High-temperature stable deep eutectic electrolyte and its application in lithium battery
The deep eutectic electrolyte formed by sulfolane and succinate with lithium salt solves the problem of lithium-ion battery decomposition and volatilization at high temperatures, forming a stable electrode and SEI film, improving the high-temperature cycle performance and safety of the battery, and is suitable for lithium-ion batteries.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- CENT SOUTH UNIV
- Filing Date
- 2026-03-27
- Publication Date
- 2026-06-05
AI Technical Summary
Traditional lithium-ion battery electrolytes are prone to decomposition and volatilization at high temperatures, leading to safety hazards and poor cycle stability. In particular, an unstable SEI film is easily formed on the surface of the negative electrode, affecting the high-temperature cycle performance of the battery.
A deep eutectic electrolyte is formed by Lewis base composed of sulfolane and succinate and Lewis acid composed of lithium bis(trifluoromethanesulfonylimide) and lithium difluorooxalateborate. Through the interaction of Lewis acid and base, a uniform and stable electrode interface film is formed on the positive electrode side and a stable SEI film is formed on the negative electrode side, thereby improving high-temperature stability and ionic conductivity.
Within a temperature range of -20℃ to 80℃, the electrolyte exhibits good viscosity and ionic conductivity, significantly improving the high and low temperature cycle stability and safety of lithium-ion batteries. In particular, it demonstrates excellent high temperature stability and cycle performance at 80℃, meeting the needs of electric vehicles and energy storage systems.
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Abstract
Description
Technical Field
[0001] This invention relates to an electrolyte, particularly a high-temperature stable deep eutectic electrolyte, and its application in lithium batteries, belonging to the field of lithium-ion battery technology. Background Technology
[0002] With the rapid development of the new energy industry, lithium-ion batteries are increasingly widely used in electric vehicles, energy storage systems, and other fields, placing higher demands on battery performance in extreme environments (especially high temperatures). Traditional lithium-ion batteries mostly use carbonate-based organic electrolytes (such as ethylene carbonate and dimethyl carbonate), but these electrolytes have low boiling points (usually below 100°C) and poor thermal stability, making them prone to decomposition and volatilization at high temperatures, and even causing safety problems such as battery leakage, short circuits, and fires. At the same time, the interfacial reaction between the electrolyte and the electrode (especially the graphite anode) intensifies at high temperatures, leading to SEI film rupture and lithium dendrite growth, which seriously affects the cycle stability and lifespan of the battery.
[0003] In existing technologies, researchers often employ methods such as adding flame retardants, introducing high-boiling-point solvents, or developing polymer electrolytes to improve high-temperature stability. Although the cycle performance of batteries improves at 60°C, performance at higher temperatures still needs further improvement. Deep eutectic solutions have attracted widespread attention due to their advantages such as good thermal and chemical stability, tunable structure, and low cost.
[0004] Existing deep eutectic electrolytes mostly use urea, ethylene glycol, etc. as hydrogen bond donors to form a eutectic system with lithium salts. However, their interfacial compatibility at high temperatures still needs improvement, especially as an unstable solid electrolyte interphase (SEI) film easily forms on the negative electrode surface, leading to dendrite growth and shortened cycle life. Chinese patent application (application publication number: CN118676431A) discloses a deep eutectic lithium-ion battery electrolyte based on molecular plastic crystals, containing the following molar fractions of raw materials: 40-60% of branched molecular plastic crystal monocarboxylic acid and 40-60% of electrolyte lithium salt. By obtaining the deep eutectic composition, the electrolyte can prevent solidification at lower temperatures, still have a certain ion conductivity, and is non-flammable, but its high-temperature cycle performance is poor. Summary of the Invention
[0005] To address the aforementioned technical problems, the first objective of this invention is to provide a high-temperature stable eutectic electrolyte that exhibits moderate viscosity and good ionic conductivity at temperatures ranging from -20°C to 80°C. This electrolyte can form a uniform and stable electrode or electrolyte interface film on the positive and negative electrode sides of a lithium-ion battery, effectively improving the cycle stability of the lithium-ion battery at both high and low temperatures.
[0006] The second objective of this invention is to provide a high-temperature stable eutectic electrolyte for use in lithium-ion batteries. This electrolyte, when used in lithium-ion batteries, can maintain good cycle stability and safety at temperatures ranging from -20°C to 80°C.
[0007] To achieve the above-mentioned technical objectives, the present invention provides a high-temperature stable deep eutectic electrolyte, which is composed of a Lewis base and a Lewis acid; the Lewis base is composed of sulfolane and succinate in a volume percentage of 60-90%:10-40%; the Lewis acid is composed of lithium bis(trifluoromethanesulfonylimide) and lithium difluorooxalateborate in a molar percentage of 40-70%:30-60%.
[0008] The deep eutectic electrolyte of the present invention is formed by Lewis acid-base interaction between sulfolane and succinate, which have Lewis base properties, and organic lithium salts (lithium bis(trifluoromethanesulfonylimide) or lithium difluorooxalateborate), which have Lewis acid properties. Among them, sulfolane contains -S(O)2- bonds, which have good oxidation stability, moderate dielectric constant and high flash point. The deep eutectic system formed by its combination with lithium bis(trifluoromethanesulfonyl)imide and lithium difluorooxalateborate is not easily decomposed or volatilized at 80℃ and has flame retardant properties, giving the deep eutectic electrolyte good high-temperature stability and solving the safety hazards of traditional electrolytes at high temperatures. Succinitriles contain double-C≡N bonds, which can form a more uniform and robust cathode / electrolyte interface (CEI) on the cathode side, effectively suppressing the irreversible phase transition of nickel-rich cathodes. At the same time, the oxalate in the lithium difluorooxalateborate (LiDFOB) organic lithium salt can preferentially decompose during cycling to form an inorganic solid electrolyte interface film (SEI film) on the graphite anode surface, suppressing the side reactions between the electrolyte and graphite at high temperatures. Lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) provides high ionic conductivity, and the two work together to improve interface stability. In summary, the deep eutectic electrolyte of the present invention extends the operating temperature range to -20℃ to 80℃, and particularly enhances the stability and cycle performance at high temperatures (80℃), which can better meet the actual needs of electric vehicles, energy storage systems and other applications that require long-term reliable operation in high-temperature environments.
[0009] As a preferred embodiment, the Lewis base is composed of sulfolane and succinate in a volume percentage of 80-90%:10-20%. Appropriately increasing the proportion of sulfolane in the Lewis base can significantly enhance the system's high-temperature resistance and flame retardancy, but it also sacrifices its ion transport efficiency at low temperatures. Conversely, appropriately increasing the proportion of succinate helps form a more robust cathode interfacial film (CEI), improving the structural stability of the high-nickel cathode, but excessive amounts may introduce the risk of oxidative decomposition. Therefore, combining sulfolane and succinate in an appropriate ratio can improve the overall performance of the electrolyte.
[0010] As a preferred embodiment, the Lewis acid is composed of lithium bis(trifluoromethanesulfonyl)imide and lithium difluorooxalate borate in a molar ratio of 40-60%:40-60%. In the Lewis acid, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) primarily provides high ionic conductivity, while lithium difluorooxalate borate (LiDFOB) preferentially constructs a stable SEI film on the graphite anode, suppressing high-temperature side reactions. Appropriately increasing the proportion of LiDFOB can further enhance interface protection, but may slightly reduce the overall conductivity. Therefore, the ratio of lithium bis(trifluoromethanesulfonyl)imide to lithium difluorooxalate borate needs to be coordinated and controlled to ensure the high-temperature stability and high ionic conductivity of the deep co-electrolyte.
[0011] As a preferred embodiment, the total concentration of Lewis acid in the deep eutectic electrolyte is 0.5~1.5M, to balance sufficient charge carrier concentration with suitable electrolyte viscosity.
[0012] This invention also provides an application of a high-temperature stable deep eutectic electrolyte in lithium-ion batteries.
[0013] As a preferred embodiment, the lithium-ion battery comprises a graphite anode and a lithium cobalt oxide cathode or a ternary cathode. The deep eutectic electrolyte of this invention is particularly suitable for mainstream graphite anode and high-nickel cathode systems, exhibiting good interfacial compatibility and full-cell cycle stability, which aligns with the current technological development roadmap for power batteries and energy storage batteries.
[0014] The method for preparing the high-temperature stable deep eutectic electrolyte of the present invention includes the following steps:
[0015] S1: Weigh out Lewis acid and Lewis base in proportion under an inert gas atmosphere;
[0016] S2: Mix the solvent, which is the Lewis base, with the lithium salt, which is the Lewis acid, and heat and stir to obtain a homogeneous and clear solution. The heating temperature is 40~50℃ and the stirring time is 0.5~1h.
[0017] The high-temperature stable deep eutectic electrolyte of this invention is used to assemble lithium-ion batteries using conventional lithium-ion battery assembly methods, such as assembling a CR2032 coin cell in the following order: negative electrode shell, negative electrode, deep eutectic electrolyte, glass fiber separator, deep eutectic electrolyte, positive electrode, and positive electrode shell. The positive electrode material is LCO or NCM811, and the negative electrode material is graphite.
[0018] Compared with existing technologies, the beneficial technical effects of the present invention are as follows:
[0019] 1) The high-temperature stable deep eutectic electrolyte provided by this invention exhibits significant synergistic effects among its components, resulting in moderate viscosity and good ionic conductivity over a wide temperature range of -20℃ to 80℃. This allows for the formation of uniform and stable electrode or electrolyte interface films on both the positive and negative electrode sides of the lithium-ion battery, effectively improving the cycle stability of the lithium-ion battery at both high and low temperatures. More specifically, sulfolane has a high boiling point (285℃) and a high flash point (166℃). The deep eutectic system formed with LiTFSI and LiDFOB is not easily decomposed or volatilized at 80℃, giving it excellent high-temperature stability. Furthermore, it possesses flame-retardant properties, solving the safety hazards of traditional electrolytes at high temperatures. The -C≡N in succinate can preferentially decompose on the positive electrode side to form a uniform and robust CEI film, effectively suppressing the irreversible phase transition of the high-nickel positive electrode, thereby improving the battery cycle performance; the oxalate in LiDFOB can form a stable SEI film on the graphite negative electrode surface, suppressing the side reactions between the electrolyte and graphite at high temperatures, while LiTFSI provides high ionic conductivity, and the two work together to improve interface stability.
[0020] The high-temperature stable deep eutectic electrolyte of this invention is used in lithium-ion batteries, breaking through the barrier that traditional high-temperature electrolytes can only improve the cycle performance of lithium-ion batteries at 60°C, achieving stable cycling at 80°C or even higher temperatures, while cycling at -20°C confirms its application potential in a wide temperature range.
[0021] The high-temperature stable deep eutectic electrolyte of the present invention uses readily available raw materials and has a simple preparation process. It does not require complex polymerization reactions or additional additives for compounding and can be obtained simply by mixing and heating. Attached Figure Description
[0022] Figure 1 The cyclic voltammetry curves are for the graphite anode half-cell prepared with the deep eutectic electrolyte in Example 1.
[0023] Figure 2 The lithium-ion transference number is calculated by chronoamperometry for the deep eutectic electrolyte in Example 1.
[0024] Figure 3 The critical current density curve of the deep eutectic electrolyte in Example 1 is shown.
[0025] Figure 4 The graphite anode half-cell prepared with the deep eutectic electrolyte in Example 1 operates at 0.5 mA / cm². 2 The current density and 0.5 mAh / cm 2 The charge-discharge curves of a symmetrical battery under the given areal capacity condition.
[0026] Figure 5 The cycling curve of the graphite anode half-cell with deep eutectic electrolyte in Example 1 at 0.5C is shown.
[0027] Figure 6 The cycling curves of the full cell assembled with the deep eutectic electrolyte and LCO cathode in Example 1 at 0.5C are shown.
[0028] Figure 7 The cycling curves of the full cell assembled with the deep eutectic electrolyte and NCM811 cathode in Example 1 at 0.5C are shown.
[0029] Figure 8 The cycling curve of the graphite anode half-cell prepared by the deep eutectic electrolyte in Example 1 at a high temperature of 80°C.
[0030] Figure 9 The cycling curve of the half-cell assembled with the deep eutectic electrolyte and NCM811 cathode in Example 1 at a low temperature of -20°C.
[0031] Figure 10 The cycling curve of the graphite anode half-cell prepared by the deep eutectic electrolyte in Example 2 at a high temperature of 70°C.
[0032] Figure 11 The cycling curve of the graphite anode half-cell prepared by the deep eutectic electrolyte in Example 3 at a high temperature of 70°C.
[0033] Figure 12 Cycling curves of the graphite anode half-cell prepared with the deep eutectic electrolyte in Comparative Example 1 at room temperature (30℃).
[0034] Figure 13 Cycling curves of the graphite anode half-cell prepared with the deep eutectic electrolyte in Comparative Example 1 at 70℃.
[0035] Figure 14 The cycling curves of the full cell assembled with deep eutectic electrolyte and NCM811 cathode in Comparative Example 2 are shown at 80°C.
[0036] Figure 15 The cycling curve of the graphite anode half-cell prepared with the electrolyte in Comparative Example 3 at a high temperature of 80℃. Detailed Implementation
[0037] To more clearly illustrate the technical content of the present invention, it is described in detail here with reference to specific embodiments and accompanying drawings. Obviously, the listed embodiments are only preferred embodiments of the present technical solution, and other technical solutions that can be obviously derived by those skilled in the art based on the disclosed technical content still fall within the protection scope of the present invention.
[0038] In this embodiment of the invention, the chemical reagents used can be obtained by purchasing or by preparing them using existing methods, and the instruments and equipment used are conventional equipment in the prior art.
[0039] Example 1
[0040] Preparation of eutectic electrolyte:
[0041] 1) In an argon glove box, weigh 0.9 mL of sulfolane, 0.1 mL of succinate, 0.145 g of LiTFSI (0.5 mmol) and 0.072 g of LiDFOB (0.5 mmol) (LiTFSI to LiDFOB molar ratio 5:5).
[0042] 2) Mix the solvent and lithium salt and stir at 50°C for 1 hour to obtain a colorless and transparent deep eutectic electrolyte (DTS).
[0043] 3) Assemble the CR2032 button cell in the following order: negative electrode shell, negative electrode, deep eutectic electrolyte, glass fiber separator, deep eutectic electrolyte, positive electrode, and positive electrode shell.
[0044] 1) Performance testing:
[0045] At room temperature, at 0.5 mA / cm 2 The current density is 0.5 mAh / cm³. 2 Under the given areal capacity conditions, charge-discharge tests were performed on the lithium symmetric battery. Long-term cycle tests at 0.5 C were conducted on the graphite anode half-cell and the full cell. Cycling tests were performed on the graphite anode half-cell at 0.2 C at 80℃. Cycling tests were performed on the half-cell assembled with the NCM811 cathode at 0.1 C at -20℃.
[0046] pass Figure 1 It can be seen that the redox reaction process of the graphite anode half-cell, as measured by cyclic voltammetry (CV), is stable in the initial three cycles.
[0047] pass Figure 2 It can be seen that the lithium-ion transference number (t) of the DTS deep eutectic electrolyte, calculated by the chronoamperometry method, is... Li+ The value is 0.82.
[0048] pass Figure 3 It is known that the critical current density (CCD) of the lithium symmetric battery assembled using DTS deep eutectic electrolyte is 2.2 mA / cm². 2 .
[0049] pass Figure 4 It can be seen that at 0.5 mA / cm 2 The current density is 0.5 mAh / cm³. 2 Under the given areal capacity conditions, the DTS deep eutectic electrolyte can be stably cycled for more than 600 hours.
[0050] pass Figure 5It can be seen that the graphite anode half-cell can stably cycle 80 times at 0.5C.
[0051] pass Figure 6 It can be seen that the full cell assembled using LCO cathode can stably cycle 200 times at 0.5C with a capacity retention rate of 75%.
[0052] pass Figure 7 It can be seen that the full cell assembled using NCM811 cathode can stably cycle 200 times at 0.5C with a capacity retention rate of 75%.
[0053] pass Figure 8 It can be seen that the graphite anode half-cell can stably cycle for more than 200 cycles at a high temperature of 80℃.
[0054] pass Figure 9 It is known that the half-cell assembled using NCM811 cathode can stably cycle for more than 100 cycles at a low temperature of -20℃.
[0055] Example 2
[0056] The difference from Example 1 is that in step 1), 0.7 mL of sulfolane and 0.3 mL of succinate sulfolane are weighed. Otherwise, the other operating steps and conditions are the same as in Example 1.
[0057] pass Figure 10 It can be seen that graphite anode half-cells become unstable after cycling for more than 120 cycles at a high temperature of 70℃.
[0058] Example 3
[0059] The difference from Example 1 is that in step 1), 0.201g LiTFSI (0.7mmol) and 0.043g LiDFOB (0.3mmol) are weighed (LiTFSI to LiDFOB molar ratio 7:3). Otherwise, the remaining operation steps and conditions are the same as in Example 1.
[0060] pass Figure 11 It can be seen that graphite anode half-cells become unstable after cycling for more than 120 cycles at a high temperature of 70℃.
[0061] Comparative Example 1
[0062] The difference from Example 1 is that sulfolane is selected as the single solvent in step 1). Otherwise, the other operating steps and conditions are the same as in Example 1.
[0063] pass Figure 12 It can be seen that the capacity of graphite anode half-cells decreases significantly when cycled at 30℃.
[0064] pass Figure 13It can be seen that graphite anode half-cells become unstable after cycling for more than 80 cycles at a high temperature of 70℃.
[0065] While sulfolane can coordinate lithium salts, its high viscosity and poor wettability limit the dissociation and migration of ion pairs. Succinate, a plastic crystal at room temperature, can also act as a hydrogen bond acceptor or diluent, effectively reducing the viscosity of mixed solvents, improving the wettability of the separator and electrode, promoting the formation of a low-melting-point eutectic structure, and increasing conductivity. Furthermore, sulfolane is incompatible with graphite anodes, easily co-intercalating and causing anode peeling. Introducing succinate can optimize the composition and structure of the anode interface film and suppress solvent co-intercalation behavior.
[0066] Comparative Example 2
[0067] The difference from Example 1 is that in step 1), a single lithium salt, LiTFSI, is selected. Otherwise, the remaining operation steps and conditions are the same as in Example 1.
[0068] pass Figure 14 It can be seen that the full cell assembled using NCM811 cathode becomes unstable after 100 cycles at 80℃.
[0069] LiTFSI alone causes severe corrosion to aluminum foil at high temperatures, leading to structural collapse and battery failure. It also struggles to form a sufficiently stable interfacial film at the cathode, resulting in numerous side reactions at high temperatures and an unstable SEI film. LiDFOB, with its higher highest occupied molecular orbital (HOMO) energy level, preferentially oxidizes and decomposes, forming a dense CEI film rich in boron / fluoride on the cathode surface. This effectively inhibits corrosion, protects the cathode, suppresses transition metal dissolution, and withstands higher voltages. In contrast, single LiDFOB lithium salts have poor solubility and cannot be completely dissolved.
[0070] Comparative Example 3
[0071] Using a conventional electrolyte (1M LiPF6+EC:EMC=3:7 Vol%), symmetrical cells, graphite anode half-cells, and full cells with the same structure were assembled. At 1 mA / cm²... 2 Current density, 1 mAh / cm 2 Under the given area and capacity conditions, charge-discharge tests were conducted on the lithium symmetric battery. Long-term cycling tests at 0.5C were performed on the graphite anode half-cell, along with constant current charge-discharge cycling tests at rates of 0.1C, 0.2C, 0.5C, 1C, 2C, 5C, and 0.1C. A 0.5C long-term cycling test was also performed on the full cell. Cycling tests were also conducted on the graphite anode half-cell at 0.2C and at a high temperature of 80℃.
[0072] pass Figure 15 It can be seen that the graphite anode half-cell is unstable during cycling at a high temperature of 80℃, and the capacity fluctuation is quite obvious.
[0073] The above description is only a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.
Claims
1. A high-temperature stable deep eutectic electrolyte, characterized in that: Composed of Lewis bases and Lewis acids; The Lewis base is composed of sulfolane and succinic anionylene in a volume percentage ratio of 60-90%:10-40%; The Lewis acid is composed of lithium bis(trifluoromethanesulfonylimide) and lithium difluorooxalateborate in a molar percentage ratio of 40-70%:30-60%.
2. The high-temperature stable deep eutectic electrolyte according to claim 1, characterized in that: The Lewis base is composed of sulfolane and succinic anionylene in a volume percentage ratio of 80-90%:10-20%.
3. The high-temperature stable deep eutectic electrolyte according to claim 1, characterized in that: The Lewis acid is composed of lithium bis(trifluoromethanesulfonylimide) and lithium difluorooxalateborate in a molar percentage ratio of 40-60%:40-60%.
4. A high-temperature stable deep eutectic electrolyte according to any one of claims 1 to 3, characterized in that: The total concentration of Lewis acid in the deep eutectic electrolyte is 0.5~1.5M.
5. The application of the high-temperature stable deep eutectic electrolyte according to any one of claims 1 to 4, characterized in that: Used in lithium-ion batteries.
6. The application of the high-temperature stable deep eutectic electrolyte according to claim 5, characterized in that: The lithium-ion battery comprises a graphite anode and a lithium cobalt oxide cathode or a ternary cathode.