CN111313071A

CN111313071A - All-vanadium redox flow battery negative electrode electrolyte and method for reducing negative electrode vanadium ion migration

Info

Publication number: CN111313071A
Application number: CN201811513702.4A
Authority: CN
Inventors: 孙佳伟; 李先锋; 张华民
Original assignee: Dalian Institute of Chemical Physics of CAS
Current assignee: Dalian Institute of Chemical Physics of CAS
Priority date: 2018-12-11
Filing date: 2018-12-11
Publication date: 2020-06-19

Abstract

The invention relates to a method for reducing vanadium ion migration of a cathode of an all-vanadium redox flow battery, which is characterized in that one or more than two of complexing agents of oxalic acid, sodium oxalate and potassium oxalate are added into the all-vanadium redox flow battery; the concentration of the complexing agent is 1 mmol/L-1 mol/L. The preferable concentration of the additive is 0.01mol/L to 0.5 mol/L. The complexing agent in the method provided by the invention can be combined with vanadium ions, so that the ionic radius of the vanadium ions is increased, the permeation rate of the vanadium ions penetrating through the membrane is reduced, the occurrence rate of side reactions is reduced, and the performance of the battery is improved. The preparation process disclosed by the invention is simple to operate, energy-saving, environment-friendly and low in cost, and can realize stable operation of the electrolyte in the battery.

Description

All-vanadium redox flow battery negative electrode electrolyte and method for reducing negative electrode vanadium ion migration

Technical Field

The invention relates to electrolyte application in the technical field of energy storage of all-vanadium redox flow batteries, in particular to a method for reducing vanadium ion migration of a cathode of an all-vanadium redox flow battery.

Background

With the continuous depletion of fossil energy and the continuous enhancement of people's environmental protection consciousness all over the world, renewable energy power generation technology is more and more favored by people. Renewable energy sources mainly include wind energy, solar energy, biomass energy, ocean energy, and the like, which are generally converted into electric energy for use. The renewable energy power generation is obviously discontinuous and unstable under the influence of conditions such as regions, weather and the like. In order to smooth and stabilize the power generation output of renewable energy sources, solve the time difference contradiction between power generation and power utilization, and improve the power quality and the reliability of a power grid, a high-efficiency energy storage technology must be developed. The full-vanadium redox flow battery (VFB) has the outstanding advantages of mutually independent and adjustable system capacity and power, rapid response, safety, reliability, environmental friendliness, long cycle life, easiness in maintenance and regeneration and the like, so that the VFB becomes one of the most promising technologies in large-scale energy storage such as renewable energy power generation, peak clipping and valley filling of a power grid, emergency and standby power stations and the like.

The electrolyte is an important component of the all-vanadium redox flow battery, the concentration and the volume of the electrolyte directly determine the capacity of the battery, and as active substances in the electrolyte are vanadium ions with different valence states, the valence state balance of the vanadium ions on the two sides of a positive electrode and a negative electrode needs to be ensured as far as possible to ensure the charging capacity of the battery. In fact, vanadium ions can cross each other through the battery diaphragm, so that valence state imbalance of the vanadium ions at two sides is caused, and coulomb efficiency is reduced. Among the four valence states of vanadium ions, the divalent vanadium ion has the smallest ionic radius, and is also the most likely to cross to the positive electrode through the membrane. To ensure the valence state balance of the positive and negative electrodes, the permeation rate of the divalent vanadium ions needs to be reduced. Therefore, the reduction of the permeation rate of the vanadium ions has practical significance on the capacity and the performance of the all-vanadium flow battery.

Disclosure of Invention

The invention provides an all-vanadium redox flow battery cathode electrolyte and a method for reducing vanadium ion migration of an all-vanadium redox flow battery cathode.

In order to achieve the purpose, the invention adopts the technical scheme that:

the invention provides a cathode electrolyte of an all-vanadium redox flow battery, which comprises a complexing agent, wherein the complexing agent is one or more than two of oxalic acid, sodium oxalate and potassium oxalate.

The concentration of the additive in the negative electrode electrolyte is 1 mmol/L-1 mol/L, preferably 0.01 mol/L-0.5 mol/L.

The negative electrode electrolyte contains V²⁺And V³⁺The concentration of vanadium ions in the sulfuric acid solution is 0.5-3 mol/L, preferably 1-2 mol/L; the concentration of the sulfate radical is 1-7 mol/L, preferably 3-5 mol/L.

The invention further provides an all-vanadium redox flow battery, and the all-vanadium redox flow battery cathode electrolyte is provided.

The battery comprises positive electrolyte, negative electrolyte and a diaphragm and is characterized in that the positive electrolyte contains V⁴⁺And V⁵⁺The concentration of vanadium ions in the sulfuric acid solution is 0.5-3 mol/L, and the concentration of sulfate radicals is 1-7 mol/L.

The membrane is a nafion membrane or a porous membrane.

In another aspect of the invention, a method for reducing vanadium ion migration of a cathode of an all-vanadium redox flow battery is provided, wherein a complexing agent is added into a cathode electrolyte, and at least one of oxalic acid, sodium oxalate and potassium oxalate is preferably selected.

The main component of the vanadium battery electrolyte applicable to the invention is a lower valence (di-or tri-valent) vanadyl-sulfuric acid system. Vanadium ion (containing V) in the negative electrode electrolyte²⁺，V³⁺Etc.) in a concentration of 0.5 to 3mol/L, sulfate radical (containing SO)₄ ^2-And HSO₄ ^-) The concentration of (b) is 1 to 7 mol/L. The preferable concentration of vanadium ions in the negative electrode electrolyte is 1-2 mol/L, and the preferable concentration of sulfate radicals is 3-5 mol/L. The membrane is a nafion membrane or a porous membrane.

Beneficial results

The negative electrode electrolyte containing the complexing agent is used, and the complexing agent can be combined with divalent vanadium ions, so that the ionic radius of the negative electrode electrolyte is increased, the permeation rate of the negative electrode electrolyte penetrating through a membrane is reduced, the occurrence rate of side reactions is reduced, and the performance of a battery is improved. The preparation process disclosed by the invention is simple to operate, energy-saving, environment-friendly and low in cost, and can ensure that the battery can efficiently and stably run for a long time.

Drawings

FIG. 1 is a schematic diagram of a vanadium ion permeation experimental apparatus

FIG. 2 is a graph showing the permeation rate curves of vanadium ions (blank experiment and experiment with complexing agent)

FIG. 3 is a self-discharge curve (blank experiment and experiment with complexing agent)

FIG. 4 shows the coulombic efficiency curve of the battery (blank experiment and experiment with complexing agent)

FIG. 5 is a graph showing the voltage efficiency of a battery (blank test and test containing a complexing agent)

Detailed Description

The following examples are further illustrative of the present invention and are not intended to limit the scope of the present invention.

Example 1

Preparing a 1.8M divalent vanadium solution by adopting an electrolysis method, dividing a sample into three groups, and performing a vanadium ion permeation experiment, wherein a testing device is shown in figure 1, the left tank is filled with the 1.8M divalent vanadium solution, the right tank is filled with the 1.8M magnesium sulfate solution, a complexing agent is not added into the first group of left tanks, 0.1M sodium metaborate is added into the second group of left tanks, 0.15M oxalic acid is added into the third group of left tanks, and the rest testing conditions of the three groups of experiments are the same. Two sides of the ion exchange membrane Nafion are respectively a 1.8M magnesium sulfate solution and a vanadium solution to be detected. The magnesium sulfate side solution was periodically sampled and tested for vanadium ion concentration, the results of which are shown in FIG. 1. As can be seen from the figure, in the three groups of samples, the concentration of vanadium ions in the oxalic acid-containing sample is lower than that in the other two groups of samples at the same time, and the slope of the straight line is smaller than that in the other two groups of samples, which indicates that the oxalic acid-containing sample has less vanadium ions permeating to the right side and has a smaller vanadium ion permeation rate. The complexing agent is obtained to reduce the permeation rate of the divalent vanadium ions.

Example 2

Preparing 1.5M divalent vanadium, dividing the sample into three groups, wherein the first group of negative electrode blank samples are prepared, 0.05M sodium tetraborate is added into the second group of negative electrode electrolyte, 0.1M sodium oxalate is added into the third group of negative electrode electrolyte, and the mixture is assembled into 48cm²The positive electrode side of the all-vanadium liquid flow single cell is 1.5M pentavalent vanadium solution, the three groups of different samples are respectively used as negative electrode electrolyte, under the condition of no current application, the cell voltage is recorded every 5 seconds, a self-discharge experiment is carried out, and the experiment result is shown in figure 3. The experimental results show that the self-discharge time of one group of experiments containing sodium oxalate is obviously longer than that of the other two groups of experiments, which shows that the complexing agent can effectively reduce the penetration rate of vanadium ions.

Comparative example

Assembling the all-vanadium redox flow battery, wherein the electrolyte of the negative electrode is a sulfuric acid solution with the concentration of trivalent vanadium ions of 1.5mol/L, and the concentration of sulfate radicals is 4 mol/L; the positive electrolyte is a sulfuric acid solution with the concentration of tetravalent vanadium ions being 1.5mol/L, the concentration of sulfate radicals being 4mol/L, and the diaphragm is a nafion membrane. The battery is at 80mA/cm²The average coulombic efficiency of the battery is 94.3% (figure 4) and the average voltage efficiency is 88.8% (figure 5) after 100 cycles of charge and discharge under the condition.

Example 3

Assembling the all-vanadium redox flow battery, wherein the electrolyte of the negative electrode is a sulfuric acid solution with the concentration of trivalent vanadium ions of 1.5mol/L, and the concentration of sulfate radicals is 4 mol/L; the positive electrolyte is a sulfuric acid solution with the concentration of tetravalent vanadium ions being 1.5mol/L, the concentration of sulfate radicals is 4mol/L, the diaphragm is a nafion membrane, oxalic acid is added into the negative electrolyte, and the concentration of the oxalic acid in the negative electrolyte is 0.2 mol/L. The battery is at 80mA/cm²The average coulombic efficiency of the cell was 96.4% with 100 cycles of charging and discharging under the conditions (fig. 4). The coulombic efficiency is improved by 2 percent compared with the comparative example, which shows that the vanadium ions are in series connection with each other slowly and the coulombic efficiency is improved.

Example 4

Assembling the all-vanadium redox flow battery, wherein the electrolyte of the negative electrode is a sulfuric acid solution with the concentration of trivalent vanadium ions of 1.5mol/L, and the concentration of sulfate radicals is 4 mol/L; the positive electrolyte is a sulfuric acid solution with the concentration of tetravalent vanadium ions being 1.5mol/L, the concentration of sulfate radicals is 4mol/L, the diaphragm is a nafion membrane, sodium oxalate is added into the negative electrolyte, and the concentration of the sodium oxalate in the negative electrolyte is 1.5 mol/L. The battery is at 80mA/cm²The average voltage efficiency of the cell was 87.5% with 100 cycles of charging and discharging under the conditions (fig. 5). The voltage efficiency is reduced by 1% compared with the comparative example, and the potential reason is that the viscosity of the electrolyte is increased due to overhigh concentration of the additive, the polarization of the battery is increased, and the voltage efficiency is reduced.

Claims

1. The all-vanadium redox flow battery cathode electrolyte is characterized in that: the cathode electrolyte comprises a complexing agent, wherein the complexing agent is one or more than two of oxalic acid, sodium oxalate and potassium oxalate.

2. The all-vanadium flow battery negative electrolyte according to claim 1, characterized in that: the concentration of the additive in the negative electrode electrolyte is 1 mmol/L-1 mol/L, preferably 0.01 mol/L-0.5 mol/L.

3. The all-vanadium flow battery negative electrolyte according to claim 1, characterized in that: the negative electrode electrolyte contains V²⁺And V³⁺The concentration of vanadium ions in the sulfuric acid solution is 0.5-3 mol/L, preferably 1-2 mol/L; the concentration of the sulfate radical is 1-7 mol/L, preferably 3-5 mol/L.

4. An all-vanadium flow battery comprising the all-vanadium flow battery negative electrolyte of any one of claims 1 to 3.

5. The all-vanadium flow battery according to claim 4, comprising a positive electrolyte, a negative electrolyte and a separator, wherein the positive electrolyte is a solution containing V⁴⁺And V⁵⁺The concentration of vanadium ions in the sulfuric acid solution is 0.5-3 mol/L, and the concentration of sulfate radicals is 1-7 mol/L.

6. The all-vanadium flow battery according to claim 4, wherein the separator is a nafion membrane or a porous membrane.

7. The method for reducing vanadium ion migration of the cathode of the all-vanadium redox flow battery is characterized in that at least one of oxalic acid, sodium oxalate and potassium oxalate is added into cathode electrolyte.