Electric double-layer capacitor electrolyte with advantages of high energy density and cost

Abstract

The invention provides the double-electric-layer capacitor electrolyte with high energy density and cost advantages, the additive of the electrolyte contains small cations to increase the degree of freedom of salt ions and reduce the viscosity, and the anion part contains hydrophobic groups and oxyphilic groups of oxyphilic functional groups on the surface of activated carbon to reduce the contact between water molecules and an electrode interface, so that the service life of the double-electric-layer capacitor is prolonged, and the service life of the double-electric-layer capacitor is prolonged. And furthermore, the gas production rate of the electrolyte is reduced, the high-rate performance is adapted, the capacity exertion is increased, and the characteristic of low cost is compatible. The capacity retention rate of an EDLC battery cell containing the preferable additive is increased to 78.2% (19.3%) from 58.9% of a blank sample after 1000 circles of 125A large-current circulation (the current of a conventional application scene of the capacity battery cell is 25A), the capacitance retention rate is increased to 78.2% (19.3%) from 58.9% of the blank sample after 1500h of high-temperature floating charge at the voltage of 65DEG C and 2.9 V, and the internal resistance growth rate is increased to 78.2% (19.3%) from 58.9% of the blank sample. According to the present invention, the preferable additive can significantly improve the capacity, such that the injection amount of the cell electrolyte can be reduced so as to reduce the production cost on the premise of maintaining the capacity unchanged, the safety is high, the process change is small, the electrochemical performance is significantly improved, and the commercialization requirement can be well met.

Description

Technical Field

[0001] This invention relates to a capacitor electrolyte, and more particularly to a double-layer capacitor electrolyte that combines high energy density and cost advantages. Background Technology

[0002] Currently, electrolyte technology for electric double-layer capacitors (EDLCs) faces multiple limitations. First, high-concentration electrolyte systems present a fundamental contradiction between ionic conductivity and solution viscosity—increasing salt concentration to improve conductivity leads to a significant increase in viscosity, which in turn limits ion migration rate and device rate performance. Second, even if the electrolyte contains only water, the porous structure of activated carbon makes complete water removal difficult. Water is distributed on the electrode surface during electrolyte wetting, interacting with oxygen-containing functional groups and triggering continuous interfacial side reactions, resulting in decreased coulombic efficiency and shortened cycle life. Furthermore, traditional electrolytes rely solely on physical adsorption to form the double layer for energy storage, lacking additional electrochemical reactions to contribute capacity. This leads to high electrolyte injection volumes and bottlenecks in improving energy density. Summary of the Invention

[0003] To address the shortcomings of the aforementioned background technology, this invention discloses an electrolyte for electric double-layer capacitors that combines high energy density and cost advantages. This is achieved by introducing competitive solvation regulating additives (such as Li-containing additives). + Na + K + Salts of small cations (such as spiro-(1,1')-bispyrrole cations SBP+ and tetraethylamine cations TEA) can preferentially bind to solvent molecules, thus preventing the salt cations that would otherwise be bound by the solvent from binding. + 1,1-Dimethylpyrrole cationic DMP + 1-Ethyl-3-methylimidazolium cationic EMI + (etc.) detach and move freely to increase the freedom of salt ions, reduce the overall viscosity of the electrolyte, and increase capacity utilization. Considering that during charging and discharging, the positive electrode potential rises to a higher value compared to the negative electrode, and the electrolyte is easily oxidized on the positive electrode surface to generate gas and by-products, the designed additives prioritize anions with functional groups that can inhibit the contact between water molecules and the positive electrode interface. The anions should contain both hydrophobic and oxygen-philic groups to achieve separation and reduce the contact between water molecules and the electrode interface. The additives have the following general formula structure.

[0004]

[0005] C represents a carbon atom, O represents an oxygen atom, and R1 can be either carbon (C) or sulfur (S). If it is C, the dashed line is absent, indicating a CO single bond; if it is sulfur, the dashed line becomes a solid line, indicating an S=O double bond. C=O or S=O are strong hydrogen bond acceptors, forming hydrogen bonds with the oxygen-containing functional groups hydroxyl (-OH) and carboxyl (-COOH) on the surface of activated carbon. A hydrophobic group R2 is introduced on the other side. R2 can be a fluoroalkane chain such as trifluoromethyl (-CF3), pentafluoroethyl (-C2F5), heptafluoropropyl (-C3F7), or perfluorooctyl (-C8F5). 17 ), perfluorohexyl (-C6F) 13 ), etc., long-chain alkyl groups such as dodecyl (-C 12 H 25 ), tetradecyl (-C 14 H 29 Aromatic groups such as phenyl (-C6H5) and naphthyl (-C) 10 H7), and siloxane groups (Si-O), etc. Considering both cost and electrical performance, this patent selects potassium perfluorobutanesulfonate (KFBS) as the electrolyte additive.

[0006] Preferably, the mass percentage of the electrolyte additive of the present invention relative to the total mass of salt and solvent is 0.01 to 5.00%.

[0007] Preferably, the salt in the electrolyte of the present invention is selected from 1,1-dimethylpyrrolidine tetrafluoroborate (DMP BF4). Alternatively, one or more of tetraethylamine tetrafluoroborate (TEA BF4), spiro-(1,1')-bispyrrolidine tetrafluoroborate (SBP BF4), 1-ethyl-3-methylimidazolium tetrafluoroborate (EMI BF4), and 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EMIm FSI) may be used.

[0008] Preferably, the solvent of the electrolyte of the present invention is selected from acetonitrile (AN). Alternatively, any one or more of propylene carbonate (PC) electrolyte, ethylene carbonate (EC) electrolyte, 3-methoxypropionitrile (MPN), and N,N-dimethylformamide (DMF) may be used.

[0009] Compared with the prior art, the advantages and positive effects of the present invention are as follows:

[0010] This invention provides a novel electrolyte additive. This additive contains small cations to increase the freedom of salt ions and reduce viscosity, while the anionic portion contains hydrophobic groups and oxygen-loving groups on the activated carbon surface to reduce the contact between water molecules and the electrode interface. This results in reduced electrolyte gas production, suitability for high-rate performance, increased capacity utilization, and low cost. In an EDLC cell containing this patented preferred additive, after 1000 cycles at a high current of 125A (the current in typical applications for this capacity cell is 25A), the capacity retention rate increased from 58.9% in the blank sample to 78.2% (a 19.3% improvement). After 1500 hours of high-temperature float charging at 65℃ and 2.9V, the capacity retention rate increased from 76.9% in the blank sample to 87.0% (a 10.1% improvement), and the internal resistance growth rate decreased from 91.72% in the blank sample to 38.9% (a 52.8% improvement). Because the additives selected in this patent can significantly improve capacity performance, the amount of electrolyte injected into the cell can be reduced to lower production costs while maintaining the same capacity. Furthermore, it offers high safety, minimal process modifications, and significant improvement in electrochemical performance, which can well meet the needs of commercialization and effectively fill the research gap in EDLC electrolytes. Attached Figure Description

[0011] Table 2 is a comparison table of the initial capacity, initial energy efficiency at 125A cycle, and capacity retention after cycling for Comparative Example 1 and Example 2.

[0012] Table 3 is a summary table of the capacity and capacity improvement rate of Comparative Example 1 and Example 2 at 65℃, 25℃ and -40℃;

[0013] Figure 1 This is a schematic diagram of the preferred additive structure for this patent;

[0014] Figure 2 The graph shows the changes in capacity, internal resistance, and thickness of Comparative Example 1 and Examples 1-3 under a high-temperature load of 2.9V and constant pressure at 65°C (concentration optimized).

[0015] Figure 3 The graph shows the changes in capacity, internal resistance, and thickness of Comparative Example 1, Example 2, Example 4, and Example 5 under a constant voltage and high temperature load of 2.9V at 65°C (cation comparison).

[0016] Figure 4 The graph shows the changes in capacity, internal resistance, and thickness of Comparative Example 1, Comparative Example 2, and Example 2 under a high-temperature load of 2.9V and constant voltage at 65°C (anion comparison).

[0017] Figure 5 The graphs show the capacity, energy efficiency, and capacity retention of Comparative Example 1 and Example 2 at 25°C and 125A high-rate cycling.

[0018] Figure 6 The discharge voltage curves for Comparative Example 1 and Example 2 at 65°C and -40°C are shown. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are only for explaining this invention and are not intended to limit this invention.

[0020] Currently, commercially available double-layer capacitor electrolytes generally use 1.0 mol / L tetraethylamine tetrafluoroborate (TEA BF4) dissolved in acetonitrile (AN) or propylene carbonate (PC) as the electrolyte. When the capacitor is cycled at high power (10-15 kW / kg), the ohmic voltage drop caused by the electrolyte accounts for about 30% of the total internal resistance of the device, thus limiting the improvement of power density. Previous attempts to introduce high dielectric constant sulfone and nitrile co-solvents have improved the salt dissociation degree, but the viscosity of the electrolyte increases significantly, which in turn reduces the ion mobility by 10-20%, offsetting the power improvement effect. Therefore, there is currently a lack of systematic research and optimization for double-layer capacitor electrolytes. It is necessary to design power-type electrolyte components without changing the main solvent system, increasing viscosity, or reducing withstand voltage, and to suppress transient concentration polarization and gas generation in order to achieve the triple goals of high power, long life, and low swelling.

[0021] This invention provides the design and application of a power electrolyte for electric double-layer capacitors. The additives introduced into this electrolyte have two highly polar parts: a strongly electronegative part and a strongly electronegative part. An appropriate chain length is adjusted in the middle, so that the overall molecular size can be adapted to the micropore size of activated carbon, facilitating adsorption and desorption, and making it easy to break bonds. While contributing some pseudocapacitance through oxidative bond breaking, it can preferentially adsorb onto both the positive and negative electrodes to form a low-polarity, highly dense interface. This reduces ion association of salt ions at the electric double layer, thereby reducing the internal resistance of liquid-phase transport and exhibiting excellent power performance: the capacity retention rate is increased from 76.3% to 90.1% during 125A high-rate cycling (normal current is 25A). Furthermore, the silicon-containing part formed by bond breaking can also synergistically remove salt anions BF4 from the electrolyte. - The HF produced by hydrolysis passesivates the Al foil, reducing the contact resistance of the aluminum conductor. The electrolyte additive configuration is as follows: Figure 1As shown. R1 and R2 both represent electron-withdrawing functional groups, which can be trihalomethyl (-CF3), thiosulfate (-SO3H), nitro (-NO3), tertiary ammonium (-R3N), cyano (-CN), halo (-X), etc.; while silicon (-Si) can be replaced by other electron-donating functional groups such as hydroxyl (-OH), amino (-NH2), aryl (-Ar), ether (-OR), ester (-COOR), etc., to achieve high polarity of the molecule as a whole.

[0022] Preferably, the additive selected in this invention is potassium perfluorobutyrate (KFBS).

[0023] Preferably, the electrolyte additive of the present invention accounts for 0.1%-3% of the total mass of the salt and solvent.

[0024] Preferably, the salt in the electrolyte of the present invention is selected from 1,1-dimethylpyrrolidine tetrafluoroborate (DMP BF4). Alternatively, one or more of tetraethylamine tetrafluoroborate (TEA BF4), spiro-(1,1')-bispyrrolidine tetrafluoroborate (SBP BF4), 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIm BF4), and 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EMIm FSI) may be used.

[0025] Preferably, the solvent of the electrolyte of the present invention is selected from acetonitrile (AN). Alternatively, any one or more of propylene carbonate (PC) electrolyte, ethylene carbonate (EC) electrolyte, and acetonitrile (AN) may be used.

[0026] Compared with the prior art, the advantages and positive effects of the present invention are as follows:

[0027] This invention provides a novel electrolyte additive. This additive contains small cations to increase the freedom of salt ions and reduce viscosity, while the anionic portion contains hydrophobic groups and oxygen-loving groups on the activated carbon surface to reduce the contact between water molecules and the electrode interface. This results in reduced electrolyte gas production, suitability for high-rate performance, increased capacity utilization, and low cost. In an EDLC cell containing this patented preferred additive, after 1000 cycles at a high current of 125A (the current in typical applications for this capacity cell is 25A), the capacity retention rate increased from 58.9% to 78.2% (a 19.3% increase) compared to the blank sample. After 1500 hours of high-temperature float charging at 65℃ and 2.9V, the capacitance retention rate and internal resistance growth rate also increased from 58.9% to 78.2% (a 19.3% increase). Because the additives selected in this patent can significantly improve capacity performance, the amount of electrolyte injected into the battery cell can be reduced to lower production costs while maintaining the same capacity. Furthermore, it offers high safety, minimal process modifications, and significant improvement in electrochemical performance, thus well meeting the needs of commercialization.

[0028] The present invention is further explained through the following more specific embodiments and comparative examples, but does not constitute any limitation.

[0029] Comparative Example 1:

[0030] (1) Electrolyte preparation: 1,1-dimethylpyrrolidine tetrafluoroborate (DMP BF4) was vacuum baked at 150°C for 8 hours. Before the salt cooled down, it was transferred to a glove box with a moisture content of <20ppm and the water was removed by molecular sieve with acetonitrile (AN) solvent for more than 24 hours. DMP BF4 was added to AN solvent to prepare a 1mol / L solution and stirred and mixed at room temperature for 10 minutes.

[0031] (2) Electrode preparation: consistent with comparative example (1).

[0032] (3) Cell assembly: consistent with comparative example (1).

[0033] Comparative Example 2:

[0034] (1) Electrolyte preparation: The electrolyte of Comparative Example 1 was mixed with potassium tetrafluoroborate (KBF4) in a ratio of 98:2 (wt) to obtain the electrolyte of Comparative Example 2.

[0035] (2) Electrode preparation: consistent with comparative example (1).

[0036] (3) Cell assembly: consistent with comparative example (1).

[0037] Example 1:

[0038] (1) Electrolyte preparation: The electrolyte of Comparative Example 1 was prepared by mixing the electrolyte of Comparative Example 1 with the additive potassium perfluorobutyrate (KFBS) at a ratio of 99:1 (wt).

[0039] (2) Electrode preparation: consistent with comparative example (1).

[0040] (3) Cell assembly: consistent with comparative example (1).

[0041] Example 2:

[0042] (1) Electrolyte preparation: The electrolyte of Example 1 was prepared by mixing the electrolyte of Comparative Example 1 with the additive potassium perfluorobutyrate (KFBS) at a ratio of 98:2 (wt).

[0043] (2) Electrode preparation: consistent with comparative example (1).

[0044] (3) Cell assembly: consistent with comparative example (1).

[0045] Example 3:

[0046] (1) Electrolyte preparation: The electrolyte of Comparative Example 1 was prepared by mixing the electrolyte of Comparative Example 1 with the additive potassium perfluorobutyrate (KFBS) at a ratio of 97:3 (wt).

[0047] (2) Electrode preparation: consistent with comparative example (1).

[0048] (3) Cell assembly: consistent with comparative example (1).

[0049] Example 4:

[0050] (1) Electrolyte preparation: The electrolyte of Example 1 was prepared by mixing the electrolyte of Comparative Example 1 with the additive sodium perfluorobutyrate (NaBF4) at a ratio of 98:2 (wt).

[0051] (2) Electrode preparation: consistent with comparative example (1).

[0052] (3) Cell assembly: consistent with comparative example (1).

[0053] Example 5:

[0054] (4) Electrolyte preparation: The electrolyte of Comparative Example 1 was prepared by mixing the electrolyte of Comparative Example 1 with the additive lithium perfluorobutyrate (LiBF4) at a ratio of 98:2 (wt).

[0055] (5) Electrode preparation: consistent with comparative example (1).

[0056] (6) Cell assembly: consistent with comparative example (1).

[0057] Performance Testing

[0058] Test method:

[0059] The capacity and internal resistance of a 900F battery cell were determined using the Maxwell six-step method. An Arbin 5V 30A 32CH device was used. The cell was allowed to stand for 10 seconds, then charged with a constant current (e.g., 25A) to the rated voltage (e.g., 2.9V), allowed to stand for 5 seconds, and then allowed to stand for another 10 seconds. The cell was then discharged with a constant current (e.g., 25A) to the set voltage (50% of the rated voltage, 1.45V), allowed to stand for 5 seconds, and steps 1 to 6 were repeated for a second test. The cutoff voltage (V1) at step 5 and the voltage (V2) after standing for 5 seconds at step 6 were recorded during the second test. The capacity was calculated as: C = I5 * (t5 - t4) / (V4 - V5). The DC internal resistance was calculated using the formula: ESR. DC =(V6-V5) / I5. The testing procedure for low-temperature DCR is the same as above. After the cell has been left to stand at the rated temperature for 2 hours, the internal resistance is tested.

[0060] The test method for high-temperature load with a voltage limit of 2.9 V at 65℃ is as follows: At room temperature, test the basic performance: voltage, internal resistance, thickness (height of top and bottom), and mass. Control the temperature of the temperature chamber at 25℃ and let it stand for 1 hour; charge it to 2.8 V with a constant current of 25A; discharge it to 1.5 V with a constant current of 25A (this step is 0.1s timing), repeat the charge and discharge cycle 3 times, and take the third time as the cell capacitor; transfer the cell to the 65℃ temperature chamber and make connections; charge it at a constant voltage of 2.8V for 168 hours (7 days); transfer the cell to room temperature and let it stand for 3 hours; repeat the above steps until the 12th week.

[0061] The test method for 25℃ 125A cycle is as follows: 1. Control the temperature at 25℃ and let it rest for 10 minutes; discharge at 25A constant current to 1.35V, charge at 25A constant current and constant voltage to 2.7V / 0.1A, charge at 2.7V constant voltage for 5 minutes, discharge at 25A constant current to 1.35V (capacity calibration C1, 1s step-off), charge at 125A constant current and constant voltage to 2.7V / 0.1A (10s step-off), discharge at 125A constant current to 1.35V (1s step-off), repeat the first two steps 1000 times.

[0062] The test method for high and low temperature discharge is as follows: control the temperature at 25℃; let it stand for 10 minutes; discharge with a constant current of 25A to 1.35V; let it stand for 1 minute; charge with a constant current and constant voltage of 25A to 2.7V / 0.1A; let it stand for 1 minute; control the temperature at 65℃; let it stand for 3 hours; discharge with a constant current of 25A to 1.05V (0.01s step-by-step); repeat the above steps to test the discharge curve at -40℃.

[0063] The above-described embodiments are preferred embodiments of the present invention, but these embodiments are not intended to limit the patent scope of the present invention. All equivalent implementations or modifications that do not depart from the spirit of the present invention should be included within the protection scope of the present invention.

[0064] The electrolyte in Comparative Example 1 was a blank sample without additives. The electrolytes in Examples 1, 2, and 3 were prepared by mixing the electrolyte from Comparative Example 1 with potassium perfluorobutyrate (KFBS) at mass ratios of 99:1, 98:2, and 97:3, respectively. The 900F cells prepared by electrolyte injection were subjected to a high-temperature load of 8 weeks at 65°C and 2.9V. Figure 1 As shown, the initial capacity of the cell after adding KFBS is about 40-50F higher than that of Comparative Example 1 (blank sample), indicating that the KFBS cations released from the additive are highly reactive. + The adsorption of KFBS contributed a small amount of Faraday capacity, which increased slightly with increasing KFBS content. After 8 weeks, the capacity retention rate significantly increased by approximately 11%. The internal resistance growth rate of Examples 1-3 decreased significantly by approximately 48%, while the internal resistance growth rates of Examples 2 and 3 were very similar. Considering both capacity and internal resistance changes, Example 2 (2.0 wt% KFBS) was preferred. To demonstrate... Figure 1 To demonstrate the universality of the structural design in double-layer capacitor electrolytes, sodium perfluorobutyrate (NaFBS, 2wt%, Example 4) and lithium perfluorobutyrate (LiFBS, 2wt%, Example 5), with structures similar to potassium perfluorobutyrate (KFBS), were designed. These electrolytes were then injected into the battery cell for a high-temperature load test at 65°C and 2.9V. The results are as follows... Figure 2 As shown: Replace the cation with Li + Na + This can also slightly increase the cell's capacity, improve capacity retention, and reduce the rate of increase in internal resistance, indicating that this patent, by introducing competitive solvation modifiers (such as those containing Li), achieves this. + Na + K + The design strategy of preferentially binding small cations (such as those in salts) to solvent molecules, allowing the previously solvent-bound salt cations to release and move freely, thus increasing the degree of freedom of salt ions and reducing the overall viscosity of the electrolyte, is significantly effective. However, the capacity retention rate is potassium salt > sodium salt > lithium salt, while the internal resistance growth rate is the opposite. This indicates that the stronger the electropositivity, the more significant the effect of reducing the overall viscosity of the electrolyte. The migration resistance of ions in the electrolyte is reduced, and more ions can reach the positive and negative electrode surfaces for adsorption and desorption in the same amount of time, contributing to the capacity. More advantageously, potassium salts are generally cheaper than structurally similar sodium and lithium salts, making them more cost-effective for commercial production.

[0065] Anionic perfluorobutyrate (FBS) - ) becomes tetrafluoroborate (BF4) -To verify the effectiveness of the anion design strategy, Comparative Example 2, containing 2wt% KBF4, showed the following high-temperature loading results: Figure 3 As shown: Comparative Example 2 contains K + Its capacity retention rate was slightly higher than that of Comparative Example 1 (about 3%), and its internal resistance growth rate was about 32% lower than that of Comparative Example 1, but lower than that of Example 2 (2wt% KFBS). This indicates that designing the anion to have a structure containing both hydrophobic and oxygen-loving groups can effectively achieve separation and reduce the contact between water molecules and the electrode interface.

[0066] Electric double-layer capacitors (EDLCs), as power devices, exhibit significantly better high-rate cycling performance than lithium-ion batteries. Therefore, to further verify the improvement of cell power performance by KFBS, a 125A high-current cycle test was conducted on the cell (the conventional cycle current is 25A). The results are shown in Table 2. Figure 4 As shown, the initial capacity of Example 2 was significantly improved, the average energy efficiency of the cycle increased from 73.8% in Comparative Example 1 (blank sample) to 85.1% (an increase of 11.3%), and the capacity retention increased from 58.7% to 75.6% (an increase of 16.9%).

[0067] Table 2

[0068] parameter Comparative Example 1-1 Comparative Examples 1-2 Example 2-1 Example 2-2 Initial capacity / F 928.03 938.67 981.33 984.12 125A Cycle Energy Efficiency / % 73.65 73.93 84.94 85.28 Capacity retention rate after 1000 laps / % 55.17 62.22 75.27 75.88

[0069] The cells from Comparative Example 1 and Example 2 were charged to a rated voltage of 2.7V at room temperature and then subjected to discharge tests at extreme temperatures of 65°C and -40°C, respectively. In Comparative Example 1, the voltage rapidly dropped to 2.41V (65°C) and 2.32V (-40°C) at the extreme temperatures, while the voltage drop in Example 2 was smaller, with initial voltages of 2.48V (65°C) and 2.51V (-40°C) at the extreme temperatures, indicating that Example 2 had fewer side reactions. At 65°C, the capacity of Example 2 was 7.93% higher than that of Comparative Example 1, and at -40°C, the capacity of Example 2 was 4.64% higher than that of Comparative Example 1, demonstrating that the preferred additive structure of this patent exhibits significant effects at both high and low temperatures.

[0070] Table 3

[0071] Temperature / °C Comparative Example 1 Example 2 Capacity improvement rate / % 65 842.4160 909.2320 7.93 25 922.1040 983.6640 6.68 -40 891.7467 933.1200 4.64

Claims

1. A double-layer capacitor electrolyte that combines high energy density and cost advantages, characterized in that, The electrolyte comprises an organic solvent, an electrolyte salt, and an additive; wherein the additive has the following general formula: C represents a carbon atom, O represents an oxygen atom, and R1 can be carbon (C) or sulfur (S). If it is C, there is no dashed line, indicating a CO single bond. If it is sulfur, the dashed line becomes a solid line, indicating an S=O double bond. C=O or S=O acts as a strong hydrogen bond acceptor, forming hydrogen bonds with the oxygen-containing functional groups hydroxyl (-OH) and carboxyl (-COOH) on the surface of activated carbon. On the other side, a hydrophobic group R2 is introduced. R2 can be a fluoroalkane chain such as trifluoromethyl (-CF3), pentafluoroethyl (-C2F5), heptafluoropropyl (-C3F7), or perfluorooctyl (-C8F5). 17 ) or perfluorohexyl (-C6F) 13 ), long-chain alkyl groups such as dodecyl (-C 12 H 25 ), tetradecyl (-C 14 H 29 Aromatic groups such as phenyl (-C6H5) and naphthyl (-C) 10 H7), and siloxane groups (Si-O).

2. The electrolyte according to claim 1, characterized in that, The additive is potassium perfluorobutyrate (KFBS).

3. The electrolyte according to claim 1, characterized in that, The electrolyte salt is one or more of the following: tetraethylamine tetrafluoroborate (TEABF4), spiro-(1,1')-bispyrrolidine tetrafluoroborate (SBP BF4), 1,1-dimethylpyrrolidine tetrafluoroborate (DMPBF4), 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIm BF4), and 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EMIm FSI).

4. The electrolyte according to claim 1, characterized in that, The concentration of the electrolyte salt is 0.5 mol / L to 1.5 mol / L.

5. The electrolyte according to claim 1, characterized in that, The organic solvent is selected from at least one of acetonitrile (AN), propylene carbonate (PC) electrolyte, ethylene carbonate (EC) electrolyte, N,N-dimethylformamide (DMF), and 3-methoxypropionitrile (MPN).

6. A method for preparing the double-layer capacitor electrolyte as described in any one of claims 1 to 4, characterized in that, The method includes the following steps: (1) Mix carbonate and nitrile organic solvents in a certain proportion, and purify them by removing impurities and water to obtain a mixed solvent; (2) At room temperature, add the salt to the mixed solvent obtained in step (1) and let it stand to dissolve to obtain the electrolyte; (3) Add 0.01 to 5.00% of the electrolyte mass to the electrolyte obtained in step (2) and let it stand to dissolve to obtain the double-layer capacitor electrolyte.

7. A double-layer capacitor, characterized in that, Includes the electrolyte as described in any one of claims 1 to 5.

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