Negative electrode electrolyte for all-vanadium redox flow battery and all-vanadium redox flow battery

Abstract

The invention discloses a negative electrode electrolyte for an all-vanadium redox flow battery and the all-vanadium redox flow battery. The negative electrode electrolyte comprises vanadium ions, sulfate ions, a solvent and an additive, the additive comprises ethylene glycol and amino acid. The invention aims to solve the problem of precipitation of low-valence vanadium ions in the electrolyte, and low-temperature stability of the low-valence vanadium ions can be improved by adding low-concentration ethylene glycol and amino acid into the electrolyte, so that the low-valence vanadium ions can stably exist at a relatively low temperature, thereby improving the low-temperature activity of the negative electrode electrolyte of the all-vanadium redox flow battery and prolonging the service life of the all-vanadium redox flow battery. And the coulombic efficiency, the energy efficiency, the voltage efficiency and the capacity retention ratio of the battery at low temperature can be effectively improved, and high-performance stable operation of the battery at low temperature is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of all-vanadium redox flow batteries, and more specifically, to a negative electrolyte for an all-vanadium redox flow battery and an all-vanadium redox flow battery. Background Art

[0002] With the development of the economy, the demand for energy is increasing day by day, and the environmental problems caused by the large consumption of fossil energy are becoming increasingly prominent. Large-scale utilization of renewable energy and realization of energy diversification have become important strategies for energy security and sustainable development in various countries around the world. However, renewable energy such as wind energy and solar energy is discontinuous and unstable, making their direct utilization difficult. Therefore, the use of energy storage technology to achieve continuous supply of renewable energy has become the key to solving the above problems. Flow batteries have become one of the most promising technologies in the large-scale energy storage market due to their flexible design (separate design of capacity and power), good safety, and long design life.

[0003] The electrolyte is an important part of the all-vanadium redox flow battery. Its concentration and volume directly determine the capacity of the battery, and the electrolyte stability directly affects the reliability and stability of the VFB during long-term operation. However, in actual operation, the solubility and stability of vanadium ions in the supporting electrolyte are limited: when the temperature is low, the low-valent vanadium ions in the negative electrolyte are prone to precipitate, which limits the application of the all-vanadium redox flow battery system in low-temperature environments. Therefore, improving the low-temperature thermal stability of the VFB negative electrolyte is particularly important for the stability and application range of the battery system. Summary of the Invention

[0004] The purpose of the present invention is to overcome the above-mentioned defects existing in the prior art, and to provide a negative electrolyte for an all-vanadium redox flow battery and an all-vanadium redox flow battery, aiming to solve the problem of precipitation of low-valent vanadium ions in the electrolyte. By adding a low concentration of additives to the electrolyte, the low-temperature stability of the low-valent vanadium ions is improved, so that they can stably exist at a lower temperature, thereby improving the low-temperature activity of the negative electrolyte of the all-vanadium redox flow battery.

[0005] To achieve the above purpose, the technical solution of the present invention is as follows:

[0006] A negative electrolyte for an all-vanadium redox flow battery, the negative electrolyte comprising vanadium ions, sulfate ions, a solvent, and an additive; the additive comprising ethylene glycol and an amino acid.

[0007] Optionally, the mass ratio of ethylene glycol to amino acid is 1:0.5 to 1:2.5.

[0008] Optionally, the amino acid comprises at least one of cysteine, glutamic acid, and glycine.

[0009] Optionally, the concentration of the amino acid in the negative electrolyte is 0.5 to 3 mol / L.

[0010] Optionally, the molar concentration ratio of the amino acid to the vanadium ion is 1:1.

[0011] Optionally, the concentration of the vanadium ion in the negative electrolyte is 0.5 to 3 mol / L.

[0012] Optionally, the concentration of the sulfate ion in the negative electrolyte is 1 to 7 mol / L.

[0013] Optionally, the concentration of the vanadium ion in the negative electrolyte is 1.5 to 2.5 mol / L.

[0014] Optionally, the concentration of the sulfate ion in the negative electrolyte is 3.5 to 5.5 mol / L.

[0015] Optionally, the vanadium ions in the negative electrolyte include at least one of divalent vanadium ions and trivalent vanadium ions.

[0016] Optionally, the sulfate ions in the negative electrolyte include SO 4 2- and HSO 4 - and at least one of them.

[0017] Optionally, the solvent is water.

[0018] The present invention also discloses a vanadium redox flow battery, which includes a positive electrode, a negative electrode, an electrolyte and a separator; the electrolyte includes a positive electrolyte and a negative electrolyte; the negative electrolyte is the above-mentioned negative electrolyte.

[0019] Optionally, the positive electrolyte includes vanadium ions, sulfate ions and a solvent.

[0020] Optionally, the concentration of the vanadium ion in the positive electrolyte is 1 to 3 mol / L.

[0021] Optionally, the vanadium ions in the positive electrolyte include at least one of tetravalent vanadium ions and pentavalent vanadium ions.

[0022] Optionally, the sulfate ions in the positive electrolyte include SO 4 2- and HSO 4 - and at least one of them.

[0023] Optionally, the concentration of the sulfate ion in the positive electrolyte is 1 to 7 mol / L.

[0024] Optionally, the solvent is water.

[0025] Optionally, the operating temperature of the all-vanadium redox flow battery is -45°C to -25°C.

[0026] Optionally, both the positive electrode and the negative electrode are made of at least one of a plate-like structure, a porous structure, a metal, and a carbon material.

[0027] Optionally, the carbon material includes at least one of carbon cloth, carbon paper, and carbon felt.

[0028] Optionally, the separator is an ion exchange membrane.

[0029] Implementing the embodiments of the present invention will have the following beneficial effects:

[0030] 1. For the negative electrolyte used in the all-vanadium redox flow battery provided by the present invention, the negative additives ethylene glycol and amino acid are used. Among them, the amino acid plays a major role in coordinating with divalent vanadium ions in a ratio of 1:1. During the reaction, the divalent vanadium ions are adsorbed by the amino acid, reducing the contact between the divalent vanadium ions and other ions, thereby improving the activity of the divalent vanadium ions, reducing the formation of precipitates in the negative electrolyte, improving the battery performance, and extending the battery life. The role of ethylene glycol in the additive is mainly to dissolve the amino acid with relatively low solubility, thereby increasing the concentration of the amino acid.

[0031] 2. For the negative electrolyte used in the all-vanadium redox flow battery provided by the present invention, the negative additives ethylene glycol and amino acid can effectively improve the Coulombic efficiency, energy efficiency, voltage efficiency, and capacity retention rate of the battery at low temperatures, realizing the high-performance and stable operation of the battery at low temperatures.

[0032] 3. The preparation process of the present invention is simple in operation, energy-saving and environmentally friendly, low in cost, and at the same time ensures that the battery can operate efficiently and stably for a long time. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 Efficiency diagrams of the all-vanadium redox flow batteries of Examples 1-3 and Comparative Example 1 at a current density of 200 mA / cm² at -20°C. 2

[0034] Figure 2 Discharge capacity diagrams of the all-vanadium redox flow batteries of Examples 1-3 and Comparative Example 1 at a current density of 200 mA / cm² at -20°C. 2

[0035] Figure 3 Efficiency diagrams of the all-vanadium redox flow batteries of Examples 2 and 4-7 at a current density of 200 mA / cm² at -20°C. 2

[0036] Figure 4 ​​​Capacity decay rate diagrams of the all-vanadium redox flow batteries of Example 2 and Examples 4-7 at -20°C and a current density of 200 mA / cm 2

[0037] Figure 5 Efficiency diagrams of the all-vanadium redox flow batteries of Example 4 and Examples 8-10 at -20°C and a current density of 200 mA / cm 2 Detailed implementation manners

[0038] The present invention will be further described below in conjunction with specific embodiments, but the present invention is not limited in any way.

[0039] Example 1

[0040] 1. Electrolyte preparation:

[0041] The electrolyte includes 30 ml of positive electrode electrolyte and 30 ml of negative electrode electrolyte.

[0042] The positive electrode electrolyte includes components with the following concentrations: 2 mol / L of pentavalent vanadium ions and 4 mol / L of sulfate radicals.

[0043] The negative electrode electrolyte includes components with the following concentrations: 2 mol / L of divalent vanadium ions, 4 mol / L of sulfate radicals, 1 mol / L of ethylene glycol, and 2 mol / L of cysteine.

[0044] 2. Battery assembly:

[0045] The battery is assembled in sequence with the positive end plate, positive bipolar plate (7.5×9.5 cm 2 ), positive electrode (6×8 cm 2 ), ion conduction membrane (Nafion212), negative electrode (6×8 cm 2 ), negative bipolar plate (7.5×9.5 cm 2 ), and negative end plate.

[0046] 3. Battery testing:

[0047] Charge and discharge at -20°C, the flow rate of the electrolyte is 50 ml / min, and the charge and discharge current density is 200 mA / cm -2 . The working voltage is from 1 V to 1.55 V.

[0048] Example 2

[0049] This example is different from Example 1 only in that: the amino acid in the negative electrode electrolyte is glycine.

[0050] Example 3

[0051] ​​This example is only different from Example 1 in that the amino acid in the negative electrolyte is glutamic acid.

[0052] Example 4

[0053] This example is only different from Example 2 in that the concentration of glycine is 2.2 mol / L.

[0054] Example 5

[0055] This example is only different from Example 2 in that the concentration of glycine is 2.4 mol / L.

[0056] Example 6

[0057] This example is only different from Example 2 in that the concentration of glycine is 2.6 mol / L.

[0058] Example 7

[0059] This example is only different from Example 2 in that the concentration of glycine is 2.8 mol / L.

[0060] Example 8

[0061] This example is only different from Example 4 in that the battery test temperature is -45 °C.

[0062] Example 9

[0063] This example is only different from Example 4 in that the battery test temperature is 0 °C.

[0064] Example 10

[0065] This example is only different from Example 4 in that the battery test temperature is -25 °C.

[0066] Comparative Example 1

[0067] This comparative example is only different from Example 1 in that ethylene glycol and cysteine are not added.

[0068] Test Example

[0069] The battery performances of Examples 1-3 and Comparative Example 1 are as Figure 1 and Figure 2 shown. It can be seen from Figure 1 that adding equal amounts of ethylene glycol and amino acids will have a certain improvement on the Coulomb voltage energy efficiency of the battery. This may be due to the influence on the activity of divalent vanadium ions in the negative electrolyte, which improves the efficiency of the battery. Among them, the addition of ethylene glycol and glycine in Example 2 has the greatest impact on the battery improvement. This may be because glycine can interact better with divalent vanadium ions. For Figure 2It can be seen that the addition of the additive also slows down the attenuation rate of the electrolyte, which is mainly due to reducing the vanadium ions in the lower valence state, reducing the generation of precipitation and thus inhibiting the attenuation.

[0070] The battery performances of Examples 2 and 4-7 are as Figures 3 - 4 shown. It can be seen from the figure that the addition of divalent vanadium ions and glycine in the ratios of 1:1, 1:1.2, 1:1.3, and 1:1.4 will also affect the battery performance. When an appropriate amount of ethylene glycol and glycine are added, the efficiency will be improved, while the addition of a large amount of organic additives will increase the viscosity of the electrolyte and decrease the conductivity, thus reducing the battery efficiency.

[0071] The battery performances of Examples 4 and 8-10 are as Figure 5 shown. The addition of ethylene glycol and amino acids in the negative electrode electrolyte is suitable for improving the battery performance at low temperatures. It can be obtained from the data in the figure that the all-vanadium redox flow battery with additives added to the negative electrode has a higher battery efficiency at low temperatures and also has good performance at high temperatures. Therefore, this additive for the negative electrode of the all-vanadium redox flow battery is an excellent additive.

[0072] The above-described embodiments merely represent several implementation manners of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the patent application. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of this invention patent shall be subject to the appended claims.

Claims

1. A negative electrode electrolyte for an all-vanadium redox flow battery, characterized in that: The negative electrode electrolyte comprises vanadium ions, sulfate ions, a solvent and an additive; The additives include ethylene glycol and amino acids.

2. The negative electrode electrolyte for all-vanadium redox flow battery according to claim 1, characterized in that: The amino acid comprises at least one of cysteine, glutamic acid and glycine; The concentration of the amino acid in the negative electrode electrolyte is 0.5 to 3 mol / L.

3. The negative electrode electrolyte for all-vanadium redox flow battery according to claim 1, characterized in that: The molar concentration ratio of the amino acid to the vanadium ion is 1:

1.

4. The negative electrode electrolyte for all-vanadium redox flow battery according to claim 1, characterized in that: The concentration of vanadium ions in the negative electrode electrolyte is 0.5 to 3 mol / L; The concentration of sulfate ions in the negative electrode electrolyte is 1-7 mol / L.

5. The negative electrode electrolyte for all-vanadium redox flow battery according to claim 4, characterized in that: The concentration of vanadium ions in the negative electrode electrolyte is 1.5 to 2.5 mol / L; The concentration of sulfate ions in the negative electrode electrolyte is 3.5 to 5.5 mol / L.

6. The negative electrode electrolyte for all-vanadium redox flow battery according to claim 1, characterized in that: The vanadium ions in the negative electrode electrolyte include at least one of divalent vanadium ions and trivalent vanadium ions; The sulfate ions in the negative electrode electrolyte include SO4 2- and HSO4 - At least one of; The solvent is water.

7. An all-vanadium liquid flow battery, characterized in that: Including positive electrode, negative electrode, electrolyte and separator; The electrolyte includes a positive electrode electrolyte and a negative electrode electrolyte; The negative electrode electrolyte is the negative electrode electrolyte according to any one of claims 1 to 6.

8. The all-vanadium redox flow battery according to claim 7, characterized in that: The positive electrode electrolyte comprises vanadium ions, sulfate ions and a solvent; The concentration of vanadium ions in the positive electrode electrolyte is 1 to 3 mol / L; The vanadium ions in the positive electrode electrolyte include at least one of tetravalent vanadium ions and pentavalent vanadium ions; The sulfate ions in the positive electrolyte include SO4 2- and HSO4 - At least one of; The concentration of sulfate ions in the positive electrode electrolyte is 1 to 7 mol / L; The solvent is water.

9. The all-vanadium redox flow battery according to claim 7, characterized in that: The operating temperature of the all-vanadium liquid flow battery is -45°C to -25°C.

10. The all-vanadium redox flow battery according to claim 7, characterized in that: The positive electrode and the negative electrode both use at least one of a metal and a carbon material with a plate-like structure or a porous structure; The carbon material comprises at least one of carbon cloth, carbon paper and carbon felt; The diaphragm is an ion exchange membrane.

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