Electrolyte and lithium ion battery

Abstract

The invention provides an electrolyte and a lithium ion battery, and relates to the technical field of lithium ion batteries. The electrolyte comprises a lithium salt, an organic solvent and an additive, the organic solvent comprises a main solvent and a cosolvent; the additive comprises a pyridine compound and other additives; the structural formula of the pyridine compound is as shown in formula I in the specification. The electrolyte provided by the invention is helpful for improving the electrochemical performance of the lithium ion battery under the conditions of high voltage and low temperature.

Description

Technical Field

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

[0002] With the rapid development of new energy electric vehicles, the low-altitude economy, and portable consumer electronics, higher demands are being placed on the performance of lithium-ion batteries. In particular, to address range anxiety in electric vehicles and for emerging applications such as lightweight low-altitude aircraft, there is an urgent need to improve the energy density of lithium-ion batteries, a key performance indicator.

[0003] To further improve battery energy density, increasing the operating cutoff voltage of existing cathode materials or developing new cathode materials with higher voltage and higher capacity would be more effective methods. However, higher cutoff voltages pose a significant challenge to the oxidation resistance of widely used carbonate-based electrolytes. Specifically, at higher operating voltages, lithium-ion batteries face material instability and severe interface problems between traditional electrolytes and electrode materials. Electrolytes are more prone to oxidation and decomposition under high voltage, which will exacerbate the continuous deterioration of the electrochemical performance and lifespan degradation of lithium-ion batteries.

[0004] Furthermore, lithium-ion batteries suitable for extreme temperature environments are a future trend, requiring the development of wide-temperature-range electrolytes to achieve application in extreme temperature scenarios. Some organic solvents with low melting points and high boiling points cannot be used in large quantities due to incompatibility with graphite anodes. For example, propylene carbonate (PC) solvent has a wide liquid range (melting point: -49.2 ℃, boiling point: 241.7 ℃) and a high flash point (132 ℃), exhibiting better non-flammability and high voltage resistance. However, in systems matched with graphite anodes, PC-based electrolyte solvents undergo continuous co-intercalation and electrolyte decomposition at the graphite anode, leading to graphite layer peeling and irreversible damage to the anode material structure, causing lithium-ion battery failure. In addition, low-melting-point ether solvents such as 1,2-dimethoxyethane (DME) and 1,3-dioxolane (DOL) also exhibit solvent co-intercalation due to their strong solvation capabilities. Therefore, how to suppress the co-intercalation behavior of such solvents in graphite anodes, form an effective electrode-electrolyte interface (SEI), and achieve rapid ion transport in low-temperature environments are key issues for the application.

[0005] Therefore, in order to improve the electrochemical stability of high-nickel ternary lithium-ion batteries at high cutoff voltages, constructing a stable and robust positive and negative electrode electrolyte interface is an urgent problem to be solved in the development of high-energy-density lithium-ion batteries. Summary of the Invention

[0006] Based on the technical problems existing in the background art, the present invention proposes an electrolyte and a lithium-ion battery.

[0007] The present invention provides an electrolyte comprising a lithium salt, an organic solvent, and additives; the organic solvent includes a main solvent and a co-solvent; the additives include pyridine compounds and other additives; the structural formula of the pyridine compounds is shown in Formula I:

[0008]

[0009] Formula I

[0010] In Formula I, R1, R2, R3, R4, and R5 are each independently selected from one or more of the following: hydrogen atom, substituted or unsubstituted C1-C5 alkyl group, substituted or unsubstituted C2-C5 alkenyl group, substituted or unsubstituted C1-C5 alkoxy group, substituted or unsubstituted aryl group, nitro group, amino group, halogen atom, hydroxyl group, and cyano group.

[0011] This invention, by adding pyridine compounds with low LUMO energy levels and high HOMO energy levels and other additives, can be simultaneously oxidized / reduced on the positive and negative electrode surfaces to form an interfacial component containing CN / NxOy / LiF, which participates in the formation of the cathode electrolyte interface.

[0012] Preferably, the pyridine compound is selected from at least one of compounds 1 to 6:

[0013]

[0014] Compound 1 Compound 2 Compound 3

[0015]

[0016] Compound 4, Compound 5, Compound 6.

[0017] The pyridine compounds of this invention contain a six-membered heterocyclic structure consisting of one nitrogen atom and five carbon atoms. This structure possesses a high highest occupied molecular orbital (HOMO) energy level and a low lowest unoccupied molecular orbital energy level, allowing for preferential oxidation or reduction of other electrolyte components under high voltage. This preferential solvent reaction broadens the electrochemical window of the electrolyte and suppresses undesirable decomposition reactions. By introducing electron-withdrawing functional groups such as fluorine, methyl, cyano, or nitro groups, oxidation-resistant interfacial components are formed, thereby reducing electrolyte decomposition under high voltage conditions and extending battery cycle life. The fluorine group exhibits a high electron-withdrawing tendency, enhancing oxidation resistance, and fluorine-containing compounds can form a more robust SEI / CEI film. The pyridine compounds provided by this invention are excellent additives for lithium-ion battery electrolytes.

[0018] Preferably, the pyridine compound includes compound 1 and compound 3, and the mass ratio of compound 1 to compound 3 is 1:1.

[0019] Preferably, the other additives are selected from one or more of vinyl sulfate, 1,3-propanesulfonyl lactone, lithium difluorophosphate, lithium difluoroborate, lithium dioxalate borate, and lithium difluorodioxalate phosphate.

[0020] The other additives mentioned above are commonly used film-forming additives in lithium-ion battery electrolytes. They can be preferentially reduced during the formation stage to form robust electrode-electrolyte interface components, improve lithium-ion transport at the interface, and hinder the co-intercalation of solvents such as PC with lithium ions. They also suppress graphite structure damage caused by solvent co-intercalation, help reduce solvent side reactions at the interface, and suppress battery gas generation.

[0021] Preferably, the main solvent is a cyclic carbonate, which is selected from one or more of ethylene carbonate, propylene carbonate, butene carbonate, fluoroethylene carbonate, and difluoroethylene carbonate; the co-solvent is selected from one or more of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, ethyl butyrate, ethyl fluoroacetate, methyl difluoroacetate, ethyl difluoroacetate, ethyl trifluoroacetate, difluoroethyl acetate, trifluoroethyl acetate, and 2,2,2-trifluoroethylmethyl carbonate.

[0022] Preferably, the main solvent accounts for A% of the mass percentage of the organic solvent, with 30 ≤ A ≤ 70%.

[0023] Preferably, the co-solvent accounts for B% of the organic solvent by mass, with 30 ≤ B ≤ 70%.

[0024] Preferably, the pyridine compound accounts for C% of the electrolyte by mass, with 0.5 ≤ C ≤ 3%.

[0025] Preferably, the other additives account for D% of the mass percentage of the electrolyte, with 0.5 ≤ D ≤ 5.

[0026] More preferably, the relationships between A, B, C, and D are as follows: 0.42≤A / B≤2.35, 0.6≤A×C×D / B≤35.

[0027] This invention controls the mass ratio of the main solvent and the co-solvent, adjusting their interaction to weaken the coordination strength of cyclic carbonates in the lithium-ion solvation structure. This reduces the desolvation energy of the solvent on the graphite anode surface, making it easier for the solvent to separate from lithium ions, thus achieving reversible lithium-ion insertion / extraction on the graphite anode. Furthermore, by adjusting the amounts of the two types of additives, the film-forming ability of pyridine additives and other additives is utilized to improve the electrolyte interface composition of the cathode / anode electrodes, forming a LiF and LiN-rich electrolyte. x O y Inorganic components such as Li3N effectively passivate the cathode interface, inhibiting further oxidative decomposition of the electrolyte. Furthermore, the two additives also participate in the first / second solvation of the lithium-ion sheath solvent, further reducing the binding affinity between lithium ions and cyclic carbonate solvents, affecting the interfacial transport behavior of lithium ions at the graphite anode, thereby reducing the desolvation energy of the solvent on the graphite surface and inhibiting Li3N oxidation. + - Co-intercalation of solvents.

[0028] Preferably, the lithium salt is selected from one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium oxalate phosphate, lithium difluorooxalate borate, lithium bis(trifluorosulfonyl)imide, and lithium bis(fluorosulfonyl)imide.

[0029] Preferably, the concentration of the lithium salt in the electrolyte is 0.5~1.5 mol / L.

[0030] Choosing an appropriate lithium salt concentration helps to maximize electrolyte conductivity and balance electrolyte dosage and viscosity.

[0031] A lithium-ion battery includes a positive electrode, a negative electrode, a separator, and the electrolyte described above.

[0032] Preferably, the positive electrode active material in the positive electrode is selected from LiNi. x Co y Mn z One or more of O2, lithium cobalt oxide, lithium manganese oxide, and lithium-rich manganese-based materials, wherein 0.6≤x≤1, 0≤y≤0.4, 0≤z≤0.4, and x+y+z=1.

[0033] Preferably, the negative electrode active material in the negative electrode is selected from one or more of artificial graphite and natural graphite.

[0034] The lithium-ion battery provided by this invention has an operating voltage range of 3.0~4.6V. The electrolyte provided by this invention helps to improve the specific capacity of lithium-ion batteries at low temperatures and effectively solves the problems of material degradation and lifespan reduction of lithium-ion batteries under high voltage.

[0035] The beneficial effects of this invention are as follows:

[0036] The electrolyte of this invention uses a cyclic carbonate solvent with high dielectric constant, high voltage resistance, and wide temperature range characteristics, and incorporates Li + - Solvents with similar binding energies can reduce electrolyte viscosity, and solvent-solvent interactions weaken the coordination strength of cyclic carbonates in the solvation structure, thereby achieving solvent desolvation on the graphite anode surface. Through the excellent film-forming ability and solvation structure regulation of additives, they participate in the solvation structure to reduce the binding ability of cyclic carbonate solvents and improve the electrode-electrolyte interface composition, thereby improving the high voltage stability on the cathode side and affecting the interfacial transport behavior of solvents on the graphite anode.

[0037] This invention improves electrolyte stability under high voltage by using solvents with high oxidation potential, wide liquid range, and high dielectric constant. Then, it introduces a competitively coordinated co-solvent to weaken the Li-dominated effect of the main solvent. + The solvation structure suppresses the co-intercalation behavior of the main solvent on the graphite anode surface. On the other hand, by adding pyridine compounds and other additives with low LUMO and high HOMO energy levels, they can be simultaneously oxidized / reduced on both the positive and negative electrode surfaces, forming an interfacial component containing CN / NxOy / LiF, which participates in the formation of the cathode-electrolyte interface. This suppresses the oxidative decomposition of the electrolyte on the surface of highly active cathode materials under high voltage, and inhibits the transformation of the layered structure of high-nickel cathode materials to rock salt phase and the dissolution of transition metal ions. Through the synergistic effect of pyridine compound additives and other additives, interface strengthening and solvation regulation are achieved, suppressing graphite structure collapse and continuous electrolyte decomposition caused by co-intercalation, enhancing the electrolyte's high-voltage tolerance, and significantly improving the cycle life degradation of lithium-ion batteries under high voltage. Simultaneously, LiF can be achieved at -20℃. + Reversible insertion / extraction improves the low-temperature performance of the electrolyte.

[0038] The electrolyte of this invention enables ternary high-nickel materials to exhibit stable cycling performance under high voltage and also to be used under low-temperature conditions. Pyridine additives and other additives work together to form a stable interfacial film, regulate the lithium-ion solvation structure and solvent-solvent interactions, improve the oxidation stability of high-nickel cathode materials, and inhibit the co-intercalation behavior of lithium ions and organic solvents in graphite anodes. This invention effectively solves the problem of incompatibility between organic solvents and graphite anodes by optimizing the electrolyte system of lithium salts, solvents, and additives, and prepares an electrolyte that can withstand both 4.6V high voltage and -20℃ low temperature conditions, improves the low-temperature specific capacity of lithium-ion batteries, and effectively solves the problems of material degradation and lifespan decay of lithium-ion batteries under high voltage. Attached Figure Description

[0039] Figure 1 This is a specific capacity-voltage curve of the button battery proposed in this invention. Detailed Implementation

[0040] The technical solution of the present invention will be described in detail through specific embodiments.

[0041] Unless otherwise specified, all materials and reagents used in the following examples and comparative examples are commercially available.

[0042] Example 1

[0043] Electrolyte preparation:

[0044] In an argon-filled glove box, with water and oxygen levels both <0.1 ppm, propylene carbonate (PC) and difluoroethyl acetate (DFEA) are mixed uniformly at a mass ratio of 1:1. Then, 1 mol / L lithium difluorooxalate borate, which has been thoroughly dried, is added. After the lithium salt is completely dissolved, 1 wt% of Compound 1 and 1.5 wt% of lithium difluorodioxalate phosphate (LiDFBOP) are added and mixed to obtain the electrolyte.

[0045] Example 2

[0046] Electrolyte preparation:

[0047] In an argon-filled glove box, with water and oxygen levels both <0.1 ppm, propylene carbonate (PC) and difluoroethyl acetate (DFEA) are mixed uniformly at a mass ratio of 1:1. Then, 1 mol / L lithium difluorooxalate borate, which has been thoroughly dried, is added. After the lithium salt is completely dissolved, 1 wt% of compound 2 and 1.5 wt% of lithium difluorodioxalate phosphate (LiDFBOP) are added and mixed to obtain the electrolyte.

[0048] Example 3

[0049] Electrolyte preparation:

[0050] In an argon-filled glove box, with water and oxygen levels both <0.1 ppm, propylene carbonate (PC) and difluoroethyl acetate (DFEA) are mixed uniformly at a mass ratio of 1:1. Then, 1 mol / L lithium difluorooxalate borate, which has been thoroughly dried, is added. After the lithium salt is completely dissolved, 1 wt% of compound 3 and 1.5 wt% of lithium difluorodioxalate phosphate (LiDFBOP) are added and mixed to obtain the electrolyte.

[0051] Example 4

[0052] Electrolyte preparation:

[0053] In an argon-filled glove box, with water and oxygen levels both <0.1 ppm, propylene carbonate (PC) and difluoroethyl acetate (DFEA) are mixed uniformly at a mass ratio of 1:1. Then, 1 mol / L lithium difluorooxalate borate, which has been thoroughly dried, is added. After the lithium salt is completely dissolved, 1 wt% of compound 4 and 1.5 wt% of lithium difluorodioxalate phosphate (LiDFBOP) are added and mixed to obtain the electrolyte.

[0054] Example 5

[0055] Electrolyte preparation:

[0056] In an argon-filled glove box, with water and oxygen levels both <0.1 ppm, propylene carbonate (PC) and difluoroethyl acetate (DFEA) are mixed uniformly at a mass ratio of 1:1. Then, 1 mol / L lithium difluorooxalate borate, which has been thoroughly dried, is added. After the lithium salt is completely dissolved, 1 wt% of compound 5 and 1.5 wt% of lithium difluorodioxalate phosphate (LiDFBOP) are added and mixed to obtain the electrolyte.

[0057] Example 6

[0058] Electrolyte preparation:

[0059] In an argon-filled glove box, with water and oxygen levels both <0.1 ppm, propylene carbonate (PC) and difluoroethyl acetate (DFEA) are mixed uniformly at a mass ratio of 1:1. Then, 1 mol / L lithium difluorooxalate borate, which has been thoroughly dried, is added. After the lithium salt is completely dissolved, 1 wt% of compound 6 and 1.5 wt% of lithium difluorodioxalate phosphate (LiDFBOP) are added and mixed to obtain the electrolyte.

[0060] Example 7

[0061] Electrolyte preparation:

[0062] In an argon-filled glove box, with water and oxygen levels both <0.1 ppm, propylene carbonate (PC) and difluoroethyl acetate (DFEA) were uniformly mixed at a mass ratio of 3:7. Then, 1 mol / L lithium difluorooxalate borate, which had been thoroughly dried, was added. After the lithium salt was completely dissolved, 1 wt% of Compound 1 and 1.5 wt% of lithium difluorodioxalate phosphate (LiDFBOP) were added and mixed to obtain the electrolyte.

[0063] Example 8

[0064] Electrolyte preparation:

[0065] In an argon-filled glove box, with water and oxygen levels both <0.1 ppm, propylene carbonate (PC) and difluoroethyl acetate (DFEA) are mixed uniformly at a mass ratio of 1:1. Then, 1 mol / L lithium difluorooxalate borate, which has been thoroughly dried, is added. After the lithium salt is completely dissolved, 0.5 wt% of compound 1, 0.5 wt% of compound 3, and 1.5 wt% of lithium difluorodioxalate phosphate (LiDFBOP) are added and mixed to obtain the electrolyte.

[0066] Comparative Example 1

[0067] Electrolyte preparation:

[0068] In an argon-filled glove box, with water and oxygen levels both <0.1 ppm, ethylene carbonate (EC) and dimethyl carbonate (DMC) are mixed uniformly at a mass ratio of 3:7. Then, 1 mol / L lithium hexafluorophosphate, which has been thoroughly dried, is added. After the lithium salt is completely dissolved, 1.5 wt% lithium difluorodioxanol phosphate is added to obtain the electrolyte.

[0069] Comparative Example 2

[0070] Electrolyte preparation:

[0071] In an argon-filled glove box, with water and oxygen levels both <0.1 ppm, propylene carbonate (PC) and difluoroethyl acetate (DFEA) are uniformly mixed at a mass ratio of 7:3. After the lithium salt is completely dissolved, 1 wt% of Compound 1 and 1.5 wt% of lithium difluorodioxanol phosphate are added to obtain the electrolyte.

[0072] Comparative Example 3

[0073] Electrolyte preparation:

[0074] In an argon-filled glove box, with water and oxygen levels both <0.1 ppm, propylene carbonate (PC) and difluoroethyl acetate (DFEA) are uniformly mixed at a mass ratio of 8:2. Then, 1 mol / L lithium difluorooxalate borate, which has been thoroughly dried, is added. After the lithium salt is completely dissolved, 1 wt% of Compound 1 and 1.5 wt% of lithium difluorodioxalate phosphate are added and mixed to obtain the electrolyte.

[0075] Comparative Example 4

[0076] Electrolyte preparation:

[0077] In an argon-filled glove box, with water and oxygen levels both <0.1 ppm, propylene carbonate (PC) and difluoroethyl acetate (DFEA) are uniformly mixed at a mass ratio of 9:1. Then, 1 mol / L lithium difluorooxalate borate, which has been thoroughly dried, is added. After the lithium salt is completely dissolved, 1 wt% of Compound 1 and 1.5 wt% of lithium difluorodioxalate phosphate are added and mixed to obtain the electrolyte.

[0078] Comparative Example 5

[0079] Electrolyte preparation:

[0080] In an argon-filled glove box, with water and oxygen levels both <0.1 ppm, 1 mol / L lithium difluorooxalate borate, after thorough drying, was added to pure propylene carbonate (PC) solvent. After the lithium salt was completely dissolved, 1 wt% of compound 1 was added to obtain the electrolyte.

[0081] Comparative Example 6

[0082] Electrolyte preparation:

[0083] In an argon-filled glove box, with water and oxygen levels both <0.1 ppm, propylene carbonate (PC) and difluoroethyl acetate (DFEA) are mixed uniformly at a mass ratio of 1:1. Then, 1 mol / L lithium difluorooxalate borate that has been thoroughly dried is added. After the lithium salt is completely dissolved, 1.5 wt% lithium difluorodioxalate phosphate is added to obtain the electrolyte.

[0084] Comparative Example 7

[0085] Electrolyte preparation:

[0086] In an argon-filled glove box, with water and oxygen levels both <0.1 ppm, propylene carbonate (PC) and difluoroethyl acetate (DFEA) are mixed uniformly at a mass ratio of 1:1. Then, 1 mol / L lithium difluorooxalate borate that has been thoroughly dried is added. After the lithium salt is completely dissolved, 1 wt% of compound 1 is added to obtain the electrolyte.

[0087] Comparative Example 8

[0088] Electrolyte preparation:

[0089] In an argon-filled glove box, with water and oxygen levels both <0.1 ppm, propylene carbonate (PC) and difluoroethyl acetate (DFEA) are mixed uniformly at a mass ratio of 1:1. Then, 1 mol / L lithium difluorooxalate borate that has been thoroughly dried is added. After the lithium salt is completely dissolved, 0.5 wt% of compound 1 and 0.5 wt% of compound 3 are added and mixed to obtain the electrolyte.

[0090] The above electrolyte is assembled with a positive electrode, a negative electrode, and a separator to form a lithium-ion battery, specifically including:

[0091] (1) Preparation of the positive electrode sheet:

[0092] LiNi, the positive electrode active material 0.8 Co 0.1 Mn 0.1O2 (NCM811), polyvinylidene fluoride (PVDF), and conductive carbon black Super-p are mixed in a weight ratio of 98:1:1. N-methylpyrrolidone (NMP) is added, and the mixture is stirred under vacuum until it is stable and homogeneous to obtain a positive electrode slurry. The positive electrode slurry is uniformly coated onto an aluminum foil with a thickness of 13μm. After the aluminum foil is dried at room temperature, it is transferred to a forced-air oven at 120℃ and dried for 12 hours. Then, it is rolled and slit to obtain a positive electrode sheet.

[0093] (2) Preparation of negative electrode sheet:

[0094] Artificial graphite (anode active material), conductive carbon black, sodium carboxymethyl cellulose (thickener), and styrene-butadiene rubber latex (binder) were mixed in a weight ratio of 96.5:1:1.5:1. Deionized water was added, and the mixture was stirred under vacuum until it was stable and homogeneous to obtain anode slurry. The anode slurry was uniformly coated onto a copper foil with a thickness of 8 μm. After the copper foil was dried at room temperature, it was transferred to a 100°C forced-air oven to dry for 12 hours. Then, the foil was rolled and slit to obtain anode sheets.

[0095] (3) Preparation of lithium-ion batteries:

[0096] 1. Method for preparing button cells:

[0097] The coin cell used to assemble the Li||Gr battery is model 2032, with a battery casing diameter of approximately 20 mm and a height of 32 mm. The coin cell assembly, from top to bottom, consists of a negative electrode casing, spring contact, gasket, lithium electrode, separator, graphite electrode, and positive electrode casing. After assembling the separator, 80 μL of electrolyte is added. The assembled battery is then carefully transferred to the worktable of a manual battery packaging machine using long-handled insulated tweezers. The hydraulic press is locked, and pressure is manually applied to 50 psi to seal the battery, completing the coin cell fabrication.

[0098] 2. Preparation method of pouch cell:

[0099] The separator is moved back and forth between the stacking platforms by a movable stacking stage, and the cut positive and negative electrode sheets are placed on top. The positive electrode sheet, separator, and negative electrode sheet are stacked in sequence, with the separator positioned between the positive and negative electrode sheets to provide isolation. Then, it is placed in an aluminum-plastic film outer packaging foil, baked, and stored in a vacuum oven to complete the cell preparation. When needed, the prepared electrolyte is injected, and after vacuum sealing, settling, formation, and capacity testing, lithium-ion battery testing can be performed.

[0100] Test case

[0101] The Li||Gr coin cell was charged and discharged. The Li||Gr half-cells obtained in the comparative and example cases were discharged to 0.005V within a voltage range of 0.005~2V. +After embedding in graphite and allowing it to stand for 30 minutes, the electrode is charged to 2V to allow Li+ ions to desorb from the graphite and migrate to the lithium metal anode for deposition. Voltage-specific capacity curves are plotted using data from the cycling process, as shown below. Figure 1 As shown.

[0102] The lithium-ion batteries underwent cycling tests at 25°C and -20°C, specifically including:

[0103] 25℃ Cycling Test: The lithium-ion batteries obtained in the comparative examples and embodiments were charged to 4.6V at a constant current of 1C in a 25℃ constant temperature chamber, then charged to 0.05C at a constant voltage, and then discharged to 3.0V at a constant current of 1C. This constitutes one charge-discharge cycle. The discharge capacity of the first 5 cycles was taken as the initial discharge capacity. When the cycle reached 300 cycles, the cycle capacity retention rate was calculated as follows: Cycle capacity retention rate at 300 cycles = (Discharge capacity at 300 cycles / Initial discharge capacity) × 100%

[0104] -20℃ Cyclic Test: The lithium-ion batteries obtained in the comparative example and the embodiment were charged to 4.6V at a constant current of 0.2C in a -20℃ constant temperature chamber, then charged at a constant voltage until the current is ≤0.05C, and then discharged to 3.0V at a constant current of 0.5C. This is one charge-discharge cycle. The discharge capacity of the first 1-5 cycles is taken as the initial discharge capacity. When the cycle reaches 200 cycles, the cycle capacity retention rate is calculated. The cycle capacity retention rate of the 200th cycle = (cycle discharge capacity of the 200th cycle / initial discharge capacity) × 100%.

[0105] The electrolyte composition and lithium-ion battery performance data of the examples and comparative examples are shown in Table 1.

[0106] Table 1

[0107] Group Electrolyte components Pyridine compound additives Other additives A / B A*C*D / B 25℃ 300-cycle capacity retention -20℃ 200-cycle capacity retention Example 1 1 mol / L LiODFBPC:DFEA = 1:1 1% Compound 1 1.5% LiDFBOP 1 1.5 91.5% 99.8% Example 2 1 mol / L LiODFBPC:DFEA = 1:1 1% Compound 2 1.5% LiDFBOP 1 1.5 86.8% 97.5% Example 3 1 mol / L LiODFBPC:DFEA = 1:1 1% Compound 3 1.5% LiDFBOP 1 1.5 89.2% 99.3% Example 4 1 mol / L LiODFBPC:DFEA = 1:1 1% Compound 4 1.5% LiDFBOP 1 1.5 88.5% 96.2% Example 5 1 mol / L LiODFBPC:DFEA = 1:1 1% Compound 5 1.5% LiDFBOP 1 1.5 85.3% 98.8% Example 6 1 mol / L LiODFBPC:DFEA = 1:1 1% Compound 6 1.5% LiDFBOP 1 1.5 86.4% 96.1% Example 7 1 mol / L LiODFBPC:DFEA=3:7 1% Compound 1 1.5% LiDFBOP 0.43 0.65 89.6% 99.2% Example 8 1 mol / L LiODFBPC:DFEA = 1:1 0.5% Compound 1, 0.5% Compound 3 1.5% LiDFBOP 1 1.5 93.9% 99.9% Comparative Example 1 <![CDATA[1mol / L LiPF6EC:DMC=3:7]]> / 1.5% LiDFBOP / / 58.0% 35.2% Comparative Example 2 1 mol / L LiODFBPC:DFEA=7:3 1% Compound 1 1.5% LiDFBOP 2.33 3.5 78.7% 85.6% Comparative Example 3 1 mol / L LiODFBPC:DFEA=8:2 1% Compound 1 1.5% LiDFBOP 4 6 Cycle exception Cycle exception Comparative Example 4 1 mol / L LiODFBPC:DFEA = 9:1 1% Compound 1 1.5% LiDFBOP 9 13.5 Cycle exception Cycle exception Comparative Example 5 1 mol / L LiODFB pure PC 1% Compound 1 / / / Cycle exception Cycle exception Comparative Example 6 1 mol / L LiODFBPC:DFEA = 1:1 / 1.5% LiDFBOP 1 / 79.5% 88.7% Comparative Example 7 1 mol / L LiODFBPC:DFEA = 1:1 1% Compound 1 / 1 / 85.7% 92.2% Comparative Example 8 1 mol / L LiODFBPC:DFEA = 1:1 0.5% Compound 1, 0.5% Compound 3 / 1 / 88.5% 93.2%

[0108] The cycling results of Examples 1 and 7 and Comparative Examples 2-5 show that the ratio of PC to DFEA solvent in the electrolyte of the present invention can significantly affect the cycling performance of lithium-ion batteries. Even with the addition of additives, pure PC solvent still cannot cycle normally, resulting in severe Li-ion degradation. + - PC co-intercalation with graphite particles triggers side reactions, severely damaging the graphite structure and preventing reversible lithium-ion intercalation / deintercalation. Similar phenomena occur with PC:DFEA ratios of 9:1 and 8:2. The optimal solvent ratio is achieved when the PC:DFEA ratio is 1:1, ensuring a high proportion of PC solvent while completely suppressing PC co-intercalation, resulting in significantly improved high-voltage and low-temperature cycling performance. A comparison of Example 8 with Examples 1 and 3 shows that the synergistic effect of the two pyridine compound additives and lithium difluorodioxalate phosphate contributes to improving the battery's cycle stability.

[0109] As shown in Table 1, the 25°C cycling data of Examples 1-7 and Comparative Example 1 indicate that when PC:DFEA = 1:1, and 1% pyridine compounds and 1.5% LiDFBOP are introduced as additives, the lithium-ion battery exhibits superior high-voltage cycling performance in the 3.0-4.6V voltage range compared to Comparative Example 1. The capacity retention after 300 cycles is between 85.3% and 91.5%. This is attributed to the high voltage stability of the high-proportion PC solvent and fluorinated solvent, which enhances the overall high-voltage capability of the electrolyte formulation. Combined with the enhancement of the cathode-electrolyte interface by the pyridine additives, the electrochemical window of the electrolyte is broadened, significantly reducing solvent oxidation reactions at the interface. The excellent film-forming ability of LiDFBOP, through preferential reduction, participates in the formation of the graphite anode SEI, further enhancing the inorganic component content of the SEI and limiting the Li... + -PC co-intercalation behavior avoids the loss of activity in the graphite anode due to structural collapse caused by co-intercalation.

[0110] The cycling results of Examples 1 and Comparative Examples 6-8 show that when only 1% of Compound 1 additive, 1.5% of LiDFBOP additive, or 0.5% of Compound 1 and 0.5% of Compound 3 additive are present, the cycling performance is lower than that of Example 1. This indicates that pyridine additives and other additives can effectively synergistically improve the oxidation resistance, inhibit co-intercalation, and low-temperature lithium-ion transport performance of the interface by constructing the electrolyte interface of the positive and negative electrodes, thereby enhancing the high-voltage cycling and low-temperature cycling performance of lithium-ion batteries.

[0111] Cycling data from Examples 1-6 and Comparative Example 1 at -20°C show that when PC:DFEA = 1:1, and 1% pyridine compound and 1.5% LiDFBOP are introduced as additives, the capacity retention of the lithium-ion battery after 200 cycles at -20°C is above 95%, with no significant capacity drop. In contrast, the 35.2% capacity retention of Comparative Example 1 indicates rapid capacity decay and inability to function properly. This is attributed to the low melting point of PC solvent and the low viscosity of DFEA solvent, which allows for high conductivity even at -20°C. The excellent film-forming ability of the pyridine additive and LiDFBOP enables the formation of a low-resistance SEI, further enhancing the lithium-ion battery's conductivity under low-temperature conditions. + This ensures the transmission capacity of lithium-ion batteries, thereby guaranteeing their long lifespan and stable cycling under low-temperature conditions.

[0112] Figure 1This is a specific capacity-voltage curve of the button cell described in this invention. The compatibility of the electrolyte with different proportions of PC solvent and the graphite anode was studied using the specific capacity-voltage curves of Li||Gr half-cells from Examples 1 and 7 and Comparative Examples 2-5. In the pure PC solvent of Comparative Example 5, the Li||Gr voltage stopped decreasing at 0.5V, fluctuated, and then gradually increased to a voltage plateau of 1V. The specific capacity corresponding to 0.5V was only a few mAh / g, indicating that Li||Gr... + -The persistent co-intercalation behavior of PC leads to graphite exfoliation, Li + It cannot be properly embedded in the graphite material. The curves of Comparative Example 3 (PC:DFEA=8:2) and Comparative Example 4 (PC:DFEA=9:1) show the same reason. The curves from Examples 1, 7, and Comparative Example 2 indicate that within the range of 30wt%~70wt%, as the voltage gradually decreases to 0.005V, Li... + Capable of continuous embedding in graphite materials, providing a specific capacity exceeding 300 mAh / g, DFEA was introduced as a co-solvent in the PC electrolyte system. The mass ratio of PC to DFEA satisfies 0.42 ≤ P / F ≤ 2.35, maximizing the proportion of PC solvent while suppressing Li + -PC co-intercalation. On the one hand, DFEA solvent and Li + The binding energy is similar to that of Li-PC, and in Li + The solvation structure can reduce the coordination number of the solvation sheath PC solvent, thereby reducing the Li... + -The desolvation energy of PC, on the other hand, by adding pyridine compounds and LiDFBOP additives, the formation of SEI is further regulated. The anion-dominated SEI rich in inorganic components, together with reasonable solvation regulation, completely inhibits Li + The co-intercalation of PC effectively protects the graphite structure and enhances the high-voltage stability of the electrode-electrolyte interface.

[0113] In summary, an electrolyte based on a high proportion of PC solvent, with the introduction of pyridine and other additives, achieves a robust and stable electrode-electrolyte interface through pre-oxidation / reduction film formation. The polymerization and ring-opening of unsaturated silicon-nitrogen pyridine additives also contributes to a denser interfacial composition, enhancing interfacial chemical stability and the electrolyte's electrochemical window to withstand harsh high-voltage operating conditions. Furthermore, the combination of a high-voltage and wide-temperature-range PC solvent with a low-viscosity co-solvent further mitigates the effects of high voltage on Li. + The binding ability of PC reduces the removal of harmful substances and avoids damage to the interface. Due to the excellent film-forming ability of the first and second additives, side reactions between the positive and negative electrodes and the electrolyte are reduced, and less by-product accumulates on the interface, thereby reducing interfacial impedance and further improving the rate performance of lithium-ion batteries.

[0114] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. An electrolyte, characterized in that, The mixture includes lithium salts, organic solvents, and additives; the organic solvents include primary solvents and co-solvents; the additives include pyridine compounds and other additives; the structural formula of the pyridine compounds is shown in Formula I: Formula I In Formula I, R1, R2, R3, R4, and R5 are each independently selected from one or more of the following: hydrogen atom, substituted or unsubstituted C1-C5 alkyl group, substituted or unsubstituted C2-C5 alkenyl group, substituted or unsubstituted C1-C5 alkoxy group, substituted or unsubstituted aryl group, nitro group, amino group, halogen atom, hydroxyl group, and cyano group.

2. The electrolyte according to claim 1, characterized in that, The pyridine compounds are selected from at least one of compounds 1 to 6: Compound 1 Compound 2 Compound 3 Compound 4, Compound 5, Compound 6.

3. The electrolyte according to claim 1, characterized in that, The main solvent is a cyclic carbonate, which is selected from one or more of ethylene carbonate, propylene carbonate, butene carbonate, fluoroethylene carbonate, and difluoroethylene carbonate; the co-solvent is selected from one or more of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, ethyl butyrate, ethyl fluoroacetate, methyl difluoroacetate, ethyl difluoroacetate, ethyl trifluoroacetate, difluoroethyl acetate, trifluoroethyl acetate, and 2,2,2-trifluoroethylmethyl carbonate.

4. The electrolyte according to claim 1, characterized in that, The main solvent accounts for A% of the mass percentage of the organic solvent, the co-solvent accounts for B% of the mass percentage of the organic solvent, the pyridine compound accounts for C% of the mass percentage of the electrolyte, and other additives account for D% of the mass percentage of the electrolyte. A, B, C, and D have the following relationship: 0.42≤A / B≤2.35, 0.6≤A×C×D / B≤35; and 30≤A≤70, 30≤B≤70, 0.5≤C≤3, 0.5≤D≤5.

5. The electrolyte according to claim 1, characterized in that, The other additives are selected from one or more of vinyl sulfate, 1,3-propanesulfonyl lactone, lithium difluorophosphate, lithium difluoroborate, lithium dioxaborate, and lithium difluorodioxaborate.

6. The electrolyte according to claim 1, characterized in that, The lithium salt is selected from one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium oxalate phosphate, lithium difluorooxalate borate, lithium bis(trifluorosulfonyl)imide, and lithium bis(fluorosulfonyl)imide; the concentration of the lithium salt in the electrolyte is 0.5~2 mol / L.

7. A lithium-ion battery, characterized in that, It includes a positive electrode, a negative electrode, a separator, and the electrolyte as described in any one of claims 1 to 6.

8. The lithium-ion battery according to claim 7, characterized in that, The positive electrode active material in the aforementioned positive electrode is selected from LiNi x Co y Mn z O2, lithium cobalt oxide, lithium manganese oxide, lithium-rich manganese-based materials or one or more thereof, wherein 0.6≤x≤1, 0≤y≤0.4, 0≤z≤0.4, and x+y+z=1; the negative electrode active material is selected from one or more of artificial graphite and natural graphite.

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