Lithium ion battery electrolyte, lithium ion battery, lithium ion battery pack and lithium ion battery pack

Abstract

The invention provides a lithium ion battery electrolyte, a lithium ion battery, a lithium ion battery pack and a lithium ion battery pack, and relates to the technical field of lithium ion battery preparation. The lithium ion battery electrolyte comprises hydrofluoroether and lithium salt, the mass percent of the hydrofluoroether in the electrolyte is 30%-36%, the mass percent of the lithium salt in the electrolyte is 20%-25%, and the lithium salt is selected from at least one of lithium bis (fluorosulfonyl) imide or lithium bis (trifluorosulfonyl) imide. The side reaction between the lithium ion battery electrolyte and the silicon-carbon negative electrode material is small, the viscosity and the density are small, and the ionic conductivity is high, so that the electrochemical performance and the cycling stability of a battery cell prepared from the electrolyte are excellent.

Description

Technical Field

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

[0002] Lithium-ion battery is a high energy density, lightweight, environmentally friendly battery, widely used in mobile power, electric vehicles, drones, smart wearables and other fields. Among them, the negative electrode material is one of the key factors that determine battery performance. The negative electrode material of traditional lithium-ion batteries is graphite, which has a low theoretical specific capacity and a long charge and discharge time, which limits the energy density and cycle life of the battery. The high specific energy lithium-ion power battery with silicon-carbon composite material as the negative electrode has a higher theoretical specific capacity, which is expected to significantly improve the energy density and power density of the battery.

[0003] However, silicon-carbon composite materials have problems such as capacity decay and volume expansion, and higher performance electrolytes are needed to match silicon-carbon composite materials to reduce the capacity decay and volume expansion caused by silicon-carbon composite materials. At present, the common high-performance commercial lithium-ion battery electrolytes include carbonate-based main solvents and lithium salts with a mass percentage of 9% to 13%. Although the electrolyte improves the performance of the battery to a certain extent, the electrolyte cannot inhibit the side reactions with the silicon-carbon negative electrode material. In order to inhibit the side reactions with the silicon-carbon negative electrode material, the existing scheme is to increase the lithium salt concentration to a lithium salt mass percentage of more than 40% in the electrolyte, so that the solvation structure of the electrolyte changes, thereby reducing the reaction activity between the electrolyte and the negative electrode material. However, increasing the mass percentage of lithium salt in the electrolyte will lead to excessively high viscosity of the electrolyte, resulting in poor electrochemical performance and cycle stability of the battery cell and excessive cost. Therefore, providing an electrolyte with a low mass percentage of lithium salt in the electrolyte and a small side reaction with the silicon-carbon negative electrode material has become a technical problem that technicians in the field need to solve urgently. Summary of the invention

[0004] 1. Technical issues to be solved

[0005] In view of the deficiencies in the prior art, the present invention provides a lithium ion battery electrolyte, a lithium ion battery, a lithium ion battery group and a lithium ion battery pack, which solve the technical problem of large side reactions between the existing lithium ion battery electrolyte and the silicon-carbon negative electrode material.

[0006] (II) Technical solution

[0007] To achieve the above objectives, the present invention is implemented through the following technical solutions:

[0008] In a first aspect, the present invention provides a lithium-ion battery electrolyte, comprising a hydrofluoroether and a lithium salt, wherein the hydrofluoroether accounts for 30% to 36% by weight of the electrolyte, the lithium salt accounts for 20% to 25% by weight of the electrolyte, and the lithium salt is selected from at least one of lithium bis(fluorosulfonyl)imide or lithium bis(trifluorosulfonyl)imide.

[0009] The lithium-ion battery electrolyte includes hydrofluoroether and lithium salt, wherein the lithium salt accounts for 20% to 25% of the electrolyte by mass, which is a relatively low percentage of the electrolyte by mass. As a "non-solvent", hydrofluoroether does not participate in the dissociation of lithium salt, but is miscible with other solvents (carbonates, sulfates, carboxylates, phosphates, ethers, etc.), so that the anions (lithium ions, etc.) and cations (hexafluorophosphate ions, bisfluorosulfonyl imide ions, etc.) in the electrolyte of the present application are more closely connected with the good solvent (cyclic carbonates, cyclic sulfates, cyclic carboxylates, cyclic phosphates, etc., ethers, etc.) molecules. The solvation structure is formed so that when the lithium salt accounts for only 20% to 25% of the electrolyte by mass, the solvation structure of the electrolyte can achieve the solvation structure of the electrolyte when the lithium salt accounts for 40% of the electrolyte by mass. Therefore, the free solvent molecules in the electrolyte of the present application are reduced, and the electrolyte has less chance to contact and react with the electrode surface, thereby reducing the side reaction between the electrolyte and the silicon-carbon negative electrode material. In addition, the viscosity and density of the electrolyte of the present application are relatively small, and the ionic conductivity is high. Therefore, the battery cell prepared by the electrolyte of the present application has excellent electrochemical performance and cycle stability, and low cost. When the lithium salt is selected from one or two of lithium bis(fluorosulfonyl)imide and lithium bis(trifluorosulfonyl)imide as the main salt, the close-shallion pair (CIP) formed by the change of the solvation structure can react on the electrode surface to form a SEI layer with a high lithium fluoride content. This substance is considered to be a more ideal SEI component, with good ion permeability and electrochemical and chemical stability, and can also improve the mechanical strength of the network SEI layer formed by the ring-opening cross-linking of fluorovinylene carbonate. When the lithium salt is selected from one or two of lithium bis(fluorosulfonyl)imide and lithium bis(trifluorosulfonyl)imide as the main salt, the required lithium salt concentration can be easily reached, and it is not easy to precipitate lithium salt due to oversaturation at low temperature, thereby improving the low temperature stability of the battery cell.

[0010] As a preferred embodiment, the electrolyte further comprises a film-forming additive, the mass percentage of the film-forming additive in the electrolyte is 0.5% to 5.0%, and the structural formula of the film-forming additive is shown in formula (1):

[0011]

[0012] Wherein, in formula (I), R1 to R3 are each independently selected from substituted or unsubstituted C1 to C6 alkyl, substituted or unsubstituted C1 to C4 alkynyl, phosphate, amino, cyano or substituted or unsubstituted C6 to C12 Any of the aryl groups, and the hydrogen on the alkyl, alkynyl and aryl groups may be optionally substituted by halogen.

[0013] The film-forming additive has a high resistance to reduction, which can ensure that it is not consumed by the reaction on the negative electrode side. Among them, the fluorosulfonyl group can be oxidized on the positive electrode side at a higher potential and form a protective solid-electrolyte interphase (SEI), which can prevent the positive electrode from being attacked by the free acid in the electrolyte, avoid the oxidation of other components of the electrolyte on the positive electrode side, and inhibit nickel dissolution. The silane group in the film-forming additive can capture the free acid in the electrolyte, prevent the free acid from reacting with the high content of fluoroethylene carbonate in the electrolyte to produce hydrofluoric acid, thereby avoiding its corrosion of the SEI on the surface of the positive and negative electrode particles and extending the battery life.

[0014] As a preferred embodiment, in the formula (I), R1 to R3 are each independently selected from substituted or unsubstituted C1 to C3 alkyl, unsubstituted C1 to C4 alkynyl, phosphate, amino, cyano or unsubstituted C6 to C 12 Any of the aryl groups, and the hydrogen on the alkyl group may be optionally substituted by halogen.

[0015] As a preferred embodiment, in the formula (I), R1 to R3 are each independently selected from any one of methyl, ethyl, tert-butyl, perfluoromethyl, ethynyl, phosphate, amino, cyano or phenyl, so that the film-forming additive containing the substituted group has a stronger binding effect on the free acid, thereby improving the cycle capacity retention rate and cycle stability of the lithium-ion battery.

[0016] As a preferred embodiment, the electrolyte also includes a diluent, and the diluent is selected from one or more of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,1,2,2-tetrafluoroethyl ethyl ether, 1-(1,1,2,2-tetrafluoroethoxy)propane, 2,2,2-trifluoroethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, and 2-methyl-1-(1,1,2,2-tetrafluoroethoxy)propane, and the mass percentage of the diluent in the electrolyte is 30% to 40%.

[0017] As a preferred embodiment, the electrolyte further includes an auxiliary additive, and the auxiliary additive is selected from one or more of vinylene carbonate, lithium difluorophosphate, lithium difluorooxalatoborate, vinyl sulfate, cyclic sulfate, cyclic sulfite, tris(trimethylsilyl)borate, tris(trimethylsilyl)phosphate or fluoroethylene carbonate, and the auxiliary additive accounts for 0.1% to 5% of the electrolyte by weight, and more preferably, the weight of the auxiliary additive accounts for 0.5% to 1.5% of the lithium ion battery electrolyte by weight, which can further improve the cycle performance, low temperature performance and flame retardant effect of the lithium ion electrolyte, thereby improving the electrochemical performance and cycle performance of the lithium ion battery.

[0018] As a preferred embodiment, the lithium salt further includes one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, and lithium bis(oxalatoborate).

[0019] As a preferred embodiment, the electrolyte also includes an organic solvent, and the organic solvent is selected from one or more of ethylene carbonate, fluoroethylene carbonate, propylene carbonate, ethyl methyl carbonate, dimethyl carbonate, butylene carbonate, diethyl carbonate, propyl acetate, ethyl propionate or propyl propionate, and the mass percentage of the organic solvent in the electrolyte is 5% to 50%.

[0020] As a preferred embodiment, the hydrofluoroether is 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, and its preferred usage is 30% to 36% of the mass of the electrolyte, thereby improving the ionic conductivity of the lithium ion electrolyte, thereby improving the electrochemical performance and cycle stability of the lithium ion battery.

[0021] In a second aspect, the present invention further provides a lithium-ion battery, which includes a silicon-based negative electrode material, a ternary positive electrode material and an electrolyte, wherein the electrolyte is the lithium-ion battery electrolyte of the first aspect. Based on the reasons described above, the lithium-ion battery exhibits excellent electrochemical performance, cycle stability and a high cycle capacity retention rate.

[0022] The above-mentioned silicon-based negative electrode material can be: nano-silicon negative electrode, silicon-oxygen negative electrode, silicon-carbon negative electrode or silicon alloy negative electrode, and the ternary positive electrode material can be nickel-cobalt-manganese ternary materials with various nickel contents (such as NCM111, NCM523, NCM622 or NCM811) and nickel-cobalt-aluminum (NCA) materials.

[0023] In a third aspect, the present invention further provides a lithium ion battery pack, the lithium ion battery pack comprising the lithium ion battery of the second aspect. The lithium ion battery pack has a higher energy density and can provide a higher capacity and voltage.

[0024] In a fourth aspect, the present invention further provides a lithium-ion battery pack, the lithium-ion battery pack comprising the lithium-ion battery pack of the third aspect. The lithium-ion battery pack can achieve high energy storage and release and has high safety performance. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are clearly and completely described. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0026] The embodiments of the present application provide a lithium-ion battery electrolyte, a lithium-ion battery, a lithium-ion battery pack and a lithium-ion battery pack, thereby solving the technical problem of large side reactions between existing lithium-ion battery electrolytes and silicon-carbon negative electrode materials, and achieving the technical effect of excellent electrochemical performance and cycle stability and low cost of the battery cells prepared by the electrolyte of the present application.

[0027] The technical solution in the embodiment of the present application is to solve the above technical problems, and the overall idea is as follows:

[0028] In the existing lithium-ion batteries, the silicon-based negative electrode materials undergo drastic volume expansion during the charge and discharge process, and the protective interface formed on the surface of the negative electrode material during the battery cell formation stage - the electrolyte intermediate phase (Solid-electrolyte inter-phase, hereinafter referred to as SEI) is repeatedly ruptured, resulting in continuous side reactions between the electrolyte and the negative electrode material, which ultimately causes the problem of poor cycle performance of the lithium-ion battery. Although increasing the mass percentage of lithium salt in the electrolyte can reduce the reaction activity between the electrolyte and the negative electrode material, it will cause the electrolyte viscosity to be too high, thereby reducing the electrochemical performance and cycle stability of the battery cell and increasing the cost.

[0029] In order to solve this problem, the lithium-ion battery electrolyte of the present invention includes hydrofluoroether and lithium salt, wherein the lithium salt accounts for 20% to 25% by mass of the electrolyte, and a lower lithium salt concentration is used while adding hydrofluoroether. The reaction activity between the electrolyte and the electrode is reduced by adjusting the solvation structure, thereby reducing the side reaction between the electrolyte and the silicon-carbon negative electrode material. In addition, the electrolyte of the present application has low viscosity and density and high ionic conductivity. Therefore, the battery cell prepared by the electrolyte of the present application has excellent electrochemical performance and cycle stability and low cost.

[0030] In addition, the lithium ion battery electrolyte of the present invention further comprises a film-forming additive, and the structure of the film-forming additive is:

[0031]

[0032] wherein R1 to R3 are each independently selected from substituted or unsubstituted C1 to C6 alkyl, substituted or unsubstituted C1 to C4 alkynyl, phosphate, amino, cyano or substituted or unsubstituted C6 to C 12 Aryl, and the hydrogen on the alkyl, alkynyl and aryl groups can be optionally replaced by halogen. The film-forming additive has a high resistance to reduction, which can ensure that it is not consumed by the reaction on the negative electrode side. Among them, the fluorosulfonyl group can be oxidized on the positive electrode side at a higher potential and form a protective solid-electrolyte interphase (SEI-electrolyte inter-phase, hereinafter referred to as SEI), which can prevent the positive electrode from being attacked by the free acid in the electrolyte, avoid the oxidation of other components of the electrolyte on the positive electrode side, and inhibit nickel dissolution. The silane group in the film-forming additive can capture the free acid in the electrolyte, prevent it from reacting with the high content of fluoroethylene carbonate in the electrolyte to produce hydrofluoric acid, thereby avoiding its corrosion of the SEI on the surface of the positive and negative electrode particles and extending the battery life.

[0033] In order to better understand the above technical solution, the above technical solution will be described in detail below in conjunction with specific implementation methods.

[0034] Example 1

[0035] This embodiment provides a method for preparing a lithium ion battery electrolyte, which is as follows:

[0036] A lithium-ion battery electrolyte was prepared in a glove box filled with argon (oxygen content ≤ 5ppm, water content ≤ 10ppm), wherein the organic solvents were ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), fluoroethylene carbonate (FEC) and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (HFE), and the organic solvents were mixed uniformly in a mass ratio of 6:8:17:8:17:44. Among them, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (HFE) accounted for 35% of the mass percentage of the electrolyte.

[0037] Then, lithium salt is added to the mixed solution, the mass of which is lithium bis(fluorosulfonyl)imide (LiFSI), accounting for 22% of the total mass of the electrolyte, and stirred evenly to fully dissolve. After the mixed solution returns to room temperature, auxiliary additives are added, which are vinylene carbonate (VC) and lithium difluorooxalatoborate (LiODFB), accounting for 0.5% and 2.0% of the total mass of the electrolyte, respectively.

[0038] Finally, a film-forming additive is added to the mixed solution, the structural formula of which is shown in formula (II). The amount of the film-forming additive is 1wt% of the total mass of the lithium-ion battery electrolyte. The mixture is stirred and mixed thoroughly.

[0039]

[0040] The film-forming additive represented by formula (II) was purchased from Liv Biotech.

[0041] The prepared electrolyte is used to prepare a lithium-ion battery as follows:

[0042] The prepared electrolyte is injected into a soft-pack battery with a designed capacity of 5 ampere hours and vacuum packaged. The positive electrode of the soft-pack battery is a nickel-cobalt-manganese ternary material, and the negative electrode is a silicon oxide-graphite mixed material. Then the battery is sequentially placed, formed, aged, and divided into different capacity steps to prepare a lithium-ion battery.

[0043] Example 2

[0044] The only difference from Example 1 is that the film-forming additive is different. The structural formula of the film-forming additive in this example is shown in Formula (III):

[0045]

[0046] The film-forming additive represented by formula (III) was purchased from Liv Biotech.

[0047] Example 3

[0048] The only difference from Example 1 is that the film-forming additive is different. The structure of the film-forming additive in this example is shown in formula (IV):

[0049]

[0050] The film-forming additive represented by formula (IV) was purchased from Liv Biotech.

[0051] Comparative Example 1

[0052] The only difference from Example 1 is that the mass ratio of the organic solvents ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), fluoroethylene carbonate (FEC) and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (HFE) is 8:11:24:11:24:22, wherein the mass percentage of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (HFE) in the electrolyte is 20%.

[0053] Comparative Example 2

[0054] The only difference from Example 1 is that the organic solvent does not contain 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (HFE), and the mass ratio of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and fluoroethylene carbonate (FEC) is 10.7:14.3:30.4:14.3:30.3.

[0055] Comparative Example 3

[0056] The only difference from Example 1 is that lithium bis(fluorosulfonyl)imide (LiFSI) accounts for 40wt% of the total mass of the lithium-ion battery electrolyte, the organic solvent does not contain 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (HFE), and the mass ratio of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC) and fluoroethylene carbonate (FEC) is 10.7:14.3:30.4:14.3:30.3. Others are the same as Example 1.

[0057] Comparative Example 4

[0058] The only difference from Example 1 is that there is no film-forming additive represented by structural formula (II).

[0059] Comparative Example 5

[0060] The only difference from Example 1 is that the amount of the film-forming additive used accounts for 0.4 wt % of the total mass of the lithium-ion battery electrolyte.

[0061] Comparative Example 6

[0062] The only difference from Example 1 is that the amount of the film-forming additive used accounts for 5.5 wt % of the total mass of the lithium-ion battery electrolyte.

[0063] Comparative Example 7

[0064] The only difference from Example 1 is that the amount of the film-forming additive used accounts for 6.0 wt % of the total mass of the lithium-ion battery electrolyte.

[0065] Comparative Example 8

[0066] The only difference from Example 1 is that the lithium salt lithium bis(fluorosulfonyl)imide (LiFSI) accounts for 11.5 wt % of the total mass of the lithium ion battery electrolyte.

[0067] Performance Testing:

[0068] The products of the embodiments and comparative examples were subjected to the following performance tests:

[0069] 1. Cycle performance test: Place the lithium-ion battery at a constant temperature of 25°C and 45°C respectively, and perform charge and discharge cycle test at 1C0 / 1C0 (C0 is the cell capacity), and record the capacity retention rate and cycle number.

[0070] 2. Cyclic impedance (DCR) growth test: Take the battery cell that has been cycle tested at 25°C, leave it for 1 hour in a fully charged state, and then discharge it at a constant current rate of 1C1, with the cut-off condition being that the discharge capacity reaches 0.5×C1Ah. After leaving it for 1 hour, discharge it at a constant current rate of 5C1 for 10 seconds, and after leaving it for 40 seconds, charge it at a constant current rate of 5C1 for 10 seconds. After leaving it for 60 minutes, discharge it at a constant current rate of 1C1 to a lower limit voltage of 2.5V, and after leaving it for 10 minutes, charge it at a constant current and constant voltage rate of 1C1 to an upper limit voltage of 4.25V, and continue the cycle test. This test is performed once before the start of the cycle, and then once every 50 cycles, where C1 is the last discharge capacity before the test.

[0071] The performance test results of the products of the above embodiments and comparative examples are shown in Table 1.

[0072] Table 1 Performance test results of the products of the embodiments and comparative examples

[0073]

[0074] From Table 1, by analyzing the test results of Example 1, Example 2 and Example 3, it can be found that when the film-forming additive of structural formula (II) (Example 1), the film-forming additive of structural formula (III) (Example 2) or the film-forming additive of structural formula (IV) (Example 3) of the present invention is used, the lithium battery exhibits excellent cycle performance and electrochemical performance; and when structural formula (II) is used, due to its stronger binding effect on free acid, the cycle capacity retention rate of the lithium battery is higher and the battery ohmic impedance is more stable.

[0075] From the test results of Example 1, Comparative Example 1 and Comparative Example 2, it can be found that when the amount of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether is reduced, its amount accounts for 20% of the mass percentage of the electrolyte, and when it is lower than 30% (Comparative Example 1), because the electrolyte does not form an ideal solvation structure to reduce the reaction activity, and there is no CIP to induce the formation of a SEI layer rich in lithium fluoride, the cycle capacity retention rate and battery ohmic impedance of the lithium battery are poor. When 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether is not added (Comparative Example 2), in addition to being unable to form an ideal solvation structure, the viscosity of the electrolyte is too high and the ionic conductivity is reduced, resulting in poor cycle capacity retention rate and battery ohmic impedance of the lithium battery. In summary, by comparing the test results of Example 1, Comparative Example 1, and Comparative Example 2, it can be found that the cycle capacity retention rate and battery ohmic impedance performance of the lithium battery prepared by the electrolyte with a low amount of hydrofluoroether or without hydrofluoroether are poor.

[0076] Comparing Example 1 with Comparative Example 3, the cycle capacity retention rate and battery ohmic impedance performance of the lithium battery prepared by the electrolyte of Example 1 of the present application are comparable to those of the lithium battery prepared by the electrolyte in which lithium bis(fluorosulfonyl)imide (LiFSI) accounts for 40 wt% of the total mass of the lithium-ion battery electrolyte.

[0077] From Table 1, it can be found that the electrolyte of the present invention includes the film-forming additive shown in structural formula (II), and the obtained lithium battery still has a high capacity retention rate and the battery ohmic impedance remains stable after 200 cycles of charge and discharge at 25°C and 45°C, respectively, and the excellent electrochemical performance and cycle stability are shown. When the film-forming additive shown in structural formula (II) is not added (Comparative Example 4), due to the lack of protection of the surface of the positive electrode material and the inability to suppress the free acid in the electrolyte, the cycle capacity retention rate and battery ohmic impedance of the lithium battery are poor.

[0078] By analyzing the test results of Example 1, Comparative Example 5, Comparative Example 6 and Comparative Example 7, it can be found that when the amount of the film-forming additive represented by the structural formula (II) accounts for 0.4wt% of the total mass of the lithium-ion battery electrolyte (Comparative Example 5), due to the low concentration, an ideal SEI layer cannot be formed on the positive electrode surface, resulting in a poor cycle capacity retention rate of the lithium battery. When the amount of the additive represented by the structural formula (II) accounts for 5.5% or 6.0% of the total mass of the lithium-ion battery electrolyte (Comparative Examples 6 and 7), since the positive electrode SEI layer has been formed, the redundant additive cannot continue to react, and thus the cycle capacity retention rate of the lithium battery is not further improved.

[0079] By analyzing the test results of Example 1 and Comparative Example 8, it can be found that when the lithium salt mass ratio of the electrolyte is reduced to 11.5% (Comparative Example 8), due to the low concentration of lithium salt, it fails to change the solvation structure and cannot form a SEI layer dominated by lithium fluoride, resulting in poor cycle capacity retention and battery ohmic impedance performance of the lithium battery.

[0080] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

[0081] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them. Although the present invention is described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some of the technical features therein by equivalents. However, these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention. Anything not described in detail in the present invention is a well-known technology to those skilled in the art.

Claims

1. A lithium ion battery electrolyte, characterized in that: The invention comprises hydrofluoroether and lithium salt, wherein the hydrofluoroether accounts for 30% to 36% by weight of the electrolyte, the lithium salt accounts for 20% to 25% by weight of the electrolyte, and the lithium salt is selected from at least one of lithium bis(fluorosulfonyl)imide and lithium bis(trifluorosulfonyl)imide.

2. The lithium ion battery electrolyte according to claim 1, characterized in that The electrolyte further comprises a film-forming additive, wherein the film-forming additive accounts for 0.5% to 5.0% by mass of the electrolyte, and the structural formula of the film-forming additive is shown in formula (1): Wherein, in formula (I), R1 to R3 are each independently selected from substituted or unsubstituted C1 to C6 alkyl, substituted or unsubstituted C1 to C4 alkynyl, phosphate, amino, cyano or substituted or unsubstituted C6 to C 12 Any of the aryl groups, and the hydrogen on the alkyl, alkynyl and aryl groups may be optionally substituted by halogen.

3. The lithium ion battery electrolyte according to claim 2, characterized in that In the formula (I), R1 to R3 are each independently selected from substituted or unsubstituted C1 to C3 alkyl, unsubstituted C1 to C4 alkynyl, phosphate, amino, cyano or unsubstituted C6 to C 12 Any of the aryl groups, and the hydrogen on the alkyl group may be optionally substituted by halogen.

4. The lithium ion battery electrolyte according to claim 2, characterized in that In the formula (I), R1 to R3 are each independently selected from any one of a methyl group, an ethyl group, a tert-butyl group, a perfluoromethyl group, an ethynyl group, a phosphoric acid group, an amino group, a cyano group or a phenyl group.

5. The lithium ion battery electrolyte according to claim 1, characterized in that The electrolyte also includes a diluent, which is selected from one or more of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,1,2,2-tetrafluoroethyl ethyl ether, 1-(1,1,2,2-tetrafluoroethoxy)propane, 2,2,2-trifluoroethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, and 2-methyl-1-(1,1,2,2-tetrafluoroethoxy)propane, and the mass percentage of the diluent in the electrolyte is 30% to 40%.

6. The lithium ion battery electrolyte according to claim 1, characterized in that The electrolyte also includes auxiliary additives, which are selected from one or more of vinylene carbonate, lithium difluorophosphate, lithium difluorooxalatoborate, vinyl sulfate, cyclic sulfate, cyclic sulfite, tris(trimethylsilyl)borate, tris(trimethylsilyl)phosphate or fluoroethylene carbonate, and the auxiliary additives account for 0.1% to 5% of the electrolyte by mass.

7. The lithium ion battery electrolyte according to claim 1, characterized in that: The lithium salt further comprises one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, and lithium bis(oxalatoborate); The hydrofluoroether is 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

8. A lithium-ion battery comprising a silicon-based negative electrode material, a ternary positive electrode material and an electrolyte, characterized in that: The electrolyte is the lithium ion battery electrolyte according to any one of claims 1 to 7.

9. A lithium-ion battery pack, characterized in that: The lithium-ion battery pack comprises the lithium-ion battery according to claim 8.

10. A lithium-ion battery pack, characterized in that: The lithium-ion battery pack comprises the lithium-ion battery pack according to claim 9.

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