Electrolyte capable of improving flame retardance and cycling stability as well as preparation method and application of electrolyte
By using a mixed co-solvent system of fluorinated esters, phosphate esters, and linear carbonates, combined with lithium salts and film-forming additives, the flame retardancy and cycle stability issues of lithium-ion battery electrolytes were solved, achieving improved energy density and safety performance.
Patent Information
- Application Number
- CN202511371092.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-09-24
- Publication Date
- 2026-02-10
AI Technical Summary
Existing lithium-ion battery electrolytes have poor flame retardancy and insufficient cycle stability, making it difficult to meet the requirements for high energy density and safety performance. In particular, they are prone to combustion and the electrode interface is unstable under high voltage and highly active materials.
A mixed co-solvent system of fluorinated esters, phosphate esters and linear carbonates was adopted, combined with lithium salts and film-forming additives, to optimize the electrolyte composition and improve flame retardancy and cycle stability.
It significantly improves the flame retardancy and self-extinguishing properties of the electrolyte, reduces viscosity and increases conductivity, extends cycle life and stabilizes the electrode interface, meeting national safety standards.
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Abstract
Description
Technical Field
[0001] This application belongs to the field of battery electrolyte technology, and in particular relates to an electrolyte with improved flame retardancy and cycle stability, its preparation method and application. Background Technology
[0002] With the advancement of global energy structure transformation goals, lithium-ion batteries have become the absolute mainstream in the fields of power batteries and energy storage due to their advantages such as high energy density, long cycle life and no memory effect. However, the energy density of current commercial lithium-ion batteries is gradually approaching its theoretical limit, making it difficult to meet the market's urgent demand for longer driving range for electric vehicles. Therefore, further improving the energy density and safety performance of batteries through material innovation and electrolyte optimization within the existing system has become a key focus of research and development in industry and academia.
[0003] Using high-capacity silicon-based anodes or high-voltage / high-nickel cathode materials is an effective way to improve battery energy density, but these technical routes also bring severe safety challenges: traditional carbonate-based electrolytes are highly flammable and can easily burn or even explode in the event of thermal runaway; secondly, more active electrode materials exacerbate the side reactions at the electrode-electrolyte interface, leading to instability of the solid electrolyte interphase (SEI) film, accelerating capacity decay, and increasing the risk of thermal runaway; the Ministry of Industry and Information Technology of China officially released GB38031-2025 "Safety Requirements for Power Batteries for Electric Vehicles" on April 3, 2025, which for the first time included "no fire and no explosion" in a mandatory national standard, imposing unprecedentedly stringent requirements on the intrinsic safety performance of batteries.
[0004] To address the flammability issue of lithium-ion batteries, researchers have proposed various solutions. For example, replacing liquid electrolytes with non-flammable solid electrolytes (such as sulfides, oxides, and polymers) can fundamentally solve the combustion problem. However, solid-state batteries still face industrialization challenges such as high interfacial impedance, high cost, and poor rate performance. Another mainstream solution is to add flame retardants, such as phosphate esters and fluorocarbonates, to liquid electrolytes. However, traditional flame retardants have drawbacks such as a narrow electrochemical window (incompatible with high-voltage cathodes), high viscosity (sacrificing ionic conductivity and rate performance), and deterioration of electrode interface stability, often making it difficult to balance safety and electrochemical performance.
[0005] Therefore, developing a novel electrolyte that can simultaneously meet the requirements of high safety, high interfacial compatibility, and good kinetic performance is of vital importance for promoting the development of high-energy-density lithium-ion batteries and meeting the latest national safety standards. Summary of the Invention
[0006] The purpose of this application is to provide an electrolyte with improved flame retardancy and cycle stability, its preparation method, and its application, so as to solve the technical problems of poor flame retardancy and poor cycle stability of existing battery electrolytes.
[0007] To achieve the above objectives, the technical solution adopted in this application is: to provide an electrolyte that improves flame retardancy and cycle stability, comprising a co-solvent, a lithium salt, and a film-forming additive; Cosolvents include fluorinated ester solvents, phosphate ester solvents, and linear carbonate solvents; By mass percentage, fluorinated ester solvents account for 10-50%, phosphate ester solvents account for 20-80%, and linear carbonate solvents account for 20-60%. The mass ratio of the film-forming additive to the phosphate ester solvent is 0.01-0.1:1.
[0008] In one embodiment, Fluorinated ester solvents are one of ethyl trifluoroacetate (ETFA), 2,2,2-trifluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), fluoroethylene carbonate (FEC), or difluoroethylene carbonate (DFEC).
[0009] In one embodiment, The phosphate ester solvent is one of trimethyl phosphate (TMP), triethyl phosphate (TEP), triethyl phosphite (TEPP), or trimethyl phosphite (TMPP).
[0010] In one embodiment, The linear carbonate solvent is one of dimethyl carbonate (DMC), diethyl carbonate (DEC), or ethyl methyl carbonate (EMC).
[0011] In one embodiment, The film-forming additive is a boron-containing additive, specifically one or two of trimethyl borate (TMB), tris(trimethylsilane)borate (TMSB), or cyclic borate (BOB-EO).
[0012] In one embodiment, The lithium salt is one or two of lithium hexafluorophosphate (LiPF6), lithium difluorophosphate (LiPO2F2), or lithium bis(difluorosulfonyl)imide (LIFSI).
[0013] In one embodiment, The molar concentration of lithium salt is 0.6-2.2 mol / L.
[0014] This application also provides a method for preparing an electrolyte with improved flame retardancy and cycle stability, comprising the following steps: mixing linear carbonate solvent, fluorinated ester solvent, and phosphate ester solvent evenly to obtain a cosolvent; adding lithium salt and film-forming additive to the cosolvent to dissolve and obtain an electrolyte.
[0015] In one embodiment, The electrolyte preparation temperature was below 30 ℃ throughout the entire process.
[0016] This application also provides an application of an electrolyte that improves flame retardancy and cycle stability. The electrolyte is used in lithium-ion batteries, and the cathode material matched with the electrolyte is one of lithium nickel cobalt manganese oxide, lithium iron phosphate, lithium cobalt oxide, organic lithium cathode, lithium-rich manganese-based cathode, or sulfur cathode.
[0017] This application provides an electrolyte for improving flame retardancy and cycle stability, its preparation method, and its application. Compared with the prior art, it has the following advantages: 1. Existing technologies using fluorinated esters alone have poor flame retardancy, with a limiting oxygen index of <30%. This electrolyte uses a mixture of fluorinated esters and phosphate ester solvents, such as triethyl phosphate with a limiting oxygen index of >40%, which can significantly improve the flame retardancy of the electrolyte. The electrolyte self-extinguishes after burning for about 2-30 seconds. 2. In the prior art, phosphate esters are easily decomposed under high pressure when used alone. This application avoids the problem of high pressure decomposition of phosphate esters by adding fluorinated esters and linear carbonates for dilution. During the cycling process, the voltage is 3-4.53 V, and it can stably cycle for 853 cycles with 80% capacity retention, which is better. 3. Traditional phosphate ester flame retardant solvents have high viscosity. This application reduces electrolyte viscosity and improves conductivity and lithium ion migration speed by mixing in a high proportion of linear carbonate. 4. Adding a small amount of borate ester additives to the electrolyte can improve the mechanical strength of the formed electrolyte interface film, reduce impedance, and improve the cycle stability of lithium-ion batteries. Detailed Implementation
[0018] To make the technical problems, technical solutions, and beneficial effects to be solved by this application clearer, this application will be further described in detail. It should be understood that the specific embodiments described herein are only for explaining this application and are not intended to limit this application.
[0019] Example 1 The electrolyte formulation, by mass percentage (the same below), is: 30% ethylene carbonate (EC), 70% EMC + 1 mol / L LiPF6, which are mixed to prepare the electrolyte.
[0020] Example 2 The electrolyte formulation is: 50% FEC, 50% TEP, and 1 mol / L LiPF6, which are mixed to prepare the electrolyte.
[0021] Example 3 The electrolyte formulation is: 33% FEC, 66% TEP, and 1 mol / L LiPF6, which are mixed to prepare the electrolyte.
[0022] Example 4 The electrolyte formulation is: 20% FEC, 80% TEP, and 1 mol / L LiPF6, which are mixed to prepare the electrolyte.
[0023] Examples 1-4 compare the flammability and thermal runaway performance of linear carbonate solvent electrolytes and fluorinated ester + phosphate co-solvent electrolyte systems. The co-solvents using fluorinated ester and phosphate solvents (Examples 2-4) compared to linear carbonate solvents (Example 1) significantly improve flame retardancy and high-temperature thermal stability. This is because the thermal decomposition of phosphate esters generates phosphorus-oxygen free radicals, which can capture high-energy hydrogen and oxygen free radicals in the combustion chain reaction. Fluorinated esters preferentially decompose on the negative electrode surface, promoting the formation of a LiF-rich solid electrolyte interface film, which can isolate the transfer of high temperature to the internal active material and prevent the electrolyte from continuously decomposing and generating gas and releasing heat on the negative electrode surface. The synergistic effect of these two factors improves the flame retardant effect of the co-solvent. The results of combustion and hot box experiments are shown in Table 1. Table 1 Comparison of flammability and thermal stability performance of Examples 1-4
[0024] Example 5 The co-solvent ratio is: 10% FEC, 20% TEP, and 70% EMC.
[0025] Example 6 The co-solvent ratio is: 10% FEC, 30% TEP, and 60% EMC.
[0026] Example 7 The co-solvent ratio is: 10% FEC, 40% TEP, and 50% EMC.
[0027] Example 8 The co-solvent ratio is: 10% FEC, 50% TEP, and 40% EMC.
[0028] Example 9 The co-solvent ratio is: 15% FEC, 40% TEP, and 45% EMC.
[0029] Example 10 The co-solvent ratio is: 20% FEC, 40% TEP, and 40% EMC.
[0030] Example 11 The co-solvent ratio is: 25% FEC, 40% TEP, and 35% EMC.
[0031] Example 12 The co-solvent ratio is: 15% FEC, 35% TEP, and 50% EMC.
[0032] Example 13 The co-solvent ratio is: 20% FEC, 30% TEP, and 50% EMC.
[0033] Example 14 The co-solvent ratio is: 25% FEC, 25% TEP, and 50% EMC.
[0034] Examples 5-14 compare the effects of different proportions of fluorinated ester solvents, phosphate ester solvents, and linear carbonate solvents in the co-solvent on battery cycle performance. Examples 5-8 show that as the linear carbonate content increases, the cycle life (capacity decay to 80% at 25 °C) increases because linear carbonate can dilute phosphate ester solvents, reduce viscosity, thereby improving conductivity and lithium-ion transport rate, and thus improving cycle life. However, linear carbonate is flammable, and an excessively high proportion cannot meet the flame retardant requirements (Examples 5-6), so its proportion in the co-solvent needs to be balanced. By continuously adjusting the proportions of fluorinated ester solvents, phosphate ester solvents, and linear carbonate solvents, the optimal ratio was obtained (Example 13), and the results are shown in Table 2. Table 2 Comparison of Cyclic Performance and Thermal Stability of Examples 5-14
[0035] Example 15 TMB was added following the co-solvent ratio of Example 13, with a TMB to TEP mass ratio of 0.01:1, and the cycle life was tested to be 670 cls.
[0036] Example 16 The difference between this embodiment and embodiment 15 is that the mass ratio of TMB to TEP is 0.05:1, and the tested cycle life is 803 cls.
[0037] Example 17 The difference between this embodiment and embodiment 15 is that the mass ratio of TMB to TEP is 0.07:1, and the tested cycle life is 786 cls.
[0038] Example 18 The difference between this embodiment and embodiment 15 is that the mass ratio of TMB to TEP is 0.1:1, and the tested cycle life is 745 cls.
[0039] The comparison of cycling performance (capacity decay to 80% at 25 °C) with different film-forming additive ratios in Examples 15-18 shows that the cycling performance first increases and then decreases with increasing dosage, because borate ester additives can inhibit PF6. - Decomposition increases LiF solubility, reduces interfacial impedance, and improves the conductivity of the interfacial electrolyte membrane, thereby improving cycle performance; however, insufficient addition limits the performance improvement, while excessive addition can easily lead to side reactions and affect cycle performance.
[0040] Example 19 Following the formulation of Example 16, 0.6 mol / L of LiPF6 was added and mixed to prepare an electrolyte.
[0041] Example 20 The difference between this embodiment and Example 19 is that 0.8 mol / L of LiPF6 was added and mixed to prepare an electrolyte.
[0042] Example 21 The difference between this embodiment and Example 19 is that 1.0 mol / L of LiPF6 was added and mixed to prepare an electrolyte.
[0043] Example 22 The difference between this embodiment and Example 19 is that 1.5 mol / L of LiPF6 was added and mixed to prepare an electrolyte.
[0044] Example 23 The difference between this embodiment and Example 19 is that 2.0 mol / L of LiPF6 was added and mixed to prepare an electrolyte.
[0045] Example 24 The difference between this embodiment and Example 19 is that 2.2 mol / L of LiPF6 was added and mixed to prepare an electrolyte.
[0046] Examples 19-24 compare the thermal stability and cycling performance (capacity decay to 80% at 25 °C) of different lithium salt additions. The role of lithium salt is to provide charge carriers. As shown in Table 3, if the lithium salt content is too low, there are not enough charge carriers to effectively transfer current and complete the chemical reaction. On the other hand, if the content is too high, more solvent will not coordinate with the lithium salt, resulting in poorer thermal stability of the electrolyte. Excessive lithium salt will significantly increase the electrolyte viscosity, reduce the ion migration rate, and lead to a decrease in conductivity. At the same time, it will aggravate side reactions, increase interfacial impedance, and impair cycle life.
[0047] Table 3 Comparison of thermal stability and cycling performance of Examples 19-24
[0048] Example 25 The co-solvent ratio is: 20% FEC, 30% TEP, 50% EMC, and 1.0 mol / L LiPF6 is added to prepare the electrolyte.
[0049] Test case Conductivity tests were conducted on two different electrolytes from Examples 4 and 25. The conductivity of Example 4 was 7.754 mS / cm, and the conductivity of Example 25 was 8.243 mS / cm. The comparison shows that mixing a high proportion of linear carbonate can reduce the viscosity of the electrolyte and improve its conductivity.
[0050] Following the proportions in Example 21, 50% EMC, 20% FEC, and 30% TEP were mixed evenly to obtain a cosolvent. 1.0 mol / L LiPF6 and 1.5% TMB were added to the cosolvent to dissolve the electrolyte. The preparation temperature remained below 30 °C throughout the process.
[0051] The electrolyte is used in lithium-ion batteries, and the cathode material matched with the electrolyte is one of lithium nickel cobalt manganese oxide, lithium iron phosphate, lithium cobalt oxide, organic lithium cathode, lithium-rich manganese-based cathode, or sulfur cathode.
[0052] The substitution of each component can be flexibly adjusted based on factors such as market prices, and will not be elaborated here.
[0053] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.
Claims
1. An electrolyte for improving flame retardancy and cycle stability, characterized in that, Including cosolvents, lithium salts, and film-forming additives; The co-solvents include fluorinated ester solvents, phosphate ester solvents, and linear carbonate solvents; By mass percentage, the fluorinated ester solvent accounts for 10-50%, the phosphate ester solvent accounts for 20-80%, and the linear carbonate solvent accounts for 20-60%. The mass ratio of the film-forming additive to the phosphate ester solvent is 0.01-0.1:
1.
2. The electrolyte for improving flame retardancy and cycle stability according to claim 1, characterized in that, The fluorinated ester solvent is one of ethyl trifluoroacetate, 2,2,2-trifluoroethyl-2,2,3,3-tetrafluoropropyl ether, fluoroethylene carbonate, or difluoroethylene carbonate.
3. The electrolyte for improving flame retardancy and cycle stability according to claim 1, characterized in that, The phosphate ester solvent is one of trimethyl phosphate, triethyl phosphate, triethyl phosphite, or trimethyl phosphite.
4. The electrolyte for improving flame retardancy and cycle stability according to claim 1, characterized in that, The linear carbonate solvent is one of dimethyl carbonate, diethyl carbonate, or ethyl methyl carbonate.
5. The electrolyte for improving flame retardancy and cycle stability according to claim 1, characterized in that, The film-forming additive is one or two of trimethyl borate, tris(trimethylsilane)borate, or cyclic borate.
6. The electrolyte for improving flame retardancy and cycle stability according to claim 1, characterized in that, The lithium salt is one or two of lithium hexafluorophosphate, lithium difluorophosphate, or lithium bis(difluorosulfonyl)imide.
7. The electrolyte for improving flame retardancy and cycle stability according to claim 1, characterized in that, The molar concentration of the lithium salt is 0.6-2.2 mol / L.
8. A method for preparing an electrolyte with improved flame retardancy and cycle stability, characterized in that, The steps are as follows: Linear carbonate solvent, fluorinated ester solvent, and phosphate ester solvent are mixed evenly to obtain a cosolvent. Lithium salt and film-forming additives are added to the cosolvent to dissolve and obtain an electrolyte.
9. The method for preparing an electrolyte with improved flame retardancy and cycle stability according to claim 8, characterized in that, The electrolyte was prepared at a temperature of 30°C.
10. An application of an electrolyte that improves flame retardancy and cycle stability, characterized in that, The electrolyte is used in lithium-ion batteries, and the cathode material matched with the electrolyte is one of lithium nickel cobalt manganese oxide, lithium iron phosphate, lithium cobalt oxide, organic lithium cathode, lithium-rich manganese-based cathode, or sulfur cathode.