High-thermal-stability ethylene carbonate electrolyte, preparation method and application thereof

Abstract

The application discloses high-thermal-stability ethylene carbonate electrolyte and a preparation method and application thereof, and belongs to the technical field of electrolyte, and is used for solving the technical problem that the high-temperature stability of ethylene carbonate electrolyte in the prior art needs to be further improved, and specifically comprises a carbonate base and a lithium salt, wherein the carbonate base comprises the following components in parts by weight: 40-50 parts of ethylene carbonate, 22-25 parts of sulfonyl-modified EC, 15-18 parts of boron-phosphorus-modified DEC, 5-8 parts of fluorine-containing reinforced polyester, and 1.8-2.2 parts of polyether amine. The sulfonyl structure is introduced into the carbonate base to enhance the thermal stability of molecules, boron-containing and phosphorus-containing synergistic interface regulation components are constructed to inhibit high-temperature side reactions, fluorine-containing reinforced polymers and a composite lithium salt system are combined to optimize the solvation structure and the stability of an interface film, and the stability of the electrolyte under high-temperature storage and high-temperature cycle conditions is improved.

Description

Technical Field

[0001] This invention relates to the field of electrolyte technology, specifically to a highly thermally stable ethylene carbonate electrolyte, its preparation method, and its application. Background Technology

[0002] With the widespread application of lithium-ion batteries in new energy vehicles, energy storage systems and high-power electronic devices, their safety and stability under high energy density, high power density and complex operating conditions are becoming increasingly prominent. As a key component in lithium-ion batteries that enables ion transport and participates in interfacial reactions, the electrolyte's thermal stability, electrochemical stability and interfacial compatibility directly determine the battery's storage performance, cycle life and safety performance under high temperature environments.

[0003] Ethylene carbonate is widely used due to its high dielectric constant, strong lithium salt solubility, and ability to form a stable solid electrolyte interphase (SEI) film. It is often used in conjunction with lithium salts such as lithium hexafluorophosphate. However, traditional ethylene carbonate and its commonly used co-solvents are prone to oxidative decomposition, solvent evaporation, and accumulation of side reactions during storage or cycling at temperatures above 45°C. This leads to increased electrolyte consumption, accelerated voltage decay, and rapid capacity decay, severely affecting the high-temperature storage performance of the battery. Furthermore, under high-temperature cycling conditions, the electrode interphase film is prone to repeated rupture and regeneration, which not only increases interfacial impedance but also induces continuous side reactions, further shortening the battery's lifespan and even causing safety hazards such as thermal runaway.

[0004] To address the aforementioned issues, the thermal stability of the electrolyte can be improved by introducing fluorinated solvents, flame retardant additives, or polymeric additives. However, a single type of additive can often only improve one aspect and cannot simultaneously achieve high-temperature storage stability, high-temperature cycling performance, and ion conduction performance. Therefore, a solution is proposed. Summary of the Invention

[0005] The purpose of this invention is to provide a high thermal stability ethylene carbonate electrolyte, its preparation method, and its application, in order to solve the technical problem that the high temperature stability of ethylene carbonate electrolytes in the prior art needs to be further improved.

[0006] The objective of this invention can be achieved through the following technical solution: a highly thermally stable ethylene carbonate electrolyte, comprising a carbonate substrate and a lithium salt, wherein the concentration of the lithium salt is 1.0 mol / L; The carbonate base comprises the following components by weight: 40-50 parts ethylene carbonate, 22-25 parts sulfone-modified EC, 15-18 parts boron-phosphorus-modified DEC, 5-8 parts fluorine-reinforced polyester, and 1.8-2.2 parts polyetheramine. The lithium salt is composed of lithium hexafluorophosphate and lithium difluorosulfonyl imide in a weight ratio of 7:3-4.

[0007] Furthermore, the preparation method of sulfone-modified EC is as follows: ethylene carbonate, 1,3-bis(chloroethylsulfonyl)propanol, acetonitrile and addition catalyst are mixed and stirred, the reaction system is heated to reflux, and the reaction is maintained at this temperature for 4-6 hours. After post-treatment, sulfone-modified EC is obtained.

[0008] The synthetic reaction formula for sulfone-modified EC is as follows:

[0009] Furthermore, the molar ratio of ethylene carbonate to 1,3-bis(chloroethyl sulfone)propanol is 2:1, the molar ratio of ethylene carbonate, acetonitrile, and catalyst is 5g:30mL:0.5g, and the addition catalyst is composed of lead chloride and triethylamine in a weight ratio of 1:3. The post-treatment includes: after the reaction is complete, the reaction system is subjected to negative pressure to remove low-boiling substances by vacuum evaporation, the reaction system is cooled to room temperature, acetone is added to the reaction system, and the mixture is stirred and dispersed for 20-30 minutes. The mixture is then filtered using a 0.2μm PTFE filter membrane, and the filtrate is transferred to a rotary evaporator with a water bath temperature of 45-55℃ to remove low-boiling substances by vacuum evaporation to obtain sulfone-modified EC.

[0010] Furthermore, the preparation method of boron-phosphorus modified DEC is as follows: under the protection of an inert gas atmosphere, triisopropylboronic acid ester, transesterification catalyst, and diethyl carbonate are mixed and stirred. The reaction system is heated to 60-80℃ and kept at this temperature for 4-5 hours. The reaction system is then cooled to 25-35℃, and diisooctyl phosphite is added dropwise to the reaction system. The reaction is kept at this temperature for 10-12 hours. After post-treatment, boron-phosphorus modified DEC is obtained.

[0011] Furthermore, the ratio of triisopropylboronic acid ester, transesterification catalyst, and diethyl carbonate is 10g:0.1g:70-80mL, the molar ratio of diisooctyl phosphite to triisopropylboronic acid ester is 1.1-1.3:1, the transesterification catalyst is p-toluenesulfonic acid, and the post-treatment includes: after the reaction is completed, the reaction system is cooled to room temperature, filtered using a 0.2μm PTFE filter membrane, the filtrate is transferred to a rotary evaporator with a water bath temperature of 70-80℃, and low-boiling substances are removed by vacuum evaporation to obtain boron-phosphorus modified DEC.

[0012] Further, the preparation method of fluorinated reinforced polyester is as follows: Under the protection of an inert gas atmosphere, octafluoro-1,6-hexanediol, 2-hydroxymethyl-1,3-propanediol, dibutyltin dilaurate, and N,N-dimethylformamide are mixed and stirred. The reaction system is heated to 60-70℃, hexamethylene diisocyanate is added to the reaction system, and the reaction is maintained at this temperature for 20-30 min. Then, glycidyl ether is added to the reaction system, and the reaction is maintained at this temperature for 40-50 min. Finally, glycidyl ether is added to the reaction system, and the reaction is maintained at this temperature for 30-40 min. After post-treatment, fluorinated reinforced polyester with a molecular weight of 500-1000 is obtained.

[0013] The synthesis reaction formula for fluorinated reinforced polyester is as follows:

[0014] Furthermore, the ratio of octafluoro-1,6-hexanediol, 2-hydroxymethyl-1,3-propanediol, dibutyltin dilaurate, N,N-dimethylformamide, and glycidyl is 5-6 g:4-5 g:0.02 g:50 mL:2-3 g, and the molar amount of hexamethylene diisocyanate is 0.55 times the molar amount of hydroxyl groups in octafluoro-1,6-hexanediol and 2-hydroxymethyl-1,3-propanediol. The post-treatment includes: after the reaction is complete, cooling the reaction system to room temperature, and... The reaction solution was placed in a 1000 Da dialysis bag, and a 500 Da dialysis bag was placed over the 1000 Da dialysis bag. The dialysis bag was then immersed in N,N-dimethylformamide and dialyzed at room temperature for 24 hours. The N,N-dimethylformamide was replaced every 4 hours. The 1000 Da dialysis bag was then removed from the 500 Da dialysis bag, and the contents of the 500 Da dialysis bag were transferred to a rotary evaporator with a water bath temperature of 95-100℃. Low-boiling-point substances were removed by vacuum evaporation to obtain fluorinated reinforced polyester.

[0015] The present invention also proposes a method for preparing a high thermal stability ethylene carbonate electrolyte, comprising the following steps: under an inert gas atmosphere, ethylene carbonate, sulfone-modified EC, boron-phosphorus-modified DEC, and fluorine-reinforced polyester are mixed and stirred, the reaction system is heated to 40-50°C, stirred and dispersed for 30-50 min, lithium salt is added to the reaction system, stirred and dispersed for 60-80 min, polyetheramine is added to the reaction system, the mixture is kept at the temperature and stirred for 20-30 min, and then naturally cooled to room temperature to obtain the ethylene carbonate electrolyte.

[0016] The present invention also proposes the application of a high thermal stability ethylene carbonate electrolyte, which is used in lithium batteries.

[0017] The present invention has the following beneficial effects: 1. This invention introduces sulfone-modified ethylene carbonate and boron-phosphorus-modified diethyl carbonate into a basic carbonate solvent system. The sulfone structure effectively increases the thermal decomposition energy barrier of carbonate molecules, suppressing solvent decomposition and side reactions at the electrode interface at high temperatures. Boron and phosphorus elements further enhance the chemical stability of the electrolyte under high-temperature storage conditions by improving the electronic structure of solvent molecules and inhibiting oxidation reactions. The two elements work synergistically to significantly reduce the high-temperature storage voltage decay rate and improve the high-temperature storage capacity retention rate while ensuring the dissolution and transport capabilities of lithium salts. A stable high-temperature working environment is constructed from the solvent and lithium salt solvation levels, enabling the electrolyte molecules to simultaneously possess high polarity, high bond energy, and flame-retardant structural characteristics.

[0018] 2. This invention also introduces fluorinated reinforced polyester as a polymeric stabilizing component. By utilizing the high bond energy of fluorine and the heat resistance of the polymer skeleton, a thermally stable and chemically inert structural support phase is constructed in the electrolyte system. This fluorinated polymer is not easily volatilized or decomposed under high temperature conditions, which can effectively inhibit the migration and rearrangement of small molecule components in the electrolyte. It also participates in the formation of a denser and heat-resistant interfacial film structure on the electrode surface, thereby reducing the rate of interfacial side reactions at high temperatures. The fluorinated reinforced polyester complements the aforementioned modified solvent system, enabling the electrolyte to exhibit superior capacity retention performance under both high-temperature storage and high-temperature cycling conditions.

[0019] 3. In addition, this invention introduces polyetheramine into the electrolyte preparation process and utilizes the amine-epoxy ring-opening condensation reaction between its amine groups and the epoxy groups on the fluorinated reinforced polyester molecular chain to construct a grafted cross-linked polymeric stable structural unit in situ within the system. This effectively anchors the flexible polyether segments onto the high-temperature resistant fluorinated polymer backbone, improving the overall structural integrity and high-temperature stability of the electrolyte while forming a stable film layer with both flexibility and heat resistance at the electrode interface. This significantly inhibits the rupture of the interface film and the accumulation of side reactions during high-temperature cycling, enabling the electrolyte to maintain a high cycle capacity retention rate under high-temperature conditions. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 The infrared spectrum of the boron-phosphorus modified DE prepared in Example 1 of this invention; Figure 2 The infrared spectrum is shown for the fluorinated reinforced polyester prepared in Example 1 of this invention. Detailed Implementation

[0022] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] In this invention, the polyetheramine is polyetheramine D400, and the content of the active ingredient is 99%.

[0024] Example 1 This embodiment provides a method for preparing a highly thermally stable ethylene carbonate electrolyte, comprising the following steps: Step 1: Preparation of sulfone-modified EC Lead chloride and triethylamine were mixed evenly at a weight ratio of 1:3 to obtain an addition catalyst; Weigh out 22.8 g of ethylene ethylene carbonate, 31.3 g of 1,3-bis(chloroethyl sulfone)propanol, 136.8 mL of acetonitrile, and 2.28 g of addition catalyst and add them to a reaction flask. Stir the mixture and heat it to reflux. Maintain the temperature for 4 h. Apply negative pressure to the reaction system and remove low-boiling substances by vacuum evaporation. Cool the reaction system to room temperature and add 300 mL of acetone. Stir and disperse for 20 min. Filter the mixture using a 0.2 μm PTFE membrane. Transfer the filtrate to a rotary evaporator at a water bath temperature of 45 °C and remove low-boiling substances by vacuum evaporation to obtain sulfone-modified EC.

[0025] In the lead chloride / triethylamine addition catalysis system, the chloroethyl segment in the 1,3-bis(chloroethylsulfonyl)propanol molecule forms an activated carbon center with significant electrophilic characteristics under the strong electron-withdrawing effect of the sulfonyl group and the synergistic activation effect of the Lewis acid. Simultaneously, the olefinic double bond in the ethylene carbonate molecule undergoes an electrophilic addition reaction as a π-electron donor, introducing a sulfonyl side chain into the ethylene carbonate structural unit via carbon-carbon bonds. During the reaction, triethylamine is used to capture acidic byproducts generated in the reaction system and stabilize the reaction environment, while lead chloride, as a Lewis acid, promotes the activation and addition process of the halocarbon. By grafting the highly thermally stable sulfonyl functional segment onto the ethylene carbonate molecule, sulfonyl-modified EC is obtained.

[0026] The sulfone-modified EC molecule introduces a high-bond-energy sulfone structure, which significantly improves the thermal stability and polarity of the solvent molecule and effectively suppresses the thermal decomposition and oxidation side reactions of carbonate molecules under high-temperature conditions. In the electrolyte system, the sulfone-modified EC can enhance the stability of the lithium salt solvation structure, reduce the voltage decay rate during high-temperature storage, and provide a chemical basis for the stable formation of the subsequent interfacial film. It is a key solvent component for improving high-temperature storage performance and cycle stability.

[0027] The proton NMR spectral data of sulfone-modified EC are as follows: 1 H NMR (400 MHz, CDCl3) δ (ppm): 6.10-5.60 (m,2H,CH2=CH-), 4.20-4.00(m,2H,-CH2-SO2-), 3.85-3.50(m,4H,-CH2-CH2-SO2-) , 2.80-2.50(m,2H,-SO2-CH2-), 1.80-1.55(m,2H,-CH2-CH2-), 1.25-1.05(t,J=7.0 Hz,3H, -CH2-CH3).

[0028] Step 2: Preparation of boron-phosphorus modified DEC Weigh out 18.8 g of triisopropylboronic acid ester, 1.9 g of p-toluenesulfonic acid transesterification catalyst, and 131.6 g of diethyl carbonate and add them to an argon-protected reaction flask. Stir the mixture and heat it to 60 °C. Maintain the temperature for 4 h. Cool the reaction flask to 25 °C and add 33.7 g of diisooctyl phosphite dropwise. Maintain the temperature for 10 h. Cool the reaction flask to room temperature and filter it using a 0.2 μm PTFE membrane. Transfer the filtrate to a rotary evaporator with a water bath temperature of 70 °C and remove low-boiling substances by vacuum evaporation to obtain boron-phosphorus modified DEC.

[0029] In the reaction, p-toluenesulfonic acid acts as a Brønsted acid catalyst, which protonates the carbonyl oxygen of the carbonate, increasing the electrophilicity of the carbonyl carbon atom. This promotes ester exchange between diethyl carbonate and borate ester, allowing boron atoms to be introduced into the carbonate molecule through a BOC bond, forming a boron-containing carbonate intermediate. Subsequently, diisooctyl phosphite is added dropwise to the system. The PH bond in the phosphite molecule undergoes further esterification or addition reactions with the active carbonyl or hydroxyl groups in the system, allowing phosphorus to be incorporated into the molecular structure in the form of a phosphate ester, forming a stable POC bond. This results in the molecule containing both boron and phosphorus functional elements, yielding boron-phosphorus modified DEC.

[0030] The introduction of boron, through its Lewis acid properties, forms weak coordination with active sites on the electrode surface, thereby reducing interfacial reactivity and decreasing the electrolyte decomposition rate. Phosphorus, in high-temperature environments, facilitates the formation of stable interfacial films containing phosphorus-containing inorganic components, improving the density and heat resistance of the interfacial film. The phosphate ester structure in boron-phosphorus modified DEC can participate in the construction of interfacial film components with high thermal stability, while boron enhances the structural integrity of the interfacial film and reduces the rate of interfacial side reactions at high temperatures. Furthermore, the strong polarity of boron-phosphorus modified DEC molecules helps optimize the solvation structure of lithium salts, improving the migration stability of lithium ions under high-temperature conditions, thus enhancing overall electrochemical performance without significantly reducing ionic conductivity.

[0031] Appendix Figure 1 In the infrared spectrum, at ~1750 cm⁻¹ -1 A strong C=O stretching vibration peak appears in the carbonate matrix, at 1260-1170 cm⁻¹. -1 The presence of a CO absorption peak indicates that the carbonate skeleton is retained; at ~1240 cm⁻¹ -1 P=O stretching vibration peaks appear at ~1040 and 840 cm⁻¹. -1 The presence of characteristic POC absorption peaks indicates the stable existence of the P=O / POC structure in boron-phosphorus modified DEC; the peaks are observed in the 1350-1380 cm⁻¹ range. -1 An absorption peak consistent with BOC was observed at ~960 cm⁻¹. -1 The presence of absorption peaks consistent with BOP indicates the formation of a new bonding environment between boron, carbonate, and phospho groups, consistent with the coupling characteristics of boron modification and BP.

[0032] Step 3: Preparation of fluorinated reinforced polyester Weigh out 50g of octafluoro-1,6-hexanediol, 40g of 2-hydroxymethyl-1,3-propanediol, 0.2g of dibutyltin dilaurate, and 500mL of N,N-dimethylformamide and add them to an argon-protected reaction flask. Stir the mixture and heat it to 60℃. Calculate the amount of hexamethylene diisocyanate to be added based on 0.55 times the molar amount of hydroxyl groups in the mixed alcohol composed of octafluoro-1,6-hexanediol and 2-hydroxymethyl-1,3-propanediol. Weigh out the calculated amount of hexamethylene diisocyanate and add it to the reaction flask. Incubate the reaction for 20 minutes. Add condensate to the reaction system. 20g of water-glycerol was used to maintain the reaction temperature for 30 minutes. The reaction flask was then cooled to room temperature. The reaction solution was placed in a 1000Da dialysis bag, and a 500Da dialysis bag was placed over the 1000Da dialysis bag. The dialysis bag was then immersed in N,N-dimethylformamide and dialyzed at room temperature for 24 hours. The N,N-dimethylformamide was replaced every 4 hours. The 1000Da dialysis bag was then removed from the 500Da dialysis bag. The contents of the 500Da dialysis bag were transferred to a rotary evaporator with a water bath temperature of 95℃. Low-boiling-point substances were removed by vacuum evaporation to obtain fluorinated reinforced polyester.

[0033] In the reaction, octafluoro-1,6-hexanediol and 2-hydroxymethyl-1,3-propanediol were added to the reaction system as mixed polyol monomers. Under the catalysis of dibutyltin dilaurate, they underwent a typical isocyanate-hydroxy addition reaction with hexamethylene diisocyanate to form urethane bonds. With the participation of multifunctional monomers, chain growth and molecular skeleton construction were achieved to form a polyurethane backbone. After the formation of the polyurethane backbone, glycidyl ether was added to the reaction system and the reaction was continued at a constant temperature. The terminal hydroxyl groups of the glycidyl ether molecule reacted with the isocyanate groups on the polyurethane backbone to form epoxy groups on the polyurethane backbone. The reaction solution was placed in 1000Da and 500Da dialysis bags and dialyzed in N,N-dimethylformamide for 24 hours with the dialysis solvent being changed periodically. This effectively removed unreacted monomers, oligomers, catalyst residues and other small molecule impurities from the reaction system, and prepared fluorinated reinforced polyesters with a molecular weight of 500-1000.

[0034] Fluorinated reinforced polyesters, due to their high bond energy CF structure and stable polymer backbone, are not prone to thermal decomposition or oxidative decomposition at high temperatures. They can exist as a stable phase in the electrolyte system, reducing the rate of side reactions during high-temperature storage and resulting in a lower high-temperature storage voltage decay rate. The fluorinated reinforced polyester molecular chains have a certain degree of flexibility and structural support, which can promote the formation of a denser, more heat-resistant, and more resilient composite interfacial film near the electrode interface. This reduces the probability of structural instability of the interfacial film during high-temperature cycling and inhibits continuous electrolyte decomposition and impedance growth. The high-purity polymer component obtained after dialysis purification can reduce the accumulation of side reactions caused by low-molecular-weight impurities under high-temperature conditions, making the performance output of the electrolyte system more stable.

[0035] In the appendix Figure 2 The approximately 2270 cm⁻¹ region was not observed in the infrared analysis spectrum. -1 The -NCO characteristic peak is observed at 1720 / 1690 cm⁻¹. -1 and 1530cm -1 The presence of a complete set of urethane C=O and NH / CN absorbance at ~1720 cm⁻¹ proves that HDI has fully reacted with the polyol to form a stable polyurethane ester backbone; -1 Strong C=O stretching vibrations occur at 1260-1050 cm⁻¹. -1 The COC and CO absorption values ​​in the range indicate the coexistence of multiple ether and ester bonds in the system, consistent with the polymer backbone structure jointly constructed by octafluoro-1,6-hexanediol, 2-hydroxymethyl-1,3-propanediol, and glycidyl ether; in the 1260-1100 cm⁻¹ range... -1 A series of strong CF / CF2 absorbances within the region (1260, 1200, 1150 cm⁻¹) -1 (etc.) and 840cm -1The vibrational signals of the nearby CF2 backbone confirm that the fluorinated diol fragment has been effectively embedded in the polymer structure, forming a fluorinated segment, at ~3320 cm⁻¹. -1 2940 / 2870cm -1 The absorption peaks indicate that the system has both hydrogen bonding and flexible aliphatic segments.

[0036] Step 4: Preparation of ethylene carbonate electrolyte Lithium hexafluorophosphate and lithium difluorosulfonyl imide were mixed evenly at a weight ratio of 7:3 to obtain the lithium salt; Weigh out the following components by weight: 40 parts ethylene carbonate, 22 parts sulfone-modified EC, 15 parts boron-phosphorus-modified DEC, and 5 parts fluorine-reinforced polyester. Add these components to an argon-protected reaction flask and stir. Heat the reaction flask to 40°C and stir for 30 minutes. Add lithium salt to the reaction flask and stir for 60 minutes. Add 1.8 parts polyetheramine to the reaction flask, keep warm and stir for 20 minutes, and allow to cool naturally to room temperature to obtain an ethylene carbonate electrolyte with a lithium concentration of 1.0 mol / L.

[0037] By adding ethylene carbonate, sulfone-modified EC, boron-phosphorus-modified DEC, and fluorinated reinforced polyester to a reaction flask in a specific ratio, and dispersing them under argon protection with heating and stirring, the viscosity of the system is reduced and the compatibility between components is improved by moderately increasing the temperature. This allows the highly polar sulfone-modified EC and boron-phosphorus-modified DEC to be uniformly distributed in the ethylene carbonate main solvent, while simultaneously promoting the stable dispersion of the fluorinated reinforced polyester in a molecular chain or microscale entangled state, providing a homogenized basis for subsequent lithium salt dissolution and solvation structure construction. Subsequently, lithium hexafluorophosphate and bis(fluorosulfonyl)imide lithium salt are mixed to form a lithium salt, which is then added to the above solvent mixture. Due to the strong electron-withdrawing and high dipole moment characteristics of the sulfone group, the sulfone-modified EC can enhance the Li-... + The coordination ability of the lithium salt is enhanced, and the stability of the solvated structure is improved. Boron-phosphorus modified DEC modulates the interfacial reaction pathway through boron- and phosphorus-containing functional groups, reducing the probability of solvent decomposition under high-temperature conditions. Compared with single lithium salts, the composite lithium salt system improves salt stability and interfacial film composition at high temperatures, enabling the electrolyte to maintain a more stable electrochemical window and lower side reaction rate in high-temperature environments. Polyetheramine molecules possess flexible polyether segments and terminal amine groups, which can act as polar segments in the electrolyte to participate in the Li... + On the one hand, it optimizes the weak coordination and migration channels, and on the other hand, it can undergo ring-opening addition reaction with the epoxy functional groups introduced in the fluorinated reinforced polyester molecules to form a certain degree of grafting or weak cross-linking structure. In the electrolyte system, it constructs a flexible segment-fluorinated skeleton synergistic structural reinforcement unit, making the electrolyte less prone to component separation and interfacial film embrittlement under high temperature conditions, while reducing the continuous accumulation of side reactions caused by repeated rupture of the interfacial film.

[0038] Example 2 This embodiment provides a method for preparing a highly thermally stable ethylene carbonate electrolyte, comprising the following steps: Step 1: Preparation of sulfone-modified EC Lead chloride and triethylamine were mixed evenly at a weight ratio of 1:3 to obtain an addition catalyst; Weigh out 22.8 g of ethylene ethylene carbonate, 31.3 g of 1,3-bis(chloroethyl sulfone)propanol, 136.8 mL of acetonitrile, and 2.28 g of addition catalyst and add them to a reaction flask. Stir the mixture and heat it to reflux. Maintain the temperature for 5 h. Apply negative pressure to the reaction system and remove low-boiling substances by vacuum evaporation. Cool the reaction system to room temperature and add 300 mL of acetone. Stir and disperse for 25 min. Filter the mixture using a 0.2 μm PTFE membrane. Transfer the filtrate to a rotary evaporator at 50 °C and remove low-boiling substances by vacuum evaporation to obtain sulfone-modified EC.

[0039] Step 2: Preparation of boron-phosphorus modified DEC Weigh out 18.8 g of triisopropylboronic acid ester, 1.9 g of p-toluenesulfonic acid transesterification catalyst, and 133.5 g of diethyl carbonate and add them to an argon-protected reaction flask. Stir the mixture and heat it to 70 °C. Maintain the temperature for 4.5 h. Cool the reaction flask to 30 °C and add 36.8 g of diisooctyl phosphite dropwise. Maintain the temperature for 11 h. Cool the reaction flask to room temperature and filter it using a 0.2 μm PTFE membrane. Transfer the filtrate to a rotary evaporator with a water bath temperature of 75 °C and remove low-boiling substances by vacuum evaporation to obtain boron-phosphorus modified DEC.

[0040] Step 3: Preparation of fluorinated reinforced polyester Weigh out 55g of octafluoro-1,6-hexanediol, 45g of 2-hydroxymethyl-1,3-propanediol, 0.2g of dibutyltin dilaurate, and 500mL of N,N-dimethylformamide and add them to an argon-protected reaction flask. Stir the mixture and heat it to 65℃. Calculate the amount of hexamethylene diisocyanate to be added based on 0.55 times the molar amount of hydroxyl groups in the mixed alcohol composed of octafluoro-1,6-hexanediol and 2-hydroxymethyl-1,3-propanediol. Weigh out the calculated amount of hexamethylene diisocyanate and add it to the reaction flask. Incubate the reaction for 25 minutes. Add condensate to the reaction system. 25g of water-glycerol was used to maintain the reaction temperature for 35 minutes. The reaction flask was then cooled to room temperature. The reaction solution was placed in a 1000Da dialysis bag, and a 500Da dialysis bag was placed over the 1000Da dialysis bag. The dialysis bag was then immersed in N,N-dimethylformamide and dialyzed at room temperature for 24 hours. The N,N-dimethylformamide was replaced every 4 hours. The 1000Da dialysis bag was then removed from the 500Da dialysis bag. The contents of the 500Da dialysis bag were transferred to a rotary evaporator with a water bath temperature of 97℃. Low-boiling-point substances were removed by vacuum evaporation to obtain fluorinated reinforced polyester.

[0041] Step 4: Preparation of ethylene carbonate electrolyte Lithium hexafluorophosphate and lithium difluorosulfonyl imide were mixed evenly at a weight ratio of 7:3.5 to obtain lithium salt; Weigh out the following components by weight: 45 parts ethylene carbonate, 23.5 parts sulfone-modified EC, 16.5 parts boron-phosphorus-modified DEC, and 6.5 parts fluorine-reinforced polyester. Add these components to an argon-protected reaction flask and stir. Heat the reaction flask to 45°C and stir for 40 min. Add lithium salt to the reaction flask and stir for 70 min. Add 2.0 parts polyetheramine to the reaction flask, keep warm and stir for 25 min, and allow to cool naturally to room temperature to obtain an ethylene carbonate electrolyte with a lithium concentration of 1.0 mol / L.

[0042] Example 3 This embodiment provides a method for preparing a highly thermally stable ethylene carbonate electrolyte, comprising the following steps: Step 1: Preparation of sulfone-modified EC Lead chloride and triethylamine were mixed evenly at a weight ratio of 1:3 to obtain an addition catalyst; Weigh out 22.8 g of ethylene carbonate, 31.3 g of 1,3-bis(chloroethyl sulfone)propanol, 136.8 mL of acetonitrile, and 2.28 g of addition catalyst and add them to a reaction flask. Stir the mixture and heat it to reflux. Maintain the temperature for 6 h. Apply negative pressure to the reaction system and remove low-boiling substances by vacuum evaporation. Cool the reaction system to room temperature and add 300 mL of acetone. Stir and disperse for 30 min. Filter the mixture using a 0.2 μm PTFE membrane. Transfer the filtrate to a rotary evaporator at 55 °C and remove low-boiling substances by vacuum evaporation to obtain sulfone-modified EC.

[0043] Step 2: Preparation of boron-phosphorus modified DEC Weigh out 18.8 g of triisopropylboronic acid ester, 1.9 g of p-toluenesulfonic acid transesterification catalyst, and 150.4 g of diethyl carbonate and add them to an argon-protected reaction flask. Stir the mixture and heat it to 80 °C. Maintain the temperature for 5 h. Cool the reaction flask to 35 °C and add 39.8 g of diisooctyl phosphite dropwise. Maintain the temperature for 12 h. Cool the reaction flask to room temperature and filter it using a 0.2 μm PTFE membrane. Transfer the filtrate to a rotary evaporator with a water bath temperature of 80 °C and remove low-boiling substances by vacuum evaporation to obtain boron-phosphorus modified DEC.

[0044] Step 3: Preparation of fluorinated reinforced polyester Weigh out 60g of octafluoro-1,6-hexanediol, 50g of 2-hydroxymethyl-1,3-propanediol, 0.2g of dibutyltin dilaurate, and 500mL of N,N-dimethylformamide and add them to an argon-protected reaction flask. Stir the mixture and heat it to 70℃. Calculate the amount of hexamethylene diisocyanate to be added based on 0.55 times the molar amount of hydroxyl groups in the mixed alcohol composed of octafluoro-1,6-hexanediol and 2-hydroxymethyl-1,3-propanediol. Weigh out the calculated amount of hexamethylene diisocyanate and add it to the reaction flask. Incubate the reaction for 30 minutes. Add desiccant to the reaction system. 30g of glycerol was used to react at a constant temperature for 40 minutes. The reaction flask was then cooled to room temperature. The reaction solution was placed in a 1000Da dialysis bag, and a 500Da dialysis bag was placed over the 1000Da dialysis bag. The dialysis bags were then immersed in N,N-dimethylformamide and dialyzed at room temperature for 24 hours. The N,N-dimethylformamide was replaced every 4 hours. The 1000Da dialysis bag was then removed from the 500Da dialysis bag. The contents of the 500Da dialysis bag were transferred to a rotary evaporator with a water bath temperature of 100℃. Low-boiling-point substances were removed by vacuum evaporation to obtain fluorinated reinforced polyester.

[0045] Step 4: Preparation of ethylene carbonate electrolyte Lithium hexafluorophosphate and lithium difluorosulfonyl imide were mixed evenly at a weight ratio of 7:4 to obtain the lithium salt. Weigh out the following components by weight: 50 parts ethylene carbonate, 25 parts sulfone-modified EC, 18 parts boron-phosphorus-modified DEC, and 8 parts fluorine-reinforced polyester. Add these components to an argon-protected reaction flask and stir. Heat the reaction flask to 50°C and stir for 50 min. Add lithium salt to the reaction flask and stir for 80 min. Add 2.2 parts polyetheramine to the reaction flask, keep warm and stir for 30 min, and allow to cool naturally to room temperature to obtain an ethylene carbonate electrolyte with a lithium concentration of 1.0 mol / L.

[0046] Comparative Example 1 The difference between this comparative example and Example 3 is that step 1 is omitted, and the sulfone-modified EC in step 4 is replaced by an equal amount of ethylene carbonate.

[0047] Comparative Example 2 The difference between this comparative example and Example 3 is that step 2 is omitted, and the boron-phosphorus modified DEC in step 4 is replaced by an equal amount of ethylene carbonate.

[0048] Comparative Example 3 The difference between this comparative example and Example 3 is that octafluoro-1,6-hexanediol was not added in step 3.

[0049] Comparative Example 4 The difference between this comparative example and Example 3 is that polyetheramine was not added in step 4.

[0050] Performance testing: Lithium iron phosphate, conductive graphite, and polyvinylidene fluoride were mixed in a weight ratio of 95:3:2, followed by N-methylpyrrolidone to prepare a slurry with a solid content of 65%. The slurry was then uniformly coated onto the positive electrode current collector aluminum foil using a small coating machine and dried in a high-temperature oven. Finally, it was rolled using a roller press to achieve a compaction density of 4.3 g / cm³. 3 The positive electrode was obtained by cutting the sample using an electrode punching machine and drying it in a vacuum oven at 85°C for 12 hours. Using lithium metal sheets as the negative electrode; The ethylene carbonate electrolytes prepared in Examples 1-3 and Comparative Examples 1-4 were used as electrolytes; Referring to the standard GB / T 43092-2023 "Test Method for Electrochemical Performance of Lithium-ion Battery Cathode Materials at High Temperature", the above-mentioned positive electrode, negative electrode and electrolyte were assembled into a coin cell sample. The high temperature storage and cycling temperatures were set to 45℃ and 80℃, respectively. The high temperature storage voltage decay rate, high temperature storage capacity retention rate and high temperature cycling capacity retention rate of the coin cell sample were measured. The specific test data are shown in Table 1 below.

[0051] Table 1 - Performance Test Data of Samples

[0052] Data Analysis: Comparative analysis of the data in Table 1 shows that the coin cell samples prepared using the ethylene carbonate electrolyte of this invention exhibit the following characteristics under high-temperature storage and cycling conditions: high-temperature storage voltage decay rate decreased to 0.5-0.7%, high-temperature storage capacity retention reached 2.1-2.4%, and high-temperature cycling capacity retention reached 98.3-98.7%. Under high-temperature storage and cycling conditions at 80°C, the high-temperature storage voltage decay rate decreased to 2.1-2.4%, the high-temperature storage capacity retention reached 98.6-98.9%, and the high-temperature cycling capacity retention reached 89.2-89.5%. The performance test data of the present invention are all superior to those of the comparative example, indicating that the present invention functionalizes the structure of ethylene carbonate solvent, introduces a sulfone group structure to enhance molecular thermal stability, constructs boron- and phosphorus-containing synergistic interface regulation components to suppress high-temperature side reactions, and combines fluorine-containing enhanced polymers and composite lithium salt systems to optimize solvation structure and interface film stability. The present invention synergistically improves the stability of electrolyte under high-temperature storage and high-temperature cycling conditions from three levels: molecular structure regulation, interface reaction path control, and in-situ structure enhancement, achieving low voltage decay rate and high capacity retention rate, and is suitable for long-term stable operation of lithium-ion batteries under high-temperature conditions.

[0053] The above description is merely an example and illustration of the structure of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described, or use similar methods to replace them, as long as they do not deviate from the structure of the invention or exceed the scope defined in the claims, all of which should fall within the protection scope of the present invention.

Claims

1. A highly thermally stable ethylene carbonate electrolyte, characterized in that, It includes a carbonate substrate and a lithium salt, wherein the concentration of the lithium salt is 1.0 mol / L; The carbonate base comprises the following components by weight: 40-50 parts ethylene carbonate, 22-25 parts sulfone-modified EC, 15-18 parts boron-phosphorus-modified DEC, 5-8 parts fluorine-reinforced polyester, and 1.8-2.2 parts polyetheramine. The lithium salt is composed of lithium hexafluorophosphate and lithium difluorosulfonyl imide in a weight ratio of 7:3-4.

2. The ethylene carbonate electrolyte with high thermal stability according to claim 1, characterized in that, The preparation method of sulfone-modified EC is as follows: ethylene carbonate, 1,3-bis(chloroethylsulfonyl)propanol, acetonitrile and addition catalyst are mixed and stirred, the reaction system is heated to reflux and kept at the temperature for 4-6 hours, and then post-processed to obtain sulfone-modified EC.

3. The ethylene carbonate electrolyte with high thermal stability according to claim 2, characterized in that, The molar ratio of ethylene carbonate to 1,3-bis(chloroethyl sulfone)propanol is 2:1, the molar ratio of ethylene carbonate, acetonitrile and catalyst is 5g:30mL:0.5g, and the addition catalyst is composed of lead chloride and triethylamine in a weight ratio of 1:

3.

4. The ethylene carbonate electrolyte with high thermal stability according to claim 1, characterized in that, The preparation method of boron-phosphorus modified DEC is as follows: under the protection of an inert gas atmosphere, triisopropylboronic acid ester, transesterification catalyst and diethyl carbonate are mixed and stirred. The reaction system is heated to 60-80℃ and kept at this temperature for 4-5 hours. The reaction system is then cooled to 25-35℃, and diisooctyl phosphite is added dropwise to the reaction system. The reaction is kept at this temperature for 10-12 hours. After post-treatment, boron-phosphorus modified DEC is obtained.

5. The ethylene carbonate electrolyte with high thermal stability according to claim 4, characterized in that, The ratio of triisopropylboronic acid ester, transesterification catalyst, and diethyl carbonate is 10g:0.1g:70-80mL, the molar ratio of diisooctyl phosphite to triisopropylboronic acid ester is 1.1-1.3:1, and the transesterification catalyst is p-toluenesulfonic acid.

6. The ethylene carbonate electrolyte with high thermal stability according to claim 1, characterized in that, The preparation method of fluorinated reinforced polyester is as follows: Under the protection of an inert gas atmosphere, octafluoro-1,6-hexanediol, 2-hydroxymethyl-1,3-propanediol, dibutyltin dilaurate, and N,N-dimethylformamide are mixed and stirred. The reaction system is heated to 60-70℃, hexamethylene diisocyanate is added to the reaction system, and the reaction is maintained at this temperature for 20-30 min. Then, glycidyl ether is added to the reaction system, and the reaction is maintained at this temperature for 40-50 min. Finally, glycidyl ether is added to the reaction system, and the reaction is maintained at this temperature for 30-40 min. After post-treatment, fluorinated reinforced polyester with a molecular weight of 500-1000 is obtained.

7. The ethylene carbonate electrolyte with high thermal stability according to claim 6, characterized in that, The ratio of octafluoro-1,6-hexanediol, 2-hydroxymethyl-1,3-propanediol, dibutyltin dilaurate, N,N-dimethylformamide, and glycidyl is 5-6g:4-5g:0.02g:50mL:2-3g, and the molar amount of hexamethylene diisocyanate is 0.55 times the molar amount of hydroxyl groups in octafluoro-1,6-hexanediol and 2-hydroxymethyl-1,3-propanediol.

8. A method for preparing a highly thermally stable ethylene carbonate electrolyte according to any one of claims 1-7, characterized in that, The process includes the following steps: Under an inert gas atmosphere, ethylene carbonate, sulfone-modified EC, boron-phosphorus-modified DEC, and fluorine-reinforced polyester are mixed and stirred. The reaction system is heated to 40-50℃ and stirred for 30-50 minutes. Lithium salt is added to the reaction system and stirred for 60-80 minutes. Polyetheramine is added to the reaction system and stirred at the same temperature for 20-30 minutes. The mixture is then allowed to cool naturally to room temperature to obtain an ethylene carbonate electrolyte.

9. The application of a highly thermally stable ethylene carbonate electrolyte, characterized in that, The ethylene carbonate electrolyte with high thermal stability as described in any one of claims 1-7 is used in lithium batteries.

Images