Ionic liquid-based perfluorinated high-voltage-resistant lithium battery electrolyte and preparation method therefor

Abstract

Disclosed are an ionic liquid-based perfluorinated high-voltage-resistant lithium battery electrolyte and a preparation method therefor. The high-voltage-resistant electrolyte is composed of an imidazolyl ionic liquid, a lithium salt, and an electrolyte additive. The ionic liquid-based electrolyte has relatively reversible and stable lithium stripping / deposition performance, exhibits good compatibility with a lithium metal / graphite negative electrode, and can also form a highly fluorinated stable electrode-electrolyte interface (CEI / SEI layer), thus improving the compatibility of the ionic liquid electrolyte with a high-voltage lithium cobaltate positive electrode, and effectively inhibiting dendrite formation and oxidation dissolution of the electrolyte, thereby achieving extremely high cycle stability and Coulombic efficiency of a lithium battery under high voltage conditions.

Description

An ionic liquid-based perfluorinated high-voltage-resistant lithium battery electrolyte and a preparation method thereof TECHNICAL FIELD

[0001] The present application belongs to the technical field of lithium battery electrolyte, and particularly relates to an ionic liquid-based perfluorinated high-voltage-resistant lithium battery electrolyte and a preparation method thereof. BACKGROUND

[0002] Traditional ester-based electrolytes based on ethylene carbonate (EC) have poor anode stability, which makes them extremely unstable for high-voltage cathodes. EC and other solvent molecules can undergo oxidation and polymerization reactions on the high-catalytic surface of the layered cathode material, thereby forming protective polycarbonate substances. However, these polycarbonate substances are still not stable enough at high voltage. Even the relatively stable Li2CO3 in the solid electrolyte layer (SEI) will be oxidized above 3.5 V, releasing oxygen or carbon dioxide, which puts higher requirements on the oxidation resistance of the electrolyte. The low anode stability of commercial EC-based electrolytes greatly limits the high-voltage cathode material, and even within the voltage range of the electrolyte, the increased resistance during overcharging and cycling easily raises the potential of the cathode to the unstable region of the electrolyte and triggers safety problems. Therefore, it is necessary to find a high-safety high-voltage-resistant electrolyte that can effectively improve the compatibility of the electrolyte and the electrode interface while maintaining excellent thermal / chemical stability. TECHNICAL PROBLEM

[0003] Ionic liquids are miscible with organic solvents, have negligible vapor pressure even at elevated temperatures, are generally chemically stable, especially thermally stable, can exhibit a wide electrochemical stability window and high ionic conductivity, and are practically non-flammable and recyclable. In addition, through the chemical design of anions and cations, ionic liquids are tunable in their properties: ions can be combined in a variety of ways to tailor several properties such as melting point, solubility, and viscosity to meet the needs of the desired application. Ionic liquids have low viscosity and high ionic conductivity, for example, 1-ethyl-3-methylimidazolium bis((trifluoromethyl)sulfonyl)imide ([EMIm]TFSI) has been applied as a suitable electrolyte in lithium-ion batteries, lithium metal batteries, and lithium / air batteries, and is an excellent choice for lithium metal batteries. Compared with traditional non-fluorinated solvents, fluorinated solvent molecules have a larger energy gap between HOMO and LUMO, and have high electronegativity, low polarizability, and high ionic potential, as well as other expected properties, and can be used in high cutoff voltage (4.5 V or even 5 V vs. Li / Li +The use of fluorinated carbonates can improve the lithium plating / delamination performance, ionic conductivity, oxidative stability and non-flammability of the electrolyte system. Therefore, it is necessary to optimize the interface chemistry / electrochemical compatibility of fluorinated solvents with electrodes, develop new high-pressure fluorinated electrolytes with high ionic conductivity and low viscosity to solve the challenges faced by lithium batteries, and promote their commercialized applications. Technical solutions

[0004] Based on the above background, the present application provides an ionic liquid-based fully fluorinated high-voltage-resistant lithium battery electrolyte and a preparation method thereof. The ionic liquid-based electrolyte has good compatibility with lithium metal / graphite negative electrodes and lithium cobalt oxide positive electrodes, and has higher safety performance. At the same time, the electrolyte overcomes the problems of short service life, low capacity and electrolyte oxidative decomposition of lithium batteries under high voltage when using traditional electrolytes. The application of the electrolyte in lithium batteries can significantly improve the cycle stability and cycle life of the batteries under high voltage.

[0005] In order to achieve the above purpose, the technical scheme of the present application is as follows:

[0006] An ionic liquid-based fully fluorinated high-voltage-resistant lithium battery electrolyte and a preparation method thereof, characterized in that the high-voltage-resistant electrolyte is composed of an ionic liquid with a double trifluoromethyl sulfonimide group (TFSI - ), a lithium salt and an electrolyte additive; the preparation method comprises three steps of solvent water removal, electrolyte semi-fluorination and electrolyte full fluorination.

[0007] Preferably, the ionic liquid with a double trifluoromethyl sulfonimide group is one of 1-ethyl-3-methyl imidazole double trifluoromethyl sulfonimide salt ([EMIm]TFSI), 1-vinyl-3-ethyl imidazole double trifluoromethyl sulfonimide salt ([VEIm]TFSI), N-butyl-N-methyl pyrrolidine double trifluoromethyl sulfonimide salt (Pyr 14 TFSI) and N-methyl-N-propyl pyrrolidine double trifluoromethyl sulfonimide salt (Pyr 13 TFSI).

[0008] Preferably, the lithium salt is one or more of lithium difluoro(oxalato)borate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium difluoro(oxalato)borate, lithium tetrafluoroborate, lithium hexafluorophosphate, lithium trifluoromethanesulfonate and lithium perchlorate.

[0009] Preferably, the electrolyte additive includes fluorinated carbonate solvents, nitrate salts and fluorine-containing diluents.

[0010] Preferably, the fluorocarbonate solvent in the electrolyte additive is one or more of fluoroethylene carbonate, fluoroethyl methyl carbonate and fluoro-diethyl carbonate; the nitrate is one or more of sodium nitrate, magnesium nitrate and lithium nitrate; and the fluorine-containing diluent is one or both of fluoroether and fluorobenzene.

[0011] The electrolyte preparation method comprises the following steps:

[0012] (1) In an argon atmosphere glove box, ion liquid with bis-trifluoromethylsulfonylimide (TFSI - ), fluorocarbonate solvent and fluorine-containing diluent are all dehydrated using 4A molecular sieves, and then used, respectively, to obtain dehydrated ion liquid with bis-trifluoromethylsulfonylimide (TFSI - ), dehydrated fluorocarbonate solvent and dehydrated fluorine-containing diluent;

[0013] (2) A proper amount of lithium salt is dissolved in a certain volume of dehydrated ion liquid with bis-trifluoromethylsulfonylimide (TFSI - ), and the solution is kept stirring until all the lithium salt is dissolved, realizing semi-fluorination of the electrolyte and obtaining a semi-fluorinated electrolyte;

[0014] (3) The three electrolyte additives (dehydrated fluorocarbonate solvent, nitrate and dehydrated fluorine-containing diluent) are sequentially added to the semi-fluorinated electrolyte, and continue to stir for 12-24 h, finally obtaining a full-fluorinated high-pressure-resistant lithium battery electrolyte based on ion liquid.

[0015] Preferably, the molar concentration of lithium salt in the electrolyte is 0.5-1.5 mol / L.

[0016] Preferably, the volume ratio of ion liquid with bis-trifluoromethylsulfonylimide (TFSI - ) in the electrolyte to fluorocarbonate solvent to fluorine-containing diluent is 3: (1-3): 1.

[0017] Preferably, the concentration of nitrate in the electrolyte is 0.1-0.3 mol / L.

[0018] The lithium battery comprises a lithium cobalt oxide positive electrode, a lithium metal or graphite negative electrode and the aforementioned full-fluorinated high-pressure-resistant electrolyte based on ion liquid. Advantages

[0019] Compared with the prior art, the present application has the following advantages:

[0020] (1) The application obtains a perfluorinated high-voltage-resistant lithium battery electrolyte based on an ionic liquid and a preparation method thereof, wherein the ionic liquid has excellent thermal stability, good ionic conductivity and a wide electrochemical window. Moreover, the ionic liquid has no flash point and does not burn itself, so that the generation of combustible substances in the battery can be greatly reduced when the ionic liquid is used as a main solvent of the electrolyte, and the safety performance of the battery is improved.

[0021] (2) The application obtains a perfluorinated high-voltage-resistant lithium battery electrolyte based on an ionic liquid and a preparation method thereof, wherein the fluorocarbon carbonate additive can fluorinate the electrolyte, thereby increasing the oxidation potential of the solvent molecules, improving the stability of the solvent in the electrolyte and effectively reducing the oxidative decomposition of the electrolyte under high-voltage (4.5 V and above) conditions.

[0022] (3) The application obtains a perfluorinated high-voltage-resistant lithium battery electrolyte based on an ionic liquid and a preparation method thereof, wherein the NO3 − and electrochemical reduction of the fluorocarbon carbonate solvent form a solid-state electrolyte film (SEI layer) rich in Li3N-LiF components at the cathode-electrolyte interface, so as to realize rapid Li + transfer and uniform Li deposition, avoid the contact between the ionic liquid and the lithium metal and improve the chemical stability between the ionic liquid and the lithium metal.

[0023] (4) The perfluorinated high-voltage-resistant lithium battery electrolyte based on an ionic liquid obtained by the application has excellent compatibility with the positive and negative electrodes. The fluorine-containing diluent has the functions of adjusting the viscosity, conductivity and wettability of the solution, and the full fluorination enables the formation of a highly fluorinated interface on the electrode surface, effectively inhibits the formation of lithium dendrites, enables the lithium battery containing the same to achieve long cycle life and high coulombic efficiency, and has higher safety performance. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 is a thermogravimetric-differential scanning calorimetric curve (TG-DSC) of the perfluorinated high-voltage-resistant lithium battery electrolyte based on an ionic liquid prepared in Example 1 of the application

[0025] Figure 2 is a non-flammability test of the perfluorinated high-voltage-resistant lithium battery electrolyte based on an ionic liquid prepared in Example 1 of the application

[0026] Figure 3 is a scanning electron microscope image of lithium deposition in a lithium symmetric battery of a 1 M LiTFSI / [EMIm]TFSI electrolyte system prepared in Comparative Example 2 of the application

[0027] Figure 4 is a scanning electron microscope image of lithium deposition in a lithium symmetric battery of a perfluorinated high-voltage-resistant lithium battery electrolyte system based on an ionic liquid prepared in Example 2 of the application

[0028] Figure 5 is the element composition ratio of SEI layer at different sputtering times after 5 cycles of the ion liquid-based perfluorinated high-pressure-resistant lithium battery electrolyte prepared in Example 3

[0029] Figure 6 is the cyclic voltammetry (CV) curve of the ion liquid-based perfluorinated high-pressure-resistant lithium battery electrolyte prepared in Example 3 of the present application and the commercial electrolyte prepared in Comparative Example 1

[0030] Figure 7 is a comparison chart of the high-pressure resistance performance of the ion liquid-based perfluorinated high-pressure-resistant lithium battery electrolyte prepared in Example 6, the 1 M LiTFSI / [EMIm]TFSI electrolyte prepared in Comparative Example 2, and the commercial electrolyte prepared in Comparative Example 1. Embodiments of the present application

[0031] The present application will be further described in conjunction with the following specific examples and drawings. The process, conditions, experimental methods, etc. for implementing the present application, except for the following specifically mentioned contents, are the general knowledge and common sense in the art, and the present application has no special limitation.

[0032] Example 1

[0033] Preparation of electrolyte: in a glove box with argon atmosphere (oxygen content ≤0.5 ppm, water content <0.01 ppm)

[0034] (1) The [EMIm]TFSI ionic liquid, fluoroethylene carbonate, and fluoroether were all dehydrated using 4A molecular sieves before use;

[0035] (2) 1.4354 g of LiTFSI (0.5 mol / L) was dissolved in 6 mL of [EMIm]TFSI ionic liquid solvent, and the solution was kept stirring until all the lithium salt was dissolved, to obtain a semi-fluorinated electrolyte;

[0036] (3) The electrolyte additives were added in sequence: 2 mL of fluoroethylene carbonate, 0.15 mol / L of lithium nitrate, and 2 mL of fluoroether, and the stirring was continued for 12 h, to obtain the ion liquid-based perfluorinated high-pressure-resistant lithium battery electrolyte.

[0037] Preparation of battery positive electrode sheet: lithium cobaltate particles, conductive carbon black Super P, and polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 8:1:1 with N-methyl pyrrolidone (NMP) to prepare a positive electrode slurry. Then, the positive electrode slurry was coated on an aluminum foil, and after 80°C baking, rolling, and die cutting, a positive electrode sheet with a diameter of 12 mm was obtained, which was dried for use (moisture content less than 100 ppm).

[0038] Battery assembly: the positive electrode sheet with a diameter of 12 mm and lithium sheet with a diameter of 14 mm were assembled into CR2032 button cell with 16 μm double-sided ceramic PP separator and the electrolyte mentioned above in the glove box;

[0039] Battery cycle test: cycle test was carried out at 25°C using the new battery test system, after 12 h of rest, charged to 4.8 V, and discharged to 2.8 V at 1.2 mA / cm 2 charged to 4.8 V, and discharged to 2.8 V at 1.2 mA / cm 2 charged to 4.7 V, and discharged to 2.8 V at 1.2 mA / cm 2 charged to 4.7 V, and discharged to 2.8 V at 1.2 mA / cm 2 charged to 4.7 V, and discharged to 2.8 V at 1.2 mA / cm

[0040] Table 1 is the cycle results comparison of the ion liquid-based perfluorinated high-pressure-resistant lithium battery electrolyte according to the present application, commercial electrolyte and 1 M LiTFSI / [EMIm]TFSI ion liquid electrolyte.

[0041] Table 2 is the characteristic parameter comparison of the ion liquid-based perfluorinated high-pressure-resistant lithium battery electrolyte according to the present application, commercial electrolyte and 1 M LiTFSI / [EMIm]TFSI ion liquid electrolyte.

[0042] Figure 1 is the thermogravimetric-differential scanning calorimetry curve (TG-DSC) of the ion liquid-based perfluorinated high-pressure-resistant lithium battery electrolyte prepared in the present embodiment, as shown in Figure 1, the ion liquid-based perfluorinated high-pressure-resistant lithium battery electrolyte does not show obvious weight loss until 400°C, indicating that the electrolyte has good thermal stability. At the same time, the non-flammable (flame) test of Figure 2 shows that the ion liquid-based perfluorinated high-pressure-resistant lithium battery electrolyte cannot be ignited even if it is in contact with the flame for 10 seconds, showing good flame retardant performance.

[0043] Example 2

[0044] Preparation of electrolyte: in the glove box under argon atmosphere (oxygen content ≤0.5 ppm, water content <0.01 ppm)

[0045] (1) The [EMIm]TFSI ion liquid, fluoroethylene carbonate and fluoroether were all dehydrated using 4A molecular sieves;

[0046] (2) 3.6172 g LiTFSI (0.7 mol / L) was dissolved in 9 mL [EMIm]TFSI ion liquid solvent, and the solution was kept stirring until all the lithium salt was dissolved, to obtain a semi-fluorinated electrolyte;

[0047] (3) Add electrolyte additives in sequence: 6 mL of fluoroethylene carbonate, 0.3 mol / L of lithium nitrate and 3 mL of fluoroether, continue to stir for 20 h, to obtain the ionic liquid-based perfluorinated high-pressure-resistant lithium battery electrolyte.

[0048] The remaining steps are the same as those in Example 1, which will not be repeated here.

[0049] The cycle results are shown in Table 1.

[0050] The characteristic parameters are shown in Table 2.

[0051] In order to intuitively show the surface morphology of the lithium metal negative electrode, the lithium symmetrical battery after 5 cycles in the ionic liquid-based perfluorinated high-pressure-resistant lithium battery electrolyte was disassembled in an Ar-filled glove box, and the deposition morphology of Li was observed using SEM. As shown in FIG. 4, the lithium deposited in the ionic liquid-based perfluorinated high-pressure-resistant lithium battery electrolyte system is more uniform, showing a flat deposition layer with tight packing, high density, low specific surface area and large particle size, and no needle-shaped lithium dendrites are observed, which ensures stable and reversible lithium plating / stripping behavior. In contrast, the lithium deposition morphology cycled in the 1 M LiTFSI / [EMIm]TFSI electrolyte system prepared in Comparative Example 2 shows a large amount of collapse and cracks, and is highly loose (FIG. 3). Also, a large amount of dendritic lithium is observed, which will eventually pierce the separator and cause internal short circuit of the battery.

[0052] Example 3

[0053] Preparation of electrolyte: In an argon atmosphere glove box (oxygen content ≤0.5 ppm, water content <0.01 ppm)

[0054] (1) The [VEIm]TFSI ionic liquid, fluoroethylene carbonate and fluoroether are all dehydrated using 4A molecular sieves;

[0055] (2) Dissolve 2.3571 g of LiFSI (0.7 mol / L) in 9 mL of [VEIm]TFSI ionic liquid solvent, and keep stirring the solution until all the lithium salt is dissolved, to obtain a semi-fluorinated electrolyte;

[0056] (3) Add electrolyte additives in sequence: 6 mL of fluoroethylene carbonate, 0.3 mol / L of lithium nitrate and 3 mL of fluoroether, continue to stir for 20 h, to obtain the ionic liquid-based perfluorinated high-pressure-resistant lithium battery electrolyte.

[0057] The remaining steps are the same as those in Example 1, which will not be repeated here.

[0058] The cycle results are shown in Table 1.

[0059] The characteristic parameters are shown in Table 2.

[0060] Figure 5 is the element composition ratio of SEI layer at different sputtering times after 5 cycles in the perfluorinated high-voltage electrolyte prepared in Example 3, the weight percentage of fluorine element in the SEI generated by cycling in the perfluorinated electrolyte is 27% to 36%, which confirms that the SEI generated by cycling in the perfluorinated electrolyte is mainly LiF, which is beneficial to alleviate the redox decomposition of the electrolyte and the side reaction on the lithium metal negative electrode.

[0061] The electrochemical stability of the electrolyte was evaluated on a stainless steel electrode by cyclic voltammetry (CV), and the results are shown in Figure 6. For the conventional lithium battery commercial electrolyte (Comparative Example 1), due to the oxidative decomposition of the carbonate solvent, there is a clear peak at 4.5 V. The irreversible composition of the carbonate-based electrolyte results in a very high negative current even at 5 V, which indicates that the conventional commercial electrolyte has poor oxidative stability at high voltage. In contrast, the perfluorinated electrolyte prepared in this example maintains a low negative and stable current level in the range of 3.0 to 6.5 V, without obvious oxidation peak, showing strong oxidative stability.

[0062] Example 4

[0063] Preparation of electrolyte: in a glove box with argon atmosphere (oxygen content ≤0.5 ppm, water content <0.01 ppm)

[0064] (1) Dissolve 1.3094 g LiFSI (0.7 mol / L) in 6 mL Pyr 13 The TFSI ionic liquid, fluoroethyl methyl carbonate and fluorobenzene are all dehydrated with 4A molecular sieves before use;

[0065] (2) Dissolve 1.3094 g LiFSI (0.7 mol / L) in 6 mL Pyr 13 TFSI ionic liquid solvent, and keep stirring the solution until all the lithium salt is dissolved to obtain a semi-fluorinated electrolyte;

[0066] (3) Add electrolyte additives in sequence: 2 mL fluoroethyl methyl carbonate, 0.2 mol / L lithium nitrate and 2 mL fluorobenzene, continue to stir for 16 h to obtain a perfluorinated high-voltage resistant lithium battery electrolyte based on ionic liquid.

[0067] The remaining steps are the same as in Example 1 and will not be repeated here.

[0068] The cycling results are shown in Table 1.

[0069] The characteristic parameters are shown in Table 2.

[0070] Example 5

[0071] Preparation of electrolyte: In a glove box under argon atmosphere (oxygen content ≤ 0.5 ppm, water content < 0.01 ppm)

[0072] (1) [EMIm]TFSI ionic liquid, fluoroethylene carbonate and fluorobenzene were all used after being dehydrated by 4A molecular sieves;

[0073] (2) 1.8706 g LiFSI (1 mol / L) was dissolved in 6 mL [EMIm]TFSI ionic liquid solvent, and the solution was kept stirring until all the lithium salt was dissolved, to obtain a semi-fluorinated electrolyte;

[0074] (3) Electrolyte additives were added in sequence: 2 mL fluoroethylene carbonate, 0.2 mol / L lithium nitrate and 2 mL fluorobenzene, and the stirring was continued for 16 h, to obtain a full-fluorinated high-pressure-resistant lithium battery electrolyte based on ionic liquid.

[0075] The remaining steps were the same as those in Example 1, which will not be repeated here.

[0076] The cycling results are shown in Table 1.

[0077] The characteristic parameters are shown in Table 2.

[0078] Example 6

[0079] Preparation of electrolyte: In a glove box under argon atmosphere (oxygen content ≤ 0.5 ppm, water content < 0.01 ppm)

[0080] (1) [EMIm]TFSI ionic liquid, fluoroethylene carbonate and fluorobenzene were all used after being dehydrated by 4A molecular sieves;

[0081] (2) 1.8706 g LiFSI (1 mol / L) was dissolved in 6 mL [EMIm]TFSI ionic liquid solvent, and the solution was kept stirring until all the lithium salt was dissolved, to obtain a semi-fluorinated electrolyte;

[0082] (3) Electrolyte additives were added in sequence: 2 mL fluoroethylene carbonate, 0.2 mol / L lithium nitrate and 2 mL fluorobenzene, and the stirring was continued for 16 h, to obtain a full-fluorinated high-pressure-resistant lithium battery electrolyte based on ionic liquid.

[0083] The remaining steps were the same as those in Example 1, which will not be repeated here.

[0084] The cycling results are shown in Table 1.

[0085] The characteristic parameters are shown in Table 2.

[0086] Figure 7 is a comparison chart of the high voltage resistance of the ionic liquid-based perfluorinated high-voltage-resistant lithium battery electrolyte prepared in the present example and the 1 M LiTFSI / [EMIm]TFSI electrolyte prepared in Comparative Example 2 and the commercial ester-based electrolyte of Comparative Example 1. As can be seen, at the same current, such as 20 µA, the electrolyte of Example 6 only begins to decompose violently at greater than 5 V, while the 1 M LiTFSI / [EMIm]TFSI electrolyte and the commercial electrolyte begin to be extremely unstable at about 4 V.

[0087] Comparative Example 1

[0088] A certain amount of lithium hexafluorophosphate was added to ethylene carbonate and dimethyl carbonate in a volume ratio of 3:7, so that the concentration relative to the lithium salt was 1.0 mol / L. Stirring was performed until the electrolyte was completely clear, and a commercial ester-based lithium battery electrolyte was obtained.

[0089] The cycling results are shown in Table 1.

[0090] The characteristic parameters are shown in Table 2.

[0091] Comparative Example 2

[0092] In an argon atmosphere glove box (oxygen content ≤0.5 ppm, water content <0.01 ppm), [EMIm]TFSI ionic liquid was dehydrated using 4A molecular sieves, and then 2.8709 g LiTFSI (1 mol / L) was dissolved in 10 mL [EMIm]TFSI ionic liquid solvent. After stirring until uniform, a 1 M LiTFSI / [EMIm]TFSI ionic liquid electrolyte without electrolyte additives was obtained.

[0093] The cycling results are shown in Table 1.

[0094] The characteristic parameters are shown in Table 2.

[0095] Figure 3 is a scanning electron microscope image of lithium deposition in a lithium symmetrical battery of the electrolyte system prepared in the present comparative example.

[0096]

[0097]

Claims

1. An ionic liquid based, perfluorinated, high voltage resistant lithium battery electrolyte and a method for its preparation, characterized in that, The high-voltage-resistant electrolyte is composed of an ionic liquid with a double trifluoromethyl sulfonimide group (TFSI - ), a lithium salt, and an electrolyte additive; the preparation method comprises three steps of solvent dewatering, electrolyte semi-fluorination, and electrolyte full-fluorination.

2. An ionic liquid based, perfluorinated, high voltage resistant lithium battery electrolyte according to claim 1, characterized in that, The ionic liquid with a double trifluoromethylsulfonylimide group is one of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide salt ([EMIm]TFSI), 1-vinyl-3-ethylimidazolium bis(trifluoromethylsulfonyl)imide salt ([VEIm]TFSI), N-butyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide salt (Pyr 14 TFSI), N-methyl-N-propylpyrrolidinium bis(trifluoromethylsulfonyl)imide salt (Pyr 13 TFSI).

3. An ionic liquid based perfluorinated high voltage resistant lithium battery electrolyte according to claim 1, wherein, The lithium salt is one or more of lithium difluoro(oxalato)borate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium bis(oxalato)borate, lithium tetrafluoroborate, lithium hexafluorophosphate, lithium trifluoromethanesulfonate, lithium perchlorate.

4. An ionic liquid based, perfluorinated, high voltage resistant lithium battery electrolyte according to claim 1, wherein, The electrolyte additive includes a fluorocarbonate solvent, a nitrate, and a fluorine-containing diluent.

5. An ionic liquid based perfluorinated high voltage resistant lithium battery electrolyte according to claim 1, wherein, The fluorocarbonate solvent in the electrolyte additive is one or more of fluorinated ethylene carbonate, fluoroethylene carbonate, fluoroethyl methyl carbonate, and fluoro-diethyl carbonate; the nitrate is one or more of sodium nitrate, magnesium nitrate, and lithium nitrate; and the fluorine-containing diluent is one or more of fluoroether and fluorobenzene.

6. An ionic liquid based, perfluorinated, high voltage resistant lithium battery electrolyte according to claim 1, wherein, The specific preparation method of the electrolyte includes the following steps: (1) In an argon atmosphere glove box, the ion liquid with bis-trifluoromethylsulfonylimide (TFSI - ) group, fluorocarbonate solvent and fluorine-containing diluent were dehydrated by 4A molecular sieve, and then used, respectively, to obtain the ion liquid with bis-trifluoromethylsulfonylimide (TFSI - ) group after dehydration, fluorocarbonate solvent after dehydration and fluorine-containing diluent after dehydration. (2) Dissolve an appropriate amount of lithium salt in a certain volume of anhydrous ionic liquid with a bistrifluoromethylsulfonylimide group (TFSI - ) and keep stirring the solution until all the lithium salt is dissolved, to achieve semi-fluorination of the electrolyte and thus obtain a semi-fluorinated electrolyte; (3) sequentially adding the three electrolyte additives (water-free fluorocarbonate solvent, water-free fluorine-containing diluent, and nitrate) into the semi-fluorinated electrolyte, continuing to stir for 12-24 h, and finally obtaining a full-fluorinated high-pressure-resistant lithium battery electrolyte based on ionic liquid.

7. An ionic liquid based, perfluorinated, high voltage resistant lithium battery electrolyte according to claim 1, wherein, The molar concentration of the lithium salt in the electrolyte is 0.5-1.5 mol / L.

8. An ionic liquid based, perfluorinated, high voltage resistant lithium battery electrolyte according to claim 1, wherein, The volume ratio of the ionic liquid with a bistrifluoromethylsulfonylimide group (TFSI - ) in the electrolyte, the fluorocarbonate-based solvent, and the fluorine-containing diluent is 3: (1-3):

1.

9. An ionic liquid based, perfluorinated, high voltage resistant lithium battery electrolyte according to claim 1, wherein, The concentration of the nitrate in the electrolyte is 0.1-0.3 mol / L.

10. An ionic liquid based, perfluorinated, high voltage resistant lithium battery electrolyte according to claim 1, wherein, The full-fluorinated high-pressure-resistant lithium battery based on ionic liquid includes a lithium cobalt oxide positive electrode, a lithium metal or graphite negative electrode, and the full-fluorinated high-pressure-resistant lithium battery electrolyte based on ionic liquid according to claims 1-9.

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