Temperature-sensitive composite material, isolating membrane, positive pole piece, negative pole piece, secondary battery and electronic device

Abstract

The invention provides a temperature-sensitive composite material, an isolating membrane, a positive pole piece, a negative pole piece, a secondary battery and an electronic device. The temperature-sensitive composite material comprises an inner core and a shell arranged on the surface of the inner core, the average particle size of the temperature-sensitive composite material is D1 [mu] m, the average particle size of the inner core is D2 [mu] m, D2 / D1 is larger than or equal to 5% and smaller than or equal to 90%, and D1 is larger than or equal to 0.1 and smaller than or equal to 50 The shell comprises a first material, the inner core comprises a second material, the melting point of the first material is T1 DEG C, 100 < = T1 < = 200, the mass ratio of the temperature-sensitive composite material after absorbing the electrolyte at T1 temperature to the mass ratio of the temperature-sensitive composite material before absorbing the electrolyte is M, and 10 < = M < = 300. The secondary battery provided by the invention has good safety performance.

Description

Technical Field

[0001] The present application relates to the field of electrochemistry technology, and particularly to a temperature-sensitive composite material, a separator, a positive electrode sheet, a negative electrode sheet, 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 has higher and higher requirements for the energy density of lithium-ion batteries. 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 temperature-sensitive composite material, a separator, a positive electrode sheet, a negative electrode sheet, a secondary battery and an electronic device to improve the safety performance of the secondary battery. The specific technical solutions are as follows:

[0004] The first aspect of the present application provides a temperature-sensitive composite material. The temperature-sensitive composite material includes a core and a shell disposed on the surface of the core. The average particle size of the temperature-sensitive composite material is D1 μm, the average particle size of the core is D2 μm, 5% ≤ D2 / D1 ≤ 90%, 0.1 ≤ D1 ≤ 50; the shell includes a first material, the core includes a second material, the melting point of the first material is T1 °C, 100 ≤ T1 ≤ 200, and the mass ratio of the temperature-sensitive composite material after absorbing the electrolyte to that before absorbing the electrolyte at the temperature of T1 is M, 10 ≤ M ≤ 300. The first material of the shell of the temperature-sensitive composite material of the present application can be softened and melted above 100 °C, and the second material of the core can absorb the electrolyte. Therefore, when the temperature-sensitive composite material of the present application is applied to a secondary battery, during the thermal abuse of the secondary battery, when the internal temperature of the electrode assembly reaches above 100 °C, the first material of the shell of the temperature-sensitive composite material begins to be softened and melted, and the released second material of the core can absorb the electrolyte, reducing the violent exothermic reaction between the electrolyte and the positive electrode sheet and the negative electrode sheet, reducing the thermal accumulation temperature rise, increasing the critical temperature of thermal runaway, reducing the risk of thermal runaway, and thus improving the safety performance of the secondary battery.

[0005] In some embodiments of the present application, 0.3 ≤ D1 ≤ 20. By controlling the value of D1 within the above range, it is beneficial to further improve the safety performance of the secondary battery.

[0006] In some embodiments of the present application, 100 ≤ T1 ≤ 150. By controlling the value of T1 within the above range, it is beneficial to further improve the safety performance of the secondary battery.

[0007] In some embodiments of the present application, the first material includes at least one of polyethylene, polypropylene, polymethyl methacrylate, polyethylene terephthalate, polystyrene, polyvinyl chloride, polybutadiene, polyacrylamide, polyacrylic acid, nylon, styrene-based elastomer, ethylene-based elastomer, melamine resin, pentadecanol, hexadecanol, heptadecanol, octadecanol, paraffin wax, alginate, animal wax, plant wax, hardened oil, fatty acid, glyceryl tristearate, glyceryl distearate, lecithin, starch, sucrose, maltodextrin, corn syrup, cellulose, chitosan, soy protein, gum arabic, gelatin or agar. The electrolyte resistance and mechanical properties of the above-mentioned first material are good and it is sensitive to temperature. The prepared temperature-sensitive composite material is applied to secondary batteries, which is beneficial to improving the safety performance of secondary batteries.

[0008] In some embodiments of the present application, the second material includes at least one of a modified superabsorbent polymer, a cellulose derivative or a silicon-based material. The superabsorbent polymer includes at least one of sodium polyacrylate, polyacrylamide, polyvinyl alcohol, polyacrylic acid or polyvinylpyrrolidone. The cellulose derivative includes at least one of carboxymethyl cellulose or hydroxypropyl methyl cellulose. The silicon-based material includes at least one of silicone rubber or fumed silica. The above-mentioned second material has a high liquid absorption capacity and can absorb a large amount of vaporized and unvaporized electrolyte at high temperature. The prepared temperature-sensitive composite material is applied to secondary batteries, which is beneficial to improving the safety performance of secondary batteries.

[0009] In some embodiments of the present application, the core further includes a third material. Based on the mass of the core, the mass percentage content of the second material is 25% to 100%, and the mass percentage content of the third material is 0% to 75%. The core includes the third material and regulates the mass percentage content of the second material and the third material within the above range, which is beneficial to supporting the structure of the temperature-sensitive composite material, reducing the probability of core collapse, maintaining the shape and structure stability of the temperature-sensitive composite material, improving its mechanical properties, absorbing vaporized and unvaporized electrolyte at high temperature, and is also beneficial to improving the processing performance of the temperature-sensitive composite material, thereby being beneficial to improving the safety performance and electrochemical performance of secondary batteries under normal operating conditions.

[0010] In some embodiments of the present application, the melting point of the third material is T2 °C, T2 ≤ T1, 40 ≤ T2 ≤ 150. By regulating the melting point of the third material within the above range, it is beneficial to improving the safety performance of secondary batteries.

[0011] In some embodiments of the present application, the melt index of the third material is from 2 g / 10 min to 20 g / 10 min. Selecting the third material with a melt index within the above range is beneficial to release the second material that absorbs liquid in the core after the outer shell of the thermosensitive composite material melts at a relatively high internal heat accumulation temperature in the secondary battery (for example, greater than 100 °C), thereby being beneficial to improving the safety performance of the secondary battery.

[0012] In some embodiments of the present application, the third material includes at least one of polyolefin resin and its modified products, ethylene-based elastomer, styrene-based elastomer, polyvinylidene fluoride, chlorinated paraffin, carboxymethyl cellulose or hydroxypropyl methylcellulose. Selecting the above third material is beneficial to improving the safety performance of the secondary battery.

[0013] The second aspect of the present application provides a separator, which includes a substrate layer and a material coating provided on at least one surface of the substrate layer. The material coating includes the thermosensitive composite material provided in the first aspect of the present application. Based on the mass of the material coating, the mass percentage content of the thermosensitive composite material is from 1% to 99.5%. Applying the above separator to a secondary battery is beneficial to improving its safety performance.

[0014] In some embodiments, the average particle size of the thermosensitive composite material applied to the separator is D1 μm, where 0.1 ≤ D1 ≤ 10. Selecting the thermosensitive composite material with the above average particle size is beneficial to forming a dense material coating, improving the mechanical strength and thermal stability of the separator, and improving the safety performance of the secondary battery.

[0015] The third aspect of the present application provides a positive electrode plate, which includes a positive electrode current collector and a positive electrode material layer provided on at least one surface of the positive electrode current collector. The positive electrode material layer includes the thermosensitive composite material provided in the first aspect of the present application. Based on the mass of the positive electrode material layer, the mass percentage content of the thermosensitive composite material is from 0.01% to 5%. Applying the above positive electrode plate to a secondary battery is beneficial to improving its safety performance.

[0016] The fourth aspect of the present application provides a negative electrode plate, which includes a negative electrode current collector and a negative electrode material layer provided on at least one surface of the negative electrode current collector. The negative electrode material layer includes the thermosensitive composite material provided in the first aspect of the present application. Based on the mass of the negative electrode material layer, the mass percentage content of the thermosensitive composite material is from 0.01% to 5%. Applying the above negative electrode plate to a secondary battery is beneficial to improving its safety performance.

[0017] The fifth aspect of the present application provides a secondary battery, which includes at least one of the separator provided in the second aspect of the present application, the positive electrode plate provided in the third aspect of the present application, or the negative electrode plate provided in the fourth aspect of the present application. The secondary battery of the present application has good safety performance.

[0018] The sixth aspect of the present application provides an electronic device, which includes the secondary battery provided by the fifth aspect of the present application. The electronic device of the present application has a long service life and good performance.

[0019] Advantages of the present application:

[0020] The present application provides a thermosensitive composite material, a separator, a positive electrode sheet, a negative electrode sheet, a secondary battery and an electronic device. The thermosensitive composite material includes a core and a shell disposed on the surface of the core. The average particle size of the thermosensitive composite material is D1 μm, and the average particle size of the core is D2 μm, where 5% ≤ D2 / D1 ≤ 90% and 0.1 ≤ D1 ≤ 50; the shell includes a first material, and the core includes a second material. The melting point of the first material is T1 °C, where 100 ≤ T1 ≤ 200. The mass ratio of the thermosensitive composite material after absorbing the electrolyte to before absorbing the electrolyte at the temperature of T1 is M, where 10 ≤ M ≤ 300. The first material of the shell of the thermosensitive composite material of the present application can be softened and melted above 100 °C, and the second material of the core can absorb the electrolyte. Therefore, when the thermosensitive composite material of the present application is applied to a secondary battery, during the thermal abuse of the secondary battery, when the internal temperature of the electrode assembly reaches above 100 °C, the first material of the shell of the thermosensitive composite material begins to be softened and melted, and the released second material of the core can absorb the electrolyte, reducing the violent exothermic reaction between the electrolyte and the positive electrode sheet and the negative electrode sheet, reducing the heat accumulation temperature rise, increasing the critical temperature of thermal runaway, reducing the risk of thermal runaway, and thus improving the safety performance of the secondary battery.

[0021] Of course, it is not necessary for any product or method implementing the present application to achieve all the above-mentioned advantages simultaneously. Description of the Drawings

[0022] 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, and those of ordinary skill in the art can also obtain other embodiments based on these drawings.

[0023] Figure 1 It is a schematic structural diagram of a thermosensitive composite material according to an implementation solution of the present application;

[0024] Figure 2 It is a schematic structural diagram of a separator along its thickness direction according to an implementation solution of the present application.

[0025] Reference numerals: thermosensitive composite material 10, shell 11, core 12; separator 20, base material layer 21, material coating layer 22, adhesive layer 23. Detailed Embodiments

[0026] Next, the technical solutions in the present application will be clearly and completely described in conjunction with the embodiments of the present application and the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all of the 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.

[0027] 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.

[0028] A first aspect of the present application provides a thermosensitive composite material. The thermosensitive composite material includes a core and a shell disposed on the surface of the core. The average particle size of the thermosensitive composite material is D1 μm, and the average particle size of the core is D2 μm, where 5% ≤ D2 / D1 ≤ 90%, 0.1 ≤ D1 ≤ 50, and preferably, 0.3 ≤ D1 ≤ 20. For example, the value of D2 / D1 can be 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 90% or a range composed of any two of these values, and the value of D1 can be 0.1, 0.3, 0.5, 1, 5, 8, 10, 12, 15, 18, 20, 25, 30, 35, 40, 45, 50 or a range composed of any two of these values. The shell includes a first material, and the core includes a second material. The melting point of the first material is T1 °C, where 100 ≤ T1 ≤ 200, and preferably, 100 ≤ T1 ≤ 150. For example, the value of T1 can be 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200 or a range composed of any two of these values. The mass ratio of the thermosensitive composite material after absorbing the electrolyte to before absorbing the electrolyte at the temperature of T1 is M, where 10 ≤ M ≤ 300. For example, the value of M can be 10, 20, 50, 80, 100, 120, 150, 170, 200, 220, 250, 280, 300 or a range composed of any two of these values. In the present application, the average particle size D1 of the thermosensitive composite material refers to the average diameter of the circumscribed circle of the largest cross-section of the thermosensitive composite material particles, and the average particle size D2 of the core refers to the average diameter of the circumscribed circle of the largest cross-section of the core. In some embodiments, the shell of the thermosensitive composite material is disposed on the entire surface of the core.

[0029] 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: decomposition of the solid electrolyte interface film (SEI film), reaction between the negative electrode active material and the electrolyte, closing and bursting of the separator, structural collapse and oxygen release of the positive electrode active material and its reaction with the electrolyte, decomposition reaction of the electrolyte, and reaction related to the binder in the secondary battery. During the above reaction process, significant heat accumulation occurs inside the secondary battery, and 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 can improve the safety performance of secondary batteries.

[0030] Based on this, in this application, through material structure design, a thermosensitive composite material with a core and a shell is obtained, and the values of D2 / D1 and D1 are regulated within the scope of this application. The first material of the shell has good electrolyte resistance and mechanical properties and is sensitive to temperature. The second material of the core has a high liquid absorption capacity, such as a large specific surface area and porosity, and can absorb a large amount of electrolyte. Moreover, when the above thermosensitive composite material is applied to secondary batteries, it has little impact on the energy density. When the temperature inside the secondary battery is relatively low, for example, less than 100 °C, the first material of the shell will not soften, melt, or break under the normal operating conditions of the secondary battery, and has a relatively large mechanical strength, which can isolate and protect the second material of the core, reducing the risk that the second material of the core contacts the electrolyte under the normal operating conditions of the secondary battery, resulting in insufficient liquid retention in the secondary battery and deteriorating the electrochemical performance. At the same time, the use of the thermosensitive composite material has little impact on the electrochemical performance of the secondary battery, which is beneficial to improving the use efficiency of the secondary battery. During the thermal abuse of the secondary battery, when the internal heat accumulation temperature is too high (for example, greater than 100 °C) and there is a risk of thermal runaway, at this time, the secondary battery begins to undergo thermochemical reactions, generating gas and heat violently. The first material of the shell begins to soften, melt, and break, releasing the second liquid-absorbing material of the core. The second material of the core absorbs the high-temperature vaporized and unvaporized electrolyte, reducing the reaction between the electrolyte and the high-potential positive electrode active material and / or the lithium-fully-embedded negative electrode active material, and reducing the heat generation of the secondary battery. Therefore, when the thermosensitive composite material of this application is applied to secondary batteries, during the thermal abuse of the secondary battery, when the temperature inside the electrode assembly reaches above 100 °C, it can reduce the violent exothermic reaction between the electrolyte and the positive electrode plate and the negative electrode plate, 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 secondary batteries on the basis of their relatively high energy density.

[0031] When the value of D2 / D1 is too small, for example, less than 5%, the core accounts for too small a proportion, the ability of the thermosensitive composite material to absorb electrolyte is limited, and the effect of reducing the violent exothermic reaction between the electrolyte and the positive electrode sheet and the negative electrode sheet is weak, which is not conducive to improving the safety performance of the secondary battery. When the value of D2 / D1 is too large, for example, greater than 90%, the core accounts for too large a proportion and the shell accounts for too small a proportion, the thermosensitive composite material has a small crush resistance limit force and poor mechanical properties, and the probability of the shell rupturing and releasing the second material of the core under normal application conditions of the secondary battery increases, and the second material of the core absorbs electrolyte, resulting in insufficient liquid retention in the secondary battery, thereby affecting the safety performance of the secondary battery and also making the electrochemical performance worse. When the value of D1 is too small, for example, less than 0.1, the preparation requirements of the thermosensitive composite material are high, the preparation cost increases, and the thickness of the shell is small at this time, it is difficult for the first material to be located on the entire surface of the core, the stability at high temperature is poor and it is difficult to play its role, and it is difficult to apply it in practice. When the value of D1 is too large, for example, greater than 50, the thermosensitive composite material with an excessively large average particle size will affect the energy density of the secondary battery, and will occupy active sites when applied in the positive electrode material layer and / or the negative electrode material layer. The thermosensitive composite material with an excessively large average particle size will deteriorate the conductive network, causing the impedance of the positive electrode sheet and / or the negative electrode sheet to increase, and lithium is easily precipitated locally, thereby affecting the safety performance and electrochemical performance of the secondary battery. And because the thickness of the isolation membrane material coating is usually small, it is difficult to apply it to the isolation membrane. When the value of T1 is too small, for example, less than 100, when the heat accumulation temperature inside the secondary battery is low, the secondary battery can still work normally at this time, but the outer shell of the thermosensitive composite material has softened and melted, and the released core second material absorbs the electrolyte, making the secondary battery insufficient in terms of liquid retention, affecting the electrochemical performance and use efficiency of the secondary battery, and the safety performance is also poor. When the value of T1 is too large, for example, greater than 200, when the heat accumulation temperature inside the secondary battery is high, the shell of the thermosensitive composite material is still not completely melted, and the second material of the core is not completely released, which affects the effect of the second material of the core absorbing liquid, and the risk of thermal runaway of the secondary battery increases, thereby affecting the safety performance of the secondary battery. When the value of M is too small, for example, less than 10, the ability of the thermosensitive composite material to absorb electrolyte is limited, and the effect of reducing the violent exothermic reaction between the electrolyte and the positive electrode sheet and the negative electrode sheet is weak, which is not conducive to improving the safety performance of the secondary battery. When the value of M is too large, for example, greater than 300, the compression resistance limit force of the thermosensitive composite material is small and the mechanical properties are poor. Under normal application conditions of the secondary battery, the probability of the shell rupture and release of the second material of the core increases, and the absorption of electrolyte by the second material of the core leads to insufficient liquid retention in the secondary battery, thereby affecting the safety performance or electrochemical performance of the secondary battery.

[0032] For example, Figure 1The figure shows a schematic structural diagram of a temperature-sensitive composite material according to an embodiment of the present application. The temperature-sensitive composite material 10 includes a core 12 and a shell 11 disposed on all surfaces of the core 12. The average particle size of the temperature-sensitive composite material 10 is D1 μm, and the average particle size of the core 12 is D2 μm.

[0033] In some embodiments, 0.005 ≤ D2 ≤ 45. For example, the value of D2 can be 0.005, 2, 5, 10, 15, 20, 25, 30, 35, 40, 45, or a range composed of any two of these values.

[0034] In some embodiments, the average thickness of the shell is H1 μm, and 0.005 ≤ H1 ≤ 23.75. For example, the value of H1 can be 0.005, 2, 5, 8, 10, 12, 15, 18, 20, 23.75, or a range composed of any two of these values. In the present application, the average thickness H1 of the shell refers to the average value of the thickness of the shell in the direction of the maximum cross-sectional diameter of the temperature-sensitive composite material particles.

[0035] In some embodiments, 10% ≤ 2H1 / D1 ≤ 95%. For example, the value of 2H1 / D1 can be 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 95%, or a range composed of any two of these values.

[0036] In some embodiments, based on the mass of the temperature-sensitive composite material, the mass percentage content of the shell is 10% to 80%, and the mass percentage content of the core is 20% to 90%. For example, the mass percentage content of the shell can be 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or a range composed of any two of these values, and the mass percentage content of the core can be 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or a range composed of any two of these values. By controlling the mass percentage content of the shell and the core within the above range, when the internal heat accumulation temperature of the secondary battery is relatively low, for example, less than 100 °C, the electrolyte resistance performance and mechanical performance of the temperature-sensitive composite material are good, and the probability of the shell breaking and releasing the second material of the core is relatively low. When the internal heat accumulation temperature of the secondary battery is relatively high, for example, greater than 100 °C, it is beneficial for the second material of the core to absorb the high-temperature vaporized and unvaporized electrolyte, reduce the violent exothermic reaction between the electrolyte and the positive electrode plate and the negative electrode plate, and reduce the temperature rise of heat accumulation, thereby being beneficial to improving the safety performance of the secondary battery.

[0037] In some embodiments of the present application, the first material includes at least one of polyethylene, polypropylene, polymethyl methacrylate, polyethylene terephthalate, polystyrene, polyvinyl chloride, polybutadiene, polyacrylamide, polyacrylic acid, nylon, styrenic elastomers, ethylene-based elastomers, melamine resin, pentadecanol, hexadecanol, heptadecanol, octadecanol, paraffin wax, alginate, animal wax, plant wax, hardened oil, fatty acid, glyceryl tristearate, glyceryl distearate, lecithin, starch, sucrose, maltodextrin, corn syrup, cellulose, chitosan, soy protein, gum arabic, gelatin or agar. Among them, styrenic elastomers are a type of thermoplastic elastomer mainly composed of styrene, having the elasticity of rubber and the processing performance of thermoplastic plastics, and may include, but are not limited to, styrene-butadiene-styrene block copolymer (SBS), hydrogenated styrene-butadiene-styrene block copolymer (SEBS), styrene-isoprene-styrene block copolymer (SIS) or hydrogenated styrene-isoprene-styrene block copolymer (SEPS); ethylene-based elastomers refer to polymer materials with elasticity formed by copolymerizing ethylene as the main monomer with other monomers (such as α-olefins), and may include, but are not limited to, ethylene-α-olefin copolymer or ethylene-propylene rubber (EPM / EPDM); alginate may include at least one of sodium alginate, potassium alginate or calcium alginate; fatty acid may include at least one of stearic acid, palmitic acid or oleic acid. The above-mentioned first material has good electrolyte resistance and mechanical properties and is sensitive to temperature. The prepared thermosensitive composite material is applied to secondary batteries, which is beneficial to improving the safety performance of secondary batteries.

[0038] In some embodiments of the present application, the second material includes at least one of modified superabsorbent polymers, cellulose derivatives or silicon-based materials. The superabsorbent polymers include at least one of sodium polyacrylate, polyacrylamide, polyvinyl alcohol (PVA), polyacrylic acid (PAA) or polyvinylpyrrolidone (PVP). The cellulose derivatives include at least one of carboxymethyl cellulose (CMC) or hydroxypropyl methyl cellulose (HPMC). The silicon-based materials include at least one of silicone rubber or fumed silica. The above-mentioned second material has high liquid absorption capacity and can absorb a large amount of vaporized and unvaporized electrolytes at high temperature. The prepared thermosensitive composite material is applied to secondary batteries, which is beneficial to improving the safety performance of secondary batteries.

[0039] In the present application, the superabsorbent polymer refers to a polymer with a strong ability to absorb electrolyte. In some embodiments, modification refers to grafting groups that are affinity for the electrolyte (such as ester solvents, including but not limited to dimethyl carbonate, ethylene carbonate, diethyl carbonate, etc.), for example, ester groups (-COOR), where R can be a hydrocarbon group, and the above hydrocarbon group can be an alkyl group (such as methyl, ethyl, etc.) or an aryl group; carbonyl groups (-C=O), etc., so that the second material can rapidly absorb the electrolyte.

[0040] In some embodiments, the following materials can be selected to react with the second material to graft groups that are affinity for the electrolyte: (1) Polyethylene glycol methyl ether acrylate (PEGMA): The ether bond therein has a polarity matching with the electrolyte (such as ethylene carbonate (EC), dimethyl carbonate (DMC), etc.), which can enhance the compatibility between the second material and the electrolyte; (2) Trifluoroethyl methacrylate (TFEMA): The fluorinated segment therein can improve the wettability of the electrolyte; (3) 2-Hydroxyethyl acrylate (HEA): The hydroxyl group therein can enhance the hydrogen bond interaction with carbonate electrolytes.

[0041] In some embodiments, the modification of the second material may include but is not limited to the following steps:

[0042] 1. Preparation of porous crosslinked PAAS gel

[0043] Materials and reagents: Sodium polyacrylate (PAAS); Crosslinking agents: Epichlorohydrin (ECH, for chemical crosslinking), Calcium chloride (CaCl2, for ionic crosslinking); Initiator: Ammonium persulfate (APS, for free radical crosslinking); Solvent: Deionized water.

[0044] (1) Gradient crosslinking process:

[0045] ① Pre-crosslinking: Prepare a 10 wt% aqueous solution of PAAS, add the crosslinking agent CaCl2 for ionic crosslinking (the concentration of CaCl2 in the above solution is 0.5 wt% to 1 wt%), stir for 1 hour to form a primary network and obtain a pre-crosslinked system solution. The purpose of the above pre-crosslinking is to rapidly form a stable skeleton and prevent the structure from collapsing during subsequent grafting.

[0046] ② Chemical crosslinking strengthening: Add the crosslinking agent epichlorohydrin ECH for chemical crosslinking (the concentration of ECH in the pre-crosslinked system solution is 1 wt% to 2 wt%) and the initiator ammonium persulfate APS (the concentration of APS in the pre-crosslinked system solution is 0.1 wt%) to the pre-crosslinked system solution, heat up to 60 °C, and react for 3 hours to 5 hours. In the above steps, the dosage of the crosslinking agent needs to be controlled to reduce the risk of limited swelling of the second material caused by over-crosslinking.

[0047] (2) Post-treatment: Dialyze with deionized water for 3 days to remove unreacted reagents, and freeze-dry to obtain porous cross-linked PAAS gel.

[0048] 2. Grafting of pro-electrolyte groups

[0049] Materials and reagents: Cross-linked PAAS gel (crushed into particles with a particle size of 50 μm to 100 μm); Polyethylene glycol methyl ether acrylate (PEGMA, Mn = 500); Initiator: 2,2'-Azobis(2-methylpropionitrile) (AIBN); Solvent: N,N-Dimethylformamide (DMF).

[0050] (1) Swelling activation: Immerse the cross-linked PAAS gel in DMF and swell for 2 hours to relax the internal network.

[0051] (2) Grafting reaction: Prepare a DMF solution containing 20 wt% PEGMA and 0.5 wt% AIBN, and add the swollen PAAS gel (the mass ratio of PAAS gel to DMF solution is 1:5). Under nitrogen protection, react at 70 °C for 12 hours, and PEGMA is grafted onto the backbone of PAAS through free radicals.

[0052] (3) Purification: Wash repeatedly with acetone to remove unreacted monomers, and vacuum dry to obtain the second material-modified PAAS particles.

[0053] In some embodiments of the present application, based on the mass of the core, the mass percentage of the second material is 25% to 100%. For example, the mass percentage of the second material can be 25%, 40%, 50%, 60%, 70%, 80%, 90%, 100% or a range composed of any two of these values. By adjusting the mass percentage of the second material in the core within the above range, when the internal heat accumulation temperature of the secondary battery is relatively high, such as greater than 100 °C, it is beneficial for the second material in the core to absorb a large amount of high-temperature vaporized and non-vaporized electrolyte, reduce the violent exothermic reaction between the electrolyte and the positive and negative electrode plates, and reduce the temperature rise of heat accumulation, thereby being beneficial to improving the safety performance of the secondary battery.

[0054] In some embodiments of the present application, the core further includes a third material, and the mass percentage content of the third material is 0% to 75%. For example, the mass percentage content of the third material can be 0%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 75% or a range composed of any two of these values. The core includes the third material and regulates the mass percentage content of the third material within the above range, which is beneficial to supporting the structure of the thermosensitive composite material, reducing the probability of core collapse, maintaining the shape and structure stability of the thermosensitive composite material, improving its mechanical properties, absorbing the vaporized and unvaporized electrolyte at high temperature, and also beneficial to improving the processing performance of the thermosensitive composite material, thereby being beneficial to improving the safety performance and electrochemical performance of the secondary battery under normal use conditions.

[0055] In some embodiments of the present application, the melting point of the third material is T2 °C, T2 ≤ T1, 40 ≤ T2 ≤ 150. For example, the value of T2 can be 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150 or a range composed of any two of these values. By regulating the melting point of the third material within the above range, when the first material of the outer shell begins to soften and melt, exposing the second material and the third material of the core, the third material can synchronously complete the melting step, achieving the effect of releasing the second material that absorbs the electrolyte, improving the liquid absorption efficiency of the second material, and thus being beneficial to improving the safety performance of the secondary battery.

[0056] In some embodiments of the present application, the melt index of the third material is 2 g / 10 min to 20 g / 10 min. For example, the melt index of the third material can be 2 g / 10 min, 4 g / 10 min, 6 g / 10 min, 8 g / 10 min, 10 g / 10 min, 12 g / 10 min, 14 g / 10 min, 16 g / 10 min, 18 g / 10 min, 20 g / 10 min or a range composed of any two of these values. The melt index reflects the flow characteristics of the material at high temperature. The larger the melt index, the better the high-temperature fluidity of the material. Selecting the third material with a melt index within the above range is beneficial to quickly releasing the second material that absorbs liquid in the core when the outer shell of the thermosensitive composite material in the secondary battery melts and breaks due to high internal heat accumulation temperature (for example, greater than 100 °C), improving the liquid absorption efficiency of the second material, and thus being beneficial to improving the safety performance of the secondary battery.

[0057] In some embodiments of the present application, the third material includes at least one of polyolefin resin and its modified products, ethylene-based elastomer, styrene-based elastomer, polyvinylidene fluoride, chlorinated paraffin, carboxymethyl cellulose, or hydroxypropyl methyl cellulose. The above polyolefin resin may include, but is not limited to, polyethylene or polypropylene. Selecting the above third material is beneficial to supporting the structure of the thermosensitive composite material, reducing the probability of core collapse, maintaining the shape and structure stability of the thermosensitive composite material, improving its mechanical properties, absorbing the vaporized and unvaporized electrolyte at high temperature, and also beneficial to improving the processing performance of the thermosensitive composite material, thereby being beneficial to improving the safety performance of the secondary battery.

[0058] In the present application, the selection of the second material and / or the third material for the core of the thermosensitive composite material needs to consider its liquid absorption capacity on the one hand and its impact on the performance of the secondary battery, such as electrochemical stability, mechanical strength, processing performance, etc. on the other hand. In some embodiments, the core can be selected by blending a second material with high liquid absorption capacity and a third material with good processing performance. For example, the second material can be selected as modified superabsorbent polymer sodium polyacrylate (the above modification refers to chemical modification, such as introducing a hydrophobic group to enable it to quickly absorb the electrolyte), and the third material can be selected as polyvinylidene fluoride (PVDF) with bonding ability and good electrolyte resistance. In some embodiments, the core can be selected by blending a second material with high liquid absorption capacity and a third material that can absorb heat by phase change after 100°C. For example, the second material can be selected as modified superabsorbent polymer sodium polyacrylate, and the third material can be selected as chlorinated paraffin that can absorb heat by phase change after 100°C. In some embodiments, the core can be selected by blending a second material with high liquid absorption capacity, a third material with good processing performance, and a third material that can absorb heat by phase change after 100°C. For example, the second material can be selected as modified superabsorbent polymer sodium polyacrylate, and the third material can be selected as polyvinylidene fluoride (PVDF) with bonding ability and good electrolyte resistance, and chlorinated paraffin that can absorb heat by phase change after 100°C. In some embodiments, the core can be selected by blending a second material with high liquid absorption capacity and a third material of cellulose type. For example, the second material can be selected as modified superabsorbent polymer sodium polyacrylate, and the third material can be selected as at least one of carboxymethyl cellulose or hydroxypropyl methyl cellulose.

[0059] The preparation of the thermosensitive composite material of the present application is not particularly limited as long as the object of the present application can be achieved. For example, the preparation of the thermosensitive composite material can adopt the micelle method or the freeze-drying method. In some embodiments, the process of preparing the thermosensitive composite material by the freeze-drying method may include but is not limited to the following steps: preparing a polymer solution of the first material of the outer shell, adding the functional second material of the inner core, mixing and dispersing, then freezing and drying, and finally obtaining the thermosensitive composite material through grinding and sieving. In some embodiments, the process of preparing the thermosensitive composite material by the micelle method may include but is not limited to the following steps: preparing a solution of the first material of the outer shell, adding an emulsifier, and maintaining the emulsification stability; introducing the inner core material (the second material, or the second material and the third material), and emulsifying to obtain an emulsion; volatilizing the solvent of the solution of the first material of the outer shell, and curing to form an outer shell on the surface of the inner core material; separating, washing, and drying to obtain the thermosensitive composite material.

[0060] In some embodiments, the process of preparing the thermosensitive composite material may include but is not limited to the following steps:

[0061] (1) Preparation of the outer shell oil phase (PP solution)

[0062] High-temperature dissolution: Heat the solvent p-xylene to 130 °C to 140 °C, add the polypropylene PP particles of the outer shell material (the mass content of PP is 5 wt% to 10 wt%), stir until completely dissolved to form a transparent viscous solution. Cool down to 80 °C to 90 °C, add Span 80 (the concentration of Span 80 in the above solution is 2 wt% to 5 wt%), and maintain the emulsification stability. In the above preparation process, the mass content of PP can be 8 wt% to balance the emulsification viscosity and the density and thickness of the finally prepared outer shell. The emulsification temperature can be 80 °C to maintain the fluidity of the oil phase and reduce the probability of premature curing of PP.

[0063] (2) Preparation of the emulsion (W / O single emulsion)

[0064] Emulsification step: The modified PAAS particles of the second material of the inner core are swollen with N,N-dimethylformamide (DMF) to prepare a gel, and the above gel is slowly added to the PP oil phase at a volume ratio of 1:3. Emulsify with a high-speed homogenizer (rotation speed of 10,000 rpm to 15,000 rpm) for 5 minutes to 10 minutes to form a W / O emulsion. The droplet size can be adjusted by controlling the rotation speed and emulsification time of the high-speed homogenizer.

[0065] (3) Solvent volatilization and curing

[0066] Phase separation and solidification: Transfer the above W / O emulsion to an aqueous phase containing 1 wt% to 3 wt% of polyoxyethylene sorbitan monooleate Tween 80 (aqueous phase emulsifier) (the volume ratio of the W / O emulsion to the aqueous phase is 1:5), and stir at 40 °C to 50 °C for 4 hours to 6 hours (the rotation speed is 300 rpm to 500 rpm). During the stirring process, add acetone (the volume proportion of acetone in the above mixed system is 10%) to accelerate the solvent diffusion, improve the density of the shell, and p-xylene gradually volatilizes, and PP precipitates on the surface of the core material to form a dense shell.

[0067] (4) Post-treatment and drying

[0068] ① Separation and washing: Centrifuge (3000 rpm, 10 minutes) to collect the microcapsules, and wash them 3 times with a mixed solution of acetone and water to remove the residual emulsifier.

[0069] ② Drying: Freeze-dry (-50 °C, 24 hours) or spray-dry (inlet temperature 80 °C, outlet temperature 50 °C) to reduce the risk of high-temperature damage to the core structure and obtain the thermosensitive composite material.

[0070] When preparing the thermosensitive composite material by the above method, generally, the D2 of the thermosensitive composite material can be regulated by controlling the rotation speed and emulsification time of the high-speed homogenizer in the preparation of the emulsion. For example, when other conditions remain unchanged, as the rotation speed of the high-speed homogenizer increases, D2 decreases; as the rotation speed of the high-speed homogenizer decreases, D2 increases. When other conditions remain unchanged, as the emulsification time prolongs, D2 decreases; as the emulsification time shortens, D2 increases.

[0071] Generally, the average particle size D1 of the thermosensitive composite material can be regulated by controlling the stirring time, rotation speed and temperature during solvent evaporation and solidification, and the two-phase ratio in the W / O emulsion. For example, when other conditions remain unchanged, as the stirring time prolongs, D1 decreases; as the stirring time shortens, D1 increases. When other conditions remain unchanged, as the stirring rotation speed increases, D1 decreases; as the stirring rotation speed decreases, D1 increases.

[0072] Generally, the melting point T1 of the first material can be regulated by controlling the molecular weight of the first material and blending the same type of materials with different molecular weights. For example, when other conditions remain unchanged, the higher the molecular weight of the first material, the larger T1; the lower the molecular weight of the first material, the smaller T1. The type of the first material usually also affects its melting point, and for different types of the first material, the melting point T1 is usually different.

[0073] Generally, the M value can be regulated by controlling the value of D2. For example, when other conditions remain unchanged, as D2 increases, the M value increases; as D2 decreases, the M value decreases.

[0074] Under normal circumstances, the melting point T2 of the third material can be regulated by controlling the molecular weight of the third material. For example, when other conditions remain unchanged, the larger the molecular weight of the third material, the larger T2; the smaller the molecular weight of the third material, the smaller T2. The type of the third material usually also affects its melting point, and different types of the third material usually have different melting points T2.

[0075] In this application, the first material, the second material, and the third material in the thermosensitive composite material can be obtained by purchase. The melting points of the first material and the third material can be tested by the "melting point test" test method provided in this application, and the melt index of the third material can be tested by the "melt index test" test method, and the required first material, second material, and third material can be selected.

[0076] The second aspect of this application provides a separator. The separator includes a substrate layer and a material coating provided on at least one surface of the substrate layer. The material coating includes the thermosensitive composite material provided in the first aspect of this application. Based on the mass of the material coating, the mass percentage of the thermosensitive composite material is 1% to 99.5%. For example, the mass percentage of the thermosensitive composite material can be 1%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 99.5% or a range composed of any two of these values.

[0077] By providing a material coating on the separator in this application, the mechanical strength and thermal stability of the separator can be improved, the wettability of the electrolyte to the separator can be improved, and the safety performance and electrochemical performance of the secondary battery can be improved. Applying the thermosensitive composite material of this application to the material coating of the separator and regulating the mass percentage of the thermosensitive composite material within the scope of this application, on the basis of having little influence on the energy density of the secondary battery, the addition amount of the thermosensitive composite material can be relatively large. When the internal heat accumulation temperature of the secondary battery is relatively high, it can absorb more electrolyte, reduce the heat generation reaction between the electrolyte and the positive electrode plate and the negative electrode plate. At the same time, the first material of the outer shell softens and melts at high temperature and can also block the pores of the separator, reducing the interaction of the by-products of the side reactions of the positive electrode plate and the negative electrode plate through the separator, and further reducing the heat generation of the reaction, thereby further improving the safety performance of the secondary battery. In addition, when the thermosensitive composite material is applied to the separator, the ion and electron transmission rates in the secondary battery are relatively high and the impedance is relatively small. During the preparation process of the separator, high-temperature treatment is not required, reducing the risk that the outer shell is prematurely damaged and affects the function of the thermosensitive composite material.

[0078] When the mass percentage of the thermosensitive composite material is too small, for example, less than 1%, the ability of the thermosensitive composite material in the material coating to absorb the electrolyte is limited, and the effect of reducing the violent exothermic reaction between the electrolyte and the positive and negative electrode plates is weak, thus affecting the safety performance of the secondary battery. When the mass percentage of the thermosensitive composite material is too large, for example, greater than 99.5%, the mechanical strength of the separator material coating is low, which affects the K value of the secondary battery, and the content of the binder in the material coating is too low, and the thermosensitive composite material is easily detached and enters the electrolyte, thus affecting the safety performance and electrochemical performance of the secondary battery and being unable to meet the manufacturability, and it is difficult to apply to the secondary battery.

[0079] In some embodiments, the average particle size of the thermosensitive composite material applied to the separator is D1 μm, where 0.1 ≤ D1 ≤ 10. Selecting the thermosensitive composite material with the above average particle size is beneficial to forming a dense material coating, improving the mechanical strength and thermal stability of the separator, and improving the safety performance of the secondary battery.

[0080] In some embodiments, the material coating further includes inorganic particles and a material coating binder. Based on the mass of the material coating, the mass percentage of the inorganic particles is 0% to 98.5%, and the mass percentage of the material coating binder is 0.5% to 15%. For example, the mass percentage of the inorganic particles can be 0%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 98.5% or a range composed of any two of these values, and the mass percentage of the material coating binder can be 0.5%, 2%, 4%, 6%, 8%, 10%, 12%, 14%, 15% or a range composed of any two of these values. There is no particular limitation on the inorganic particles in this application. For example, the inorganic particles can include but are not limited to at least one of silicon oxide, aluminum 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. There is no particular limitation on the material coating binder in this application. For example, the material coating binder can include but are 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.

[0081] In some embodiments, the separator membrane comprises a substrate layer, a material coating disposed on one surface of the substrate layer, and an adhesive layer disposed on the other surface of the substrate layer. In other embodiments, the separator membrane comprises a substrate layer, a material coating disposed on one surface of the substrate layer, and an adhesive layer disposed on the surface of the material coating away from the substrate layer. In still other embodiments, the separator membrane comprises a substrate layer, an adhesive layer disposed on one surface of the substrate layer, and a material coating and an adhesive layer sequentially disposed on the other surface of the substrate layer. The adhesive layer comprises a polymer, and there is no particular limitation on the above polymer in the present application. For example, 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).

[0082] Exemplarily, as Figure 2 shown, define the length direction of the separator membrane itself as X and the thickness direction as Y. The separator membrane generally has a long side and a short side, and the above length direction is the extension direction of the long side of the separator membrane. It should be understood that the above definition of the direction is for the purpose of conveniently describing the present application. The separator membrane 20 comprises a substrate layer 21, an adhesive layer 23 disposed on one surface of the substrate layer 21, and a material coating 22 and an adhesive layer 23 sequentially disposed on the other surface of the substrate layer 21.

[0083] There is no particular limitation on the substrate layer in the present application as long as the purpose of the present application can be achieved. 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 membrane, a polyethylene porous membrane, a polypropylene non-woven fabric, a polyethylene non-woven fabric, or a polypropylene - polyethylene - polypropylene porous composite film may be used.

[0084] There is no particular limitation on the thickness of the material coating in the present application as long as the purpose of the present application can be achieved. For example, the thickness of the material coating may be 1 μm to 5 μm. There is no particular limitation on the thickness of the separator membrane in the present application as long as the purpose of the present application can be achieved. For example, the thickness of the separator membrane may be 3 μm to 30 μm.

[0085] The third aspect of the present application provides a positive electrode sheet, which comprises a positive electrode current collector and a positive electrode material layer disposed on at least one surface of the positive electrode current collector. The positive electrode material layer comprises the thermosensitive composite material provided by the first aspect of the present application. Based on the mass of the positive electrode material layer, the mass percentage content of the thermosensitive composite material is 0.01% to 5%. For example, the mass percentage content of the thermosensitive composite material may be 0.01%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or any range composed of any two of these values.

[0086] The thermosensitive composite material of the present application is applied to the positive electrode plate, and the mass percentage content of the thermosensitive composite material is adjusted within the scope of the present application. On the basis of the good electrochemical performance of the secondary battery, the contact area between the thermosensitive composite material and the positive electrode active material is larger. When the internal heat accumulation temperature of the secondary battery is relatively high, it can directly absorb the electrolyte inside the positive electrode plate, reduce the violent exothermic reaction between the electrolyte and the positive electrode plate, and has a higher action efficiency. The addition amount of the thermosensitive composite material can be relatively small, and the impact on the energy density of the secondary battery is also small. At the same time, when applied to the positive electrode plate, the requirement for the average particle size of the thermosensitive composite material is relatively low, which is also conducive to reducing the preparation cost. Therefore, applying the above positive electrode plate to the secondary battery is beneficial to improving its safety performance, and at the same time, the secondary battery has a high energy density and good electrochemical performance.

[0087] When the mass percentage content of the thermosensitive composite material is too small, for example, less than 0.01%, the ability of the thermosensitive composite material in the positive electrode plate to absorb the electrolyte is limited, and the effect of reducing the violent exothermic reaction between the electrolyte and the positive electrode plate and the negative electrode plate is weak, thus affecting the safety performance of the secondary battery. When the mass percentage content of the thermosensitive composite material is too large, for example, greater than 5%, it affects the energy density of the secondary battery. At the same time, it occupies too many active sites in the positive electrode material layer, deteriorates the conductive network, increases the impedance of the positive electrode plate, and increases the risk of local lithium deposition, thus affecting the electrochemical performance of the secondary battery.

[0088] In the present application, "the positive electrode plate includes a positive electrode current collector and a positive electrode material layer provided on at least one surface of the positive electrode current collector" means that the positive electrode material layer can be provided on one surface of the positive electrode current collector along its thickness direction, or can be provided on both surfaces of the positive electrode current collector along its thickness direction. It should be noted that the "surface" here can be the entire area of the surface of the positive electrode current collector or a partial area of the surface of the positive electrode current collector. There is no special limitation in the present application as long as the purpose of the present application can be achieved.

[0089] In some embodiments, the positive electrode material layer further includes a positive electrode active material, which includes a substance capable of reversibly intercalating and deintercalating active ions such as lithium ions. Based on the mass of the positive electrode material layer, the mass percentage of the positive electrode active material is 82% to 99%. For example, the mass percentage of the positive electrode active material can be 82%, 84%, 86%, 88%, 90%, 92%, 94%, 95%, 96%, 98%, 99%, or a range composed of any two of these values. 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. There is no particular limitation on the positive electrode active material in this application, as long as the purpose of this 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 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) or at least one of them.

[0090] In some embodiments, the positive electrode material layer further includes a positive electrode conductive agent and a positive electrode binder. Based on the mass of the positive electrode material layer, the mass percentage content of the positive electrode conductive agent is 0.2% to 7%, and the mass percentage content of the positive electrode binder is 0.2% to 7%. For example, the mass percentage content of the positive electrode conductive agent can be 0.2%, 0.8%, 1.2%, 1.5%, 2%, 3%, 4%, 5%, 6%, 7%, or a range composed of any two of these values. The mass percentage content of the positive electrode binder can be 0.2%, 0.8%, 1.2%, 1.5%, 2%, 3%, 4%, 5%, 6%, 7%, or a range composed of any two of these values. There is no particular limitation on the positive electrode conductive agent and the positive electrode binder in this application, as long as the purpose of this application can be achieved. For example, the positive electrode conductive agent can 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 can include, but is not limited to, at least one of acetylene black or Ketjen black. The above-mentioned carbon nanotubes can include, but are not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The above-mentioned carbon fibers can include, but are not limited to, vapor-grown carbon fibers (VGCF) and / or nanofibers. The above-mentioned metal materials can include, but are not limited to, metal powders and / or metal fibers. Specifically, the metal can include, but is not limited to, at least one of copper, nickel, aluminum, or silver. The above-mentioned conductive polymers can include, but are not limited to, at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene, or polypyrrole. For example, the positive electrode binder can 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.

[0091] There is no particular limitation on the positive electrode current collector in this application, as long as the purpose of this 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.

[0092] There is no particular limitation on the thickness of the positive electrode current collector in this application, as long as the purpose of this application can be achieved. For example, the thickness of the positive electrode current collector can be 5 μm to 10 μm. There is no particular limitation on the thickness of the positive electrode material layer in this application, as long as the purpose of this application can be achieved. For example, the thickness of the single-sided positive electrode material layer can be 50 μm to 120 μm.

[0093] Optionally, the positive electrode tab may further include a conductive layer 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 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 above conductive layer. For example, the conductive agent for the conductive layer may be at least one of the above positive electrode conductive agents, and the binder for the conductive layer may be at least one of the above positive electrode binders.

[0094] The fourth aspect of the present application provides a negative electrode tab, which includes a negative electrode current collector and a negative electrode material layer provided on at least one surface of the negative electrode current collector. The negative electrode material layer includes the thermosensitive composite material provided in the first aspect of the present application. Based on the mass of the negative electrode material layer, the mass percentage content of the thermosensitive composite material is 0.01% to 5%. For example, the mass percentage content of the thermosensitive composite material may be 0.01%, 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.

[0095] Applying the thermosensitive composite material of the present application to the negative electrode tab and controlling the mass percentage content of the thermosensitive composite material within the scope of the present application, on the basis of the good electrochemical performance of the secondary battery, the contact area between the thermosensitive composite material and the negative electrode active material is larger. When the internal heat accumulation temperature of the secondary battery is relatively high, it can directly absorb the electrolyte inside the negative electrode tab, reduce the violent exothermic reaction between the electrolyte and the negative electrode tab, and the action efficiency is higher. The addition amount of the thermosensitive composite material can be relatively small, and the impact on the energy density of the secondary battery is also small. At the same time, when applied to the negative electrode tab, the requirement for the average particle size of the thermosensitive composite material is relatively low, which is also beneficial to reducing the preparation cost. Therefore, applying the above negative electrode tab to the secondary battery is beneficial to improving its safety performance, and at the same time, the secondary battery has a relatively high energy density and good electrochemical performance.

[0096] When the mass percentage content of the thermosensitive composite material is too small, for example, less than 0.01%, the ability of the thermosensitive composite material in the negative electrode tab to absorb the electrolyte is limited, and the effect of reducing the violent exothermic reaction between the electrolyte and the positive electrode tab and the negative electrode tab is weak, thus affecting the safety performance of the secondary battery. When the mass percentage content of the thermosensitive composite material is too large, for example, greater than 5%, it affects the energy density of the secondary battery. At the same time, it occupies too many active sites in the negative electrode material layer, deteriorates the conductive network, increases the impedance of the negative electrode tab, and increases the risk of local lithium plating, thus affecting the electrochemical performance of the secondary battery.

[0097] In this application, "the negative electrode sheet includes a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector" means that the negative electrode material layer can be disposed on one surface of the negative electrode current collector along its thickness direction, or can be disposed on both surfaces of the negative electrode 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 electrode current collector or a partial area of the surface of the negative electrode current collector. There is no special limitation in this application, as long as the purpose of this application can be achieved.

[0098] In some embodiments, the negative electrode material layer includes a negative electrode active material. Based on the mass of the negative electrode material layer, the mass percentage content of the negative electrode active material is 82% to 99%. For example, the mass percentage content of the negative electrode active material can be 82%, 84%, 86%, 88%, 90%, 92%, 94%, 95%, 96%, 98%, 99% or a range composed of any two of these values. There is no special limitation on the negative electrode active material in this application, as long as the purpose of this application can be achieved. For example, the negative electrode active material can include but is not limited to natural graphite, artificial graphite, mesocarbon 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 alloys.

[0099] In some embodiments, the negative electrode material layer further includes a negative electrode conductive agent and a negative electrode binder. Based on the mass of the negative electrode material layer, the mass percentage content of the negative electrode conductive agent is 0.2% to 7%, and the mass percentage content of the negative electrode binder is 0.2% to 7%. For example, the mass percentage content of the negative electrode conductive agent can be 0.2%, 0.8%, 1.2%, 1.5%, 2%, 3%, 4%, 5%, 6%, 7% or a range composed of any two of these values, and the mass percentage content of the negative electrode binder can be 0.2%, 0.8%, 1.2%, 1.5%, 2%, 3%, 4%, 5%, 6%, 7% or a range composed of any two of these values. There is no special limitation on the negative electrode conductive agent and the negative electrode binder in this application, as long as the purpose of this application can be achieved. 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.

[0100] There is no special limitation on the negative electrode current collector in this application, as long as the purpose of this 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.

[0101] The present application places no particular limitation on the thickness of the negative electrode material layer and the thickness of the negative electrode current collector, as long as the object of the present application can be achieved. For example, the thickness of the single-sided negative electrode material layer can be 30 μm to 120 μm, and the thickness of the negative electrode current collector can be 4 μm to 15 μm.

[0102] 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 places 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 places no particular limitation on the conductive agent for the conductive layer and the binder for the conductive layer in the above conductive layer. For example, the conductive agent for the conductive layer may be at least one of the above positive electrode conductive agents, and the binder for the conductive layer may be at least one of the above positive electrode binders.

[0103] The fifth aspect of the present application provides a secondary battery, which includes at least one of the separator provided in the second aspect of the present application, the positive electrode sheet provided in the third aspect of the present application, or the negative electrode sheet provided in the fourth aspect of the present application. The secondary battery of the present application has good safety performance.

[0104] In the present application, the secondary battery further includes an electrolyte, which includes a lithium salt and a non-aqueous solvent.

[0105] The present application places no particular limitation on the lithium salt, as long as the object of the present application can be achieved. For example, the lithium salt may 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 places no particular limitation on the content of the lithium salt in the electrolyte, as long as the object of the present application can be achieved.

[0106] The present application places no particular limitation on the non-aqueous solvent, as long as the object of the present application can be achieved. For example, the non-aqueous solvent may include, but is not limited to, at least one of carbonate compounds, carboxylate compounds, ether compounds, or other organic solvents.

[0107] 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, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate. The present application has no particular limitation on the content of the non-aqueous solvent in the electrolyte as long as the object of the present application can be achieved.

[0108] The secondary battery further includes a housing for accommodating 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 has no particular limitation on 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.

[0109] 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.

[0110] 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 the positive electrode sheet, the separator, and the negative electrode sheet in sequence, and winding, folding, etc. as needed to obtain a wound structure electrode assembly, placing the electrode assembly into a housing, injecting an electrolyte into the housing and sealing it to obtain a secondary battery; or, stacking the positive electrode sheet, the separator, and the negative electrode sheet in sequence, and then fixing the four corners of the entire laminated structure with tape to obtain a laminated structure electrode assembly, 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 and discharging.

[0111] The sixth aspect of the present application provides an electronic device, and the electronic device includes the secondary battery provided in the fifth aspect of the present application. The electronic device of the present application has a long service life and good performance.

[0112] 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 head-mounted stereo headset, 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.

[0113] Examples

[0114] 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.

[0115] Testing methods and equipment:

[0116] Average particle size test

[0117] After discharging the lithium-ion battery at 0.2C until 3V, disassemble it to obtain a separator membrane or a positive electrode sheet or a negative electrode sheet sample including the thermosensitive composite material. After cleaning the above sample with dimethyl carbonate (DMC), dry it at 60°C. Use an IB-19520CCP ion polishing instrument to polish the cross-section of the sample along the thickness direction, and then use a scanning electron microscope to observe the above cross-section. Measure the diameters of the circumscribed circles of the largest cross-sections of 32 thermosensitive composite material particles and the diameters of the circumscribed circles of the largest cross-sections of the cores, and calculate the average values respectively to obtain the average particle size D1 of the thermosensitive composite material and the average particle size D2 of the core, and calculate D2 / D1.

[0118] Melting point test

[0119] After discharging the lithium-ion battery at 0.2C until 3V, disassemble it to obtain a separator membrane or a positive electrode sheet or a negative electrode sheet sample including the thermosensitive composite material. After cleaning the above sample with dimethyl carbonate (DMC), dry it at 60°C. Use an energy dispersive X-ray spectrometer (EDS) to scan the surface of the sample perpendicular to the thickness direction to obtain the element distribution in the thermosensitive composite material particles. Scrape off the material coating or the positive electrode material layer or the negative electrode material layer to obtain the test sample powder of the material coating or the positive electrode material layer or the negative electrode material layer. Use an X-ray diffractometer to test the above sample powder to obtain the XRD diffraction pattern.

[0120] At the same time, referring to the ASTM D3418-2021 standard method for measuring the polymer transition temperature, melting enthalpy and crystallinity by differential scanning calorimetry, use a differential scanning calorimeter (model DSC214), take 5mg of the test sample powder, and heat it from 30°C to 400°C at a rate of 10°C / min in an N2 environment. According to the generated DSC curve and the above EDS and XRD test results, obtain the melting point T1 of the first material, or the melting point T1 of the first material and the melting point T2 of the third material.

[0121] Melt index test

[0122] Use a melt index instrument to crush the third material into small particles to ensure the uniformity of the sample. Set the test temperature to 230°C and the load to 2.16 kg. Put the sample into the barrel of the melt index instrument, heat it to the set temperature to ensure that the sample is completely melted. Apply the load to make the molten third material pass through the standard die. Record the weight of the third material passing through the die within a certain time. Calculate the melt index of the third material through the following formula: Melt index (MFR) = weight of the third material passing through the die (g) / test time (min).

[0123] Mass ratio test of the thermosensitive composite material before and after absorbing the electrolyte

[0124] Dry 10 g of the thermosensitive composite material in a vacuum drying oven at 40 °C for 6 h to remove the adsorbed moisture or solvent. In an argon atmosphere glove box with a water content of less than 10 ppm, uniformly mix ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC) according to a mass ratio of 10:30:60 to obtain a base solvent. Add lithium salt LiPF6 and stir evenly to obtain an electrolyte. Among them, based on the total mass of the electrolyte, the mass percentage content of lithium salt LiPF6 is 12.5%, and the balance is the base solvent. Place the thermosensitive composite material in a container containing a sufficient amount of electrolyte to ensure complete immersion. Place the container in a constant temperature oil bath, set the temperature to 85 °C, and keep it immersed at a constant temperature for 24 hours. After the immersion is completed, quickly cool it to room temperature. Use a centrifuge to remove the free electrolyte on the surface of the thermosensitive composite material. Finally, use an analytical balance to weigh the mass of the treated thermosensitive composite material again to obtain the mass ratio of the thermosensitive composite material after absorbing the electrolyte at 85 °C to that before absorbing the electrolyte.

[0125] Adopt the same test method as above, set the temperature of the constant temperature oil bath to the melting point of the first material of the outer shell, and test the mass ratio M of the thermosensitive composite material after absorbing the electrolyte to that before absorbing the electrolyte at the melting point temperature of the first material of the outer shell.

[0126] Test on the crush-resistant limit force of the thermosensitive composite material

[0127] Place 15 g of the thermosensitive composite material in a columnar container with a fixed volume and fix it on a mechanical vibration device for vibration. The vibration frequency is 50 ± 5 times / min, the vibration amplitude is 3 ± 0.1 mm, and the vibration time is 3 min. Use a universal material testing machine to gradually apply pressure to the thermosensitive composite material sample at a rate of 175 mm / min, record the displacement-pressure curve during the process, and define the pressure at the position where the curve shows an obvious pressure mutation step as the crush-resistant limit force of the thermosensitive composite material. Characterize the mechanical properties of the thermosensitive composite material by the crush-resistant limit force of the thermosensitive composite material. The greater the crush-resistant limit force, the better the mechanical properties of the thermosensitive composite material; the smaller the crush-resistant limit force, the worse the mechanical properties of the thermosensitive composite material.

[0128] Test on the highest temperature through the hot box test

[0129] Adjust the temperature of the constant temperature furnace to 25 °C. For each example and comparative example, 100 lithium-ion batteries were taken as samples and placed in the constant temperature furnace for 5 minutes. Then, the lithium-ion batteries were discharged at a constant current of 0.2C to 3.0V, left standing 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 left standing 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, and 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 at that temperature for 60 minutes. Take a photo after the test 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. The highest temperature at which the lithium-ion battery passes the hot box test is used to characterize the safety performance of the lithium-ion battery. 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.

[0130] Example 1-1

[0131] <Preparation of Thermosensitive Composite Material>

[0132] 1. Modification of the Second Core Material

[0133] 1.1 Preparation of Porous Crosslinked PAAS Gel

[0134] Materials and Reagents: Sodium Polyacrylate (PAAS); Crosslinking Agents: Epichlorohydrin (ECH, for chemical crosslinking), Calcium Chloride (CaCl2, for ionic crosslinking); Initiator: Ammonium Persulfate (APS, for free radical crosslinking); Solvent: Deionized Water.

[0135] ① Gradient Crosslinking Process:

[0136] Pre-crosslinking: Prepare a 10wt% aqueous solution of PAAS, add the crosslinking agent CaCl2 for ionic crosslinking (the concentration of CaCl2 in the above solution is 0.8wt%), stir for 1 hour to form a primary network, and obtain a pre-crosslinked system solution.

[0137] Chemical crosslinking strengthening: Add epichlorohydrin ECH (the concentration of ECH in the pre-crosslinked system solution is 1.5 wt%) and ammonium persulfate APS (the concentration of APS in the pre-crosslinked system solution is 0.1 wt%) as crosslinking agents for chemical crosslinking to the pre-crosslinked system solution, heat up to 60 °C, and react for 4 hours.

[0138] ② Post-treatment: Dialyze with deionized water for 3 days to remove unreacted reagents, and freeze-dry to obtain porous crosslinked PAAS gel.

[0139] 1.2 Grafting of electrolyte-friendly groups

[0140] Materials and reagents: Crosslinked PAAS gel (ground into particles with a particle size of 50 μm to 100 μm); poly(ethylene glycol) methyl ether acrylate (PEGMA, Mn = 500); initiator: azobisisobutyronitrile (AIBN); solvent: N,N-dimethylformamide (DMF).

[0141] ① Swelling activation: Immerse the crosslinked PAAS gel in DMF for 2 hours to relax the internal network.

[0142] ② Grafting reaction: Prepare a DMF solution containing 20 wt% PEGMA and 0.5 wt% AIBN, and add the swollen PAAS gel (the mass ratio of PAAS gel to DMF solution is 1:5). Under nitrogen protection, react at 70 °C for 12 hours, and PEGMA is grafted onto the backbone of PAAS through free radicals.

[0143] ③ Purification: Wash repeatedly with acetone to remove unreacted monomers, and dry in vacuum to obtain the second material-modified sodium polyacrylate PAAS particles.

[0144] 2. Preparation of thermosensitive composite materials

[0145] 2.1 Preparation of the outer shell oil phase (PP solution)

[0146] High-temperature dissolution: Heat the solvent p-xylene to 135 °C, add polypropylene PP particles as the outer shell material (the mass content of PP is 8 wt%), stir until completely dissolved to form a transparent viscous solution. Cool down to 80 °C, add Span 80 (the concentration of Span 80 in the above solution is 4 wt%) to maintain emulsion stability.

[0147] 2.2 Preparation of emulsion (W / O single emulsion)

[0148] Emulsification step: Swell the core second material-modified PAAS particles with N,N-dimethylformamide (DMF) to prepare a gel, and slowly add the above gel to the PP oil phase at a volume ratio of 1:3. Emulsify with a high-speed homogenizer (rotation speed of 12000 rpm) for 8 minutes to form a W / O emulsion.

[0149] 2.3 Solvent evaporation and curing

[0150] Phase separation and curing: Transfer the above W / O emulsion to an aqueous phase containing 1 wt% Tween 80 (aqueous phase emulsifier) (the volume ratio of the W / O emulsion to the aqueous phase is 1:5), and stir at 45 °C for 5 hours (rotation speed is 400 rpm). During the stirring process, add acetone (the volume ratio of acetone in the above mixed system is 10%) to accelerate the solvent diffusion and improve the density of the outer shell. p-Xylene gradually volatilizes, and PP precipitates on the surface of the core material to form a dense outer shell.

[0151] 2.4 Post-treatment and drying

[0152] ① Separation and washing: Centrifuge (3000 rpm, 10 minutes) to collect the microcapsules, and wash them 3 times with a mixed solution of acetone and water to remove the residual emulsifier.

[0153] ② Drying: Freeze-dry (-50 °C, 24 hours) to obtain the temperature-sensitive composite material.

[0154] <Preparation of the separator membrane>

[0155] Use a porous polyethylene film with a thickness of 5 μm (provided by Celgard) as the base layer of the separator membrane. Mix the temperature-sensitive composite material, inorganic particle alumina, and material coating binder polyvinylidene fluoride (PVDF) in a mass ratio of 30:68:2, add deionized water as the solvent, and mix evenly under the action of a vacuum mixer to obtain a material coating slurry with a solid content of 75 wt%. Coat it evenly on one surface of the base layer, and dry it at 50 °C to obtain a material coating with a thickness of 2 μm. Then, coat the adhesive layer PVDF on the surface of the material coating away from the base layer and the other surface of the base layer without the material coating, and dry it at 50 °C to form an adhesive layer with a thickness of 1 μm each, obtaining a separator membrane with a material coating and an adhesive layer sequentially arranged on one side of the base layer and an adhesive layer arranged on the other side.

[0156] <Preparation of the positive electrode sheet>

[0157] The positive electrode active material lithium cobalt oxide (LiCoO₂), the positive electrode conductive agent conductive carbon black (Super P), and the positive electrode binder polyvinylidene fluoride are mixed in a mass ratio of 97.9∶0.9∶1.2, and N-methylpyrrolidone (NMP) is added as a solvent to prepare a slurry with a solid content of 75 wt%. After vacuum stirring evenly, the 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, the above steps are repeated 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 electrode 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 tap density of the positive electrode material layer is 4.2 g / cm 3 。

[0158] <Preparation of negative electrode plate>

[0159] 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 45 wt%. After being stirred evenly by a vacuum mixer, the negative electrode slurry is obtained. The negative electrode slurry is evenly coated on one surface of a negative electrode current collector copper foil with a thickness of 6 μm and dried at 90 °C to obtain a negative electrode plate with a single-sided coated negative electrode material layer. Then, the above steps are repeated on the other surface of the copper foil to obtain a negative electrode plate with a double-sided coated negative electrode material layer. After drying at 90 °C, it is cold-pressed, and then cut into pieces and the electrode tabs are welded to obtain a negative electrode plate with a specification of 78 mm × 875 mm for use. Among them, the thickness of the single-sided negative electrode material layer is 54.5 μm, and the tap density of the negative electrode material layer is 1.7 g / cm 3 。

[0160] <Preparation of electrolyte>

[0161] 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 evenly mixed in a mass ratio of 10∶30∶60 to obtain a basic solvent, and the lithium salt LiPF₆ is added and stirred evenly to obtain an electrolyte. Among them, based on the total mass of the electrolyte, the mass percentage content of the lithium salt LiPF₆ is 12.5%, and the balance is the basic solvent.

[0162] <Preparation of lithium-ion battery>

[0163] Stack the prepared positive electrode sheet, separator, and negative electrode sheet in sequence, with the separator in the middle of the positive electrode sheet and the negative electrode sheet to play an insulating role, and wind them to obtain an electrode assembly, where the side of the separator with the material coating faces the positive electrode sheet. Put the electrode assembly into an aluminum-plastic film packaging bag, remove moisture at 80 °C, inject the prepared electrolyte, and obtain a lithium-ion battery through processes such as vacuum packaging, standing, forming, degassing, and trimming. Among them, the upper limit voltage for forming is 4.5 V, the forming temperature is 85 °C, and the forming standing time is 2 h.

[0164] Examples 1-2 to Examples 1-9

[0165] Except for adjusting the corresponding preparation parameters according to Table 1, the rest are the same as in Example 1-1. Among them, in the preparation of the 2.1 outer shell oil phase of Examples 1-4, the solvent was changed to tetrahydrofuran; by controlling the rotation speed and emulsification time of the high-speed homogenizer in the preparation of the 2.2 emulsion and the stirring time and rotation speed in the 2.3 solvent evaporation and curing, the average particle size D1 of the thermosensitive composite material, the average particle size D2 of the core, and D2 / D1 are as shown in Table 1.

[0166] Examples 1-10 to Examples 1-11

[0167] Except for adjusting the corresponding preparation parameters according to Table 1, the rest are the same as in Example 1-1. Among them, the mass percentage content of the binder in the material coating of Example 1-10 is the same as that in Example 1-1, and the mass percentage content of the inorganic particles changes accordingly; in Example 1-11, inorganic particles are not used, and the mass percentage content of the binder in the material coating is 0.5%.

[0168] Example 2-1

[0169] Except for using the following preparation method in the preparation of the 2.2 emulsion in <Preparation of Thermosensitive Composite Material>, the rest are the same as in Example 1-1.

[0170] <Preparation of Thermosensitive Composite Material>

[0171] 2.2 Preparation of Emulsion

[0172] Except for swelling the third material, chlorinated paraffin, and modified PAAS particles with N,N-dimethylformamide (DMF) to prepare a gel, the rest are the same as in Example 1-1. Among them, based on the mass of the core, the mass percentage content of the second material and the third material, the melting point T2 of the third material, and the melt index are as shown in Table 2.

[0173] Examples 2-2 to Examples 2-4

[0174] Except for adjusting the corresponding preparation parameters according to Table 2, the rest are the same as in Example 2-1.

[0175] Example 3-1

[0176] Except for the preparation methods of the temperature-sensitive composite material, the positive electrode sheet, the separator, and the lithium-ion battery, the rest are the same as in Example 1-1.

[0177] <Preparation of Temperature-Sensitive Composite Material>

[0178] Except for adjusting the rotation speed of the high-speed homogenizer and the emulsification time in the preparation of 2.2 emulsion, and the stirring time and rotation speed in 2.3 solvent evaporation and curing, so that the average particle size D1 of the temperature-sensitive composite material, the average particle size D2 of the core, and D2 / D1 are as shown in Table 3, the rest are the same as in Example 1-1.

[0179] <Preparation of Positive Electrode Sheet>

[0180] Except for mixing the positive electrode active material lithium cobalt oxide (LiCoO2), the temperature-sensitive composite material, the positive electrode conductive agent carbon black (Super P), and the positive electrode binder polyvinylidene fluoride in a mass ratio of 95.4:2.5:0.9:1.2, the rest are the same as in Example 1-1.

[0181] <Preparation of Separator>

[0182] Use a porous polyethylene film with a thickness of 7 μm (provided by Celgard) as the separator.

[0183] <Preparation of Lithium-Ion Battery>

[0184] Stack the above-prepared positive electrode sheet, separator, and negative electrode sheet in sequence, with the separator in the middle of the positive electrode sheet and the negative electrode sheet to play a separating role, and wind to obtain an electrode assembly. Put the electrode assembly into an aluminum-plastic film packaging bag, dehydrate at 80 °C, inject the electrolyte prepared above, and obtain a lithium-ion battery through processes such as vacuum packaging, standing, formation, degassing, and trimming. Among them, the upper limit voltage of formation is 4.5 V, the formation temperature is 85 °C, and the formation standing time is 2 h.

[0185] Examples 3-2 to 3-7

[0186] Except for adjusting the corresponding preparation parameters according to Table 3, the rest are the same as in Example 3-1. Among them, by adjusting the rotation speed of the high-speed homogenizer and the emulsification time in the preparation of 2.2 emulsion, and the stirring time and rotation speed in 2.3 solvent evaporation and curing, the average particle size D1 of the temperature-sensitive composite material, the average particle size D2 of the core, and D2 / D1 are as shown in Table 3; when the mass percentage content of the temperature-sensitive composite material changes, the mass percentage content of the positive electrode active material changes accordingly, and the mass percentage contents of the positive electrode conductive agent and the positive electrode binder remain unchanged.

[0187] Example 3-8

[0188] Except for the following preparation methods for <Preparation of Thermosensitive Composite Material>, <Preparation of Negative Electrode Plate>, <Preparation of Separator>, and <Preparation of Lithium-Ion Battery>, the rest are the same as in Example 1-1.

[0189] <Preparation of Thermosensitive Composite Material>

[0190] Except for adjusting the rotation speed and emulsification time of the high-speed homogenizer in the preparation of 2.2 emulsion and the stirring time and rotation speed in 2.3 solvent evaporation and curing so that the average particle size D1 of the thermosensitive composite material, the average particle size D2 of the core, and D2 / D1 are as shown in Table 3, the rest are the same as in Example 1-1.

[0191] <Preparation of Negative Electrode Plate>

[0192] Except for mixing the negative electrode active material artificial graphite, thermosensitive composite material, negative electrode binder styrene-butadiene rubber, and negative electrode conductive agent acetylene black in a mass ratio of 97.39∶0.01∶1.4∶1.2, the rest are the same as in Example 1-1.

[0193] <Preparation of Separator>

[0194] Use a porous polyethylene film with a thickness of 7 μm (provided by Celgard) as the separator.

[0195] <Preparation of Lithium-Ion Battery>

[0196] Stack the above-prepared positive electrode plate, separator, and negative electrode plate in sequence, with the separator in the middle of the positive electrode plate and the negative electrode plate to play a separating role, and wind to obtain an electrode assembly. Put the electrode assembly into an aluminum-plastic film packaging bag, remove moisture at 80 °C, inject the above-prepared electrolyte, and obtain a lithium-ion battery through processes such as vacuum packaging, standing, forming, degassing, and trimming. Among them, the upper limit voltage of forming is 4.5 V, the forming temperature is 85 °C, and the forming standing time is 2 h.

[0197] Examples 3-9 to 3-10

[0198] Except for adjusting the corresponding preparation parameters according to Table 3, the rest are the same as in Example 3-8. Among them, when the mass percentage content of the thermosensitive composite material changes, the mass percentage content of the negative electrode active material changes accordingly, and the mass percentage contents of the negative electrode conductive agent and the negative electrode binder remain unchanged.

[0199] Comparative Example 1-1

[0200] Except for the following preparation methods for <Preparation of Separator> and <Preparation of Lithium-Ion Battery>, the rest are the same as in Example 1-1.

[0201] <Preparation of Separator>

[0202] A porous polyethylene film with a thickness of 7 μm (provided by Celgard) was used as the separator membrane.

[0203] <Preparation of Lithium-Ion Batteries>

[0204] The above-prepared positive electrode sheet, separator membrane, and negative electrode sheet were stacked in sequence, with the separator membrane placed between the positive electrode sheet and the negative electrode sheet to play a separating role, and then wound to obtain an electrode assembly. The electrode assembly was placed into an aluminum-plastic film packaging bag, dehydrated at 80 °C, and the above-prepared electrolyte was injected. After vacuum packaging, standing, formation, degassing, trimming and other processes, a lithium-ion battery was obtained. Among them, the upper limit voltage of formation was 4.5 V, the formation temperature was 85 °C, and the formation standing time was 2 h.

[0205] Comparative Example 1-2

[0206] Except that polypropylene particles with the parameters shown in Table 1 were directly used for the separator membrane in <Preparation of Thermosensitive Composite Materials> (i.e., the thermosensitive composite material only contains the shell material), the rest was the same as in Example 1-1.

[0207] Comparative Example 1-3

[0208] Except that the following preparation method was used in <Preparation of Thermosensitive Composite Materials>, the rest was the same as in Example 1-1.

[0209] <Preparation of Thermosensitive Composite Materials>

[0210] The modified PAAS particles obtained in the modification of the second material of the core were directly used for the separator membrane after being pulverized, that is, the thermosensitive composite material only contains the core material. Among them, the average particle size D1 of the thermosensitive composite material, the average particle size D2 of the core, and D2 / D1 are shown in Table 1.

[0211] Comparative Examples 1-4 to Comparative Examples 1-7

[0212] Except that the corresponding preparation parameters were adjusted according to Table 1, the rest was the same as in Example 1-1. Among them, in the preparation of the oil phase of the shell in Comparative Example 1-5, the solvent was replaced with tetrahydrofuran; by controlling the rotation speed and emulsification time of the high-speed homogenizer in the preparation of the emulsion in 2.2 and the stirring time and rotation speed in the solvent evaporation and curing in 2.3, the average particle size D1 of the thermosensitive composite material, the average particle size D2 of the core, and D2 / D1 are shown in Table 1.

[0213] Comparative Examples 1-8 to Comparative Examples 1-9

[0214] Except for adjusting the corresponding preparation parameters according to Table 1, the rest is the same as in Example 1-1. Among them, the mass percentage content of the material coating binder in Comparative Examples 1-8 is the same as that in Example 1-1, and the mass percentage content of the inorganic particles changes accordingly; in Comparative Example 1-9, no inorganic particles are used, and the mass percentage content of the material coating binder is 0.2%.

[0215] Comparative Example 3-1

[0216] Except that the polypropylene particles with the parameters shown in Table 3 selected in <Preparation of Thermosensitive Composite Material> are directly used for the positive electrode sheet (i.e., the thermosensitive composite material only contains the shell material), the rest is the same as in Example 3-1.

[0217] Comparative Example 3-2

[0218] Except that in <Preparation of Positive Electrode Sheet>, the thermosensitive composite material obtained by the following preparation method is used, the rest is the same as in Example 3-1.

[0219] <Preparation of Thermosensitive Composite Material>

[0220] The modified PAAS particles obtained in the modification of 1. the second material of the core are directly used for the positive electrode sheet after being pulverized, that is, the thermosensitive composite material only contains the core material. Among them, the average particle size D1 of the thermosensitive composite material, the average particle size D2 of the core, and D2 / D1 are shown in Table 3.

[0221] Comparative Examples 3-3 to Comparative Example 3-5

[0222] Except for adjusting the corresponding preparation parameters according to Table 3, the rest is the same as in Example 3-1. Among them, by regulating the rotation speed and emulsification time of the high-speed homogenizer in the preparation of 2.2 emulsion and the stirring time and rotation speed in the solvent evaporation and curing of 2.3, the average particle size D1 of the thermosensitive composite material, the average particle size D2 of the core, and D2 / D1 are shown in Table 3; when the mass percentage content of the thermosensitive composite material changes, the mass percentage content of the positive electrode active material changes accordingly, and the mass percentage contents of the positive electrode conductive agent and the positive electrode binder remain unchanged.

[0223] Comparative Example 3-6

[0224] Except that the polypropylene particles with the parameters shown in Table 3 selected in <Preparation of Thermosensitive Composite Material> are directly used for the negative electrode sheet (i.e., the thermosensitive composite material only contains the shell material), the rest is the same as in Example 3-8.

[0225] Comparative Example 3-7

[0226] Except that in <Preparation of Negative Electrode Sheet>, the thermosensitive composite material obtained by the following preparation method is used, the rest is the same as in Example 3-8.

[0227] <Preparation of Thermosensitive Composite Material>

[0228] The modified PAAS particles obtained in the modification of the second material of the core are directly used for the negative electrode sheet after being pulverized, that is, the thermosensitive composite material only contains the core material. Among them, the average particle size D1 of the thermosensitive composite material, the average particle size D2 of the core, and D2 / D1 are shown in Table 3.

[0229] Comparative Examples 3-8

[0230] Except for adjusting the corresponding preparation parameters according to Table 3, the rest are the same as in Examples 3-8. Among them, when the mass percentage content of the thermosensitive composite material changes, the mass percentage content of the negative electrode active material changes accordingly, and the mass percentage contents of the negative electrode conductive agent and the negative electrode binder remain unchanged.

[0231] The preparation parameters and performance parameters of each example and comparative example are shown in Tables 1 to 3.

[0232]

[0233] It can be seen from Examples 1-1 to 1-11 and Comparative Examples 1-1 to 1-9 that the thermosensitive composite material has the structure of this application, and by adjusting the values of D2 / D1, D1, T1, and M within the scope of this application, the pressure collapse limit force of the thermosensitive composite material is greater. Applying it to the material coating of the separator and adjusting the mass percentage content of the thermosensitive composite material within the scope of this application, the highest temperature of the prepared lithium-ion battery passing the hot box test is higher, indicating that the mechanical properties of the thermosensitive composite material of this application are good and the safety performance of the lithium-ion battery is good. In the lithium-ion battery of Comparative Example 1-1, there is no thermosensitive composite material. In Comparative Examples 1-2 and 1-3, the thermosensitive composite material does not contain both the core and the shell at the same time. In Comparative Examples 1-4 and 1-5, the melting point T1 of the first material of the shell of the thermosensitive composite material is not within the scope of this application. In Comparative Examples 1-6 and 1-7, the D2 / D1 value of the thermosensitive composite material is not within the scope of this application. In Comparative Examples 1-8 and 1-9, the mass percentage content of the thermosensitive composite material in the material coating is not within the scope of this application. The pressure collapse limit force of the thermosensitive composite materials of Comparative Examples 1-1 to 1-9 is smaller, the highest temperature of the lithium-ion battery passing the hot box test is lower, or a lithium-ion battery cannot be prepared, indicating that the mechanical properties of the thermosensitive composite material are poor and the safety performance of the lithium-ion battery is poor.

[0234] The melting point T1 of the first material of the outer shell usually affects the safety performance of the lithium-ion battery. It can be seen from Examples 1-1 to 1-4 and Comparative Examples 1-4 to 1-5 that when the melting point T1 of the first material is within the scope of the present application, the pressure collapse limit force of the thermosensitive composite material is relatively large, and the maximum temperature of the lithium-ion battery passing the hot box test is relatively high, indicating that the thermosensitive composite material of the present application has good mechanical properties and the lithium-ion battery has good safety performance. In Comparative Examples 1-4 to 1-5, the melting point T1 of the first material in the thermosensitive composite material is not within the scope of the present application, the pressure collapse limit force of the thermosensitive composite material is relatively small, and the maximum temperature of the lithium-ion battery passing the hot box test is relatively low, indicating that the safety performance of the lithium-ion battery is poor.

[0235] The value of D2 / D1 usually affects the safety performance of the lithium-ion battery. It can be seen from Example 1-1, Examples 1-5 to 1-6, and Comparative Examples 1-6 to 1-7 that when the value of D2 / D1 is within the scope of the present application, the pressure collapse limit force of the thermosensitive composite material is relatively large, and the maximum temperature of the lithium-ion battery passing the hot box test is relatively high, indicating that the thermosensitive composite material of the present application has good mechanical properties and the lithium-ion battery has good safety performance. In Comparative Examples 1-6 to 1-7, the value of D2 / D1 of the thermosensitive composite material is not within the scope of the present application, the pressure collapse limit force of the thermosensitive composite material is relatively small, and the maximum temperature of the lithium-ion battery passing the hot box test is relatively low, indicating that the safety performance of the lithium-ion battery is poor.

[0236] The mass percentage content of the thermosensitive composite material in the material coating usually affects the safety performance of the lithium-ion battery. It can be seen from Example 1-1, Examples 1-10 to 1-11, and Comparative Examples 1-8 to 1-9 that when the mass percentage content of the thermosensitive composite material in the material coating is within the scope of the present application, the maximum temperature of the lithium-ion battery passing the hot box test is relatively high, indicating that the lithium-ion battery of the present application has good safety performance. In Comparative Examples 1-8 and 1-9, the mass percentage content of the thermosensitive composite material in the material coating is not within the scope of the present application. In Comparative Example 1-8, the maximum temperature of the lithium-ion battery passing the hot box test is relatively low, indicating that the safety performance of the lithium-ion battery is poor. In Comparative Example 1-9, due to the too low mechanical strength of the separator material coating, it cannot meet the manufacturability, and the lithium-ion battery cannot be prepared.

[0237] The types of the first material and the second material usually affect the safety performance of the lithium-ion battery. It can be seen from Examples 1-1 to 1-4 and Example 1-9 that when the first material and the second material within the scope of the present application are selected, the pressure collapse limit force of the thermosensitive composite material is relatively large, and the maximum temperature of the lithium-ion battery passing the hot box test is relatively high, indicating that the thermosensitive composite material of the present application has good mechanical properties and the lithium-ion battery has good safety performance.

[0238] Table 2

[0239]

[0240] Note: " / " in Table 2 indicates no corresponding parameter.

[0241] The mass percentage contents of the second material and the third material in the core usually affect the safety performance of the lithium-ion battery. It can be seen from Examples 1-1, 2-1 to 2-2 that when the mass percentage contents of the second material and the third material in the core are within the scope of the present application, the pressure collapse limit force of the thermosensitive composite material is relatively large, and the maximum temperature of the lithium-ion battery passing the hot box test is relatively large, indicating that the thermosensitive composite material of the present application has good mechanical properties and the lithium-ion battery has good safety performance.

[0242] The type, melting point and melt index of the third material usually affect the safety performance of the lithium-ion battery. It can be seen from Examples 2-1 to 2-4 that when the type, melting point and melt index of the third material are within the scope of the present application, the pressure collapse limit force of the thermosensitive composite material is relatively large, and the maximum temperature of the lithium-ion battery passing the hot box test is relatively large, indicating that the thermosensitive composite material of the present application has good mechanical properties and the lithium-ion battery has good safety performance.

[0243] Table 3

[0244]

[0245]

[0246] Note: " / " in Table 3 indicates no corresponding parameter, and "-" indicates that the lithium-ion battery cannot be prepared.

[0247] The value of D1 usually affects the safety performance of the lithium-ion battery. It can be seen from Examples 3-1 to 3-5, Comparative Examples 3-3 to 3-4 that when the value of D1 is within the scope of the present application, the pressure collapse limit force of the thermosensitive composite material is relatively large, and the maximum temperature of the lithium-ion battery passing the hot box test is even larger, indicating that the thermosensitive composite material of the present application has good mechanical properties and the lithium-ion battery has good safety performance. In Comparative Examples 3-3 to 3-4, the D1 value of the thermosensitive composite material is not within the scope of the present application. In Comparative Example 3-3, it is difficult to completely wrap due to the small thickness of the outer shell, and the stability of the thermosensitive composite material at high temperature is poor and difficult to apply, so the lithium-ion battery cannot be prepared. In Comparative Example 3-4, the pressure collapse limit force of the thermosensitive composite material is even smaller, and the maximum temperature of the lithium-ion battery passing the hot box test is smaller, indicating that the mechanical properties of the thermosensitive composite material are poor and the safety performance of the lithium-ion battery is poor.

[0248] The mass percentage content of the temperature-sensitive composite material in the positive electrode material layer usually affects the safety performance of the lithium-ion battery. It can be seen from Example 3-1, Examples 3-6 to 3-7, and Comparative Example 3-5 that when the mass percentage content of the temperature-sensitive composite material in the positive electrode material layer is within the scope of this application, the maximum temperature of the lithium-ion battery passing the hot box test is higher, indicating that the safety performance of the lithium-ion battery is good. However, in Comparative Example 3-5, the mass percentage content of the temperature-sensitive composite material in the positive electrode material layer is not within the scope of this application. Although the maximum temperature of the lithium-ion battery passing the hot box test is relatively high, it will affect the energy density of the lithium-ion battery. At the same time, it occupies too many active sites in the positive electrode material layer, deteriorates the conductive network, increases the impedance of the positive electrode sheet, increases the risk of local lithium deposition, and makes the electrochemical performance (such as cycle performance, storage performance) of the lithium-ion battery poor.

[0249] The mass percentage content of the temperature-sensitive composite material in the negative electrode material layer usually affects the safety performance of the lithium-ion battery. It can be seen from Examples 3-8 to 3-10 and Comparative Example 3-8 that when the mass percentage content of the temperature-sensitive composite material in the negative electrode material layer is within the scope of this application, the maximum temperature of the lithium-ion battery passing the hot box test is higher, indicating that the safety performance of the lithium-ion battery is good. However, in Comparative Example 3-8, the mass percentage content of the temperature-sensitive composite material in the negative electrode material layer is not within the scope of this application. Although the maximum temperature of the lithium-ion battery passing the hot box test is relatively high, it will affect the energy density of the lithium-ion battery. At the same time, it occupies too many active sites in the negative electrode material layer, deteriorates the conductive network, increases the impedance of the negative electrode sheet, increases the risk of local lithium deposition, and makes the electrochemical performance (such as cycle performance, storage performance) of the lithium-ion battery poor.

[0250] 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 "comprising", "including" 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 also includes elements inherent to such process, method or article.

[0251] Each embodiment in this specification is described in a related manner. The same or similar parts between each embodiment can be referred to each other. The key point of each embodiment is to illustrate the differences from other embodiments.

[0252] The above are only the preferred embodiments of this application and are not intended to limit this application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of this application shall be included within the scope of protection of this application.

Claims

1. A thermosensitive composite material, comprising a core and a shell disposed on the surface of the core, wherein the average particle size of the thermosensitive composite material is D1 μm, the average particle size of the core is D2 μm, 5%≤D2 / D1≤90%, 0.1≤D1≤50; The shell includes a first material, the core includes a second material, the melting point of the first material is T1°C, 100≤T1≤200, and the mass ratio of the temperature-sensitive composite material after absorbing the electrolyte at the T1 temperature to that before absorbing the electrolyte is M, 10≤M≤300.

2. The temperature-sensitive composite material according to claim 1, wherein: 0.3≤D1≤20。 3. The thermosensitive composite material according to claim 1, wherein: 100≤T1≤150。 4. The temperature-sensitive composite material according to claim 1, wherein: The first material includes at least one of polyethylene, polypropylene, polymethyl methacrylate, polyethylene terephthalate, polystyrene, polyvinyl chloride, polybutadiene, polyacrylamide, polyacrylic acid, nylon, styrene elastomer, ethylene elastomer, melamine resin, pentadecanol, hexadecanol, heptadecanol, octadecyl alcohol, paraffin, alginate, animal wax, vegetable wax, hardened oil, fatty acid, tristearin, distearin, lecithin, starch, sucrose, maltodextrin, corn syrup, cellulose, chitosan, soy protein, gum arabic, gelatin or agar.

5. The temperature-sensitive composite material according to claim 1, wherein: The second material includes at least one of a modified super absorbent polymer, a cellulose derivative or a silicon-based material, the super absorbent polymer includes at least one of sodium polyacrylate, polyacrylamide, polyvinyl alcohol, polyacrylic acid or polyvinyl pyrrolidone, the cellulose derivative includes at least one of carboxymethyl cellulose or hydroxypropyl methyl cellulose, and the silicon-based material includes at least one of silicone rubber or fumed silica.

6. The thermosensitive composite material according to any one of claims 1 to 5, wherein: The core further comprises a third material. Based on the mass of the core, the mass percentage of the second material is 25% to 100%, and the mass percentage of the third material is 0% to 75%.

7. The temperature-sensitive composite material according to claim 6, wherein: The melting point of the third material is T2°C, T2≤T1, 40≤T2≤150.

8. The temperature-sensitive composite material according to claim 6, wherein: The third material has a melt index of 2 g / 10 min to 20 g / 10 min.

9. The temperature-sensitive composite material according to claim 6, wherein: The third material includes at least one of polyolefin resin and modified products thereof, ethylene elastomer, styrene elastomer, polyvinylidene fluoride, chlorinated paraffin, carboxymethyl cellulose or hydroxypropyl methyl cellulose.

10. An isolation membrane, comprising a substrate layer and a material coating arranged on at least one surface of the substrate layer, wherein the material coating comprises the temperature-sensitive composite material according to any one of claims 1 to 9, and based on the mass of the material coating, the mass percentage of the temperature-sensitive composite material is 1% to 99.5%.

11. The isolation film according to claim 10, wherein: The average particle size D1 μm of the temperature-sensitive composite material satisfies: 0.1≤D1≤10.

12. A positive electrode plate, comprising a positive electrode collector and a positive electrode material layer arranged on at least one surface of the positive electrode collector, wherein the positive electrode material layer comprises the temperature-sensitive composite material according to any one of claims 1 to 9, and the mass percentage of the temperature-sensitive composite material is 0.01% to 5% based on the mass of the positive electrode material layer.

13. A negative electrode plate, comprising a negative electrode current collector and a negative electrode material layer arranged on at least one surface of the negative electrode current collector, the negative electrode material layer comprising the temperature-sensitive composite material according to any one of claims 1 to 9, and based on the mass of the negative electrode material layer, the mass percentage of the temperature-sensitive composite material is 0.01% to 5%. 14 . A secondary battery, comprising at least one of the separator according to claim 10 or 11 , the positive electrode sheet according to claim 12 , or the negative electrode sheet according to claim 13 . 15 . An electronic device comprising the secondary battery according to claim 14 .

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