Electrolyte and lithium ion battery

Abstract

The application belongs to the technical field of power batteries, and specifically discloses an electrolyte and a lithium ion battery. The electrolyte comprises an electrolyte, a solvent and an additive, the additive at least comprises a first additive and a second additive, the first additive is a siloxyl compound containing an unsaturated bond as shown in formula (I), and the second additive is a carbodiimide compound as shown in formula (II). The combination of the two additives can effectively solve the negative influence caused by the expansion of the silicon negative electrode, improve the cycle performance and initial impedance of the battery, and improve the overall performance and safety of the battery.

Description

Technical Field

[0001] This invention relates to the field of power battery technology, and in particular to an electrolyte and a lithium-ion battery. Background Technology

[0002] Lithium-ion batteries are widely used in electric vehicles due to their high energy density and long cycle life. However, with the development of the electric vehicle industry, driving range has become a major limiting factor for the further development of lithium-ion batteries. Silicon anodes are widely considered the superior choice for next-generation products due to their high theoretical capacity. However, silicon anodes suffer from significant volume expansion during lithium insertion / extraction, leading to poor battery cycle performance. Furthermore, when conventional electrolytes are applied to silicon anodes, the SEI film continuously thickens during the expansion and contraction of the silicon anode, consuming active lithium and further degrading the cycle performance of the lithium-ion battery.

[0003] Therefore, developing new electrolytes suitable for use with silicon anode systems to improve the cycle performance of lithium-ion batteries and enhance their overall performance is beneficial for overcoming the limitations of existing technologies, thereby promoting the development of silicon anode system batteries and improving the commercial application prospects of silicon anodes. Summary of the Invention

[0004] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide an electrolyte and a lithium-ion battery. By adding new additives to the electrolyte and then applying them to the lithium-ion battery, the battery cycle performance can be improved, the overall battery performance can be enhanced, and the negative impact of the current silicon anode expansion can be solved, thereby improving the prospects for large-scale commercialization of silicon anodes.

[0005] To achieve the above and other related objectives, the present invention provides an electrolyte comprising an electrolyte, a solvent, and additives, wherein the additives include at least a first additive and a second additive, wherein the first additive is selected from siloxy compounds containing unsaturated bonds as shown in formula (I):

[0006]

[0007] In formula (I), R1, R2, R3, R4 and R5 are selected from at least one of tert-butyl, 1,1-dimethoxyethyl ether, or 1,1-diethylpropyl.

[0008] The second additive is selected from carbodiimide compounds with the general chemical formula (II):

[0009] R6-N=C=N-R7

[0010] (II),

[0011] In formula (II), R6 and R7 are selected from at least one of substituted or unsubstituted alkyl groups having 1 to 12 carbon atoms, substituted or unsubstituted alkenyl groups having 2 to 12 carbon atoms, or substituted or unsubstituted cycloalkyl groups having 3 to 12 carbon atoms; if substituted, the substituent is a halogen or an alkyl group having 1 to 12 carbon atoms.

[0012] Furthermore, based on the total mass of the electrolyte, the mass percentage of the first additive is 0.1% to 3%.

[0013] Furthermore, based on the total mass of the electrolyte, the mass percentage of the second additive is 0.01% to 1%.

[0014] Furthermore, the electrolyte is a lithium salt, which is selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(trifluoromethyl)sulfonylimide, lithium dioxalate borate, lithium difluorodioxalate phosphate, lithium difluorooxalate borate, lithium difluorophosphate, or lithium trifluoromethylsulfonate.

[0015] Furthermore, the lithium salt includes lithium hexafluorophosphate and lithium difluorosulfonylimide, and the mass percentage of lithium hexafluorophosphate in the electrolyte is greater than the mass percentage of lithium difluorosulfonylimide in the electrolyte.

[0016] Furthermore, based on the total mass of the electrolyte, the mass percentage of lithium hexafluorophosphate is 11% to 15%, and the mass percentage of lithium difluorosulfonylimide is 1% to 3%.

[0017] Furthermore, the solvent is selected from at least one of carbonate solvents, carboxylic acid ester solvents, ether solvents, or nitrile solvents.

[0018] The present invention also provides a lithium-ion battery comprising the electrolyte as described above.

[0019] Furthermore, the lithium-ion battery includes a negative electrode sheet, the negative electrode sheet includes a negative current collector and a negative active material layer coated on at least one side surface of the negative current collector, the negative active material layer includes a negative active material;

[0020] The negative electrode active material is selected from at least one of silicon, silicon oxide, or silicon carbide; or, the negative electrode active material includes a first negative electrode active component and a second negative electrode active component, wherein the first negative electrode active component is selected from at least one of silicon, silicon oxide, or silicon carbide, and the second negative electrode active component is selected from at least one of graphite, soft carbon, hard carbon, artificial graphite, or natural graphite.

[0021] Furthermore, the lithium-ion battery includes a positive electrode sheet, the positive electrode sheet includes a positive current collector and a positive active material layer coated on at least one surface of the positive current collector, the positive active material layer includes a positive active material;

[0022] The positive electrode active material is selected from at least one of lithium nickel manganese oxide, lithium iron phosphate, lithium manganese iron phosphate, lithium cobalt oxide, lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt manganese oxide, or lithium nickel cobalt aluminum oxide.

[0023] As described above, the electrolyte and lithium-ion battery of the present invention have the following beneficial effects:

[0024] 1. The present invention adds two additives to the electrolyte, namely the first additive, a siloxy compound containing unsaturated bonds as shown in formula (I), and the second additive, a carbodiimide compound as shown in formula (II). The combination of the two can effectively suppress the negative impact of silicon anode expansion. The first additive contains -Si-O-Si- groups that react with residual silanol groups on the silicon anode surface to form new Si-O-Si bonds, thus fixing the first additive to the silicon anode surface. The R groups in the first additive are sterically hindered groups (such as tert-butyl, 1,1-dimethoxyethyl ether, and 1,1-diethylpropyl). Their main function is to diffuse outwards due to steric hindrance when the silicon anode expands, significantly reducing the fresh exposed surface area caused by the volume expansion of the silicon anode. The first additive also contains unsaturated bonds, which can polymerize adjacent first additives, reducing the failure of the first additive due to the breaking of Si-O-Si bonds. Furthermore, the Si-O-Si bonds formed by the reaction of the first additive with silanol groups are easily attacked by hydrofluoric acid (HF) in the electrolyte, leading to the breaking of Si-O bonds and reducing the effectiveness of the first additive. Therefore, it is used in conjunction with a second additive. The main function of the second additive is to absorb water and acid in the electrolyte, reducing the impact of HF formation on the first additive.

[0025] 2. The present invention also limits the amount of additives in the electrolyte. Only by reasonably controlling the amount of the first additive and the second additive within a specific range can the negative impact of silicon anode expansion be effectively suppressed, and the best balance point be found between effectively improving battery cycle performance and initial impedance and ensuring battery performance, thereby effectively improving the overall performance and safety of the battery.

[0026] In summary, applying the electrolyte provided by this invention to lithium-ion batteries based on silicon anode systems can effectively solve the negative impact of silicon anode expansion, thereby effectively improving the overall performance of the battery and enhancing battery safety, thus improving the prospects for large-scale commercialization of silicon anodes. Detailed Implementation

[0027] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0028] In this invention, unless otherwise stated, the term "multiple" means two or more.

[0029] The character " / " indicates that the objects before and after it are in an "or" relationship. For example, A / B means: A or B.

[0030] The term "and / or" describes an association between objects, indicating that three relationships can exist. For example, A and / or B means: A or B, or A and B.

[0031] One embodiment of the present invention provides an electrolyte comprising an electrolyte, a solvent, and an additive, wherein the additive comprises at least a first additive and a second additive, and the first additive is selected from siloxy compounds containing unsaturated bonds as shown in formula (I):

[0032]

[0033] In formula (I), R1, R2, R3, R4 and R5 are selected from at least one of tert-butyl, 1,1-dimethoxyethyl ether, or 1,1-diethylpropyl.

[0034] The second additive is selected from carbodiimide compounds with the general chemical formula (II):

[0035] R6-N=C=N-R7

[0036] (II),

[0037] In formula (II), R6 and R7 are selected from at least one of substituted or unsubstituted alkyl groups having 1 to 12 carbon atoms, substituted or unsubstituted alkenyl groups having 2N12 carbon atoms, or substituted or unsubstituted cycloalkyl groups having 3N12 carbon atoms; if substituted, the substituent is a halogen or an alkyl group having 1 to 12 carbon atoms.

[0038] In lithium-ion batteries, the electrolyte plays a crucial role in conducting ions, providing ion channels, and maintaining chemical stability. The various components of the electrolyte can be categorized according to their function and dosage as electrolyte lithium salt, solvent, and additives. Lithium salt primarily provides lithium ions to form ion channels. In the entire electrochemical system of the battery, the directional movement of lithium ions and electrons generates electricity. Lithium salt has a significant impact on the energy density, power density, wide electrochemical window, cycle life, and safety performance of lithium batteries. The solvent dissolves the lithium salt and additives within it. Additives, added in small amounts to the electrolyte, are numerous and each plays a different role, such as improving the battery's high and low temperature performance, cycle performance, and film-forming properties.

[0039] In the above embodiments of the present invention, two additives are added to the electrolyte: a first additive, a siloxy compound containing unsaturated bonds as shown in formula (I), and a second additive, a carbodiimide compound as shown in formula (II). The combination of the two can effectively suppress the negative effects caused by the expansion of the silicon anode. The first additive contains -Si-O-Si- groups that react with residual silanol groups on the silicon anode surface to form new Si-O-Si bonds, thus fixing the first additive to the silicon anode surface. The R groups in the first additive are sterically hindered groups (such as tert-butyl, 1,1-dimethoxyethyl ether, and 1,1-diethylpropyl). Their main function is to diffuse outwards due to steric hindrance when the silicon anode expands, significantly reducing the fresh exposed surface area caused by the volume expansion of the silicon anode. The first additive also contains unsaturated bonds, which can polymerize adjacent first additives, reducing the failure of the first additive due to the breaking of Si-O-Si bonds. Furthermore, the Si-O-Si bonds formed by the reaction of the first additive with silanol groups are easily attacked by hydrofluoric acid (HF) in the electrolyte, leading to the breaking of Si-O bonds and reducing the effectiveness of the first additive. Therefore, it is used in conjunction with a second additive. The main function of the second additive is to absorb water and acid in the electrolyte, reducing the impact of HF formation on the first additive.

[0040] In some embodiments, the mass percentage of the first additive is 0.1% to 3%, preferably 0.1% to 1%, based on the total mass of the electrolyte. Excessive use of the first additive, exceeding the 3% threshold, will affect the battery's impedance and cycle performance. Conversely, insufficient use of the first additive, below the critical value of 0.1%, will not effectively improve battery cycle performance or reduce battery impedance.

[0041] In some embodiments, the mass percentage of the second additive is 0.01% to 1%, preferably 0.1% to 0.3%, based on the total mass of the electrolyte. If the amount of the second additive is too high, exceeding the 1% threshold, the cell performance cannot be further improved. Conversely, if the amount of the second additive is too low, below the critical value of 0.01%, the battery cycle performance and battery impedance cannot be effectively improved.

[0042] Therefore, by reasonably controlling the dosage of the first additive and the second additive within the scope defined in the above embodiments, the negative impact of silicon anode expansion can be effectively suppressed, and the best balance can be found between effectively improving battery cycle performance and initial impedance and ensuring battery performance, thereby effectively improving the overall performance and safety of the battery.

[0043] In some embodiments, the electrolyte is a lithium salt selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(trifluoromethyl)sulfonylimide, lithium dioxolane borate, lithium difluorodioxolane phosphate, lithium difluorooxolane borate, lithium difluorophosphate, or lithium trifluoromethylsulfonate.

[0044] In some embodiments, the lithium salt comprises lithium hexafluorophosphate and lithium bisfluorosulfonylimide, and the mass percentage of lithium hexafluorophosphate in the electrolyte is greater than the mass percentage of lithium bisfluorosulfonylimide in the electrolyte.

[0045] In some embodiments, based on the total mass of the electrolyte, the mass percentage of lithium hexafluorophosphate is 11% to 15%, and the mass percentage of lithium difluorosulfonylimide is 1% to 3%.

[0046] In some embodiments, the solvent is selected from at least one of carbonate solvents, carboxylic acid ester solvents, ether solvents, or nitrile solvents. Examples of carbonate solvents include ethylene carbonate, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, fluoroethylene carbonate, and polycarbonate. Examples of carboxylic acid ester solvents include ethyl formate, ethyl acetate, propyl acetate, ethyl propionate, and propyl propionate. Examples of ether solvents include ethylene glycol dimethyl ether and diethanol diethyl ether. Examples of nitrile solvents include acetonitrile, propionitrile, butyronitrile, and valerate. This invention does not limit the type of solvent; a single solvent or a mixture of solvents can be used.

[0047] Another embodiment of the present invention provides a lithium-ion battery, including the electrolyte as described above, and further including a casing and a bare cell disposed within the casing, the bare cell including a positive electrode, a separator and a negative electrode.

[0048] In one specific embodiment, the method for preparing the lithium-ion battery includes the following steps: stacking a positive electrode, a separator, and a negative electrode sequentially, ensuring that a separator is present between any positive and negative electrode; obtaining a multi-layered stack by winding; and inserting this stack as a bare cell into a battery casing. Finally, injecting electrolyte into the casing once or in multiple stages, so that the bare cell is completely immersed in the electrolyte. In other words, the electrolyte is injected and fills the entire internal space of the battery, and the positive electrode, separator, and negative electrode are completely immersed in the electrolyte.

[0049] In some embodiments, the negative electrode sheet includes a negative current collector and a negative active material layer coated at least on one surface of the negative current collector, the negative active material layer including a negative active material; the negative active material is selected from at least one of silicon, silicon oxide, or silicon carbide; or, the negative active material includes a first negative active component and a second negative active component, the first negative active component being selected from silicon, silicon oxide (SiO2), or silicon carbide. x The first negative electrode active component is selected from at least one of the following: (x < 2) or silicon carbide compounds. The second negative electrode active component is selected from at least one of graphite, soft carbon, hard carbon, artificial graphite, or natural graphite. The mass ratio of the first negative electrode active component to the second negative electrode active component can be, for example, 2–20:8–98. Furthermore, the negative electrode current collector is selected from, for example, any one of copper foil current collector, composite copper foil current collector, carbon current collector, foamed copper current collector, or stainless steel current collector. The thickness of the negative electrode current collector is, for example, 8 μm to 15 μm. In one specific embodiment, the negative electrode current collector is, for example, copper foil, and the thickness of the copper foil is, for example, 13 μm.

[0050] In some embodiments, the negative electrode active material layer includes a negative electrode active material, a conductive agent, a binder, and a thickener, etc., and the mass ratio of the negative electrode active material, conductive agent, binder, and thickener can be, for example, (90-96):(1-2):(1-3):(2-5). The conductive agent is selected from, for example, any one or more of conductive carbon black, acetylene black, Ketjen black, carbon nanotubes, or graphene. The binder is selected from, for example, any one or more of carboxymethyl cellulose sodium (CMC-Na), polyvinylidene fluoride, polyethylene oxide, polyamide, polypropylene, polyacrylate, polyethylene ether, polymethyl methacrylate, polyhexamethylene propylene, or styrene-butadiene rubber. The thickener is selected from, for example, CMC-Na.

[0051] In one specific embodiment, the negative electrode active material is selected, for example, from silicon suboxide (SiO), the conductive agent is selected, for example, from acetylene black, and the binder is selected, for example, from sodium carboxymethyl cellulose. The negative electrode active material, conductive agent, and binder are mixed, for example, at a mass ratio of 96:2:2, and deionized water is added. The mixture is then stirred evenly under vacuum to obtain a negative electrode slurry. The negative electrode slurry is coated onto copper foil, then air-dried at room temperature and transferred to an oven for drying. After cold pressing and slitting, the negative electrode sheet is obtained. In other embodiments, the negative electrode sheet can also be obtained by any other method of forming a negative electrode sheet.

[0052] In some embodiments, the positive electrode sheet includes a positive current collector and a positive active material layer coated at least on one surface of the positive current collector. The positive active material layer includes a positive active material. The positive active material is selected from at least one of lithium nickel manganese oxide, lithium iron phosphate, lithium manganese iron phosphate, lithium cobalt oxide, lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt manganese oxide, or lithium nickel cobalt aluminum oxide, preferably at least one of lithium iron phosphate, lithium nickel cobalt manganese oxide, or lithium nickel cobalt aluminum oxide. Further, in some embodiments, the positive active material is selected from ternary positive electrode materials, such as those with the chemical formula Li. x Ni y Co z Mn t M γ O 2-δ The ternary cathode material, wherein M is selected from at least one of Cr, Zr, Ca, Mg, Cu, Ti, Al, Mo, W, or Zn, with 0.9 < x < 1.1, 0.65 ≤ y < 1.0, 0 ≤ z < 0.5, 0 ≤ t < 0.5, y + z + t + γ = 1, and 0 ≤ δ ≤ 0.1, is used to improve the energy density and cycle life of lithium-ion batteries. Furthermore, the cathode current collector is, for example, a foil formed by surface treatment of nickel, titanium, aluminum, silver, stainless steel, or carbon. Besides foil, the cathode current collector can also be used in any one or more combinations of various forms such as film, mesh, porous, foam, or non-woven fabric. The thickness of the cathode current collector is, for example, 8 μm to 15 μm. Further, in a specific embodiment, the cathode current collector is, for example, an aluminum foil, and the thickness of the aluminum foil is, for example, 13 μm.

[0053] In some embodiments, the positive electrode active material layer includes a positive electrode active material, a binder, and a conductive agent, etc., and the mass ratio of the positive electrode active material, the conductive agent, and the binder can be, for example, (90-98):(1-5):(1-5). The binder is selected from, for example, any one or more of polyvinylidene fluoride (PVDF), poly(ethylene oxide) (PEO), polyamide (PA), polyacrylonitrile (PAN), polyacrylate (polyacrylate), polyvinyl ether (polyvinyl ether), polymethyl methacrylate (PMMA), ethylene-propylene-diene terpolymer (EPDM), polyhexanefluoropropylene (polyhexafluoropropylene), or polymerized styrene-butadiene rubber (SBR). The conductive agent is selected from, for example, any one or more of conductive carbon black (SuperP), acetylene black, carbon nanotubes, or graphene.

[0054] In one specific embodiment, the positive electrode active material is, for example, LiNi. 0.8 Mn 0.1 Co 0.1 02. The binder is selected from polyvinylidene fluoride, and the conductive agent is selected from acetylene black. The positive electrode active material, conductive agent, and binder are mixed in a mass ratio of 95:3:2, and an organic solvent is added. The mixture is stirred under vacuum until the system is homogeneous to obtain a positive electrode slurry. The organic solvent is selected from N-methylpyrrolidone (NMP). The positive electrode slurry is uniformly coated onto aluminum foil, then air-dried at room temperature and transferred to an oven for drying. The positive electrode sheet is obtained through cold pressing and slitting. In other embodiments, the positive electrode sheet can also be obtained by any other method of forming the positive electrode sheet.

[0055] In some embodiments, the diaphragm is, for example, a polyethylene (PE) membrane, a polypropylene (PP) membrane, a glass fiber membrane, or a composite membrane, and the thickness of the diaphragm is, for example, 9 μm to 15 μm.

[0056] In some embodiments, the separator includes a base membrane and a coating applied to the base membrane. The base membrane is, for example, a PE membrane, a PP membrane, a glass fiber membrane, or a composite membrane, and the thickness of the separator is, for example, 8 μm to 10 μm; the coating is, for example, a nano-alumina coating, and the coating thickness is, for example, 2 μm to 4 μm.

[0057] The following specific examples illustrate the present invention in detail. It should also be understood that the following examples are only for specific illustrative purposes and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention are within the scope of protection of the present invention. The specific process parameters, etc., in the following examples are merely examples within a suitable range; that is, those skilled in the art can make appropriate selections within the appropriate range based on the description herein, and are not intended to be limited to the specific values ​​in the examples below.

[0058] According to the amounts of the first and second additives in the electrolytes of Example 1N12 and Comparative Examples 1-3 shown in Table 1, and the electrolyte, positive electrode, negative electrode and separator were prepared according to the following method, and then lithium-ion batteries were made and their performance was tested. The test results are shown in Table 1.

[0059] 1. Preparation of electrolyte:

[0060] In an argon-filled glove box with a moisture content of less than 0.1 ppm and an oxygen content of less than 0.1 ppm, ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate were mixed uniformly at a mass ratio of 3:5:2 to obtain a mixed solvent. Then, dried lithium hexafluorophosphate and lithium difluorosulfonyl imide, along with a first additive and / or a second additive, were added to the mixed solvent and mixed thoroughly to obtain an electrolyte. In the obtained electrolyte, based on a total electrolyte mass percentage of 100%, the mass percentage of lithium hexafluorophosphate was 13%, the mass percentage of lithium difluorosulfonyl imide was 2%, and the mass percentage of the mixed solvent was adjusted according to the amounts (i.e., mass percentages) of the first and second additives.

[0061] In Examples 1-9 and Example 12, R1, R2, R3, R4 and R5 of the first additive are all tert-butyl (), in Example 10, R1, R2, R3, R4 and R5 of the first additive are all 1,1-dimethoxyethyl ether (DME), and in Example 11, R1, R2, R3, R4 and R5 of the first additive are all 1,1-diethylpropyl (DME).

[0062] In Example 1N11, R6 and R7 of the second additive were both methyl, while in Example 12, R6 and R7 of the second additive were both fluoromethyl.

[0063] 2. Preparation of the positive electrode sheet:

[0064] LiNi, the positive electrode active material 0.8 Mn 0.1 Co 0.1O2, conductive agent acetylene black, and binder polyvinylidene fluoride were mixed in a mass ratio of 95:3:2, and N-methylpyrrolidone was added. The mixture was stirred under vacuum until the system was homogeneous to obtain a positive electrode slurry. The positive electrode slurry was uniformly coated onto an aluminum foil with a thickness of 13 μm, then air-dried at room temperature and transferred to an oven for drying. After cold pressing and slitting, the positive electrode sheet was obtained.

[0065] 3. Preparation of the negative electrode sheet:

[0066] The negative electrode active material silicon suboxide, conductive agent acetylene black, and binder sodium carboxymethyl cellulose were mixed at a mass ratio of 96:2:2. Deionized water was added, and the mixture was stirred evenly under vacuum to obtain a negative electrode slurry. The negative electrode slurry was coated onto a copper foil with a thickness of 13 μm, then air-dried at room temperature and transferred to an oven for drying. After cold pressing and slitting, the negative electrode sheet was obtained. 4. Preparation of the separator:

[0067] An 8μm polyethylene membrane was selected as the base membrane, and a 3μm thick nano-alumina coating was coated on the base membrane to obtain the separator.

[0068] 5. Battery manufacturing:

[0069] The positive electrode, separator, and negative electrode are wound sequentially, with the separator positioned between the positive and negative electrodes to act as a separator, resulting in a cylindrical bare cell. This cell is then placed in a circular casing, dried in a vacuum oven, injected with the electrolyte prepared above, and sealed to allow electrolyte formation, thus obtaining a lithium-ion battery.

[0070] 6. Performance testing methods:

[0071] 6.1 Loop Testing:

[0072] At 25°C, the lithium-ion battery was charged at a constant current of 1 / 3C to 4.25V, and then charged at a constant voltage to a current of 0.05C. The battery was then discharged at a constant current of 1 / 3C to 2.5V. The capacity C0 was recorded. This charge-discharge cycle was repeated 1000 times, and the discharge capacity C1 after 1000 cycles was recorded. The cycle capacity retention rate of the battery was calculated using the following formula:

[0073] Cyclic capacity retention rate = C1 / C0 * 100%.

[0074] 6.2 Direct Current Resistance (DCR) Growth Rate Test:

[0075] At 25°C, charge an uncycled lithium-ion battery at a constant current of 1 / 3C to 4.25V, then charge at a constant voltage to a current of 0.05C. Discharge the battery at a constant current of 1 / 3C to 2.5V. Repeat the above charging steps and record the charging capacity as C1. Discharge the battery at a constant current of 1 / 3C to (50% * C1) and record the initial voltage as V2. Discharge the battery at a constant current of 1C for 30 seconds and record the final voltage as V3. Calculate DCR1 using the following formula:

[0076] DCR1=(V2-V3) / (C1*1).

[0077] The cells were tested using the same method after cycling, and the results were recorded as DCR2. The DCR growth rate was then calculated using the following formula:

[0078] DCR growth rate = DCR2 / DCR1*100%.

[0079] Table 1

[0080] First additive dosage / % Second additive dosage / % Cyclic capacity retention rate / % DCR growth rate / % Example 1 0.1 0.1 79.4％ 39.9％ Example 2 0.5 0.1 83.4％ 31.5％ Example 3 1 0.1 83.3％ 32.6％ Example 4 0.5 0.2 88.6％ 21.7％ Example 5 0.5 0.3 88.2％ 22.4％ Example 6 3 0.1 83.2％ 33.1％ Example 7 0.5 0.01 75.6％ 60.8％ Example 8 0.5 1 88.4％ 23.4％ Example 9 0.01 0.1 74.2％ 58.2％ Example 10 0.5 0.2 87.6％ 23.7％ Example 11 0.5 0.2 87.3％ 24.1％ Example 12 0.5 0.2 88.7％ 23.7％ Comparative Example 1 0.5 0 75.7％ 60.3％ Comparative Example 2 0 0.2 74.3％ 59.2％ Comparative Example 3 0 0 73.1％ 64.0％

[0081] From the data in Table 1, the following conclusions can be drawn:

[0082] Comparing Examples 4, 10-12 with Comparative Example 1N3, it can be seen that the combination of the first additive and the second additive is necessary to effectively improve battery cycle performance and reduce battery impedance.

[0083] Comparing Examples 1-3, 6, and 9 with Comparative Example 2, it can be seen that as the dosage of the first additive increases from 0.1% to 3%, the battery cycle capacity retention rate first increases and then decreases, while the DCR growth rate first decreases and then increases. Both effectively improve battery cycle performance and reduce battery impedance. However, too little dosage or no addition of the first additive to the electrolyte cannot effectively improve battery cycle performance or reduce battery impedance; while excessive dosage will affect battery impedance and cycle performance. Therefore, the dosage of the first additive is suitable to be controlled within the range of 0.1% to 3%, with the optimal dosage being 0.1% to 1%.

[0084] Comparing Examples 2, 4, 5, 7, and 8 with Comparative Example 1, it can be seen that as the dosage of the second additive increases from 0.1% to 1%, the battery cycle capacity retention rate first increases and then decreases, while the DCR growth rate first decreases and then increases. Both effectively improve battery cycle performance and reduce battery impedance. However, too little dosage or no addition of the second additive to the electrolyte cannot effectively improve battery cycle performance or reduce battery impedance; while excessive dosage will not further improve cell performance. Therefore, the dosage of the first additive is suitable to be controlled within the range of 0.01% to 1%, with the optimal dosage being 0.1% to 0.3%.

[0085] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. An electrolyte, characterized in that, Includes electrolytes, solvents, and additives; The electrolyte is a lithium salt, which includes lithium hexafluorophosphate and lithium difluorosulfonylimide, and the mass percentage of lithium hexafluorophosphate in the electrolyte is greater than the mass percentage of lithium difluorosulfonylimide in the electrolyte. The additives include at least a first additive and a second additive, wherein the first additive is selected from siloxy compounds containing unsaturated bonds, as shown in formula (I): (Ⅰ)， In formula (Ⅰ), R1, R2, R3, R4 and R5 are selected from at least one of tert-butyl, 1,1-dimethoxyethyl ether, or 1,1-diethylpropyl. The second additive is selected from carbodiimide compounds with the general chemical formula (II): (Ⅱ)， In formula (II), R6 and R7 are selected from at least one of substituted or unsubstituted alkyl groups having 1 to 12 carbon atoms, substituted or unsubstituted alkenyl groups having 2 to 12 carbon atoms, or substituted or unsubstituted cycloalkyl groups having 3 to 12 carbon atoms; if substituted, the substituent is a halogen or an alkyl group having 1 to 12 carbon atoms.

2. The electrolyte according to claim 1, characterized in that: Based on the total mass of the electrolyte, the mass percentage of the first additive is 0.1% to 3%.

3. The electrolyte according to claim 1, characterized in that: Based on the total mass of the electrolyte, the mass percentage of the second additive is 0.01% to 1%.

4. The electrolyte according to claim 1, characterized in that: The lithium salt further includes at least one of lithium tetrafluoroborate, lithium bis(trifluoromethyl)sulfonylimide, lithium dioxalate borate, lithium difluorodioxalate phosphate, lithium difluorooxalate borate, lithium difluorophosphate, or lithium trifluoromethylsulfonate.

5. The electrolyte according to claim 1, characterized in that: Based on the total mass of the electrolyte, the mass percentage of lithium hexafluorophosphate is 11% to 15%, and the mass percentage of lithium difluorosulfonylimide is 1% to 3%.

6. The electrolyte according to claim 1, characterized in that: The solvent is selected from at least one of carbonate solvents, carboxylic acid ester solvents, ether solvents, or nitrile solvents.

7. A lithium-ion battery, characterized in that: Includes the electrolyte as described in any one of claims 1 to 6.

8. The lithium-ion battery according to claim 7, characterized in that: It includes a negative electrode sheet, the negative electrode sheet including a negative current collector and a negative active material layer coated on at least one surface of the negative current collector, the negative active material layer including a negative active material; The negative electrode active material is selected from at least one of silicon, silicon oxide, or silicon carbide; or, the negative electrode active material includes a first negative electrode active component and a second negative electrode active component, wherein the first negative electrode active component is selected from at least one of silicon, silicon oxide, or silicon carbide, and the second negative electrode active component is selected from at least one of graphite, soft carbon, or hard carbon.

9. The lithium-ion battery according to claim 7, characterized in that: The positive electrode includes a positive current collector and a positive active material layer coated on at least one surface of the positive current collector, the positive active material layer including a positive active material; The positive electrode active material is selected from at least one of lithium iron phosphate, lithium manganese iron phosphate, lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, or lithium nickel cobalt aluminum oxide.

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