thickness of the bonding layer is H3 μm, where 1 ≤ H3 ≤ 3. Providing a bonding layer on the surface of any electrolyte-resistant layer of the adhesive film and controlling the value of H3 within the above range can fix the adhesive film and have a small impact on the energy density of the secondary battery, thereby being beneficial to improving the safety performance of the secondary battery.

[0010] In some embodiments of the present application, the adhesive layer includes at least one of epoxy resin, acrylate, polyurethane, silicone glue, polyvinyl alcohol, silicone rubber, ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, polyethylene, or polypropylene. Selecting the above adhesive layer materials is beneficial for fixing the adhesive film, thereby facilitating the improvement of the safety performance of the secondary battery.

[0011] In some embodiments of the present application, the mass growth rate of the adhesive film after soaking in the electrolyte at 85°C for 24 hours is 0.01% to 2%. The mass growth rate of the adhesive film after soaking in the electrolyte at 85°C for 24 hours within the above range indicates that the adhesive film has good electrolyte resistance at relatively low temperatures (e.g., less than 100°C), thereby facilitating the improvement of the usage efficiency of the secondary battery on the basis of good safety performance.

[0012] In some embodiments of the present application, the tensile strength of the adhesive film is 10 MPa to 120 MPa. The tensile strength of the adhesive film within the above range indicates that the adhesive film has good mechanical properties, thereby facilitating the improvement of the safety performance and usage efficiency of the secondary battery.

[0013] The second aspect of the present application provides a secondary battery, which includes an electrode assembly, a housing, and the adhesive film provided in the first aspect of the present application. The adhesive film is disposed inside the housing, and based on the volume inside the housing, the volume ratio of the adhesive film is 0.1% to 5%. The secondary battery of the present application has good safety performance and high energy density at the same time.

[0014] In some embodiments of the present application, the electrode assembly is a wound structure, and the adhesive film is disposed in the inner empty foil area of the electrode assembly. The inner empty foil area refers to the current collector area where no active material is provided starting from the starting position of the pole piece winding. Disposing the adhesive film at the above position is beneficial for improving the safety performance of the secondary battery, and the secondary battery also has a high energy density.

[0015] In some embodiments of the present application, the adhesive film is disposed between the outer surface of the electrode assembly and the housing. Disposing the adhesive film at the above position is beneficial for improving the safety performance of the secondary battery, and the secondary battery also has a high energy density.

[0016] The third aspect of the present application provides an electronic device, which includes the secondary battery provided in the second aspect of the present application. The electronic device of the present application has a long service life and good performance.

[0017] Advantages of the present application:

[0018] The present application provides an adhesive film, a secondary battery, and an electronic device. The adhesive film includes a heat-absorbing layer and an electrolyte-resistant layer. The electrolyte-resistant layer is disposed on two surfaces of the heat-absorbing layer respectively. The thickness of the adhesive film is H μm, the thickness of the heat-absorbing layer is H1 μm, and the sum of the thicknesses of the two electrolyte-resistant layers is H2 μm. 10 ≤ H ≤ 200, 50% ≤ H1 / H ≤ 80%, 20% ≤ H2 / H ≤ 50%. The melting point of the electrolyte-resistant layer is greater than or equal to 100 °C. The heat absorption enthalpy value of the adhesive film in the range of 25 °C to 300 °C is 220 J / cm 3 to 1500 J / cm 3 . In the adhesive film of the present application, the electrolyte-resistant layer can be softened and melted above 100 °C, and the heat-absorbing layer can absorb heat. Therefore, when the adhesive film of the present application is applied to a secondary battery, during the thermal abuse of the secondary battery, when the temperature inside the electrode assembly reaches above 100 °C, the electrolyte-resistant layer of the adhesive film begins to be softened and melted, and the heat-absorbing layer can absorb more heat, thereby reducing the temperature inside the secondary battery, increasing the thermal runaway critical temperature, reducing the thermal runaway risk, and further improving the safety performance of the secondary battery.

[0019] Of course, it is not necessary for any product or method implementing the present application to achieve all the above-mentioned advantages simultaneously. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, other embodiments can also be obtained based on these drawings.

[0021] Figure 1 is a schematic structural diagram of the adhesive film in an implementation scheme of the present application along its thickness direction;

[0022] Figure 2 is a schematic structural diagram of the adhesive film in another implementation scheme of the present application along its thickness direction.

[0023] Reference numerals: adhesive film 10, heat-absorbing layer 11, electrolyte-resistant layer 12, adhesive layer 13. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0024] The following will clearly and completely describe the technical solutions in the present application in conjunction with the embodiments of the present application and the drawings. Obviously, the described embodiments are only some embodiments of the present application, rather than all embodiments. All other embodiments obtained by those skilled in the art based on the present application belong to the scope of protection of the present application.

[0025] It should be noted that in the specific embodiments of the present application, a lithium-ion battery is used as an example of a secondary battery to explain the present application. However, the secondary battery of the present application is not limited to lithium-ion batteries.

[0026] The first aspect of the present application provides a film, which includes a heat-absorbing layer and an electrolyte-resistant layer. The electrolyte-resistant layer is respectively disposed on two surfaces of the heat-absorbing layer. The thickness of the film is H μm, the thickness of the heat-absorbing layer is H1 μm, and the sum of the thicknesses of the two electrolyte-resistant layers is H2 μm, where 10 ≤ H ≤ 200, 50% ≤ H1 / H ≤ 80%, and 20% ≤ H2 / H ≤ 50%. For example, the value of H can be 10, 30, 50, 80, 100, 130, 150, 180, 200, or a range composed of any two of these values; the value of H1 / H can be 50%, 52%, 55%, 58%, 60%, 62%, 65%, 68%, 70%, 72%, 75%, 78%, 80%, or a range composed of any two of these values; the value of H2 / H can be 20%, 22%, 25%, 28%, 30%, 32%, 35%, 38%, 40%, 42%, 45%, 48%, 50%, or a range composed of any two of these values. The melting point of the electrolyte-resistant layer is greater than or equal to 100 °C. In some embodiments, the melting point of the electrolyte-resistant layer is 100 °C to 400 °C. For example, the melting point of the electrolyte-resistant layer can be 100 °C, 130 °C, 150 °C, 180 °C, 200 °C, 230 °C, 250 °C, 280 °C, 300 °C, 320 °C, 350 °C, 380 °C, 400 °C, or a range composed of any two of these values. The heat absorption enthalpy value of the film in the range of 25 °C to 300 °C is 220 J / cm 3 to 1500 J / cm 3 For example, the heat absorption enthalpy value of the film in the range of 25 °C to 300 °C can be 220 J / cm 3 、300 J / cm 3 、400 J / cm 3 、500 J / cm 3 、600 J / cm 3 、700 J / cm 3 、750 J / cm 3 、800 J / cm 3 、850 J / cm 3 、900 J / cm 3 、1000 J / cm 3 、1100 J / cm 3 、1200 J / cm 3 、1400 J / cm 3 、1500 J / cm 3 or a range composed of any two of these values.

[0027] The inventors' research found that during the thermal abuse of secondary batteries, the components in the electrode assembly react when heated, which can be summarized into the following six types of side reactions: the decomposition of the solid electrolyte interface film (SEI film), the reaction between the negative electrode active material and the electrolyte, the closing and bursting of the separator, the structural collapse and oxygen release of the positive electrode active material and its reaction with the electrolyte, the decomposition reaction of the electrolyte, and the reaction related to the binder in the secondary battery. During the above reaction process, significant heat accumulation will occur inside the secondary battery. A large amount of oxidizing or reducing gases are generated during the entire heat accumulation process, causing the housing to expand and deform, squeezing the electrode assembly until thermal runaway occurs. For the entire above-mentioned thermochemical reaction chain, developing targeted safety technologies to interrupt one of the reaction steps, or reducing the heat generation of a certain type of side reaction, or increasing the heat dissipation during the reaction process, or increasing the heat absorption during the temperature rise process inside the secondary battery before the thermal runaway temperature can improve the safety performance of the secondary battery.

[0028] Based on this, in this application, by designing the structure of the adhesive film, an adhesive film with a heat absorption layer and an electrolyte-resistant layer is obtained, and the values of H, H1 / H, and H2 / H are regulated within the scope of this application. The electrolyte-resistant layer has good electrolyte resistance and mechanical properties and is sensitive to temperature. The heat absorption layer can absorb the heat inside the secondary battery, and applying the above adhesive film to the secondary battery has little impact on the energy density. When the temperature inside the secondary battery is relatively low, such as less than 100 °C, the electrolyte-resistant layer will not melt and break under the normal application conditions of the secondary battery and has a relatively large mechanical strength, which can isolate and protect the heat absorption layer, reducing the probability of the heat absorption layer material dissolving into the electrolyte. At this time, the heat absorbed by the heat absorption layer of the adhesive film is also less, and the use of the adhesive film has little impact on the electrochemical performance of the secondary battery, which is beneficial to improving the use efficiency of the secondary battery. However, when the internal heat accumulation temperature of the secondary battery is too high (such as greater than 100 °C) during the thermal abuse process and there is a risk of thermal runaway, at this time, the secondary battery begins to undergo thermochemical reactions, generating gas and heat violently, and the electrolyte-resistant layer begins to soften and melt, and the heat absorption layer material is gradually released. The heat absorption layer can absorb more heat, reducing the temperature inside the secondary battery. Therefore, applying the adhesive film of this application to the secondary battery can absorb the heat inside the secondary battery during the thermal abuse process of the secondary battery, reduce the temperature rise of heat accumulation, increase the critical temperature of thermal runaway, and reduce the risk of thermal runaway, thereby improving the safety performance of the secondary battery on the basis of the secondary battery having a high energy density.

[0029] When the value of the thickness H of the adhesive film is too small, for example, less than 10, the tensile strength of the adhesive film is small, the mechanical properties are poor, and while the secondary battery loses a certain energy density, the heat absorption capacity of the adhesive film is limited, and the effect of reducing the thermal accumulation temperature rise is weak, which is not conducive to improving the safety performance of the secondary battery. When the value of the thickness H of the adhesive film is too large, for example, greater than 200, on the one hand, the manufacturing cost is increased, and on the other hand, the energy density of the secondary battery is reduced. When the value of H1 / H is too small and the value of H2 / H is too large, for example, the value of H1 / H is less than 50% and the value of H2 / H is greater than 50%, while the secondary battery loses a certain energy density, the heat absorption capacity of the adhesive film is limited, and the effect of reducing the thermal accumulation temperature rise is weak, and the effect of improving the safety performance of the secondary battery is weak. When the value of H1 / H is too large and the value of H2 / H is too small, for example, the value of H1 / H is greater than 80% and the value of H2 / H is less than 20%, the tensile strength of the adhesive film is small, the mechanical properties are poor, and the adhesive film is easily damaged during use, and the heat absorption layer material may dissolve in the electrolyte, affecting the electrochemical performance of the secondary battery (such as cycle performance, high-temperature storage performance, kinetic performance, etc.), resulting in a reduced cycle life. When the melting point of the electrolyte-resistant layer is too small, for example, less than 100 °C, when the internal thermal accumulation temperature of the secondary battery is relatively low, the secondary battery can still operate normally at this time, but the electrolyte-resistant layer has melted, and the heat absorption layer material may dissolve in the electrolyte, affecting the electrochemical performance and service efficiency of the secondary battery, and the probability of the adhesive film melting is relatively large during the preparation process of the lithium-ion battery, so it is also more difficult to apply the adhesive film to the secondary battery. When the endothermic enthalpy value of the adhesive film in the range of 25 °C to 300 °C is too small, for example, less than 220 J / cm 3 , while the secondary battery loses a certain energy density, the heat absorption capacity of the adhesive film is limited, and the effect of reducing the thermal accumulation temperature rise is weak, which is not conducive to improving the safety performance of the secondary battery. When the endothermic enthalpy value of the adhesive film in the range of 25 °C to 300 °C is too large, for example, greater than 1500 J / cm 3 , there are few choices of heat absorption layer materials that meet the above endothermic enthalpy value, the preparation difficulty is large, and the application to the secondary battery is difficult.

[0030] Exemplarily, as Figure 1 shown, define the length direction of the adhesive film itself as X and the thickness direction as Y. The adhesive film usually has a long side and a short side, and the above length direction is the extension direction of the long side of the adhesive film. It should be understood that the above definition of the direction is for the purpose of facilitating the description of the present application. The adhesive film 10 includes a heat absorption layer 11 and an electrolyte-resistant layer 12, and the electrolyte-resistant layer 12 is respectively disposed on two surfaces of the heat absorption layer 11.

[0031] In some embodiments, 5 ≤ H1 ≤ 160. For example, the value of H1 can be 5, 20, 50, 80, 100, 120, 140, 160 or a range composed of any two of these values.

[0032] In some embodiments, 2 ≤ H2 ≤ 100. For example, the value of H2 can be 2, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, or a range composed of any two of these numerical values. In this application, the thicknesses of the two electrolyte-resistant layers can be the same or different. Preferably, the thicknesses of the two electrolyte-resistant layers are the same.

[0033] In this application, the area of the electrolyte-resistant layer is larger than the area of the heat-absorbing layer, so that the electrolyte-resistant layer can completely cover the heat-absorbing layer. There is no particular limitation on the area of the adhesive film in this application, and a suitable area can be selected according to the size of the secondary battery and the heat absorption requirement, as long as the purpose of this application can be achieved. For example, the area of the adhesive film can be from 1 mm 2 to 10 6 mm 2 , and it can be selected according to the actual area of the secondary battery. The sizes of existing secondary batteries are diverse and the application area range is large, and the preparation process of the adhesive film is sufficient to meet the area requirements of existing secondary batteries.

[0034] In some embodiments of this application, the heat-absorbing layer includes a first material, and based on the mass of the heat-absorbing layer, the mass percentage of the first material is 30% to 100%. For example, the mass percentage of the first material can be 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%, or a range composed of any two of these numerical values. By adjusting the mass percentage of the first material in the heat-absorbing layer within the above range, it is beneficial to increase the heat absorption enthalpy value of the adhesive film so that it can absorb more heat and reduce the temperature inside the secondary battery, thereby being beneficial to improving the safety performance of the secondary battery.

[0035] In some embodiments of the present application, the first material includes at least one of an organic phase change material or an inorganic phase change material. The organic phase change material includes at least one of paraffin, polyethylene glycol, fatty acid, fatty alcohol or n-hexadecane. The above-mentioned fatty acid may include, but is not limited to, at least one of stearic acid, palmitic acid or oleic acid. The above-mentioned fatty alcohol may include, but is not limited to, at least one of dodecanol, tetradecanol, hexadecanol, octadecanol or docosanol. The inorganic phase change material includes at least one of sodium sulfate decahydrate (Na2SO4·10H2O), magnesium sulfate heptahydrate (MgSO4·7H2O), calcium nitrate tetrahydrate (Ca(NO3)2·4H2O), sodium nitrate dihydrate (NaNO3·2H2O), sodium carbonate decahydrate (Na2CO3·10H2O), calcium chloride hexahydrate (CaCl2·6H2O), magnesium chloride hexahydrate (MgCl2·6H2O), sodium hydrogen phosphate dodecahydrate (Na2HPO4·12H2O), sodium borate decahydrate (Na2B4O7·10H2O), magnesium chloride (MgCl2), sodium chloride (NaCl), aluminum hydroxide (Al(OH)3), magnesium hydroxide (Mg(OH)2) or a metal alloy. The above-mentioned metal alloy may include, but is not limited to, at least one of a tin-bismuth alloy, an indium-tin alloy or a bismuth-tin-zinc alloy. The above-mentioned first material can absorb heat and is prepared into a gel film for use in secondary batteries, which is beneficial to improving the safety performance of secondary batteries.

[0036] In some embodiments of the present application, the heat-absorbing layer further includes a second material, and based on the mass of the heat-absorbing layer, the mass percentage content of the second material is 0% to 70%. For example, the mass percentage content of the second material may be 0%, 10%, 20%, 30%, 40%, 50%, 60%, 70% or a range composed of any two of these values. The heat-absorbing layer includes the second material and regulates the mass percentage content of the second material within the above range. The second material has good plastic deformation ability, which is beneficial to improving its processing performance to form a film of the heat-absorbing layer while the gel film has good heat-absorbing ability, thereby being beneficial to improving the safety performance of secondary batteries.

[0037] In some embodiments of the present application, the second material includes at least one of polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polyimide (PI), polyvinyl chloride (PVC), polystyrene (PS), polycarbonate (PC), polyurethane (PU), polyamide (PA), polytetrafluoroethylene (PTFE), polymethyl methacrylate (PMMA), polyoxymethylene (POM), polyphenylene sulfide (PPS), polyetheretherketone (PEEK), polyetherimide (PEI), polyacrylonitrile (PAN), or polyvinyl alcohol (PVA). The above-mentioned second material has good plastic deformation ability. Selecting the above-mentioned second material is beneficial to improving the processing performance of the adhesive film to form the heat absorption layer, thereby being beneficial to improving the safety performance of the secondary battery.

[0038] In some embodiments, paraffin can be selected as the first material of the heat absorption layer, and polyethylene (PE) and / or polypropylene (PP) can be selected as the second material of the heat absorption layer. In some other embodiments, hydrated salt inorganic phase change materials can be selected as the first material of the heat absorption layer, such as sodium sulfate decahydrate (Na2SO4·10H2O), magnesium sulfate heptahydrate (MgSO4·7H2O), calcium nitrate tetrahydrate (Ca(NO3)2·4H2O), sodium nitrate dihydrate (NaNO3·2H2O), sodium carbonate decahydrate (Na2CO3·10H2O), calcium chloride hexahydrate (CaCl2·6H2O), magnesium chloride hexahydrate (MgCl2·6H2O), sodium hydrogen phosphate dodecahydrate (Na2HPO4·12H2O), sodium borate decahydrate (Na2B4O7·10H2O), and polyethylene (PE) and / or polypropylene (PP) can be selected as the second material of the heat absorption layer.

[0039] In some embodiments of the present application, the electrolyte-resistant layer includes at least one of polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polyimide (PI), polyvinyl chloride (PVC), polystyrene (PS), polycarbonate (PC), polyurethane (PU), polyamide (PA), polytetrafluoroethylene (PTFE), polymethyl methacrylate (PMMA), polyoxymethylene (POM), polyphenylene sulfide (PPS), polyetheretherketone (PEEK), polyetherimide (PEI), polyacrylonitrile (PAN), or polyvinyl alcohol (PVA). The electrolyte-resistant layer material has good electrolyte resistance and mechanical properties and is sensitive to temperature. Preparing it into an adhesive film and applying it to the secondary battery is beneficial to improving the safety performance of the secondary battery.

[0040] In some embodiments of the present application, a bonding layer is provided on the surface of any electrolyte-resistant layer of the adhesive film away from the heat-absorbing layer, and the thickness of the bonding layer is H3 μm, where 1 ≤ H3 ≤ 3. For example, the value of H3 can be 1, 1.2, 1.4, 1.6, 1.8, 2, 2.2, 2.4, 2.6, 2.8, 3 or a range composed of any two of these values. Providing a bonding layer on the surface of any electrolyte-resistant layer of the adhesive film and controlling the value of H3 within the above range can fix the adhesive film and have a relatively small impact on the energy density of the secondary battery, which is beneficial to reducing the risk that the adhesive film moves during the use of the secondary battery and affects the electrochemical performance of the secondary battery, thereby being beneficial to improving the safety performance of the secondary battery.

[0041] Exemplarily, as Figure 2 shown, the length direction of the adhesive film itself is defined as X, and the thickness direction is defined as Y. The adhesive film 10 includes a heat-absorbing layer 11, an electrolyte-resistant layer 12, and a bonding layer 13. The electrolyte-resistant layer 12 is provided on both surfaces of the heat-absorbing layer 11 respectively, and a bonding layer 13 is provided on the surface of one of the electrolyte-resistant layers 12 away from the heat-absorbing layer 11.

[0042] In some embodiments of the present application, the bonding layer includes at least one of epoxy resin, acrylate, polyurethane, silicone rubber, polyvinyl alcohol, organosilica gel, ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, polyethylene, or polypropylene. Selecting the above bonding layer materials is beneficial to fixing the adhesive film, reducing the risk that the adhesive film moves during the use of the secondary battery and affects the electrochemical performance of the secondary battery, thereby being beneficial to improving the safety performance of the secondary battery.

[0043] In some embodiments of the present application, the mass growth rate of the adhesive film after being immersed in the electrolyte at 85°C for 24 hours is 0.01% to 2%. For example, the mass growth rate of the adhesive film after being immersed in the electrolyte at 85°C for 24 hours can be 0.01%, 0.2%, 0.4%, 0.6%, 0.8%, 1.0%, 1.2%, 1.4%, 1.6%, 1.8%, 2% or a range composed of any two of these values. The mass growth rate of the adhesive film after being immersed in the electrolyte at 85°C for 24 hours within the above range indicates that the adhesive film has good electrolyte resistance at a relatively low temperature (for example, less than 100°C), can isolate and protect the heat-absorbing layer under the normal application conditions of the secondary battery, reduce the probability of the heat-absorbing layer material dissolving into the electrolyte, and the use of the adhesive film has a relatively small impact on the electrochemical performance of the secondary battery, thereby being beneficial to improving the use efficiency of the secondary battery on the basis of the secondary battery having good safety performance.

[0044] In some embodiments of the present application, the tensile strength of the adhesive film is 10 MPa to 120 MPa. For example, the tensile strength of the adhesive film can be 10 MPa, 30 MPa, 50 MPa, 70 MPa, 90 MPa, 100 MPa, 120 MPa, or a range composed of any two of these values. When the tensile strength of the adhesive film is within the above range, it indicates that the mechanical properties of the adhesive film are good, the risk of fracture and damage during application to secondary batteries is small, which is conducive to reducing the probability of the heat-absorbing layer material dissolving into the electrolyte under normal use conditions, and thus is conducive to improving the safety performance and service efficiency of secondary batteries.

[0045] The present application does not particularly limit the preparation method of the adhesive film, as long as the purpose of the present application can be achieved. For example, in some embodiments, the preparation of the adhesive film may include but is not limited to the following steps: The particles of the electrolyte-resistant layer material and the particles of the heat-absorbing layer material (the first material, or the first material and the second material) are respectively conveyed to a screw extruder through a vacuum suction feeder, melted and plasticized at high temperature, and then co-extruded and cast through three dies, where two dies are used for the preparation of the electrolyte-resistant layer and one die is used for the preparation of the heat-absorbing layer, to obtain a three-layer structure of electrolyte-resistant layer / heat-absorbing layer / electrolyte-resistant layer. It is cooled to room temperature for forming and cured at normal temperature to obtain the adhesive film.

[0046] In some other embodiments, the preparation of the adhesive film may include but is not limited to the following steps: (1) The particles of the electrolyte-resistant layer material are conveyed to a screw extruder through a vacuum suction feeder, melted and plasticized at high temperature, extruded and cast through a die, cooled to room temperature for forming, and cured at normal temperature to obtain the first electrolyte-resistant layer. (2) The particles of the electrolyte-resistant layer material and the particles of the heat-absorbing layer material (the first material, or the first material and the second material) are respectively conveyed to a screw extruder through a vacuum suction feeder, melted and plasticized at high temperature, and then co-extruded and cast through two dies, cooled to room temperature for forming, and cured at normal temperature to obtain a two-layer structure of heat-absorbing layer / second electrolyte-resistant layer. Subsequently, high-temperature and high-humidity treatment is carried out to make the first material of the heat-absorbing layer hydrate again to restore the high heat-absorbing enthalpy value. (3) The first electrolyte-resistant layer and the heat-absorbing layer / second electrolyte-resistant layer are thermally pressed and compounded to obtain the adhesive film.

[0047] In still some other embodiments, the preparation of the adhesive film may include but is not limited to the following steps: The particles of the electrolyte-resistant layer material are conveyed to a screw extruder through a vacuum suction feeder, melted and plasticized at high temperature, extruded and cast through a die, cooled to room temperature for forming, and cured at normal temperature to obtain the electrolyte-resistant layer. An adhesive is respectively coated on one surface of the two electrolyte-resistant layers, and the particles of the heat-absorbing layer material (the first material, or the first material and the second material) are coated on the surface of the electrolyte-resistant layer provided with the adhesive. The two electrolyte-resistant layers are stacked (the surfaces coated with the heat-absorbing layer material are opposite), and thermally pressed and compounded to obtain the adhesive film.

[0048] In some embodiments, a film-forming process, such as casting, blow molding, calendering, etc., is required during the preparation of the adhesive film. When there is a high-temperature step with a temperature greater than 100 °C during the preparation process, if the first material of the heat-absorbing layer is a hydrated salt-based inorganic phase change material, the above material is prone to dehydration and lose its heat-absorbing ability at high temperatures. Therefore, high-temperature and high-humidity treatment is required during the preparation of the adhesive film, specifically storing it for 24 h to 60 h in a temperature range of 25 °C to 60 °C and a humidity range of 75% to 95% RH, so that the hydrated salt-based inorganic phase change material rehydrates and restores its high heat-absorbing enthalpy value.

[0049] In the present application, the melting point of the electrolyte-resistant layer can be regulated by controlling the molecular weight of the electrolyte-resistant layer material and blending the same type of materials with different molecular weights. For example, when other conditions remain unchanged, the larger the molecular weight of the electrolyte-resistant layer material, the higher the melting point; the smaller the molecular weight of the electrolyte-resistant layer material, the lower the melting point. The type of the electrolyte-resistant layer material also affects its melting point.

[0050] In the present application, the heat-absorbing enthalpy value of the adhesive film in the range of 25 °C to 300 °C can be regulated by controlling the value of H1 / H. For example, when other conditions remain unchanged, the larger the value of H1 / H, the larger the heat-absorbing enthalpy value of the adhesive film in the range of 25 °C to 300 °C; the smaller the value of H1 / H, the smaller the heat-absorbing enthalpy value of the adhesive film in the range of 25 °C to 300 °C. The type of the first material of the heat-absorbing layer also affects the heat-absorbing enthalpy value of the adhesive film in the range of 25 °C to 300 °C.

[0051] In the present application, the first material and the second material in the electrolyte-resistant layer and the heat-absorbing layer of the adhesive film can be obtained by purchase, and the melting point of the electrolyte-resistant layer is tested by the "melting point test" test method provided in the present application, and the heat-absorbing enthalpy value of the adhesive film is tested by the "heat-absorbing enthalpy value test" test method, and the required electrolyte-resistant layer, the first material and the second material of the heat-absorbing layer are selected.

[0052] The second aspect of the present application provides a secondary battery, which includes an electrode assembly, a housing, and the adhesive film provided in the first aspect of the present application. The adhesive film is disposed inside the housing, and based on the volume inside the housing, the volume ratio of the adhesive film is 0.1% to 5%. For example, the volume ratio of the adhesive film can be 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or a range composed of any two of these values.

[0053] Apply the adhesive film of the present application to a secondary battery and adjust the volume ratio of the adhesive film within the scope of the present application. On the basis of having a relatively small impact on the energy density of the secondary battery, when the internal heat accumulation temperature of the secondary battery is too high (for example, greater than 100 °C), the adhesive film can absorb the internal heat, reduce the internal temperature of the secondary battery, increase the thermal runaway critical temperature, and reduce the risk of thermal runaway, thereby improving the safety performance of the secondary battery on the basis of the secondary battery having a high energy density. When the volume ratio of the adhesive film is too small, for example, less than 0.1%, while the secondary battery loses a certain amount of energy density, the heat absorption capacity of the adhesive film is limited, and the effect of reducing the temperature rise of heat accumulation is weak, and the effect of improving the safety performance of the secondary battery is weak. When the volume ratio of the adhesive film is too large, for example, greater than 5%, it affects the energy density of the secondary battery.

[0054] In some embodiments of the present application, the electrode assembly is a wound structure, and the adhesive film is disposed in the inner empty foil area of the electrode assembly. Specifically, the adhesive film can be disposed in the inner positive current collector empty foil area of the electrode assembly, or can be disposed in the inner negative current collector empty foil area of the electrode assembly. The position selection of the adhesive film needs to consider the balance between the energy density and thermal safety performance of the secondary battery. For a wound electrode assembly, there will be a temperature difference between the inner layer and the outer layer when the internal temperature of the secondary battery rises, and the temperature rise of the inner layer is greater than that of the outer layer. Disposing the adhesive film in the inner empty foil area of the electrode assembly is more conducive to absorbing the internal heat of the secondary battery, improving the heat absorption efficiency of the adhesive film, reducing the temperature rise of heat accumulation, and thus being beneficial to improving the safety performance of the secondary battery, and the secondary battery also has a high energy density.

[0055] In some embodiments of the present application, the adhesive film is disposed between the outer surface of the electrode assembly and the housing. At this time, the electrode assembly can be a wound structure or a stacked structure. The position selection of the adhesive film needs to consider the balance between the energy density and thermal safety performance of the secondary battery. In some embodiments, the adhesive film can be disposed at a position with a relatively large gap between the outer surface of the electrode assembly and the housing to reduce the impact on the energy density of the secondary battery. In other embodiments, the adhesive film can replace the end adhesive of the outermost layer of the electrode assembly or be compounded with the end adhesive (for example, styrene-isoprene-styrene (SIS) block copolymer). Disposing the adhesive film at the above positions is beneficial to improving the safety performance of the secondary battery, and the secondary battery also has a high energy density.

[0056] In the present application, the electrode assembly includes a positive electrode tab. The positive electrode tab includes a positive current collector and a positive electrode material layer disposed on at least one surface of the positive current collector. The above-mentioned "positive electrode material layer disposed on at least one surface of the positive current collector" means that the positive electrode material layer can be disposed on one surface of the positive current collector along its own thickness direction, or can be disposed on both surfaces of the positive current collector along its own thickness direction. It should be noted that the "surface" here can be the entire area of the positive current collector or a partial area of the positive current collector, and the present application has no special limitation as long as the purpose of the present application can be achieved.

[0057] The present application has no special limitation on the positive current collector as long as the purpose of the present application can be achieved. For example, it can include aluminum foil, aluminum alloy foil or a composite current collector (such as an aluminum-carbon composite current collector), etc.

[0058] The positive electrode material layer of the present application includes a positive electrode active material, and the positive electrode active material includes a substance that can reversibly insert and extract active ions such as lithium ions. The positive electrode material layer can be one layer or multiple layers, and each layer in the multiple positive electrode material layers can contain the same or different positive electrode active materials. The present application has no special limitation on the positive electrode active material as long as the purpose of the present application can be achieved. For example, the positive electrode active material can include, but is not limited to, at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminate, lithium iron phosphate, lithium-rich manganese-based material, lithium cobalt oxide (LiCoO2), lithium manganese oxide, lithium manganese iron phosphate or lithium titanate. The above-mentioned lithium nickel cobalt manganese oxide can include LiNi 0.95 Co 0.03 Mn 0.02 O2(Ni95), LiNi 0.91 Co 0.03 Mn 0.06 O2(Ni91), LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM811), LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM622), LiNi 0.5 Co 0.2 Mn 0.3 O2(NCM523) or LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2(NCM111) and the like.

[0059] The positive electrode material layer of the present application further includes a positive electrode conductive agent and a positive electrode binder. The present application has no particular limitation on the positive electrode conductive agent and the positive electrode binder in the positive electrode material layer, as long as the object of the present application can be achieved. For example, the positive electrode conductive agent may include, but is not limited to, at least one of conductive carbon black, carbon nanotubes (CNTs), carbon fibers, flake graphite, graphene, metal materials, or conductive polymers. The conductive carbon black may include, but is not limited to, at least one of acetylene black or Ketjen black. The above carbon nanotubes may include, but are not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The above carbon fibers may include, but are not limited to, vapor-grown carbon fibers (VGCF) and / or nanofibers. The above metal 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 above conductive polymers may include, but are not limited to, at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene, or polypyrrole. For example, the positive electrode binder may include, but is not limited to, at least one of polyacrylic acid, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyvinyl alcohol, carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, polyimide, polyamideimide, styrene-butadiene rubber, or polyvinylidene fluoride. The present application has no particular limitation on the mass ratio of the positive electrode active material, the positive electrode conductive agent, and the positive electrode binder in the positive electrode material layer. Those skilled in the art can select according to actual needs as long as the object of the present application can be achieved.

[0060] The present application has no particular limitation on the thickness of the positive electrode current collector, as long as the object of the present application can be achieved. For example, the thickness of the positive electrode current collector may be 6 μm to 25 μm. The present application has no particular limitation on the thickness of the positive electrode material layer, as long as the object of the present application can be achieved. For example, the thickness of the single-sided positive electrode material layer may be 50 μm to 120 μm.

[0061] Optionally, the positive electrode sheet may further include a conductive layer, and the conductive layer is located between the positive electrode current collector and the positive electrode material layer. The present application has no particular limitation on the composition of the conductive layer, and it may be a commonly used conductive layer in the art. For example, the conductive layer includes a conductive layer conductive agent and a conductive layer binder. The present application has no particular limitation on the conductive layer conductive agent and the conductive layer binder in the conductive layer. For example, the conductive layer conductive agent may be at least one of the above positive electrode conductive agents, and the conductive layer binder may be at least one of the above positive electrode binders.

[0062] In the present application, the electrode assembly includes a negative electrode tab. The negative electrode tab includes a negative current collector and a negative electrode material layer disposed on at least one surface of the negative current collector. The statement that "the negative electrode tab includes a negative current collector and a negative electrode material layer disposed on at least one surface of the negative current collector" means that the negative electrode material layer can be disposed on one surface of the negative current collector along its thickness direction, or can be disposed on both surfaces of the negative current collector along its thickness direction. It should be noted that the "surface" here can be the entire area of the surface of the negative current collector, or a partial area of the surface of the negative current collector. There is no special limitation in the present application, as long as the purpose of the present application can be achieved.

[0063] There is no special limitation on the negative current collector in the present application, as long as the purpose of the present application can be achieved. For example, it can include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam or a composite current collector. Exemplarily, the composite current collector can be a lithium-copper composite current collector, a carbon-copper composite current collector, a nickel-copper composite current collector or a titanium-copper composite current collector, etc.

[0064] The negative electrode material layer of the present application includes a negative electrode active material. There is no special limitation on the negative electrode active material in the present application, as long as the purpose of the present application can be achieved. For example, the negative electrode active material can include, but is not limited to, natural graphite, artificial graphite, mesophase carbon microbeads, hard carbon, soft carbon, silicon, silicon-carbon composite, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, lithiated TiO2-Li4Ti5O with a spinel structure 12 or at least one of Li-Al alloy.

[0065] The negative electrode material layer of the present application can also include a negative electrode conductive agent and a negative electrode binder. For example, the negative electrode conductive agent can be at least one of the above-mentioned positive electrode conductive agents, and the negative electrode binder can be at least one of the above-mentioned positive electrode binders. There is no special limitation on the mass ratio of the negative electrode active material, the negative electrode conductive agent and the negative electrode binder in the negative electrode material layer. Those skilled in the art can select according to actual needs, as long as the purpose of the present application can be achieved.

[0066] There is no special limitation on the thickness of the negative electrode material layer and the thickness of the negative current collector in the present application, as long as the purpose of the present application can be achieved. For example, the thickness of the negative electrode material layer can be 80 μm to 100 μm, and the thickness of the negative current collector can be 4 μm to 15 μm.

[0067] Optionally, the negative electrode sheet may further include a conductive layer, which is located between the negative electrode current collector and the negative electrode material layer. The present application has no particular limitation on the composition of the conductive layer, and it may be a commonly used conductive layer in the art. For example, the conductive layer includes a conductive agent for the conductive layer and a binder for the conductive layer. The present application has no particular limitation on the conductive agent for the conductive layer and the binder for the conductive layer in the conductive layer. For example, the conductive agent for the conductive layer may be at least one of the above-mentioned conductive agents for the positive electrode, and the binder for the conductive layer may be at least one of the above-mentioned binders for the positive electrode.

[0068] In the present application, the electrode assembly includes a separator. The present application has no particular limitation on the separator, as long as it can achieve the purpose of the present application. For example, the material of the separator may include, but is not limited to, at least one of polyolefins (PO) mainly composed of polyethylene (PE) and polypropylene (PP), polyester (for example, polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex or aramid. The type of the separator may include at least one of a woven film, a non-woven film, a microporous film, a composite film, a rolled film or a spun film.

[0069] In some embodiments, the separator may include a substrate layer and a surface treatment layer. The substrate layer may be a non-woven fabric or a composite film having a porous structure, and the material of the substrate layer may include at least one of polyethylene, polypropylene, polyethylene terephthalate or polyimide. Optionally, a polypropylene porous film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric or a polypropylene-polyethylene-polypropylene porous composite film may be used.

[0070] 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, an inorganic layer, or a layer formed by mixing a polymer and an inorganic substance.

[0071] In some embodiments, the inorganic layer includes ceramic particles and an inorganic layer binder. The present application has no particular limitation on the ceramic particles. For example, the ceramic particles may include at least one of silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, aluminum hydroxide, magnesium hydroxide, calcium hydroxide or barium sulfate. The present application has no particular limitation on the inorganic layer binder. For example, the inorganic layer binder may be at least one of the above-mentioned binders for the positive electrode. In some embodiments, the polymer layer includes a polymer, and the material of the polymer may include, but is not limited to, at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyethylene ether, polyvinylidene fluoride or poly(vinylidene fluoride-hexafluoropropylene).

[0072] In the present application, the thickness of the separator film is not particularly limited as long as the object of the present application can be achieved. For example, the thickness of the separator film can be 3 μm to 20 μm.

[0073] In the present application, the secondary battery further includes an electrolyte, and the electrolyte includes a lithium salt and a non-aqueous solvent.

[0074] The present application does not particularly limit the lithium salt as long as the object of the present application can be achieved. For example, the lithium salt can include, but is not limited to, at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, Li2SiF6, lithium bis(oxalato)borate (LiBOB), or lithium difluoroborate. The present application does not particularly limit the content of the lithium salt in the electrolyte as long as the object of the present application can be achieved.

[0075] The present application does not particularly limit the non-aqueous solvent as long as the object of the present application can be achieved. For example, the non-aqueous solvent can include, but is not limited to, at least one of carbonate compounds, carboxylate compounds, ether compounds, or other organic solvents.

[0076] The above-mentioned carbonate compounds may include, but are not limited to, at least one of chain carbonate compounds, cyclic carbonate compounds, or fluorinated carbonate compounds. The above-mentioned 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 above-mentioned cyclic carbonate compounds may include, but are not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), or vinylene ethylene carbonate (VEC). The above-mentioned fluorinated carbonate compounds may include, but are not limited to, at least one of fluorinated ethylene 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 trifluoromethyl ethylene carbonate. The above-mentioned carboxylic 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, decanolide, valerolactone, or caprolactone. The above-mentioned 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 above-mentioned 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-imidazolidinone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate. The present application does not particularly limit the content of the non-aqueous solvent in the electrolyte, as long as the object of the present application can be achieved.

[0077] The secondary battery further includes a housing for accommodating the adhesive film, the positive electrode sheet, the separator, the negative electrode sheet, and the electrolyte, as well as other components known in the field of secondary batteries. The present application does not limit the above-mentioned other components. The present application does not particularly limit the housing, and it may be a housing well-known in the art, as long as the object of the present application can be achieved. For example, the housing may be a hard shell housing or a flexible housing. The material of the hard shell housing may be metal. The present application does not limit the type of metal, and a metal hard shell housing known in the art may be used, as long as the object of the present application can be achieved. The flexible housing may be a metal plastic film, such as an aluminum plastic film, a steel plastic film, etc.

[0078] The secondary battery of the present application is not particularly limited and may include any device that undergoes an electrochemical reaction. In some embodiments, the secondary battery may include, but is not limited to, a lithium-ion secondary battery (lithium-ion battery), a lithium polymer secondary battery, or a lithium-ion polymer secondary battery, etc.

[0079] The preparation process of the secondary battery of the present application is well-known to those skilled in the art and is not particularly limited in the present application. For example, the preparation process of the secondary battery may include, but is not limited to, the following steps: stacking a positive electrode sheet, a separator, a negative electrode sheet, and a separator in sequence, and winding, folding, etc. as needed to obtain a wound electrode assembly with a wound structure, setting a glue film at a suitable position of the electrode assembly, then placing the electrode assembly into a housing, injecting an electrolyte into the housing and sealing it to obtain a secondary battery; or stacking a positive electrode sheet, a separator, a negative electrode sheet, and a separator in sequence, and then fixing the four corners of the entire laminated structure with tape to obtain a laminated electrode assembly, setting a glue film at a suitable position of the electrode assembly, then placing the electrode assembly into a housing, injecting an electrolyte into the housing and sealing it to obtain a secondary battery. In addition, an overcurrent protection element, a guide plate, etc. may be placed in the housing as needed to prevent the pressure inside the secondary battery from rising and overcharging / discharging.

[0080] The third aspect of the present application provides an electronic device, which includes the secondary battery provided by the second aspect of the present application. The electronic device of the present application has a long service life and good performance.

[0081] The electronic device of the present application is not particularly limited and may be any electronic device known in the prior art. In some embodiments, the electronic device may include, but is not limited to, a laptop computer, a pen-input computer, a mobile computer, an e-book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a headset stereo earphone, a video recorder, a liquid crystal TV, a portable cleaner, a portable CD player, a minidisc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, an automobile, a motorcycle, a moped, a bicycle, a lighting fixture, a toy, a game console, a clock, a power tool, a flash, a camera, a large household battery, and a lithium-ion capacitor, etc.

[0082] Examples

[0083] Hereinafter, examples and comparative examples are given to more specifically illustrate the embodiments of the present application. Various tests and evaluations are carried out according to the following methods. In addition, unless otherwise specified, "parts" and "%" are based on mass.

[0084] Testing methods and equipment:

[0085] Thickness Test

[0086] After discharging the lithium-ion battery at 0.2C to 3V, disassemble it to obtain the adhesive film. After cleaning the adhesive film with dimethyl carbonate (DMC), dry it at 60°C. Cut the adhesive film and polish the cross-section of the adhesive film along the thickness direction with argon ion polishing. Then use a scanning electron microscope (OXFORD·EDS) to observe and measure the thicknesses of the adhesive film, heat-absorbing layer, electrolyte-resistant layer, and bonding layer at three positions of the above cross-section. After taking the average value, obtain the thickness H of the adhesive film, the thickness H1 of the heat-absorbing layer, the sum H2 of the thicknesses of the electrolyte-resistant layer, and the thickness H3 of the bonding layer, and calculate H1 / H and H2 / H.

[0087] Melting point test

[0088] After discharging the lithium-ion battery at 0.2C to 0V, disassemble it to obtain the adhesive film. After cleaning the adhesive film with dimethyl carbonate (DMC), dry it at 60°C, and obtain the electrolyte-resistant layer by blade peeling. Refer to ASTM D3418-2021 Standard Test Method for Polymer Transition Temperatures, Enthalpies of Fusion, and Crystallinities by Differential Scanning Calorimetry. Use a differential scanning calorimeter (model DSC214), sample 5mg of the electrolyte-resistant layer material, and heat it from 30°C to 400°C at a rate of 10°C / min in an N2 environment. Obtain the melting point of the electrolyte-resistant layer according to the generated DSC curve.

[0089] Heat absorption enthalpy value test

[0090] Refer to the national standard "Thermal Analysis Test Method for Thermal Stability of Substances" (GB / T 13464-2008), and use a differential scanning calorimeter (model DSC214) to conduct thermogravimetric / heat absorption and exothermic (TG-DSC) tests. Introduce nitrogen inert gas, set the gas source pressure in the range of 0.01MPa to 0.04MPa, set the purge gas flow rate in the range of 30mL / min to 60mL / min, and set the protective gas N2 flow rate in the range of 15mL / min to 20mL / min. Place the adhesive film sample in the crucible and place the crucible on the bracket. Run the heating program at a heating rate of 10°C / min to obtain the corresponding thermogravimetric / heat absorption and exothermic (TG / DSC) curve. According to the TG / DSC curve, combined with the volume of the adhesive film sample, calculate the heat absorption enthalpy of the adhesive film in the temperature range of 25°C to 300°C, and obtain the heat absorption enthalpy value of the adhesive film in the range of 25°C to 300°C.

[0091] Mass growth rate test of the adhesive film after soaking in the electrolyte at 85°C for 24h

[0092] In an argon atmosphere glove box with a water content of less than 10 ppm, ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC) were uniformly mixed in a mass ratio of 10:30:60 to obtain a base solvent. Then, lithium salt LiPF6 was added and stirred evenly to obtain an electrolyte. Among them, based on the total mass of the electrolyte, the mass percentage of lithium salt LiPF6 was 12.5%, and the balance was the base solvent.

[0093] The film was dried in a vacuum drying oven at 40 °C for 6 h to remove adsorbed moisture or solvent. The mass of the film was weighed and recorded as M1 mg. The film was placed in a container containing sufficient electrolyte to ensure complete immersion. Then, the container was placed in an 85 °C constant temperature oven, baked for 24 h, taken out, left to stand at room temperature for 30 min, and then the electrolyte was poured out. The soaked film was dried in the air for 10 min, and the mass of the film at this time was weighed and recorded as M2 mg. The mass growth rate (%) of the film after soaking in the electrolyte at 85 °C for 24 h = (M2 - M1) / M1 × 100%.

[0094] Tensile strength test

[0095] At 25 °C, using a high-speed tensile testing machine, a film sample with a length of 3 cm and a width of 0.8 cm was cut. The tensile testing machine clamped the two ends of the film sample at the same size distance in the length direction, and the sample was stretched at 180°. The experimental parameters were set as a span of 2 mm and a stretching speed of 175 mm / min. The maximum tensile force F (unit: N) at which the film broke was obtained. Combining with the cross-sectional area A (unit: mm 2 ) of the film sample, the tensile strength σ = F / A was calculated by the formula, and the tensile strength σ (unit: MPa) of the film was measured.

[0096] Highest temperature test by hot box test

[0097] Adjust the temperature of the constant temperature furnace to 25°C. For each example and comparative example, 100 lithium-ion batteries are taken as samples and placed in the constant temperature furnace for 5 minutes of static placement. Then, the lithium-ion batteries are discharged at a constant current of 0.2C to 3.0V, statically placed for 10 minutes, charged at a constant current of 0.7C to 4.5V, charged at a constant voltage of 4.5V to 0.025C, and statically placed for 10 minutes. Take a photo before the hot box test, measure the voltage of the lithium-ion battery to make it at 100% SOC (state of charge), attach the temperature sensing wire to the surface of the lithium-ion battery, then put the lithium-ion battery into the heating furnace chamber, start heating from 25°C at a heating rate of 5±2°C / min to the target temperature (for example, 120°C, 125°C, 126°C, 127°C, 128°C, 129°C, 130°C, 132°C, 133°C, etc.) and keep it warm for 60 minutes. Take a photo after the test is over and measure the voltage of the lithium-ion battery. If the lithium-ion battery does not catch fire or explode, it indicates that it passes the hot box test. Record the highest temperature that each lithium-ion battery can pass. The highest temperature that 100 lithium-ion batteries can completely pass is recorded as the highest temperature at which the lithium-ion battery passes the hot box test. Characterize the safety performance of the lithium-ion battery by the highest temperature at which the lithium-ion battery passes the hot box test. The higher the highest temperature at which the lithium-ion battery passes the hot box test, the better the safety performance of the lithium-ion battery; the lower the highest temperature at which the lithium-ion battery passes the hot box test, the worse the safety performance of the lithium-ion battery.

[0098] Energy density test

[0099] Under the condition of 25°C, charge the lithium-ion battery at a constant current of 0.2C to the cut-off voltage of 4.5V, then charge at a constant voltage of 4.5V until the current is less than 0.05C. After static placement for 5 minutes, discharge at a constant current of 0.2C to the cut-off voltage of 3.0V and statically place for 5 minutes. Record the energy of the above discharge process as the discharge energy E. Calculate the volume V (mm 3 ) = length × width × height. Calculate the energy density of the lithium-ion battery according to the following formula: Energy density (Wh / L) = E / V×10 6 .

[0100] Example 1-1

[0101] <Preparation of the adhesive film>

[0102] (1) Convey the particles of the electrolyte-resistant layer material polypropylene to the screw extruder through a vacuum feeding machine, gradually melt and plasticize in the temperature range of 10 MPa and 180°C to 250°C, then extrude and cast through the die head at 230°C and 5 MPa, cool to room temperature for molding, and cure at normal temperature for 24 hours to obtain the first electrolyte-resistant layer.

[0103] (2) The particles of the electrolyte-resistant layer material polypropylene and the first material of the heat-absorbing layer, sodium sulfate decahydrate, are respectively conveyed to a screw extruder by a vacuum feeder, and are progressively melted and plasticized in a temperature range of 10 MPa and 180 °C to 250 °C. Then, they are co-extruded and cast through two dies at 230 °C and 5 MPa, cooled to room temperature for molding, and cured at room temperature for 24 h to obtain a two-layer structure of the heat-absorbing layer / second electrolyte-resistant layer. Store it in an environment of 40 °C and 80% RH humidity for 48 h to rehydrate the first material of the heat-absorbing layer and restore the high heat-absorbing enthalpy value.

[0104] (3) The first electrolyte-resistant layer and the heat-absorbing layer / second electrolyte-resistant layer are thermocompression bonded at 1 MPa and 100 °C to obtain a film with a structure of the first electrolyte-resistant layer / heat-absorbing layer / second electrolyte-resistant layer. Among them, the melting point, H, H1 / H, and H2 / H values of the electrolyte-resistant layer are shown in Table 1, and the thicknesses of the first electrolyte-resistant layer and the second electrolyte-resistant layer are the same.

[0105] (4) Coat an epoxy resin adhesive layer on the surface of the first electrolyte-resistant layer away from the heat-absorbing layer, and the thickness H3 of the adhesive layer is 2 μm.

[0106] <Preparation of the positive electrode plate>

[0107] Mix the positive electrode active material lithium cobaltate (LiCoO2), the positive electrode conductive agent conductive carbon black (Super P), and the positive electrode binder polyvinylidene fluoride in a mass ratio of 97.9:0.9:1.2, add N-methylpyrrolidone (NMP) as a solvent, and formulate a slurry with a solid content of 75 wt%. After vacuum stirring evenly, a positive electrode slurry is obtained. The positive electrode slurry is evenly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 10 μm, and dried at 90 °C to obtain a positive electrode plate with a single-sided coated positive electrode material layer. Then, repeat the above steps on the other surface of the aluminum foil to obtain a positive electrode plate with a double-sided coated positive electrode material layer. After drying at 90 °C, it is cold-pressed, and then cut into pieces and the tabs are welded to obtain a positive electrode plate with a specification of 74 mm × 867 mm for use. Among them, the thickness of the single-sided positive electrode material layer is 42 μm, and the compaction density of the positive electrode material layer is 4.3 g / cm 3 .

[0108] <Preparation of the negative electrode plate>

[0109] The negative electrode active material artificial graphite, the negative electrode binder styrene butadiene rubber, and the negative electrode conductive agent acetylene black are mixed in a mass ratio of 97.4:1.4:1.2, and deionized water is added as a solvent to prepare a slurry with a solid content of 45wt%. The negative electrode slurry is obtained after being stirred evenly by a vacuum mixer. The negative electrode slurry is evenly coated on one surface of a negative electrode current collector copper foil with a thickness of 6μm, and dried at 90°C to obtain a negative electrode sheet coated with a negative electrode material layer on one side. Then repeat the above steps on the other surface of the copper foil to obtain a negative electrode sheet coated with a negative electrode material layer on both sides. After drying at 90°C, cold pressing is performed, and then cutting and welding of the pole ears are performed to obtain a negative electrode sheet with a specification of 78mm×875mm for standby use. Among them, the thickness of the single-sided negative electrode material layer is 54.5μm, and the compaction density of the negative electrode material layer is 1.7g / cm 3 .

[0110] <Isolation film>

[0111] A polyethylene porous polymer film with a thickness of 5 μm (manufacturer: Celgard Membrane Co., Ltd., USA) was used as a separator.

[0112] <Preparation of Electrolyte>

[0113] In an argon atmosphere glove box with a water content of less than 10 ppm, ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC) are uniformly mixed at a mass ratio of 10:30:60 to obtain a base solvent, and lithium salt LiPF6 is added and stirred to obtain an electrolyte. Among them, based on the total mass of the electrolyte, the mass percentage of lithium salt LiPF6 is 12.5%, and the remainder is the base solvent.

[0114] <Preparation of lithium-ion batteries>

[0115] The positive electrode sheet, separator, negative electrode sheet and separator prepared above are stacked in order, so that the separator is between the positive electrode sheet and the negative electrode sheet to play an isolating role, and the electrode assembly is wound. The adhesive film is bonded to the outer surface of the electrode assembly, and the electrode assembly is placed in an aluminum-plastic film packaging bag so that the adhesive film is located between the outer surface of the electrode assembly and the aluminum-plastic film packaging bag, and the moisture is removed at 80°C, and the electrolyte prepared above is injected, and the lithium-ion battery is obtained through vacuum packaging, standing, formation (the upper limit voltage of formation is 4.5V, the formation temperature is 85°C, and the formation standing time is 2h), degassing, trimming and other processes. Among them, based on the volume inside the shell, the volume ratio of the adhesive film is shown in Table 1.

[0116] Example 1-2 to Example 1-9

[0117] Except for adjusting the corresponding preparation parameters according to Table 1, the rest is the same as in Example 1-1. Among them, in the <Preparation of the Gel Film>, when the first materials of the electrolyte-resistant layer and the heat-absorbing layer change, the temperatures in steps (1) to (3) change accordingly so that the electrolyte-resistant layer and the heat-absorbing layer can be melt-plasticized, extruded and cast, and hot-pressed and laminated.

[0118] Example 2-1

[0119] Except for using the following preparation method in step (2) of the <Preparation of the Gel Film>, the rest is the same as in Example 1-1.

[0120] <Preparation of the Gel Film>

[0121] (2) Except for separately conveying the particles of the polypropylene material of the electrolyte-resistant layer, the mixture of the first material sodium sulfate decahydrate of the heat-absorbing layer and the second material polypropylene of the heat-absorbing layer to the screw extruder through a vacuum suction feeder, the rest is the same as in Example 1-1. Among them, based on the mass of the heat-absorbing layer, the mass percentage contents of the first material and the second material are shown in Table 2.

[0122] Examples 2-2 to 2-4

[0123] Except for adjusting the corresponding preparation parameters according to Table 2, the rest is the same as in Example 2-1.

[0124] Example 2-5

[0125] Except for bonding the gel film in the empty foil area of the positive current collector in the <Preparation of the Lithium-Ion Battery> and being located in the inner empty foil area of the electrode assembly after winding, the rest is the same as in Example 1-1.

[0126] Comparative Example 1

[0127] Except for not carrying out the preparation of the gel film and not using the gel film in the <Preparation of the Lithium-Ion Battery>, the rest is the same as in Example 1-1.

[0128] Comparative Example 2

[0129] Except for using the following preparation method in the <Preparation of the Gel Film>, the rest is the same as in Example 1-1.

[0130] <Preparation of the Gel Film>

[0131] Convey the particles of the polypropylene material of the electrolyte-resistant layer to the screw extruder through a vacuum suction feeder, progressively melt and plasticize in the temperature range of 10 MPa and 180 °C to 250 °C, then extrude and cast at 230 °C and 5 MPa through a die head, cool to room temperature and form, and cure at room temperature for 24 h to obtain the electrolyte-resistant layer. The melting point, H, H1 / H, and H2 / H values of the electrolyte-resistant layer are shown in Table 1. Coat an epoxy resin adhesive layer on one surface of the electrolyte-resistant layer, and the thickness H3 of the adhesive layer is 2 μm.

[0132] Comparative Example 3

[0133] Except that the following preparation method is adopted for <Preparation of the Adhesive Film>, the rest is the same as that of Example 1-1.

[0134] <Preparation of the Adhesive Film>

[0135] Mix the first material of the endothermic layer, sodium sulfate decahydrate, and polypropylene in a mass ratio of 90:10, and convey it to a screw extruder through a vacuum feeder. Gradually melt and plasticize it in the temperature range of 10 MPa and 180°C to 250°C, and then extrude and cast it at 230°C and 5 MPa through a die head, cool it to room temperature for molding, and cure it at room temperature for 24 h to obtain the endothermic layer. The values of H, H1 / H, and H2 / H are shown in Table 1. Store it in an environment of 40°C and 80% RH humidity for 48 h to make the first material of the endothermic layer hydrate again to restore the high endothermic enthalpy value. Coat an epoxy resin adhesive layer on one surface of the endothermic layer, and the thickness H3 of the adhesive layer is 2 μm.

[0136] Comparative Examples 4 to 9

[0137] Except that the corresponding preparation parameters are adjusted according to Table 1, the rest is the same as that of Example 1-1. Among them, when the electrolyte-resistant layer and the first material of the endothermic layer change in <Preparation of the Adhesive Film>, the temperature in steps (1) to (3) changes accordingly so that the electrolyte-resistant layer and the endothermic layer can be melt-plasticized, extruded and cast, and hot-pressed and compounded.

[0138] Comparative Example 10

[0139] Except that the following preparation method is adopted for <Preparation of the Adhesive Film>, the rest is the same as that of Example 1-1.

[0140] <Preparation of the Adhesive Film>

[0141] Convey the particles of the electrolyte-resistant layer material, polypropylene, to a screw extruder through a vacuum feeder. Gradually melt and plasticize it in the temperature range of 10 MPa and 180°C to 250°C, and then extrude and cast it at 230°C and 5 MPa through a die head, cool it to room temperature for molding, and cure it at room temperature for 24 h to obtain the electrolyte-resistant layer. Seal deionized water in the middle of two electrolyte-resistant layers to obtain the adhesive film, where the melting point, H, H1 / H, and H2 / H values of the electrolyte-resistant layer are shown in Table 1, and the thicknesses of the two electrolyte-resistant layers are the same. Coat an epoxy resin adhesive layer on one surface of the electrolyte-resistant layer, and the thickness H3 of the adhesive layer is 2 μm.

[0142] The preparation parameters and performance parameters of each example and comparative example are shown in Tables 1 to 2.

[0143]

[0144] As can be seen from Examples 1-1 to 1-9 and Comparative Examples 1 to 10, in this application, by designing the structure of the adhesive film and regulating H, H1 / H, H2 / H, the melting point of the electrolyte-resistant layer, and the endothermic enthalpy value of the adhesive film in the range of 25°C to 300°C within the scope of this application, the adhesive film has a relatively high tensile strength and a relatively small mass growth rate after being immersed in the electrolyte at 85°C for 24 hours. When it is applied to a lithium-ion battery and the volume ratio of the adhesive film is regulated within the scope of this application, the highest temperature of the lithium-ion battery obtained by the hot box test is higher, indicating that the adhesive film of this application has good mechanical properties, the lithium-ion battery has good safety performance, and at the same time has a high energy density. In the lithium-ion battery of Comparative Example 1, there is no adhesive film. In Comparative Examples 2 and 3, the adhesive film does not simultaneously include an endothermic layer and an electrolyte-resistant layer. In Comparative Examples 4 to 7, H, H1 / H, and H2 / H of the adhesive film are not simultaneously within the scope of this application. In Comparative Example 8, the melting point of the electrolyte-resistant layer of the adhesive film is not within the scope of this application. In Comparative Examples 9 and 10, the endothermic enthalpy value of the adhesive film in the range of 25°C to 300°C is not within the scope of this application. The highest temperature of the lithium-ion batteries in Comparative Examples 1 to 10 obtained by the hot box test is lower, indicating that the safety performance of the lithium-ion battery is poor, and / or the energy density of the lithium-ion battery is low, and the lithium-ion battery cannot simultaneously take into account safety performance and energy density.

[0145] The thickness H of the adhesive film and the volume ratio of the adhesive film will affect the safety performance and energy density of the lithium-ion battery. As can be seen from Examples 1-1 to 1-3 and Comparative Examples 4 to 5, when the value of H and the volume ratio of the adhesive film are too small, such as in Comparative Example 4, the tensile strength of the adhesive film is small, and the mass growth rate after being immersed in the electrolyte at 85°C for 24 hours is large, and the highest temperature of the lithium-ion battery obtained by the hot box test is lower; when the value of H and the volume ratio of the adhesive film are too large, such as in Comparative Example 5, although the highest temperature of the lithium-ion battery obtained by the hot box test is relatively high, the energy density of the lithium-ion battery is too low, indicating that the safety performance of the lithium-ion battery is poor, or the energy density of the lithium-ion battery is low, and the lithium-ion battery cannot simultaneously take into account safety performance and energy density. When the value of H and the volume ratio of the adhesive film are within the scope of this application, the tensile strength of the adhesive film is large, the mass growth rate after being immersed in the electrolyte at 85°C for 24 hours is small, and the highest temperature of the lithium-ion battery obtained by the hot box test is higher, indicating that the adhesive film of this application has good mechanical properties, the lithium-ion battery has good safety performance, and at the same time has a high energy density.

[0146] The values of H1 / H and H2 / H can affect the safety performance of lithium-ion batteries. It can be seen from Examples 1-1, 1-4 to 1-5, and Comparative Examples 6 to 7 that when the value of H1 / H is too small and the value of H2 / H is too large, such as in Comparative Example 6, the maximum temperature at which the lithium-ion battery passes the hot box test is lower; when the value of H1 / H is too large and the value of H2 / H is too small, such as in Comparative Example 7, the tensile strength of the film is small, the mass growth rate after soaking in the electrolyte at 85°C for 24 hours is large, the mechanical properties of the film are poor, and it is easily damaged during the use of the lithium-ion battery, resulting in a reduced cycle life and deterioration of the performance of the lithium-ion battery (such as cycle performance, high-temperature storage performance, kinetic performance, etc.), indicating that the safety performance or electrochemical performance of the lithium-ion battery is poor and cannot be taken into account at the same time. When the values of H1 / H and H2 / H are within the scope of this application, the tensile strength of the film is large, the mass growth rate after soaking in the electrolyte at 85°C for 24 hours is small, and the maximum temperature at which the prepared lithium-ion battery passes the hot box test is higher, indicating that the film of this application has good mechanical properties, the lithium-ion battery has good safety performance, and at the same time has a high energy density.

[0147] The melting point of the electrolyte-resistant layer can affect the safety performance of lithium-ion batteries. It can be seen from Examples 1-1, 1-6 to 1-7, and Comparative Example 8 that when the melting point of the electrolyte-resistant layer is too small, such as in Comparative Example 8, the film is easily melted at a lower temperature, affecting the use efficiency of the lithium-ion battery, and the probability of the film melting during the preparation of the lithium-ion battery is relatively large, making it difficult to apply to lithium-ion batteries. When the melting point of the electrolyte-resistant layer is within the scope of this application, the tensile strength of the film is large, the mass growth rate after soaking in the electrolyte at 85°C for 24 hours is small, and the maximum temperature at which the prepared lithium-ion battery passes the hot box test is higher, indicating that the film of this application has good mechanical properties, the lithium-ion battery has good safety performance, and at the same time has a high energy density.

[0148] The endothermic enthalpy value of the film in the range of 25°C to 300°C can affect the safety performance of lithium-ion batteries. It can be seen from Examples 1-1, 1-8 to 1-9, and Comparative Examples 9 to 10 that when the endothermic enthalpy value of the film is too small, such as in Comparative Example 9, the maximum temperature at which the lithium-ion battery passes the hot box test is lower, indicating that the safety performance of the lithium-ion battery is poor; when the endothermic enthalpy value of the film is too large, such as in Comparative Example 10, it is difficult to prepare the film and it is difficult to apply to lithium-ion batteries. When the endothermic enthalpy value of the film is within the scope of this application, the tensile strength of the film is large, the mass growth rate after soaking in the electrolyte at 85°C for 24 hours is small, and the maximum temperature at which the prepared lithium-ion battery passes the hot box test is higher, indicating that the film of this application has good mechanical properties, the lithium-ion battery has good safety performance, and at the same time has a high energy density.

[0149] Table 2

[0150]

[0151] Note: " / " in Table 2 indicates no corresponding parameter.

[0152] The mass percentage contents of the first material and the second material of the heat-absorbing layer can affect the safety performance of the lithium-ion battery. It can be seen from Examples 1-1, 2-1 to 2-3 that when the mass percentage contents of the first material and the second material of the heat-absorbing layer are within the scope of this application, the tensile strength of the adhesive film is relatively large, the mass growth rate after soaking in the electrolyte at 85 °C for 24 h is relatively small, and the highest temperature of the lithium-ion battery prepared through the hot box test is relatively high, indicating that the adhesive film of this application has good mechanical properties, the lithium-ion battery has good safety performance, and at the same time has a high energy density.

[0153] The type of the second material of the heat-absorbing layer can affect the safety performance of the lithium-ion battery. It can be seen from Examples 2-1 and 2-4 that when the second material of the heat-absorbing layer within the scope of this application is selected, the tensile strength of the adhesive film is relatively large, the mass growth rate after soaking in the electrolyte at 85 °C for 24 h is relatively small, and the highest temperature of the lithium-ion battery prepared through the hot box test is relatively high, indicating that the adhesive film of this application has good mechanical properties, the lithium-ion battery has good safety performance, and at the same time has a high energy density.

[0154] The position of the adhesive film can affect the safety performance of the lithium-ion battery. It can be seen from Examples 1-1 and 2-5 that when the position of the adhesive film is set within the scope of this application, the tensile strength of the adhesive film is relatively large, the mass growth rate after soaking in the electrolyte at 85 °C for 24 h is relatively small, and the highest temperature of the lithium-ion battery prepared through the hot box test is relatively high, indicating that the adhesive film of this application has good mechanical properties, the lithium-ion battery has good safety performance, and at the same time has a high energy density.

[0155] It should be noted that in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variant thereof are intended to cover non-exclusive inclusion, so that a process, method or article including a series of elements not only includes those elements, but also includes other elements not expressly listed, or further includes elements inherent to such process, method or article.

[0156] Each embodiment in this specification is described in a related manner. For the same or similar parts between each embodiment, reference can be made to each other. The key point of each embodiment is to illustrate the differences from other embodiments.

[0157] The above are only the preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present application shall be included within the scope of protection of the present application.

Claims

1. A film comprising a heat absorption layer and an electrolyte resistant layer, wherein the electrolyte resistant layers are respectively arranged on two surfaces of the heat absorption layer, the thickness of the film is H μm, the thickness of the heat absorption layer is H1 μm, the sum of the thicknesses of the two electrolyte resistant layers is H2 μm, 10≤H≤200, 50%≤H1 / H≤80%, 20%≤H2 / H≤50%, The melting point of the electrolyte resistant layer is greater than or equal to 100°C, and the endothermic enthalpy of the adhesive film in the range of 25°C to 300°C is 220 J / cm 3 Up to 1500J / cm 3 .

2. The adhesive film according to claim 1, wherein: The melting point of the electrolyte resistant layer is 100°C to 400°C.

3. The adhesive film according to claim 1, wherein: The heat absorption layer comprises a first material, and based on the mass of the heat absorption layer, the mass percentage of the first material is 30% to 100%, The first material includes at least one of an organic phase change material or an inorganic phase change material, the organic phase change material includes at least one of paraffin, polyethylene glycol, fatty acid, fatty alcohol or n-hexadecane, and the inorganic phase change material includes at least one of sodium sulfate decahydrate, magnesium sulfate heptahydrate, calcium nitrate tetrahydrate, sodium nitrate dihydrate, sodium carbonate decahydrate, calcium chloride hexahydrate, magnesium chloride hexahydrate, sodium phosphate dodecahydrate, sodium borate decahydrate, magnesium chloride, sodium chloride, aluminum hydroxide, magnesium hydroxide or a metal alloy.

4. The adhesive film according to claim 3, wherein: The heat absorption layer further comprises a second material, and based on the mass of the heat absorption layer, the mass percentage of the second material is 0% to 70%, The second material includes at least one of polyethylene, polypropylene, polyethylene terephthalate, polyimide, polyvinyl chloride, polystyrene, polycarbonate, polyurethane, polyamide, polytetrafluoroethylene, polymethyl methacrylate, polyoxymethylene, polyphenylene sulfide, polyetheretherketone, polyetherimide, polyacrylonitrile or polyvinyl alcohol.

5. The adhesive film according to claim 1, wherein: The electrolyte-resistant layer includes at least one of polyethylene, polypropylene, polyethylene terephthalate, polyimide, polyvinyl chloride, polystyrene, polycarbonate, polyurethane, polyamide, polytetrafluoroethylene, polymethyl methacrylate, polyoxymethylene, polyphenylene sulfide, polyetheretherketone, polyetherimide, polyacrylonitrile or polyvinyl alcohol.

6. The adhesive film according to claim 1, wherein: A bonding layer is provided on a surface of any one of the electrolyte-resistant layers of the adhesive film away from the heat-absorbing layer, and a thickness of the bonding layer is H3 μm, 1≤H3≤3.

7. The adhesive film according to claim 6, wherein: The bonding layer includes at least one of epoxy resin, acrylate, polyurethane, silicone glue, polyvinyl alcohol, organic silica gel, ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, polyethylene or polypropylene.

8. The adhesive film according to any one of claims 1 to 7, wherein The mass growth rate of the adhesive film after being immersed in an electrolyte at 85° C. for 24 hours is 0.01% to 2%.

9. The adhesive film according to any one of claims 1 to 7, wherein The tensile strength of the adhesive film is 10 MPa to 120 MPa.

10. A secondary battery comprising an electrode assembly, a shell and the adhesive film according to any one of claims 1 to 9, wherein the adhesive film is arranged inside the shell, and based on the volume inside the shell, the volume of the adhesive film accounts for 0.1% to 5%.

11. The secondary battery according to claim 10, wherein The electrode assembly is a winding structure, and the adhesive film is arranged in the inner hollow foil area of ​​the electrode assembly.

12. The secondary battery according to claim 10, wherein The adhesive film is arranged between the outer surface of the electrode assembly and the shell. 13 . An electronic device comprising the secondary battery according to claim 10 .

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