Multifunctional electrolyte and lithium ion battery

Abstract

The application discloses a multifunctional electrolyte and a lithium ion battery. The multifunctional electrolyte comprises a first additive and a second additive, the first additive comprises 3-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-1-p-tolylsulfonyl-1H-pyrrolo[2,3-b]pyridine-5-carbonitrile, and the chemical structure of the second additive is shown in formula I: wherein R1, R2 and R3 are each independently selected from any one of -CH2CF3, -CHCF3CF3 and -CH2CF2CHF2. The application has the advantages of improving the cycle performance and rate performance of the lithium battery and reducing the risk of thermal runaway.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium batteries, in particular to a multifunctional electrolyte and a lithium ion battery. BACKGROUND

[0002] Lithium ion batteries have become the first choice for producing pure electric vehicles in the automotive industry due to their high energy density, low self-discharge, long service life, green environmental protection, reasonable cost and other advantages. However, the current negative electrode material mainly based on graphite has been unable to meet the market demand for high specific capacity of lithium batteries

[0003] High specific capacity negative electrode materials are an important breakthrough for improving the energy density of lithium ion batteries. Silicon-based materials are considered to be the most likely negative electrode material to replace graphite because of their high theoretical specific capacity, suitable discharge potential, and relatively abundant reserves in nature. However, there are many problems in the commercial application of elemental silicon in lithium ion batteries. First, the volume expansion problem of silicon-based materials as negative electrodes during battery cycling may cause active particle breakage, electrode powdering, and active material shedding. Second, the silicon negative electrode undergoes a large volume expansion during the first cycle, which leads to the formation of a solid electrolyte interface film (SEI) and consumes lithium ions, reducing the first coulombic efficiency. During the cycling process, the repeated growth and rupture of the SEI film at the interface of the electrode material greatly affect the cycle stability. More seriously, under high temperature conditions, severe side reactions and interface instability will accelerate the degradation of lithium ion batteries. At the same time, high temperature conditions will also increase the risk of thermal runaway of the battery, causing battery safety problems. SUMMARY

[0004] To solve the problems in the prior art, the present application provides a multifunctional electrolyte and a lithium ion battery.

[0005] In a first aspect, the present application provides a multifunctional electrolyte, which adopts the following technical solution:

[0006] A multifunctional electrolyte includes a first additive and a second additive. The first additive includes 3-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-1-p-tolylsulfonyl-1H-pyrrolo[2,3-b]pyridine-5-carbonitrile. The chemical structure of the second additive is shown in Formula I:

[0007]

[0008] wherein R1, R2, R3 are each independently selected from any one of -CH2CF3, -CHCF3CF3, -CH2CF2CHF2.

[0009] The present application uses the first additive and the second additive in combination, the N atom on the cyano group in the first additive can be coordinated with the dioxaborolane group due to having a lone pair of electrons, which can complex with the hydrogen atoms in the HF and water molecules in the electrolyte, thereby playing a role of removing water and suppressing acid to improve the stability of the electrolyte and the stability of the silicon-containing negative electrode in the electrolyte, thereby improving the stability of the negative electrode interface and avoiding the decline of the cycle performance of the lithium battery caused by the expansion of the silicon negative electrode; at the same time, the second additive contains trivalent phosphorus, which will be preferentially oxidized compared with the first additive, and the trivalent phosphorus removes the oxygen generated at the positive electrode interface, and the oxidation decomposition generates a protective layer containing alkyl phosphorus, thereby forming a protective CEI film on the electrode interface, which can effectively inhibit the decomposition of the electrolyte and the dissolution of transition metal ions at the positive electrode, avoiding the negative impact of the dissolution of transition metal ions on the stability of the SEI film, thereby further improving the stability of the SEI film formation at the negative electrode and improving the thermal stability of the electrolyte, which all help to further improve the cycle performance of the silicon-containing negative electrode.

[0010] Further, the second additive cooperates with the first additive, the sulfonyl group in the first additive and the fluorine element in the second additive cooperate to significantly improve the fire-retardant effect of the electrolyte, thereby improving the fast-charging safety of the lithium battery; at the same time, the pyridine group in the first additive cooperates with the fluorine element in the second additive, which not only can improve the ion conductivity of the electrolyte, but also can form LiF with high ion conductivity, which all help to improve the cycle performance and rate performance of the lithium battery.

[0011] Preferably, the second additive includes tris(1,1,1,3,3,3-hexafluoro-2-propyl) phosphite.

[0012] The structural formula of N,O-bis(trimethylsilyl) trifluoroacetamide is The CAS number is 1434747-57-5; the structural formula of tris(1,1,1,3,3,3-hexafluoro-2-propyl) phosphite is The CAS number is 66470-81-3.

[0013] Preferably, the mass fraction of the first additive in the electrolyte is 0.5%-2%.

[0014] Preferably, the mass fraction of the second additive in the electrolyte is 0.5%-1.5%.

[0015] By controlling the proportions of the first and second additives in the electrolyte, on the one hand, the stability of the electrolyte is improved, and on the other hand, a stable electrolyte environment is provided for the film formation of the second additive at the positive electrode. This helps the two to work together, improving the stability of the positive and negative electrode interfacial films while leveraging the synergistic effect of the sulfonyl groups, pyridine groups, and fluorine elements in the additives. This not only improves the flame retardant properties of the electrolyte but also helps to further improve the cycle performance of the lithium battery.

[0016] Preferably, it also includes an organic solvent, a lithium salt, and a lithium salt additive.

[0017] Preferably, the lithium salt additive includes at least one of lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, and lithium tetrafluoroborate.

[0018] Preferably, the lithium salt additive accounts for 0.2%-3% of the mass of the electrolyte.

[0019] This application, by adding lithium salt additives to the electrolyte, helps to further improve the high-temperature stability and rate performance of the electrolyte.

[0020] Preferably, the lithium salt comprises lithium hexafluorophosphate; the concentration of the lithium salt is 1-1.5 mol / L.

[0021] Batteries using a mixed electrolyte of LiTFSI and LiPF6 exhibit high capacity retention, especially under high temperature conditions, where this mixed electrolyte provides better rate performance.

[0022] Preferably, the organic solvent includes at least one of linear carbonates and cyclic carbonates.

[0023] Preferably, the linear carbonate includes at least one of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, and methyl propyl carbonate; the cyclic carbonate includes at least one of ethylene carbonate, fluoroethylene carbonate, and propylene carbonate.

[0024] Preferably, the mass ratio of the linear carbonate to the cyclic carbonate is 60-80:20-40.

[0025] By using linear and cyclic carbonates as solvents, it is helpful to adjust the electrolyte to a suitable viscosity, thereby generating a stable SEI film on the surface of the negative electrode active material. Furthermore, it can improve the ionic conductivity and chemical stability of the electrolyte, thus helping the first and second additives to exert a long-term synergistic effect in the electrolyte, and further helping to improve the cycle performance, flame retardant performance and rate performance of lithium batteries.

[0026] Secondly, this application provides a lithium-ion battery, which adopts the following technical solution:

[0027] A lithium ion battery comprising a positive electrode sheet, a separator, a negative electrode sheet, and the multifunctional electrolyte as described above. DETAILED DESCRIPTION

[0028] For better understanding and implementation, the technical solutions of the present application will be described clearly and completely in combination with examples below. Obviously, the described examples are only a part of the embodiments of the present application, but not all the embodiments.

[0029] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description herein is for describing the specific embodiments only and is not intended to be limiting of the present application.

[0030] Unless otherwise indicated, all numbers expressing quantities of ingredients, reaction conditions, and so forth used in the specification and claims are to be understood as approximations as the term "about" is used herein. Thus, unless otherwise indicated, the numerical parameters set forth in the specification and claims are approximations that can vary depending on the desired properties sought to be obtained by the compositions of the present application.

[0031] As used herein, "and / or" means one or all of the listed items.

[0032] As used herein "comprises" and "comprising" are used in their open-ended, non-limiting sense to encompass both the stated features and additional not specified features.

[0033] All percentages in the present application are weight percentages, unless otherwise indicated.

[0034] As used in the description of the application herein, the terms "a," "an," and "the" are intended to include "at least one," or "one or more," unless otherwise indicated. For example, the phrase "a component" as used herein is intended to include one or more components, and thus, a mixture of more than one component is also encompassed by the term.

[0035] Example 1

[0036] 1. Preparation of electrolyte

[0037] The mass ratio of the first additive in the electrolyte is 1.2%, the mass ratio of the second additive is 1%, the mass ratio of linear carbonate to cyclic carbonate in the organic solvent is 70:30, and the lithium salt concentration is 1.3 mol / L.

[0038] The first additive is 3-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-1-p-tolylsulfonyl-1H-pyrrolo[2,3-b]pyridine-5-carbonitrile, and the second additive is tris(1,1,1,3,3,3-hexafluoro-2-propyl)phosphite, and the structural formula is The CAS number is 66470-81-3.

[0039] The lithium salt is lithium hexafluorophosphate.

[0040] The linear carbonate is diethyl carbonate DEC, methyl ethyl carbonate EMC, and the cyclic carbonate is fluorinated ethylene carbonate FEC, propylene carbonate PC (DEC: EMC: FEC: PC = 25:45:10:20).

[0041] The linear carbonate and the cyclic carbonate are stirred, and after being uniformly mixed, a first mixture is obtained; the lithium salt is added to the first mixture and stirred, and after being uniformly mixed, a second mixture is obtained; the first additive and the second additive are added to the second mixture and stirred, and after being uniformly mixed, an electrolyte is obtained.

[0042] 2. Preparation of positive electrode sheet

[0043] The ternary material NCM (LiNi 0.9 Co 0.05 Mn 0.05 O2) positive active material, the binder PVDF (polyvinylidene fluoride), and the conductive agent SP (conductive carbon black Super-P) are mixed and stirred uniformly at a mass ratio of 96:1.8:2.2 to obtain a positive electrode slurry, and then the positive electrode slurry is coated on an aluminum foil through a coating process, and after drying and cold pressing, a positive electrode sheet is obtained.

[0044] 3. Preparation of negative electrode sheet

[0045] The silicon-carbon negative electrode material, the conductive agent SP (conductive carbon black Super-P), SWCNT (single-walled carbon nanotube), and the binder PAA (polyacrylic acid) are mixed and stirred uniformly at a mass ratio of 83.5:8:0.5:8 to obtain a negative electrode slurry, and the solid content is controlled at 30%, and then the negative electrode slurry is coated on a copper foil current collector through a coating process, and after vacuum drying and cold pressing, a negative electrode sheet is obtained.

[0046] 4. Selection of separator film

[0047] Polyethylene (PE) + ceramic is selected as the separator film of the lithium ion battery.

[0048] 5. Preparation of lithium ion battery

[0049] The positive electrode sheet, the separator, and the negative electrode sheet are stacked in sequence, the separator is between the positive electrode sheet and the negative electrode sheet to play a role of isolation, and then a bare battery cell is obtained; the bare battery cell is placed in an outer packaging shell, electrolyte is injected after drying, and a soft package lithium ion battery is obtained through processes such as vacuum packaging, standing, formation, and shaping.

[0050] Example 2

[0051] 1. Preparation of electrolyte

[0052] The mass ratio of the first additive in the electrolyte is 0.5%, the mass ratio of the second additive is 1.5%, the mass ratio of linear carbonate and cyclic carbonate in the organic solvent is 60:40, and the lithium salt concentration is 1.5 mol / L.

[0053] The first additive is 3-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-1-p-tolylsulfonyl-1H-pyrrolo[2,3-b]pyridine-5-carbonitrile, and the structural formula of the second additive is CAS No. is 2241-68-1;

[0054] The lithium salt is lithium hexafluorophosphate;

[0055] The linear carbonate is methyl ethyl carbonate EMC and methyl propyl carbonate MPC, and the cyclic carbonate is ethylene carbonate EC and propylene carbonate PC (EMC: MPC: EC: PC = 15:45:15:25);

[0056] The linear carbonate and the cyclic carbonate are stirred, and after uniform stirring, a first mixture is obtained; the lithium salt is added to the first mixture and stirred, and after uniform stirring, a second mixture is obtained; the first additive and the second additive are added to the second mixture and stirred, and after uniform stirring, the electrolyte is obtained.

[0057] 2. Preparation of positive electrode sheet

[0058] The ternary material NCM (LiNi 0.9 Co 0.05 Mn 0.05 O2) positive active material, binder PVDF (polyvinylidene fluoride), and conductive agent SP (conductive carbon black Super-P) are mixed and stirred uniformly at a mass ratio of 96:1.8:2.2 to obtain a positive electrode slurry, then the positive electrode slurry is coated on an aluminum foil through a coating process, and after drying and cold pressing, a positive electrode sheet is obtained.

[0059] 3. Preparation of negative electrode sheet

[0060] The silicon-carbon negative electrode material, conductive agent SP (conductive carbon black Super-P), SWCNT (single-walled carbon nanotube), and binder PAA (polyacrylic acid) are mixed and stirred uniformly at a mass ratio of 83.5:8:0.5:8 to obtain a negative electrode slurry, and the solid content is controlled at 30%. Then, the negative electrode slurry is coated on the copper foil current collector through a coating process, and the negative electrode sheet is obtained after vacuum drying and cold pressing.

[0061] 4. Selection of separator film

[0062] Polyethylene (PE) + ceramic is selected as the separator film of the lithium ion battery.

[0063] 5. Preparation of lithium ion battery

[0064] The above positive electrode sheet, separator film, and negative electrode sheet are stacked in order, with the separator film between the positive electrode sheet and the negative electrode sheet to play a separating role, and then a bare cell is obtained. The bare cell is placed in an outer packaging shell, dried, and then injected with electrolyte. After vacuum packaging, standing, formation, shaping, and other processes, a soft-pack lithium ion battery is obtained.

[0065] Example 3

[0066] 1. Preparation of electrolyte

[0067] The mass ratio of the first additive in the electrolyte is 2%, the mass ratio of the second additive is 0.5%, the mass ratio of linear carbonate to cyclic carbonate in the organic solvent is 80:20, and the lithium salt concentration is 1 mol / L.

[0068] The first additive is 3-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-1-p-tolylsulfonyl-1H-pyrrolo[2,3-b]pyridine-5-carbonitrile, and the structural formula of the second additive is CAS No. 370-69-4;

[0069] The lithium salt is lithium hexafluorophosphate;

[0070] The linear carbonate is dimethyl carbonate DMC, diethyl carbonate DEC, and methyl propyl carbonate MPC, and the cyclic carbonate is ethylene carbonate EC (DMC:DEC:MPC:EC=25:45:10:20).

[0071] The linear carbonate and the cyclic carbonate are stirred, and after stirring and mixing uniformly, a first mixture is obtained. The lithium salt is added to the first mixture and stirred, and after stirring and mixing uniformly, a second mixture is obtained. The first additive and the second additive are added to the second mixture and stirred, and after stirring and mixing uniformly, the electrolyte is obtained.

[0072] 2. Preparation of positive electrode sheet

[0073] The ternary material NCM (LiNi 0.9 Co 0.05 Mn 0.05 O2) positive electrode active material, a binder PVDF (polyvinylidene fluoride), and a conductive agent SP (conductive carbon black Super-P) are mixed in a mass ratio of 96:1.8:2.2 to obtain a positive electrode slurry, which is then coated on an aluminum foil through a coating process, dried, and cold-pressed to obtain a positive electrode sheet.

[0074] 3. Preparation of a negative electrode sheet

[0075] The silicon-carbon negative electrode material, the conductive agent SP (conductive carbon black Super-P), SWCNT (single-walled carbon nanotubes), and the binder PAA (polyacrylic acid) are mixed in a mass ratio of 83.5:8:0.5:8 to obtain a negative electrode slurry with a solid content of 30%, which is then coated on a copper foil current collector through a coating process, vacuum-dried, and cold-pressed to obtain a negative electrode sheet.

[0076] 4. Selection of a separator film

[0077] Polyethylene (PE) + ceramic is selected as the separator film of the lithium ion battery.

[0078] 5. Preparation of a lithium ion battery

[0079] The above positive electrode sheet, the separator film, and the negative electrode sheet are stacked in order with the separator film between the positive electrode sheet and the negative electrode sheet to serve as a separator, and a bare cell is obtained. The bare cell is placed in an outer packaging shell, dried, and then injected with electrolyte. After vacuum packaging, standing, formation, shaping, and other processes, a soft-pack lithium ion battery is obtained.

[0080] Example 4

[0081] The difference between this example and Example 1 is that the electrolyte further includes a lithium salt additive (lithium bisfluorosulfonylimide LiFSI), and the mass fraction of the lithium salt additive in the electrolyte is 0.3%. The remaining steps and parameter settings are consistent with those of Example 1.

[0082] Example 5

[0083] The difference between this example and Example 1 is that the electrolyte further includes a lithium salt additive (lithium bis-trifluoromethanesulfonylimide LiTFSi), and the mass fraction of the lithium salt additive in the electrolyte is 3%. The remaining steps and parameter settings are consistent with those of Example 1.

[0084] Example 6

[0085] The difference between this embodiment and embodiment 1 is that the electrolyte further comprises a lithium salt additive (lithium tetrafluoroborate LiBF4), and the mass percentage of the lithium salt additive in the electrolyte is 0.5%; the remaining steps and parameter settings are consistent with embodiment 1.

[0086] Embodiment 7

[0087] The difference between this embodiment and embodiment 1 is that the mass percentage of the first additive in the electrolyte is 3%, and the mass percentage of the second additive in the electrolyte is 0.1%; the remaining steps and parameter settings are consistent with embodiment 1.

[0088] Embodiment 8

[0089] The difference between this embodiment and embodiment 1 is that the mass percentage of the first additive in the electrolyte is 0.2%, and the mass percentage of the second additive in the electrolyte is 2.5%; the remaining steps and parameter settings are consistent with embodiment 1.

[0090] Embodiment 9

[0091] The difference between this embodiment and embodiment 1 is that ethyl propionate (EP) is used instead of linear carbonate in embodiment 1; the remaining steps and parameter settings are consistent with embodiment 1.

[0092] Embodiment 10

[0093] The difference between this embodiment and embodiment 1 is that the mass percentage of linear carbonate and cyclic carbonate is 20:80; the remaining steps and parameter settings are consistent with embodiment 1.

[0094] Comparative Example 1

[0095] The difference between this comparative example and embodiment 1 is that the electrolyte does not contain the first additive and the second additive; the remaining steps and parameter settings are consistent with embodiment 1.

[0096] Comparative Example 2

[0097] The difference between this comparative example and embodiment 1 is that the electrolyte does not contain the first additive; the remaining steps and parameter settings are consistent with embodiment 1.

[0098] Comparative Example 3

[0099] The difference between this comparative example and embodiment 1 is that the electrolyte does not contain the second additive; the remaining steps and parameter settings are consistent with embodiment 1.

[0100] Comparative Example 4

[0101] The difference between this comparative example and embodiment 1 is that the structural formula of the first additive is CAS No. 2752449-73-1; other steps and parameter settings are consistent with Example 1.

[0102] Comparative Example 5

[0103] This comparative example is different from Example 1 in that the structural formula of the second additive is CAS No. 66559-58-8; other steps and parameter settings are consistent with Example 1.

[0104] Test method

[0105] I. First coulombic efficiency test of lithium battery

[0106] The first coulombic efficiency of the lithium battery in the above examples and comparative examples was tested, and the specific test steps were as follows: under the condition of 25℃, the lithium ion battery was charged to 4.2V at 0.33C rate, and then discharged to 2.5V at 0.33C rate, and the first coulombic efficiency of the lithium ion battery was calculated.

[0107] First coulombic efficiency (%) = lithium ion battery 0.33C first discharge total capacity / lithium ion battery 0.33C first charge total capacity x 100%.

[0108] II. Cycle performance test of lithium battery

[0109] 2.1. Lithium battery cycle capacity retention rate at room temperature

[0110] The lithium battery in the above examples and comparative examples was tested for cycle capacity retention rate at room temperature, and the specific test steps were as follows: under the condition of 25℃, the lithium ion battery was charged to 4.2V at 1C rate, and then discharged to 2.5V at 1C rate, and the first charge-discharge cycle was carried out, and the lithium ion battery was charged and discharged according to the above method for 1000 cycles, and the capacity retention rate of the lithium ion battery after 1000 cycles of charge-discharge at 1C / 1C was calculated.

[0111] 2.2. Lithium battery cycle capacity retention rate at high temperature

[0112] The lithium battery in the above examples and comparative examples was subjected to normal temperature cycle capacity retention rate test, and the specific test steps were as follows: under the condition of 45°C, the lithium ion battery was subjected to constant current and constant voltage charging to 4.2V at 1C rate, the cutoff current was 0.05C, and the lithium ion battery was allowed to stand for 10 min, then the lithium ion battery was subjected to constant current discharging to 2.5V at 1C rate, and the lithium ion battery was allowed to stand for 10 min, which was one cycle of charging and discharging. The lithium ion battery was subjected to charging and discharging cycle for 1000 times according to the above method, and the capacity retention rate after 1000 cycles of charging and discharging of the lithium ion battery at 1C / 1C was calculated.

[0113] The capacity retention rate (%) of the lithium ion battery after N cycles = (discharge capacity of the Nth cycle / first discharge capacity) x 100%, and N was the cycle number of the lithium ion battery.

[0114] III. Rate performance test

[0115] The lithium battery in the above examples and comparative examples was subjected to rate performance test, and the specific test steps were as follows: under the condition of 25°C, the lithium ion battery was subjected to constant current discharging to 2.5V at 1C rate, and the lithium ion battery was allowed to stand for 10 min, then the lithium ion battery was subjected to constant current and constant voltage charging to 4.2V at 6C rate, the cutoff current was 0.05C, and the lithium ion battery was allowed to stand for 10 min, and the constant current charging capacity Q1 and the total constant current and constant voltage charging capacity Q2 of the lithium ion battery were recorded. The 6C rate charging constant current charging ratio was calculated according to the following formula: 6C rate charging constant current charging ratio = constant current charging capacity Q1 / total constant current and constant voltage charging capacity Q2 x 100%.

[0116] IV. Safety performance test

[0117] The lithium battery in the above examples and comparative examples was subjected to thermal runaway test, and the specific test steps were as follows: the test sample was heated from room temperature to 45±2°C in the cavity, and after standing for 90 min, the change of battery temperature rise rate was detected. If the temperature rise was more than 0.2°C in 10 min (i.e. SHR>0.02°C / min), it was considered that the self-heat reaction occurred in the battery, and the adiabatic environment was maintained until the thermal runaway of the battery occurred. If the temperature rise was not more than 0.2°C in 10 min (i.e. SHR≤0.02°C / min), the next step temperature rise test was continued. Each temperature step was 5°C, and the steps were repeated at each step. The ARC test temperature range was 45-300°C, the initial self-heating temperature was T1 (temperature rise rate SHR>0.02°C / min), and the initial thermal runaway temperature T2 (temperature rise rate SHR>1°C / min).

[0118] Table 1

[0119]

[0120] In combination with Examples 1-3, Comparative Examples 1-5 and Table 1, it can be seen that, by using the first additive and the second additive in combination in the present application, not only can the stability of the electrolyte be improved to improve the stability of the negative electrode interface film, but also a protective layer containing alkyl phosphorus can be formed on the surface of the positive electrode to effectively inhibit the dissolution of transition metal ions at the positive electrode and avoid the negative impact of transition metal ions on the film-forming stability of the negative electrode SEI film, which helps to improve the cycle capacity retention rate and thermal stability of the lithium battery; and the combination of the sulfonyl group, the pyridyl group and the fluorine element in the two additives not only improves the flame retardance of the electrolyte, but also helps to improve the ionic conductivity of the electrolyte, thereby further improving the self-heat generation starting temperature and the rate performance of the lithium battery.

[0121] In combination with Example 1, Examples 4-6 and Table 1, it can be seen that, by adding a suitable lithium salt additive to the electrolyte, the ionic conductivity of the electrolyte can be improved, which helps to improve the cycle capacity retention rate of the lithium battery.

[0122] In combination with Example 1, Examples 7-8 and Table 1, it can be seen that, when the amount of the first additive and the second additive is too high or too low, it is not conducive to improving the stability of the positive electrode interface film and the negative electrode interface film, which will reduce the combination effect of the sulfonyl group, the pyridyl group and the fluorine element in the additive, and is not conducive to improving the flame retardance of the electrolyte and the cycle performance of the lithium battery, so the cycle performance and the self-heat generation starting temperature of the lithium battery of Examples 7-8 are lower than those of the lithium battery of Example 1.

[0123] In combination with Example 1, Examples 9-10 and Table 1, it can be seen that, by selecting a cyclic carbonate and a linear carbonate as the organic solvent and controlling the mass ratio of the cyclic carbonate to the linear carbonate, the stability of the electrolyte can be improved, which provides a stable environmental basis for the combination of the first additive and the second additive, and the surface of the negative electrode active material can be uniformly filmed, so the cycle performance and the initial efficiency performance of the lithium battery of Examples 9-10 are lower than those of the lithium battery of Example 1.

[0124] The above examples are only used to illustrate the technical solutions of the present application and not to limit the protection scope of the present application. Although the present application has been described in detail with reference to the above examples, it should be understood by those skilled in the art that the technical solutions of the present application can be modified or replaced equivalently, but these modifications or replacements are within the protection scope of the present application.

Claims

1. A multifunctional electrolyte, characterized by: The electrolyte comprises a first additive, a second additive and an organic solvent, the first additive comprises 3-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-1-p-tolylsulfonyl-1H-pyrrolo[2,3-b]pyridine-5-carbonitrile; the chemical structure of the second additive is shown in formula I: ； wherein R1, R2, R3 are each independently selected from any one of -CH2CF3, -CHCF3CF3, -CH2CF2CHF2; the mass percentage of the first additive in the electrolyte is 0.5%-2%; the mass percentage of the second additive in the electrolyte is 0.5%-1.5%; the organic solvent comprises linear carbonate and cyclic carbonate.

2. The multifunctional electrolyte according to claim 1, characterized in that: Further comprising a lithium salt and a lithium salt additive.

3. The multifunctional electrolyte according to claim 2, characterized in that: The lithium salt additive comprises at least one of lithium bisfluorosulfonimide, lithium bis-trifluoromethanesulfonimide, lithium tetrafluoroborate.

4. The multifunctional electrolyte according to claim 2, wherein: The mass percentage of the lithium salt additive in the electrolyte is 0.2%-3%.

5. The multifunctional electrolyte according to claim 2, wherein: The linear carbonate comprises at least one of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate and methyl propyl carbonate; the cyclic carbonate comprises at least one of ethylene carbonate, fluorinated ethylene carbonate, propylene carbonate.

6. The multifunctional electrolyte according to claim 2, wherein: The mass ratio of the linear carbonate to the cyclic carbonate is 60-80:20-40.

7. A lithium-ion battery, characterized by: The electrolyte comprises a first additive, a second additive and an organic solvent, the first additive comprises 3-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-1-p-tolylsulfonyl-1H-pyrrolo[2,3-b]pyridine-5-carbonitrile; the chemical structure of the second additive is shown in formula I: wherein R1, R2, R3 are each independently selected from any one of -CH2CF3, -CHCF3CF3, -CH2CF2CHF2; the mass percentage of the first additive in the electrolyte is 0.5%-2%; the mass percentage of the second additive in the electrolyte is 0.5%-1.5%; the organic solvent comprises linear carbonate and cyclic carbonate. Further comprising a lithium salt and a lithium salt additive. The lithium salt additive comprises at least one of lithium bisfluorosulfonimide, lithium bis-trifluoromethanesulfonimide, lithium tetrafluoroborate. The mass percentage of the lithium salt additive in the electrolyte is 0.2%-3%. The linear carbonate comprises at least one of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate and methyl propyl carbonate; the cyclic carbonate comprises at least one of ethylene carbonate, fluorinated ethylene carbonate, propylene carbonate. The mass ratio of the linear carbonate to the cyclic carbonate is 60-80:20-40. The electrolyte comprises a first additive, a second additive and an organic solvent, the first additive comprises 3-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-1-p-tolylsulfonyl-1H-pyrrolo[2,3-b]pyridine-5-carbonitrile; the chemical structure of the second additive is shown in formula I: wherein R1, R2, R3 are each independently selected from any one of -CH2CF3, -CHCF3CF3, -CH2CF2CHF2; the mass percentage of the first additive in the electrolyte is 0.5%-2%; the mass percentage of the second additive in the electrolyte is 0.5%-1.5%; the organic solvent comprises linear carbonate and cyclic carbonate. Further comprising a lithium salt and a lithium salt additive. The lithium salt additive comprises at least one of lithium bisfluorosulfonimide, lithium bis-trifluoromethanesulfonimide, lithium tetrafluoroborate. The mass percentage of the lithium salt additive in the electrolyte is 0.2%-3%. The linear carbonate comprises at least one of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate and methyl

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