Lithium ion battery electrolyte, preparation method and application of sulfonamide additive

Abstract

The application relates to a lithium ion battery electrolyte, a preparation method and application of a sulfonamide additive, and belongs to the technical field of lithium ion batteries. The lithium ion battery electrolyte comprises a lithium salt, an organic solvent and a sulfonamide additive; the sulfonamide additive is prepared by the following method: alcohol and chlorosulfonic acid are reacted at -10-15 DEG C to obtain an intermediate; without separating the intermediate, an amine and an acid-binding agent are directly added to the reaction system, the pH value of the system is controlled to be 9-10, and the sulfonamide additive is obtained through reaction. The electrolyte can form a stable CEI film rich in inorganic substances on the surface of a high-nickel ternary positive electrode, inhibits material microcracks and side reactions, and significantly improves the cycle performance of the battery. Meanwhile, the preparation process of the sulfonamide additive avoids separation of an intermediate product, is safe, and is suitable for large-scale production.

Description

Technical Field

[0001] This application belongs to the field of lithium-ion battery technology, and specifically relates to a method for preparing lithium-ion battery electrolyte and sulfonamide additives and their applications. Background Technology

[0002] Lithium-ion batteries are widely used in portable electronic devices, electric vehicles, and energy storage systems due to their advantages such as high energy density, long cycle life, and no memory effect. As market demands for battery energy density continue to increase, high-nickel ternary cathode materials (such as LiNi) are becoming increasingly important. x Co y Mn z O2 or LiNi x Co y Al z O2 (where x+y+z=1, x>0.8) has become a research hotspot due to its high specific capacity. However, high-nickel ternary materials face severe interfacial stability problems under high-voltage operation. During charging and discharging, the repeated insertion and extraction of lithium ions causes drastic changes in the lattice parameters of the cathode material, leading to stress concentration within the particles and subsequently the generation and propagation of bulk microcracks. These microcracks not only increase the contact area between the cathode material and the electrolyte, exacerbating interfacial side reactions, but also cause the dissolution of transition metal ions, ultimately resulting in rapid capacity decay and decreased safety performance of the battery.

[0003] To improve the interfacial stability of high-nickel ternary materials, sulfonamide additives are considered a cost-effective solution. Sulfonamide compounds (such as tetraethylsulfonamide and tetramethylsulfonamide) are believed to oxidize and decompose on the cathode surface to form a positive electrode electrolyte interfacial film (CEI film), thereby inhibiting the continuous decomposition of the electrolyte. However, existing sulfonamide additives still have the following limitations in practical applications: First, the preparation processes of sulfonamide additives pose safety risks and are difficult to scale up. Traditional methods for preparing sulfonamide compounds mainly include the reaction of amines with sulfonyl chlorides or the alkylation of sulfonamides. In the former, the intermediate sulfonyl chloride is highly susceptible to hydrolysis, requiring extremely high humidity control in the production environment, and the hydrolysis products severely affect the purity of the final sulfonamide additive. In the latter, strong alkaline reagents such as sodium hydride are often required, which can react violently or even explode upon contact with water, posing significant safety hazards. Furthermore, existing preparation processes typically involve the separation and purification of intermediate products, resulting in cumbersome procedures and high costs, making it difficult to meet the demands of the lithium battery industry for large-scale industrial production.

[0004] Secondly, the purity and impurity control of sulfonamide additives affect electrolyte performance. Due to the limitations of the aforementioned preparation processes, commercially available or conventionally prepared sulfonamide additives often contain residual moisture, acidic impurities, or unreacted intermediates. These impurities are prone to decomposition under the high-voltage environment of the battery, leading to a decrease in the oxidative decomposition potential of the electrolyte. This not only prevents the formation of a dense and stable CEI film but may also induce side reactions such as gas generation, weakening the protective effect that sulfonamide additives should provide.

[0005] Finally, single sulfonamide additives are insufficient to meet the synergistic requirements of high-voltage systems. Existing electrolyte systems often focus only on the introduction of sulfonamide additives themselves, neglecting the synergistic compatibility effects between sulfonamide additives and solvents or lithium salts. For example, traditional carbonate solvents are prone to oxidative decomposition and gas generation under high voltage, while single lithium salts (such as LiPF6) are prone to generating HF that corrodes the cathode material at high temperatures or in the presence of trace amounts of water. Without suitable co-solvents (such as sulfone solvents) and mixed lithium salt systems, even with the use of sulfonamide additives, it is difficult to fully realize their protective role in high-nickel ternary systems, resulting in limited improvement in the battery's long-cycle performance.

[0006] Therefore, developing a safe, low-cost, and scalable method for preparing sulfonamide additives, and optimizing its compatibility with specific solvents and lithium salt systems to solve the problems of interface stability and cycle life of high-nickel ternary cathode materials under high voltage, has become an urgent technical challenge in the field of lithium-ion battery technology. Summary of the Invention

[0007] The purpose of this application is to provide a method for preparing lithium-ion battery electrolytes and sulfonamide additives, as well as their applications. This aims to solve the technical problems of the degradation of cycle performance of existing high-nickel ternary cathode materials under high-voltage operation due to interfacial side reactions, and the fact that traditional sulfonamide additive preparation processes have problems such as easy hydrolysis of raw materials, significant reaction safety hazards, and unsuitability for large-scale production.

[0008] In a first aspect, this application provides a lithium-ion battery electrolyte, comprising: Lithium salts, including lithium hexafluorophosphate and lithium difluorosulfonylimide; Organic solvents, including carbonate solvents and sulfone solvents; A sulfonamide additive, wherein the sulfonamide additive is prepared by the following method: reacting an alcohol with chlorosulfonic acid at -10 to 15°C to obtain an intermediate; wherein the alcohol is methanol or ethanol, and the molar ratio of the alcohol to chlorosulfonic acid is 1.05 to 1.2:1; without separating the intermediate, directly adding an amine and an acid-binding agent to the reaction system, controlling the pH of the system to be 9 to 10, and reacting to obtain the sulfonamide additive; wherein the amine is dimethylamine or diethylamine.

[0009] In conjunction with the first aspect of this application, in some embodiments, the total concentration of the lithium salt is 0.01M to 3M; and the lithium hexafluorophosphate accounts for 40% to 99.9% of the total mass of the lithium hexafluorophosphate and lithium difluorosulfonylimide.

[0010] In conjunction with the first aspect of this application, in some embodiments, the carbonate solvent is a mixture of methyl ethyl carbonate and ethylene carbonate; the sulfone solvent is one or more of sulfolane, methyl ethyl sulfone, dimethyl sulfone, and diethyl sulfone.

[0011] In conjunction with the first aspect of this application, in some embodiments, the carbonate solvent accounts for 60% to 99.9% of the total weight of the carbonate solvent and the sulfone solvent; the sulfone solvent accounts for 0.1% to 40% of the total weight of the carbonate solvent and the sulfone solvent; and the methyl ethyl carbonate accounts for 65% to 99.9% of the weight of the carbonate solvent.

[0012] In conjunction with the first aspect of this application, in some embodiments, the sulfonamide additive accounts for 0.01% to 5% of the total weight of the carbonate solvent and the sulfone solvent.

[0013] In conjunction with the first aspect of this application, in some embodiments, the reaction time of alcohol and chlorosulfonic acid at -10 to 15°C is 1 to 3 hours; after adding amines and acid-binding agents to the reaction system, the temperature is controlled at 20 to 30°C, and the reaction time is 1 to 1.5 hours.

[0014] In conjunction with the first aspect of this application, in some embodiments, the acid-binding agent is sodium hydroxide powder or potassium hydroxide powder.

[0015] In conjunction with the first aspect of this application, in some embodiments, the electrolyte is prepared by the following method: first, a carbonate solvent, a sulfone solvent and a sulfonamide additive are mixed evenly, and then the lithium salt is added to dissolve it; during the dissolution of the lithium salt, the ambient temperature of the electrolyte is controlled to be 0-10°C.

[0016] Secondly, this application provides a lithium-ion battery, including a positive electrode, a negative electrode, a separator, and the above-mentioned electrolyte; the positive electrode is a high-nickel ternary positive electrode material; the negative electrode is lithium metal or graphite; and the battery operates in the voltage range of 2.75V to 4.4V.

[0017] Thirdly, this application provides a method for preparing a sulfonamide additive, comprising: reacting an alcohol with chlorosulfonic acid at -10 to 15°C to obtain an intermediate; wherein the alcohol is methanol or ethanol, and the molar ratio of the alcohol to chlorosulfonic acid is 1.05 to 1.2:1; without separating the intermediate, directly adding an amine and an acid-binding agent to the reaction system, controlling the pH of the system to be 9 to 10, and reacting to obtain the sulfonamide additive; wherein the amine is dimethylamine or diethylamine.

[0018] Compared with the prior art, this application has at least the following beneficial effects: 1. The sulfonamide additive preparation method provided in this application has the advantages of high safety and low cost. Compared with the traditional amine and sulfonyl chloride preparation method or sulfonamide alkylation preparation method, this application adopts an aminosulfonate preparation method (one-pot, two-step process), avoiding the use of strongly alkaline reagents such as sodium hydride, which is prone to explosion upon contact with water, thus significantly reducing the safety risks in the production process. Simultaneously, by controlling the low-temperature reaction conditions (-10 to 15°C) and the raw material molar ratio, the hydrolysis side reaction of the intermediate sulfonyl chloride is effectively suppressed. Due to the one-pot process, there is no need to separate intermediate products, reducing intermediate separation and purification steps, which not only lowers production costs and equipment requirements, making it more suitable for large-scale industrial production, but also reduces intermediate product exposure and processing steps, lowering the risk of introducing moisture and acidic impurities. Experimental data show that the electrolyte prepared using the additive using this method has a higher oxidative decomposition potential, indicating that this method effectively improves the electrochemical stability of the additive and reduces the content of easily decomposable impurities.

[0019] 2. The electrolyte provided in this application exhibits high oxidation stability and a wide electrochemical window. This application significantly improves the overall performance of the electrolyte through the synergistic effect of a specific formulation. Thanks to the combination of high-purity sulfonamide additives and sulfone solvents, the oxidative decomposition potential of the electrolyte at high voltage is enhanced, surpassing electrolyte systems with commonly used commercial additives. Furthermore, the introduction of sulfone solvents broadens the electrochemical window of the electrolyte, effectively suppressing the gas generation problem caused by the oxidative decomposition of traditional carbonate solvents at high potentials, thus improving battery safety. Simultaneously, the use of a mixed lithium salt system of lithium hexafluorophosphate and lithium difluorosulfonylimide reduces the corrosion of the cathode material surface caused by the HF generated from the reaction of trace amounts of water with LiPF6, further ensuring the long-term stability of the electrolyte.

[0020] 3. When applied to lithium-ion batteries using high-nickel ternary cathode materials, this electrolyte exhibits excellent cycle stability. Under high-voltage operating conditions, the battery retains a high capacity retention rate after long cycles, significantly better than the comparative example. The electrolyte of this application effectively mitigates the volume change of the cathode material caused by repeated lithium-ion intercalation and deintercalation, suppresses the generation and propagation of microcracks in the particulate bulk phase, and maintains the integrity of the cathode structure, thus solving the technical problem of microcrack generation and performance degradation in high-nickel ternary materials due to volume changes under high voltage.

[0021] 4. This application utilizes a synergistic mechanism of additive decomposition and solvent compatibility to form a more protective CEI film on the cathode surface. Sulfonamide additives preferentially oxidize and decompose under high voltage, forming a CEI film rich in inorganic substances such as Li3N and Li2SO3, as well as alkyl lithium. The mixed structure of inorganic and organic components enhances the mechanical strength and flexibility of the CEI film, enabling it to better adapt to the volume expansion of the cathode material and prevent film rupture. The dense CEI film effectively blocks direct contact between the cathode active material and the electrolyte, reducing the dissolution of transition metal ions and the continuous consumption of electrolyte, thus achieving a balance between long cycle life and high safety in the battery. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below in conjunction with the embodiments of this application. Obviously, the described embodiments are only some, not all, of the embodiments of this application. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0023] In the field of lithium-ion battery electrolytes, sulfonamide compounds have been disclosed in numerous patent documents as additives or co-solvents. For example, CN113061102A reports the use of sulfonate ester compounds with sulfonamide structures as electrolyte additives. However, there are no commercially available products of these sulfonate ester compounds, and their complex structures make them difficult to synthesize. N,N,N',N'-tetramethylsulfonamide (hereinafter referred to as tetramethylsulfonamide) and N,N,N',N'-tetraethylsulfonamide (hereinafter referred to as tetraethylsulfonamide) have been documented in the field of organic chemistry for many years and are often seen as organic synthesis intermediates, solvents, or specific reaction reagents in public chemical databases and early literature. According to existing research data, tetraethylsulfonamide has indeed been used as a component of lithium-ion battery electrolytes, but there are no reports of tetramethylsulfonamide itself being used directly as a solvent or additive in lithium-ion battery electrolytes.

[0024] The applicant used commercially available tetramethylsulfonamide and tetraethylsulfonamide as electrolyte additives and found that the capacity retention rate was only about 60% after 400 cycles. This experimental result indicates that directly using these two commercially available sulfonamides as electrolyte additives has a very limited effect on improving the long-cycle stability of batteries under the current testing system, and may even have a negative impact.

[0025] Under the same conditions, the applicant added tetramethylsulfonamide and tetraethylsulfonamide, prepared by the following method, to the electrolyte and found that the capacity retention rate reached about 85% after 400 cycles. Preparation method: An alcohol and chlorosulfonic acid were reacted at -10 to 15°C to obtain an intermediate; the alcohol was methanol or ethanol, and the molar ratio of the alcohol to chlorosulfonic acid was 1.05 to 1.2:1; without separating the intermediate, an amine and an acid-binding agent were directly added to the reaction system, controlling the pH of the system to 9 to 10, and the reaction yielded the sulfonamide additive; the amine was dimethylamine or diethylamine.

[0026] Trace amounts of moisture and metal ion impurities (such as Na) are commonly found in commercially available chemicals. + K + Fe 3+ Residual solvents or synthesis byproducts can severely catalyze electrolyte decomposition and damage the electrode interface, leading to rapid capacity decay. Based on the above results, the applicant speculates that the self-made product is likely to have a much higher purity than commercially available tetramethylsulfonamide and tetraethylsulfonamide.

[0027] Based on this, this application uses the self-made product in a lithium-ion battery electrolyte, which comprises: Lithium salts, including lithium hexafluorophosphate (LiPF6) and lithium difluorosulfonylimide (LiFSI); Organic solvents, including carbonate solvents and sulfone solvents; A sulfonamide additive, wherein the sulfonamide additive is prepared by the following method: reacting an alcohol with chlorosulfonic acid at -10 to 15°C to obtain an intermediate; wherein the alcohol is methanol or ethanol, and the molar ratio of the alcohol to chlorosulfonic acid is 1.05 to 1.2:1; without separating the intermediate, directly adding an amine and an acid-binding agent to the reaction system, controlling the pH of the system to be 9 to 10, and reacting to obtain the sulfonamide additive; wherein the amine is dimethylamine or diethylamine.

[0028] This electrolyte has a low additive decomposition voltage (4.1~4.15V), at which a CEI film can be formed; it also has a high electrolyte oxidation decomposition potential (5.82~5.91V), which is much higher than the electrolyte oxidation decomposition potential of commercially available products; and when this electrolyte is applied to ternary lithium-ion batteries, it can make the batteries have good capacity retention performance, with a capacity retention rate of about 85% after 400 cycles.

[0029] In some embodiments of this application, the total concentration and mixing ratio of lithium salts are optimized and limited. Specifically, the total concentration of lithium salts is 0.01M to 3M. If the lithium salt concentration is too low, the number of migratable lithium ions in the electrolyte is insufficient, which will lead to a significant increase in battery internal resistance and a decrease in rate performance; if the concentration is too high, the electrolyte viscosity will increase, the ion migration rate will decrease, and lithium salt precipitation or excessive cost may occur. In addition, this application adopts a mixed lithium salt system of lithium hexafluorophosphate and lithium difluorosulfonylimide, and limits the lithium hexafluorophosphate to account for 40% to 99.9% of the total mass of the two. This specific mixing strategy aims to exert a synergistic effect: on the one hand, LiPF6 can form a stable passivation film on the surface of aluminum current collector to prevent current collector corrosion, so a high proportion (≥50%) is required; on the other hand, LiFSI has higher thermal stability and dissociation degree, and the introduction of a small amount of LiFSI (i.e., LiPF6 proportion ≤99.9%) helps to weaken the tendency of LiPF6 to react with trace water to generate HF, thereby reducing the corrosion risk of HF on high-nickel ternary cathode materials. When the LiPF6 content is within the specific range mentioned above, the mixed lithium salt can form an optimal synergy with the sulfonamide additives and sulfone co-solvents specific in this application, ensuring both the high ionic conductivity of the electrolyte and effectively suppressing interfacial side reactions, thereby significantly improving the cycle stability of the high-nickel ternary battery under high temperature and high voltage. Preferably, the total concentration of the lithium salt is 1.5~2.5M; more specifically, the total concentration of the lithium salt is 1.8~2.2M; in the embodiments of this application, the total concentration of the lithium salt is 2M. In the mixed lithium salt system, the molar percentage of lithium hexafluorophosphate is 70% (i.e., 1.4M).

[0030] In some embodiments of this application, the composition of the organic solvent has been specifically selected and optimized. The carbonate solvent is a mixture of ethyl methyl carbonate (EMC) and ethylene carbonate (EC). Ethyl carbonate has a high dielectric constant, which facilitates the dissociation of lithium salts and can participate in the formation of the SEI film on the negative electrode surface, ensuring the stability of the negative electrode interface. Ethyl methyl carbonate has a low viscosity and melting point, which helps improve the ionic conductivity and low-temperature discharge performance of the electrolyte. The use of this mixture aims to balance the electrochemical window, ionic conductivity, and film-forming properties of the electrolyte, providing a basic electrochemical environment for the battery. The sulfone solvent is one or more of sulfolane (SL), methyl ethyl sulfone (EMS), dimethyl sulfone (DMS), and diethyl sulfone (DES). Sulfone solvents have excellent high-voltage oxidation resistance; their introduction can effectively broaden the electrochemical window of the electrolyte and suppress the oxidative decomposition and gas generation of traditional carbonate solvents at high voltages (>4.4V). More importantly, the sulfone solvent and sulfonamide additives in this application exhibit a synergistic effect. The stable high-pressure environment provided by the sulfone solvent facilitates the preferential oxidation and decomposition of the sulfonamide additives on the cathode surface, forming a dense CEI film rich in inorganic matter. This effectively protects the high-nickel ternary cathode material, alleviates the formation of microcracks caused by volume expansion, and improves the cycle life and safety performance of the battery. Preferably, the mass ratio of methyl ethyl carbonate to ethylene carbonate is 7:3 to 9:1, for example, 7:3, 8:2, or 9:1.

[0031] In a preferred embodiment of this application, the mass ratio of each solvent component has been further optimized to balance the ionic conductivity, low-temperature performance, and high-voltage stability of the electrolyte. Specifically, the carbonate solvent accounts for 60% to 99.9% of the total weight of the carbonate and sulfone solvents, and the sulfone solvent accounts for 0.1% to 40% of the total weight of the carbonate and sulfone solvents. Although sulfone solvents have excellent high-pressure oxidation resistance, their viscosity is relatively high. If the content is too high (above 40%), it will lead to a significant increase in electrolyte viscosity, hindering ion migration, reducing low-temperature discharge performance, and worsening the wettability of the electrode. If the content is too low (below 0.1%), it will be difficult to effectively suppress the decomposition and gas generation of the carbonate solvent under high voltage. Therefore, controlling the sulfone solvent within the above-mentioned specific range can both broaden the electrochemical window and maintain good electrolyte fluidity. In addition, the methyl ethyl carbonate accounts for 65% to 99.9% of the weight of the carbonate solvents. Ethyl methyl carbonate, as a linear carbonate, has low viscosity and melting point. A high proportion of ethyl methyl carbonate helps reduce the overall viscosity of the electrolyte, improves ionic conductivity, and enhances the electrolyte's wetting and penetration ability in the pores of the high-nickel cathode. The remaining ethylene carbonate provides the necessary dielectric constant to support lithium salt dissociation. This specific solvent ratio, together with the sulfonamide additives and mixed lithium salts described in this application, creates a synergistic effect, ensuring that the electrolyte exhibits low impedance, high stability, and long cycle life under high-voltage, high-nickel systems. Preferably, ethyl methyl carbonate accounts for 70% of the weight of the carbonate solvent.

[0032] In some embodiments of this application, the sulfonamide additive accounts for 0.01% to 5% of the total weight of the carbonate solvent and sulfone solvent. This specific content range is set based on a comprehensive balance between the cathode film formation effect and the overall electrochemical performance of the electrolyte. If the additive content is too low (below 0.01 wt%), the CEI film formed on the surface of the high-nickel ternary cathode may not be dense or complete enough, making it difficult to effectively suppress the oxidative decomposition of the electrolyte under high voltage and the generation of microcracks in the cathode material; if the content is too high (above 5 wt%), the excessive additive will not only increase the electrolyte viscosity and reduce the ionic conductivity, but may also generate gas due to excessive decomposition, affecting the cycle stability and safety of the battery. With the specific sulfone co-solvent and mixed lithium salt system of this application, controlling the additive content within the range of 0.01% to 5% ensures that the sulfonamide additive preferentially oxidizes and decomposes before the solvent, forming a stable protective layer rich in inorganic matter, while not affecting the normal transport of lithium ions, thereby achieving a significant improvement in the cycle life and safety of the high-nickel ternary battery under high voltage. Preferably, the additive content is 0.5wt% to 1wt%.

[0033] In some embodiments of this application, the sulfonamide additive is a mixture of tetraethylsulfonamide and tetramethylsulfonamide, and the mass of tetraethylsulfonamide accounts for 50% to 100% of the total mass of tetraethylsulfonamide and tetramethylsulfonamide. This specific range is primarily based on the difference in solubility of the two sulfonamide compounds in the electrolyte system and the complementarity of their film-forming properties. Compared to tetramethylsulfonamide, tetraethylsulfonamide has superior solubility in mixed solvents of carbonates and sulfones, and is particularly resistant to precipitation at low temperatures, ensuring the homogeneity and stability of the electrolyte system. Simultaneously, the CEI film formed by the decomposition of tetraethylsulfonamide exhibits good flexibility, better adapting to the volume expansion of high-nickel cathode materials. If the proportion of tetraethylsulfonamide is too low (below 50 wt%), i.e., the content of tetramethylsulfonamide is too high, it may lead to a decrease in the solubility of the additive in the electrolyte, especially under low temperature or high concentration lithium salt conditions, which can easily cause crystallization and precipitation, clogging the positive electrode pores and increasing the battery's internal resistance. In addition, excessive tetramethylsulfonamide may lead to an excessively high proportion of inorganic components in the formed CEI film, increasing its brittleness and making it prone to breakage during cycling. Therefore, controlling the mass proportion of tetraethylsulfonamide to above 50% can ensure that the additive is fully dissolved and uniformly distributed, synergistically forming a dense and flexible protective film with sulfone co-solvents. This maximizes its protective effect on the high-nickel ternary positive electrode while ensuring electrolyte stability, thereby improving the battery's cycle life. Preferably, the proportion of tetraethylsulfonamide is between 70 wt% and 90 wt%.

[0034] In some embodiments of this application, the reaction temperature and time during the preparation of sulfonamide additives are precisely controlled to ensure the smooth implementation of the one-pot process and the stability of product quality. Specifically, the reaction time of alcohol and chlorosulfonic acid at -10 to 15°C is 1 to 3 hours. This low-temperature condition is designed to suppress the hydrolysis side reaction of sulfonyl chloride intermediates, reduce the generation of acidic impurities and water, and avoid a decrease in the oxidation potential of the subsequent electrolyte due to excessive impurities; while the reaction time of 1 to 3 hours ensures the full conversion of raw materials, avoiding the influence of residual raw materials on subsequent steps or the introduction of additional impurities due to incomplete reaction. After adding amines and acid-binding agents to the reaction system, the temperature is controlled at 20 to 30°C, and the reaction time is 1 to 1.5 hours. The reaction at 20 to 30°C not only reduces energy consumption and operational difficulty, and avoids additive decomposition or side reactions that may be caused by high temperatures, but also the 1 to 1.5 hours time is sufficient to ensure the complete amination reaction, while preventing the product stability from decreasing due to excessively long reaction time. By synergistically controlling the above reaction conditions, this application can effectively reduce the introduction of impurities and improve the electrochemical stability of the obtained sulfonamide additives without separating intermediate products. When this highly stable additive is applied to the electrolyte, it helps to form a more stable CEI film, thereby indirectly verifying the positive contribution of the preparation process to the final battery cycle performance. Preferably, the reaction time is 1.2 h.

[0035] In some embodiments of this application, the acid-binding agent is sodium hydroxide powder or potassium hydroxide powder. The selection of these two bases as acid-binding agents is primarily based on a comprehensive consideration of their neutralization efficiency, cost-effectiveness, and process safety. During the amination reaction, hydrogen chloride byproducts are generated. If not neutralized in time, the acidic environment may cause the sulfonamide additives to decompose or trigger other side reactions, affecting product stability. Sodium hydroxide or potassium hydroxide is a strong base, which can quickly and effectively neutralize the acid generated in the reaction. Combined with pH control (e.g., pH 9-10), this ensures the reaction system is in a suitable alkaline environment, promoting the reaction to proceed completely towards the formation of sulfonamides. These two acid-binding agents are widely available and inexpensive, helping to reduce the overall preparation cost of the additives. By selecting specific acid-binding agents and controlling their addition amount, residual acidic impurities in the reaction system can be effectively reduced, thereby improving the electrochemical stability of the obtained sulfonamide additives. This allows them to participate more stably in the formation of the CEI film in subsequent electrolyte applications, ensuring the cycle performance of high-nickel ternary batteries. Preferably, the pH is controlled at 9.5-9.7.

[0036] In some embodiments of this application, the preparation sequence and temperature conditions of the electrolyte are specifically controlled to maximize the chemical stability of the electrolyte components. Specifically, the electrolyte is prepared by first uniformly mixing carbonate solvents, sulfone solvents, and sulfonamide additives, and then adding the lithium salt to dissolve it. This order of addition aims to ensure that the sulfonamide additives are fully dispersed and dissolved in a low-viscosity solvent system, avoiding the increase in system viscosity or ionic strength caused by adding the lithium salt first, which would affect the uniform distribution of the additives. Furthermore, the ambient temperature of the electrolyte is controlled at 0–10°C when dissolving the lithium salt. The dissolution process of lithium salts (especially lithium hexafluorophosphate) is usually exothermic, and lithium hexafluorophosphate is sensitive to heat and moisture; high temperatures accelerate its hydrolysis to generate HF acidic substances. By strictly controlling the temperature within the low-temperature range of 0–10°C, the thermal decomposition and hydrolysis reactions of the lithium salt during the preparation process can be effectively suppressed, reducing the generation of HF, while avoiding the potential impact of high temperatures on the structural stability of the sulfonamide additives. This low-temperature formulation process helps to obtain electrolytes with lower impurity content and higher chemical stability, thereby reducing corrosion of high-nickel ternary cathode materials in subsequent battery applications, ensuring the integrity of the CEI film, and ultimately improving the cycle life and safety performance of the battery.

[0037] This application provides a lithium-ion battery, including a positive electrode, a negative electrode, a separator, and the above-mentioned electrolyte; the positive electrode is a high-nickel ternary positive electrode material; the negative electrode is lithium metal or graphite; the battery operates in the voltage range of 2.75V to 4.4V.

[0038] This application selects high-nickel materials with a nickel content higher than 0.8% to pursue higher specific capacity and energy density. However, such materials are extremely sensitive to electrolyte stability and are prone to lattice distortion, microcrack propagation, and transition metal ion dissolution. The specific electrolyte system of this application can form a stable CEI film rich in inorganic matter on the surface of the positive electrode, effectively suppressing interfacial side reactions and microcrack generation, thereby matching the high activity characteristics of high-nickel materials. The negative electrode is lithium metal or graphite, which can form a stable SEI film with the electrolyte of this application, ensuring the lithium ion insertion / extraction efficiency at the negative electrode interface. In addition, the battery operates in the voltage range of 2.75V to 4.4V. The cutoff voltage of 4.4V is in the high-voltage operating range. Traditional electrolytes are prone to oxidation and decomposition at this voltage, producing gas. However, the electrolyte of this application, thanks to the wide electrochemical window of the sulfone cosolvent and the protective effect of the highly stable sulfonamide additive, can withstand high voltage stress and reduce the risk of gas production. This combination of a high-nickel cathode and a high-voltage electrolyte system fully leverages the advantages of the electrolyte in suppressing HF corrosion and improving interface stability, significantly enhancing the cycle life and safety performance of lithium-ion batteries under high energy density conditions.

[0039] The following are specific embodiments of this application. Unless otherwise specified, the raw materials used in this application are all commercially available products.

[0040] The self-made sulfonamide additives used in the following examples are all target products prepared by the following method (taking self-made tetramethylsulfonamide as an example): 1. Preparation of methanesulfonyl chloride: Methanol (CH3OH) reacts with chlorosulfonic acid (ClSO3H) at low temperature to produce methyl chlorosulfonate (CH3OSO2Cl) and hydrochloric acid (HCl). The molar ratio of methanol to chlorosulfonic acid is 1.05:1, the reaction temperature is -10℃, and the reaction time is 1.2h.

[0041] 2. Formation of sulfonamides: Without separating methyl chlorosulfonate, dimethylamine and an acid-binding agent (sodium hydroxide powder) were directly added to the reaction system. The pH was controlled at 9.5, and the reaction was carried out at 20-30℃ for 1.2 hours to obtain the target product. The molar ratio of diethylamine to methanol was 1:2.2, and the molar ratio of sodium hydroxide to methanol was 3:1.1. The reaction mechanism is as follows: (1) The first step of substitution between methyl chlorosulfonate and dimethylamine: CH3OSO2Cl + 2(CH3)2NH → (CH3)2NSO2OCH3 + (CH3)2NH2Cl; (2) The intermediate product is then dehydrogenated by one molecule of dimethylamine: (CH3)2NSO2OCH3+(CH3)2NH→(CH3)2NSO2N(CH3)2+CH3OH; (3) NaOH binds acid to neutralize hydrochloric acid: (CH3)2NH2Cl+NaOH→(CH3)2NH+NaCl+H2O).

[0042] The self-made tetraethylsulfonamide used in the following examples is prepared using the same method as the self-made tetramethylsulfonamide described above, except that methanol is replaced with ethanol and dimethylamine is replaced with diethylamine.

[0043] In the following embodiments, the electrolyte is prepared in the following order: first, carbonate solvents, sulfone solvents, and sulfonamide additives are added to the sample vial sequentially and mixed thoroughly. Then, lithium salt is added. To reduce the temperature rise caused by the exothermic reaction of lithium salt dissolution, the external temperature of the sample vial is controlled between 0-10°C.

[0044] In the following examples and comparative examples, the total lithium salt concentration of 2M was kept consistent as the basic parameter, while the other variables were adjusted gradient.

[0045] Example 1 The lithium-ion battery electrolyte provided in this embodiment is composed of the following components: Lithium salt: Total concentration 2M, 15.2g lithium hexafluorophosphate + 18.7g lithium difluorosulfonylimide; Organic solvents: 100g carbonates (methyl ethyl carbonate: ethylene carbonate mass ratio 7:3) + 30g sulfones (sulfolane: methyl ethyl sulfone mass ratio 1:1); Additive: 1g of homemade sulfonamide additive (tetramethylsulfonamide).

[0046] Example 2 The lithium-ion battery electrolyte provided in this embodiment is composed of the following components: Lithium salt: Total concentration 2M, 22.8g lithium hexafluorophosphate + 9.35g lithium difluorosulfonylimide; Organic solvents: 100g carbonates (methyl ethyl carbonate: ethylene carbonate mass ratio 8:2) + 30g sulfones (sulfolane: methyl ethyl sulfone: dimethyl sulfone mass ratio 1:1:1); Additive: 1.5g of homemade sulfonamide additive (tetraethylsulfonamide).

[0047] Example 3 The lithium-ion battery electrolyte provided in this embodiment is composed of the following components: Lithium salt: Total concentration 2M, 26.6g lithium hexafluorophosphate + 4.675g lithium difluorosulfonylimide; Organic solvents: 100g carbonates (methyl ethyl carbonate: ethylene carbonate mass ratio 9:1) + 30g sulfones (sulfolane: methyl ethyl sulfone: dimethyl sulfone mass ratio 1:1:1); Additives: 1.5g of homemade sulfonamide additive (tetraethylsulfonamide:tetramethylsulfonamide in a 1:1 mass ratio).

[0048] Comparative Example 1 The lithium-ion battery electrolyte provided in this comparative example is composed of the following components: Lithium salt: completely consistent with Example 1, total concentration 2M, 15.2g lithium hexafluorophosphate + 18.7g lithium difluorosulfonylimide; Organic solvent: 130g pure carbonate (methyl ethyl carbonate: ethylene carbonate mass ratio 7:3), no sulfone solvent added; Additives: No additives.

[0049] Comparative Example 2 The lithium-ion battery electrolyte provided in this comparative example is composed of the following components: Lithium salt: completely consistent with Example 1, total concentration 2M, 15.2g lithium hexafluorophosphate + 18.7g lithium difluorosulfonylimide; Organic solvent: exactly the same as in Example 1, 100g carbonate (methyl ethyl carbonate to ethylene carbonate in a mass ratio of 7:3) + 30g sulfone (sulfolane: methyl ethyl sulfone in a mass ratio of 1:1). Additives: No additives.

[0050] Comparative Example 3 The lithium-ion battery electrolyte provided in this comparative example is composed of the following components: Lithium salt: completely consistent with Example 1, total concentration 2M, 15.2g lithium hexafluorophosphate + 18.7g lithium difluorosulfonylimide; Organic solvent: exactly the same as Comparative Example 1, 130g of pure carbonate (mass ratio of methyl ethyl carbonate to ethylene carbonate is 7:3). Additive: 1g of sulfonamide additive (tetraethylsulfonamide).

[0051] Comparative Example 4 The lithium-ion battery electrolyte provided in this comparative example is composed of the following components: Lithium salt: completely consistent with Example 1, total concentration 2M, 15.2g lithium hexafluorophosphate + 18.7g lithium difluorosulfonylimide; Organic solvent: exactly the same as in Example 1, 100g carbonate (mass ratio of methyl ethyl carbonate to ethylene carbonate is 7:3) + 30g sulfone (ratio of sulfolane to methyl ethyl sulfone is 1:1). Additive: 1g of commercial sulfonamide additive (tetramethylsulfonamide, only the source is different from Example 1).

[0052] Comparative Example 5 The lithium-ion battery electrolyte provided in this comparative example is composed of the following components: Lithium salt: completely consistent with Example 1, total concentration 2M, 15.2g lithium hexafluorophosphate + 18.7g lithium difluorosulfonylimide; Organic solvent: exactly the same as in Example 1, 100g carbonate (mass ratio of methyl ethyl carbonate to ethylene carbonate is 7:3) + 30g sulfone (ratio of sulfolane to methyl ethyl sulfone is 1:1). Additive: 1g of commercial sulfonamide additive (tetraethylsulfonamide).

[0053] Comparative Example 6 The lithium-ion battery electrolyte provided in this comparative example is composed of the following components: Lithium salt: completely consistent with Example 3, total concentration 2M, 26.6g lithium hexafluorophosphate + 4.675g lithium difluorosulfonylimide; Organic solvent: exactly the same as in Example 3, 100g carbonate (methyl ethyl carbonate to ethylene carbonate in a mass ratio of 9:1) + 30g sulfone (sulfolane to methyl ethyl sulfone to dimethyl sulfone in a ratio of 1:1:1). Additives: 1.5g of commercially available sulfonamide additives (tetraethylsulfonamide:tetramethylsulfonamide in a mass ratio of 2:1, the source and ratio of which are different from those in Example 3).

[0054] Comparative Example 7 The lithium-ion battery electrolyte provided in this comparative example is composed of the following components: Lithium salt: completely consistent with Example 3, total concentration 2M, 26.6g lithium hexafluorophosphate + 4.675g lithium difluorosulfonylimide; Organic solvent: exactly the same as in Example 3, 100g carbonate (mass ratio of methyl ethyl carbonate to ethylene carbonate is 9:1) + 30g sulfone (ratio of sulfolane to methyl ethyl sulfone to dimethyl sulfone is 1:1:1). Additives: 1.5g of self-made sulfonamide additive (tetraethylsulfonamide:tetramethylsulfonamide in a mass ratio of 3:1, only the ratio is different from that in Example 3).

[0055] application: The above electrolyte is applied to lithium metal as the negative electrode and high-nickel ternary cathode material LiNi. 0.8 Co 0.1 Mn 0.1 In a battery with O2 as the positive electrode and glass fiber as the separator, the battery was activated for 5 cycles using a 0.1C / 0.1C constant current charge-discharge cycle within a voltage range of 2.75–4.4V, followed by a 1C / 1C constant current charge-discharge cycle for cyclic testing. The capacity retention rate at the 400th cycle relative to the 6th cycle was recorded. The results are listed in Table 1.

[0056] Table 1

[0057] The test results above show that the sulfonamide additives and sulfone solvents provided in this application, when used in the electrolyte, can produce an electrolyte with a lower sulfonamide additive decomposition voltage (i.e., CEI film formation voltage) and a higher electrolyte oxidation decomposition potential. Furthermore, applying this electrolyte to ternary lithium-ion batteries can enhance the battery's capacity retention performance. Simultaneously, the electrolyte with the self-made sulfonamide additive has a higher oxidation decomposition potential than the electrolyte with the commercially available sulfonamide additive, indicating that the self-made sulfonamide additive has higher purity and completely avoids the influence of impurities or moisture.

[0058] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A lithium-ion battery electrolyte, characterized in that, Include: Lithium salts, including lithium hexafluorophosphate and lithium difluorosulfonylimide; Organic solvents, including carbonate solvents and sulfone solvents; A sulfonamide additive, wherein the sulfonamide additive is prepared by the following method: reacting an alcohol with chlorosulfonic acid at -10 to 15°C to obtain an intermediate; wherein the alcohol is methanol or ethanol, and the molar ratio of the alcohol to chlorosulfonic acid is 1.05 to 1.2:1; without separating the intermediate, directly adding an amine and an acid-binding agent to the reaction system, controlling the pH of the system to be 9 to 10, and reacting to obtain the sulfonamide additive; wherein the amine is dimethylamine or diethylamine.

2. The electrolyte according to claim 1, characterized in that, The total concentration of the lithium salt is 0.01M to 3M; the lithium hexafluorophosphate accounts for 40% to 99.9% of the total mass of the lithium hexafluorophosphate and lithium difluorosulfonylimide.

3. The electrolyte according to claim 1, characterized in that, The carbonate solvent is a mixture of methyl ethyl carbonate and ethylene carbonate; the sulfone solvent is one or more of sulfolane, methyl ethyl sulfone, dimethyl sulfone, and diethyl sulfone.

4. The electrolyte according to claim 3, characterized in that, The carbonate solvent accounts for 60% to 99.9% of the total weight of the carbonate solvent and sulfone solvent; the sulfone solvent accounts for 0.1% to 40% of the total weight of the carbonate solvent and sulfone solvent; and the methyl ethyl carbonate accounts for 65% to 99.9% of the weight of the carbonate solvent.

5. The electrolyte according to claim 1, characterized in that, The sulfonamide additives account for 0.01% to 5% of the total weight of the carbonate solvents and sulfone solvents.

6. The electrolyte according to claim 1, characterized in that, The reaction time of alcohol with chlorosulfonic acid at -10 to 15°C is 1 to 3 hours; after adding amines and acid-binding agents to the reaction system, the temperature is controlled at 20 to 30°C and the reaction time is 1 to 1.5 hours.

7. The electrolyte according to claim 1, characterized in that, The acid-binding agent is sodium hydroxide powder or potassium hydroxide powder.

8. The electrolyte according to claim 1, characterized in that, The electrolyte is prepared by the following method: first, a carbonate solvent, a sulfone solvent and a sulfonamide additive are mixed evenly, and then the lithium salt is added to dissolve it; when dissolving the lithium salt, the ambient temperature of the electrolyte is controlled to be 0-10℃.

9. A lithium-ion battery, characterized in that, The battery includes a positive electrode, a negative electrode, a separator, and an electrolyte as described in any one of claims 1 to 8; the positive electrode is a high-nickel ternary cathode material; the negative electrode is lithium metal or graphite; and the battery operates in a voltage range of 2.75V to 4.4V.

10. A method for preparing a sulfonamide additive, characterized in that, include: The alcohol was reacted with chlorosulfonic acid at -10 to 15°C to obtain an intermediate; The alcohol is methanol or ethanol, and the molar ratio of the alcohol to chlorosulfonic acid is 1.05 to 1.2:

1. Without separating the intermediate, the amine and acid-binding agent are directly added to the reaction system, and the pH of the system is controlled to be 9 to 10 to obtain the sulfonamide additive. The amine is dimethylamine or diethylamine.

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