Lithium ion electrolyte and lithium ion battery thereof

Abstract

The present invention relates to the field of lithium battery technology, and discloses a lithium ion electrolyte and a lithium ion battery thereof. The electrolyte contains an organic solvent, a lithium salt and a first additive, wherein the first additive is at least one of 3,4-difluoropyrrole, 3,4-ditrifluoromethylpyrrole, 3,4-dipentafluoroethylpyrrole, 3,4-difluoromethylpyrrole, 3,4-difluorothiophene, 3,4-difluorobenzothiophene and 3,4-difluorofuran. According to the lithium ion electrolyte of the present invention, a polymer is formed by the first additive, thereby forming a SEI film with low internal resistance and high stability, promoting lithium ion conduction, and improving the charge and discharge performance and cycle performance of the lithium ion battery in a low temperature environment.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and in particular to a lithium ion electrolyte and a lithium ion battery thereof. Background Art

[0002] Lithium-ion batteries, using lithium iron phosphate and graphite as positive and negative electrodes, have rapidly increased their market share in electric vehicles and large-scale energy storage, with total installed capacity increasing significantly. Lithium-ion electrolyte, one of the four key materials in lithium batteries, functions to stably conduct lithium ions. The electrolyte conducts ions between the positive and negative electrodes in the battery, crucial for achieving high voltage and high specific energy.

[0003] At present, the research directions of lithium-ion electrolytes mainly include: high specific energy electrolytes, high power electrolytes, wide temperature electrolytes, safety electrolytes and flame retardant electrolytes. Among them, the development of low-temperature electrolytes for lithium iron phosphate batteries still has certain limitations and cannot fully meet the charge, discharge and cycle performance of lithium batteries under low temperature conditions. This is mainly reflected in the following aspects: (1) Most existing electrolytes use solvents such as ethylene carbonate, dimethyl carbonate, and diethyl carbonate as the main solvents. These solvents have high melting points and are solid at low temperature conditions. They have low ionic conductivity and are easy to cause lithium deposition in the battery, which cannot meet the charge, discharge and cycle performance of lithium-ion batteries in low temperature environments; (2) Most existing electrolytes use vinylene carbonate as a film-forming additive. The content of vinylene carbonate will directly affect the charge, discharge and cycle performance of the battery under low temperature conditions. This electrolyte containing a single component film-forming agent can no longer meet the low temperature performance of the battery; (3) Existing electrolytes use lithium hexafluorophosphate as a lithium salt. Single-component lithium salts cannot meet the charge, discharge and cycle performance of lithium-ion batteries under low temperature conditions.

[0004] Patent application CN111710909B discloses a lithium battery electrolyte, a preparation method, and a lithium-ion battery thereof. These applications relate to the field of lithium batteries and provide a lithium-ion electrolyte with excellent low-temperature performance and high conductivity. The raw material formula includes an electrolyte matrix and polymer monomers. The polymer monomers include at least one naphthalene ring monomer containing an amino group and at least one monomer containing two carboxyl groups. However, amino substituents of naphthalene have a certain alkalinity and can produce side reactions with lithium ions, thereby reducing the charge-discharge performance and cycling performance of the lithium-ion battery under low-temperature conditions.

[0005] Therefore, there is an urgent need to develop a lithium battery electrolyte that can enable the lithium battery to still have good charge and discharge performance and cycle performance in a low temperature environment. Summary of the Invention

[0006] The purpose of the present invention is to overcome the problems of lithium battery electrolyte in the prior art, such as high freezing point, high viscosity, poor wettability, low lithium ion migration rate, high internal resistance and poor stability of SEI film, which lead to reduced charge and discharge performance and cycle performance of lithium ion batteries in low temperature environments. A lithium battery electrolyte and a lithium ion battery thereof are provided. The invention reduces the freezing point and viscosity of the electrolyte, improves the wettability, promotes lithium ion conduction, forms an SEI film with low internal resistance and high stability, thereby improving the charge and discharge performance and cycle performance of the lithium ion battery in low temperature environments.

[0007] In order to achieve the above-mentioned object, the present invention provides a lithium ion electrolyte on the one hand, which contains an organic solvent, a lithium salt and a first additive, wherein the first additive is at least one of 3,4-difluoropyrrole, 3,4-ditrifluoromethylpyrrole, 3,4-dipentafluoroethylpyrrole, 3,4-difluoromethylpyrrole, 3,4-difluorothiophene, 3,4-difluorobenzothiophene and 3,4-difluorofuran.

[0008] Preferably, based on the total weight of the electrolyte, the content of the first additive is 1-5 wt %.

[0009] Preferably, the concentration of the lithium salt is 0.8-1.2 mol / L.

[0010] Preferably, the electrolyte further contains a second additive, and the second additive is at least one of hexafluorobenzene, tetrafluoronaphthalene, hexafluoronaphthalene and octafluoronaphthalene.

[0011] Preferably, based on the total weight of the electrolyte, the content of the second additive is 1-3 wt %.

[0012] Preferably, the electrolyte further contains a third additive, and the third additive is vinylene carbonate and / or vinyl sulfate.

[0013] Preferably, based on the total weight of the electrolyte, the content of the third additive is 3-5 wt %.

[0014] Preferably, the lithium salt is lithium hexafluorophosphate and / or lithium bis(trifluoromethanesulfonyl)imide.

[0015] Preferably, in the electrolyte, the concentration of the lithium hexafluorophosphate is 0.7-1.0 mol / L, and the concentration of the lithium bis(trifluoromethanesulfonyl)imide is 0.05-0.2 mol / L.

[0016] Preferably, the organic solvent contains at least one of dimethyl carbonate, diethyl carbonate, ethyl acetate, ethylene carbonate, tetrahydrofuran and dipropylene glycol dimethyl ether.

[0017] Preferably, in the organic solvent, based on the total mass of the organic solvent, the content of ethyl acetate is 35-40 wt %, the content of diethyl carbonate is 10-15 wt %, and the content of dimethyl carbonate is 20-25 wt %.

[0018] Preferably, the electrolyte further contains a flame retardant.

[0019] Preferably, based on the total weight of the electrolyte, the content of the flame retardant is 0.5-1 wt%.

[0020] Preferably, the flame retardant is at least one of trimethyl phosphate, trimethyl phosphate and diethyl phosphate.

[0021] A second aspect of the present invention provides a lithium-ion battery, which includes a positive electrode, a negative electrode and an electrolyte, wherein the positive electrode and the negative electrode are placed in the electrolyte, and the electrolyte is the electrolyte described above.

[0022] Through the above technical solution, inorganic lithium salts such as lithium fluoride are formed by introducing 3,4-fluorine-substituted pyrrole, thiophene and furan. In addition, pyrrole, thiophene and furan form free radicals and polymers during the electrochemical process, thereby forming a thinner and more ion-conductive SEI film, thereby improving the charge and discharge performance and cycle performance of lithium-ion batteries in low-temperature environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 1 is the charge capacity curve of Example 1 and Comparative Example 1 at -20°C;

[0024] Figure 2 1 is the discharge capacity curve of Example 1 and Comparative Example 1 at -20°C;

[0025] Figure 3 The discharge capacity curves of Example 1 and Comparative Example 1 were tested in a cycle at 0°C. DETAILED DESCRIPTION

[0026] The following describes the specific embodiments of the present invention in detail with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention and are not intended to limit the present invention.

[0027] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0028] The lithium-ion electrolyte of the present invention contains an organic solvent, a lithium salt, and a first additive, wherein the first additive is at least one of 3,4-difluoropyrrole, 3,4-ditrifluoromethylpyrrole, 3,4-dipentafluoroethylpyrrole, 3,4-difluoromethylpyrrole, 3,4-difluorothiophene, 3,4-difluorobenzothiophene, and 3,4-difluorofuran. The lithium-ion electrolyte of the present invention helps form a SEI film with low internal resistance and high stability, thereby improving the charge-discharge performance and cycle performance of lithium-ion batteries in low-temperature environments.

[0029] In the present invention, the first additive can undergo redox reaction on the electrode surface to promote the formation of a dense and stable SEI film.

[0030] In the present invention, in order to form a SEI film with better ion conductivity, the first additive is preferably at least one of 3,4-difluoropyrrole, 3,4-difluorothiophene, 3,4-difluorobenzothiophene and 3,4-difluorofuran.

[0031] In the lithium ion electrolyte of the present invention, the content of the first additive may be 1-5 wt %, preferably 1-4 wt %, based on the total weight of the electrolyte.

[0032] In the lithium ion electrolyte of the present invention, the concentration of the lithium salt may be 0.8-1.2 mol / L, preferably 0.9-1.1 mol / L.

[0033] In the lithium ion electrolyte of the present invention, the electrolyte may further contain a second additive, and the second additive may be at least one of hexafluorobenzene, tetrafluoronaphthalene, hexafluoronaphthalene and octafluoronaphthalene.

[0034] In the present invention, the second additive can improve the contact performance between the electrolyte and the electrode, thereby improving the performance and efficiency of the battery.

[0035] In the present invention, a SEI film with high stability and low impedance is formed by the combined action of the first additive and the second additive, thereby improving the wettability of the electrolyte and thus improving the cycle performance of the battery in a low temperature environment.

[0036] In the present invention, in order to improve the wetting performance of the electrolyte, the second additive is preferably octafluoronaphthalene.

[0037] In the lithium ion electrolyte of the present invention, the content of the second additive may be 1-3 wt %, preferably 1.2-2.2 wt %, based on the total weight of the electrolyte.

[0038] In the lithium ion electrolyte of the present invention, based on the total weight of the electrolyte, the total content of the first additive and the second additive may be less than 10 wt %, preferably 2-7 wt %.

[0039] In the lithium ion electrolyte of the present invention, the electrolyte may further contain a third additive, and the third additive may be vinylene carbonate and / or vinyl sulfate.

[0040] In the present invention, the third additive can promote the formation of a stable and effective SEI film on the surface of the electrode material.

[0041] In the present invention, in order to improve the charge-discharge and cycle performance of the battery in a low-temperature environment, the third additive is preferably vinylene carbonate and vinyl sulfate.

[0042] In the lithium ion electrolyte of the present invention, the content of the third additive may be 3-5 wt %, preferably 4-5 wt %, based on the total weight of the electrolyte.

[0043] In the present invention, to form a highly stable and low-impedance SEI film, the mass ratio of the first additive, the second additive, and the third additive is preferably (1-2):1:(2-4), and more preferably (1-1.5):1:(2-3). This electrolyte ratio is more conducive to forming an SEI film with a higher elastic modulus, making the SEI film less susceptible to breakage during graphite expansion, reducing SEI film regeneration and active lithium loss, and extending the battery cell life.

[0044] In the present invention, based on the total weight of the electrolyte, the total content of the first additive, the second additive and the third additive may be 5-15 wt %, preferably 7-11 wt %.

[0045] In the lithium ion electrolyte of the present invention, the lithium salt may be lithium hexafluorophosphate and / or lithium bis(trifluoromethanesulfonyl)imide.

[0046] In the present invention, in order to meet the demand for lithium ions during charge, discharge and cycle of the battery in a low temperature environment, the lithium salt is preferably lithium hexafluorophosphate and lithium bis(trifluoromethanesulfonyl)imide.

[0047] In the lithium ion electrolyte of the present invention, the concentration of the lithium hexafluorophosphate may be 0.7-1.0 mol / L, preferably 0.8-0.9 mol / L; the concentration of the lithium bis(trifluoromethanesulfonyl)imide may be 0.05-0.2 mol / L, preferably 0.05-0.15 mol / L.

[0048] In the lithium-ion electrolyte of the present invention, the organic solvent may include at least one of dimethyl carbonate, diethyl carbonate, ethyl acetate, ethylene carbonate, tetrahydrofuran, and dipropylene glycol dimethyl ether. To lower the freezing point of the organic solvent and thereby prevent it from solidifying at low temperatures, thereby reducing electrical conductivity and lithium deposition in the battery, ethyl acetate is preferably the highest content of the organic solvent.

[0049] In the present invention, in order to reduce the viscosity of the electrolyte, thereby reducing polarization and improving the charge and discharge performance of the battery, the organic solvent preferably contains tetrahydrofuran, dimethyl carbonate, diethyl carbonate and ethyl acetate.

[0050] In the lithium ion electrolyte of the present invention, in order to lower the freezing point of the organic solvent, in the organic solvent, based on the total mass of the organic solvent, the content of ethyl acetate is preferably 35-40wt%, more preferably 36-38wt%; the content of diethyl carbonate is preferably 10-15wt%, more preferably 12-14wt%; and the content of dimethyl carbonate is preferably 20-25wt%, more preferably 22-25wt%.

[0051] In the lithium ion electrolyte of the present invention, in order to reduce the flammability of the electrolyte and improve the safety of the battery, the electrolyte preferably further contains a flame retardant.

[0052] In the lithium ion electrolyte of the present invention, the content of the flame retardant may be 0.5-1 wt %, preferably 0.75-1 wt %, based on the total weight of the electrolyte.

[0053] In the lithium-ion electrolyte of the present invention, the flame retardant may be at least one of trimethyl phosphate, dimethyl phosphate, and diethyl phosphate. In order to improve the charge-discharge and cycle performance of the battery in a low-temperature environment, the flame retardant is preferably trimethyl phosphate.

[0054] In some embodiments, the lithium ion electrolyte of the present invention contains an organic solvent, a lithium salt, a first additive, a second additive, and a third additive; wherein the organic solvent is at least one of dimethyl carbonate, diethyl carbonate, ethyl acetate, ethylene carbonate, tetrahydrofuran, and dipropylene glycol dimethyl ether; the lithium salt is lithium hexafluorophosphate and / or lithium bistrifluoromethanesulfonyl imide, the first additive is at least one of 3,4-difluoropyrrole, 3,4-ditrifluoromethylpyrrole, 3,4-dipentafluoroethylpyrrole, 3,4-difluoromethylpyrrole, 3,4-difluorothiophene, 3,4-difluorobenzothiophene, and 3,4-difluorofuran, and the second additive is at least one of hexafluorobenzene, tetrafluoronaphthalene, hexafluoronaphthalene, and octafluoronaphthalene. At least one, the third additive is vinylene carbonate and / or vinyl sulfate; in the organic solvent, based on the total mass of the organic solvent, the content of ethyl acetate is 35-40wt%, the content of diethyl carbonate is 10-15wt%, and the content of dimethyl carbonate is 20-25wt%; in the electrolyte, the concentration of lithium hexafluorophosphate is 0.7-1.0mol / L, and the concentration of lithium bistrifluoromethanesulfonyl imide is 0.05-0.2mol / L; based on the total weight of the electrolyte, the content of the first additive is 1-5wt%, the content of the second additive is 1-3wt%, and the content of the third additive is 3-5wt%.

[0055] In other embodiments, the lithium ion electrolyte of the present invention contains an organic solvent, a lithium salt, a first additive, a second additive, a third additive and a flame retardant; wherein the organic solvent is tetrahydrofuran, dimethyl carbonate, diethyl carbonate and ethyl acetate; the lithium salt is lithium hexafluorophosphate and lithium bistrifluoromethanesulfonyl imide, the first additive is at least one of 3,4-difluoropyrrole, 3,4-difluorothiophene, 3,4-difluorobenzothiophene and 3,4-difluorofuran, the second additive is octafluoronaphthalene, the third additive is vinylene carbonate and vinyl sulfate, the flame retardant can be at least one of trimethyl phosphate, dimethyl phosphate and diethyl phosphate; in the organic solvent In the electrolyte, based on the total mass of the organic solvent, the content of ethyl acetate is 36-38wt%, the content of diethyl carbonate is 12-14wt%, and the content of dimethyl carbonate is 22-25wt%; in the electrolyte, the concentration of lithium hexafluorophosphate is 0.8-0.9mol / L, and the concentration of lithium bistrifluoromethanesulfonyl imide is 0.05-0.15mol / L; based on the total weight of the electrolyte, the content of the first additive is 1-4wt%, the content of the second additive is 1.2-2.2wt%, the content of the third additive is 4-5wt%, and the content of the flame retardant is 0.5-1wt%.

[0056] The present invention also provides a lithium-ion battery comprising a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode and the negative electrode are disposed in the electrolyte, and the electrolyte is the electrolyte described above. The lithium-ion battery according to the present invention exhibits excellent wettability, charge-discharge performance, and cycle performance even in low-temperature environments.

[0057] In the lithium-ion battery of the present invention, the positive electrode of the battery may be lithium iron phosphate, and the negative electrode of the battery may be graphite.

[0058] The lithium ion electrolyte and lithium ion battery of the present invention are further described below by way of examples. The examples are implemented based on the technical solution of the present invention, and provide detailed implementation methods and specific operating processes, but the scope of protection of the present invention is not limited to the following examples.

[0059] The experimental methods in the following examples, unless otherwise specified, are all conventional methods in the art. The experimental materials used in the following examples, unless otherwise specified, are all commercially available.

[0060] Example 1

[0061] 25 parts by weight of ethylene carbonate, 22 parts by weight of dimethyl carbonate, 12 parts by weight of diethyl carbonate, and 34 parts by weight of ethyl acetate were mixed, and 2.6 parts by weight of vinylene carbonate, 2 parts by weight of vinyl sulfate, 1.2 parts by weight of 3,4-difluoropyrrole, and 1.2 parts by weight of octafluoronaphthalene were added to the mixed organic solvent. The mixture was ultrasonicated for 30 minutes, and then lithium hexafluorophosphate and lithium bistrifluoromethanesulfonyl imide were added until the concentration of lithium hexafluorophosphate reached 0.9 mol / L and the concentration of lithium bistrifluoromethanesulfonyl imide reached 0.1 mol / L. The mixture was ultrasonicated until the lithium hexafluorophosphate and lithium bistrifluoromethanesulfonyl imide were completely dissolved.

[0062] Wettability test: 19g of the above electrolyte was manually injected into the battery cell. The cell was then aged at a 25°C dew point for 4 days before undergoing formation and volume separation. After formation and volume separation, the cell was disassembled and the mass of the free electrolyte was measured. The electrode wettability was observed, and the presence of lithium deposition at the negative electrode edge was recorded in Table 1.

[0063] Low temperature charge and discharge performance test: Under normal temperature conditions, the battery cells separated in the wettability test were discharged at 0.25C to 2.0V, then the cells were placed in a dew point space at -20℃ for 10 hours, and finally the battery was charged at 0.25C with a constant current, and the cut-off voltage was 3.5V. Under normal temperature conditions, the battery cells separated in the wettability test were charged at 0.25C to 3.5V, then the cells were placed in a dew point space at -20℃ for 5 hours, and finally the cells were discharged at 0.25C to 2.5V, and the charge and discharge curves of the battery cells were recorded. Figure 1 and Figure 2 , record the charge capacity and discharge capacity in Table 1.

[0064] Low temperature cycle performance test:

[0065] (1) Capacity calibration:

[0066] Charging: At room temperature, charge the cells after capacity separation in the wettability test at a constant current and constant voltage of 0.25C to 3.5V, then cut off at 0.02C, and then leave them for 30 minutes;

[0067] Discharge: At room temperature, discharge the cells after capacity separation in the wettability test at a constant current of 0.25C to 2.0V, and then leave them for 30 minutes;

[0068] Repeat the charge and discharge three times, and record the third discharge capacity as the battery's nominal discharge capacity C0;

[0069] (2) Place the battery aside for another 10 hours, keeping the battery temperature at 0°C, charge the battery to 3.5V at a constant current and constant voltage of 0.25C0, place it aside for another 30 minutes, discharge the battery to 2.0V at a constant current of 0.25C0, and place it aside for another 30 minutes;

[0070] (3) Cycle step (2) 5000 times. Record the discharge capacity curve at Figure 3 .

[0071] Example 2

[0072] 24 parts by weight of tetrahydrofuran, 23 parts by weight of dimethyl carbonate, 11 parts by weight of diethyl carbonate, and 32 parts by weight of ethyl acetate were mixed, and 2.6 parts by weight of vinylene carbonate, 2 parts by weight of vinyl sulfate, 2.2 parts by weight of 3,4-difluorothiophene, 2.2 parts by weight of hexafluoronaphthalene, and 1 part by weight of trimethyl phosphate were added to the mixed organic solvent. The mixture was ultrasonicated for 30 minutes, and then lithium hexafluorophosphate and lithium bistrifluoromethanesulfonyl imide were added until the concentration of lithium hexafluorophosphate reached 0.8 mol / L and the concentration of lithium bistrifluoromethanesulfonyl imide reached 0.2 mol / L. The mixture was ultrasonicated until the lithium hexafluorophosphate and lithium bistrifluoromethanesulfonyl imide were completely dissolved.

[0073] The wettability test, low-temperature charge-discharge performance test, and low-temperature cycle performance test were conducted according to Example 1 and are recorded in Table 1.

[0074] Example 3

[0075] 22 parts by weight of dipropylene glycol dimethyl ether, 19.5 parts by weight of dimethyl carbonate, 13 parts by weight of diethyl carbonate, and 34 parts by weight of ethyl acetate were mixed, and 2 parts by weight of vinylene carbonate, 2 parts by weight of vinyl sulfate, 4.8 parts by weight of 3,4-difluorofuran, 2.2 parts by weight of tetrafluoronaphthalene, and 0.5 parts by weight of trimethyl phosphate were added to the mixed organic solvent. The mixture was ultrasonicated for 30 minutes, and then lithium hexafluorophosphate and lithium bistrifluoromethanesulfonyl imide were added until the concentration of lithium hexafluorophosphate reached 0.9 mol / L and the concentration of lithium bistrifluoromethanesulfonyl imide reached 0.05 mol / L. The mixture was ultrasonicated until the lithium hexafluorophosphate and lithium bistrifluoromethanesulfonyl imide were completely dissolved.

[0076] The wettability test, low-temperature charge-discharge performance test, and low-temperature cycle performance test were conducted according to Example 1 and are recorded in Table 1.

[0077] Example 4

[0078] 23 parts by weight of tetrahydrofuran, 21 parts by weight of dimethyl carbonate, 11 parts by weight of diethyl carbonate, and 34 parts by weight of ethyl acetate were mixed, and 2.6 parts by weight of vinylene carbonate, 2.4 parts by weight of vinyl sulfate, 2.8 parts by weight of 3,4-difluorobenzothiophene, 2.2 parts by weight of tetrafluoronaphthalene, and 1 part by weight of trimethyl phosphate were added to the mixed organic solvent. The mixture was ultrasonicated for 30 minutes, and then lithium hexafluorophosphate and lithium bistrifluoromethanesulfonyl imide were added until the concentration of lithium hexafluorophosphate reached 0.9 mol / L and the concentration of lithium bistrifluoromethanesulfonyl imide reached 0.1 mol / L. The mixture was ultrasonicated until the lithium hexafluorophosphate and lithium bistrifluoromethanesulfonyl imide were completely dissolved.

[0079] The wettability test, low-temperature charge-discharge performance test, and low-temperature cycle performance test were conducted according to Example 1 and are recorded in Table 1.

[0080] Comparative Example 1

[0081] A lithium ion electrolyte was prepared according to the method of Example 1, except that 1.2 parts by weight of 3,4-difluoropyrrole and 1.2 parts by weight of octafluoronaphthalene were replaced by 2.4 parts by weight of ethylene carbonate.

[0082] The wettability test, low temperature charge and discharge performance test and low temperature cycle performance test were tested according to Example 1 and recorded in Table 1. Figure 1-3 .

[0083] Comparative Example 2

[0084] A lithium ion electrolyte was prepared according to the method of Example 1, except that 1.2 parts by weight of 3,4-difluoropyrrole was replaced with 1.2 parts by weight of ethylene carbonate, and the results are recorded in Table 1.

[0085] Table 1

[0086] Example No. Is lithium deposition occurring? Charging capacity (Ah) Discharge capacity (Ah) Example 1 no 4.37 3.95 Example 2 no 4.52 4.11 Example 3 no 4.31 3.89 Example 4 no 4.43 4.12 Comparative Example 1 yes 3.50 3.25 Comparative Example 2 yes 3.74 3.31

[0087] From the results in Table 1, it can be seen that the embodiments using the lithium ion electrolyte and lithium ion battery of the present invention have good wettability, and have good charge and discharge performance and cycle performance in a low temperature environment.

[0088] pass Figure 1 and Figure 2 It can be seen that the low-temperature charge and discharge capability of Example 1 is significantly better than that of Comparative Example 1, indicating that the embodiments using the lithium ion electrolyte and lithium ion battery of the present invention have more excellent charge and discharge performance.

[0089] pass Figure 3 It can be seen that the low-temperature cycle decay of Example 1 is slow, while the capacity of Comparative Example 1 begins to decay significantly after about 100 cycles, indicating that the embodiments using the lithium ion electrolyte and lithium ion battery of the present invention have better cycle performance.

[0090] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A lithium ion electrolyte, characterized in that The electrolyte contains an organic solvent, a lithium salt and a first additive, wherein the first additive is at least one of 3,4-difluoropyrrole, 3,4-ditrifluoromethylpyrrole, 3,4-dipentafluoroethylpyrrole, 3,4-difluoromethylpyrrole and 3,4-difluorofuran.

2. The electrolyte according to claim 1, characterized in that Based on the total weight of the electrolyte, the content of the first additive is 1-5 wt %.

3. The electrolyte according to claim 1 or 2, characterized in that The concentration of the lithium salt is 0.8-1.2 mol / L.

4. The electrolyte according to claim 1, characterized in that The electrolyte further contains a second additive, which is at least one of hexafluorobenzene, tetrafluoronaphthalene, hexafluoronaphthalene and octafluoronaphthalene.

5. The electrolyte according to claim 4, characterized in that Based on the total weight of the electrolyte, the content of the second additive is 1-3 wt %.

6. The electrolyte according to claim 1, characterized in that The electrolyte further contains a third additive, which is vinylene carbonate and / or vinyl sulfate.

7. The electrolyte according to claim 6, characterized in that Based on the total weight of the electrolyte, the content of the third additive is 3-5 wt %.

8. The electrolyte according to any one of claims 1, 2 and 4-7, characterized in that The lithium salt is lithium hexafluorophosphate and / or lithium bis(trifluoromethanesulfonyl)imide.

9. The electrolyte according to claim 8, characterized in that In the electrolyte, the concentration of the lithium hexafluorophosphate is 0.7-1.0 mol / L, and the concentration of the lithium bis(trifluoromethanesulfonyl)imide is 0.05-0.2 mol / L.

10. The electrolyte according to any one of claims 1, 2 and 4-7, characterized in that The organic solvent contains at least one of dimethyl carbonate, diethyl carbonate, ethyl acetate, ethylene carbonate, tetrahydrofuran and dipropylene glycol dimethyl ether.

11. The electrolyte according to claim 10, characterized in that In the organic solvent, based on the total mass of the organic solvent, the content of ethyl acetate is 35-40wt%, the content of diethyl carbonate is 10-15wt%, and the content of dimethyl carbonate is 20-25wt%.

12. The electrolyte according to any one of claims 1, 2 and 4-7, characterized in that The electrolyte also contains a flame retardant.

13. The electrolyte according to claim 12, characterized in that Based on the total weight of the electrolyte, the content of the flame retardant is 0.5-1 wt %.

14. The electrolyte according to claim 12, characterized in that The flame retardant is at least one of trimethyl phosphate, dimethyl phosphate and diethyl phosphate.

15. A lithium-ion battery comprising a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode and the negative electrode are placed in the electrolyte, characterized in that: The electrolyte is the electrolyte according to any one of claims 1 to 14.

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