Electrolyte and lithium ion battery

Abstract

The application provides an electrolyte and a lithium ion battery. The electrolyte comprises an organic solvent, LiPF6 and an additive, wherein the additive comprises vinyltrimethoxysilane, pyridinium propane sulfonate and bis(trimethylsilyl) sulfate. The vinyltrimethoxysilane additive can form an organic polymer containing an unsaturated bond and a cross-polymerization network containing Si-O-Si bonds on the surface of a silicon negative electrode, thereby improving the mechanical strength and flexibility of the SEI film. The pyridinium propane sulfonate and the bis(trimethylsilyl) sulfate can form a small amount of a positive electrode protective film containing a sulfur compound, and can also form an unstable solid electrolyte passivation film on the surface of the negative electrode while being easily decomposed on the surface of the positive electrode. Through the synergistic effect of the above three additives, the cycle performance, high and low temperature performance of the battery are effectively improved, and the service life of the battery is prolonged.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion batteries, in particular to an electrolyte and a lithium ion battery. BACKGROUND

[0002] Classic film-forming additives such as FEC, VC, PS, DTD, etc. play an important role in lithium ion batteries, but with the increase of silicon doping ratio and the continuous development of high-voltage materials, conventional additives cannot meet the needs of long cycle and wide temperature working environment. From the current commercial application, DTD can significantly improve the high-temperature storage and high-temperature cycle performance of the battery, and it is the best additive among sulfate compounds, but the cost of DTD is relatively high, and the low-temperature storage requirement brings inconvenience to the transportation and storage of electrolyte; VC has oxidation stability problems after film formation in high-temperature and high-voltage systems, which leads to a series of metathesis, PS performs well in inhibiting gas production, but it is easy to be continuously oxidized with the positive electrode, the membrane impedance increases, and the internal resistance and DCR increase rapidly in long cycle, and PS has the defect of great harm to the body, which has been banned in some countries.

[0003] High-capacity negative electrode materials are an important breakthrough for improving the energy density of lithium ion batteries. Compared with graphite negative electrode, silicon-carbon negative electrode has obvious advantages in compaction density and specific capacity. It is difficult to further improve the graphite negative electrode material, and the theoretical energy density of 372 mAh / g is also far from the theoretical energy density of 4200 mAh / g of silicon negative electrode material. Suitable discharge potential and relatively abundant reserves in nature are considered to be the most likely negative electrode material to replace graphite.

[0004] However, there are many problems in the commercial application of elemental silicon in lithium ion batteries. On the one hand, the lithium ion deintercalation and intercalation process in silicon material will produce internal stress in its interior, which will cause volume expansion and damage to the material structure, and may cause problems such as breakage of active particles, pulverization of electrode, and shedding of active material; on the other hand, due to the change in the volume of silicon, the solid electrolyte interface film (SEI) will be broken, and the newly exposed silicon will produce a new SEI film, which will continuously consume lithium ions in the electrolyte, reducing the first coulomb efficiency. Finally, during the cycle process, due to the volume change of the electrode material, the SEI film of the silicon negative electrode interface repeatedly grows and breaks, the lithium source is rapidly consumed, and a series of problems such as rapid capacity decay, which greatly affects the cycle stability.

[0005] In summary, in the research and development process of silicon negative electrode material lithium ion batteries, selecting appropriate additives and developing matching liquid injection and formation methods are particularly crucial for improving the first coulomb efficiency of lithium batteries, improving cycle stability, reducing internal resistance, and improving high and low temperature working performance, etc. SUMMARY

[0006] The main objective of this application is to provide an electrolyte and a lithium-ion battery to solve the problems of poor cycle performance and poor high and low temperature performance of lithium-ion batteries that include silicon anode materials in the prior art.

[0007] To achieve the above objectives, according to one aspect of this application, an electrolyte is provided comprising an organic solvent, LiPF6, and additives, including vinyltrimethoxysilane, pyridinium propanesulfonate, and bis(trimethylsilyl)sulfate.

[0008] Furthermore, the mass of vinyltrimethoxysilane accounts for 0.1–5 wt% of the total mass of the electrolyte, the mass of pyridinium propanesulfonate accounts for 0.1–5 wt% of the total mass of the electrolyte, and the mass of bis(trimethylsilyl)sulfate accounts for 0.1–5 wt% of the total mass of the electrolyte.

[0009] Furthermore, the mass ratio of vinyltrimethoxysilane, pyridinium propanesulfonate, and bis(trimethylsilyl)sulfate is 0.1–3:0.1–3:0.1–3.

[0010] Furthermore, the electrolyte also includes a first additive, which includes lithium difluorooxalate borate and fluoroethylene carbonate, wherein the mass of lithium difluorooxalate borate accounts for 0.3 to 1 wt% of the total mass of the electrolyte, and / or the mass of fluoroethylene carbonate accounts for 1 to 12 wt% of the total mass of the electrolyte.

[0011] Furthermore, the mass ratio of the additive to the first auxiliary agent is 0.3 to 1:1 to 12.

[0012] Furthermore, the electrolyte also includes a second additive, which includes C4H6N2 and / or LiPO2F2, wherein the mass of C4H6N2 accounts for 0.5 to 1.5 wt% of the total mass of the electrolyte, and / or the mass of LiPO2F2 accounts for 0.1 to 1 wt% of the total mass of the electrolyte.

[0013] Furthermore, the organic solvent includes ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl propionate, and propyl propionate; wherein the mass ratio of ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl propionate, and propyl propionate is 10–20:5–15:5–15:5–15:45–60.

[0014] Furthermore, the mass of LiPF6 accounts for 10–15 wt% of the total mass of the electrolyte.

[0015] Further, by mass percentage, the electrolyte comprises 0.1–3 wt% vinyltrimethoxysilane, 0.1–3 wt% pyridinium propanesulfonate, 0.1–3 wt% bis(trimethylsilyl)sulfate, 10–15 wt% LiPF6, and an organic solvent; and / or, the electrolyte comprises 0.1–3 wt% vinyltrimethoxysilane, 0.1–3 wt% pyridinium propanesulfonate, 0.1–3 wt% bis(trimethylsilyl)sulfate, 10–15 wt% LiPF6, 0.3–1 wt% lithium difluorooxalate borate, 1–12 wt% fluoroethylene carbonate, 0.5–1.5 wt% C4H6N2, 0.3–1 wt% LiPO2F2, and an organic solvent.

[0016] According to another aspect of this application, a lithium-ion battery is provided, including a positive electrode, a negative electrode, and an electrolyte, wherein the electrolyte is the electrolyte described above.

[0017] By applying the technical solution of this application, this application provides an electrolyte that can improve the electrical performance of lithium-ion batteries, including silicon anode materials, through optimization of the additive combination. Specifically, the vinyltrimethoxysilane additive used in this application can form an organic polymer containing unsaturated bonds and a cross-polymer network containing Si-O-Si bonds on the surface of the silicon anode, thereby improving the mechanical strength and flexibility of the SEI film. Pyridinium propanesulfonate and bis(trimethylsilyl)sulfate can form sulfur-containing compounds in small amounts as positive electrode protective films, or they can form unstable solid electrolyte passivation films on the anode surface while being easily decomposed on the positive electrode surface. They can also react with the SEI of the organic polymer containing unsaturated bonds formed by the vinyltrimethoxysilane additive, inhibiting further decomposition of the organic polymer's SEI and thus modifying the SEI. The synergistic effect of the above three additives can form a protective layer with a three-dimensional network on the cathode of the battery, providing a cross-linking protective layer and forming an SEI with high electrical conductivity and high thermal stability. This balances the various performance characteristics of the battery, effectively improves the battery's cycle performance and high and low temperature performance, extends the battery's service life, and solves the problem of the harmful effects of PS on the body. Detailed Implementation

[0018] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present application will now be described in detail with reference to the embodiments.

[0019] As analyzed in the background section, existing lithium-ion batteries, including those using silicon anode materials, suffer from poor cycle performance and poor performance at high and low temperatures. To address this issue, this application provides an electrolyte and a lithium-ion battery.

[0020] In a typical embodiment of this application, an electrolyte is provided, comprising an organic solvent, LiPF6, and additives, including vinyltrimethoxysilane, pyridinium propanesulfonate, and bis(trimethylsilyl)sulfate.

[0021] This application provides an electrolyte that improves the electrical performance of lithium-ion batteries, including silicon anode materials, through optimization of the additive combination. Specifically, the vinyltrimethoxysilane additive used in this application can form an organic polymer containing unsaturated bonds and a cross-polymerized network containing Si-O-Si bonds on the surface of the silicon anode, improving the mechanical strength and flexibility of the SEI film. Pyridinium propanesulfonate and bis(trimethylsilyl)sulfate can form a small amount of sulfur-containing compounds that form the positive electrode protective film. They can also form an unstable solid electrolyte passivation film on the anode surface while being easily decomposed on the positive electrode surface. Furthermore, they can react with the SEI of the organic polymer containing unsaturated bonds formed by the vinyltrimethoxysilane additive, inhibiting further decomposition of the organic polymer's SEI and thus modifying the SEI. Through the synergistic effect of these three additives, a protective layer with a three-dimensional network can be formed on the cathode of the battery, providing a cross-linked protective layer and forming an SEI with high conductivity and high thermal stability. This balances various battery performance aspects, effectively improving the battery's cycle performance, high and low temperature performance, extending battery life, and addressing the significant health hazards associated with polystyrene (PS).

[0022] In one embodiment of this application, the mass of the above-mentioned vinyltrimethoxysilane accounts for 0.1 to 5 wt% of the total mass of the electrolyte, the mass of propanesulfonic acid pyridinium salt accounts for 0.1 to 5 wt% of the total mass of the electrolyte, and the mass of bis(trimethylsilyl)sulfate accounts for 0.1 to 5 wt% of the total mass of the electrolyte.

[0023] Too high or too low a concentration is not conducive to the effective formation of the required SEI film, or leads to increased electrolyte cost and decreased performance. This application further limits the content of additives, which is more conducive to the formation of organic polymers containing unsaturated bonds and cross-polymerized networks containing Si-O-Si bonds on the silicon anode surface, as well as the formation of SEI reaction of organic polymers containing unsaturated bonds, inhibiting further decomposition of the organic polymer SEI, improving the mechanical strength and flexibility of the SEI film, thereby helping to improve the first coulombic efficiency of the battery, improve cycle stability, reduce internal resistance and improve high and low temperature performance, while also helping to reduce costs.

[0024] In one embodiment of this application, the mass ratio of the above-mentioned vinyltrimethoxysilane, pyridinium propanesulfonate and bis(trimethylsilyl)sulfate is 0.1-3:0.1-3:0.1-3.

[0025] By controlling the ratio of the three additives within the above range, the synergistic effect of the three additives can form a protective layer with a three-dimensional network on the cathode of the battery, which acts as a cross-linked protective layer. This helps to promote the uniform formation of the SEI film, improve its mechanical strength and flexibility, reduce the increase of internal resistance and the rupture of the SEI film during the cycle, thereby extending the battery life and improving battery safety.

[0026] In one embodiment of this application, the electrolyte further includes a first additive, which includes lithium difluorooxalate borate and fluoroethylene carbonate, wherein the mass of lithium difluorooxalate borate accounts for 0.3 to 1 wt% of the total mass of the electrolyte, and / or the mass of fluoroethylene carbonate accounts for 1 to 12 wt% of the total mass of the electrolyte.

[0027] Lithium difluorooxalate borate and fluoroethylene carbonate can enhance the stability of the SEI film and the lithium-ion insertion / extraction efficiency in the electrode material. By controlling the content of lithium difluorooxalate borate and fluoroethylene carbonate within the above-mentioned range, it is beneficial to improve the initial coulombic efficiency of the battery, enhance the stability of the battery at high temperature and high voltage, thereby extending the cycle life of the battery. At the same time, it is also beneficial to reduce the internal resistance of the battery at low temperature and improve the low-temperature performance of the battery.

[0028] In one embodiment of this application, the mass ratio of the above-mentioned additive to the first auxiliary agent is 0.3 to 1: 1 to 12.

[0029] By controlling the mass ratio of the additive to the first auxiliary agent within the above range, the synergistic effect of the additive and the first auxiliary agent is more conducive to enhancing the stability of the SEI film and the insertion / extraction efficiency of lithium ions in the electrode material. It is also more conducive to promoting the uniform formation of the SEI film, improving the capacity retention rate of the battery under high temperature storage conditions, reducing battery thickness expansion, and also helping to reduce capacity decay during battery cycling, thereby improving the cycle stability and safety of the battery.

[0030] In one embodiment of this application, the electrolyte further includes a second additive, which includes C4H6N2 and / or LiPO2F2, wherein the mass of C4H6N2 accounts for 0.5 to 1.5 wt% of the total mass of the electrolyte, and / or the mass of LiPO2F2 accounts for 0.1 to 1 wt% of the total mass of the electrolyte.

[0031] C4H6N2 and LiPO2F2 promote the formation of the SEI film, enhancing its stability and conductivity. LiPO2F2 also improves the battery's high-temperature performance and cycle stability. By controlling the content of C4H6N2 and LiPO2F2 within the aforementioned ranges, it is beneficial to improve the battery's discharge capacity at low temperatures, enhance its cycle stability and storage performance under high-temperature conditions, and also reduce the rate of internal resistance increase during cycling, thus extending the battery's lifespan.

[0032] In one embodiment of this application, the organic solvent includes ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl propionate, and propyl propionate; wherein the mass ratio of ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl propionate, and propyl propionate is 10-20:5-15:5-15:5-15:45-60.

[0033] Organic solvents provide the basic electrochemical environment for the electrolyte, which is crucial to battery performance, especially affecting lithium-ion transport efficiency and SEI film formation. By controlling the combination and ratio of organic solvents within the above-mentioned range, it is beneficial to improve the conductivity of the electrolyte, reduce internal losses of the battery during charging and discharging, promote the stable formation of the SEI film, improve the battery's cycle efficiency and high and low temperature performance, and extend the battery's lifespan.

[0034] In one embodiment of this application, the mass of the LiPF6 described above accounts for 10 to 15 wt% of the total mass of the electrolyte.

[0035] LiPF6, as a lithium salt, is a key component of the electrolyte. Its concentration directly affects the electrolyte's conductivity and the battery's electrochemical performance, including the conductivity of lithium ions and the battery's cycle stability. By controlling the LiPF6 concentration within the aforementioned range, it is beneficial to improve the battery's conductivity, thereby increasing the battery's charge and discharge efficiency. Simultaneously, it reduces performance degradation and safety issues caused by excessively high or low LiPF6 concentrations in the electrolyte, ultimately improving the battery's overall performance.

[0036] In one embodiment of this application, the electrolyte comprises, by weight percentage, 0.1–3 wt% vinyltrimethoxysilane, 0.1–3 wt% pyridinium propanesulfonate, 0.1–3 wt% bis(trimethylsilyl)sulfate, 10–15 wt% LiPF6, and an organic solvent; and / or, the electrolyte comprises 0.1–3 wt% vinyltrimethoxysilane, 0.1–3 wt% pyridinium propanesulfonate, 0.1–3 wt% bis(trimethylsilyl)sulfate, 10–15 wt% LiPF6, 0.3–1 wt% lithium difluorooxalate borate, 1–12 wt% fluoroethylene carbonate, 0.5–1.5 wt% C4H6N2, 0.3–1 wt% LiPO2F2, and an organic solvent.

[0037] Controlling the concentration of each component in the electrolyte within the aforementioned range helps each component to exert its optimal electrochemical effect within that specific concentration range. Through the synergistic effect of these components, it is more conducive to achieving a comprehensive improvement in battery performance, thereby enhancing battery cycle efficiency, thermal stability and safety, extending battery life, and improving battery performance under high and low temperature conditions. This provides a reliable technical foundation for high-energy-density, high-safety lithium-ion batteries.

[0038] In another typical embodiment of this application, a lithium-ion battery is provided, including a positive electrode, a negative electrode, and an electrolyte, wherein the electrolyte is the electrolyte described above.

[0039] Lithium-ion batteries containing the aforementioned electrolytes have higher energy density, longer cycle life, better high and low temperature performance, and higher safety and reliability, making them suitable for various portable electronic products, electric vehicles, and energy storage systems.

[0040] The beneficial technical effects of this application will be explained below with reference to specific embodiments and comparative examples.

[0041] Example 1

[0042] A method for preparing a lithium-ion battery includes the following steps performed sequentially:

[0043] Preparation of electrolyte: In a nitrogen-filled glove box (H2O content < 0.5 ppm), ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl propionate, and propyl propionate were mixed in a mass ratio of 15:10:10:10:55 to obtain a mixed solution. Then, 0.30 wt% vinyltrimethoxysilane, 0.30 wt% pyridinium propanesulfonate, 0.50 wt% bis(trimethylsilyl)sulfate, 15 wt% LiPF6, 0.50 wt% lithium difluorooxalate borate, 10 wt% fluoroethylene carbonate, 1.00 wt% C4H6N2, and 0.30 wt% LiPO2F2 were slowly added to the 72.1 wt% mixed solution and stirred until homogeneous to obtain the lithium-ion battery electrolyte.

[0044] Preparation of the positive electrode: The positive electrode active materials LCO, CNT, SP and PVDF are thoroughly mixed in a mass ratio of 98:0.6:0.7:0.7, coated on aluminum foil, dried and cold-pressed to obtain the positive electrode sheet;

[0045] Preparation of the negative electrode: Silicon-carbon negative electrode material, conductive carbon black, single-walled carbon nanotubes and binder polyacrylic acid are mixed in a mass ratio of 80:9:1:10 and then added to deionized water as a solvent. After being mixed evenly, the mixture is coated on copper foil, dried, and cold-pressed to obtain the negative electrode sheet.

[0046] Example 2

[0047] The difference from Example 1 is that the content of vinyltrimethoxysilane is 0.50 wt%, the mass percentage of the mixed solution is 71.9 wt%, and the remaining components are the same as in Example 1, ultimately yielding a lithium-ion battery.

[0048] Example 3

[0049] The difference from Example 1 is that the content of vinyltrimethoxysilane is 1.0 wt%, the mass percentage of the mixed solution is 71.4 wt%, and the remaining components are the same as in Example 1, ultimately yielding a lithium-ion battery.

[0050] Example 4

[0051] The difference from Example 1 is that the content of vinyltrimethoxysilane is 1.5 wt%, the mass percentage of the mixed solution is 70.9 wt%, and the remaining components are the same as in Example 1, ultimately yielding a lithium-ion battery.

[0052] Example 5

[0053] The difference from Example 1 is that the content of vinyltrimethoxysilane is 2.0 wt%, the mass percentage of the mixed solution is 70.4 wt%, and the remaining components are the same as in Example 1, ultimately yielding a lithium-ion battery.

[0054] Example 6

[0055] The difference from Example 1 is that the content of bis(trimethylsilyl)sulfate is 1.0 wt%, the mass percentage of the mixed solution is 71.6 wt%, and the remaining components are the same as in Example 1, ultimately yielding a lithium-ion battery.

[0056] Example 7

[0057] The difference from Example 1 is that the content of bis(trimethylsilyl)sulfate is 1.5 wt%, the mass percentage of the mixed solution is 71.1 wt%, and the remaining components are the same as in Example 1, ultimately yielding a lithium-ion battery.

[0058] Example 8

[0059] The difference from Example 1 is that the content of bis(trimethylsilyl)sulfate is 2.0 wt%, the mass percentage of the mixed solution is 70.6 wt%, and the remaining components are the same as in Example 1, ultimately yielding a lithium-ion battery.

[0060] Example 9

[0061] The difference from Example 1 is that the content of bis(trimethylsilyl)sulfate is 3.00 wt%, the mass percentage of the mixed solution is 69.6 wt%, and the remaining components are the same as in Example 1, ultimately yielding a lithium-ion battery.

[0062] Example 10

[0063] The difference from Example 1 is that the content of propanesulfonic acid pyridinium salt is 0.50 wt%, the mass percentage of the mixed solution is 71.9 wt%, and the remaining components are the same as in Example 1, ultimately yielding a lithium-ion battery.

[0064] Example 11

[0065] The difference from Example 1 is that the content of propanesulfonic acid pyridinium salt is 1.00 wt%, the mass percentage of the mixed solution is 71.4 wt%, and the remaining components are the same as in Example 1, ultimately yielding a lithium-ion battery.

[0066] Example 12

[0067] The difference from Example 1 is that 2.00 wt% of vinyltrimethoxysilane, 1.0 wt% of propanesulfonic acid pyridinium salt, and 3.0 wt% of bis(trimethylsilyl)sulfate were added to the electrolyte, and the mass percentage of the mixed solution was 67.2 wt%. The remaining components were the same as in Example 1, and a lithium-ion battery was finally obtained.

[0068] Example 13

[0069] The difference from Example 12 is that 3.00 wt% of vinyltrimethoxysilane, 3.00 wt% of pyridinium propanesulfonate, and 3.00 wt% of bis(trimethylsilyl)sulfate were added to the electrolyte, and the mass percentage of the mixed solution was 64.2 wt%. The remaining components were the same as in Example 1, and a lithium-ion battery was finally obtained.

[0070] Example 14

[0071] The difference from Example 1 is that 3.00 wt% of vinyltrimethoxysilane, 3.00 wt% of pyridinium propanesulfonate, and 3.00 wt% of bis(trimethylsilyl)sulfate were added to the electrolyte, while fluoroethylene carbonate and C4H6N2 were not added. The mass percentage of the mixed solution was 75.2 wt%, and a lithium-ion battery was finally obtained.

[0072] Example 15

[0073] The difference from Example 13 is that 0.1 wt% of vinyltrimethoxysilane, 0.1 wt% of propanesulfonic acid pyridinium salt, and 3.00 wt% of bis(trimethylsilyl)sulfate were added to the electrolyte, and the mass percentage of the mixed solution was 70.0 wt%, thus obtaining a lithium-ion battery.

[0074] Example 16

[0075] The difference from Example 1 is that 0.1 wt% of vinyltrimethoxysilane, 0.1 wt% of propanesulfonic acid pyridinium salt, and 0.1 wt% of bis(trimethylsilyl)sulfate were added to the electrolyte, and the mass percentage of the mixed solution was 72.9 wt%, which finally yielded a lithium-ion battery.

[0076] Example 17

[0077] The difference from Example 1 is that the electrolyte was prepared as follows: 5.0 wt% vinyltrimethoxysilane, 4.0 wt% pyridinium propanesulfonate, and 5.0 wt% bis(trimethylsilyl)sulfate, with a mixed solution mass percentage of 59.2 wt%, ultimately yielding a lithium-ion battery.

[0078] Example 18

[0079] The difference from Example 1 is that the electrolyte is prepared as follows: 0.5 wt% vinyltrimethoxysilane, 0.5 wt% propanesulfonic acid pyridinium salt, 0.5 wt% bis(trimethylsilyl)sulfate, 1.0 wt% lithium difluorooxalate borate, and 12 wt% fluoroethylene carbonate. The ratio of the total mass of vinyltrimethoxysilane, propanesulfonic acid pyridinium salt, and bis(trimethylsilyl)sulfate to the total mass of lithium difluorooxalate borate and fluoroethylene carbonate is 0.75:6.5, thus obtaining a lithium-ion battery.

[0080] Example 19

[0081] The difference from Example 1 is that the electrolyte is prepared as follows: 1.00 wt% vinyltrimethoxysilane, 1.00 wt% propanesulfonic acid pyridinium salt, 1.00 wt% bis(trimethylsilyl)sulfate, 1.00 wt% lithium difluorooxalate borate, and 12.00 wt% fluoroethylene carbonate, and the ratio of the total mass of vinyltrimethoxysilane, propanesulfonic acid pyridinium salt, and bis(trimethylsilyl)sulfate to the total mass of lithium difluorooxalate borate and fluoroethylene carbonate is 1.5:6.5, thus obtaining a lithium-ion battery.

[0082] Example 20

[0083] The difference from Example 1 is that the electrolyte is prepared as follows: 4.00 wt% vinyltrimethoxysilane, 4.00 wt% propanesulfonic acid pyridinium salt, 4.00 wt% bis(trimethylsilyl)sulfate, 1.00 wt% lithium difluorooxalate borate, and 12.00 wt% fluoroethylene carbonate, and the ratio of the total mass of vinyltrimethoxysilane, propanesulfonic acid pyridinium salt, and bis(trimethylsilyl)sulfate to the total mass of lithium difluorooxalate borate and fluoroethylene carbonate is 6:6.5, thus obtaining a lithium-ion battery.

[0084] Example 21

[0085] The difference from Example 1 is that lithium difluorooxalate borate and fluoroethylene carbonate are not added to the electrolyte, and the mass percentage of the mixed solution is 82.6 wt%, ultimately yielding a lithium-ion battery.

[0086] Comparative Example 1

[0087] The difference from Example 1 is that the electrolyte was prepared without the addition of vinyltrimethoxysilane, pyridinium propanesulfonate and bis(trimethylsilyl)sulfate. The mass percentage of the mixed solution was 73.2 wt%, and the remaining components were the same as in Example 1, resulting in a lithium-ion battery.

[0088] Comparative Example 2

[0089] The difference from Example 1 is that the electrolyte was prepared without the addition of pyridinium propanesulfonate and bis(trimethylsilyl)sulfate. The mass percentage of the mixed solution was 72.9 wt%, and the remaining components were the same as in Example 1, resulting in a lithium-ion battery.

[0090] Comparative Example 3

[0091] The difference from Example 1 is that the electrolyte was prepared without the addition of vinyltrimethoxysilane and bis(trimethylsilyl)sulfate, the mass percentage of the mixed solution was 72.9 wt%, and the remaining components were the same as in Example 1, resulting in a lithium-ion battery.

[0092] Comparative Example 4

[0093] The difference from Example 1 is that the electrolyte was prepared without the addition of vinyltrimethoxysilane and pyridinium propanesulfonate. The mass percentage of the mixed solution was 72.7 wt%, and the remaining components were the same as in Example 1, resulting in a lithium-ion battery.

[0094] Performance testing:

[0095] Cyclic performance test: The lithium-ion battery was charged at a constant current and constant voltage rate of 1C to 4.5V at 25℃ and 45℃ respectively, with a cutoff current of 0.05C, and allowed to rest for 10 minutes. Then, the lithium-ion battery was discharged at a constant current rate of 1C to 3.0V, and allowed to rest for 10 minutes. This constitutes one charge-discharge cycle. The capacity retention rate (%) of the lithium-ion battery after N cycles = (discharge capacity of the Nth cycle / initial discharge capacity) × 100%, where N is the number of cycles of the lithium-ion battery.

[0096] High-temperature storage performance test: First, the formed battery was charged and discharged at 1.0C to 3.0V at room temperature, and the initial thickness was recorded; then it was charged at 0.2C constant current and constant voltage to 4.5V, and cut off at 0.02C; then discharged at 0.2C constant current to 3.0V; this was recorded as the initial capacity; then it was charged at 0.2C constant current and constant voltage to 4.5V, and cut off at 0.02C; after the battery was stored in a 60℃ constant temperature chamber for 7 days, the battery was removed, and the hot thickness was measured (the hot thickness was recorded at the temperature chamber). After resting for 2 hours, it was discharged at 0.2C constant current to 3.0V, and this was recorded as the residual capacity; then it was charged at 0.2C constant current and constant voltage to 4.5V, and cut off at 0.02C; after resting for 10 minutes; finally, it was discharged at 0.2C constant current to 3.0V; the recovered capacity was recorded.

[0097] The thermal expansion rate of the battery after 7 days of storage at 60℃ is calculated as follows: (thermal thickness - initial thickness) / initial thickness * 100%.

[0098] Battery capacity retention rate after 7 days of storage at 60℃ = (residual capacity / initial capacity) * 100%.

[0099] Battery capacity recovery rate after 7 days of storage at 60℃ = (recovered capacity / initial capacity) * 100%.

[0100] The test results are listed in Table 1.

[0101] Table 1

[0102]

[0103]

[0104] As can be seen from the above description, the embodiments of this application achieve the following technical effects:

[0105] This application provides an electrolyte that improves the electrical performance of lithium-ion batteries, including silicon anode materials, through optimization of the additive combination. Specifically, the vinyltrimethoxysilane additive used in this application can form an organic polymer containing unsaturated bonds and a cross-polymerized network containing Si-O-Si bonds on the surface of the silicon anode, improving the mechanical strength and flexibility of the SEI film. Pyridinium propanesulfonate and bis(trimethylsilyl)sulfate can form a small amount of sulfur-containing compounds that form the positive electrode protective film. They can also form an unstable solid electrolyte passivation film on the anode surface while being easily decomposed on the positive electrode surface. Furthermore, they can react with the SEI of the organic polymer containing unsaturated bonds formed by the vinyltrimethoxysilane additive, inhibiting further decomposition of the organic polymer's SEI and thus modifying the SEI. Through the synergistic effect of these three additives, a protective layer with a three-dimensional network can be formed on the cathode of the battery, providing a cross-linked protective layer and forming an SEI with high conductivity and high thermal stability. This balances various battery performance aspects, effectively improving the battery's cycle performance, high and low temperature performance, extending battery life, and addressing the significant health hazards associated with polystyrene (PS).

[0106] The above are merely preferred embodiments of this application and are not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. An electrolyte, characterized in that, The electrolyte includes an organic solvent, LiPF6, and additives, the additives including vinyltrimethoxysilane, pyridinium propanesulfonate, and bis(trimethylsilyl)sulfate. The mass ratio of the vinyltrimethoxysilane, the pyridinium propanesulfonate, and the bis(trimethylsilyl)sulfate is 0.1~3:0.1~3:0.1~3; The mass of the vinyltrimethoxysilane is 0.1-5 wt% of the total mass of the electrolyte, the mass of the propanesulfonic acid pyridinium salt is 0.1-5 wt% of the total mass of the electrolyte, and the mass of the bis(trimethylsilyl)sulfate is 0.1-5 wt% of the total mass of the electrolyte.

2. The electrolyte according to claim 1, characterized in that, The electrolyte further includes a first additive, which includes lithium difluorooxalate borate and fluoroethylene carbonate, wherein the mass of lithium difluorooxalate borate accounts for 0.3 to 1 wt% of the total mass of the electrolyte, and / or the mass of fluoroethylene carbonate accounts for 1 to 12 wt% of the total mass of the electrolyte.

3. The electrolyte according to claim 2, characterized in that, The mass ratio of the additive to the first auxiliary agent is 0.3~1.5:1~12.

4. The electrolyte according to claim 1, characterized in that, The electrolyte further includes a second additive, which includes C4H6N2 and / or LiPO2F2, wherein the mass of C4H6N2 accounts for 0.5 to 1.5 wt% of the total mass of the electrolyte, and / or the mass of LiPO2F2 accounts for 0.1 to 1.0 wt% of the total mass of the electrolyte.

5. The electrolyte according to claim 1, characterized in that, The organic solvent includes ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl propionate, and propyl propionate; wherein the mass ratio of ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl propionate, and propyl propionate is 10~20:5~15:5~15:5~15:45~60.

6. The electrolyte according to claim 1, characterized in that, The mass of LiPF6 accounts for 10-15 wt% of the total mass of the electrolyte.

7. The electrolyte according to claim 1, characterized in that, The electrolyte comprises, by weight percentage, 0.1-3 wt% of the vinyltrimethoxysilane, 0.1-3 wt% of the pyridinium propanesulfonate, 0.1-3 wt% of the bis(trimethylsilyl)sulfate, 10-15 wt% of the LiPF6, and an organic solvent; and / or, the electrolyte comprises 0.1-3 wt% of the vinyltrimethoxysilane, 0.1-3 wt% of the pyridinium propanesulfonate, 0.1-3 wt% of the bis(trimethylsilyl)sulfate, 10-15 wt% of the LiPF6, 0.3-1 wt% of lithium difluorooxalateborate, 1-12 wt% of fluoroethylene carbonate, 0.5-1.5 wt% of C4H6N2, 0.3-1.0 wt% of LiPO2F2, and an organic solvent.

8. A lithium-ion battery, comprising a positive electrode, a negative electrode, and an electrolyte, characterized in that, The electrolyte is any one of claims 1 to 7.

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