An all-vanadium redox flow battery electrolyte containing composite additives

Abstract

The present invention belongs to the technical field of all-vanadium redox flow batteries and discloses an all-vanadium redox flow battery electrolyte containing a composite additive. Potassium chloride and potassium sulfate are dissolved as additives into the all-vanadium redox flow battery electrolyte. The all-vanadium redox flow battery electrolyte containing the composite additive has a vanadium ion concentration range of 1 to 2 mol / L, a sulfate concentration range of 3 to 5 mol / L, a phosphate concentration range of 0.05 to 0.4 mol / L, a potassium chloride concentration range of 0.091 to 0.366 mol / L, and a potassium sulfate concentration range of 0.039 to 0.157 mol / L. The preparation process of the present invention is simple to operate, potassium chloride and potassium sulfate are inexpensive, energy-saving and environmentally friendly, and can also ensure stable operation of the electrolyte during battery circulation.

Description

Technical Field

[0001] The invention belongs to the technical field of all-vanadium redox flow batteries, and in particular relates to an all-vanadium redox flow battery electrolyte containing a composite additive. Background Art

[0002] In the existing technology, the testing of flow battery electrolyte additives mainly focuses on thermal stability testing. + Add additives to the electrolyte and conduct thermal stability test, mainly through this method to conduct preliminary screening of additives. 2+ The electrochemical activity of the electrolyte was evaluated by CV test.

[0003] Existing sulfuric acid system electrolyte additives will affect the performance and capacity retention of the battery, resulting in a short battery life, poor performance and weak endurance. There is an urgent need for a liquid flow battery electrolyte that can solve the above problems. Summary of the Invention

[0004] In order to overcome the shortcomings of the existing technology, the present invention provides an all-vanadium liquid flow battery electrolyte containing a composite additive. The all-vanadium liquid flow battery electrolyte improves the high-temperature stability of the entire electrolyte without affecting the low-temperature stability of the negative electrode electrolyte. It can be used in both the positive and negative electrode electrolytes of the all-vanadium liquid flow battery without the problem of distinguishing between the positive and negative electrode electrolytes.

[0005] The above-mentioned object of the present invention is achieved through the following technical scheme: an all-vanadium redox flow battery electrolyte containing a composite additive, characterized in that the composite additive in the all-vanadium redox flow battery electrolyte containing a composite additive is potassium chloride + potassium sulfate; the all-vanadium redox flow battery electrolyte containing a composite additive has a vanadium ion concentration range of 1 to 2 mol / L, a sulfate concentration range of 3 to 5 mol / L, a phosphate concentration range of 0.05 to 0.4 mol / L, a potassium chloride concentration range of 0.091 to 0.366 mol / L, and a potassium sulfate concentration range of 0.039 to 0.157 mol / L.

[0006] Furthermore, the total vanadium ions in the all-vanadium redox flow battery electrolyte containing the composite additive are V 3+ / V 4+ The molar concentration ratio is 1.

[0007] Furthermore, the vanadium ion concentration of the all-vanadium redox flow battery electrolyte containing the composite additive is in the range of 1.5 to 1.7 mol / L.

[0008] Furthermore, the sulfate concentration of the all-vanadium redox flow battery electrolyte containing the composite additive is in the range of 4 to 4.2 mol / L.

[0009] Furthermore, the phosphate concentration of the all-vanadium redox flow battery electrolyte containing the composite additive is in the range of 0.05 to 0.3 mol / L.

[0010] Furthermore, the concentration of potassium chloride in the composite additive is 0.091 mol / L.

[0011] Furthermore, the concentration of potassium sulfate in the composite additive is 0.039 mol / L.

[0012] The beneficial effects of the present invention compared with the prior art are:

[0013] 1. It can significantly improve the high-temperature stability of the positive electrolyte without affecting the low-temperature stability of the negative electrolyte. The electrolyte of the present invention can be used in both the positive and negative electrolytes of all-vanadium redox flow batteries, eliminating the problem of electrolyte cross-contamination.

[0014] 2. The addition of an appropriate amount of sulfate ions in the present invention improves the conductivity of the electrolyte, thereby improving the coulombic efficiency and voltage efficiency of the battery. An appropriate amount of chloride ions plays a complexing role, which can inhibit the VO2 + The electrostatic repulsion between the appropriate amount of potassium ions in the additive and the vanadium ions makes the latter more evenly dispersed, thereby improving the stability of the positive and negative electrolytes.

[0015] 3. The preparation process of the present invention is simple to operate, potassium chloride and potassium sulfate are cheap, energy-saving and environmentally friendly, and can achieve stable operation of the electrolyte during the battery cycle. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0017] Figure 1 is a graph showing the CV test results of Example 4;

[0018] Figure 2 This is a discharge capacity curve diagram of Example 5. DETAILED DESCRIPTION

[0019] The present invention is described in detail below by specific examples, but the scope of protection of the present invention is not limited. Unless otherwise specified, the experimental methods adopted in the present invention are all conventional methods, and the experimental equipment, materials, reagents, etc. used can be obtained from commercial channels.

[0020] Example 1

[0021] Take the electrolyte of the all-vanadium flow battery, the electrolyte vanadium ion concentration range is 1.65mol / L, the sulfate concentration range is 4mol / L, and the phosphate concentration range is 0.1mol / L. Ensure that the positive and negative electrode volumes are equal. First, at 80mA / cm 2 The battery was charged at a constant current until the open circuit voltage of the single cell reached 1.55V, and then continued to charge at a constant voltage of 1.55V until the battery SOC reached 100%. The battery used Chemours NR212 ion exchange membrane as the diaphragm, impregnated hard graphite plate as the current collector, and carbon felt as the electrode. The electrode area was 48cm 2 After charging is completed, the electrolyte on the positive electrode side of the battery with a SOC of 100% is taken for backup.

[0022] To 10mL of the positive electrode electrolyte, potassium chloride (KCl) and potassium sulfate (K2SO4) in different molar ratios were slowly added in batches. Three parallel samples were prepared for each group of samples. After complete dissolution, they were placed in a 45°C water bath for observation. The time when precipitation appeared in each group of samples was recorded. The stability time of the positive electrode electrolyte after adding different molar ratios of KCl and K2SO4 is shown in Table 1. According to the results in Table 1, adding a certain amount of KCl and K2SO4 can greatly improve the stability of the positive electrode electrolyte. Among them, the positive electrode pentavalent vanadium with 0.091M KCl and 0.039M K2SO4 has the longest stability time, which can reach 192h. This is because the composite additives and the VO2 in the electrolyte + Complexation occurs, thereby inhibiting VO2 + of precipitation.

[0023] Table 1 Stability time of pentavalent vanadium solution with different amounts in a 45°C water bath

[0024]

[0025]

[0026] Example 2

[0027] To 35 mL of a blank 3.5-valent electrolyte, 0.091 M KCl and 0.039 M K₂SO₄ were added. The solution was placed in a 50 mL centrifuge tube. A carbon felt measuring 50 mm (length x width x thickness) x 10 mm (length x width x thickness) x 4.35 mm was then added. After complete dissolution, the tube was sealed and stored at -15°C. The results were observed and recorded every other day. A blank control group was established, and three replicates were prepared for each group to ensure the accuracy of the stability results. The low-temperature stability results for the blank control group and the composite additive control group are shown in Table 2. The purpose of adding the carbon felt was to introduce crystal nuclei into the electrolyte, which facilitates the evaluation of the electrolyte's stability in practical applications. The results in Table 2 demonstrate that the composite additive had no negative impact on the low-temperature stability of the initial 3.5-valent electrolyte.

[0028] Table 2 Stability time of 3.5-valent electrolyte with addition of 0.091M KCl and 0.039M K2SO4 at -15℃

[0029]

[0030] Example 3

[0031] Take the blank initial electrolyte, the positive and negative volumes are equal, and 2 The constant current charging was stopped after the single cell OCV reached 1.367 V (corresponding to SOC of 35%), and the negative electrode electrolyte was taken for backup.

[0032] 0.091M KCl and 0.039M K₂SO₄ were added to 35mL of the negative electrolyte solution, placed in a 50mL centrifuge tube, and then a carbon felt (length × width × thickness = 50mm × 10mm × 4.35mm) was added. After complete dissolution, the solution was sealed and stored at -15°C. The results were observed and recorded every other day. A blank control group was established, and three replicates were prepared for each group to ensure the accuracy of the results. The low-temperature stability results of the negative electrolyte solutions for the blank control group and the group with the composite additive are shown in Table 3. The stability results in Table 3 indicate that the composite additive has no negative impact on the low-temperature stability of the low-SOC negative electrolyte solution.

[0033] Table 3 Stability time of low SOC negative electrode electrolyte with addition of 0.091M KCl and 0.039M K2SO4 at -15℃

[0034]

[0035] Example 4

[0036] The electrolyte used in this example was prepared by dissolving VOSO4 to obtain 0.75M VO 2+ +1.5M SO4 2- electrolyte, to VO 2+ 0.091M KCl and 0.039M K2SO4 were added to the electrolyte and completely dissolved before use in CV testing. A blank group experiment was also set up. The CV test used three electrodes, an R232 straight saturated calomel electrode as the reference electrode, a platinum wire as the counter electrode, and an impregnated graphite plate as the working electrode. The effective area of ​​the working electrode was 1cm 2 The rest of the parts are sealed with insulating tape. The cyclic voltammetry test scan voltage range is 0.7V-1.15V, and the scan rate is 10mV / s. The CV test results are as follows Figure 1 shown.

[0037] Depend on Figure 1 It can be seen that the addition of 0.091M KCl and 0.039M K2SO4 additives has no obvious effect on the electrochemical properties of the electrolyte.

[0038] Example 5

[0039] Take 160mL of blank electrolyte, add 0.091M KCl and 0.039M K2SO4, and keep it for use after it is completely dissolved. The volume of positive and negative electrolytes in the blank group and the composite additive group is 80mL respectively. The battery uses an ion exchange membrane as a separator, an impregnated hard graphite plate as a current collector, and carbon felt as an electrode. The electrode area is 48cm 2 The constant current charge and discharge was carried out in a water bath at 50°C, with a voltage range of 1-1.55V and a current density of 80mA / cm 2 The capacity decay curve within 200 cycles is as follows: Figure 2 The average performance is shown in Table 4.

[0040] From Table 4 and Figure 2 The results show that the addition of 0.091M KCl and 0.039M K2SO4 to the electrolyte improves the battery's voltage efficiency and energy efficiency. Battery capacity decay can be caused by the precipitation of vanadium ions at the positive electrode or the migration of electrolytes between the positive and negative electrodes. The appropriate amounts of potassium chloride and potassium sulfate in the present invention complex with vanadium ions, significantly inhibiting the migration rate of electrolytes between the positive and negative electrodes compared to the blank control, thereby reducing battery capacity decay and improving battery capacity retention, enabling long-term stable operation of the all-vanadium redox flow battery.

[0041] Table 4 Average performance

[0042]

[0043] The above-described embodiments are only preferred embodiments of the present invention, and are not intended to be all feasible embodiments of the present invention. Any obvious modifications made by a person skilled in the art without departing from the principles and spirit of the present invention should be considered to be included within the scope of protection of the claims of the present invention.

Claims

1. An all-vanadium redox flow battery electrolyte containing a composite additive, characterized in that: The composite additive in the all-vanadium redox flow battery electrolyte containing the composite additive is potassium chloride + potassium sulfate; the vanadium ion concentration of the all-vanadium redox flow battery electrolyte containing the composite additive is in the range of 1.5 to 1.7 mol / L, the sulfate concentration is in the range of 4 to 4.2 mol / L, the phosphate concentration is in the range of 0.05 to 0.3 mol / L, the potassium chloride concentration is 0.091 mol / L, and the potassium sulfate concentration is 0.039 mol / L; the V in the total vanadium ion in the all-vanadium redox flow battery electrolyte containing the composite additive is 0. 3+ / V 4+ The molar concentration ratio is 1.

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