Wide-temperature-range and high-voltage lithium ion battery electrolyte containing amide solvent and preparation method of wide-temperature-range and high-voltage lithium ion battery electrolyte

Abstract

The invention relates to the technical field of electrolytes, in particular to a wide-temperature-range high-voltage lithium ion battery electrolyte containing an amide solvent and a preparation method of the wide-temperature-range high-voltage lithium ion battery electrolyte. The fluorinated amide solvent comprises a main solvent and a cosolvent, the main solvent comprises one or more of perfluoro-2-methyl pyrrolidone, perfluoro-N-methyl pyrrolidone, perfluoro-epsilon-caprolactam, N, N-difluoroethyl formamide and trifluoroacetamide, and the cosolvent comprises one or more of perfluoro-2-methyl pyrrolidone, perfluoro-N-methyl pyrrolidone, perfluoro-epsilon-caprolactam, N, N-difluoroethyl formamide and trifluoroacetamide. The lithium salt comprises one or more of lithium bis (fluorosulfonyl) imide, lithium bis (trifluoromethanesulfonyl) imide, lithium bis (oxalato) borate, lithium difluoro (oxalato) borate and lithium tetrafluoroborate; the functional additives comprise a high-voltage additive, a temperature-adaptive additive and a flame retardant. The obtained electrolyte can maintain good electrochemical performance in a wide temperature range, has high voltage stability, improves the energy density and safety of the lithium ion battery, and prolongs the cycle life of the lithium ion battery.

Description

Technical Field

[0001] The present invention relates to the technical field of electrolytes, and in particular to an amide solvent-containing wide-temperature-range high-voltage lithium-ion battery electrolyte and a preparation method thereof. Background Art

[0002] With the rapid development of new energy technologies, lithium-ion batteries have been widely used in electric vehicles, energy storage systems, and other fields. However, existing lithium-ion battery electrolytes still face numerous challenges in wide temperature range and high voltage performance. At low temperatures, electrolyte viscosity increases, reducing lithium ion migration rates and leading to reduced battery charge and discharge performance. At high temperatures, the electrolyte is prone to side reactions such as decomposition and oxidation, affecting battery safety and cycle life.

[0003] In recent years, high-voltage systems have become an important direction for improving battery energy density. However, conventional electrolytes are very likely to cause lattice collapse of positive electrode materials and oxidative decomposition of the electrolyte itself under high voltage, which limits further breakthroughs in battery performance. Amide solvents have unique molecular structures and physical and chemical properties, showing excellent adaptability to a wide temperature range and high voltage stability: their low freezing point characteristics can effectively reduce the low-temperature viscosity of the electrolyte and promote the rapid migration of lithium ions; at the same time, the strong interaction between the amide group and the electrode surface can form a stable interfacial protective film, inhibiting the occurrence of side reactions under high voltage. Therefore, the development of wide-temperature-range, high-voltage lithium-ion battery electrolytes based on amide solvents is of great practical significance for promoting the development of new energy technologies. Summary of the Invention

[0004] The purpose of the present invention is to provide a wide-temperature range, high-voltage lithium-ion battery electrolyte containing an amide solvent and a preparation method thereof. The obtained electrolyte can maintain good electrochemical properties over a wide temperature range while having high voltage stability, thereby improving the energy density, safety and cycle life of the lithium-ion battery.

[0005] To achieve the above objectives, the present invention provides a wide-temperature range, high-voltage lithium-ion battery electrolyte containing an amide solvent, the electrolyte comprising a fluorinated amide solvent, a lithium salt, and a functional additive;

[0006] The fluorinated amide solvent includes a main solvent and a co-solvent, the main solvent includes one or more of perfluoro-2-methylpyrrolidone, perfluoro-N-methylpyrrolidone, perfluoro-ε-caprolactam, N,N-difluoroethylformamide, and trifluoroacetamide, and the co-solvent includes one or more of fluoroethylene carbonate, difluoroethylene carbonate, methyl fluoroacetate, ethyl trifluoropropionate, bis(2,2,2-trifluoroethyl) ether, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether;

[0007] The lithium salt includes one or more of lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(oxalatoborate), lithium difluorooxalatoborate, and lithium tetrafluoroborate;

[0008] Functional additives include high voltage additives, temperature adaptability additives and flame retardants.

[0009] Preferably, the volume ratio of the main solvent to the co-solvent is 1:1-1:3.

[0010] More preferably, the main solvent is perfluoro-2-methylpyrrolidone, and the co-solvent is a mixture of fluoroethylene carbonate and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0011] The present invention uses fluorinated amide as the main solvent, and its highly fluorinated molecular structure has excellent chemical stability and thermal stability. During the operation of the battery, the highly fluorinated structure makes the solvent molecules less likely to be oxidized and decomposed, and can withstand strong oxidation in a high-voltage environment, thereby effectively avoiding problems such as decomposition and gas production of the electrolyte, and providing a stable dielectric environment for the high-voltage operation of the battery. At the same time, fluorinated amide solvents have a low freezing point and a high boiling point, which broadens the liquid temperature range of the electrolyte. They are not easy to solidify in low-temperature environments, ensuring the normal transmission of lithium ions in the electrolyte; they are also not easy to volatilize in high-temperature environments, maintaining the stability of the electrolyte concentration and realizing wide-temperature application of the battery.

[0012] The present invention uses fluoroesters or fluoroethers as co-solvents, which can form a good mixed system with the main solvent and optimize the physical and chemical properties of the electrolyte. On the one hand, it can reduce the viscosity of the electrolyte and increase the migration rate of lithium ions in the electrolyte, thereby improving the charge and discharge performance of the battery; on the other hand, the co-solvent molecules can participate in the formation of a stable solid electrolyte interface (SEI) film on the electrode surface. During the first charge and discharge process of the battery, the co-solvent molecules preferentially undergo reduction and decomposition on the electrode surface to form a uniform, dense SEI film with good ionic conductivity. This film can not only prevent the electrolyte from further side reactions with the electrode, thereby improving the cycle stability and safety of the battery, but also promote the rapid insertion and extraction of lithium ions, thereby enhancing the performance of the battery at different temperatures.

[0013] Preferably, the concentration of lithium salt in the electrolyte is 1.2-1.5 mol / L.

[0014] More preferably, the lithium salt in the electrolyte is lithium bis(fluorosulfonyl)imide as the main lithium salt, with lithium bis(oxalatoborate) as the auxiliary lithium salt. Lithium bis(fluorosulfonyl)imide has high conductivity and good thermal stability, is not easily decomposed at high voltage, and effectively improves the charge and discharge performance and cycle life of the battery. Lithium bis(oxalatoborate) synergistically forms a dense and stable SEI film and CEI film on the electrode surface, inhibiting the decomposition of the electrolyte and improving the high-voltage stability and safety of the battery.

[0015] The lithium salt used in this invention has high ionic conductivity and good solubility, allowing it to fully ionize in fluorinated amide solvents to form a highly concentrated lithium ion solution. During battery charging, lithium ions are released from the positive electrode material, migrate through the electrolyte, and become embedded in the negative electrode material; the discharge process is the opposite.

[0016] The anionic portion of the lithium salt can interact with fluorinated amide solvent molecules to form a stable solvation sheath structure constructed by coordination bonds and electrostatic interactions between lithium ions, amide solvent molecules, and lithium salt anions. This structure consists of a tightly bound first solvation shell (composed of direct coordination between lithium ions and oxygen / nitrogen atoms of solvent molecules) on the inner layer and a weaker second solvation shell on the outer layer. The solvation sheath structure helps improve the transmission efficiency of lithium ions at the interface between the electrolyte and electrode materials, reducing battery polarization, thereby improving the battery's charge and discharge capacity and cycle performance.

[0017] Preferably, the volume fraction of the high voltage additive is 1-3%, and the high voltage additive includes one or more of trimethyl borate, tris(trimethylsilyl)borate, lithium difluorophosphate, triallyl phosphate, vinyl sulfate, and 1,3-propane sultone.

[0018] More preferably, the high-pressure additive is trimethyl borate.

[0019] The high-voltage additive of the present invention has a strong electron-withdrawing effect. Under high voltage conditions, it undergoes oxidative decomposition on the cathode surface, forming a high-impedance, highly stable passivation film. This effectively inhibits irreversible phase transitions and structural damage in the cathode material under high voltage, preventing further side reactions between the electrolyte and the cathode material, thereby improving the stability of the cathode material and the battery's high-voltage tolerance. For example, BOx species generated by the decomposition of the auxiliary lithium salt lithium bis(oxalatoborate) can co-construct a "gradient" CEI film (with a BO-rich outer layer and a LiF-rich inner layer) with the BO network derived from trimethyl borate, reducing interfacial impedance.

[0020] Preferably, the volume fraction of the temperature adaptability additive is 1-3%, and the temperature adaptability additive includes one or more of tetramethylene sulfone, vinylene carbonate, and benzimidazole.

[0021] More preferably, the temperature adaptability additive is a mixture of tetramethylene sulfone and benzimidazole.

[0022] The temperature-adaptable additive of the present invention reduces the viscosity of the electrolyte, increases the diffusion rate of lithium ions, and enhances the low-temperature charge and discharge capabilities of the battery in a low-temperature environment; in a high-temperature environment, it participates in the formation of a more stable SEI film and positive electrode passivation film, inhibits the decomposition of the electrolyte and the corrosion of the electrode material, and improves the high-temperature stability and safety of the battery.

[0023] Preferably, the volume fraction of the flame retardant is 0.5-2%, and the flame retardant includes one or more of trimethyl phosphate, hexamethylphosphoric triamide, and tris(2,2,2-trifluoroethyl) phosphate.

[0024] The present invention also provides a method for preparing the above-mentioned wide-temperature-range high-voltage lithium-ion battery electrolyte containing an amide solvent, comprising the following steps:

[0025] S1. Mixing the main solvent and the co-solvent at room temperature under stirring to obtain a fluorinated amide solvent;

[0026] S2. Add lithium salt to the fluorinated amide solvent of S1. After the addition is complete, increase the stirring speed and stir at a temperature of 30-40° C. until the lithium salt is completely dissolved to form a clear and transparent solution;

[0027] S3. Add the high voltage additive and the temperature adaptability additive to the solution of S2. After the addition is complete, adjust the stirring speed and stir at room temperature for 30-45 minutes;

[0028] S4. Add flame retardant to S3, adjust the stirring speed again, and stir at room temperature for 20-30 minutes to obtain an electrolyte;

[0029] S5. Filter the electrolyte obtained in S4 through a 0.22 μm microporous filter membrane, then transfer it to a dry, sealed container and fill it with argon for protection, thereby obtaining a wide temperature range, high voltage lithium-ion battery electrolyte containing an amide solvent.

[0030] Preferably, the stirring speed in S1 is 200-250 r / min, and the stirring is carried out at room temperature for 30-45 min.

[0031] The present invention controls the stirring speed in S1 within the above range, which can not only provide sufficient shear force to promote the thorough mixing of the two solvents and avoid local concentration differences, but also effectively control the heat accumulation caused by excessive stirring during the stirring process, and prevent the solvent from volatilizing or chemically reacting due to temperature increase; at the same time, a moderate rotation speed can reduce the mechanical stress during the stirring process, avoid damage to the molecular structure of the solvent, ensure the stability of the physical and chemical properties of the mixed solvent, and provide a uniform and reliable basic solvent system for the subsequent preparation of the electrolyte.

[0032] Preferably, in S2, the stirring speed is increased to 300-400 r / min, and the stirring is carried out at a temperature of 30-40° C. for 30-60 min.

[0033] The present invention increases the stirring speed in S2 to the above range, thereby enhancing the material mixing efficiency. A higher stirring speed can effectively increase the collision frequency between the components, prompting the amide solvent, lithium salt and additives to be quickly and evenly dispersed, thereby avoiding uneven electrolyte performance caused by local concentration differences. At the same time, this speed range can generate moderate shear force, accelerate the dissolution process of the lithium salt, and help eliminate bubbles generated during the mixing process, ensuring the uniformity and stability of the electrolyte system, thereby improving the overall performance of wide-temperature high-voltage lithium-ion batteries.

[0034] Preferably, the stirring speed in S3 is adjusted to 200-250 r / min, and the stirring speed in S4 is adjusted to 150-200 r / min.

[0035] The present invention controls the stirring speed in S3 within the above range. The purpose is to avoid safety risks such as excessive bubbles in the electrolyte or even splashing caused by excessively high rotation speed, while providing a shear force sufficient to quickly disperse the high-voltage additive at room temperature, and to achieve sufficient and uniform dispersion of the additive within 30-45 minutes, thereby ensuring the uniformity and stability of the mixing of the various components of the electrolyte.

[0036] The present invention controls the stirring speed in S4 within the above range to ensure uniform mixing of the entire electrolyte system. A rotation speed that is too low will lead to insufficient mixing efficiency, making it impossible to fully disperse the solute and solvent, resulting in uneven electrolyte concentration; a rotation speed that is too high may introduce too many bubbles, exacerbating the contact between the electrolyte and air, leading to solvent volatilization or additive decomposition, and the shear force generated may destroy the solute molecular structure. 150-200r / min can provide sufficient stirring kinetic energy to promote the mass transfer process and achieve full mixing of the components, while avoiding the negative effects caused by excessive stirring, ensuring the stability and uniformity of the electrolyte system.

[0037] The present invention uses the above-mentioned wide-temperature range high-voltage lithium-ion battery electrolyte containing an amide solvent and the beneficial effects of the preparation method thereof:

[0038] (1) Fluorinated amide solvents keep the electrolyte at low viscosity at low temperatures, ensuring rapid migration of lithium ions; they remain stable at high temperatures without decomposition or volatilization, allowing the battery to operate normally within the temperature range of -60°C to 80°C, thus broadening the battery's operating temperature range.

[0039] (2) Through the synergistic effect of lithium salts and high-voltage additives, a stable electrode interface film can be formed under high voltage, effectively inhibiting the structural destruction of the positive electrode material and the decomposition of the electrolyte, enabling the battery to operate stably at high voltage and improving the energy density of the battery.

[0040] (3) The addition of temperature-adaptive additives and flame retardants enhances the stability and safety of the battery at different temperatures and reduces safety hazards such as thermal runaway. At the same time, the stable electrode interface film and electrolyte system effectively reduce the polarization of the battery and improve the cycle life of the battery.

[0041] The technical solution of the present invention is further described in detail below through examples. DETAILED DESCRIPTION

[0042] The present invention will be further described below with reference to the following embodiments. Unless otherwise defined, technical or scientific terms used herein shall have the same meanings as those commonly understood by persons of ordinary skill in the art to which the present invention pertains. The above-mentioned features or features described in the specific examples of the present invention may be combined in any manner. These specific embodiments are intended only to illustrate the present invention and are not intended to limit the scope of the present invention.

[0043] Example 1

[0044] The present invention provides a wide-temperature-range, high-voltage lithium-ion battery electrolyte containing an amide solvent. The main solvent is perfluoro-2-methylpyrrolidone, and the co-solvent is a mixture of fluoroethylene carbonate and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (volume ratio of 3:2). The volume ratio of the main solvent to the co-solvent is 1:1. The lithium salt is lithium bis(fluorosulfonyl)imide as the main lithium salt, and lithium bis(oxalatoborate) as the auxiliary lithium salt. The lithium salt concentration is 1.2 mol / L. The high-voltage additive is trimethyl borate, with a volume fraction of 1%; the temperature adaptability additive is vinylene carbonate, with a volume fraction of 1%; and the flame retardant is trimethyl phosphate, with a volume fraction of 0.5%.

[0045] The preparation method comprises the following steps:

[0046] S1. Add the above main solvent and co-solvent in a volume ratio of 1:1 into a dry, clean container, and stir at room temperature at a speed of 200 r / min for 30 minutes to obtain a fluorinated amide solvent.

[0047] S2. Add lithium salt to the fluorinated amide solvent in S1 to make the concentration of lithium salt 1.2 mol / L. After the addition is completed, increase the stirring speed to 300 r / min and stir at 35°C for 60 min until the lithium salt is completely dissolved to form a clear and transparent solution.

[0048] S3. Add the high voltage additive and the temperature adaptability additive to the solution of S2. After the addition is completed, adjust the stirring speed to 200 r / min and stir at room temperature for 45 minutes.

[0049] S4. Add flame retardant to S3, adjust the stirring speed to 150 r / min again, and stir at room temperature for 30 min to obtain an electrolyte.

[0050] S5. Filter the electrolyte obtained in S4 through a 0.22 μm microporous filter membrane, then transfer it to a dry, sealed container and fill it with argon for protection, thereby obtaining a wide temperature range, high voltage lithium-ion battery electrolyte containing an amide solvent.

[0051] Example 2

[0052] The present invention provides a wide-temperature-range, high-voltage lithium-ion battery electrolyte containing an amide solvent. The main solvent is perfluoro-N-methylpyrrolidone, and the co-solvent is a mixture of difluoroethylene carbonate and bis(2,2,2-trifluoroethyl) ether (volume ratio of 3:2). The volume ratio of the main solvent to the co-solvent is 1:2. The lithium salt is lithium bistrifluoromethanesulfonyl imide as the main lithium salt, and lithium difluorooxalatoborate as the auxiliary lithium salt. The lithium salt concentration is 1.3 mol / L. The high-voltage additive is trimethyl borate, with a volume fraction of 2%; the temperature adaptability additive is vinylene carbonate, with a volume fraction of 2%; and the flame retardant is trimethyl phosphate, with a volume fraction of 1%.

[0053] The preparation method comprises the following steps:

[0054] S1. Add the above main solvent and co-solvent in a volume ratio of 1:1 into a dry, clean container, and stir at room temperature at a speed of 220 r / min for 45 minutes to obtain a fluorinated amide solvent.

[0055] S2. Add lithium salt to the fluorinated amide solvent in S1 to make the concentration of lithium salt 1.3 mol / L. After the addition is completed, increase the stirring speed to 350 r / min and stir at 40°C for 60 min until the lithium salt is completely dissolved to form a clear and transparent solution.

[0056] S3. Add the high voltage additive and the temperature adaptability additive to the solution of S2. After the addition is completed, adjust the stirring speed to 220 r / min and stir at room temperature for 45 minutes.

[0057] S4. Add flame retardant to S3, adjust the stirring speed to 180 r / min again, and stir at room temperature for 30 min to obtain an electrolyte.

[0058] S5. Filter the electrolyte obtained in S4 through a 0.22 μm microporous filter membrane, then transfer it to a dry, sealed container and fill it with argon for protection, thereby obtaining a wide temperature range, high voltage lithium-ion battery electrolyte containing an amide solvent.

[0059] Example 3

[0060] The present invention provides a wide-temperature-range, high-voltage lithium-ion battery electrolyte containing an amide solvent. The main solvent is N,N-difluoroethylformamide, and the cosolvent is a mixture of methyl fluoroacetate and bis-1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (volume ratio is 3:2). The volume ratio of the main solvent to the cosolvent is 1:3. The lithium salt is lithium bis(fluorosulfonyl)imide as the main lithium salt, and lithium bis(oxalatoborate) as the auxiliary lithium salt. The lithium salt concentration is 1.5 mol / L. The high-voltage additive is trimethyl borate, with a volume fraction of 3%; the temperature adaptability additive is vinylene carbonate, with a volume fraction of 3%; and the flame retardant is trimethyl phosphate, with a volume fraction of 2%.

[0061] The preparation method comprises the following steps:

[0062] S1. Add the above main solvent and co-solvent in a volume ratio of 1:1 into a dry, clean container, and stir at room temperature at a speed of 250 r / min for 45 minutes to obtain a fluorinated amide solvent.

[0063] S2. Add lithium salt to the fluorinated amide solvent in S1 to make the concentration of lithium salt 1.5 mol / L. After the addition is completed, increase the stirring speed to 400 r / min and stir at 40°C for 60 min until the lithium salt is completely dissolved to form a clear and transparent solution.

[0064] S3. Add the high voltage additive and the temperature adaptability additive to the solution of S2. After the addition is completed, adjust the stirring speed to 250 r / min and stir at room temperature for 45 minutes.

[0065] S4. Add flame retardant to S3, adjust the stirring speed to 200 r / min again, and stir at room temperature for 30 minutes to obtain an electrolyte.

[0066] S5. Filter the electrolyte obtained in S4 through a 0.22 μm microporous filter membrane, then transfer it to a dry, sealed container and fill it with argon for protection, thereby obtaining a wide temperature range, high voltage lithium-ion battery electrolyte containing an amide solvent.

[0067] Comparative Example 1

[0068] The electrolyte composition is composed of ethylene carbonate and dimethyl carbonate (1:1 volume ratio) as the main solvents, and ethyl methyl carbonate as the co-solvent, with a volume ratio of 1:1. The lithium salt is lithium hexafluorophosphate at a concentration of 1.0 mol / L. No high-voltage additives, temperature-adaptive additives, or flame retardants are added. This electrolyte is a traditional carbonate-based lithium-ion battery electrolyte formulation.

[0069] Preparation method: add the main solvent and co-solvent to a dry container, stir and mix them evenly at a speed of 200-250r / min; then add lithium salt and continue stirring until completely dissolved; finally filter through a 0.22μm microporous filter membrane, then transfer to a dry, sealed container, fill with argon gas for protection, and obtain a lithium-ion battery electrolyte.

[0070] Comparative Example 2

[0071] Taking Example 1 as a reference, the difference from Example 1 is that no high voltage additive, temperature adaptability additive and flame retardant are added to the lithium ion battery electrolyte. The preparation method is the same as that of Example 1.

[0072] Comparative Example 3

[0073] The difference from Example 1 is that no flame retardant is added to the lithium ion battery electrolyte. The preparation method is the same as that of Example 1.

[0074] The electrolytes prepared in Examples 1-3 and Comparative Examples 1-3 were assembled into lithium-ion batteries. The positive electrode material was lithium iron phosphate, the negative electrode material was graphite, and Cellgard 2500 was used as the separator. Constant current charge and discharge tests were conducted within the 2.75-4.6 V voltage range. After charging at 0.5 C, the batteries were cycled 1000 times at -60°C, -40°C, -20°C, 0°C, 20°C, 40°C, 60°C, and 80°C. The results are shown in Table 1-2.

[0075] Table 1 Capacity retention rate of lithium-ion batteries assembled in Examples 1-3

[0076]

[0077] Table 2 Capacity retention rate of lithium-ion batteries assembled in Comparative Examples 1-3

[0078]

[0079]

[0080] As can be seen from Tables 1 and 2, under an extremely low temperature environment of -60°C, Comparative Example 1 cannot be effectively discharged, while Examples 1-3 can still achieve an initial discharge specific capacity of 60-70 mAh / g at 0.5C. As the temperature rises to -40°C, the initial discharge specific capacity of Examples 1-3 increases to 100-120 mAh / g. Although Comparative Examples 2 and 3 have discharge capabilities, their specific capacities are only 60-70 mAh / g, and Comparative Example 1 is only 15 mAh / g. In terms of capacity retention after 1000 cycles, at -60°C, Examples 1-3 can reach 65%-70%, respectively, while Comparative Examples 2 and 3 are only 50%-55%, and Comparative Example 1 cannot be cycled. This shows that the fluorinated amide solvent and temperature-adaptive additive in the electrolyte of the present invention effectively reduce the low-temperature viscosity of the electrolyte and increase the lithium ion migration rate. At the same time, the stable SEI film ensures the normal reaction of the electrode interface at low temperatures, so that the battery still has good charge and discharge performance and cycle stability in an extremely low temperature environment.

[0081] When the temperature reaches 80°C, the initial discharge specific capacity of Examples 1-3 can still be maintained at 175-195 mAh / g, and the capacity retention rate after 1000 cycles is 78%-84%. In contrast, the initial discharge specific capacity of Comparative Examples 1-3 drops to 100-140 mAh / g, and the capacity retention rate after 1000 cycles is only 40%-69%. In the electrolyte of the present invention, the high chemical and thermal stability of the main solvent, as well as the stable electrode interface film formed by the flame retardant and temperature adaptability additives at high temperatures, effectively inhibit the decomposition of the electrolyte and the corrosion of the electrode material, ensuring the performance and safety of the battery in high temperature environments.

[0082] During the high-voltage charge and discharge process of 2.75-4.6V, Examples 1-3 effectively suppressed the structural destruction of the positive electrode material and the decomposition of the electrolyte by virtue of the stable passivation film formed on the surface of the positive electrode by the high-voltage additive. After 1000 cycles at various temperatures, the capacity retention rate was significantly higher than that of the comparative example. For example, at 20°C, the capacity retention rate of Examples 1-3 after 1000 cycles was 83%-87%, while that of Comparative Example 1-3 was only 55%-75%. At the same time, the high voltage stability of the electrolyte of the present invention makes the battery's first discharge specific capacity at different temperatures more advantageous, indicating that it can achieve efficient transmission of lithium ions and electrode reactions at high voltage, thereby improving the energy density and cycle life of the battery.

[0083] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solutions of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A wide temperature range, high voltage lithium ion battery electrolyte containing an amide solvent, characterized in that: The electrolyte includes a fluorinated amide solvent, a lithium salt and a functional additive; The fluorinated amide solvent includes a main solvent and a co-solvent, the main solvent includes one or more of perfluoro-2-methylpyrrolidone, perfluoro-N-methylpyrrolidone, perfluoro-ε-caprolactam, N,N-difluoroethylformamide, and trifluoroacetamide, and the co-solvent includes one or more of fluoroethylene carbonate, difluoroethylene carbonate, methyl fluoroacetate, ethyl trifluoropropionate, bis(2,2,2-trifluoroethyl) ether, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether; The lithium salt includes one or more of lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(oxalatoborate), lithium difluorooxalatoborate, and lithium tetrafluoroborate; Functional additives include high voltage additives, temperature adaptability additives and flame retardants.

2. The wide temperature range, high voltage lithium ion battery electrolyte containing an amide solvent according to claim 1, characterized in that: The volume ratio of the main solvent to the co-solvent is 1:1-1:

3.

3. The wide temperature range, high voltage lithium ion battery electrolyte containing an amide solvent according to claim 1, characterized in that: The concentration of lithium salt in the electrolyte is 1.2-1.5 mol / L.

4. The wide temperature range, high voltage lithium ion battery electrolyte containing an amide solvent according to claim 1, characterized in that: The volume fraction of the high voltage additive is 1-3%, and the high voltage additive includes one or more of trimethyl borate, tris(trimethylsilyl)borate, lithium difluorophosphate, triallyl phosphate, vinyl sulfate, and 1,3-propane sultone.

5. The wide temperature range high voltage lithium ion battery electrolyte containing an amide solvent according to claim 1, characterized in that: The volume fraction of the temperature adaptability additive is 1-3%, and the temperature adaptability additive includes one or more of tetramethylene sulfone, vinylene carbonate, and benzimidazole.

6. The wide temperature range high voltage lithium ion battery electrolyte containing an amide solvent according to claim 1, characterized in that: The volume fraction of the flame retardant is 0.5-2%, and the flame retardant includes one or more of trimethyl phosphate, hexamethylphosphoric triamide, and tris(2,2,2-trifluoroethyl) phosphate.

7. A method for preparing a wide temperature range high voltage lithium ion battery electrolyte containing an amide solvent according to any one of claims 1 to 6, characterized in that: The following steps are involved: S1. Mixing the main solvent and the co-solvent at room temperature under stirring to obtain a fluorinated amide solvent; S2. Add lithium salt to the fluorinated amide solvent of S1. After the addition is complete, increase the stirring speed and stir at a temperature of 30-40° C. until the lithium salt is completely dissolved to form a clear and transparent solution; S3. Add the high voltage additive and the temperature adaptability additive to the solution of S2. After the addition is complete, adjust the stirring speed and stir at room temperature for 30-45 minutes; S4. Add flame retardant to S3, adjust the stirring speed again, and stir at room temperature for 20-30 minutes to obtain an electrolyte; S5. Filter the electrolyte obtained in S4 through a 0.22 μm microporous filter membrane, then transfer it to a dry, sealed container and fill it with argon for protection, thereby obtaining a wide temperature range, high voltage lithium-ion battery electrolyte containing an amide solvent.

8. The method for preparing a wide temperature range high voltage lithium ion battery electrolyte containing an amide solvent according to claim 7, characterized in that: The stirring speed in S1 is 200-250 r / min, and the stirring is carried out at room temperature for 30-45 minutes.

9. The method for preparing a wide temperature range high voltage lithium ion battery electrolyte containing an amide solvent according to claim 7, characterized in that: In S2, the stirring speed is increased to 300-400 r / min, and the mixture is stirred at a temperature of 30-40°C for 30-60 min.

10. The method for preparing a wide temperature range high voltage lithium ion battery electrolyte containing an amide solvent according to claim 7, characterized in that: The stirring speed in S3 is adjusted to 200-250 r / min, and the stirring speed in S4 is adjusted to 150-200 r / min.

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