Preparation method of low-cost high-specific-energy battery electrolyte and application thereof

Abstract

The application relates to a preparation method of a low-cost high-specific-energy battery electrolyte and application thereof and relates to the technical field of lithium metal battery electrolytes. The application realizes the synergistic regulation of the solvation structure of an electrolyte and the electrode interface reaction by constructing a propyl acetate (EP) / fluorinated ethylene carbonate (FEC) / tetrahydrofuran (THF) composite solvent system, taking lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) as a main lithium salt and introducing lithium difluoro(oxalato)borate (LiDFOB) functional lithium salt, so that the cycle stability and the rate performance of a high-nickel positive electrode / lithium metal battery are improved. The low-cost high-specific-energy battery electrolyte prepared by the application has the advantages of a wide electrochemical stability window, excellent interface compatibility and good comprehensive performance balance, still maintains excellent rate capacity output capacity at an extremely low temperature of -30 DEG C, is suitable for the application of high-energy-density lithium metal batteries, and simultaneously shows excellent high-rate capacity retention capacity and long-term cycle stability.

Description

Technical Field

[0001] This invention relates to the field of lithium metal battery electrolyte technology, specifically to a method for preparing a low-cost, high-energy-density battery electrolyte and its application. Background Technology

[0002] With the rapid development of new energy vehicles and high-end energy storage systems, higher demands are being placed on the energy density and lifespan of lithium-ion and lithium metal batteries. Ternary cathode materials, due to their high specific capacity and operating voltage, are considered an important cathode choice for achieving high-energy-density batteries; while lithium metal anodes, due to their extremely high theoretical specific capacity, have become the ideal anode for next-generation battery systems. However, when ternary cathodes and lithium metal anodes are directly coupled, the stability of the electrolyte-electrode interface becomes particularly prominent, severely restricting the practical application of this type of battery.

[0003] Currently widely used commercial electrolytes are typically based on carbonate solvents and use lithium hexafluorophosphate (LiPF6) as the lithium salt. Under high-voltage ternary cathode operating conditions, commercial electrolytes are prone to oxidative decomposition, leading to interfacial film instability, transition metal dissolution, and a continuous increase in impedance. Simultaneously, on the lithium metal anode side, traditional electrolytes struggle to induce the formation of a uniform and dense solid electrolyte interfacial film, easily causing lithium dendrite growth, continuous electrolyte consumption, and a decrease in coulombic efficiency, thereby affecting the battery's cycle life and safety.

[0004] To address these issues, researchers have attempted to optimize the electrolyte system by introducing novel lithium salts, low-viscosity solvents, and functional additives. LiTFSI exhibits high thermal stability and ionic conductivity, while carboxylic acid ester solvents offer low viscosity and good transport properties, which are beneficial for improving the overall kinetic characteristics of the electrolyte. Furthermore, boron- and nitrogen-containing lithium salt additives show potential advantages in regulating the chemical composition of the electrode interface. However, current technologies still lack an electrolyte system capable of simultaneously stabilizing the interface on both sides of the high-voltage ternary cathode and the lithium metal anode, making it difficult to balance the high-voltage stability of the cathode with the long-term cycling reliability of the anode.

[0005] Therefore, it is necessary to develop a multi-component synergistic composite electrolyte that, through the rational combination of the main lithium salt, solvent system and functional additive salts, forms a stable protective structure at the interface between the ternary cathode and the lithium metal anode, thereby improving the overall electrochemical performance of NCM / / Li batteries under high voltage conditions. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a method for preparing a low-cost, high-energy-density battery electrolyte and its application.

[0007] This invention constructs a composite solvent system of ethyl propionate (EP) / fluoroethylene carbonate (FEC) / tetrahydrofuran (THF), with lithium bis(trifluoromethanesulfonylimide) (LiTFSI) as the main lithium salt and introduces LiDFOB functional lithium salt to achieve synergistic regulation of electrolyte solvation structure and electrode interface reaction, thereby improving the cycle stability and rate performance of high-nickel cathode / lithium metal batteries.

[0008] A method for preparing a low-cost, high-energy-density battery electrolyte is specifically carried out according to the following steps:

[0009] Lithium bis(trifluoromethanesulfonyl)imide was added to a container, followed by ethyl propionate and magnetic stirring. Then, fluoroethylene carbonate was added and magnetic stirring continued. Tetrahydrofuran was added and magnetic stirring continued. Finally, lithium difluorooxalateborate was added and the reaction was stirred to obtain a low-cost, high-energy-density battery electrolyte.

[0010] Advantages of this invention:

[0011] I. Compared with commercial electrolytes, the low-cost, high-energy-density battery electrolyte prepared by this invention can effectively suppress side reactions at the positive electrode interface under high voltage conditions and construct a stable and dense interfacial film structure on the surface of the lithium metal negative electrode, thereby reducing interfacial impedance and improving the cycle stability and coulombic efficiency of the battery.

[0012] II. The low-cost, high-energy-density battery electrolyte prepared by this invention has the advantages of a wide electrochemical stability window, excellent interfacial compatibility, and good overall performance balance. It still maintains excellent rate capacity output capability at an extreme low temperature of -30℃, and is suitable for high-energy-density lithium metal battery applications.

[0013] III. In high areal density (12 mg·cm³) -2 Under the same conditions, the low-cost, high-energy-density battery electrolyte prepared by this invention exhibits excellent high-rate capacity retention and long-term cycling stability in NCM811 / / Li half-cells, while commercial carbonate electrolytes show rapid capacity decay under the same conditions, indicating obvious interface failure and kinetic limitations. Attached Figure Description

[0014] Figure 1 Raman spectra of PCFB, PCF3B, PCF5B, and PCF;

[0015] Figure 2 To utilize PCFB, PCF3B, PCF5B and PCF electrolytes and a low-load NCM811 electrode (2.3 mg / cm²), respectively. 2 Rate performance graph of assembled NCM811 / / Li half-cell;

[0016] Figure 3To utilize PCFB and low-load NCM811 (2.3 mg / cm³) 2 Assembled NCM811 / / Li half-cells and utilizing BE37 and low-load NCM811 (2.3 mg / cm³). 2 Charge-discharge curves of assembled NCM811 / / Li half-cells at different rates;

[0017] Figure 4 To utilize PCFB and high-load NCM811 (12 mg / cm³) 2 Assembled NCM811 / / Li half-cell and its utilization

[0018] BE37 and high-load NCM811 (12 mg / cm³) 2 Rate plot of assembled NCM811 / / Li half-cell;

[0019] Figure 5 To utilize PCFB and high-load NCM811 (12 mg / cm³) 2 The NCM811 / / Li half-cell was assembled and utilized with BE37 and a high loading of NCM811 (12 mg / cm³). 2 Long-cycle diagram of assembled NCM811 / / Li half-cell at 1C charge / 2C discharge;

[0020] Figure 6 for Figure 5 Impedance spectra of the battery collected in real time during charging and discharging. The left figure shows the impedance spectrum obtained using BE37 and a high-load NCM811 (12 mg / cm²). 2 The right figure shows an NCM811 / / Li half-cell assembled using PCFB and a high-load NCM811 (12 mg / cm³). 2 Assembled NCM811 / / Li half-cell;

[0021] Figure 7 To employ a 20μm thin lithium anode and a high-load NCM811 electrode (12mg / cm²) 2 Cyclic performance diagram of assembled NCM811 / / Li half-cell;

[0022] Figure 8 The graph shows the ionic conductivity test results of BE37 and PCFB electrolytes at different temperatures.

[0023] Figure 9 To utilize PCFB and high-load NCM811 (12 mg / cm³) 2 The NCM811 / / Li half-cell was assembled and utilized with BE37 and a high loading of NCM811 (12 mg / cm³). 2 Rate curve of assembled NCM811 / / Li half-cell at -30℃;

[0024] Figure 10 Impedance diagrams of NCM811 / / NCM81 symmetrical cells at different temperatures are shown. The left diagram shows the NCM811 / / NCM811 symmetrical cell assembled using BE37 electrolyte, and the right diagram shows the NCM811 / / NCM811 symmetrical cell assembled using PCFB electrolyte. Detailed Implementation

[0025] Specific Implementation Method 1: This implementation method is a low-cost, high-energy-density battery electrolyte preparation method, specifically completed according to the following steps:

[0026] Lithium bis(trifluoromethanesulfonyl)imide was added to a container, followed by ethyl propionate and magnetic stirring. Then, fluoroethylene carbonate was added and magnetic stirring continued. Tetrahydrofuran was added and magnetic stirring continued. Finally, lithium difluorooxalateborate was added and the reaction was stirred to obtain a low-cost, high-energy-density battery electrolyte.

[0027] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the preparation of the low-cost, high-energy-density battery electrolyte is completed inside a glove box; the H2O concentration inside the glove box is <0.01ppm, and the O2 concentration is <0.01ppm. Other steps are the same as in Specific Implementation Method One.

[0028] Specific Implementation Method 3: This implementation method differs from Specific Implementation Method 1 or 2 in that the volume ratio of ethyl propionate, fluoroethylene carbonate, and tetrahydrofuran is (80~90):(10~20):10. Other steps are the same as in Specific Implementation Method 1 or 2.

[0029] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that the volume ratio of ethyl propionate, fluoroethylene carbonate, and tetrahydrofuran is 85:15:10. The other steps are the same as in Specific Implementation Methods One to Three.

[0030] Specific Implementation Method Five: This implementation method differs from Specific Implementation Methods One to Four in that the concentration of lithium bis(trifluoromethanesulfonyl)imide in the low-cost, high-energy-density battery electrolyte is 0.8 mol / L to 1.2 mol / L. The other steps are the same as in Specific Implementation Methods One to Four.

[0031] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One to Five in that the concentration of lithium bis(trifluoromethanesulfonyl)imide in the low-cost, high-energy-density battery electrolyte is 1 mol / L. The other steps are the same as in Specific Implementation Methods One to Five.

[0032] Specific Implementation Method Seven: The difference between this implementation method and Specific Implementation Methods One to Six is ​​that the concentration of lithium difluorooxalate borate in the low-cost, high-energy-density battery electrolyte is 0.1 mol / L to 0.5 mol / L. The other steps are the same as in Specific Implementation Methods One to Six.

[0033] Specific Implementation Method Eight: The difference between this implementation method and Specific Implementation Methods One to Seven is that the concentration of lithium difluorooxalate borate in the low-cost, high-energy-density battery electrolyte is 0.3 mol / L. The other steps are the same as in Specific Implementation Methods One to Seven.

[0034] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Methods One to Eight in that the magnetic stirring time is 10-30 minutes; the stirring reaction time is 1-2 hours. Other steps are the same as in Specific Implementation Methods One to Eight.

[0035] Specific Implementation Method 10: This implementation method is the application of a low-cost, high-energy-density battery electrolyte in ternary cathode materials / lithium metal anode batteries.

[0036] The beneficial effects of the present invention are verified using the following embodiments:

[0037] Example 1: A method for preparing a low-cost, high-energy-density battery electrolyte (PCFB), specifically comprising the following steps:

[0038] In a glove box filled with argon (H2O < 0.01 ppm, O2 < 0.01 ppm), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) was added to the container, followed by ethyl propionate (EP). The mixture was magnetically stirred at 300 rpm for 10 min, then fluoroethylene carbonate (FEC) was added, and the mixture was magnetically stirred at 300 rpm for another 10 min. Tetrahydrofuran (THF) was then added, and the mixture was magnetically stirred at 300 rpm for 30 min. Finally, lithium difluorooxalate borate (LiDFOB) was added, and the mixture was magnetically stirred at 300 rpm for 2 h to obtain a low-cost, high-energy-density battery electrolyte (denoted as PCFB).

[0039] The volume ratio of ethyl propionate, fluoroethylene carbonate and tetrahydrofuran is 85:15:10.

[0040] The concentration of lithium bis(trifluoromethanesulfonyl)imide in the low-cost, high-energy-density battery electrolyte is 1 mol / L;

[0041] The concentration of lithium difluorooxalate borate in the low-cost, high-energy-density battery electrolyte is 0.1 mol / L.

[0042] Example 2: The difference between this example and Example 1 is that the concentration of lithium difluorooxalate borate in the low-cost, high-energy-density battery electrolyte is 0.3 mol / L; the resulting low-cost, high-energy-density battery electrolyte is designated PCF3B. All other steps and parameters are the same as in Example 1.

[0043] Example 3: The difference between this example and Example 1 is that the concentration of lithium difluorooxalate borate in the low-cost, high-energy-density battery electrolyte is 0.5 mol / L; the resulting low-cost, high-energy-density battery electrolyte is designated PCF5B. All other steps and parameters are the same as in Example 1.

[0044] Comparative Example 1: The difference between this example and Example 1 is that the concentration of lithium difluorooxalate borate in the low-cost, high-energy-density battery electrolyte is 0 mol / L; the resulting electrolyte is denoted as PCF. All other steps and parameters are the same as in Example 1.

[0045] Comparative Example 2: LiPF6 was dissolved in a mixture of EC (ethylene carbonate) and EMC (ethyl methyl carbonate) (the volume ratio of EC to EMC was 3:7) to obtain an electrolyte (denoted as BE37); the concentration of LiPF6 in the electrolyte was 1 mol / L.

[0046] To investigate the effect of LiDFOB addition on the solvation structure of the electrolyte, Raman spectroscopy was performed on different electrolyte systems. For example... Figure 1 As shown;

[0047] Figure 1 Raman spectra of PCFB, PCF3B, PCF5B, and PCF;

[0048] from Figure 1 It can be seen that after the addition of LiDFOB, the relevant characteristic peaks in the electrolyte showed significant changes, indicating that Li... + The coordination environment between LiDFOB and the solvent and anion is regulated. As the concentration of LiDFOB increases, the solvation structure gradually changes, indicating that LiDFOB can participate in the Li... + The first solvation shell regulates the ion coordination environment.

[0049] Preparation of NCM811 electrode sheets (low loading NCM811-2.3 mg / cm²) 2 High load NCM 811-12mg / cm 2 ):

[0050] 1. Raw material drying: Conductive carbon black Super-P, NCM811 powder and PVDF powder are placed in a vacuum oven at 80℃ and dried for 24 hours.

[0051] II. Preparation of slurry:

[0052] 2.3mg-NCM811 slurry preparation: Weigh 0.1g Super-P powder, 0.1g PVDF powder, and 1.8g NCM811 powder, grind them manually in a mortar for 25min, add the ground powder to a slurry bottle, use anhydrous NMP (N-methylpyrrolidone) as solvent, add 3.5mL NMP to the slurry bottle, and stir with a magnetic stirrer at 300rpm for 12h;

[0053] Preparation of 12mg-NCM811 slurry: Weigh 0.6g Super-P powder, 0.6g PVDF powder and 4.8g NCM811 powder and add them to a homogenizer. Add 10mL of anhydrous NMP to the homogenizer and stir for 12h under vacuum and at 300rpm.

[0054] III. Electrode Coating

[0055] 2.3mg-NCM811 electrode: Coated 50 microns using slurry from the slurry bottle;

[0056] 12mg-NCM811 electrode: The slurry is coated to a thickness of 600 microns using a homogenizer;

[0057] IV. Drying the electrode sheets: Place them in a vacuum oven and dry them at 80℃ for 12 hours;

[0058] V. Rolling: All dried electrode sheets need to be rolled. The rolling pressure for 2.3mg-NCM811 electrode sheets is 4 tons and the holding pressure is 20 seconds; the rolling pressure for 12mg-NCM811 electrode sheets is 3 tons and the holding pressure is 1 minute.

[0059] VI. Cut the two different load electrodes into 12mm diameter round pieces using a cutting machine to obtain the low-load NCM811 electrode (2.3mg / cm²). 2 ) and high-load NCM811 electrode (12mg / cm) 2 It is used for subsequent button cell assembly.

[0060] The NCM811 positive electrode prepared above was transferred to a glove box filled with argon atmosphere (H2O < 0.01 ppm, O2 < 0.01 ppm). Using the NCM811 positive electrode as the working electrode, a lithium metal sheet as the counter electrode and reference electrode, a polyolefin membrane as the separator, and the electrolyte prepared in the examples or comparative examples as the electrolyte, a CR2032 type NCM811 / / Li coin cell was assembled.

[0061] Specifically, the positive electrode shell, NCM811 positive electrode sheet, separator, lithium metal sheet, gasket, spring sheet, and negative electrode shell are placed in sequence, and electrolyte is added dropwise at the interface between the separator and the electrode, 30µL each time, twice, for a total of 60µL, so that the electrolyte fully wets the interface between the positive electrode sheet, separator, and lithium sheet; then, a button cell sealing machine is used for pressing and sealing to obtain an NCM811 / / Li half cell.

[0062] The NCM811 cathode sheet includes a low-load NCM811 cathode sheet and a high-load NCM811 cathode sheet. The active material areal loading of the low-load NCM811 cathode sheet is 2.3 mg / cm³. 2 It is mainly used for rate performance testing and charge-discharge curve testing at different rates; the active material areal loading of the high-load NCM811 positive electrode is 12 mg / cm³. 2 It is mainly used for high load rate performance testing, long cycle testing, in-situ impedance testing and low temperature rate performance testing.

[0063] remove Figure 7 Except for the lithium-poor conditions shown in the test, all other NCM811 / / Li half-cells used a lithium metal sheet with a thickness of approximately 450 μm as the negative electrode. Figure 7 The test shown uses a lithium metal sheet with a thickness of approximately 20 μm as the negative electrode to evaluate the stabilizing effect of the electrolyte of the present invention on the lithium metal negative electrode interface under low excess lithium conditions.

[0064] To further determine the optimal addition amount, rate performance tests were conducted in NCM811 / / Li half-cells. Figure 2 As shown;

[0065] Figure 2 To utilize PCFB, PCF3B, PCF5B and PCF electrolytes and a low-load NCM811 electrode (2.3 mg / cm²), respectively. 2 Rate performance graph of assembled NCM811 / / Li half-cell;

[0066] Under different LiDFOB concentrations, the batteries exhibited significantly different rate performances. The PCFB electrolyte showed the best capacity retention at high rates, while increasing the LiDFOB concentration to 0.3M and 0.5M significantly increased battery polarization and decreased rate performance. These results indicate that an appropriate amount of LiDFOB can optimize the electrode interface structure and improve kinetic performance, while excessive addition may increase ion migration resistance, which is detrimental to high-rate operation.

[0067] The results in summary indicate that the optimal electrochemical performance can be obtained by introducing 0.1 M LiDFOB into the EP / FEC / THF composite solvent system.

[0068] Figure 3 To utilize PCFB and low-load NCM811 (2.3 mg / cm³) 2 Assembled NCM811 / / Li half-cells and utilizing BE37 and low-load NCM811 (2.3 mg / cm³). 2 Charge-discharge curves of assembled NCM811 / / Li half-cells at different rates;

[0069] from Figure 3 It can be seen that, due to the small electrode thickness and low ion diffusion resistance under this load condition, the test results can effectively reflect the influence of the electrolyte on the reversible lithium insertion / extraction reaction and high voltage stability of the cathode material.

[0070] Test results show that the battery using the electrolyte PCFB prepared by this invention exhibits a lower polarization voltage and better overlap of charge and discharge curves in the high voltage region, indicating that the electrolyte can stably support the reversible electrochemical reaction of the high-nickel cathode without introducing additional side reactions.

[0071] Figure 4 To utilize PCFB and high-load NCM811 (12 mg / cm³) 2 Assembled NCM811 / / Li semi-electric

[0072] The pool utilizes BE37 and high-load NCM811 (12 mg / cm³). 2 The assembled NCM811 / / Li half-cell has a multiple of

[0073] Rate graph;

[0074] Figure 4 The interfacial stability and kinetic compatibility of the electrolyte of the present invention under high areal capacity and high current density conditions were verified.

[0075] from Figure 4 It can be seen that: at the positive electrode surface density of 12 mg·cm⁻¹ -2 Under the conditions described above, the NCM811 / / Li half-cell using the electrolyte PCFB of this invention can still maintain a high specific capacity output during the high-rate test from 1C to 4C, and shows good capacity recovery capability in the rate recovery test; in contrast, the control cell using commercial carbonate electrolyte rapidly decays in capacity under high-rate conditions and is difficult to recover.

[0076] Figure 5 To utilize PCFB and high-load NCM811 (12 mg / cm³) 2 The NCM811 / / Li half-cell was assembled and utilized with BE37 and a high loading of NCM811 (12 mg / cm³). 2Long-cycle diagram of assembled NCM811 / / Li half-cell at 1C charge / 2C discharge;

[0077] like Figure 5 As shown, in long-term cycling tests under high areal density NCM811 cathode conditions, the half-cell using the electrolyte of this invention still maintains a capacity retention of about 91.5% after about 270 cycles, while the capacity retention of the comparative cell using commercial carbonate electrolyte is only about 21.6%. This indicates that the electrolyte of this invention can significantly improve the cycling stability of the high nickel cathode system under lithium metal anode conditions.

[0078] To further elucidate the mechanism by which the electrolyte of this invention enhances the electrochemical performance of the battery, in-situ electrochemical impedance spectroscopy was performed in the NCM811 / / Li half-cell system. For example... Figure 6 As shown, this test dynamically tracks the formation and evolution of the electrode / electrolyte interface impedance by acquiring impedance spectra in real time during the actual charging and discharging process of the battery.

[0079] Figure 6 for Figure 5 Impedance spectra of the battery collected in real time during charging and discharging. The left figure shows the impedance spectrum obtained using BE37 and a high-load NCM811 (12 mg / cm²). 2 The right figure shows an NCM811 / / Li half-cell assembled using PCFB and a high-load NCM811 (12 mg / cm³). 2 Assembled NCM811 / / Li half-cell;

[0080] Test results show that the interfacial impedance of the battery using the electrolyte PCFB of the present invention increases slowly and remains stable during cycling, indicating that the electrolyte can form a stable and low-impedance interfacial film structure on the electrode surface, thus providing reliable mechanistic support for its excellent electrochemical performance under high load and high rate conditions.

[0081] To further evaluate the interfacial stability of the electrolyte of this invention in lithium anode bias engineering applications, a cathode loading of 12 mg·cm⁻¹ was used. -2 In the NCM811 / / Li half-cell, a lithium anode with a thickness of approximately 20 μm was used for cycle testing. Apart from this test, all other NCM811 / / Li half-cells used a lithium sheet with a thickness of approximately 450 μm as the anode. Because the available lithium in the system is significantly reduced under the 20 μm thin lithium condition, the battery is highly sensitive to side reactions at the lithium anode interface and lithium deposition behavior, thus effectively amplifying the differences in lithium anode stability among different electrolyte systems.

[0082] Figure 7 To employ a 20μm thin lithium anode and a high-load NCM811 electrode (12mg / cm²) 2Cyclic performance diagram of assembled NCM811 / / Li half-cell;

[0083] Figure 7 The results showed that the control battery using commercial carbonate electrolyte rapidly decreased in capacity during cycling and failed after about 40 cycles; in contrast, the battery using the electrolyte PCFB of the present invention was able to maintain a high specific capacity output after 100 cycles, showing a significantly improved cycle stability.

[0084] To verify that the electrolyte of the present invention can still maintain a high Li content under the conditions of the solvent and lithium salt combination, + The transmission capacity was assessed to provide fundamental kinetic support for stable electrochemical performance under high load and high rate conditions. Ionic conductivity was tested, and the results are as follows: Figure 8 As shown;

[0085] Figure 8 The graph shows the ionic conductivity test results of BE37 and PCFB electrolytes at different temperatures.

[0086] Figure 8 The test results show that for BE37, the Z' intercept shifts significantly to the right as the temperature increases from 20°C to -30°C, and the impedance increases significantly, especially at -20°C and -30°C. However, under the same conditions, the Z' increase is much smaller for PCFB, and it still maintains a low overall impedance level at -30°C.

[0087] To further verify the practical electrochemical application capability of the electrolyte PCFB of the present invention under low-temperature conditions, based on the above 12 mg / cm 2 A high-load NCM811 / / Li half-cell system was subjected to gradient rate charge-discharge tests at -30℃, using charge-discharge rates of 0.05C, 0.1C, 0.2C, 0.5C, and 1C. The low-temperature output and polarization characteristics of the PCFB electrolyte and the commercial BE37 electrolyte were compared. Figure 9 As shown.

[0088] Figure 9 To utilize PCFB and high-load NCM811 (12 mg / cm³) 2 The NCM811 / / Li half-cell was assembled and utilized with BE37 and a high loading of NCM811 (12 mg / cm³). 2 Rate curve of assembled NCM811 / / Li half-cell at -30℃;

[0089] The results of the -30℃ low temperature gradient rate test show that ( Figure 9 The NCM811 / / Li half-cell assembled using PCFB electrolyte achieved a first discharge specific capacity of ~180 mAh·g at a 0.05C rate.-1 Even with a rate increase to 1C, it can still maintain ~80mAh·g -1 The effective capacity output demonstrates excellent low-temperature rate adaptability; while the commercial BE37 electrolyte has a discharge specific capacity of only ~170 mAh·g at a rate of 0.05C. -1 Furthermore, the capacity drops sharply after the rate is increased to 0.5C, and there is almost no effective capacity output at 1C rate (<10mAh·g). -1 This indicates that its ion transport kinetics are severely limited at -30℃.

[0090] The assembly method of NCM811 / / NCM811 symmetrical cells is as follows: First, a high-load NCM811 electrode (12mg / cm³) is used. 2 An NCM811 / / Li half-cell was assembled with lithium plates and charged with constant current to bring the NCM811 electrodes to the same state of charge (50% SOC). The battery was then disassembled in an argon glove box, and two NCM811 electrodes with the same state of charge were taken as the two electrodes of the symmetrical battery. A polyolefin separator was placed in the middle and the corresponding electrolyte was added to assemble the NCM811 / / NCM811 symmetrical battery. After the battery was allowed to stand and equilibrate at a set temperature, an electrochemical impedance spectroscopy test was performed.

[0091] To eliminate the influence of the lithium anode, the effect of the present invention's electrolyte PCFB on the NCM811 cathode / electrolyte interface impedance was evaluated separately to clarify the true source of impedance reduction and performance improvement. Symmetrical impedance tests of NCM811 / / NCM811 at different temperatures were performed as follows: Figure 10 As shown;

[0092] Figure 10 Impedance diagrams of NCM811 / / NCM811 symmetrical cells at different temperatures are shown. The left diagram shows the NCM811 / / NCM811 symmetrical cell assembled using BE37 electrolyte, and the right diagram shows the NCM811 / / NCM811 symmetrical cell assembled using PCFB electrolyte.

[0093] The NCM811 / / NCM811 symmetrical impedance test, under the condition of eliminating the influence of the lithium metal anode, can focus on reflecting the cathode / electrolyte interface film (CEI), the low-temperature conductivity of the electrolyte, and the Li... + The influence of factors such as desolvation kinetics on interfacial impedance;

[0094] Test results show that, compared with commercial carbonate electrolytes, the electrolyte PCFB of this invention significantly reduces the interfacial impedance of NCM811 / / NCM811 symmetrical cells under conditions of -10°C to -30°C, and the impedance growth trend is gradual. This indicates that the electrolyte can form a stable and low-impedance interfacial structure on the positive electrode surface, thus further verifying its contribution to improving battery dynamic performance from the positive electrode side.

Claims

1. A method of preparing a low cost high specific energy battery electrolyte, characterized in that The preparation method is specifically carried out according to the following steps: Lithium bis(trifluoromethanesulfonyl)imide was added to a container, followed by ethyl propionate and magnetic stirring. Then, fluoroethylene carbonate was added and magnetic stirring continued. Tetrahydrofuran was added and magnetic stirring continued. Finally, lithium difluorooxalateborate was added and the reaction was stirred to obtain a low-cost, high-energy-density battery electrolyte.

2. The method for preparing a low-cost, high-energy-density battery electrolyte according to claim 1, characterized in that... The preparation of the low-cost, high-energy-density battery electrolyte is completed inside a glove box; the glove box contains H2O < 0.01 ppm and O2 < 0.01 ppm.

3. The method for preparing a low-cost, high-energy-density battery electrolyte according to claim 1, characterized in that... The volume ratio of ethyl propionate, fluoroethylene carbonate and tetrahydrofuran is (80~90):(10~20):

10.

4. The method for preparing a low-cost, high-energy-density battery electrolyte according to claim 3, characterized in that... The volume ratio of ethyl propionate, fluoroethylene carbonate, and tetrahydrofuran is 85:15:

10.

5. The method for preparing a low-cost, high-energy-density battery electrolyte according to claim 1, characterized in that... The concentration of lithium bis(trifluoromethanesulfonyl)imide in the low-cost, high-energy-density battery electrolyte is 0.8 mol / L to 1.2 mol / L.

6. The method for preparing a low-cost, high-energy-density battery electrolyte according to claim 5, characterized in that... The concentration of lithium bis(trifluoromethanesulfonyl)imide in the low-cost, high-energy-density battery electrolyte is 1 mol / L.

7. The method for preparing a low-cost, high-energy-density battery electrolyte according to claim 1, characterized in that... The concentration of lithium difluorooxalate borate in the low-cost, high-energy-density battery electrolyte is 0.1 mol / L to 0.5 mol / L.

8. The method for preparing a low-cost, high-energy-density battery electrolyte according to claim 7, characterized in that... The concentration of lithium difluorooxalate borate in the low-cost, high-energy-density battery electrolyte is 0.3 mol / L.

9. The method for preparing a low-cost, high-energy-density battery electrolyte according to claim 1, characterized in that... The magnetic stirring time is 10 min to 30 min; the stirring reaction time is 1 h to 2 h.

10. The application of the low-cost, high-energy-density battery electrolyte prepared by the preparation method according to claim 1, characterized in that... Application of low-cost, high-energy-density battery electrolytes in ternary cathode / lithium metal anode batteries.

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