Perfluoro eutectic electrolyte for wide-temperature-range lithium battery and preparation method of perfluoro eutectic electrolyte
By designing a perfluorinated eutectic electrolyte, the problems of flammability, explosiveness, and increased viscosity at low temperatures in lithium-ion batteries have been solved, achieving high-efficiency electrolyte performance over a wide temperature range and improving battery safety and cycle life.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-23
- Publication Date
- 2026-03-27
AI Technical Summary
Traditional liquid ester electrolytes in existing lithium-ion batteries are flammable and explosive, and pose a risk of combustion or explosion under extreme conditions. The electrode/electrolyte interface is unstable, affecting the battery's durability and safety. Eutectic electrolytes have increased viscosity at low temperatures, leading to reduced ion mobility and affecting electrolyte conductivity. Solvent molecules are prone to decomposition and reaction with lithium metal, consuming lithium metal and causing electrochemical interface instability.
The perfluorinated eutectic electrolyte is composed of fluorinated lithium salt, fluorinated mixed solvent and fluorinated ester additive. The mixed solvent includes fluorinated amide and fluorinated nitrile compounds. Through specific molar ratio and additive ratio, a high-voltage resistant and non-flammable electrolyte is formed, which is suitable for wide temperature range lithium batteries.
The perfluorinated eutectic electrolyte remains liquid in a wide temperature range of -50℃ to 100℃, which enhances high-temperature stability, improves compatibility with high-voltage cathodes, inhibits lithium dendrite growth, extends battery cycle life, and improves battery safety and electrochemical performance.
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Figure CN121748545A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a wide-temperature-range perfluorinated eutectic electrolyte for lithium batteries and its preparation method, belonging to the technical field of electrolyte preparation. Background Technology
[0002] With the increasing demand for high-energy-density and high-safety energy storage devices, existing lithium-ion batteries with graphite anodes (theoretical specific energy density of approximately 350 Wh / kg) are no longer sufficient to meet the needs, necessitating the development of next-generation high-energy-density materials. Lithium metal anodes, with their ultra-high theoretical specific capacity (3860 mAh / g) and extremely low redox potential (-3.040 Vvs. SHE), are considered an ideal alternative to graphite anodes. Nickel-rich layered oxide (NCM) cathode materials, when matched with lithium metal anodes, can construct battery systems with ultra-high energy density (approximately 500 Wh / kg). However, achieving large-scale commercial application of high-energy-density lithium metal battery devices still faces challenges. While traditional liquid ester-based electrolytes (such as carbonates) are often used to match lithium metal anodes and high-voltage cathodes (such as NCMs), their high volatility and flammability pose a risk of combustion or explosion under extreme conditions. Furthermore, durability and safety issues caused by electrode / electrolyte interface instability also severely hinder their application in next-generation high-energy-density devices. Therefore, it is crucial to develop novel electrolytes that are non-flammable and stable and compatible with lithium metal and high-voltage cathodes.
[0003] Amide, nitrile, and sulfone eutectic electrolytes have become a research hotspot due to their advantages such as non-flammability, wide electrochemical window, and low cost. Among them, nitrile and sulfone eutectic electrolyte systems have shown potential value in high-voltage battery systems. However, amide-based electrolytes have relatively weak oxidation resistance, making them unsuitable for high-voltage cathode materials and limiting their application in high-voltage battery systems. Furthermore, eutectic electrolytes still need to overcome the following problems: increased viscosity at low temperatures creates a poor kinetic environment, reducing ion mobility and affecting electrolyte conductivity, thus impacting its cycling performance over a wide temperature range; the active groups such as amide and nitrile groups in the solvent molecules are prone to decomposition and continuously react with lithium metal, consuming lithium metal and leading to electrochemical interface instability. These are all issues that cannot be ignored in the preparation of novel eutectic electrolytes. Summary of the Invention
[0004] This invention proposes a perfluorinated eutectic electrolyte suitable for wide-temperature-range lithium batteries, which has the characteristics of high voltage resistance and non-flammability.
[0005] To achieve the above objectives, the present invention adopts the following technical solution:
[0006] A perfluorinated eutectic electrolyte suitable for high-voltage, non-flammable, and wide-temperature-range lithium batteries is disclosed. The electrolyte comprises a fluorinated lithium salt, a fluorinated mixed solvent, and a fluorinated ester additive. The mixed solvent includes fluorinated amides and fluorinated nitriles, with a molar ratio of 10:1 to 1:10. The molar ratio of the fluorinated lithium salt to the fluorinated mixed solvent is 10:1 to 1:10. The fluorinated ester additive accounts for 0.5% to 20% of the total electrolyte mass.
[0007] Preferably, the mixed solvent comprises fluorinated amides and fluorinated nitriles, with a molar ratio of 4:1 to 1:1; the molar ratio of the fluorinated lithium salt to the fluorinated mixed solvent is 1:3 to 1:6; and the fluorinated ester additive accounts for 5% to 10% of the total electrolyte by mass. Electrolytes within this range have a low eutectic temperature of -50°C and a wide liquid phase temperature range; simultaneously, the electrolyte assembly... Stainless steel battery systems have a high voltage resistance of >6V.
[0008] Furthermore, the fluorinated lithium salt is one or more of lithium hexafluorophosphate (LiPF6), lithium hexafluoroarsenate (LiAsF6), lithium tetrafluoroborate (LiBF4), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium difluorooxalateborate (LiODFB), lithium difluorophosphate (LiPO2F2), and lithium difluorosulfonylimide (LiFSI).
[0009] Furthermore, the fluorinated amide compound is one or more of fluoroacetamide, difluoroacetamide, trifluoroacetamide, N-methyltrifluoroacetamide, 2,2,2-trifluoro-N,N-dimethylacetamide, 2-amino-N-(2,2,2-trifluoroethyl)acetamide and their structural derivatives.
[0010] Furthermore, the fluorinated nitrile compound is one or more of 3-(2,2,2-trifluoroethoxy)propionitrile, 2-fluoroadiponitrile, 2,2-difluorosuccinate and their structural derivatives.
[0011] Furthermore, the fluorinated additive is one or more of the following: fluoroethylene carbonate, ethyl difluorocarbonate, ethyl trifluorocarbonate, methyl trifluoropropionate, diethyl fluoromalonate, trifluoroethyl methyl carbonate, methyl 3,3,3-trifluoropropionate, and their structural derivatives.
[0012] A wide-temperature-range perfluoroamide-based eutectic electrolyte for lithium batteries and its preparation method, the preparation method comprising the following steps:
[0013] (1) Fluorine-containing lithium salt and fluorine-containing amide compound are mixed in a certain molar ratio and heated and stirred at a certain temperature until a clear and transparent liquid is obtained. The mixture is then cooled to room temperature to obtain a binary perfluorinated eutectic electrolyte.
[0014] (2) A certain amount of fluorinated nitrile compound was added to the above electrolyte and cooled and allowed to stand to obtain a ternary perfluorinated eutectic electrolyte.
[0015] (3) Add fluorine-containing additives to the ternary perfluorinated eutectic electrolyte obtained in step (2) at a mass ratio of 0.5% to 20%, heat, stir evenly, and let stand and cool to obtain a clear and transparent perfluorinated eutectic electrolyte.
[0016] The electrolyte preparation process is carried out in a glove box filled with argon gas, with a water content of <0.1ppm and an oxygen content of 0.3ppm.
[0017] The mixed solvent comprises a fluoroamide and a fluoronitrile mixed solvent with a molar ratio of 10:1 to 1:10, more preferably 4:1 to 1:1; the fluorinated lithium salt and the fluorinated mixed solvent have a molar ratio of 10:1 to 1:10, more preferably 1:3 to 1:6; and the fluorinated ester additive accounts for 0.5% to 20% of the total electrolyte by mass, more preferably 5% to 10%.
[0018] This electrolyte is suitable for lithium batteries.
[0019] The lithium battery includes a positive electrode, a negative electrode, a separator, and an electrolyte. The positive electrode is one or more of the following ternary materials: lithium cobalt oxide, lithium manganese iron phosphate, lithium manganese oxide, lithium nickel manganese oxide, nickel cobalt manganese oxide, and lithium nickel cobalt manganese oxide. The negative electrode is one or more of the following: lithium metal, graphite, silicon anode, silicon-carbon anode, silicon suboxide, and lithium titanate. The separator is one of the following: polyethylene (PE), polypropylene (PP), PP / PE / PP three-layer composite membrane, GF / A glass fiber separator, GF / F glass fiber separator, and GF / D glass fiber separator.
[0020] The beneficial effects of this invention are as follows:
[0021] Carbonyl groups in traditional amide electrolytes ( Oxygen atoms pair with lithium ions (Li + The strong coordination effect of fluorinated amides limits the wide temperature range performance of the electrolyte, and its antioxidant capacity is weak. However, the perfluorinated eutectic electrolyte system constructed by fluorinated amides and fluorinated nitriles has multiple advantages: (1) The low volatility of fluorinated amides and the low melting point of fluorinated nitriles enable the perfluorinated eutectic electrolyte formed by the two to remain liquid in a wide temperature range of -50℃ to 100℃, which significantly widens the liquid phase temperature window and enhances high temperature stability. (2) The cyano group of fluorinated nitriles ( The strong electron-withdrawing ability, combined with the synergistic effect of fluorine, significantly enhances the system's antioxidant properties and improves its compatibility with high-voltage cathodes; simultaneously, the nitrile and amide groups ( Intermolecular hydrogen bonds formed between () (3) Fluoroamide-containing The group weakens the amide carbonyl oxygen through electron-withdrawing effect. ) and Li + The binding energy allows some anions to enter Li. + The solvation structure reduces free solvent molecules and facilitates the formation of solvation clusters; fluoronitriles, with their high dielectric constant and low viscosity, provide a favorable kinetic environment for lithium ions, and their weak coordination further promotes the formation of Li-ion clusters. + During the rapid desolventizing process at the electrode interface, the two components, after mixing, can synergistically form a solvation sheath with low binding energy, allowing more anions to enter the solvation sheath. This is beneficial for the formation of LiF-containing compounds on the electrode surface. An interface layer with stable components. On the negative electrode side, fluorinated amide compounds preferentially reduce and decompose to form a high-modulus layer. It can effectively suppress volume expansion and dendrite growth, achieving uniform lithium ion deposition; on the positive electrode side, the cyano group in the fluorinated nitrile compound ( These compounds can form coordination bonds with transition metal ions (such as cobalt and nickel) in the cathode material, reducing the dissolution of transition metal ions. Simultaneously, their preferential oxidation and decomposition on the cathode side can form a dense and uniform solid electrolyte film, effectively blocking the dissolution of transition metals. The synergistic effect of fluoronitriles and fluoroamides can effectively improve battery cycle life. Attached Figure Description
[0022] Figure 1 Linear cyclic voltammetry (LSV) tests were conducted on the perfluorinated eutectic electrolytes prepared in the comparative examples and embodiments of this invention.
[0023] Figure 2 The images are optical images of Example 1 of the present invention after being left to stand for 12 hours at 25°C and -20°C, respectively, and optical images of Comparative Example 3 after being left to stand for 12 hours at 25°C, -20°C, and -50°C, respectively.
[0024] Figure 3 These are optical images of Embodiments 2 and 5 of the present invention, taken after being left to stand for 12 hours at 25°C and -50°C, respectively.
[0025] Figure 4 The bar chart shows the statistical performance and coulombic efficiency of the perfluorinated eutectic electrolytes prepared in the comparative examples and embodiments of this invention when applied to high-voltage lithium metal batteries.
[0026] Figure 5 The graph shows the rate cycling performance of the perfluorinated eutectic electrolyte prepared in Example 5 of this invention applied to a high-voltage lithium metal battery.
[0027] Figure 6The graph shows the cycle performance of the perfluorinated eutectic electrolytes prepared in Comparative Examples 2, 3, and 5 of this invention when applied to high-voltage lithium metal batteries. Detailed Implementation
[0028] The specific embodiments of the present invention are described in detail through the following examples, but the scope of protection is not limited thereto:
[0029] Comparative Example 1 (using a binary eutectic electrolyte as a comparative example and a ternary eutectic electrolyte as an example)
[0030] LiTFSI and acetamide were mixed in a molar ratio of 1:3 and placed in a sample vial. The mixture was stirred at 60°C until clear and transparent, and then cooled to room temperature to obtain a binary eutectic electrolyte. This electrolyte was used in a full cell with lithium metal as the negative electrode and NMC523 as the positive electrode, and tested at a charge / discharge rate of 0.5C within a voltage range of 3-4.5V.
[0031] Comparative Example 2
[0032] LiTFSI and acetamide were mixed in a molar ratio of 1:3 and placed in a sample vial. The mixture was stirred at 60°C until clear and transparent, and then cooled to room temperature to obtain a binary eutectic electrolyte. 5% (w / w) of fluoroethylene carbonate was added to the obtained binary eutectic electrolyte, and the mixture was allowed to stand at room temperature for 5 minutes. The electrolyte was then used in a full cell with lithium metal as the negative electrode and NMC523 as the positive electrode, and tested at a charge / discharge rate of 0.5C within a voltage range of 3-4.5V.
[0033] Comparative Example 3
[0034] Step 1: Mix LiTFSI and difluoroacetamide in a molar ratio of 1:3 in a sample vial and stir at 60°C until clear and transparent. Cool to room temperature to obtain a perfluorinated binary eutectic electrolyte. Add 5% (w / w) of fluoroethylene carbonate to the obtained binary perfluorinated eutectic electrolyte, mix, and let stand at room temperature for 5 minutes. Use this solution in a full cell with lithium metal as the negative electrode and NMC523 as the positive electrode, and test the charge / discharge rate at 0.5C within a voltage range of 3-4.5V.
[0035] Example 1
[0036] LiTFSI, acetamide, and succinate were mixed in a molar ratio of 1:3:1 and placed in a sample vial. The mixture was stirred at 60°C until clear and transparent, and then cooled to room temperature to obtain a ternary eutectic electrolyte. 5% (w / w) of fluoroethylene carbonate was added to the obtained ternary eutectic electrolyte, and the mixture was allowed to stand at room temperature for 5 minutes. The electrolyte was then used in a full cell with lithium metal as the negative electrode and NMC523 as the positive electrode, and tested at a charge / discharge rate of 0.5C within a voltage range of 3-4.5V.
[0037] Example 2
[0038] LiTFSI, difluoroacetamide, and 2,2-difluorosuccinate were mixed in a molar ratio of 1:3:1 and placed in a sample vial. The mixture was stirred at 60°C until clear and transparent, and then cooled to room temperature to obtain a perfluorinated ternary eutectic electrolyte. 5% (w / w) of fluoroethylene carbonate was added to the obtained perfluorinated ternary eutectic electrolyte, and the mixture was allowed to stand at room temperature for 5 minutes. The electrolyte was then used in a full cell with lithium metal as the negative electrode and NMC523 as the positive electrode, and tested at a charge / discharge rate of 0.5C within a voltage range of 3-4.5V.
[0039] Example 3
[0040] LiTFSI, difluoroacetamide, and 2,2-difluorosuccinate were mixed in a molar ratio of 1:3:1 and placed in a sample vial. The mixture was stirred at 60°C until clear and transparent, and then cooled to room temperature to obtain a perfluorinated ternary eutectic electrolyte. 10% (w / w) of fluoroethylene carbonate was added to the obtained perfluorinated ternary eutectic electrolyte, and the mixture was allowed to stand at room temperature for 5 minutes. The electrolyte was then used in a full cell with lithium metal as the negative electrode and NMC523 as the positive electrode, and tested at a charge / discharge rate of 0.5C within a voltage range of 3-4.5V.
[0041] Example 4
[0042] LiTFSI, difluoroacetamide, and 2,2-difluorosuccinate were mixed in a molar ratio of 1:3:1 and placed in a sample vial. The mixture was stirred at 60°C until clear and transparent, and then cooled to room temperature to obtain a perfluorinated ternary eutectic electrolyte. 5% (w / w) of diethyl fluoromalonate was added to the obtained perfluorinated ternary eutectic electrolyte, and the mixture was allowed to stand at room temperature for 5 minutes. The electrolyte was then used in a full cell with lithium metal as the negative electrode and NMC523 as the positive electrode, and tested at a charge / discharge rate of 0.5C within a voltage range of 3-4.5V.
[0043] Example 5
[0044] LiTFSI, difluoroacetamide, and 2,2-difluorosuccinate were mixed in a molar ratio of 1:3:3 and placed in a sample vial. The mixture was stirred at 60°C until clear and transparent, and then cooled to room temperature to obtain a perfluorinated ternary eutectic electrolyte. 5% (w / w) of fluoroethylene carbonate was added to the obtained perfluorinated ternary eutectic electrolyte, and the mixture was allowed to stand at room temperature for 5 minutes. The electrolyte was then used in a full cell with lithium metal as the negative electrode and NMC523 as the positive electrode, and tested at a charge / discharge rate of 0.5C within a voltage range of 3-4.5V.
[0045] Example 6
[0046] LiTFSI, difluoroacetamide, and 2,2-difluorosuccinate were mixed in a molar ratio of 1:4:1 and placed in a sample vial. The mixture was stirred at 60°C until clear and transparent, and then cooled to room temperature to obtain a perfluorinated ternary eutectic electrolyte. 5% (w / w) of fluoroethylene carbonate was added to the obtained perfluorinated ternary eutectic electrolyte, and the mixture was allowed to stand at room temperature for 5 min. The electrolyte was then used in a full cell with lithium metal as the negative electrode and NMC523 as the positive electrode, and tested at a charge / discharge rate of 0.5C within a voltage range of 3-4.5V.
[0047] Example 7
[0048] LiTFSI, 2-amino-N-(2,2,2-trifluoroethyl)acetamide, and 2-fluoroadiponitrile were mixed in a molar ratio of 1:3:1 and placed in a sample vial. The mixture was stirred at 60°C until clear and transparent, and then cooled to room temperature to obtain a perfluorinated ternary eutectic electrolyte. 5% (w / w) of fluoroethylene carbonate was added to the obtained perfluorinated ternary eutectic electrolyte, and the mixture was allowed to stand at room temperature for 5 min. The electrolyte was then used in a full cell with lithium metal as the negative electrode and NMC523 as the positive electrode, and the charge / discharge rate was tested at 0.5C within a voltage range of 3-4.5V.
[0049] A nickel-cobalt-manganese ternary cathode material (NCM523), commercially available Super P conductive carbon, and a binder (PVDF) were dispersed in N-methylpyrrolidone (NMP) at a mass ratio of 8:1:1 to form a slurry. This slurry was then uniformly coated onto copper foil and vacuum-dried at 60 °C for 12 h. The resulting slurry was then cut into 14 mm diameter discs to serve as the cathode. A Li / NCM battery was assembled using a 16 mm lithium sheet as the anode, Celgard 2325 as the separator, and NCM as the cathode. The electrolyte used was the same as that prepared in Comparative Examples 1-3 and Examples 1-7. CR2016 coin cells were assembled in a glove box filled with high-purity argon. The Li / NCM batteries were charged and discharged at different temperatures and a 0.5 C rate.
[0050] from Figure 1 It can be seen that, compared with Comparative Examples 2 and 3, the oxidation stability of the battery systems in Examples 2 and 5 is significantly improved. In particular, the ternary perfluorinated eutectic electrolyte assembled in Example 5, which is a mixture of LiTFSI, difluoroacetamide, and 2,2-difluorosuccinate in a molar ratio of 1:3:3 and with the addition of 5% fluoroethylene carbonate, is significantly improved. The stainless steel battery system exhibits a high voltage resistance of >6V. Furthermore, the improvement in the high voltage resistance of the electrolyte system is positively correlated with the addition content of fluorinated nitrile compounds. This is mainly because, in the examples, nitrile groups ( The fluorine group has a low electron cloud density, which can suppress nucleophilic attack to some extent. Simultaneously, the fluorine-containing group can raise the HOMO energy level of the molecule, thus effectively improving the antioxidant stability of amide compounds. Furthermore, the nitrile group (… ) and amide group ( Intermolecular hydrogen bonds formed between ) This will enhance electron delocalization and further stabilize the HOMO orbital, effectively compensating for the shortcomings of amide groups in withstanding high voltage.
[0051] from Figure 2 It can be seen that the non-fluorinated ternary eutectic electrolyte in Example 1, consisting of LiTFSI, acetamide, and succinate in a molar ratio of 1:3:1, exhibits significant solid-phase precipitation and becomes viscous at -20°C. In contrast, the perfluorinated binary eutectic electrolyte in Comparative Example 3 maintains a good liquid state at -50°C, but suffers from excessively high overall viscosity. Furthermore, amide systems themselves exhibit poor high-voltage resistance. To balance low-temperature performance and oxidation stability, fluorinated nitrile compounds, such as... Figure 3 As shown, in Example 2, the components were fully fluorinated and fluoroethylene carbonate was added, allowing the electrolyte to remain in the liquid phase at -20°C, but it still solidified at -50°C. This indicates that simply performing perfluorination without properly adjusting the component ratio is insufficient to achieve a sufficiently low eutectic temperature. In Example 5, a ternary perfluorinated eutectic electrolyte was prepared by mixing LiTFSI, difluoroacetamide, and 2,2-difluorosuccinate in a molar ratio of 1:3:3, with the addition of 5% fluoroethylene carbonate. This further increased the molar ratio of fluoronitrile compounds in the fluorinated system, successfully preparing a perfluorinated ternary eutectic electrolyte with a low eutectic temperature of -50°C and a wide liquid phase temperature range. Furthermore, the ternary perfluorinated eutectic electrolyte exhibited suitable viscosity across the entire temperature range.
[0052] Figure 4 The perfluorinated eutectic electrolytes prepared in the comparative examples and embodiments of this invention are assembled... The full-cell system is presented in a statistical histogram showing the cycle performance and coulombic efficiency within a voltage range of 3-4.5V. To better analyze the histogram, the following table provides a brief explanation of the results. The symbols and data in the table have the following meanings:
[0053] Cycle life (the number of cycles required for capacity to drop to 80%) is denoted as Cycles@80%.
[0054] Coulombic efficiency at 80% capacity retention is denoted as CE@80%.
[0055] Lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), acetamide (AC), succinate (SN), difluoroacetamide (dFAC), 2,2-difluorosuccinate (DFSN), diethyl fluoromalonate (DEM-2F), 2-amino-N-(2,2,2-trifluoroethyl)acetamide (TFEAE)
[0056]
[0057] As shown in the bar chart and table, the binary eutectic electrolyte system composed of lithium salt, acetamide, and fluoroamide exhibits poor cycle performance, failing after less than 100 cycles. Adding a certain molar ratio of fluoroamide compounds to the binary eutectic electrolyte significantly improves the cycle stability of the resulting ternary perfluorinated eutectic electrolyte. In Example 2, the ternary perfluorinated eutectic electrolyte prepared by mixing LiTFSI, difluoroacetamide, and 2,2-difluorosuccinate in a molar ratio of 1:3:1, with the addition of 5% fluoroethylene carbonate, maintained 80% capacity retention and 99% coulombic efficiency after 500 cycles at a charge-discharge rate of 0.5C. In Example 5, a ternary perfluorinated eutectic electrolyte was prepared by mixing LiTFSI, difluoroacetamide, and 2,2-difluorosuccinate in a molar ratio of 1:3:3 and adding 5% fluoroethylene carbonate. After 600 cycles at a charge-discharge rate of 0.5C, the electrolyte retained 80% of its capacity and had a coulombic efficiency of 99.2%.
[0058] from Figure 5 , Figure 6 It can be seen that the ternary perfluorinated eutectic electrolyte assembled in Example 5, which is a mixture of LiTFSI, difluoroacetamide, and 2,2-difluorosuccinate in a molar ratio of 1:3:3 and with the addition of 5% fluoroethylene carbonate, is effective. The proposed full-cell system exhibits high reversible specific capacity and minimal capacity decay at rates of 0.2C, 0.5C, 1.0C, and 2.0C within a voltage range of 3-4.5V. When the current density recovers to 0.5C, there is almost no capacity loss. At a charge-discharge rate of 0.5C, after 600 cycles, the capacity retention is 80%, and the coulombic efficiency is 99.2%.
[0059] The mechanism that produces this effect is mainly:
[0060] (1) Constructing a good solvation structure: containing strong electron-withdrawing properties Amide compounds with a group can effectively weaken the amide group. The originally excessively strong coordination interactions between them. This weakening effect can break the original tight solvation shell, allowing for the formation of anionic (e.g., ...) bonds. (etc.) provides access to Li +The opportunity for solvation of the sheath arises, forming an anion-involved solvation structure. Simultaneously, the coordination of nitrile compounds with lithium ions can enable Li... + With their low solvation energy, fluoronitriles further weaken this coordination, placing lithium ions in a more loose solvation environment. Simultaneously, the cyano group of fluoronitriles... The strong electron-withdrawing ability, combined with fluorine, synergistically enhances antioxidant properties; nitrile groups ( ) and amide group ( Intermolecular hydrogen bonds formed between ) This will enhance electron delocalization and further stabilize HOMO orbitals, effectively improving compatibility with high-voltage cathode materials.
[0061] Optimize the electrode / electrolyte interface: Groups and The groups themselves have poor compatibility with highly active lithium metal anodes. They easily initiate continuous and uncontrollable side reactions on the anode surface. These malignant side reactions continuously consume active lithium and electrolyte, hindering the formation of a uniform, dense, and protective solid electrolyte membrane (SEI). Such inferior or incomplete SEI films cannot effectively suppress the uncontrollable growth of lithium dendrites, leading to the generation of a large number of "dead lithium" deposits, severely impairing the battery's cycle life and safety. Conversely, carrying... Amide and nitrile compounds with functional groups (i.e., fluoroamides and fluoronitriles) exhibit an optimizing effect on interfacial behavior. The groups help to construct a dense, stable, and ionicly conductive solid electrolyte membrane. This optimized SEI membrane can effectively act as a physical and chemical barrier, significantly inhibiting the continuous decomposition of subsequent electrolytes, the piercing growth of lithium dendrites, and the formation of a large number of dead lithium, thereby improving the interfacial stability and long-cycle performance of the battery.
[0062] The basic principles, main features and advantages of this invention have been explained. The described embodiments are only for illustrating the principles of the invention and not for limiting the scope of protection. Those skilled in the art can make several modifications or improvements to the technical solutions (including but not limited to component substitution, parameter adjustment or application extension) without departing from the concept of this invention. All such modifications and variations are within the scope of protection defined by the claims and their equivalents.
Claims
1. A perfluorinated eutectic electrolyte suitable for high-voltage, non-flammable, and wide-temperature-range lithium batteries, comprising a fluorinated lithium salt, a fluorinated mixed solvent, and a fluorinated ester additive; wherein, The molar ratio of the fluorinated lithium salt to the fluorinated mixed solvent is 10:1 to 1:10, and the fluorinated ester additive accounts for 0.5% to 20% of the total electrolyte by mass. The mixed solvent includes fluorinated amides and fluorinated nitrile compounds, with a molar ratio of 10:1 to 1:
10.
2. The electrolyte according to claim 1, characterized in that: The fluorinated lithium salt is one or more of lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium tetrafluoroborate, lithium bis(trifluoromethanesulfonyl)imide, lithium difluorooxalateborate, lithium difluorophosphate, and lithium difluorosulfonylimide.
3. The electrolyte according to claim 1, characterized in that: The fluorinated amide compound is one or more of fluoroacetamide, difluoroacetamide, trifluoroacetamide, N-methyltrifluoroacetamide, 2,2,2-trifluoro-N,N-dimethylacetamide, and 2-amino-N-(2,2,2-trifluoroethyl)acetamide.
4. The electrolyte according to claim 1, characterized in that: The fluoronitrile compound is 3-(2,2,2-trifluoroethoxy)propionitrile and / or 2-fluoroadiponitrile and 2,2-difluorosuccinate.
5. The electrolyte according to claim 1, characterized in that: The fluorinated additive is one or more of the following: fluoroethylene carbonate, ethyl difluorocarbonate, ethyl trifluorocarbonate, methyl trifluoropropionate, diethyl fluoromalonate, trifluoroethyl methyl carbonate, and methyl 3,3,3-trifluoropropionate.
6. The method for preparing the electrolyte according to any one of claims 1-5, characterized in that, The preparation method includes the following steps: (1) Mix fluorinated lithium salt and fluorinated amide compound in a certain proportion, heat and stir until a clear and transparent liquid is obtained, and cool to room temperature to obtain a binary perfluorinated eutectic electrolyte; (2) A fluorinated nitrile compound was added to the binary perfluorinated eutectic electrolyte, and the mixture was cooled and allowed to stand to obtain a ternary perfluorinated eutectic electrolyte; (3) Add fluorine-containing additives to the ternary perfluorinated eutectic electrolyte at a mass ratio of 0.5% to 20%, heat, stir evenly, and let stand and cool to obtain a clear and transparent perfluorinated eutectic electrolyte.
7. The preparation method according to claim 6, characterized in that, The electrolyte preparation process is carried out in a glove box filled with argon gas, with a water content of <0.1ppm and an oxygen content of 0.3ppm.
8. The application of the electrolyte according to any one of claims 1-5, characterized in that: This electrolyte is suitable for lithium batteries.
9. The application according to claim 8, characterized in that: The lithium battery includes a positive electrode, a negative electrode, a separator, and an electrolyte.
10. The application according to claim 9, characterized in that: The positive electrode is made of one or more of the following ternary materials: lithium cobalt oxide, lithium manganese iron phosphate, lithium manganese oxide, lithium nickel manganese oxide, nickel cobalt manganese oxide, and lithium nickel cobalt manganese oxide. The negative electrode is one or more of lithium metal, graphite, silicon negative electrode, silicon-carbon negative electrode, silicon suboxide and lithium titanate; The diaphragm is one of the following: polyethylene film, polypropylene film, PP / PE / PP three-layer composite film, GF / A glass fiber diaphragm, GF / F glass fiber diaphragm, and GF / D glass fiber diaphragm.