Lithium ion battery electrolyte and preparation method thereof

Abstract

The application relates to the technical field of battery materials, and particularly discloses a lithium ion battery electrolyte and a preparation method thereof. The lithium ion battery electrolyte comprises the following raw materials: an organic solvent, a lithium salt and an additive; the additive comprises an additive A, fluoroethylene carbonate, a boron-containing lithium salt additive and / or a phosphorus-containing lithium salt additive; and the additive A is one or more of silane compounds containing unsaturated bonds. The unsaturated silane, the fluoroethylene carbonate and the boron / phosphorus lithium salt compound system can form an elastic interpenetrating network SEI film on a silicon-carbon negative electrode, adapt to volume expansion, avoid film layer rupture and reconstruction, construct a dense CEI film on a positive electrode, inhibit HF generation and transition metal dissolution, and significantly improve the initial coulomb efficiency, reversible capacity and long-term cycle stability of the battery.

Description

Technical Field

[0001] This application relates to the field of battery materials technology, and more specifically, to a lithium-ion battery electrolyte and its preparation method. Background Technology

[0002] Lithium-ion batteries have become the core energy storage device in the new energy field due to their advantages such as high energy density and long cycle life. Silicon materials have become the preferred new generation of anode materials due to their ultra-high theoretical specific capacity. However, silicon materials can expand more than three times in volume during lithium insertion / extraction cycles, which can easily damage the solid electrolyte interphase (SEI) film on the surface of the anode, leading to the shedding of active materials and rapid capacity decay. At the same time, the SEI film is repeatedly regenerated and destroyed during charging and discharging, continuously consuming lithium ions and film-forming additives, making it impossible to form a stable SEI film, further aggravating capacity decay and reducing charging and discharging efficiency.

[0003] In the prior art, patent application CN119419361A discloses a lithium-ion battery electrolyte and its application. The electrolyte contains lithium salt, carbonate organic solvent, and a composite additive system. The additive includes difluoromaleic anhydride as shown in Formula I, which reduces and decomposes on the electrode surface to form an SEI film based on rigid polycarbonate and lithium fluoride. Due to its defective elasticity and extensibility, the SEI film is prone to repeated rupture and reconstruction under stress, continuously consuming active lithium and electrolyte, resulting in battery capacity decay and shortened cycle life. At the same time, this structure significantly increases the negative electrode interface impedance, degrades the battery's low-temperature discharge performance and rate performance, and cannot synergistically construct a stable positive electrode CEI film. It also has no inhibitory effect on the dissolution of transition metals in nickel-rich positive electrodes, and cannot meet the requirements for long-term cycle life and comprehensive performance of batteries. Summary of the Invention

[0004] To improve the long-term cycle performance of lithium-ion batteries, this application provides a lithium-ion battery electrolyte and its preparation method.

[0005] In a first aspect, this application provides a lithium-ion battery electrolyte, which adopts the following technical solution: A lithium-ion battery electrolyte comprises the following raw materials: an organic solvent, a lithium salt, and additives; The additives include additive A, fluoroethylene carbonate, boron-containing lithium salt additives and / or phosphorus-containing lithium salt additives; additive A is one or more silane compounds containing unsaturated bonds; The structural formula of the silane compound containing unsaturated bonds is: ; Wherein, R1 is a vinyl group, and R2, R3, and R4 are one of alkyl, alkoxy, alkenyl, fluoroalkyl, fluoroalkoxy, fluoroalkenyl, benzene ring, and cyano groups, respectively. The fluorine substitution in the fluoroalkyl, fluoroalkoxy, and fluoroalkenyl groups includes partial or complete fluorine substitution. By employing the above technical solution, using a composite additive system of unsaturated silane compounds (additive A), fluoroethylene carbonate, boron-containing lithium salt additives, or phosphorus-containing lithium salt additives, combined with a suitable organic solvent and lithium salt, a stable SEI film with an elastic interpenetrating network structure can be formed in situ on the silicon-carbon anode surface. This film can adapt to the volume changes of the silicon anode during the lithium insertion-deintercalation process, preventing the SEI film from rupturing and reconstructing due to expansion stress, thus fundamentally reducing the continuous consumption of lithium ions and electrolyte, and significantly improving the initial coulombic efficiency, reversible capacity, and long-term cycle stability of the battery. Simultaneously, unsaturated silane compounds can induce the formation of tightly bonded, structurally sound compounds on the nickel-rich cathode surface. The dense silicate-silane polymer CEI film, combined with boron / phosphorus lithium salt additives, efficiently removes hydrofluoric acid (HF) from the electrolyte, stabilizes lithium salts, and inhibits transition metal dissolution, reducing positive electrode side reactions and irreversible phase transitions, thus further extending battery cycle life. In addition, fluoroethylene carbonate can synergistically enhance the flexibility and density of the SEI film, improve interface stability and ion transport efficiency, enabling the electrolyte of this invention to significantly improve high-temperature long-cycle performance at 45°C while greatly improving low-temperature discharge capacity retention and enhancing battery safety and stability at high temperatures. This achieves a balance between long-term cycle life, high and low temperature adaptability, and high safety, making it particularly suitable for silicon-carbon anode-nickel-rich cathode lithium-ion battery systems.

[0006] Preferably, the additive A accounts for 0.1%-10% of the electrolyte by mass, more preferably 1%.

[0007] The additive A includes, but is not limited to, one or more of the following: vinyltrimethylsilane, divinyldimethylsilane, trivinylmethylsilane, tetravinylsilane, 3-cyanopropyltrimethoxysilane, 3-cyanopropyltriethoxysilane, 2-cyanoethyltriethoxysilane; more preferably 2-cyanoethyltriethoxysilane or tetravinylsilane.

[0008] By adopting the above technical solution, 2-cyanoethyltriethoxysilane or tetravinylsilane as additive A can enable the electrolyte to form a more stable and flexible interpenetrating network structure SEI film on the surface of silicon-carbon anode. 2-cyanoethyltriethoxysilane contains both cyano and ethoxysilane groups. The cyano group can enhance the film strength and improve the interfacial adhesion, while the ethoxysilane can bond with the anode surface and induce the formation of a dense and stable silicate interface layer, which significantly inhibits the expansion of silicon anode and reduces side reactions. Tetravinylsilane contains multiple polymerizable vinyl groups, which can quickly crosslink on the anode surface to form a highly elastic and deformation-resistant three-dimensional network structure, better adapting to the large volume changes of silicon anode, avoiding repeated rupture and reconstruction of the SEI film, and simultaneously synergistically improving the density of the cathode CEI film, inhibiting hydrofluoric acid corrosion and transition metal dissolution, so that the battery can achieve more outstanding comprehensive performance improvement in terms of high temperature long cycle, low temperature discharge, safety and stability.

[0009] Preferably, the fluoroethylene carbonate accounts for 5%-20% of the electrolyte by mass, and more preferably 8%-12%.

[0010] Preferably, the boron-containing lithium salt additive or the phosphorus-containing lithium salt additive accounts for 0.1%-0.8% of the electrolyte mass fraction, more preferably 0.3%.

[0011] Preferably, the boron-containing lithium salt additive is one or more of lithium bis(oxalato)borate, lithium tetrafluoroborate, and lithium difluorooxalato)borate.

[0012] Preferably, the phosphorus-containing lithium salt additive is one or both of lithium tetrafluorodioxazophosphate and lithium difluorodioxazophosphate.

[0013] Preferably, the lithium salt is one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(oxalate)borate, lithium difluorooxalateborate, lithium difluorophosphate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethanesulfonyl)imide; more preferably, it is lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, or lithium bis(trifluoromethanesulfonyl)imide.

[0014] By adopting the above scheme, lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethanesulfonyl)imide, either in combination or individually, can balance the ionic conductivity, dissociation degree, thermal stability, and interfacial compatibility of the electrolyte: lithium hexafluorophosphate has sufficient dissociation and high ionic conductivity, ensuring excellent rate and power output performance of the battery, and is the most mature and stable mainstream lithium salt for lithium-ion batteries; lithium bis(fluorosulfonyl)imide has strong dissociation ability and low interfacial impedance, which can significantly improve the low-temperature discharge performance and cycle stability of the battery, while suppressing side reactions and gas generation; lithium bis(trifluoromethanesulfonyl)imide has extremely strong thermal stability, is resistant to hydrolysis, and does not easily produce hydrofluoric acid, which can greatly improve the stability of the electrolyte in high-temperature environments and protect the electrode structure from corrosion; the three can be used synergistically or individually to maintain the stability of the electrolyte performance over a wide temperature range, effectively reduce interfacial impedance, reduce lithium salt decomposition, and improve battery cycle life and safety reliability, especially suitable for the silicon-carbon anode-nickel-rich cathode system's requirement for highly stable and long-life electrolytes.

[0015] Preferably, the organic solvent is one or more of carbonates, carboxylic acid esters, and / or ether solvents; the carbonate is one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, fluoropropylene carbonate, difluoropropylene carbonate, and methyl ethyl carbonate; the carboxylic acid ester is one or more of ethyl acetate, ethyl propionate, propyl acetate, ethyl propionate, fluoroethyl acetate, ethyl propionate, and propyl fluoroacetate; the ether solvent is one or two of ethylene glycol dimethyl ether and diethylene glycol dimethyl ether; the organic solvent is further preferably a mixture of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, ethyl propionate, and ethylene glycol dimethyl ether.

[0016] By adopting the above technical solution, a mixed organic solvent system composed of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, ethyl propionate, and ethylene glycol dimethyl ether can achieve multiple synergistic effects of high dielectric constant, low viscosity, excellent low-temperature performance, and strong interfacial wettability: ethylene carbonate and propylene carbonate have high dielectric constants, which can efficiently promote lithium salt dissociation, improve electrolyte ionic conductivity, and stabilize the negative electrode interface; methyl ethyl carbonate has low viscosity and good flowability, which can significantly reduce the system viscosity and improve lithium-ion migration rate and battery rate performance; ethyl propionate, as a carboxyl group... Ester solvents, with moderate flash points and excellent low-temperature fluidity, can effectively improve the low-temperature discharge performance of batteries and enhance the wetting effect on silicon-carbon anodes. Ethylene glycol dimethyl ether, as an ether solvent, has outstanding interfacial compatibility, which can further reduce interfacial impedance and improve the stability of the SEI film during cycling. The combination of five solvents takes into account high dielectric, low viscosity, wide temperature range, high wetting and high stability, making the electrolyte perform better in high-temperature long-cycle, low-temperature discharge and safety stability, and highly adaptable to the stringent use requirements of silicon-carbon anode-nickel-rich cathode lithium-ion batteries.

[0017] Preferably, the raw material further includes additive B; additive B is one or more of 1,3-propanesulfonate lactone, vinylene carbonate, vinyl sulfate, propylene sulfite, 1,3-propenesulfonate lactone, dimethyl sulfite, and diethyl sulfite; and additive B accounts for 0.1%-3% of the electrolyte by mass.

[0018] By adopting the above technical solution, adding an appropriate amount of additive B to the electrolyte can rapidly form a uniform, dense, and stable SEI film with moderate impedance on the electrode surface. This effectively suppresses side reactions and gas generation behavior of the electrolyte during charging and discharging, reduces lithium salt decomposition and active lithium loss, and improves battery formation efficiency and initial coulombic efficiency. At the same time, it can enhance interface stability, and synergistically enhance the toughness and mechanical strength of the SEI film with additive A and fluoroethylene carbonate, better adapting to the volume expansion changes of the silicon-carbon anode, suppressing film rupture and repeated reconstruction, and significantly improving the battery's cycle life, high-temperature storage stability, and safety performance. This enables the electrolyte to achieve a more comprehensive performance improvement in terms of long-cycle, high and low temperature adaptability, and reliability.

[0019] Secondly, this application provides a method for preparing a lithium-ion battery electrolyte, employing the following technical solution: A method for preparing a lithium-ion battery electrolyte includes the following steps: The organic solvent was cooled to below 10°C, and lithium salt was added in batches, stirring until the lithium salt dissolved after each addition to obtain the basic electrolyte. The remaining raw materials are added sequentially to the base electrolyte and mixed evenly to obtain the lithium-ion battery electrolyte.

[0020] The above-mentioned technical solution and preparation method avoid exothermic decomposition and side reactions by using low temperature control and batch dissolution of lithium salts, ensuring uniform and stable electrolyte composition, improving batch consistency and production safety, and ensuring the complete preservation of additive activity.

[0021] In summary, this application has the following beneficial effects: 1. This application adopts a composite system of unsaturated silane, fluoroethylene carbonate and boron / phosphorus lithium salt, which can form an elastic interpenetrating network SEI film on the silicon-carbon anode, adapt to volume expansion and avoid film layer rupture and reconstruction. At the same time, a dense CEI film is constructed on the cathode to suppress HF generation and transition metal dissolution, which significantly improves the initial coulombic efficiency, reversible capacity and long-term cycle stability of the battery.

[0022] 2. This application preferably uses a compound solvent of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, ethyl propionate and ethylene glycol dimethyl ether to balance high dielectric constant, low viscosity and excellent low temperature fluidity, improve lithium salt dissociation and interface wettability, effectively reduce interface impedance, and simultaneously improve battery performance in high and low temperature, rate performance and cycle stability.

[0023] 3. This application utilizes the synergistic effect of additive B and the main additive to rapidly form a uniform and stable SEI film, suppress charging and discharging side reactions and gas generation, reduce active lithium loss, and enhance the toughness and mechanical strength of the film layer, further improving the high-temperature storage stability and safety performance of the battery, making the electrolyte more suitable for the silicon-carbon anode-nickel-rich cathode system. Detailed Implementation

[0024] The present application will be further described in detail below with reference to the embodiments.

[0025] Unless otherwise specified, the raw materials used in the embodiments and comparative examples of this application are all commercially available.

[0026] Example 1 This embodiment provides a method for preparing a lithium-ion battery, including the following steps: (1) Preparation of positive electrode sheet LiNi, the positive electrode active material x CO y Mn z O2, binder polyvinylidene fluoride (PVDF), and SP (Super P) are mixed in a mass ratio of 96:2:2. N-methylpyrrolidone (NMP) is added, and the mixture is stirred under the action of a cantilever electric mixer until a uniform positive electrode active slurry is formed. The positive electrode active slurry is evenly coated on both sides of an aluminum foil, then dried in a vacuum drying oven. After rolling and punching, a positive electrode sheet with a thickness of 112μm is obtained. (2) Preparation of negative electrode plate The active materials for the negative electrode, artificial graphite, silicon, sodium carboxymethyl cellulose (CMC-Na), styrene-butadiene rubber (SBR), polyacrylic acid (PAA), and conductive carbon black (SP), were mixed in a mass ratio of 82:10:2:1:1.5:2.5. Deionized water was added, and the mixture was stirred under the action of a cantilever electric mixer until a uniform negative electrode active slurry was formed. The negative electrode active slurry was uniformly coated on both sides of a copper foil, and then dried in a vacuum drying oven. After rolling and punching, a negative electrode sheet with a thickness of 77 μm was obtained. (3) Preparation of electrolyte In an argon-filled glove box (H2O < 0.1 ppm, O2 < 0.01 ppm), organic solvents (200 g ethylene carbonate, 100 g propylene carbonate, 500 g methyl ethyl carbonate, and 200 g dimethyl carbonate) were mixed uniformly according to the mass ratio to obtain a mixed solution. Then, lithium salt (1.0 mol / L lithium hexafluorophosphate) was added in three batches according to the mass percentage to prepare a basic electrolyte. The mixed solution was cooled to below 10°C before each addition of lithium salt. Subsequently, additives with different mass percentages (0.1 g 2-cyanoethyltriethoxysilane, 0.5 g vinylene carbonate, 0.5 g 1,3-propanesulfonyl lactone, 12 g fluoroethylene carbonate, and 0.3 g lithium difluorooxalate borate) were added to the basic electrolyte to obtain the final electrolyte. (4) Battery preparation The positive electrode from step (1), the negative electrode from step (2), and the separator (PP / PEP / PP porous membrane with a thickness of 16μm) were stacked according to the cell design of 5 negative electrodes and 4 positive electrodes. Then, the cells were placed in the cut aluminum-plastic film and baked at 85℃ for 24h before electrolyte injection. Next, the aluminum-plastic film was vacuum-evacuated and heat-sealed. The sealed cells were left to stand at room temperature for 12h and then formed at room temperature. They were charged to 4.2V with a constant current of 0.1C. After formation, vacuum degassing was performed to remove the gas generated inside the cells and heat-sealed again. Finally, constant current charge and discharge was performed at 1C rate to obtain the battery.

[0027] Example 2 This embodiment is basically the same as that of embodiment 1, except that in step (3) the preparation of electrolyte: in a glove box filled with argon (H2O < 0.1 ppm, O2 < 0.01 ppm), organic solvents (200 g of ethylene carbonate, 100 g of propylene carbonate, 400 g of methyl ethyl carbonate, and 300 g of dimethyl carbonate) are mixed evenly according to the mass ratio to obtain a mixed solution. Then, lithium salt (1.0 mol / L lithium hexafluorophosphate) is added in three batches according to the mass percentage to prepare a basic electrolyte. Before each addition of lithium salt, the mixed solution needs to be cooled to below 10°C. Subsequently, additives with different mass percentages (0.1 g of 2-cyanoethyltriethoxysilane, 0.5 g of vinylene carbonate, 0.5 g of 1,3-propanesulfonyl lactone, 10 g of fluoroethylene carbonate, and 0.3 g of lithium difluorooxalate borate) are added to the basic electrolyte to obtain the electrolyte.

[0028] Example 3 This embodiment is basically the same as that of embodiment 1, except that in step (3) the preparation of electrolyte: in a glove box filled with argon (H2O < 0.1 ppm, O2 < 0.01 ppm), organic solvents (200 g of ethylene carbonate, 100 g of propylene carbonate, 500 g of methyl ethyl carbonate, and 200 g of ethyl acetate) are mixed evenly according to the mass ratio to obtain a mixed solution. Then, lithium salt (1.0 mol / L lithium hexafluorophosphate) is added in three batches according to the mass percentage to prepare a basic electrolyte. Before each addition of lithium salt, the mixed solution needs to be cooled to below 10°C. Subsequently, additives with different mass percentages (0.1 g of 2-cyanoethyltriethoxysilane, 0.5 g of vinylene carbonate, 0.5 g of 1,3-propanesulfonate lactone, 8 g of fluoroethylene carbonate, and 0.3 g of lithium difluorooxalate borate) are added to the basic electrolyte to obtain the electrolyte.

[0029] Example 4 This embodiment is basically the same as that of embodiment 1, except that in step (3) the preparation of electrolyte: in a glove box filled with argon (H2O < 0.1 ppm, O2 < 0.01 ppm), organic solvents (200 g of ethylene carbonate, 100 g of propylene carbonate, 500 g of methyl ethyl carbonate, and 200 g of ethyl propionate) are mixed evenly according to the mass ratio to obtain a mixed solution. Then, lithium salt (1.0 mol / L lithium hexafluorophosphate) is added in three batches according to the mass percentage to prepare a basic electrolyte. Before each addition of lithium salt, the mixed solution needs to be cooled to below 10°C. Subsequently, additives with different mass percentages (0.2 g of 2-cyanoethyltriethoxysilane, 0.5 g of vinylene carbonate, 1.0 g of 1,3-propanesulfonyl lactone, 12 g of fluoroethylene carbonate, and 0.3 g of lithium difluorooxalate borate) are added to the basic electrolyte to obtain the electrolyte.

[0030] Example 5 This embodiment is basically the same as that of embodiment 1, except that in step (3) the preparation of electrolyte: in a glove box filled with argon (H2O < 0.1 ppm, O2 < 0.01 ppm), organic solvents (200 g of ethylene carbonate, 100 g of propylene carbonate, 500 g of methyl ethyl carbonate, and 200 g of dimethyl carbonate) are mixed evenly according to the mass ratio to obtain a mixed solution. Then, lithium salts (0.8 mol / L lithium hexafluorophosphate and 0.2 mol / L lithium difluorosulfonyl imide) are added in three batches according to the mass percentage to prepare a basic electrolyte. Before each addition of lithium salt, the mixed solution needs to be cooled to below 10°C. Subsequently, additives with different mass percentages (0.1 g of 2-cyanoethyltriethoxysilane, 0.5 g of vinylene carbonate, 0.5 g of 1,3-propanesulfonyl lactone, 12 g of fluoroethylene carbonate, and 0.3 g of lithium difluorodioxarate phosphate) are added to the basic electrolyte to obtain the electrolyte.

[0031] Example 6 This embodiment is basically the same as that of embodiment 1, except that in step (3) the preparation of electrolyte: in a glove box filled with argon (H2O < 0.1 ppm, O2 < 0.01 ppm), organic solvents (200 g of ethylene carbonate, 100 g of propylene carbonate, 500 g of methyl ethyl carbonate, and 200 g of dimethyl carbonate) are mixed evenly according to the mass ratio to obtain a mixed solution. Then, lithium salt (1.0 mol / L lithium hexafluorophosphate) is added in three batches according to the mass percentage to prepare a basic electrolyte. Before each addition of lithium salt, the mixed solution needs to be cooled to below 10°C. Then, additives with different mass percentages (0.1 g 2-cyanoethyltriethoxysilane, 0.5 g vinylene carbonate, 0.5 g 1,3-propanesulfonate lactone, 12 g fluoroethylene carbonate, 0.2 g vinyl sulfate, and 0.3 g lithium difluorooxalate borate) are added to the basic electrolyte to obtain the electrolyte.

[0032] Example 7 This embodiment is basically the same as that of embodiment 1, except that in step (3) the preparation of electrolyte: in a glove box filled with argon (H2O < 0.1 ppm, O2 < 0.01 ppm), organic solvents (200 g of ethylene carbonate, 100 g of propylene carbonate, 500 g of methyl ethyl carbonate, and 200 g of dimethyl carbonate) are mixed evenly according to the mass ratio to obtain a mixed solution. Then, lithium salt (1.0 mol / L lithium hexafluorophosphate) is added in three batches according to the mass percentage to prepare a basic electrolyte. Before each addition of lithium salt, the mixed solution needs to be cooled to below 10°C. Subsequently, additives with different mass percentages (0.5 g of 2-cyanoethyltriethoxysilane, 0.5 g of vinylene carbonate, 0.5 g of 1,3-propanesulfonyl lactone, 12 g of fluoroethylene carbonate, and 0.3 g of lithium difluorooxalate borate) are added to the basic electrolyte to obtain the electrolyte.

[0033] Example 8 This embodiment is basically the same as that of embodiment 1, except that in step (3) the preparation of electrolyte: in a glove box filled with argon (H2O < 0.1 ppm, O2 < 0.01 ppm), organic solvents (200 g of ethylene carbonate, 100 g of propylene carbonate, 500 g of methyl ethyl carbonate, and 200 g of dimethyl carbonate) are mixed evenly according to the mass ratio to obtain a mixed solution. Then, lithium salt (1.0 mol / L lithium hexafluorophosphate) is added in three batches according to the mass percentage to prepare a basic electrolyte. Before each addition of lithium salt, the mixed solution needs to be cooled to below 10°C. Subsequently, additives with different mass percentages (0.1 g tetravinylsilane, 0.5 g vinylene carbonate, 0.5 g 1,3-propanesulfonyl lactone, 12 g fluoroethylene carbonate, and 0.3 g lithium difluorooxalate borate) are added to the basic electrolyte to obtain the electrolyte.

[0034] Example 9 This embodiment is basically the same as that of embodiment 1, except that in step (3) the preparation of electrolyte: in a glove box filled with argon (H2O < 0.1 ppm, O2 < 0.01 ppm), organic solvents (200 g of ethylene carbonate, 100 g of propylene carbonate, 500 g of methyl ethyl carbonate, and 200 g of dimethyl carbonate) are mixed evenly according to the mass ratio to obtain a mixed solution. Then, lithium salt (1.0 mol / L lithium hexafluorophosphate) is added in three batches according to the mass percentage to prepare a basic electrolyte. Before each addition of lithium salt, the mixed solution needs to be cooled to below 10°C. Subsequently, additives with different mass percentages (0.3 g tetravinylsilane, 0.5 g vinylene carbonate, 0.5 g 1,3-propanesulfonyl lactone, 12 g fluoroethylene carbonate, and 0.3 g lithium difluorodioxarate phosphate) are added to the basic electrolyte to obtain the electrolyte.

[0035] Example 10 This embodiment is basically the same as that of embodiment 1, except that in step (3) the preparation of electrolyte: in a glove box filled with argon (H2O < 0.1 ppm, O2 < 0.01 ppm), organic solvents (200 g of ethylene carbonate, 100 g of propylene carbonate, 500 g of methyl ethyl carbonate, and 200 g of ethylene glycol dimethyl ether) are mixed evenly according to the mass ratio to obtain a mixed solution. Then, lithium salt (1.0 mol / L lithium hexafluorophosphate) is added in three batches according to the mass percentage to prepare a basic electrolyte. Before each addition of lithium salt, the mixed solution needs to be cooled to below 10°C. Subsequently, additives with different mass percentages (0.3 g tetravinylsilane, 0.5 g vinylene carbonate, 0.5 g 1,3-propanesulfonyl lactone, 12 g fluoroethylene carbonate, and 0.3 g lithium difluorodioxarate phosphate) are added to the basic electrolyte to obtain the electrolyte.

[0036] Comparative Example 1 This embodiment is basically the same as that of embodiment 1, except that in step (3) the preparation of electrolyte: in a glove box filled with argon (H2O < 0.1 ppm, O2 < 0.01 ppm), organic solvents (200 g of ethylene carbonate, 100 g of propylene carbonate, 500 g of methyl ethyl carbonate, and 200 g of dimethyl carbonate) are mixed evenly according to the mass ratio to obtain a mixed solution. Then, lithium salt (2.5 mol / L lithium hexafluorophosphate) is added in three batches according to the mass percentage to prepare a basic electrolyte. Before each addition of lithium salt, the mixed solution needs to be cooled to below 10°C. Subsequently, additives with different mass percentages (0.1 g of 2-cyanoethyltriethoxysilane, 0.5 g of vinylene carbonate, 0.5 g of 1,3-propanesulfonyl lactone, 12 g of fluoroethylene carbonate, and 0.3 g of lithium difluorooxalate borate) are added to the basic electrolyte to obtain the electrolyte.

[0037] Comparative Example 2 This embodiment is basically the same as that of embodiment 1, except that in step (3) the preparation of electrolyte: in a glove box filled with argon (H2O < 0.1 ppm, O2 < 0.01 ppm), organic solvents (200 g of ethylene carbonate, 100 g of propylene carbonate, and 700 g of methyl ethyl carbonate) are mixed evenly according to the mass ratio to obtain a mixed solution. Then, lithium salt (1.0 mol / L lithium hexafluorophosphate) is added in three batches according to the mass percentage to prepare a basic electrolyte. Before each addition of lithium salt, the mixed solution needs to be cooled to below 10°C. Subsequently, additives with different mass percentages (0.1 g 2-cyanoethyltriethoxysilane, 0.5 g vinylene carbonate, 0.5 g 1,3-propanesulfonyl lactone, 2 g fluoroethylene carbonate, and 0.3 g lithium difluorooxalate borate) are added to the basic electrolyte to obtain the electrolyte.

[0038] Comparative Example 3 This embodiment is basically the same as that of embodiment 1, except that in step (3) the preparation of electrolyte: in a glove box filled with argon (H2O < 0.1 ppm, O2 < 0.01 ppm), organic solvents (200 g of ethylene carbonate, 100 g of propylene carbonate, 500 g of methyl ethyl carbonate, and 200 g of dimethyl carbonate) are mixed evenly according to the mass ratio to obtain a mixed solution. Then, lithium salt (1.0 mol / L lithium hexafluorophosphate) is added in three batches according to the mass percentage to prepare a basic electrolyte. Before each addition of lithium salt, the mixed solution needs to be cooled to below 10°C. Subsequently, additives (0.1 g of 2-cyanoethyltriethoxysilane, 0.5 g of vinylene carbonate, and 0.5 g of 1,3-propanesulfonate lactone) with different mass percentages are added to the basic electrolyte to obtain the electrolyte.

[0039] Comparative Example 4 This embodiment is basically the same as that of embodiment 1, except that in step (3) the preparation of electrolyte: in a glove box filled with argon (H2O < 0.1 ppm, O2 < 0.01 ppm), organic solvents (200 g of ethylene carbonate, 100 g of propylene carbonate, 500 g of methyl ethyl carbonate, and 200 g of dimethyl carbonate) are mixed evenly according to the mass ratio to obtain a mixed solution. Then, lithium salt (1.0 mol / L lithium hexafluorophosphate) is added in three batches according to the mass percentage to prepare a basic electrolyte. Before each addition of lithium salt, the mixed solution needs to be cooled to below 10°C. Subsequently, additives with different mass percentages (0.5 g of vinylene carbonate, 0.5 g of 1,3-propanesulfonate lactone, and 12 g of fluoroethylene carbonate) are added to the basic electrolyte to obtain the electrolyte.

[0040] Testing standards: The batteries obtained in each of the above embodiments and comparative examples were subjected to the following tests, and the test results are shown in Table 1.

[0041] 1. Cyclic performance test: The batteries obtained in each embodiment and each comparative example were charged and discharged at 45°C at a rate of 1C within the range of 2.8V-4.2V for 500 cycles. The discharge capacity in the first cycle and the discharge capacity in the 500th cycle were tested. The capacity in the 500th cycle was divided by the capacity in the first cycle to obtain the cycle capacity retention rate.

[0042] 2. Safety test: After cycling, charge the battery to 4.2V at a constant current and constant voltage rate of 1C, with a cutoff current of 0.05C, and then store it at 130℃ for 10 minutes to observe whether the battery catches fire or explodes.

[0043] 3. Low-temperature discharge performance test: The batteries obtained in each embodiment and each comparative example were subjected to three charge-discharge cycles at a 1C rate at room temperature. The discharge capacity of the third cycle was recorded as Q0. The fully charged batteries were placed at -20℃ for 4 hours and then discharged at a 0.2C rate to 3V. The discharge capacity was recorded as Q1. The discharge capacity retention rate at -20℃ can be calculated. Low-temperature discharge capacity retention rate (%) = Q1 / Q0 × 100.

[0044] Table 1 Performance test data of lithium-ion batteries in Examples 1-10 and Comparative Examples 1-4

[0045] Referring to Table 1, the comparative test results of Examples 1-10 and Comparative Examples 1-4 show that the electrolyte of the present invention, when applied to silicon-carbon anode-nickel-rich cathode lithium-ion batteries, exhibits significant improvements in three key indicators: long-term cycling at 45℃, low-temperature discharge at -20℃, and safety in a 130℃ hot box. The batteries in the Examples 1-10 achieved a capacity retention rate of 81.3%-86.3% after 500 cycles at 45℃ and a discharge capacity retention rate of 81.2%-85.6% at -20℃. Furthermore, they did not ignite or explode after 10 minutes of storage at 130℃. In contrast, the comparative examples, lacking unsaturated silane compounds, having insufficient fluoroethylene carbonate, and either not being paired with boron / phosphorus-containing lithium salts or having excessively high lithium salt concentrations, achieved a cycle retention rate of only 78.1% at its highest and 54.7% at its lowest, and a discharge retention rate of only 83.5% at its highest and 23.4% at its lowest, with all of them exhibiting signs of ignition. The above results fully demonstrate that the present invention, through the synergistic effect of unsaturated bond silane compounds, fluoroethylene carbonate, boron / phosphorus lithium salts, a compound solvent system, and a suitable lithium salt concentration, can construct a stable and flexible interpenetrating network SEI film and a dense CEI film on the electrode surface. This effectively inhibits silicon anode expansion, reduces electrolyte decomposition, removes hydrofluoric acid, and inhibits transition metal dissolution, significantly improving the battery's long-term cycle stability, low-temperature discharge performance, and high-temperature safety performance. The absence of any key component or parameters exceeding the preferred range will lead to a significant decline in battery performance or even safety hazards.

[0046] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A lithium-ion battery electrolyte, characterized in that, Including the following raw materials: organic solvents, lithium salts, and additives; The additives include additive A, fluoroethylene carbonate, boron-containing lithium salt additives and / or phosphorus-containing lithium salt additives; additive A is one or more silane compounds containing unsaturated bonds; The structural formula of the silane compound containing unsaturated bonds is: ； Wherein, R1 is a vinyl group, and R2, R3, and R4 are one of alkyl, alkoxy, alkenyl, fluoroalkyl, fluoroalkoxy, fluoroalkenyl, benzene ring, and cyano groups, respectively. The fluorine substitution in the fluoroalkyl, fluoroalkoxy, and fluoroalkenyl groups includes partial or complete fluorine substitution.

2. The lithium-ion battery electrolyte according to claim 1, characterized in that, The additive A accounts for 0.1%-10% of the electrolyte by mass. The additive A includes, but is not limited to, one or more of the following: vinyltrimethylsilane, divinyldimethylsilane, trivinylmethylsilane, tetravinylsilane, 3-cyanopropyltrimethoxysilane, 3-cyanopropyltriethoxysilane, 2-cyanoethyltriethoxysilane; more preferably 2-cyanoethyltriethoxysilane or tetravinylsilane.

3. The lithium-ion battery electrolyte according to claim 1, characterized in that, The fluoroethylene carbonate accounts for 5%-20% of the electrolyte by mass.

4. The lithium-ion battery electrolyte according to claim 1, characterized in that, The boron-containing lithium salt additive or the phosphorus-containing lithium salt additive accounts for 0.1%-0.8% of the electrolyte mass fraction.

5. The lithium-ion battery electrolyte according to claim 1, characterized in that, The boron-containing lithium salt additive is one or more of lithium bis(oxalato)borate, lithium tetrafluoroborate, and lithium difluorooxalato)borate.

6. The lithium-ion battery electrolyte according to claim 1, characterized in that, The phosphorus-containing lithium salt additive is one or both of lithium tetrafluorodioxazophosphate and lithium difluorodioxazophosphate.

7. The lithium-ion battery electrolyte according to claim 1, characterized in that, The lithium salt is one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(oxalate)borate, lithium difluorooxalateborate, lithium difluorophosphate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethanesulfonyl)imide.

8. The lithium-ion battery electrolyte according to claim 1, characterized in that, The organic solvent is one or more of carbonates, carboxylic acid esters, and / or ether solvents; the carbonate is one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, fluoropropylene carbonate, difluoropropylene carbonate, and methyl ethyl fluorocarbonate; the carboxylic acid ester is one or more of ethyl acetate, ethyl propionate, propyl acetate, ethyl fluoropropionate, and propyl fluoroacetate; and the ether solvent is one or two of ethylene glycol dimethyl ether and diethylene glycol dimethyl ether.

9. The lithium-ion battery electrolyte according to claim 1, characterized in that, The raw materials also include additive B; additive B is one or more of 1,3-propanesulfonate lactone, vinylene carbonate, vinyl sulfate, propylene sulfite, 1,3-propenesulfonate lactone, dimethyl sulfite, and diethyl sulfite; additive B accounts for 0.1%-3% of the electrolyte by mass.

10. A method for preparing a lithium-ion battery electrolyte according to any one of claims 1-9, characterized in that, Includes the following steps: The organic solvent was cooled to below 10°C, and lithium salt was added in batches, stirring until the lithium salt dissolved after each addition to obtain the basic electrolyte. The remaining raw materials are added sequentially to the base electrolyte and mixed evenly to obtain the lithium-ion battery electrolyte.

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