CN113948318B - High-pressure water system electrolyte and preparation method and application thereof - Google Patents

Abstract

The invention discloses a medium-high-voltage water-based electrolyte, a preparation method thereof and an application in supercapacitors, belonging to the field of preparation of water-based supercapacitors. In the invention, salt solute is added to ionized water or distilled water to obtain a mixed solution, and additives are added to the mixed solution to obtain a high-pressure water-based electrolyte. The preparation method can control the conductivity, viscosity and electrochemical stability window of the electrolyte by controlling the solute, the type of the additive, and the content of the additive; the hydrophobicity of the surface of the electrode material can be adjusted through the additive, thereby enhancing the adsorption of the electrolyte on its surface . The prepared high-pressure water-based electrolyte is harmless to the environment, non-toxic, nonflammable, and low in cost, and has broad application prospects in supercapacitors.

Description

A kind of high-pressure aqueous electrolyte and its preparation method and application

technical field

The invention belongs to the field of preparation of water-based supercapacitors, and in particular relates to a high-pressure water-based electrolyte, a preparation method thereof, and an application thereof in supercapacitors.

Background technique

可知，影响超级电容器能量密度的主要因素有电极材料、工作电压等，提升超级电容器的能量密度可以通过增加比容量(C)或提高电压窗口(U)来实现。目前提高电压窗口是提高超级电容器能量密度最为有效的方法。超级电容器的电压窗口主要由电解液决定，常用于超级电容器的电解液分为水系、有机系、离子液体及固态电解液。有机系超级电容器可以提供稳定的宽电压窗口(≥2.5V)，但它的缺点是离子导电性低、具有可燃性和毒性。和有机系类似，离子液体超级电容器的电压窗口虽可高达4.0V，然而离子液体的电导率比有机系的更低，而且电解液具有较高的黏度从而增加等效串联电阻(ESR)，导致较差的功率性能和倍率特性。此外，这两种电解液对水敏感，所以在制备过程中要求更加严格，成本更高。对于固态超级电容器来说，因其在室温下具有很低的离子导电性而受到一定的限制。与以上的非水系超级电容器相比，水系超级电容器通常具有更大的比容，更高的功率密度，这是因为水系电解液离子尺寸更小，电导率更高，更重要的是这种电解液对环境友好、成本低廉，可进行大规模的生产。因此，水系电解液成为超级电容器研究领域的热点。然而，由于水的分解电压只有1.23V，所以水系超级电容器的电化学稳定窗口很窄，这也是目前限制水系超级电容器发展的主要原因。As an electrochemical energy storage device, supercapacitors have attracted extensive attention due to their ultrahigh power density and excellent cycle life. However, the relatively low energy density limits their further practical applications. According to the formula

It can be seen that the main factors affecting the energy density of supercapacitors are electrode materials, operating voltage, etc., and the energy density of supercapacitors can be increased by increasing the specific capacity (C) or increasing the voltage window (U). At present, increasing the voltage window is the most effective way to increase the energy density of supercapacitors. The voltage window of a supercapacitor is mainly determined by the electrolyte. The electrolytes commonly used in supercapacitors are divided into aqueous systems, organic systems, ionic liquids, and solid electrolytes. Organic supercapacitors can provide a stable wide voltage window (≥2.5V), but their disadvantages are low ionic conductivity, flammability and toxicity. Similar to the organic system, although the voltage window of the ionic liquid supercapacitor can be as high as 4.0V, the conductivity of the ionic liquid is lower than that of the organic system, and the electrolyte has a higher viscosity, which increases the equivalent series resistance (ESR), resulting in Poor power performance and rate characteristics. In addition, these two electrolytes are sensitive to water, so the requirements in the preparation process are more stringent and the cost is higher. Solid-state supercapacitors are limited by their low ionic conductivity at room temperature. Compared with the above non-aqueous supercapacitors, aqueous supercapacitors usually have larger specific capacity and higher power density, because the aqueous electrolyte ion size is smaller, the conductivity is higher, and more importantly, this electrolysis The liquid is environmentally friendly, low in cost, and can be produced on a large scale. Therefore, aqueous electrolyte has become a hot spot in the field of supercapacitor research. However, since the decomposition voltage of water is only 1.23V, the electrochemical stability window of aqueous supercapacitors is very narrow, which is the main reason that currently limits the development of aqueous supercapacitors.

There are two main methods to broaden the electrochemical window of aqueous supercapacitors: one is to design special electrode materials to expand the electrochemical stability window. For example, Zhao et al prepared an aqueous supercapacitor with vertically grown MnO ₂ on carbon nanofibers as the electrode material, and its electrochemical stability window is about 2V. Wang and Dai et al. used electrochemical deposition to deposit _MnO2 -based electrodes and assembled them into asymmetric supercapacitors. The electrochemical stability window of this capacitor was 2.2V, and the capacity retention rate after 5000 cycles was 88.6%. Although this method can expand the electrochemical stability window of aqueous supercapacitors to above 2 V, the electrochemical performance will be greatly degraded after thousands of cycles. Another approach to improve the stability window of aqueous supercapacitors is to assemble symmetrical supercapacitors with carbon-based materials as electrodes and a special aqueous electrolyte. These special aqueous electrolytes have high overpotentials, which can broaden the electrochemical stability window. For example, the invention patent CN104134549A discloses a supercapacitor using magnesium nitrate aqueous solution as the electrolyte and an electrochemical window of 1.2V to 1.9V. Wang et al. used graphite as the electrode and neutral sodium sulfate as the electrolyte to make a supercapacitor with a working voltage of 1.8V. Although this method can widen the voltage window, the voltage is relatively small for practical applications, and the energy density of the device has not been further improved.

Contents of the invention

The present invention aims at the problems of small electrochemical stability window and low energy density of the current water-based supercapacitor, and provides a high-pressure water-based electrolyte, its preparation method and application in supercapacitors, thereby increasing the working voltage and energy density of the supercapacitor.

In order to achieve the above object, the present invention adopts the following technical solutions to achieve:

The invention discloses a method for preparing a high-pressure water-based electrolyte, which comprises the following steps:

1) Add the salt solute into deionized water or distilled water, and stir until the salt solute is completely dissolved to obtain a mixed solution;

The salt solute is one or more of sulfate, ammonium salt and iminium salt; the mass fraction of the sulfate in the formed mixed solution is 1% to 19%, and the ammonium salt in the formed mixed solution The mass fraction of the imide salt in the formed mixed solution is 0.1% to 10%;

2) adding additives to the mixed solution to react to obtain a high-pressure water-based electrolyte;

The additive is one or more of a water-repelling agent, a hydrogen remover, an additive for increasing working voltage, an additive for suppressing or eliminating water vapor, and a surfactant;

The mass fractions of the waterproof mixture, the hydrogen remover, the additive for increasing the working voltage, the additive for suppressing or eliminating water vapor, and the surfactant in the prepared high-pressure aqueous electrolyte are 0.1%-50%, 0.2%-30%, respectively. %, 0.1% to 20%, 0.05% to 10%, and 0.5% to 30%.

Further, in step 1), the sulfate salt includes one or more of sodium sulfate, lithium sulfate and potassium sulfate; the ammonium salt includes ammonium phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate and ammonium sulfate One or more of them; the imide salt includes one or more of sodium bistrifluoromethanesulfonimide, lithium bistrifluoromethanesulfonimide and zinc bistrifluoromethanesulfonimide.

Further, in step 2), the waterproofing agent is acetonitrile, dimethylformamide, ethylene glycol, isopropanol, phosphoric acid, hypophosphorous acid, ammonium hypophosphite, ammonium dihydrogen phosphate, ammonium adipate, One or more of ammonium pentaborate, ammonium phosphate, silicic acid compound and aluminum salt.

Further, in step 2), the hydrogen remover is one of resorcinol, p-nitrophenol, p-nitrobenzoic acid, dimethyl sulfoxide, p-nitrobenzyl alcohol and p-benzoquinone or Several kinds.

Further, in step 2), the additive for increasing the working voltage is citric acid or tartaric acid or a mixture of the two.

Further, in step 2), the additive for suppressing or eliminating water vapor is one or more of polyvinyl alcohol, polyethylene glycol, glucose, sucrose, mannitol and polypropylene amine.

Further, in step 2), the surfactant is sodium vinyl sulfonate, sodium allyl sulfonate, sodium allyloxy hydroxypropyl sulfonate, sodium methacrylate hydroxypropyl sulfonate and styrene sulfonic acid One or more of sodium.

The invention also discloses the high-pressure water-based electrolyte prepared by the above-mentioned method.

The invention also discloses the application of the above-mentioned high-pressure water electrolyte in supercapacitors.

Compared with the prior art, the present invention has the following beneficial effects:

In the preparation method of a high-pressure water-based electrolyte disclosed in the present invention, the conductivity, viscosity and electrochemical stability window of the electrolyte can be controlled by controlling the type of solute, the additive, and the content of the additive during the preparation process; due to the carbon electrode material It is hydrophobic in itself, and the functional groups in the water-repelling agent, hydrogen scavenger, additive to increase the working voltage, additive to suppress or eliminate water vapor, and the surfactant are closely combined with the oxygen-containing functional groups on the surface of the carbon electrode by hydrogen bonds. The surface of the carbon electrode is fully infiltrated, and the ions in the electrolyte can reach and adsorb on the electrode surface more easily, thereby enhancing the energy storage capacity of the supercapacitor and increasing the specific capacity and energy density of the supercapacitor.

Compared with the organic or ionic liquid electrolyte, the high-pressure water-based electrolyte prepared by the above-mentioned preparation method of the high-pressure water-based electrolyte in the present invention has lower prices because the solute of the electrolyte is mainly sulfate, ammonium salt and imide salt. Inorganic salt, the solvent is deionized water, the water-based electrolyte thus configured is non-toxic and harmless compared with the organic electrolyte; although organic additives are added to the water-based electrolyte, the content of these additives is very small, so it is not easy to combustion.

The high-pressure aqueous electrolyte prepared by the present invention is applied to a supercapacitor, and the specific capacity of the prepared supercapacitor is 90F/g; after 10,000 cycles, the retention rate is close to 90%, the Coulombic efficiency is close to 100%, and the electrochemical stability When the window is 2-3V, the working voltage and energy density of the supercapacitor are improved, and it has beneficial electrochemical properties such as high capacity and long life.

Description of drawings

Fig. 1 is the optical photograph of the high-pressure aqueous electrolyte prepared in the embodiment of the present invention 1;

Fig. 2 is the cyclic voltammetry characteristic curve under different voltage windows of the supercapacitor assembled by the high-pressure aqueous electrolyte in Example 1 of the present invention;

Fig. 3 is the optical photograph of the high-pressure aqueous electrolyte prepared in the embodiment of the present invention 2;

Fig. 4 is the cyclic voltammetry characteristic curve under different voltage windows of the supercapacitor assembled by the high-pressure aqueous electrolyte in Example 2 of the present invention;

Fig. 5 is the optical photo of the high-pressure aqueous electrolyte prepared in the embodiment of the present invention 3;

Fig. 6 is the cyclic voltammetry characteristic curve under different voltage windows of the supercapacitor assembled by the high-pressure aqueous electrolyte in Example 3 of the present invention;

Fig. 7 is a cyclic voltammetry characteristic curve of a supercapacitor assembled with the high-pressure aqueous electrolyte in Example 4 of the present invention under different voltage windows.

detailed description

In order to enable those skilled in the art to better understand the solutions of the present invention, the following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only It is an embodiment of a part of the present invention, but not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts shall fall within the protection scope of the present invention.

It should be noted that the terms "first" and "second" in the description and claims of the present invention and the above drawings are used to distinguish similar objects, but not necessarily used to describe a specific sequence or sequence. It is to be understood that the data so used are interchangeable under appropriate circumstances such that the embodiments of the invention described herein can be practiced in sequences other than those illustrated or described herein. Furthermore, the terms "comprising" and "having", as well as any variations thereof, are intended to cover a non-exclusive inclusion, for example, a process, method, system, product or device comprising a sequence of steps or elements is not necessarily limited to the expressly listed instead, may include other steps or elements not explicitly listed or inherent to the process, method, product or apparatus.

The present invention is described in further detail below in conjunction with accompanying drawing:

Example 1

A method for preparing a high-pressure water-based electrolyte, comprising the following steps:

Step 1: Weigh 2.8g of analytically pure Na ₂ SO ₄ into 100mL of deionized water or distilled water, stir to dissolve it completely, and obtain a mixed solution with a mass fraction of 2.72%;

Step 2: Ammonium dihydrogen phosphate is added to the above mixed solution as a water-repellent mixture, and then p-nitrobenzoic acid is added to the above mixed solution as a hydrogen remover to obtain a high-pressure water-based electrolyte, wherein the water-resistant mixture and hydrogen remover The mass fractions of the electrolyte in the high-pressure water system are 1% and 0.3% respectively;

The electrolyte prepared above was used as the supercapacitor aqueous electrolyte, and the aluminum-based carbon nanotube was used as the electrode material to assemble the symmetrical supercapacitor. The above-assembled device was used for performance tests such as cyclic voltammetry, impedance, constant current charge and discharge, and cycle stability with a Princeton electrochemical workstation. The test results are as follows:

The electrolyte solution prepared in this embodiment is shown in Figure 1, from which it can be seen that the electrolyte solution is a colorless and transparent liquid. Figure 2 shows the cyclic voltammetry characteristic curves (CV) of the above devices under different voltage windows, and the test voltage ranges are 0-2V, 0-2.4V, 0-2.6V, 0-2.8V and 0-3V. It can be seen from the figure that with the increase of the voltage window, the CV curve gradually produces polarization, which may be caused by water decomposition. Therefore, in this experiment, the voltage stability window we selected is 2.4V. It can be seen that the prepared high-pressure aqueous electrolyte has excellent supercapacitor characteristics under different voltage windows.

Example 2

The difference from the preparation conditions of the high-pressure aqueous electrolyte in Example 1 is that the addition of additives and surfactants to suppress or eliminate water vapor are polyethylene glycol and sodium vinyl sulfonate, and other condition parameters are the same as in Example 1 to obtain a high-pressure The water-based electrolyte, wherein the mass fractions of the water-repellent mixture, the hydrogen remover, the additive for suppressing water vapor, and the surfactant in the high-pressure water-based electrolyte are 1%, 0.3%, 0.2% and 0.7%, respectively.

The electrolyte prepared above was used as the supercapacitor aqueous electrolyte, and the aluminum-based carbon nanotube was used as the electrode material to assemble the symmetrical supercapacitor. The above-assembled device was used for performance tests such as cyclic voltammetry, impedance, constant current charge and discharge, and cycle stability with a Princeton electrochemical workstation. The test results are as follows:

The electrolyte solution prepared in this embodiment is shown in Figure 3, from which it can be seen that the electrolyte solution is a colorless and transparent liquid. Figure 4 shows the cyclic voltammetry characteristic curves of the above devices under different voltage windows. It can be seen from Figure 4 that a small polarization phenomenon occurs when the voltage window is increased to 2.8V or even 3V. This is because the addition of additives further inhibits the decomposition of water, thus making the voltage window of the aqueous electrolyte wider. It can be seen that changing the additive type of the electrolyte can change the electrochemical window of the device, which reflects the wide applicability of the electrolyte.

Example 3

The difference from the preparation conditions of the high-pressure water-based electrolyte in Example 1 is that the water-repellent mixture used is ammonium hypophosphite, the hydrogen remover is p-nitrophenol, and other condition parameters are the same as those in Example 1 to obtain a high-pressure water-based electrolyte, wherein The mass fractions of the water-repellent mixture and the hydrogen remover in the high-pressure aqueous electrolyte are 5% and 1%, respectively.

The electrolyte prepared above was used as the supercapacitor aqueous electrolyte, and the aluminum-based carbon nanotube was used as the electrode material to assemble the symmetrical supercapacitor. The above-assembled device was used for performance tests such as cyclic voltammetry, impedance, constant current charge and discharge, and cycle stability with a Princeton electrochemical workstation. The test results are as follows:

The electrolyte solution prepared in this embodiment is shown in Figure 5, from which it can be seen that the electrolyte solution is a colorless and transparent liquid. Figure 6 shows the cyclic voltammetry characteristic curves of the above devices under different voltage windows. It can be seen from Fig. 6 that the CV curves obtained when changing the types of hydrogen scavenger and anti-alloying agent are different. When the voltage window is 2.6V, the CV curve shows a nice rectangle. Therefore, it shows that the electrolyte prepared under this condition also has a wide voltage window.

Example 4

The difference from the preparation conditions of the high-pressure water-based electrolyte in Example 1 is that the electrolyte salt is analytically pure Li ₂ SO ₄ with a mass fraction of 10.9%, and other condition parameters are the same as in Example 1. A high-pressure water-based electrolyte is obtained, in which The mass fractions of ammonium dihydrogen phosphate mixture and p-nitrobenzoic acid hydrogen remover in the high-pressure aqueous electrolyte are 1% and 0.3%, respectively.

The electrolyte prepared above was used as the supercapacitor aqueous electrolyte, and the aluminum-based carbon nanotube was used as the electrode material to assemble the symmetrical supercapacitor. The above-assembled device was used for performance tests such as cyclic voltammetry, impedance, constant current charge and discharge, and cycle stability with a Princeton electrochemical workstation. The test results are as follows:

Figure 7 shows the cyclic voltammetry characteristic curves of the above devices under different voltage windows. It can be seen from the figure that when the voltage window is 0-2V, the CV curve basically remains rectangular, and when the voltage window is further expanded, polarization occurs and the water in the electrolyte begins to decompose. It can be seen that changing the electrolyte salt in the high-pressure water-based electrolyte can also expand the voltage range to varying degrees, indicating that the electrolyte additive can be applied to different electrolyte salts.

In Examples 5 to 7, the types of solutes in the electrolyte, the types and mass fractions of additives are adjusted differently, and supercapacitors are prepared with these electrolytes and their electrochemical performance is tested. The detailed data are shown in Table 1 and Table 2.

Comparative example 1: take sodium sulfate as solute, deionized water as solvent, the mass fraction of sodium sulfate in deionized water is 2.72%, assemble supercapacitor with this electrolyte, used electrode material and assembly method are the same as embodiment 1. The properties of supercapacitors are shown in Table 3.

Comparative example 2: using lithium sulfate as the solute and deionized water as the solvent. The mass fraction of lithium sulfate in deionized water is 10.9%, and the electrochemical performance of the supercapacitor assembled with this electrolyte (assembly method is the same as in Example 1) is shown in Table 3.

Comparative example 3: using ammonium dihydrogen phosphate as the solute and deionized water as the solvent. The mass fraction of ammonium dihydrogen phosphate in deionized water is 5%, and the electrochemical performance of the supercapacitor assembled with this electrolyte (assembly method is the same as in Example 1) is shown in Table 3.

Comparative example 4: using ammonium dihydrogen phosphate as the solute and deionized water as the solvent. The mass fraction of ammonium dihydrogen phosphate in deionized water is 12%, and the electrochemical properties of the supercapacitor assembled with this electrolyte (assembly method is the same as in Example 1) are shown in Table 3.

Comparative example 5: using diammonium hydrogen phosphate as the solute and deionized water as the solvent. The mass fraction of diammonium hydrogen phosphate in deionized water is 2%, and the electrochemical performance of the supercapacitor assembled with this electrolyte (assembly method is the same as in Example 1) is shown in Table 3.

Table 1 Electrolyte composition and content and supercapacitor performance comparison

Table 2 Electrolyte composition and content and supercapacitor performance comparison

Table 3 Electrolyte composition and content and supercapacitor performance comparison

It can be seen from the data in Table 1-3 that the voltage window and specific capacity of the supercapacitor obtained without adding any additives to the electrolyte are relatively small, and the capacity retention rate is low. The voltage window of the supercapacitor obtained by adding different types and contents of additives to the aqueous electrolyte prepared by different solutes is further expanded, from the original 1.8V to about 2.8V. In addition, the specific capacity and cycle retention of the assembled aqueous supercapacitors are further improved.

The above content is only to illustrate the technical ideas of the present invention, and cannot limit the protection scope of the present invention. Any changes made on the basis of the technical solutions according to the technical ideas proposed in the present invention shall fall within the scope of the claims of the present invention. within the scope of protection.

Claims (4)

1. A preparation method of a high-pressure water system electrolyte is characterized by comprising the following steps:

1) Adding the salt solute into deionized water or distilled water, and stirring until the salt solute is completely dissolved to obtain a mixed solution;

the salt solute is one or more of sulfate, ammonium salt and imine salt; the mass fraction of the sulfate in the formed mixed solution is 1-19%, the mass fraction of the ammonium salt in the formed mixed solution is 0.5-30%, and the mass fraction of the iminium salt in the formed mixed solution is 0.1-10%;

2) Adding an additive into the mixed solution for reaction to obtain a high-pressure water system electrolyte;

the additive is one or more of a waterproof agent, a hydrogen eliminating agent, an additive for improving working voltage, an additive for inhibiting or eliminating water vapor and a surfactant;

the mass fractions of the waterproof agent, the hydrogen scavenger, the additive for improving the working voltage, the additive for inhibiting or eliminating water vapor and the surfactant in the prepared high-pressure water system electrolyte are respectively 0.1-50%, 0.2-30%, 0.1-20%, 0.05-10% and 0.5-30%;

the waterproof agent is one or more of acetonitrile, dimethylformamide, ethylene glycol, isopropanol, phosphoric acid, hypophosphorous acid, ammonium hypophosphite, ammonium dihydrogen phosphate, ammonium adipate, ammonium pentaborate, ammonium phosphate, sodium silicate and aluminum phosphate;

the dehydrogenation agent is one or more of resorcinol, p-nitrophenol, p-nitrobenzoic acid, dimethyl sulfoxide, p-nitrobenzol and p-benzoquinone;

the additive for improving the working voltage is citric acid or tartaric acid or a mixture of the two;

the additive for inhibiting or eliminating water vapor is one or more of polyvinyl alcohol, polyethylene glycol, glucose, sucrose, mannitol and polyacrylamide;

the surfactant is one or more of sodium vinyl sulfonate, sodium allyl sulfonate, sodium allyloxy hydroxypropyl sulfonate, sodium hydroxypropyl methacrylate sulfonate and sodium styrene sulfonate.

2. The method according to claim 1, wherein in step 1), the sulfate comprises one or more of sodium sulfate, lithium sulfate, and potassium sulfate; the ammonium salt comprises one or more of ammonium phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate and ammonium sulfate; the imide salt comprises one or more of bis (trifluoromethanesulfonyl) imide sodium, bis (trifluoromethanesulfonyl) imide lithium and bis (trifluoromethanesulfonyl) imide zinc.

3. A high-pressure aqueous electrolyte obtained by the method for producing a high-pressure aqueous electrolyte according to any one of claims 1 to 2.

4. Use of the high-pressure aqueous electrolyte according to claim 3 in a supercapacitor.

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