An electrolyte additive composition for improving high-temperature cycle life of a battery, an electrolyte comprising the same, and a preparation method thereof

Abstract

This application relates to an electrolyte additive composition for improving the high-temperature cycle life of batteries, an electrolyte containing the same, and a method for preparing the same, relating to the field of lithium-ion battery technology. The electrolyte additive composition includes a dynamic network framework builder, a thermally triggered crosslinking agent, and lithium difluorophosphate. By introducing the dynamic network framework builder, it electrochemically polymerizes on the electrode surface to form a polymer network containing borate ester side groups, which can buffer volume changes at high temperatures to maintain the physical integrity of the interface. The key component, the thermally triggered crosslinking agent, releases highly active groups when a specific temperature is reached, which on the one hand efficiently complexes and fixes harmful substances, and on the other hand chemically crosslinks with active sites, improving the thermomechanical stability of the film. Lithium difluorophosphate provides a stable substrate for the above-mentioned organic functional layer, together ensuring that the battery has a low interface degradation rate under high-temperature conditions, ultimately achieving an improvement in high-temperature cycle life and a substantial enhancement in thermal safety performance.

Description

Technical Field

[0001] This application relates to the field of lithium-ion battery technology, specifically to an electrolyte additive composition for improving the high-temperature cycle life of batteries, an electrolyte containing the same, and a method for preparing the same. Background Technology

[0002] With the rapid development of new energy vehicles and large-scale energy storage industries, the energy density and service environment requirements of lithium-ion batteries are constantly increasing. However, in high-temperature environments above 45°C, the performance degradation and safety risks of batteries increase dramatically. The root cause of this problem lies mainly in the deterioration of the stability of the electrode-electrolyte interface. High temperatures accelerate the oxidative decomposition of conventional carbonate electrolytes, damaging the structure of the positive electrode material, while also causing the solid electrolyte interface film of the negative electrode to thicken and rupture, continuously consuming active lithium. In addition, the hydrolysis reaction of lithium salts in the electrolyte is also intensified, producing acidic substances that corrode the internal components of the battery.

[0003] Currently, research on electrolyte technology to improve the high-temperature performance of batteries mainly focuses on the following directions: First, using solvents with higher boiling and flash points, such as carboxylic acid esters or sulfone solvents, to improve the thermal stability of the electrolyte itself, but this usually sacrifices low-temperature performance and ionic conductivity; Second, adding single-function film-forming additives, such as vinylene carbonate or vinyl sulfate, in order to form a more stable protective layer on the electrode surface, but the interfacial films formed by such additives are mostly static structures, which are prone to cracking due to changes in electrode volume during long-term high-temperature cycling and cannot be repaired; Third, introducing compounds with flame-retardant functions, such as organophosphorus compounds, to improve the thermal safety of batteries, however, these additives often have a negative impact on the electrochemical performance of batteries.

[0004] Therefore, it is of great significance to develop an electrolyte that can maintain long-term interface stability at high temperatures and improve the high-temperature cycle life and safety of batteries. Summary of the Invention

[0005] This application provides an electrolyte additive composition for improving the high-temperature cycle life of batteries, an electrolyte containing the same, and a method for preparing the same, which has the effect of maintaining long-term interface stability at high temperatures and improving the high-temperature cycle life and safety of batteries.

[0006] In a first aspect, the electrolyte additive composition for improving the high-temperature cycle life of batteries provided in this application adopts the following technical solution: An electrolyte additive composition for improving the high-temperature cycle life of batteries, comprising the following components by weight: 1.5-2.5 parts of dynamic network framework builder, 2.0-4.0 parts of thermally triggered crosslinking agent, and 1.0-1.5 parts of film-forming initiator; The dynamic network framework builder is 2-vinyl-4,4,5,5-tetramethyl-1,3,2-dioxoboronylcyclohexane; the film-forming initiator is lithium difluorophosphate. The thermally triggered crosslinking agent is a compound having the following structure: (R'-NH-CO-O-(CH2)3)3Si-O-Si((CH2)3-O-CO-NH-R')3.

[0007] By employing the above technical solution, lithium difluorophosphate preferentially decomposes at a lower potential, forming a dense underlying film rich in inorganic components such as lithium fluoride and phosphates on the surface of both the positive and negative electrodes in situ. This film not only has high ionic conductivity, effectively inhibiting surface oxidation of the positive electrode material and dissolution of transition metal ions, but more importantly, it provides a stable substrate for the subsequent growth of organic polymer films.

[0008] Secondly, during the initial charging and early cycling phases of the battery, vinyl borate pinacol ester (2-vinyl-4,4,5,5-tetramethyl-1,3,2-dioxoboronylcyclopentane) undergoes polymerization initiation on the negative electrode surface using its vinyl functional groups, forming a polymer substrate film containing borate ester side groups. This polymer layer has a low LUMO energy level, and its electron-rich oxygen and boron atoms can complex and fix phosphorus pentafluoride generated by high-temperature decomposition in the electrolyte through Lewis acid-base interactions, thereby reducing the electrolyte acidity. Simultaneously, its unique structure possesses a certain degree of micro-conformation adjustment capability, endowing the interfacial film with preliminary flexibility.

[0009] When the battery temperature abnormally rises to the safety warning range of 90-120℃ during high-temperature cycling, the chemical reaction of the thermally triggered crosslinking agent is activated. The end-capping groups in its molecular structure dissociate, releasing highly reactive isocyanate groups. These groups can chemically crosslink with active sites on the interfacial film caused by thermal damage or electrolyte decomposition products, repairing the damaged SEI film and constructing a denser polyurethane / polyurea network. Simultaneously, the siloxane bonds in the crosslinking agent's main chain not only provide flexible segments, effectively dissipating the volume expansion stress of the electrode material during high-temperature charging and discharging, preventing film embrittlement, but also, under extreme conditions, the Si-O bonds can act as sacrificial components, preferentially consuming the highly corrosive hydrofluoric acid in the electrolyte through chemical reactions, converting it into stable fluorosilanes, thereby cutting off the chain reaction leading to thermal runaway.

[0010] The inorganic bottom layer ensures ion transport and chemical stability, the organic outer layer provides mechanical protection, and the thermal triggering mechanism provides additional cross-linking enhancement and acid removal capabilities at high temperatures, thereby improving the battery's high-temperature cycle life and safety.

[0011] Optionally, R' in the thermally triggered crosslinking agent is a group with the following structure: -N=C(CH3)(C2H5).

[0012] Optionally, the preparation method of the thermally triggered crosslinking agent includes the following steps: S1. Under inert atmosphere and ice bath conditions, an anhydrous toluene solution containing methyl ethyl ketone oxime is added dropwise to an anhydrous toluene solution containing hexa(3-propyl isocyanate)disiloxane, while controlling the reaction temperature below 10°C. The molar ratio of hexa(3-propyl isocyanate)disiloxane to methyl ethyl ketone oxime is 1:6.0-6.6. S2. After the addition is complete, add 0.03-0.08 wt% of dibutyltin dilaurate as a catalyst; S3. Heat the reaction system to 55-65℃ and stir for 6-10 hours. S4. After the reaction is complete, the toluene solvent is removed by rotary evaporation at 30-45℃ and a pressure below 10 kPa. S5. The crude product obtained in S4 is purified by silica gel column chromatography. A mixed solvent of ethyl acetate and petroleum ether with a volume ratio of 1:3-6 is used as the eluent. The target fraction is collected and the solvent is removed. The product is then vacuum dried at 50-70℃ and a pressure below 0.5 Pa for 18-30 h to obtain the thermally triggered crosslinking agent.

[0013] By employing the above technical solution, firstly, the dropwise reaction under an inert atmosphere and ice bath low-temperature conditions effectively inhibits side reactions such as hydrolysis or dimerization of the highly reactive isocyanate (-NCO) groups in the raw material hexa(3-propyl isocyanate)disiloxane with water vapor, ensuring the integrity of the reaction starting material. Secondly, the reaction is carried out at 55-65℃ for a sufficient time under catalysis, promoting the quantitative conversion of methyl ethyl ketone oxime and -NCO groups into a thermally reversible oxime carbamate structure, which is the key chemical conversion to achieve temperature-triggered function. Subsequent washing and drying operations remove soluble byproducts and water, while rotary evaporation gently removes most of the solvent. Silica gel column chromatography purification is a key purification step, which can effectively separate and enrich the target product, removing unreacted raw materials, catalyst residues, and byproducts with similar molecular weights. Finally, long-term drying under high temperature and high vacuum conditions removes trace solvents and adsorbed water, ensuring that the product maintains chemical inertness and stability during subsequent electrolyte preparation and battery injection. The entire process ultimately ensures that the obtained crosslinking agent remains stable during normal battery storage and operation, and can controllably release active -NCO groups within a preset high-temperature window, thus providing the material prerequisite for subsequent crosslinking repair reactions at the electrode interface.

[0014] Optionally, in step S1, the isocyanate group content of the hexa(3-propyl isocyanate)disiloxane is greater than 19.0%, and the moisture content is less than 50 ppm.

[0015] By employing the above technical solution, an isocyanate group content greater than 19.0% ensures the molecular purity and structural integrity of hexa(3-propyl isocyanate)disiloxane, thereby enabling the precise synthesis of the target product. Simultaneously, controlling the moisture content below 50 ppm effectively suppresses hydrolysis side reactions of the isocyanate groups during storage and pretreatment before synthesis.

[0016] Optionally, the thermally triggered crosslinking agent is a light yellow to colorless transparent viscous liquid that undergoes thermal deblocking in the temperature range of 90-120°C, releasing active isocyanate groups.

[0017] By adopting the above technical solution, the component remains stable during normal battery operation and storage, and will not interfere with the electrochemical process, thereby ensuring the long-term stability and cycle performance of the system. When the battery reaches the trigger temperature due to abnormal heating, it can respond immediately, and the released active groups quickly participate in the cross-linking reaction at the interface, strengthening and repairing the electrode protective film.

[0018] Secondly, the electrolyte provided in this application for improving the high-temperature cycle life of batteries adopts the following technical solution: An electrolyte for improving the high-temperature cycle life of batteries, comprising the following components by weight: 4.5-8 parts of electrolyte additive composition and 92.0-95.5 parts of base electrolyte; The basic electrolyte is a mixed solvent of ethylene carbonate and methyl ethyl carbonate containing lithium hexafluorophosphate, wherein the volume ratio of ethylene carbonate to methyl ethyl carbonate is 3-4:6-7.

[0019] By employing the above technical solution, ethylene carbonate provides the necessary high dielectric constant, ensuring the full dissociation of lithium salt and its participation in the construction of a stable initial interfacial film. Meanwhile, the dominant methyl ethyl carbonate reduces the overall viscosity and freezing point of the system, ensuring the electrolyte maintains good ion mobility and chemical stability over a wide temperature range, especially at high temperatures. This creates an ideal solution environment for the dissolution and efficient operation of functional additives. Secondly, limiting the total content of the additive composition to 4.5-8 parts ensures that sufficient functional molecules can effectively migrate to the electrode interface and construct the required dynamic protective network, while avoiding the risks of decreased electrolyte conductivity, increased viscosity, or new side reactions that may result from excessive addition.

[0020] Optionally, the basic electrolyte has a water content of less than 20 ppm and a free acid content of less than 50 ppm (calculated as hydrofluoric acid).

[0021] By adopting the above technical solution, the key component with high reactivity—vinyl borate pinacol ester—and the thermally triggered crosslinking agent are ensured to remain chemically inert before being injected into the battery, preventing unintended hydrolysis or polymerization that could lead to deactivation. Simultaneously, the low-humidity, low-acid environment maximally suppresses the hydrolysis side reactions of lithium hexafluorophosphate, reducing the formation of corrosive byproducts at the electrode interface.

[0022] Thirdly, this application provides a method for preparing an electrolyte that improves the high-temperature cycle life of a battery, the method comprising the following steps: S1. In an inert atmosphere and an environment where the water and oxygen content are both below 10 ppm, add lithium difluorophosphate to the basic electrolyte at 20-30℃ and stir at a rate of 200-400 rpm for 2-4 hours. S2. While maintaining the same temperature and stirring conditions, add 2-vinyl-4,4,5,5-tetramethyl-1,3,2-dioxoboronylcyclohexane to the solution obtained in step S1 and continue stirring for 0.5-1 h. S3. While maintaining the same temperature and stirring conditions, add a thermally triggered crosslinking agent to the solution obtained in step S2, increase the stirring rate to 400-600 rpm, and continue stirring at 20-30℃ for 10-14 hours to obtain an electrolyte that improves the high-temperature cycle life of the battery.

[0023] By adopting the above technical solution, the order of component addition corresponds to the electrochemical logic of film formation and function of each component inside the battery: first, a stable inorganic bottom layer is constructed, then a dynamic polymer framework is built, and finally, a crosslinking agent in an undetermined state is introduced, laying the chemical foundation for intelligent triggering repair at high temperatures. Secondly, the entire process is carried out in an inert environment with a water and oxygen content of less than 10 ppm at 20-30°C, effectively preventing hydrolysis or premature reaction of additives during the formulation stage, ensuring the chemical integrity of functional molecules, and thus ensuring the long-term stability of the electrolyte before storage and injection. Finally, by controlling the stirring rate and time, it is ensured that the thermally triggered crosslinking agent can be fully and uniformly dispersed in the electrolyte, forming a homogeneous and stable solution system. At the same time, the mild room temperature conditions avoid unexpected side reactions or premature activation of the crosslinking agent that may be caused by stirring heat.

[0024] In summary, this application includes at least one of the following beneficial technical effects: 1. By introducing vinyl borate pinacol ester, an electrochemical polymerization process is performed on the electrode surface to form a polymer network containing borate ester side groups. This network utilizes the conformational flexibility of the borate ester structure to buffer volume changes at high temperatures, maintaining the physical integrity of the interface. The key component, the thermally triggered crosslinking agent, releases highly active groups upon reaching a specific temperature. On one hand, it utilizes the electron-rich nitrogen and oxygen sites in its molecular structure to efficiently complex and fix Lewis acid-type harmful substances such as phosphorus pentafluoride, which can trigger chain decomposition, through Lewis acid-base interactions; or it eliminates hydrogen fluoride through a sacrificial reaction, curbing the continuous consumption of electrolyte. On the other hand, it chemically crosslinks with the active sites on the vinyl borate pinacol ester network, forming a composite interface layer that combines flexible siloxane segments and rigid boron-oxygen nodes, improving the thermomechanical stability of the membrane. Simultaneously, lithium difluorophosphate preferentially constructs a dense and lithium fluoride-rich inorganic underlayer, providing a stable substrate for the aforementioned organic functional layers and effectively suppressing oxidation reactions at the cathode interface. These mechanisms work synergistically to ensure a low interface degradation rate in the battery under high-temperature conditions, ultimately achieving improved high-temperature cycle life and substantial enhancement of thermal safety performance. Detailed Implementation

[0025] Preparation Example 1 The thermally triggered crosslinking agent is prepared by the following steps: S1. Under inert atmosphere and ice bath conditions, an anhydrous toluene solution containing 6.3 mol of methyl ethyl ketone oxime is added dropwise to an anhydrous toluene solution containing 1 mol of hexa(3-propyl isocyanate)disiloxane, while controlling the reaction temperature below 10℃. The isocyanate group content of hexa(3-propyl isocyanate)disiloxane is greater than 19.0%, and the water content is less than 50 ppm. S2. After the addition is complete, add 0.05wt% dibutyltin dilaurate as a catalyst; S3. Heat the reaction system to 60°C and stir for 8 hours. S4. After the reaction is complete, the toluene solvent is removed by rotary evaporation at 35°C and a pressure below 10 kPa. S5. The crude product obtained in S4 was purified by silica gel column chromatography using a mixture of ethyl acetate and petroleum ether (volume ratio 1:4.5) as the eluent. After collecting the target fraction and removing the solvent, the product was vacuum dried for 24 hours at 60°C and a pressure below 0.5 Pa to obtain a light yellow to colorless transparent viscous liquid. This liquid can undergo thermal deblocking in the temperature range of 90-120°C, releasing a thermally triggered crosslinking agent with active isocyanate groups. This thermally triggered crosslinking agent is a compound with the structure of formula (I): (R'-NH-CO-O-(CH2)3)3Si-O-Si((CH2)3-O-CO-NH-R')3 (I) Wherein, R' is a group having the structure of formula (II): -N=C(CH3)(C2H5) (II)。

[0026] Preparation Example 2 The thermally triggered crosslinking agent differs from that in Preparation Example 1 in that the methyl ethyl ketone oxime in step S1 is replaced with an equimolar amount of acetone oxime, resulting in a thermally triggered crosslinking agent R' of -N=C(CH3)2.

[0027] Example 1 An electrolyte for improving the high-temperature cycle life of batteries, comprising the following components by weight: 7 parts of electrolyte additive composition and 93 parts of base electrolyte; The basic electrolyte is a mixed solvent of ethylene carbonate and methyl ethyl carbonate containing lithium hexafluorophosphate, wherein the volume ratio of ethylene carbonate to methyl ethyl carbonate is 3:7. The electrolyte additive composition comprises, by weight, the following components: 2.0 parts of 2-vinyl-4,4,5,5-tetramethyl-1,3,2-dioxoboronylcyclohexane, 3.0 parts of thermally triggered crosslinking agent, and 1.2 parts of lithium difluorophosphate; Specifically, the thermally triggered crosslinking agent was obtained using Preparation Example 1; 2-vinyl-4,4,5,5-tetramethyl-1,3,2-dioxoboronylcyclopentane was a colorless liquid with a purity greater than 99% and a water content less than 50 ppm; the basic electrolyte had a water content less than 20 ppm and a free acid content (calculated as hydrofluoric acid) less than 50 ppm.

[0028] A method for preparing an electrolyte that improves the high-temperature cycle life of a battery, the method comprising the following steps: S1. In an inert atmosphere and an environment where the water and oxygen content are both below 10 ppm, lithium difluorophosphate is added to the basic electrolyte at 25°C and stirred at 300 rpm for 3 hours. S2. While maintaining the same temperature and stirring conditions, add 2-vinyl-4,4,5,5-tetramethyl-1,3,2-dioxoboronylcyclopentane to the solution obtained in step S1 and continue stirring for 1 hour. S3. Maintaining the same temperature and stirring conditions, add a thermally triggered crosslinking agent to the solution obtained in step S2, increase the stirring rate to 500 rpm, and continue stirring at 25°C for 12 hours to obtain an electrolyte that improves the high-temperature cycle life of the battery.

[0029] Example 2 An electrolyte for improving the high-temperature cycle life of batteries differs from that in Example 1 in that the electrolyte additive composition comprises, by weight, the following components: 1.5 parts of 2-vinyl-4,4,5,5-tetramethyl-1,3,2-dioxoboronylcyclohexane, 2.0 parts of thermally triggered crosslinking agent, and 1.0 part of lithium difluorophosphate.

[0030] Example 3 An electrolyte for improving the high-temperature cycle life of batteries differs from that in Example 1 in that the electrolyte additive composition comprises, by weight, the following components: 2.5 parts of 2-vinyl-4,4,5,5-tetramethyl-1,3,2-dioxoboronylcyclohexane, 4.0 parts of thermally triggered crosslinking agent, and 1.5 parts of lithium difluorophosphate.

[0031] Example 4 An electrolyte for improving the high-temperature cycle life of batteries differs from that in Example 1 in that the volume ratio of ethylene carbonate to methyl ethyl carbonate in the basic electrolyte is 4:6.

[0032] Example 5 An electrolyte for improving the high-temperature cycle life of batteries differs from that in Example 1 in that the volume ratio of ethylene carbonate to ethyl methyl carbonate in the basic electrolyte is 2:8.

[0033] Comparative Example 1 An electrolyte for improving the high-temperature cycle life of batteries differs from Example 1 in that the electrolyte additive composition is replaced with an equal amount of basic electrolyte.

[0034] Comparative Example 2 An electrolyte for improving the high-temperature cycle life of batteries differs from that in Example 1 in that the thermally triggered crosslinking agent is replaced with an equal amount of hexa(3-propyl isocyanate)disiloxane, and lithium difluorophosphate is replaced with an equal amount of lithium phosphate.

[0035] Comparative Example 3 An electrolyte for improving the high-temperature cycle life of batteries differs from that of Example 1 in that 2-vinyl-4,4,5,5-tetramethyl-1,3,2-dioxoborane is replaced with an equal amount of ethylene boric acid, and lithium difluorophosphate is replaced with an equal amount of lithium phosphate.

[0036] Comparative Example 4 An electrolyte for improving the high-temperature cycle life of batteries differs from that in Example 1 in that the thermally triggered crosslinking agent is replaced with an equal amount of hexa(3-propyl isocyanate)disiloxane, and 2-vinyl-4,4,5,5-tetramethyl-1,3,2-dioxoborane is replaced with an equal amount of ethyleneboric acid.

[0037] Comparative Example 5 An electrolyte for improving the high-temperature cycle life of batteries differs from that of Example 1 in that the thermally triggered crosslinking agent is replaced with an equal amount of a mixture of 2-vinyl-4,4,5,5-tetramethyl-1,3,2-dioxoboronylcyclohexane and lithium difluorophosphate mixed in a mass ratio of 5:3.

[0038] Comparative Example 6 An electrolyte for improving the high-temperature cycle life of batteries differs from Example 1 in that the thermally triggered crosslinking agent is specifically obtained using Preparation Example 1.

[0039] Detection example High-temperature long-cycle test: The battery is placed in a 60℃ constant temperature chamber and cycled at 1C / 1C charge and discharge (3.0-4.4V). The capacity decay curve is recorded and the capacity retention rate is detected after the 500th cycle. High-temperature storage test: The battery charged to 4.4V was placed in an 80℃ oven for 7 days. After cooling, its capacity recovery rate, thickness expansion rate and DC internal resistance (DCR) growth rate were measured. Interfacial impedance evolution test: Electrochemical impedance spectroscopy was performed on the battery before cycling and after the 300th cycle. The increase in interfacial film impedance (R_film) was quantified by fitting an equivalent circuit. Thermal safety test: The positive and negative electrode sheets were recovered from the cycled battery, mixed with fresh electrolyte and sealed in a high-pressure crucible. The temperature was increased by 5℃ / min, and the onset temperature of the first significant exothermic peak (T_dec, onset) was recorded. A fully charged pouch battery (design capacity 2Ah) was subjected to a heating-wait-search test, and the thermal runaway trigger temperature (T_tr) was recorded. The specific test results are shown in Table 1.

[0040] Table 1

[0041] As can be seen from the performance test data in Table 1 of Examples 1-5, 2-vinyl-4,4,5,5-tetramethyl-1,3,2-dioxoboronylcyclohexane, thermally triggered crosslinking agent, and lithium difluorophosphate constitute a broad and effective optimization ratio window. The ratios within this range can maintain long-term interface stability at high temperatures and improve the high-temperature cycle life and safety of the battery.

[0042] As shown in Table 1 of the performance test data of Examples 1 and Comparative Examples 2-4, Comparative Example 2 improved cycling and thermal stability, but the improvement in thermal runaway temperature was limited, proving that a single dynamic framework is insufficient to fully cope with severe thermal abuse. Comparative Example 3 had a high thermal runaway temperature but poor cycling performance, indicating that without a good substrate and dynamic framework, its thermally triggered crosslinking cannot construct an effective long-term cycling protective layer. Comparative Example 4 provided good initial cycling and oxidation resistance, but its thermal safety and long-term impedance control were average, lacking long-term effectiveness.

[0043] As can be seen from the performance test data in Table 1 of Example 1 and Comparative Example 6, the main component that plays a role in the thermal crosslinking agent is the isocyanate group it releases, which achieves interfacial crosslinking through the isocyanate group.

[0044] As can be seen from the performance test data in Table 1 of Example 1, Comparative Example 1, and Comparative Example 5, the deep synergistic effect of the system composed of 2-vinyl-4,4,5,5-tetramethyl-1,3,2-dioxoboronylcyclohexane, thermally triggered crosslinking agent, and lithium difluorophosphate is strongly demonstrated.

[0045] Please note that the technical features of the above embodiments can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments have been described. However, as long as the combination of these technical features does not contradict each other, it should be considered within the scope of this specification. The above embodiments only illustrate several implementation methods of this application, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be pointed out that for those skilled in the art, several modifications and improvements can be made without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. An electrolyte additive composition for improving high temperature cycle life of a battery, characterized by, By weight, it comprises the following components: 1.5-2.5 parts of dynamic network framework builder, 2.0-4.0 parts of thermally triggered crosslinking agent, and 1.0-1.5 parts of film-forming initiator; The dynamic network framework builder is 2-vinyl-4,4,5,5-tetramethyl-1,3,2-dioxoboronylcyclohexane; the film-forming initiator is lithium difluorophosphate. The thermally triggered crosslinking agent is a compound having the following structure: (R'-NH-CO-O-(CH2)3)3Si-O-Si((CH2)3-O-CO-NH-R')3.

2. The electrolyte additive composition for improving the high-temperature cycle life of a battery according to claim 1, characterized in that, In the thermally triggered crosslinking agent, R' is a group with the following structure: -N=C(CH3)(C2H5).

3. The electrolyte additive composition for improving the high-temperature cycle life of a battery according to claim 1, characterized in that, The preparation method of the thermally triggered crosslinking agent includes the following steps: S1. Under inert atmosphere and ice bath conditions, an anhydrous toluene solution containing methyl ethyl ketone oxime is added dropwise to an anhydrous toluene solution containing hexa(3-propyl isocyanate)disiloxane, while controlling the reaction temperature below 10°C. The molar ratio of hexa(3-propyl isocyanate)disiloxane to methyl ethyl ketone oxime is 1:6.0-6.

6. S2. After the addition is complete, add 0.03-0.08 wt% of dibutyltin dilaurate as a catalyst; S3. Heat the reaction system to 55-65℃ and stir for 6-10 hours. S4. After the reaction is complete, the toluene solvent is removed by rotary evaporation at 30-45℃ and a pressure below 10 kPa. S5. The crude product obtained in S4 is purified by silica gel column chromatography. A mixed solvent of ethyl acetate and petroleum ether with a volume ratio of 1:3-6 is used as the eluent. The target fraction is collected and the solvent is removed. The product is then vacuum dried at 50-70℃ and a pressure below 0.5 Pa for 18-30 h to obtain the thermally triggered crosslinking agent.

4. The electrolyte additive composition for improving the high-temperature cycle life of a battery according to claim 2, characterized in that, In step S1, the isocyanate group content of the hexa(3-propyl isocyanate)disiloxane is greater than 19.0%, and the moisture content is less than 50 ppm.

5. The electrolyte additive composition for improving the high-temperature cycle life of a battery according to claim 1, characterized in that, The dynamic network skeleton builder is a colorless liquid with a purity greater than 99% and a water content of less than 50 ppm.

6. The electrolyte additive composition for improving the high-temperature cycle life of a battery according to claim 1, characterized in that, The thermally triggered crosslinking agent is a light yellow to colorless transparent viscous liquid that undergoes thermal deblocking in the temperature range of 90-120℃, releasing active isocyanate groups.

7. An electrolyte for improving the high-temperature cycle life of a battery according to any one of claims 1-6, characterized in that, By weight, it comprises the following components: 4.5-8 parts of electrolyte additive composition and 92.0-95.5 parts of base electrolyte; The basic electrolyte is a mixed solvent of ethylene carbonate and methyl ethyl carbonate containing lithium hexafluorophosphate, wherein the volume ratio of ethylene carbonate to methyl ethyl carbonate is 3-4:6-7.

8. The electrolyte for improving the high-temperature cycle life of a battery according to claim 7, characterized in that, The basic electrolyte has a water content of less than 20 ppm and a free acid content (calculated as hydrofluoric acid) of less than 50 ppm.

9. A method for preparing an electrolyte to improve the high-temperature cycle life of a battery according to claims 7-8, characterized in that, The preparation method includes the following steps: S1. In an inert atmosphere and an environment where the water and oxygen content are both below 10 ppm, add lithium difluorophosphate to the basic electrolyte at 20-30℃ and stir at a rate of 200-400 rpm for 2-4 hours. S2. While maintaining the same temperature and stirring conditions, add 2-vinyl-4,4,5,5-tetramethyl-1,3,2-dioxoboronylcyclohexane to the solution obtained in step S1 and continue stirring for 0.5-1 h. S3. While maintaining the same temperature and stirring conditions, add a thermally triggered crosslinking agent to the solution obtained in step S2, increase the stirring rate to 400-600 rpm, and continue stirring at 20-30℃ for 10-14 hours to obtain an electrolyte that improves the high-temperature cycle life of the battery.

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