Bismuth-containing modified electrolyte, all-vanadium redox flow battery, and preparation method and application thereof

Abstract

The present invention relates to a bismuth-containing modified electrolyte, a vanadium redox flow battery, and a preparation method and application thereof, belonging to the technical field of vanadium redox flow batteries. The bismuth-containing modified electrolyte includes a vanadium electrolyte, a bismuth salt is added as a catalyst to the vanadium electrolyte, and a hydroxycarboxylic acid complexing agent is added; the molar ratio of the bismuth salt to the hydroxycarboxylic acid complexing agent is 6-8:0.6-0.8. In the present invention, a catalyst and a complexing agent are added to the electrolyte, and Bi metal is deposited on the electrode during the battery charging process, increasing the active sites of the electrode, which helps to improve the energy efficiency of the battery. At the same time, the catalyst can improve the capacity retention rate of the flow battery, greatly simplify the process steps, and reduce the cost.

Description

Technical Field

[0001] The present invention relates to the technical field of all-vanadium redox flow batteries, and particularly relates to a bismuth-containing modified electrolyte, an all-vanadium redox flow battery, and a preparation method and application thereof. Background Art

[0002] In recent years, environmental pollution and energy crisis have gradually attracted people's attention. In order to alleviate the energy crisis and reduce the impact of environmental pollution, it has become extremely urgent to use clean energy to replace traditional fossil energy. Although technologies such as solar energy and wind energy are relatively mature at present, they have the problem of instability. As an electrochemical energy storage technology, flow batteries have gradually become one of the core solutions to solve the volatility of renewable energy and the demand for long-term energy storage since they were proposed in the 1970s. However, the hydrogen evolution side reaction and cost problems existing in current flow batteries restrict the improvement of the energy density of flow batteries and large-scale commercial production.

[0003] The electrode and the electrolyte are two important components in a flow battery. Among them, the electrode is the place where the electrochemical reaction occurs and is a key material directly affecting the energy density of the flow battery. The electrolyte contains active substances, and the flow battery realizes the storage and release of energy through the redox reaction of the active substances in the electrolyte.

[0004] The electrode reaction kinetics of an all-vanadium redox flow battery depends on an efficient catalyst to improve the reaction kinetics and electrochemical activity of the flow battery. Different efficient catalysts are attached to the electrode to increase the active sites of the carbon felt electrode, thereby improving the overall reaction rate. In addition, different catalysts can also catalytically act on different active substances in a targeted manner. Because of this characteristic, the attachment of catalysts has been widely favored by researchers. Different catalysts have different catalytic mechanisms. The catalytic mechanism of Bi-based catalysts is mainly that the Bi element attached to the carbon felt electrode reacts with H + in the solution to generate an intermediate of BiH x . On the one hand, this intermediate can inhibit the occurrence of the hydrogen evolution reaction, and on the other hand, it can promote the mutual conversion process between V 2+ and V 3+ in the electrolyte, thereby improving the energy efficiency of the battery. The electrolyte can directly affect the battery capacity. To increase the capacity of the flow battery, a larger amount of electrolyte needs to be used. However, as the reaction proceeds, the ion exchange membrane cannot completely isolate the exchange of vanadium ions between the positive and negative electrodes, which will lead to the attenuation of the battery capacity. However, by adding additives to the electrolyte, this situation can be effectively alleviated, thereby improving the capacity retention rate of the battery.

[0005] Traditional catalysts need to be loaded on the electrode surface by means of coating, electrodeposition, etc. However, they have the following problems: (1) The process is complex, and the loading process requires multiple steps of treatment, with high costs and difficulty in scaling up; (2) Catalyst shedding: During the cycling process, the catalyst sheds due to changes in the electrode volume or electrolyte flushing, resulting in a decrease in activity; (3) Uneven distribution: Fixed loading easily leads to uneven distribution of the catalyst, affecting the reaction efficiency. In order to obtain a vanadium redox flow battery that can be used to improve the capacity retention rate of the redox flow battery and can act on the carbon felt electrode, further research is still needed. Summary of the Invention

[0006] The purpose of the present invention is to provide a bismuth-containing modified electrolyte, a vanadium redox flow battery, a preparation method thereof, and an application, in order to solve the above problems.

[0007] The purpose of the present invention is achieved through the following technical solutions:

[0008] A bismuth-containing modified electrolyte, comprising a vanadium electrolyte, wherein a bismuth salt is added as a catalyst to the vanadium electrolyte, and a hydroxycarboxylic acid complexing agent is added;

[0009] The molar ratio of the bismuth salt to the hydroxycarboxylic acid complexing agent is 6-8:0.6-0.8. Further preferably, the molar ratio of the bismuth salt to the hydroxycarboxylic acid complexing agent is 7:0.7.

[0010] In the present invention, a catalyst and a complexing agent are added to the electrolyte, and Bi metal is deposited on the electrode during the battery charging process, increasing the active sites of the electrode, which helps to improve the energy efficiency of the battery; at the same time, this catalyst can improve the capacity retention rate of the redox flow battery, greatly simplify the process steps, and reduce costs.

[0011] As a preferred technical solution of the present invention, the vanadium electrolyte is a 3.5-valent vanadium ion electrolyte. Preferably, the vanadium electrolyte is 1.7 mol / L 3.5-valent vanadium ions in 3 mol / L H2SO4.

[0012] As a preferred technical solution of the present invention, the bismuth salt includes one or more of bismuth trichloride and bismuth nitrate, and preferably bismuth trichloride.

[0013] As a preferred technical solution of the present invention, the hydroxycarboxylic acid complexing agent includes one or more of citric acid and tartaric acid, and preferably citric acid.

[0014] As a preferred technical solution of the present invention, in the vanadium electrolyte, the concentration of the bismuth salt is 0.05-0.2 mol / L, preferably 0.08-0.15 mol / L, and most preferably 0.1 mol / L.

[0015] A method for preparing a bismuth-containing modified electrolyte comprises the following steps: using a vanadium electrolyte as a solvent, and using a bismuth salt and a hydroxycarboxylic acid complexing agent as solutes, and stirring and mixing them uniformly to obtain the electrolyte.

[0016] As a preferred technical solution of the present invention, the mixed electrolyte is allowed to stand and then filtered to remove solid impurities.

[0017] The invention discloses an application of a bismuth-containing modified electrolyte, wherein the bismuth-containing modified electrolyte is used for preparing an electrolyte for an all-vanadium liquid flow battery.

[0018] An all-vanadium liquid flow battery uses the above-mentioned bismuth-containing modified electrolyte as the electrolyte, belonging to an all-vanadium liquid flow battery with both electrodes and electrolyte modified. The all-vanadium liquid flow battery of the present invention uses a bismuth-containing modified electrolyte to deposit Bi on the electrode during the battery charging process, thereby increasing the active sites of the electrode and modifying and optimizing the electrode, which helps to improve the energy efficiency of the battery, improve the capacity retention rate of the liquid flow battery, simplify the process steps, and reduce costs.

[0019] A method for preparing an all-vanadium liquid flow battery comprises the following steps:

[0020] S1. Using bismuth chloride and citric acid as solutes and 3.5-valent vanadium ion electrolyte as solvent, the solute and solvent are mixed and stirred evenly;

[0021] S2, after the electrolyte prepared in S1 is allowed to stand, it is filtered to remove solid impurities to obtain a modified electrolyte;

[0022] S3. The electrolyte prepared in S2 is used in an all-vanadium liquid flow battery. As the battery is charged, the Bi element in the electrolyte is deposited on the surface of the carbon felt, and returns to the solution during the discharge process.

[0023] As a preferred technical solution of the present invention, the amount of the solute in step S1 is: bismuth chloride is 0.07mmol~35mmol, citric acid is 0.07mmol~35mmol, and the solvent is a mixture of trivalent vanadium ion solution and tetravalent vanadium ion solution in a ratio of 1:1.

[0024] As a preferred technical solution of the present invention, the electrolyte is allowed to stand for 10-40 minutes in step S2.

[0025] As a preferred technical solution of the present invention, the bipolar plates used in the liquid flow battery are flexible graphite plates with a thickness of 0.6~2mm, the electrodes are carbon felt with a thickness of 2.0~4.6mm, and the diaphragm is a proton exchange membrane, preferably Nafion117, with a thickness of 40~117μm.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] In the present invention, a bismuth salt (such as bismuth chloride) is mixed with a complexing agent (such as citric acid) and then directly dissolved in the electrolyte in a direct dissolution manner to form a dynamic homogeneous catalytic system, Bi³⁺ / Bi 0 directly participates in the redox reaction in the electrolyte, avoiding the problem of interface shedding of traditional solid-supported catalysts; the present invention does not require an electrode preloading step, and directly configuring an electrolyte containing Bi 3+ can achieve the catalytic function; Bi³⁺ can be dynamically adsorbed on the electrode surface during charge and discharge to form active sites, and the catalytic activity is maintained through dissolution-redeposition after cycling.

[0028] The process steps of the present invention are simple and time-saving, do not affect the original battery structure, system and assembly method, and can greatly reduce the workload and thus reduce the cost during the commercialization process. The present invention can improve the energy efficiency of the all-vanadium redox flow battery. At a current density of 200 mA / cm², the energy efficiency can reach 81.5%. The present invention can improve the capacity retention rate of the flow battery. After 40 charge-discharge cycles, compared with the blank control group, the capacity retention rate is increased from 71.83% to 93.13%. -2 Figure 15 is an experimental graph of the energy efficiency and current density of Example 1 of the present invention and the control group; Description of the Drawings

[0029] Figure 1 Figure 19 is an experimental graph of the discharge capacity of Example 1 of the present invention and the control group versus the number of cycles;

[0030] Figure 2 Figure 23 is an experimental graph of the Coulombic efficiency and voltage efficiency of Example 1 of the present invention and the control group versus the current density.

[0031] Figure 3 Figure 24 is an experimental graph of the Coulombic efficiency and voltage efficiency of Example 1 of the present invention and the control group versus the current density. Detailed Embodiments

[0032] The present invention will be described in detail below. Those not described in detail in the present invention are all publicly known technical solutions in the art.

[0033] Example 1

[0034] Prepare an all-vanadium redox flow battery containing a bismuth-based catalyst. The preparation method is specifically as follows:

[0035] Measure 70 mL of electrolyte as the solvent respectively. The electrolyte is specifically a mixed solution of 1.7 mol / L trivalent vanadium ions and 3 mol / L H2SO4. Weigh 7 mmol of bismuth chloride solid and 0.7 mmol of citric acid, place them in the measured electrolyte and stir evenly (stir with a magnetic stirrer) to obtain a bismuth-modified electrolyte;

[0036] Let the prepared electrolyte stand for 20 min and then filter it (filter with a Buchner funnel) to remove the existing solid impurities.

[0037] The prepared electrolyte above was used in the assembled all-vanadium redox flow battery for charge and discharge tests, and Nafion 117 was used as the diaphragm. The electrolyte was circulated in the battery by a pump. After the activation process, V was in the electrolyte on the negative electrode side 3+ , and the electrolyte on the positive electrode side was VO 2+ . At a current density of 200 mA cm -2 , the energy efficiency of the all-vanadium redox flow battery using the prepared electrolyte above was 81.5%. After 40 cycles, the capacity retention rate was 93.13%. The summary of the performance of the flow battery is shown in Table 1.

[0038] Example 2

[0039] The preparation method was the same as that of Example 1, except that 14 mmol of bismuth chloride solid was added.

[0040] Using the same detection method for testing, the energy efficiency of the all-vanadium redox flow battery using the prepared electrolyte above was 80.4%. After 40 cycles, the capacity retention rate was 91.15%. The summary of the performance of the flow battery is shown in Table 1.

[0041] Example 3

[0042] The preparation method was the same as that of Example 1, except that 7 mmol of bismuth nitrate solid was added.

[0043] Using the same detection method for testing, the energy efficiency of the all-vanadium redox flow battery using the prepared electrolyte above was 79.7%. After 40 cycles, the capacity retention rate was 89.92%. The summary of the performance of the flow battery is shown in Table 1.

[0044] Example 4

[0045] The preparation method was the same as that of Example 1, except that 0.7 mmol of tartaric acid was added.

[0046] Using the same detection method for testing, the energy efficiency of the all-vanadium redox flow battery using the prepared electrolyte above was 80.2%. After 40 cycles, the capacity retention rate was 86.35%. The summary of the performance of the flow battery is shown in Table 1.

[0047] Comparative Example 1

[0048] The preparation method was the same as that of Example 1, except that 7 mmol of bismuth chloride solid was not added.

[0049] Using the same detection method for testing, the energy efficiency of the all-vanadium redox flow battery using the prepared electrolyte above was 78.1%. After 40 cycles, the capacity retention rate was 71.83%. The summary of the performance of the flow battery is shown in Table 1.

[0050] Comparative Example 2

[0051] The preparation method was the same as that of Example 1, except that the metal catalyst therein was replaced with an equimolar amount of iron salt (FeCl3·6H2O) instead of BiCl3.

[0052] Using the same detection method for testing, the energy efficiency of the electrolyte prepared above when applied to a vanadium redox flow battery was 79.3%, and the capacity retention rate after 40 cycles was 75.43%. The performance summary of the flow battery is shown in Table 1.

[0053] Comparative Example 3

[0054] The preparation method was the same as that of Example 1, except that the metal catalyst therein was replaced with an equimolar amount of antimony salt (SbCl3) instead of BiCl3.

[0055] Using the same detection method for testing, the energy efficiency of the electrolyte prepared above when applied to a vanadium redox flow battery was 78.5%, and the capacity retention rate after 40 cycles was 80.19%. The performance summary of the flow battery is shown in Table 1.

[0056] Comparative Example 4

[0057] The preparation method was the same as that of Example 1, except that the complexing agent citric acid was replaced with an equimolar amount of EDTA.

[0058] Using the same detection method for testing, the energy efficiency of the electrolyte prepared above when applied to a vanadium redox flow battery was 79.5%, and the capacity retention rate after 40 cycles was 83.62%. The performance summary of the flow battery is shown in Table 1.

[0059] Table 1

[0060] Catalyst Complexing agent Energy efficiency / % Capacity retention rate / % Example 1 <![CDATA[BiCl3]]> Citric acid 81.5 93.13 Example 2 <![CDATA[BiCl3]]> Citric acid 80.4 91.15 Example 3 <![CDATA[Bi(NO3)3]]> Citric acid 79.7 89.92 Example 4 <![CDATA[BiCl3]]> Tartaric acid 80.2 86.35 Comparative example 1 None Citric acid 78.1 71.83 Comparative example 2 <![CDATA[FeCl3·6H2O]]> Citric acid 79.3 75.43 Comparative example 3 <![CDATA[SbCl3]]> Citric acid 78.5 80.19 Comparative example 4 <![CDATA[BiCl3]]> EDTA 79.5 83.62

[0061] As can be seen from Table 1, in the embodiments of the present invention, BiCl3 or Bi(NO3)3 is used as a catalyst, and citric acid or tartaric acid is used as a complexing agent, which are superior to all comparative examples in terms of energy efficiency and capacity retention. In particular, in Example 1, compared with Comparative Example 1 without a catalyst (capacity retention of 71.83%), BiCl3 significantly improves the reaction activity and stability; compared with other catalysts (FeCl3·6H2O, SbCl3), its capacity retention advantage is particularly prominent (93.13% VS 75.43% - 80.19%), indicating that BiCl3 more effectively inhibits the attenuation of the electrode material. At the same time, as a complexing agent, citric acid further improves the capacity retention compared with EDTA (93.13% VS 83.62%). The inventor speculates that this may be related to optimizing the metal coordination environment. Examples 1 and 2 achieve an energy efficiency exceeding 80% and a capacity retention exceeding 90%, indicating that BiCl3 and citric acid have a significant synergistic effect and have significant technical advantages in high-efficiency energy conversion and long cycle life.

[0062] Blank control group

[0063] A blank control group comparison experiment was also conducted in the present invention using a vanadium electrolyte without adding BiCl3 and citric acid as the blank control group.

[0064] For the specific experimental results, please refer to Figures 1 to 3 , and the experimental results show that the present invention can improve the energy efficiency of the all-vanadium redox flow battery. At a current density of 200 mA / cm -2 , the energy efficiency can reach 81.5%. The present invention can improve the capacity retention of the flow battery. After 40 charge-discharge cycles, compared with the blank control group, the capacity retention increases from 71.83% to 93.13%. Compared with the blank control group, the technical solution of adding bismuth chloride and citric acid to the electrolyte in the present invention is significantly superior to the blank control group in terms of energy efficiency, discharge capacity, Coulomb efficiency, and voltage efficiency, indicating that the technical solution of the present invention has significant technological progress.

[0065] The above description of the embodiments is for the convenience of those of ordinary skill in the art to understand and use the invention. Obviously, those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative labor. Therefore, the present invention is not limited to the above embodiments, and the improvements and modifications made by those skilled in the art without departing from the scope of the present invention should be within the protection scope of the present invention.

Claims

1. A bismuth-containing modified electrolyte, including a vanadium electrolyte, characterized in that: A bismuth salt is added to the vanadium electrolyte as a catalyst, and a hydroxycarboxylic acid complexing agent is added; The molar ratio of the bismuth salt to the hydroxycarboxylic acid complexing agent is 7:0.7; The bismuth salt is bismuth trichloride, and in the vanadium electrolyte, the concentration of the bismuth salt is 0.05-0.2 mol / L; The hydroxycarboxylic acid complexing agent is citric acid; The vanadium electrolyte is a mixture of 1.7 mol / L 3.5-valent vanadium ions and 3 mol / L H2SO4.

2. A method for preparing a bismuth-containing modified electrolyte as claimed in claim 1, characterized in that: The vanadium electrolyte is used as a solvent, and bismuth salt and hydroxycarboxylic acid complexing agent are used as solutes, and the mixture is stirred and evenly mixed to obtain the product.

3. The method for preparing a bismuth-containing modified electrolyte according to claim 2, characterized in that: The mixed electrolyte is allowed to stand and then filtered to remove solid impurities.

4. An application of the bismuth-containing modified electrolyte as claimed in claim 1, characterized in that: The bismuth-containing modified electrolyte is used to prepare the electrolyte of the all-vanadium liquid flow battery.

5. An all-vanadium liquid flow battery, characterized in that: The bismuth-containing modified electrolyte according to claim 1 is used as the electrolyte.

6. A method for preparing an all-vanadium redox flow battery as claimed in claim 5, characterized in that: The following steps are involved: S1. Using bismuth chloride and citric acid as solutes and 3.5-valent vanadium ion electrolyte as solvent, the solute and solvent are mixed and stirred evenly; S2, after the electrolyte prepared in S1 is allowed to stand, it is filtered to remove solid impurities to obtain a modified electrolyte; S3. The electrolyte prepared in S2 is used in an all-vanadium liquid flow battery. As the battery is charged, the Bi element in the electrolyte is deposited on the surface of the carbon felt, and returns to the solution during the discharge process.

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