Super capacitor electrolyte and super capacitor

Abstract

The invention discloses a super capacitor electrolyte and a super capacitor, and relates to the technical field of super capacitors, the super capacitor electrolyte comprises an electrolyte, a solvent and a functional additive; the electrolyte comprises spiro quaternary ammonium tetrafluoroborate and triethyl methyl ammonium tetrafluoroborate; the solvent comprises acetonitrile and sulfolane; the functional additive is a compound with a crown ether structure prepared through a thiol-ene click reaction; the addition amount of the functional additive is 1-10% of that of the solvent. The supercapacitor electrolyte system can resist high voltage and has wide temperature adaptability, that is, the supercapacitor electrolyte system has good high temperature resistance and low temperature resistance, so that the application requirement of a supercapacitor in a complex and severe environment is met.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of supercapacitors, and particularly relates to a supercapacitor electrolyte and a supercapacitor. BACKGROUND

[0002] As a new type of energy storage device, supercapacitors have a wide application prospect in the fields of new energy vehicles, rail transit, smart grids and consumer electronics due to their high power density, long cycle life and fast charging and discharging speed. However, the performance of supercapacitors, especially the performance of the electrolyte thereof, is significantly affected by the ambient temperature, which seriously restricts the application of supercapacitors in extreme environments.

[0003] In a high-temperature environment, the chemical stability of the solvent and the electrolyte salt in the conventional organic electrolyte will be significantly reduced. This will cause the electrolyte to easily decompose and generate gas, and trigger a series of side reactions. The direct consequence is that the internal resistance of the supercapacitor increases sharply, the capacity rapidly decays, and even there is a risk of explosion. In addition, high temperature also accelerates the degradation of the electrode or the electric double layer of the electrolyte interface, affecting the long-term cycle stability of the device.

[0004] In a low-temperature environment, the physical properties of the organic electrolyte will change adversely. Its viscosity will rise sharply, resulting in a significant decrease in the ion migration rate. At the same time, the ion dissociation degree of the electrolyte salt will decrease, reducing the concentration of free-moving carriers in the electrolyte. Under the combined action of these two factors, the internal resistance of the supercapacitor increases significantly, causing its power characteristics to deteriorate sharply, and its capacity to decrease substantially, and even it cannot start and work normally at low temperature.

[0005] In addition, in order to achieve high energy density, the industry generally pursues higher operating voltage. However, increasing the voltage will exacerbate the decomposition side reactions at high temperature, and put forward more stringent requirements on the electrochemical window and thermal stability of the electrolyte. The conventional electrolyte system on the market is difficult to achieve high operating voltage while also considering excellent high-temperature resistance and low-temperature resistance.

[0006] Therefore, it is urgent to develop a new type of supercapacitor electrolyte system that can achieve high voltage resistance while also having wide temperature adaptability, i.e., good high-temperature resistance and low-temperature resistance, to meet the application requirements of supercapacitors in complex and harsh environments. SUMMARY

[0007] The purpose of the present application is to provide a supercapacitor electrolyte to solve the problem that the capacitor cannot simultaneously satisfy high voltage resistance and high or low temperature resistance in the prior art.

[0008] The purpose of the present application is also to provide a supercapacitor for use in high-voltage, high-temperature or low-temperature working environments.

[0009] In a first aspect, the present application provides a supercapacitor electrolyte, comprising an electrolyte, a solvent and a functional additive; The electrolyte comprises a spirocyclic quaternary ammonium tetrafluoroborate and a triethylmethylammonium tetrafluoroborate; The solvent comprises acetonitrile and sulfolane; The functional additive is a compound with crown ether structure prepared by a thiol-ene click reaction; The functional additive is added in an amount of 1% to 10% of the solvent.

[0010] By adopting the above technical solution, the electrolyte of the present application adopts a spirocyclic quaternary ammonium tetrafluoroborate, the spirocyclic cation of which has the characteristics of large steric hindrance and high electrochemical stability, providing a wide electrochemical window for the electrolyte, which is the basis for realizing high energy density. At the same time, it is supplemented by a triethylmethylammonium tetrafluoroborate with a small molecular size, the small cation of which can migrate more quickly and effectively infiltrate the micropores of the electrode, thereby improving the rate performance and low-temperature performance. The two constitute a mixed salt system of large and small ions, taking into account both high voltage and high ionic conductivity.

[0011] The solvent is a mixed system of acetonitrile and sulfolane. Among them, acetonitrile has low viscosity, responsible for providing extremely high ionic conductivity and excellent power characteristics; while sulfolane has high boiling point and good thermal stability, responsible for widening the upper limit of the working temperature of the electrolyte, improving safety and further widening the electrochemical window.

[0012] The compound with crown ether structure is synthesized by a thiol-ene click reaction. The unique cavity structure of the crown ether can selectively recognize and complex the spirocyclic or quaternary ammonium cation in the electrolyte, forming a stable host-guest complex, which can promote its migration number in the electrolyte, especially in the micropores of the electrode, thereby significantly improving the charge and discharge rate and the capacity retention rate at low temperature; in addition, the benzene ring structure of the crown ether cooperates with the sulfolane to improve the thermal stability and flame retardant performance of the electrolyte system.

[0013] Preferably, the raw materials of the compound with crown ether structure include 4-vinylbenzo-15-crown-5 and a thiol compound in a molar ratio of 1: (0.8-1.2).

[0014] Preferably, the thiol compound includes one or a combination of 11-mercaptoundecylphosphonic acid, polyethylene glycol dithiol and mercaptopropyl-terminated polydimethylsiloxane.

[0015] Preferably, the compound with crown ether structure is prepared by the following preparation method: 4-vinylbenzo-15-crown-5 is added to a solvent, stirred and dissolved, then a thiol compound is added, stirred, a photoinitiator is added and irradiated with ultraviolet light for 30-60 min, washed and dried.

[0016] Preferably, the photoinitiator includes benzophenone, benzoin compound.

[0017] Preferably, the mass ratio of acetonitrile and sulfolane is (5-10):(1-5).

[0018] Preferably, the mass ratio of spirocyclic quaternary ammonium tetrafluoroborate and triethylmethylammonium tetrafluoroborate is (1-3):(0.1-0.5).

[0019] Preferably, the electrolyte further includes a diluent; the diluent includes a fluoroalkyl ether and / or a fluoroalkyl sulfonate.

[0020] Preferably, the addition amount of the diluent is 10%-30% of the mass of the solvent.

[0021] More preferably, the fluoroalkyl ether includes 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether; the fluoroalkyl sulfonate includes 2,2,2-trifluoroethyl trifluoromethanesulfonate.

[0022] In a second aspect, the present application also provides a supercapacitor.

[0023] Preferably, the lower limit of the working temperature of the supercapacitor is -40℃.

[0024] The beneficial effects of the present application are: 1. By using the electrolyte of the present application, excellent wide-temperature performance can be achieved, especially maintaining high ionic conductivity at low temperature. The present application uses a mixed electrolyte system of large and small ions composed of spirocyclic quaternary ammonium tetrafluoroborate and triethylmethylammonium tetrafluoroborate and a low-viscosity acetonitrile solvent to ensure the migration ability of ions at low temperature; at the same time, the functional additive with crown ether structure can selectively complex cations, further improving the transference number. This makes the supercapacitor work stably at -40℃ and a wider temperature range.

[0025] 2. By using the electrolyte of the present application, high working voltage and excellent high-temperature stability can be achieved. The spirocyclic quaternary ammonium salt provides a wide electrochemical window, and the high-boiling sulfolane solvent and the crown ether additive containing benzene ring cooperate to significantly improve the thermal stability and flame retardance of the electrolyte system DETAILED DESCRIPTION

[0026] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the specific embodiments of the present application are described in detail below.

[0027] A supercapacitor electrolyte, comprising an electrolyte, a solvent and a functional additive; The electrolyte comprises a spirocyclic quaternary ammonium tetrafluoroborate and a triethylmethylammonium tetrafluoroborate; The solvent comprises acetonitrile and sulfolane; The functional additive is a compound with a crown ether structure prepared through a thiol-ene click reaction; The functional additive is added in an amount of 1% to 10% of the solvent.

[0028] By adopting the above technical solution, the electrolyte of the application adopts a spirocyclic quaternary ammonium tetrafluoroborate, the spirocyclic cation of which has the characteristics of large steric hindrance and high electrochemical stability, thereby providing a wide electrochemical window for the electrolyte and being the basis for realizing high energy density. Meanwhile, the electrolyte is supplemented with a triethylmethylammonium tetrafluoroborate with a small molecular size, the small cation of which can migrate more quickly and effectively infiltrate the micropores of the electrode, thereby improving the rate performance and low-temperature performance. The two constitute a mixed salt system with synergistic large and small ions, which takes into account both high voltage and high ionic conductivity.

[0029] The solvent is a mixed system of acetonitrile and sulfolane. The acetonitrile has low viscosity and is responsible for providing extremely high ionic conductivity and excellent power characteristics; while the sulfolane has a high boiling point and good thermal stability, and is responsible for widening the upper limit of the working temperature of the electrolyte, improving safety and further widening the electrochemical window.

[0030] The compound with a crown ether structure is synthesized through a thiol-ene click reaction. The unique cavity structure of the crown ether can selectively recognize and complex the spirocyclic or quaternary ammonium cation in the electrolyte to form a stable host-guest complex, which can promote the number of migrations of the electrolyte, especially in the micropores of the electrode, thereby significantly improving the charge and discharge rate and the capacity retention rate at low temperature; in addition, the benzene ring structure of the crown ether cooperates with the sulfolane to improve the thermal stability and flame retardant performance of the electrolyte system.

[0031] In some embodiments, the raw material of the compound with a crown ether structure comprises 4-vinylbenzo-15-crown-5 and a mercapto compound in a molar ratio of 1: (0.8-1.2). By adopting this range of molar ratio, the functional group ratio of the vinyl group to the mercapto group in the reactants can be ensured to be reasonable, thereby ensuring that the thiol-ene click reaction is complete and effectively avoiding side reactions caused by excessive amounts of any raw material.

[0032] In some embodiments, the mercapto compound includes a combination of one or more of 11-mercapto-undecylphosphonic acid, polyethylene glycol dithiol, and mercaptopropyl-terminated polydimethylsiloxane; the use of 11-mercapto-undecylphosphonic acid can further introduce a phosphonate group on the basis of the crown ether structure, which can play a synergistic flame-retardant effect with the benzene ring in the crown ether; the use of polyethylene glycol dithiol can construct an additive with a longer flexible chain segment or network structure, enhancing its viscosity adjustment capability for the electrolyte; and the use of mercaptopropyl-terminated polydimethylsiloxane can introduce the excellent high and low temperature resistance, hydrophobicity, and chain flexibility of silicone into the additive molecule, significantly improving the flowability of the electrolyte at extreme temperatures and enhancing its flame-retardant performance.

[0033] In some embodiments, the compound with a crown ether structure is obtained by the following preparation method: 4-vinylbenzo-15-crown-5 is added to a solvent, stirred and dissolved, then a mercapto compound is added, stirred, a photoinitiator is added, and irradiated with ultraviolet light for 30-60 min, and then washed and dried to obtain the product.

[0034] The solvent includes a combination of one or more of tetrahydrofuran, N,N-dimethylformamide, and toluene.

[0035] The synthesis of the compound with a crown ether structure is performed by a mercapto-alkene click reaction. Specifically, 4-vinylbenzo-15-crown-5 and a mercapto compound undergo a highly efficient mercapto-alkene radical addition reaction under the action of a photoinitiator and ultraviolet light irradiation. This reaction has the advantages of mild conditions, fast reaction rate, high selectivity, and few by-products.

[0036] In some embodiments, the photoinitiator includes benzophenone, α-hydroxyacetone, and benzoin; the benzophenone includes benzophenone and 4-methylbenzophenone; the α-hydroxyacetone includes Irgacure 184 and Irgacure 1173; and the benzoin includes benzoin dimethyl ether, benzoin ethyl ether, and benzoin isopropyl ether.

[0037] In some embodiments, the mass ratio of acetonitrile to sulfolane is (5-10):(1-5); by using acetonitrile and sulfolane with this mass ratio, the electrolyte can have a sufficiently high boiling point and flash point while ensuring low viscosity and high conductivity, thereby achieving an optimal balance between high power output and high temperature safety. If the proportion of acetonitrile is too low, the viscosity of the electrolyte is too large, affecting the power characteristics; and if the proportion of sulfolane is too low, the improvement effect on thermal stability and voltage window is limited.

[0038] In some embodiments, the mass ratio of the spirocyclic quaternary ammonium tetrafluoroborate and triethylmethylammonium tetrafluoroborate is (1-3):(0.1-0.5); by using the two electrolyte salts with the mass ratio, enough large-size cations can be ensured to exist in the electrolyte to ensure high-voltage stability, and appropriate small-size cations can be ensured to exist to optimize the rate performance and low-temperature performance.

[0039] In some embodiments, the electrolyte further comprises a diluent; the diluent comprises a fluoroalkyl ether and / or a fluoroalkyl sulfonate. More preferably, the fluoroalkyl ether comprises 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether; the fluoroalkyl sulfonate comprises 2,2,2-trifluoroethyl trifluoromethanesulfonate.

[0040] The added amount of the diluent is 5%-20% of the mass of the electrolyte.

[0041] The electrolyte of the present application further comprises a diluent, by adding a fluoroalkyl ether and / or a fluoroalkyl sulfonate, the electrochemical window of the electrolyte can be further widened, especially the oxidation decomposition resistance is improved, and the working voltage of the supercapacitor is improved in cooperation with the electrolyte salt. At the same time, such fluorinated solvents generally have excellent flame retardant properties and low melting points, and can synergistically act with sulfolane and functional additives to improve the safety and low-temperature performance of the entire electrolyte system.

[0042] A supercapacitor, the lower limit working temperature of the supercapacitor is -40℃. The supercapacitor is an electric double-layer supercapacitor, and the electrode is an activated carbon porous electrode.

[0043] The supercapacitor added with the electrolyte of the present application can work at high and low temperatures in cooperation with the electrolyte with different size ions, low freezing point acetonitrile and high boiling point sulfolane solution, diluent containing fluorine element and crown ether functional additive capable of promoting ion migration, and also has high voltage resistance.

[0044] The specific embodiments of the present application are described in detail below, but it should be understood that the protection scope of the present application is not limited by the specific embodiments.

[0045] Preparation Example

[0046] Preparation Example 1, a compound with a crown ether structure, is prepared by the following preparation method: 1 mmol of 4-vinylbenzo-15-crown-5 ether-5 was added to 100 mL of tetrahydrofuran, after stirring and dissolving, 11-mercaptyl undecyl phosphonic acid was added, stirred for 2 h, Irgacure 1173 was added and irradiated with ultraviolet light of wavelength 365 nm for 30 min, washed with methanol and dried to obtain, wherein the molar ratio of 4-vinylbenzo-15-crown-5 ether-5 and 11-mercaptyl undecyl phosphonic acid is 1:1.

[0047] Preparation Example 2, a compound with crown ether structure, is different from Preparation Example 1 only in that the same mass of mercaptopropyl terminated polydimethylsiloxane is used to replace 11-mercaptyl undecyl phosphonic acid in Preparation Example 1.

[0048] Example

[0049] Example 1, a supercapacitor, is prepared by the following preparation method: In a glove box, 7 parts of acetonitrile and 3 parts of sulfolane were mixed into a composite organic solvent, 1 part of spirocyclic quaternary ammonium tetrafluoroborate, 0.2 parts of triethylmethylammonium tetrafluoroborate and 1 part of 2,2,2-trifluoroethyl trifluoromethanesulfonate were added to the composite organic solvent, and then 0.5 parts of the crown ether structure compound prepared in Preparation Example 1 was added to obtain an electrolyte for supercapacitors; After the active carbon, conductive carbon black and binder were mixed uniformly, they were coated on an aluminum current collector, dried, compacted, and cut into two electrode sheets of the same size and weight. Then the electrode sheets, a polypropylene / polytetrafluoroethylene composite separator and the above-mentioned electrolyte for supercapacitors were assembled and sealed to obtain a supercapacitor, the water and oxygen content in the glove box was less than 0.01 ppm.

[0050] Example 2, a supercapacitor, is different from Example 1 only in that the same mass of the crown ether structure compound prepared in Preparation Example 2 is used to replace the crown ether structure compound prepared in Example 1.

[0051] Example 3, a supercapacitor, is different from Example 1 only in that the addition amount of the crown ether structure compound is 0.8 parts.

[0052] Comparative Example

[0053] Comparative Example 1, a supercapacitor, is different from Example 1 only in that no functional additive is added.

[0054] Comparative Example 2, a supercapacitor, is different from Example 1 only in that no diluent is added.

[0055] Comparative Example 3, a supercapacitor, is different from Example 1 only in that the addition amount of the functional additive is 15% of the solvent.

[0056] Comparative Example 4, a supercapacitor, differs from Example 1 only in that the amount of functional additive added is 0.1%.

[0057] Performance testing

[0058] 1. Charge-discharge experiment: The batteries provided in the examples and control group were subjected to charge-discharge experiments at a voltage of 3.2V, 85°C, and 85%RH humidity. 2. Electrolyte combustion time test: 5g of the electrolyte prepared in the examples and comparative examples was added into the battery case, and the battery was ignited. The ignition time was 5s. After the fire source was removed, the time was recorded. The final combustion time was the ratio of the time recorded to the mass of the electrolyte. 3. High and low temperature test: The electrolytes obtained in Examples 1 to 3 and Comparative Examples 1 to 5 were placed in a high and low temperature alternating test chamber. The temperatures were set to 60℃ and -40℃, and their conductivity was measured at different temperatures.

[0059] The results of the above performance tests are shown in Table 1: Table 1 Performance test results

[0060] According to Table 1, and in conjunction with Example 1 and Comparative Example 1, it can be seen that the internal resistance change rate, capacity decay rate, 30-minute leakage current, electrolyte combustion time, and ionic conductivity at 60℃ and -40℃ of Comparative Example 1 are all lower than those of Example 1. The reason for this is that Comparative Example 1 did not add functional additives, so the electrolyte system lacked the effect of crown ether structure compounds. Crown ethers cannot complex cations through their hole structures to increase ion mobility, resulting in increased internal resistance, decreased low-temperature conductivity, and accelerated capacity decay. At the same time, the synergistic flame-retardant effect of the benzene ring structure of crown ethers and sulfolane is also missing, making the electrolyte easier to burn and shortening the combustion time.

[0061] Combining Example 1 and Comparative Example 2, it can be seen that the internal resistance change rate, capacity decay rate, 30-minute leakage current, electrolyte combustion time, and ionic conductivity at 60℃ and -40℃ of Comparative Example 2 are all lower than those of Example 1. This is because Comparative Example 2 did not add a diluent, thus the electrolyte system lacks the crucial function of a diluent. The absence of a fluorinated diluent leads to a narrower electrochemical window and weakened antioxidant capacity, resulting in increased side reactions at high voltages, manifested as a higher capacity decay rate and increased leakage current. Simultaneously, its excellent flame-retardant properties and melting point-lowering effect are not utilized, leading to a shorter combustion time and poorer electrolyte fluidity at low temperatures, resulting in a significant decrease in ionic conductivity at -40℃.

[0062] Combining Example 1 and Comparative Example 3, it can be seen that the internal resistance change rate, capacity decay rate, 30-minute leakage current, electrolyte combustion time, and ionic conductivity at 60°C and -40°C of Comparative Example 3 are all lower than those of Example 1. The reason for this is that the amount of functional additive added in Comparative Example 3 is 15% of the solvent. The excessive amount of additive exceeds its solubility limit in the electrolyte, increases the viscosity of the electrolyte, and hinders the free migration of ions, thereby leading to a decrease in ionic conductivity and an increase in internal resistance. Excessive additive may also cause uncontrollable side reactions or physical adsorption at the electrode interface, accelerating capacity decay and impairing rate performance. In addition, an inappropriately high amount of additive may also disrupt the component balance of the electrolyte system, affecting its overall thermal stability and flame retardant efficiency.

[0063] Combining Example 1 and Comparative Example 4, it can be seen that the internal resistance change rate, capacity decay rate, 30-minute leakage current, electrolyte combustion time, and ionic conductivity at 60℃ and -40℃ of Comparative Example 4 are all lower than those of Example 1. The reason is that the amount of functional additive added in Comparative Example 4 is only 0.1% of the solvent, which is seriously insufficient. It cannot form an effective concentration in the electrolyte to play its key role in promoting ion migration, resulting in limited improvement in ionic conductivity at low temperatures and no significant improvement in internal resistance performance. At the same time, the low concentration also prevents the crown ether structure from fully binding with cations to stabilize the electrode interface, leading to accelerated capacity decay and increased leakage current. In terms of flame retardancy, the low content also prevents it from producing an effective synergistic effect with sulfolane, resulting in a combustion time similar to that without the additive, and the safety is not effectively improved.

[0064] The above-disclosed embodiments are merely a few specific examples of the present invention. However, the embodiments of the present invention are not limited thereto, and any variations that can be conceived by those skilled in the art should fall within the protection scope of the present invention.

Claims

1. A supercapacitor electrolyte, characterized in that, Including electrolytes, solvents, and functional additives; The electrolyte comprises spirocyclic ammonium tetrafluoroborate and triethylmethylammonium tetrafluoroborate; The solvent includes acetonitrile and sulfolane; The functional additive is a compound with a crown ether structure prepared by a mercapto-olefin click reaction; The amount of the functional additive added is 1% to 10% of the solvent.

2. The supercapacitor electrolyte according to claim 1, characterized in that, The raw materials for the compound having a crown ether structure include 4-vinylbenzo-15-crown ether-5 and a mercapto compound in a molar ratio of 1:(0.8 to 1.2).

3. The supercapacitor electrolyte according to claim 2, characterized in that, The thiol compound includes one or more of 11-mercaptoundecyl phosphate, polyethylene glycol dithiol, and mercaptopropyl-terminated polydimethylsiloxane.

4. The supercapacitor electrolyte according to claim 3, characterized in that, The substance having a crown ether structure is obtained by the following preparation method: Add 4-vinylbenzo-15-crown ether-5 to a solvent, stir to dissolve, add a thiol compound, stir, add a photoinitiator, and irradiate with ultraviolet light for 30-60 minutes. Wash and dry to obtain the final product.

5. The supercapacitor electrolyte according to claim 4, characterized in that, The photoinitiators include benzophenones and benzoin compounds.

6. The supercapacitor electrolyte according to claim 1, characterized in that, The mass ratio of acetonitrile to sulfolane is (5-10):(1-5).

7. The supercapacitor electrolyte according to claim 1, characterized in that, The mass ratio of the spirocyclic quaternary ammonium tetrafluoroborate salt to triethylmethylammonium tetrafluoroborate salt is (1-3):(0.1-0.5).

8. The supercapacitor electrolyte according to claim 1, characterized in that, The electrolyte also includes a diluent; the diluent includes fluoroalkyl ethers and / or fluoroalkyl sulfonates.

9. A supercapacitor comprising the supercapacitor electrolyte according to any one of claims 1 to 8.

10. A supercapacitor according to claim 9, characterized in that, The lower limit operating temperature of the supercapacitor is -40℃.

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