4.5v high-voltage wide-temperature-range ternary lithium ion battery electrolyte, preparation method and application thereof

Abstract

This invention discloses a 4.5V high-voltage, wide-temperature-range ternary lithium-ion battery electrolyte, its preparation method, and its application. The electrolyte comprises a non-aqueous organic solvent, LiPF6 at a concentration of 0.68~0.96 mol / L, LiDFOB at a concentration of 0.32~0.40 mol / L, LiBF4 at a concentration of 0.1~0.16 mol / L, and a composite additive. The composite additive is a mixture of tetrahydro-2-(trifluoromethyl)furan and 1,3,6-hexanetrionitrile. This invention also discloses the preparation method of this electrolyte and its application in lithium-ion batteries. Through the specific ratio of the three lithium salts and the synergistic effect of the composite additive, this invention enables the battery to maintain excellent cycle stability and discharge capacity within a wide temperature range of -20~45℃, while simultaneously imparting lower ohmic impedance, interfacial film impedance, and charge transfer impedance. This invention improves the application performance of lithium-ion batteries in wide-temperature-range, high-voltage scenarios, expanding their production applicability in electric vehicles, energy storage systems, and other fields.

Description

Technical Field

[0001] This invention relates to the field of electrolyte technology, specifically to a 4.5V high-voltage wide-temperature-range ternary lithium-ion battery electrolyte, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries, with their high energy density and long cycle life, have been widely used in electric vehicles and other fields. Among them, ternary cathode materials (lithium nickel cobalt manganese oxide) have become key materials for improving battery energy density due to their high specific capacity and operating voltage platform. As the requirements for driving range of electric vehicles continue to increase, raising the charging cut-off voltage to 4.5V has become the main technical path to further release the energy density of ternary materials.

[0003] However, the increase in voltage poses a severe challenge to the electrolyte system. The electrochemical stability window of existing commercial electrolytes is generally below 4.5V. At high voltages, the electrolyte is prone to oxidative decomposition on the positive electrode surface. Simultaneously, the highly active positive electrode material catalyzes side reactions, leading to the dissolution of transition metal ions such as nickel, cobalt, and manganese. This disrupts the positive electrode crystal structure and allows these ions to migrate to the negative electrode, damaging the solid electrolyte interfacial film and ultimately causing rapid capacity decay. Furthermore, electric vehicles require batteries to operate stably in environments ranging from -20°C to 45°C, placing even higher demands on electrolyte formulation design.

[0004] Patent CN105355970B discloses "A Ternary Cathode Material Lithium-ion Battery Electrolyte," which aims to improve the battery's cycle performance and high-temperature storage performance by adding a compound system of fluoroethylene carbonate, sulfur-containing organic compounds, and fluorinated ethers. The technical solution of this patent mainly targets a 4.35V operating voltage; the stability of its composite additive combination at higher voltages (4.5V) has not been proven, and its specification only focuses on room temperature cycling and 60℃ high-temperature storage, without addressing improvements in low-temperature performance.

[0005] Another patent, CN116779970A, entitled "A 4.5V High-Voltage Ternary Lithium-ion Battery Electrolyte and Its Preparation Method and Application," further attempts to increase the operating voltage to 4.5V. It employs a mixed lithium salt of lithium hexafluorophosphate and lithium difluorosulfonylimide, combined with fluorinated carbonate and pentafluoroethoxycyclotriphosphazene. Although this scheme is designed for a high voltage of 4.5V, it also only focuses on cycle performance at room temperature (25°C), without mentioning low-temperature discharge or cycle performance, nor conducting a systematic study on high-temperature stability.

[0006] In summary, for ternary lithium batteries, existing electrolyte technologies are still unable to ensure stable and long-lasting cycle performance across a wide temperature range in a 4.5V high-voltage operating environment. This technological bottleneck has not yet been effectively overcome. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the prior art and provide a 4.5V high-voltage wide-temperature-range ternary lithium-ion battery electrolyte, its preparation method and application, to solve the technical problem that "existing ternary battery electrolytes are difficult to achieve stable cycling over a wide temperature range at a high voltage of 4.5V".

[0008] To achieve the above objectives, the present invention is implemented using the following technical solution: In a first aspect, the present invention provides a 4.5V high-voltage wide-temperature-range ternary lithium-ion battery electrolyte, comprising: a non-aqueous organic solvent, a first lithium salt, a second lithium salt, a third lithium salt, and a composite additive; the first lithium salt is LiPF6, and its concentration in the electrolyte is 0.68~0.96 mol / L; the second lithium salt is LiDFOB, and its concentration in the electrolyte is 0.32~0.4 mol / L; the third lithium salt is LiBF4, and its concentration in the electrolyte is 0.1~0.16 mol / L; the composite additive comprises a first additive and a second additive, the first additive being tetrahydro-2-(trifluoromethyl)furan, and the second additive being 1,3,6-hexanetrionitrile; the non-aqueous organic solvent is prepared by mixing ethylene carbonate and dimethyl carbonate.

[0009] Secondly, the present invention provides a method for preparing a 4.5V high-voltage wide-temperature-range ternary lithium-ion battery electrolyte, comprising the following steps: under a dry inert atmosphere, ethylene carbonate and dimethyl carbonate are mixed to form a non-aqueous organic solvent, a first lithium salt, a second lithium salt and a third lithium salt are added to the solvent, and a composite additive is added, and the mixture is stirred until completely dissolved to obtain the electrolyte.

[0010] Furthermore, the mass ratio of ethylene carbonate to dimethyl carbonate is 1:(1~2).

[0011] Furthermore, the molar ratio of the first lithium salt, the second lithium salt, and the third lithium salt is (5.25~6.8):(2.5~3.2):1.

[0012] Furthermore, the mass ratio of the composite additive to the non-aqueous organic solvent is (0.02~0.1):1.

[0013] Furthermore, the volume ratio of the first additive and the second additive in the composite additive is (3~6):1.

[0014] Thirdly, the present invention provides an application of a 4.5V high-voltage wide-temperature-range ternary lithium-ion battery electrolyte in lithium-ion batteries, wherein the lithium-ion battery includes a cell and an electrolyte, and the cell includes a positive electrode, a negative electrode and a separator.

[0015] Compared with the prior art, the beneficial effects achieved by the present invention are: (1) This invention combines three lithium salts, lithium hexafluorophosphate, lithium difluorooxalate borate and lithium tetrafluoroborate, in a specific molar ratio, and uses tetrahydro-2-(trifluoromethyl)furan and 1,3,6-hexanetrionitrile as composite additives. This can effectively suppress the side reactions between the positive electrode and the electrolyte at a high voltage of 4.5V, significantly reduce the dissolution of transition metals, and thus greatly improve the room temperature cycling stability of the battery at a high voltage of 4.5V.

[0016] (2) The composite additive introduced in this invention is composed of tetrahydro-2-(trifluoromethyl)furan and 1,3,6-hexanetrionitrile in a specific ratio. Tetrahydro-2-(trifluoromethyl)furan has a low melting point, low viscosity and good antioxidant properties, which can significantly improve the ionic conductivity of the electrolyte and the wettability of the electrode interface at low temperatures; 1,3,6-hexanetrionitrile forms a stable complex layer with the transition metal ions on the positive electrode surface through its three cyano groups, inhibiting metal dissolution and assisting in the construction of a low-impedance interface film. The two work synergistically to greatly reduce the interface impedance and achieve stable cycling under a wide temperature range (-20~45℃).

[0017] (3) The present invention demonstrates by electrochemical impedance spectroscopy test at -20℃ that the composite additive and ternary lithium salt compound system can significantly reduce ohmic impedance, interfacial film impedance and charge transfer impedance under low temperature environment. The formula is simple, the preparation process is easy to control, and the raw materials are widely available, making it suitable for large-scale industrial production. Attached Figure Description

[0018] Figure 1 The graph shows the room temperature cycling performance of lithium-ion batteries prepared with the electrolytes described in the various embodiments and comparative examples of the present invention at 25°C and 4.5V.

[0019] Figure 2 This is a comparison chart showing the discharge capacity retention rate of lithium-ion batteries prepared with the electrolytes described in the various embodiments and comparative examples of the present invention at temperatures ranging from -20°C to 45°C.

[0020] Figure 3 This is a schematic diagram of the structure of the composite additive of the present invention. Detailed Implementation

[0021] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0022] The technical concept of this invention lies in addressing the technical deficiency of existing lithium-ion battery electrolytes in maintaining wide-temperature-range cycle stability at a high voltage of 4.5V. This is achieved by compounding three lithium salts—lithium hexafluorophosphate (LiPF6), lithium difluorooxalate borate (LiDFOB), and lithium tetrafluoroborate (LiBF4)—in a specific molar ratio, and using tetrahydro-2-(trifluoromethyl)furan and 1,3,6-hexanetrionitrile as functional composite additives. The ternary lithium salts work synergistically to form a stable and low-resistance passivation film at the positive and negative electrode interfaces, effectively suppressing side reactions and metal dissolution under high voltage. Tetrahydro-2-(trifluoromethyl)furan, due to the low melting point and low viscosity of its fluorine atoms, significantly reduces the viscosity increase of the electrolyte at low temperatures and maintains good ion mobility. This compound can preferentially adsorb onto the electrode surface to form a thin and dense LiF-rich interfacial film, greatly reducing interfacial impedance. 1,3,6-Hexanetrionitrile, as a low-temperature flexible film-forming and high-voltage complexing aid, has three cyano groups (-CN) in its molecule with strong coordination ability, which can preferentially form a stable complex layer with the transition metal ions (Ni, Co, Mn) exposed on the positive electrode surface at low temperatures, effectively inhibiting metal dissolution. The two exhibit a synergistic effect at low temperatures: tetrahydro-2-(trifluoromethyl)furan maintains the low viscosity and high ionic conductivity of the electrolyte, ensuring rapid migration of lithium ions in the liquid phase, while 1,3,6-Hexanetrionitrile, through the anchoring effect of the cyano groups at the electrode / electrolyte interface, further reduces the interfacial charge transfer impedance and stabilizes the existing interfacial film structure. Therefore, the electrolyte of this invention achieves stable cycling in a wide temperature range from -20°C to 45°C under a high voltage of 4.5V, significantly improving the overall application performance of lithium-ion batteries.

[0023] Based on the above technical concept, the present invention realizes the electrolyte solution through the following specific proportions and preparation steps.

[0024] Prepare the electrolyte in a glove box filled with argon gas, with less than 10 ppm of gaseous water. First, mix ethylene carbonate and dimethyl carbonate in a mass ratio of 1:(1~2) to form a solvent. Add LiPF6, LiDFOB and LiBF4 in a molar ratio of (5.25~6.8):(2.5~3.2):1 to the solvent. Then add a composite additive at a mass ratio of 2~10% of the solvent. After mixing and stirring, the electrolyte is obtained and stored in a -10℃ refrigerator for later use.

[0025] Preferably, the composite additive is prepared by mixing tetrahydro-2-(trifluoromethyl)furan and 1,3,6-hexanetrionitrile in a volume ratio of (3~6):1.

[0026] Preferably, the concentration of LiPF6 in the electrolyte is 0.68~0.96 mol / L.

[0027] Preferably, the concentration of LiDFOB is 0.32~0.4 mol / L.

[0028] Preferably, the concentration of LiBF4 is 0.1~0.16 mol / L.

[0029] The technical effects of the present invention will be further illustrated below with reference to specific embodiments, comparative examples and application examples, but the scope of protection of the present invention is not limited thereto.

[0030] Example 1; Electrolyte was prepared in a glove box filled with argon gas, with gaseous water content less than 10 ppm. A composite additive was prepared by first mixing tetrahydro-2-(trifluoromethyl)furan and 1,3,6-hexanetrionitrile at a volume ratio of 3:1. Ethylene carbonate and dimethyl carbonate were mixed at a mass ratio of 1:1 to form a solvent. LiPF6, LiDFOB, and LiBF4 were added to this solvent in a molar ratio of 6.8:3.2:1, followed by the addition of a composite additive at a mass ratio of 2% of the solvent. After mixing and stirring, the electrolyte was obtained and stored at -10℃ for later use. The concentrations of LiPF6, LiDFOB, and LiBF4 in the electrolyte were 0.68 mol / L, 0.32 mol / L, and 0.1 mol / L, respectively.

[0031] Example 2; Electrolyte was prepared in a glove box filled with argon gas, with gaseous water concentrations less than 10 ppm. A composite additive was prepared by first mixing tetrahydro-2-(trifluoromethyl)furan and 1,3,6-hexanetrionitrile at a volume ratio of 4:1. Ethylene carbonate and dimethyl carbonate were mixed at a mass ratio of 1:1.5 to form a solvent. LiPF6, LiDFOB, and LiBF4 were added to this solvent in a molar ratio of 6:3:1, followed by the addition of a 5% (by mass) composite additive. After mixing and stirring, the electrolyte was obtained and stored at -10°C for later use. The concentrations of LiPF6, LiDFOB, and LiBF4 in the electrolyte were 0.72 mol / L, 0.36 mol / L, and 0.12 mol / L, respectively.

[0032] Example 3; Electrolyte was prepared in a glove box filled with argon gas, with gaseous water concentrations less than 10 ppm. A composite additive was prepared by first mixing tetrahydro-2-(trifluoromethyl)furan and 1,3,6-hexanetrionitrile at a volume ratio of 6:1. Ethylene carbonate and dimethyl carbonate were mixed at a mass ratio of 1:2 to form a solvent. LiPF6, LiDFOB, and LiBF4 were added to this solvent in a molar ratio of 5.25:2.5:1, followed by the addition of a composite additive at 10% of the solvent mass. After mixing and stirring, the electrolyte was obtained and stored at -10°C for later use. The concentrations of LiPF6, LiDFOB, and LiBF4 in the electrolyte were 0.84 mol / L, 0.4 mol / L, and 0.16 mol / L, respectively.

[0033] Comparative Example 1; Electrolyte was prepared in a glove box filled with argon gas, with gaseous water content less than 10 ppm. A composite additive was prepared by first mixing tetrahydro-2-(trifluoromethyl)furan and 1,3,6-hexanetrionitrile at a volume ratio of 4:1. Ethylene carbonate and dimethyl carbonate were mixed at a mass ratio of 1:1.5 to form a solvent. LiPF6 was added to this solvent, followed by 5% (by mass) of the composite additive. After mixing and stirring, the electrolyte was obtained and stored at -10°C for later use. The concentration of LiPF6 in the electrolyte was 1.2 mol / L.

[0034] Comparative Example 2; The electrolyte was prepared in a glove box filled with argon gas, with gaseous water content less than 10 ppm. First, ethylene carbonate and dimethyl carbonate were mixed in a mass ratio of 1:1.5 to form a solvent. Then, LiPF6, LiDFOB, and LiBF4 were added to this solvent in a molar ratio of 6:3:1. Next, 1,3,6-hexanetrionitrile was added at 5% of the solvent mass. After mixing and stirring, the electrolyte was obtained and stored at -10℃ for later use. The concentrations of LiPF6, LiDFOB, and LiBF4 in the electrolyte were 0.72 mol / L, 0.36 mol / L, and 0.12 mol / L, respectively.

[0035] Application examples 1-5; (1) Preparation of positive electrode: Polyvinylidene fluoride is uniformly dissolved in N-methylpyrrolidone. By mass percentage, 96.5% of ternary (lithium nickel cobalt manganese oxide) positive electrode material, 2% of conductive carbon nanotubes, and 1.5% of binder polyvinylidene fluoride solution are mixed and stirred evenly to obtain a positive electrode slurry with a solid content of 68.4%. The positive electrode slurry is coated on the current collector, and then dried, calendered, and slit to obtain a positive electrode that can be directly stacked. (2) Preparation of negative electrode: Graphite: conductive agent carbon nanotube: binder styrene-butadiene rubber: thickener sodium carboxymethyl cellulose are mixed in a mass ratio of 97.2:0.6:1:1.3 and stirred. Deionized water is added at the same time for dispersion. The negative electrode slurry is prepared by high-speed stirring. The slurry is coated on the surface of copper foil and then dried, rolled and slit in sequence to obtain a negative electrode that can be directly stacked. (3) Preparation of electrolyte: The specific components and preparation steps of the electrolyte correspond to Examples 1-3 and Comparative Examples 1-2, respectively; (4) Battery assembly: The positive and negative electrode sheets obtained in the above steps are stacked alternately with the separator using a Z-shaped stacking process. The separator is a polyethylene base film with a ceramic layer coated on one side (base film thickness 12μm, ceramic layer thickness 2μm). After stacking, the cells are hot-pressed and shaped, the tabs are welded, and the cells are installed in an aluminum-plastic film shell. After top sealing and side sealing, the soft-pack battery core is injected with electrolyte, formed, and finally sealed to obtain a lithium-ion battery.

[0036] Test and Results Analysis The prepared soft-pack battery cells and the corresponding electrolytes of each embodiment and comparative example were labeled as samples E1, E2, E3, C1, and C2 according to the preparation method of the application example, and the following tests were performed.

[0037] High and low temperature cycling performance test: The tested pouch cells (E1, E2, E3, C1, C2) were cycled in a 45℃ constant temperature chamber and a -20℃ low temperature chamber, respectively. Charging regime: 0.5C constant current charging to 4.5V, then constant voltage charging until the current drops to 0.05C, followed by 5 minutes of rest; 0.5C constant current discharging to 3.0V. The first discharge capacity of the cell in the first cycle at the corresponding test temperature was taken as 100% of the baseline, and the capacity retention rate was calculated. Capacity retention rate (%) after N cycles = discharge capacity in the Nth cycle at this temperature / first discharge capacity in the first cycle at this temperature × 100%. Each test group used an independent cell, and the results are shown in Table 1.

[0038] Table 1

[0039] As shown in Table 1, Examples E1 to E3 demonstrate that the composite additive composed of the ternary lithium salt complex system described in this invention and tetrahydro-2-(trifluoromethyl)furan and 1,3,6-hexanetrionitrile can significantly improve the cycle stability of the battery over a wide temperature range (-20~45℃) at a high voltage of 4.5V. Specifically, the optimal formulation E2 maintained a capacity retention of 90.1% after 400 cycles at 45℃ and 82.7% after 200 cycles at -20℃, proving that this combination effectively suppresses interfacial side reactions and capacity decay under high and low temperature environments.

[0040] When Comparative Example 1 (C1) uses only a single lithium salt, LiPF6, without the synergistic film-forming effect of LiDFOB and LiBF4, its high and low temperature cycling performance is significantly reduced even when the same composite additives are added. This indicates that the combination of ternary lithium salts is indispensable for constructing a stable, low-impedance interface film.

[0041] When the composite additive in Comparative Example 2 (C2) lacked tetrahydro-2-(trifluoromethyl)furan and only used 1,3,6-hexanetrionitrile, the electrolyte exhibited the worst cycling stability at both high and low temperatures, with only 63.8% stability after 200 cycles at -20℃. This demonstrates that tetrahydro-2-(trifluoromethyl)furan is a key component for improving wide-temperature-range cycling performance by reducing low-temperature viscosity and assisting in the formation of a LiF-rich interfacial film.

[0042] Room temperature cycling performance test: At 25℃, charge at a constant current of 0.5C to 4.5V, then switch to constant voltage charging until the current drops to 0.05C, let stand for 5 minutes, and then discharge at a constant current of 0.5C to 3.0V. Record the initial discharge capacity. Cycle according to the above steps, and record the capacity retention rate of each cell from 0 to 700 cycles. The results are shown in […]. Figure 1 .

[0043] like Figure 1 As shown, the horizontal axis represents the number of charge-discharge cycles, and the vertical axis represents the capacity retention rate. The capacity retention rate of all batteries decreases with increasing cycle count. Battery E2 exhibits the slowest degradation, maintaining a capacity retention rate of over 95% after 700 cycles. Batteries C1 and C2 show the fastest degradation, with their capacity retention rates dropping to 86-88% after 700 cycles. E1 and E3 show moderate degradation rates, with capacity retention rates of approximately 93% and 90%, respectively, after 700 cycles. It is evident that the electrolyte using a ternary mixed lithium salt with a molar ratio of 6:3:1 and an appropriate amount of composite additives exhibits the best high-voltage cycling stability, while the comparative examples lacking tetrahydro-2-(trifluoromethyl)furan or using only a single lithium salt show relatively faster degradation rates.

[0044] Low-temperature electrochemical impedance spectroscopy test: After the soft-pack battery cell under test was placed in a constant temperature chamber at -20℃ for 4 hours until the temperature reached equilibrium, its AC impedance spectrum was measured using an electrochemical workstation with a frequency range of 100kHz to 0.01Hz and an AC amplitude of 5mV applied. The ohmic resistance (RΩ), interfacial film resistance (Rf), and charge transfer resistance (Rct) were obtained by fitting with an equivalent circuit. The specific results are shown in Table 2.

[0045] Table 2

[0046] As shown in Table 2, Examples 1-3 demonstrate that the composite additive composed of tetrahydro-2-(trifluoromethyl)furan and 1,3,6-hexanetrionitrile described in this invention, combined with a ternary lithium salt (LiPF6, LiDFOB, LiBF4) complex system, can significantly reduce the ohmic impedance (RΩ), interfacial film impedance (Rf), and charge transfer impedance (Rct) of the electrolyte at -20℃. In Example 2, the Rct is as low as 33.6mΩ, and the total impedance is only 53.6mΩ, proving that this ratio can effectively improve the transport dynamics of lithium ions in the electrolyte bulk and at the interface at low temperatures, thereby improving the low-temperature discharge performance.

[0047] Comparative Example 1 (C1), although the same composite additive was added, only a single lithium salt LiPF6 was used, and its Rct was as high as 62.5 mΩ, and the total impedance was 95.0 mΩ, which was much higher than any of the embodiments. This shows that without the synergistic film-forming effect of LiDFOB and LiBF4, it is difficult to construct a low-impedance interface film. Therefore, the ternary lithium salt composite of the present invention is essential to reduce low-temperature impedance.

[0048] The composite additive in Comparative Example 2 (C2) lacked tetrahydro-2-(trifluoromethyl)furan, and the RΩ, Rf, and Rct of the electrolyte were the highest among all samples; this indicates that it is difficult to fully exert the effect of reducing interfacial impedance by using cyano additives alone.

[0049] Wide-temperature-range discharge performance testing: A DC discharge capacity testing method was used to characterize the performance of batteries with various electrolyte systems within a temperature range of -20 to 45°C. The batteries were first fully charged under standard conditions at 25°C, then transferred to the corresponding temperature environment and allowed to stand until the internal temperature of the battery reached equilibrium with the ambient temperature. Afterward, a constant current was used to discharge the batteries to the termination voltage, and the discharge capacity at different temperatures was recorded. Using the discharge capacity at 25°C as a baseline, the capacity retention rate at each temperature was recorded. The capacity retention rate (%) at this temperature was calculated as: (Discharge capacity at this temperature / Discharge capacity at 25°C) × 100%. Results are shown in [Figure / Table / Incomplete]. Figure 2 .

[0050] like Figure 2As shown, the capacity retention of all batteries in the application examples decreased with decreasing temperature, indicating a significant impact of low temperature on battery discharge performance. Among them, the electrolytes of the examples (E1, E2, E3) showed significantly better capacity retention at low temperatures than the comparative electrolytes (C1, C2). In particular, at -20°C, the capacity retention of the electrolyte of Example 2 remained at 78.5%, while the capacity retention of the electrolyte of Comparative Example 1 (C1), which used only a single lithium salt LiPF6, was 72.6% at -20°C. The electrolyte of Comparative Example 2 (C2) only added 1,3,6-hexanetrionitrile, lacking the antioxidant effect of tetrahydro-2-(trifluoromethyl)furan, resulting in the most significant decrease in low-temperature performance, with a capacity retention of only 69.2% at -20°C. Under normal temperature and high temperature (45°C) conditions, the differences in capacity retention among the battery groups were relatively small.

[0051] Figure 3 This is a schematic diagram of the structural formula of the composite additive of the present invention, wherein, Figure 3 (a) is the structural formula of the first additive, tetrahydro-2-(trifluoromethyl)furan. Figure 3 (b) shows the structural formula of the second additive, 1,3,6-hexanetrionitrile. In the first additive, a trifluoromethyl group is attached to the carbon atom at position 2 of the tetrahydrofuran ring. The strong electron-withdrawing fluorine atom effectively improves antioxidant properties and reduces low-temperature viscosity. The three cyano groups in the second additive can complex transition metal ions and enhance the flexibility of the interfacial film. When used in combination with various lithium salts, both can synergistically improve the electrical performance of lithium-ion batteries under high voltage and wide temperature range.

[0052] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No markings in the claims should be construed as limiting the scope of the claims.

Claims

1. A 4.5V high-voltage, wide-temperature-range ternary lithium-ion battery electrolyte, characterized in that, include: Non-aqueous organic solvents, first lithium salt, second lithium salt, third lithium salt, and composite additives; The first lithium salt is LiPF6, and its concentration in the electrolyte is 0.68~0.96 mol / L; The second lithium salt is LiDFOB, and its concentration in the electrolyte is 0.32~0.4 mol / L; The third lithium salt is LiBF4, and its concentration in the electrolyte is 0.1~0.16 mol / L; The composite additive includes a first additive and a second additive. The first additive is a halogen-substituted furan compound, and the second additive is 1,3,6-hexanetrionitrile.

2. The electrolyte according to claim 1, characterized in that, The non-aqueous organic solvent is prepared by mixing ethylene carbonate and dimethyl carbonate.

3. The electrolyte according to claim 1, characterized in that, The first additive is tetrahydro-2-(trifluoromethyl)furan.

4. A method for preparing an electrolyte as described in any one of claims 1-3, characterized in that, The process includes the following steps: under a dry, inert atmosphere, ethylene carbonate and dimethyl carbonate are mixed to form a non-aqueous organic solvent. A first lithium salt, a second lithium salt, and a third lithium salt are added to the solvent, followed by the addition of a composite additive. The mixture is stirred until completely dissolved to obtain the electrolyte.

5. The method according to claim 4, characterized in that, The mass ratio of ethylene carbonate to dimethyl carbonate is 1:(1~2).

6. The method according to claim 4, characterized in that, The molar ratio of the first lithium salt, the second lithium salt, and the third lithium salt is (5.25~6.8):(2.5~3.2):

1.

7. The method according to claim 4, characterized in that, The mass ratio of the composite additive to the non-aqueous organic solvent is (0.02~0.1):

1.

8. The method according to claim 4, characterized in that, The volume ratio of the first additive to the second additive in the composite additive is (3~6):

1.

9. The application of the electrolyte according to any one of claims 1-3 in a lithium-ion battery.

10. The application according to claim 9, characterized in that, The lithium-ion battery includes a cell and an electrolyte, and the cell includes a positive electrode, a negative electrode, and a separator.

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