Low-temperature electrolyte, preparation method thereof and lithium battery

Abstract

The invention provides a low-temperature electrolyte, a preparation method thereof and a lithium battery, and relates to the technical field of lithium batteries. The method provided by the invention comprises the following steps: adding a lithium salt and an electrolyte additive into an organic solvent, stirring and dissolving to obtain a low-temperature electrolyte; and the electrolyte additive comprises at least one of lithium nonafluoro-1-butane sulfonate, potassium bis (nonafluoro-1-butane sulfonimide) and potassium perfluorobutanesulfonate. The low-temperature electrolyte can effectively improve the ionic conductivity of the lithium battery, optimizes an SEI film and a CEI film on the surface of an electrode to inhibit the growth of lithium dendrites and the decomposition of the electrolyte, and reduces the energy barrier of lithium ions in the desolvation process during transmission to improve the capacity retention ratio of the lithium battery at low temperature.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium batteries, in particular to a low-temperature electrolyte, a preparation method thereof and a lithium battery. BACKGROUND

[0002] With the acceleration of global energy transformation, lithium-ion batteries have become the core components of electric vehicles, portable electronic devices and energy storage systems due to their high energy density and long cycle life.

[0003] However, the conventional lithium battery electrolyte (usually lithium hexafluorophosphate as lithium salt, and solvent based on a mixture of carbonate solvents such as ethylene carbonate, dimethyl carbonate and methyl ethyl carbonate) performs significantly poorly in low-temperature environments. When the temperature is below 0℃, the ionic conductivity of the electrolyte drops sharply (for example, to less than 20% of the normal temperature at -20℃), resulting in rapid capacity decay and reduced charging rate of the battery at low temperatures. This is due to the high melting point of the solvent, increased viscosity of the electrolyte, significantly increased energy barrier for lithium ion transport desolvation process, and deteriorated interfacial reaction (formation of SEI / CEI film), as well as the initiation of lithium dendrite growth and electrolyte decomposition, reducing battery life and posing safety risks.

[0004] Existing technologies attempt to improve performance by adding low-temperature additives (such as fluoroethylene carbonate or vinylene carbonate) or optimizing solvent ratios, but these solutions often have limitations: liquid additives may sacrifice high-temperature stability or increase costs, making it difficult to balance dielectric constant, viscosity, melting point and electrochemical stability. For example, CN103107364A reports the addition of vinylene carbonate to the electrolyte, and the lithium battery using the electrolyte can achieve a discharge specific capacity of about 90% of the normal temperature at -20℃, but the performance improvement is limited below -40℃, with a discharge specific capacity of only about half of the normal temperature. CN120261712A reports the use of fluoro-, chloro- and bromo-acetic acid ethyl ester as liquid additives in electrolytes, and the specific capacity of the graphite half-cell using the electrolyte in Example 4 has little decay at 0℃ and -10℃ compared to the normal temperature, but the specific capacity is less than 50% of the normal temperature at -30℃, and even less than 20% of the normal temperature at -40℃. These limitations restrict the promotion of lithium batteries in cold regions or seasons.

[0005] Therefore, there is an urgent need to provide a solution to improve the above problems. SUMMARY

[0006] The present application relates to the technical field of lithium batteries, in particular to a low-temperature electrolyte, a preparation method thereof and a lithium battery.

[0007] In a first aspect, the present application provides a preparation method of a low-temperature electrolyte, comprising: adding a lithium salt and an electrolyte additive into an organic solvent to stir and dissolve to obtain a low-temperature electrolyte; the electrolyte additive comprises at least one of lithium nonafluoro-1-butanesulfonate, potassium bisnonaflate, and potassium perfluorobutane sulfonate.

[0008] Optionally, the organic solvent comprises a mixture of carboxylic acid ester and carbonic acid ester; the volume percentage of the carboxylic acid ester in the mixture is 70%-95%; the volume percentage of the carbonic acid ester in the mixture is 5%-30%.

[0009] Optionally, the carboxylic acid ester comprises at least one of methyl acetate, methyl difluoroacetate, methyl trifluoroacetate, ethyl acetate, ethyl fluoroacetate, ethyl difluoroacetate, and ethyl trifluoroacetate.

[0010] Optionally, the carbonic acid ester comprises at least one of ethylene carbonate, fluoroethylene carbonate, and vinylene carbonate.

[0011] Optionally, the lithium salt comprises at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, and lithium tetrafluoroborate.

[0012] Optionally, the concentration of the lithium salt is 0.5 mol / L-2 mol / L.

[0013] Optionally, the concentration of the electrolyte additive is 0.05 mol / L-0.2 mol / L.

[0014] Optionally, under an inert atmosphere, the lithium salt and the electrolyte additive are added into the organic solvent, and after stirring at 0℃-45℃ for 2h-6h, the mixture is left to stand for 6h-15h.

[0015] In a second aspect, the present application further provides a low-temperature electrolyte prepared by any of the above optional preparation methods, wherein the lithium salt and the electrolyte additive are completely dissolved in the low-temperature electrolyte; and the low-temperature electrolyte is a completely transparent liquid without any precipitate.

[0016] In a third aspect, the present application further provides an application of the low-temperature electrolyte prepared by any of the above optional preparation methods in lithium batteries, comprising any of the following aspects:

[0017] (1) improving the ionic conductivity of the lithium battery;

[0018] (2) inhibiting the growth of lithium dendrites, and improving the service life and safety of the lithium battery;

[0019] (3) improving the capacity retention rate of the lithium battery at low temperature.

[0020] In a fourth aspect, the present application provides a lithium battery, comprising a positive electrode, a negative electrode, a separator and the low-temperature electrolyte prepared by any of the optional preparation methods.

[0021] Optionally, the positive electrode comprises at least one of lithium cobaltate, ternary lithium and lithium iron phosphate.

[0022] Optionally, the negative electrode comprises a lithium sheet.

[0023] Optionally, the separator comprises at least one of a polyethylene separator, a polypropylene separator and a polyethylene / polypropylene composite separator. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 The ion conductivity-temperature relationship graph of Comparative Example 1;

[0025] Figure 2 The ion conductivity-temperature relationship graph of Comparative Example 2;

[0026] Figure 3 The ion conductivity-temperature relationship graph of Example 1;

[0027] Figure 4 The ion conductivity-temperature relationship graph of Example 2;

[0028] Figure 5 The ion conductivity-temperature relationship graph of Example 3;

[0029] Figure 6 The ion conductivity-temperature relationship graph of Example 4;

[0030] Figure 7 The ion conductivity-temperature relationship graph of Example 5;

[0031] Figure 8 The ion conductivity-temperature relationship graph of Example 6;

[0032] Figure 9 The ion conductivity-temperature relationship graph of Example 7;

[0033] Figure 10 The room-temperature cycle capacity graph of the lithium battery using Comparative Example 1 as the electrolyte;

[0034] Figure 11 The room-temperature cycle capacity graph of the lithium battery using Comparative Example 2 as the electrolyte;

[0035] Figure 12 The room-temperature cycle capacity graph of the lithium battery using Example 1 as the electrolyte;

[0036] Figure 13Cycle capacity chart at normal temperature for a lithium battery using Example 2 as electrolyte;

[0037] Figure 14 Cycle capacity chart at normal temperature for a lithium battery using Example 3 as electrolyte;

[0038] Figure 15 Cycle capacity chart at normal temperature for a lithium battery using Example 4 as electrolyte;

[0039] Figure 16 Cycle capacity chart at normal temperature for a lithium battery using Example 5 as electrolyte;

[0040] Figure 17 Cycle capacity chart at normal temperature for a lithium battery using Example 6 as electrolyte;

[0041] Figure 18 Cycle capacity chart at normal temperature for a lithium battery using Example 7 as electrolyte;

[0042] Figure 19 Charge-discharge curve chart at -35°C and at normal temperature for a lithium battery using Comparative Example 1 as electrolyte;

[0043] Figure 20 Charge-discharge curve chart at -35°C and at normal temperature for a lithium battery using Comparative Example 2 as electrolyte;

[0044] Figure 21 Charge-discharge curve chart at -35°C and at normal temperature for a lithium battery using Example 1 as electrolyte;

[0045] Figure 22 Charge-discharge curve chart at -35°C and at normal temperature for a lithium battery using Example 2 as electrolyte.

[0046] Figure 23 Charge-discharge curve chart at -35°C and at normal temperature for a lithium battery using Example 3 as electrolyte;

[0047] Figure 24 Charge-discharge curve chart at -35°C and at normal temperature for a lithium battery using Example 4 as electrolyte;

[0048] Figure 25 Charge-discharge curve chart at -35°C and at normal temperature for a lithium battery using Example 5 as electrolyte;

[0049] Figure 26 Charge-discharge curve chart at -35°C and at normal temperature for a lithium battery using Example 6 as electrolyte.

[0050] Figure 27The charge-discharge curves at -35℃ and normal temperature of the lithium battery using Example 7 as the electrolyte are shown in the following figures. DETAILED DESCRIPTION

[0051] In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below. Obviously, the described embodiments are only some but not all of the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the scope of the present application. Unless otherwise defined, the technical terms or scientific terms used herein should be understood as the common meanings thereof by those of ordinary skill in the art.

[0052] The present application provides a preparation method of a low-temperature electrolyte, comprising: adding a lithium salt and an electrolyte additive into an organic solvent to stir and dissolve to obtain a low-temperature electrolyte; the electrolyte additive comprises at least one of lithium nonafluoro-1-butanesulfonate, potassium bisnonafluoro-1-butanesulfonimide and potassium perfluorobutylsulfonate.

[0053] In fact, the SEI film (solid electrolyte interface film) of the lithium battery is a protective film formed on the surface of the lithium ion battery negative electrode, mainly produced by the reduction of the electrolyte on the negative electrode surface during the first charging process, composed of inorganic and organic compounds. The key role of this film is to passivate the electrode surface, inhibit the continuous decomposition of the electrolyte, reduce the interface impedance, and prevent the growth of lithium dendrites, thereby significantly improving the cycle life, safety and energy efficiency of the battery. A stable SEI film can reduce capacity attenuation and is the cornerstone of high performance and long life of the battery, and its quality is affected by factors such as temperature and electrolyte formula. Similarly, the CSEI film (cathode surface solid electrolyte interface film, referred to as CEI film) is produced by the oxidation of the electrolyte on the positive electrode surface during the first charging process, and its main role is to prevent the continuous decomposition of the electrolyte on the positive electrode surface (especially lithium cobaltate, ternary and other high-voltage positive electrodes).

[0054] In addition, the solvation structure refers to the dynamic coordination shell formed by the electrostatic interaction between lithium ions and solvent molecules in the electrolyte during battery operation; and the desolvation process is the key step of lithium ions breaking away from the solvent molecules and embedding into the electrode material at the electrode interface. The energy barrier of this process (desolvation energy) directly affects the ion migration rate and interface reaction kinetics, and is also the main reason for the capacity reduction of lithium batteries at low temperature.

[0055] The electrolyte additive provided by the application is a solute type additive, which can introduce anions rich in F, S and other elements without affecting the dielectric constant, viscosity, melting point and electrochemical stability of the electrolyte solvent, can preferentially decompose on the surface of the negative electrode and the positive electrode to form a thin and uniform SEI and CEI film rich in inorganic components such as LiF, Li2S, Li2SO3, KF, K2S and K2SO3, and has lower charge transfer impedance, higher ion transmission efficiency and can prevent further decomposition of the electrolyte compared with the SEI and CEI film formed by the ordinary electrolyte, which is mainly composed of organic components such as LiOCO2CH3, LiOCO2C2H5, LiO2C-CO2R (R is an alkyl group). The strong coordination between the sulfonic acid group (-SO3) at one end of the anion introduced by the electrolyte additive and the lithium ion enables the anion to preferentially enter the solvation structure of the lithium ion, and the perfluoro group (-C4F9) at the other end of the anion repels the solvent molecules by the negative nature of the fluorine atoms, thereby reducing the number of solvent molecules in the solvation structure of the lithium ion and lowering the energy barrier of the solvent molecules in the desolvation process.

[0056] In some embodiments, the organic solvent used includes a mixture of carboxylic acid ester and carbonic acid ester; wherein the volume percentage of carboxylic acid ester in the mixture is 70%-95%; and the volume percentage of carbonic acid ester in the mixture is 5%-30%.

[0057] In some embodiments, the carboxylic acid ester used includes at least one of methyl acetate, methyl difluoroacetate, methyl trifluoroacetate, ethyl acetate, ethyl fluoroacetate, ethyl difluoroacetate, and ethyl trifluoroacetate.

[0058] In some embodiments, the carbonic acid ester used includes at least one of vinyl carbonate, fluoro-vinyl carbonate, and vinylene carbonate.

[0059] In some embodiments, the lithium salt used includes at least one of lithium bis-trifluoromethanesulfonimide, lithium bis-fluorosulfonimide, lithium bis-oxalato-borate, lithium difluoro-oxalato-borate, and lithium tetrafluoroborate.

[0060] In some embodiments, the concentration of the lithium salt used is 0.5 mol / L-2 mol / L.

[0061] In some embodiments, the concentration of the electrolyte additive used is 0.05 mol / L-0.2 mol / L.

[0062] In some embodiments, the lithium salt and the electrolyte additive are added to the organic solvent under an inert atmosphere, stirred at 0℃-45℃ for 2h-6h, and then left to stand for 6h-15h.

[0063] The application also provides a low-temperature electrolyte prepared by any of the above embodiments, wherein the lithium salt and the electrolyte additive are completely dissolved in the low-temperature electrolyte; and the low-temperature electrolyte is a completely transparent liquid without any precipitate.

[0064] The application also provides an application of the low-temperature electrolyte prepared by any of the above embodiments in a lithium battery, including any of the following aspects:

[0065] (1) improving the ionic conductivity of the lithium battery;

[0066] (2) inhibiting the growth of lithium dendrites, improving the service life and safety of the lithium battery;

[0067] (3) improving the capacity retention rate of the lithium battery at low temperature.

[0068] The application also provides a lithium battery, which comprises a positive electrode, a negative electrode, a separator and the low-temperature electrolyte prepared by any of the above optional preparation methods.

[0069] In some embodiments, the positive electrode comprises at least one of lithium cobaltate, ternary lithium and lithium iron phosphate.

[0070] In some embodiments, the negative electrode comprises a lithium sheet.

[0071] In some embodiments, the separator comprises at least one of a polyethylene separator, a polypropylene separator and a polyethylene / polypropylene composite separator.

[0072] Comparative Example 1

[0073] The comparative example 1 provides a preparation method of an electrolyte, which comprises the following steps:

[0074] S1, 3.33 mL of ethylene carbonate, 3.33 mL of dimethyl carbonate and 3.33 mL of methyl ethyl carbonate are added to a glass bottle, and a magnetic stirrer (1000 r / min) is used for continuous stirring for 1 h until the mixture is uniformly mixed to obtain a mixed organic solvent (the volume ratio of the three is 1:1:1);

[0075] S2, 1.519 g of lithium hexafluorophosphate is added to 10 mL of the mixed organic solvent, and the solution is stirred at 30°C using a magnetic stirrer (1000 r / min) for 3 h until the lithium salt is completely dissolved. After standing for 12 h, no solid is precipitated and the solution remains colorless and transparent, and the electrolyte is obtained.

[0076] Comparative Example 2

[0077] The comparative example 2 provides a preparation method of an electrolyte, which comprises the following steps:

[0078] S1, 9 mL of methyl acetate and 1 mL of fluoroethylene carbonate were added into a glass bottle, and stirred continuously for 1 h with a magnetic stirrer (1000 r / min) until mixed uniformly to obtain a mixed organic solvent (volume ratio of 9:1);

[0079] S2, 2.871 g of lithium bis-trifluoromethylsulfonylimide was added into 10 mL of the mixed organic solvent, and stirred for 3 h at 30°C with a magnetic stirrer (1000 r / min) until the lithium salt was completely dissolved. After standing for 12 h, no solid was precipitated, and the solution remained colorless and transparent, thereby obtaining the electrolyte.

[0080] Example 1

[0081] The present example 1 provides a preparation method of a low-temperature electrolyte, comprising the following steps:

[0082] S1, 9 mL of methyl acetate and 1 mL of fluoroethylene carbonate were added into a glass bottle, and stirred continuously for 1 h with a magnetic stirrer (1000 r / min) until mixed uniformly to obtain a mixed organic solvent (volume ratio of 9:1);

[0083] S2, 2.871 g of lithium bis-trifluoromethylsulfonylimide and 0.306 g of lithium nonafluoro-1-butanesulfonate were added into 10 mL of the mixed organic solvent, and stirred continuously for 3 h at 30°C with a magnetic stirrer (1000 r / min) until the lithium salt and the electrolyte additive were completely dissolved. After standing for 12 h, no solid was precipitated, and the solution remained colorless and transparent, thereby obtaining the electrolyte.

[0084] Example 2

[0085] The present example 2 provides a preparation method of a low-temperature electrolyte, which is different from example 1 in that 2.871 g of lithium bis-trifluoromethylsulfonylimide and 0.712 g of lithium nonafluoro-1-butanesulfonate were added into 10 mL of the mixed organic solvent in step S2.

[0086] Example 3

[0087] The present example 3 provides a preparation method of a low-temperature electrolyte, which is different from example 1 in that 2.871 g of lithium bis-trifluoromethylsulfonylimide, 0.306 g of lithium nonafluoro-1-butanesulfonate, and 0.310 g of potassium bis-nonafluoro-1-butanesulfonylimide were added into 10 mL of the mixed organic solvent in step S2.

[0088] Example 4

[0089] This embodiment 4 provides a preparation method of a low-temperature electrolyte, which is different from that of embodiment 1 in that 2.871 g of lithium bis-trifluoromethylsulfonylimide, 0.306 g of lithium nonafluoro-1-butanesulfonate and 0.619 g of potassium bis-nonafluoro-1-butanesulfonylimide are added to 10 mL of the mixed organic solvent in step S2.

[0090] Embodiment 5

[0091] This embodiment 5 provides a preparation method of a low-temperature electrolyte, which is different from that of embodiment 1 in that 2.871 g of lithium bis-trifluoromethylsulfonylimide, 0.306 g of lithium nonafluoro-1-butanesulfonate and 0.169 g of potassium perfluorobutylsulfonate are added to 10 mL of the mixed organic solvent in step S2.

[0092] Embodiment 6

[0093] This embodiment 6 provides a preparation method of a low-temperature electrolyte, which is different from that of embodiment 1 in that 2.871 g of lithium bis-trifluoromethylsulfonylimide, 0.306 g of lithium nonafluoro-1-butanesulfonate and 0.338 g of potassium perfluorobutylsulfonate are added to 10 mL of the mixed organic solvent in step S2.

[0094] Embodiment 7

[0095] This embodiment 7 provides a preparation method of a low-temperature electrolyte, which is different from that of embodiment 1 in that 2.871 g of lithium bis-trifluoromethylsulfonylimide, 0.306 g of lithium nonafluoro-1-butanesulfonate, 0.310 g of potassium bis-nonafluoro-1-butanesulfonylimide and 0.169 g of potassium perfluorobutylsulfonate are added to 10 mL of the mixed organic solvent in step S2.

[0096] Preparation of lithium battery

[0097] (1) Preparation of positive electrode sheet: 0.8 g of lithium cobaltate positive electrode material, 0.1 g of conductive carbon black and 0.1 g of polyvinylidene fluoride were added to a glass bottle, and a magnetic stirrer (500 r / min) was used for continuous stirring for 3 h to uniformly mix them, then 3.5 g of N-methylpyrrolidone was added and stirring was continued at 30°C for 12 h to prepare conductive slurry, and the conductive slurry was coated on the surface of a dry and clean carbon-coated aluminum foil with a thickness of 170 μm and dried in a 70°C vacuum drying oven for 12 h to prepare a lithium cobaltate positive electrode sheet;

[0098] (2) The electrolyte provided by comparative example 1, comparative example 2 and embodiment 1, embodiment 2, embodiment 3, embodiment 4, embodiment 5, embodiment 6 and embodiment 7, lithium cobaltate electrode sheet, Celgard 2500 separator and 0.6 mm thick lithium sheet were respectively packaged to prepare button lithium batteries.

[0099] Performance test and result

[0100] (1) Celgared 2500 separator (thickness L = 25 μm) was impregnated with the electrolyte provided by Comparative Example 1, Comparative Example 2 and Example 1, Example 2, Example 3, Example 4, Example 5, Example 6, Example 7 respectively, and the said separator was clamped with a stainless steel gasket (area S = 2.01 cm 2 ) as a counter electrode to detect the impedance R at -10℃, 0℃, 10℃, 20℃, 30℃, 40℃ by an electrochemical workstation. The ion conductivity σ = L / (R*S) was taken as the ordinate, and 1000 / T (T is the Kelvin temperature) as the abscissa, a linear relationship curve was obtained, and the results are shown in Figures 1 to 9 .

[0101] It can be seen from Figures 1 to 9 that the low temperature electrolyte provided by the examples has higher ion conductivity at each temperature compared with the comparative examples.

[0102] (2) The lithium batteries prepared from the electrolyte provided by Comparative Example 1, Comparative Example 2, Example 1, Example 2, Example 3, Example 4, Example 5, Example 6, Example 7 were respectively tested at 25℃ with a rate of 2C and a charge-discharge voltage of 2.75V-4.45V by a new battery test cabinet, and the specific capacity cycle scatter plot was drawn, and the results are shown in Figures 10 to 18 .

[0103] It can be seen from Figures 10 to 18 that the lithium batteries prepared from the electrolyte provided by Example 1, Example 2, Example 3, Example 4, Example 5, Example 6, Example 7 still have discharge specific capacity of 87.08%, 79.2%, 80.6%, 77.5%, 79.9%, 83.1%, 93.7% of the initial value after 300 cycles, which has good cycle life.

[0104] (3) The lithium batteries prepared from the electrolyte provided by Comparative Example 1, Comparative Example 2, Example 1, Example 2, Example 3, Example 4, Example 5, Example 6, Example 7 were respectively tested at 25℃ and -35℃ with a rate of 0.1C and a charge-discharge voltage of 2.75V-4.45V by a new battery test cabinet, and the specific capacity voltage plot was drawn, and the results are shown in Figures 19 to 27 .

[0105] It can be seen from Figures 19 to 27It can be seen that the lithium batteries prepared from the electrolyte provided by Example 1, Example 2, Example 3, Example 4, Example 5, Example 6 and Example 7 have discharge specific capacity at -35℃ that can retain 84.2%, 85.7%, 80.6%, 79.1%, 86.5%, 83.2%, 91.3% of that at normal temperature, respectively, and have excellent low-temperature performance.

[0106] While the embodiments of the application have been illustrated and described in detail, it will be apparent to those skilled in the art that various modifications and changes can be made therein without departing from the scope and spirit of the application as described in the claims. Moreover, the application described herein can have other embodiments and be practiced or carried out in various ways.

Claims

1. A method for preparing a low-temperature electrolyte, characterized in that, include: A low-temperature electrolyte is obtained by adding lithium salt and electrolyte additive to an organic solvent and stirring to dissolve them; the electrolyte additive includes at least one of lithium nonafluoro-1-butanesulfonate, potassium bisnonafluoro-1-butanesulfonylimide, and potassium perfluorobutylsulfonate.

2. The method according to claim 1, characterized in that, The organic solvent comprises a mixture of carboxylic acid esters and carbonates; the carboxylic acid esters account for 70%-95% of the mixture by volume; and the carbonates account for 5%-30% of the mixture by volume.

3. The method according to claim 2, characterized in that, The carboxylic acid ester includes at least one of methyl acetate, methyl difluoroacetate, methyl trifluoroacetate, ethyl acetate, ethyl fluoroacetate, ethyl difluoroacetate, and ethyl trifluoroacetate; and / or, the carbonate includes at least one of ethylene carbonate, fluoroethylene carbonate, and vinylene carbonate.

4. The method according to claim 1, characterized in that, The lithium salt includes at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium di(oxalate)borate, lithium di(fluorooxalate)borate, and lithium tetra(fluoroborate).

5. The method according to claim 1, characterized in that, The concentration of the lithium salt is 0.5 mol / L to 2 mol / L; and / or the concentration of the electrolyte additive is 0.05 mol / L to 0.2 mol / L.

6. The method according to claim 1, characterized in that, Under an inert atmosphere, lithium salt and electrolyte additives are added to an organic solvent, stirred at 0℃-45℃ for 2h-6h, and then allowed to stand for 6h-15h.

7. A low-temperature electrolyte prepared by the preparation method according to any one of claims 1 to 6, characterized in that, The lithium salt and electrolyte additives in the low-temperature electrolyte are completely dissolved; the low-temperature electrolyte is a completely transparent liquid without any precipitates.

8. The application of a low-temperature electrolyte prepared by any one of claims 1 to 6 or the low-temperature electrolyte as described in claim 7 in lithium batteries, characterized in that, Including any of the following aspects: (1) Improve the ionic conductivity of lithium batteries; (2) Inhibit the growth of lithium dendrites and improve the lifespan and safety of lithium batteries; (3) Improve the capacity retention rate of lithium batteries at low temperatures.

9. A lithium battery, characterized in that, It includes a positive electrode, a negative electrode, a separator, and a low-temperature electrolyte prepared by any one of the preparation methods described in claims 1 to 6, or a low-temperature electrolyte as described in claim 7.

10. The lithium battery according to claim 9, characterized in that, The positive electrode includes at least one of lithium cobalt oxide, ternary lithium, and lithium iron phosphate; and / or, the negative electrode includes a lithium sheet; and / or, the separator includes at least one of polyethylene separator, polypropylene separator, and polyethylene / polypropylene composite separator.

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