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

Abstract

The invention relates to a bismuth-containing modified electrolyte, an all-vanadium redox flow battery and a preparation method and application of the all-vanadium redox flow battery, and belongs to the technical field of all-vanadium redox flow batteries. The bismuth-containing modified electrolyte comprises a vanadium electrolyte, bismuth salt is added into the vanadium electrolyte to serve as a catalyst, and a hydroxyl carboxylic 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). According to the invention, the catalyst and the complexing agent are added into the electrolyte, the Bi elementary substance is deposited on the electrode through the charging process of the battery, the active sites of the electrode are increased, and the energy efficiency of the battery is improved. Meanwhile, the catalyst can improve the capacity retention ratio 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 liquid flow batteries, and in particular to a bismuth-containing modified electrolyte, an all-vanadium liquid 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 is urgent to use clean energy to replace traditional fossil energy. Although solar energy, wind energy and other technologies are relatively mature, they still have the problem of instability. As an electrochemical energy storage technology, flow battery has gradually become one of the core solutions to solve the volatility of renewable energy and long-term energy storage needs since it was proposed in the 1970s. However, the hydrogen evolution side reaction and cost issues in flow batteries currently restrict the improvement of flow battery energy density and commercial large-scale production.

[0003] Electrodes and electrolytes are two important components of flow batteries. Electrodes are the place where electrochemical reactions occur and are the key materials that directly affect the energy density of flow batteries. Electrolytes contain active substances. Flow batteries store and release energy through redox reactions of active substances in the electrolyte.

[0004] The electrode reaction kinetics of the all-vanadium liquid flow battery relies on high-efficiency catalysts to improve the reaction kinetics and electrochemical activity of the liquid flow battery. Different high-efficiency 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 catalyze different active substances in a targeted manner. It is precisely because of this feature that 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 attached to the carbon felt electrode reacts with H in the solution. + The reaction generates BiH x The intermediate can inhibit the occurrence of hydrogen evolution reaction on the one hand, and promote the V 2+ With V 3+ The mutual conversion process between vanadium ions and vanadium ions can improve the energy efficiency of the battery. The electrolyte can directly affect the capacity of the battery. To increase the capacity of the flow battery, more electrolyte is needed. However, as the reaction proceeds, the ion membrane cannot completely isolate the exchange of vanadium ions between the positive and negative electrodes, which will cause the battery capacity to decay. However, by adding additives to the electrolyte, this situation can be effectively alleviated, thereby improving the battery capacity retention rate.

[0005] Traditional catalysts need to be loaded on the electrode surface by coating, electrodeposition, etc., but they have the following problems: (1) The process is complex, the loading process requires multiple steps, the cost is high and it is difficult to scale up; (2) Catalyst shedding: During the cycle, the catalyst shedding occurs due to changes in electrode volume or electrolyte flushing, resulting in decreased activity; (3) Uneven distribution: Fixed loading can easily lead to uneven catalyst distribution, affecting reaction efficiency. Further research is needed to obtain an all-vanadium flow battery that can be used to improve the capacity retention rate of flow batteries and can act on carbon felt electrodes. Summary of the invention

[0006] The purpose of the present invention is to provide a bismuth-containing modified electrolyte, an all-vanadium liquid flow battery, and a preparation method and application thereof 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 includes a vanadium electrolyte, a bismuth salt is added as a catalyst, and a hydroxycarboxylic acid complexing agent is added to the vanadium electrolyte;

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

[0010] The present invention utilizes catalysts and complexing agents added to the electrolyte, and deposits Bi on the electrode during the battery charging process, thereby increasing the active sites of the electrode and helping to improve the energy efficiency of the battery; at the same time, the catalyst can improve the capacity retention rate of the liquid flow battery, greatly simplifying the process steps and reducing 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 ion and 3 mol / L H 2 SO 4 .

[0012] As a preferred technical solution of the present invention, the bismuth salt includes one or more of bismuth trichloride and bismuth nitrate, 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, 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] The present invention mixes a bismuth salt (such as bismuth chloride) and a complexing agent (such as citric acid) and then directly dissolves them in an electrolyte in a direct dissolution manner to form a dynamic homogeneous catalytic system. 0 Directly participate in the redox reaction in the electrolyte, avoiding the interface shedding problem of traditional solid-supported catalysts; the present invention does not require an electrode pre-loading step, and directly configures Bi 3+ The catalytic function can be realized by using an electrolyte; Bi³⁺ can be dynamically adsorbed on the electrode surface and form active sites during the charge and discharge process, and maintain catalytic activity through dissolution-redeposition after cycling.

[0028] The process steps of the present invention are simple and time-saving, and do not affect the original battery structure, system and assembly method. In the process of commercialization, the workload can be greatly reduced, thereby reducing costs. The present invention can improve the energy efficiency of all-vanadium liquid flow batteries. -2 At a current density of , the energy efficiency can reach 81.5%. The present invention can improve the capacity retention rate of the flow battery. After 40 charge and discharge cycles, compared with the blank control group, the capacity retention rate is increased from 71.83% to 93.13%. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 The energy efficiency and current density experimental diagram of Example 1 of the present invention and the control group;

[0030] Figure 2 This is an experimental diagram of the discharge capacity versus cycle number of Example 1 of the present invention and the control group;

[0031] Figure 3 The experimental diagrams are of the coulombic efficiency, voltage efficiency and current density of Example 1 of the present invention and the control group. DETAILED DESCRIPTION

[0032] The present invention is described in detail below. All matters not described in detail in the present invention are technical solutions already disclosed in the art.

[0033] Example 1

[0034] An all-vanadium liquid flow battery containing a bismuth-based catalyst is prepared, and the preparation method is specifically as follows:

[0035] 70 mL of electrolyte was taken as solvent, wherein the electrolyte contained 1.7 mol / L 3.5-valent vanadium ions and 3 mol / L H 2 SO 4 7 mmol of bismuth chloride solid and 0.7 mmol of citric acid are weighed into the measured electrolyte and stirred evenly (using a magnetic stirrer) to obtain a bismuth-containing modified electrolyte;

[0036] The prepared electrolyte was allowed to stand for 20 min and then filtered (using a Buchner funnel) to remove any solid impurities.

[0037] The prepared electrolyte was used in the assembled all-vanadium liquid flow battery for charge and discharge tests. The diaphragm was Nafion117. The electrolyte was circulated in the battery by a pump. After the activation process, the electrolyte on the negative electrode side was V 3+ , the electrolyte on the positive electrode side is VO 2+ At 200mA cm -2 At the current density, the energy efficiency of the electrolyte prepared as above applied to the all-vanadium flow battery is 81.5%, and the capacity retention rate is 93.13% after 40 cycles. The performance of the flow battery is summarized in Table 1.

[0038] Example 2

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

[0040] The same detection method was used for testing. The energy efficiency of the electrolyte prepared above in the all-vanadium flow battery was 80.4%, and the capacity retention rate was 91.15% after 40 cycles. The performance of the flow battery is summarized in Table 1.

[0041] Example 3

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

[0043] The same detection method was used for testing. The energy efficiency of the electrolyte prepared above in the all-vanadium flow battery was 79.7%. The capacity retention rate after 40 cycles was 89.92%. The performance of the flow battery is summarized in Table 1.

[0044] Example 4

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

[0046] The same detection method was used for testing. The energy efficiency of the electrolyte prepared above in the all-vanadium flow battery was 80.2%. The capacity retention rate after 40 cycles was 86.35%. The performance of the flow battery is summarized in Table 1.

[0047] Comparative Example 1

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

[0049] The same detection method was used for testing. The energy efficiency of the electrolyte prepared above in the all-vanadium flow battery was 78.1%. The capacity retention rate after 40 cycles was 71.83%. The performance of the flow battery is summarized in Table 1.

[0050] Comparative Example 2

[0051] The preparation method is the same as that of Example 1, except that the metal catalyst is replaced by BiCl 3 Replace with an equal amount of iron salt (FeCl 3 6H 2 O).

[0052] The same detection method was used for testing. The energy efficiency of the electrolyte prepared above in the all-vanadium flow battery was 79.3%. The capacity retention rate after 40 cycles was 75.43%. The performance of the flow battery is summarized in Table 1.

[0053] Comparative Example 3

[0054] The preparation method is the same as that of Example 1, except that the metal catalyst is replaced by BiCl 3 Replace with an equal amount of antimony salt (SbCl 3 ).

[0055] The same detection method was used for testing. The energy efficiency of the electrolyte prepared above in the all-vanadium flow battery was 78.5%, and the capacity retention rate was 80.19% after 40 cycles. The performance of the flow battery is summarized in Table 1.

[0056] Comparative Example 4

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

[0058] The same detection method was used for testing. The energy efficiency of the electrolyte prepared above in the all-vanadium flow battery was 79.5%. The capacity retention rate after 40 cycles was 83.62%. The performance of the flow battery is summarized in Table 1.

[0059] Table 1 catalyst Complexing agent Energy efficiency / % Capacity retention rate / % Example 1 <![CDATA[BiCl 3 ]]> Citric Acid 81.5 93.13 Example 2 <![CDATA[BiCl 3 ]]> Citric Acid 80.4 91.15 Example 3 <![CDATA[Bi(NO 3 ) 3 ]]> Citric Acid 79.7 89.92 Example 4 <![CDATA[BiCl 3 ]]> tartaric acid 80.2 86.35 Comparative Example 1 none Citric Acid 78.1 71.83 Comparative Example 2 <![CDATA[FeCl 3 ·6H 2 O]]> Citric Acid 79.3 75.43 Comparative Example 3 <![CDATA[SbCl 3 ]]> Citric Acid 78.5 80.19 Comparative Example 4 <![CDATA[BiCl 3 ]]> EDTA 79.5 83.62

[0060] As can be seen from Table 1, the embodiment of the present invention uses BiCl 3 or Bi(NO 3 ) 3 As a catalyst, citric acid or tartaric acid as a complexing agent is superior to all comparative examples in terms of energy efficiency and capacity retention rate, especially Example 1. Compared with Comparative Example 1 without catalyst (71.83% capacity retention rate), BiCl 3The reaction activity and stability are significantly improved; compared with other catalysts (FeCl 3 6H 2 O、SbCl 3 ), its capacity retention rate advantage is particularly prominent (93.13% VS 75.43%~80.19%), which shows that BiCl 3 More effectively inhibit electrode material degradation. At the same time, citric acid as a complexing agent compared with EDTA further improved the capacity retention rate (93.13% VS 83.62%). The inventors speculate that this may be related to the optimization of the metal coordination environment. Example 1 and Example 2 achieved energy efficiency exceeding 80% and capacity retention exceeding 90%, indicating that BiCl 3 It has a significant synergistic effect with citric acid and possesses significant technical advantages in terms of efficient energy conversion and long cycle life.

[0061] Blank control group

[0062] Without adding BiCl 3 The vanadium electrolyte containing citric acid and vanadium electrolyte was used as a blank control group, and the present invention also conducted a blank control group comparative experiment.

[0063] For detailed experimental results, see Figures 1 to 3 The experimental results show that the present invention can improve the energy efficiency of all-vanadium liquid flow batteries at 200mAcm -2 At a current density of , the energy efficiency can reach 81.5%. The present invention can improve the capacity retention rate of the flow battery. After 40 charge and discharge cycles, the capacity retention rate is increased from 71.83% to 93.13% compared with the blank control group. Compared with the blank control group, the technical solution of the present invention of adding bismuth chloride and citric acid to the electrolyte is significantly better than 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 technical progress.

[0064] The above description of the embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that 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 work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the scope of protection 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 6-8:0.6-0.

8.

2. A bismuth-containing modified electrolyte according to claim 1, characterized in that: The vanadium electrolyte is a 3.5-valent vanadium ion electrolyte.

3. A bismuth-containing modified electrolyte according to claim 1, characterized in that: The bismuth salt includes one or more of bismuth trichloride and bismuth nitrate.

4. A bismuth-containing modified electrolyte according to claim 1, characterized in that: The hydroxycarboxylic acid complexing agent includes one or more of citric acid and tartaric acid.

5. The bismuth-containing modified electrolyte according to claim 1, characterized in that: In the vanadium electrolyte, the concentration of the bismuth salt is 0.05-0.2 mol / L.

6. 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.

7. The method for preparing a bismuth-containing modified electrolyte according to claim 6, characterized in that: The mixed electrolyte is allowed to stand and then filtered to remove solid impurities.

8. 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.

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

10. A method for preparing an all-vanadium redox flow battery as claimed in claim 9, 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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