Electrolyte and battery

Abstract

An electrolyte and a battery. The electrolyte comprises a fluorine‑containing oxalic acid lithium salt and a functional additive; the functional additive has a structure as represented by formula (1), wherein R1 is selected from at least one of a linear alkyl group having 1-6 carbon atoms and a substituted or unsubstituted aromatic group; and R2 and R3 are each independently selected from at least one of a halogen atom and a substituted or unsubstituted alkyl group having 1-10 carbon atoms. The electrolyte can ensure that the battery meets high energy density requirements and fast charging requirements, and improve the cycle stability of the battery.

Description

An electrolyte, a battery

[0001] Priority information

[0002] This application claims priority and benefits to patent application No. 202411222205.4, filed with the China National Intellectual Property Administration on September 2, 2024, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This invention relates to an electrolyte, and more particularly to an electrolyte and a battery, belonging to the field of lithium-ion battery technology. Background Technology

[0004] Lithium-ion batteries, due to their high energy density, high power density, good cycle performance, no memory effect, and environmental friendliness, are widely used in various electronic products such as mobile communication devices, mobile cameras, laptops, and smartphones. They are also a strong candidate for future power supply systems in electric vehicles. With the expansion of application areas, especially the rapid development of electric vehicles, the market is demanding higher energy density and faster charging capabilities from lithium-ion batteries.

[0005] Currently, battery energy density can be increased by using high voltage and silicon-based materials as the negative electrode active material, while fast charging requires higher current densities. However, high voltage and high current densities can lead to problems such as silicon-based material expansion and positive electrode metal dissolution, severely affecting the battery's cycle stability.

[0006] Therefore, there is an urgent need to explore solutions that can meet the requirements of high energy density and fast charging while maintaining excellent cycle stability. Summary of the Invention

[0007] This invention provides an electrolyte that can improve the cycle stability of lithium-ion batteries under fast charging conditions.

[0008] This invention provides a battery that exhibits excellent cycle performance in fast-charging mode.

[0009] One aspect of the present invention provides an electrolyte comprising a fluorinated oxalate lithium salt and functional additives;

[0010] The functional additive has the structure of formula (1);

[0011] Wherein, R1 is selected from at least one of a chain alkyl group having 1 to 6 carbon atoms, or a substituted or unsubstituted aromatic group; R2 and R3 are independently selected from at least one of a halogen atom, or a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms.

[0012] In the electrolyte described above, the functional additive is selected from compounds represented by formulas (2), (3), and (4):

[0013] In the electrolyte described above, the fluorinated oxalate lithium salt is selected from at least one of lithium difluorooxalate borate, lithium tetrafluorooxalate phosphate, and lithium difluorodi(oxalate) phosphate.

[0014] In the electrolyte described above, the molar ratio of the fluorinated oxalate lithium salt to the functional additive is 1:(0.2-6.5).

[0015] The electrolyte as described above also includes hexamethylene diisocyanate.

[0016] In the electrolyte as described above, the hexamethylene diisocyanate has a mass percentage content of 0.1%-2% in the electrolyte.

[0017] In the electrolyte described above, the molar ratio of hexamethylene diisocyanate to the functional additive is 1:(0.2-10).

[0018] In the electrolyte as described above, the functional additive has a mass percentage content of 1%-10% in the electrolyte;

[0019] And / or, the fluorinated oxalate lithium salt has a mass percentage content of 0.5%-5% in the electrolyte.

[0020] The electrolyte as described above further includes a first additive, wherein the first additive is selected from at least one of vinylene carbonate, fluoroethylene carbonate, ethylene ethylene carbonate, ethylene sulfate, 1,3-propanesulfonate lactone, 1,3-propenesulfonate lactone, vinyl sulfite, tris(trimethylsilane)borate, and tris(trimethylsilane)phosphate; the first additive is present in the electrolyte at a mass percentage of 0.1%-5%; and / or,

[0021] It also includes a second additive, which is selected from at least one of lithium hexafluorophosphate, lithium perchlorate, lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, and lithium hexafluoroarsenate; the second additive has a mass percentage content of 10%-20% in the electrolyte.

[0022] The electrolyte described above further includes a non-aqueous organic solvent selected from at least one 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.

[0023] The non-aqueous organic solvent in the electrolyte has a mass percentage of 50%-85%.

[0024] In another aspect, the present invention provides a battery comprising the electrolyte as described above.

[0025] The battery described above also includes a ternary cathode and a silicon-containing anode.

[0026] The ternary cathode material includes NCM cathode material with the molecular formula LiNi. a Co b Mn c O2, where a, b, and c satisfy a+b+c=1;

[0027] Silicon-containing anode sheets include anode active materials, which in turn include silicon-based materials.

[0028] The electrolyte of the present invention combines a fluorinated oxalate lithium salt with a functional additive having the structure of Formula 1, thereby leveraging the synergistic effect of the functional additive and the fluorinated oxalate lithium salt to form a dense SEI film and improve the cycle stability of the battery under fast charging conditions.

[0029] The battery of the present invention is prepared based on the electrolyte described above, and the battery has excellent cycle stability in fast charging mode. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0031] In one aspect, the present invention provides an electrolyte comprising a fluorinated oxalate lithium salt and a functional additive; the functional additive having the structure of formula (1);

[0032] R1 is selected from at least one of a chain alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted aromatic group; R2 and R3 are independently selected from at least one of a halogen atom, a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms.

[0033] This invention does not limit the specific type of fluorinated oxalate lithium salt, and conventional fluorinated oxalate lithium salts in the art can be used.

[0034] The functional additive of the present invention is a compound with the structure shown in Formula 1, which is a disulfonate compound.

[0035] In this invention, R1 is selected from at least one of a chain alkyl group having 1-6 carbon atoms, a substituted or unsubstituted aromatic group. A substituted aromatic group in this invention refers to a group in which the hydrogen atom on the aromatic ring is replaced by another atom or group, such as tolyl. An unsubstituted aromatic group refers to a group in which the hydrogen atom on the aromatic ring is not replaced by another atom or group, i.e., phenyl.

[0036] In this invention, R2 and R3 are independently selected from at least one of halogen atoms and substituted or unsubstituted alkyl groups having 1-10 carbon atoms.

[0037] Specifically, R2 and R3 are independently selected from halogen atoms, alkyl groups having 1-10 carbon atoms, or haloalkyl groups having 1-10 carbon atoms. For example, R2 and R3 are independently selected from at least one of fluorine atoms, methyl, ethyl, propyl, butyl, pentyl, hexyl, isopropyl, isobutyl, sec-butyl, tert-butyl, isopentyl, isohexyl, fluoromethyl, fluoroethyl, fluoropropyl, fluorobutyl, fluoropentyl, fluorohexyl, fluoroisopropyl, fluoroisobutyl, fluorosec-butyl, fluorotert-butyl, fluoroisopentyl, or fluoroisohexyl.

[0038] According to the above-mentioned solution provided by the present invention, when the electrolyte includes functional additives and fluorinated oxalate lithium salts, the lithium-ion battery can not only meet the requirements of high energy density and fast charging, but also has relatively excellent cycle stability. The inventors analyzed the principle and believe that the reason may be that fluorinated oxalate lithium salts have good high-temperature performance, high conductivity and cycle capacity, which is beneficial for preparing electrolytes suitable for fast-charging batteries. However, the hydrofluoric acid generated by fluorine will corrode the SEI and CEI films, causing a decrease in the high-temperature storage capacity of the battery, and further leading to increased gas production and a decrease in battery performance. At the same time, the nickel-cobalt-manganese ternary material commonly used in the positive electrode of the medium-nickel high-voltage silicon-carbon anode system will undergo a Co disproportionation reaction in the battery reaction. The dissolved cobalt ions combine with oxalate ions to form cobalt oxalate precipitate, which will accumulate on the positive electrode, increasing impedance and decreasing battery performance. Functional additives can complement the advantages and disadvantages of fluorinated oxalate lithium salts. The functional additive has a disulfonate structure, which can effectively inhibit the damage caused by metal dissolution. For batteries with cobalt-containing cathodes, it can inhibit the formation of cobalt oxalate precipitation and suppress the gas generation problem of oxalate at the cathode, thereby ensuring the cycle stability of the battery under high voltage and high rate conditions.

[0039] Furthermore, in one specific embodiment of the present invention, the functional additive is selected from compounds represented by formulas (2), (3), and (4):

[0040] Furthermore, in one specific embodiment of the present invention, the fluorinated oxalate lithium salt is selected from at least one of lithium difluorooxalate borate, lithium tetrafluorooxalate phosphate, and lithium difluorodi(oxalate) phosphate.

[0041] When the above-mentioned types of fluorinated oxalate lithium salts are selected, it helps to improve high-temperature cycling performance and high-temperature conductivity, as well as SEI film formation, thereby helping to optimize fast charging performance.

[0042] Furthermore, in one specific embodiment of the present invention, the molar ratio of fluorinated oxalate lithium salt to functional additive is 1:(0.2-6.5).

[0043] Specifically, the molar ratio of fluorinated oxalate lithium salt to functional additive is 1:(0.2-6.5). For example, the molar ratio of fluorinated oxalate lithium salt to functional additive includes, but is not limited to, 1:0.2, 1:0.5, 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:6.5 or any combination thereof.

[0044] When the molar ratio of fluorinated oxalate lithium salt to functional additives is within the above range, the fluorinated oxalate lithium salt and functional additives have a better synergistic effect, which makes the battery form a more stable SEI film, better suppresses the expansion of silicon-based materials in the negative electrode and the dissolution of transition metal ions in the positive electrode, and makes the battery exhibit higher cycle performance and high temperature performance.

[0045] Furthermore, in one specific embodiment of the present invention, hexamethylene diisocyanate is also included.

[0046] When the electrolyte includes fluorinated oxalate lithium salts and functional additives, fluorine readily generates hydrofluoric acid. The N=C=O structure in hexamethylene diisocyanate (HDI) can complex with hydrofluoric acid, which helps to capture free hydrofluoric acid, reduce its corrosion on the battery, control the acidity of the electrolyte, and thus suppress the negative effects of hydrofluoric acid on the battery, ensuring the cycle stability of the battery.

[0047] Furthermore, in one specific embodiment of the present invention, the mass percentage of hexamethylene diisocyanate in the electrolyte is 0.1%-2%.

[0048] In detail, the mass percentage of hexamethylene diisocyanate in the electrolyte includes, but is not limited to, 0.1%, 0.5%, 1.0%, 1.5%, 2%, or any combination thereof.

[0049] When the mass percentage of hexamethylene diisocyanate in the electrolyte is within the above range, the inhibitory effect of hexamethylene diisocyanate on hydrofluoric acid can be better exerted, ensuring the cycle stability of the battery.

[0050] Furthermore, in one specific embodiment of the present invention, the functional additive has a mass percentage content of 1%-10% in the electrolyte; and / or, the fluorinated oxalate lithium salt has a mass percentage content of 0.5%-5% in the electrolyte.

[0051] In detail, the mass percentage of functional additives in the electrolyte includes, but is not limited to, a range of 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or any two of these.

[0052] The mass percentage of fluorinated oxalate lithium salts in the electrolyte includes, but is not limited to, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or any combination thereof.

[0053] When the mass percentage of functional additives and fluorinated oxalate lithium salts in the electrolyte meets the above range, the synergistic effect among the three can be further improved, enabling the battery to have high energy density, fast charging capability, and superior cycle stability.

[0054] Furthermore, in one specific embodiment of the present invention, it further includes a first additive selected from at least one of vinylene carbonate, fluoroethylene carbonate, ethylene ethylene carbonate, ethylene sulfate, 1,3-propanesulfonate lactone, 1,3-propenesulfonate lactone, vinyl sulfite, tris(trimethylsilane)borate, and tris(trimethylsilane)phosphate; the first additive has a mass percentage content of 0.1%-5% in the electrolyte; and / or, it further includes a second additive selected from at least one of lithium hexafluorophosphate, lithium perchlorate, lithium difluorosulfonylimide, lithium difluorophosphate, and lithium hexafluoroarsenate; the second additive has a mass percentage content of 10%-20% in the electrolyte.

[0055] The first and second additives help improve the ionic conductivity of the electrolyte, further optimizing the battery and improving fast-charging cycle stability.

[0056] In detail, the mass percentage of the first additive in the electrolyte includes, but is not limited to, 0.5%, 1%, 2%, 5%, 7%, 10%, 13%, 15%, 18%, 20%, or any combination thereof.

[0057] The second additive has a mass percentage in the electrolyte including, but not limited to, 10%, 12%, 14%, 16%, 18%, 20%, or any combination thereof.

[0058] Furthermore, in one specific embodiment of the present invention, a non-aqueous organic solvent is further included, wherein the non-aqueous organic solvent is selected from at least one of propylene carbonate, methyl ethyl 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; the mass percentage of the non-aqueous organic solvent in the electrolyte is 50%-85%.

[0059] When the above-mentioned non-aqueous organic solvents are selected, they can serve as solvent carriers for the electrolyte, helping to separate cations and anions in the electrolyte and transfer charge between electrodes. At the same time, they can improve the overall conductivity of the electrolyte, which is beneficial to the battery's charge and discharge efficiency and energy density.

[0060] In detail, the mass percentage of non-aqueous organic solvents in the electrolyte includes, but is not limited to, 50%, 60%, 70%, 80%, 85%, or any combination thereof.

[0061] When the mass percentage of organic solvent is within the above range, the conductivity of the electrolyte can be further improved, thereby improving the cycle performance of the battery to a greater extent.

[0062] In another aspect, the present invention provides a battery comprising the electrolyte as described above.

[0063] Because it includes the electrolyte mentioned above, this battery achieves excellent cycle stability while meeting the requirements of high energy density and fast charging.

[0064] In one specific embodiment, in addition to the electrolyte provided by this invention, the battery also includes a positive electrode, a negative electrode, and a separator. During the charging and discharging process, active ions repeatedly insert and extract between the positive and negative electrode. The electrolyte acts as a conductor of ions between the positive and negative electrode. The separator, positioned between the positive and negative electrode, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through. Specifically:

[0065] Furthermore, in one specific embodiment of the present invention, the battery further includes a ternary cathode sheet and a silicon-containing anode sheet; the ternary cathode sheet includes an NCM cathode material with the molecular formula LiNi. a Co b Mn c O2, where a, b, and c satisfy a+b+c=1; the silicon-containing negative electrode includes a negative electrode active material, which includes at least one of silicon oxide compound or silicon-carbon composite.

[0066] In detail, the molecular formula of the NCM cathode material is LiNi. a Co b Mn c O2, where a, b, and c satisfy a+b+c=1.

[0067] In one specific embodiment, the positive electrode material is selected from one of NCM613, NCM333, NCM523, NCM622, and NCM811, with NCM613 being preferred.

[0068] The silicon-containing anode sheet includes an anode active material, which includes at least one of silicon oxide compounds or silicon-carbon composites.

[0069] Among them, silicon oxide compounds or silicon-carbon compounds commonly used in the art can be selected. For example, silicon-carbon composites include, but are not limited to, at least one of SiO@C with theoretical specific capacities of 420 mAh / g, 450 mAh / g, and 550 mAh / g, or Si@C with theoretical specific capacities of 400 mAh / g, 500 mAh / g, 600 mAh / g, and 650 mAh / g.

[0070] In one specific embodiment, the negative electrode active material also includes carbon-based materials, such as graphite, mesophase carbon microspheres, hard carbon materials, soft carbon materials, etc.

[0071] When a battery meets the above requirements, it is classified as a medium-nickel high-voltage silicon-carbon battery. Medium-nickel high-voltage silicon-carbon batteries have high energy density, high voltage platform, long cycle life and fast charging capability. Therefore, medium-nickel high-voltage silicon-carbon batteries are expected to play an important role in electric vehicles, portable electronic devices and energy storage systems, and contribute to the development of sustainable energy.

[0072] This invention does not limit the compaction density of ternary cathode sheets and silicon-containing anode sheets. In one specific embodiment, the compaction density of the ternary cathode sheet is 1-5 g / cm³. 3 The compaction density of silicon-containing anode sheets is 1-4 g / cm³. 3 .

[0073] The battery provided by this invention has an operating voltage of ≥4.4V.

[0074] In one specific embodiment, the positive current collector includes a metal foil or a composite current collector. For example, aluminum foil can be used as the metal foil. The composite current collector includes a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0075] In one specific embodiment, the positive electrode active material layer further includes a binder, which includes at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0076] In one specific embodiment, the positive electrode active material layer further includes a conductive agent. For example, the conductive agent includes at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0077] In one specific embodiment, the negative electrode active material layer may further include a binder, a conductive agent, and other additives. For example, the binder may include at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethyl methacrylate (PMAA), and carboxymethyl chitosan (CMCS); the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, single-walled carbon nanotubes, graphene, and carbon nanofibers; and the additives may include thickeners, such as sodium carboxymethyl cellulose (CMC-Na).

[0078] It is understood that the battery also includes a separator. This invention does not impose any particular limitation on the type of separator; any porous separator with good chemical and mechanical stability can be selected. For example, the separator material includes at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film.

[0079] The batteries in this application may be in the form of individual battery cells, battery modules, or battery packs.

[0080] The present invention will be further described in detail below with reference to embodiments, but the implementation of the present invention is not limited thereto.

[0081] Example 1

[0082] The electrolyte preparation method provided in this embodiment includes the following steps:

[0083] In a glove box with qualified water and oxygen content (moisture <10ppm, oxygen <1ppm), a non-aqueous organic solvent composed of ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC) in a mass ratio of 1:2.8:2.8:6 is added to a lithium salt containing fluorinated oxalate and functional additives. After thorough mixing and stirring, an electrolyte is obtained.

[0084] The preparation methods of the electrolytes provided in Examples 1-39 and Comparative Examples 1-4 are basically the same as those in Example 1, but there are differences in the raw material formulations. When the raw materials include not only fluorinated oxalate lithium salts and functional additives, other types of raw materials are added simultaneously with the fluorinated oxalate lithium salts and functional additives. The specific parameters of the raw material formulations are shown in Table 1.

[0085] Table 1

[0086] (2) A high-voltage nickel-silicon-carbon anode battery was prepared using the above electrolyte:

[0087] 1) Preparation of positive electrode sheet: NCM613 Zhenhua / 6000A positive electrode active material, conductive agent SP, conductive agent CNT (Tiannai LB107-44), and binder PVDF (Soway 5130) were mixed in a weight ratio of 95:3:0.5:1.5, and N-methylpyrrolidone (NMP) was added. The mixture was stirred under vacuum to obtain a positive electrode slurry. The positive electrode slurry was uniformly coated onto an aluminum foil with a thickness of 16μm. The coated aluminum foil was then baked in an oven with three different temperature gradients. After that, the positive electrode sheet was rolled to control the compaction density of the positive electrode sheet to 3.4g / cm3, and then cut to obtain the positive electrode sheet.

[0088] 2) Negative electrode preparation: Graphite / Zichen silicon carbide 550-M5-230415 negative electrode active material, conductive agent SP, binder SBR (JSR-104A), thickener CMC (crt30000PA), and solvent CNT were mixed in a weight ratio of 94.94:1.5:2:1.5:0.06. CNT solvent was added, and the mixture was stirred under vacuum to obtain a negative electrode slurry. The negative electrode slurry was uniformly coated onto a 9μm thick copper foil; after baking in ovens with three different temperature gradients, the negative electrode was rolled to control the compaction density to 1.6 g / cm³, and then die-cut to obtain the negative electrode sheet.

[0089] 3) Preparation of the diaphragm

[0090] A 16μm thick double-layer PP ceramic was selected.

[0091] 4) Preparation of lithium-ion batteries

[0092] The prepared positive electrode, separator, and negative electrode are stacked, punched, and assembled to obtain a bare cell without electrolyte filling. The bare cell is placed in an outer packaging foil, and the prepared electrolyte is injected into the dried bare cell. After vacuum sealing, standing, formation, shaping, and sorting, the desired lithium-ion battery is obtained.

[0093] (3) Performance tests were conducted on the above-mentioned medium-nickel high-voltage silicon-carbon anode battery:

[0094] 1) High-Temperature Storage Performance Test: The lithium-ion battery was placed in a 60℃ constant temperature chamber for 6 hours, and then subjected to two charge-discharge cycles at a 1C current, with a test voltage window of 2.75~4.4V. Before storage, the gas production (water displacement method) and DCR were measured at full charge (100% SOC). After storage for 7, 15, 30, 45, and 60 days, the DCR, remaining capacity, and capacity recovery rate were tested respectively. The gas production was tested using the water displacement method, the specific process of which is as follows: The battery cell was hooked onto the bottom hook of an electronic scale before storage, with the cell submerged in a beaker of water. The scale reading was recorded as m. 初始 (This is the initial weight), in grams; the same method is used to test the stored battery cells, and the electronic scale reading is recorded as m2 (i.e., the weight after drainage), in grams; according to Archimedes' principle, the amount of gas produced by drainage (m3) = (initial weight - weight after drainage) / density of water, where the density of water is 1 g / cm³. 3 The test results are shown in Table 2.

[0095] Capacity recovery rate (%) = (Capacity recovered after storage / Initial capacity) × 100%.

[0096] Capacity remaining rate (%) = Remaining capacity after discharge / Initial capacity × 100%.

[0097] Gas production from drainage (m3) = (initial weight - weight after drainage) / density of water.

[0098] 2) High-temperature cycle performance test: The lithium-ion battery was placed in a constant temperature chamber at 45℃ and left to stand for 5 minutes. Then, the lithium-ion battery was subjected to 1500 charge-discharge cycles at a current of 1C. The test voltage window was 2.75~4.5V. The DCR was measured at 50, 100, 200, 300, 400 and 500 cycles before the cycle and at the full charge (100% SOC) state. The test results are shown in Table 2.

[0099] 3) Room temperature cycle performance test: The lithium-ion battery was placed in a test chamber with a set temperature of 25℃ and left to stand for 5 minutes. Then, the lithium-ion battery was subjected to 1500 charge-discharge cycles at a current of 1C. The test voltage window was 2.75~4.5V. The DCR was measured at 50, 100, 200, 300, 400 and 500 cycles before the cycle and at the full charge (100% SOC) state. The test results are shown in Table 2.

[0100] Table 2

[0101] Table 2 shows that, based on the comparison of Examples 1-39 and Comparative Examples 1-4, the functional additives and fluorinated oxalate lithium salts can work synergistically to improve the cycle stability of the battery under fast charging conditions. A comparison of Examples 5 and 6 with Examples 1-4 shows that a functional additive content between 1% and 10% is more beneficial to the battery's cycle stability. A comparison of Examples 10 and 11 with Examples 1 and 7-9 shows that a fluorinated oxalate lithium salt content between 0.5% and 5% results in superior cycle stability. A comparison of Examples 12 and 17 with Examples 13-16 shows that the hexamethylene diisocyanate content should not be too high or too low. Examples 20-25 show that a first additive content between 0.1% and 5% is beneficial to the battery's cycle stability.

[0102] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An electrolyte, characterized in that, Including lithium salts containing fluorinated oxalate and functional additives; The functional additive has the structure of formula (1); R1 is selected from at least one of a chain alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted aromatic group; R2 and R3 are independently selected from at least one of a halogen atom, a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms.

2. The electrolyte according to claim 1, characterized in that, The functional additives are selected from compounds shown in formulas (2), (3), and (4):

3. The electrolyte according to claim 1 or 2, characterized in that, The fluorinated oxalate lithium salt is selected from at least one of lithium difluorooxalate borate, lithium tetrafluorooxalate phosphate, and lithium difluorodi(oxalate) phosphate.

4. The electrolyte according to any one of claims 1-3, characterized in that, The molar ratio of the fluorinated oxalate lithium salt to the functional additive is 1:(0.2-6.5).

5. The electrolyte according to any one of claims 1-3, characterized in that, It also includes hexamethylene diisocyanate.

6. The electrolyte according to claim 5, characterized in that, The hexamethylene diisocyanate in the electrolyte has a mass percentage of 0.1%-2%.

7. The electrolyte according to any one of claims 1-6, characterized in that, The functional additive has a mass percentage content of 1%-10% in the electrolyte; And / or, the fluorinated oxalate lithium salt has a mass percentage content of 0.5%-5% in the electrolyte.

8. The electrolyte according to any one of claims 1-7, characterized in that, It also includes a first additive selected from at least one of vinylene carbonate, fluoroethylene carbonate, ethylene ethylene carbonate, ethylene sulfate, 1,3-propanesulfonate lactone, 1,3-propenesulfonate lactone, vinyl sulfite, tris(trimethylsilane)borate, and tris(trimethylsilane)phosphate; the first additive is present in the electrolyte at a mass percentage of 0.1%-5%; and / or, It also includes a second additive, which is selected from at least one of lithium hexafluorophosphate, lithium perchlorate, lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, and lithium hexafluoroarsenate; the second additive has a mass percentage content of 10%-20% in the electrolyte.

9. The electrolyte according to any one of claims 1-8, characterized in that, It also includes non-aqueous organic solvents, wherein the non-aqueous organic solvents are selected from at least one 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. The non-aqueous organic solvent in the electrolyte has a mass percentage of 50%-85%.

10. A battery, characterized in that, Includes the electrolyte as described in any one of claims 1-9.

11. The battery according to claim 10, characterized in that, It also includes ternary cathode plates and silicon-containing anode plates; The ternary cathode material includes NCM cathode material with the molecular formula LiNi. a Co b Mn c O2, where a, b, and c satisfy a+b+c=1; The silicon-containing anode sheet includes an anode active material, which includes at least one of a silicon oxide compound or a silicon-carbon composite.

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