Electrolyte for lithium ion battery with low discharge cut-off voltage and silicon negative electrode as well as preparation method and application of electrolyte
By optimizing the electrolyte composition and discharge cutoff voltage, a stable SEI film and protective layer are formed, solving the problems of insufficient capacity release and poor cycle performance of silicon anode lithium-ion batteries at low discharge cutoff voltage. This achieves high capacity retention and low expansion rate, improving the battery's deep discharge cycle performance and range.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-30
- Publication Date
- 2026-03-27
AI Technical Summary
Silicon anode lithium-ion batteries do not fully release their capacity at low discharge cutoff voltages, have poor deep discharge cycle performance, and face high risks of copper foil corrosion and capacity decay, as well as foil breakage.
A stable SEI film with high LiF content is formed by using a specific ratio of electrolyte components, including solvents, additives, lithium salts and dinitrile compounds, to inhibit defluorination corrosion and improve the toughness of the SEI film. By adjusting the discharge cutoff voltage to 2.0~2.75V to satisfy a specific relationship, a protective layer is formed to inhibit copper foil corrosion.
It significantly improves the capacity release and deep discharge cycle performance of silicon anode lithium-ion batteries, avoids the risk of capacity drop and foil breakage, and enhances battery life and cycle stability.
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Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the technical field of lithium ion batteries, in particular to an electrolyte for a low discharge cut-off voltage silicon negative electrode lithium ion battery and a preparation method and application thereof. BACKGROUND
[0002] With the improvement of the performance of electronic devices, the power consumption will also increase, so the long endurance capability of lithium ion batteries is becoming more and more important. The energy density of the battery can be effectively improved by doping silicon in the negative electrode, thereby improving the endurance capability of the lithium ion battery. However, the SEI of the silicon negative electrode is more fragile than that of graphite, and there is a huge volume change in the production process. Therefore, after introducing silicon material into the negative electrode active material, the cycle performance of the lithium ion battery will be significantly deteriorated. When the battery is discharged to a voltage of 3.0V, a part of the capacity in the silicon negative electrode is not released, and the proportion is high. Therefore, when the discharge cut-off voltage of the battery is set to 2.75V or even 2.5V, the capacity of the silicon negative electrode can be fully released. However, when the battery is deeply discharged (defined as the discharge step cut-off voltage ≤2.75V) and discharged at a large rate, the negative electrode is easy to reach over-discharge state, which causes the copper foil current collector of the negative electrode to dissolve, and the active material loses contact with the current collector, thereby causing capacity attenuation, and even in the process of cycling, there is a risk of broken foil, causing capacity to drop.
[0003] Therefore, a kind of electrolyte for low discharge cut-off voltage silicon negative electrode lithium ion battery which can significantly improve the cycle performance of system and its preparation method and application are researched. SUMMARY
[0004] The purpose of the present application is to provide an electrolyte for low discharge cut-off voltage silicon negative electrode lithium ion battery and its preparation method and application, which solves the problem of poor cycle performance of existing silicon negative electrode lithium ion battery.
[0005] In order to achieve the above-mentioned purpose of the application, the present application provides the following technical scheme: The present application provides an electrolyte for low discharge cut-off voltage silicon negative electrode lithium ion battery, which comprises the following components by mass fraction: 48~86 parts of solvent, 0.3~3 parts of additive, 6.1~21 parts of lithium salt and 0.3~2.5 parts of dinitrile compound.
[0006] Preferably, the solvent includes one or more of vinyl carbonate, propylene carbonate, diethyl carbonate, propyl propionate, fluoroethylene carbonate, difluoroethylene carbonate, 3,3,3-trifluoro propylene carbonate, dimethyl carbonate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, ethyl butyrate, methyl butyrate, butyl butyrate and ethyl difluoroacetate.
[0007] Preferably, the additive has the structural formula shown in Formula I:
[0008] Formula I
[0009] Among them, R1 and R2 are independently C2~C10 carbonate groups or C2~C10 sulfate groups.
[0010] Preferably, the lithium salt includes LiPF6 and an auxiliary lithium salt, wherein the auxiliary lithium salt is one or more selected from lithium difluorophosphate, lithium tetrafluoroborate, lithium difluorooxalate borate, lithium difluorooxalate phosphate, lithium tetrafluorooxalate phosphate, lithium bis(trifluoromethyl)sulfonylimide, lithium bis(trifluoromethyl)sulfonylimide, and lithium 4,5-dicyano-2-trifluoromethyl-imidazolium. The mass ratio of LiPF6 to auxiliary lithium salt is 6~16:0.1~5.
[0011] Preferably, the dinitrile compound is one or more selected from malononitrile, succinic anhydride, glutaronitrile, isoprene, ethyl succinic anhydride, methyl isoprene, 2-propyl malononitrile, and adiponitrile.
[0012] The present invention also provides a method for preparing an electrolyte for a low discharge cutoff voltage silicon anode lithium-ion battery, wherein the preparation method comprises mixing a solvent, an additive, a lithium salt and a dinitrile compound to obtain the electrolyte.
[0013] The present invention also provides the application of an electrolyte for a low discharge cutoff voltage silicon anode lithium-ion battery in a silicon anode lithium-ion battery, wherein the lower limit voltage of the silicon anode lithium-ion battery is 2~3V.
[0014] Preferably, in the silicon anode, the anode active material includes carbon and a silicon-containing anode material, wherein the silicon-containing anode material is SiC and / or SiO; The negative electrode active material contains 7.5 to 25 parts by mass of silicon and 75 to 92.5 parts by mass of carbon.
[0015] Preferably, the mass fraction of the additive is denoted as a, the mass fraction of the lithium salt is denoted as b, the mass fraction of the dinitrile compound is denoted as x, the mass fraction of the silicon-containing anode material in the anode active material is denoted as y, and the lower limit voltage of the silicon anode lithium-ion battery is denoted as z. The relationship between a, b, x, y, and z is shown below: ① When 2.5 ≤ z ≤ 2.75, the relation is 10 ≤ a × b + x 2 +y / 3+z 2 ≤50; ② When 2.0 ≤ z < 2.5, the relation is 3 ≤ a / b + x + y / 5 + 2z 2 ≤40.
[0016] As can be seen from the above technical solution, compared with the prior art, the present invention has the following beneficial effects: This invention addresses the technical pain points of insufficient capacity release and poor deep discharge cycle performance (copper foil corrosion, capacity decay, and foil breakage) in silicon anode lithium-ion batteries under low discharge cutoff voltage. Through optimization of the electrolyte additive system and parameter matching, the discharge cutoff voltage is lowered to 2.0~2.75V. Furthermore, electrolyte components (additives, lithium salt, and dinitrile compounds) are matched according to a specific formula. Through the synergistic effect of these three components—lithium salt facilitates the formation of a stable SEI film with high LiF content, dinitrile compounds form a protective layer on the copper foil surface to inhibit corrosion caused by defluorination, and additives improve the SEI—the invention achieves this. The film's toughness mitigates the volume expansion damage of the silicon anode, not only fully releasing the silicon anode's capacity and improving battery life, but also significantly improving the battery's deep discharge cycle performance. This allows the battery to maintain high capacity retention and low thickness expansion rate after 500 cycles at room temperature and 400 cycles at high temperature, avoiding the risk of capacity drop and foil breakage. At the same time, by limiting the components and discharge cutoff voltage through parameter relationships, a balance between battery capacity utilization and cycle performance is achieved. Moreover, this system has strong compatibility and is suitable for anode systems with silicon-based material content of 7.5% to 25%, showing significant overall performance advantages compared to batteries with excessively low or high silicon content. Detailed Implementation
[0017] This invention provides an electrolyte for a low-discharge-cut-voltage silicon anode lithium-ion battery, comprising the following components in parts by mass: 48-86 parts solvent, 0.3-3 parts additives, 6.1-21 parts lithium salt and 0.3-2.5 parts dinitrile compounds.
[0018] In this invention, the solvent is preferably 55-80 parts by mass, more preferably 60-75 parts, and even more preferably 65-70 parts by mass. The additive is preferably 0.5 to 2.8 parts by mass, more preferably 1 to 2.5 parts, and even more preferably 1.5 to 2 parts by mass. The lithium salt is preferably 8 to 18 parts by mass, more preferably 10 to 16 parts by mass, and even more preferably 12 to 15 parts by mass. The preferred mass fraction of the dinitrile compound is 0.5 to 2.2 parts, more preferably 0.8 to 2 parts, and even more preferably 1 to 1.5 parts.
[0019] In this invention, the solvent includes one or more of the following: ethylene carbonate, propylene carbonate, diethyl carbonate, propyl propionate, fluoroethylene carbonate, difluoroethylene carbonate, 3,3,3-trifluoropropylene carbonate, dimethyl carbonate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, ethyl butyrate, methyl butyrate, butyl butyrate, and ethyl difluoroacetate.
[0020] In this invention, the additive has the structural formula shown in Formula I:
[0021] Formula I
[0022] Among them, R1 and R2 are preferably C2~C10 carbonate groups or C2~C10 sulfate groups.
[0023] In this invention, the additive is preferably A1, A2, or A3; The structural formula of A1 is: ; The structural formula of A2 is: ; The structural formula of A3 is: .
[0024] In this invention, the additive can improve the cycling performance of the system.
[0025] In this invention, the lithium salt includes LiPF6 and an auxiliary lithium salt, wherein the auxiliary lithium salt is one or more selected from lithium difluorophosphate, lithium tetrafluoroborate, lithium difluorooxalate borate, lithium difluorooxalate phosphate, lithium tetrafluorooxalate phosphate, lithium bis(trifluoromethyl)sulfonylimide, lithium bis(trifluoromethyl)sulfonylimide, and lithium 4,5-dicyano-2-trifluoromethyl-imidazolium. The preferred mass ratio of LiPF6 to auxiliary lithium salt is 6~16:0.1~5, more preferably 8~14:2~4, and even more preferably 10~12:2.5~3.
[0026] In this invention, the dinitrile compound is one or more selected from malononitrile, succinic anionyl, glutaronitrile, isoprene, ethyl succinic anionyl, methyl isoprene, 2-propyl malononitrile, and adiponitrile.
[0027] In this invention, lithium salt is beneficial for generating SEI with higher LiF content, but at the same time, defluorination will be more severe during high temperature and long cycle, which will aggravate the corrosion of silicon particles and copper foil, leading to copper foil corrosion. Introducing dinitrile compounds into the electrolyte can form a protective layer on the surface of copper foil, inhibiting the corrosion of copper foil by defluorination and deep discharge cycle.
[0028] The present invention also provides a method for preparing an electrolyte for a low discharge cutoff voltage silicon anode lithium-ion battery, wherein the preparation method comprises mixing a solvent, an additive, a lithium salt, a dinitrile compound and a silicon-containing anode material.
[0029] The present invention also provides the application of an electrolyte for a low discharge cutoff voltage silicon anode lithium-ion battery in a silicon anode lithium-ion battery, wherein the lower limit voltage of the silicon anode lithium-ion battery is 2~3V.
[0030] In this invention, the lower limit voltage of the silicon anode lithium-ion battery is preferably 2.2~2.8V, more preferably 2.3~2.7V, and even more preferably 2.4~2.5V.
[0031] In this invention, the mass fraction of the additive is denoted as a, the mass fraction of the lithium salt is denoted as b, the mass fraction of the dinitrile compound is denoted as x, the mass fraction of the silicon-containing anode material in the anode active material is denoted as y, and the lower limit voltage of the silicon anode lithium-ion battery is denoted as z. The relationship between the above data is shown below: ① When 2.5 ≤ z ≤ 2.75, the relation is 10 ≤ a × b + x 2 +y / 3+z 2 ≤50; ② When 2.0 ≤ z < 2.5, the relation is 3 ≤ a / b + x + y / 5 + 2z 2 ≤40.
[0032] When the above parameters satisfy the above relationship and each parameter is within the specified range, the capacity of the lithium-ion battery can be fully utilized and the deep discharge cycle performance of the battery can also reach the best. When the above relationship is less than the lower limit and all parameters are within the specified range, the battery capacity is high, but the battery's deep discharge (defined as discharge lower limit voltage ≤ 2.75V) cycle performance is poor. When the above relationship is greater than the upper limit and all parameters are within the specified range, the battery capacity is poor, but the battery's deep discharge cycle performance is better.
[0033] In this invention, the silicon anode lithium-ion battery includes a positive electrode, a negative electrode, a separator, and the electrolyte described above. The diaphragm is preferably Xingyuan single-layer diaphragm SD216102; The method for preparing the positive electrode sheet is as follows: The positive electrode active material, conductive agent, binder and solvent are mixed to obtain positive electrode slurry. The positive electrode slurry is coated on the current collector, and then dried, cold pressed, trimmed, cut, slit and dried again in sequence. Finally, aluminum tabs are welded to obtain the positive electrode sheet. The preferred positive electrode active material is lithium cobalt oxide, the preferred conductive agent is Super P, the preferred binder is polyvinylidene fluoride, and the preferred solvent is N-methylpyrrolidone. The mass ratio of the positive electrode active material, the conductive agent, and the binder is 97.5:1:1.5. The current collector is preferably aluminum foil, and the coating amount is 0.243 g / 1540 mm. 2 ; In the primary and secondary drying processes, the temperature is preferably 80-90℃, more preferably 82-88℃, and even more preferably 85-86℃, and the time is preferably 2-5h, more preferably 2.5-4.5h, and even more preferably 3-4h.
[0034] The method for preparing the negative electrode sheet is as follows: The negative electrode active material, conductive agent, thickener, binder and solvent are mixed to obtain a negative electrode slurry. The negative electrode slurry is coated on the current collector, and then the negative electrode sheet is obtained by sequentially drying, cold pressing, trimming, cutting, slitting and drying again, followed by welding aluminum tabs. The negative electrode active material preferably includes carbon and a silicon-containing negative electrode material. The silicon-containing negative electrode material is preferably SiC and / or SiO. The mass fraction of the silicon-containing negative electrode material in the negative electrode active material is preferably 7.5-25 parts, more preferably 10-22 parts, and even more preferably 12-15 parts. The mass fraction of carbon is preferably 75-92.5 parts, more preferably 78-90 parts, and even more preferably 80-85 parts. The specific capacity of the negative electrode active material is preferably 1400-1950 mAh / g, more preferably 1450-1900 mAh / g, and even more preferably 1500-1700 mAh / g. The conductive agent is carbon nanotubes, the thickener is sodium carboxymethyl cellulose, the binder is polyacrylic acid, and the solvent is water. The mass ratio of the negative electrode active material, conductive agent, thickener, and binder is 97.6:0.5:0.7:1.2. The current collector is preferably copper foil, and the coating amount is 0.102 g / 1540 mm. 2 ; In the primary and secondary drying processes, the temperature is preferably 80-90℃, more preferably 82-88℃, and even more preferably 85-86℃, and the time is preferably 10-15h, more preferably 11-14h, and even more preferably 12-13h.
[0035] The battery is prepared by: The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes, and then wound to obtain a bare battery. The bare battery is placed in an aluminum-plastic film outer packaging, and the electrolyte is injected into the dried battery. The battery is then encapsulated, left to stand, formed, shaped, and tested for capacity to complete the preparation of the lithium-ion soft-pack battery.
[0036] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.
[0037] In the embodiments and comparative examples of this invention, the number of parts refers to parts by mass.
[0038] Example 1
[0039] A solvent is obtained by mixing ethylene carbonate, polycarbonate, diethyl carbonate, and propyl propionate in a mass ratio of 15:15:35:35. The electrolyte is obtained by mixing 14.5 parts of lithium salt (LiPF6 and lithium difluorooxalate borate (LiODFB) in a mass ratio of 14:0.5), 1.5 parts of Al, 1.5 parts of succinic anion, and 82.5 parts of solvent.
[0040] The raw material composition and dosage of Examples 2-15 and Comparative Examples 1-15 are shown in Table 1, wherein the composition of the solvent is the same as that of Example 1.
[0041] Table 1. Raw material composition and dosage of Examples 2-15 and Comparative Examples 1-15
[0042] In Table 1, B represents bis(trimethylsilyl)sulfate.
[0043] Application Example 1
[0044] The battery was prepared using the electrolyte obtained in Example 1. The specific preparation steps are as follows: Preparation of positive electrode: Lithium cobalt oxide, Super P, and polyvinylidene fluoride were mixed in a mass ratio of 97.5:1:1.5, and then N-methylpyrrolidone was added to obtain a positive electrode slurry. The obtained positive electrode slurry was then used at a concentration of 0.243 g / 1540 mm. 2 The coating amount is applied to the aluminum foil, dried at 85℃ for 4 hours, then cold-pressed, then trimmed, cut, and slit, and dried under vacuum at 85℃ for 4 hours. Aluminum tabs are then welded to obtain the positive electrode sheet. Preparation of negative electrode: The negative electrode active material (graphite to SiC mass ratio of 85:15), carbon nanotubes, sodium carboxymethyl cellulose, and polyacrylic acid were mixed in a mass ratio of 97.6:0.5:0.7:1.2, and then water was added to obtain the negative electrode slurry. The obtained negative electrode slurry was then mixed at a mass ratio of 0.102 g / 1540 mm. 2 The coating amount is applied to the copper foil surface, dried at 85℃ for 4 hours, then cold-pressed, then trimmed, cut, and slit, and dried under vacuum at 85℃ for 12 hours. Aluminum tabs are then welded to obtain the negative electrode sheet. Battery manufacturing: The positive electrode, separator (Xingyuan single-layer separator SD216102), and negative electrode are stacked in sequence, with the separator in the middle of the positive and negative electrodes, and wound to obtain a bare battery. The bare battery is placed in an aluminum-plastic film outer packaging, and the electrolyte is injected into the dried battery. The battery is then encapsulated, left to stand, formed, shaped, and tested for capacity to complete the preparation of the lithium-ion soft pack battery, with a discharge lower limit voltage of 2.5V.
[0045] Application Examples 2-11
[0046] Batteries were prepared using the electrolytes obtained in Examples 2-11, with the specific preparation method being the same as in Application Example 1.
[0047] Application Example 12
[0048] A battery was prepared using the electrolyte obtained in Example 12, except that the mass ratio of graphite to SiC in Application Example 1 was 85:15, which was replaced with the mass ratio of graphite to SiC was 90:10. The other steps were the same as in Application Example 1.
[0049] Application Example 13
[0050] A battery was prepared using the electrolyte obtained in Example 13, except that the mass ratio of graphite to SiC in Application Example 1 was 85:15, which was replaced with the mass ratio of graphite to SiC was 80:20. The other steps were the same as in Application Example 1.
[0051] Application Example 14
[0052] A battery was prepared using the electrolyte obtained in Example 14, with the lower limit voltage of all discharge steps set to 2.75V, and the other steps being the same as in Application Example 1.
[0053] Example 15
[0054] A battery was prepared using the electrolyte obtained in Example 15. The lower limit voltage for all discharge steps was set to 2.25V, and the other steps were the same as in Application Example 1.
[0055] Application Comparative Examples 1-8
[0056] Batteries were prepared using the electrolytes obtained in Comparative Examples 1 to 8, respectively, with the specific preparation steps being the same as in Application Example 1.
[0057] Application Comparison Example 9
[0058] A battery was prepared using the electrolyte obtained in Comparative Example 9. The phrase "the mass ratio of graphite to SiC is 85:15" in Application Example 1 was replaced with "graphite". The other steps were the same as in Application Example 1.
[0059] Application Comparison Example 10
[0060] A battery was prepared using the electrolyte obtained in Comparative Example 10. The phrase "the mass ratio of graphite to SiC is 85:15" in Application Example 1 was replaced with "the mass ratio of graphite to SiC is 95:5". The other steps were the same as in Application Example 1.
[0061] Application Comparative Example 11
[0062] A battery was prepared using the electrolyte obtained in Comparative Example 11. The "mass ratio of graphite to SiC is 85:15" in Application Example 1 was replaced with "mass ratio of graphite to SiC is 70:30". The other steps were the same as in Application Example 1.
[0063] Application Comparative Examples 12-13
[0064] Batteries were prepared using the electrolytes obtained in Comparative Examples 12 and 13, respectively, with the specific preparation steps being the same as in Application Example 1.
[0065] Application Comparative Example 14
[0066] A battery was prepared using the electrolyte obtained in Comparative Example 14. The lower limit voltage of all discharge steps was set to 1.8V, and the other steps were the same as in Application Example 1.
[0067] Application Comparative Example 15
[0068] A battery was prepared using the electrolyte obtained in Comparative Example 15. The lower limit voltage of all discharge steps was set to 3.2V, and the other steps were the same as in Application Example 1.
[0069] The batteries obtained from corresponding use cases 1-15 and application comparison cases 1-15 were subjected to the following performance tests, and the test results are shown in Table 2.
[0070] Discharge capacity test: The battery is charged at a constant current of 1.5C to 4.55V, and then switched to constant voltage charging until the current drops to 0.02C; then it is discharged at a constant current of 0.7C to the set lower limit voltage. This step is repeated 3 times, and the average value is recorded as the average capacity.
[0071] Room temperature cycling performance test: At 25℃, charge at a constant current of 1.5C to 4.55V, then switch to constant voltage charging until the current drops to 0.02C; then discharge at a constant current of 0.7C to the set lower limit voltage, repeating this cycle 500 times. Record the discharge capacity of the first cycle and the discharge capacity of the 500th cycle, and calculate the capacity retention rate using the following formula: Capacity retention rate = (Discharge capacity at week 500 ÷ Discharge capacity at week 1) × 100%, Thickness expansion rate = (full charge thickness in week 500 ÷ full charge thickness in week 1) × 100%.
[0072] High-temperature cycling performance test: At 45℃, charge at a constant current of 1.5C to 4.55V, then switch to constant voltage charging until the current drops to 0.02C; then discharge at a constant current of 0.7C to the set lower limit voltage, repeating this cycle 400 times. Record the discharge capacity of the first cycle and the discharge capacity of the 400th cycle, and calculate the capacity retention rate using the following formula: Capacity retention rate = (Discharge capacity at week 400 ÷ Discharge capacity at week 1) × 100% Thickness expansion rate = (full charge thickness in week 400 ÷ full charge thickness in week 1) × 100%.
[0073] Table 2 Battery performance test results of Application Examples 1-15 and Comparative Application Examples 1-15
[0074] As can be seen from Tables 1 and 2, when the relevant parameters of the lithium-ion battery satisfy the relevant formulas and all parameters are within the specified range, the lithium-ion battery capacity can be fully utilized, and the battery's deep discharge cycle performance can also reach its optimal level. At this point, the additives, lithium salts, and dinitrile compounds work synergistically to ensure the battery has a high capacity, achieving longer driving range, while also suppressing copper foil corrosion that may occur during deep discharge, thus reducing the rapid capacity decay caused by copper foil corrosion due to deep discharge.
[0075] When equations ① and ② are less than the lower limit and all parameters are within the specified range, the battery's capacity is high, but its deep discharge (defined as a lower discharge limit voltage ≤ 2.75V) cycle performance is poor. At this point, the battery's impedance is low, and its capacity is high, but the electrolyte provides insufficient protection for the copper foil. Under deep discharge conditions, the copper foil is highly susceptible to corrosion, leading to capacity decay or even electrode breakage, ultimately resulting in a significant drop in capacity.
[0076] When equations ① and ② are greater than their upper limits, and all parameters are within their specified ranges, the battery's capacity utilization is poor, but its deep discharge cycle performance is superior. At this point, the battery's impedance is higher, but the electrolyte's inhibitory effect on copper foil corrosion is optimal, which helps improve the battery's cycle performance.
[0077] Some examples in the comparative examples meet the range of the equation, but the design of their specific parameters does not meet the requirements, or they use compounds that are not the required additives for comparison. Their performance is still worse than that of Example 1, which further illustrates that only when the invention point is fully met can the overall performance of the battery reach the optimal level.
[0078] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.
Claims
1. An electrolyte for a low-discharge-cut-voltage silicon anode lithium-ion battery, characterized in that, The components include the following parts by mass: 48-86 parts solvent, 0.3-3 parts additives, 6.1-21 parts lithium salt and 0.3-2.5 parts dinitrile compounds.
2. The electrolyte for a low discharge cutoff voltage silicon anode lithium-ion battery according to claim 1, characterized in that, The solvent includes one or more of the following: ethylene carbonate, propylene carbonate, diethyl carbonate, propyl propionate, fluoroethylene carbonate, difluoroethylene carbonate, 3,3,3-trifluoropropylene carbonate, dimethyl carbonate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, ethyl butyrate, methyl butyrate, butyl butyrate, and ethyl difluoroacetate.
3. The electrolyte for a low discharge cutoff voltage silicon anode lithium-ion battery according to claim 2, characterized in that, The structural formula of the additive is shown in Formula I: Formula I Among them, R1 and R2 are independently C2~C10 carbonate groups or C2~C10 sulfate groups.
4. The electrolyte for a low discharge cutoff voltage silicon anode lithium-ion battery according to claim 2 or 3, characterized in that, The lithium salt includes LiPF6 and an auxiliary lithium salt, wherein the auxiliary lithium salt is one or more selected from lithium difluorophosphate, lithium tetrafluoroborate, lithium difluorooxalate borate, lithium difluorooxalate phosphate, lithium tetrafluorooxalate phosphate, lithium bis(trifluoromethyl)sulfonylimide, lithium bis(trifluoromethyl)sulfonylimide, and lithium 4,5-dicyano-2-trifluoromethyl-imidazolium. The mass ratio of LiPF6 to auxiliary lithium salt is 6~16:0.1~5.
5. The electrolyte for a low discharge cutoff voltage silicon anode lithium-ion battery according to claim 4, characterized in that, The dinitrile compounds are one or more selected from malononitrile, succinic anhydride, glutaronitrile, isoprenatrile, ethyl succinic anhydride, methyl isoprenatrile, 2-propyl malononitrile, and adiponitrile.
6. A method for preparing an electrolyte for a low-discharge-cut-voltage silicon anode lithium-ion battery according to any one of claims 1 to 5, characterized in that, The preparation method involves mixing a solvent, an additive, a lithium salt, and a dinitrile compound.
7. The application of the electrolyte for a low discharge cutoff voltage silicon anode lithium-ion battery according to any one of claims 1 to 5 in a silicon anode lithium-ion battery, characterized in that, The lower limit voltage of the silicon anode lithium-ion battery is 2~3V.
8. The application of the electrolyte for a low discharge cutoff voltage silicon anode lithium-ion battery according to claim 7 in a silicon anode lithium-ion battery, characterized in that, In the silicon anode, the anode active material includes carbon and silicon-containing anode material, wherein the silicon-containing anode material is SiC and / or SiO; The negative electrode active material contains 7.5 to 25 parts by mass of silicon and 75 to 92.5 parts by mass of carbon.
9. The application of the electrolyte for a low discharge cutoff voltage silicon anode lithium-ion battery according to claim 7 or 8 in a silicon anode lithium-ion battery, characterized in that, Let a denote the mass fraction of the additive, b denote the mass fraction of the lithium salt, x denote the mass fraction of the dinitrile compound, y denote the mass fraction of the silicon-containing anode material in the anode active material, and z denote the lower limit voltage of the silicon anode lithium-ion battery. The relationship between a, b, x, y, and z is shown below: ① When 2.5 ≤ z ≤ 2.75, the relation is 10 ≤ a × b + x 2 +y / 3+z 2 ≤50; ② When 2.0 ≤ z < 2.5, the relation is 3 ≤ a / b + x + y / 5 + 2z 2 ≤40.