Electrolyte based on silicon-sulfur synergistic multifunctional electrolyte additive, supercapacitor and application thereof in wind power energy storage

Abstract

This invention discloses an electrolyte, a supercapacitor, and their application in wind power energy storage based on a silicon-sulfur synergistic multifunctional electrolyte additive, belonging to the field of supercapacitor technology. The additive is composed of 4-(triethoxysilyl)phenyl isothiocyanate and diphenylphosphimide in a mass ratio of (0.4~1.2):(0.3~0.9). Through the efficient acid removal of the isothiocyanate group, the chemical anchoring of the siloxane group, and the stabilizing effect of the phenyl conjugation, it synergizes with the flame retardant and ion transport regulation functions of the phosphorimide to construct a stable interface with high temperature resistance and high ion conductivity. The electrolyte contains the additive, a composite lithium salt (LiPF6 / LiFSI / LiPO2F2), a five-element functional solvent (FEC / EC / PC / DEC / EMC), and auxiliary film-forming components (VC / DTD / PST), which synergistically solve the problems of acid corrosion, interface instability, and solvent decomposition at high temperatures. The supercapacitor exhibits low free acidity and high capacity retention after 28 days of storage at 55°C, high capacity retention after 350 high-temperature cycles, and short self-extinguishing time, meeting the high reliability requirements of extreme operating conditions such as wind power energy storage.

Description

Technical Field

[0001] This invention belongs to the field of supercapacitor technology, specifically relating to an electrolyte based on a silicon-sulfur synergistic multifunctional electrolyte additive, a supercapacitor, and its application in wind power energy storage. Background Technology

[0002] With the surge in demand for power storage devices from new energy power generation, smart grids, and rail transportation, the high power and long cycle life advantages of supercapacitors are becoming increasingly prominent. However, as application scenarios continue to expand and deepen, supercapacitors often need to operate stably for extended periods in extreme environments such as high temperature and high humidity, posing a severe challenge to the electrolyte, one of their key materials. Currently, commercial supercapacitors generally use electrolyte systems based on lithium salts (LiPF6) and organic carbonate solvents. This system exhibits a series of interrelated failure mechanisms under high-temperature conditions, severely limiting the high-temperature reliability and cycle life of the devices.

[0003] First, electrolyte acidity runaway and material corrosion occur. Under high-temperature conditions, the hydrolysis reaction of lithium salts (especially LiPF6) is significantly aggravated, continuously generating highly corrosive hydrofluoric acid (HF). HF not only directly attacks and dissolves active components and transition metal ions in the electrode material, leading to electrode structure damage and a decrease in effective active surface area, but also triggers a chain reaction of electrolyte decomposition. The dissolved transition metal ions further catalyze the redox decomposition of the electrolyte, forming a vicious cycle and causing irreversible capacity loss. Second, electrode-electrolyte interface instability occurs. During high-temperature cycling, the chemical and mechanical stability of the solid electrolyte interfacial film (CEI film) formed on the electrode material surface deteriorates, making it prone to rupture and repeated reconstruction. This unstable interfacial film leads to a sharp increase in interfacial impedance, hindering rapid ion transport, while increasing the active sites for side reactions, exacerbating the continuous consumption of electrolyte and the degradation of electrode materials, ultimately manifesting as rapid capacity decay at high temperatures. Third, electrolyte solvents are prone to thermal oxidation and decomposition. High-temperature conditions accelerate the oxidative decomposition reaction of organic solvents under high pressure. The decomposition products include gases such as carbon dioxide (CO2) and oxygen (O2). These gases accumulate within the sealed supercapacitor casing, generating internal pressure that causes the device to swell, potentially leading to sealing failure and safety risks. Fourthly, there are limitations and a lack of synergy in the functions of additives. To alleviate these problems, existing technologies often introduce various functional additives, such as acid scavengers, film-forming additives, and overcharge protection additives. However, these additives are mostly designed based on a single functional group or a single mechanism of action. For example, some phosphorus and nitrogen compounds can capture HF, and some sulfur- or boron-containing compounds help form a stable interfacial film. However, this strategy has significant shortcomings. A single additive cannot simultaneously address multiple failure modes such as acid corrosion, interfacial instability, and solvent decomposition at high temperatures; different additives often lack effective synergistic effects and may even interfere with each other, affecting the physicochemical properties of the main salt and solvent; the existing additive molecular structure design lacks innovation and has limited adaptability to extreme operating conditions. The limited adaptability of existing additives to extreme conditions such as high temperature and high voltage makes it difficult to support the long-term reliability requirements of supercapacitors in harsh environments such as wind power storage.

[0004] In response to the comprehensive requirements of wind power energy storage systems for high-temperature stability, power response, and cycle life, there is an urgent need to develop a new type of additive that can achieve multiple functions synergistically at the molecular level. Through the organic combination of multiple functional groups and the synergistic effect between components, it is necessary to systematically solve comprehensive problems such as electrolyte acidity control, interface stability, ion transport, and safety protection at high temperatures. Summary of the Invention

[0005] To address the comprehensive requirements of wind power energy storage systems for high-temperature stability, power response, and cycle life, there is an urgent need to develop a novel additive capable of achieving synergistic effects of multiple functions at the molecular level. This additive aims to systematically solve the current technical challenges of acidity control, interface stability, ion transport, and safety protection of electrolytes at high temperatures through the organic combination of multiple functional groups and synergistic effects between components. This invention aims to provide an electrolyte, a supercapacitor, and its application in wind power energy storage based on a silicon-sulfur synergistic multifunctional electrolyte additive. An innovative silicon-sulfur synergistic multifunctional electrolyte additive is designed. Through the efficient acid removal of isothiocyanate groups, the chemical anchoring film formation of triethoxysilane groups, and the conjugated stabilizing effect of phenyl groups, combined with the flame retardant enhancement and ion transport regulation functions of phosphorimide, and combined with composite lithium salts, a five-element functional solvent, and auxiliary film-forming components, a novel electrolyte system is constructed that can comprehensively improve the high-temperature storage and cycle performance of supercapacitors, making it particularly suitable for high-temperature, high-load extreme operating conditions such as wind power energy storage.

[0006] To achieve the above objectives, the present invention employs the following technical solution: This invention provides a multifunctional electrolyte additive with silicon-sulfur synergy, which is composed of 4-(triethoxysilyl)phenyl isothiocyanate and diphenylphosphamide; the mass ratio of 4-(triethoxysilyl)phenyl isothiocyanate to diphenylphosphamide is (0.4~1.2):(0.3~0.9). 4-(triethoxysilyl)phenyl isothiocyanate molecules simultaneously contain isothiocyanate groups (-N=C=S), triethoxysilyl groups (-Si(OEt)3), and phenyl conjugated structures, breaking through the functional limitations of traditional single-functional group additives and achieving a multi-functional integration of "acid removal, interface enhancement, and ion transport regulation"; -N=C=S undergoes addition reactions with H2O and HF in the electrolyte (-N=C=S + H2O → -NH-CO-SH; -N=C=S + HF → -NH-CO-SF), rapidly removing acidic impurities; triethoxysilyl hydrolysis generates silanol groups (-SiOH), which form hydrogen bonds with hydroxyl groups on the electrode surface, and the phenyl conjugated structure achieves π-π stacking, synergistically decomposing products to construct a dense organic-inorganic composite CEI membrane. The membrane layer is rich in LiF, SiO2, and polythiourea structures, inhibiting side reactions between the electrolyte and the electrode; the coordination of thioether bonds with transition metal ions reduces ion dissolution and avoids catalytic electrolyte decomposition. Containing phosphoryl groups (-PO2-) and imine groups (-NH-), it possesses both flame-retardant and interfacial synergistic functions, complementing 4-(triethoxysilyl)phenyl isothiocyanate; the imine groups form hydrogen bonds with the thiol groups (-SH) of 4-(triethoxysilyl)phenyl isothiocyanate, further densifying the CEI film and improving the film's oxidation resistance; the phosphoryl groups form weak coordination with lithium ions, reducing the migration energy barrier and improving ionic conductivity.

[0007] The mass ratio of 4-(triethoxysilyl)phenyl isothiocyanate to diphenylphosphamide is (0.6~1.0):(0.3~0.9).

[0008] Preferably, the mass ratio of 4-(triethoxysilyl)phenyl isothiocyanate to diphenylphosphamide is 1:1.

[0009] This invention provides a silicon-sulfur synergistic multifunctional electrolyte, characterized in that, based on 100% of the total electrolyte mass, it comprises the aforementioned silicon-sulfur synergistic multifunctional electrolyte additive, 12-15% composite lithium salt, and 1.5-2.0% auxiliary film-forming components, with the balance being a pentacetic functional solvent; the total content of the silicon-sulfur synergistic multifunctional electrolyte additive is 0.9%-1.9%. The composite lithium salt is composed of lithium hexafluorophosphate, lithium difluorosulfonylimide and lithium difluorophosphate; The five-element functional solvent is prepared from fluoroethylene carbonate, ethylene carbonate, propylene carbonate, diethyl carbonate and methyl ethyl carbonate; The auxiliary film-forming component consists of vinylene carbonate, vinyl sulfate, and 1,3-propenesulfonate lactone.

[0010] The mass ratio of lithium hexafluorophosphate, lithium difluorosulfonylimide, and lithium difluorophosphate is (8~11):(2~4):(0.5~1.2).

[0011] The volume ratio of the fluoroethylene carbonate, ethylene carbonate, propylene carbonate, diethyl carbonate and methyl ethyl carbonate is (7~9):(15~17):(11~13):(12~13):(41~47).

[0012] In the auxiliary film-forming components, the mass ratio of vinylene carbonate, vinyl sulfate, and 1,3-propenesulfonate lactone is (0.3~0.6):(0.4~1.2):(0~1.0).

[0013] This invention provides a method for preparing a silicon-sulfur synergistic multifunctional electrolyte, comprising the following steps: S1, under an inert atmosphere, the five-element functional solvent is mixed and cooled, and a composite lithium salt is added under stirring. The mixture is stirred until completely dissolved to obtain a mixed solution. S2, the aforementioned silicon-sulfur synergistic multifunctional electrolyte additive and film-forming auxiliary components are added sequentially to the mixed solution, and the solution is gradually aged to obtain a silicon-sulfur synergistic multifunctional electrolyte.

[0014] In S1, the cooling temperature is 0~4℃, and the amount of composite lithium salt added is 12%~15% of the total mass in the electrolyte.

[0015] S2 is specifically as follows: at a temperature of 6~10℃, add 4-(triethoxysilyl)phenyl isothiocyanate, ultrasonically disperse for 25~35 min, then add diphenylphosphimide, stir for 30~40 min; raise the temperature to 15~20℃, add the film-forming auxiliary component, stir for 30~40 min; raise the temperature to 20~30℃ and keep warm for 40~50 min to obtain a silicon-sulfur synergistic multifunctional electrolyte.

[0016] This invention provides a supercapacitor, comprising a positive electrode, a negative electrode, a separator, and the aforementioned silicon-sulfur synergistic multifunctional electrolyte; Preferably, the active material of the positive electrode is NCM811 ternary material, and the active material of the negative electrode is a composite of graphite and soft carbon.

[0017] This invention provides the aforementioned silicon-sulfur synergistic multifunctional electrolyte additive, or the aforementioned silicon-sulfur synergistic multifunctional electrolyte, or the aforementioned supercapacitor in a wind power energy storage system.

[0018] Compared with the prior art, the present invention achieves the following technical effects: The present invention provides a silicon-sulfur synergistic multifunctional electrolyte additive, 4-(triethoxysilyl)phenyl isothiocyanate, which simultaneously contains isothiocyanate groups (-N=C=S), triethoxysilyl groups (-Si(OEt)3), and a phenyl conjugated structure. This overcomes the functional limitations of traditional single-functional group additives, achieving a multifunctional integration of "acid removal, interface enhancement, and ion transport regulation." The triethoxysilyl group hydrolyzes to generate silanol groups (-SiOH), which form hydrogen bonds with hydroxyl groups on the electrode surface. The phenyl conjugated structure achieves π-π... Stacking and synergistic decomposition products construct a dense organic-inorganic composite CEI membrane. The membrane layer is rich in LiF, SiO2, and polythiourea structures, inhibiting side reactions between the electrolyte and electrodes. The coordination of thioether bonds with transition metal ions reduces ion dissolution and avoids catalytic electrolyte decomposition. Diphenylphosphorimide, containing phosphoryl groups (-PO2-) and imine groups (-NH-), possesses both flame-retardant and interfacial synergistic functions, complementing 4-(triethoxysilyl)phenyl isothiocyanate. The imine groups form hydrogen bonds with the thiol groups (-SH) of 4-(triethoxysilyl)phenyl isothiocyanate, further densifying the CEI membrane and improving its oxidation resistance. The phosphoryl groups form weak coordination with lithium ions, lowering the migration barrier and improving ionic conductivity.

[0019] The multifunctional electrolyte with silicon-sulfur synergy provided by this invention consists of binary synergistic additives, composite lithium salts, pentagonal functional solvents, and auxiliary film-forming components. LiPF6 provides high ionic conductivity, LiFSI enhances thermal stability and interfacial compatibility, and LiPO2F2 further strengthens the compactness of the CEI membrane. The mixture of these three components inhibits lithium salt hydrolysis and balances ion transport efficiency and high-temperature stability. Ethylene carbonate (EC) promotes lithium salt dissociation, ethyl methyl carbonate (EMC) enhances ion mobility, FEC strengthens CEI membrane stability, PC improves electrolyte thermal stability, and DEC adjusts system viscosity. The pentagonal compound achieves a balance of high dielectric, low viscosity, high boiling point, and strong compatibility. The auxiliary film-forming components, in combination with the binary synergistic additives, further optimize the SEI / CEI membrane structure, improve membrane flexibility and cycle resistance, and inhibit electrolyte decomposition and gas generation.

[0020] The electrolyte preparation method provided by this invention adopts a low-temperature dispersion-stepwise compounding-gradient maturation process to ensure that each component is uniformly dispersed and that its synergistic effect is fully utilized.

[0021] The supercapacitor provided by this invention exhibits excellent high-temperature resistance due to its electrolyte system employing a silicon-sulfur synergistic multifunctional additive system. Diphenylphosphimide provides phosphorus-based flame retardant properties, and its synergistic effect with 4-(triethoxysilyl)phenyl isothiocyanate shortens the self-extinguishing time of the electrolyte to 40-48 seconds, significantly superior to the flammability of traditional electrolytes. The use of a five-element functional solvent (FEC / EC / PC / DEC / EMC) achieves a balance between high dielectric strength, low viscosity, high boiling point, and a wide electrochemical window. Combined with the thermal stability advantages of the composite lithium salt (LiPF6 / LiFSI / LiPO2F2), the supercapacitor can operate stably over a wide temperature range. Under the aforementioned synergistic mechanism, after 28 days of storage at 55°C, the free acidity of this invention is as low as 28.5-38.9 ppm, and the capacity retention rate is as high as 94.0%-95.5%; after 350 high-temperature cycles, the capacity retention rate remains above 93.0%. Compared with the comparative examples (the capacity retention of Comparative Example 1 without silicon-sulfur additives was only 84.2%, and that of Comparative Example 3 with traditional electrolyte was only 80.5%), the high-temperature performance of the supercapacitor of the present invention is significantly improved, which fully demonstrates the superiority of the matching design of silicon-sulfur synergistic additive system with NCM811 cathode and graphite / soft carbon anode under high-temperature conditions.

[0022] The application provided by this invention is that the supercapacitor achieves multiple technical effects, such as stable high-nickel positive electrode interface, complete negative electrode structure, efficient ion transport, and excellent high-temperature performance, through the matching design of silicon-sulfur synergistic multifunctional electrolyte and specific electrode materials. It can meet the high reliability requirements of supercapacitors under extreme conditions such as wind power energy storage, and provides key material support for high-reliability energy storage in the field of wind power and other new energy. Detailed Implementation

[0023] To enable those skilled in the art to better understand the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. 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 should fall within the scope of protection of the present invention.

[0024] Where specific experimental steps or conditions are not specified in the embodiments, they can be performed according to the conventional experimental steps or conditions described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available products. In this invention, unless otherwise specified, all experimental materials used are commercially available commodities well-known to those skilled in the art.

[0025] Example 1 This embodiment provides a silicon-sulfur synergistic multifunctional electrolyte additive and an electrolyte. The electrolyte includes a silicon-sulfur synergistic multifunctional electrolyte additive, a composite lithium salt, a pentacetic functional solvent, and film-forming auxiliary components. The specific preparation steps are as follows: Step 1: Five-element functional solvent Solvent system (by volume percentage): fluoroethylene carbonate (FEC): 7%, ethylene carbonate (EC): 17%, propylene carbonate (PC): 11%, diethyl carbonate (DEC): 13%, methyl ethyl carbonate (EMC): 47%. The above five organic solvents are mixed in a dry container in proportion, and the mixed solvent system is cooled to 2°C using a low-temperature thermostat.

[0026] Step 2: Dissolving the composite lithium salt The composite lithium salt system (as a percentage of the total electrolyte mass): Total lithium salt content: 13 wt%; Specific ratio: LiPF6: LiFSI: LiPO2F2 = 4:1:0.5 (mass ratio). Under low temperature (2℃) and continuous stirring conditions, the composite lithium salt was slowly added to the mixed solvent in step one. After the addition was complete, the system was kept at a low temperature, and stirring was continued for 80 minutes until all lithium salts were completely dissolved, forming a clear and transparent mixed solution.

[0027] Step 3: Dispersion of multifunctional electrolyte additives with silicon-sulfur synergy Multifunctional electrolyte additive with silicon-sulfur synergy (by weight of total electrolyte): 4-(triethoxysilyl)phenyl isothiocyanate: 0.6 wt%; diphenylphosphamide: 0.6 wt%. The system temperature was slightly increased to 8°C. First, 4-(triethoxysilyl)phenyl isothiocyanate was added and ultrasonically dispersed for 30 minutes to ensure complete pre-dissolution and dispersion. Then, diphenylphosphimide was added, and mechanical stirring was carried out for 35 minutes to ensure homogeneity.

[0028] Step 4: Mixing of film-forming components Auxiliary film-forming components (percentage of total electrolyte mass): vinylene carbonate (VC): 0.4 wt%, vinyl sulfate (DTD): 0.6 wt%, 1-propylene-1,3-sulfonyl lactone (PST): 0.8 wt%. The system temperature was raised to 18°C, and VC, DTD and PST were added sequentially, while stirring continuously for 35 minutes to ensure that all additives were fully mixed.

[0029] Step 5: Electrolyte maturation The electrolyte system was gradually heated to 25°C at a rate of 0.8°C / min. After reaching the target temperature, it was kept at this temperature for 45 minutes to allow the components to fully interact and stabilize, ultimately obtaining a homogeneous and stable silicon-sulfur synergistic multifunctional electrolyte.

[0030] Based on the aforementioned silicon-sulfur synergistic multifunctional electrolyte, supercapacitors are assembled: Cathode: Prepared using NCM811 (LiNi) 0.8 Co 0.1 Mn 0.1 The ternary composite positive electrode with O2 as the main active material has an active material areal density of 11 mg / cm³. 2 .

[0031] Negative electrode: A composite negative electrode sheet of graphite and soft carbon was prepared, with an active material areal density of 9 mg / cm³. 2 .

[0032] Assembly: Inside the glove box, using a CR2025 button cell casing, with the above-mentioned positive and negative electrode sheets as working electrodes and a lithium metal sheet as the counter electrode / reference electrode, inject 78 μL of the silicon-sulfur synergistic multifunctional electrolyte prepared in step five. Encapsulation: After electrolyte injection, the battery is vacuum sealed and left to stand at room temperature for 24 hours to allow the electrolyte to fully wet the electrodes, thus completing the assembly of the supercapacitor.

[0033] Example 2 Based on Example 1, this embodiment provides a silicon-sulfur synergistic multifunctional electrolyte additive and electrolyte. The only difference between this embodiment and Example 1 is that the amount of 4-(triethoxysilyl)phenyl isothiocyanate added is 0.8%, and the rest is the same as in Example 1.

[0034] Example 3 This embodiment provides a silicon-sulfur synergistic multifunctional electrolyte additive and electrolyte based on Example 1. The only difference between this embodiment and Example 1 is that the amount of 4-(triethoxysilyl)phenyl isothiocyanate added is 1.0%, and the rest is the same as in Example 1.

[0035] Example 4 This embodiment provides a silicon-sulfur synergistic multifunctional electrolyte additive and electrolyte based on Example 1. The only difference between this embodiment and Example 1 is that the amount of diphenylphosphine imide added is 0.3%, while the rest is the same as in Example 1.

[0036] Example 5 The amount of diphenylphosphine added was 0.9%, and everything else was the same as in Example 1.

[0037] Example 6 This embodiment provides a silicon-sulfur synergistic multifunctional electrolyte additive and electrolyte based on Example 1. The only difference between this embodiment and Example 1 is that it contains 1.2% vinyl sulfate (without PST), and the rest is the same as Example 1.

[0038] Example 7 This embodiment provides a silicon-sulfur synergistic multifunctional electrolyte additive and electrolyte based on Embodiment 1. The only difference between this embodiment and Embodiment 1 is that the amount of vinylene carbonate added is 0.6%, while the rest is the same as in Embodiment 1.

[0039] Example 8 This embodiment provides a silicon-sulfur synergistic multifunctional electrolyte additive and electrolyte based on Embodiment 1. The only difference between this embodiment and Embodiment 1 is that the composite lithium salt is adjusted to LiPF6 10% + LiFSI 3% + LiPO2F2 0.5%, while the rest is the same as in Embodiment 1.

[0040] Example 9 This embodiment provides a silicon-sulfur synergistic multifunctional electrolyte additive and electrolyte based on Embodiment 1. The only difference between this embodiment and Embodiment 1 is that the volume ratio of the five-component solvent is adjusted to: FEC 9%, EC 15%, PC 13%, DEC 12%, EMC 41%, while the rest is the same as in Embodiment 1.

[0041] Example 10 This embodiment provides a silicon-sulfur synergistic multifunctional electrolyte additive and electrolyte based on Embodiment 1. The only difference between this embodiment and Embodiment 1 is that the positive electrode active material is a single NCM811, while the rest is the same as in Embodiment 1.

[0042] Example 11 This embodiment provides a silicon-sulfur synergistic multifunctional electrolyte additive and electrolyte based on Embodiment 1. The only difference between this embodiment and Embodiment 1 is that the positive electrode active material is a single NCM811, while the rest is the same as in Embodiment 1.

[0043] Comparative Example 1 Comparative Example 1 is based on Example 1, except that 4-(triethoxysilyl)phenyl isothiocyanate and diphenylphosphamide were not added; otherwise, it is the same as Example 1.

[0044] Comparative Example 2 Comparative Example 2 is based on Example 1, except that only 0.6% of 4-(triethoxysilyl)phenyl isothiocyanate was added, and diphenylphosphamide was not added. Otherwise, it is the same as Example 1.

[0045] Comparative Example 3 Step 1: Prepare the solvent according to the following volume ratios: FEC 7%, EC 17%, DEC 13%, EMC 63%, add 13% LiPF6 at 25℃, and stir for 30 minutes to dissolve; Step 2: Add 0.4% VC and 0.6% DTD, stir for 60 minutes to obtain the conventional electrolyte; Step 3: Prepare the supercapacitor according to the electrode and assembly process of Example 1.

[0046] Test method: Free acid content: The electrolyte was poured into an aluminum-plastic film using a dropper, sealed, and stored in a 55°C oven for 7 days. The free acid content was then tested using the organic amine method.

[0047] Capacitance retention (storage) test: The supercapacitor was stored in a 55℃ constant temperature oven for 28 days. Before storage, it was charged and discharged 3 times at 25℃ and 0.5C rate, and the initial discharge capacity C0 was recorded. After storage, it was naturally cooled to 25℃ and charged and discharged 3 times at 0.5C rate. The third discharge capacity C1 was recorded. Capacitance retention rate = (C1 / C0) × 100%.

[0048] Cyclic capacity retention test: Charge-discharge cycle test was performed at 55℃ and 1C rate, and the initial discharge capacity C0 and the discharge capacity C after 350 cycles were recorded. 350 Cyclic capacity retention rate = (C 350 / C0)×100%, using the Landian CT2001A charge and discharge tester.

[0049] Self-extinguishing time test: According to UL94 standard, take 0.5 mL of electrolyte sample and drop it onto degreased cotton (mass 1 g), ignite the degreased cotton with an alcohol lamp, and record the time it takes for the flame to extinguish itself after the flame source is removed. If it does not extinguish within 60 seconds, it is recorded as "non-flammable". Perform three parallel tests and take the average value.

[0050] The performance of the supercapacitor was tested, and the results are shown in the table below.

[0051]

[0052] As shown in the table above, this invention successfully constructed a high-performance, high-safety electrolyte system by introducing a silicon-sulfur synergistic multifunctional additive (4-(triethoxysilyl)phenyl isothiocyanate + diphenylphosphamide) into the traditional lithium-ion battery electrolyte system, combined with a composite lithium salt, a pentacetic solvent, and an auxiliary film-forming agent. Test results demonstrate that this system exhibits significant synergistic advantages over traditional electrolytes (comparative example) in suppressing acidity growth, improving high-temperature storage and cycle stability, and enhancing safety.

[0053] Silicon additive content (Examples 1 vs 2 vs 3): As the content of 4-(triethoxysilyl)phenyl isothiocyanate increased from 0.6% to 1.0%, the free acid content continuously decreased (34.7→28.5 ppm), and the storage retention rate slightly improved (94.6%→95.5%), but the cycle retention rate and flame retardancy decreased slightly. This indicates that the acid removal effect of this additive is positively correlated with concentration, but excessive amounts have a slight negative impact on the interface or kinetics.

[0054] Phosphorus additive content (Examples 1 vs 4 vs 5): When the diphenylphosphine imide content varied within the range of 0.3%-0.9%, 0.6% showed the best overall performance. A lower content (0.3%, Example 4) resulted in slightly poorer acidity control and a longer flame retardant time; a higher content (0.9%, Example 5) resulted in a slightly shorter flame retardant time. This indicates that it has an optimal synergistic ratio with the silicon additive.

[0055] Compared to Example 1, the absence of phosphorus additive (Comparative Example 2) only resulted in the loss of diphenylphosphine imide, leading to weakened acidity control, decreased capacity retention, and a flammable electrolyte. This strongly demonstrates the irreplaceable role of diphenylphosphine imide in flame retardancy and synergistic stabilization. Comparative Example 1 (without any silicon-sulfur additives): performance was the worst across the board (failure to remove acid, rapid capacity decay), highlighting the key role of the silicon-sulfur additive system in performance improvement. Comparative Example 2 (with only silicon additives): performance was between that of Example 1 and Comparative Example 1, but it lost its flame retardancy. This demonstrates that diphenylphosphine imide is the core of achieving the "sulfur" function in "silicon-sulfur synergy" (phosphorus / sulfur-related functional groups contribute to flame retardancy and specific film formation), and both are indispensable. Comparative Example 3 (conventional electrolyte): using a single LiPF6 salt and a simplified solvent, it had the worst performance and the longest self-extinguishing time (61 seconds, but combustion characteristics may vary depending on the solvent system). This indicates that a complete composite salt, functional solvent, and additive system together form the foundation for high performance.

[0056] This invention successfully designs a multifunctional electrolyte with silicon-sulfur synergy. Its core innovation lies in the introduction of two functional additives: "silicon-based isothiocyanate" and "phosphorimide." The synergistic mechanism is as follows: the former primarily acts as "acid removal and passivation," eliminating destructive impurities at the source; the latter primarily acts as "synergistic film formation and flame retardancy," constructing a stable and robust electrode interface and enhancing intrinsic safety. Together with composite lithium salts and functional solvents, these two additives achieve comprehensive protection of the electrode interface (especially the highly active NCM811 cathode), resulting in a breakthrough balance and improvement in high-temperature storage stability, long cycle life, and safety. All performance indicators are significantly superior to traditional electrolyte systems.

[0057] 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 to the technical solution 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 multifunctional electrolyte additive with silicon-sulfur synergy, characterized in that, It is composed of 4-(triethoxysilyl)phenyl isothiocyanate and diphenylphosphamide; the mass ratio of 4-(triethoxysilyl)phenyl isothiocyanate to diphenylphosphamide is (0.4~1.2):(0.3~0.9).

2. The multifunctional electrolyte additive with silicon-sulfur synergy according to claim 1, characterized in that, The mass ratio of 4-(triethoxysilyl)phenyl isothiocyanate to diphenylphosphamide is (0.6~1.0):(0.3~0.9).

3. A silicon-sulfur synergistic multifunctional electrolyte, characterized in that, Based on the total mass of the electrolyte (100%), it includes a silicon-sulfur synergistic multifunctional electrolyte additive as described in claim 1 or 2, 12-15% composite lithium salt, and 1.5-2.0% auxiliary film-forming components, with the balance being a pentacetic functional solvent; the total content of the silicon-sulfur synergistic multifunctional electrolyte additive is 0.9%-1.9%. The composite lithium salt is composed of lithium hexafluorophosphate, lithium difluorosulfonylimide and lithium difluorophosphate; The five-element functional solvent is prepared from fluoroethylene carbonate, ethylene carbonate, propylene carbonate, diethyl carbonate and methyl ethyl carbonate; The auxiliary film-forming component consists of vinylene carbonate, vinyl sulfate, and 1,3-propenesulfonate lactone.

4. The silicon-sulfur synergistic multifunctional electrolyte according to claim 3, characterized in that, The mass ratio of lithium hexafluorophosphate, lithium difluorosulfonylimide, and lithium difluorophosphate is (8~11):(2~4):(0.5~1.2).

5. The silicon-sulfur synergistic multifunctional electrolyte according to claim 3, characterized in that, The volume ratio of the fluoroethylene carbonate, ethylene carbonate, propylene carbonate, diethyl carbonate and methyl ethyl carbonate is (7~9):(15~17):(11~13):(12~13):(41~47).

6. The silicon-sulfur synergistic multifunctional electrolyte according to claim 3, characterized in that, In the auxiliary film-forming components, the mass ratio of vinylene carbonate, vinyl sulfate, and 1,3-propenesulfonate lactone is (0.3~0.6):(0.4~1.2):(0~1.0).

7. A method for preparing a silicon-sulfur synergistic multifunctional electrolyte according to any one of claims 3 to 6, characterized in that, Includes the following steps: S1, under an inert atmosphere, the five-element functional solvent is mixed and cooled, and a composite lithium salt is added under stirring. The mixture is stirred until completely dissolved to obtain a mixed solution. S2, raise the system temperature to 6~10℃, add 4-(triethoxysilyl)phenyl isothiocyanate, ultrasonically disperse for 25~35min, then add diphenylphosphimide, stir for 30~40min; raise the temperature to 15~20℃, add the film-forming auxiliary component and stir for 30~40min; then raise the temperature to 20~30℃ at a gradient rate of 0.5~1℃ / min, hold for 40~50min to mature, and obtain a silicon-sulfur synergistic multifunctional electrolyte.

8. The method for preparing a silicon-sulfur synergistic multifunctional electrolyte according to claim 7, characterized in that, In S1, the amount of the composite lithium salt added is 12% to 15% of the total mass of the electrolyte.

9. A supercapacitor, characterized in that, Includes a positive electrode, a negative electrode, a separator, and a silicon-sulfur synergistic multifunctional electrolyte as described in any one of claims 3-6; The active material of the positive electrode is NCM811 ternary material, and the active material of the negative electrode is a composite of graphite and soft carbon.

10. The silicon-sulfur synergistic multifunctional electrolyte additive as described in claim 1 or 2, or the silicon-sulfur synergistic multifunctional electrolyte as described in any one of claims 3 to 6, or the application of the supercapacitor as described in claim 9 in a wind power energy storage system.

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