Electrolyte, preparation method and lithium ion battery containing same

Abstract

The present invention provides an electrolyte, a preparation method and a lithium-ion battery containing the same. The electrolyte includes: a lithium salt, a non-aqueous organic solvent and an additive, and the additive includes an additive A and an additive B. In the present invention, by adding additives A and B to the electrolyte, a stable interface film can be formed at the electrolyte-electrode material interface. In addition, the ‑C≡N bond functional group in additive A can combine with H2O in the electrolyte, thereby reducing the decomposition reaction of the lithium salt LiPF6 in the electrolyte to produce the Lewis strong acid PF5 when it comes into contact with water; the ‑Si bond contained in additive B can further remove HF in the electrolyte, reduce the acidity of the system, and thus reduce the damage to the interface film caused by side reactions. Moreover, the ‑P free radicals in additives A and additive B can combine with the active oxygen in the system, reduce the dissolution of transition metals, and stabilize the structure of the positive electrode material. The electrolyte can significantly improve the high-temperature performance of the lithium-ion battery.

Description

Technical Field

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

[0002] As people pay more attention to the depletion of non-renewable energy and environmental pollution, renewable clean energy is developing rapidly. Among them, lithium-ion batteries, with their high energy density, long cycle life, low self-discharge rate, and environmental friendliness, have been widely used in consumer electronics, new energy vehicles, and other power battery products.

[0003] However, at present, lithium-ion batteries still have problems such as poor endurance, which limits their application in power products, especially automotive lithium-ion batteries. The electrical properties of lithium-ion batteries are closely related to the electrolyte. At the electrolyte-electrode material interface, if a stable and dense passivation film cannot be formed, the positive / negative electrode materials will be exposed to the electrolyte. Affected by the moisture and acidity in the electrolyte, adverse factors such as changes in the surface structure of the positive electrode material, precipitation of metal ions, gas escape, and diffusion of metal ions to the negative electrode to destroy the SEI film will occur, causing the cycle life of the battery to continue to deteriorate. This degradation is more serious in a high-temperature environment. Based on this bottleneck problem, relevant workers have done a lot of research. Chinese patent CN110416613A discloses an electrolyte that can improve the cycle and safety performance of lithium-ion batteries. The electrolyte is prepared by combining a special non-aqueous organic solvent and an additive, and then combining an electrolyte stabilizer and a lithium salt. This invention proposes to form a highly stable protective film on the surface of the negative electrode material to protect the negative electrode material, but it does not provide an effective solution to problems such as the dissolution of active oxygen and transition metal ions that may occur in the positive electrode material. Summary of the Invention

[0004] In view of this, the present invention provides an electrolyte, a preparation method and a lithium-ion battery containing the same. The electrolyte provided in the present invention can not only form a stable interfacial film, but also reduce the acidity of the system, bind the active oxygen in the system, effectively stabilize the electrode material structure, and significantly improve the high-temperature performance of the lithium-ion battery.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0006] In a first aspect, the present invention provides an electrolyte, comprising: a lithium salt, a non-aqueous organic solvent, and an additive; wherein the additive comprises an additive A and an additive B, and the chemical structure of the additive A is shown in Formula 1:

[0007]

[0008] Wherein, R1 is selected from halogen, substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkynyl, substituted or unsubstituted cycloalkyl, substituted or unsubstituted alkoxy; if substituted, the substituent is any one of C1-C5 alkyl, C2-C5 alkenyl, C2-C5 alkynyl, C3-C5 cycloalkyl, and halogen;

[0009] The chemical structural formula of the additive B is shown in Formula 2:

[0010]

[0011] Furthermore, the lithium salt is lithium hexafluorophosphate; or the lithium salt includes lithium hexafluorophosphate and further includes at least one of lithium difluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(oxalatoborate) and lithium difluorooxalatoborate.

[0012] Furthermore, the non-aqueous organic solvent is selected from any two or more of propylene carbonate, ethyl methyl carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, fluoroethylene carbonate, γ-butyrolactone, sulfolane, methyl formate, ethyl formate, propyl formate, butyl formate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, and butyl butyrate.

[0013] Furthermore, the additive A is selected from at least one of the following compounds I to IV:

[0014]

[0015] Furthermore, the additives also include additive C; the additive C is selected from at least one of vinylene carbonate (VC), fluoroethylene carbonate (FEC), vinyl ethylene carbonate (VEC), ethylene sulfate (DTD), 1,3-propane sultone (PS), vinyl sulfite (ES), tris(trimethylsilyl) borate (TMSB), tris(trimethylsilyl) phosphate (TMSP), lithium bis(oxalatoborate) (LiBOB), lithium difluorooxalatoborate (LiODFB), and lithium difluorobis(oxalatophosphate) (LiODFP); and / or the amount of the additive C added is 0.5wt% to 3wt% of the total mass of the electrolyte.

[0016] Furthermore, the amount of the additive A added is 0.5 wt% to 3 wt% of the total mass of the electrolyte; and / or the amount of the additive B added is 0.5 wt% to 3 wt% of the total mass of the electrolyte.

[0017] Furthermore, the amount of the lithium salt added is 12 wt% to 18 wt% of the total mass of the electrolyte; and / or the amount of the non-aqueous organic solvent added is 70 wt% to 80 wt% of the total mass of the electrolyte.

[0018] In a second aspect, the present invention provides a method for preparing the electrolyte as described above, wherein the preparation method is:

[0019] The lithium salt and the additive are added to the non-aqueous organic solvent and mixed evenly to obtain the electrolyte.

[0020] In a third aspect, the present invention provides a lithium-ion battery comprising the electrolyte described above.

[0021] Furthermore, the lithium-ion battery also includes a positive electrode sheet, a negative electrode sheet and a separator.

[0022] The beneficial effects of the above technical solution of the present invention are as follows:

[0023] The present invention provides an electrolyte comprising: a lithium salt, a non-aqueous organic solvent, and additives; wherein the additives include additive A and additive B, wherein additive A is represented by formula 1 above, and additive B is represented by formula 2 above. By adding additives A and B to the electrolyte, a stable interfacial film can be formed at the electrolyte-electrode material interface. Furthermore, the -C≡N functional group in additive A can bind with H₂O in the electrolyte, thereby reducing the decomposition reaction of the lithium salt LiPF₆ in the electrolyte to produce the Lewis acid PF₅ upon contact with water. Furthermore, the -C≡N bond can complex transition metal ions, preventing metal ion deposition at the negative electrode. The -Si bond contained in additive B can further scavenge HF from the electrolyte, reducing the acidity of the system and thus reducing damage to the interfacial film caused by side reactions. Furthermore, the -P radicals in additives A and B can bind to active oxygen in the system, reducing transition metal dissolution and stabilizing the structure of the positive electrode material. Experiments have demonstrated that the combined use of additives A and B significantly improves the high-temperature performance of lithium-ion batteries. DETAILED DESCRIPTION

[0024] In order to further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than for limiting the present invention.

[0025] In a first aspect, the present invention provides an electrolyte, comprising: a lithium salt, a non-aqueous organic solvent, and an additive; wherein the additive comprises an additive A and an additive B, and the chemical structure of the additive A is shown in Formula 1:

[0026]

[0027] Wherein, R1 is selected from halogen, substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkynyl, substituted or unsubstituted cycloalkyl, substituted or unsubstituted alkoxy; if substituted, the substituent is any one of C1-C5 alkyl, C2-C5 alkenyl, C2-C5 alkynyl, C3-C5 cycloalkyl, and halogen;

[0028] The chemical structural formula of the additive B is shown in Formula 2:

[0029]

[0030] In order to solve the problems of film formation stability and high-temperature performance of lithium-ion batteries, the present invention provides an electrolyte comprising additives A and additives B, wherein additive A is shown in formula 1 above, and additive B is shown in formula 2 above. In the present invention, by adding additives A and additives B to the electrolyte, a stable interface film can be formed at the electrolyte-electrode material interface. Specifically, additive A forms a film by ring-opening polymerization to form an organic compound or inorganic compound containing or not containing Li; additive B forms a film by bond breaking to form an interface film rich in substances such as -POF. In addition, the -C≡N bond functional group in additive A can combine with H2O in the electrolyte, thereby reducing the decomposition reaction of the lithium salt LiPF6 in the electrolyte to produce the Lewis strong acid PF5 when it comes into contact with water. At the same time, the -C≡N bond can also complex transition metal ions to avoid the deposition of metal ions at the negative electrode. The -Si bond contained in additive B can further remove HF in the electrolyte, reduce the acidity of the system, and thus reduce the damage to the interface film caused by side reactions. Furthermore, the -P radicals in Additives A and B can bind to active oxygen in the system, reducing transition metal dissolution and stabilizing the cathode material structure. Experiments have shown that the combined use of Additives A and B can significantly improve the high-temperature performance of lithium-ion batteries.

[0031] According to some embodiments of the present invention, the lithium salt is lithium hexafluorophosphate; or the lithium salt includes lithium hexafluorophosphate and further includes at least one of lithium difluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(oxalatoborate), and lithium difluorooxalatoborate. In the electrolyte provided by the present invention, the lithium salt included therein may include only lithium hexafluorophosphate, or, in addition to lithium hexafluorophosphate, may also include other types of lithium salts, such as lithium difluorophosphate and lithium tetrafluoroborate.

[0032] According to some embodiments of the present invention, the non-aqueous organic solvent is selected from any two or more of propylene carbonate, ethyl methyl carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, fluoroethylene carbonate, γ-butyrolactone, cyclopentane, methyl formate, ethyl formate, propyl formate, butyl formate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, and butyl butyrate.

[0033] According to some embodiments of the present invention, the non-aqueous organic solvent may be a mixture of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, and dimethyl carbonate.

[0034] According to some embodiments of the present invention, the additive A is selected from at least one of the following compounds I to IV:

[0035]

[0036] According to some embodiments of the present invention, the additive further includes an additive C; the additive C is selected from at least one of vinylene carbonate (VC), fluoroethylene carbonate (FEC), vinyl ethylene carbonate (VEC), ethylene sulfate (DTD), 1,3-propane sultone (PS), vinyl sulfite (ES), tris(trimethylsilyl) borate (TMSB), tris(trimethylsilyl) phosphate (TMSP), lithium bis(oxalatoborate) (LiBOB), lithium difluorooxalatoborate (LiODFB), and lithium difluorobis(oxalatophosphate) (LiODFP); and / or the amount of the additive C added is 0.5 wt% to 3 wt% of the total mass of the electrolyte.

[0037] In addition to functional additives such as Additives A and B, the electrolyte provided by the present invention also includes a conventional additive, Additive C. These additives generally serve the same purpose: forming a film before the solvent, preventing the solvent from decomposing and forming the film first, which could cause battery bloating. However, different types of Additive C have different film-forming effects and compositions, so different additive combinations are selected for different project requirements. For example, to improve high-temperature performance, additives with higher film-forming impedance, such as 1,3-propane sultone (PS) and lithium bis(oxalatoborate) (LiBOB), are selected, while to improve low-temperature performance, low-impedance additives, such as ethylene sulfate (DTD) and ethylene sulfite (ES), are selected.

[0038] According to some embodiments of the present invention, the amount of additive A added is 0.5 wt% to 3 wt% of the total mass of the electrolyte. Specifically, the amount of additive A added can be 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, or 3 wt% of the total mass of the electrolyte.

[0039] According to some embodiments of the present invention, the amount of additive B added is 0.5 wt% to 3 wt% of the total mass of the electrolyte. Specifically, the amount of additive B added can be 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, or 3 wt% of the total mass of the electrolyte.

[0040] According to some embodiments of the present invention, the amount of the lithium salt added is 12 wt% to 18 wt% of the total mass of the electrolyte. Specifically, the amount of the lithium salt added can be 12 wt%, 13%, 14% wt%, 15% wt%, 16% wt%, 17% wt%, or 18% wt% of the total mass of the electrolyte.

[0041] According to some embodiments of the present invention, the amount of the non-aqueous organic solvent added is 70 wt % to 80 wt % of the total mass of the electrolyte.

[0042] In a second aspect, the present invention provides a method for preparing the electrolyte as described above, wherein the preparation method is:

[0043] The lithium salt and the additive are added to the non-aqueous organic solvent and mixed evenly to obtain the electrolyte.

[0044] In a third aspect, the present invention provides a lithium-ion battery comprising the electrolyte described above.

[0045] According to some embodiments of the present invention, the lithium-ion battery further includes a positive electrode sheet, a negative electrode sheet, and a separator.

[0046] According to some embodiments of the present invention, the active material of the positive electrode sheet is at least one of lithium manganese oxide, lithium iron phosphate, nickel cobalt lithium manganese oxide ternary material, lithium nickel manganese oxide, and lithium-rich manganese-based material.

[0047] According to some embodiments of the present invention, the active material of the negative electrode sheet is at least one of graphite, hard carbon, soft carbon, mesophase carbon microbeads, silicon-based negative electrode materials and lithium-containing metal composite oxide materials.

[0048] The present invention will be further described below through some specific examples.

[0049] Unless otherwise specified, the experimental methods used in the following examples are conventional methods; the reagents, materials, etc. used in the following examples are all commercially available unless otherwise specified.

[0050] The compounds I to IV described in the following examples and comparative examples are the following compounds:

[0051]

[0052] Example 1

[0053] Lithium-ion battery preparation

[0054] (1) Preparation of positive electrode sheet

[0055] The positive electrode active material lithium nickel cobalt manganese oxide (NCM), the binder polyvinylidene fluoride (PVDF), and the conductive agent acetylene black were mixed in a weight ratio of 96.5:2:1.5, N-methylpyrrolidone (NMP) was added, and the mixture was stirred under the action of a vacuum mixer until the mixed system became a positive electrode slurry with uniform fluidity; the positive electrode slurry was evenly coated on an aluminum foil with a thickness of 7 μm; the coated aluminum foil was baked in an oven with 5 different temperature gradients, and then dried in an oven at 120°C for 8 hours, and then rolled and slit to obtain a positive electrode sheet.

[0056] (2) Preparation of negative electrode sheet

[0057] The negative electrode active material artificial graphite, thickener sodium carboxymethyl cellulose (CMC-Na), binder styrene-butadiene rubber, conductive agent acetylene black, and conductive agent single-walled carbon nanotube (SWCNT) were mixed in a weight ratio of 95.9:1:2:1:0.1, and deionized water was added to obtain a negative electrode slurry under the action of a vacuum mixer; the negative electrode slurry was evenly coated on a copper foil with a thickness of 6 μm; and the negative electrode sheet was obtained after drying (temperature: 85°C, time: 5 h), rolling and die-cutting.

[0058] (3) Preparation of electrolyte

[0059] In an argon-filled glove box (moisture <10 ppm, oxygen <1 ppm), ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed in a mass ratio of 25:5:65:5. 14.5 wt.% of fully dried lithium salt LiPF6, 0.5 wt.% of compound I, 0.5 wt.% of additive B, 1 wt% of ethylene sulfate (DTD), and 2 wt% of 1,3-propane sultone (PS) were quickly added to the mixed solution and stirred to obtain an electrolyte (see Table 1 for the electrolyte composition).

[0060] (4) Preparation of diaphragm

[0061] A coated polyethylene diaphragm with a thickness of 8 μm was selected.

[0062] (5) Preparation of lithium-ion batteries

[0063] The positive electrode sheet, separator, and negative electrode sheet prepared above are wound to obtain a bare cell without liquid injection; the bare cell is placed in an outer packaging foil, and the electrolyte prepared in step (3) is injected into the dried bare cell. After vacuum packaging, standing, forming, shaping, sorting and other processes, the desired lithium-ion battery is obtained.

[0064] Examples 2 to 13

[0065] The preparation methods of the positive electrode sheet, negative electrode sheet, separator, and lithium-ion battery in Examples 2 to 13 are the same as those in Example 1, except that the additives in the electrolyte are different. For the specific composition of the electrolyte, see Table 1 (the non-aqueous organic solvent and lithium salt in the electrolyte are the same as those in Example 1).

[0066] Comparative Examples 1-5

[0067] The preparation methods of the positive electrode sheet, negative electrode sheet, separator and lithium-ion battery in Comparative Examples 1 to 5 are the same as those in Example 1, except that the additives in the electrolyte are different. For the specific composition of the electrolyte, see Table 1 (the non-aqueous organic solvent and lithium salt in the electrolyte are the same as those in Example 1).

[0068] Table 1 Types and amounts of additives in the electrolytes of Comparative Examples 1 to 5 and Examples 1 to 13

[0069]

[0070]

[0071] The electrochemical performance of the lithium-ion batteries obtained in the above comparative examples 1 to 5 and examples 2 to 13 was tested:

[0072] (1) Acidity test: The electrolytes of the above examples and comparative examples were sampled for acidity testing, and then placed in sealed aluminum bottles. The aluminum bottles were vacuum-sealed with aluminum-plastic film and then stored in a thermostat set at 60° C. for 15 days. After that, the electrolyte acidity was sampled and tested.

[0073] (2) 55℃ high temperature cycling test: The obtained battery was placed in a (55±2)℃ environment and allowed to stand for 2-3 hours. When the battery body reached (55±2)℃, the battery was charged to an upper limit voltage of 4.25V at a constant current and constant voltage of 1C, with a cutoff current of 0.05C. After the battery was fully charged, it was left for 5 minutes and then discharged at a constant current of 1C to a cutoff voltage of 3.0V. The highest discharge capacity of the first three cycles was recorded as the initial capacity Q1. When the cycle reached 300 cycles, the last discharge capacity of the battery was recorded as Q2. The capacity retention rate of the battery was calculated and the results were recorded as shown in Table 2. The calculation formula used is as follows: Capacity retention rate (%) = Q2 / Q1×100%.

[0074] (3) 85℃ high temperature test: The obtained battery was placed in a (25±2)℃ environment, and the formed battery was charged at 1C constant current and constant voltage to an upper limit voltage of 4.25V, with a cutoff current of 0.05C, and then discharged to 3.0V with 1C constant current, and then charged at 1C constant current and constant voltage to an upper limit voltage of 4.25V, with a cutoff current of 0.05C. After being placed in an 85℃ environment for 12 hours, the gas composition test was performed using a gas chromatograph.

[0075] (4) Normal temperature DCIR test: At 25±2°C, the battery was fully charged at 1C, then adjusted to 50% SOC, discharged at 2C for 15s, and charged at 2C for 15s. The DCIR test results are shown in Table 2.

[0076] Table 2 Test results of lithium ion batteries of Comparative Examples 1 to 5 and Examples 2 to 13

[0077]

[0078]

[0079] It can be seen from the results of Comparative Examples 1-5 and Example 1 that the high-temperature performance can be significantly improved without significantly increasing DCIR by using additives A and B in combination. It is speculated that the possible mechanism for producing this effect is: the -C≡N functional group in additive A having the structure shown in Formula 1 can combine with H2O in the electrolyte, reducing the decomposition reaction of LiPF6 to produce Lewis strong acid PF5 when it comes into contact with water, but some HF will still be generated. At this time, the -Si contained in the functional additive B added can further remove HF in the electrolyte, reduce the acidity of the system, and reduce the damage to the interface film caused by side reactions. Moreover, the -P radicals in additives A and additive B can combine with the active oxygen in the system, reduce the dissolution caused by the combination of transition metals and active oxygen, and stabilize the structure of the positive electrode material. By using the two functional additives in combination, not only can a stable interface film be formed, but the acidity in the electrolyte is also significantly reduced, thereby improving the high-temperature performance of the lithium-ion battery.

[0080] It can be seen from the results of Comparative Examples 2-3, Examples 1-2 and Examples 6-7 that the optimal range of the content of Additive A is 0.5wt%-3wt%. It is speculated that the possible mechanism for this effect is: when the content of functional additive A is too low, H2O in the electrolyte cannot be effectively removed, resulting in no significant improvement in performance; when the content of additive A is too high, although it can improve film formation stability and cycle performance, it will increase DCIR internal resistance and may deteriorate low-temperature performance.

[0081] It can be seen from the results of Comparative Examples 4-5, Examples 2 and Examples 8-10 that the optimal range of the content of Additive B is 0.5wt%-3wt%. It is speculated that the possible mechanism for producing this effect is: when the content of Additive B is too low, it cannot further effectively remove the possible HF, resulting in failure to prevent its damage to the interface film; when the content of Additive B is too high, the DCIR internal resistance will increase, which may deteriorate the low-temperature performance.

[0082] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. An electrolyte, characterized in that: The electrolyte comprises: lithium salts, non-aqueous organic solvents and additives; The additives include additive A and additive B, and the chemical structure of additive A is shown in Formula 1: Wherein, R1 is selected from halogen, substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkynyl, substituted or unsubstituted cycloalkyl, substituted or unsubstituted alkoxy; if substituted, the substituent is any one of C1-C5 alkyl, C2-C5 alkenyl, C2-C5 alkynyl, C3-C5 cycloalkyl, and halogen; The chemical structural formula of the additive B is shown in Formula 2: The amount of the additive A added is 0.5 wt% to 3 wt% of the total mass of the electrolyte, and the amount of the additive B added is 0.5 wt% to 3 wt% of the total mass of the electrolyte.

2. The electrolyte according to claim 1, characterized in that The lithium salt is lithium hexafluorophosphate; Or the lithium salt includes lithium hexafluorophosphate and at least one of lithium difluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(oxalatoborate) and lithium difluorooxalatoborate.

3. The electrolyte according to claim 1, characterized in that The non-aqueous organic solvent is selected from any two or more of propylene carbonate, ethyl methyl carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, fluoroethylene carbonate, γ-butyrolactone, sulfolane, methyl formate, ethyl formate, propyl formate, butyl formate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, and butyl butyrate.

4. The electrolyte according to claim 1, characterized in that The additive A is selected from at least one of the following compounds I to IV:

5. The electrolyte according to claim 1, characterized in that The additives also include additive C; The additive C is selected from at least one of vinylene carbonate (VC), fluoroethylene carbonate (FEC), vinyl ethylene carbonate (VEC), ethylene sulfate (DTD), 1,3-propane sultone (PS), vinyl sulfite (ES), tris(trimethylsilyl)borate (TMSB), tris(trimethylsilyl)phosphate (TMSP), lithium bis(oxalatoborate) (LiBOB), lithium difluorooxalatoborate (LiODFB), and lithium difluorobis(oxalatophosphate) (LiODFP); and / or The amount of the additive C added is 0.5 wt% to 3 wt% of the total mass of the electrolyte.

6. The electrolyte according to claim 1, characterized in that The amount of the lithium salt added is 12 wt% to 18 wt% of the total mass of the electrolyte; and / or The amount of the non-aqueous organic solvent added is 70 wt% to 80 wt% of the total mass of the electrolyte.

7. The method for preparing an electrolyte according to any one of claims 1 to 6, characterized in that: The preparation method is: The lithium salt and the additive are added to the non-aqueous organic solvent and mixed evenly to obtain the electrolyte.

8. A lithium-ion battery, characterized in that: The lithium ion battery comprises the electrolyte according to any one of claims 1 to 7.

9. The lithium-ion battery according to claim 8, characterized in that It also includes positive electrode sheet, negative electrode sheet and separator.

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