Electrolyte additive for aluminum foil and application thereof

Abstract

The invention belongs to the technical field of electrolyte additives, and discloses an electrolyte additive for aluminum foil and application thereof.The electrolyte additive for aluminum foil comprises an organic solvent, electrolyte lithium salt, a sulfur-containing additive and a compound, and the organic solvent comprises cyclic carbonate and chain carbonate; the cyclic carbonate comprises at least one of ethylene carbonate and propylene carbonate, the chain carbonate comprises two or three of diethyl carbonate, dimethyl carbonate and methyl ethyl carbonate, and the total mass ratio of the cyclic carbonate to the chain carbonate is (35-45): (55-65); according to the invention, the problem that the lithium bis (fluorosulfonyl) imide corrodes the aluminum foil under high voltage in the prior art is solved, and the comprehensive performance of the supercapacitor can be improved.

Description

Technical Field

[0001] This invention relates to the field of electrolyte additives, and more specifically to an electrolyte additive for aluminum foil and its application. Background Technology

[0002] Supercapacitors are a new type of high-performance energy storage device, falling between traditional capacitors and batteries. Their core advantages lie in their extremely high power density, enabling rapid charging and discharging within seconds, and a cycle life of hundreds of thousands of cycles, far exceeding that of batteries. They store energy through electrostatic adsorption on the electrode surface (double-layer principle) or rapid redox reactions (pseudocapacitance). No chemical reactions occur during charging and discharging, resulting in high efficiency, low heat generation, and good safety. They are primarily used in scenarios requiring instantaneous high power, such as energy recovery in electric vehicles, braking energy storage in rail transit, power compensation in smart grids, and backup power for consumer electronics, overcoming the shortcomings of insufficient battery power and low energy density of traditional capacitors.

[0003] In recent years, high-voltage supercapacitor technology has received widespread attention as a key pathway to improve the energy density of electrochemical energy storage devices. With the increasingly urgent need for higher energy density supercapacitors, continuously increasing the operating voltage has become a crucial step. Lithium bisfluorosulfonyl imide (LiFSI) is considered an ideal lithium salt to replace traditional lithium hexafluorophosphate (LiPF6) due to its excellent ionic conductivity, thermal stability, and superior film-forming ability at the anode interface.

[0004] However, LiFSI performs better at high voltages (typically >4.2V vs. Li / Li). + Under certain conditions, the aluminum foil current collector will be severely corroded, a fatal flaw that severely restricts its application in advanced supercapacitor systems such as high-voltage ternary capacitors (e.g., NCM811, NCA). In existing technologies, while using a mixed salt of LiFSI and LiPF6 can alleviate corrosion to some extent, it sacrifices the high conductivity advantage of LiFSI; adding conventional corrosion inhibitors has limited effectiveness or negatively impacts the overall electrochemical performance of the supercapacitor.

[0005] Therefore, developing a novel additive that can efficiently inhibit the corrosion of aluminum foil by LiFSI without affecting or even improving the overall performance of supercapacitors has become a technical challenge that urgently needs to be overcome in this field. Summary of the Invention

[0006] The purpose of this invention is to provide an electrolyte additive for aluminum foil and its application, so as to overcome the problems existing in the prior art. This invention solves the problem of lithium bis(fluorosulfonyl)imide corroding aluminum foil under high voltage in the prior art, and can also improve the overall performance of supercapacitors.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: In a first aspect, the present invention provides a compound for aluminum foil having the structure shown in general formula I (CAS: 145193-98-2):

[0008] General formula I.

[0009] In a second aspect, the present invention provides an electrolyte additive for aluminum foil, comprising: Organic solvents, lithium electrolytes, sulfur-containing additives, and compounds.

[0010] In some embodiments, the organic solvent includes cyclic carbonates and chain carbonates.

[0011] In some embodiments, the cyclic carbonate includes at least one of ethylene carbonate and propylene carbonate; The chain carbonates include two or three of diethyl carbonate, dimethyl carbonate, and methyl ethyl carbonate.

[0012] In some embodiments, the total mass of the cyclic carbonate and the chain carbonate is (35-45):(55-65).

[0013] In some embodiments, the sulfur-containing additive includes at least one of vinyl sulfate (DTD), methylene methane disulfonate (MMDS), and 1,3-propenesulfonate lactone (PST); The electrolyte lithium salt is lithium hexafluorophosphate.

[0014] In some embodiments, a lithium salt additive is further included, wherein the lithium salt additive includes at least one of lithium difluorophosphate (LiPO2F2) and lithium bis(oxalatoborate) (LiBOB).

[0015] In some embodiments, the mass ratio of the compound, the sulfur-containing additive, and the lithium salt additive is (0.8–1.5):(1.8–3):(3.5–4.8).

[0016] In some embodiments, the electrolyte lithium salt is lithium hexafluorophosphate (LiPF6), and the mass percentage of the electrolyte lithium salt is 10% to 15%.

[0017] Thirdly, the present invention provides an application of an electrolyte additive for aluminum foil in a supercapacitor.

[0018] The above technical solution has the following advantages or beneficial effects: In a first aspect, the present invention provides a compound for aluminum foil, wherein the aluminum oxide (Al2O3) passivation film on the surface of the aluminum foil is a protective layer, and under high voltage, FSI- The anion undergoes oxidative decomposition to produce fluoride ions (F). - ); F - It reacts with aluminum oxide (Al₂O₃ + 6F₂) - + 3H₂O → 2AlF₃ + 6OH⁻ - This process dissolves the protective film, and after the passivation film is partially damaged, the underlying active aluminum substrate is exposed to the electrolyte, undergoing oxidation and dissolution under high voltage: Al → Al³ + + 3e - Al³ + It will react with components in the electrolyte (such as FSI) - The benzoindoline cation combines with the lithium to form a complex (such as Al(FSI)3), which further hydrolyzes to produce products such as AlF3, causing a sharp increase in DCR and resulting in a rapid drop in the cycle. The benzoindoline cation carries a positive charge, which preferentially adsorbs onto the surface of the negatively charged aluminum foil current collector (relative to the increased lithium potential) through electrostatic interactions. This adsorption forms an initial, dynamic "molecular barrier" that can block free FSI in the electrolyte. - Anions directly approach the alumina passivation film on the aluminum foil surface, thus mitigating FSI from the very first step. - Chemical attack on the passivation film; as the voltage continues to rise into the operating window of the ternary supercapacitor (typically >4.2V vs. Li / Li), + Benzoindoline cations undergo preferential electrochemical oxidation at a specific, lower potential before the basic electrolyte solvent and LiFSI salt decompose. This oxidation reaction is usually irreversible, and its decomposition products are deposited in situ and uniformly on the aluminum foil surface. This newly formed film is tightly bonded to the aluminum foil, making up for the defects of the natural alumina film and forming a denser and more stable artificial protective layer.

[0019] Secondly, this invention provides an electrolyte additive for aluminum foil. By introducing a specific compound, which works synergistically with sulfur-containing additives, lithium electrolyte salts, and organic solvents, the corrosion resistance of aluminum foil in high-voltage electrolytes is significantly improved. This compound preferentially adsorbs on the aluminum foil surface and forms a dense and stable protective film, effectively inhibiting electrolyte decomposition and the corrosion of aluminum foil by hydrogen fluoride. At the same time, the sulfur-containing additive helps to form a more robust cathode interface layer, further enhancing the electrochemical stability of the aluminum foil. This synergistic effect enables lithium-ion batteries using this additive to have better cycle life and capacity retention, especially under high-voltage operating conditions, while effectively preventing battery performance degradation and safety hazards caused by aluminum foil corrosion.

[0020] In some embodiments, the electrolyte additive of the present invention, through the use of an organic solvent system combining cyclic carbonates and chain carbonates, produces a significant synergistic effect with the compound and other components. Cyclic carbonates (such as ethylene carbonate) have high dielectric constants, which can effectively promote lithium salt dissociation and participate in the formation of a stable and dense SEI film. Chain carbonates (such as dimethyl carbonate) provide lower viscosity, which greatly improves the low-temperature performance and ionic conductivity of the electrolyte. The combination of the two achieves efficient ion transport over a wide temperature range while ensuring film quality. This solvent system provides an optimal medium environment for the compound and sulfur-containing additives to fully exert their synergistic protective effect on aluminum foil and inhibit corrosion, thereby jointly ensuring the excellent long-cycle stability and safety of the battery, especially the high-voltage battery.

[0021] In some embodiments, the electrolyte additive of the present invention achieves deep synergy and performance optimization of each component by specifically defining the types and compounding methods of cyclic and chain carbonates; the selected ethylene carbonate and / or propylene carbonate can form a tough interfacial protective layer, while the chain carbonates (at least two compounded) create an ideal medium environment with both high ionic conductivity and a wide liquid range through synergistic solubilization and viscosity reduction; this solvent system not only ensures the full dissolution and efficient migration of lithium salt and functional additives, but more importantly, it provides the best reaction and mass transfer conditions for the compound and sulfur-containing additives to jointly construct a uniform, dense and stable composite protective film on the aluminum foil surface, thereby effectively inhibiting aluminum foil corrosion even under extreme voltage and temperature, and comprehensively improving the high-voltage life and safety reliability of the battery.

[0022] In some embodiments, the electrolyte additive of the present invention achieves an optimal balance between high dielectric constant and low viscosity in the solvent system by precisely controlling the mass ratio of cyclic carbonate to chain carbonate at (35-45):(55-65). This ratio ensures that the cyclic carbonate is sufficient to fully dissolve lithium salt and synergistically form a stable and dense SEI / CEI film with the film-forming additive. At the same time, the sufficient amount of chain carbonate effectively reduces the viscosity of the system, ensuring extremely high ionic conductivity and excellent wettability. This optimized ratio creates an ideal mass transfer environment for the uniform adsorption and efficient collaboration of the compound and sulfur-containing additive at the electrode interface (especially the aluminum foil surface), enabling it to quickly build a robust passivation layer, thereby achieving ultimate suppression of aluminum foil corrosion under high pressure conditions and significantly improving the rate performance, cycle stability and high-temperature storage performance of the battery.

[0023] In some embodiments, the electrolyte additive of the present invention specifically defines the sulfur-containing additive as at least one of vinyl sulfate (DTD), methylene disulfonate (MMDS), and 1,3-propenesulfonate lactone (PST), and generates multiple composite effects with lithium hexafluorophosphate electrolyte salt and compounds. These sulfur-containing additives preferentially undergo electrochemical reduction / oxidation on the surfaces of the negative and positive electrode aluminum foils, participating in the construction of a robust, dense, and high-quality interface protective film rich in sulfides / sulfonates. This interface film can effectively inhibit the etching of aluminum foil by hydrogen fluoride generated by the decomposition of lithium hexafluorophosphate in the presence of trace amounts of water. At the same time, it synergistically complements the protective layer formed by the compounds, jointly constructing a highly efficient barrier. Thus, under harsh conditions such as high pressure and high temperature, it greatly improves the corrosion resistance and electrochemical window stability of the aluminum foil, ensuring the battery's excellent long cycle life and safety performance.

[0024] In some embodiments, the electrolyte additive of the present invention achieves optimal synergy among core functional components by precisely limiting the mass ratio of the compound, sulfur-containing additive, and lithium salt additive to (0.8–1.5):(1.8–3):(3.5–4.8). Under this golden ratio, the competitive adsorption and reaction of the three additives at the electrode interface (especially the aluminum foil surface) reach a dynamic equilibrium, enabling them to quickly and orderly construct a multidimensional composite protective film with high ionic conductivity, excellent chemical stability, and superior mechanical strength. This composite film has distinct layers and a dense structure, effectively blocking electrolyte corrosion and HF attack in all aspects, while ensuring efficient lithium-ion conduction. The synergistic effect fundamentally suppresses corrosion perforation and interfacial impedance growth of the aluminum foil, thereby endowing high-voltage lithium-ion batteries with unprecedented cycle life, rate performance, and safety reliability.

[0025] In some embodiments, the electrolyte additive of the present invention achieves an optimal balance between ensuring sufficient ionic conductivity and optimal interfacial film formation by precisely controlling the concentration of lithium hexafluorophosphate (LiPF6) at 10%~15%. This concentration range provides sufficient free lithium ions to ensure the rate performance of the battery while avoiding the increase in viscosity and decrease in ion mobility caused by excessively high concentrations. More importantly, this concentration can produce deep synergy with precisely proportioned functional additives, providing an ideal ionic environment for them to efficiently and orderly synergistically construct a highly stable multidimensional composite protective film at the electrode interface, thereby fundamentally enhancing the anti-corrosion effect on aluminum foil and jointly ensuring the excellent high-voltage and cycle performance of the battery.

[0026] Thirdly, this invention provides an application of an electrolyte additive for aluminum foil in a supercapacitor. This application applies the aforementioned electrolyte additive to a supercapacitor, and through the synergistic effect of the components, a dense and stable composite protective film is constructed on the surface of the aluminum foil current collector, significantly enhancing its resistance to electrolyte corrosion under high voltage, high frequency and wide temperature range conditions. This application can effectively suppress capacitance decay, reduce internal resistance and greatly improve cycle life, providing a key material solution for the development of advanced supercapacitors with high energy density and long life. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the general formula I structure of an electrolyte additive for aluminum foil according to some embodiments of this specification. Detailed Implementation

[0028] In the following description, only certain exemplary embodiments are briefly described. As those skilled in the art will recognize, the described embodiments can be modified in various ways without departing from the spirit or scope of the invention. Therefore, the drawings and description are considered to be exemplary in nature and not restrictive.

[0029] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0030] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] Figure 1 This is a schematic diagram of a general formula I structure for an electrolyte additive for aluminum foil, as shown in some embodiments of this specification. The main objective of this invention is to provide a lithium salt, electrolyte, and supercapacitor for passivating aluminum foil, so as to solve the problem of capacitance drop caused by increased impedance due to aluminum foil corrosion in related technologies.

[0032] Example 1: This embodiment provides an electrolyte additive for aluminum foil. According to the mass percentage of the components, the electrolyte additive used in this embodiment consists of: 83.9% organic solvent, 1.8% sulfur-containing additive, 3.5% lithium salt additive, 10% electrolyte lithium salt, and 0.8% a compound for aluminum foil. The organic solvent is composed of cyclic carbonates and chain carbonates. Calculated with the total mass of the organic solvent as 100%, the ratio of the total mass of cyclic carbonates to the total mass of chain carbonates is 35:65. The cyclic carbonates are a mixture of 25% ethylene carbonate (EC) and 10% propylene carbonate (PC), and the chain carbonates are a mixture of 45% diethyl carbonate (DEC) and 20% dimethyl carbonate (DMC). The electrolyte lithium salt is 10% lithium hexafluorophosphate (LiPF6). The sulfur-containing additive is 1.8% vinyl sulfate (DTD); The lithium salt additive is 3.5% lithium difluorophosphate (LiPO2F2). The 0.8% compound for aluminum foil has the structure shown in general formula I:

[0033] General formula I.

[0034] The method for preparing an electrolyte additive for aluminum foil provided in this embodiment is as follows: Step 1: Synthesize a chlorinated, methylated acridine precursor, using 5-chloro-1-methylacridinium as the core structure, through electrophilic substitution or nitrogen quaternization reactions. Raw materials: 5-chloroacridinium, methylating agent (e.g., iodomethane), organic solvent (e.g., acetonitrile). Reaction process: Dissolve 5-chloroacridinium in acetonitrile, add excess iodomethane, and heat under reflux for several hours to methylate the nitrogen atom on the acridine ring, generating 5-chloro-1-methylacridinium iodomonium salt.

[0035] Step 2: Preparation of trifluoroborate by ion exchange; iodide ions are replaced with trifluoroborate ions through an ion exchange reaction. Raw materials: 5-chloro-1-methylacridinium iodide, sodium tetrafluoroborate, water or methanol. Reaction process: Dissolve 5-chloro-1-methylacridinium iodide in water (or methanol), add an equal amount of sodium tetrafluoroborate, stir for a period of time, and the product (target compound) will precipitate due to its low solubility. After filtration, washing, and drying, 5-chloro-1-methylacridinium trifluoroborate (the compound mentioned in the question) is obtained.

[0036] The following embodiment provides a method for preparing an electrolyte additive for aluminum foil: In an argon-filled glove box (water content <10 ppm, oxygen content <1 ppm), ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and dimethyl carbonate (DMC) are first mixed according to the above proportions to form an organic solvent component. Subsequently, under continuous stirring, lithium hexafluorophosphate (LiPF6), ethylene sulfate (DTD), lithium difluorophosphate (LiPO2F2), and the compound are added to the organic solvent in sequence until all components are completely dissolved and a homogeneous, clear electrolyte additive for flame retardancy is formed.

[0037] Example 2: This embodiment provides an electrolyte additive for aluminum foil. According to the mass percentage of the components, the electrolyte additive used in this embodiment consists of: 75.7% organic solvent, 3% sulfur-containing additive, 4.8% lithium salt additive, 15% electrolyte lithium salt, and 1.5% a compound for aluminum foil. The organic solvent is composed of cyclic carbonates and chain carbonates. Calculated with the total mass of the organic solvent as 100%, the ratio of the total mass of cyclic carbonates to the total mass of chain carbonates is 45:55. The cyclic carbonates are a mixture of 25% ethylene carbonate (EC) and 20% propylene carbonate (PC), and the chain carbonates are a mixture of 20% diethyl carbonate (DEC), 20% dimethyl carbonate (DMC), and 15% ethyl methyl carbonate (EMC). The electrolyte lithium salt is 15% lithium hexafluorophosphate (LiPF6). The sulfur-containing additive is 3% methylene disulfonate (MMDS). The lithium salt additive is 4.8% lithium bis(oxalato)borate (LiBOB). The 0.8% compound for aluminum foil has the structure shown in general formula I:

[0038] General formula I.

[0039] The method for preparing an electrolyte additive for aluminum foil provided in this embodiment is as follows: Step 1: Synthesize a chlorinated, methylated acridine precursor, using 5-chloro-1-methylacridinium as the core structure, through electrophilic substitution or nitrogen quaternization reactions. Raw materials: 5-chloroacridinium, methylating agent (e.g., iodomethane), organic solvent (e.g., acetonitrile). Reaction process: Dissolve 5-chloroacridinium in acetonitrile, add excess iodomethane, and heat under reflux for several hours to methylate the nitrogen atom on the acridine ring, generating 5-chloro-1-methylacridinium iodomonium salt.

[0040] Step 2: Preparation of trifluoroborate by ion exchange; iodide ions are replaced with trifluoroborate ions through an ion exchange reaction. Raw materials: 5-chloro-1-methylacridinium iodide, sodium tetrafluoroborate, water or methanol. Reaction process: Dissolve 5-chloro-1-methylacridinium iodide in water (or methanol), add an equal amount of sodium tetrafluoroborate, stir for a period of time, and the product (target compound) will precipitate due to its low solubility. After filtration, washing, and drying, 5-chloro-1-methylacridinium trifluoroborate (the compound mentioned in the question) is obtained.

[0041] The following embodiment provides a method for preparing an electrolyte additive for aluminum foil: In an argon-filled glove box (water content <10 ppm, oxygen content <1 ppm), ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) are mixed according to the above proportions to form an organic solvent component. Subsequently, under continuous stirring, lithium hexafluorophosphate (LiPF6), methylene disulfonate (MMDS), lithium bis(oxalato)borate (LiBOB), and the compound are added sequentially to the organic solvent until all components are completely dissolved and a homogeneous, clear electrolyte additive for flame retardancy is formed.

[0042] Example 3: This embodiment provides an electrolyte additive for aluminum foil. According to the mass percentage of the components, the electrolyte additive used in this embodiment consists of: 79.8% organic solvent, 2% sulfur-containing additive, 4.2% lithium salt additive, 13% electrolyte lithium salt, and 1% a compound for aluminum foil. The organic solvent is composed of cyclic carbonates and chain carbonates. Calculated with the total mass of the organic solvent as 100%, the ratio of the total mass of cyclic carbonates to the total mass of chain carbonates is 40:60. The cyclic carbonates are a mixture of 25% ethylene carbonate (EC) and 15% propylene carbonate (PC), and the chain carbonates are a mixture of 30% diethyl carbonate (DEC), 20% dimethyl carbonate (DMC), and 10% ethyl methyl carbonate (EMC). The electrolyte lithium salt is 13% lithium hexafluorophosphate (LiPF6). The sulfur-containing additive is 2% 1,3-propenesulfonyl lactone (PST). The lithium salt additive is a mixture of 2% lithium difluorophosphate (LiPO2F2) and 2.2% lithium bis(oxalate-borate) (LiBOB); The 1% compound for aluminum foil has the structure shown in general formula I:

[0043] General formula I.

[0044] The method for preparing an electrolyte additive for aluminum foil provided in this embodiment is as follows: Step 1: Synthesize a chlorinated, methylated acridine precursor, using 5-chloro-1-methylacridinium as the core structure, through electrophilic substitution or nitrogen quaternization reactions. Raw materials: 5-chloroacridinium, methylating agent (e.g., iodomethane), organic solvent (e.g., acetonitrile). Reaction process: Dissolve 5-chloroacridinium in acetonitrile, add excess iodomethane, and heat under reflux for several hours to methylate the nitrogen atom on the acridine ring, generating 5-chloro-1-methylacridinium iodomonium salt.

[0045] Step 2: Preparation of trifluoroborate by ion exchange; iodide ions are replaced with trifluoroborate ions through an ion exchange reaction. Raw materials: 5-chloro-1-methylacridinium iodide, sodium tetrafluoroborate, water or methanol. Reaction process: Dissolve 5-chloro-1-methylacridinium iodide in water (or methanol), add an equal amount of sodium tetrafluoroborate, stir for a period of time, and the product (target compound) will precipitate due to its low solubility. After filtration, washing, and drying, 5-chloro-1-methylacridinium trifluoroborate (the compound mentioned in the question) is obtained.

[0046] The following embodiment provides a method for preparing an electrolyte additive for aluminum foil: In an argon-filled glove box (water content <10 ppm, oxygen content <1 ppm), according to the above proportions, first mix ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC). The mixture is then mixed to form an organic solvent component. Subsequently, under continuous stirring, lithium hexafluorophosphate (LiPF6), 1,3-propenesulfonate lactone (PST), lithium difluorophosphate (LiPO2F2), and lithium bis(oxalato)borate (LiBOB) and other compounds are added sequentially to the organic solvent until all components are completely dissolved and a homogeneous, clear electrolyte additive for flame retardancy is formed.

[0047] Comparative Example 1: This comparative example provides an electrolyte that differs from Example 1 only in that it does not contain functional lithium salts; otherwise, it is the same as Example 1.

[0048] Comparative Example 2: This comparative example provides an electrolyte that differs from Example 1 only in that it does not contain functional lithium salts, and the amount of lithium difluorosulfonylimide added is increased to 15%, while the rest is the same as Example 1.

[0049] This invention provides an electrochemical device that uses graphite as the negative electrode active material. A negative electrode slurry is prepared by mixing graphite, conductive agent acetylene black, binder CMC, and PAA in a certain proportion. The negative electrode slurry is coated onto a copper foil current collector and vacuum dried to obtain a negative electrode sheet. NCA is used as the positive electrode active material. A positive electrode slurry is prepared by mixing the positive electrode active material, conductive agent acetylene black, binder PVDF, and CNT in a certain mass ratio. The positive electrode slurry is coated onto an aluminum foil current collector and vacuum dried to obtain a positive electrode sheet. The electrolytes prepared in the examples and comparative examples are then assembled with the above-mentioned positive electrode sheet, negative electrode sheet, and separator to form a supercapacitor.

[0050] The electrical performance of the supercapacitor was tested, and the results are shown in Table 1.

[0051]

[0052] Comparing Examples 1-3 and Comparative Example 1, it can be seen that as the amount of functional lithium salt added increases, the aluminum content in the electrolyte decreases. The difference in aluminum content between electrolytes with 1% and 3% addition is not significant, indicating that the optimal addition amount is 1%. Comparative Examples 1 and 2 show that increasing the content of lithium difluorosulfonylimide increases aluminum dissolution.

[0053] The aluminum oxide (Al2O3) passivation film on the surface of the aluminum foil is supposed to be a protective layer, but under high voltage, FSI - The anion undergoes oxidative decomposition to produce fluoride ions (F). - F - It reacts with aluminum oxide (Al₂O₃ + 6F₂) - + 3H₂O → 2AlF₃ + 6OH⁻ - This process dissolves the protective film, and after the passivation film is partially damaged, the underlying active aluminum substrate is exposed to the electrolyte, undergoing oxidation and dissolution under high voltage: Al → Al³ + + 3e - Al³ + It will react with components in the electrolyte (such as FSI) - These compounds combine to form complexes (such as Al(FSI)3), which are then further hydrolyzed to produce products such as AlF3, causing a sharp increase in DCR and resulting in a cyclical plunge.

[0054] This invention provides an electrolyte additive for aluminum foil. By introducing a specific compound, which works synergistically with sulfur-containing additives, lithium electrolyte salts, and organic solvents, the corrosion resistance of aluminum foil in high-voltage electrolytes is significantly improved. This compound preferentially adsorbs on the aluminum foil surface and forms a dense and stable protective film, effectively inhibiting electrolyte decomposition and hydrogen fluoride erosion of the aluminum foil. Simultaneously, the sulfur-containing additive helps form a more robust cathode interface layer, further enhancing the electrochemical stability of the aluminum foil. This synergistic effect enables lithium-ion batteries using this additive to exhibit superior cycle life and capacity retention, especially under high-voltage operating conditions, while effectively preventing battery performance degradation and safety hazards caused by aluminum foil corrosion.

[0055] The benzoindoline cation carries a positive charge and preferentially adsorbs onto the surface of the negatively charged aluminum foil current collector (relative to the increased lithium potential) via electrostatic interactions. This adsorption forms an initial, dynamic "molecular barrier" that blocks free FSI in the electrolyte. - Anions directly approach the alumina passivation film on the aluminum foil surface, thus mitigating FSI from the very first step. - Chemical attack on the passivation film. As the voltage continues to rise into the operating window of the ternary supercapacitor (typically >4.2V vs. Li / Li),... + Benzoindoline cations undergo preferential electrochemical oxidation at a specific, lower potential before decomposition in the base electrolyte solvent and LiFSI salt. This oxidation reaction is typically irreversible, and its decomposition products are deposited in situ and uniformly on the aluminum foil surface. This newly formed film bonds tightly to the aluminum foil, compensating for the deficiencies of the natural alumina film and forming a denser and more stable artificial protective layer. The foregoing has shown and described the basic principles, main features, and advantages of the present invention. It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the scope of the invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0056] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can be appropriately combined to form other embodiments that can be understood by those skilled in the art. The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A compound for use in aluminum foil, characterized in that, It has the structure shown in general formula I: General formula I.

2. An electrolyte additive for aluminum foil, characterized in that, include: Organic solvents, lithium electrolytes, sulfur-containing additives, and compounds as described in claim 1.

3. The electrolyte additive for aluminum foil according to claim 2, characterized in that, The organic solvents include cyclic carbonates and chain carbonates.

4. The electrolyte additive for aluminum foil according to claim 3, characterized in that, The cyclic carbonate includes at least one of ethylene carbonate and propylene carbonate; The chain carbonates include two or three of diethyl carbonate, dimethyl carbonate, and methyl ethyl carbonate.

5. The electrolyte additive for aluminum foil according to claim 3, characterized in that, The total mass of the cyclic carbonate and the chain carbonate is (35-45):(55-65).

6. The electrolyte additive for aluminum foil according to claim 2, characterized in that, The sulfur-containing additive includes at least one of vinyl sulfate, methylene disulfonate, and 1,3-propenesulfonate lactone. The electrolyte lithium salt is lithium hexafluorophosphate.

7. The electrolyte additive for aluminum foil according to claim 2, characterized in that, It also includes lithium salt additives, which include at least one of lithium difluorophosphate and lithium bis(oxalato)borate.

8. An electrolyte additive for aluminum foil according to claim 7, characterized in that, The mass ratio of the compound, the sulfur-containing additive, and the lithium salt additive is (0.8–1.5):(1.8–3):(3.5–4.8).

9. An electrolyte additive for aluminum foil according to claim 8, characterized in that, The electrolyte lithium salt is lithium hexafluorophosphate, and the mass percentage of the electrolyte lithium salt is 10%~15%.

10. The application of an electrolyte additive for aluminum foil as described in any one of claims 2 to 9 in a supercapacitor.

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