Thermosensitive crosslinking electrolyte, preparation method thereof and electrochemical energy storage device

Abstract

The invention relates to the field of electrochemical energy storage devices, and discloses a thermosensitive cross-linking electrolyte, a preparation method thereof and an electrochemical energy storage device, the electrolyte comprises an organic solvent, a thermosensitive cross-linking agent, an electrolyte salt, a thermal initiator and a flame retardant synergist; wherein the structure of the thermosensitive cross-linking agent is N, N '-(4, 4'-methylene diphenyl) bismaleimide (BMI) containing a carbon-carbon double bond (-C = C-). According to the thermosensitive cross-linked electrolyte, when the internal temperature of the electrolyte reaches 180-200 DEG C, the initiator is cracked to generate free radicals, the cross-linking agent forms a three-dimensional network within 10-60 s, after gelatinization, the solvent vapor pressure is reduced by more than or equal to 60%, the gas generation rate is reduced by more than or equal to 70%, the ionic conductivity is kept to be greater than or equal to 30% of an initial value, the buffer requirement before power failure is met, and the self-extinguishing time is less than or equal to 5 s (UL-94V-0 level); therefore, gas production is inhibited, thermal runaway is blocked, the non-combustible effect is achieved, and the requirements of active safety and high-power performance can be met.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical energy storage devices, and particularly relates to a thermosensitive crosslinked electrolyte and its preparation method, as well as an electric double-layer capacitor (EDLC) and a high-power lithium-ion capacitor. More specifically, it relates to introducing a thermosensitive crosslinking agent into the electrolyte, which forms a three-dimensional network in situ when the temperature reaches a set threshold, thereby suppressing gas production, blocking thermal runaway, and achieving a non-flammable effect. Background Technology

[0002] Existing technologies mainly rely on passive venting structures such as explosion-proof valves, which only open when the internal pressure reaches 1.0–1.5 MPa. This fails to suppress gas generation at the source, and the instantaneous release of large amounts of flammable gas and electrolyte mist can still cause flame ejection and secondary combustion. While flame-retardant solvents (trimethyl phosphate TMP, tripropyl phosphate TPP, or high-fluorinated ether HFE) can improve non-flammability, their viscosity at room temperature is >3 cP and rises sharply to >20 cP at -40°C, resulting in a 30–60% increase in DC internal resistance. Moreover, their cost is 5–8 times that of conventional carbonates, making it difficult to meet the requirements of high power, low-temperature start-up, and commercialization. Solid or gel electrolytes need to be cross-linked before film formation, are already solid at room temperature, have an interfacial impedance >10 Ω cm², and have a fixed transition temperature. They are incompatible with a wide range of solvent systems such as AN and DMC, and lack an active internal shutdown mechanism with an "adjustable temperature threshold," making it impossible to achieve self-curing at high temperatures while balancing power, cost, and process compatibility.

[0003] Therefore, the industry urgently needs to develop an electrolyte system that is low viscosity at room temperature, cross-links instantly upon reaching the set temperature, retains ion channels after cross-linking, and is non-flammable, in order to fill the technological gap that balances "active safety" and "high power performance". Summary of the Invention

[0004] To address the shortcomings of the prior art, this invention provides a thermosensitive cross-linked electrolyte that, when the internal temperature of the electrolyte reaches 180-200℃, self-crosslinks to form a three-dimensional network and gels, thereby suppressing gas production, blocking thermal runaway, and achieving a non-flammable effect, thus meeting the requirements of both "active safety" and "high power performance".

[0005] Another object of the present invention is to provide a method for preparing such a thermosensitive crosslinked electrolyte.

[0006] Another object of the present invention is to provide the application of such a thermosensitive crosslinked electrolyte.

[0007] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0008] A thermosensitive crosslinking electrolyte comprises an organic solvent, a thermosensitive crosslinking agent, an electrolyte salt, a thermal initiator, and an optional flame retardant synergist; wherein the thermosensitive crosslinking agent has a structure of R¹-N=N-R² or R¹-C≡C-R², wherein R¹ and R² are C4-C12 hydrocarbon groups containing alkenyl, epoxy, or siloxane side chains; preferably, the thermosensitive crosslinking agent is N,N′-(4,4′-methylenediphenyl)bismaleimide (BMI) containing a carbon-carbon double bond (-C=C-);

[0009] Preferably, the mass concentration of the thermosensitive crosslinking agent is 0.1-5 wt%.

[0010] In this invention, the electrolyte salt is at least one of tetraethylamine tetrafluoroborate (TEA BF4), spiro-(1,1')-bispyrrolidine tetrafluoroborate (SBP BF4), and 1,1-dimethylpyrrolidine tetrafluoroborate (DMP BF4); or at least one of lithium hexafluorophosphate (LiPF6), lithium bisfluorosulfonylimide (LiFSI), and lithium bis(trifluoromethylsulfonyl)imide (LiTFSI).

[0011] In this invention, the concentration of the electrolyte salt is 0.5 mol / L to 2.0 mol / L.

[0012] In this invention, the organic solvent is selected from at least one of propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), methyl propionate (MP), acetonitrile (ACN), 3-methoxypropionitrile (MPN), propionitrile (PN), butyronitrile (BN), dimethylformamide (DMF), methyl formate (MF), ethyl formate (EF), ethyl acetate (EA), methyl acetate (MA), and fluoroethers.

[0013] Preferably, the organic solvent has a mass concentration of 50-90 wt%.

[0014] In this invention, the thermal initiator is selected from at least one of dicumyl peroxide (DCP), azobisisobutyronitrile (AIBN), and tert-butyl peroxide (TBPB);

[0015] Preferably, the mass concentration of the thermal initiator is 0.01-1 wt%.

[0016] In this invention, the flame retardant synergist is selected from one or both of triphenyl phosphate (TPP) and triethyl phosphate (TEP);

[0017] Preferably, the mass concentration of the flame retardant synergist is 0-2.0 wt%, more preferably 0.1-2.0 wt%.

[0018] In another aspect of the present invention, the aforementioned method for preparing the thermosensitive crosslinked electrolyte includes the following steps:

[0019] (1) The organic solvent is purified by removing impurities and water to obtain purified organic solvent;

[0020] (2) At room temperature, the electrolyte salt is added to the purified organic solvent obtained in step (1) and allowed to stand to dissolve, thus obtaining the electrolyte solution;

[0021] (3) Add a thermal initiator to the electrolyte obtained in step (2) and let it stand to dissolve;

[0022] (4) Add an optional flame retardant synergist to the electrolyte obtained in step (3) to obtain the thermosensitive crosslinked electrolyte.

[0023] In another aspect, a double-layer capacitor includes the aforementioned thermosensitive crosslinked electrolyte or the thermosensitive crosslinked electrolyte prepared by the aforementioned preparation method; wherein the electrolyte salt is at least one of tetraethylamine tetrafluoroborate (TEA BF4), spiro-(1,1')-bispyrrolidine tetrafluoroborate (SBP BF4), and 1,1-dimethylpyrrolidine tetrafluoroborate (DMP BF4).

[0024] In another aspect, a lithium-ion capacitor includes the aforementioned thermosensitive crosslinked electrolyte or the thermosensitive crosslinked electrolyte prepared by the aforementioned preparation method; wherein the electrolyte salt is selected from at least one of lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium bis(trifluoromethylsulfonyl)imide (LiTFSI).

[0025] Compared with the prior art, the advantages and positive effects of the present invention are as follows:

[0026] The thermosensitive crosslinking agent in the thermosensitive crosslinking electrolyte of this invention is stable at 20-60 °C. When the internal temperature of the electrolyte reaches 180-200 °C, the initiator decomposes to generate free radicals, and the crosslinking agent forms a three-dimensional network within 10-60 s. After gelation: the solvent vapor pressure decreases by ≥60%; the gas generation rate decreases by ≥70%; the ionic conductivity remains at ≥30% of the initial value, meeting the buffering requirements before power failure; and the self-extinguishing time is ≤5s, achieving the UL-94V-0 level. Attached Figure Description

[0027] Figure 1 This is a graph showing the change in cell thickness under high-temperature load of 65°C and 2.9V voltage limit for comparative examples and embodiments of the present invention. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are only for explaining this invention and are not intended to limit this invention.

[0029] In one specific embodiment of the present invention, a thermosensitive crosslinking electrolyte includes an organic solvent, a thermosensitive crosslinking agent, an electrolyte salt, a thermal initiator, and an optional flame retardant synergist; wherein the thermosensitive crosslinking agent is N,N′-(4,4′-methylenediphenyl)bismaleimide (BMI) containing a carbon-carbon double bond (-C=C-).

[0030] In a preferred embodiment, a thermosensitive crosslinked electrolyte comprises: a) an electrolyte salt with a concentration of 0.5-2M, selected from at least one of TEABF4, LiPF6, LiFSI, NaTFSI, etc.;

[0031] Preferably, the electrolyte salt of the present invention is selected from spiro-(1,1')-bispyrrolidine tetrafluoroborate (SBP BF4), or any one or more of tetraethylamine tetrafluoroborate (TEA BF4), 1,1-dimethylpyrrolidine tetrafluoroborate (DMP BF4), 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIm BF4), and 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EMIm FSI).

[0032] b) Organic solvents: accounting for 50-90 wt% of the total weight, selected from one or a mixture of several of acetonitrile (AN), dimethyl carbonate (DMC), methyl propionate (MP), fluoroethers, etc.

[0033] Preferably, the organic solvent of the electrolyte of the present invention is selected from acetonitrile (ACN), or any one or more of propylene carbonate (PC) electrolyte, ethylene carbonate (EC) electrolyte, and acetonitrile (ACN).

[0034] c) Thermosensitive crosslinking agent: 0.1-5 wt%, which is N,N′-(4,4′-methylenediphenyl)bismaleimide (BMI) containing carbon-carbon double bonds (-C=C-);

[0035] Preferably, the thermosensitive crosslinking agent of the present invention is 1 wt% bismaleimide.

[0036] d) Thermal initiator: 0.01-1 wt%, selected from at least one of dicumyl peroxide (DCP), azobisisobutyronitrile (AIBN), and tert-butyl peroxide (TBPB), with a decomposition temperature of 50-130℃;

[0037] Preferably, the thermal initiator of the electrolyte of the present invention is 0.05 wt% dicumyl peroxide (DCP).

[0038] e) Optional flame retardant synergist: 0-2 wt%, preferably 0.1-2 wt%, selected from triphenyl phosphate (TPP) or triethyl phosphate (TEP).

[0039] Preferably, the flame retardant synergist of the electrolyte of the present invention is 0.1 wt% triphenyl phosphate (TPP).

[0040] In the electrolyte of this invention, a thermosensitive crosslinking agent with a specific structure is introduced. Under the action of an initiator, the agent crosslinks to form a three-dimensional network at a certain temperature. After gelation, the solvent vapor pressure decreases by ≥60%, the gas generation rate decreases by ≥70%, and the ionic conductivity remains at ≥30% of the initial value, meeting the buffering requirements before power failure. The self-extinguishing time is ≤5s (UL-94V-0 level), thereby suppressing gas generation, blocking thermal runaway, and achieving a non-flammable effect. This can meet the requirements of both "active safety" and "high power performance".

[0041] The present invention will be further explained and illustrated below through more specific embodiments, but these do not constitute any limitation.

[0042] The main raw materials involved in the following examples can all be purchased through commercial channels, and are all of industrial grade or above, without any special restrictions.

[0043] The main test methods involved in the following embodiments are as follows:

[0044] Test method:

[0045] The test method for high-temperature load with a voltage limit of 2.9V at 65℃ is as follows: At room temperature, test the basic performance: voltage, internal resistance, thickness (height of top and bottom), and mass. Control the temperature of the temperature chamber at 25℃ and let it stand for 1 hour; charge it to 2.9V with a constant current of 25A; discharge it to 1.5V with a constant current of 25A (this step is 0.1s timing), repeat the charge and discharge cycle 3 times, and take the third time as the cell capacitor; transfer the cell to the 65℃ temperature chamber and connect it; charge it at a constant voltage of 2.9V for 168 hours (7 days); transfer the cell to room temperature and let it stand for 3 hours; repeat the above steps until the 12th week.

[0046] The method for testing ionic conductivity is as follows: use a standard solution to rinse and calibrate the probe of the conductivity meter, place the electrolyte in a temperature chamber at the target temperature for 1 hour, take it out, quickly rinse the probe of the conductivity meter with the electrolyte, directly measure the conductivity of the solution, and convert it to a standard value through built-in temperature compensation. Each group of electrolytes is measured twice and the average value is taken.

[0047] Example 1

[0048] (1) Pre-synthesis of bismaleimide-ethylene glycol diacrylate (BMI-EGDMA) copolymer: 8.40 g of bismaleimide (BMI), 7.00 g of ethylene glycol diacrylate (EGDMA), and 0.046 g of azobisisobutyronitrile (AIBN) were weighed in a glove box and dissolved in 70 g of acetonitrile (AN) solution. Initial chain growth was carried out by heating and stirring at 75 °C for 3 h, and then the temperature was raised to 90 °C and stirred for 1 h to complete chain transfer and form crosslinking points, resulting in a light yellow transparent oligomer solution L-AN. The solution was cooled to room temperature and sealed for later use.

[0049] (2) Electrolyte preparation: Spiro-(1,1')-bispyrrolidine tetrafluoroborate (SBP BF4) was vacuum-baked at 150°C for 8 hours. Before the salt cooled down, it was transferred to a glove box with a moisture content of <20 ppm for cooling. The AN solvent was dehydrated using molecular sieves for more than 24 hours. 27.8 g of SBP BF4 was added to 72.2 g of AN to prepare a 100 g 1 mol / L salt solution. 2 g of L-AN prepolymer solution (2 wt%) was added to the salt solution, followed by 0.3 wt% DCP to provide free radicals, initiating chain copolymerization of the carbon-carbon double bonds of BMI and EGDMA to form a three-dimensional cross-linked network. Finally, 2 wt% triphenyl phosphate (TPP) was added, and the mixture was magnetically stirred at 25 °C for 30 min to obtain a colorless and transparent liquid.

[0050] (3) Electrode preparation: Both positive and negative electrode sheets are made by coating aluminum foil after uniformly mixing activated carbon YP, conductive agent SP and binder PA in a mass ratio of 90:5:5.

[0051] (4) Cell assembly: The symmetrical electrodes and cellulose membrane are wound and assembled into the shell and injected with the electrolyte prepared in step (2) to form a 600 F cylindrical cell (safety valve pressure 3.0 MPa). The cell is transferred to a temperature chamber and heated from 25°C to 85°C at a rate of 5°C / min. The temperature is held for 30 min, and the electrolyte gels within 10–15 s to form a three-dimensional network.

[0052] Example 2

[0053] (1) Pre-synthesis of bismaleimide-ethylene glycol diacrylate (BMI-EGDMA) copolymer: L-AN was prepared in the same way as in Example 1, cooled to room temperature, and stored for later use.

[0054] (2) Electrolyte preparation: SBP BF4 was vacuum-baked at 150°C for 8 hours. Before the salt cooled down, it was transferred to a glove box with a moisture content of <20 ppm for cooling. The AN solvent was dehydrated using molecular sieves for more than 24 hours. 27.8 g of SBP BF4 was added to 72.2 g of AN to prepare a 100 g 1 mol / L salt solution. 2 g of L-AN prepolymer solution (2 wt%) was added to the salt solution, and then 0.2 wt% DCP was added to provide free radicals, initiating the chain copolymerization of the carbon-carbon double bonds of BMI and EGDMA to form a three-dimensional cross-linked network. The mixture was magnetically stirred at 25 °C for 30 min to obtain a colorless and transparent liquid.

[0055] (3) Electrode preparation: Both positive and negative electrode sheets are made by coating aluminum foil after uniformly mixing activated carbon YP, conductive agent SP and binder PA in a mass ratio of 90:5:5.

[0056] (4) Cell assembly: The symmetrical electrodes and cellulose membrane are wound and assembled into the shell and injected with the electrolyte prepared in step (2) to form a 600 F cylindrical cell (safety valve pressure 3.0 MPa). The cell is transferred to a temperature chamber and heated from 25 °C to 85 °C at a rate of 5 °C / min. The temperature is held for 30 min, and the electrolyte gels within 10-15 s to form a three-dimensional network.

[0057] Example 3

[0058] (1) Pre-synthesis of bismaleimide-ethylene glycol diacrylate (BMI-EGDMA) copolymer: L-AN was prepared in the same way as in Example 1, cooled to room temperature, and stored for later use.

[0059] (2) Electrolyte preparation: SBP BF4 was vacuum-baked at 150°C for 8 hours. Before the salt cooled down, it was transferred to a glove box with a moisture content of <20 ppm for cooling. The AN solvent was dehydrated using molecular sieves for more than 24 hours. 27.8 g of SBP BF4 was added to 72.2 g of AN to prepare a 100 g 1 mol / L salt solution. 2 g of L-AN prepolymer solution (2 wt%) was added to the salt solution, and then 0.3 wt% DCP was added to provide free radicals, initiating the chain copolymerization of the carbon-carbon double bonds of BMI and EGDMA to form a three-dimensional cross-linked network. The solution was magnetically stirred at 25 °C for 30 min to obtain a colorless and transparent liquid.

[0060] (3) Electrode preparation: Both positive and negative electrode sheets are made by coating aluminum foil after uniformly mixing activated carbon YP, conductive agent SP and binder PA in a mass ratio of 90:5:5.

[0061] (4) Cell assembly: The symmetrical electrodes and cellulose membrane are wound and assembled into the shell and injected with the electrolyte prepared in step (2) to form a 600 F cylindrical cell (safety valve pressure 3.0 MPa). The cell is transferred to a temperature chamber and heated from 25 °C to 85 °C at a rate of 5 °C / min. The temperature is held for 30 min, and the electrolyte gels within 10-15 s to form a three-dimensional network.

[0062] Example 4

[0063] (1) Pre-synthesis of bismaleimide-ethylene glycol diacrylate (BMI-EGDMA) copolymer: L-AN was prepared in the same way as in Example 1, cooled to room temperature, and stored for later use.

[0064] (2) Electrolyte preparation: SBP BF4 was vacuum-baked at 150°C for 8 hours. Before the salt cooled down, it was transferred to a glove box with a moisture content of <20 ppm for cooling. The AN solvent was dehydrated using molecular sieves for more than 24 hours. 27.8 g of SBP BF4 was added to 72.2 g of AN to prepare a 100 g 1 mol / L salt solution. 1 g of L-AN prepolymer solution (1 wt%) was added to the salt solution, followed by 0.3 wt% DCP to provide free radicals, initiating chain copolymerization of the carbon-carbon double bonds of BMI and EGDMA to form a three-dimensional cross-linked network. The solution was magnetically stirred at 25 °C for 30 min to obtain a colorless and transparent liquid.

[0065] (3) Electrode preparation: Both positive and negative electrode sheets are made by coating aluminum foil after uniformly mixing activated carbon YP, conductive agent SP and binder PA in a mass ratio of 90:5:5.

[0066] (4) Cell assembly: The symmetrical electrodes and cellulose membrane are wound and assembled into the shell and injected with the electrolyte prepared in step (2) to form a 600 F cylindrical cell (safety valve pressure 3.0 MPa). The cell is transferred to a temperature chamber and heated from 25 °C to 85 °C at a rate of 5 °C / min. The temperature is held for 30 min, and the electrolyte gels within 10-15 s to form a three-dimensional network.

[0067] Comparative Example 1

[0068] (1) Electrolyte preparation: Spiro-(1,1')-bispyrrolidine tetrafluoroborate (SBP BF4) was vacuum baked at 150°C for 8 hours. Before the salt cooled down, it was transferred to a glove box with a moisture content of <20ppm and the water was removed from the AN solvent using molecular sieve for more than 24 hours. SBP BF4 was added to ACN solvent to prepare a 1mol / L solution without adding any additives or initiators. The solution was stirred and mixed at room temperature for 10 minutes.

[0069] (2) Electrode preparation: Same as in Example (1).

[0070] (3) Cell assembly: The symmetrical electrodes and cellulose membrane are wound and assembled into the shell and injected with the electrolyte prepared in step (1) to form a 600 F cylindrical cell (safety valve pressure 3.0 MPa). The cell is not heated and stored.

[0071] Comparative Example 2

[0072] (1) Electrolyte preparation: Spiro-(1,1')-bispyrrolidine tetrafluoroborate (SBP BF4) was vacuum baked at 150°C for 8 hours. Before the salt cooled down, it was transferred to a glove box with a moisture content of <20ppm and cooled. The AN solvent was dehydrated using molecular sieves for more than 24 hours. SBP BF4 was added to ACN solvent to prepare a 1mol / L solution, and 2 wt% of flame retardant additive triphenyl phosphate (TPP) was added. The mixture was stirred and mixed at room temperature for 10 minutes.

[0073] (2) Electrode preparation: Same as in Example (1).

[0074] (3) Cell assembly: The symmetrical electrodes and cellulose membrane are wound and assembled into the shell and injected with the electrolyte prepared in step (1) to form a 600 F cylindrical cell (safety valve pressure 3.0 MPa). The cell is not heated and stored.

[0075] As can be seen, BMI in Example 1 provides a high-rigidity, flame-retardant framework, but BMI itself has a high homopolymerization temperature (≈ 180 ℃), requiring copolymerization with olefin monomers such as EGDMA to significantly reduce the activation energy of the reaction. EGDMA has the characteristics of low viscosity, easy initiation, and low shrinkage. In the presence of DCP, it can rapidly open the ring and crosslink at 80 ℃, significantly reducing the reaction temperature of the thermosensitive agent crosslinking. The prepared electrolytes all have good fluidity in the injection state and do not affect the injection process. Table 1 shows the ionic conductivity-temperature relationship of the electrolyte before and after thermosensitive crosslinking in Example 1. The ionic conductivity increases with increasing temperature. After crosslinking, the overall value shifts downward by about 30% in parallel, with the slope remaining unchanged, indicating that the crosslinking network does not destroy the ion migration channels.

[0076] Table 1. Ionic conductivity-temperature data of electrolyte before and after thermosensitive crosslinking in Example 1.

[0077] Temperature / °C Before crosslinking σ / mS cm⁻¹ After crosslinking, σ / mS cm⁻¹ -40 12.1 8.6 -20 25.3 18.0 0 38.9 27.8 25 58.4 42.1 40 68.7 49.5 60 78.2 56.3 85 86.5 61.0

[0078] In addition, the viscosity of the electrolytes in each example and comparative example was measured using a rotational viscometer (NDJ-5S, #1 rotor, 60 rpm, n=3). The data are shown in Table 2. Comparative Example 1, as a blank sample, had the lowest viscosity. The electrolyte viscosity increased by 0.38 mPa·s upon the introduction of TPP, and increased by 3-4 times after the introduction of the crosslinking agent and initiator. However, it is close to the literature value of 1 M SBP BF4PC electrolyte, and the viscosity increase is within a reasonable range. The BMI-EGDMA prepolymer content added in Example 4 was lower, and the viscosity was 1.18 mPa·s lower than that in Example 1, indicating that the crosslinking network has a greater impact on viscosity than the flame retardant TPP.

[0079] Table 2 Viscosity of electrolytes in comparative examples and embodiments at 25°C

[0080] Group Thermosensitive crosslinking agent Initiator (wt%) Flame retardant Viscosity / mPa·s (25 ℃) Comparative Example 1 — — — 0.88 Comparative Example 2 — — 2.0 wt% TPP 1.36 Example 1 2 wt% BMI-EGDMA prepolymer 0.3 wt% DCP 2.0 wt% TPP 3.87 Example 2 2 wt% BMI-EGDMA prepolymer 0.2 wt% DCP — 3.68 Example 3 2 wt% BMI-EGDMA prepolymer 0.3 wt% DCP — 3.76 Example 4 1 wt% BMI-EGDMA prepolymer 0.3 wt% DCP — 2.69

[0081] Figure 1 To illustrate the cell thickness changes in the comparative examples and embodiments under a high-temperature load of 65°C and a voltage upper limit of 2.9V, the safety valve pressure of the cells during assembly was 3.0 MPa, resulting in more pronounced thickness changes. Furthermore, to accelerate cell degradation, the conventional upper voltage limit was increased from 2.7V to 2.9V. Comparative Example 1, a blank control group without any crosslinking agents or flame retardants, showed significant bulging after week 8 due to the easy decomposition and gas production of AN. Comparative Example 2, with the addition of 2 wt% TPP, exhibited slightly reduced bulging due to the relatively more stable thermal stability of phosphate esters compared to AN. Example 2, with the addition of 2 wt% BMI-EGDMA prepolymer and 0.2 wt% DCP, showed significantly lower cell thickness growth in the later stages of the high-temperature load compared to Comparative Examples 1 and 2, indicating that the rigid-flexible channel network constructed by the crosslinking agent effectively improved the thermal stability of the electrolyte and reduced the vapor pressure inside the cell at high temperatures. In Example 3, slightly increasing the DCP content further reduced bulging, indicating that a DCP content of 0.3 wt% was more suitable. Example 1, which further incorporated 2.0 wt% liquid flame retardant TPP, exhibited the lowest bulging, indicating extremely low internal vapor pressure and minimal electrolyte decomposition during high-temperature loading.

[0082] Self-extinguishing tests (SETs) were conducted on 1g of electrolyte from Examples 1, 3, and 4, and Comparative Examples 1 and 2, respectively, in a closed incubator. The combustion times were as follows: the blank sample (Comparative Example 1) had the longest combustion time of 45 s; Comparative Example 2, with the addition of 2.0 wt% TPP, had a self-extinguishing time reduced by 13 s; Example 4, with only 1 wt% BMI-EGDMA prepolymer and 0.3 wt% DCP, was still combustible; while Example 1, with 2 wt% BMI-EGDMA prepolymer, 0.3 wt% DCP, and 2.0 wt% TPP, was completely non-flammable, indicating that the optimal content of BMI-EGDMA prepolymer is 2 wt%. The combination of cross-linked network and flame retardant greatly improves the safety of the battery cell.

[0083] Table 3 Self-extinguishing combustion timetables for Examples 1 and 3 and Comparative Examples 1 and 2

[0084] Group Thermosensitive crosslinking agent Initiator (wt%) Flame retardant Self-extinguishing time (s) Comparative Example 1 — — — 45 Comparative Example 2 — — 2.0 wt% TPP 32 Example 1 2 wt% BMI-EGDMA prepolymer 0.3 wt% DCP 2.0 wt% TPP 0 Example 3 2 wt% BMI-EGDMA prepolymer 0.3 wt% DCP — 13 Example 4 1 wt% BMI-EGDMA prepolymer 0.3 wt% DCP — 11

[0085] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A heat-sensitive crosslinking electrolyte, characterized by, The organic solvent, the heat-sensitive crosslinking agent, the electrolyte salt, the thermal initiator, and the optional flame-retardant synergist; wherein the heat-sensitive crosslinking agent has a structure of R¹-N=N-R² or R¹-C≡C-R², wherein R¹ and R² are C4-C12 hydrocarbon groups containing alkenyl, epoxy or siloxane side chains.

2. The heat-sensitive crosslinking electrolyte according to claim 1, characterized in that, The heat-sensitive crosslinking agent is N,N'-(4,4'-methylene diphenyl) bismaleimide (BMI) containing a carbon-carbon double bond (-C=C-). Preferably, the mass concentration of the heat-sensitive crosslinking agent is 0.1-5 wt%.

3. The heat-sensitive crosslinking electrolyte according to claim 1, wherein The electrolyte salt is at least one of tetraethylammonium tetrafluoroborate (TEABF4), spiro-(1,1')-bipyrrolidinium tetrafluoroborate (SBPBF4), and 1,1-dimethylpyrrolidinium tetrafluoroborate (DMPBF4), or at least one selected from lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium bis(trifluoromethylsulfonyl)imide (LiTFSI).

4. The heat-sensitive crosslinking electrolyte according to claim 3, characterized in that, The concentration of the electrolyte salt is 0.5 mol / L-2.0 mol / L.

5. The heat-sensitive crosslinking electrolyte according to claim 1, wherein The organic solvent is at least one selected from propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), methyl propionate (MP), acetonitrile (ACN), 3-methoxypropionitrile (MPN), propionitrile (PN), butyronitrile (BN), dimethylformamide (DMF), methyl formate (MF), ethyl formate (EF), ethyl acetate (EA), methyl acetate (MA), and fluoroether. Preferably, the mass concentration of the organic solvent is 50-90 wt%.

6. The heat-sensitive crosslinking electrolyte according to claim 1, wherein The thermal initiator is at least one selected from dicumyl peroxide (DCP), azobis(isobutyronitrile) (AIBN), and tert-butyl peroxybenzoate (TBPB). Preferably, the mass concentration of the thermal initiator is 0.01-1 wt%.

7. The heat-sensitive crosslinking electrolyte according to claim 1, wherein The flame-retardant synergist is one or both of triphenyl phosphate (TPP) and triethyl phosphate (TEP). Preferably, the mass concentration of the flame-retardant synergist is 0.1-2.0 wt%.

8. The process for the preparation of the heat-sensitive crosslinking electrolyte according to any one of claims 1 to 7, characterized in that, The method comprises the following steps: (1) purifying the organic solvent by removing impurities and water to obtain a purified organic solvent; (2) adding the electrolyte salt to the purified organic solvent obtained in step (1) at room temperature and standing for dissolution to obtain an electrolyte; (3) adding the thermal initiator to the electrolyte obtained in step (2) and standing for dissolution; (4) adding the optional flame-retardant synergist to the electrolyte obtained in step (3) to obtain the heat-sensitive crosslinked electrolyte.

9. An electric double layer capacitor characterized by The heat-sensitive crosslinked electrolyte prepared by the method of any one of claims 1-7 or claim 8; wherein the electrolyte salt is at least one of tetraethylammonium tetrafluoroborate (TEABF4), spiro-(1,1')-bipyrrolidinium tetrafluoroborate (SBPBF4), and 1,1-dimethylpyrrolidinium tetrafluoroborate (DMPBF4).

10. A lithium-ion capacitor, characterized by, The heat-sensitive cross-linking electrolyte according to any one of claims 1-7 or prepared by the method according to claim 8; wherein the electrolyte salt is at least one selected from lithium hexafluorophosphate (LiPF6), lithium bisfluorosulfonylimide (LiFSI), lithium bis(trifluoromethylsulfonyl)imide (LiTFSI).

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