Composition for local high-concentration electrolyte, local high-concentration electrolyte, preparation method and application of local high-concentration electrolyte, and lithium ion battery

Abstract

The invention relates to the technical field of lithium ion batteries, and discloses a composition for a local high-concentration electrolyte, the local high-concentration electrolyte, a preparation method and application of the local high-concentration electrolyte, and a lithium ion battery. The composition contains a composite lithium salt, a solvent, a diluent and a film-forming additive, based on the total mass of the composition, the content of the composite lithium salt is 0.5-5 wt%, the content of the solvent is 15-55.5 wt%, the content of the diluent is 40-85 wt%, and the content of the film-forming additive is 3-10 wt%. The composite lithium salt is a combination of lithium hexafluorophosphate, lithium nitrate, lithium bis (fluorosulfonyl) imide, lithium tetrafluoroborate and lithium difluoro (oxalato) borate in a molar mass ratio of 1: (0.5-2): (0.5-2): (0.5-2): (0.5-2). According to the local high-concentration electrolyte provided by the invention, the compatibility of the electrolyte and a graphite negative electrode can be remarkably improved, the ionic conductivity of the electrolyte is improved, and the cycle performance of the electrolyte is improved.

Description

Technical Field

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

[0002] Lithium iron phosphate batteries are currently the most widely used energy storage battery due to cost, safety, and environmental considerations. However, they can still experience safety incidents under external thermal, mechanical, and electrical abuse, posing significant challenges to the safe and stable operation of energy storage systems.

[0003] The use of phosphate ester solvents can produce flame-retardant and safe electrolytes, significantly improving the safety of lithium-ion batteries. However, due to the poor compatibility of phosphate ester solvents with graphite anodes, the electrical performance of lithium-ion batteries is severely affected. Improving the compatibility of phosphate ester electrolytes with graphite anodes through rational electrolyte formulation design is a current research focus.

[0004] Locally concentrated electrolytes have been a research hotspot in the field of lithium-ion batteries in recent years. They are a new type of electrolyte system based on a combination of high-concentration electrolytes and diluents. The formation of a unique lithium-ion solvation structure involving anions can effectively solve the compatibility problem between phosphate solvents and graphite negative electrodes. However, the low ionic conductivity leads to large battery polarization, limiting its application in practical-level batteries. Furthermore, due to its reliance on a high proportion of lithium salts or fluoroether diluents, it also has the defect of high cost.

[0005] For example, CN119069797A discloses a wide-temperature flame-retardant electrolyte, its preparation method, and its application. By combining the advantages of a locally high-concentration electrolyte, this solution overcomes the instability issues of low-concentration electrolytes at the positive and negative electrode interfaces, as well as the high cost and high viscosity of high-concentration electrolytes. However, this solution requires a relatively high lithium salt content (20 wt%) and a highly fluorinated diluent (TFNP), resulting in high electrolyte costs. Furthermore, the solution suffers from low ionic conductivity, hindering its practical application in batteries.

[0006] Therefore, there is an urgent need to develop a new type of local high-concentration electrolyte suitable for the field of lithium-ion batteries, which can improve ionic conductivity and reduce costs while combining the advantages of existing local high-concentration electrolytes to meet the application needs of actual lithium-ion batteries. Summary of the Invention

[0007] The purpose of the present invention is to solve the problems of low ion conductivity and high cost in the locally high-concentration electrolyte used in lithium-ion batteries in the prior art.

[0008] In order to achieve the above-mentioned object, the first aspect of the present invention provides a composition for local high-concentration electrolyte, which contains a complex lithium salt, a solvent, a diluent and a film-forming additive;

[0009] Based on the total mass of the composition, the content of the composite lithium salt is 0.5-5wt%, the content of the solvent is 15-55.5wt%, the content of the diluent is 40-85wt%, and the content of the film-forming additive is 3-10wt%;

[0010] The composite lithium salt is a combination of lithium hexafluorophosphate, lithium nitrate, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate and lithium difluorooxalatoborate in a molar mass ratio of 1:0.5-2:0.5-2:0.5-2:0.5-2.

[0011] The second aspect of the present invention provides a method for preparing a local high-concentration electrolyte, which is performed using the composition for the local high-concentration electrolyte described in the first aspect, and comprises: mixing a mixture containing the composition for the local high-concentration electrolyte to obtain the local high-concentration electrolyte.

[0012] The third aspect of the present invention provides a local high-concentration electrolyte prepared by the method described in the second aspect.

[0013] The fourth aspect of the present invention provides the use of the local high-concentration electrolyte described in the third aspect in a lithium-ion battery.

[0014] A fifth aspect of the present invention provides a lithium-ion battery, comprising: a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator; the electrolyte is the local high-concentration electrolyte described in the third aspect.

[0015] Compared with the prior art, the present invention has at least the following beneficial effects:

[0016] (1) The lithium salt content in the locally high-concentration electrolyte provided by the present invention is low, and the diluent is cheap and readily available, which can significantly reduce the overall cost of the electrolyte;

[0017] (2) The present invention can significantly enhance the interaction between anions and cations in a local high-concentration electrolyte by compounding lithium hexafluorophosphate, lithium nitrate, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate and lithium difluorooxalatoborate in a specific ratio as a composite lithium salt, and controlling the content of the composite lithium salt to 0.5-5wt%, and using a solvent, a diluent and a film-forming agent in combination, thereby optimizing the electrolyte solvation structure, significantly improving the compatibility of the electrolyte with the graphite negative electrode, and improving the ionic conductivity of the electrolyte;

[0018] (3) The present invention uses a specific composite lithium salt combination to prepare a local high-concentration electrolyte, which can optimize the electrode / electrolyte interface structure and improve the electrolyte circulation performance;

[0019] (4) The present invention uses a combination of a specific compound lithium salt and a phosphate solvent to prepare a local high-concentration electrolyte, which can further improve the safety of the electrolyte and reduce the heat generated by its reaction with the graphite negative electrode at high temperature. DETAILED DESCRIPTION

[0020] 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.

[0021] As mentioned above, the first aspect of the present invention provides a composition for local high-concentration electrolyte, which contains a complex lithium salt, a solvent, a diluent and a film-forming additive;

[0022] Based on the total mass of the composition, the content of the composite lithium salt is 0.5-5wt%, the content of the solvent is 15-55.5wt%, the content of the diluent is 40-85wt%, and the content of the film-forming additive is 3-10wt%;

[0023] The composite lithium salt is a combination of lithium hexafluorophosphate, lithium nitrate, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate and lithium difluorooxalatoborate in a molar mass ratio of 1:0.5-2:0.5-2:0.5-2:0.5-2.

[0024] Preferably, the composite lithium salt is a combination of lithium hexafluorophosphate, lithium nitrate, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate and lithium difluorooxalatoborate in a molar mass ratio of 1:0.8-1.2:0.8-1.2:0.8-1.2:0.8-1.2.

[0025] More preferably, the composite lithium salt is a combination of lithium hexafluorophosphate, lithium nitrate, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, and lithium difluorooxalatoborate in a molar mass ratio of 1:0.8-0.85:1.1-1.2:0.9-1:0.8-1.2. The inventors have discovered that the electrolyte obtained under this preferred embodiment has higher ionic conductivity and, when applied to lithium-ion batteries, can significantly improve the battery's rate performance without affecting the battery's long-term cycling performance.

[0026] Preferably, the content of the composite lithium salt is 0.5-1.5 wt %, the content of the solvent is 40.5-55.5 wt %, the content of the diluent is 40-53 wt %, and the content of the film-forming additive is 4-5 wt %. The inventors have found that the electrolyte obtained under this preferred embodiment has higher ionic conductivity.

[0027] Preferably, the diluent is selected from at least one of 2-phenylpropane, m-fluorotoluene, fluorobenzene, and 1,3,5-trifluorobenzene.

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

[0029] More preferably, the film-forming additive is selected from 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.

[0030] Preferably, the solvent is selected from at least two of trimethyl phosphate, triethyl phosphate, tributyl phosphate, triphenyl phosphate, and dimethyl methyl phosphate.

[0031] As mentioned above, the second aspect of the present invention provides a method for preparing a local high-concentration electrolyte, which is carried out using the composition for the local high-concentration electrolyte described in the first aspect, and includes: mixing a mixture containing the composition for the local high-concentration electrolyte to obtain the local high-concentration electrolyte.

[0032] It should be noted that in the present invention, there are no particular requirements for the mixing conditions for preparing the local high-concentration electrolyte by mixing the composition for the local high-concentration 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.

[0033] As mentioned above, the third aspect of the present invention provides a local high-concentration electrolyte prepared by the method described in the second aspect.

[0034] As mentioned above, the fourth aspect of the present invention provides the use of the local high-concentration electrolyte described in the third aspect in a lithium-ion battery.

[0035] As mentioned above, the fifth aspect of the present invention provides a lithium-ion battery, which includes: a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator; the electrolyte is the local high-concentration electrolyte described in the third aspect.

[0036] 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.

[0037] 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.

[0038] raw material:

[0039] Lithium hexafluorophosphate: CAS number 21324-40-3, purchased from Shanghai MacLean Biochemical Technology Co., Ltd.

[0040] Lithium nitrate: CAS number 7790-69-4, purchased from Shanghai MacLean Biochemical Technology Co., Ltd.

[0041] Lithium bis(fluorosulfonyl)imide: CAS number 9002-81-7, purchased from Shanghai MacLean Biochemical Technology Co., Ltd.

[0042] Lithium tetrafluoroborate: CAS number 14283-07-9, purchased from Shanghai MacLean Biochemical Technology Co., Ltd.

[0043] Lithium difluorooxalatoborate: CAS number 409071-16-5, purchased from Shanghai MacLean Biochemical Technology Co., Ltd.

[0044] Lithium trifluoromethanesulfonate: CAS number 33454-82-9, purchased from Shanghai MacLean Biochemical Technology Co., Ltd.

[0045] Lithium difluorophosphate: CAS number 24389-25-1, purchased from Shanghai MacLean Biochemical Technology Co., Ltd.

[0046] Trimethyl phosphate: CAS number 512-56-1, purchased from Shanghai MacLean Biochemical Technology Co., Ltd.

[0047] Triethyl phosphate: CAS number 78-40-0, purchased from Shanghai MacLean Biochemical Technology Co., Ltd.

[0048] Tributyl phosphate: CAS number 126-73-8, purchased from Shanghai MacLean Biochemical Technology Co., Ltd.

[0049] Dimethyl methyl phosphate: CAS number 756-79-6, purchased from Shanghai MacLean Biochemical Technology Co., Ltd.

[0050] Triphenyl phosphate: CAS number 13674-84-5, purchased from Shanghai MacLean Biochemical Technology Co., Ltd.

[0051] Benzene: CAS number 71-43-2, purchased from Shanghai MacLean Biochemical Technology Co., Ltd.

[0052] Toluene: CAS number 108-88-3, purchased from Shanghai MacLean Biochemical Technology Co., Ltd.

[0053] 2-Phenylpropane: CAS number 98-82-8, purchased from Shanghai MacLean Biochemical Technology Co., Ltd.;

[0054] m-Fluorotoluene: CAS number 352-70-5, purchased from Shanghai MacLean Biochemical Technology Co., Ltd.

[0055] Fluorobenzene: CAS number 462-06-6, purchased from Shanghai MacLean Biochemical Technology Co., Ltd.

[0056] 1,3,5-Trifluorobenzene: CAS number 372-38-3, purchased from Shanghai MacLean Biochemical Technology Co., Ltd.;

[0057] Polyolefin separator: Celgard 2400 separator, 25 μm thick, single-layer PP material, 41% porosity, purchased from Celgard Company, USA;

[0058] Commercial lithium iron phosphate cathode: surface density of 12 mg / cm 2 , active material accounts for 95.4wt%, purchased from Shenzhen Kejing Zhida Technology Co., Ltd.;

[0059] Commercial graphite anode: surface density 5.8 mg / cm 2 , active substances accounted for 95.5wt% and were purchased from Shenzhen Kejing Zhida Technology Co., Ltd.

[0060] Example 1

[0061] This example is used to illustrate that the local high-concentration electrolyte provided by the present invention is prepared using the following steps:

[0062] In an argon-protected glove box (H2O and O2 contents are both less than 0.1 ppm), 53.5 g of solvent, 1.5 g of composite lithium salt, and 40.5 g of m-fluorotoluene were stirred at 25°C for 12 h (stirring speed is 600 rpm), and then 4.5 g of film-forming additive was added and stirred and mixed for 12 h to obtain the local high-concentration electrolyte S1;

[0063] The solvent is a combination of trimethyl phosphate, triethyl phosphate and dimethyl methyl phosphate in a mass ratio of 1:1:0.5;

[0064] The film-forming additive is a combination of methylene methanedisulfonate, vinyl sulfate, fluoroethylene carbonate and vinylene carbonate in a mass ratio of 1:1:1:3.5;

[0065] The composite lithium salt is a combination of lithium hexafluorophosphate, lithium nitrate, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate and lithium difluorooxalatoborate in a molar mass ratio of 1:0.8:1.1:0.9:0.8.

[0066] Example 2

[0067] In an argon-protected glove box (H2O and O2 contents are both less than 0.1 ppm), 45.5 g of solvent, 1.0 g of composite lithium salt and 48.5 g of m-fluorotoluene were stirred at 25°C for 12 h (stirring speed is 600 rpm), and then 5 g of film-forming additive was added and the stirring and mixing were continued for 12 h to obtain the local high-concentration electrolyte S2;

[0068] The solvent is a combination of trimethyl phosphate, triethyl phosphate and dimethyl methyl phosphate in a mass ratio of 1:1:1;

[0069] The film-forming additive is a combination of methylene methanedisulfonate, vinyl sulfate, fluoroethylene carbonate and vinylene carbonate in a mass ratio of 1:1:1:3.5;

[0070] The composite lithium salt is a combination of lithium hexafluorophosphate, lithium nitrate, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate and lithium difluorooxalatoborate in a molar mass ratio of 1:0.85:1.2:1:1.2.

[0071] Example 3

[0072] This embodiment is carried out using a process similar to that of Example 1, except that, in this embodiment, the amount of the composite lithium salt is controlled to be the same as that of Example 1, but the composite lithium salt is a combination of lithium hexafluorophosphate, lithium nitrate, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, and lithium difluorooxalatoborate in a molar mass ratio of 1:1:1:1:1.

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

[0074] A locally high-concentration electrolyte S3 is prepared.

[0075] Example 4

[0076] This embodiment is carried out using a process similar to that of Example 1, except that the total amount of the composite lithium salt, solvent, diluent and film-forming additive is controlled to be the same as that of Example 1, but the amount of the composite lithium salt is 5g, the amount of the solvent is 50g, the amount of the diluent is 40.5g, and the amount of the film-forming additive is 4.5g.

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

[0078] A locally high-concentration electrolyte S4 is prepared.

[0079] Example 5

[0080] This embodiment is carried out using a process similar to that of Example 1, except that, in this embodiment, the amount of the composite lithium salt is controlled to be the same as that of Example 1, but the composite lithium salt is a combination of lithium hexafluorophosphate, lithium nitrate, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, and lithium difluorooxalatoborate in a molar mass ratio of 1:2:2:2:2.

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

[0082] A locally high-concentration electrolyte S5 is prepared.

[0083] Comparative Example 1

[0084] In an argon-protected glove box (H2O and O2 contents less than 0.1 ppm), 1.25 g of lithium hexafluorophosphate was added to 2.50 g of ethylene carbonate, 3.0 g of ethyl methyl carbonate, and 2.5 g of dimethyl carbonate. The mixture was stirred at 25°C for 12 hours to fully dissolve the lithium salts. Subsequently, 0.35 g of vinylene carbonate, 0.10 g of fluoroethylene carbonate, 0.10 g of vinyl sulfate, and 0.10 g of methylene methanedisulfonate were added and mixed thoroughly. This yielded electrolyte DS1.

[0085] Comparative Example 2

[0086] This comparative example is carried out using a process similar to that of Example 1, except that the total amount of the composite lithium salt, solvent, diluent and film-forming additive is controlled to be the same as that of Example 1, but the amount of the composite lithium salt is 0.4g, the amount of the solvent is 49.6g, the amount of the diluent is 45.5g, and the amount of the film-forming additive is 4.5g.

[0087] The rest are the same as in Example 1.

[0088] The electrolyte DS2 was prepared.

[0089] Comparative Example 3

[0090] This comparative example is carried out using a process similar to that of Example 1, except that the total amount of the composite lithium salt, solvent, diluent and film-forming additive is controlled to be the same as that of Example 1, but the amount of the composite lithium salt is 8g, the amount of the solvent is 42g, the amount of the diluent is 45.5g, and the amount of the film-forming additive is 4.5g.

[0091] The rest are the same as in Example 1.

[0092] The electrolyte DS3 was prepared.

[0093] Comparative Example 4

[0094] This comparative example was carried out using a process similar to that of Example 3, except that the amount of the composite lithium salt in this comparative example was the same as that in Example 3, but the composite lithium salt was a combination of lithium hexafluorophosphate, lithium nitrate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, and lithium difluorooxalatoborate in a molar mass ratio of 1:1:1:1:1.

[0095] The rest are the same as in Example 3.

[0096] The electrolyte DS4 was prepared.

[0097] Comparative Example 5

[0098] This comparative example was carried out using a process similar to that of Example 3, except that the amount of the composite lithium salt in this comparative example was the same as that in Example 3, but the composite lithium salt was a combination of lithium trifluoromethanesulfonate, lithium nitrate, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, and lithium difluorooxalatoborate in a molar mass ratio of 1:1:1:1:1.

[0099] The rest are the same as in Example 3.

[0100] The electrolyte DS5 was prepared.

[0101] Comparative Example 6

[0102] This comparative example was carried out using a process similar to that of Example 3, except that the amount of the composite lithium salt in this comparative example was the same as that in Example 3, but the composite lithium salt was a combination of lithium hexafluorophosphate, lithium nitrate, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, and lithium difluorophosphate in a molar mass ratio of 1:1:1:1:1.

[0103] The rest are the same as in Example 3.

[0104] Electrolyte DS6 was prepared.

[0105] Comparative Example 7

[0106] This comparative example was carried out using a process similar to that of Example 3, except that the amount of the composite lithium salt in this comparative example was the same as that in Example 3, but the composite lithium salt was a combination of lithium hexafluorophosphate, lithium nitrate, lithium bis(fluorosulfonyl)imide, and lithium tetrafluoroborate in a molar mass ratio of 1:1:1:1.

[0107] The rest are the same as in Example 3.

[0108] Electrolyte DS7 was prepared.

[0109] Comparative Example 8

[0110] This comparative example was carried out using a process similar to that of Example 3, except that the amount of the composite lithium salt in this comparative example was the same as that in Example 3, but the composite lithium salt was a combination of lithium bistrifluoromethanesulfonyl imide, lithium nitrate, lithium bisfluorosulfonyl imide, and lithium difluorooxalatoborate in a molar mass ratio of 1:1:1:1.

[0111] The rest are the same as in Example 3.

[0112] The electrolyte DS8 was prepared.

[0113] Comparative Example 9

[0114] This comparative example was carried out using a process similar to that of Example 3, except that the amount of the composite lithium salt in this comparative example was the same as that in Example 3, but the composite lithium salt was a combination of lithium hexafluorophosphate, lithium nitrate, lithium bis(fluorosulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate and lithium difluorooxalatoborate in a molar mass ratio of 1:1:1:1:1:1:1.

[0115] The rest are the same as in Example 3.

[0116] The electrolyte DS9 was prepared.

[0117] Test Example 1

[0118] This test example exemplarily tests the ionic conductivity of the electrolyte obtained in the above example, as well as the electrochemical performance of the electrolyte after being applied to the battery, including battery cycle performance test and battery rate performance test, as follows:

[0119] Ionic conductivity test: The electrolyte was tested at room temperature of 25°C using a Leimagnetic conductivity tester DDB-303A. The ionic conductivity of each electrolyte was recorded. The test results are shown in Table 1.

[0120] A commercial lithium iron phosphate positive electrode, a commercial graphite negative electrode, a commercial separator and the electrolyte prepared in each example are assembled into a battery to obtain a safe lithium-ion battery.

[0121] Battery cycle performance test: The Wuhan Land charge and discharge tester was used for charge and discharge tests. Specifically, within the voltage range of 2.5-3.65V, the battery was first activated three times at a 0.1C rate, and then charge and discharge cycles were performed 100 times at a 0.5C rate. The capacity retention rate = 100th cycle discharge capacity / 1st cycle discharge capacity. The test results are shown in Table 1.

[0122] Battery high-voltage cycle performance test: The Wuhan Land charge and discharge tester was used for charge and discharge tests. Specifically, within the voltage range of 2.5-3.65V, the battery was first activated three times at a 0.1C rate, and then the charge and discharge cycles were performed five times at 1C, 2C, and 3C rates within the voltage range of 2.5-4.5V. The average discharge capacity at each rate was recorded. The test results are shown in Table 1.

[0123] Table 1

[0124]

[0125]

[0126] As can be seen from Table 1, the local high-concentration electrolyte provided by the present invention has higher ionic conductivity. When applied to lithium-ion batteries, it can significantly improve the battery rate performance without affecting the long-term cycle performance of the battery.

[0127] 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 local high-concentration electrolyte, characterized in that: The composition contains a composite lithium salt, a solvent, a diluent and a film-forming additive; Based on the total mass of the composition, the content of the composite lithium salt is 0.5-5wt%, the content of the solvent is 15-55.5wt%, the content of the diluent is 40-85wt%, and the content of the film-forming additive is 3-10wt%; The composite lithium salt is a combination of lithium hexafluorophosphate, lithium nitrate, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate and lithium difluorooxalatoborate in a molar mass ratio of 1:0.5-2:0.5-2:0.5-2:0.5-2.

2. The composition according to claim 1, characterized in that The composite lithium salt is a combination of lithium hexafluorophosphate, lithium nitrate, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate and lithium difluorooxalatoborate in a molar mass ratio of 1:0.8-1.2:0.8-1.2:0.8-1.2:0.8-1.

2.

3. The composition according to claim 2, characterized in that The composite lithium salt is a combination of lithium hexafluorophosphate, lithium nitrate, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate and lithium difluorooxalatoborate in a molar mass ratio of 1:0.8-0.85:1.1-1.2:0.9-1:0.8-1.

2.

4. The composition according to any one of claims 1 to 3, characterized in that The content of the composite lithium salt is 0.5-1.5 wt %, the content of the solvent is 40.5-55.5 wt %, the content of the diluent is 40-53 wt %, and the content of the film-forming additive is 4-5 wt %.

5. The composition according to any one of claims 1 to 4, characterized in that The diluent is selected from at least one of 2-phenylpropane, m-fluorotoluene, fluorobenzene, and 1,3,5-trifluorobenzene.

6. The composition according to any one of claims 1 to 5, characterized in that The film-forming additive is selected from 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 a local high-concentration electrolyte, characterized in that: The method is carried out using the composition for local high-concentration electrolyte according to any one of claims 1 to 6, and comprises: mixing a mixture containing the composition for local high-concentration electrolyte to obtain the local high-concentration electrolyte.

8. The local high-concentration electrolyte prepared by the method according to claim 7.

9. Use of the local high-concentration electrolyte according to claim 8 in a lithium-ion battery.

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

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