High-temperature electrolyte for supercapacitors

Abstract

The application relates to a high-temperature electrolyte for supercapacitors. The high-temperature electrolyte comprises an electrolyte and an organic solvent, the organic solvent comprises a nitrile compound and an aryl sulfone compound, and the electrolyte is a quaternary ammonium salt with a concentration of 0.7-1.4 mol / L. Through the overall improvement of the electrolyte, the flash point and gas production of the electrolyte are effectively improved, so that the electrolyte has excellent high-temperature performance and good flame retardance, and the safe use range of the supercapacitor at high temperature is widened.

Description

Technical Field

[0001] This invention relates specifically to the field of double-layer capacitor technology, and more specifically to a high-temperature electrolyte for supercapacitors. Background Technology

[0002] Supercapacitors are a new type of energy storage device that falls between capacitors and batteries. They possess high power density and energy storage characteristics while also enabling rapid charging and discharging. Compared to batteries and traditional capacitors, supercapacitors offer advantages such as high power density, long cycle life, wide operating temperature range, and environmental friendliness. With societal progress and continuous technological development, supercapacitors are finding applications in an increasing number of fields, including new energy vehicles, wind power generation systems, smart grids, urban rail transit, and automotive start-stop systems.

[0003] With the expanding applications of supercapacitors, especially in special environments where they operate at high temperatures (≥65℃) for extended periods, supercapacitors cannot maintain high power and long lifespan. Therefore, it is essential to develop an electrolyte that can operate stably and safely at high temperatures.

[0004] Currently, supercapacitors widely use acetonitrile electrolytes based on tetraethylammonium tetrafluoroborate. However, acetonitrile has a flash point of 5.6℃, resulting in a relatively low overall flash point for the electrolyte. The boiling point of acetonitrile (78℃) limits the upper limit of the operating temperature of acetonitrile electrolyte systems. Experiments have shown that operating temperatures above 65℃ can lead to capacitor combustion, gas expansion, and rupture. Furthermore, some high-temperature resistant supercapacitors on the market add chain alkyl sulfones to the electrolyte, which increases the operating temperature but reduces the electrolyte's conductivity and increases its DC internal resistance. Additionally, the high proportion of acetonitrile in commercially available high-temperature resistant electrolytes still poses a significant risk of combustion and fire. Summary of the Invention

[0005] The purpose of this invention is to provide a high-temperature electrolyte for supercapacitors that can operate stably under high-temperature conditions (up to 85°C).

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A high-temperature electrolyte for supercapacitors, the high-temperature electrolyte comprising an electrolyte and an organic solvent, the organic solvent comprising nitrile compounds and aryl sulfone compounds, and the electrolyte being a quaternary ammonium salt with a concentration of 0.7–1.4 mol / L.

[0008] Preferably, the organic solvent is composed of the nitrile compound and the aryl sulfone compound.

[0009] Preferably, the mass of the aryl sulfone compound fed into the feed is 10% to 40% of the total mass of the organic solvent.

[0010] Preferably, the nitrile compound is acetonitrile (CAS: 75-05-8) and / or 3-methoxypropionitrile (CAS: 110-67-8); and / or, the aryl sulfone compound is difluoromethylphenyl sulfone (CAS: 1535-65-5) and / or diphenyl sulfone (CAS: 127-63-9).

[0011] Preferably, the nitrile compound is a mixture of acetonitrile and 3-methoxypropionitrile, wherein the mass of acetonitrile fed is 30% to 65% of the total mass of the organic solvent.

[0012] Preferably, the electrolyte is N,N-dimethylpyrrolidone tetrafluoroborate (CAS No.: 69444-51-5) and / or 5,5-spirobispyrrolidone tetrafluoroborate (CAS No.: 129211-47-8).

[0013] Preferably, the high-temperature electrolyte for the supercapacitor further includes a flame retardant, which is a compound containing a phosphazene group.

[0014] More preferably, the mass of the flame retardant is 0.5% to 10% of the total mass of the organic solvent.

[0015] More preferably, the flame retardant is ethoxy(pentafluoro)cyclotriphosphazene (CAS No.: 33027-66-6) and / or phenoxy(pentafluoro)cyclotriphosphazene (CAS No.: 33027-68-8).

[0016] Preferably, the high-temperature electrolyte for the supercapacitor is a mixture of electrolyte, flame retardant, and organic solvent.

[0017] A supercapacitor, the supercapacitor comprising a high-temperature electrolyte for supercapacitors.

[0018] Preferably, the supercapacitor is a double-layer supercapacitor, and its electrodes are porous activated carbon electrodes, with the distance between the two electrodes being on the nanometer scale.

[0019] Specifically, the distance between the two electrodes is 50nm to 100nm.

[0020] Due to the application of the above-mentioned technical solution, the present invention has the following advantages compared with the prior art:

[0021] This invention improves the electrolyte formulation for supercapacitors, enabling the electrolyte to operate normally at high temperatures (up to 85°C) with high capacity retention and low DC internal resistance growth rate. Furthermore, the addition of phosphazene flame retardants significantly enhances the flame retardant effect of the electrolyte, further expanding its application in high-temperature flame retardancy. Attached Figure Description

[0022] Figure 1 The NMR spectrum of N,N-dimethylpyrrolidineonium tetrafluoroborate;

[0023] Figure 2 The NMR spectrum of 5,5-spirobispyrrolomium tetrafluoroborate. Detailed Implementation

[0024] The present invention will be further described below with reference to embodiments, but the present invention is not limited to the following embodiments. The implementation conditions used in the embodiments can be further adjusted according to different requirements of specific applications, and the implementation conditions not specified are conventional conditions in this industry.

[0025] To address the issues of poor performance and inadequate flame retardancy of existing supercapacitor electrolytes under high-temperature conditions, the inventors conducted extensive research and experimental verification, ultimately proposing a high-temperature electrolyte for supercapacitors.

[0026] According to the present invention, the high-temperature electrolyte comprises an electrolyte and an organic solvent, wherein the organic solvent comprises nitrile compounds and aryl sulfone compounds, and the electrolyte is a quaternary ammonium salt with a concentration of 0.7 to 1.4 mol / L.

[0027] In the supercapacitor electrolyte of this invention, the organic solvent is composed of a combination of nitrile compounds and aryl sulfone compounds. The boiling points and flash points of the nitrile compounds and aryl sulfone compounds used in this invention are shown in Table 1 below.

[0028] Table 1

[0029] Acetonitrile 3-Methoxypropionitrile Difluoromethylphenyl sulfone diphenyl sulfone Boiling point ℃ 81 165.5 289.5 378 Flash point ℃ 5.6 61 128.9 226.8

[0030] Table 1 shows that both difluoromethylphenyl sulfone and diphenyl sulfone have high boiling and flash points. In the experiment, nitriles were used as the base solvent, and one or two aryl sulfones were added to the electrolyte. As the amount added increased, the high-temperature performance of the electrolyte improved.

[0031] Furthermore, when the mass of aryl sulfone compounds is greater than 40% of the solvent mass, the electrolyte viscosity will increase and the conductivity will decrease, resulting in a reduction in the performance of the electrolyte. When the amount of aryl sulfone compounds is too low, it will not be able to achieve the effect of high temperature resistance.

[0032] Preferably, the aryl sulfone compound accounts for 10% to 40% of the solvent mass.

[0033] Furthermore, the acetonitrile content is 30% to 65% of the total solvent mass. When the acetonitrile content is too high, there is a risk of deflagration. When the content is too low, it will reduce the overall conductivity of the electrolyte, increase the viscosity, and affect the electrical performance.

[0034] Furthermore, the electrolyte and solvent are mixed to prepare a basic electrolyte solution.

[0035] Furthermore, the addition of flame retardants effectively improves the flame retardant properties of the electrolyte. However, when the amount of flame retardant added exceeds 10%, it will reduce the conductivity of the electrolyte and the discharge capacity of the capacitor. Excessive addition will also increase the cost of the electrolyte.

[0036] Preferably, the amount of flame retardant added is 0.5% to 10% of the mass of the base electrolyte.

[0037] Preferably, in the high-temperature flame-retardant electrolyte, the flame retardant is one or a combination of two of ethoxy(pentafluoro)cyclotriphosphazene and / or phenoxy(pentafluoro)cyclotriphosphazene, which have flame-retardant effects.

[0038] Preferably, the electrolyte concentration in the supercapacitor electrolyte is 0.7–1.4 mol / L. Actual data analysis revealed that when the electrolyte concentration is below 0.7 mol / L, the electrolyte conductivity decreases, failing to meet the electrical performance requirements of the supercapacitor; when the electrolyte concentration is above 1.4 mol / L, the electrolyte viscosity increases, and the conductivity decreases, thereby reducing the electrolyte's discharge performance.

[0039] Preferably, in the electrolyte of the supercapacitor, the electrolyte is a quaternary ammonium salt, selected from one or a combination of N,N-dimethylpyrrolidone ammonium tetrafluoroborate and 5,5-spirobispyrrolidone ammonium tetrafluoroborate.

[0040] The technical solutions and effects of this application are further illustrated below with reference to specific embodiments and comparative examples, but these embodiments should not be construed as limiting the scope of protection of the claims of this invention.

[0041] Unless otherwise specified, all reagents and raw materials used in this invention are commercially available products.

[0042] In this invention, unless otherwise specified, "%" represents a percentage by mass.

[0043] In this invention, the synthesis method of N,N-dimethylpyrrolidineonium tetrafluoroborate ammonium is derived from patent CN105448538A (right holder: Jiangsu Guotai Chaowei New Materials Co., Ltd.).

[0044] The specific synthesis method is as follows:

[0045] (1) First, add 200g of sodium hydroxide to 1333g of high-purity water to prepare a 13% sodium hydroxide aqueous solution, and then draw it into a 5L stainless steel high-pressure reactor. Then, while stirring, draw in 630g of 1,4-dichlorobutane, and finally introduce 236.5g of dimethylamine. Stir the reaction solution for 30min until uniform, turn on the electric heating to raise the temperature to 90℃ and react for 10 hours. During the reaction, control the pressure at 0.1MPa~1.0MPa. After returning to room temperature, release 2388g of the synthesis reaction solution.

[0046] (2) The above-mentioned synthetic reaction solution was vacuum dehydrated at 110°C on a rotary evaporator to obtain 968g of powder-solid mixture;

[0047] (3) Add 968g of anhydrous ethanol to the above solid mixture, stir for 60min, and then filter to obtain 1600g of ethanol solution of N,N-dimethylpyrrolidone chloride.

[0048] (4) Add 525g of ammonium tetrafluoroborate to the above ethanol solution of N,N-dimethylpyrrolidone onion chloride, reflux at 100°C for 8 hours, cool to 25°C and filter to obtain an ethanol solution of N,N-dimethylpyrrolidone onion tetrafluoroborate.

[0049] (5) The above-mentioned ethanol solution of N,N-dimethylpyrrolidone tetrafluoroborate was crystallized at a low temperature of -20℃, and then filtered to obtain high-purity N,N-dimethylpyrrolidone tetrafluoroborate crystals. The filtrate was recovered and used as an anhydrous organic solvent for the preparation of the next batch of N,N-dimethylpyrrolidone tetrafluoroborate.

[0050] (6) The above N,N-dimethylpyrrolidone tetrafluoroborate crystals were vacuum dried at 120°C for 8 hours to obtain 900g of high-purity anhydrous N,N-dimethylpyrrolidone tetrafluoroborate.

[0051] The purity of the product analyzed by ion chromatography was 99.8%, and the yield reached 96.27%.

[0052] ICP testing revealed: Na + 3ppm, K + 1.5ppm, Fe 3+ 0.8ppm, Ca 2+ 0.9ppm.

[0053] Potentiometric titration: Cl - 0.5ppm.

[0054] The synthesis method of 5,5-spirobispyrrolomethylene tetrafluoroborate ammonium is derived from patent CN104387386B (rights holder: Jiangsu Guotai Chaowei New Materials Co., Ltd.).

[0055] The specific synthesis method is as follows: In a three-necked flask, 105 g (1 mol) of NH4BF4, 254 g (2 mol) of 1,4-dichlorobutane, 276 g (2.1 mol) of K2CO3, and 2000 ml of deionized water were added sequentially. The mixture was refluxed at atmospheric pressure for 10 h, and the resulting reaction solution was concentrated to a product content of 21%. After cooling the concentrated solution, the residue was removed by filtration. The resulting filtrate was further concentrated to a paste-like solid with a product content of 75%. An appropriate amount of ethanol was added, and the mixture was stirred and crystallized at -10 °C for 10 h. After filtration, colorless and transparent crystals were obtained. The crystals were dried under vacuum for 24 h to obtain 184 g of colorless crystalline spiro1,1'-bispyrrole quaternary ammonium salt of tetrafluoroborate. The molar yield was 86.3%.

[0056] 1H NMR results: 1H NMR (400MHz, D2O): δ=2.17(8*H,4*CH2), δ=3.49(8*H,4*4CH2), δ=4.8(D2O).

[0057] Ion chromatography yielded a product purity of 99.9%.

[0058] ICP testing revealed: Na + 0.9ppm, K + 3ppm, Fe 3+ 0.2ppm, Ca 2+ 0.6ppm.

[0059] Potentiometric titration: Cl - 3.1ppm.

[0060] In this invention, the moisture content of each raw material is ensured to be less than 10 ppm before preparing the electrolyte.

[0061] The specific preparation method for the electrolyte is as follows:

[0062] Step 1: In a glove box where the water and oxygen content is less than 1 ppm (mass percentage), mix nitrile compounds and aryl sulfone compounds to form a composite organic solvent.

[0063] Step 2: Add electrolyte to the composite organic solvent and stir thoroughly until a homogeneous liquid is formed. This liquid is the base electrolyte.

[0064] Step 3: Add flame retardant at a mass equivalent to 0.5% to 10% of the base electrolyte to prepare the high-temperature flame-retardant electrolyte for the supercapacitor.

[0065] The following examples are all prepared according to different proportions of the above method.

[0066] Example 1

[0067] In a glove box where the water and oxygen content is below 1 ppm (mass percentage), acetonitrile, 3-methoxypropionitrile, and difluoromethylphenyl sulfone are mixed in a mass ratio of 60:25:15 to form a composite organic solvent. 0.8 mol / L of N,N-dimethylpyrrolidone ontium tetrafluoroborate is added to the composite solvent and stirred until a homogeneous liquid is formed. This is the base electrolyte. Then, 2% of the flame retardant ethoxy(pentafluoro)cyclotriphosphazene is added to the base electrolyte to prepare a high-temperature flame-retardant electrolyte for supercapacitors.

[0068] Example 2

[0069] In a glove box where the water and oxygen content is below 1 ppm (mass percentage), acetonitrile, 3-methoxypropionitrile, and difluoromethyl sulfone are mixed in a mass ratio of 55:15:30 to form a composite organic solvent. 0.75 mol / L of N,N-dimethylpyrrolidone ontium tetrafluoroborate is added to the composite solvent and stirred until a homogeneous liquid is formed. This electrolyte serves as the base electrolyte. Then, 8% of the flame retardant ethoxy(pentafluoro)cyclotriphosphazene is added to the base electrolyte to prepare a high-temperature flame-retardant electrolyte for supercapacitors.

[0070] Example 3

[0071] In a glove box where the water and oxygen content is below 1 ppm (mass percentage), acetonitrile, 3-methoxypropionitrile, and diphenyl sulfone are mixed in a mass ratio of 60:25:15 to form a composite organic solvent. 1.0 mol / L of N,N-dimethylpyrrolidone ontium tetrafluoroborate is added to the composite solvent and stirred until a homogeneous liquid is formed. This electrolyte serves as the base electrolyte. Then, 5% of a flame retardant phenoxy(pentafluoro)cyclotriphosphazene is added to the base electrolyte to prepare a high-temperature flame-retardant electrolyte for supercapacitors.

[0072] Example 4

[0073] In a glove box where the water and oxygen content is below 1 ppm (mass percentage), acetonitrile, 3-methoxypropionitrile, and diphenyl sulfone are mixed in a mass ratio of 55:15:30 to form a composite organic solvent. 1.0 mol / L of N,N-dimethylpyrrolidone ontium tetrafluoroborate is added to the composite solvent and stirred until a homogeneous liquid is formed. This electrolyte serves as the base electrolyte. Then, 5% of a flame retardant phenoxy(pentafluoro)cyclotriphosphazene is added to the base electrolyte to prepare a high-temperature flame-retardant electrolyte for supercapacitors.

[0074] Example 5

[0075] In a glove box where the water and oxygen content is below 1 ppm (mass percentage), acetonitrile, 3-methoxypropionitrile, and difluoromethyl sulfone are mixed in a mass ratio of 50:40:10 to form a composite organic solvent. 0.8 mol / L of 5,5-spirobispyrroleonium tetrafluoroborate is added to the composite solvent and stirred until a homogeneous liquid is formed. This electrolyte serves as the base electrolyte. Then, 3% of the flame retardant ethoxy(pentafluoro)cyclotriphosphazene is added to the base electrolyte to prepare a high-temperature flame-retardant electrolyte for supercapacitors.

[0076] Example 6

[0077] In a glove box where the water and oxygen content is below 1 ppm (mass percentage), acetonitrile, 3-methoxypropionitrile, and difluoromethyl sulfone are mixed in a mass ratio of 50:25:25 to form a composite organic solvent. 0.8 mol / L of 5,5-spirobispyrroleonium tetrafluoroborate is added to the composite solvent and stirred until a homogeneous liquid is formed. This electrolyte serves as the base electrolyte. Then, 6% of the flame retardant ethoxy(pentafluoro)cyclotriphosphazene is added to the base electrolyte to prepare a high-temperature flame-retardant electrolyte for supercapacitors.

[0078] Example 7

[0079] In a glove box with water and oxygen content below 1 ppm (mass percentage), acetonitrile, 3-methoxypropionitrile, and diphenyl sulfone were mixed in a mass ratio of 40:40:20 to form a composite organic solvent. 1.0 mol / L of 5,5-spirobispyrroleonium tetrafluoroborate was added to the composite solvent and stirred until a homogeneous liquid was formed. This electrolyte served as the base electrolyte. Then, 4% of the flame retardant ethoxy(pentafluoro)cyclotriphosphazene and 1% of the flame retardant phenoxy(pentafluoro)cyclotriphosphazene were added to the base electrolyte to prepare a high-temperature flame-retardant electrolyte for supercapacitors.

[0080] Example 8

[0081] In a glove box with water and oxygen content below 1 ppm (mass percentage), acetonitrile, 3-methoxypropionitrile, and diphenyl sulfone were mixed in a mass ratio of 55:20:25 to form a composite organic solvent. 1.0 mol / L of 5,5-spirobispyrroleonium tetrafluoroborate was added to the composite solvent and stirred until a homogeneous liquid was formed. This electrolyte served as the base electrolyte. Then, 5% of the flame retardant ethoxy(pentafluoro)cyclotriphosphazene and 2% of the flame retardant phenoxy(pentafluoro)cyclotriphosphazene were added to the base electrolyte to prepare a high-temperature flame-retardant electrolyte for supercapacitors.

[0082] Example 9

[0083] In a glove box where the water and oxygen content is below 1 ppm (mass percentage), acetonitrile, 3-methoxypropionitrile, difluoromethylphenyl sulfone, and diphenyl sulfone are mixed in a mass ratio of 35:30:25:10 to form a composite organic solvent. 0.9 mol / L of N,N-dimethylpyrrolidone ontium tetrafluoroborate is added to the composite solvent and stirred until a homogeneous liquid is formed. This electrolyte serves as the base electrolyte. Then, 6% of the flame retardant ethoxy(pentafluoro)cyclotriphosphazene is added to the base electrolyte to prepare a high-temperature flame-retardant electrolyte for supercapacitors.

[0084] Example 10

[0085] In a glove box where the water and oxygen content is below 1 ppm (mass percentage), acetonitrile, 3-methoxypropionitrile, difluoromethylphenyl sulfone, and diphenyl sulfone are mixed in a mass ratio of 40:25:25:10 to form a composite organic solvent. 1.0 mol / L of N,N-dimethylpyrrolidone ontium tetrafluoroborate is added to the composite solvent and stirred until a homogeneous liquid is formed. This electrolyte serves as the base electrolyte. Then, phenoxy(pentafluoro)cyclotriphosphazene, equivalent to 6% of the flame retardant in the base electrolyte, is added to prepare a high-temperature flame-retardant electrolyte for supercapacitors.

[0086] Example 11

[0087] In a glove box where the water and oxygen content is below 1 ppm (mass percentage), acetonitrile, 3-methoxypropionitrile, difluoromethylphenyl sulfone, and diphenyl sulfone are mixed in a mass ratio of 35:35:20:10 to form a composite organic solvent. 1.0 mol / L of 5,5-spirobispyrroleonium tetrafluoroborate is added to the composite solvent and stirred until a homogeneous liquid is formed. This electrolyte serves as the base electrolyte. Then, 4% of the flame retardant phenoxy(pentafluoro)cyclotriphosphazene is added to the base electrolyte to prepare a high-temperature flame-retardant electrolyte for supercapacitors.

[0088] Example 12

[0089] In a glove box where the water and oxygen content is below 1 ppm (mass percentage), acetonitrile, 3-methoxypropionitrile, difluoromethylphenyl sulfone, and diphenyl sulfone are mixed in a mass ratio of 40:40:10:10 to form a composite organic solvent. 1.2 mol / L of 5,5-spirobispyrroleonium tetrafluoroborate is added to the composite solvent and stirred until a homogeneous liquid is formed. This electrolyte serves as the base electrolyte. Then, 4% of the flame retardant phenoxy(pentafluoro)cyclotriphosphazene is added to the base electrolyte to prepare a high-temperature flame-retardant electrolyte for supercapacitors.

[0090] Example 13

[0091] In a glove box where the water and oxygen content is below 1 ppm (mass percentage), acetonitrile, 3-methoxypropionitrile, difluoromethylphenyl sulfone, and diphenyl sulfone are mixed in a mass ratio of 55:35:5:5 to form a composite organic solvent. 1.2 mol / L of N,N-dimethylpyrrolidone ontium tetrafluoroborate is added to the composite solvent and stirred until a homogeneous liquid is formed. This electrolyte serves as the base electrolyte. Then, 3% of the flame retardant ethoxy(pentafluoro)cyclotriphosphazene is added to the base electrolyte to prepare a high-temperature flame-retardant electrolyte for supercapacitors.

[0092] Example 14

[0093] In a glove box where the water and oxygen content is below 1 ppm (mass percentage), acetonitrile, 3-methoxypropionitrile, difluoromethylphenyl sulfone, and diphenyl sulfone are mixed in a mass ratio of 60:30:5:5 to form a composite organic solvent. 1.2 mol / L of N,N-dimethylpyrrolidone ontium tetrafluoroborate is added to the composite solvent and stirred until a homogeneous liquid is formed. This electrolyte serves as the base electrolyte. Then, 3% of the flame retardant phenoxy(pentafluoro)cyclotriphosphazene is added to the base electrolyte to prepare a high-temperature flame-retardant electrolyte for supercapacitors.

[0094] Example 15

[0095] In a glove box where the water and oxygen content is below 1 ppm (mass percentage), acetonitrile, 3-methoxypropionitrile, difluoromethylphenyl sulfone, and diphenyl sulfone are mixed in a mass ratio of 60:30:5:5 to form a composite organic solvent. 1.3 mol / L of 5,5-spirobispyrroleonium tetrafluoroborate is added to the composite solvent and stirred until a homogeneous liquid is formed. This electrolyte serves as the base electrolyte. Then, 2% of the flame retardant ethoxy(pentafluoro)cyclotriphosphazene is added to the base electrolyte to prepare a high-temperature flame-retardant electrolyte for supercapacitors.

[0096] Example 16

[0097] In a glove box where the water and oxygen content is below 1 ppm (mass percentage), acetonitrile, 3-methoxypropionitrile, and difluoromethylphenyl sulfone are mixed in a mass ratio of 55:30:15 to form a composite organic solvent. 1.3 mol / L of 5,5-spirobispyrroleonium tetrafluoroborate is added to the composite solvent and stirred until a homogeneous liquid is formed. This electrolyte serves as the base electrolyte. Then, 2% of the flame retardant phenoxy(pentafluoro)cyclotriphosphazene is added to the base electrolyte to prepare a high-temperature flame-retardant electrolyte for supercapacitors.

[0098] Example 17

[0099] In a glove box where the water and oxygen content is below 1 ppm (mass percentage), acetonitrile, 3-methoxypropionitrile, difluoromethylphenyl sulfone, and diphenyl sulfone are mixed in a mass ratio of 60:25:10:5 to form a composite organic solvent. 1.0 mol / L N,N-dimethylpyrrolidone tetrafluoroborate and 0.3 mol / L 5,5-spirobispyrrolidone tetrafluoroborate are added to the composite solvent and stirred until a homogeneous liquid is formed. This is the base electrolyte. Then, 3% of the flame retardant phenoxy(pentafluoro)cyclotriphosphazene is added to the base electrolyte to prepare a high-temperature flame-retardant electrolyte for supercapacitors.

[0100] Example 18

[0101] In a glove box where the water and oxygen content is below 1 ppm (mass percentage), acetonitrile, 3-methoxypropionitrile, difluoromethylphenyl sulfone, and diphenyl sulfone are mixed in a mass ratio of 30:55:10:5 to form a composite organic solvent. 0.8 mol / L N,N-dimethylpyrrolidone tetrafluoroborate and 0.5 mol / L 5,5-spirobispyrrolidone tetrafluoroborate are added to the composite solvent and stirred until a homogeneous liquid is formed. This is the base electrolyte. Then, 2% of the flame retardant ethoxy(pentafluoro)cyclotriphosphazene is added to the base electrolyte to prepare a high-temperature flame-retardant electrolyte for supercapacitors.

[0102] Example 19

[0103] In a glove box where the water and oxygen content is below 1 ppm (mass percentage), acetonitrile, 3-methoxypropionitrile, and diphenyl sulfone are mixed in a mass ratio of 60:20:20 to form a composite organic solvent. 0.7 mol / L N,N-dimethylpyrrolidone tetrafluoroborate and 0.4 mol / L 5,5-spirobispyrrolidone tetrafluoroborate are added to the composite solvent and stirred until a homogeneous liquid is formed. This is the base electrolyte. Then, 3% of the flame retardant phenoxy(pentafluoro)cyclotriphosphazene is added to the base electrolyte to prepare a high-temperature flame-retardant electrolyte for supercapacitors.

[0104] Example 20

[0105] In a glove box where the water and oxygen content is below 1 ppm (mass percentage), acetonitrile, 3-methoxypropionitrile, and difluoromethylphenyl sulfone are mixed in a mass ratio of 55:35:10 to form a composite organic solvent. Then, 0.5 mol / L N,N-dimethylpyrrolidone tetrafluoroborate and 0.8 mol / L 5,5-spirobispyrrolidone tetrafluoroborate are added to the composite solvent and stirred until a homogeneous liquid is formed. This is the base electrolyte. Then, 2% of the flame retardant phenoxy(pentafluoro)cyclotriphosphazene is added to the base electrolyte to prepare a high-temperature flame-retardant electrolyte for supercapacitors.

[0106] Example 21

[0107] In a glove box where the water and oxygen content is below 1 ppm (mass percentage), acetonitrile, 3-methoxypropionitrile, difluoromethylphenyl sulfone, and diphenyl sulfone are mixed in a mass ratio of 35:35:5:25 to form a composite organic solvent. 0.5 mol / L N,N-dimethylpyrrolidone tetrafluoroborate and 0.4 mol / L 5,5-spirobispyrrolidone tetrafluoroborate are added to the composite solvent and stirred until a homogeneous liquid is formed. This is the base electrolyte. Then, 3% of the flame retardant ethoxy(pentafluoro)cyclotriphosphazene and 3% of phenoxy(pentafluoro)cyclotriphosphazene are added to the base electrolyte to prepare a high-temperature flame-retardant electrolyte for supercapacitors.

[0108] Comparative Example 1

[0109] An electrolyte for supercapacitors was prepared by adding 1.0 mol / L N,N-dimethylpyrrolidone ontium tetrafluoroborate to acetonitrile solvent in a glove box where the water and oxygen content was less than 1 ppm (mass percentage).

[0110] Comparative Example 2

[0111] An electrolyte for supercapacitors was prepared by adding 1.0 mol / L of 5,5-spirobispyrroleon tetrafluoroborate to acetonitrile solvent in a glove box where the water and oxygen content was less than 1 ppm (mass percentage).

[0112] Comparative Example 3

[0113] Electrolyte for supercapacitors is prepared by adding 1.0 mol / L tetraethylammonium tetrafluoroborate (TEABF4) to acetonitrile solvent in a glove box where the water and oxygen content is less than 1 ppm (mass percentage).

[0114] Comparative Example 4

[0115] In a glove box with water and oxygen content below 1 ppm (mass percentage), 0.5 mol / L N,N-dimethylpyrrolidone tetrafluoroborate and 0.4 mol / L 5,5-spirobispyrrolidone tetrafluoroborate were added to acetonitrile solvent and stirred until a homogeneous liquid was obtained, thus preparing the electrolyte for supercapacitors.

[0116] Comparative Example 5

[0117] In a glove box where the water and oxygen content is less than 1 ppm (mass percentage), acetonitrile and sulfolane are mixed at a mass ratio of 80:20 to form a composite organic solvent. 1 mol / L of 5,5-spirobispyrroleon tetrafluoroborate is added to the composite organic solvent and stirred to form a homogeneous liquid, thus preparing the electrolyte for supercapacitors.

[0118] Table 2 shows the formulations for the examples and comparative examples.

[0119] Table 2

[0120]

[0121]

[0122] In Table 2, TEABF4 in Comparative Example 3 is tetraethylammonium tetrafluoroborate.

[0123] The supercapacitor used in this invention is a cylindrical supercapacitor (cylindrical, 1.5 cm in diameter and 3.0 cm in height). The supercapacitor electrode material is composed of activated carbon, acetylene black, and binder in an 8:1:1 ratio, with a thickness of 300 μm. The activated carbon material is coated onto aluminum foil using a film rolling process to form the supercapacitor electrode. The electrode spacing in the supercapacitor is 50–100 nm, and the designed capacitance is 25 F.

[0124] The final supercapacitor was made by injecting electrolyte into a 25F supercapacitor in an environment where the water and oxygen content was less than 1 ppm (mass percentage). The high-temperature aging performance and DC internal resistance of the supercapacitor were then tested on a battery test cabinet.

[0125] High-temperature aging and internal resistance testing method: A new capacitor is fabricated and placed in a high-temperature chamber. Parameters are set on the battery test cabinet: voltage range 0.1–2.7V, discharge current 1875mA / F. First, it is charged and discharged at room temperature (25℃) for 25 cycles. The average discharge capacity and DC internal resistance are taken to obtain the initial discharge capacity and initial DC internal resistance at 25℃. Then, the temperature is raised to 85℃ and charged at a constant voltage of 2.7V for 1500 hours. After this period, the capacitor temperature is lowered to room temperature (25℃) and maintained for 24 hours. Then, parameters are set on the battery test cabinet: voltage range 0.1–2.7V, discharge current 1875mA / F. The capacitor is charged and discharged for 25 cycles. The average discharge capacity and DC internal resistance are taken to obtain the discharge capacity and DC internal resistance after 1500 hours at 85℃ constant voltage.

[0126] Self-extinguishing time test method: Place 5 grams of electrolyte in a 25 ml crucible, ignite it, and test the change in its self-extinguishing time. Ignite quickly and record the time from when the ignition device is removed until the flame automatically extinguishes; this is the self-extinguishing time. Test each electrolyte 5 times and take the average value. Use the self-extinguishing time per unit mass of electrolyte as the standard to compare the flame retardant performance of different electrolytes.

[0127] Table 3 shows the high-temperature aging data, and Table 4 shows the DC internal resistance and electrolyte self-extinguishing data.

[0128] Table 3 High-temperature aging data

[0129]

[0130]

[0131] Table 4

[0132]

[0133]

[0134] *In Comparative Example 3, some of the supercapacitors bulged and cracked during high-temperature aging.

[0135] As shown in Table 3, the introduction of difluoromethyl sulfone and diphenyl sulfone organic solvents into the electrolyte of this invention can significantly improve the high-temperature performance of the electrolyte. For example, the electrolyte in Example 7 has an organic solvent of acetonitrile / 3-methoxypropionitrile / diphenyl sulfone in a mass ratio of 40:40:20, an electrolyte of 1 mol / L 5,5-spirobispyrrolidon tetrafluoroborate, and flame retardants of 4% ethoxy(pentafluoro)cyclotriphosphazene and 1% phenoxy(pentafluoro)cyclotriphosphazene. After being kept at an ambient temperature of 85°C for 1500 hours, the capacity retention rate is as high as 84.53% and the internal resistance growth rate is only 349% (relative to the initial value at 25°C). This electrolyte has a significant improvement in high-temperature performance and flame retardancy compared with the current mainstream acetonitrile single-system electrolytes (such as Comparative Example 1, Comparative Example 2, and Comparative Example 3).

[0136] While improving high-temperature performance, the safety of the electrolyte also faces greater challenges. This invention significantly improves the flame retardancy of the electrolyte by adding compounds containing phosphazene groups. Data in Table 4 shows that the addition of flame retardants greatly reduces the self-extinguishing time of the electrolyte. Furthermore, this excellent flame retardant effect is inseparable from the nitrile and aryl sulfone organic solvents selected in this invention.

[0137] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A high-temperature electrolyte for supercapacitors, characterized in that: The high-temperature electrolyte comprises an electrolyte and an organic solvent. The organic solvent is composed of nitrile compounds and aryl sulfone compounds. The mass of the aryl sulfone compounds is 10% to 40% of the total mass of the organic solvent. The electrolyte is N,N-dimethylpyrrolidone tetrafluoroborate and / or 5,5-spirobispyrrolidone tetrafluoroborate. The electrolyte is a quaternary ammonium salt with a concentration of 0.7 to 1.4 mol / L.

2. The high-temperature electrolyte for supercapacitors according to claim 1, characterized in that: The nitrile compounds are acetonitrile and / or 3-methoxypropionitrile; and / or, the aryl sulfone compounds are difluoromethylphenyl sulfone and / or diphenyl sulfone.

3. The high-temperature electrolyte for supercapacitors according to claim 1, characterized in that: The nitrile compound is a mixture of acetonitrile and 3-methoxypropionitrile, wherein the mass of acetonitrile fed is 30% to 65% of the total mass of the organic solvent.

4. The high-temperature electrolyte for supercapacitors according to claim 1, characterized in that: The high-temperature electrolyte for the supercapacitor also includes a flame retardant, which is a compound containing a phosphazene group.

5. The high-temperature electrolyte for supercapacitors according to claim 4, characterized in that: The mass of the flame retardant added is 0.5% to 10% of the total mass of the organic solvent; And / or, the flame retardant is ethoxy(pentafluoro)cyclotriphosphazene and / or phenoxy(pentafluoro)cyclotriphosphazene.

6. A supercapacitor, characterized in that, The supercapacitor includes the high-temperature electrolyte for supercapacitors as described in any one of claims 1 to 5.

7. The supercapacitor according to claim 6, characterized in that, The supercapacitor is a double-layer supercapacitor, and its electrodes are porous activated carbon electrodes, with a distance of 50-100 nm between the two electrodes.

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