Lithium-ion battery electrolyte and lithium-ion battery

Abstract

This application relates to a lithium-ion battery electrolyte and a lithium-ion battery. The electrolyte comprises a lithium salt, an organic solvent, and an additive, wherein the additive comprises an organophosphate lithium salt and the organic solvent comprises a sulfone compound. The solution provided in this application can improve the high-temperature cycling performance and high-temperature storage performance of lithium cobalt oxide lithium-ion batteries at high voltages.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to an electrolyte for a lithium-ion battery and a lithium-ion battery. Background Art

[0002] In related technologies, to delay the failure of lithium cobalt oxide (LCO) materials during cycling at high voltages, manufacturers primarily employ aluminum doping strategies to stabilize the cathode material's lattice structure at high voltages. However, excessive aluminum doping reduces the actual gram capacity of the lithium-ion battery's cathode material, thereby reducing the cell's energy density. Therefore, the aluminum doping level is limited and cannot be excessively high. Given this limitation, other strategies are needed to stabilize the cathode material's lattice structure at high voltages.

[0003] To delay the failure of LCO during cycling at high voltages, improving the electrolyte is currently a relatively low-cost strategy. For example, adding some commonly used additives such as nitrile additives to the electrolyte can improve performance, but the improvement effect on lithium-ion batteries is limited.

[0004] Therefore, it is necessary to develop a multifunctional additive to improve the cycling performance of lithium-ion batteries at high voltages. Summary of the Invention

[0005] In order to solve or partially solve the problems existing in the related art, the present application provides an electrolyte for a lithium ion battery and a lithium ion battery, which can improve the cycle performance of lithium cobalt oxide batteries under high voltage.

[0006] In a first aspect, the present application provides an electrolyte for a lithium-ion battery, comprising a lithium salt, an organic solvent, and an additive, wherein the additive comprises an organic lithium phosphate salt, and the structural formula of the organic lithium phosphate salt is as follows:

[0007]

[0008] The organic solvent includes a sulfone compound.

[0009] In some embodiments, the content of the sulfone compound is greater than 10% of the total mass of the electrolyte;

[0010] Preferably, the content of the sulfone compound is 10% to 20% of the total mass of the electrolyte.

[0011] In some embodiments, the content of the organic lithium phosphate salt is 0.3% to 2% of the total mass of the electrolyte;

[0012] Preferably, the content of the organic lithium phosphate salt is 0.3% to 1.5% of the total mass of the electrolyte.

[0013] In some embodiments, the sulfone compound is selected from sulfolane, dimethyl sulfone, methyl ethyl sulfone, diethyl sulfone, methyl propyl sulfone, ethyl propyl sulfone, dipropyl sulfone or at least one of the monofluorinated or polyfluorinated substituted compounds corresponding to the above seven sulfone compounds.

[0014] In some embodiments, the additive further comprises a nitrile compound;

[0015] Preferably, the nitrile compound is selected from at least one of adiponitrile, succinonitrile, 1,3,6-hexanetricarboxylic acid nitrile, trans-hexenedinitrile, fumaronitrile, 1,2-bis(cyanoethoxy)ethane or 1,2,3-tris(cyanoethoxy)propane;

[0016] More preferably, the content of the nitrile compound is 2% to 5% of the total mass of the electrolyte.

[0017] In some embodiments, the additive further comprises fluoroethylene carbonate;

[0018] Preferably, the content of the fluoroethylene carbonate is 6% to 10% of the total mass of the electrolyte.

[0019] In some embodiments, the organic solvent further comprises at least two of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl formate, propyl propionate, methyl butyrate, and ethyl difluoroacetate.

[0020] In some embodiments, the lithium salt includes at least one of lithium hexafluorophosphate, lithium difluorophosphate, lithium tetrafluoroborate, lithium bisfluorooxalatoborate, lithium bisoxalatoborate, lithium bisfluorosulfonyl imide, lithium bistrifluoromethylimide, lithium difluorooxalatophosphate, or lithium perchlorate;

[0021] Preferably, the content of the lithium salt is 10% to 20% of the total mass of the electrolyte.

[0022] A second aspect of the present application provides a lithium-ion battery, which includes a positive electrode sheet, a negative electrode sheet, a separator and the electrolyte described in any one of the above items, wherein the separator is placed between the positive electrode sheet and the negative electrode sheet.

[0023] In some embodiments, the positive electrode plate comprises lithium cobalt oxide and aluminum, and the content of the aluminum is less than 8500 ppm; and / or

[0024] The charging cut-off voltage of the lithium-ion battery is above 4.53V.

[0025] The technical solution provided by this application may have the following beneficial effects:

[0026] The electrolyte of the present application can adjust the lithium ion solvation structure by adding organic lithium phosphate additives, and can form a film on the positive electrode of the battery, thereby stabilizing the positive electrode structure and improving the cycle performance and high-temperature storage performance of the lithium cobalt oxide battery; the organic lithium phosphate can also inhibit the side reaction between the positive electrode material and the electrolyte, and the organic lithium phosphate that has not formed a film can also capture the active oxygen released by the lithium cobalt oxide, thereby preventing the solvent from being oxidized and producing gas to cause safety risks. In addition, sulfone compounds can improve the overall antioxidant properties of the electrolyte, and sulfone compounds are excellent solvents for organic lithium phosphates, thereby increasing the solubility of phosphates in the electrolyte and further strengthening the protection of the electrolyte to the positive electrode of the battery. The lithium cobalt oxide lithium ion battery using this electrolyte has good high-temperature cycle performance and high-temperature storage performance at high voltage.

[0027] The electrolyte of the present application is applied to lithium-ion batteries. When the additives simultaneously include organic lithium phosphate salts, nitrile compounds and fluoroethylene carbonate, by limiting the corresponding mass proportions of each in the electrolyte, and containing an appropriate amount of sulfone compound solvent in the organic solvent, an appropriate amount of organic lithium phosphate salts can be dissolved in the electrolyte, thereby ensuring the high-temperature and high-voltage electrical properties and high-temperature storage performance of the lithium-ion battery; the appropriate addition of nitrile compounds can better ensure the high-temperature and high-voltage electrical properties of the lithium-ion battery; the appropriate addition of fluoroethylene carbonate can form a stable and low-impedance SEI film at the negative electrode, thereby effectively reducing the consumption of nitrile additives, while also preventing the solvent of the sulfone compound from damaging the negative electrode material. In such a design, different additives and solvents complement each other, and the overall cycle performance of lithium cobalt oxide lithium-ion batteries at high voltages is significantly improved.

[0028] It should be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present application. DETAILED DESCRIPTION

[0029] To facilitate understanding of the present invention, the present invention will be described in detail below. However, before describing the present invention in detail, it should be understood that the present invention is not limited to the specific embodiments described. It should also be understood that the terminology used herein is for the purpose of describing specific embodiments only and is not intended to be limiting.

[0030] Where a numerical range is provided, it will be understood that each intervening value between the upper and lower limits of the range and any other specified or intervening values ​​in the specified range is encompassed within the present invention. The upper and lower limits of these smaller ranges may be independently included in smaller ranges and are also encompassed within the present invention, subject to any explicitly excluded limits in the specified range. Where a specified range includes one or two limits, ranges excluding either or both of those included limits are also encompassed within the present invention. It will also be understood that the term "and / or" as used herein refers to and includes any or all possible combinations of one or more associated listed items. In the description of this application, "a plurality of" means two or more, unless otherwise specifically defined. "One or more" means one or more, unless otherwise specifically defined.

[0031] Unless otherwise defined, all terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention pertains. Although any methods and materials or equivalents to those described herein may also be used in the practice or testing of the present invention, preferred methods and materials are now described.

[0032] In related technologies, when the positive electrode material of a lithium-ion battery is lithium cobalt oxide, due to its own material structure, lithium cobalt oxide is prone to irreversible phase transition under high voltage (excessive delithiation), and its layered lattice structure is unstable. Accompanied by crystal plane slip, atomic rearrangement causes drastic changes in unit cell parameters, dislocation of grain boundaries, and surface stress changes causing particle rupture. In addition, side reactions caused by the oxidation and decomposition of the electrolyte, oxygen escape, dissolution of cobalt metal, and other problems lead to battery performance failure.

[0033] The present application provides an electrolyte for a lithium-ion battery, which can improve the high-temperature and high-voltage electrical performance and high-temperature storage performance of the lithium-ion battery.

[0034] An electrolyte for a lithium-ion battery provided in one embodiment of the present application includes a lithium salt, an organic solvent, and an additive, wherein the additive includes an organic lithium phosphate salt, and the structural formula of the organic lithium phosphate salt is as follows:

[0035]

[0036] Organic solvents include sulfone compounds.

[0037] The electrolyte of the present application can adjust the lithium ion solvation structure by adding organic lithium phosphate additives, and can form a film on the positive electrode of the battery, thereby stabilizing the positive electrode structure and improving the cycle performance and high-temperature storage performance of the lithium cobalt oxide battery; the organic lithium phosphate can also inhibit the side reaction between the positive electrode material and the electrolyte, and the organic lithium phosphate that has not formed a film can also capture the active oxygen released by the lithium cobalt oxide, thereby preventing the solvent from being oxidized and producing gas to cause safety risks. In addition, sulfone compounds can improve the overall antioxidant properties of the electrolyte, and sulfone compounds are excellent solvents for organic lithium phosphates, thereby increasing the solubility of phosphates in the electrolyte and further strengthening the protection of the electrolyte to the positive electrode. The lithium cobalt oxide lithium ion battery using this electrolyte has good high-temperature cycle performance and high-temperature storage performance at high voltage.

[0038] In some embodiments, the content of the organic lithium phosphate salt is 0.3% to 2% of the total mass of the electrolyte. If the content of the organic lithium phosphate salt is higher than 2% of the total mass of the electrolyte, more sulfone compound solvents need to be introduced to ensure the solubility of the organic lithium phosphate salt. However, a large amount of sulfone compounds will not only damage the negative electrode material of the battery, but also increase the viscosity of the electrolyte, affecting the use of the electrolyte at room temperature and low temperature. If the content of the organic lithium phosphate salt is lower than 0.3% of the total mass of the electrolyte, the electrical performance of the lithium ion battery cannot be significantly improved. Preferably, the content of the organic lithium phosphate salt is 0.3% to 1.5% of the total mass of the electrolyte. An appropriate amount of organic lithium phosphate salt can ensure the high-temperature and high-voltage electrical performance and high-temperature storage performance of the lithium ion battery.

[0039] In some embodiments, the sulfone compound content is greater than 10% of the total mass of the electrolyte. Preferably, the sulfone compound content is 10% to 20% of the total mass of the electrolyte. If the sulfone compound content is too low, the amount of organophosphate lithium salt used will be limited, making it impossible to dissolve sufficient organophosphate lithium salt, and the improvement in the solvent's antioxidant properties will be limited. If the sulfone compound content is too high, it will damage the battery's negative electrode material and increase the electrolyte viscosity, affecting the electrolyte's use at both room and low temperatures.

[0040] Optionally, the sulfone compound is selected from sulfolane, dimethyl sulfone, methyl ethyl sulfone, diethyl sulfone, methyl propyl sulfone, ethyl propyl sulfone or dipropyl sulfone, or at least one of the monofluorinated or polyfluorinated substituted compounds corresponding to the foregoing seven sulfone compounds.

[0041] In some embodiments, the additive further comprises a nitrile compound. The content of the nitrile compound is 2% to 5% of the total mass of the electrolyte. It is understandable that the nitrile additive can chelate with the positive electrode material, on the one hand reducing the side reaction between LCO and the electrolyte, and on the other hand also providing electrons to the delithiated LCO to stabilize the LCO. If the amount of the nitrile additive used in the total content of the electrolyte is less than 1%, it is easy to cause the gas production of the lithium-ion battery to drop during high-temperature circulation. If the amount of the nitrile additive used in the total content of the electrolyte is greater than 6%, the positive and negative electrode impedances are worsened, and lithium plating is easily caused under normal temperature or low-temperature circulation conditions of the lithium-ion battery. Therefore, in the present application, the amount of the nitrile additive used in the total content of the electrolyte is 2% to 5%, which can better ensure the high-temperature and high-voltage electrical performance of the lithium-ion battery.

[0042] In some embodiments, the nitrile compound is selected from at least one of adiponitrile, succinonitrile, 1,3,6-hexanetricarboxylic acid nitrile, trans-hexenedinitrile, fumaronitrile, 1,2-bis(cyanoethoxy)ethane, and 1,2,3-tris(cyanoethoxy)propane.

[0043] In some embodiments, the additive further comprises fluoroethylene carbonate (FEC). In some embodiments, the content of fluoroethylene carbonate is 6% to 10% of the total mass of the electrolyte. For example, the content of fluoroethylene carbonate can be 6%, 6.5%, 7%, 8%, 9%, 10%, etc. of the total mass of the electrolyte, which is only illustrative and not limiting. Among them, when applied to lithium-ion batteries, fluoroethylene carbonate can form a stable and low-impedance SEI film at the negative electrode, thereby effectively reducing the consumption of nitrile additives. In particular, when the amount of fluoroethylene carbonate used accounts for 6% to 10% of the total mass of the electrolyte, it can prevent the solvent of the sulfone compound from damaging the negative electrode material. When the content of fluoroethylene carbonate is higher than 10% of the total mass of the electrolyte, the lithium-ion battery is prone to gassing, and thus cannot achieve a better protection effect.

[0044] In some embodiments, the organic solvent further comprises at least two of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl formate, propyl propionate, methyl butyrate, and ethyl difluoroacetate.

[0045] In some embodiments, the lithium salt comprises 10% to 20% of the total mass of the electrolyte. In some embodiments, the lithium salt comprises at least one of lithium hexafluorophosphate, lithium difluorophosphate, lithium tetrafluoroborate, lithium bisfluorooxalatoborate, lithium bisoxalatoborate, lithium bisfluorosulfonyl imide, lithium bistrifluoromethylimide, lithium difluorooxalatophosphate, or lithium perchlorate.

[0046] The electrolyte of the present application has a simplified overall composition. When the additives simultaneously include organic lithium phosphate salts, nitrile compounds and fluoroethylene carbonate, by limiting the corresponding mass proportions of each in the electrolyte, and containing an appropriate amount of sulfone compound solvent in the organic solvent, an appropriate amount of organic lithium phosphate salts can be dissolved in the electrolyte, thereby ensuring the high temperature and high voltage electrical properties and high temperature storage performance of the lithium ion battery; the appropriate addition of nitrile compounds can better ensure the high temperature and high voltage electrical properties of the lithium ion battery; the appropriate addition of fluoroethylene carbonate can form a stable and low impedance SEI film at the negative electrode, thereby effectively reducing the consumption of nitrile additives, while also preventing the solvent of the sulfone compound from damaging the negative electrode material. In such a design, different additives and solvents complement each other, and the overall cycle performance of lithium cobalt oxide lithium ion batteries at high voltage is significantly improved.

[0047] An embodiment of the present application further provides a lithium-ion battery, and the lithium-ion battery of the present application includes the electrolyte in any of the above embodiments.

[0048] Furthermore, the lithium-ion battery of the present application also includes a positive electrode sheet, a negative electrode sheet and a separator, wherein the separator is placed between the positive electrode sheet and the negative electrode sheet. After being prepared into a bare cell through a lamination process, a finished battery can be obtained through relevant processes. For example, the bare cell is placed in an aluminum-plastic film for packaging, and then vacuum packaging, standing, formation, shaping and other processes are performed to complete the preparation of the lithium-ion battery. No further details will be given here.

[0049] In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode material disposed on the positive electrode current collector, wherein the positive electrode material includes a positive electrode active material, the positive electrode active material includes lithium cobalt oxide and aluminum, and the content of the aluminum element is less than 8500 ppm.

[0050] In some embodiments, the positive electrode material further comprises a conductive agent, a binder, and a solvent. Specifically, the positive electrode active material, the conductive agent, the binder, and the solvent can be mixed in a predetermined mass ratio to prepare a positive electrode slurry, which is then coated on a positive electrode current collector, dried, roll-pressed, and cut into pieces to obtain positive electrode sheets of a predetermined size.

[0051] In some embodiments, a negative electrode sheet includes a negative electrode current collector and a negative electrode material disposed on the negative electrode current collector. The negative electrode material may include a negative electrode active material, a conductive agent, a binder, a thickener, and a solvent. For example, according to related art, the negative electrode active material, the conductive agent, the binder, the thickener, and the solvent are mixed in a predetermined mass ratio to prepare a negative electrode slurry. The slurry is then coated on the negative electrode current collector, dried, rolled, and cut into pieces to obtain a negative electrode sheet of a predetermined size.

[0052] The current collector, conductive agent, binder, solvent, and other materials used in the positive and negative electrode materials can be selected based on relevant technologies and are not limited here. The separator can be made of, for example, polyethylene, polypropylene, self-woven fabric, non-woven fabric, or a synthetic resin microporous membrane, and can be selected based on relevant technologies and are not limited here.

[0053] In some embodiments, the charging cut-off voltage of the lithium-ion battery of the present application is greater than 4.53 V. For example, the charging cut-off voltage is 4.53 V.

[0054] To make the present invention easier to understand, the present invention will be further described in detail below with reference to the following examples. These examples are merely illustrative and do not limit the scope of application of the present invention. Unless otherwise specified, the raw materials or components used in the present invention can be obtained through commercial channels or conventional methods.

[0055] 1. Preparation of electrolyte

[0056] Example 1

[0057] In an argon-filled glove box (moisture <1ppm, oxygen <1ppm), ethylene carbonate (EC) and propyl propionate (PP) were mixed at a mass ratio of EC:PP = 25:75 to prepare a mixed organic solvent. To this mixed organic solvent, 10% by weight of the total electrolyte solution was followed by 15% by weight of lithium hexafluorophosphate (LiPF6), 4% by weight of the total electrolyte solution was followed by 4% by weight of succinonitrile (SN), 8% by weight of fluoroethylene carbonate (FEC), and 0.3% by weight of an organic lithium phosphate. The electrolyte was then stirred thoroughly to obtain the desired solution.

[0058] The difference between Examples 2 to 10 and Example 1 is the different types and proportions of the corresponding components, and the specific differences are shown in Table 1 below.

[0059] The difference between Comparative Examples 1 to 4 and Example 1 is the different types and proportions of the corresponding components, as shown in Table 1 below. Where % is mentioned, it is expressed as a percentage by weight of the total weight of the electrolyte, and the mass percentage of the mixed organic solvent is the remaining value after deducting the mass percentages of other components.

[0060] Table 1

[0061]

[0062] Note: The sulfone compound FMES in Example 10 is trifluoromethyl ethyl sulfone, which is a polyfluorinated compound of methyl ethyl sulfone.

[0063] 2. Preparation of lithium-ion batteries

[0064] According to the electrolytes prepared in Examples 1 to 11 and Comparative Examples 1 to 4, corresponding lithium-ion batteries were prepared according to the following methods.

[0065] (1) Preparation of positive electrode sheet. The positive electrode active material lithium cobalt oxide (LCO), conductive agent carbon black and binder polyvinylidene fluoride (PVDF), carbon nanotubes (CNT) were mixed in the solvent N-methylpyrrolidone at a mass ratio of 96.5:1:1.8:0.7, and stirred thoroughly to form a uniform positive electrode slurry. The slurry was then coated on the surface of the positive electrode current collector aluminum foil. After drying, rolling, and slitting, the compacted density was 4.1 g / cm 3 The positive electrode.

[0066] (2) Preparation of negative electrode sheet. The negative electrode active material graphite, conductive agent carbon black, binder styrene butadiene rubber, and thickener sodium carboxymethyl cellulose were mixed in an appropriate amount of deionized water solvent at a mass ratio of 96.7:0.5:1.5:1.3 to form a uniform negative electrode slurry. The slurry was then coated on the surface of the negative electrode current collector copper foil. After drying, rolling, and slitting, the compacted density was 1.65 g / cm 3 The negative electrode.

[0067] (3) Preparation of lithium-ion batteries. Using a PE porous polymer film as a separator, the positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator positioned between the positive and negative electrode sheets to act as an isolation device. The stacked electrode sheets and separator are then wound to form a core, which is then placed in a pre-punched aluminum-plastic film bag. After vacuum packaging, standing, and chemical formation, the lithium-ion battery is prepared.

[0068] 3. Battery performance test

[0069] The lithium-ion batteries prepared in Examples 1 to 11 and Comparative Examples 1 to 4 were subjected to the following tests.

[0070] 1) 60℃ cycle performance test

[0071] Test conditions: At 60°C, charge the divided lithium-ion battery at a constant current and constant voltage of 0.5C to 4.53V, with a cut-off current of 0.05C. Then discharge it at a constant current of 0.5C to 3.0V. Repeat this cycle for 100 charge and discharge cycles. Calculate the capacity retention rate of the battery after the 100th cycle using the following formula:

[0072] The 100th cycle capacity retention rate (%) = (100th cycle discharge capacity / first cycle discharge capacity) × 100%.

[0073] 2) Thickness test at 60°C

[0074] At room temperature, charge the lithium-ion battery to 4.53V at a constant current and constant voltage of 0.5C, with a cutoff current of 0.05C. Measure the initial fully charged thickness of the battery. Store the battery at 60°C for 30 days, and measure the thickness after storage. Calculate the thickness expansion rate of each battery using the following formula:

[0075] Thickness expansion rate = thickness after storage / initial full-charge thickness × 100%

[0076] The test results of the lithium-ion batteries are shown in Table 2 below.

[0077] Table 2

[0078]

[0079] According to Examples 1 to 3, increasing the amount of organic lithium phosphate at 0.3% to 1.5% can improve the high-temperature cycle performance of lithium-ion batteries. According to Comparative Examples 1 to 2, adding a sulfone compound solvent alone can significantly reduce the gas production during high-temperature storage of the battery from the perspective of thickness expansion rate. According to Examples 1 to 6, increasing the sulfone compound solvent from 10% to 15% can improve the battery's cycle performance and reduce storage gas production. According to Examples 4 to 9, Example 11 and Comparative Example 4, when the sulfone compound solvent content is higher than 15%, the battery's cycle performance will be reduced, and increasing the amount of FEC can offset and improve the high-temperature cycle performance; however, when the FEC is higher than 10%, the battery's high-temperature storage gas production performance deteriorates again. According to Examples 9 to 10, the fluorosulfone compound solvent has better cycle performance than TS, but slightly worse storage performance. According to Examples 4 to 6 and Comparative Example 3, increasing the sulfone compound solvent to 30% and the organic lithium phosphate to 1.8% at the same time will seriously deteriorate the cycle performance of the battery cell.

[0080] Regarding the above embodiment, its specific implementation has been described in detail in the embodiment of the method, and will not be elaborated again here.

[0081] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0082] It should be noted that the embodiments described above are only used to explain the present application and do not constitute any limitation to the present application. The present application has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory words, rather than restrictive words. The present application may be modified as specified within the scope of the claims of the present application, and the present application may be revised without departing from the scope and spirit of the present application. Although the present application described therein relates to specific methods, materials and embodiments, it does not mean that the present application is limited to the specific examples disclosed therein. On the contrary, the present application can be extended to all other methods and applications with the same function.

Claims

1. An electrolyte for a lithium ion battery, characterized in that The electrolyte comprises a lithium salt, an organic solvent and an additive, wherein the additive comprises an organic lithium phosphate salt, the content of the organic lithium phosphate salt is 0.3% to 2% of the total mass of the electrolyte, and the structural formula of the organic lithium phosphate salt is as follows: The organic solvent includes a sulfone compound, and the content of the sulfone compound is greater than 10% of the total mass of the electrolyte; The additives further include nitrile compounds and fluoroethylene carbonate. The content of the nitrile compounds is 2% to 5% of the total mass of the electrolyte, and the content of the fluoroethylene carbonate is 6% to 10% of the total mass of the electrolyte.

2. The electrolyte according to claim 1, wherein: The content of the sulfone compound is 10% to 20% of the total mass of the electrolyte.

3. The electrolyte according to claim 2, characterized in that: The content of the organic lithium phosphate salt is 0.3% to 1.5% of the total mass of the electrolyte.

4. The electrolyte according to claim 1, wherein: The sulfone compound is selected from sulfolane, dimethyl sulfone, methyl ethyl sulfone, diethyl sulfone, methyl propyl sulfone, ethyl propyl sulfone, dipropyl sulfone or at least one of the monofluorinated or polyfluorinated substituted compounds corresponding to the above seven sulfone compounds.

5. The electrolyte according to claim 1, wherein: The nitrile compound is selected from at least one of adiponitrile, succinonitrile, 1,3,6-hexanetricarboxylic acid nitrile, trans-hexenedinitrile, fumaronitrile, 1,2-bis(cyanoethoxy)ethane or 1,2,3-tris(cyanoethoxy)propane.

6. The electrolyte according to claim 1, wherein: The organic solvent further comprises at least two of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl formate, propyl propionate, methyl butyrate, and ethyl difluoroacetate.

7. The electrolyte according to claim 1, wherein: The lithium salt includes at least one of lithium hexafluorophosphate, lithium difluorophosphate, lithium tetrafluoroborate, lithium bisfluorooxalatoborate, lithium bisoxalatoborate, lithium bisfluorosulfonyl imide, lithium bistrifluoromethylimide, lithium difluorooxalatophosphate or lithium perchlorate.

8. The electrolyte according to claim 7, characterized in that: The content of the lithium salt is 10% to 20% of the total mass of the electrolyte.

9. A lithium-ion battery, characterized in that: The electrolyte comprises a positive electrode sheet, a negative electrode sheet, a separator and the electrolyte according to any one of claims 1 to 8, wherein the separator is placed between the positive electrode sheet and the negative electrode sheet.

10. The lithium-ion battery according to claim 9, wherein: The positive electrode plate comprises lithium cobalt oxide and aluminum, and the content of the aluminum is less than 8500 ppm; and / or The charging cut-off voltage of the lithium-ion battery is above 4.53V.

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