Composition for electrolyte, electrolyte as well as preparation method and application of electrolyte

Abstract

The invention relates to the technical field of lithium ion batteries, and discloses a composition for an electrolyte, the electrolyte as well as a preparation method and application of the electrolyte. The composition contains a lithium salt, a solvent, a film-forming additive and a composite additive, based on the total mass of the composition, the content of the lithium salt is 9.5-15 wt%, the content of the solvent is 65-90 wt%, the content of the film-forming additive is 2-5 wt%, and the content of the composite additive is 0.1-3 wt%. The composite additive is a combination of lithium phosphate difluoro bis (oxalate) and 2, 6-difluoronicotinonitrile in a content mass ratio of 1: (0.55-1.8). After the electrolyte provided by the invention is applied to a battery, the interface impedance of a negative electrode can be remarkably reduced, the interface stability of a single-particle graphite negative electrode is improved, the rate capability and the cycle performance of the battery are improved, meanwhile, the oxidation resistance of the electrolyte can be improved, the oxygenolysis of the electrolyte in long-term operation is slowed down, and the dissolution of transition metal of a positive electrode is inhibited.

Description

Technical Field

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

[0002] As an important component of electrochemical energy storage systems, lithium-ion batteries play a vital role in new energy systems. In order to improve the economic efficiency of electrochemical energy storage systems, the development of long-life lithium-ion batteries has become a current research focus. Single-grain graphite anodes have a smaller specific surface area and exhibit better interfacial stability than conventional secondary granulated graphite, and therefore have been widely studied and applied in long-life lithium-ion battery research. However, due to the large particle size of single-grain graphite, its rate performance is poor and needs to be optimized through the regulation of the anode / electrolyte interface.

[0003] Currently, there are relatively few strategies for optimizing electrolytes for single-particle graphite negative electrodes. Most of them follow the experience of secondary granulated graphite research. The electrolyte design tends to improve interface stability, but this may lead to an increase in the interface impedance of the single-particle graphite negative electrode, thereby affecting the rate performance of lithium-ion batteries.

[0004] CN119764554A discloses an electrolyte composition characterized by comprising a lithium salt, a film-forming additive, an organic solvent, and an auxiliary agent. The lithium salt comprises 6-20% by weight, the film-forming additive comprises 2-6% by weight, the organic solvent comprises 75-90% by weight, and the auxiliary agent comprises 2-10% by weight, based on the total weight of the electrolyte. The auxiliary agent is a combination of 4-iodophthalonitrile and 6-fluoro-nicotinonitrile in a mass ratio of 1:0.5-2. While this solution significantly improves the high-temperature stability and performance of single-grain graphite anodes, the strong film-forming effect results in lower battery energy efficiency at room temperature. Summary of the Invention

[0005] The purpose of the present invention is to solve the problems of poor room temperature rate performance and battery energy efficiency, poor electrolyte antioxidant performance, easy dissolution of positive electrode transition metal, lithium plating at the negative electrode, and rapid high-temperature cycle capacity decay in the existing single-particle graphite negative electrode.

[0006] In order to achieve the above-mentioned object, the first aspect of the present invention provides a composition for an electrolyte, wherein the composition contains a lithium salt, a solvent, a film-forming additive and a composite additive;

[0007] Based on the total mass of the composition, the content of the lithium salt is 9.5-15wt%, the content of the solvent is 65-90wt%, the content of the film-forming additive is 2-5wt%, and the content of the composite additive is 0.1-3wt%;

[0008] The composite additive is a combination of lithium difluorobis(oxaloyl)phosphate and 2,6-difluoronicotinonitrile in a mass ratio of 1:0.55-1.8.

[0009] The second aspect of the present invention provides a method for preparing an electrolyte, which is carried out using the electrolyte composition described in the first aspect, and comprises: mixing a mixture containing the electrolyte composition to obtain the concentrated electrolyte.

[0010] The third aspect of the present invention provides an electrolyte prepared by the method described in the second aspect.

[0011] The fourth aspect of the present invention provides use of the electrolyte described in the third aspect in a lithium ion battery with a single-particle graphite negative electrode.

[0012] A fifth aspect of the present invention provides a lithium-ion battery, comprising: a positive electrode, a single-particle graphite negative electrode, an electrolyte, and a separator; the electrolyte is the electrolyte described in the third aspect.

[0013] Compared with the prior art, the present invention has at least the following beneficial effects:

[0014] (1) The electrolyte provided by the present invention regulates the negative electrode interface composition through the synergistic effect of lithium difluorobis(oxalato)phosphate and 2,6-difluoronicotinonitrile, forming a thin, dense and stable negative electrode / electrolyte interface film, which can significantly reduce the negative electrode interface impedance and improve the battery rate performance;

[0015] (2) The electrolyte provided by the present invention can improve the interfacial stability of single-particle graphite negative electrodes and increase the battery cycle life.

[0016] (3) The electrolyte provided by the present invention can improve the antioxidant capacity of the electrolyte, slow down the oxidative decomposition of the electrolyte during long-term operation, and inhibit the dissolution of the positive electrode transition metal. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 1 is a rate performance test diagram of the electrolytes obtained in Example 1 and Comparative Example 1 provided by the present invention after being applied to batteries;

[0018] Figure 2 This is a test chart of the cycle performance of the electrolytes obtained in Example 1 and Comparative Example 1 provided by the present invention after being applied to batteries. DETAILED DESCRIPTION

[0019] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0020] As mentioned above, the first aspect of the present invention provides a composition for an electrolyte, the composition comprising a lithium salt, a solvent, a film-forming additive and a composite additive;

[0021] Based on the total mass of the composition, the content of the lithium salt is 9.5-15wt%, the content of the solvent is 65-90wt%, the content of the film-forming additive is 2-5wt%, and the content of the composite additive is 0.1-3wt%;

[0022] The composite additive is a combination of lithium difluorobis(oxaloyl)phosphate and 2,6-difluoronicotinonitrile in a mass ratio of 1:0.55-1.8.

[0023] Preferably, the composite additive is a combination of lithium difluorobis(oxaloyl)phosphate and 2,6-difluoronicotinonitrile in a mass ratio of 1:1-1.5.

[0024] More preferably, the composite additive is a combination of lithium difluorobis(oxalatophosphate) and 2,6-difluoronicotinonitrile in a mass ratio of 1:1-1.2. The inventors have found that the electrolyte obtained under this preferred embodiment exhibits superior rate performance and battery energy efficiency when used in batteries, while also exhibiting improved antioxidant properties and reduced positive electrode transition metal dissolution.

[0025] Preferably, based on the total mass of the composition, the lithium salt content is 12.5-14.5wt%, the solvent content is 80-85wt%, the film-forming additive content is 2-4wt%, and the composite additive content is 2-3wt%. The inventors have found that the electrolyte obtained under this preferred embodiment, when used in a battery, has superior rate performance and battery energy efficiency, while also having improved antioxidant capacity and lower positive electrode transition metal dissolution.

[0026] Preferably, the lithium salt is selected from at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium perchlorate, lithium nitrate, lithium difluoroborooxalate, lithium tetrafluoroborate, lithium bis(trifluoromethylsulfonyl)imide, and lithium trifluoromethanesulfonate.

[0027] Preferably, the solvent is selected from at least three of ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, propylene carbonate, γ-butyrolactone, methyl acetate, propyl acetate, and butyl acetate.

[0028] Preferably, the film-forming additive is at least two of vinylene carbonate, vinyl sulfate, fluoroethylene carbonate, methylene methanedisulfonate, 1,3-propane sultone, and vinyl ethylene carbonate.

[0029] Preferably, the solvent is a combination of ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate in a mass ratio of 1:1-1.5:0.8-1.2.

[0030] More preferably, the lithium salt is a combination of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide in a mass ratio of 1:0.7-0.9. The inventors have found that the electrolyte obtained under this preferred embodiment exhibits superior rate performance and battery energy efficiency when used in batteries, while also exhibiting improved antioxidant capacity and reduced positive electrode transition metal dissolution.

[0031] Further preferably, the film-forming additive is a combination of methylene methanedisulfonate, vinyl sulfate, fluoroethylene carbonate, and vinylene carbonate in a mass ratio of 1:0.8-1.2:0.8-1.2:2-4. The inventors have found that the electrolyte obtained under this preferred embodiment, when used in a battery, exhibits superior rate performance and battery energy efficiency, while also having improved antioxidant capacity and lower positive electrode transition metal dissolution.

[0032] As mentioned above, the second aspect of the present invention provides a method for preparing an electrolyte, which is performed using the electrolyte composition described in the first aspect, and comprises: mixing a mixture containing the electrolyte composition to obtain the electrolyte.

[0033] It should be noted that in the present invention, there are no particular requirements for the mixing conditions for preparing the electrolyte composition by mixing the electrolyte. Conventional methods in the art can be used, and the order of adding different raw materials can be adjusted to ensure sufficient mixing. The present invention will not be described in detail here, and those skilled in the art should not be construed as limiting the present invention.

[0034] As mentioned above, the third aspect of the present invention provides an electrolyte prepared by the method described in the second aspect.

[0035] As mentioned above, the fourth aspect of the present invention provides the use of the electrolyte described in the third aspect in a lithium-ion battery with a single-particle graphite negative electrode.

[0036] As mentioned above, the fifth aspect of the present invention provides a lithium-ion battery, which includes: a positive electrode, a single-particle graphite negative electrode, an electrolyte and a separator; the electrolyte is the electrolyte described in the third aspect.

[0037] It should be noted that the present invention has no special requirements for the assembly process of the above-mentioned lithium-ion battery, and it can be assembled using methods known in the art. The present invention will not describe them one by one here, and those skilled in the art should not understand this as a limitation of the present invention.

[0038] The present invention will be described in detail below by way of examples. In the following examples, unless otherwise specified, all raw materials used are commercially available.

[0039] raw material

[0040] Lithium difluorobis(oxaloyl)phosphate: CAS number 678966-16-0, purchased from Hubei Qianmosheng Biotechnology Co., Ltd.

[0041] 2,6-Difluoronicotinonitrile: CAS number 869557-17-5, Shanghai MacLean Biochemical Technology Co., Ltd.

[0042] Lithium hexafluorophosphate: CAS number 21324-40-3, purchased from Suzhou Duoduo Reagent Co., Ltd.

[0043] Lithium bis(fluorosulfonyl)imide: CAS number 9002-81-7, purchased from Suzhou Duoduo Reagent Co., Ltd.

[0044] Lithium bis(trifluoromethanesulfonyl)imide: CAS number 90076-65-6, purchased from Suzhou Duoduo Reagent Co., Ltd.

[0045] Ethylene carbonate: CAS number 96-49-1, purchased from Suzhou Duoduo Reagent Co., Ltd.

[0046] Dimethyl carbonate: CAS number 616-38-6, purchased from Suzhou Duoduo Reagent Co., Ltd.

[0047] Ethyl methyl carbonate: CAS number 623-53-0, purchased from Suzhou Duoduo Reagent Co., Ltd.

[0048] Vinylene carbonate: CAS number 872-36-6, purchased from Suzhou Duoduo Reagent Co., Ltd.

[0049] Ethylene sulfate: CAS number 1072-53-3, purchased from Suzhou Duoduo Reagent Co., Ltd.

[0050] Fluoroethylene carbonate: CAS number 114435-02-8, purchased from Suzhou Duoduo Reagent Co., Ltd.

[0051] Methylene methanedisulfonate: CAS number 99591-74-9, purchased from Suzhou Duoduo Reagent Co., Ltd.

[0052] Polyolefin separator: Celgard 2400 separator, 25 μm thick, single-layer PP material, 41% porosity, purchased from Celgard Company, USA;

[0053] Commercial lithium iron phosphate cathode: surface density of 13.5 mg / cm 2 , active material accounts for 95.3wt%, purchased from Shenzhen Kejing Zhida Technology Co., Ltd.;

[0054] Commercial single-particle graphite anode: surface density 6.3 mg / cm 2 , active material accounts for 95.3wt% and is purchased from Hunan Rongli New Material Technology Co., Ltd.

[0055] Example 1

[0056] In an argon-protected glove box (H2O and O2 contents were both less than 0.1 ppm), 13.5 g of lithium salt, 81.5 g of solvent, 3 g of film-forming additive, and 2 g of composite additive were stirred at 25°C for 6 h (stirring speed was 600 rpm) to obtain electrolyte S1;

[0057] The composite additive is a combination of lithium difluorobis(oxaloyl)phosphate and 2,6-difluoronicotinonitrile in a mass ratio of 1:1;

[0058] The film-forming additive is a combination of methylene methanedisulfonate, vinyl sulfate, fluoroethylene carbonate and vinylene carbonate in a mass ratio of 1:1:1:3;

[0059] The solvent is a combination of ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate in a mass ratio of 1:1.26:1;

[0060] The lithium salt is a combination of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide in a mass ratio of 1:0.8.

[0061] Example 2

[0062] In an argon-protected glove box (H2O and O2 contents were both less than 0.1 ppm), 12.5 g of lithium salt, 82.5 g of solvent, 2 g of film-forming additive, and 3 g of composite additive were stirred at 25°C for 6 h (stirring speed was 600 rpm) to obtain electrolyte S2;

[0063] The composite additive is a combination of lithium difluorobis(oxaloyl)phosphate and 2,6-difluoronicotinonitrile in a mass ratio of 1:1.2;

[0064] The film-forming additive is a combination of methylene methanedisulfonate, vinyl sulfate, fluoroethylene carbonate and vinylene carbonate in a mass ratio of 1:0.9:1.2:2;

[0065] The solvent is a combination of ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate in a mass ratio of 1:1.5:0.8;

[0066] The lithium salt is a combination of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide in a mass ratio of 1:0.9.

[0067] Example 3

[0068] This example is carried out using a process similar to that of Example 1, except that the amount of the solvent in this example is controlled to be the same as that in Example 1, but the solvent is a combination of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate in a mass ratio of 1:1.51:1.46.

[0069] The rest are the same as in Example 1.

[0070] The electrolyte S3 was prepared.

[0071] Example 4

[0072] This embodiment is carried out using a process similar to that of Embodiment 1, except that an equal mass of lithium hexafluorophosphate is used to replace the lithium salt in Embodiment 1.

[0073] The rest are the same as in Example 1.

[0074] Electrolyte S4 was prepared.

[0075] Example 5

[0076] This example is carried out using a process similar to that of Example 1, except that an equal mass of vinylene carbonate is used in this example to replace the film-forming additive in Example 1.

[0077] The rest are the same as in Example 1.

[0078] Electrolyte S5 was prepared.

[0079] Example 6

[0080] This example is carried out using a process similar to that of Example 1, except that the amount of the composite additive used in this example is the same as that in Example 1, but the composite additive is a combination of lithium difluorobis(oxaloyl)phosphate and 2,6-difluoronicotinonitrile in a mass ratio of 1:1.5.

[0081] The rest are the same as in Example 1.

[0082] Electrolyte S6 was prepared.

[0083] Comparative Example 1

[0084] This comparative example uses commercial lithium-ion battery electrolyte, and the preparation method is as follows:

[0085] A solvent, lithium hexafluorophosphate and vinylene carbonate are mixed to obtain an electrolyte DS1; based on the total volume of the electrolyte DS1, the amount of the lithium hexafluorophosphate is such that the content of the lithium hexafluorophosphate is 1 mol / L; based on the total mass of the electrolyte DS1, the amount of the vinylene carbonate is such that the content of the vinylene carbonate is 2.5 wt%.

[0086] Comparative Example 2

[0087] This comparative example was carried out using a process similar to that of Example 1, except that no composite additive was added and the amount of solvent was changed to 83.5 g.

[0088] The rest are the same as in Example 1.

[0089] The electrolyte DS2 was prepared.

[0090] Comparative Example 3

[0091] This comparative example was carried out using a process similar to that of Example 1, except that lithium difluorobis(oxaloyl)phosphate of the same mass as that of the composite additive in Example 1 was used instead of the composite additive in Example 1 (ie, 2,6-difluoronicotinonitrile was not added).

[0092] The rest are the same as in Example 1.

[0093] The electrolyte DS3 was prepared.

[0094] Comparative Example 4

[0095] This comparative example was carried out using a process similar to that of Example 1, except that the composite additive in Example 1 was replaced with 2,6-difluoronicotinonitrile of the same mass as that in Example 1 (ie, lithium difluorobis(oxalophosphate) was not added).

[0096] The rest are the same as in Example 1.

[0097] The electrolyte DS4 was prepared.

[0098] Comparative Example 5

[0099] This comparative example was carried out using a process similar to that of Example 1, except that the amount of the composite additive used in this comparative example was the same as that in Example 1, but the composite additive was a combination of lithium difluorobis(oxaloyl)phosphate and 2,6-difluoronicotinonitrile in a mass ratio of 1:2.

[0100] The rest are the same as in Example 1.

[0101] The electrolyte DS5 was prepared.

[0102] Comparative Example 6

[0103] This comparative example was carried out using a process similar to that of Example 1, except that the amount of the composite additive used in this comparative example was the same as that in Example 1, but the composite additive was a combination of lithium difluorobis(oxaloyl)phosphate and 2,6-difluoronicotinonitrile in a mass ratio of 1:0.5.

[0104] The rest are the same as in Example 1.

[0105] Electrolyte DS6 was prepared.

[0106] Comparative Example 7

[0107] This comparative example was carried out using a process similar to that of Example 1, except that an equal mass of lithium difluorobisoxalatoborate was used to replace the lithium difluorobisoxalatophosphate in Example 1.

[0108] The rest are the same as in Example 1.

[0109] Electrolyte DS7 was prepared.

[0110] Comparative Example 8

[0111] This comparative example was carried out using a process similar to that of Example 1, except that an equal mass of fluoroacetonitrile was used to replace the 2,6-difluoronicotinonitrile in Example 1.

[0112] The rest are the same as in Example 1.

[0113] The electrolyte DS8 was prepared.

[0114] Comparative Example 9

[0115] This comparative example was carried out using a process similar to that of Example 1, except that an equal mass of 6-fluoro-nicotinonitrile was used to replace the 2,6-difluoronicotinonitrile in Example 1.

[0116] The rest are the same as in Example 1.

[0117] The electrolyte DS9 was prepared.

[0118] Comparative Example 10

[0119] This comparative example was carried out using a process similar to that of Example 1, except that, in this comparative example, the amount of the composite additive was 4 g, and the amount of the adjustment solvent was 79.5 g.

[0120] The rest are the same as in Example 1.

[0121] The electrolyte DS10 was prepared.

[0122] Test Example 1

[0123] A commercial lithium iron phosphate cathode, a commercial single-grain graphite anode, a commercial separator, and the electrolyte prepared in the above example were assembled into a battery to obtain a lithium-ion battery. The obtained lithium-ion battery was subjected to performance tests, including electrolyte rate performance tests and cycle performance tests, as follows:

[0124] Electrolyte rate performance test (lithium-ion battery cycle test in a blue electric charge and discharge tester):

[0125] (1) Charge and discharge the battery three times at a rate of 0.1C within the voltage range of 2.5-3.65V to fully activate the battery;

[0126] (2) Within the voltage range of 2.5-3.65V, five charge-discharge cycle tests were performed at rates of 0.5C, 1C, 2C, and 3C, and the average discharge capacity at each rate was recorded. The test results are shown in Table 1.

[0127] Battery cycle performance test (cycle test on a blue power charge and discharge tester)

[0128] (1) Charge and discharge the battery three times at a rate of 0.1C within the voltage range of 2.5-3.65V to fully activate the battery;

[0129] (2) Charge and discharge cycle tests were performed at a rate of 0.5C within a voltage range of 2.5-3.65V, and the discharge capacity retention rate after 100 cycles was recorded, where the discharge capacity retention rate = discharge capacity at the 100th cycle / discharge capacity at the first cycle at 0.5C * 100%. The test results are shown in Table 2.

[0130] Table 1

[0131]

[0132] Table 2

[0133] Discharge capacity retention after 100 cycles (%) Example 1 98.47 Example 2 98.43 Example 3 98.12 Example 4 97.89 Example 5 97.65 Example 6 97.32 Comparative Example 1 95.31 Comparative Example 2 95.34 Comparative Example 3 95.81 Comparative Example 4 95.54 Comparative Example 5 95.02 Comparative Example 6 94.89 Comparative Example 7 94.83 Comparative Example 8 94.88 Comparative Example 9 94.75 Comparative Example 10 94.61

[0134] It can be seen from the results in Table 1 and Table 2 that the electrolyte provided by the present invention has better rate performance and cycle stability after being applied to the battery.

[0135] The present invention also provides an exemplary rate performance test diagram of the electrolyte obtained in Example 1 and Comparative Example 1 after being applied to the battery, as shown in FIG. Figure 1 As shown in the figure, it can be seen that the capacity of Example 1 is more stable than that of Comparative Example 1 at each rate, which fully proves its significant improvement on rate performance.

[0136] The present invention also provides exemplary cycle performance test diagrams of the electrolyte obtained in Example 1 and Comparative Example 1 after being applied to the battery, as shown in FIG. Figure 2As shown in the figure, it can be seen that the cycle performance of the lithium ion battery obtained in Example 1 is very stable and significantly better than that of Comparative Example 1.

[0137] Test Example 2

[0138] Aluminum foil, lithium sheet, commercial separator, and the electrolyte prepared in the previous example were assembled into a battery to obtain an Al|Li half-cell. A commercial lithium iron phosphate positive electrode, a commercial single-grain graphite negative electrode, a commercial separator, and the electrolyte prepared in the previous example were assembled into a battery to obtain a lithium-ion battery. The half-cell was subjected to an oxidation window test, and the lithium-ion battery was subjected to an iron dissolution test, as follows:

[0139] Oxidation window test (half-cell tested on Chenhua CHI tester):

[0140] (1) Perform a linear voltammetric sweep test on the half-cell with a voltage range from open circuit voltage to 6 V and a sweep rate of 0.1 mV s -1 ;

[0141] (2) Record current density reaches 100 μA cm -2 The voltage value of the test is shown in Table 3.

[0142] Iron dissolution test (cycle test in a Blue Electric charge and discharge tester, and test the iron content in the graphite negative electrode by Thermo Fisher ICP-OES):

[0143] (1) Charge and discharge the battery three times at a rate of 0.1C within the voltage range of 2.5-3.65V to fully activate the battery;

[0144] (2) Within the voltage range of 2.5-3.65 V, 100 charge-discharge cycle tests were performed at a rate of 0.5 C. After the test, the battery was disassembled to obtain the graphite negative electrode. The iron content in the graphite was tested by ICP-OES. The test results are shown in Table 3.

[0145] Table 3

[0146]

[0147]

[0148] From the results in Table 3, it can be seen that the electrolyte provided by the present invention has significantly better oxidation stability, can significantly reduce the oxidation decomposition current under the same high voltage conditions, and inhibit the iron dissolution of the lithium iron phosphate positive electrode during the cycle.

[0149] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A composition for an electrolyte, characterized in that The composition contains lithium salt, solvent, film-forming additive and composite additive; Based on the total mass of the composition, the content of the lithium salt is 9.5-15wt%, the content of the solvent is 65-90wt%, the content of the film-forming additive is 2-5wt%, and the content of the composite additive is 0.1-3wt%; The composite additive is a combination of lithium difluorobis(oxaloyl)phosphate and 2,6-difluoronicotinonitrile in a mass ratio of 1:0.55-1.

8.

2. The composition according to claim 1, characterized in that The composite additive is a combination of lithium difluorobis(oxaloyl)phosphate and 2,6-difluoronicotinonitrile in a mass ratio of 1:1-1.

5.

3. The composition according to claim 2, characterized in that The composite additive is a combination of lithium difluorobis(oxaloyl)phosphate and 2,6-difluoronicotinonitrile in a mass ratio of 1:1-1.

2.

4. The composition according to any one of claims 1 to 3, characterized in that Based on the total mass of the composition, the content of the lithium salt is 12.5-14.5 wt %, the content of the solvent is 80-85 wt %, the content of the film-forming additive is 2-4 wt %, and the content of the composite additive is 2-3 wt %.

5. The composition according to any one of claims 1 to 3, characterized in that The lithium salt is selected from at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium perchlorate, lithium nitrate, lithium difluoroborate, lithium tetrafluoroborate, lithium bis(trifluoromethylsulfonyl)imide, and lithium trifluoromethanesulfonate; and / or, the solvent is selected from at least three of ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, propylene carbonate, γ-butyrolactone, methyl acetate, propyl acetate, and butyl acetate; And / or, the film-forming additive is at least two of vinylene carbonate, vinyl sulfate, fluoroethylene carbonate, methylene methanedisulfonate, 1,3-propane sultone, and vinyl ethylene carbonate.

6. The composition according to claim 5, characterized in that The solvent is a combination of ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate in a mass ratio of 1:1-1.5:0.8-1.2; And / or, the lithium salt is a combination of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide in a mass ratio of 1:0.7-0.9; And / or, the film-forming additive is a combination of methylene methanedisulfonate, vinyl sulfate, fluoroethylene carbonate and vinylene carbonate in a mass ratio of 1:0.8-1.2:0.8-1.2:2-4.

7. A method for preparing an electrolyte, characterized in that: The method is carried out using the electrolyte composition according to any one of claims 1 to 6, and comprises: mixing a mixture containing the electrolyte composition to obtain the electrolyte.

8. The electrolyte prepared by the method according to claim 7.

9. Use of the electrolyte according to claim 8 in a lithium ion battery with a single-particle graphite negative electrode.

10. A lithium ion battery, characterized in that: The lithium-ion battery comprises: a positive electrode, a single-particle graphite negative electrode, an electrolyte and a separator; the electrolyte is the electrolyte according to claim 8.

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