Electrolyte additive, electrolyte and lithium ion battery

Abstract

The invention provides an electrolyte additive, an electrolyte and a lithium ion battery. The electrolyte additive comprises a compound I, the compound I contains R1 and R2 groups, R1 and R2 are independently selected from any one of hydrogen and alkoxy substituted by a substituent group, and the substituent group is alkyl containing a P-O bond and / or a P = O bond; r1 and R2 are not hydrogen at the same time. The compound I can optimize the chemical characteristics of an electrode interface, significantly improve the cycle life and the high-temperature storage performance of the battery, and can generate a controllable oxidation-reduction reaction on the surfaces of the positive and negative electrodes to form a compact solid electrolyte interface film with excellent ionic conductivity; according to the present invention, with the composite material, the continuous decomposition of the electrolyte, the dissolution of the metal ions and the gas production side reaction can be effectively inhibited, the HF generated in the electrolyte can be combined, the corrosion of the HF on the electrode material can be reduced, and the cycle life and the high-temperature storage performance of the battery assembled by the positive electrode active material and the negative electrode active material can be improved;

Description

Technical Field

[0001] This application belongs to the field of lithium-ion battery technology, specifically relating to an electrolyte additive, an electrolyte, and a lithium-ion battery. Background Technology

[0002] Lithium-ion batteries are now widely used in power, energy storage, and electronic products, leading to increasingly higher demands on their energy density, cycle performance, high-temperature performance, and safety. Improving battery cycle life and high-temperature performance is a pressing issue that needs to be addressed.

[0003] Currently available commercial electrolytes are prone to decomposition at high temperatures or high voltages, leading to a chain reaction of reactions such as the dissolution of transition metals in the positive electrode and the rupture of the SEI film in the negative electrode, resulting in capacity decay and the risk of thermal runaway. Therefore, how to provide an electrolyte that can improve the high-temperature performance of lithium-ion batteries is a problem that needs to be solved. Summary of the Invention

[0004] The purpose of this application is to provide an electrolyte additive, an electrolyte, and a lithium-ion battery, aiming to solve the problem of unstable performance of the electrolyte in existing lithium-ion batteries at high temperatures.

[0005] The first embodiment of this application provides an electrolyte additive, comprising compound I, the structural formula of which is shown in Formula I:

[0006] Formula I; R1 and R2 are each independently selected from hydrogen and alkoxy groups substituted with substituents, wherein the substituents are alkyl groups containing PO bonds and / or P=O bonds; R1 and R2 are not both hydrogen.

[0007] In some embodiments, R1 and R2 are each independently selected from... , , and Any one of them; R3 and R4 are each independently selected from , , , and Any one of them.

[0008] In some embodiments, compound I is selected from any one of the compounds shown in Formulas I-1 to I-8:

[0009] The second embodiment of this application provides an electrolyte including the electrolyte additives in any of the above embodiments, wherein the mass percentage of the electrolyte additives in the electrolyte is 0.1~10%.

[0010] In some embodiments, the electrolyte further includes lithium salt and organic solvent; The lithium salt in the electrolyte has a mass percentage of 5-20%; The organic solvent accounts for 70-90% by mass in the electrolyte.

[0011] In some embodiments, the electrolyte further includes auxiliary additives; the auxiliary additives include at least one of ester compounds, nitrile compounds, silicon-based compounds, sulfur-containing compounds, and lithium salt compounds.

[0012] In some embodiments, the electrolyte additive and the auxiliary additive satisfy the following: 0.1%≤w1+w2≤10%; and 0.1≤w1 / w2≤1; In the formula, w1 is the mass percentage of the electrolyte additive in the electrolyte, and w2 is the mass percentage of the auxiliary additive in the electrolyte.

[0013] In some embodiments, the mass ratio of the ester compound, the nitrile compound, the silicon-based compound, the sulfur-containing compound, and the lithium salt compound is 0~3%:0~3%:0~3%:0~5%:0~6%.

[0014] In some embodiments, the lithium salt includes at least one of lithium hexafluorophosphate, lithium bisfluorosulfonylimide, lithium tetrafluoroborate, and lithium bistrifluoromethylsulfonylimide.

[0015] In some embodiments, the organic solvent includes at least one selected from ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethyl acetate, ethyl propionate, propyl propionate, and 1,1,2,3-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0016] In some embodiments, the ester compound includes at least one of vinylene carbonate, fluoroethylene carbonate, and methyl (2,2,2-trifluoroethyl) carbonate.

[0017] In some embodiments, the nitrile compound includes at least one selected from butadionitrile, glutaronitrile, octadionitrile, 1,3,6-hexanetrionitrile, 1,3,5-pentanetrionitrile, and methoxypropionitrile.

[0018] In some embodiments, the sulfur-containing compound includes at least one of 1,3-propanesulfonate lactone, 1,3-propenesulfonate lactone, vinyl sulfate, and vinylene sulfate.

[0019] In some embodiments, the lithium salt compound is selected from at least one of lithium difluorophosphate, lithium bis(oxalate)borate, lithium difluorooxalateborate, and lithium difluorooxalate phosphate.

[0020] The third embodiment of this application provides a lithium-ion battery, including a positive electrode, a negative electrode, a separator, and an electrolyte as described in any of the above embodiments; the high-temperature storage capacity retention rate (60d, 60℃) of the lithium-ion battery is 50~90%, and the high-temperature storage volume expansion rate (60d, 60℃) is 5~50%.

[0021] This application provides an electrolyte additive comprising compound I, wherein compound I contains R1 and R2 groups, wherein R1 and R2 are each independently selected from hydrogen and alkoxy groups substituted with substituents, and the substituents are alkyl groups containing PO bonds and / or P=O bonds; R1 and R2 are not both hydrogen. By adding compound I, which contains PO bonds and / or P=O bonds, to the electrolyte, this application can optimize the chemical properties of the electrode interface, significantly improve the cycle life and high-temperature storage performance of the battery. It can not only induce a controllable redox reaction on the positive and negative electrode surfaces to form a dense and ionicly conductive solid electrolyte interphase (SEI / CEI) film, effectively suppressing the continuous decomposition of the electrolyte, the dissolution of metal ions, and gas generation side reactions, but also bind to HF generated in the electrolyte, reducing the corrosion of electrode materials by HF. This can improve cycle life and enhance high-temperature storage performance for batteries assembled from positive and negative electrode active materials. Detailed Implementation

[0022] The technical solutions of this application will be clearly and completely described below with reference to the embodiments therein. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0023] In the description of this application, it should be noted that "multiple" means two or more, unless otherwise explicitly specified. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, features defined with "first" or "second" may explicitly or implicitly include one or more features.

[0024] The compounds of this application can be synthesized via synthetic routes including methods similar to those known in the field of chemistry, particularly with reference to the description contained herein. Starting materials are generally available from commercial sources or can be readily prepared using methods known to those skilled in the art. For illustrative purposes, the reaction schemes described below illustrate possible routes for synthesizing the compounds of this application and key intermediates. For a more detailed description of each reaction step, see the Examples section below. Those skilled in the art will recognize that other suitable starting materials, reagents, and synthetic routes can be used to synthesize the compounds of this application and their various derivatives.

[0025] Unless otherwise stated, the term "alkyl" as used herein refers to a saturated aliphatic hydrocarbon group, which may be straight-chain or branched. For example, the term "C1-C6 alkyl" refers to an alkyl group containing 1, 2, 3, 4, 5, or 6 carbon atoms (e.g., methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, 1-methylbutyl, 2-methylbutyl, 3-methylbutyl, neopentyl, hexyl, 2-methylpentyl, etc.). Similarly, the alkyl portion (i.e., alkyl) of alkoxy, alkylacyl, alkylphosphate, alkylsulfonyl, and alkylaminosulfonyl groups has the same definition above. For example, the term "C1-C3 alkyl" refers to an alkyl group containing 1, 2, or 3 carbon atoms (e.g., methyl, ethyl, propyl, and isopropyl). Alkyl groups may be substituted or unsubstituted, and when substituted, the substituents may be substituted at any usable link.

[0026] Unless otherwise stated, the term "alkoxy" as used herein refers to -O-alkyl, where alkyl is as defined in this application.

[0027] The following disclosure provides many different embodiments or examples for implementing different structures of this application. To simplify the disclosure of this application, the configuration and arrangement of specific examples are described below. Of course, these are merely examples and are not intended to limit this application.

[0028] The first embodiment of this application provides an electrolyte additive, including compound I, the structural formula of which is shown in Formula I:

[0029] Formula I; R1 and R2 are each independently selected from hydrogen and alkoxy groups substituted with substituents, and the substituents are alkyl groups containing PO bonds and / or P=O bonds; R1 and R2 are not both hydrogen.

[0030] It is understandable that the basic structure of compound I is an ethylene carbonate group, which has a high dielectric constant and can form a film to protect the negative electrode of the battery. When a P=O bond exists in compound I, the oxygen atom in the P=O bond can combine with HF generated in the electrolyte during battery charging and discharging to form a stable POF structure, reducing the corrosion of electrode materials by HF. It can also stabilize highly reactive high oxidation state transition metal ions, such as Ni, generated on the surface of the electrode material. 4+ This reduces side reaction gas production; the PO bond can be oxidized on the positive electrode surface to form P=O bonds, and generate an inorganic-organic composite CEI film rich in P=O bonds, effectively inhibiting electrolyte oxidative decomposition and transition metal (such as Ni) reactions. 3+ The PO bond dissolves, reducing the loss of active lithium and thus improving the cycle stability and high-temperature stability of the battery. Furthermore, the phosphite formed by the PO bond decomposes at high temperatures to generate PO· radicals, which combine with H· from the combustion chain reaction (H· + PO· → HPO), achieving gas-phase flame retardancy and further improving the high-temperature safety of lithium-ion batteries.

[0031] In some embodiments, R1 and R2 are each independently selected from... , , and Any one of them; R3 and R4 are each independently selected from , , , and Any one of them.

[0032] It is understandable that the above-mentioned preferred groups all contain heterocyclic structures, which have strong electronegativity and can further help to form a dense protective film on the negative electrode surface of the battery, thereby improving the battery's high-temperature and cycle performance and reducing gas generation during storage.

[0033] In some embodiments, compound I is selected from any one of compounds I-1 to I-8 as shown below:

[0034] The second embodiment of this application provides an electrolyte including the electrolyte additives in any of the above embodiments, wherein the mass percentage of the electrolyte additives in the electrolyte is 0.1~10%.

[0035] It is understandable that the mass percentage of electrolyte additives in the electrolyte can be any value from 0.1%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or any value within a range of any two values. When the proportion of electrolyte additives in the electrolyte meets the above range, it can effectively inhibit the dissolution of transition metals and the oxidative decomposition of the electrolyte, while avoiding excessive addition that leads to an excessively thick electrode interface film, resulting in increased battery impedance and decreased cycle performance and high-temperature performance.

[0036] In some embodiments, the electrolyte further includes lithium salt and organic solvent; The mass percentage of lithium salt in the electrolyte is 5-20%; It is understandable that the mass percentage of lithium salt in the electrolyte can be any value from 5%, 10%, 15%, 20%, or any value within a range of any two values.

[0037] The organic solvent accounts for 70-90% of the mass percentage in the electrolyte.

[0038] It is understandable that the mass percentage of organic solvent in the electrolyte can be any value from 70%, 75%, 80%, 85%, 90%, or any range between two of these values. When the amounts of lithium salt and organic solvent added to the electrolyte meet the above ranges, it can further ensure that the electrolyte has good electrical performance.

[0039] In some embodiments, the electrolyte further includes auxiliary additives; the auxiliary additives include at least one of ester compounds, nitrile compounds, silicon-based compounds, sulfur-containing compounds, and lithium salt compounds.

[0040] It is understandable that ester compounds, silicon-based compounds, and sulfur-containing compounds can improve the high-temperature resistance of electrolytes, nitrile compounds can improve the high-voltage resistance of electrolytes, and sulfur-containing compounds and lithium salt compounds can reduce impedance.

[0041] In some embodiments, the electrolyte additive and auxiliary additives satisfy the following: 0.1%≤w1+w2≤10%; and 0.1≤w1 / w2≤1; In the formula, w1 is the mass percentage of electrolyte additives in the electrolyte, and w2 is the mass percentage of auxiliary additives in the electrolyte.

[0042] It is understandable that the value of w1+w2 can be any value from 0.1%, 0.5%, 1%, 2%, 4%, 6%, 8%, 10%, or any value within the range of any two values. The value of w1 / w2 can be any value from 0.1, 0.2, 0.4, 0.5, 0.6, 0.8, 1, or any value within the range of any two values. By controlling the total amount and ratio of electrolyte additives and auxiliary additives to meet the above value ranges, a balance can be achieved between good high-temperature cycling performance and low impedance in the electrolyte.

[0043] In some embodiments, the mass ratio of ester compounds, nitrile compounds, silicon-based compounds, sulfur-containing compounds and lithium salt compounds is 0~3%:0~3%:0~3%:0~5%:0~6%.

[0044] In some embodiments, the lithium salt includes at least one of lithium hexafluorophosphate, lithium bisfluorosulfonylimide, lithium tetrafluoroborate, and lithium bistrifluoromethylsulfonylimide.

[0045] In some embodiments, the organic solvent includes at least one selected from ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethyl acetate, ethyl propionate, propyl propionate, and 1,1,2,3-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0046] In some embodiments, the ester compound includes at least one of vinylene carbonate, fluoroethylene carbonate, and methyl (2,2,2-trifluoroethyl) carbonate.

[0047] In some embodiments, the nitrile compound includes at least one selected from succinic anionyl nitrile, glutaronitrile, octanoic anionyl nitrile, 1,3,6-hexanetrionitrile, 1,3,5-pentanetrionitrile, and methoxypropionitrile.

[0048] In some embodiments, the sulfur-containing compound includes at least one of 1,3-propanesulfonate lactone, 1,3-propenesulfonate lactone, vinyl sulfate, and vinylene sulfate.

[0049] In some embodiments, the lithium salt compound is selected from at least one of lithium difluorophosphate, lithium bis(oxalate)borate, lithium difluorooxalateborate, and lithium difluorooxalate phosphate.

[0050] The third embodiment of this application provides a lithium-ion battery, including a positive electrode, a negative electrode, a separator, and an electrolyte as described in any of the above embodiments; the high-temperature storage capacity retention rate (60d, 60°C) of the lithium-ion battery is 50-90%, and the high-temperature storage volume expansion rate (60d, 60°C) is 5-50%.

[0051] Specifically, the positive electrode includes a positive electrode active material, which includes at least one of lithium nickel cobalt manganese oxide, lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, and lithium nickel cobalt aluminum oxide; the negative electrode includes a negative electrode active material, which includes at least one of soft carbon, hard carbon, artificial graphite, natural graphite, graphene, silicon oxide, or silicon carbide; the separator is one of polyethylene (PE) separator, polypropylene (PP) separator, PP / PE / PP three-layer composite membrane, polyimide (PI), and polyacrylonitrile (PAN).

[0052] The electrolyte additive, electrolyte, and lithium-ion battery provided in this application are described below with reference to specific embodiments: Example 1 This embodiment provides an electrolyte, which, based on 100% of the total mass of the electrolyte, comprises the following components: Compound I-1: 2%; Vinylene carbonate: 1%; Lithium bis(oxalate) phosphate: 0.2%; Lithium difluorophosphate: 0.6%; Lithium hexafluorophosphate: 11%; Lithium difluorosulfonylimide: 2.7%; Ethyl methyl carbonate: 41.25%; Ethylene carbonate: 24.75%; Diethyl carbonate: 16.5%.

[0053] The electrolyte was prepared as follows: The electrolyte was prepared in a glove box with a nitrogen content of 99.999%, an actual oxygen content of 0.1 ppm, and a moisture content of 0.1 ppm. Based on 100% of the total mass of the non-aqueous electrolyte, 24.75% ethylene carbonate, 41.25% methyl ethyl carbonate, and 16.5% diethyl carbonate (battery-grade organic solvent) were mixed evenly. Then, 11% lithium hexafluorophosphate and 2.7% lithium difluorosulfonyl imide (fully dried) were added to the above non-aqueous solvent. Additives of 2% compound 1.1, 0.6% lithium difluorophosphate, 1% ethylene carbonate, and 0.2% lithium bis(oxalate) phosphate were added to prepare the non-aqueous electrolyte for lithium-ion batteries.

[0054] The lithium-ion battery is prepared using the above electrolyte, and the preparation method is as follows: The positive electrode active material NCM811, conductive agent conductive carbon black, binder PVDF, and carbon nanotubes were thoroughly mixed in an N-methylpyrrolidone solvent system at a mass ratio of 96.5:1.5:1.5:0.5. The mixture was then coated onto aluminum foil, dried, and hot-pressed to obtain the positive electrode sheet with an areal density of 250 g / m³.2 The compacted density is 3.5 g / cm³. 3 .

[0055] The negative electrode active material graphite, conductive agent conductive carbon black, binder CMC, and SBR were thoroughly mixed in a deionized water solvent system at a mass percentage of 95.1:1.5:1.4:2.0. The mixture was then coated onto Cu foil, dried, and cold-pressed to obtain the negative electrode sheet with an areal density of 160 g / m³. 2 The compacted density is 1.55 g / cm³. 3 .

[0056] A diaphragm was obtained by using a 9μm thick polyethylene (PE) base film and coating a 2μm ceramic coating on both sides of the base film.

[0057] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to act as an insulator. The stacked electrodes then form a bare cell.

[0058] After the bare battery cell is placed in an aluminum-plastic film and baked at 80°C to remove moisture, the corresponding electrolyte is injected and the cell is sealed. Then, after processes such as settling, hot and cold pressing, formation, high-temperature settling, and capacity testing, the finished soft-pack lithium-ion secondary battery is obtained.

[0059] Examples 2-13 Examples 2-13 are similar to the electrolyte in Example 1, except for the adjustment of the components and the proportions of addition, see Table 1.

[0060] Comparative Example 1 The difference between this comparative example and Example 1 is that, with the total mass of the non-aqueous electrolyte being 100%, compound I is not added, and the amount of non-aqueous solvent is adjusted to make the total electrolyte amount 100%. The other raw materials, proportions, and mass percentages of each component are the same as in Example 1.

[0061] Comparative Examples 2-3 Comparative Examples 2 and 3 are similar to the electrolyte in Example 1, except for the adjustment of the components and the proportions of addition, see Table 1.

[0062] Table 1

[0063] Performance testing of lithium-ion batteries: (1) Lithium-ion battery cycle performance test The lithium-ion battery was placed in a 25°C constant temperature chamber and left to stand for 30 minutes to allow it to reach a constant temperature. The battery was then charged at a constant current of 1C to a voltage of 4.25V, followed by charging at a constant voltage of 4.25V to a current of 0.05C, and then discharging at a constant current of 1C to a voltage of 2.75V. This constitutes one charge-discharge cycle. This cycle was repeated three times, and the discharge capacity of the last cycle was taken as the initial capacity of the lithium-ion battery. Starting from the initial capacity of 100%, the charge-discharge cycles were repeated until the discharge capacity decreased to 80%. The test was then stopped, and the number of cycles was recorded as an indicator of the lithium-ion battery's cycle performance.

[0064] Meanwhile, the cycle performance of lithium-ion batteries at 45°C was tested, and the testing method was the same as the 25°C cycle performance test mentioned above, except for the temperature difference.

[0065] (2) High-temperature storage test of lithium-ion batteries (60 degrees Celsius, storage for 60 days) The lithium-ion battery was placed in a 25°C constant temperature chamber and left to stand for 30 minutes to allow it to reach a constant temperature. It was then charged at a constant current of 0.33C to 4.25V, then charged at a constant voltage to a current of 0.05C, and finally discharged at a constant current of 0.33C to 2.75V. This cycle was repeated three times, and the discharge capacity of the last cycle was taken as the initial capacity of the lithium-ion battery. The tested lithium-ion battery was then transferred to a 60°C constant temperature chamber for storage for 60 days. After 60 days of storage, the battery was transferred to a 25°C constant temperature chamber and left to stand for 60 minutes. It was then discharged at a constant current of 0.33C to 2.75V, and the discharge capacity was recorded as the remaining capacity of the lithium-ion battery. It was then charged at a constant current of 0.33C to 4.25V, then charged at a constant voltage to a current of 0.05C, and finally discharged at a constant current of 0.33C to 2.8V, and the discharge capacity was recorded as the recoverable capacity of the lithium-ion battery. The above are used as the performance indicators for high-temperature storage of the battery. The lithium-ion battery was placed in a 25°C constant temperature chamber and left to stand for 30 minutes to allow it to reach a constant temperature. First, it was charged at a constant current of 1C until the voltage reached 4.25V, then charged at a constant voltage until the current reached 0.05C. After charging, the cell volume was measured using the water displacement method (V1). The tested lithium-ion battery was then transferred to a 60°C constant temperature chamber for storage for 60 days. After 60 days of storage, the battery was transferred to a 25°C constant temperature chamber and left to stand for 60 minutes. After the battery returned to room temperature, the cell volume was measured again using the water displacement method (V2). The cell volume expansion rate was calculated using the following formula. This is used as a performance indicator of the battery's high-temperature gas production.

[0066] .

[0067] The test results are shown in Table 2.

[0068] Table 2

[0069] The experimental comparison data shows that, as can be seen from the comparison between the examples and the comparative examples: Example 3: After 1000 cycles at 25°C, the capacity retention rate was still 86.2% (an improvement of 23.7% compared to Comparative Example 1). After 1000 cycles at 45°C, the capacity retention rate was still 86.0% (an improvement of 25.8% compared to Comparative Example 1). After 60 days of storage at 60°C, the capacity retention rate was still 84.4% (an improvement of 21.0% compared to Comparative Example 1), the capacity recovery rate was as high as 86.7% (an improvement of 18.5% compared to Comparative Example 1), and the volume expansion rate was only 17.7% (a decrease of 22.1% compared to Comparative Example 1).

[0070] Comparative Example 1 (without the additive): Cyclic performance and high-temperature performance deteriorated significantly, verifying the key role of the additive.

[0071] Comparative Example 2 (excess additive): Compared with the above examples, the cycle performance and high temperature performance are deteriorated but better than Comparative Example 1. Excessive addition will lead to performance degradation, but it is still better than not adding.

[0072] Comparative Example 3 (too little of the additive): Compared with the above examples, the cycle performance and high temperature performance are deteriorated, but better than Comparative Example 1. Too little additive will also lead to performance degradation, but it is still better than not adding it.

[0073] The electrolyte additives, electrolytes, and lithium-ion batteries provided in the embodiments of this application have been described in detail above. Specific examples have been used in this application to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the technical solutions and core ideas of this application. Those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. An electrolyte additive, characterized in that, Including compound I, the structural formula of which is shown in Formula I: Formula I; R1 and R2 are each independently selected from hydrogen and alkoxy groups substituted with substituents, wherein the substituents are alkyl groups containing PO bonds and / or P=O bonds; R1 and R2 are not both hydrogen.

2. The electrolyte additive according to claim 1, characterized in that, R1 and R2 are each independently selected from , , and Any one of them; R3 and R4 are each independently selected from , , , and Any one of them.

3. The electrolyte additive according to claim 2, characterized in that, Compound I is selected from any one of the compounds shown in Formulas I-1 to I-8: 。 4. An electrolyte, characterized in that, The electrolyte additive includes any one of claims 1 to 3, wherein the electrolyte additive is present in the electrolyte at a mass percentage of 0.1 to 10%.

5. The electrolyte according to claim 4, characterized in that, It also includes lithium salts and organic solvents; The lithium salt in the electrolyte has a mass percentage of 5-20%; The organic solvent accounts for 70-90% by mass in the electrolyte.

6. The electrolyte according to claim 5, characterized in that, It also includes auxiliary additives; the auxiliary additives include at least one of ester compounds, nitrile compounds, silicon-based compounds, sulfur-containing compounds and lithium salt compounds.

7. The electrolyte according to claim 6, characterized in that, The electrolyte additive and the auxiliary additive satisfy the following: 0.1%≤w1+w2≤10%; and 0.1≤w1 / w2≤1; In the formula, w1 is the mass percentage of the electrolyte additive in the electrolyte, and w2 is the mass percentage of the auxiliary additive in the electrolyte.

8. The electrolyte according to claim 6, characterized in that, The mass ratio of the ester compound, the nitrile compound, the silicon-based compound, the sulfur-containing compound, and the lithium salt compound is 0~3:0~3:0~3:0~5:0~6.

9. The electrolyte according to claim 6, characterized in that, The lithium salt comprises at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, and lithium bis(trifluoromethylsulfonyl)imide; and / or, The organic solvent includes at least one selected from ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethyl acetate, ethyl propionate, propyl propionate, and 1,1,2,3-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether; and / or, The ester compounds include at least one of vinylene carbonate, fluorovinyl carbonate, and methyl (2,2,2-trifluoroethyl) carbonate; and / or, The nitrile compounds include at least one selected from butadionitrile, glutaronitrile, octanoic acid, 1,3,6-hexanetrionitrile, 1,3,5-pentanetrionitrile, and methoxypropionitrile; and / or, The sulfur-containing compound includes at least one selected from 1,3-propanesulfonate lactone, 1,3-propenesulfonate lactone, vinyl sulfate, and vinylene sulfate; and / or, The lithium salt compound is selected from at least one of lithium difluorophosphate, lithium bis(oxalate)borate, lithium difluorooxalateborate, and lithium difluorooxalate phosphate.

10. A lithium-ion battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, characterized in that, The electrolyte is any one of claims 4 to 9; the high-temperature storage capacity retention rate (60 days, 60°C) of the lithium-ion battery is 50 to 90%, and the high-temperature storage volume expansion rate (60 days, 60°C) is 5 to 50%.

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