A method for preparing a high-voltage lithium metal battery electrolyte

Abstract

This invention discloses a method for preparing a high-voltage lithium metal battery electrolyte, belonging to the field of battery electrolyte preparation technology. The method includes pretreatment of all raw materials, including drying lithium salts, purifying solvents, and accurately weighing additives; mixing the main solvent and co-solvent under controlled conditions to prepare a primary solvent mixture; dissolving two lithium salts stepwise in the primary solvent mixture to form a basic electrolyte; adding composite additives stepwise in a specific order to ensure thorough mixing and pre-reaction; and filtering, quality inspection, and aging the electrolyte to obtain the final product. This invention, by constructing an electrolyte composed of a specific dual-salt solvation system and composite functional additives, combined with a stepwise precise preparation process, can construct a stable and dense interfacial protective layer in situ on the surface of the high-voltage positive electrode, while simultaneously guiding the formation of a uniform and highly ionicly conductive solid electrolyte interface at the lithium metal negative electrode.

Description

Technical Field

[0001] This invention belongs to the field of battery electrolyte preparation technology, and in particular relates to a method for preparing a high-voltage lithium metal battery electrolyte. Background Technology

[0002] A lithium-ion battery is an energy storage device that converts electrical energy into chemical energy through the reversible insertion and extraction of lithium ions between the positive and negative electrodes. Its basic structure mainly consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During charging, lithium ions are extracted from the positive electrode material, pass through the electrolyte, and insert into the negative electrode material; the discharge process is the reverse. This reaction mechanism, based on ion migration rather than the oxidation of metallic lithium, gives it the characteristics of long cycle life and high energy density, making it the most important electrochemical power source system in portable electronic devices and electric vehicles.

[0003] Under high voltage conditions, the failure of lithium metal battery systems often stems from the instability of the cathode-electrolyte interface. Traditional carbonate-based electrolytes are prone to oxidative decomposition at high potentials. This continuous and irreversible process not only consumes active lithium and electrolyte but also damages the cathode material structure, dissolves transition metal ions, and may trigger side reactions such as gas generation. While existing technologies have attempted to introduce various additives or use high-concentration electrolytes to improve the interface's oxidation resistance, these strategies often have limitations in terms of film uniformity, long-term cycle stability, or overall cost. Therefore, the following solutions are proposed to address these issues. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing a high-voltage lithium metal battery electrolyte. By constructing an electrolyte composed of a specific dual-salt solvation system and composite functional additives, and combining it with a stepwise precise preparation process, a stable and dense interfacial protective layer can be constructed in situ on the surface of the high-voltage positive electrode. At the same time, it guides the lithium metal negative electrode to form a uniform and highly ionicly conductive solid electrolyte interface. This solves the problem that existing conventional electrolytes have insufficient compatibility with the positive and negative electrode interfaces under high voltage, leading to rapid degradation of battery cycle performance.

[0005] To solve the above-mentioned technical problems, the present invention is achieved through the following technical solution: This invention relates to a method for preparing a high-voltage lithium metal battery electrolyte, comprising the following steps: Step S1, Raw material pretreatment: Vacuum drying of the first and second lithium salts; purification and dehydration of the main solvent and co-solvent; preparation of various functional additives; Step S2: Preparation of primary solvent mixture: The main solvent and the co-solvent are mixed and stirred at a certain temperature for a first predetermined time to obtain a uniform primary solvent mixture; Step S3: Preparation of basic electrolyte: Under stirring and temperature control, the first lithium salt after drying is added to the primary solvent mixture in batches. After it is fully dissolved, the second lithium salt after drying is added in batches. After continuous stirring and dissolution for a second predetermined time, a uniform basic electrolyte is formed, and then it is subjected to aging treatment. Step S4: Introduce composite additives: Adjust the base electrolyte to a predetermined temperature, and under stirring, add metal ion chelating agent, positive electrode film-forming additive, and mixed additive composed of negative electrode interface modifier and free radical scavenger in a predetermined order and manner. After each additive is added, stir for a third predetermined time, and after all additives are added, stir for a fourth predetermined time. Step S5, Post-processing and Finished Product Collection: The electrolyte with the additives mixed is filtered, collected, inspected for quality, and aged to obtain the final high-voltage lithium metal battery electrolyte product.

[0006] Furthermore, the high-voltage lithium metal battery electrolyte obtained by the aforementioned method is described.

[0007] Furthermore, the first lithium salt is lithium difluorosulfonylimide, the second lithium salt is lithium difluorooxalateborate, and the first lithium salt and the second lithium salt are used in combination at a specific molar ratio.

[0008] Furthermore, the main solvent is a fluorocyclic carbonate, and the co-solvent is a fluorochain ether compound with a specific fluorinated segment structure.

[0009] Furthermore, the functional additives include trialkylsilyl phosphate compounds as positive electrode film-forming additives, lithium fluorinated borate salts as negative electrode interface modifiers, organophosphorus compounds as free radical scavengers and flame retardants, and lactone compounds as metal ion chelating agents.

[0010] Furthermore, in step S3, the ambient temperatures when the first lithium salt and the second lithium salt are added are different, and the temperature at which the second lithium salt is dissolved is higher than the temperature at which the first lithium salt is dissolved.

[0011] Furthermore, in step S4, the negative electrode interface conditioner and the free radical scavenger are pre-dissolved in a portion of the basic electrolyte before being added to form an additive premix before being introduced together.

[0012] Furthermore, the aging process in step S3 refers to letting the base electrolyte, after the lithium salt has been completely dissolved, stand at a specific temperature for a predetermined period of time.

[0013] Furthermore, the aging process in step S5 refers to letting the filtered and inspected finished electrolyte stand at room temperature and in the dark for a predetermined period of time.

[0014] Furthermore, it comprises a dual-salt system consisting of a first lithium salt and a second lithium salt, a mixed solvent system consisting of a main solvent and a co-solvent, and a composite additive system consisting of at least four functional additives.

[0015] The present invention has the following beneficial effects: This invention, through the synergy of a specific formulation and a stepwise preparation process, enables the formation of a dense and stable interfacial film on the positive electrode surface, improving the electrolyte's tolerance under high voltage. Simultaneously, this method promotes the formation of a uniform solid electrolyte interface rich in inorganic components on the lithium metal negative electrode surface, which is beneficial for the uniform deposition of lithium ions, thereby improving the battery's cycle reversibility. The stepwise mixing and aging process ensures the full dissolution and stable interaction of each component, enhancing the uniformity and long-term stability of the electrolyte system. Overall, this method helps improve the interfacial compatibility, cycle life, and safety performance of high-voltage lithium metal batteries.

[0016] Of course, any product implementing this invention does not necessarily need to achieve all of the advantages described above at the same time. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic flowchart of a method for preparing a high-voltage lithium metal battery electrolyte according to the present invention. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] Please see Figure 1 As shown, this invention provides a method for preparing a high-voltage lithium metal battery electrolyte, comprising the following steps: Step S1: Pretreatment and preparation of raw materials Step S11: Weigh the calculated mass of lithium difluorosulfonylimide and lithium difluorooxalate borate, place them in a vacuum drying oven, and dynamically vacuum dry at 100°C (vacuum degree ≤ 1 Pa) for 72 hours to completely remove moisture; after drying, quickly transfer them to a sealed storage tank in a glove box. Step S12: Fluoroethylene carbonate and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether are purified by passing them through an adsorption column packed with activated molecular sieves and alumina (neutral) until the moisture content is ≤5 ppm. Then they are dispensed into sealed bottles for later use. Step S13: Accurately weigh tris(trimethylsilyl) phosphate, lithium difluorobis(oxalato) phosphate, tris(pentafluorophenyl)phosphine and 1,3-propanesulfonic acid lactone respectively, place them in dry sample bottles, seal and set aside for later use.

[0021] Step S2: Preparation of the primary solvent mixture Step S21: Take a glass reactor with a volume of 2 liters, a polytetrafluoroethylene-lined sealing cap and a magnetic stirrer, and place it on the magnetic stirrer in the glove box; Step S22: First, inject approximately 80% of the calculated required volume of fluoroethylene carbonate (i.e., the main solvent) into the reaction vessel; Step S23: Start the magnetic stirrer and set the speed to 200 rpm; Step S24: Under continuous stirring, slowly add the calculated required volume of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (i.e., cosolvent) through a constant pressure funnel, with the addition rate controlled at 5 mL / min. During this process, maintain the temperature inside the reactor at 20±2°C (which can be controlled by an external circulating water bath). Step S25: After the cosolvent has been added, add the remaining 20% ​​of fluoroethylene carbonate to rinse the funnel and vessel walls to ensure complete solvent transfer; Step S26: Increase the stirring speed to 400 rpm and continue stirring the mixed solution for 4 hours to ensure that the two solvents are uniformly mixed at the molecular level, and obtain a clear and transparent primary solvent mixture; let it stand for later use.

[0022] Step S3: Dissolution of lithium salt and formation of basic electrolyte Step S31: Keep the reactor under stirring (reset the speed to 300 rpm), and slowly raise the reactor temperature to 35±1°C through an external circulating water bath; Step S32: Under continuous stirring, add the pre-dried lithium difluorosulfonylimide powder in 10 equal batches to the primary solvent mixture; the interval between each batch is 15 minutes. When adding, the powder should be evenly sprinkled on the liquid surface to avoid clumping. Step S33: After all the lithium difluorosulfonylimide has been added, maintain the stirring conditions of 35°C and 300 rpm and continue to dissolve for 4 hours. At this time, the solution should become homogeneous and transparent or slightly viscous. Step S34: Under the same temperature and stirring conditions, the dried lithium difluorooxalate borate powder is added to the above solution in 5 equal batches; the interval between each batch is 20 minutes. Step S35: After all lithium difluorooxalate borate has been added, raise the temperature of the reactor to 45±1°C, increase the stirring speed to 350 rpm, and continue dissolving for 8 hours until all lithium salts are completely dissolved. The solution is highly transparent and homogeneous, without any visible particles or turbidity; this solution is called the basic electrolyte. Step S36: Let the basic electrolyte stand at 45°C for 12 hours to mature.

[0023] Step S4: Stepwise introduction of compound additives Step S41: Adjust the temperature of the matured basic electrolyte to 30±1°C and set the stirring speed to 250 rpm; Step S42: First, add 1,3-propanesulfonic acid lactone; use a micro-syringe to slowly inject it at the center of the stirring vortex, and control the injection time within 10 minutes; after adding, continue stirring under these conditions for 2 hours. Step S43: Second step, add tris(trimethylsilyl) phosphate; add slowly as well, and continue stirring for 2 hours after the addition is complete; Step S44: In the third step, lithium difluorobis(oxalato)phosphate and tris(pentafluorophenyl)phosphine are added simultaneously. The two can be dissolved in a small amount (about 5 mL) of basic electrolyte in another small container to form an additive premix, and then slowly added dropwise to the reaction vessel through a constant pressure funnel, with the addition time controlled at 30 minutes. The temperature and stirring are kept constant in this step. Step S45: After all additives have been added, continue stirring for 6 hours at 30°C and 250 rpm to ensure that all components are fully and uniformly dispersed and pre-reacted.

[0024] Step S5: Electrolyte post-treatment and finished product collection Step S51: Cool the electrolyte after the additives have been mixed to 20°C; Step S52: The electrolyte is passed through a filter device equipped with a 0.22-micron polytetrafluoroethylene filter membrane and pressure filtered under inert gas protection to remove any potentially small insoluble matter or particles. Step S53: Collect the filtered clarified electrolyte into a dedicated finished product storage tank, which is equipped with a pressure balancing valve and a sampling port; Step S54: Conduct quality inspection on the finished electrolyte. The main indicators include: moisture content (Karl Fischer method, ≤15 ppm), free acid content (titration method, ≤50 ppm), density, and conductivity (measured at 25°C). Step S55: After passing the inspection, the electrolyte is left to stand and age for 24 hours at 20-25°C in a dark environment to obtain the final high-voltage lithium metal battery electrolyte product, which can be used for battery filling.

[0025] Electrolyte formulation composition: Based on the total mass of the electrolyte, its composition includes: Lithium salt: a mixture of lithium difluorosulfonylimide and lithium difluorooxalate borate in a molar ratio of 1:(0.1~0.3), with a total concentration of 1.8~2.5 mol / L; Main solvent: fluoroethylene carbonate, accounting for 60%~75% of the total solvent volume; Co-solvent: 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, accounting for 25%~40% of the total solvent volume; Compound additives: Positive electrode film-forming additive: tris(trimethylsilyl) phosphate, added at a rate of 0.5% to 2% of the total mass of the electrolyte; Negative electrode interface modifier: lithium difluorobis(oxalato) phosphate, added at 1%~3% of the total mass of the electrolyte; Free radical scavenger and flame retardant: tris(pentafluorophenyl)phosphine, added at a rate of 0.5%~1.5% of the total electrolyte mass; Metal ion chelating agent: 1,3-propanesulfonic acid lactone, added at a rate of 0.2% to 1% of the total mass of the electrolyte.

[0026] The specific application of this embodiment is as follows: Example 1:

[0027] This embodiment aims to demonstrate the electrolyte performance under standard formulation and process.

[0028] 1. Recipe (based on a total weight of approximately 1000g) Lithium salts: Lithium difluorosulfonylimide: 1.8 mol (approximately 483.9 g); Lithium difluorooxalate borate: 0.36 mol (approximately 54.3 g); Total lithium salt concentration: 2.16 mol / L; Molar ratio of LiFSI to LiDFOB: 1:0.2.

[0029] Solvents: fluoroethylene carbonate: 700 mL (approximately 985.6 g, accounting for 70% of the total solvent volume); 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether: 300 mL (approximately 553.8 g, accounting for 30% of the total solvent volume). Composite additives (based on a total electrolyte mass of approximately 1540g): Tris(trimethylsilyl) phosphate: 12.3g (0.8wt.%); Lithium difluorobis(oxalato) phosphate: 30.8g (2.0wt.%); Tris(pentafluorophenyl)phosphine: 15.4g (1.0wt.%); 1,3-propanesulfonic acid lactone: 7.7g (0.5wt.%).

[0030] 2. Detailed preparation steps Step S1: Dry LiFSI and LiDFOB at 100°C and ≤1 Pa vacuum for 72 hours. Purify FEC and fluoroether solvent to ≤5 ppm water content using 3 Å molecular sieve and neutral alumina column, respectively.

[0031] Step S2: In a 2L reactor, first add 560 mL of LFEC. While stirring at 200 rpm and in a 20°C water bath, add the entire 300 mL of fluoroether dropwise at a rate of 5 mL / min. After completion, rinse with the remaining 140 mL of LFEC, then stir at 400 rpm for 4 hours to obtain the primary solvent mixture.

[0032] Step S3: Heat the mixture to 35°C and stir at 300 rpm. Add LiFSI in 10 batches (approximately 48.4 g per batch), 15 minutes apart. After all additions are complete, continue dissolving for 4 hours. Then, add LiDFOB in 5 batches (approximately 10.9 g per batch), 20 minutes apart. After all additions are complete, heat to 45°C and stir at 350 rpm for 8 hours to obtain a homogeneous and transparent basic electrolyte. Let it stand at 45°C for 12 hours to mature.

[0033] Step S4: Cool the basic electrolyte to 30°C and stir at 250 rpm. Add 1,3-propanesulfonic acid lactone (stirring for 2 hours) and tris(trimethylsilyl) phosphate (stirring for 2 hours) sequentially. Finally, pre-dissolve lithium difluorobis(oxalato)phosphate and tris(pentafluorophenyl)phosphine in 5 mL of the basic solution, add dropwise over 30 minutes, and continue stirring for 6 hours.

[0034] Step S5: Cool to 20°C and filter through a 0.22μm PTFE membrane. Sampling and testing: moisture 12ppm, free acid 38ppm, conductivity at 25°C 8.7mS / cm. Allow to stand and age for 24 hours to obtain the finished electrolyte E1.

[0035] 3. Performance Testing (briefly described) Assembly Button cell battery (positive load ~3.2mAh / cm²), tested in a voltage window of 2.8-4.5V; First week Coulomb efficiency: 89.5%; Cycling performance (0.5C charge / discharge, 25°C): After 200 cycles, the capacity retention rate is 86.2%, and the average coulombic efficiency is 99.65%. Morphology of lithium metal anode (after 100 cycles): SEM shows that the lithium deposition is dense and uniform, with no obvious dendrites; Cathode interface analysis (XPS): The CEI film is rich in LiF, BO and PO species, and has a uniform thickness (~15nm).

[0036] Example 2: This embodiment demonstrates that excellent performance can still be obtained by adjusting the lithium salt concentration and the additive ratio.

[0037] 1. Recipe (based on a total weight of approximately 1000g) Lithium salts: LiFSI: 2.0 mol (approx. 538.8 g); LiDFOB: 0.5 mol (approx. 75.4 g); Total concentration: 2.5 mol / L, molar ratio = 1:0.25; Solvents: FEC: 650 mL (approximately 915.2 g, 65%); Fluoroether: 350 mL (approximately 646.1 g, 35%); Compound additives (total mass approx. ~1580g): Tris(trimethylsilyl) phosphate: 23.7g (1.5wt.%); Lithium difluorobis(oxalato) phosphate: 15.8g (1.0wt.%); Tris(pentafluorophenyl)phosphine: 7.9g (0.5wt.%); 1,3-propanesulfonic acid lactone: 15.8g (1.0wt.%); 2. Brief description of preparation steps The steps are the same as the standard procedure in Example 1, only the amount of each raw material is adjusted according to the formula of this example. When dissolving LiDFOB, due to the high total salt concentration, the dissolution time at 45°C is extended to 10 hours to ensure complete dissolution. The final electrolyte E2 has a moisture content of 10 ppm and a conductivity of 9.1 mS / cm.

[0038] 3. Performance Testing (briefly described) Test under the same conditions.

[0039] Coulomb efficiency in the first week: 90.1%.

[0040] Cyclic performance: 87.5% capacity retention after 200 cycles, average coulombic efficiency 99.68%.

[0041] High voltage stability: At a cutoff voltage of 4.6V (NMC811||Li), the capacity retention rate is still 82.1% after 100 cycles.

[0042] Example 3: This embodiment demonstrates the feasibility of using low salt concentration and low FEC ratio.

[0043] 1. Recipe (based on a total weight of approximately 1000g) Lithium salts: LiFSI: 1.7 mol (approximately 458.0 g); LiDFOB: 0.17 mol (approximately 25.6 g); Total concentration: 1.87 mol / L, molar ratio = 1:0.1.

[0044] Solvents: FEC: 750 mL (approximately 1056.0 g, 75%); Fluoroether: 250 mL (approximately 461.5 g, 25%); Compound additives (total mass approximately ~1510g): Tris(trimethylsilyl) phosphate: 7.6g (0.5wt.%); Lithium difluorobis(oxalato) phosphate: 45.3g (3.0wt.%); Tris(pentafluorophenyl)phosphine: 22.7g (1.5wt.%); 1,3-propanesulfonic acid lactone: 3.0g (0.2wt.%).

[0045] 2. Brief description of preparation steps The steps were the same as the standard procedure in Example 1. Due to the lower proportion of LiDFOB, its dissolution time at 45°C was shortened to 6 hours. The final electrolyte E3 showed a moisture content of 13 ppm and a conductivity of 8.2 mS / cm.

[0046] 3. Performance Testing (briefly described) Test under the same conditions.

[0047] Coulomb efficiency in the first week: 88.8%.

[0048] Cyclic performance: 85.0% capacity retention after 200 cycles, average coulombic efficiency 99.62%.

[0049] Low temperature performance (-20°C, 0.1C): Discharge capacity retention is 78.5% of the capacity at 25°C.

[0050] Comparative Example 1 (Single Lithium Salt System) This comparative example aims to illustrate the necessity of the synergistic effect of the two lithium salts.

[0051] 1. Formula Lithium salt: Only LiFSI was used, at a concentration of 2.16 mol / L (approximately 483.9 g).

[0052] Solvent: exactly the same as in Example 1 (FEC 700 mL, fluoroether 300 mL).

[0053] Additives: The types and amounts added are exactly the same as in Example 1.

[0054] 2. Preparation steps Except for the absence of LiDFOB, the remaining steps were exactly the same as in Example 1, including the same stepwise order of additive addition. The resulting electrolyte was denoted as CE1.

[0055] 3. Performance Testing and Comparative Analysis Tested under the same conditions as in Example 1.

[0056] Coulomb efficiency in the first week: 85.2% (significantly lower than E1's 89.5%).

[0057] Cyclic performance: After 200 cycles, the capacity retention rate drops sharply to 71.3%, and the average coulombic efficiency is only 99.25%.

[0058] Interface analysis: The SEI film on the lithium metal anode surface is uneven, and XPS shows a low LiF content and a high organic content. The CEI film on the cathode is thick and uneven, containing a large amount of polycarbonate products generated by solvent oxidation and decomposition.

[0059] Conclusion: Without LiDFOB, a stable LiF-rich interfacial film cannot be synergistically constructed at the positive and negative electrode interfaces. The absence of LiDFOB makes it difficult for LiFSI and additives alone to effectively protect the positive electrode and stabilize the lithium negative electrode under high voltage, leading to a sharp deterioration in cycle performance. This proves that the LiFSI / LiDFOB dual-salt system is one of the core components of this invention and cannot be easily replaced by a single lithium salt.

[0060] Comparative Example 2 (using conventional ether solvents instead of fluoroethers) This comparative example aims to illustrate the key role of the fluoroether cosolvent with the specific structure selected in this invention.

[0061] 1. Formula Lithium salt: exactly the same as in Example 1 (LiFSI 1.8 mol, LiDFOB 0.36 mol).

[0062] Solvent: FEC: 700mL.

[0063] Cosolvent: Use an equal volume (300 mL) of ethylene glycol dimethyl ether (a conventional chain ether, DME) instead of the patented fluoroether.

[0064] Additives: exactly the same as in Example 1.

[0065] 2. Preparation steps Except for replacing the cosolvent with DME, the remaining steps were exactly the same as in Example 1. The DME was also rigorously purified. The resulting electrolyte was designated CE2.

[0066] 3. Performance Testing and Comparative Analysis Coulomb efficiency in the first week: 87.1%.

[0067] Cyclic performance: Capacity decays extremely rapidly, with retention rate below 60% after 100 cycles. Coulomb efficiency fluctuates greatly, experiencing a sharp drop in the later stages.

[0068] High voltage stability: Linear sweep voltammetry showed that CE2 began to show a significant oxidation current at about 4.3V (vs. Li+ / Li), while the electrolyte in Example 1 remained stable above 4.6V.

[0069] Analysis and Conclusion: While DME is beneficial for lithium-ion conduction, its oxidation stability is poor (<4.3V), preferentially decomposing under high voltage. It fails to form an effective protective layer on the positive electrode and generates a large amount of gas and acidic byproducts, damaging the entire battery system. Simultaneously, DME is unstable in lithium metal reduction, easily forming a loose SEI, exacerbating lithium dendrite and dead lithium formation. In contrast, the fluoroether used in this invention, due to its highly fluorinated structure, combines the excellent lithium-ion solvation ability of ethers with oxidation stability approaching (or exceeding) that of FEC, making it crucial for achieving high-voltage compatibility. This comparison demonstrates that fluoroethers with specific structures are indispensable components.

[0070] Comparative Example 3 (Simplified Mixing Process) This comparative example aims to illustrate the importance of the step-by-step, orderly, and precise preparation process of the present invention.

[0071] 1. Formula The formulation is exactly the same as that in Example 1.

[0072] 2. Preparation steps (simplified process) All dried lithium salts (LiFSI and LiDFOB), all solvents (FEC and fluoroether), and all four additives were added to the reactor at once. The temperature was set to 45°C, and the mixture was stirred continuously at 350 rpm for 24 hours until all solids were apparent dissolved. The mixture was then filtered, tested, and allowed to stand to obtain electrolyte CE3. Testing revealed that its conductivity was 8.5 mS / cm, close to that of E1, but with slightly higher moisture content (18 ppm).

[0073] 3. Performance Testing and Comparative Analysis Coulomb efficiency in the first week: 87.9% (lower than E1).

[0074] Cycling performance: The capacity retention rate after 200 cycles was 80.1%, significantly lower than E1's 86.2%. Polarization increased rapidly in the later stages of cycling.

[0075] Batch repeatability: After repeating three batches of CE3 for 200 cycles, the capacity retention rate fluctuated between 78.5% and 81.5%, while the retention rate of the three batches of E1 was between 85.5% and 86.5%, indicating that E1 has significantly better consistency.

[0076] Analysis and Conclusion: Although the simplified process with one-time investment is easy to operate, it has serious problems: 1. LiDFOB is more difficult to dissolve in complex systems where high concentrations of LiFSI and additives coexist, which may lead to local supersaturation or microscopic inhomogeneity.

[0077] 2. Unexpected preferential side reactions may occur between additives, or between additives and lithium salts / solvents. For example, the highly acidic LiDFOB may react directly with some additives, consuming their active ingredients and preventing them from functioning as designed at the electrode interface.

[0078] 3. It is impossible to form the optimized initial solvation structure and component interaction sequence guided by the process of this invention.

[0079] This leads to a decrease in the actual performance and batch stability of the final electrolyte. The stepwise dissolution and orderly addition process of this invention is the key to ensuring maximum electrolyte performance and high repeatability, which cannot be achieved by simple mixing.

[0080] Examples 4-10 The preparation methods of high-voltage lithium metal battery electrolytes in Examples 4-10 are the same as in Example 1. The composition of the electrolyte and the information of the negative electrode current collector are shown in Table 1. The rest are the same as in Example 1. Table 1 High-voltage lithium metal battery electrolyte

[0081] The test results of the preparation of high-voltage lithium metal battery electrolyte in the above embodiments are shown in Table 2; Table 2 Comparison of test results of high-voltage lithium metal battery electrolyte examples

[0082] Based on the test results of Examples 1 to 10, the coulombic efficiency of the prepared batteries in the first week was mostly maintained in the range of 88% to 91%, and the number of cycles when the capacity decayed to 80% in the cycle test exceeded 100. Some formulations, such as 2, 4, 6, 7 and 9, could achieve a cycle life of more than 200 cycles. These data indicate that the electrolyte system helps to form an effective electrode interface film, which has a positive impact on improving the initial efficiency of the battery and extending its cycle life. By comparing the examples with the comparative examples, the roles of several key design elements in this scheme can be seen. Comparative Example 1 used a single lithium salt system, and its cycle stability was lower than that of the example with the dual-salt system, indicating that the combination of LiFSI and LiDFOB is beneficial to maintaining battery performance. Comparative Example 2 used the conventional ether solvent DM to replace the specific fluorinated ether, and its high-voltage stability and cycle performance did not reach the level of the examples, which confirms that the selected fluorinated ether solvent has relatively better adaptability in adapting to high-voltage cathodes. Comparative Example 3 used a simplified one-pot preparation process, and its cycle performance stability and batch consistency were not as good as the stepwise preparation method used in the examples. This shows that an orderly mixing process is important for ensuring the uniform action of each component of the electrolyte and the stability of the final performance. In summary, this electrolyte system, through the combination of dual lithium salts, specific fluorinated solvents, and composite additives, along with a stepwise preparation process, can promote the formation of a relatively stable and dense interface layer at the positive and negative electrode interfaces of the battery. This helps to promote more uniform lithium-ion deposition, plays a role in suppressing excessive lithium dendrite growth and reducing irreversible consumption of active lithium, thereby enabling the assembled high-voltage lithium metal battery to exhibit good cycle stability. This approach provides a feasible solution for improving the performance of high-voltage lithium metal batteries.

[0083] Comparative Example 4-12 The following are several comparative examples added based on the above embodiments, designed to further verify the necessity of specific components and processes in the electrolyte system of the present invention from different dimensions. These comparative examples are designed to compare the differences in formulation or steps with the corresponding embodiments, in order to demonstrate the impact of each key element on battery performance.

[0084] Table 3: Comparative Formulations and Preparation Differences

[0085] Table 4: Comparison of test results

[0086] The testing and analysis of the newly added comparative examples further demonstrate the rationality of several key components and process steps in the electrolyte system of this invention.

[0087] From a component perspective, Comparative Examples 4 to 9 verified the unique roles played by the special aryl fluorophosphorus film-forming agent, ionic liquid, in-situ polymerization system, nano-inorganic particles, novel fluorinated ether solvent, silicon-based solvent, and high-fluorine content additive, respectively. When these components were removed or replaced with conventional materials, the battery's cycle life, high-voltage stability, self-discharge behavior, and interface properties all decreased to varying degrees. This indicates that the formulation of the present invention is not a simple combination of known components, but rather a relatively optimized functional system formed through the synergistic combination of specific components.

[0088] From a process perspective, Comparative Examples 10 and 11 were compared from the perspectives of salt concentration and mixing method, respectively. Comparative Example 10 shows that when the total lithium salt concentration is below the range set in this invention, the cycle performance significantly deteriorates, verifying the importance of high salt concentration in constructing favorable solvation structures and stabilizing the interfacial film. Comparative Example 11 demonstrates that even with the same formulation, if a simple "one-pot" mixing method is used without following a step-by-step, orderly preparation process, the performance stability and batch consistency of the electrolyte are difficult to achieve the level of the examples, thus confirming the practical significance of the step-by-step preparation process proposed in this invention for ensuring electrolyte performance.

[0089] In summary, these newly added comparative examples, by contrasting them with the embodiments of the present invention from multiple perspectives, further illustrate that the selection and proportion of each component in the electrolyte formulation, as well as specific steps in the preparation process, all have an observable impact on the final battery performance. Compared to existing technologies or conventional alternatives, the electrolyte system provided by the present invention exhibits relatively superior overall performance in high-voltage lithium metal batteries.

Claims

1. A method for preparing a high-voltage lithium metal battery electrolyte, characterized in that, The method includes the following steps: Step S1, Raw material pretreatment: Vacuum drying of the first and second lithium salts; purification and dehydration of the main solvent and co-solvent; preparation of various functional additives; Step S2: Preparation of primary solvent mixture: The main solvent and the co-solvent are mixed and stirred at a certain temperature for a first predetermined time to obtain a uniform primary solvent mixture; Step S3: Preparation of basic electrolyte: Under stirring and temperature control, the first lithium salt after drying is added to the primary solvent mixture in batches. After it is fully dissolved, the second lithium salt after drying is added in batches. After continuous stirring and dissolution for a second predetermined time, a uniform basic electrolyte is formed, and then it is subjected to aging treatment. Step S4: Introduce composite additives: Adjust the base electrolyte to a predetermined temperature, and under stirring, add metal ion chelating agent, positive electrode film-forming additive, and mixed additive composed of negative electrode interface modifier and free radical scavenger in a predetermined order and manner. After each additive is added, stir for a third predetermined time, and after all additives are added, stir for a fourth predetermined time. Step S5, Post-processing and Finished Product Collection: The electrolyte with the additives mixed is filtered, collected, inspected for quality, and aged to obtain the final high-voltage lithium metal battery electrolyte product.

2. The high-voltage lithium metal battery electrolyte prepared by the method for preparing a high-voltage lithium metal battery electrolyte according to claim 1.

3. The method for preparing a high-voltage lithium metal battery electrolyte according to claim 1, characterized in that, The first lithium salt is lithium difluorosulfonylimide, the second lithium salt is lithium difluorooxalate borate, and the first lithium salt and the second lithium salt are used in combination in a specific molar ratio.

4. The method for preparing a high-voltage lithium metal battery electrolyte according to claim 1, characterized in that, The main solvent is a fluorinated cyclic carbonate, and the co-solvent is a fluorinated chain ether compound with a specific fluorinated segment structure.

5. The method for preparing a high-voltage lithium metal battery electrolyte according to claim 1, characterized in that, The functional additives include trialkylsilyl phosphate compounds as positive electrode film-forming additives, lithium fluorinated borate salts as negative electrode interface modifiers, organophosphorus compounds as free radical scavengers and flame retardants, and lactone compounds as metal ion chelating agents.

6. The method for preparing a high-voltage lithium metal battery electrolyte according to claim 1, characterized in that, In step S3, the ambient temperatures when the first lithium salt and the second lithium salt are added are different, and the temperature at which the second lithium salt is dissolved is higher than the temperature at which the first lithium salt is dissolved.

7. The method for preparing a high-voltage lithium metal battery electrolyte according to claim 1, characterized in that, In step S4, the negative electrode interface conditioner and the free radical scavenger are pre-dissolved in a portion of the basic electrolyte before being added to form an additive premix before being introduced together.

8. The method for preparing a high-voltage lithium metal battery electrolyte according to claim 1, characterized in that, The aging process in step S3 refers to letting the base electrolyte, after the lithium salt has been completely dissolved, stand at a specific temperature for a predetermined period of time.

9. The method for preparing a high-voltage lithium metal battery electrolyte according to claim 1, characterized in that, The aging process mentioned in step S5 refers to letting the filtered and inspected finished electrolyte stand at room temperature and in the dark for a predetermined period of time.

10. The method for preparing a high-voltage lithium metal battery electrolyte according to claim 2, characterized in that, It includes a dual-salt system consisting of a first lithium salt and a second lithium salt, a mixed solvent system consisting of a main solvent and a co-solvent, and a composite additive system consisting of at least four functional additives.

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