Folic acid-added low-temperature electrolyte and lithium battery

Abstract

The invention relates to the technical field of lithium batteries, in particular to a folic acid-added low-temperature electrolyte and a lithium battery. The low-temperature electrolyte comprises a lithium salt, a non-aqueous organic solvent and an additive, the additive is folic acid, the weight percentage content of the additive is 0.01-1wt%, the non-aqueous organic solvent is a mixture of cyclic carbonate, chain carbonate, carboxylic ester and nitrile, and the concentration of the lithium salt is 0.1-4M. The cyclic carbonate compound accounts for 15-50% of the volume of the non-aqueous organic solvent; the chain carbonate accounts for 40-75% of the volume of the non-aqueous organic solvent; the nitrile accounts for 10%-60% of the volume of the non-aqueous organic solvent. By adopting the electrolyte added with folic acid, the charging and discharging capacities of the lithium battery at low temperature are improved.

Description

Technical Field

[0001] The invention relates to the technical field of lithium batteries, and more particularly to a low-temperature electrolyte and a lithium battery added with folic acid. Background Art

[0002] Lithium-ion batteries have become the focus of current energy storage equipment research and development due to their significant advantages such as high operating voltage, power, energy density, low self-discharge rate and long life. Although lithium-ion batteries have broad prospects, their performance has dropped sharply in cold regions such as Northwest and Northeast my country and in low-temperature environments in winter, becoming a bottleneck restricting the stable operation of electronic equipment. Therefore, how to improve the energy density of batteries and ensure cycle stability under low-temperature conditions has become a technical problem that needs to be overcome urgently.

[0003] The root cause of the limited performance of lithium-ion batteries at low temperatures can be attributed to multiple factors such as the obstruction of lithium ion diffusion in the positive and negative electrode materials, the reduction of interfacial charge transfer efficiency, and the slowdown of lithium ion diffusion in the electrolyte.

[0004] The interfacial charge transfer process is directly related to the performance of battery capacity. In low temperature environments, the desolvation process of lithium ions becomes slow, making it difficult to smoothly cross the electrode-electrolyte interface, which in turn causes polarization to intensify, resulting in a significant decrease in discharge capacity. In view of this, it has become an urgent task for scientific research and industry to innovate and optimize the existing lithium battery system to significantly improve its capacity retention ability in low temperature environments.

[0005] In the prior art, researchers have introduced folic acid into electrolytes to enhance the high-temperature energy storage characteristics of batteries. For example, patent KR1020120090113A involves a lithium battery electrolyte composed of a non-aqueous organic solvent and a vitamin lithium salt electrolyte. However, there are few reports on the technology of using folic acid in combination with special non-aqueous organic solvents to prepare excellent lithium battery low-temperature electrolytes. Summary of the invention

[0006] The purpose of the present invention is to provide a low-temperature electrolyte and a lithium battery with added folic acid, which solve the problems of decreased discharge platform, capacity attenuation and large charging polarization of lithium batteries at low temperatures. By adding additives, the low-temperature impedance of the battery can be effectively reduced and the low-temperature performance of the battery can be improved.

[0007] To achieve the above-mentioned purpose, the present invention provides a low-temperature electrolyte added with folic acid, wherein the low-temperature electrolyte comprises a lithium salt, a non-aqueous organic solvent and an additive, wherein the additive is folic acid, and its weight percentage content is 0.01wt%-1wt%, and the non-aqueous organic solvent comprises at least two of cyclic carbonates, nitriles, carboxylates, and chain carbonates, and the concentration of the lithium salt is 0.1-4M.

[0008] Preferably, the present invention provides a low-temperature electrolyte added with folic acid, the low-temperature electrolyte comprising a lithium salt, a non-aqueous organic solvent and an additive, the additive being folic acid, the weight percentage content of which is 0.01wt%-1wt%, the non-aqueous organic solvent containing cyclic carbonate compounds, chain carbonate compounds, nitriles, or the non-aqueous organic solvent containing cyclic carbonate compounds, chain carbonate compounds;

[0009] The lithium salt concentration is 0.1-4M, preferably 1-1.5M.

[0010] Preferably, the weight percentage content of the additive is 0.01wt%-0.1wt%.

[0011] Preferably, the lithium salt is one or more combinations of LiPF6, LiClO4, LiBF4, LiAsF6, LiBC4O8, LiBC2O4F2, LiN(SO2CF3)2 or LiN(SO2F)2.

[0012] Preferably, the cyclic carbonate compound is one or more combinations of ethylene carbonate, halogenated ethylene carbonate, propylene carbonate, halogenated propylene carbonate, butylene carbonate, and halogenated butylene carbonate, and its volume accounts for 15-50% of the volume of the non-aqueous organic solvent, preferably 20-42%, and more preferably 20-40%.

[0013] Preferably, the linear carbonate is one or more of dimethyl carbonate, diethyl carbonate (DEC), ethyl methyl carbonate or methyl propyl carbonate, and its volume accounts for 40-75% of the volume of the non-aqueous organic solvent, more preferably 45%-65%.

[0014] Preferably, the nitrile is one or more combinations of acetonitrile, propionitrile, (iso)butyronitrile or (iso)valeronitrile, and its volume accounts for 10% to 60% of the volume of the non-aqueous organic solvent, preferably 20 to 40%, more preferably 25 to 35%, and even more preferably 28 to 32%.

[0015] The non-aqueous organic solvent may also contain carboxylate, which is one or more of methyl acetate, ethyl acetate, propyl acetate, butyl formate, butyl formate or butyl acetate, and its volume accounts for 0-50% of the volume of the non-aqueous organic solvent.

[0016] As one of the preferred embodiments, the non-aqueous organic solvent is composed of isobutyronitrile (IBN), ethyl methyl carbonate (EMC), fluoroethylene carbonate (FEC), and diethyl carbonate (DEC) in a volume ratio of isobutyronitrile (IBN): ethyl methyl carbonate (EMC): fluoroethylene carbonate (FEC): diethyl carbonate (DEC) = 2.8-3.2: 0.8-1.2: 0.8-1.2: 4.8-5.2 (v:v). This of course includes the non-aqueous organic solvent being composed of isobutyronitrile (IBN), ethyl methyl carbonate (EMC), fluoroethylene carbonate (FEC), and diethyl carbonate (DEC) in a volume ratio of isobutyronitrile (IBN): ethyl methyl carbonate (EMC): fluoroethylene carbonate (FEC): diethyl carbonate (DEC) = 3:1:1:5. At this time, by adding 0.05-0.06wt% folic acid (0.05-0.06% folic acid relative to the total mass of the electrolyte) and 1.1-1.3M lithium hexafluorophosphate (LiPF6), a low-temperature electrolyte with extremely excellent electrical properties can be obtained.

[0017] As one of the preferred schemes, the non-aqueous organic solvent is composed of ethylene carbonate (EC), ethyl methyl carbonate (EMC), fluoroethylene carbonate (FEC), and diethyl carbonate (DEC), and the volume ratio is ethylene carbonate (EC): ethyl methyl carbonate (EMC): fluoroethylene carbonate (FEC): diethyl carbonate (DEC) = 0.8~1.2:1.8~2.2:0.8~1.2:5.8~6.2. It is further preferred that the volume ratio is ethylene carbonate (EC): ethyl methyl carbonate (EMC): fluoroethylene carbonate (FEC): diethyl carbonate (DEC) = 1:2:1:6.

[0018] A lithium battery comprises a battery housing and a positive electrode, a negative electrode, a diaphragm and an electrolyte located in the battery housing, wherein the electrolyte is the above-mentioned low-temperature electrolyte.

[0019] Preferably, the positive electrode includes a positive electrode collector and a positive electrode material located on the positive electrode collector, and the positive electrode material is one or more combinations of lithium cobalt oxide, lithium nickel manganese oxide, lithium nickel oxide, lithium manganese oxide, nickel cobalt manganese ternary positive electrode material, nickel cobalt aluminum positive electrode material, and lithium manganese-rich positive electrode material.

[0020] Preferably, the negative electrode comprises a negative electrode current collector and a negative electrode material located on the negative electrode current collector, and the negative electrode material is one or more combinations of graphite, hard carbon, soft carbon, silicon-carbon composite material, silicon-oxygen-carbon composite material, metallic lithium, and metallic lithium alloy.

[0021] Preferably, the separator is one or more combinations of a polyolefin porous membrane, a non-woven fabric or fiber coating, a ceramic coating, and an inorganic solid electrolyte coating.

[0022] Preferably, a lithium battery further comprises an aluminum-plastic film; the aluminum-plastic film is composed of at least two layers of a PP layer, an aluminum foil layer, and a nylon layer.

[0023] Therefore, the present invention adopts the above-mentioned low-temperature electrolyte and lithium battery with added folic acid to solve the problems of lithium battery discharge platform drop, capacity attenuation, low-temperature cycle capacity attenuation and large charging polarization at low temperatures.

[0024] The obtained low-temperature electrolyte is prepared into an NCM523|| soft carbon lithium-ion battery according to a lithium battery preparation method; in a 1Ah NCM523|| soft carbon lithium-ion battery, the electrolyte provided by the present invention can effectively improve the low-temperature charging capacity of the battery, and the charging capacity of the obtained battery at -40°C and a current density of 200mA is greater than 590mAh, and can reach 635-645mAh after optimization.

[0025] The obtained low-temperature electrolyte was prepared into a button cell of NCM811||Li according to the lithium battery preparation method; at -40 degrees, 20mA g -1 At a current density of 1.38 W, the discharge capacity is greater than 136 mAh g -1 After optimization, it can reach 157~160mAh g -1 .

[0026] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a charging voltage-capacity diagram of a lithium battery prepared from electrolyte comparative example 1;

[0028] Figure 2 is a charging voltage-capacity diagram of a lithium battery prepared from electrolyte comparative example 2;

[0029] Figure 3 is a discharge voltage-capacity diagram of a lithium battery prepared from electrolyte Example 1-1;

[0030] Figure 4 3 is a discharge voltage-capacity diagram of the lithium battery prepared by electrolyte Example 1-2.

[0031] Figure 5 is a charging voltage-capacity diagram of lithium batteries prepared from electrolyte examples 1-3;

[0032] Figure 6 is a charging voltage-capacity diagram of a lithium battery prepared from electrolyte Example 2-1;

[0033] Figure 7 is a discharge voltage-capacity diagram of a lithium battery prepared from electrolyte Example 2-2;

[0034] Figure 8 3 is a discharge voltage-capacity diagram of the lithium battery prepared by electrolyte Example 2-3.

[0035] Fig. 9 is a charging voltage-capacity diagram of a lithium battery prepared from electrolyte comparative example 3;

[0036] Fig.10 This is a discharge voltage-capacity diagram of the lithium battery prepared by electrolyte comparative example 4. DETAILED DESCRIPTION

[0037] The present invention provides a low-temperature electrolyte added with folic acid, comprising a lithium salt, a non-aqueous organic solvent and an additive, wherein the additive is folic acid, and the weight percentage content thereof is 0.01wt%-1wt%, the non-aqueous organic solvent is a mixture of cyclic carbonate and chain carbonate, and the lithium salt concentration is 0.1-4M. Preferably, the weight percentage content of the additive is 0.01wt%-0.1wt%.

[0038] In the non-aqueous organic solvent system used, an appropriate amount of folic acid as an additive can participate in the formation of a high-quality positive electrode material interface film (CEI). The formed CEI has rich lithium oxynitride and amorphous carbon components, which can effectively block the contact between the positive electrode material and the electrolyte, accelerate the migration of lithium ions at the interface, and improve the low-temperature capacity retention rate and coulomb efficiency of the battery. Moreover, in this non-aqueous organic solvent system, an appropriate amount of folic acid as an additive can form a solid electrolyte film (SEI) rich in lithium nitride and amorphous carbon at the interface of lithium metal negative electrode / graphite / soft carbon / hard carbon / silicon oxygen / silicon carbon negative electrode. The formed SEI can accelerate the diffusion of lithium ions, reduce the polarization of the battery, improve the discharge platform of the battery, and reduce the charging polarization of the battery. Therefore, the aforementioned low-temperature electrolyte can effectively improve the performance of the battery at low temperatures.

[0039] The molecular structure of folic acid is as follows:

[0040]

[0041] The lithium salt is one or more combinations of LiPF6, LiClO4, LiBF4, LiAsF6, LiBC4O8, LiBC2O4F2, LiN(SO2CF3)2 or LiN(SO2F)2. The cyclic carbonate is one or more combinations of ethylene carbonate, propylene carbonate or butylene carbonate. The chain carbonate is one or more combinations of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate or methyl propyl carbonate. The nitrile is one or more combinations of acetonitrile, propionitrile, (iso)butyronitrile or (iso)valeronitrile. The carboxylate is one or more combinations of methyl acetate, ethyl acetate, propyl acetate, butyl formate, butyl formate or butyl acetate. A mixture of a cyclic carbonate with a high dielectric constant, a nitrile organic solvent and a low-viscosity chain carbonate, a carboxylate organic solvent is used as a solvent for a low-temperature electrolyte of a lithium-ion battery, so that the mixture of the organic solvent has high ionic conductivity, high dielectric constant and low viscosity at the same time.

[0042] A lithium battery, comprising a battery housing and a positive electrode, a negative electrode, a diaphragm and an electrolyte located in the battery housing, wherein the electrolyte is the above-mentioned low-temperature electrolyte. The positive electrode comprises a positive electrode current collector and a positive electrode material located on the positive electrode current collector, wherein the positive electrode material is one or more combinations of lithium cobalt oxide, lithium nickel manganese oxide, lithium nickel oxide, lithium manganese oxide, nickel cobalt manganese ternary positive electrode material, nickel cobalt aluminum positive electrode material, and lithium-rich manganese base. The negative electrode comprises a negative electrode current collector and a negative electrode material located on the negative electrode current collector, wherein the negative electrode material is one or more combinations of graphite, hard carbon, soft carbon, silicon-carbon composite material, silicon-oxygen-carbon composite material, metallic lithium, and an alloy of metallic lithium. The diaphragm is one or more combinations of a polyolefin porous film, a non-woven fabric or fiber coating, a ceramic coating, and an inorganic solid electrolyte coating, and the aluminum-plastic film is one or more combinations of a PP layer, an aluminum foil layer, and a nylon layer.

[0043] The technical solution of the present invention is further described below through the accompanying drawings and embodiments.

[0044] The low-temperature electrolyte provided by the present invention is suitable for various conventional lithium batteries, such as conventional lithium-ion batteries and lithium metal batteries.

[0045] The present invention is further described below by way of examples.

[0046] The method for preparing the electrolyte of the embodiment and comparative example into a lithium battery is as follows:

[0047] Lithium metal battery: In a glove box (H2O <0.1ppm, O2 <0.1ppm), assemble the positive electrode shell → NCM811 electrode → electrolyte → diaphragm → electrolyte → lithium sheet → negative electrode shell from bottom to top, and then transfer to a tablet press for stamping and packaging to obtain a completed lithium metal battery.

[0048] Lithium-ion battery: In a dry room with a dew point less than -40°C, assemble NCM523 pole piece → diaphragm → soft carbon negative pole piece → ... in sequence, and finally use aluminum-plastic film to package, weld the pole ears, inject electrolyte, and obtain a completed 1Ah lithium-ion battery.

[0049] The electrochemical performance of the assembled battery was tested using Xinwei testing equipment. The above lithium battery was placed in a -40℃ low temperature box for 4 hours and then subjected to constant current charge and discharge tests.

[0050] This example is used to illustrate the electrolyte disclosed in the present invention.

[0051] Comparative Example 1

[0052] In a glove box filled with argon (H2O<0.1ppm, O2<0.1ppm), weigh an appropriate amount of lithium hexafluorophosphate (LiPF6) and dissolve it in a non-aqueous organic solution to obtain a base electrolyte. Lithium salt concentration: 1.2M lithium hexafluorophosphate (LiPF6); the non-aqueous organic solvent is composed of isobutyronitrile (IBN), ethyl methyl carbonate (EMC), fluoroethylene carbonate (FEC), and diethyl carbonate (DEC) in a volume ratio of isobutyronitrile (IBN): ethyl methyl carbonate (EMC): fluoroethylene carbonate (FEC): diethyl carbonate (DEC) = 3:1:1:5 (v:v), and comparative example 1 is obtained.

[0053] The obtained low-temperature electrolyte is prepared into NCM523|| soft carbon lithium-ion battery according to the lithium battery preparation method;

[0054] In the 1AhNCM523 soft carbon lithium-ion battery, the battery capacity assembled with Comparative Example 1 is 504mAh at -40°C and a current density of 200mA (see Appendix Figure 1 ).

[0055] Comparative Example 2

[0056] The electrolyte was prepared according to the method of Example 1, except that the organic solvent in the base electrolyte consisted of ethylene carbonate (EC), ethyl methyl carbonate (EMC), fluoroethylene carbonate (FEC), and diethyl carbonate (DEC) in a volume ratio of EC:EMC:FEC:DEC=1:2:1:6 (v:v), to obtain Comparative Example 2.

[0057] The obtained low-temperature electrolyte is prepared into NCM811|| soft carbon lithium-ion battery according to the lithium battery preparation method;

[0058] As attached Figure 2 , using the button cell of NCM811||Li of Comparative Example 2, at -40 degrees, 20mA g -1At a current density of , the discharge capacity is 133.84 mAh g -1 .

[0059] Example 1-1

[0060] The electrolyte was prepared according to the method of Comparative Example 1, except that 0.05 wt % of folic acid was added to the base electrolyte, and Example 1-1 was obtained after stirring evenly.

[0061] The obtained low-temperature electrolyte is prepared into NCM523|| soft carbon lithium-ion battery according to the lithium battery preparation method;

[0062] In a 1AhNCM523 soft carbon lithium ion battery, the electrolyte provided by the present invention can effectively improve the low temperature charging capacity of the battery. The battery of Example 1-1 has a charging capacity of 642mAh at -40°C and a current density of 200mA (see Appendix). Figure 3 ).

[0063] Example 1-2

[0064] The other conditions are the same as those of Example 1-1, except that the non-aqueous organic solvent is composed of isobutyronitrile (IBN), ethyl methyl carbonate (EMC), fluoroethylene carbonate (FEC), and diethyl carbonate (DEC) in a volume ratio of isobutyronitrile (IBN): ethyl methyl carbonate (EMC): fluoroethylene carbonate (FEC): diethyl carbonate (DEC) = 2:1:1:6,

[0065] The obtained low-temperature electrolyte is prepared into NCM523|| soft carbon lithium-ion battery according to the lithium battery preparation method;

[0066] In a 1AhNCM523 soft carbon lithium ion battery, the electrolyte provided by the present invention can effectively improve the low temperature charging capacity of the battery. The battery of Example 1-2 has a charging capacity of 637.3mAh at -40°C and a current density of 200mA (see Appendix). Figure 4 ).

[0067] Examples 1-3

[0068] The other conditions are the same as those of Example 1-1, except that the non-aqueous organic solvent is composed of isobutyronitrile (IBN), ethyl methyl carbonate (EMC), fluoroethylene carbonate (FEC), and diethyl carbonate (DEC) in a volume ratio of isobutyronitrile (IBN): ethyl methyl carbonate (EMC): fluoroethylene carbonate (FEC): diethyl carbonate (DEC) = 4:1:1:4.

[0069] The obtained low-temperature electrolyte is prepared into a NCM523|| soft carbon lithium-ion battery according to the lithium battery preparation method; in a 1Ah NCM523|| soft carbon lithium-ion battery, the electrolyte provided by the present invention can effectively improve the low-temperature charging capacity of the battery, and the battery of Example 1-3 is used at -40°C and a current density of 200mA to have a charging capacity of 592.1mAh (see Appendix Figure 5 ).

[0070] Example 2-1

[0071] The electrolyte was prepared according to the method of comparative example 2, except that 0.1 wt% of folic acid was added to the base electrolyte, and the mixture was stirred evenly to obtain Example 2-1. The obtained low-temperature electrolyte was prepared into a button cell of NCM811||Li according to the lithium battery preparation method; at -40 degrees, 20 mA g -1 At a current density of 1.547 W, the discharge capacity is 158.91 mAh g -1 (Attached Figure 6 ).

[0072] Example 2-2

[0073] The other conditions are the same as those in Example 2-1, except that the non-aqueous organic solvent is composed of ethylene carbonate (EC), ethyl methyl carbonate (EMC), fluoroethylene carbonate (FEC), and diethyl carbonate (DEC) in a volume ratio of EC:EMC:FEC:DEC=2:1:1:6.

[0074] The obtained low-temperature electrolyte was prepared into a button cell of NCM811||Li according to the lithium battery preparation method; at -40 degrees, 20mA g -1 At a current density of 1.547 W, the discharge capacity is 157.3 mAh g -1 (Attached Figure 7 ).

[0075] Example 2-3

[0076] The other conditions are the same as those in Example 2-1, except that the non-aqueous organic solvent is composed of ethylene carbonate (EC), ethyl methyl carbonate (EMC), fluoroethylene carbonate (FEC), and diethyl carbonate (DEC) in a volume ratio of EC:EMC:FEC:DEC=0:3:1:6.

[0077] The obtained low-temperature electrolyte was prepared into a button cell of NCM811||Li according to the lithium battery preparation method; at -40 degrees, 20mA g -1 At a current density of 1.38, the discharge capacity is 136.6 mAh g -1 (Attached Figure 8 ).

[0078] Comparative Example 3

[0079] The other conditions are the same as those of Example 1-1, except that the non-aqueous organic solvent is composed of isobutyronitrile (IBN), ethyl methyl carbonate (EMC), fluoroethylene carbonate (FEC), and diethyl carbonate (DEC) in a volume ratio of isobutyronitrile (IBN): ethyl methyl carbonate (EMC): fluoroethylene carbonate (FEC): diethyl carbonate (DEC) = 0:2:2:6,

[0080] The obtained low-temperature electrolyte is prepared into a NCM523|| soft carbon lithium-ion battery according to the lithium battery preparation method; in a 1Ah NCM523|| soft carbon lithium-ion battery, the electrolyte provided by the present invention can effectively improve the low-temperature charging capacity of the battery, and the battery of Example 1-3 is used at -40°C and a current density of 200mA. The charging capacity is 294mAh (attached Fig. 9 )

[0081] Comparative Example 4

[0082] The other conditions are the same as those in Example 2-1, except that the non-aqueous organic solvent is composed of ethylene carbonate (EC), ethyl methyl carbonate (EMC), fluoroethylene carbonate (FEC), and diethyl carbonate (DEC) in a volume ratio of EC:EMC:FEC:DEC=5:2:3:0.

[0083] The obtained low-temperature electrolyte was prepared into a button cell of NCM811||Li according to the lithium battery preparation method; at -40 degrees, 20mA g -1 At a current density of 1.34 W, the discharge capacity is 37 mAh g -1 (Attached Fig.10 ).

[0084] Therefore, the present invention adopts the above-mentioned low-temperature electrolyte and lithium battery with added folic acid to improve the charging capacity and discharging capacity of the battery at low temperatures.

[0085] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A low-temperature electrolyte with added folic acid, characterized in that : The low-temperature electrolyte includes a lithium salt, a non-aqueous organic solvent and an additive, wherein the additive is folic acid, and its weight percentage content is 0.01wt%-1wt%, and the non-aqueous organic solvent contains cyclic carbonate compounds, chain carbonate compounds, nitriles, or the non-aqueous organic solvent contains cyclic carbonate compounds and chain carbonate compounds; The lithium salt concentration is 0.1-4M; The cyclic carbonate compound is one or more of ethylene carbonate, halogenated ethylene carbonate, propylene carbonate, halogenated propylene carbonate, butylene carbonate, and halogenated butylene carbonate, and the volume thereof accounts for 15 to 50% of the volume of the non-aqueous organic solvent; The chain carbonate is one or more of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate or methyl propyl carbonate, and its volume accounts for 40-75% of the volume of the non-aqueous organic solvent; The nitrile is one or more of acetonitrile, propionitrile, isobutyronitrile or isovaleronitrile, and its volume accounts for 10% to 60% of the volume of the non-aqueous organic solvent; The lithium salt is one or more combinations of LiPF6, LiClO4, LiBF4, LiAsF6, LiBC4O8, LiBC2O4F2, LiN(SO2CF3)2 or LiN(SO2F)2.

2. The low-temperature electrolyte containing folic acid according to claim 1, characterized in that :The weight percentage content of the additive is 0.01wt%-0.1wt%.

3. The low-temperature electrolyte containing folic acid according to claim 1, characterized in that : The lithium salt concentration is 1 to 1.5M.

4. The low-temperature electrolyte containing folic acid according to claim 1, characterized in that : The volume of the cyclic carbonate compound accounts for 20 to 42% of the volume of the non-aqueous organic solvent, and more preferably 20 to 40%; The volume of the linear carbonate accounts for 40% to 75% of the volume of the non-aqueous organic solvent, and more preferably 45% to 65%; The nitrile is one or more combinations of acetonitrile, propionitrile, isobutyronitrile or isovaleronitrile, and its volume accounts for 20-40% of the volume of the non-aqueous organic solvent, more preferably 25-35%, and even more preferably 28-32%.

5. The low-temperature electrolyte containing folic acid according to claim 1, characterized in that : The non-aqueous organic solvent also contains carboxylic acid ester, which is one or more combinations of methyl acetate, ethyl acetate, propyl acetate, butyl formate, butyl formate or butyl acetate, and its volume accounts for 0-50% of the volume of the non-aqueous organic solvent.

6. The low-temperature electrolyte containing folic acid according to claim 5, characterized in that : The non-aqueous organic solvent is composed of isobutyronitrile, ethyl methyl carbonate, fluoroethylene carbonate and diethyl carbonate, in a volume ratio of isobutyronitrile:ethyl methyl carbonate:fluoroethylene carbonate:diethyl carbonate=2.8-3.2:0.8-1.2:0.8-1.2:4.8-5.2; or The non-aqueous organic solvent is composed of ethylene carbonate, ethyl methyl carbonate, fluoroethylene carbonate and diethyl carbonate, and the volume ratio is ethylene carbonate: ethyl methyl carbonate: fluoroethylene carbonate: diethyl carbonate = 0.8-1.2: 1.8-2.2: 0.8-1.2: 5.8-6.

2.

7. A lithium battery, characterized in that : comprising a battery shell and a positive electrode, a negative electrode, a separator and an electrolyte located in the battery shell, wherein the electrolyte is the low-temperature electrolyte according to any one of claims 1 to 7.

8. A lithium battery according to claim 8, characterized in that : The positive electrode includes a positive electrode current collector and a positive electrode material located on the positive electrode current collector, wherein the positive electrode material is one or more combinations of lithium cobalt oxide, lithium nickel manganese oxide, lithium nickel oxide, lithium manganese oxide, nickel cobalt manganese ternary positive electrode material, nickel cobalt aluminum positive electrode material, and lithium-rich manganese-based positive electrode material; The negative electrode comprises a negative electrode current collector and a negative electrode material on the negative electrode current collector, wherein the negative electrode material is one or more combinations of graphite, hard carbon, soft carbon, silicon-carbon composite material, silicon-oxygen-carbon composite material, metallic lithium, and metallic lithium alloy. The separator is one or more combinations of a polyolefin porous membrane, a non-woven fabric or fiber coating, a ceramic coating, and an inorganic solid electrolyte coating.

Images