Application of betaine electrolyte to broadening ammonium ion supercapacitor

Abstract

According to the technology and application for broadening the working voltage of the ammonium ion supercapacitor through the betaine electrolyte additive, the experiment method is easy to operate, efficient and stable, the prepared NH4AC and betaine mixed solution serves as the aqueous ammonium ion supercapacitor electrolyte, the hydrogen evolution and oxygen evolution problem is solved, the stable voltage window is broadened, and the application range is wide. The technology provides a new thought for solving the problem of hydrogen evolution and oxygen evolution of the aqueous electrolyte, and lays a foundation for subsequent research on aqueous energy storage.

Description

Technical Field

[0001] The invention belongs to the field of electrochemical energy storage, relates to a betaine electrolyte additive to broaden the working voltage technology of ammonium ion supercapacitors and its application, and specifically relates to an aqueous ammonium ion supercapacitor. Background Art

[0002] Lithium-ion batteries are a type of energy storage device that is widely known and used. They are the main type of commercial batteries and have advantages such as high energy density, long cycle life, and low self-discharge rate. However, in high temperature environments, the internal chemical reaction rate of lithium-ion batteries will be accelerated, causing the battery to overheat and have the risk of ignition and explosion. In addition, the metal resources required for the more efficient positive electrode materials of lithium batteries are relatively scarce, which leads to increased costs. Therefore, there is an urgent need for a cheap, safe, and efficient energy storage system.

[0003] Aqueous supercapacitors use water as electrolyte, which is non-flammable, non-explosive, and has stable chemical properties. Even under extreme conditions such as high temperature, short circuit, and needle puncture, they will not have thermal runaway, fire, explosion, and other dangerous situations like lithium-ion batteries, and can provide higher safety protection for the use environment. + 、Na + , K + etc. Non-metallic charge carrier NH4 + With a lower molar mass (18 g mol -1 ), small hydration radius, low cost and abundant resources, so the development of ammonium ion supercapacitors has great prospects. However, when the voltage of aqueous ammonium ion supercapacitors exceeds 1.23V, the water in the electrolyte will decompose and release hydrogen or oxygen. This hydrogen and oxygen evolution reaction will cause the working voltage of aqueous ammonium ion supercapacitors to be usually low, which seriously affects the final energy storage performance and causes the device to bulge or even explode. It can be seen that solving the problem of hydrogen and oxygen evolution in aqueous electrolytes has become a difficult problem that cannot be overcome in improving the efficiency of aqueous supercapacitors.

[0004] In the prior art, there are reports on introducing additives to change the water structure in the electrolyte and inhibit the decomposition of water. At present, there are studies (Adv. Mater. 2020, 32, 2000074 and Angew. Chem. Int. Ed. 2022, 61, e202213757) that by adding sucrose molecules to the electrolyte, the sucrose-water hydrogen bond destroys the continuity of the water-water hydrogen bond network, thereby significantly inhibiting the decomposition of water and the dissolution of the main substance. Summary of the invention

[0005] The purpose of the present invention is to provide an ammonium ion electrolyte that adds betaine to broaden the working voltage of an ammonium ion supercapacitor. The following technical scheme is adopted: betaine is added to the electrolyte to improve the problem of hydrogen and oxygen evolution in the aqueous electrolyte, thereby broadening the working voltage of the aqueous ammonium ion supercapacitor and finally improving the electrochemical energy storage performance.

[0006] According to a first aspect of the present invention, the present invention provides an ammonium ion electrolyte comprising ammonium ions, betaine and water. The ammonium ion electrolyte of the present invention can be used to broaden the operating voltage of aqueous ammonium ion supercapacitors.

[0007] Preferably, the ammonium ion electrolyte contains 100 mL 1 mol L -1 The amount of betaine added to the NH4AC aqueous solution is from 0.1 g to a saturated concentration, preferably 0.6-1.3 g; for example, 0.6 g, 0.9 g or 1.3 g.

[0008] According to a second aspect of the present invention, the present invention provides an aqueous symmetrical ammonium ion supercapacitor, wherein the aqueous symmetrical ammonium ion supercapacitor uses two expanded graphite electrodes of equal mass as positive and negative electrodes, the ammonium ion electrolyte described in the first aspect is used as the electrolyte of the aqueous symmetrical ammonium ion supercapacitor, and the electrolyte group is encapsulated in a battery shell.

[0009] According to a third aspect of the present invention, the present invention provides a method for preparing the symmetrical ammonium ion supercapacitor of the second aspect, comprising the following steps:

[0010] a. Prepare expanded graphite as an electrode material for aqueous ammonium ion supercapacitors;

[0011] b. mixing the ammonium-containing electrolyte and betaine in different proportions to obtain different mixed solutions;

[0012] c. The expanded graphite was used as the working electrode and the mixed solution containing betaine was used as the electrolyte of the aqueous ammonium ion supercapacitor for electrochemical testing;

[0013] d, Assemble symmetrical ammonium ion supercapacitors and test their electrochemical performance.

[0014] Preferably, the preparation of the expanded graphite in step a is completed by high-temperature expansion of graphene oxide prepared by the Hummers method.

[0015] Preferably, the ammonium-containing electrolyte in step b has a concentration of 1 mol L -1 NH4AC aqueous solution.

[0016] Preferably, the ammonium-containing electrolyte and betaine in step b are mixed uniformly in different proportions, and the mixture is 100 mL 1 mol L -1Different amounts of betaine were added into the NH4AC aqueous solution, and the added amounts of betaine were 0.6 g, 0.9 g and 1.3 g.

[0017] Preferably, the electrochemical test in step c is performed using a three-electrode test, with expanded graphite as the positive electrode, a platinum wire electrode as the counter electrode, and a saturated calomel cell electrode as the reference electrode. The electrolyte is 10 ml of the 1 mol L -1 NH4AC and betaine mixed electrolyte.

[0018] Preferably, the electrochemical test content of step c is to test the linear scan LSV curve and cyclic voltammetry CV curve of the expanded graphite electrode in all the above mixed electrolytes.

[0019] Preferably, the symmetrical ammonium ion supercapacitor in step d is encapsulated in a CR2032 battery case with two expanded graphite electrodes of the same mass as the positive and negative electrodes and a mixed solution of 0.9 g of betaine added as the electrolyte. The electrochemical test content is the CV curve at different scan rates and the constant current charge and discharge curve at different current densities.

[0020] The present invention provides an ammonium ion electrolyte containing a betaine additive obtained by the preparation method described in the above technical scheme, and the electrolyte is used for the application of an aqueous ammonium ion supercapacitor using expanded graphite as an electrode material. The experimental method is simple and efficient to operate, the prepared product is stable, and the prepared betaine ammonium ion electrolyte can significantly broaden the working voltage of the expanded graphite-based ammonium ion supercapacitor. This technology provides a new idea for solving the problem of hydrogen and oxygen evolution in aqueous electrolytes, and lays a foundation for subsequent research on aqueous energy storage.

[0021] The results of certain embodiments of the present invention show that the hydrogen and oxygen evolution problems of the expanded graphite electrode in the NH4AC electrolyte after adding betaine are significantly improved, especially in 1M NH4AC-0.9g betaine / H2O electrolyte, the expanded graphite works stably in the voltage range of -0.9V-0.9V in the three-electrode system, without obvious hydrogen and oxygen evolution signals, and the operating voltage of the assembled symmetrical ammonium ion supercapacitor can be widened to 2V. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Scanning electron microscope image of expanded graphite;

[0023] Figure 2 Expanded graphite XRD pattern;

[0024] Figure 3LSV curves of expanded graphite electrode in 1M NH4AC, 1M NH4AC-0.6g betaine / H2O, 1M NH4AC-0.9g betaine / H2O, and 1M NH4AC-1.3g betaine / H2O electrolytes, with a scan rate of 10mV·s -1 ;

[0025] Figure 4 CV curves of expanded graphite electrode in 1M NH4AC, 1M NH4AC-0.6g betaine / H2O, 1M NH4AC-0.9g betaine / H2O, and 1M NH4AC-1.3g betaine / H2O electrolytes, with a scan rate of 10mV·s -1 ;

[0026] Figure 5 CV curve (left) and constant current charge-discharge curve (right) of expanded graphite symmetrical ammonium ion supercapacitor in 1M NH4AC-0.9g betaine / H2O electrolyte. DETAILED DESCRIPTION

[0027] Example 1

[0028] a. Weigh 2g natural graphite powder and mix it with 2g NaNO3, then disperse it in 46mL concentrated sulfuric acid and stir it evenly; then add 6g KMnO4 powder and transfer it to an oil bath and heat it at 35℃; after 90 minutes, add 120mL deionized water and stir it evenly, and raise the temperature to 90℃; after heating for 20 minutes, add 6mL 30wt% H2O2 aqueous solution to the solution to obtain a golden precipitate; after centrifugal washing with deionized water, vacuum drying is performed to obtain graphene oxide (GO). Next, the tubular furnace is passed through argon and heated to 1000℃ under argon atmosphere, and then the GO powder is quickly placed in the furnace and heated for 10s to obtain expanded graphite.

[0029] b. Expanded graphite and binder polytetrafluoroethylene were mixed in a mass ratio of 9:1 to prepare an electrode paste, which was coated on a conductive carbon paper with a length and width of 1.2 cm×2 cm and dried at 60°C for at least 12 hours.

[0030] c, prepare 1 mol L -1 100 ml of 1 mol / L NH4AC aqueous solution was mixed with 9 g of betaine powder, and ultrasonicated for 15 minutes until the betaine powder was completely dissolved and the solution was colorless and transparent, which was recorded as 1M NH4AC-0.9 g betaine / H2O.

[0031] d. Take 10 ml of the above 1M NH4AC-0.9g betaine / H2O solution as the electrolyte, assemble a three-electrode system with expanded graphite electrode as the working electrode, platinum wire as the counter electrode, and saturated calomel electrode as the reference electrode, and perform linear sweep test and cyclic voltammetry test.

[0032] Example 2

[0033] The expanded graphite prepared in Example 1 and the binder polytetrafluoroethylene were mixed in a mass ratio of 9:1 to prepare an electrode paste, which was coated on a conductive carbon paper with a length and width of 1.2 cm × 2 cm and dried at 60°C for at least 12 hours. A three-electrode system was assembled with the expanded graphite electrode as the working electrode, the platinum wire as the counter electrode, and the saturated calomel electrode as the reference electrode. -1 Linear sweep test and cyclic voltammetry test were performed in NH4AC solution.

[0034] Example 3

[0035] The expanded graphite prepared in Example 1 and the binder polytetrafluoroethylene were mixed in a mass ratio of 9:1 to form an electrode paste, which was coated on a 1.2 cm × 2 cm conductive carbon paper and dried at 60°C for at least 12 hours. A three-electrode system was assembled with an expanded graphite electrode as the working electrode, a platinum wire as the counter electrode, and a saturated calomel electrode as the reference electrode. 0.6 g of betaine powder was added to 100 ml of 1 mol / L NH4AC, and ultrasonicated for 15 minutes until the betaine powder was completely dissolved, and the solution was colorless and transparent, recorded as 1M NH4AC-0.6 g betaine / H2O. 10 mL of 1M NH4AC-0.6 g betaine / H2O solution was taken as an electrolyte for linear sweep test and cyclic voltammetry test.

[0036] Example 4

[0037] The expanded graphite prepared in Example 1 and the binder polytetrafluoroethylene were mixed in a mass ratio of 9:1 to form an electrode paste, which was coated on a conductive carbon paper with a length and width of 1.2 cm × 2 cm and dried at 60°C for at least 12 hours. A three-electrode system was assembled with an expanded graphite electrode as the working electrode, a platinum wire as the counter electrode, and a saturated calomel electrode as the reference electrode. 13g of betaine powder was added to 100ml of 1mol / L NH4AC aqueous solution, and ultrasonicated for 15 minutes until the betaine powder was completely dissolved, and the solution was colorless and transparent, recorded as 1M NH4AC-1.3g betaine / H2O. 10mL of 1M NH4AC-1.3g betaine / H2O solution was taken as the electrolyte for linear sweep test and cyclic voltammetry test.

[0038] Example 5

[0039] Two pieces of expanded graphite electrodes of the same mass were used as positive and negative electrodes, a glass fiber membrane was used as a separator, and a 1M NH4AC-0.9g betaine / H2O mixed solution was used as an electrolyte. They were successively encapsulated in a CR2032 battery shell to assemble into a symmetrical ammonium ion supercapacitor, and cyclic voltammetry and constant current charge-discharge tests were carried out.

[0040] Example 6

[0041] Commercial activated carbon YP-50 and binder polytetrafluoroethylene were mixed in a mass ratio of 9:1 to form an electrode paste, which was coated on a conductive carbon paper with a length and width of 1.2 cm × 2 cm and dried at 60°C for at least 12 hours. A three-electrode system was assembled with YP-50 electrode as the working electrode, platinum wire as the counter electrode, and saturated calomel electrode as the reference electrode, and its LSV and CV curves were measured in 1M NH4AC-0.9g betaine / H2O electrolyte. Two pieces of YP-50 electrodes with the same mass were taken and assembled into a button-type 2032 symmetrical ammonium ion supercapacitor with 1M NH4AC-0.9g betaine / H2O as the electrolyte, and cyclic voltammetry and constant current charge and discharge tests were carried out.

[0042] The LSV curves of the expanded graphite electrode as the working electrode in 1M NH4AC, 1M NH4AC / 0.6g betaine / H2O, 1M NH4AC / 0.9g betaine / H2O, and 1M NH4AC / 1.3g betaine / H2O electrolytes are shown in FIG. Figure 3 As shown in the figure. From the LSV test results, it can be seen that the electrochemical stability window of the expanded graphite electrode in 1M NH4AC electrolyte without betaine is 2.34V, and the stability window can be significantly widened to 3.16V after adding betaine. With the increase of the amount of betaine, the hydrogen and oxygen evolution currents gradually decrease, and the window is slightly widened, but when it continues to increase to 1.3g, the corresponding electrochemical stability window almost no longer changes and reaches saturation.

[0043] The CV curves of the expanded graphite electrode as the working electrode in 1M NH4AC, 1M NH4AC / 0.6g betaine / H2O, 1M NH4AC / 0.9g betaine / H2O, and 1M NH4AC / 1.3g betaine / H2O electrolytes are shown in Figure 1. Figure 4As shown. In the 1M NH4AC electrolyte without betaine, the expanded graphite electrolysis showed obvious oxygen evolution and hydrogen evolution peak signals at 0.64V and -0.74V in the range of -0.9-0.9V. After adding 0.6g betaine, the hydrogen evolution peak was significantly weakened. When the amount of betaine added was increased to 0.9g, the oxygen evolution situation was also significantly improved. When the amount of betaine added was further increased to 1.3g, the integral area of ​​the CV curve decreased, and the corresponding expanded graphite electrode energy storage capacity decreased. Through the comparison of the three-electrode tests of corresponding examples 1 to 4, the expanded graphite electrode has better and more stable performance in the electrolyte with an addition ratio of 1M NH4AC / 0.9g betaine / H2O.

[0044] Examples 5 and 6 are ammonium ion supercapacitors formed by assembling expanded graphite and YP-50 as electrodes, respectively, and using 1M NH4AC / 9g betaine / H2O as electrolyte. The working voltage can be extended to 2V, but expanded graphite has a higher specific capacitance. The electrochemical test results of expanded graphite symmetrical ammonium ion supercapacitors are shown in Figure 2. Figure 5 As shown, the test potential range is 0-2V, at 10, 20, 30, 50, 70 and 100mV·s -1 The CV curves at different scan rates do not show any hydrogen evolution and oxygen evolution redox peaks, indicating that the expanded graphite electrode can stably operate at 0-2 V. These curves show a large integrated area and a rectangular shape, indicating high capacitance, high rate and good capacitance behavior. -1 All curves show a symmetrical triangle shape when the constant current charge and discharge are performed at a current density of 1A·g. According to the discharge curve, based on the total mass of the two electrodes, the expanded graphite -1 The highest specific capacitance of 29.5 F g was obtained -1 , the energy density is 58.9Wh kg -1 , while YP-50 is 27.1F g -1 (54.2Wh kg -1 ). This once again confirms that adding betaine to the electrolyte can broaden the operating voltage of ammonium ion supercapacitors and thus achieve the purpose of improving the energy density of the device.

[0045] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. An ammonium ion electrolyte comprising ammonium ions, betaine and water.

2. The ammonium ion electrolyte according to claim 1, wherein 100 mL 1 mol L -1 The amount of betaine added to the NH4AC aqueous solution is from 0.1 g to a saturated concentration, preferably 0.6-1.3 g; for example, 0.6 g, 0.9 g or 1.3 g.

3. An aqueous symmetrical ammonium ion supercapacitor, wherein the aqueous symmetrical ammonium ion supercapacitor uses two expanded graphite electrodes of equal mass as positive and negative electrodes, the ammonium ion electrolyte according to claim 1 is used as the aqueous symmetrical ammonium ion supercapacitor electrolyte, and the electrolyte is encapsulated in a battery shell.

4. A method for preparing the aqueous symmetrical ammonium ion supercapacitor according to claim 3, comprising the following steps: a. Preparation of expanded graphite as electrode material for aqueous ammonium ion supercapacitors; b. mixing the ammonium-containing electrolyte and betaine in different proportions to obtain different mixed solutions; c Expanded graphite was used as the working electrode, and the mixed solution containing betaine was used as the electrolyte of aqueous ammonium ion supercapacitor for electrochemical testing; d Assemble symmetrical ammonium ion supercapacitors and test their electrochemical performance.

5. The preparation method according to claim 4, characterized in that: The preparation of the expanded graphite in step a is completed by expanding the graphene oxide prepared by the Hummers method at high temperature.

6. The preparation method according to claim 4, characterized in that: The ammonium-containing electrolyte in step b has a concentration of 1 mol L - 1 NH4AC aqueous solution.

7. The preparation method according to claim 4, characterized in that: The ammonium electrolyte and betaine in step b are mixed uniformly in different proportions, and the mixture is 100 mL 1 mol L -1 Different amounts of betaine were added into the NH4AC aqueous solution, and the added amounts of betaine were 0.6 g, 0.9 g and 1.3 g.

8. The preparation method according to claim 4, characterized in that: The electrochemical test in step c is performed using a three-electrode test, with expanded graphite as the positive electrode, a platinum wire electrode as the counter electrode, and a saturated calomel cell electrode as the reference electrode; the electrolyte is 10 ml of the 1 mol L prepared in step b. -1 NH4AC and betaine mixed electrolyte.

9. The preparation method according to claim 4, characterized in that: The electrochemical test content of step c is to test the linear scan LSV curve and cyclic voltammetry CV curve of the expanded graphite electrode in all the above mixed electrolytes.

10. The preparation method according to claim 4, characterized in that: In step d, the symmetrical ammonium ion supercapacitor is encapsulated in a CR2032 battery shell with two expanded graphite electrodes of the same mass and a mixed solution with 0.9 g of betaine added as the positive and negative electrodes and the electrolyte group respectively; the electrochemical test content is the CV curve at different scan rates and the constant current charge and discharge curve at different current densities.

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