阅读说明：本技术 一种提高水系电化学电容器工作电压的电解液 (Electrolyte for improving working voltage of aqueous electrochemical capacitor ) 是由 黄妙逢 杨嘉杰 郑思容 任小莲 巨新 陈森 于 2019-09-29 设计创作，主要内容包括：本发明提供一种提高水系电化学电容器工作电压的电解液,属于电化学电容器技术领域。该电解液由电解质和溶剂组成,其中,电解质为具有疏水端的离子,如脂肪醇聚氧乙烯醚硫酸钠、十二烷基硫酸钠等离子型表面活性剂,或醋酸钠、醋酸钾等有机盐；溶剂为低分子量聚氧乙烯和水的混合溶液。本发明采用具有疏水端的离子作为电解质。当电极施加电压后,离子带电端将被吸附到电极表面,而离子的疏水端可以阻止水溶剂与电极接触,达到将电极和水溶剂分隔开的效果,从而阻碍水溶剂的分解。聚氧乙烯可以增加有机盐的溶解度同时减少电解液中自由水的含量,从而提高电解液的工作电压。本发明制备方法简单,电解液价格低廉、对环境友好,对电极等不会腐蚀破坏。(The invention provides an electrolyte for improving the working voltage of a water-system electrochemical capacitor, belonging to the technical field of electrochemical capacitors. The electrolyte consists of an electrolyte and a solvent, wherein the electrolyte is ions with hydrophobic ends, such as fatty alcohol-polyoxyethylene ether sodium sulfate, lauryl sodium sulfate and other ionic surfactants, or sodium acetate, potassium acetate and other organic salts; the solvent is a mixed solution of low molecular weight polyethylene oxide and water. The present invention employs ions having hydrophobic ends as electrolytes. When voltage is applied to the electrode, the ion charged end is adsorbed to the surface of the electrode, and the hydrophobic end of the ion can prevent the water solvent from contacting with the electrode, so that the effect of separating the electrode and the water solvent is achieved, and the decomposition of the water solvent is hindered. The polyoxyethylene can increase the solubility of the organic salt and reduce the content of free water in the electrolyte, thereby improving the working voltage of the electrolyte. The preparation method is simple, the electrolyte is low in price and environment-friendly, and the electrode and the like cannot be corroded and damaged.)

1. An electrolyte for improving the working voltage of a water-based electrochemical capacitor is characterized in that: the electrolyte is a mixed solution of polyoxyethylene and water, and is dissolved in the solvent to obtain an electrolyte, and the ion concentration in the electrolyte is ensured to be 0.5-6 mol/Kg.

2. The aqueous electrochemical capacitor operating voltage increasing electrolyte of claim 1, wherein: the ionic surfactant comprises fatty alcohol-polyoxyethylene ether sodium sulfate and lauryl sodium sulfate.

3. The aqueous electrochemical capacitor operating voltage increasing electrolyte of claim 1, wherein: the organic salt and alkali salt include sodium acetate, potassium hydroxide, and potassium acetate.

4. The aqueous electrochemical capacitor operating voltage increasing electrolyte of claim 1, wherein: the mass ratio of polyoxyethylene to water in the solvent is 1: 1-9:1.

Technical Field

The invention relates to the technical field of electrochemical capacitors, in particular to an electrolyte for improving the working voltage of a water-system electrochemical capacitor.

Background

The super capacitor (electrochemical capacitor) has gained wide scientific research attention due to its high power density, fast charge and discharge capability and super long cycle stability. The main problems faced by current electrochemical capacitors are: compared with secondary batteries such as lithium ion batteries, electrochemical capacitors have difficulty in meeting the demand of various electric devices for high energy storage density due to their low energy density.

In order to obtain higher energy storage density, the capacitance of the electrode is increased. The storage density of the electrochemical capacitor is improved by increasing the specific surface area of an electrode material or obtaining pseudo capacitance by a composite metal oxide and the like. If the formula E is 0.5CU²Compared with the capacitance C, the energy storage density is directly proportional to the square of the working voltage U of the electrochemical capacitor, so the influence of the working voltage on the energy storage density is more obvious. The energy density can be obviously improved by increasing the working voltage, under the condition of unchanging the capacitance, the working voltage is increased to N times, and the energy density is increased by N²And (4) doubling.

The operating voltage of an electrochemical capacitor is related to the electrolyte. Electrochemical capacitor electrolytes can be classified mainly into organic, aqueous, ionic liquid, and gel depending on the components of the electrolyte solution used. Organic electrolytes generally can withstand voltages of 2.5 to 4V without decomposition, and thus the use of organic electrolytes is an important method for achieving high energy storage density. However, organic electrolytes have significant drawbacks, and the use of organic electrolytes can lead to a reduction in capacitance and power. More noteworthy are the problems of environmental pollution of organic electrolytes and the drawbacks of flammability and explosiveness.

The aqueous electrolyte has a larger specific capacitance and better power performance than the organic electrolyte. And the price is low, the environment is protected, and the safety problems that organic electrolyte is flammable and easy to explode and the like do not exist. However, aqueous electrolytes have a significant disadvantage, namely low operating voltages. Because the thermodynamically stable potential of water is only around 1.23V. Water hydrolyzes at a lower voltage than organic electrolytes. Therefore, the improvement of the hydrolysis voltage of the water solvent in the water-based supercapacitor electrolyte becomes the key for realizing the high-performance water-based electrochemical capacitor.

The method for improving the working voltage of the aqueous electrolyte mainly comprises the following steps: a pair of redox reaction substances are added into the electrolyte to introduce a redox reaction with rapid reaction kinetics so as to inhibit a water decomposition reaction, a surface modification and the like, or a metal salt electrolyte with high hydration energy such as lithium sulfate and the like is adopted.

In recent years, an electrolyte called "water in salt" has been developed (Science,350,938(2015)), which is an ultra-high concentration organic salt, and based on this concept, a plurality of ultra-high concentration electrolytes are used for aqueous electrochemical energy storage, and these ultra-high concentration electrolytes can improve the electrochemical window of aqueous electrolytes and increase the operating voltage of aqueous electrolytes (about 3V, which is much greater than that of ordinary aqueous electrolytes by 1.23V). However, the ultra-high concentration of the electrolyte is limited to the electrolyte having ultra-high solubility (such as bis (trifluoromethyl) sulfonyl imide salt). These electrolytes are generally relatively expensive, and the ultra-high concentration of electrolyte means that a large amount of electrolyte is required, which further increases the cost of the electrolyte. The invention develops the water system electrolyte without the need of salt with ultrahigh solubility, so that the conventional electrolyte salt can realize a high potential window under the conventional concentration, and the electrolyte can be used for a water system high-voltage electrochemical energy storage device.

Disclosure of Invention

The invention provides an electrolyte for improving the working voltage of an aqueous electrochemical capacitor, aiming at the problem of low working voltage of an aqueous electrolyte caused by hydrolysis.

The electrolyte comprises electrolyte and solvent, wherein the electrolyte is ionic surfactant with a hydrophobic end, or organic salt or alkali salt, the solvent is mixed solution of polyoxyethylene and water, the electrolyte is dissolved in the solvent to obtain the electrolyte, and the ion concentration in the electrolyte is ensured to be 0.5-6 mol/Kg.

Wherein, the ionic surfactant comprises fatty alcohol polyoxyethylene ether sodium sulfate, lauryl sodium sulfate and the like, and the organic salt and the alkali salt comprise sodium acetate, potassium hydroxide, potassium acetate and the like.

The mass ratio of polyoxyethylene to water in the solvent is 1: 1-9:1.

The ionic surfactant having a hydrophobic end used in the present invention is an electrolyte, for example: sodium fatty alcohol polyoxyethylene ether sulfate, sodium dodecyl sulfate and the like. The electrolyte having the above function can be electrolyzed in an aqueous solvent into ions having a hydrophobic end. Sodium fatty alcohol-polyoxyethylene ether sulfate is taken as an example: RO (CH2CH2O) n-SO₄Na ionizes RO (CH2CH2O) n-SO in water₄ ^2-And Na⁺. For anion RO (CH2CH2O)12-SO₄ ^2-One end of which is SO₄ ^2-The charged carrier has the same anion action as common metal salts, and RO (CH2CH2O)12 is a hydrophobic end, and can repel aqueous solution and prevent water from contacting with electrodes, thereby inhibiting hydrolysis and improving the working voltage of aqueous electrolyte.

The electrolyte is mainly characterized in that ions with hydrophobic ends, such as fatty alcohol-polyoxyethylene ether sodium sulfate, lauryl sodium sulfate and the like, are used as electrolytes. The ion concentration of the electrolyte solution can be 0.5-6 mol/Kg, so as to obtain different hydrolysis voltages and ion mobility.

On the other hand, the invention can reduce or eliminate free water in the electrolyte, thereby hindering the decomposition of water in the solvent and further achieving the effect of improving the voltage of the aqueous electrolyte. The invention obtains the high-pressure water-based electrolyte with the voltage of more than 3V based on the principle.

The present invention uses a conventional organic salt or alkali metal hydroxide as an electrolyte, and polyoxyethylene and the like and water as a solvent to obtain a high-voltage aqueous electrolyte. Substances such as polyoxyethylene which have a strong effect on water can reduce or even eliminate free water in the solvent, thereby improving the operating voltage of the aqueous electrolyte.

The solvent of the invention is a mixed solution of polyoxyethylene and water, and the mass fraction of (polyoxyethylene) in the mixed solvent is 50-90% according to the difference of working voltage and working power. Depending on the mass fraction, a potential window of 2-3V can be obtained.

The technical scheme of the invention has the following beneficial effects:

in the scheme, the method for preparing the electrolyte is simple and universal, and the working voltage of most of water-system electrochemical capacitors can be easily improved; in the method for improving the voltage of the electrochemical capacitor, the electrolyte with the functions is basically daily chemical products such as sodium dodecyl benzene sulfonate, sodium acetate and the like, is low in price, environment-friendly (even can be used for treating environmental pollution) and good in stability; the invention has no corrosion damage to electrochemical capacitors such as electrodes and the like, and has simple requirements on operating environment.

Drawings

FIG. 1 is a comparison of an electrolyte solution for increasing the operating voltage of an aqueous electrochemical capacitor according to the present invention with a conventional aqueous electrolyte solution, wherein (a) is the conventional aqueous electrolyte solution and (b) is the aqueous electrolyte solution according to the present invention;

FIG. 2 is a comparison of potential windows of a fatty alcohol-polyoxyethylene ether sodium sulfate electrolyte and a sodium sulfate electrolyte prepared in an embodiment of the present invention;

FIG. 3 is a comparison of sodium dodecyl sulfate electrolyte and sodium sulfate electrolyte potential windows prepared in examples of the present invention;

FIG. 4 is a cyclic voltammetry curve of a supercapacitor according to an embodiment of the present invention, with a voltage sweep rate of 0.005V/s and a working potential of 1.5-2.2V;

FIG. 5 is a cyclic voltammetry curve of a supercapacitor according to an embodiment of the present invention, with a voltage sweep rate of 0.01V/s and a working potential of 1.5-2.6V;

FIG. 6 is a graph of the coulombic efficiency of the super capacitor at different operating voltages according to the embodiment of the invention;

fig. 7 is a comparison of the potential windows of the electrolytes of the present invention and conventional electrolytes.

Detailed Description

In order to make the technical problems, technical solutions and advantages of the present invention more apparent, the following detailed description is given with reference to the accompanying drawings and specific embodiments.

The invention provides an electrolyte for improving the working voltage of an aqueous electrochemical capacitor, aiming at the problem of low working voltage caused by hydrolysis of the existing aqueous electrolyte.

The electrolyte comprises an electrolyte and a solvent, wherein the electrolyte is ions with hydrophobic ends, the solvent is a mixed solution of polyoxyethylene and water, the electrolyte is dissolved in the solvent to obtain the electrolyte, and the ion concentration in the electrolyte is ensured to be 0.5-6 mol/Kg.

The design idea of the invention is as follows: since the water decomposition voltage is relatively low, when a voltage is applied to the electrodes (water decomposition voltage is reached), hydrolysis reaction occurs at the interface where the water solvent contacts the electrodes or the water solvent contacts the electrodes. Then, if the water in the electrolyte is not allowed to easily reach the electrode surface or the electrolyte-electrode interface, the decomposition of water can be hindered or even prevented. The invention is based on this principle to increase the operating voltage of the electrolyte. The present invention employs ions having hydrophobic ends as electrolytes. When voltage is applied to the electrode, the ionic charged end is adsorbed to the surface of the electrode, and the hydrophobic end of the ion can prevent the water solvent from contacting with the electrode (as shown in figure 1), so that the electrode and the water solvent are separated, and the decomposition of the water solvent is hindered.

The following description is given with reference to specific examples.