Electrolyte additive, electrolyte and lithium ion battery

Abstract

The application discloses an electrolyte additive, an electrolyte and a lithium ion battery, and relates to the technical field of electrolytes.The electrolyte comprises an electrolyte additive, and the electrolyte additive comprises 2,4,6-(methoxysulfonyl)methyl-2,4,6-trimethylcyclotrisiloxane shown in formula I.The additive with the structure of the application can improve the cycle performance of the lithium ion battery by the synergistic effect of the siloxane ring structure, the methyl group and the methoxysulfonyl group and other functional groups, and can improve the defects of the thermal stability, the chemical stability, the long-term stability, the side reaction, the quality of the covering layer, the solubility, the compatibility, the viscosity and the volatility of other additives.

Description

TECHNICAL FIELD

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

[0002] Lithium ion batteries have been widely used in many fields such as mobile phones, notebook computers, electric vehicles and energy storage cabinets due to their high energy density, long cycle life, low self-discharge rate, no memory effect, stable output voltage, fast charging and discharging and environmental protection. With the continuous development of these application fields, the performance requirements of lithium ion batteries are also increasing. Among them, the cycle performance is one of the key indicators to measure the quality and service life of lithium ion batteries, which is of great significance to ensure the stability and reliability of the battery during long-term use.

[0003] However, the current commercial lithium ion batteries still have certain limitations in terms of cycle performance. During the charging and discharging cycle of the battery, various factors will cause the performance of the battery to gradually decline. For example, the structure and performance of the electrode material will change, the positive electrode material may have problems such as structure collapse and active material loss, and the negative electrode material may face situations such as volume expansion and SEI film rupture. At the same time, the electrolyte will also decompose during the cycle process, and will have side reactions with the electrode material, which will all lead to an increase in the internal resistance of the battery and a decrease in the capacity, thereby shortening the cycle life of the battery.

[0004] As an important component of lithium ion batteries, electrolyte has a crucial influence on the performance of the battery. Among them, the use of electrolyte additives is an effective means to improve the performance of the battery. Suitable additives can form a stable protective film on the electrode surface, inhibit the decomposition of the electrolyte and the degradation of the electrode material, adjust the ion conductivity and viscosity of the electrolyte, and thus improve the cycle performance of the battery. For example, some additives can preferentially react on the electrode surface to form a stable SEI film or CEI film, reduce the side reactions between the electrode and the electrolyte, and protect the electrode material; other additives can interact with lithium salts in the electrolyte to improve the dissociation state of the lithium salts and increase the ion conduction efficiency. Therefore, the development of new electrolyte additives has important research value and practical application prospects for improving the cycle performance of lithium ion batteries.

[0005] Through research and analysis of the electrolyte additives developed by the prior art, it is found that these additives still have the following defects:

[0006] 1. Poor thermal stability:

[0007] In high-temperature environments or high-rate charging and discharging, the internal temperature of lithium-ion batteries rises, and the chemical bond energy of many compounds, including electrolyte additives, is difficult to withstand high-temperature stress. For example, the chemical bonds in some additives are prone to breakage at high temperatures, leading to molecular structure destruction and thermal decomposition reactions. Thermal decomposition products can change the chemical composition of the electrolyte, possibly generating some poorly conductive substances, reducing the ionic conductivity of the electrolyte. At the same time, decomposition products can also react with electrode materials, forming undesirable deposits on the electrode surface, increasing the internal resistance of the battery. The increase in battery internal resistance leads to increased energy loss during charging and discharging, and the battery heats up further. This further accelerates the structural destruction of the electrode material and the decomposition of the electrolyte, forming a vicious cycle, ultimately reducing the battery capacity retention rate and significantly shortening the cycle life. For example, when electric vehicles drive at high speed for a long time or charge in hot environments, the internal temperature of the battery rises, and additives with poor thermal stability can accelerate the deterioration of battery performance.

[0008] 2. Low chemical stability:

[0009] The working environment of lithium-ion batteries is complex, and additives in the electrolyte can react with a variety of substances. Some specific functional groups in the molecular structure of the additives have high reactivity, and during the battery operation process, they are prone to chemical reactions with lithium salts, solvent molecules, trace impurities (such as water, acid, base, etc.), or active substances generated during battery charging and discharging in the electrolyte. These reactions can change the structure and properties of the additives themselves, causing them to lose their original functions, such as being unable to effectively form stable protective films or regulate electrolyte performance. At the same time, reaction products can interfere with the transport of lithium ions, reducing the ionic conductivity of the electrolyte and affecting the charging and discharging efficiency of the battery. In the long term, the continuous reaction of additives with low chemical stability can lead to an unstable internal chemical environment in the battery, accelerating the corrosion of electrode materials and the decomposition of electrolyte, thereby reducing the cycle life and capacity retention rate of the battery.

[0010] 3. Insufficient long-term stability:

[0011] As the number of battery charging and discharging cycles increases and the use time extends, the stability of some additives in the battery system gradually decreases. For example, the protective film formed by some additives may age, crack, or dissolve during long-term cycling. The destruction of the protective film can expose the electrode surface to the electrolyte again, triggering undesirable reactions between the electrode material and the electrolyte, such as corrosion of the electrode material and decomposition of the electrolyte. This leads to an increase in battery internal resistance and exacerbation of polarization during charging and discharging, resulting in gradual degradation of battery capacity. Insufficient long-term stability can also cause changes in the concentration of additives in the electrolyte, affecting their synergistic effect with other components and further reducing the cycle performance of the battery. For example, a decrease in the concentration of additives can weaken their protective effect on the electrode, making it difficult to effectively suppress the occurrence of side reactions.

[0012] 4. Too high reactivity leads to side reactions:

[0013] Some additives have high reactivity and are prone to unwanted side reactions with other components in the electrolyte. The new compounds generated by side reactions can have poor electrochemical properties, such as reducing the conductivity of the electrolyte, increasing the self-discharge rate of the battery, etc. An increase in the self-discharge rate will accelerate the loss of electrical energy during the resting process, reducing the efficiency of the battery. These side reactions also consume effective components in the electrolyte, reducing the performance of the electrolyte, accelerating the chemical reactions inside the battery, leading to increased heat generation, accelerated aging of electrode materials and electrolyte, and ultimately reducing the cycle life and performance stability of the battery.

[0014] 5. The quality of the coating layer affects the internal resistance and performance of the battery:

[0015] The quality of the coating layer formed by the additives on the electrode surface has a significant impact on the internal resistance of the battery. If the coating layer is uneven, loose, or has poor adhesion to the electrode material, the charge transfer and ion diffusion will be hindered during the charging and discharging process of the battery. An uneven coating layer will cause excessive local current density, accelerating the local loss of electrode materials; a loose coating layer is prone to electrolyte penetration into the electrode interior, triggering side reactions. These situations will increase the internal resistance of the battery, generating more heat during the charging and discharging process. The accumulation of heat further accelerates the chemical reactions inside the battery, reducing the charging and discharging efficiency and power performance, especially during high-rate charging and discharging, the battery performance decreases more obviously. In the long term, the quality problem of the coating layer will cause the battery capacity to decay rapidly and the cycle life to be shortened.

[0016] 6. Limited solubility and changes affect cycle performance:

[0017] Some additives have limited solubility in non-aqueous solvents, and this solubility problem is more pronounced in low-temperature environments. Low temperature will reduce the solubility of the additive, making it prone to precipitation. Precipitation will block the electrode channels, hinder the transport of lithium ions, and increase the internal resistance of the battery. This makes the polarization phenomenon more severe during the charging and discharging process of the battery, reducing the charging and discharging rate, especially in low-temperature environments, the discharge capacity and charging rate of the battery decrease significantly. When the composition of the electrolyte solvent changes, such as solvent evaporation, additive decomposition, etc., the solubility of the additive may also change, causing crystallization and precipitation, etc. This will destroy the uniformity of the electrolyte, affect ion conduction, and further affect the cycle performance of the battery, reducing the capacity retention rate and performance stability of the battery during the cycle process.

[0018] 7. Unwanted reactions with battery components affect the cycle:

[0019] Some additives can have adverse reactions with electrode materials, electrolyte salts or other additives in the battery. For example, chemical reactions with the positive electrode material can destroy the crystal structure of the positive electrode material, affect its electrochemical activity, and reduce the lithium storage capacity of the positive electrode material. Interactions with electrolyte salts can change the dissociation state of the salt, affect the conduction of lithium ions, and reduce the conductivity of the battery. Incompatibility with other additives can interfere with the normal functioning of the additives and prevent the expected improvement in battery performance. These adverse reactions can lead to a deterioration of the chemical environment inside the battery, accelerate the degradation of electrode materials and the decomposition of electrolytes, increase the internal resistance of the battery, reduce the charge and discharge efficiency and cycle life, and severely affect the cycle performance of the battery.

[0020] 8. Viscosity and volatility issues affect cycling:

[0021] Some additives have high viscosity, which increases the overall viscosity of the electrolyte. High-viscosity electrolytes hinder the rapid migration of ions, increasing the internal resistance of the battery and reducing the charge and discharge rate of the battery. During high-current charging and discharging, polarization is intensified, the battery generates a lot of heat, and the cycle life and safety of the battery are affected. High viscosity also makes the processing and filling process of the electrolyte difficult, which can lead to uneven distribution of the electrolyte in the battery, further affecting the performance consistency of the battery. Some additives have volatility, and if not properly sealed during battery use or production, solvent evaporation can change the composition of the electrolyte. Volatilization can change the concentration of the additive, affecting its improvement effect on battery performance; at the same time, the vapor of the volatilized solvent can be flammable, posing a safety hazard, and solvent evaporation can cause changes in the internal pressure of the battery, increasing the risk of battery bulging and leakage, indirectly affecting the cycle performance of the battery. SUMMARY

[0022] To solve the above problems, the present application provides an electrolyte additive, as well as an electrolyte and a lithium ion battery comprising the additive.

[0023] In order to achieve the above-mentioned purpose of the present application, the following technical solutions are adopted:

[0024] In a first aspect, the present application provides an electrolyte additive, the electrolyte additive comprising 2,4,6-(methoxysulfonyl)methyl-2,4,6-trimethylcyclotrisiloxane represented by Formula I:

[0025]

[0026] In some embodiments, the 2,4,6-(methoxysulfonyl)methyl-2,4,6-trimethylcyclotrisiloxane is prepared by the following method:

[0027] A nucleophilic substitution reaction is carried out between 2,4,6-triethyl-2,4,6-trimethylcyclotrisiloxane (15901-49-2) and methyl methanesulfonate (66-27-3) to produce 2,4,6-(methoxysulfonyl)methyl-2,4,6-trimethylcyclotrisiloxane.

[0028] Specifically, the following steps are included:

[0029] Raw material preparation:

[0030] 2,4,6-triethyl-2,4,6-trimethylcyclotrisiloxane: 100 g (about 0.35 moles, adjusted according to actual purity) of 2,4,6-triethyl-2,4,6-trimethylcyclotrisiloxane is prepared, with a purity of more than 95% to ensure smooth reaction and product quality.

[0031] Methyl methanesulfonate: as an alkylating agent, it is used to react with the ethyl group on 2,4,6-triethyl-2,4,6-trimethylcyclotrisiloxane. The amount of methyl methanesulfonate is usually in excess to ensure complete reaction. Generally, 150 g (about 1.2 moles) of methyl methanesulfonate can be used, with a purity requirement of more than 98%.

[0032] Selection and pretreatment of reaction container:

[0033] A dry four-necked flask equipped with stirring device, thermometer and reflux condenser is selected as the reaction container, and its volume can be selected according to the amount of raw materials, for example, a 500 ml four-necked flask is more appropriate. Before use, the four-necked flask is purged with nitrogen for 15-20 minutes to remove air and moisture in the bottle, preventing unnecessary reactions of raw materials and products with oxygen or moisture.

[0034] Raw material addition and mixing:

[0035] The prepared 2,4,6-triethyl-2,4,6-trimethylcyclotrisiloxane and methyl methanesulfonate are added to the four-necked flask in turn, and the stirring device is turned on under nitrogen protection, with the stirring speed controlled at 300-500 rpm to ensure that the raw materials are fully mixed and uniform.

[0036] Reaction condition control and reaction progress:

[0037] The temperature is slowly raised to the reaction temperature, which is set between 80-120 °C, preferably 100 °C. At this temperature, the reaction system is kept in a reflux state, and the reaction time lasts for 12-24 hours. During this process, the methyl group in methyl methanesulfonate undergoes a nucleophilic substitution reaction with the ethyl group on 2,4,6-triethyl-2,4,6-trimethylcyclotrisiloxane, gradually forming 2,4,6-(methoxysulfonyl)methyl-2,4,6-trimethylcyclotrisiloxane. The reaction temperature is closely monitored by a thermometer during the reaction to ensure that the temperature fluctuation range is within ±2 °C of the set temperature, to ensure the stability of the reaction and the selectivity of the product.

[0038] Reaction monitoring and progress determination:

[0039] The reaction progress is regularly monitored by thin layer chromatography (TLC) or gas chromatography (GC). Every 2-3 hours, a small amount of the reaction mixture is taken for analysis. When the chromatographic peak area of the raw material 2,4,6-triethyl-2,4,6-trimethylcyclotrisiloxane decreases to a certain extent (e.g. less than 5%), and the chromatographic peak area of the target product 2,4,6-(methoxysulfonyl)methyl-2,4,6-trimethylcyclotrisiloxane no longer increases significantly, it can be determined that the reaction is basically complete.

[0040] Cooling and extraction:

[0041] After the reaction is completed, the heating is stopped, and the reaction system is naturally cooled to room temperature. Then the reaction mixture is transferred to a separatory funnel, and an appropriate amount of organic solvent (such as ethyl acetate) is added for extraction. The amount of ethyl acetate can be 1-2 times the volume of the reaction mixture. The separatory funnel is shaken thoroughly to transfer the product to the organic phase, and after the layers are separated, the organic phase is collected.

[0042] Washing and drying:

[0043] The organic phase is washed with deionized water 2-3 times, with each time using 0.5-1 times the volume of the organic phase to remove unreacted methyl methanesulfonate and other water-soluble impurities. Then the organic phase is dried through a column of anhydrous sodium sulfate to remove the water in it, obtaining a dry organic solution.

[0044] Separation and purification:

[0045] The dry organic solution is subjected to rotary evaporation to remove the organic solvent, obtaining the crude product. The crude product is further purified by vacuum distillation or column chromatography. In vacuum distillation, the pressure is controlled at 1-5 mm of mercury, and the fraction with a specific boiling point range (e.g. 150-160 °C / 1-5 mm of mercury) is collected, which is the purified 2,4,6-(methoxysulfonyl)methyl-2,4,6-trimethylcyclotrisiloxane, with a purity of more than 98%.

[0046] In a second aspect, the present invention provides an electrolyte comprising the above-mentioned electrolyte additives.

[0047] The electrolyte comprises a lithium salt, an anhydrous organic solvent, and electrolyte additives, wherein the electrolyte additives include 2,4,6-(methoxysulfonyl)methyl-2,4,6-trimethylcyclotrisiloxane as shown in Formula I and other additives.

[0048] Preferably, the mass percentage of 2,4,6-(methoxysulfonyl)methyl-2,4,6-trimethylcyclotrisiloxane in the electrolyte is 0.1%-10%, more preferably 0.1%-5%, and even more preferably 0.1%-1%.

[0049] Preferably, the other additives are selected from at least one of vinylene carbonate (VC), fluoroethylene carbonate (FEC), vinyl sulfate (DTD), vinyl sulfite (ES), adiponitrile (SN), succinic anionyl (ADN), 1,3,6-hexanetrionitrile, lithium bis(oxalato)borate (LiBOB), lithium difluorooxalato)borate (LiDFOB), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), tri(trimethylsilane)borate (TMSB), tri(trimethylsilane)phosphate (TMSP), sulfolane (SL), methyl sulfolane, 1,3-propanesulfonate lactone (PS), 1,4-butanesulfonate lactone, methanedisulfonate methylene (MMDS), ethylene disulfonate methylene, lithium difluorophosphate (LiPO2F2), ethylene ethylene carbonate (VEC), cyclohexylbenzene, and 1,3-propenylsulfonate lactone (PST).

[0050] Preferably, the mass percentage of other additives in the electrolyte is 0.01-20%.

[0051] Preferably, the lithium salt is selected from at least one of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide.

[0052] Preferably, the concentration of lithium salt in the electrolyte is 0.8M-1.4M.

[0053] Preferably, the anhydrous organic solvent is selected from at least one of carbonates, halocarbonates, carboxylic esters, propionates, fluoroethers, aromatic hydrocarbons, or haloaromatic hydrocarbons.

[0054] Preferably, the carbonate is at least one of ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), or ethyl methyl carbonate (EMC).

[0055] Preferably, the halogenated carbonate is at least one selected from fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), difluoropropylene carbonate, ethyl trifluorocarbonate, trifluoroethyl methyl carbonate, trifluoromethyl ethylene carbonate, 4-trifluoromethyl ethylene carbonate, chloroethylene carbonate, di(2,2,2-trifluoroethyl) carbonate, methyl trifluoropropionate, ethyl 3,3,3-trifluoroethyl carbonate, methyl 2-(trifluoromethyl)benzoate, ethyl 4,4,4-trifluorobutyrate, and 1,1,1,3,3,3-hexafluoroisopropyl acrylate.

[0056] Preferably, the carboxylic acid ester is at least one selected from ethyl propionate, ethyl acetate, methyl acetate, propyl butyrate, propyl acetate, isopropyl acetate, butyl propionate, isopropyl propionate, or ethyl butyrate.

[0057] Preferably, the propionate is at least one of methyl propionate (EM), ethyl propionate (EP), or propyl propionate (PP).

[0058] Preferably, the electrolyte contains 60%-80% by mass of anhydrous organic solvent.

[0059] Thirdly, the present invention provides a lithium-ion battery comprising the electrolyte described above.

[0060] Technical effects:

[0061] The additive molecule of this invention contains functional groups such as a siloxane ring structure, methyl groups, and methoxysulfonyl groups. The siloxane ring structure has a certain degree of stability, the methyl group can affect the spatial structure and solubility of the molecule, and the methoxysulfonyl group has unique chemical activity. The synergistic effect of these functional groups is expected to provide a new approach to improve battery performance.

[0062] The core structural feature of the additive of this invention is the unique combination of (methoxysulfonyl)methyl substituents at positions 2, 4, and 6 with a trimethylcyclotrisiloxane core. Compared with other compounds, the presence and connection position of the methoxysulfonyl group are highly specific, differing from existing compounds in their overall molecular structure, relative positional relationship with other functional groups, and the nature of the connecting bonds. In this invention, the methoxysulfonyl group is tightly linked to the siloxane ring and methyl group through specific chemical bonds, forming a unique electron cloud distribution and spatial conformation. This structural design lays the foundation for its performance enhancement.

[0063] Improved thermal stability:

[0064] The silicon-oxygen ring structure in the molecule has high bond energy, which can resist the energy impact of temperature rise under high temperature environment or high charge and discharge rate, and is not prone to breakage or rearrangement. Compared with some compounds with poor thermal stability, the silicon-oxygen ring structure can effectively maintain the integrity of the molecule and reduce the occurrence of thermal decomposition reactions.

[0065] The stability of the silicon oxide ring structure helps maintain the chemical composition of the electrolyte, preventing the formation of poorly conductive substances due to additive decomposition, thereby maintaining the ionic conductivity of the electrolyte and reducing the risk of increased battery internal resistance due to thermal effects. For lithium-ion batteries operating under high-temperature conditions, such as electric vehicle batteries operating in hot climates or generating significant heat during fast charging, this can significantly improve battery thermal stability, reduce the rate of capacity retention loss, and extend cycle life.

[0066] Improved chemical stability:

[0067] The methoxysulfonyl functional group possesses a degree of chemical inertness, which reduces unnecessary reactions with lithium salts, solvent molecules, and active substances generated during battery charging and discharging in the complex operating environment of a battery. Compared to some more reactive functional groups, it reduces the likelihood of the additive's own structure being damaged, thus maintaining the additive's effectiveness.

[0068] This chemical inertness helps maintain the original functions of additives in the electrolyte, such as stably forming a protective film on the electrode surface or regulating electrolyte performance, ensuring the stability of lithium-ion transport channels, reducing the problem of decreased ionic conductivity caused by chemical reactions, thereby improving the charging and discharging efficiency of the battery, maintaining the chemical stability of the battery during long-term use, slowing down the corrosion of electrode materials and the decomposition rate of electrolyte, which is beneficial to extending the cycle life of the battery and improving the capacity retention rate.

[0069] Enhanced long-term stability:

[0070] There is a synergistic effect among the siloxane ring structure, functional groups such as methyl and methoxysulfonyl groups. The siloxane ring structure provides basic molecular skeleton stability, the methyl group helps to fill the molecular space and reduce the influence of external factors on the molecular structure, and the methoxysulfonyl group plays a role in chemical stability.

[0071] During long-term cycling, this synergistic effect can stabilize additive molecules and reduce the performance degradation caused by changes in molecular structure. For example, the protective film formed by the additive can remain intact over a long period of time, effectively preventing the electrode surface from being re-exposed to the electrolyte, avoiding adverse reactions between the electrode material and the electrolyte, thereby reducing the rate of increase in battery internal resistance, reducing the severity of polarization, maintaining stable battery capacity, and significantly enhancing the long-term stability of the battery.

[0072] Inhibition of side reactions:

[0073] The overall structural design of the additive molecules ensures that its reactivity is within a suitable range. It avoids being too inactive to form an effective protective film or perform other beneficial functions on the electrode surface, while also avoiding excessively high reactivity that could lead to unnecessary side reactions with other components in the electrolyte.

[0074] Compared to some additives that easily trigger side reactions, 2,4,6-(methoxysulfonyl)methyl-2,4,6-trimethylcyclotrisiloxane avoids adverse reactions with the electrolyte lithium salt, thus maintaining the dissociation equilibrium of the lithium salt and ensuring normal lithium ion concentration and transport. Simultaneously, it reduces the formation of side reaction products, avoiding their negative impacts on electrolyte conductivity and self-discharge rate, thereby improving battery cycle life and performance stability.

[0075] Optimization of overlay quality:

[0076] The presence of functional groups such as methyl and methoxysulfonyl groups may affect the process and quality of SEI coating formation on the electrode surface. They can promote a more uniform and dense coating formation and enhance the adhesion between the coating and the electrode material.

[0077] A uniform and dense capping layer can effectively reduce the obstruction of charge transfer and ion diffusion, and lower the risk of excessive local current density and side reactions caused by electrolyte penetration. Compared with poor capping layer quality, an optimized capping layer can reduce battery internal resistance, reduce heat generation during charging and discharging, and improve charging and discharging efficiency and power performance, especially at high charging and discharging rates, which helps to extend battery cycle life and maintain a high capacity retention rate.

[0078] Improved solubility:

[0079] Functional groups such as methyl groups can improve the solubility of additives in non-aqueous solvents. At low temperatures, although the overall solubility may still be affected to some extent, the likelihood of precipitation is reduced compared to additives with poor solubility.

[0080] Good solubility helps additives disperse uniformly in the electrolyte, ensuring the uniformity of their functions, such as forming a protective film on the electrode surface. When the composition of the electrolyte solvent changes, such as solvent evaporation or additive decomposition, relatively stable solubility can also reduce the occurrence of problems such as crystallization, maintain the uniformity of the electrolyte, and facilitate lithium-ion transport. This reduces the risk of increased battery internal resistance due to solubility issues, improves battery cycle performance under different temperature conditions, and reduces fluctuations in capacity retention.

[0081] Improved compatibility with battery components:

[0082] The additive's structural design ensures good compatibility with electrode materials, electrolyte salts, and other additives in the battery. Its molecular structure does not react adversely with the cathode material, thus avoiding damage to the cathode material's crystal structure and maintaining its electrochemical activity and lithium storage capacity.

[0083] It maintains good interaction with electrolyte salts, does not interfere with the dissociation state of the salts, and ensures normal lithium-ion conduction. When coexisting with other additives in the electrolyte, it works synergistically without mutual interference or performance degradation, jointly achieving the goal of improving battery performance, reducing the deterioration of the internal chemical environment of the battery due to compatibility issues, and contributing to improved battery cycle life and overall performance.

[0084] Improvements in viscosity and volatility:

[0085] The molecular structure of the additive prevents it from excessively increasing the viscosity of the electrolyte. Compared to some high-viscosity additives, it maintains a relatively suitable ion migration rate in the electrolyte, reducing the problems of increased battery internal resistance and reduced charge / discharge rates caused by increased viscosity.

[0086] In terms of volatility, the functional groups in the molecular structure give the additives relatively low volatility. During battery use or production, even under certain temperature and pressure conditions, it can reduce problems such as changes in additive concentration, safety hazards, and changes in internal battery pressure caused by solvent evaporation, maintain the relative stability of the electrolyte composition, and indirectly improve the battery's cycle performance and safety.

[0087] The present invention has been described in detail above; however, the above embodiments are merely illustrative in nature and are not intended to limit the invention. Furthermore, this document is not limited to the foregoing prior art or the invention itself, or to any theory described in the following embodiments. Attached Figure Description

[0088] Figure 1 To prepare 2,4,6-(methoxysulfonyl)methyl-2,4,6-trimethylcyclotrisiloxane 1 HNMR spectrum. Detailed Implementation

[0089] The present invention will be further described below with reference to the embodiments. It should be noted that the following embodiments are provided for illustrative purposes only and do not constitute a limitation on the scope of protection of the present invention.

[0090] Unless otherwise specified, the raw materials, reagents, and methods used in the embodiments are all conventional raw materials, reagents, and methods in the art.

[0091] Preparation Example: Synthesis of 2,4,6-(methoxysulfonyl)methyl-2,4,6-trimethylcyclotrisiloxane

[0092] Add 100g (approximately 0.35 mol) of 2,4,6-triethyl-2,4,6-trimethylcyclotrisiloxane (95% purity) and 150g (approximately 1.2 mol) of methyl methanesulfonate (98% purity) to a 500 mL dry four-necked flask equipped with a stirrer, thermometer, and reflux condenser (purge the flask with nitrogen for 15-20 minutes before use). Under nitrogen protection, turn on the stirrer and stir at 400 rpm to ensure thorough mixing of the raw materials. Slowly raise the temperature to 100°C and maintain reflux for 24 hours. The reaction process was monitored regularly. After the reaction was complete, the reaction mixture was extracted with ethyl acetate, and the organic phase was collected. The organic phase was washed 2-3 times with deionized water, and then dried using an anhydrous sodium sulfate drying column to obtain a dry organic solution. This solution was then subjected to rotary evaporation to obtain a crude product. The crude product was then subjected to vacuum distillation at a pressure controlled at 3 mmHg. The fraction collected at 155 °C / 3 mmHg was the purified 2,4,6-(methoxysulfonyl)methyl-2,4,6-trimethylcyclotrisiloxane with a purity of 98%. 1 H NMR spectrum as follows Figure 1 As shown, the structure is as shown in Equation I.

[0093]

[0094] A lithium-ion battery assembled with an electrolyte containing 2,4,6-(methoxysulfonyl)methyl-2,4,6-trimethylcyclotrisiloxane was selected as an example. A lithium-ion battery assembled with a conventional electrolyte that does not contain 2,4,6-(methoxysulfonyl)methyl-2,4,6-trimethylcyclotrisiloxane and a lithium-ion battery assembled with an electrolyte containing other structural additives were selected as comparative examples.

[0095] The specific steps for preparing the electrolyte in the glove box (H2O < 5 ppm) are as follows:

[0096] (1) Under the protection of nitrogen or inert gas, the anhydrous organic solvent molecular sieve is dehydrated to obtain anhydrous organic solvent;

[0097] (2) Add an appropriate amount of lithium salt to an anhydrous organic solvent, stir and cool to obtain a mixture;

[0098] (3) Add an appropriate amount of additive to the mixture to obtain 2000g of electrolyte, which is then placed in a fluorinated bottle.

[0099] A lithium-ion battery is assembled using an electrolyte, wherein the positive electrode material of the lithium-ion battery is a ternary material (LiNi). 0.6Co 0.2 Mn 0.2 O2), the negative electrode material is artificial graphite, the designed capacity is 60Ah, and the liquid injection volume is 2.3±0.5g / Ah.

[0100] Example 1:

[0101] The non-aqueous organic solvent used in the electrolyte is EC:EMC (v:v) = 30:70; lithium salts: 0.8M lithium hexafluorophosphate (LiPF6) and 0.4M lithium bisfluorosulfonylimide (LiFSI). Additives: 1 wt.% VC, 0.5 wt.% FEC, 1 wt.% DTD, 0.5 wt.% LiDFOB, 0.5 wt.% TMSP, 1 wt.% PS, 0.5 wt.% LiPO2F2, with compound I added at 8 wt.%.

[0102] Example 2:

[0103] The non-aqueous organic solvent used in the electrolyte is EC:EMC (v:v) = 30:70; lithium salts: 0.8M lithium hexafluorophosphate (LiPF6) and 0.4M lithium bisfluorosulfonylimide (LiFSI). Additives: 1 wt.% VC, 0.5 wt.% FEC, 1 wt.% DTD, 0.5 wt.% LiDFOB, 0.5 wt.% TMSP, 1 wt.% PS, 0.5 wt.% LiPO2F2, with compound I added at 4 wt.%.

[0104] Example 3:

[0105] The non-aqueous organic solvent used in the electrolyte is EC:EMC (v:v) = 30:70; lithium salts: 0.8M lithium hexafluorophosphate (LiPF6) and 0.4M lithium bisfluorosulfonylimide (LiFSI). Additives: 1 wt.% VC, 0.5 wt.% FEC, 1 wt.% DTD, 0.5 wt.% LiDFOB, 0.5 wt.% TMSP, 1 wt.% PS, 0.5 wt.% LiPO2F2, with compound I added at 0.5 wt.%.

[0106] Comparative Example 1:

[0107] The non-aqueous organic solvent used in the electrolyte is: EC:EMC (v:v) = 30:70; lithium salt: 1.2M lithium hexafluorophosphate (LiPF6).

[0108] Comparative Example 2:

[0109] The non-aqueous organic solvent used in the electrolyte is: EC:EMC (v:v) = 30:70; lithium salts: 0.8M lithium hexafluorophosphate (LiPF6) and 0.4M lithium bisfluorosulfonylimide (LiFSI).

[0110] Comparative Example 3:

[0111] The non-aqueous organic solvent used in the electrolyte is EC:EMC (v:v) = 30:70; lithium salts: 0.8M lithium hexafluorophosphate (LiPF6) and 0.4M lithium bisfluorosulfonylimide (LiFSI). Additives: 1 wt.% VC, 0.5 wt.% FEC, 1 wt.% DTD, 0.5 wt.% LiDFOB, 0.5 wt.% TMSP, 1 wt.% PS, and 0.5 wt.% LiPO2F2.

[0112] Comparative Example 4:

[0113] The only difference between this comparative example and Example 3 is that the compound of Formula I is replaced with the compound shown in Formula II (hexamethylcyclotrisiloxane, CAS Registry No. 541-05-9).

[0114]

[0115] Comparative Example 5:

[0116] The only difference between this comparative example and Example 3 is that the compound of Formula I is replaced with the compound shown in Formula III (1,3,5-tris(2,2,2-acetonitrile)-1,3,5-trimethylcyclotrisiloxane, patent CN111883831A).

[0117]

[0118] Comparative Example 6:

[0119] The only difference between this comparative example and Example 3 is that the compound of Formula I is replaced with the compound of Formula IV, 1,3,5-tris(3,3,3-propionitrile)-1,3,5-trimethylcyclotrisiloxane (patent CN111883831A).

[0120]

[0121] The assembled lithium-ion batteries in the comparative examples and embodiments were subjected to 1C charge-discharge cycles at 25°C to test capacity retention within a voltage range of 2.75–4.2V. The results are shown in Table 1.

[0122] Table 1. Room Temperature Cycling Performance Test

[0123] 1000 turns 2000 turns 3000 turns 4000 turns 5000 turns Comparative Example 1 29.3％ 24.0％ 14.5％ 0.0％ 0.0％ Comparative Example 2 61.1％ 56.4％ 46.6％ 31.5％ 11.3％ Comparative Example 3 85.5％ 80.8％ 70.5％ 55.0％ 35.0％ Comparative Example 4 83.3％ 78.3％ 68.5％ 53.3％ 33.1％ Comparative Example 5 90.0％ 85.3％ 75.9％ 60.2％ 40.2％ Comparative Example 6 88.6％ 83.1％ 73.9％ 58.3％ 38.8％ Example 1 98.6％ 96.8％ 94.4％ 92.1％ 90.9％ Example 2 99.6％ 97.5％ 95.7％ 93.5％ 91.3％ Example 3 100.0％ 98.8％ 96.2％ 94.7％ 92.0％

[0124] The assembled lithium-ion batteries in the comparative examples and embodiments were subjected to 1C charge-1C discharge cycles at 45°C to test capacity retention within a voltage range of 2.75–4.2V. The results are shown in Table 2.

[0125] Table 2 High-Temperature Cyclic Performance Test

[0126] 1000 turns 2000 turns 3000 turns 4000 turns Comparative Example 1 29.6％ 19.9％ 0.0％ 0.0％ Comparative Example 2 60.0％ 50.6％ 30.0％ 0.3％ Comparative Example 3 86.9％ 76.2％ 56.2％ 26.9％ Comparative Example 4 84.7％ 74.1％ 54.8％ 24.0％ Comparative Example 5 91.2％ 81.3％ 61.8％ 31.9％ Comparative Example 6 89.3％ 79.0％ 53.8％ 24.9％ Example 1 95.0％ 92.1％ 89.1％ 87.9％ Example 2 96.2％ 93.4％ 90.0％ 88.3％ Example 3 98.4％ 95.1％ 92.5％ 90.1％

[0127] The results show that adding 2,4,6-(methoxysulfonyl)methyl-2,4,6-trimethylcyclotrisiloxane additive to the electrolyte can effectively improve the cycle performance of lithium-ion batteries and has good application prospects.

[0128] The above embodiments are merely illustrative of the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein, without departing from the spirit and substance defined by the claims of the present invention; and such modifications or substitutions are still within the scope defined by the claims of the present invention.

Claims

1. An electrolyte additive, characterized in that, The electrolyte additive comprises 2,4,6-(methoxysulfonyl)methyl-2,4,6-trimethylcyclotrisiloxane as shown in Formula I: Formula I; The mass percentage of 2,4,6-(methoxysulfonyl)methyl-2,4,6-trimethylcyclotrisiloxane in the electrolyte is 0.1%-10%.

2. The electrolyte additive according to claim 1, characterized in that, The 2,4,6-(methoxysulfonyl)methyl-2,4,6-trimethylcyclotrisiloxane was prepared by the following method: Nucleophilic substitution reaction of 2,4,6-triethyl-2,4,6-trimethylcyclotrisiloxane and methyl methanesulfonate yields 2,4,6-(methoxysulfonyl)methyl-2,4,6-trimethylcyclotrisiloxane.

3. The electrolyte additive according to claim 2, characterized in that, The molar ratio of 2,4,6-triethyl-2,4,6-trimethylcyclotrisiloxane to methyl methanesulfonate is 0.35:1.

2.

4. The electrolyte additive according to claim 2, characterized in that, The reaction temperature is 80-120℃, and the reaction time is 12-24h.

5. An electrolyte, characterized in that, The electrolyte comprises the electrolyte additive as described in any one of claims 1-4, a lithium salt, and an anhydrous organic solvent; The electrolyte additives include 2,4,6-(methoxysulfonyl)methyl-2,4,6-trimethylcyclotrisiloxane as shown in Formula I and other additives.

6. The electrolyte according to claim 5, characterized in that, The other additives are selected from at least one of vinylene carbonate (VC), fluoroethylene carbonate (FEC), vinyl sulfate (DTD), vinyl sulfite (ES), adiponitrile (SN), succinic anionyl (ADN), 1,3,6-hexanetrionitrile, lithium bis(oxalato)borate (LiBOB), lithium difluorooxalato)borate (LiDFOB), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), tri(trimethylsilane)borate (TMSB), tri(trimethylsilane)phosphate (TMSP), sulfolane (SL), methyl sulfolane, 1,3-propanesulfonate lactone (PS), 1,4-butanesulfonate lactone, methanedisulfonate methylene (MMDS), ethylene disulfonate methylene, lithium difluorophosphate (LiPO2F2), ethylene ethylene carbonate (VEC), cyclohexylbenzene, and 1,3-propenylsulfonate lactone (PST).

7. The electrolyte according to claim 5, characterized in that, The lithium salt is selected from at least one of lithium hexafluorophosphate and lithium difluorosulfonylimide; The concentration of lithium salt in the electrolyte is 0.8M-1.4M.

8. The electrolyte according to claim 5, characterized in that, The anhydrous organic solvent is selected from at least one of carbonates, halocarbonates, carboxylic esters, propionates, fluoroethers, aromatic hydrocarbons, or haloaromatic hydrocarbons. The electrolyte contains 60%-80% by mass of anhydrous organic solvent.

9. A lithium-ion battery, characterized in that, The lithium-ion battery includes the electrolyte as described in any one of claims 5-8.

Images