An asymmetric organic sulfonamide lithium salt, a preparation method and application thereof

Abstract

The application discloses an asymmetric organic sulfonamide lithium salt and a preparation method and application thereof, relates to the technical field of lithium metal batteries, and the asymmetric organic sulfonamide lithium salt is Li(TFEEC-FSI) containing a trifluoroether ester-fluorosulfonylimide branched chain and Li(EEC-FSI) containing an ether ester-fluorosulfonylimide branched chain, and a modified electrolyte is prepared by adding the asymmetric organic lithium salt and LiNO3 into a carbonate-based electrolyte; the modified electrolyte optimizes Li + solvation structure, improves Li + ion migration number, increases CBE apparent donor number to increase LiNO3 solubility, regulates an electrode / electrolyte interface to form a stable SEI film, realizes uniform lithium deposition, and improves the rate performance, cycle stability and low-temperature adaptability of a lithium metal battery, and the energy density of a 5.0 Ah grade Li||NCM811 soft package battery is 472 Wh kg ‑1 .

Description

Technical Field

[0001] This application belongs to the field of lithium metal battery technology, and particularly relates to an asymmetric organic sulfonamide-based lithium salt, its preparation method and application. Background Technology

[0002] Lithium metal batteries have an extremely high theoretical specific capacity (3860 mAh g) due to the lithium metal anode. -1 With its extremely low standard electrode potential (-3.04 VVs. SHE), lithium metal is considered a core choice for next-generation high-energy-density energy storage devices, showing broad application prospects in electric vehicles, large-scale energy storage power stations, and other fields. However, lithium metal anodes are prone to dendrite growth during cycling, leading to instability at the electrode / electrolyte interface. The resulting solid electrolyte interphase (SEI) film is easily broken and remodeled, causing problems such as reduced battery coulombic efficiency and shortened cycle life. In severe cases, it can even puncture the separator and cause a short circuit, hindering the commercialization of lithium metal batteries.

[0003] To address these issues, researchers have developed various strategies, among which electrolyte modification is one of the most practical and economical methods. Lithium nitrate (LiNO3), a classic electrolyte additive, can form a stable SEI film rich in Li3N on the lithium metal surface, effectively inhibiting lithium dendrite growth. However, LiNO3 has extremely low solubility in conventional carbonate-based electrolytes (CBE), making it difficult to fully utilize its capabilities in practical applications and limiting the improvement of modification effects.

[0004] Organic lithium salts, as a key component of electrolytes, have molecular structures that directly affect the properties of Li. + Solvation structure, ion migration behavior, and interfacial film formation properties. While traditional symmetrical organic lithium salts (such as LiTFSI) can improve electrolyte conductivity, they also play a role in regulating Li... + Its ability to solubilize the environment, improve LiNO3 solubility, and synergistically stabilize the interface is limited. Therefore, it is necessary to develop a method that optimizes LiNO3's solubility. + Novel organic lithium salts with solvation structures, improved LiNO3 solubility, and controlled interfacial film-forming properties have become key technological requirements for overcoming the performance bottleneck of lithium metal batteries. Summary of the Invention

[0005] Technical problem solved: This application provides an asymmetric organic sulfonamide-based lithium salt, its preparation method and application, which solves the technical problems of low LiNO3 solubility in conventional carbonate-based electrolytes, poor cycle stability of lithium metal batteries and insufficient energy density in the prior art.

[0006] Objective of the Invention: This application provides an asymmetric organic sulfonamide-based lithium salt, its preparation method, and its application. Through its unique molecular structure design, it achieves a synergistic effect with LiNO3, solving the interface stability and electrolyte performance defects of lithium metal batteries and improving the overall battery performance. Firstly, two asymmetric organic lithium salts, Li(TFEEC-FSI) and Li(EEC-FSI), are designed and synthesized. By introducing trifluoroether ester or ether ester polar branches and combining them with fluorosulfonamide anions, an asymmetric structure with a high dipole moment is constructed. Secondly, the above-mentioned asymmetric organic lithium salts and LiNO3 are added as synergistic additives to conventional carbonate-based electrolytes to prepare modified electrolytes. The strong cation-anion interaction and high apparent donor number of the organic lithium salts are utilized to optimize the LiNO3 content. + The method involves three main aspects: first, solubilizing the structure and improving the solubility of LiNO3; second, applying the modified electrolyte to lithium metal batteries, and achieving uniform lithium deposition by synergistically regulating the composition and structure of the SEI film, thereby improving the battery's rate performance, cycle stability, and low-temperature adaptability.

[0007] Technical solution: A method for preparing an asymmetric organosulfonamide lithium salt, wherein the asymmetric organosulfonamide lithium salt is Li (TFEEC-FSI) containing a trifluoroether ester-fluorosulfonamide branch or Li (EEC-FSI) containing an ether ester-fluorosulfonamide branch, wherein the preparation method of Li (TFEEC-FSI) containing a trifluoroether ester-fluorosulfonamide branch includes the following specific steps: The first step is to prepare fluorosulfonyl isocyanate: Under a nitrogen atmosphere, 30 mmol of chlorosulfonyl isocyanate and 10 mmol of antimony trifluoride (1.79 g) are mixed in a 100 mL round-bottom flask by molar ratio, and after stirring magnetically at 90 °C for 24 h, fluorosulfonyl isocyanate is obtained by distillation at 80 °C. The second step was to prepare ({[2-(2,2,2-trifluoroethoxy)ethoxy]carbonyl})(fluorosulfonyl)imide: Under a nitrogen atmosphere, 80 mL of anhydrous dichloromethane and 20 mmol of 2-(2,2,2-trifluoroethoxy)ethanol (2.96 g) were added to a two-necked round-bottom flask by molar volume ratio. After cooling to 0 °C and maintaining the temperature for 10 min, 21 mmol of fluorosulfonyl isocyanate obtained in the first step was added dropwise. The mixture was stirred at room temperature for 8 h, and after removing the solvent, the product ({[2-(2,2,2-trifluoroethoxy)ethoxy]carbonyl})(fluorosulfonyl)imide was obtained. The third step is to prepare Li(TFEEC-FSI): Under a nitrogen atmosphere, 25 mmol of ({[2-(2,2,2-trifluoroethoxy)ethoxy]carbonyl})(fluorosulfonyl)imide obtained in the second step and 50 mL of anhydrous diethyl ether were added to a double-necked round-bottom flask at a molar volume ratio. After cooling to -78°C and maintaining the temperature for 15 min, 10 mmol of n-butyllithium was added dropwise. The mixture was stirred at room temperature for 1 h. After removing the solvent, the target product Li(TFEEC-FSI) was obtained.

[0008] Furthermore, the preparation method of the ether ester-fluorosulfonyl imide-branched Li(EEC-FSI) includes the following specific steps: Step 1, Preparation of fluorosulfonyl isocyanate: Under a nitrogen atmosphere, 30 mmol of chlorosulfonyl isocyanate and 10 mmol of antimony trifluoride (1.79 g) were mixed in a 100 mL round-bottom flask by molar ratio, and after magnetic stirring at 90 °C for 24 h, fluorosulfonyl isocyanate was obtained by distillation at 80 °C. Step 2, Preparation of ({[2-(ethoxy)ethoxy]carbonyl})(fluorosulfonyl)imide: Under a nitrogen atmosphere, 80 mL of anhydrous dichloromethane and 20 mmol of 2-ethoxyethanol were added to a two-necked round-bottom flask at a molar volume ratio. After cooling to 0 °C and maintaining the temperature for 10 min, 21 mmol of the fluorosulfonyl isocyanate prepared in Step 1 was added dropwise. The mixture was stirred at room temperature for 8 h. After removing the solvent, the product ({[2-(ethoxy)ethoxy]carbonyl})(fluorosulfonyl)imide was obtained. Step 3, Preparation of Li(EEC-FSI): Under a nitrogen atmosphere, 25 mmol of ({[2-(ethoxy)ethoxy]carbonyl})(fluorosulfonyl)imide obtained in step 2 and 50 mL of anhydrous diethyl ether were added to a double-necked round-bottom flask at a molar volume ratio. After cooling to -78°C and maintaining the temperature for 15 min, 10 mmol of n-butyllithium was added dropwise. The mixture was stirred at room temperature for 1 h. After removing the solvent, the target product Li(EEC-FSI) was obtained.

[0009] An asymmetric organic sulfonamide lithium salt prepared by any of the above preparation methods, wherein the asymmetric organic sulfonamide lithium salt is as shown in Formula I: Formula I In the formula, R is an alkane with 5 or fewer carbon atoms or a fluorinated substituted alkane.

[0010] This application also discloses the application of the asymmetric organic sulfonamide lithium salt prepared by any of the above preparation methods in modified electrolytes. The Li(TFEEC-FSI) and lithium nitrate LiNO3 are added as synergistic additives to carbonate-based electrolyte CBE and stirred in a constant temperature water bath at 60°C for 2-4 hours until LiNO3 is completely dissolved to obtain a clear and transparent Li(TFEEC-FSI)+LiNO3 / CBE modified electrolyte.

[0011] Furthermore, the concentration of Li(TFEEC-FSI) in the modified electrolyte is 0.15 M, and the concentration of LiNO3 is 0.1 M.

[0012] Furthermore, the carbonate-based electrolyte CBE is prepared by dissolving 1.0 M lithium hexafluorophosphate (LiPF6) in a co-solvent of ethylene carbonate (EC) and diethyl carbonate (DEC), with a volume ratio of EC:DEC = 1:1.

[0013] This application also discloses the application of asymmetric organic sulfonamide-based lithium salts prepared by any of the above-described preparation methods in lithium metal batteries, including Li||LFP batteries, Li||NCM811 batteries, and 5.0Ah-grade Li||NCM811 pouch batteries; the battery assembly process is carried out in an argon glove box or a dry room with a dew point below -50°C, wherein the H2O and O2 content in the argon glove box is <0.12500 polypropylene membrane, and the modified electrolyte prepared by the asymmetric organic sulfonamide-based lithium salt is used as the modified electrolyte in the lithium metal battery.

[0014] Furthermore, the Li||LFP battery and Li||NCM811 battery are coin cells. The coin cells use a CR2032 type casing, with lithium metal foil as the negative electrode, LFP or NCM811 as the positive electrode, and a polypropylene PP porous membrane as the separator. After being injected with the modified electrolyte, they are encapsulated.

[0015] Furthermore, the positive electrode of the Li||NCM811 battery is a high-load NCM811 electrode with an areal mass loading of 14.9-15.0 mg cm⁻¹. -2 The voltage window is 2.8-4.4V; the positive electrode of the 5.0Ah grade Li||NCM811 pouch cell uses a double-sided high-load NCM811 electrode.

[0016] Beneficial effects: 1. Significant advantages of asymmetric organolithium salt structure design: The Li(TFEEC-FSI) and Li(EEC-FSI) prepared in this invention adopt an asymmetric molecular structure. The strong polarity of the trifluoroether ester or ether ester side chains endows the molecule with a high dipole moment, which can react with Li + Stable coordination is formed, and the strong electron-withdrawing ability of the fluorosulfonamide anion enhances the interaction between cations and anions, significantly optimizing Li... + Solvation structure, making Li + The mobility number is increased to above 0.5, reducing concentration polarization; 2. Outstanding synergistic solubilizing effect: The ether / trifluoroether ester branches of the asymmetric organic lithium salt can increase the apparent donor number of the electrolyte, thereby increasing the solubility of LiNO3 in conventional carbonate-based electrolytes from below 0.05 M to 0.1 M, achieving full dissolution of LiNO3 and playing an interfacial regulation role, solving the core pain point of low solubility of LiNO3 in traditional electrolytes; 3. Significantly improved interface stability: In the modified electrolyte, Li(TFEEC-FSI) and LiNO3 work synergistically to form a composite SEI film rich in Li3N, LiF and organic esters on the surface of the lithium metal anode. This film has high ionic conductivity, low electronic conductivity and good mechanical toughness, which can effectively inhibit lithium dendrite growth and achieve uniform lithium deposition. This allows the Li||NCM811 coin cell to retain more than 92% of its capacity after 100 cycles at 0.5 C rate. 4. Excellent overall battery performance: The energy density of a 5.0Ah-grade Li||NCM811 pouch battery using the modified electrolyte of this invention can reach 472 Wh kg. -1 Far exceeding traditional carbonate-based electrolyte batteries (approximately 400 Wh kg) -1 Meanwhile, at a low temperature of -20℃, the capacity retention rate at a 0.2 C discharge rate reaches 75% of the room temperature capacity, demonstrating good low-temperature adaptability and obvious advantages in low-temperature energy storage scenarios. 5. Simple preparation process and strong compatibility: The organic lithium salt synthesis steps of the present invention are simple, the raw materials are readily available, and the reaction conditions are mild (no high temperature and high pressure required), making it suitable for large-scale production; the preparation of the modified electrolyte only requires simple mixing and stirring, and it is highly compatible with existing lithium metal battery production processes, making it easy to promote industrialization. Attached Figure Description

[0017] Figure 1 The diagram shows the molecular structure of the asymmetric lithium salt synthesized in Examples 1 and 2 of this application. Figure 2 The asymmetric lithium salt synthesized in Example 1 of this application 1 H NMR spectrum; Figure 3 The asymmetric lithium salt synthesized in Example 1 of this application 13 C NMR spectrum; Figure 4 The asymmetric lithium salt synthesized in Example 1 of this application 19 F nuclear magnetic resonance spectrum; Figure 5 The asymmetric lithium salt synthesized in Example 1 of this application 7 Li NMR spectrum; Figure 6 The asymmetric lithium salt synthesized in Example 2 of this application1 H NMR spectrum; Figure 7 The asymmetric lithium salt synthesized in Example 2 of this application 13 C NMR spectrum; Figure 8 The asymmetric lithium salt synthesized in Example 2 of this application 19 F nuclear magnetic resonance spectrum; Figure 9 The asymmetric lithium salt synthesized in Example 2 of this application 7 Li NMR spectrum; Figure 10 The images show the cycle performance and optical photographs of a pouch cell based on the Li(TFEEC-FSI)+LiNO3 / CBE modified electrolyte prepared in Example 3 of this application. The left image is a cycle performance graph, and the right image is an optical photograph. Detailed Implementation

[0018] To make the objectives and advantages of this invention clearer, the invention will be specifically described below with reference to embodiments. It should be understood that the following text is merely used to describe one or more specific embodiments of the invention and does not strictly limit the scope of protection specifically claimed by the invention.

[0019] Example 1: A method for synthesizing an asymmetric organosulfonamide lithium salt Li (TFEEC-FSI), comprising the following specific steps: Step 1, Synthesis of fluorosulfonyl isocyanate: In a 100 mL round-bottom flask under a nitrogen atmosphere, 30 mmol of chlorosulfonyl isocyanate (3.87 g) and 10 mmol of antimony trifluoride (1.79 g) were mixed in a molar ratio. A spherical condenser was installed, and the flask was placed on a heat-collecting, constant-temperature magnetic stirrer at 500 rpm and 90 °C for 24 h. After stirring, the condenser was removed, and a distillation apparatus was used. The oil bath temperature was set to 80 °C, and the vacuum distillation was performed at 0.08 MPa. The fraction collected at 45-47 °C yielded 18.2 mmol of fluorosulfonyl isocyanate (2.01 g), with a yield of 60.7%. The second step involved the synthesis of the imide intermediate ({[2-(2,2,2-trifluoroethoxy)ethoxy]carbonyl})(fluorosulfonyl)imide: Under a nitrogen atmosphere, 80 mL of anhydrous dichloromethane and 20 mmol of 2.96 g of 2-(2,2,2-trifluoroethoxy)ethanol were added to a 250 mL double-necked round-bottom flask at a molar volume ratio. The flask was placed in an ice bath, and a thermometer was inserted to monitor the system temperature. After the temperature stabilized at 0 °C and was maintained for 10 min, 21 mmol of the fluorosulfonyl isocyanate prepared in the first step was added dropwise through a constant-pressure dropping funnel at a dropping rate of 1 drop / second, while maintaining the system temperature ≤5 °C during the addition process. After the addition was complete, the ice bath was removed, and the mixture was stirred at 400 rpm for 8 hours at room temperature (25°C). After the reaction was completed, the reaction solution was transferred to a rotary evaporator, and anhydrous dichloromethane was removed under reduced pressure at 40°C to obtain 10.23 g of 37.5 mmol pale yellow oily liquid ({[2-(2,2,2-trifluoroethoxy)ethoxy]carbonyl})(fluorosulfonyl)imide intermediate, yield 91.5%. The third step is the preparation of Li(TFEEC-FSI): Under a nitrogen atmosphere, 25 mmol of 6.82 g of ({[2-(2,2,2-trifluoroethoxy)ethoxy]carbonyl})(fluorosulfonyl)imide obtained in the second step and 50 mL of anhydrous diethyl ether were added to a 250 mL double-necked round-bottom flask. The flask was placed in a liquid nitrogen-ethanol low-temperature bath, cooled to -78 °C and kept at this temperature for 15 min. Then, 10 mmol of n-butyllithium was dissolved in 6.25 mL of 1.6 M hexane solution to prepare an n-butyllithium solution. The n-butyllithium solution was added dropwise through a constant-pressure dropping funnel at a dropping rate of 1 drop / second, and the system temperature was kept ≤-70 °C during the dropping process. After the addition was complete, the cryogenic bath was slowly removed, and the temperature was naturally raised to room temperature (25°C). Stirring continued for 1 hour. After the reaction was complete, anhydrous diethyl ether was removed under reduced pressure at 40°C to obtain a white solid. This solid was transferred to a vacuum drying oven and dried under vacuum at 60°C for 24 hours to obtain 7.12 g of 23.8 mmol Li(TFEEC-FSI) product, with a yield of 95.2%. High-performance liquid chromatography (HPLC) analysis showed that the product purity was ≥99.0%.

[0020] Example 2, a method for synthesizing an asymmetric organic sulfonamide lithium salt Li (EEC-FSI), comprising the following specific steps: Step 1, Synthesis of fluorosulfonyl isocyanate: In a 100 mL round-bottom flask under a nitrogen atmosphere, 30 mmol of chlorosulfonyl isocyanate (3.87 g) and 10 mmol of antimony trifluoride (1.79 g) were mixed in a molar ratio. A spherical condenser was installed, and the flask was placed on a heat-collecting, constant-temperature magnetic stirrer at 500 rpm and 90 °C for 24 h. After stirring, the condenser was removed, and a distillation apparatus was used. The oil bath temperature was set to 80 °C, and the vacuum distillation was performed at 0.08 MPa. The fraction collected at 45-47 °C yielded 18.2 mmol of fluorosulfonyl isocyanate (2.01 g), with a yield of 60.7%. The second step involves the synthesis of the imide intermediate ({[2-(ethoxy)ethoxy]carbonyl})(fluorosulfonyl)imide: Under a nitrogen atmosphere, 80 mL of anhydrous dichloromethane and 1.80 g of 20 mmol 2-ethoxyethanol were added to a 250 mL double-necked round-bottom flask at a molar volume ratio. The flask was placed in an ice bath, and a thermometer was inserted to monitor the system temperature. After the temperature stabilized at 0 °C and was kept at that temperature for 10 min, 2.32 g of 21 mmol of the fluorosulfonyl isocyanate prepared in the first step was added dropwise through a constant-pressure dropping funnel at a dropping rate of 1 drop / second. During the dropping process, the system temperature was kept ≤5 °C. After the addition was complete, the ice bath was removed, and the mixture was stirred at 400 rpm for 8 hours at room temperature (25°C). After the reaction was completed, the reaction solution was transferred to a rotary evaporator, and anhydrous dichloromethane was removed under reduced pressure at 40°C to obtain 8.52 g of 38.1 mmol pale yellow oily liquid ({[2-(ethoxy)ethoxy]carbonyl})(fluorosulfonyl)imide intermediate, with a yield of 93.0%. The third step is the preparation of Li(EEC-FSI): Under a nitrogen atmosphere, 5.69 g of 25 mmol of ({[2-(ethoxy)ethoxy]carbonyl})(fluorosulfonyl)imide obtained in the second step and 50 mL of anhydrous diethyl ether were added to a 250 mL double-necked round-bottom flask. The flask was placed in a liquid nitrogen-ethanol low-temperature bath, cooled to -78 °C and kept at that temperature for 15 min. Then, 10 mmol of n-butyllithium was dissolved in 6.25 mL of 1.6 M hexane solution to prepare n-butyllithium solution. The n-butyllithium solution was added dropwise through a constant pressure dropping funnel at a dropping rate of 1 drop / second, and the system temperature was kept ≤-70 °C during the dropping process. After the addition was complete, the cryogenic bath was slowly removed, and the temperature was naturally raised to room temperature (25°C). Stirring continued for 1 hour. After the reaction was complete, anhydrous diethyl ether was removed under reduced pressure at 40°C to obtain a white solid. This solid was transferred to a vacuum drying oven and dried under vacuum at 60°C for 24 hours to obtain 5.80 g of 24.1 mmol Li(EEC-FSI) product, with a yield of 96.4%. High-performance liquid chromatography (HPLC) analysis showed that the product purity was ≥99.0%.

[0021] Example 3: Application of asymmetric organic sulfonamide lithium salt in the preparation of modified electrolyte Li(TFEEC-FSI)+LiNO3 / CBE. First, carbonate-based electrolyte CBE was prepared: In an argon glove box, 50 mL of ethylene carbonate (EC) and 50 mL of diethyl carbonate (DEC) were mixed, and 15.20 g of 1.0 M lithium hexafluorophosphate (LiPF6) was added. The mixture was magnetically stirred at 500 rpm for 2 h until LiPF6 was completely dissolved, resulting in a clear and transparent CBE. Subsequently, 2.26 g of 0.15 M Li(TFEEC-FSI) prepared in Example 1 and 0.69 g of 0.1 M LiNO3 were added to the above CBE. The mixture was placed in a 60°C constant temperature water bath and stirred at 400 rpm for 2.5 h. Samples were taken every 30 min during the process until LiNO3 was completely dissolved, resulting in a clear and transparent modified electrolyte Li(TFEEC-FSI)+LiNO3 / CBE. According to the moisture content tester, the electrolyte moisture content of the polypropylene film is ≤152500.

[0022] Comparative Example 1: Pure CBE electrolyte. Only the above-mentioned CBE was prepared without any additives, serving as a blank control.

[0023] Comparative Example 2, LiNO3 / CBE electrolyte. Only 0.1 M LiNO3 was added to CBE. After stirring at 60°C for 4 hours, a large amount of LiNO3 remained undissolved, and the system was turbid. After centrifugation, the supernatant was collected, and the actual solubility of LiNO3 was determined to be 0.018 M.

[0024] Example 4: Application of asymmetric organic sulfonamide lithium salts in lithium metal batteries, assembly and performance testing of lithium metal batteries: Battery Assembly: Li||NCM811 button cell assembly. In an argon-filled glove box, using a CR2032 battery case as a carrier, the positive electrode shell and a high-load NCM811 positive electrode sheet (12 mm diameter, areal mass load 14.95 mg cm⁻¹) were placed sequentially. -2 Surface capacity 3.02 mAh cm -2 The following materials were prepared: a PP porous separator (16 mm in diameter), the modified electrolyte prepared in Example 3 (50 μL injected into each battery), lithium metal foil (14 mm in diameter and 50 μm in thickness), a spring sheet, and a negative electrode shell. The materials were sealed using a battery sealing machine and left to stand for 12 hours for later use.

[0025] 5.0Ah-grade Li||NCM811 pouch cell assembly. The assembly was performed in a dry chamber with a dew point below -50°C, using double-sided high-load NCM811 cathode sheets (100 mm × 50 mm, single-sided areal mass loading 24.0 mg cm⁻¹). -2 Single-sided capacity 4.8 mAh / cm³ -2The battery cell was assembled using a stacking process with lithium metal foil (102 mm × 52 mm, 50 μm thick) and a polyethylene / polypropylene composite separator (104 mm × 54 mm). The modified electrolyte prepared in Example 3 was injected (12.5 g), vacuum-sealed, and left to stand for 24 h before formation treatment.

[0026] Comparative Example 3: Using the pure CBE electrolyte of Comparative Example 1, a Li||NCM811 coin cell was assembled according to the method of Example 4.

[0027] Comparative Example 4: Using the LiNO3 / CBE electrolyte of Comparative Example 2, a Li||NCM811 coin cell was assembled according to the method of Example 4.

[0028] Performance testing: Electrochemical performance testing: The coin cells of Example 4, Comparative Examples 3 and 4 were subjected to cycle performance testing using a CT-3008W battery testing system. The test conditions were 2.8-4.4V (vs. Li / Li). + ), 0.5 C charge / discharge rate; the rate performance test conditions are 2.8-4.4V, charged and discharged at 0.2 C, 0.5 C, 1 C, 2 C and 5 C rates respectively, with 5 cycles at each rate; the low temperature performance test conditions are -20℃, 0.2 C rate charge / discharge.

[0029] Test results: After 100 cycles at 0.5 C rate, the coin cell of Example 4 retained 92.3% of its capacity and had an average coulombic efficiency of 99.6%; its discharge specific capacity at 0.2 C rate was 192.5 mAh g. -1 The specific capacity at a 5C rate discharge is 158.2 mAh g. -1 The rate performance retention rate was 82.2%; the capacity retention rate at -20℃ and 0.2C discharge was 75.1% of the room temperature capacity. In contrast, the coin cell of Comparative Example 3 retained only 65.8% of its capacity after 100 cycles, and its 5C rate discharge specific capacity was 102.4 mAh g⁻¹. -1 The discharge capacity retention rate at -20℃ was 42.3%; the capacity retention rate of the coin cell in Comparative Example 4 was 78.5% after 100 cycles, and the specific capacity at a 5C rate discharge was 125.6 mAh g. -1 The discharge capacity retention rate at -20℃ is 58.7%.

[0030] Soft-pack battery performance test: After formation at 0.1 C, the 5.0 Ah soft-pack battery of Example 5 retained 94.8% of its capacity after 50 cycles at 0.3 C rate. The energy density was calculated to be 472 Wh kg by weighing method. -1The discharge capacity retention rate at -20℃ and 0.2 C rate is 74.8% of the room temperature capacity, demonstrating excellent performance in practical applications.

[0031] The above description is merely a preferred embodiment of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention. Structures and preparation methods not specifically described or explained in this invention, unless otherwise specified or limited, shall be implemented according to conventional methods in the art.

Claims

1. A method for preparing an asymmetric organosulfonamide lithium salt, characterized in that, The asymmetric organic sulfonamide lithium salt is either Li (TFEEC-FSI) containing a trifluoroether ester-fluorosulfonamide branch or Li (EEC-FSI) containing an ether ester-fluorosulfonamide branch. The preparation method of Li (TFEEC-FSI) containing a trifluoroether ester-fluorosulfonamide branch includes the following specific steps: The first step is to prepare fluorosulfonyl isocyanate: Under a nitrogen atmosphere, 30 mmol of chlorosulfonyl isocyanate and 10 mmol of antimony trifluoride (1.79 g) are mixed in a 100 mL round-bottom flask by molar ratio, and after stirring magnetically at 90 °C for 24 h, fluorosulfonyl isocyanate is obtained by distillation at 80 °C. The second step was to prepare ({[2-(2,2,2-trifluoroethoxy)ethoxy]carbonyl})(fluorosulfonyl)imide: Under a nitrogen atmosphere, 80 mL of anhydrous dichloromethane and 20 mmol of 2-(2,2,2-trifluoroethoxy)ethanol (2.96 g) were added to a two-necked round-bottom flask by molar volume ratio. After cooling to 0 °C and maintaining the temperature for 10 min, 21 mmol of fluorosulfonyl isocyanate obtained in the first step was added dropwise. The mixture was stirred at room temperature for 8 h, and after removing the solvent, the product ({[2-(2,2,2-trifluoroethoxy)ethoxy]carbonyl})(fluorosulfonyl)imide was obtained. The third step is to prepare Li(TFEEC-FSI): Under a nitrogen atmosphere, 25 mmol of ({[2-(2,2,2-trifluoroethoxy)ethoxy]carbonyl})(fluorosulfonyl)imide obtained in the second step and 50 mL of anhydrous diethyl ether were added to a double-necked round-bottom flask at a molar volume ratio. After cooling to -78°C and maintaining the temperature for 15 min, 10 mmol of n-butyllithium was added dropwise. The mixture was stirred at room temperature for 1 h. After removing the solvent, the target product Li(TFEEC-FSI) was obtained.

2. The method for preparing an asymmetric organic sulfonamide lithium salt according to claim 1, characterized in that: The preparation method of the ether ester-fluorosulfonyl imide branched Li(EEC-FSI) includes the following specific steps: Step 1, Preparation of fluorosulfonyl isocyanate: Under a nitrogen atmosphere, 30 mmol of chlorosulfonyl isocyanate and 10 mmol of antimony trifluoride (1.79 g) were mixed in a 100 mL round-bottom flask by molar ratio, and after magnetic stirring at 90 °C for 24 h, fluorosulfonyl isocyanate was obtained by distillation at 80 °C. Step 2, Preparation of ({[2-(ethoxy)ethoxy]carbonyl})(fluorosulfonyl)imide: Under a nitrogen atmosphere, 80 mL of anhydrous dichloromethane and 20 mmol of 2-ethoxyethanol were added to a two-necked round-bottom flask at a molar volume ratio. After cooling to 0 °C and maintaining the temperature for 10 min, 21 mmol of the fluorosulfonyl isocyanate prepared in Step 1 was added dropwise. The mixture was stirred at room temperature for 8 h. After removing the solvent, the product ({[2-(ethoxy)ethoxy]carbonyl})(fluorosulfonyl)imide was obtained. Step 3, Preparation of Li(EEC-FSI): Under a nitrogen atmosphere, 25 mmol of ({[2-(ethoxy)ethoxy]carbonyl})(fluorosulfonyl)imide obtained in step 2 and 50 mL of anhydrous diethyl ether were added to a double-necked round-bottom flask at a molar volume ratio. After cooling to -78°C and maintaining the temperature for 15 min, 10 mmol of n-butyllithium was added dropwise. The mixture was stirred at room temperature for 1 h. After removing the solvent, the target product Li(EEC-FSI) was obtained.

3. An asymmetric organosulfonamide lithium salt prepared by the method of claim 1 or 2, characterized in that: The asymmetric organic sulfonamide lithium salt is shown in Formula I: Equation I In the formula, R is an alkane with 5 or fewer carbon atoms or a fluorinated substituted alkane.

4. The application of an asymmetric organic sulfonamide lithium salt prepared by the method of claim 1 or 2 in the preparation of modified electrolytes, characterized in that: The Li(TFEEC-FSI) and lithium nitrate LiNO3 were added as synergistic additives to the carbonate-based electrolyte CBE and stirred in a constant temperature water bath at 60°C for 2-4 hours until the LiNO3 was completely dissolved, resulting in a clear and transparent Li(TFEEC-FSI)+LiNO3 / CBE modified electrolyte.

5. The application according to claim 4, characterized in that: The concentration of Li(TFEEC-FSI) in the modified electrolyte is 0.15 M, and the concentration of LiNO3 is 0.1 M.

6. The application according to claim 4, characterized in that: The carbonate-based electrolyte CBE is prepared by dissolving 1.0 M lithium hexafluorophosphate (LiPF6) in a co-solvent of ethylene carbonate (EC) and diethyl carbonate (DEC), with a volume ratio of EC:DEC = 1:

1.

7. The application of an asymmetric organic sulfonamide-based lithium salt prepared by the method of claim 1 or 2 in a lithium metal battery, characterized in that: The lithium metal battery includes Li||LFP battery, Li||NCM811 battery and 5.0Ah-grade Li||NCM811 pouch battery; the battery assembly process is carried out in an argon glove box or a dry room with a dew point below -50°C, wherein the argon glove box contains H2O and O2 content < 0.12500 polypropylene membrane, and the modified electrolyte prepared by the asymmetric organic sulfonamide lithium salt is used as the modified electrolyte in the lithium metal battery.

8. The application according to claim 7, characterized in that: The Li||LFP battery and Li||NCM811 battery are button cells. The button cells use a CR2032 type casing, with lithium metal foil as the negative electrode, LFP or NCM811 as the positive electrode, and a polypropylene (PP) porous membrane as the separator. After the modified electrolyte is injected, the cells are encapsulated.

9. The application according to claim 7, characterized in that: The positive electrode of the Li||NCM811 battery is a high-load NCM811 electrode with an areal mass loading of 14.9-15.0 mg cm⁻¹. -2 The voltage window is 2.8-4.4V; the positive electrode of the 5.0Ah grade Li||NCM811 pouch cell uses a double-sided high-load NCM811 electrode.

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