Electrolyte additive, electrolyte and lithium ion battery

Abstract

The invention 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-trimethyl cyclotrisiloxane as shown in a formula I which is described in the specification. According to the additive with the structure, through the synergistic effect of functional groups such as a silicon-oxygen ring structure, methyl and methoxysulfonyl, the defects of thermal stability, chemical stability, long-term stability, side reaction, covering layer quality, solubility, compatibility, viscosity and volatility of other additives are overcome, and the cycle performance of the lithium ion battery can be effectively improved.

Description

Technical Field

[0001] The invention relates to the technical field of lithium ion battery electrolyte, and in particular to an electrolyte additive, an electrolyte and a lithium ion battery. Background Art

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

[0003] However, the current commercial lithium-ion batteries still have certain limitations in terms of cycle performance. During the battery's charge and discharge cycle, a variety of factors will cause the battery performance to gradually decline. For example, the structure and performance of the electrode material will change, the positive electrode material may experience structural collapse, loss of active substances and other problems, and the negative electrode material may face volume expansion, SEI membrane rupture and other situations. At the same time, the electrolyte will also decompose during the cycle process and have side reactions with the electrode material, which will lead to an increase in the battery's internal resistance and capacity decay, thereby shortening the battery's cycle life.

[0004] As an important component of lithium-ion batteries, electrolyte has a vital impact on battery performance. Among them, the use of electrolyte additives is an effective means to improve battery performance. 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, and adjust the ionic conductivity and viscosity of the electrolyte, thereby improving 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 the lithium salt in the electrolyte, improve the dissociation state of the lithium salt, and improve 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 the research and analysis of electrolyte additives developed by existing technologies, it is found that these additives still have the following defects:

[0006] 1. Poor thermal stability:

[0007] In high temperature environments or when charging and discharging at high rates, the internal temperature of lithium-ion batteries rises, and the chemical bonds of many compounds (including electrolyte additives) are difficult to withstand high temperature stress. For example, the chemical bonds in some additives are easily broken at high temperatures, resulting in the destruction of the molecular structure and thermal decomposition reactions. The thermal decomposition products will change the chemical composition of the electrolyte, and may generate some substances with poor conductivity, which will reduce the ionic conductivity of the electrolyte. At the same time, the decomposition products may also react with the electrode materials to form undesirable deposits on the electrode surface, increasing the internal resistance of the battery. The increase in the internal resistance of the battery will lead to increased energy loss during charging and discharging, and increased battery heating. This further accelerates the structural destruction of the electrode material and the decomposition of the electrolyte, forming a vicious cycle, which ultimately reduces the battery capacity retention rate and significantly shortens the cycle life. For example, when electric vehicles are driving at high speed for a long time or charging in a hot environment, the internal temperature of the battery rises, and additives with poor thermal stability will accelerate the deterioration of battery performance.

[0008] 2. Low chemical stability:

[0009] The working environment of lithium-ion batteries is complex, and the additives in the electrolyte may react with a variety of substances. Specific functional groups in the molecular structure of some additives have high reactivity. During the operation of the battery, they are prone to chemical reactions with lithium salts, solvent molecules, trace impurities (such as water, acid, alkali, etc.) in the electrolyte, or active substances produced during the battery charging and discharging process. These reactions will change the structure and properties of the additives themselves, causing them to lose their original functions, such as being unable to effectively form a stable protective film or adjust the performance of the electrolyte. At the same time, the reaction products may interfere with the transmission of lithium ions, reduce the ionic conductivity of the electrolyte, and affect the charging and discharging efficiency of the battery. In the long run, the continuous reaction of additives with low chemical stability will lead to an unstable chemical environment inside the battery, accelerate the corrosion of electrode materials and the decomposition of the 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 charge and discharge cycles increases and the usage time increases, 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 cycles. The destruction of the protective film will re-expose the electrode surface to the electrolyte, triggering adverse 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 the internal resistance of the battery, an increase in polarization during the charge and discharge process, and a gradual decay of the battery capacity. Insufficient long-term stability may also cause changes in the concentration of additives in the electrolyte, affecting its synergistic effect with other components and further reducing the battery's cycle performance. For example, a reduction in the concentration of additives may weaken their protective effect on the electrode and fail to effectively inhibit the occurrence of side reactions.

[0012] 4. Excessive reaction activity leads to side reactions:

[0013] Some additives have high reactivity and are prone to unnecessary side reactions with other components in the electrolyte. New compounds generated by side reactions may have poor electrochemical properties, such as reducing the conductivity of the electrolyte and increasing the self-discharge rate of the battery. The increase in the self-discharge rate will accelerate the loss of battery power during the static process, reducing the battery's efficiency. These side reactions will also consume the effective ingredients in the electrolyte, reduce the performance of the electrolyte, accelerate the chemical reactions inside the battery, increase the heat generation of the battery, accelerate the aging of the electrode materials and electrolyte, and ultimately reduce the cycle life and performance stability of the battery.

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

[0015] The quality of the coating formed by additives on the electrode surface has an important influence on the internal resistance of the battery. If the coating is uneven, loose, or has weak adhesion to the electrode material, charge transfer and ion diffusion will be hindered during the battery charging and discharging process. Uneven coatings can lead to excessive local current density, accelerating local loss of electrode materials; loose coatings can easily allow electrolyte to penetrate into the interior of the electrode, triggering side reactions. These conditions will increase the internal resistance of the battery and cause the battery to generate more heat during charging and discharging. The accumulation of heat further accelerates the chemical reactions inside the battery, reducing the charging and discharging efficiency and power performance, especially at high-rate charging and discharging, where the battery performance declines more significantly. In the long run, coating quality issues can lead to faster battery capacity decay and shorter cycle life.

[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 prominent in low-temperature environments. Low temperatures can reduce the solubility of additives, making them more susceptible to precipitation. Precipitation can clog electrode pores, hinder the transmission of lithium ions, and increase the internal resistance of the battery. This intensifies the polarization of the battery during charging and discharging, reduces the charging and discharging rate, and significantly reduces the discharge capacity and charging rate of the battery in low-temperature environments. When the composition of the electrolyte solvent changes, such as solvent volatilization and additive decomposition, the solubility of the additive may also change, resulting in problems such as crystal precipitation. This can destroy the uniformity of the electrolyte, affect ion conduction, and further affect the cycle performance of the battery, causing the battery to have a lower capacity retention rate during the cycle and unstable performance.

[0018] 7. Adverse reactions with battery components affect circulation:

[0019] Some additives may react adversely with electrode materials, electrolyte salts or other additives in the battery. For example, chemical reactions with positive electrode materials may 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 may change the dissociation state of the salt, affect the conduction of lithium ions, and reduce the conductivity of the battery. When incompatible with other additives, they will interfere with the normal functioning of the additives and fail to achieve the expected battery performance improvement effect. These adverse reactions will cause the internal chemical environment of the battery to deteriorate, accelerate the loss of electrode materials and the decomposition of the electrolyte, increase the internal resistance of the battery, reduce the charge and discharge efficiency and cycle life, and seriously affect the cycle performance of the battery.

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

[0021] Some additives have high viscosity, which will increase the overall viscosity of the electrolyte. High-viscosity electrolytes hinder the rapid migration of ions, increase the internal resistance of the battery, and reduce the charge and discharge rate of the battery. When charging and discharging at high currents, polarization is aggravated, the battery heats up severely, and the cycle life and safety of the battery are affected. High viscosity also brings difficulties to the processing and infusion of the electrolyte, which may cause uneven distribution of the electrolyte inside the battery, further affecting the performance consistency of the battery. Some additives are volatile. During the use or production of the battery, if the sealing is not done properly, solvent volatilization will cause changes in the composition of the electrolyte. Volatilization may change the concentration of the additive, affecting its effect on improving battery performance; at the same time, the volatilized solvent vapor may have a certain degree of flammability, posing a safety hazard, and solvent volatilization will cause changes in the internal pressure of the battery, increasing the risk of battery bulging and leakage, and indirectly affecting the cycle performance of the battery. Summary of the invention

[0022] In order to solve the above problems, the present invention provides an electrolyte additive, and an electrolyte and a lithium ion battery comprising the additive.

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

[0024] In a first aspect, the present invention provides an electrolyte additive, wherein the electrolyte additive comprises 2,4,6-(methoxysulfonyl)methyl-2,4,6-trimethylcyclotrisiloxane as shown in Formula I:

[0025]

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

[0027] 2,4,6-Triethyl-2,4,6-trimethylcyclotrisiloxane (15901-49-2) and methyl methanesulfonate (66-27-3) undergo nucleophilic substitution reaction to generate 2,4,6-(methoxysulfonyl)methyl-2,4,6-trimethylcyclotrisiloxane.

[0028] Specifically, the steps include:

[0029] Raw materials preparation:

[0030] 2,4,6-Triethyl-2,4,6-trimethylcyclotrisiloxane: prepare 100 g (about 0.35 moles, adjusted according to the actual purity) of 2,4,6-triethyl-2,4,6-trimethylcyclotrisiloxane, the purity of which should reach more than 95% to ensure the smooth progress of the reaction and the quality of the product.

[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 excessive to ensure the complete reaction. Generally, 150g (about 1.2 moles) of methyl methanesulfonate can be used, and its purity is required to be above 98%.

[0032] Reaction vessel selection and pretreatment:

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

[0034] Raw material addition and mixing:

[0035] The prepared 2,4,6-triethyl-2,4,6-trimethylcyclotrisiloxane and methyl methanesulfonate were added into a four-necked flask in sequence. Under nitrogen protection, the stirring device was turned on and the stirring speed was controlled at 300-500 rpm to ensure that the raw materials were fully mixed.

[0036] Reaction condition control and reaction progress:

[0037] Slowly raise the temperature to the reaction temperature, the reaction temperature 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 to gradually generate 2,4,6-(methoxysulfonyl)methyl-2,4,6-trimethylcyclotrisiloxane. During the reaction, the reaction temperature is closely monitored by a thermometer 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 process judgment:

[0039] The reaction progress is monitored regularly by thin layer chromatography (TLC) or gas chromatography (GC). A small amount of the reaction mixture is taken for analysis every 2-3 hours. 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 judged that the reaction is basically completed.

[0040] Cooling and extraction:

[0041] After the reaction is completed, stop heating and let the reaction system cool naturally to room temperature. Then transfer the reaction mixture to a separatory funnel and add an appropriate amount of organic solvent (such as ethyl acetate) for extraction. The amount of ethyl acetate can be 1-2 times the volume of the reaction mixture. Fully shake the separatory funnel to transfer the product to the organic phase. After standing and stratifying, collect the organic phase.

[0042] Washing and drying:

[0043] The organic phase is washed with deionized water for 2-3 times, with the amount of water used each time being 0.5-1 times the volume of the organic phase, to remove unreacted methyl methanesulfonate and other water-soluble impurities. The organic phase is then dried through an anhydrous sodium sulfate drying column to remove the water therein and obtain a dry organic solution.

[0044] Separation and purification:

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

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

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

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

[0049] Preferably, the other additives are selected from vinylene carbonate (VC), fluoroethylene carbonate (FEC), vinyl sulfate (DTD), vinyl sulfite (ES), adiponitrile (SN), succinonitrile (ADN), 1,3,6-hexanetrinitrile, lithium bis(oxalatoborate) (LiBOB), lithium difluorooxalatoborate (LiDFOB), lithium bis(trifluoromethanesulfonyl imide) (LiTFSI), tris(trimethylsilyl) borate (TMSB), tris(trimethylsilyl) phosphate (TMSP), sulfolane (SL), methyl sulfolane, 1,3-propane sultone (PS), 1,4-butane sultone, methylene disulfonate (MMDS), ethylene disulfonate, lithium difluorophosphate (LiPO 2 F 2 ), vinyl ethylene carbonate (VEC), cyclohexylbenzene, and 1,3-propene sultone (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, halogenated carbonates, carboxylates, propionates, fluoroethers, aromatic hydrocarbons or halogenated aromatic 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 of fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), difluoropropylene carbonate, trifluoroethyl acetate, trifluoroethyl methyl carbonate, trifluoromethylethylene carbonate, 4-trifluoromethylethylene carbonate, chloroethylene carbonate, di(2,2,2-trifluoroethyl) carbonate, methyl trifluoropropionate, 3,3,3-trifluoroethyl acetate, 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 of ethyl propionate, ethyl acetate, methyl acetate, propyl butyrate, propyl acetate, isopropyl acetate, butyl propionate, isopropyl propionate or ethyl butyrate.

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

[0058] Preferably, the mass percentage of the anhydrous organic solvent in the electrolyte is 60%-80%.

[0059] In a third aspect, the present invention provides a lithium-ion battery comprising the above-mentioned electrolyte.

[0060] Technical effect:

[0061] The additive molecules of the present invention contain functional groups such as silicon-oxygen ring structure, methyl group, methoxysulfonyl group, etc. The silicon-oxygen ring structure has a certain 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 way to improve battery performance.

[0062] The core structural feature of the additive of the present invention is the combination of the unique (methoxysulfonyl) methyl substituents at the 2, 4, and 6 positions and the trimethylcyclotrisiloxane core. Compared with other compounds, the existence mode and connection position of the methoxysulfonyl group are highly specific, and the layout in the overall molecular structure, the relative position relationship with other functional groups, and the nature of the connecting bond are different from the existing compounds. In the present invention, the methoxysulfonyl group is closely connected to the siloxane ring and the methyl group through a specific chemical bond, forming a unique electron cloud distribution and spatial conformation. This structural design lays the foundation for its performance improvement.

[0063] Improved thermal stability:

[0064] The silicon-oxygen ring structure in the molecule has a high bond energy. It can resist the energy impact caused by the temperature rise in high temperature environment or high rate charge and discharge, and is not easy to break or rearrange. 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-oxygen ring structure helps maintain the chemical composition of the electrolyte, prevents the production of poorly conductive substances due to the decomposition of additives, thereby maintaining the ionic conductivity of the electrolyte and reducing the risk of increased battery internal resistance due to thermal effects. This can significantly improve the thermal stability of lithium-ion batteries operating under high temperature conditions, such as electric vehicle batteries operating in hot climates or when the battery generates a lot of heat during rapid charging, reduce the reduction in capacity retention, and extend the cycle life.

[0066] Improved chemical stability:

[0067] The methoxysulfonyl functional group has a certain degree of chemical inertness. In the complex working environment of the battery, it can reduce unnecessary reactions with lithium salts, solvent molecules in the electrolyte, and active substances generated during the battery charging and discharging process. Compared with some functional groups with higher reactivity, it can reduce the possibility of the additive's own structure being destroyed and maintain the effectiveness of the additive.

[0068] This chemical inertness helps maintain the original functions of the additive in the electrolyte, such as stably forming a protective film on the electrode surface or adjusting the electrolyte performance, ensuring the stability of the lithium ion transmission channel, and reducing the problem of decreased ion conductivity caused by chemical reactions, thereby improving the battery's charge and discharge efficiency, maintaining the battery's chemical stability during long-term use, slowing down the corrosion of electrode materials and the decomposition rate of the electrolyte, and helping to extend the battery's cycle life and improve capacity retention.

[0069] Enhanced long-term stability:

[0070] There is a synergistic effect between the siloxane ring structure, methyl and methoxysulfonyl functional groups. The siloxane ring structure provides basic molecular skeleton stability, the methyl group helps fill the molecular space and reduce the impact 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 keep the additive molecules stable and reduce the performance degradation of the additives caused by changes in the molecular structure. For example, the protective film formed by the additives can remain intact for a long time, effectively preventing the electrode surface from being re-exposed to the electrolyte and avoiding the adverse reaction between the electrode material and the electrolyte, thereby reducing the rate of increase in the battery's internal resistance, reducing the degree of polarization, maintaining the stability of the battery capacity, and significantly enhancing the long-term stability of the battery.

[0072] Suppression of side effects:

[0073] The overall structural design of the additive molecule keeps its reactivity within an appropriate range. It will neither fail to form an effective protective film on the electrode surface or play other beneficial functions due to low reactivity, nor will it cause excessive unnecessary side reactions with other components in the electrolyte due to high reactivity.

[0074] Compared with some additives that easily cause side reactions, 2,4,6-(methoxysulfonyl)methyl-2,4,6-trimethylcyclotrisiloxane can avoid adverse reactions with electrolyte lithium salts, thereby maintaining the dissociation balance of lithium salts and ensuring the normal concentration and transmission of lithium ions. At the same time, it reduces the generation of side reaction products, avoids the negative effects of these products on the reduction of electrolyte conductivity and the increase of self-discharge rate, and is conducive to improving the cycle life and performance stability of the battery.

[0075] Optimization of cover quality:

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

[0077] The uniform and dense covering layer can effectively reduce the obstacles to charge transfer and ion diffusion, and reduce the risk of excessive local current density and electrolyte penetration-induced side reactions. Compared with the case of poor quality covering layer, the optimized covering layer can reduce the internal resistance of the battery, reduce the heat generated during the charging and discharging process, and improve the charging and discharging efficiency and power performance, especially at high-rate charging and discharging, which helps to extend the cycle life of the battery 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. Although the overall solubility may still be affected to a certain extent in low temperature environments, the possibility of precipitation at low temperatures is reduced compared to additives with poor solubility.

[0080] Good solubility helps the additives to disperse evenly in the electrolyte, ensuring the uniformity of its functions such as forming a protective film on the electrode surface. When the composition of the electrolyte solvent changes, such as solvent volatilization or additive decomposition, its relatively stable solubility can also reduce the occurrence of problems such as crystallization, maintain the uniformity of the electrolyte, and facilitate the transmission of lithium ions, thereby reducing the risk of increased battery internal resistance due to solubility problems, improving the battery's cycle performance under different temperature conditions, and reducing fluctuations in capacity retention.

[0081] Improved compatibility with battery components:

[0082] The structural design of the additive makes it compatible with the electrode materials, electrolyte salts and other additives in the battery. Its molecular structure will not cause adverse chemical reactions with the positive electrode material, thereby avoiding damage to the crystal structure of the positive electrode material and maintaining the electrochemical activity and lithium storage capacity of the positive electrode material.

[0083] It can maintain good interaction with electrolyte salts, does not interfere with the dissociation state of salts, and ensures the normal conduction of lithium ions. When it coexists with other additives in the electrolyte, it can work together without interfering with each other or reducing each other's performance, and jointly achieve the goal of improving battery performance, reduce the deterioration of the internal chemical environment of the battery caused by compatibility issues, and is conducive to improving the cycle life and overall performance of the battery.

[0084] Improvement of viscosity and volatility issues:

[0085] The molecular structure of the additive prevents it from excessively increasing the viscosity of the electrolyte. Compared with some high-viscosity additives, it can maintain a relatively appropriate ion migration rate in the electrolyte, reducing the increase in battery internal resistance and the decrease in charge and discharge rate caused by increased viscosity.

[0086] In terms of volatility, the functional groups in the molecular structure make the additives relatively volatile. During the use or production of the battery, even under certain temperature and pressure conditions, it can reduce the changes in additive concentration, safety hazards, and changes in internal battery pressure caused by solvent volatilization, 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, but the above embodiments are only illustrative in nature and are not intended to limit the present invention. In addition, this article is not limited by any theory described in the above prior art or invention content or the following examples. BRIEF DESCRIPTION OF THE DRAWINGS

[0088] Figure 1 The prepared 2,4,6-(methoxysulfonyl)methyl-2,4,6-trimethylcyclotrisiloxane 1 HNMR spectrum. DETAILED DESCRIPTION

[0089] The present invention is further described below in conjunction with examples. It should be noted that the following examples are provided for illustrative purposes only and do not constitute a limitation on the scope of protection claimed for the present invention.

[0090] Unless otherwise specified, the raw materials, reagents, methods, etc. used in the examples are conventional raw materials, reagents, methods in the art.

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

[0092] 100 g (about 0.35 moles) of 2,4,6-triethyl-2,4,6-trimethylcyclotrisiloxane (purity 95%) and 150 g (about 1.2 moles) of methyl methanesulfonate (purity 98%) were added into a 500 ml dry four-necked flask equipped with a stirring device, a thermometer and a reflux condenser (before use, the four-necked flask was purged with nitrogen for 15-20 minutes). Under nitrogen protection, the stirring device was turned on and the stirring speed was controlled at 400 rpm to fully mix the raw materials. The temperature was slowly raised to 100° C. and the reflux state was maintained for reaction for 24 hours. The reaction process was monitored regularly. After the reaction was completed, the reaction mixture was extracted with ethyl acetate, the organic phase was collected, and the organic phase was washed with deionized water 2-3 times. The organic phase was then dried through an anhydrous sodium sulfate drying column to obtain a dry organic solution, which was subjected to rotary evaporation to obtain a crude product. The crude product was then subjected to reduced pressure distillation, and the pressure was controlled at 3 mm Hg. The fraction at 155°C / 3 mm Hg was collected, which was the purified 2,4,6-(methoxysulfonyl)methyl-2,4,6-trimethylcyclotrisiloxane with a purity of 98%. 1 H NMR spectrum Figure 1 As shown, the structure is shown in Formula 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, and a lithium-ion battery assembled with a conventional electrolyte not containing 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] In the glove box (H 2 The specific steps for preparing the electrolyte (O<5ppm) are as follows:

[0096] (1) dehydrating an anhydrous organic solvent molecular sieve under the protection of nitrogen or inert gas to obtain an anhydrous organic solvent;

[0097] (2) adding an appropriate amount of lithium salt to an anhydrous organic solvent, stirring and cooling to obtain a mixed solution;

[0098] (3) Add appropriate amount of additives to the mixed solution to obtain 2000 g of electrolyte, which is placed in a fluorination bottle.

[0099] The positive electrode material of the lithium-ion battery is a ternary material (LiNi0.6 Co 0.2 Mn 0.2 O 2 ), the negative electrode material is artificial graphite, the design capacity is 60Ah, and the injection volume is 2.3±0.5g / Ah.

[0100] Embodiment 1:

[0101] The non-aqueous organic solvent used in the electrolyte is: EC:EMC (v:v) = 30:70; lithium salt: concentration of 0.8M lithium hexafluorophosphate (LiPF 6 ), with a concentration of 0.4 M lithium bis(fluorosulfonyl)imide (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.% LiPO 2 F 2 , the added amount of the compound of formula I is 8 wt.%.

[0102] Embodiment 2:

[0103] The non-aqueous organic solvent used in the electrolyte is: EC:EMC (v:v) = 30:70; lithium salt: concentration of 0.8M lithium hexafluorophosphate (LiPF 6 ), with a concentration of 0.4 M lithium bis(fluorosulfonyl)imide (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.% LiPO 2 F 2 , the added amount of the compound of formula I is 4 wt.%.

[0104] Embodiment 3:

[0105] The non-aqueous organic solvent used in the electrolyte is: EC:EMC (v:v) = 30:70; lithium salt: concentration of 0.8M lithium hexafluorophosphate (LiPF 6 ), with a concentration of 0.4 M lithium bis(fluorosulfonyl)imide (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.% LiPO 2 F 2 , the added amount of the compound of formula I is 0.5wt.%.

[0106] Comparative Example 1:

[0107] The non-aqueous organic solvent used in the electrolyte is: EC:EMC (v:v) = 30:70; lithium salt: concentration is 1.2M lithium hexafluorophosphate (LiPF 6 ).

[0108] Comparative Example 2:

[0109] The non-aqueous organic solvent used in the electrolyte is: EC:EMC (v:v) = 30:70; lithium salt: concentration of 0.8M lithium hexafluorophosphate (LiPF 6 ), with a concentration of 0.4 M lithium bis(fluorosulfonyl)imide (LiFSI).

[0110] Comparative Example 3:

[0111] The non-aqueous organic solvent used in the electrolyte is: EC:EMC (v:v) = 30:70; lithium salt: concentration of 0.8M lithium hexafluorophosphate (LiPF 6 ), with a concentration of 0.4 M lithium bis(fluorosulfonyl)imide (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.% LiPO 2 F 2 .

[0112] Comparative Example 4:

[0113] The difference between this comparative example and Example 3 is that the compound of formula I is replaced by the compound of formula II (hexamethylcyclotrisiloxane, CAS registration number is 541-05-9).

[0114]

[0115] Comparative Example 5:

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

[0117]

[0118] Comparative Example 6:

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

[0120]

[0121] The lithium-ion batteries assembled in the comparative example and the embodiment were placed in an environment of 25°C and cycled at 1C charge and 1C discharge to test the capacity retention rate, with a voltage range of 2.75 to 4.2V. The results are shown in Table 1:

[0122] Table 1 Normal temperature cycle performance test

[0123] 1000 laps 2000 laps 3000 laps 4000 laps 5000 laps 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 lithium-ion batteries assembled in the comparative example and the embodiment were placed in an environment of 45°C and cycled at 1C charge and 1C discharge to test the capacity retention rate, with a voltage range of 2.75 to 4.2V. The results are shown in Table 2:

[0125] Table 2 High temperature cycle performance test

[0126] 1000 laps 2000 laps 3000 laps 4000 laps 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] It can be seen from the results 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 a good application prospect.

[0128] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions described in the above embodiments may be modified, or some or all of the technical features thereof may be replaced by equivalents, without departing from the spirit and essence of the claims of the present invention; and these modifications or replacements are still within the scope defined by the claims of the present invention.

Claims

1. An electrolyte additive, characterized in that: The electrolyte additive includes 2,4,6-(methoxysulfonyl)methyl-2,4,6-trimethylcyclotrisiloxane shown in Formula I:

2. The electrolyte additive according to claim 1, characterized in that: The 2,4,6-(methoxysulfonyl)methyl-2,4,6-trimethylcyclotrisiloxane is prepared by the following method: 2,4,6-triethyl-2,4,6-trimethylcyclotrisiloxane and methyl methanesulfonate are subjected to a nucleophilic substitution reaction to generate 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°C and the reaction time is 12-24h.

5. An electrolyte, characterized in that: The electrolyte comprises the electrolyte additive according to any one of claims 1 to 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 mass percentage of the 2,4,6-(methoxysulfonyl)methyl-2,4,6-trimethylcyclotrisiloxane in the electrolyte is 0.1%-10%.

7. 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), succinonitrile (ADN), 1,3,6-hexanetrinitrile, lithium bis(oxalatoborate) (LiBOB), lithium difluorooxalatoborate (LiDFOB), lithium bis(trifluoromethanesulfonylimide) (LiTFSI), tris(trimethylsilyl)borate (TMSB), tris(trimethylsilyl)phosphate (TMSP), sulfolane (SL), methyl sulfolane, 1,3-propane sultone (PS), 1,4-butane sultone, methylene methanedisulfonate (MMDS), ethylene methanedisulfonate, lithium difluorophosphate (LiPO2F2), vinyl ethylene carbonate (VEC), cyclohexylbenzene, and 1,3-propene sultone (PST).

8. The electrolyte according to claim 5, characterized in that The lithium salt is selected from at least one of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide; The concentration of lithium salt in the electrolyte is 0.8M-1.4M.

9. The electrolyte according to claim 5, characterized in that The anhydrous organic solvent is selected from at least one of carbonates, halogenated carbonates, carboxylates, propionates, fluoroethers, aromatic hydrocarbons or halogenated aromatic hydrocarbons; The mass percentage of the anhydrous organic solvent in the electrolyte is 60%-80%.

10. A lithium ion battery, characterized in that: The lithium-ion battery comprises the electrolyte according to any one of claims 5 to 9.

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