A high-voltage lithium metal battery electrolyte based on synergistic effect of multi-fluorinated solvents

Abstract

The application provides a high-voltage lithium metal battery electrolyte based on synergistic effect of multi-fluorinated solvents, and relates to the field of electrolytes. The raw materials of the high-voltage lithium metal battery electrolyte based on synergistic effect of multi-fluorinated solvents include lithium salt, cyclic fluorinated carbonate, linear fluorinated carboxylic acid ester and fluorine-containing aromatic hydrocarbon. In the high-performance electrolyte, the molar content of the fluorine-containing aromatic hydrocarbon is 5-20%; the molar ratio of the cyclic fluorinated carbonate, the linear fluorinated carboxylic acid ester and the fluorine-containing aromatic hydrocarbon is 0.3-0.6:0.3-0.6:0.05-0.3. Through the rigidity film forming of the cyclic fluorinated carbonate, the flexibility viscosity reduction of the linear fluorinated carboxylic acid ester and the interface wetting and shielding of the fluorine-containing aromatic hydrocarbon, the perfluorinated electrolyte system with high-voltage stability, excellent kinetics and long cycle life is successfully constructed.

Description

Technical Field

[0001] This application relates to the field of electrolytes, and more particularly to a high-voltage lithium metal battery electrolyte based on the synergistic effect of polyfluorinated solvents. Background Technology

[0002] With the urgent demand for extended battery life from new energy vehicles and portable electronic devices, lithium batteries are rapidly evolving towards higher energy density and higher operating voltage. In particular, battery systems using high-nickel ternary materials (such as NCM811) as the positive electrode and metallic lithium as the negative electrode have attracted significant attention due to their extremely high theoretical specific capacity. However, existing commercial carbonate electrolyte systems (mainly composed of EC, DMC, EMC, etc.) exhibit poor oxidation stability under high voltage (≥4.5V) conditions, easily decomposing and generating gas, leading to increased battery impedance and rapid capacity decay. Simultaneously, these non-fluorinated solvents struggle to form a dense and stable solid electrolyte interphase (SEI) film on the metallic lithium surface, failing to effectively suppress lithium dendrite growth and posing serious safety hazards.

[0003] To improve interfacial stability, fluoroethylene carbonate (FEC) is often introduced into electrolytes as a film-forming additive or co-solvent. Although FEC possesses excellent anti-reduction properties and can induce the formation of an inorganic interfacial layer rich in lithium fluoride (LiF), its high viscosity and high melting point limit its large-scale application. High FEC content leads to a significant decrease in the electrolyte's ionic conductivity, and its large surface tension reduces the wettability of the electrolyte to the polypropylene separator and thick electrodes, severely restricting the battery's rate charge / discharge performance and low-temperature operation capability.

[0004] To address viscosity issues, existing technologies typically employ a locally high-concentration electrolyte (LHCE) strategy, which involves introducing hydrofluoroethers (such as TTE) as diluents. However, hydrofluoroether diluents are generally "inert," meaning they do not dissolve lithium salts and hardly participate in the construction of the solvation shell. This leads to microscopic and even macroscopic phase separation within the electrolyte, causing localized polarization of lithium salt concentration. Furthermore, inert diluents cannot effectively participate in the interfacial film formation reaction, making it difficult to provide additional chemical protection for the high-voltage cathode or active anode.

[0005] Therefore, there is an urgent need to develop a perfluorinated electrolyte system that can eliminate traditional inert diluents and simultaneously achieve low viscosity, high wettability, and high-pressure film-forming stability of all components. Summary of the Invention

[0006] The purpose of this application is to provide a high-voltage lithium metal battery electrolyte based on the synergistic effect of polyfluorinated solvents, so as to solve the common problems in existing high-voltage electrolyte systems, such as the high viscosity of film-forming agents leading to limited fast-charging performance, and the poor compatibility between inert diluents and lithium salts and their non-participation in film formation in traditional local high-concentration electrolytes.

[0007] To achieve the above objectives, the first aspect of this application provides a high-voltage lithium metal battery electrolyte based on the synergistic effect of polyfluorinated solvents, the raw materials of which include lithium salts, cyclic fluorinated carbonates, linear fluorinated carboxylic esters and fluorinated aromatic hydrocarbons. In high-performance electrolytes, the molar percentage of the fluorinated aromatic hydrocarbons is 5%-20%; The molar ratio of the cyclic fluorocarbonate, the linear fluorocarboxylic acid ester, and the fluorinated aromatic hydrocarbon is 0.3-0.6:0.3-0.6:0.05-0.3.

[0008] Optionally, the molar ratio of the cyclic fluorocarbonate to the linear fluorocarboxylic acid ester is 1-3:1-3.

[0009] Optionally, the molar ratio of the cyclic fluorocarbonate, the linear fluorocarboxylic acid ester, and the fluorinated aromatic hydrocarbon is 0.42:0.42:0.16.

[0010] Optionally, in the high-performance electrolyte, the molar concentration of the lithium salt is 0.5-2.0 M.

[0011] Optionally, the lithium salt includes at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium hexafluorophosphate, lithium tetrafluoroborate, and lithium difluorooxalate borate.

[0012] Optionally, the lithium salt comprises lithium bis(trifluoromethanesulfonyl)imide and / or lithium bis(fluorosulfonyl)imide.

[0013] Optionally, the cyclic fluorocarbonate includes at least one of fluoroethylene carbonate, difluoroethylene carbonate, and trifluoromethylethylene carbonate.

[0014] Optionally, the linear fluorocarboxylic acid ester includes at least one of methyl difluoroacetate, ethyl difluoroacetate, methyl trifluoroacetate, and methyl 2,2-difluoropropionate.

[0015] Optionally, the fluorinated aromatic hydrocarbon includes at least one of 1,3,5-trifluorobenzene, hexafluorobenzene, tetrafluorobenzene, and difluorobenzene.

[0016] Compared with the prior art, the beneficial effects of this application include: The high-voltage lithium metal battery electrolyte provided in this application, based on the synergistic effect of polyfluorinated solvents, retains cyclic fluorocarbonate as the main solvent in the construction of the film-forming framework. Utilizing its high dielectric constant and unique cyclic stress structure, FEC preferentially undergoes a ring-opening reaction at the negative electrode interface, constructing an inorganic rigid interface layer rich in lithium fluoride (LiF), thereby effectively suppressing lithium dendrite growth. However, given that the high viscosity and high melting point of FEC itself limit the lithium-ion transport kinetics, this application does not use conventional non-fluorinated linear esters (poor antioxidant properties) or hydrofluoroethers (poor compatibility) for dilution. Instead, it introduces linear fluorocarboxylic acid esters as a key regulating component. The linear fluorocarboxylic acid ester molecules have extremely low viscosity and small steric hindrance, effectively dispersing the strong dipole interactions between FEC molecules, significantly reducing the overall viscosity of the system and improving ionic conductivity. Simultaneously, as a fluorinated carboxylic acid ester, the linear fluorocarboxylic acid ester has good lithium salt solubility, avoiding the risk of local salt precipitation, and can also serve as an active fluorine source. The application modifies and reinforces the interface of the electrolyte. Furthermore, addressing the issues of high surface tension and difficulty in wetting polypropylene microporous membranes and thick electrodes in perfluorinated systems, as well as the requirement for cathode stability at high voltages above 4.3V, this application introduces fluorinated aromatic hydrocarbons with a planar rigid structure as functional additives. These aromatic hydrocarbons, utilizing their unique low surface tension and excellent lipophilicity, significantly reduce the contact angle between the electrolyte and the membrane, accelerating the physical wetting process of the electrolyte inside the battery, thereby greatly improving the battery's rate charge / discharge performance. In addition, utilizing the high chemical stability and spatial shielding effect of fluorinated aromatic rings, fluorinated aromatic hydrocarbons can preferentially adsorb onto the surface of the high-energy cathode, forming a physical isolation layer that blocks direct contact between the active solvent and the high-valence cathode material. In summary, this application successfully constructs a perfluorinated electrolyte system that balances high-voltage stability, excellent kinetics, and long cycle life through the synergistic effect of rigid film formation by cyclic fluorinated carbonates, flexible viscosity reduction by linear fluorinated carboxylic esters, and interfacial wetting and shielding by fluorinated aromatic hydrocarbons. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation on the scope of this application.

[0018] Figure 1 The Tafel polarization curves and exchange current densities of Example 1, Comparative Example 1, and Comparative Example 2 are shown in the comparison graph. Figure 2 The images show contact angle test results on the polypropylene diaphragm surface for Examples 1, 1, and 2. Figure 3The graph shows a comparison of the discharge specific capacity of the batteries assembled in Example 1, Comparative Example 1, and Comparative Example 2 at different discharge rates from 0.2C to 5C. Figure 4 Comparison of SEM microstructures of lithium metal deposited on copper foil surfaces in Example 1, Comparative Example 1, and Comparative Example 2; Figure 5 The graph shows a comparison of LSV stability tests at different temperatures for Example 1 and Comparative Example 2. Detailed Implementation

[0019] First, the solution provided in this application will be explained in more detail as follows: This application provides a high-voltage lithium metal battery electrolyte based on the synergistic effect of polyfluorinated solvents, the raw materials of which include lithium salt, cyclic fluorinated carbonate, linear fluorinated carboxylic acid ester and fluorinated aromatic hydrocarbon; In high-performance electrolytes, the molar percentage of the fluorinated aromatic hydrocarbons is 5%-20%; Optionally, in the high-performance electrolyte, the molar percentage of fluorinated aromatic hydrocarbons can be any value between 5%, 10%, 15%, 20%, or 5-20%. It should be noted that this ratio is sufficient to improve wettability and provide high-pressure protection, without affecting the solubility of lithium salts due to excessive non-polar components. The molar ratio of the cyclic fluorocarbonate, the linear fluorocarboxylic acid ester, and the fluorinated aromatic hydrocarbon is 0.3-0.6:0.3-0.6:0.05-0.3.

[0020] Optionally, the molar ratio of cyclic fluorocarbonate, linear fluorocarboxylic acid ester and fluorinated aromatic hydrocarbon can be any value between (0.3:0.3:0.05), (0.4:0.3:0.05), (0.5:0.3:0.05), (0.6:0.3:0.05), (0.3:0.5:0.05), (0.3:0.6:0.05), (0.3:0.3:0.1), (0.3:0.3:0.2), (0.3:0.3:0.3) or 0.3-0.6:0.3-0.6:0.05-0.3.

[0021] It should be noted that this application abandons the traditional physical mixing strategy based on "good solvent + inert diluent" and instead adopts a homogeneous control strategy based on "complementary fluorinated solvents with different spatial configurations". The aim is to achieve a comprehensive improvement in macroscopic electrochemical performance by differentiating the viscosity, dielectric constant and surface tension of each component.

[0022] The mechanism of action is as follows: Rigid film formation mechanism: Cyclic fluorocarbonate is used as the main film-forming agent. It utilizes its high ring strain and preferential reduction characteristics to construct a rigid solid electrolyte interphase (SEI) rich in inorganic lithium fluoride (LiF) in situ on the negative electrode surface. This interphase film has a high mechanical modulus and can effectively physically block the longitudinal piercing growth of lithium dendrites.

[0023] Flexible viscosity reduction and acceleration mechanism: Linear fluorocarboxylic acid esters act as kinetic modifiers, utilizing their low-steric-resistance linear structure to interweave within the solvent network, disrupting dipole interactions to reduce system viscosity. Simultaneously, the weak solvation effect of the linear fluorocarboxylic acid esters on lithium ions effectively lowers the desolvation energy barrier, thereby significantly enhancing the interfacial charge transfer rate and meeting the requirements of fast charging.

[0024] Interfacial wetting and high-voltage shielding mechanism: Fluorinated aromatic hydrocarbons, with their planar rigid structure and lipophilicity, significantly reduce the surface tension of perfluorinated electrolytes, improving the physical wetting of the microporous membrane. Furthermore, fluorinated aromatic hydrocarbons preferentially adsorb onto the surface of the high-voltage cathode through π-electron interactions, forming an antioxidant physical shielding layer that blocks the decomposition of the active solvent, ensuring high-voltage stability.

[0025] In some embodiments, the molar ratio of the cyclic fluorocarbonate to the linear fluorocarboxylic acid ester is 1-3:1-3.

[0026] Optionally, the molar ratio of cyclic fluorocarbonate to linear fluorocarboxylic acid ester can be any value between 1:1, 1:2, 1:3, 2:1, 3:1, or 1-3:1-3.

[0027] It is important to note that within this range, cyclic fluorocarbonates provide sufficient film-forming sources, while linear fluorocarboxylic acids provide sufficient fluidity, achieving an optimal viscosity / film-forming balance.

[0028] In some embodiments, the molar ratio of the cyclic fluorocarbonate, the linear fluorocarboxylic acid ester, and the fluorinated aromatic hydrocarbon is 0.42:0.42:0.16.

[0029] In some embodiments, the molar concentration of the lithium salt in the high-performance electrolyte is 0.5-2.0 M.

[0030] Optionally, in the high-performance electrolyte, the molar concentration of the lithium salt can be any value between 0.5M, 1M, 1.5M, 2M, or 0.5-2M.

[0031] In some embodiments, the lithium salt includes at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium hexafluorophosphate, lithium tetrafluoroborate, and lithium difluorooxalate borate.

[0032] Preferably, the lithium salt comprises lithium bis(trifluoromethanesulfonyl)imide and / or lithium bis(fluorosulfonyl)imide, which effectively improves the low dielectric constant characteristics and antioxidant requirements.

[0033] In some embodiments, the cyclic fluorocarbonate includes at least one of fluoroethylene carbonate, difluoroethylene carbonate, and trifluoromethylethylene carbonate.

[0034] Preferably, the cyclic fluorocarbonate includes fluoroethylene carbonate.

[0035] It is important to note that, compared to ethylene difluorocarbonate or ethylene trifluoromethyl carbonate, fluoroethylene carbonate (FEC) achieves the optimal balance between film formation potential and film quality. FEC possesses a suitable ring strain and preferential reduction potential, enabling it to initiate the ring-opening reaction on the surface of the lithium metal anode, thus constructing a dense and inorganic LiF-rich rigid SEI film in situ, effectively suppressing lithium dendrite growth. Excessive fluorination (such as with ethylene difluorocarbonate) can lead to overly vigorous reduction reactions, increased side reactions, and increased gas production; while the introduction of trifluoromethyl groups significantly increases steric hindrance, causing the already high viscosity of the system to spike further, severely hindering lithium-ion transport kinetics.

[0036] In some embodiments, the linear fluorocarboxylic acid ester includes at least one of methyl difluoroacetate, ethyl difluoroacetate, methyl trifluoroacetate, and methyl 2,2-difluoropropionate.

[0037] Preferably, the linear fluorocarboxylic acid ester includes methyl difluoroacetate.

[0038] It is important to note that compared to other linear esters such as ethyl difluoroacetate or methyl trifluoroacetate, methyl difluoroacetate (MDFA) possesses minimal steric hindrance and optimal solvation regulation. The extremely small size of the methyl ester groups in MDFA allows for most efficient insertion into the FEC molecular network, disrupting strong dipole interactions and thus minimizing the system's macroscopic viscosity. Simultaneously, moderate difluoro substitution preserves good solubility for lithium salts while also improving the solubility of Li. + This creates a well-balanced weak solvation effect, significantly reducing the desolvation energy barrier during fast charging. If perfluorinated or derivatives containing more fluorine atoms (such as methyl trifluoroacetate) are used, their excessively strong electron-withdrawing effect will drastically reduce the solubility of lithium salts, increasing the risk of localized salt precipitation.

[0039] In some embodiments, the fluorinated aromatic hydrocarbon includes at least one of 1,3,5-trifluorobenzene, hexafluorobenzene, tetrafluorobenzene, and difluorobenzene.

[0040] Preferably, the fluoroaromatic hydrocarbon includes 1,3,5-trifluorobenzene.

[0041] It is important to note that compared to hexafluorobenzene, tetrafluorobenzene, or difluorobenzene, 1,3,5-trifluorobenzene (TFB) possesses a highly symmetrical planar rigid structure and an optimal degree of fluorination. This meta-symmetric structure endows it with exceptionally good lipophilicity and extremely low surface tension, maximizing the improvement of the physical wetting problem of perfluorinated systems on polypropylene (PP) microporous membranes and thick electrodes. Simultaneously, the three 1,3,5-alternating fluorine atoms ensure sufficient high-voltage oxidation resistance (forming a π-electron shielding layer to protect the positive electrode) while avoiding the problems of increased melting point and decreased compatibility with polar systems caused by excessive fluorine content, as seen in hexafluorobenzene. This perfectly guarantees the homogeneous stability of the electrolyte over a wide temperature range (e.g., 273 K to 303 K). This application overcomes the shortcomings of single solvents in viscosity, wettability, and film-forming properties through the complementary combination of three fluorinated solvents with different spatial configurations, achieving a comprehensive improvement in macroscopic electrochemical performance.

[0042] The implementation schemes of this application will be described in detail below with reference to specific embodiments. However, those skilled in the art will understand that the following embodiments are only for illustrating this application and should not be regarded as limiting the scope of this application. Unless otherwise specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments used without specified manufacturers are all conventional products that can be purchased commercially.

[0043] Example 1 The first aspect of this application provides a high-voltage lithium metal battery electrolyte based on the synergistic effect of polyfluorinated solvents, the raw materials of which include lithium bis(trifluoromethanesulfonyl)imide (LITFSI), fluoroethylene carbonate (FEC), methyl difluoroacetate (MDFA) and 1,3,5-trifluorobenzene (TFB).

[0044] The molar concentration of lithium salt is 1M, the molar proportion of fluorinated aromatic hydrocarbons is 16%, and the molar ratio of FEC, MDFA and TFB is 0.4:0.42:0.16. This dosage is within the optimal balance window between rigid film formation and flexible viscosity reduction, aiming to provide optimal interfacial dynamics and dense lithium deposition morphology.

[0045] The second aspect of this application provides a method for preparing a high-voltage lithium metal battery electrolyte based on the synergistic effect of polyfluorinated solvents, specifically: In an argon-filled glove box (water and oxygen content <0.1 ppm), liquid FEC, MDFA, and TFB are first mixed evenly in the above proportions to form a homogeneous mixed solvent; then, metered LiTFSI is slowly added and fully dissolved under magnetic stirring until the solution is clear and transparent, thus obtaining the high-voltage lithium metal battery electrolyte (F3) based on the synergistic effect of polyfluorinated solvents.

[0046] Example 2 The difference from Example 1 is that the molar concentration of lithium salt is 1.5 M, and the molar ratio of FEC, MDFA and TFB is 0.5:0.35:0.15.

[0047] Example 3 The difference from Example 1 is that the lithium salt is replaced with an equimolar amount of lithium bis(fluorosulfonyl)imide; and the methyl difluoroacetate is replaced with an equimolar amount of methyl 2,2-difluoropropionate.

[0048] Comparative Example 1 The difference from Example 1 is that the molar ratio of FEC, MDFA and TFB is 0.625:0.125:0.25.

[0049] The high-voltage lithium metal battery electrolyte (F4) prepared in this comparative example, based on the synergistic effect of polyfluorinated solvents, significantly reduced the content of low-viscosity MDFA compared to Example 1, leading to an increase in system viscosity; meanwhile, the TFB content increased slightly. This comparative example was used to verify the negative impact on kinetics and rate performance when the content of linear carboxylic acid ester MDFA was insufficient.

[0050] Comparative Example 2 The difference from Example 1 is that the high-voltage lithium metal battery electrolyte based on the synergistic effect of polyfluorinated solvents in Example 1 is replaced with a commercial electrolyte, namely 1.0 M LiPF6 dissolved in a mixed solvent of EC and DEC with a volume ratio of 1:1.

[0051] The commercial electrolyte (BASE) provided in this comparative example serves as a performance benchmark for existing technologies, used to compare the advantages of perfluorinated systems.

[0052] Comparative Example 3 The difference from Example 1 is that no fluoroethylene carbonate (FEC) is added.

[0053] Comparative Example 4 The difference from Example 1 is that methyl difluoroacetate (MDFA) is not added.

[0054] Comparative Example 5 The difference from Example 1 is that 1,3,5-trifluorobenzene (TFB) is not added.

[0055] Comparative Example 6 The difference from Example 1 is that fluoroethylene carbonate (FEC) is replaced with ethylene carbonate.

[0056] This application also conducts performance tests on the high-voltage lithium metal battery electrolytes based on the synergistic effect of polyfluorinated solvents provided in the above embodiments and comparative examples. The specific test results are shown in Table 1.

[0057] Test Item 1: Interface kinetics testing (Tafel curve analysis) was performed on the above examples and comparative examples. Tafel polarization curves were tested using a Li-Li symmetric cell to evaluate the interfacial charge transfer impedance. The Tafel polarization curves and exchange current densities of Example 1 (labeled F3), Comparative Example 1 (labeled F4), and Comparative Example 2 (labeled BASE) are compared as follows: Figure 1 As shown.

[0058] Test Item 2: Wetting Test (Contact Angle Analysis) The physical wetting ability of the electrolyte on the polypropylene membrane surface is evaluated by measuring the contact angle of the electrolyte. The contact angle tests on the polypropylene membrane surfaces of Example 1 (labeled F3), Comparative Example 1 (labeled F4), and Comparative Example 2 (labeled BASE) are shown. Figure 2 As shown.

[0059] Test Item 3: Rate Performance Test. The assembled Li||NCM811 batteries were subjected to charge-discharge tests from 0.2C to 5C at 303K. The discharge specific capacity of the batteries assembled in Example 1 (labeled F3), Comparative Example 1 (labeled F4), and Comparative Example 2 (labeled BASE) at different rates from 0.2C to 5C was compared as follows: Figure 3 As shown.

[0060] Test Item 4: Lithium Deposition Morphology Characterization (SEM Analysis) The deposition state of lithium metal on the copper foil surface was observed using scanning electron microscopy. The SEM microstructures of lithium metal deposited on the copper foil surface in Example 1 (labeled F3), Comparative Example 1 (labeled F4), and Comparative Example 2 (labeled BASE) are compared as follows: Figure 4 As shown, Comparative Example 2 (BASE) exhibits a typical moss-like or dendritic morphology, with a loose and porous lithium layer, posing a significant risk of dead lithium and short circuits. While the lithium deposition in Comparative Example 1 (F4) is relatively dense, some irregular stacking and porosity are still observed. Example 1 (F3), on the other hand, exhibits an extremely dense, smooth, large-particle deposition morphology with clear grain boundaries and no dendrite growth. This directly confirms that the LiF-rich inorganic interface film generated on the negative electrode surface in Example 1 possesses extremely high mechanical strength and interfacial energy, enabling it to induce uniform lateral deposition of lithium ions.

[0061] Test Item 5: Linear Scan Volt-Ampere Curve Display. The LSV stability tests of Example 1 (labeled F3) and Comparative Example 2 (labeled BASE) at different temperatures are compared. Figure 5As shown in the figure, linear sweep voltammetry (LSV) curves reveal that all electrolytes exhibit high oxidation stability at a low temperature of 273 K. However, when the ambient temperature rises to 303 K, the oxidation decomposition current of the commercial electrolyte (BASE) in Comparative Example 2 shows an exponential and dramatic increase in the high-voltage region, indicating that its interfacial film rapidly loses its protective function under heating conditions, leading to a serious risk of thermal runaway. In contrast, the LSV curves of Example 1 (F3) show extremely high overlap during the heating process from 273 K to 303 K, with no significant drift between the peak voltage and background current. This temperature-insensitive electrochemical characteristic confirms that the fluorine-rich interfacial film constructed in this application has excellent thermal stability, effectively suppressing side reactions under high temperature and high pressure, and ensuring the safe operation of the battery over a wide temperature range.

[0062] Table 1 Performance Tests

[0063] analyze: Experimental results show that the exchange current density i0 in Example 1 is as high as 0.6889 mA cm⁻¹. -2 The exchange current density of Comparative Example 1 is 0.4786 mA cm⁻¹. -2 Comparative Example 2, however, only showed 0.0584 mA cm⁻¹. -2 The kinetic performance of Example 1 is more than 10 times that of commercial electrolytes. Compared with Comparative Example 1, Example 1, with its sufficient MDFA content, effectively reduced the desolvation barrier of the solvation shell, demonstrating the key role of MDFA in improving kinetics in perfluorinated systems. Further comparison shows that the exchange current density of Comparative Example 4 (without MDFA) drops drastically, reaching only 0.1450 mA cm⁻¹. -2 Furthermore, the discharge specific capacity drops sharply to 68 mA hg at a 5C rate. -1 This contrasts sharply with the excellent performance of Example 1, further confirming the irreplaceable role of linear fluorocarboxylic acid esters (MDFAs) in enhancing kinetics through flexible viscosity reduction. Furthermore, the exchange current densities of Example 2 (1.5M high salt concentration and adjusted solvent ratio) and Example 3 (replaced with lithium bis(fluorosulfonyl)imide and methyl 2,2-difluoropropionate) reached 0.5924 mA cm⁻¹, respectively. -2 and 0.7105 mA cm -2 It maintained 162 mA hg at 5C rate. -1 and 178 mA hg -1 The high specific capacity further confirms that the different concentrations and combinations of substances disclosed in this application can effectively overcome the kinetic bottleneck of the perfluorinated system and have wide applicability.

[0064] The contact angle of Example 1 was 55.5 degrees, that of Comparative Example 1 was 52.2 degrees, and that of Comparative Example 2 was 52.7 degrees. Analysis of the results shows that although Comparative Example 1 had the smallest contact angle due to its slightly higher TFB content, the commercial electrolytes of Example 1 and Comparative Example 2 were at the same level. This demonstrates that by introducing the fluorinated aromatic hydrocarbon TFB, this application successfully overcomes the high surface tension defect of perfluorinated solvents, ensuring rapid penetration of the electrolyte into the membrane pores and meeting the standards for engineering applications.

[0065] Example 1 (F3) maintains the highest capacity across the entire rate range, especially under extreme fast charging conditions at 5C, where its discharge specific capacity remains at approximately 175 mA hg. -1 In contrast, Comparative Example 1 (F4) exhibits a capacity decay of approximately 130 mA hg at 5C. -1 In contrast, two commercial electrolytes (BASE) showed almost no capacity loss at such high rates. This result confirms that although Comparative Example 1 had slightly better wettability, its rate performance was far inferior to Example 1, indicating that after wettability meets basic requirements, the interfacial kinetics determined by the MDFA content is the bottleneck restricting fast charging capability. Conversely, Comparative Example 3 (without FEC), lacking a core film-forming framework, could not construct an inorganic rigid interface layer rich in lithium fluoride (LiF), resulting in a poor discharge performance at 5C, only about 45 mA hg. -1 Furthermore, this application investigated Comparative Example 6 (where the cyclic fluorocarbonate FEC was replaced with non-fluorinated ethylene carbonate EC). The results showed that although the contact angle remained at a good level of 54.2 degrees under the influence of TFB, its 5C discharge specific capacity dropped sharply to approximately 42 mA hg. -1 Furthermore, the exchange current density significantly decreased to 0.3150 mAcm⁻¹. -2 This indicates that traditional non-fluorinated carbonates (ECs) are highly susceptible to oxidative decomposition under high voltage and cannot induce the formation of a structurally stable inorganic protective layer on the surface of lithium metal anodes. The comparative results across multiple dimensions strongly confirm that the perfluorinated solvent system constructed in this application (rigid film-forming main solvent, flexible viscosity-reducing diluent, and interfacial wetting additive) is indispensable. Only through the synergistic effect of these three components can a true leap in both fast-charging performance and cycle life of high-voltage lithium metal batteries be achieved.

[0066] Therefore, this application has overcome the fast-charging performance bottleneck of perfluorinated electrolytes: by regulating linear fluorocarboxylic acid esters (such as MDFA), the viscosity and interfacial impedance of the system are significantly reduced without sacrificing high-voltage stability. Experiments show that the interfacial exchange current density of the electrolyte in this application is increased to more than 10 times that of commercial electrolytes, and it can still maintain high capacity performance at a high rate of 5C, achieving a qualitative leap in the fast-charging performance of high-voltage lithium metal batteries.

[0067] This application solves the engineering problem of poor wettability in perfluorinated systems: addressing the defect that perfluorinated solvents are usually difficult to wet polypropylene membranes, this application successfully reduces the contact angle of the electrolyte to a commercial level by introducing fluorinated aromatic hydrocarbons (such as TFB). This excellent physical wettability not only ensures the smooth flow of ion transport channels, but also significantly improves the injection efficiency, clearing away the key obstacles to the engineering application of perfluorinated electrolytes.

[0068] A dense, dendrite-free lithium deposition was achieved: This application utilizes the synergistic effect of various components to induce a dense, flat, chunky lithium deposition morphology on the negative electrode surface, fundamentally inhibiting the growth of moss-like or dendritic lithium dendrites. This dense deposition structure effectively reduces dead lithium accumulation and electrolyte consumption, significantly extending the battery's cycle life and improving safety.

[0069] Balancing high voltage stability and intrinsic safety: The perfluorinated formulation used in this application has an intrinsic oxidation resistance window exceeding 5.0V, making it perfectly compatible with high-voltage cathode materials. Simultaneously, the perfluorinated solvent itself has low flammability, significantly improving the thermal stability and safety of high-energy-density batteries under extreme operating conditions.

[0070] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

[0071] Furthermore, those skilled in the art will understand that although some embodiments herein include certain features included in other embodiments but not others, combinations of features from different embodiments are intended to be within the scope of this application and form different embodiments. For example, any of the claimed embodiments can be used in any combination. The information disclosed in this background section is intended only to enhance the understanding of the general background of this application and should not be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

Claims

1. A high-voltage lithium metal battery electrolyte based on the synergistic effect of polyfluorinated solvents, characterized in that, Its raw materials include lithium salts, cyclic fluorocarbonates, linear fluorocarboxylic acid esters, and fluorinated aromatic hydrocarbons; In high-performance electrolytes, the molar percentage of the fluorinated aromatic hydrocarbons is 5%-20%; The molar ratio of the cyclic fluorocarbonate, the linear fluorocarboxylic acid ester, and the fluorinated aromatic hydrocarbon is 0.3-0.6:0.3-0.6:0.05-0.

3.

2. The high-voltage lithium metal battery electrolyte based on the synergistic effect of polyfluorinated solvents according to claim 1, characterized in that, The molar ratio of the cyclic fluorocarbonate to the linear fluorocarboxylic acid ester is 1-3:1-3.

3. The high-voltage lithium metal battery electrolyte based on the synergistic effect of polyfluorinated solvents according to claim 1, characterized in that, The molar ratio of the cyclic fluorocarbonate, the linear fluorocarboxylic acid ester, and the fluorinated aromatic hydrocarbon is 0.42:0.42:0.

16.

4. The high-voltage lithium metal battery electrolyte based on the synergistic effect of polyfluorinated solvents according to claim 1, characterized in that, In the high-performance electrolyte, the molar concentration of the lithium salt is 0.5-2.0 M; The lithium salt includes at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium hexafluorophosphate, lithium tetrafluoroborate, and lithium difluorooxalate borate.

5. The high-voltage lithium metal battery electrolyte based on the synergistic effect of polyfluorinated solvents according to claim 4, characterized in that, The lithium salt includes lithium bis(trifluoromethanesulfonyl)imide and / or lithium bis(fluorosulfonyl)imide.

6. The high-voltage lithium metal battery electrolyte based on the synergistic effect of polyfluorinated solvents according to claim 1, characterized in that, The cyclic fluorocarbonate includes at least one of fluoroethylene carbonate, difluoroethylene carbonate, and trifluoromethylethylene carbonate.

7. The high-voltage lithium metal battery electrolyte based on the synergistic effect of polyfluorinated solvents according to claim 1, characterized in that, The linear fluorocarboxylic acid esters include at least one of methyl difluoroacetate, ethyl difluoroacetate, methyl trifluoroacetate, and methyl 2,2-difluoropropionate.

8. The high-voltage lithium metal battery electrolyte based on the synergistic effect of polyfluorinated solvents according to any one of claims 1-7, characterized in that, The fluorinated aromatic hydrocarbons include at least one of 1,3,5-trifluorobenzene, hexafluorobenzene, tetrafluorobenzene, and difluorobenzene.

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