Low self-discharge supercapacitor electrolyte, preparation method and application thereof

Abstract

The application provides a supercapacitor electrolyte with low self-discharge, a preparation method and application thereof, raw materials of the supercapacitor electrolyte include organic solvents, ammonium salt and pyridine oxide; the organic solvents are one or more of acetonitrile, fluoroacetonitrile, propionitrile, butyronitrile and isobutyronitrile; the ammonium salt is tetraethylamine bistrifluoromethylsulfonylimide or tetraethylammonium bis(trifluoromethanesulfonyl)imide; and the pyridine oxide is pyridine-N-oxide, 4-methylpyridine oxide or 3-methylpyridine oxide. By selective use of specific additives and optimized configuration of electrolyte salt, the supercapacitor electrolyte of the application can effectively reduce the self-discharge rate of the supercapacitor and significantly improve the energy utilization efficiency of the capacitor.

Description

Technical Field

[0001] This invention relates to the field of supercapacitor electrolytes, specifically to a low self-discharge supercapacitor electrolyte, its preparation method, and its application. Background Technology

[0002] Supercapacitors, as energy storage devices with high power density and long cycle life, are widely used in grid frequency regulation and portable electronic devices. However, their severe self-discharge problem leads to rapid decay of stored charge, significantly reducing energy utilization efficiency.

[0003] US Patent Application Publication No. US7879486B2 discloses a supercapacitor electrolyte with improved electrochemical stability, wherein the electrolyte contains one or more organic salts containing FSI anions. These electrolytes are used to increase the operating voltage window of the supercapacitor, but do not mention reducing self-discharge. Chinese Patent Application Publication No. CN104640197A describes a non-water-soluble electrolyte for supercapacitors, the formulation of which includes 1-ethyl-3-methylimidazolium tetrafluoroborate (EMImBF4) dissolved in a mixed solvent of propylene carbonate (PC) and diethyl carbonate (DEC), aiming to improve the cycling stability of the capacitor, but does not involve specific additives. Agents are used to reduce self-discharge rate; Japanese patent application JP2015114917A describes a non-aqueous electrolyte for supercapacitors, which contains a high concentration of imidazole ionic liquid and a specific ratio of acetonitrile (AN) to improve the energy density of the capacitor. However, it does not address the self-discharge problem. US patent application US20160251572A1 describes a low-volatility electrolyte containing FSI and TFSI anions. This electrolyte is suitable for lithium-ion batteries and supercapacitors. Its main purpose is to broaden the electrochemical stability window and maintain a high ionic conductivity, but it does not specify any measures to reduce the self-discharge of the capacitor.

[0004] While existing supercapacitor electrolytes have achieved significant improvements in electrochemical stability, operating voltage window, cycle stability, energy density, and ionic conductivity, a common problem remains: they fail to effectively address the self-discharge phenomenon in supercapacitors. This leads to rapid decay of stored charge, thereby affecting the energy utilization efficiency of supercapacitors. Specifically, patent applications such as US7879486B2, CN104640197A, JP2015114917A, and US20160251572A1, although each improves different properties of the electrolyte through various means, have not revealed any improvements in reducing the self-discharge rate. Summary of the Invention

[0005] The purpose of this invention is to provide a low self-discharge supercapacitor electrolyte, its preparation method, and its application, in order to overcome the shortcomings of the prior art. By selectively using specific additives and optimizing the configuration of electrolyte salts, this invention enables the supercapacitor electrolyte to effectively reduce the self-discharge rate of supercapacitors and significantly improve the energy utilization efficiency of capacitors.

[0006] This invention is achieved through the following technical solution: A low self-discharge supercapacitor electrolyte, wherein the raw materials of the supercapacitor electrolyte include organic solvents, ammonium salts and pyridine oxides; The organic solvent is one or more selected from acetonitrile, fluoroacetonitrile, propionitrile, butyronitrile, and isobutyronitrile; The ammonium salt is tetraethylamine bis(fluorosulfonyl)imide salt or tetraethylammonium bis(trifluoromethanesulfonyl)imide salt; The pyridine oxide is pyridine-N-oxide, 4-methylpyridine oxide, or 3-methylpyridine oxide.

[0007] Furthermore, in the electrolyte of the supercapacitor, the concentration of ammonium salt is 0.1~3 mol / L; pyridine oxide accounts for 10%~50% of the total volume of pyridine oxide and organic solvent.

[0008] Furthermore, the organic solvent is a mixture of fluoroacetonitrile and propionitrile.

[0009] Furthermore, the volume ratio of the fluoroacetonitrile to the propionitrile is 1:1.

[0010] Furthermore, the ammonium salt is tetraethylamine difluorosulfonyl imide salt.

[0011] Furthermore, the concentration of tetraethylamine difluorosulfonyl imide salt in the supercapacitor electrolyte is 1 mol / L.

[0012] Furthermore, the pyridine oxide is 3-methylpyridine oxide.

[0013] Furthermore, in the electrolyte of the supercapacitor, 3-methylpyridine oxide accounts for 10% of the total volume of 3-methylpyridine oxide and organic solvent.

[0014] A method for preparing a low self-discharge supercapacitor electrolyte involves heating pyridine oxide to a liquid state, then adding the liquid pyridine oxide to an organic solvent to obtain a mixed solution, and dissolving an ammonium salt in the mixed solution to obtain the low self-discharge supercapacitor electrolyte.

[0015] Application of a low self-discharge supercapacitor electrolyte in supercapacitors.

[0016] Compared with the prior art, the present invention has the following beneficial technical effects: The low self-discharge supercapacitor electrolyte of this invention uses a fluorinated solvent, which widens the electrochemical window of the electrolyte. The ammonium salt used has a larger anion, resulting in higher ionic conductivity of the electrolyte. Fluorination of organic solvents significantly reduces the solubility of the system, thus affecting the degree of dissociation of the dissolved salt and reducing the ionic conductivity of the electrolyte. In this invention, the fluorinated solvent is combined with a large anionic ammonium salt to ensure both the stability of the electrochemical window and the ionic conductivity of the electrolyte. However, a larger anion means a lower electron cloud density and poorer polarity, resulting in weaker interactions when adsorbed onto the electric double layer, easily triggering self-discharge relaxation. The introduction of pyridine oxide additives, through their high polarity, allows for the adsorption and binding of anions through strong cation-anion interactions between the central positively charged nitrogen atom and the anion, and also through the adsorption of negatively charged oxygen atoms on the electrode surface, thereby anchoring ions to stabilize the interfacial electric double layer and reduce the self-discharge rate of the supercapacitor. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly described below. The following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained from these drawings without creative effort.

[0018] Figure 1 These are effect diagrams of some embodiments of the present invention. Detailed Implementation

[0019] The present invention will now be described in detail: A low self-discharge supercapacitor electrolyte, wherein the raw materials of the supercapacitor electrolyte include an organic solvent, an ammonium salt (as an electrolyte salt), and pyridine oxide (as an additive). The organic solvent is one or more selected from acetonitrile, fluoroacetonitrile, propionitrile, butyronitrile, and isobutyronitrile; The ammonium salt is tetraethylamine bis(fluorosulfonyl)imide salt or tetraethylammonium bis(trifluoromethanesulfonyl)imide salt; The pyridine oxide is pyridine-N-oxide, 4-methylpyridine oxide, or 3-methylpyridine oxide.

[0020] In the electrolyte of the supercapacitor, the concentration of ammonium salt is 0.1~3 mol / L; pyridine oxide accounts for 10%~50% of the total volume of pyridine oxide and organic solvent.

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Unless otherwise specified, the methods and experimental equipment used in the following embodiments are conventional methods and instruments.

[0022] Example 1 A low self-discharge supercapacitor electrolyte comprises an organic solvent of fluoroacetonitrile and propionitrile mixed in a 1:1 volume ratio, and an electrolyte salt of 1 mol / L tetraethylfluorosulfonylimide ammonium. The additive is 3-methylpyridine oxide, comprising 10% by volume of the total solvent (total volume of 3-methylpyridine oxide and organic solvent).

[0023] The electrolyte is prepared as follows: 3-methylpyridine oxide is heated to 50°C and melted, then added to a mixed solvent formed by mixing acetonitrile and propionitrile in a 1:1 volume ratio. Tetraethylfluorosulfonylimide ammonium is then dissolved in this solvent. This electrolyte salt ratio effectively reduces the self-discharge phenomenon of the supercapacitor, improves the capacitor's charge retention capacity, and thus enhances the overall energy utilization efficiency. The electrolyte prepared in this way not only enhances the stability of the supercapacitor but also significantly improves its long-term energy storage performance, enabling it to exhibit excellent electrochemical performance and energy management capabilities in various environments. Through this optimization, the self-discharge rate of the supercapacitor is significantly reduced, and the capacity retention rate is improved. Especially under long-term storage conditions, it can maintain a high charge level, significantly improving the energy utilization efficiency in applications.

[0024] Example 2 A low self-discharge supercapacitor electrolyte uses fluoroacetonitrile as the organic solvent and 1 mol / L tetraethylfluorosulfonylimide ammonium as the electrolyte salt. The additive is 20% by volume of 3-methylpyridine oxide (the total volume of 3-methylpyridine oxide and organic solvent).

[0025] The electrolyte preparation method of this embodiment is as follows: 3-methylpyridine oxide is heated to 50°C to melt, then added to the organic solvent fluoroacetonitrile, and then tetraethylfluorosulfonamide ammonium is dissolved therein.

[0026] Example 3 A low self-discharge supercapacitor electrolyte uses acetonitrile as the organic solvent and 1 mol / L tetraethylfluorosulfonylimide ammonium as the electrolyte salt. The additive is 30% by volume of 3-methylpyridine oxide, which constitutes 30% of the total solvent (the total volume of 3-methylpyridine oxide and the organic solvent).

[0027] The electrolyte preparation method of this embodiment is as follows: 3-methylpyridine oxide is heated to 50°C to melt, then added to the organic solvent acetonitrile, and then tetraethylfluorosulfonamide ammonium is dissolved therein.

[0028] Example 4 A low self-discharge supercapacitor electrolyte uses propionitrile as the organic solvent and 1 mol / L tetraethylfluorosulfonylimide ammonium as the electrolyte salt. The additive is 3-methylpyridine oxide, which accounts for 40% of the total solvent (the total volume of 3-methylpyridine oxide and organic solvent).

[0029] The electrolyte preparation method of this embodiment is as follows: 3-methylpyridine oxide is heated to 50°C to melt, then added to the organic solvent propionitrile, and then tetraethylfluorosulfonamide ammonium is dissolved therein.

[0030] Example 5 A low self-discharge supercapacitor electrolyte uses nitrile butadiene as the organic solvent and 1 mol / L tetraethylfluorosulfonylimide ammonium as the electrolyte salt. The additive is 10% by volume of 3-methylpyridine oxide in the total solvent (total volume of 3-methylpyridine oxide and organic solvent).

[0031] The electrolyte preparation method of this embodiment is as follows: 3-methylpyridine oxide is heated to 50°C to melt, then added to the organic solvent butyronitrile, and then tetraethylfluorosulfonylimide ammonium is dissolved therein.

[0032] Example 6 A low self-discharge supercapacitor electrolyte uses isobutyronitrile as the organic solvent and tetraethylfluorosulfonylimide ammonium as the electrolyte salt. The additive is 3-methylpyridine oxide, which accounts for 10% of the total solvent (the total volume of 3-methylpyridine oxide and organic solvent).

[0033] The electrolyte preparation method of this embodiment is as follows: 3-methylpyridine oxide is heated to 50°C to melt, then added to the organic solvent isobutyronitrile, and then tetraethylfluorosulfonylimide ammonium is dissolved therein.

[0034] Example 7 A low self-discharge supercapacitor electrolyte comprises an organic solvent of fluoroacetonitrile, acetonitrile, and propionitrile in a 1:1:1 volume ratio, and an electrolyte salt of 1 mol / L tetraethylfluorosulfonylimide ammonium. The additive is 10% by volume of 3-methylpyridine oxide (the total volume of 3-methylpyridine oxide and the organic solvent).

[0035] The electrolyte preparation method of this embodiment is as follows: 3-methylpyridine oxide is heated to 50°C to melt, and then added to a mixed solvent formed by mixing fluoroacetonitrile, acetonitrile and propionitrile in a volume ratio of 1:1:1. Then, tetraethylfluorosulfonamide ammonium is dissolved in it.

[0036] Example 8 A low self-discharge supercapacitor electrolyte comprises an organic solvent of fluoroacetonitrile and propionitrile mixed in a 1:1 volume ratio, and an electrolyte salt of 0.1 mol / L tetraethylfluorosulfonylimide ammonium. The additive is 3-methylpyridine oxide, comprising 10% by volume of the total solvent (the total volume of 3-methylpyridine oxide and the organic solvent).

[0037] The electrolyte preparation method in this embodiment differs from that in Example 1 in that the concentration of the dielectric salt is selected differently.

[0038] Example 9 A low self-discharge supercapacitor electrolyte comprises an organic solvent of fluoroacetonitrile and propionitrile mixed in a 1:1 volume ratio, and an electrolyte salt of 3 mol / L tetraethylfluorosulfonylimide ammonium. The additive is 10% by volume of 3-methylpyridine oxide (the total volume of 3-methylpyridine oxide and the organic solvent).

[0039] The difference between the electrolyte preparation method in this embodiment and that in Example 1 lies in the selection of the concentration of the dielectric salt.

[0040] Example 10 A low self-discharge supercapacitor electrolyte uses fluoroacetonitrile and propionitrile mixed in a 1:1 volume ratio as an organic solvent, and the electrolyte salt is 1 mol / L tetraethylammonium bis(trifluoromethaneyl)imide salt. The additive is 3-methylpyridine oxide, accounting for 10% of the total solvent (total volume of 3-methylpyridine oxide and organic solvent).

[0041] The electrolyte preparation method in this embodiment differs from that in Example 1 in that the choice of dielectric salt is different.

[0042] Example 11 A low self-discharge supercapacitor electrolyte uses fluoroacetonitrile and propionitrile mixed in a 1:1 volume ratio as an organic solvent, and the electrolyte salt is 0.1 mol / L tetraethylammonium bis(trifluoromethaneyl)imide salt. The additive is 3-methylpyridine oxide, accounting for 10% of the total solvent (total volume of 3-methylpyridine oxide and organic solvent).

[0043] The electrolyte preparation method in this embodiment is the same as that in Example 10, except that the concentration of the dielectric salt is different.

[0044] Example 12 A low self-discharge supercapacitor electrolyte uses fluoroacetonitrile and propionitrile mixed in a 1:1 volume ratio as an organic solvent, and the electrolyte salt is 3 mol / L tetraethylammonium bis(trifluoromethaneyl)imide salt. The additive is 10% by volume of 3-methylpyridine oxide in the total solvent (total volume of 3-methylpyridine oxide and organic solvent).

[0045] The electrolyte preparation method in this embodiment is the same as that in Example 10, except that the concentration of the dielectric salt is different.

[0046] Example 13 A low self-discharge supercapacitor electrolyte uses fluoroacetonitrile and propionitrile mixed in a 1:1 volume ratio as an organic solvent, the electrolyte salt includes 1 mol / L of tetraethylfluorosulfonylimide ammonium, and the additive is 3-methylpyridine oxide accounting for 50% of the total solvent (the total volume of 3-methylpyridine oxide and organic solvent).

[0047] The electrolyte preparation method in this embodiment is the same as that in Example 1, except that the proportion of additives in the total solvent is different.

[0048] Example 14 A supercapacitor electrolyte with low self-discharge uses fluoroacetonitrile and propionitrile mixed in a 1:1 volume ratio as an organic solvent, the electrolyte salt includes 1 mol / L of tetraethylfluorosulfonylimide ammonium, and the additive is pyridine-N-oxide accounting for 10% of the total solvent (the total volume of pyridine-N-oxide and organic solvent).

[0049] The electrolyte preparation method in this embodiment differs from that in Example 1 in that the choice of additives is different.

[0050] Example 15 A supercapacitor electrolyte with low self-discharge uses fluoroacetonitrile and propionitrile mixed in a 1:1 volume ratio as an organic solvent, the electrolyte salt includes 1 mol / L of tetraethylfluorosulfonylimide ammonium, and the additive is 4-methylpyridine oxide accounting for 10% of the total solvent (the total volume of 4-methylpyridine oxide and organic solvent).

[0051] The electrolyte preparation method in this embodiment differs from that in Example 1 in that the choice of additives is different.

[0052] Comparative Example 1 A low self-discharge supercapacitor electrolyte uses a 1:1 volume ratio of fluoroacetonitrile and propionitrile as an organic solvent, and the electrolyte salt includes 1 mol / L tetraethylfluorosulfonamide ammonium. The electrolyte preparation method in this embodiment differs from that in Example 1 in that no additives are introduced.

[0053] In the preparation of the electrolyte, in Example 2, the salt could not be completely dissolved due to the poor solvation ability of the electrolyte. The solvents used in the electrolytes of Examples 3, 4, 5, and 6 had good redox stability, but their stability was significantly reduced when used in combination with the dielectric salt, making them unsuitable for direct use as solvents. The results are shown in Table 1. Furthermore, the ionic conductivity of the electrolyte obtained by mixing the three organic solvents in Example 7 was lower than that of Example 1.

[0054] Table 1 Redox Potential Window of Examples

[0055] In addition, during the preparation of the electrolyte, the additives in Examples 14 and 15 have high melting points and cannot be dissolved by heating and mixing (preparation method of Example 1). Instead, the volume ratio can be converted to weight and the solid is dissolved in a solvent. However, this will reduce the fluidity of the electrolyte and thus reduce the ionic conductivity of the electrolyte. The results are shown in Table 2.

[0056] Table 2 Ionic conductivity of the examples

[0057] Based on the above indicators, self-discharge tests were conducted on Examples 1, 8, 10, 15, and the comparative example, and the results are as follows. Figure 1 As shown. By Figure 1 It can be seen that the self-discharge rate of the examples is significantly improved compared to the comparative examples. This is because the pyridine additive, as a specific adsorption additive, helps stabilize the electrolyte, providing active sites and anchoring effects for the storage of anions and cations at the interface, thus reducing self-discharge. Comparing Examples 1, 8, and 10, it can be seen that the concentration and type of dielectric salt affect both the electrochemical window and ionic conductivity of the electrolyte, and determine the self-discharge rate of the capacitor. At low concentrations, due to the lower anion concentration, the effect of concentration diffusion is greater, resulting in a higher self-discharge rate. Furthermore, the degree of dissociation of tetraethylammonium bis(trifluoromethaneyl)imide salt is lower than that of tetraethylfluorosulfonylimide ammonium, making the capacitor more prone to self-discharge after charging, thus resulting in slightly inferior performance.

[0058] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Anyone skilled in the art can make various modifications and alterations without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be determined by the claims.

Claims

1. A low self-discharge supercapacitor electrolyte, characterized in that, The raw materials for the supercapacitor electrolyte include organic solvents, ammonium salts, and pyridine oxides; The organic solvent is one or more selected from acetonitrile, fluoroacetonitrile, propionitrile, butyronitrile, and isobutyronitrile; The ammonium salt is tetraethylammonium bis(trifluoromethanesulfonyl)imide salt or tetraethylammonium bis(trifluoromethanesulfonyl)imide salt; The pyridine oxide is pyridine-N-oxide, 4-methylpyridine oxide, or 3-methylpyridine oxide.

2. The low self-discharge supercapacitor electrolyte according to claim 1, characterized in that, In the electrolyte of the supercapacitor, the concentration of ammonium salt is 0.1~3 mol / L; pyridine oxide accounts for 10%~50% of the total volume of pyridine oxide and organic solvent.

3. The low self-discharge supercapacitor electrolyte according to claim 1, characterized in that, The organic solvent is a mixture of fluoroacetonitrile and propionitrile.

4. The low self-discharge supercapacitor electrolyte according to claim 3, characterized in that, The volume ratio of the fluoroacetonitrile to the propionitrile is 1:

1.

5. The low self-discharge supercapacitor electrolyte according to claim 3, characterized in that, The ammonium salt is tetraethylamine difluorosulfonyl imide salt.

6. A low self-discharge supercapacitor electrolyte according to claim 5, characterized in that, The concentration of tetraethylamine difluorosulfonyl imide salt in the supercapacitor electrolyte is 1 mol / L.

7. The low self-discharge supercapacitor electrolyte according to claim 3, characterized in that, The pyridine oxide is 3-methylpyridine oxide.

8. The low self-discharge supercapacitor electrolyte according to claim 7, characterized in that, In the electrolyte of the supercapacitor, 3-methylpyridine oxide accounts for 10% of the total volume of 3-methylpyridine oxide and organic solvent.

9. A method for preparing a low self-discharge supercapacitor electrolyte according to any one of claims 1-8, characterized in that, Pyridine oxide is heated to a liquid state, and then the liquid pyridine oxide is added to an organic solvent to obtain a mixed solution. Ammonium salt is dissolved in the mixed solution to obtain a supercapacitor electrolyte with low self-discharge.

10. The application of a low self-discharge supercapacitor electrolyte according to any one of claims 1-8 in a supercapacitor.

Images