Phase transition heat responsive electrolyte and lithium ion battery

Abstract

The application relates to the technical field of lithium ion batteries, and provides a phase transition thermal response electrolyte and a lithium ion battery. The phase transition thermal response electrolyte comprises a lithium salt, a first solvent, a second solvent, a thermal decomposition type free radical initiator, and a reaction monomer; wherein the first solvent is one or more selected from propylene carbonate, trimethyl phosphate, triethyl phosphate and sulfolane; the second solvent is one or more selected from 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, bis(2,2,2-trifluoroethyl) ether, hydrofluoroether and fluorobenzene; and the reaction monomer is one or more selected from a bismaleimide monomer, a vinyl carbonate monomer and an acrylate monomer. The lithium ion battery electrolyte is the aforementioned phase transition thermal response electrolyte. The electrolyte of the application inhibits reaction at normal temperature and quickly triggers reaction at high temperature.

Description

Technical Field

[0001] This application relates to the field of lithium-ion battery technology, specifically to a phase transition thermally responsive electrolyte and a lithium-ion battery. Background Technology

[0002] With the rapid development of energy storage technology and electric transportation, lithium-ion batteries have been widely used due to their high energy density and long cycle life. However, under abnormal operating conditions such as high temperature, overcharging, and internal short circuits, the electrolyte is prone to decomposition reactions, generating large amounts of gas and heat, which is one of the key factors inducing battery thermal runaway or even fire and explosion. Therefore, developing an electrolyte system with intrinsic safety is of great significance for improving the safety performance of lithium-ion batteries.

[0003] To address these issues, existing technologies have proposed various safe electrolyte design strategies, such as introducing flame-retardant solvents, adding flame retardants, and constructing thermoresponsive electrolyte systems. Thermoresponsive electrolytes, in particular, can form gels or solid structures through chemical reactions upon temperature increases, thereby suppressing electrolyte flow and blocking side reactions. However, existing thermoresponsive electrolytes typically rely on highly reactive functional components, which may still undergo slow spontaneous reactions under normal or moderate temperature conditions. This can lead to increased electrolyte viscosity, impaired ion transport, and deterioration of electrode interface performance, ultimately affecting the long-term cycle stability of the battery.

[0004] Furthermore, existing technologies primarily rely on the direct influence of temperature on the reaction rate, lacking effective control over the spatial distribution and local concentration of reactants, making it difficult to simultaneously achieve both "room temperature stability" and "rapid high-temperature response." At room temperature, reactants are in a uniform distribution state, and even at low reaction rates, it is still difficult to completely avoid the occurrence of side reactions; while under high-temperature conditions, reactants fail to achieve effective enrichment in the system, limiting the triggering efficiency of the thermal response process.

[0005] Therefore, there is an urgent need to develop a novel electrolyte system that can suppress the reaction at room temperature and rapidly trigger the reaction at high temperature. By regulating the temperature-responsive phase transition behavior of the solvent environment, the spatial distribution and high-temperature enrichment of reactants can be achieved, thereby improving the safety of the battery under abnormal operating conditions while ensuring its normal operation. Summary of the Invention

[0006] The present invention aims to solve the above-mentioned problems in the prior art and provide a phase transition thermal response electrolyte and lithium-ion battery that can ensure normal operation and high safety of the battery under high temperature conditions.

[0007] To achieve the above objectives, the first aspect of this application provides a phase transition thermally responsive electrolyte, comprising: a lithium salt, a first solvent, a second solvent, a thermally decomposable free radical initiator, and a reactive monomer;

[0008] Wherein, the first solvent is one or more selected from propylene carbonate, trimethyl phosphate, triethyl phosphate, and sulfolane; The second solvent is selected from one or more of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, bis(2,2,2-trifluoroethyl) ether, hydrofluoroether, and fluorobenzene; The thermally decomposable free radical initiator is a thermally decomposable free radical initiator; The reaction monomers are selected from one or more of bismaleimide monomers, vinyl carbonate monomers, and acrylate monomers.

[0009] Preferably, in the phase transition heat-responsive electrolyte described above, the mass content of the first solvent is 20-70 wt% and the mass content of the second solvent is 10-70 wt%, based on the total mass of the electrolyte.

[0010] In the aforementioned phase transition thermally responsive electrolyte, preferably, the thermally decomposable free radical initiator is selected from one or more of tert-butylperoxide-2-ethylhexanoate, tert-butylperoxybenzoate, dicumyl peroxide, and tert-amylperoxybenzoate.

[0011] Preferably, in the aforementioned phase transition thermally responsive electrolyte, the thermally decomposable free radical initiator has a mass content of 0.1-5 wt% in the electrolyte. More preferably, it has a mass content of 0.3-3 wt%.

[0012] Preferably, in the aforementioned phase transition heat-responsive electrolyte, the mass content of the reactive monomer in the electrolyte is 0.5~20 wt%. More preferably, it is 1~10 wt%.

[0013] In the aforementioned phase transition thermally responsive electrolyte, preferably, the bismaleimide monomer is 1,1′-(methylenedi-p-phenylene)bismaleimide and / or ethylidene bismaleimide; The vinyl carbonate monomers are selected from one or more of vinylene carbonate, 4-vinyl-1,3-dioxolane-2-one and 4-vinyl-1,3-dioxane-2-one; The acrylate monomers are selected from one or more of polyethylene glycol diacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, and pentaerythritol tetraacrylate.

[0014] Preferably, in the aforementioned phase transition thermally responsive electrolyte, the lithium salt is selected from one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium difluorooxalateborate, and lithium bis(oxalateborate); the mass content of the lithium salt in the electrolyte is 5-20 wt%. More preferably, it is 7-15 wt%.

[0015] Preferably, the phase transition heat-responsive electrolyte further includes an additive, wherein the mass content of the additive in the electrolyte does not exceed 10 wt%.

[0016] In the aforementioned phase transition thermally responsive electrolyte, preferably, the additive is selected from one or more of fluoroethylene carbonate, vinylene carbonate, methane disulfonate, vinyl sulfate, and 1,3-propane sulpholactone.

[0017] The phase transition thermally responsive electrolyte of this application does not rely solely on temperature increase to improve the polymerization rate, but achieves a balance between room temperature stability and high-temperature rapid response through the synergistic effect between a specific first solvent, a second solvent, a thermally decomposable free radical initiator, and the reactants.

[0018] The first solvent is selected from highly polar solvents such as propylene carbonate, trimethyl phosphate, triethyl phosphate, and sulfolane. These solvents possess high dielectric constants and strong lithium salt dissolving capabilities, enabling them to form polar microphase regions and preferentially dissolve highly polar reactive monomers such as bismaleimide monomers and vinyl carbonate monomers. Taking bismaleimide monomers as an example, their molecules contain two imide groups, exhibiting strong polarity. Their solubility in the first solvent, such as propylene carbonate and trimethyl phosphate, is significantly higher than their solubility in the second solvent, a weakly polar fluorinated solvent. Therefore, they preferentially accumulate in the polar microregions formed by the first solvent.

[0019] The second solvent is selected from weak solvent-type fluorinated solvents such as 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, bis(2,2,2-trifluoroethyl) ether, hydrofluoroether, and fluorobenzene. These solvents have weak miscibility with the first solvent at room temperature, forming a stable microphase separation structure; simultaneously, they exhibit good solubility for thermally decomposable free radical initiators. Taking peroxide thermally decomposable free radical initiators such as tert-butylperoxide-2-ethylhexanoate and tert-butylperoxybenzoate as examples, their molecules have long hydrophobic alkyl chains and weak polarity, making them more easily distributed in the low-polarity microregions formed by the fluorinated second solvent. Therefore, under room temperature conditions, the thermally decomposable free radical initiator and the reactant monomer are enriched in different microregions, significantly reducing their contact probability and effective collision frequency, and inhibiting slow polymerization, spontaneous thickening, or gelation of the electrolyte at room temperature.

[0020] Furthermore, this application employs thermally decomposable free radical initiators, rather than azo initiators, ionic initiators, or lithium salt-induced initiators. Azo initiators, such as azobisisobutyronitrile (AIBN), exhibit high decomposition rates near room temperature, easily leading to premature polymerization of the electrolyte during storage. Ionic initiators are susceptible to the effects of lithium salts, trace amounts of water, or electrode surfaces, inducing side reactions at room temperature and making it difficult to ensure long-term storage stability. In contrast, thermally decomposable peroxide initiators such as tert-butylperoxide-2-ethylhexanoate and tert-butylperoxybenzoate are relatively stable at room temperature, rapidly decomposing to generate free radicals only within the range of 100–140°C. Therefore, they can ensure long-term stability of the system at room temperature while rapidly triggering polymerization reactions at high temperatures.

[0021] This application further prefers to use bismaleimide monomers. The double bond in the bismaleimide molecule is affected by the electron-withdrawing effect of the adjacent imide group, and its room temperature polymerization activity is low. Therefore, even if it comes into contact with a small amount of free radicals at room temperature, it is not easy to undergo rapid polymerization. However, under high temperature conditions, when a large amount of thermally decomposable free radical initiator is decomposed, bismaleimide can still undergo rapid cross-linking polymerization to form a dense gel network.

[0022] When the temperature rises above the phase transition temperature, the first and second solvents change from partially miscible to a homogeneously miscible system, disrupting the original microphase structure. The thermally decomposable free radical initiator and the reactant monomers change from a spatially isolated state to a uniformly contacted state. Simultaneously, the high temperature significantly promotes the rapid decomposition of peroxide thermally decomposable free radical initiators such as tert-butylperoxide-2-ethylhexanoate, leading to a rapid increase in free radical concentration. Meanwhile, the polymerization rate of monomers such as bismaleimide increases significantly at high temperatures, resulting in gelation of the system within tens of seconds. Therefore, this application does not simply rely on "high temperature → faster reaction," but rather achieves the technical effect of long-term room-temperature stability and rapid high-temperature response through a dual synergistic mechanism of "room-temperature spatial isolation – high-temperature miscible contact" and "low-temperature stable thermally decomposable free radical initiator – high-temperature rapid decomposition thermally decomposable free radical initiator."

[0023] A second aspect of this application provides a lithium-ion battery, wherein the electrolyte of the lithium-ion battery is the phase transition thermally responsive electrolyte described above.

[0024] Compared with the prior art, this application has the following beneficial effects: (1) The present invention constructs a temperature-sensitive solvent system by using a highly polar first solvent and a weak solvent second solvent. Under normal temperature conditions, a microphase separation structure is formed, so that the thermally decomposable free radical initiator and the reactant monomer are distributed in different microphase regions, thereby reducing the contact probability between reactants, effectively suppressing spontaneous reactions under normal temperature conditions, and improving the room temperature stability of the electrolyte. Under high temperature conditions, the temperature-sensitive solvent system undergoes a phase transformation and forms a homogeneous miscible system, which enables the thermally decomposable free radical initiator and the reactant monomer to come into rapid contact. At the same time, the high temperature promotes the decomposition of the thermally decomposable free radical initiator, thereby significantly improving the polymerization reaction rate and realizing the rapid triggering of thermal response behavior.

[0025] (2) This invention utilizes the phase transition that occurs when the temperature of the electrolyte increases during battery operation to regulate the spatial distribution of reactants. Based on this characteristic, the electrolyte maintains good electrochemical performance under normal operating conditions and suppresses electrolyte fluidity and side reaction processes through polymerization reaction under abnormally high operating conditions, thereby improving the safety performance of lithium-ion batteries. Detailed Implementation

[0026] To facilitate understanding of this application, the following description will be more comprehensive and detailed in conjunction with preferred embodiments, but the scope of protection of this application is not limited to the following specific embodiments.

[0027] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of this application.

[0028] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods, and all solvents used are of analytical grade.

[0029] The relevant materials involved in this application may be, but are not limited to, the following sources: propylene carbonate (CAS No. 108-32-7), trimethyl phosphate (CAS No. 512-56-1), triethyl phosphate (CAS No. 78-40-0), and sulfolane (CAS No. 126-33-0) were purchased from Sinopharm Group; 1,1,2,2-Tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (CAS No. 16627-68-2), bis(2,2,2-trifluoroethyl) ether (CAS No. 333-36-8), and fluorobenzene (CAS No. 462-06-6) were purchased from Aladdin. tert-Butyl peroxide-2-ethylhexanoate (CAS No. 3006-82-4), tert-Butyl peroxybenzoate (CAS No. 614-45-9), and dicumyl peroxide (CAS No. 80-43-3) were purchased from Aladdin. Bismaleimide (CAS No. 13676-54-5) was purchased from TCI; Fluorinated vinyl carbonate (CAS No. 114435-02-8), vinylene carbonate (CAS No. 872-36-6), and 1,3-propane sulpholactone (CAS No. 1120-71-4) were purchased from Aladdin. Lithium hexafluorophosphate (CAS No. 21324-40-3) and lithium difluorosulfonyl imide (CAS No. 171611-11-3) were purchased from Shanghai Maclean Biochemical Technology Co., Ltd.

[0030] Polyolefin membrane: Celgard 2400 membrane, 25μm thick, single-layer PP material, 41% porosity, purchased from Celgard, USA; Commercial lithium iron phosphate cathode: areal density 12 mg / cm³ 2 The active substance content was 95.4 wt%, purchased from Shenzhen Kejing Zhida Technology Co., Ltd. Commercial graphite anode: areal density 5.8 mg / cm³ 2 The active substance content is 95.5 wt%, purchased from Shenzhen Kejing Zhida Technology Co., Ltd.

[0031] In the following examples and comparative examples, room temperature refers to 25±2℃.

[0032] Example 1: The phase transition thermally responsive electrolyte of this embodiment includes: LiPF6, propylene carbonate (PC), 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), tert-butyl peroxide-2-ethylhexanoate, bismaleimide (BMI), and fluoroethylene carbonate. The mass content of LiPF6 is 9.14 wt%, the mass content of propylene carbonate is 33.34 wt%, the mass content of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether is 50.01 wt%, the mass content of tert-butyl peroxide-2-ethylhexanoate is 0.83 wt%, the mass content of bismaleimide is 4.17 wt%, and the mass content of fluoroethylene carbonate is 2.51 wt%.

[0033] The preparation method of the phase transition heat-responsive electrolyte in this embodiment includes the following specific steps: In an argon-protected glove box, propylene carbonate (PC) was mixed with 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), and LiPF6 was added. The mixture was stirred for 12 h until completely dissolved. Then, bismaleimide (BMI) and tert-butyl peroxide-2-ethylhexanoate (TBPO) were added, and the mixture was stirred for another 6 h. Finally, fluoroethylene carbonate (FEC) was added, and the mixture was stirred until homogeneous to obtain the electrolyte.

[0034] Example 2: The phase transition thermally responsive electrolyte of this embodiment includes: LiFSI, trimethyl phosphate (TMP), 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), tert-butyl peroxide-2-ethylhexanoate, bismaleimide (BMI), and fluoroethylene carbonate. The mass content of LiFSI is 11.30 wt%, the mass content of trimethyl phosphate is 40.69 wt%, the mass content of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether is 40.69 wt%, the mass content of tert-butyl peroxide-2-ethylhexanoate is 0.81 wt%, the mass content of bismaleimide is 4.07 wt%, and the mass content of fluoroethylene carbonate is 2.44 wt%.

[0035] The raw materials were prepared according to the formulation of the phase transition heat-responsive electrolyte in this embodiment, and the phase transition heat-responsive electrolyte was prepared according to the same preparation method as in Example 1.

[0036] Example 3: The phase transition thermally responsive electrolyte of this embodiment includes: LiPF6, propylene carbonate (PC), bis(2,2,2-trifluoroethyl) ether (BTFE), tert-butyl peroxide-2-ethylhexanoate, bismaleimide (BMI), and fluoroethylene carbonate. The mass content of LiPF6 is 11.11 wt%, the mass content of propylene carbonate is 24.46 wt%, the mass content of bis(2,2,2-trifluoroethyl) ether is 57.08 wt%, the mass content of tert-butyl peroxide-2-ethylhexanoate is 0.82 wt%, the mass content of bismaleimide is 4.08 wt%, and the mass content of fluoroethylene carbonate is 2.45 wt%.

[0037] The raw materials were prepared according to the formulation of the phase transition heat-responsive electrolyte in this embodiment, and the phase transition heat-responsive electrolyte was prepared according to the same preparation method as in Example 1.

[0038] Example 4: The phase transition thermally responsive electrolyte of this embodiment includes: LiPF6, propylene carbonate (PC), 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), tert-butyl peroxide-2-ethylhexanoate, bismaleimide (BMI), and fluoroethylene carbonate. The mass content of LiPF6 is 9.19 wt%, the mass content of propylene carbonate is 33.54 wt%, the mass content of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether is 50.31 wt%, the mass content of tert-butyl peroxide-2-ethylhexanoate is 0.25 wt%, the mass content of bismaleimide is 4.19 wt%, and the mass content of fluoroethylene carbonate is 2.52 wt%.

[0039] The raw materials were prepared according to the formulation of the phase transition heat-responsive electrolyte in this embodiment, and the phase transition heat-responsive electrolyte was prepared according to the same preparation method as in Example 1.

[0040] Example 5: The phase transition thermally responsive electrolyte of this embodiment includes: LiPF6, propylene carbonate (PC), 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), tert-butyl peroxide-2-ethylhexanoate, bismaleimide (BMI), and fluoroethylene carbonate. The mass content of LiPF6 is 9.49 wt%, the mass content of propylene carbonate is 34.61 wt%, the mass content of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether is 51.92 wt%, the mass content of tert-butyl peroxide-2-ethylhexanoate is 0.87 wt%, the mass content of bismaleimide is 0.52 wt%, and the mass content of fluoroethylene carbonate is 2.59 wt%.

[0041] The raw materials were prepared according to the formulation of the phase transition heat-responsive electrolyte in this embodiment, and the phase transition heat-responsive electrolyte was prepared according to the same preparation method as in Example 1.

[0042] Example 6: The phase transition thermally responsive electrolyte of this embodiment includes: LiPF6, propylene carbonate (PC), 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), tert-butyl peroxide-2-ethylhexanoate, bismaleimide (BMI), and fluoroethylene carbonate. The mass content of LiPF6 is 8.66 wt%, the mass content of propylene carbonate is 20.53 wt%, the mass content of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether is 61.58 wt%, the mass content of tert-butyl peroxide-2-ethylhexanoate is 1.03 wt%, the mass content of bismaleimide is 5.13 wt%, and the mass content of fluoroethylene carbonate is 3.07 wt%.

[0043] The raw materials were prepared according to the formulation of the phase transition heat-responsive electrolyte in this embodiment, and the phase transition heat-responsive electrolyte was prepared according to the same preparation method as in Example 1.

[0044] Example 7: The phase transition thermally responsive electrolyte of this embodiment includes: LiPF6, propylene carbonate (PC), 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), tert-butyl peroxide-2-ethylhexanoate, bismaleimide (BMI), and fluoroethylene carbonate. The mass content of LiPF6 is 7.89 wt%, the mass content of propylene carbonate is 28.78 wt%, the mass content of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether is 43.18 wt%, the mass content of tert-butyl peroxide-2-ethylhexanoate is 3.60 wt%, the mass content of bismaleimide is 14.39 wt%, and the mass content of fluoroethylene carbonate is 2.16 wt%.

[0045] The raw materials were prepared according to the formulation of the phase transition heat-responsive electrolyte in this embodiment, and the phase transition heat-responsive electrolyte was prepared according to the same preparation method as in Example 1.

[0046] Example 8: The phase transition thermally responsive electrolyte of this embodiment includes: LiPF6, propylene carbonate (PC), 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), tert-butyl peroxide-2-ethylhexanoate, bismaleimide (BMI), and fluoroethylene carbonate. The mass content of LiPF6 is 9.91 wt%, the mass content of propylene carbonate is 69.30 wt%, the mass content of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether is 11.88 wt%, the mass content of tert-butyl peroxide-2-ethylhexanoate is 0.99 wt%, the mass content of bismaleimide is 4.95 wt%, and the mass content of fluoroethylene carbonate is 2.97 wt%.

[0047] The raw materials were prepared according to the formulation of the phase transition heat-responsive electrolyte in this embodiment, and the phase transition heat-responsive electrolyte was prepared according to the same preparation method as in Example 1.

[0048] Comparative Example 1: The electrolyte in this comparative example includes: LiPF6, ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), vinylene carbonate, fluoroethylene carbonate, vinyl sulfate, and methanedisulfonate. The mass content of LiPF6 is 11.34 wt%, ethylene carbonate is 27.47 wt%, dimethyl carbonate is 27.47 wt%, ethyl methyl carbonate is 28.31 wt%, vinylene carbonate is 2.92 wt%, fluoroethylene carbonate is 0.83 wt%, ethylene sulfate is 0.83 wt%, and methanedisulfonate is 0.83 wt%.

[0049] The preparation method of the electrolyte in this comparative example is as follows: Ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) are mixed, LiPF6 is added, and the mixture is stirred until homogeneous. Then, vinylene carbonate, fluoroethylene carbonate, ethylene sulfate, and methane disulfonate are added and mixed until homogeneous to obtain the electrolyte.

[0050] Comparative Example 2: The phase transition thermal response electrolyte of this comparative example includes: LiPF6, ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), tert-butyl peroxide-2-ethylhexanoate, bismaleimide (BMI), and fluoroethylene carbonate. The mass content of LiPF6 is 11.01 wt%, ethylene carbonate is 26.97 wt%, dimethyl carbonate is 26.97 wt%, ethyl methyl carbonate is 26.97 wt%, tert-butyl peroxide-2-ethylhexanoate is 0.90 wt%, bismaleimide is 4.48 wt%, and fluoroethylene carbonate is 2.70 wt%.

[0051] The preparation method of the phase transition heat-responsive electrolyte in this comparative example includes the following specific steps: In an argon-protected glove box, ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) were mixed, and then LiPF6 was added and stirred for 12 h until completely dissolved. Subsequently, bismaleimide (BMI) and tert-butyl peroxide-2-ethylhexanoate (TBPO) were added, and stirring was continued for 6 h. Finally, fluoroethylene carbonate (FEC) was added and mixed evenly to obtain the electrolyte.

[0052] Comparative Example 3: The electrolyte composition and preparation method of this comparative example differ from those of Example 1 only in that the second solvent 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) is replaced with an equal amount of dimethyl carbonate (DMC). All other components and contents are exactly the same as those in Example 1.

[0053] Comparative Example 4: The electrolyte in this comparative example comprises: LiPF6, propylene carbonate (PC), 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), tert-butyl peroxide-2-ethylhexanoate, bismaleimide (BMI), and fluoroethylene carbonate. The mass content of LiPF6 is 8.64 wt%, the mass content of propylene carbonate is 31.50 wt%, the mass content of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether is 47.26 wt%, the mass content of tert-butyl peroxide-2-ethylhexanoate is 6.30 wt%, the mass content of bismaleimide is 3.94 wt%, and the mass content of fluoroethylene carbonate is 2.36 wt%.

[0054] Prepare raw materials according to the formulation of the phase transition heat-responsive electrolyte in this comparative example, and prepare the phase transition heat-responsive electrolyte according to the same preparation method as in Example 1.

[0055] Comparative Example 5: The only difference between the electrolyte composition and preparation method of this comparative example and Example 1 is that the first solvent, propylene carbonate (PC), is replaced with an equal amount of dimethyl carbonate (DMC).

[0056] Comparative Example 6: The only difference between the electrolyte composition and preparation method of this comparative example and Example 1 is that the second solvent 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) is replaced with an equal amount of methyl ethyl carbonate (EMC).

[0057] Comparative Example 7: The only difference between the electrolyte composition and preparation method of this comparative example and Example 1 is that the reactive monomer bismaleimide (BMI) is replaced with an equal amount of methyl methacrylate (MMA).

[0058] Comparative Example 8: The difference between the electrolyte composition and preparation method of this comparative example and Example 1 is that the thermally decomposable free radical initiator tert-butyl peroxide-2-ethylhexanoate is replaced with an equal amount of azobisisobutyronitrile (AIBN).

[0059] Preparation of lithium-ion batteries: The electrolytes prepared in each example and comparative example were assembled into lithium-ion batteries with commercial lithium iron phosphate cathodes, commercial graphite anodes, and commercial polyolefin separators.

[0060] The electrolyte and lithium-ion battery prepared above were subjected to performance tests, including electrolyte room temperature storage test, electrolyte high temperature response test, battery cycle performance test, and battery thermal runaway test.

[0061] in: Electrolyte room temperature storage experiment: Each electrolyte was sealed in a glass sample bottle and stored in a dark environment at 25°C. The appearance changes of the electrolyte were recorded at regular intervals. The test results are shown in Table 1.

[0062] Electrolyte high temperature response experiment: Each electrolyte sample was placed in a constant temperature oil bath at 120℃, and the time required for the electrolyte to change from the initial state to the fully gelled state was recorded. The test results are shown in Table 1.

[0063] Table 1: Room temperature storage stability and high temperature response of electrolyte

[0064] As shown in Table 1, the electrolytes in the examples remained transparent and homogeneous after 3 months of storage, with no significant increase in viscosity or gelation observed; in contrast, Comparative Example 2 (a conventional thermally responsive electrolyte) showed significant gelation within 7 days. These results indicate that the electrolyte of this invention significantly improves the room temperature stability of thermally responsive electrolytes. In a 120°C constant-temperature oil bath, the electrolytes in the examples completely gelled within 70 seconds, while Comparative Example 2 (a conventional thermally responsive electrolyte) required nearly 3 minutes to completely gel. These results demonstrate that the electrolyte of this invention exhibits rapid response characteristics under high-temperature conditions. The response times of Comparative Examples 2, 3, 5, 6, and 7 were generally long, even approaching 3 minutes (especially Comparative Examples 2 and 3). In real battery thermal runaway, these speeds are too slow to respond in time and have poor safety. Comparative Examples 4 (26s) and 8 (58s) also had fast high-temperature responses, but Comparative Example 4 gelled in 2 days at room temperature and Comparative Example 8 gelled in 5 days at room temperature. This shows that simply pursuing speed is not the goal. A balance must be struck between room temperature stability and high-temperature response. Electrolytes that are too fast but lack stability have no commercial value.

[0065] Battery cycle performance test: The Wuhan Land charge and discharge tester was used for charge and discharge test. Specifically, within the voltage range of 2.5-3.65V, the battery was first activated three times at a rate of 0.1C, and then charged and discharged 100 times at a rate of 0.5C. The test results are shown in Table 2.

[0066] Battery thermal runaway test: The fully charged battery (100% SOC) was placed in a heating furnace and heated to 200℃ at a rate of 5℃ / min. The thermal runaway state of the battery was recorded, and the results are shown in Table 2.

[0067] Table 2: Cyclic performance test and thermal runaway test of lithium batteries

[0068] As can be seen from the experimental data in Table 2, the lithium-ion battery of the present invention retains a capacity retention rate of over 95% after 100 cycles, while the lithium batteries of Comparative Examples 2-8 show significant degradation in cycle performance. These results indicate that the system of the present invention maintains good electrochemical performance while retaining its thermal response capability, which should be related to its good storage stability.

[0069] Meanwhile, the lithium-ion batteries in Examples 1-3 of the present invention showed no significant changes, and the lithium-ion batteries in Examples 4-8 only showed slight swelling without open flame or severe thermal runaway. In contrast, Comparative Example 1 (conventional commercial electrolyte) showed severe thermal runaway at around 150°C, and the lithium-ion batteries in Comparative Examples 2-8 all showed swelling. The results indicate that the electrolyte of the present invention can significantly improve the thermal safety performance of the battery at high temperatures.

[0070] The above are merely preferred embodiments of this application. It should be noted that this application is not limited to the above embodiments. For those skilled in the art, several improvements and modifications can be made without departing from the principles of this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should also be considered within the scope of protection of this application.

Claims

1. A phase transition thermally responsive electrolyte, characterized in that, include: Lithium salt, first solvent, second solvent, thermally decomposable free radical initiator, and reactant monomer; Wherein, the first solvent is one or more selected from propylene carbonate, trimethyl phosphate, triethyl phosphate, and sulfolane; The second solvent is selected from one or more of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, bis(2,2,2-trifluoroethyl) ether, hydrofluoroether, and fluorobenzene; The reaction monomers are selected from one or more of bismaleimide monomers, vinyl carbonate monomers, and acrylate monomers.

2. The phase transition thermally responsive electrolyte according to claim 1, characterized in that, Based on the total mass of the electrolyte, the mass content of the first solvent is 20~70 wt%, and the mass content of the second solvent is 10~70 wt%.

3. The phase transition thermally responsive electrolyte according to claim 1, characterized in that, The thermally decomposable free radical initiator is selected from one or more of tert-butylperoxide-2-ethylhexanoate, tert-butylperoxybenzoate, dicumyl peroxide, and tert-amylperoxybenzoate.

4. The phase transition thermally responsive electrolyte according to claim 3, characterized in that, The thermally decomposable free radical initiator has a mass content of 0.1~5 wt% in the electrolyte.

5. The phase transition thermally responsive electrolyte according to claim 1, characterized in that, The mass content of the reactant in the electrolyte is 0.5~20 wt%.

6. The phase transition thermally responsive electrolyte according to claim 1, characterized in that, The bismaleimide monomer is 1,1′-(methylenebis-p-phenylene)bismaleimide and / or ethylidene bismaleimide; The vinyl carbonate monomers are selected from one or more of vinylene carbonate, 4-vinyl-1,3-dioxolane-2-one and 4-vinyl-1,3-dioxane-2-one; The acrylate monomers are selected from one or more of polyethylene glycol diacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, and pentaerythritol tetraacrylate.

7. The phase transition thermally responsive electrolyte according to claim 1, characterized in that, The lithium salt is selected from one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium difluorooxalateborate, and lithium bis(oxalateborate); the mass content of the lithium salt in the electrolyte is 5-20 wt%.

8. The phase transition thermally responsive electrolyte according to claim 1, characterized in that, The electrolyte also includes additives, and the mass content of the additives in the electrolyte does not exceed 10 wt%.

9. The phase transition thermally responsive electrolyte according to claim 8, characterized in that, The additive is selected from one or more of fluoroethylene carbonate, vinylene carbonate, methanedisulfonate, vinyl sulfate, and 1,3-propanesulfonyl lactone.

10. A lithium-ion battery, characterized in that, The electrolyte of the lithium-ion battery is the phase transition thermally responsive electrolyte as described in any one of claims 1 to 9.

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