Electrolytes for Supercapacitors and Their Preparation Methods

Abstract

This application provides an electrolyte for supercapacitors and a method for preparing the same. The electrolyte comprises a mixture of an electrolyte functional additive, an organic solvent, and a lithium salt. The general structural formula of the electrolyte functional additive is as follows: ; wherein R1 is independently selected from any one of hydrogen, substituted or unsubstituted alkoxy groups, and sulfate groups; R2 is independently selected from any one of hydrogen and sulfate groups; and R3 is independently selected from any one of hydrogen, aldehyde, cyano, and substituted sulfonyl groups. This additive, through the synergistic effect of multiple functional groups within the molecule, can simultaneously form a stable protective layer at the positive and negative electrode interfaces, effectively inhibiting electrolyte decomposition and transition metal dissolution, and improving interfacial ionic conductivity and mechanical strength. Simultaneously, its specific structure can capture harmful substances in the electrolyte, regulate the lithium-ion solvation structure, significantly improve the high-temperature storage stability, rate performance, and high and low temperature discharge retention rate of supercapacitors, and simultaneously optimize energy density, cycle life, and safety.

Description

Technical Field

[0001] This application relates to the technical field of supercapacitors, and more specifically to electrolytes used in supercapacitors and methods for their preparation. Background Technology

[0002] With the rapid development of high energy density hybrid supercapacitors, their electrolyte systems still face a series of technical bottlenecks and challenges that urgently need to be addressed in practical applications, which seriously restrict the further improvement of device performance and long-term reliability.

[0003] First, under wide voltage window operating conditions, the electrode-electrolyte interface exhibits significantly insufficient stability, easily triggering continuous interfacial side reactions. This leads to the decay of active materials and increased interfacial impedance, resulting in a rapid decline in cycle life. Second, under high-temperature conditions, the lithium hexafluorophosphate (LiPF6) and fluoroethylene carbonate in the electrolyte composition are unstable together, easily decomposing and generating large amounts of gas, causing device gas expansion problems. This not only affects the safety of the physical structure but may also accelerate performance degradation. Furthermore, traditional electrolyte additives have limited functions and cannot synergistically address multiple issues: for example, conventional film-forming additives, while improving the interface, often sacrifice ionic conductivity; flame-retardant additives, while enhancing safety, may deteriorate electrochemical performance. This difficulty in achieving synergistic performance makes simultaneously achieving high energy density, long cycle life, and high safety a significant challenge.

[0004] Furthermore, existing technologies focus solely on optimizing the function of electrolyte additives themselves, neglecting the synergistic adaptation between the post-assembly process and the additives. When a supercapacitor is first assembled, the film formation process of the additives at the electrode interface is often insufficient and uneven, resulting in a high initial interfacial impedance. Unreacted additives are also prone to concentrated decomposition during subsequent cycles, exacerbating localized side reactions. Although some aging processes are used, these are mostly long-term temperature holding at a single temperature, which cannot match the stepwise film-forming characteristics of the additives, making it difficult to achieve interfacial film densification and stabilization, and thus failing to fully utilize the performance advantages of the additives.

[0005] Therefore, there is an urgent need for a solution that combines functional additives with a suitable aging process to simultaneously address issues such as interface stability, high-temperature gas expansion, and performance degradation. Summary of the Invention

[0006] This application proposes an electrolyte for supercapacitors and a method for preparing the same, in order to overcome the deficiencies of the prior art.

[0007] According to a first aspect of the embodiments of this application, an electrolyte for a supercapacitor is provided, the electrolyte comprising a mixture of an electrolyte functional additive, an organic solvent, and a lithium salt, wherein the general structural formula of the electrolyte functional additive is as follows:

[0008] ;

[0009] R1 is independently selected from any one of hydrogen, substituted or unsubstituted alkoxy, and sulfate ester group; R2 is independently selected from any one of hydrogen and sulfate ester group; R3 is independently selected from any one of hydrogen, aldehyde, cyano, and substituted sulfonyl group.

[0010] According to a second aspect of this application, a method for preparing an electrolyte for a supercapacitor as described above is provided, comprising:

[0011] To obtain functional additives for organic solvents, lithium salts, and electrolytes;

[0012] The organic solvent, the lithium salt, and the electrolyte functional additive are mixed and stirred under an inert atmosphere to obtain the electrolyte.

[0013] In some embodiments, the electrolyte functional additive is added to the electrolyte at an amount of 0.5% to 1% of the total mass of the electrolyte.

[0014] In some embodiments, the electrolyte functional additive is selected from at least one of the following compounds:

[0015] ;

[0016] ;

[0017] ;

[0018] ;

[0019] ;

[0020] .

[0021] In some embodiments, mixing and stirring the organic solvent, the lithium salt, and the electrolyte functional additive includes:

[0022] Add auxiliary additives;

[0023] The auxiliary additive includes at least one of 1,3-propenesulfonate lactone and 1,3-propanesulfonate lactone, and the amount of the auxiliary additive added to the electrolyte is 0.5% to 1.5% of the total mass of the electrolyte.

[0024] In some embodiments, the mixing and stirring of the organic solvent, the lithium salt, and the electrolyte functional additive further includes:

[0025] Add lithium salt additives;

[0026] The lithium salt additive includes at least one of lithium difluorophosphate and lithium difluorooxalate borate, and the amount of the lithium salt additive added to the electrolyte is 0.5% to 1.0% of the total mass of the electrolyte.

[0027] In some embodiments, the organic solvent includes cyclic carbonates and chain carbonates;

[0028] Based on the total mass of organic solvents of 100%, the cyclic carbonates include fluoroethylene carbonate and ethylene carbonate, with the total mass percentage of the fluoroethylene carbonate and ethylene carbonate being 20% ​​to 23%; the chain carbonates include dimethyl carbonate at a mass percentage of 50% to 65% and methyl ethyl carbonate at a mass percentage of 15% to 25%.

[0029] In some embodiments, the lithium salt is lithium hexafluorophosphate, and the mass fraction of the lithium salt in the electrolyte is 12% to 15%.

[0030] In some embodiments, the mixing temperature is 5°C to 15°C, and the mixing time is 2 hours to 4 hours.

[0031] In some embodiments, the auxiliary additive is 1,3-propenesulfonate lactone, and the amount of 1,3-propenesulfonate lactone added is 0.5% of the total mass of the electrolyte.

[0032] According to a third aspect of this application, a synergistic aging process for a supercapacitor is provided. This process is implemented after assembling the supercapacitor using the aforementioned electrolyte and is a segmented aging process designed to enhance the interaction between the electrolyte functional additives and the electrode interface. Specifically, it includes:

[0033] 1. First stage of low-temperature pre-aging: Place the assembled supercapacitor in an environment of 30~40℃ and keep it warm for 8~12 hours;

[0034] 2. Second stage of high-temperature deep aging: The supercapacitor that has undergone low-temperature pre-aging is placed in an environment of 50~60℃ and kept at that temperature for 12~24 hours;

[0035] 3. Natural cooling: The supercapacitors that have undergone high-temperature deep aging are allowed to cool naturally to room temperature with the environment, thus completing the synergistic aging process.

[0036] In some embodiments, both stages of the synergistic aging process are carried out in an inert atmosphere (argon or nitrogen) to avoid side reactions caused by contact between the electrolyte and oxygen or moisture during the aging process.

[0037] The beneficial effects of the electrolyte for supercapacitors and its preparation method, as well as the synergistic aging process in the embodiments of this application, include at least the following: The embodiments of this application integrate multiple functional groups into a single molecule through the unique molecular structure of the electrolyte functional additive. The fluorosulfonate group, as a strong electron-withdrawing and reactive group, cooperates with various functional groups (such as alkoxy, sulfate, aldehyde, cyano, substituted sulfonyl, etc.) that can be flexibly selected at the R1, R2, and R3 sites, allowing a single additive molecule to simultaneously undertake multiple tasks such as interfacial film formation, electrolyte stabilization, and improved safety. This overcomes the shortcomings of traditional single-functional additives where performance synergy is difficult to achieve. The additive molecule can preferentially react on the positive and negative electrode surfaces, constructing a stable interfacial protective layer (SEI / CEI film), significantly optimizing electrode interface stability. Based on the high reactivity of the fluorosulfonate group itself, it easily decomposes at the electrode interface to form fluorine- and sulfur-containing inorganic components, improving the density and ionic conductivity of the interfacial film. Through the sulfate group at the R1 site and the R2... The sulfate ester group at the R3 site can further enhance the organic-inorganic composite structure of the interfacial film, especially improving its stability under high temperature and high voltage. This stable interfacial film can effectively inhibit the continuous decomposition of the electrolyte under a wide voltage window, thereby significantly extending the cycle life of the supercapacitor. In this general formula, the optional strong electron-withdrawing group (such as aldehyde, cyano, or substituted sulfonyl group) at the R3 site can significantly improve the antioxidant capacity of the additive molecule itself, thereby increasing the overall decomposition voltage of the electrolyte. This allows the supercapacitor using this electrolyte to operate at a higher operating voltage, laying the foundation for improving energy density. In addition, the selectable range of substituents R1, R2, and R3 in the general formula provides the possibility of customizing the performance of the additive for different supercapacitor systems.

[0038] Furthermore, lithium hexafluorophosphate (LiPF6) and fluoroethylene carbonate (FEC) are unstable together. LiPF6 promotes the decomposition of FEC. LiPF6 reacts with water to decompose into PF5. Under the catalysis of PF5, FEC undergoes ring-opening to form fluorinated polymers. This indicates that FEC-based electrolytes are more prone to decomposition, leading to increased electrolyte acidity. However, the addition of functional additives stabilizes the LiPF6 and FEC system through a synergistic effect of "capturing harmful substances + regulating the interfacial film + stabilizing solvation": on the one hand, cyano groups and methoxy groups capture HF and PF5 generated from LiPF6 hydrolysis, inhibiting their catalytic decomposition of FEC; on the other hand, fluorosulfonyl groups are preferentially reduced on the electrode surface, co-constructing a dense SEI / CEI film with FEC products. Cyano groups can also adsorb onto the positive electrode to inhibit transition metal dissolution and electrolyte oxidation. Simultaneously, fluorosulfonyl groups and methoxy groups regulate the LiPF6 content. + The solvated sheath layer alleviates the damage of FEC to the solvated structure, inhibits the dissociation imbalance of LiPF6, and fundamentally suppresses the side reactions between the two.

[0039] Key Synergistic Effect of Functional Additives and Co-aging Process: One of the core innovations of this application lies in constructing a synergistic system of "functional additive molecular design - segmented aging process adaptation," which achieves ordered and dense film formation of additives through segmented temperature control, maximizing the performance advantages of additives.

[0040] The synergistic effect of the first stage of low-temperature pre-aging: The low-temperature environment of 30~40℃ provides suitable thermodynamic conditions for the preferential adsorption and initial film formation of functional additives, avoiding the problems of slow film formation and uneven distribution of additives at room temperature. In this stage, active functional groups such as cyano groups and fluorosulfonyl groups in the functional additive molecules can be slowly and uniformly adsorbed on the positive and negative electrode surfaces, initially forming a thin interfacial film, laying the foundation for subsequent deep film formation; at the same time, the low-temperature environment can inhibit the rapid hydrolysis of LiPF6, reduce HF generation, avoid excessive consumption of active functional groups by HF, and ensure the effective utilization rate of additives.

[0041] The second stage involves the synergistic effect of high-temperature deep aging: A high-temperature environment of 50-60℃ promotes further decomposition and cross-linking reactions of additive molecules adsorbed on the electrode surface, transforming the initially formed thin interfacial film into a dense and stable organic-inorganic composite SEI / CEI film. Specifically, high temperature accelerates the decomposition of fluorosulfonyloxy groups, generating more fluorine- and sulfur-containing inorganic components (such as LiF and Li2SO3), enhancing the mechanical strength and ionic conductivity of the interfacial film. Simultaneously, the benzene ring structure in the functional additive molecules undergoes slight cross-linking at high temperatures, forming an interpenetrating network structure with the film-forming products of auxiliary additives (such as PST), further improving the stability and anti-swelling ability of the interfacial film. Furthermore, the high-temperature environment allows the PF5 generated from the reaction of residual trace amounts of water in the electrolyte with LiPF6 to be fully captured by the cyano groups of the functional additives, reducing its corrosion of the electrode material and damage to the interfacial film.

[0042] Synergistic Enhancement: The synergistic effect of segmented aging process and functional additives can improve the film formation efficiency of the interface film. Ultimately, this results in: significantly reduced interfacial impedance, improving the rate performance of supercapacitors; enhanced inhibition of electrolyte decomposition by the interface film, reducing gas generation at high temperatures and lowering device gas expansion rate; and improved long-term stability of the interface film, further enhancing the capacity retention of supercapacitors during high-temperature storage and cycling.

[0043] In summary, this application, by introducing functional additives with the specific general structure and combining them with a suitable segmented synergistic aging process, achieves synergistic optimization of interface stability, electrochemical window, high-temperature safety, and long-term reliability through a systematic "material design-process adaptation" approach. This provides key electrolyte and process solutions for the preparation of high-energy-density, long-life supercapacitors. Attached Figure Description

[0044] Figure 1 This is a schematic flowchart illustrating a method for preparing an electrolyte for a supercapacitor according to an embodiment of this application.

[0045] Figure 2 This is a schematic diagram of the current change in the electrochemical window according to an embodiment of this application;

[0046] Figure 3 A schematic diagram illustrating the change in capacity retention rate during high-rate charging according to an embodiment of this application;

[0047] Figure 4 This is a schematic diagram illustrating the change of free acid in an embodiment of this application. Detailed Implementation

[0048] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the embodiments of this application, and not all embodiments. The components of the embodiments of this application described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0049] Therefore, the following detailed description of the embodiments of the present application provided in the accompanying drawings is not intended to limit the scope of the claimed embodiments of the present application, but merely to illustrate selected embodiments of the present application. Other embodiments obtained by those skilled in the art based on the embodiments of the present application without inventive effort are all within the scope of protection of the embodiments of the present application.

[0050] In related technologies, multifunctional electrolyte additives can integrate multiple functional groups through molecular design to achieve synergistic effects in electrode interface regulation, electrolyte stability, and safety protection. For example, their molecules can simultaneously contain reducing groups such as cyano and sulfonate groups, preferentially constructing a nitrogen- / sulfur-rich organic-inorganic composite SEI film on the negative electrode surface to inhibit electrolyte decomposition and broaden the electrochemical window; simultaneously, oxidizing groups such as phosphorus and fluorine can be introduced to form a stable CEI layer at the positive electrode interface, effectively blocking transition metal catalytic side reactions; in addition, flame-retardant units (such as phosphorus and halogens) can be introduced to improve the intrinsic safety of the electrolyte through gas-phase free radical quenching mechanisms, and specially designed conjugated structures can also participate in the formation of the interfacial electric double layer to improve specific capacitance. Such multifunctional additives aim to achieve simultaneous optimization of interfacial stability, electrochemical performance, and safety through intramolecular synergy with multiple effects, providing a key material solution for the development of next-generation high-energy-density, long-life supercapacitors. However, existing technologies have not co-designed the additives with the aging process after device assembly, resulting in poor film formation and the inability to fully realize the performance advantages of the additives.

[0051] This application discloses an electrolyte for supercapacitors and its preparation method, aiming to solve the problems of low capacity decay, low rate discharge, and low high and low temperature discharge retention rate of supercapacitors during high-temperature storage in related technologies.

[0052] The electrolyte comprises a mixture of electrolyte functional additives, organic solvents, and lithium salts.

[0053] In some embodiments, the general structural formula of the electrolyte functional additive is as follows:

[0054] ;

[0055] R1 is independently selected from any one of hydrogen, substituted or unsubstituted alkoxy, and sulfate ester group; R2 is independently selected from any one of hydrogen and sulfate ester group; R3 is independently selected from any one of hydrogen, aldehyde, cyano, and substituted sulfonyl group.

[0056] See attached document Figure 1 As shown, this application discloses a method for preparing an electrolyte for a supercapacitor as described above, the method comprising the following steps 110-120.

[0057] Step 110: Obtain organic solvent, lithium salt and electrolyte functional additive.

[0058] In some embodiments, the electrolyte functional additive is added to the electrolyte at a rate of 0.5% to 1% of the total mass of the electrolyte, by weight percentage.

[0059] In some embodiments, the electrolyte functional additive is selected from at least one of the following compounds:

[0060] Formula I-1, whose compound registration number (CAS) is 1692870-14-6;

[0061] Formula I-2, whose compound registration number (CAS) is 1839621-24-7;

[0062] Formula I-3, whose compound registration number (CAS) is 1839621-08-7;

[0063] Formula I-4, whose compound registration number (CAS) is 2411296-20-1;

[0064] Formula I-5, whose compound registration number (CAS) is 2411294-98-7;

[0065] Formula I-6, whose compound registration number (CAS) is 2411220-25-0.

[0066] In some embodiments, the organic solvent includes cyclic carbonates and chain carbonates.

[0067] For example, based on 100% of the total mass of organic solvent, the cyclic carbonate includes fluoroethylene carbonate and ethylene carbonate, with the total mass of the fluoroethylene carbonate and ethylene carbonate accounting for 20% to 23%; the chain carbonate includes 50% to 65% by mass of dimethyl carbonate and 15% to 25% by mass of ethyl methyl carbonate.

[0068] In some embodiments, the lithium salt is lithium hexafluorophosphate, and the mass fraction of the lithium salt in the electrolyte is 12% to 15%.

[0069] Step 120: Under an inert atmosphere, the organic solvent, the lithium salt, and the electrolyte functional additive are mixed and stirred to obtain the electrolyte.

[0070] In some embodiments, mixing the organic solvent, the lithium salt, and the electrolyte functional additive includes adding an auxiliary additive. The auxiliary additive includes at least one of 1,3-propenesulfonate lactone and 1,3-propanesulfonate lactone, and the amount of the auxiliary additive added to the electrolyte is 0.5% to 1.5% of the total mass of the electrolyte.

[0071] For example, the auxiliary additive is 1,3-propenesulfonate lactone, and the amount of 1,3-propenesulfonate lactone added is 0.5% of the total mass of the electrolyte.

[0072] In some embodiments, mixing and stirring the organic solvent, the lithium salt, and the electrolyte functional additive further includes adding a lithium salt additive. The lithium salt additive includes at least one of lithium difluorophosphate and lithium difluorooxalate borate, and the amount of the lithium salt additive added to the electrolyte is 0.5% to 1.0% of the total mass of the electrolyte.

[0073] In some embodiments, the mixing temperature is 5°C to 15°C, and the mixing time is 2 hours to 4 hours.

[0074] The supercapacitor co-aging process disclosed in the application includes the following steps 210-230:

[0075] Step 210: Assemble the supercapacitor: Assemble the supercapacitor using the above-mentioned electrolyte, positive electrode, negative electrode, and separator;

[0076] Step 220: First stage of low temperature pre-aging: Place the assembled supercapacitor in an argon atmosphere at 30~40℃ and keep it at that temperature for 8~12 hours;

[0077] Step 230: Second stage of high temperature deep aging: Place the supercapacitor that has undergone low temperature pre-aging in an argon atmosphere at 50~60℃ and keep it at that temperature for 12~24h.

[0078] Step 240: Natural cooling: Allow the supercapacitor that has undergone high-temperature deep aging to cool naturally to room temperature with the environment to complete the synergistic aging process.

[0079] This application embodiment utilizes the unique molecular structure of the electrolyte functional additive to integrate multiple functional groups into a single molecule. Simultaneously, a segmented synergistic aging process is employed to achieve a synergistic effect between film formation and interfacial stability. The fluorosulfonate group, as a strongly electron-withdrawing and reactive group, can be combined with various functional groups (such as alkoxy, sulfate, aldehyde, cyano, and substituted sulfonyl groups) that can be flexibly selected at the R1, R2, and R3 sites. This allows a single additive molecule to simultaneously undertake multiple tasks such as interfacial film formation, electrolyte stabilization, and enhanced safety, overcoming the shortcomings of traditional single-functional additives where performance synergy is difficult to achieve. This additive molecule can preferentially react on the positive and negative electrode surfaces, constructing a robust interfacial protective layer (SEI / CEI film), significantly optimizing electrode interfacial stability. Based on the high reactivity of the fluorosulfonate group itself, it easily decomposes at the electrode interface during aging to form fluorine- and sulfur-containing inorganic components, improving the density and ionic conductivity of the interfacial film. Through the sulfate group at the R1 site and… The sulfate ester group at the R2 site further enhances the organic-inorganic composite structure of the interfacial film, particularly improving its stability under high temperature and high voltage. This stable interfacial film effectively inhibits the continuous decomposition of the electrolyte within a wide voltage window, thus significantly extending the cycle life of the supercapacitor. In this general structure, the optional strong electron-withdrawing groups (such as aldehydes, cyanos, or substituted sulfonyl groups) at the R3 site can significantly improve the antioxidant capacity of the additive molecule itself, thereby increasing the overall decomposition voltage of the electrolyte. This allows supercapacitors using this electrolyte to operate at higher operating voltages, laying the foundation for improved energy density. Furthermore, the selectable range of substituents for R1, R2, and R3 in the general formula provides the possibility for customized adjustment of additive performance for different supercapacitor systems. In summary, this application, by introducing functional additives with this specific general structure and a suitable synergistic aging process, achieves synergistic optimization of interfacial stability, electrochemical window, and overall compatibility through a systematic "materials-process" design scheme, providing a key electrolyte and process solution for the preparation of high-energy-density, long-life supercapacitors. The following embodiments of this application disclose an electrolyte for supercapacitors, its preparation method, and a specific implementation process of a synergistic aging process. This specific implementation process includes Examples 1-20 and Comparative Examples 1-4. Example 1: Based on the mass percentage of the components, the electrolyte formulation used in this example is as follows: Electrolyte functional additive (Formula I-2): 0.5%, LiODFB: 0.5%, PST: 0.5%, LiPF6: 15%, with the remainder being organic solvent components. The organic solvent components in the above electrolyte formulation consist of fluoroethylene carbonate, ethylene carbonate, dimethyl carbonate, and methyl ethyl carbonate. Based on the total volume of the organic solvent being 100%, the volume percentage of fluoroethylene carbonate is 2%, ethylene carbonate is 21%, dimethyl carbonate is 55%, and methyl ethyl carbonate is 22%.The electrolyte was prepared by the following method: under an argon atmosphere, the compound shown in Formula I-2, lithium difluorooxalate borate, 1,3-propenesulfonate lactone, and lithium hexafluorophosphate were added to an organic solvent formed by mixing fluoroethylene carbonate, methyl ethyl carbonate, ethylene carbonate, and dimethyl carbonate, and the mixture was stirred at 10°C for 3 hours to obtain the electrolyte.

[0080] The supercapacitor assembly and aging process includes, for example: using graphite as the negative electrode active material, preparing a negative electrode slurry by mixing graphite, conductive agent, and binder in a mass percentage of 97.4:1.5:1.1, coating the negative electrode slurry onto a copper foil current collector, and vacuum drying to obtain a negative electrode sheet; using NCM811-blended activated carbon as the positive electrode active material, preparing a positive electrode slurry by mixing the positive electrode active material, conductive agent, and binder in a mass ratio of 96.5:1.7:1.8, coating the positive electrode slurry onto an aluminum foil current collector, and vacuum drying to obtain a positive electrode sheet; assembling the supercapacitor with the above electrolyte, the above positive electrode sheet, the negative electrode sheet, and the separator; and then implementing a synergistic aging process: holding at 35℃ for 10 hours (low-temperature pre-aging), holding at 55℃ for 18 hours (high-temperature deep aging), and naturally cooling to room temperature.

[0081] Example 2: In this example, the amount of electrolyte functional additive added is used as a variable. The amount of electrolyte functional additive added is 0.7%, and the rest is the same as in Example 1.

[0082] Example 3: In this example, the amount of electrolyte functional additive added is used as a variable. The amount of electrolyte functional additive added is 1%, and the rest is the same as in Example 1.

[0083] Example 4: The electrolyte functional additive in this example is the compound shown in Formula I-3, and the addition amount is 0.5%. The rest is the same as in Example 1.

[0084] Example 5: The electrolyte functional additive in this example is the compound shown in Formula I-4, and the addition amount is 0.5%, and the rest is the same as in Example 1.

[0085] Example 6: The electrolyte functional additive in this example is the compound shown in Formula I-5, and the addition amount is 0.5%, and the rest is the same as in Example 1.

[0086] Example 7: The electrolyte functional additive in this example is the compound shown in Formula I-6, with an addition amount of 0.5%, and the rest is the same as in Example 1.

[0087] Example 8: This example uses the electrolyte formulation used in Example 1 as a reference, and the amount of sulfur-containing additives included in the formulation as a variable. The difference from Example 1 is that the amount of PST added is adjusted to 0.7%, and the rest is the same as Example 1.

[0088] Example 9: This example uses the electrolyte formulation used in Example 1 as a reference, and the amount of sulfur-containing additives included in the formulation as a variable. The difference from Example 1 is that the amount of PST added is adjusted to 1%, and the rest is the same as Example 1.

[0089] Example 10: This example uses the electrolyte formulation used in Example 1 as a reference, and the sulfur-containing additives included in the formulation as variables. The difference from Example 1 is that PST is replaced with PS, and the amount added is 0.5%. Everything else is the same as in Example 1.

[0090] Example 11: This example uses the electrolyte formulation used in Example 1 as a reference, and the types of lithium salt additives included in the formulation as variables. The difference from Example 1 is that the amount of LiODFB added is 1%, and the rest is the same as Example 1.

[0091] Example 12: This example uses the electrolyte formulation used in Example 1 as a reference, and the types of lithium salt additives included in the formulation as variables. The difference from Example 1 is that the amount of LiODFB added is 0.5%, and lithium difluorophosphate is added at the same amount of 0.5%. Everything else is the same as in Example 1.

[0092] Example 13: This example uses the electrolyte formulation used in Example 1 as a reference, and the content of lithium hexafluorophosphate included in the formulation as a variable. The difference from Example 1 is that the content of lithium hexafluorophosphate is adjusted to 13.5%, and the content of the organic solvent component is reduced by the same mass. Everything else is the same as in Example 1.

[0093] Example 14: This example uses the electrolyte formulation used in Example 1 as a reference, and the content of lithium hexafluorophosphate in the formulation is used as a variable. The difference from Example 1 is that the content of lithium hexafluorophosphate is adjusted to 12%, and the content of the organic solvent component is reduced by the same mass. Everything else is the same as in Example 1.

[0094] Example 15: This example uses the low-temperature pre-aging temperature of the synergistic aging process as a variable. The difference from Example 1 is that the low-temperature pre-aging temperature is adjusted to 30°C and the holding time is 12 hours. Everything else is the same as Example 1.

[0095] Example 16: This example uses the low-temperature pre-aging temperature of the synergistic aging process as a variable. The difference from Example 1 is that the low-temperature pre-aging temperature is adjusted to 40°C and the holding time is 8 hours. The rest is the same as Example 1.

[0096] Example 17: This example uses the high temperature deep aging temperature of the synergistic aging process as a variable. The difference from Example 1 is that the high temperature deep aging temperature is adjusted to 50°C and the holding time is 24 hours. Everything else is the same as Example 1.

[0097] Example 18: This example uses the high temperature deep aging temperature of the synergistic aging process as a variable. The difference from Example 1 is that the high temperature deep aging temperature is adjusted to 60°C and the holding time is 12 hours. The rest is the same as Example 1.

[0098] Example 19: This example uses "no low-temperature pre-aging" as the variable. The difference from Example 1 is that only high-temperature aging at 55°C for 18 hours is performed, without the low-temperature pre-aging step. Everything else is the same as Example 1.

[0099] Example 20: This example uses "single high-temperature aging" as the variable. The difference from Example 1 is that the aging process is replaced with 55℃ holding for 28 hours (single high-temperature aging, the total time is the same as the total time of the two aging stages in Example 1). Everything else is the same as Example 1.

[0100] Comparative Example 1: The only difference between this comparative example and Example 1 is that the comparative example does not contain electrolyte functional additives, and the electrolyte functional additives in the electrolyte formulation of Example 1 are replaced by organic solvent components of equal mass. Otherwise, it is the same as Example 1.

[0101] Comparative Example 2: This comparative example uses the electrolyte formulation of Comparative Example 1 as a reference. The difference from Comparative Example 1 is that benzenesulfonyl fluoride was added to the formulation of Comparative Example 1 at a dosage of 0.5%. All other aspects are the same as Comparative Example 1. The general formula of benzenesulfonyl fluoride is shown below:

[0102] .

[0103] Comparative Example 3: The only difference between this comparative example and Example 1 is that no aging process is performed after the supercapacitor is assembled; otherwise, it is the same as Example 1.

[0104] Comparative Example 4: The only difference between this comparative example and Example 1 is that the synergistic aging process is replaced with aging at room temperature of 25°C for 28 hours (the total time is the same as the total aging time of the two stages in Example 1), and everything else is the same as Example 1.

[0105] In this application, the electrolytes prepared in Examples 1-20 and Comparative Examples 1-4 were used to assemble supercapacitors with the aforementioned positive electrode, negative electrode, and separator. The supercapacitors were then subjected to initial DCR and capacity retention tests at 60°C for 30 days. For example, the specific results of the supercapacitor's test data are shown in Table 1 below:

[0106] Table 1: Results of Examples and Comparative Examples

[0107]

[0108] The verification of the effects of the functional additives included, for example, a comparison between Comparative Example 1 and Example 1. It was found that without the electrolyte functional additive described in this application, the initial DCR of the supercapacitor was as high as 11.5 mΩ, the capacity retention rate after 30 days of storage at 60°C was only 78.2%, and the gas expansion rate was 6.8%. However, in Example 1, with the addition of 0.5% of the I-2 functional additive, the initial DCR decreased to 8.5 mΩ, the capacity retention rate increased to 91.5%, and the gas expansion rate was only 2.1%. This indicates that the functional additive of this application can significantly reduce interfacial impedance and suppress electrolyte decomposition and gas generation at high temperatures by forming a stable SEI / CEI film at the electrode interface, thereby improving the storage stability of the device. Meanwhile, Comparative Example 2, using a traditional benzenesulfonyl fluoride additive, had an initial DCR of 10.3 mΩ, a capacity retention rate of 82.6%, and a gas expansion rate of 5.5%, all inferior to Example 1. This demonstrates that the multi-functional group synergistic design (fluorosulfonyloxy, cyano, etc.) of the functional additive of this application has advantages over traditional single-functional additives in terms of interface regulation and electrolyte stability.

[0109] The key role of the synergistic aging process is, but is not limited to, the following: A comparison of Example 1 with Comparative Examples 3 and 4 clearly shows the impact of the aging process: Comparative Example 3, without aging, had an initial DCR of 10.8 mΩ, a capacity retention rate of 80.5%, and a gas expansion rate of 5.9%; Comparative Example 4, aged at room temperature, had an initial DCR of 10.2 mΩ, a capacity retention rate of 83.3%, and a gas expansion rate of 5.2%; while Example 1, using the synergistic aging process of "35℃ pre-aging for 10 h + 55℃ deep aging for 18 h," showed significantly optimized performance in all aspects. This is because segmented synergistic aging enables the orderly film formation of additives: the low-temperature pre-aging stage allows functional additives to be uniformly adsorbed onto the electrode surface, initially constructing a thin interfacial film; the high-temperature deep aging stage promotes the full decomposition and cross-linking of additives, forming a dense and stable organic-inorganic composite film, thereby maximizing the performance advantages of the additives.

[0110] The influence of aging process parameters, for example, is as follows: Examples 15-18 verified the rationality of the process window by adjusting the temperature and time parameters of the synergistic aging process. Specifically, within the parameter range of 30-40℃ pre-aging for 8-12 hours and 50-60℃ deep aging for 12-24 hours (Examples 1, 15-18), the initial DCR was below 8.9 mΩ, the capacity retention rate was above 90.3%, and the gas expansion rate was below 2.6%, demonstrating stable performance. However, Example 19, lacking low-temperature pre-aging, only underwent aging at 55℃ for 18 hours, resulting in an initial DCR of 9.5 mΩ, a capacity retention rate of 88.6%, and a gas expansion rate of 3.1%. Example 20, employing only high-temperature aging (55℃ for 28 hours), had an initial DCR of 9.3 mΩ, a capacity retention rate of 89.2%, and a gas expansion rate of 2.9%, all inferior to Example 1. This demonstrates that the segmented synergistic mode of "low-temperature pre-aging + high-temperature deep aging" can avoid problems such as uneven film formation and insufficient film density caused by single-temperature aging, and is a key process step to ensure the high performance of devices.

[0111] The synergistic effect of process and materials is illustrated by the comprehensive data from Examples 1-3 and 15-18, which show that when the functional additives and synergistic aging process are compatible, the device can stably achieve excellent performance with "initial DCR ≤ 8.9 mΩ, capacity retention ≥ 90.3% after 30 days of storage at 60℃, and gas expansion rate ≤ 2.6%". The absence or replacement of either component leads to significant performance degradation, fully demonstrating the scientific validity and necessity of the systematic approach of "material molecular design - process adaptation" in this application, and providing reliable material and process support for the fabrication of high-stability supercapacitors.

[0112] from Figures 2-4 It is known that using this functional additive can also broaden the electrochemical window, improve rate charging performance, and inhibit acidity growth, which is mainly attributed to the synergistic effect of the functional additive and the aging process.

[0113] It is understood that the above embodiments are merely exemplary implementations used to illustrate the principles of this application, and this application is not limited thereto. For those skilled in the art, various modifications and improvements can be made without departing from the spirit and substance of this application, and these modifications and improvements are also considered to be within the scope of protection of this application.

Claims

1. An electrolyte for supercapacitors, characterized in that, The electrolyte comprises a mixture of electrolyte functional additives, organic solvents, and lithium salts. The general structural formula of the electrolyte functional additives is as follows: ； R1 is independently selected from any one of hydrogen, substituted or unsubstituted alkoxy, and sulfate ester group; R2 is independently selected from any one of hydrogen and sulfate ester group; R3 is independently selected from any one of hydrogen, aldehyde, cyano, and substituted sulfonyl group.

2. A method for preparing the electrolyte for supercapacitors as described in claim 1, characterized in that, include: To obtain functional additives for organic solvents, lithium salts, and electrolytes; The organic solvent, the lithium salt, and the electrolyte functional additive are mixed and stirred under an inert atmosphere to obtain the electrolyte.

3. The method according to claim 2, characterized in that, The electrolyte functional additive is added to the electrolyte at a rate of 0.5% to 1% of the total mass of the electrolyte.

4. The method according to claim 2, characterized in that, The electrolyte functional additive is selected from at least one of the following compounds: ； ； ； ； ； 。 5. The method according to claim 2, characterized in that, The step of mixing and stirring the organic solvent, the lithium salt, and the electrolyte functional additive includes: Add auxiliary additives; The auxiliary additive includes at least one of 1,3-propenesulfonate lactone and 1,3-propanesulfonate lactone, and the amount of the auxiliary additive added to the electrolyte is 0.5% to 1.5% of the total mass of the electrolyte.

6. The method according to claim 2, characterized in that, The step of mixing and stirring the organic solvent, the lithium salt, and the electrolyte functional additive further includes: Add lithium salt additives; The lithium salt additive includes at least one of lithium difluorophosphate and lithium difluorooxalate borate, and the amount of the lithium salt additive added to the electrolyte is 0.5% to 1.0% of the total mass of the electrolyte.

7. The method according to claim 2, characterized in that, The organic solvents include cyclic carbonates and chain carbonates; Based on the total mass of organic solvents of 100%, the cyclic carbonates include fluoroethylene carbonate and ethylene carbonate, with the total mass percentage of the fluoroethylene carbonate and ethylene carbonate being 20% ​​to 23%; the chain carbonates include dimethyl carbonate at a mass percentage of 50% to 65% and methyl ethyl carbonate at a mass percentage of 15% to 25%.

8. The method according to claim 2, characterized in that, The lithium salt is lithium hexafluorophosphate, and the mass fraction of the lithium salt in the electrolyte is 12% to 15%.

9. The method according to claim 2, characterized in that, The mixing temperature is 5°C to 15°C, and the mixing time is 2 hours to 4 hours.

10. The method according to claim 5, characterized in that, The auxiliary additive is 1,3-propenesulfonate lactone, and the amount of 1,3-propenesulfonate lactone added is 0.5% of the total mass of the electrolyte.

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