CN116266507A - A high-voltage redox type composite electrolyte for supercapacitors and its preparation method and application - Google Patents

Abstract

The application provides a high-voltage redox type composite electrolyte for supercapacitors and its preparation method and application, including solvents, electrolytes and additives; the additives are selected from at least one of zinc iodide, copper iodide or iron iodide The electrolyte is selected from at least one of zinc chloride, zinc bromide or ferric chloride; the concentration of the electrolyte is 5-20M; the concentration of the additive is 1-5M. This application reduces the number of free water molecules by using a high-concentration salt electrolyte and broadens the working voltage; by adding additives containing double redox couples, the Faraday reaction capacity is introduced into the positive and negative electrodes at the same time to increase the specific capacity and show a higher Coulombic efficiency and cycle stability. The electrolyte solution of the present application has a simple formula, low cost, and environmental protection, and is applicable to the field of large-scale electrochemical energy storage.

Description

A high-voltage redox-type composite electrolyte for supercapacitors and its preparation Methods and Applications

technical field

The application relates to a high-voltage redox type composite electrolyte for supercapacitors and its preparation method and application, belonging to the field of electrochemical energy storage.

Background technique

A supercapacitor is an energy storage device between a traditional capacitor and a battery. It stores energy through ion adsorption and desorption at the interface between the electrode and the electrolyte or fast redox reactions on the surface and near the surface, so it has a high power density. and long-term cycle stability, it is regarded as a promising energy storage device. Supercapacitors are mainly composed of electrodes, electrolytes, and diaphragms. The improvement of their electrochemical performance is usually through the modification and optimization of electrode materials, such as the development of electrode materials with Faraday process pseudocapacitance to increase their specific capacity.

In recent years, scientists have also developed methods to modify the electrolyte to improve the performance of supercapacitors. Redox couples (I ⁰ / _I ^- _{, Br} ⁰ _/ Br ^- , Cu ²⁺ /Cu, Fe ³⁺ /Fe ²⁺ ) increase the Faradaic reaction process to increase the specific capacity. However, the introduction of a pair of redox couples only reacts at the positive or negative electrodes, and the increase in the capacity of a single electrode will aggravate the asymmetric behavior of the device electrodes, which usually leads to a decrease in the coulombic efficiency of the device and an increase in instability, limiting the further development of the energy density. improve.

Water-based electrolytes are safe and environment-friendly, making them the preferred electrolytes. However, the decomposition voltage of water is only 1.23V, which leads to low energy density of supercapacitors assembled from this electrolyte. When working under high voltage for a long time, the capacity decays quickly and cycle The short lifespan greatly limits the application of aqueous electrolytes in supercontainers.

Contents of the invention

In response to the above problems, the present application aims to provide a high-voltage redox type composite electrolyte for supercapacitors, which is to add transition metal iodide in high-concentration salt (zinc chloride (ZnCl ₂ )) electrolyte (such as zinc iodide (ZnI ₂ ), copper iodide (CuI ₂ ), iron iodide (FeI ₃ ), etc.) as additives to improve the electrochemical performance of supercapacitors such as energy density, specific capacity, and cycle stability.

According to one aspect of the present application, there is provided a high-voltage redox-type composite electrolyte for supercapacitors, including solvents, electrolytes and additives;

The additive is selected from at least one of zinc iodide, copper iodide or iron iodide; it can significantly increase its specific capacity, and exhibit high coulombic efficiency and cycle stability. Taking _ZnI2 as an example, the mechanism of a supercapacitor is that during the charging and discharging process, the positive electrode oxidizes ^I- ions to form _I2 simple substance, and then part of the _I2 simple substance combines with ^I- to form _I3- ^which is adsorbed on the electrode surface. Wherein I ^- complexes with zinc ions in the high-concentration salt electrolyte to form a compound ion [ZnI _x (OH ₂ ) _4-x ] ^2-x (x=0-2), which reduces the formation of I ₃ ^- . Zn ²⁺ at the negative electrode is reduced to Zn simple substance, which is deposited on the surface of the electrode.

Described electrolyte is selected from at least one in zinc chloride, zinc bromide or ferric chloride; Taking zinc chloride as example, _ZnCl has a solubility up to 30m (mol/Kg) in water at room temperature, and high-concentration zinc The combination of ions and water molecules in the solution through the van der Waals force greatly reduces the number of free water molecules in the solution, inhibits the decomposition of water under high pressure, and increases the working voltage of the aqueous electrolyte. When used in supercapacitors, it improves the capacitor energy density. In addition, the high-concentration electrolyte hinders the dissociation of redox couples, inhibits self-discharge, and improves Coulombic efficiency.

The concentration of the electrolyte is 5-20M; the concentration of the additive is 1-5M.

The solvent is water.

In the high-voltage redox composite electrolyte solution for supercapacitors, the concentration of the electrolyte is 10-20M.

In the high-voltage redox type composite electrolyte for supercapacitors, the concentration of the additive is 1-3M.

According to another aspect of the present application, there is provided a method for preparing the above-mentioned high-voltage redox composite electrolyte for supercapacitors, at least including the following steps:

The raw materials containing electrolyte and additives are mixed with water to obtain the high-voltage redox type composite electrolyte for supercapacitor.

The dosage ratio of the electrolyte, additives and water is 5-20mol: 1-5M: 1000g

The raw material contains silicon dioxide powder;

The ratio of the mass of the silica powder to the total mass of the electrolyte, additives and water is 1:10.

The mixing process includes magnetic stirring.

According to another aspect of the present application, a supercapacitor is provided, including a positive pole, a negative pole and an electrolyte;

The electrolyte is selected from the above-mentioned high-voltage redox composite electrolyte for supercapacitors or the high-voltage redox composite electrolyte for supercapacitors prepared by the above preparation method.

The positive electrode or/and is selected from graphene;

The supercapacitor includes a diaphragm.

At a current density of 0.1mA cm ^-2 , the voltage window is 0-1.35V; after 5300 cycles, it still has a specific discharge capacity of 93mAh cm ^-3 , a capacity retention rate of 92.1%, and a coulombic efficiency of 99%.

The beneficial effect that this application can produce comprises:

1) The preparation method of the high-voltage redox type composite electrolyte for supercapacitors provided by this application has a simple synthesis method, is simple and easy to implement, and is easy to expand production.

2) The composite electrolyte solution provided by this application has high safety, excellent ionic conductivity and voltage window, and introduces Faradaic reactions at the positive and negative electrodes at the same time. The supercapacitor assembled with the composite electrolyte has excellent electrochemical performance.

3) In this application, adding zinc iodide (ZnI ₂ ), copper iodide (CuI ₂ ), iron iodide (FeI ₃ ) and other transition metal iodides to the high-concentration brine electrolyte can significantly increase the energy density of supercapacitors, Specific capacity while ensuring the Coulombic efficiency and cycle stability of the two-electrode test.

Description of drawings

Fig. 1 is the water-based graphene-based micro-supercapacitor prepared in Example 1 of the present application. Figure a is an optical microscope image of some microcapacitors. Figure b is the height distribution diagram of the dotted line in Figure a.

Fig. 2 is the linear sweep voltammetry curve of the water-based graphene-based micro-supercapacitor assembled with the high-voltage redox composite electrolyte in Example 1 of the present application, with a sweep speed of 1 mV s ^-1 .

Fig. 3 is the cyclic voltammetry curve of the water-based graphene-based micro-supercapacitor assembled with the high-voltage redox composite electrolyte in Example 1 of the present application. The scanning range is 0-1.35V, and the scanning speed is 1mV s ^-1 .

Figure 4 is the cycle curve of the water-based graphene-based micro-supercapacitor assembled with a high-voltage redox composite electrolyte in Example 1 of the present application, wherein the voltage window is 0-1.35V, and the current density is 0.1mA cm ^-2 .

Fig. 5 is the cyclic voltammetry curve of the water-based graphene-based micro-supercapacitor assembled with 15m ZnCl ₂ electrolyte, the scanning range is 0-1.35V, and the scanning speed is 1mV s ^-1 .

Detailed ways

The present application will be described in detail below in conjunction with the examples. It should be understood that the following embodiments are only used to illustrate the present application, not to limit the present application.

Unless otherwise specified, the raw materials in the examples of the present application were purchased through commercial channels. Those who do not indicate the specific conditions in the examples are carried out according to the conventional conditions or the conditions suggested by the manufacturer. The reagents or instruments used were not indicated by the manufacturer, and they were all conventional products that could be purchased from the market.

Analytic method is as follows in the embodiment of the application:

Using CHI 760E electrochemical workstation (Shanghai Chenhua Instrument Co., Ltd.) to test electrochemical impedance spectroscopy (EIS) (performed at a frequency of 105Hz to 10-2Hz, with an AC amplitude of 5mV) and linear sweep voltammetry curves (voltage range of 0 to 1.35V with a scan rate of 1-10mV s ^-1 ).

Use LAND CT2001A battery system (Wuhan Landian Electronics Co., Ltd.) for constant current charge/discharge test (voltage range is 0-1.35V).

The characteristics and performance of the present application will be described in further detail below in conjunction with the examples.

Example 1

Preparation of electrolyte solution: Add 3.192g _ZnI2 powder and 20.445g _ZnCl2 powder into a sample bottle, add 10ml deionized water, stir with a magnetic stirrer at room temperature for 5h, stirring speed 500rpm, mix well, and prepare 1m _ZnI2 + 15m ZnCl ₂ high pressure redox composite electrolyte. In order to reduce the fluidity of the electrolyte, it is advisable to mix silica powder at a mass ratio (silica powder:composite electrolyte) of 1:10 to form a hydrogel electrolyte to further improve safety.

Preparation of supercapacitor: Graphite paper (122mg) was used as the working electrode, metal platinum was used as the counter electrode, 7mol L ^{- 1} KOH solution was used as the electrolyte, and a positive voltage of 10V was applied to electrochemically strip the graphite paper for 2h. The electrochemically exfoliated graphene (EG) obtained by exfoliation was washed with deionized water until the pH value was 7.0, and then dispersed with 500ml of ethanol to form an EG dispersion. Take 1ml of the dispersion liquid to the two stages of the interdigitated grinding tool, vacuum filter and transfer further to obtain interdigitated EG symmetrical electrodes with polyethylene terephthalate (PET) film as the substrate. Take a sufficient amount of hydrogel electrolyte and apply it on the EG symmetrical electrode to obtain a water-based graphene-based micro-supercapacitor. As shown in Figure 1, the two stages have four fingers respectively, the finger length is 12 mm, the finger width is 1 mm, the finger spacing is 1 mm, and the thickness is 2.1 μm.

Electrochemical performance test: CHI 760E electrochemical workstation was used for linear scan test (scanning speed 1mVs ^-1 ). Figure 2 shows the linear sweep voltage and volt-ampere curves of the water-based graphene-based micro-supercapacitor assembled with a high-voltage redox composite electrolyte. It can be seen that the decomposition voltage of the electrolyte is greater than 2.1V, which is much higher than the decomposition voltage of water, which is 1.2V. The cyclic voltammetry curve of the test line was tested by CHI 760E electrochemical workstation (the voltage range is 0-1.35V, and the scan rate is 1mV/s). Figure 3 is the cyclic voltammetry curve of the water-based graphene-based micro-supercapacitor assembled with a high-voltage redox-type composite electrolyte. It can be seen that sharp redox peaks appear at 1.27V and 1.12V, respectively. Use the LAND CT2001A battery system for constant current charge/discharge test (voltage range is 0-1.35V). Figure 4 is the cycle curve of the water-based graphene-based micro-supercapacitor assembled with a high-voltage redox composite electrolyte in Example 1 of the present application. It can be seen that at a current density of 0.1mA cm ^-2 , the voltage window is 0-1.35V , the water-based graphene-based micro-supercapacitor assembled with a high-voltage redox composite electrolyte still has a discharge specific capacity of 93mAh cm ^-3 after 5300 cycles, a capacity retention rate of 92.1%, and a Coulombic efficiency of 99%, which are very excellent. stability.

Comparative example 1

Add 20.445g of _ZnCl2 powder into the sample bottle, and add 10ml of deionized water, stir with a magnetic stirrer at room temperature for 5h at a stirring speed of 500rpm, mix well, and prepare a 15m _ZnCl2 electrolyte. The preparation and assembly of graphene-based micro-supercapacitors are the same as in Example 1. The cyclic voltammetry curve of the test line was tested by CHI 760E electrochemical workstation (the voltage range is 0-1.35V, and the scan rate is 1mV/s). Figure 5 is the cyclic voltammetry curve of a water-based graphene-based micro-supercapacitor assembled with a 15m ZnCl ₂ electrolyte. It can be seen that the capacitor only exhibits standard electric double layer capacitance characteristics.

The above are only a few embodiments of the application, and do not limit the application in any form. Although the application is disclosed as above with preferred embodiments, it is not intended to limit the application. Any skilled person familiar with this field, Without departing from the scope of the technical solution of the present application, any changes or modifications made using the technical content disclosed above are equivalent to equivalent implementation cases, and all belong to the scope of the technical solution.

Claims (10)

1. A high-voltage redox type composite electrolyte for supercapacitors, characterized in that it includes solvents, electrolytes and additives; The additive is selected from at least one of zinc iodide, copper iodide or iron iodide; The electrolyte is selected from at least one of zinc chloride, zinc bromide or ferric chloride; The concentration of the electrolyte is 5-20M; the concentration of the additive is 1-5M. 2. The high-voltage redox type composite electrolyte for supercapacitor according to claim 1, wherein the solvent is water. 3. The high-voltage redox composite electrolyte for supercapacitor according to claim 1, characterized in that, in the high voltage redox composite electrolyte for supercapacitor, the concentration of the electrolyte is 10- 20M. 4. The high-voltage redox type composite electrolyte for supercapacitor according to claim 1, characterized in that, in the high voltage redox type composite electrolyte for supercapacitor, the concentration of the additive is 1～ 3M. 5. a preparation method for the high-pressure redox type composite electrolytic solution for supercapacitor claimed in claim 1, is characterized in that, comprises the following steps at least: The raw materials containing electrolyte and additives are mixed with water to obtain the high-voltage redox type composite electrolyte for supercapacitor. 6 . The preparation method according to claim 5 , characterized in that, the dosage ratio of the electrolyte, the additive and water is 5-20 mol: 1-5M: 1000 g. 7. the preparation method according to claim 5, is characterized in that, contains silicon dioxide powder in the described raw material; The ratio of the mass of the silicon dioxide powder to the total mass of the electrolyte, additives and water is 1:10-15. 8. A supercapacitor, characterized in that, comprises positive pole, negative pole and electrolyte; The electrolyte is selected from the high-voltage redox composite electrolyte for supercapacitors described in any one of claims 1 to 4 or the high-voltage redox composite electrolyte for supercapacitors prepared by the preparation method described in claims 5 to 7. Prototype composite electrolyte. 9. supercapacitor according to claim 8, is characterized in that, described positive electrode or/and is selected from graphene; The supercapacitor includes a diaphragm. 10. The supercapacitor according to claim 8, characterized in that, at a current density of 0.1mA cm ^-2 , the voltage window is 0-1.35V; after 5300 cycles, it still has a discharge specific capacity of 93mAh cm ^-3 , The capacity retention rate is 92.1%, and the Coulombic efficiency is 99%.

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