Method for preparing all-vanadium redox flow battery electrolyte based on vanadium pentoxide and formic acid one-step method

Abstract

The invention discloses a method for preparing an all-vanadium redox flow battery electrolyte based on a vanadium pentoxide and formic acid one-step method. The method comprises the following steps: dissolving vanadium pentoxide by using a dilute sulfuric acid solution, adding a reducing agent formic acid, adding a catalyst such as platinum carbon (Pt / C), continuously heating and stirring, sampling and detecting, cooling, filtering and the like. According to the method disclosed by the invention, efficient and low-cost preparation of the 3.5-valent vanadium electrolyte is realized through a simplified technological process and a reasonable raw material ratio, and the method is suitable for an all-vanadium redox flow battery system; the prepared electrolyte has high purity, good electrochemical performance and stable charge and discharge performance.

Description

Technical Field

[0001] The invention belongs to the technical field of liquid flow batteries, and specifically relates to a method for preparing an all-vanadium liquid flow battery electrolyte based on vanadium pentoxide and formic acid in a one-step process. Background Art

[0002] The worsening global energy crisis is prompting countries to vigorously develop renewable energy. However, the intermittent and unstable nature of renewable energy poses a severe challenge to the reliability and stability of the power system. In this context, finding efficient, safe, and low-cost energy storage technology has become one of the keys to the solution. Liquid flow batteries have attracted much attention because they can achieve independent regulation of energy and power, and are particularly suitable for long-term, large-scale energy storage scenarios.

[0003] As an important member of the flow battery family, all-vanadium flow battery (VFB) has become one of the ideal energy storage options due to its unique advantages - long life, high safety, wide voltage range, fast response capability, and easy recovery and recycling of vanadium electrolyte. In all-vanadium flow batteries, the performance and quality of the electrolyte directly affect the overall performance, cycle life and cost efficiency of the battery. However, traditional vanadium electrolyte preparation methods usually rely on multi-step chemical reactions and complex process flows, which are not only costly and inefficient, but also easily introduce impurities, reducing the purity and electrochemical properties of the electrolyte.

[0004] The valence regulation and purity of the electrolyte of the all-vanadium liquid flow battery is one of the key factors that determine its performance. Generally, the valence range of the electrolyte is between +2 and +5. The positive and negative electrolytes undergo reversible redox reactions during the battery charging and discharging process to achieve the storage and release of electrical energy. The 3.5-valent vanadium electrolyte has unique advantages and can be used as a universal electrolyte for positive and negative electrodes in commercial use. Therefore, the development of an efficient preparation method for high-purity 3.5-valent vanadium electrolyte is of great significance to improving the commercial application potential of all-vanadium liquid flow batteries.

[0005] Chinese patent application CN 117902626 A discloses a method and device for preparing vanadium electrolyte from crude vanadium, the method comprising: (1) providing a crude vanadium raw material solution, adjusting the pH value to 8-9, and then adding an impurity remover to perform a primary impurity removal to obtain a primary impurity removal product; (2) adding 1.2-5 times the theoretical amount of vanadium as a reducing agent sodium thiosulfate and sulfuric acid to the primary impurity removal product to control the solution pH to 1.5-4, and performing a primary reduction to obtain a primary reduction product and filter residue containing tetravalent vanadium; (3) adjusting the pH of the primary reduction product to 2-5, performing a secondary impurity removal to obtain a secondary impurity removal liquid; (4) extracting and stripping the secondary impurity removal liquid to obtain an extraction product containing a tetravalent vanadium electrolyte; (5) electrolytically reducing the extraction product to obtain a 3.5-valent vanadium electrolyte. It can be seen that the method has complicated steps and is time-consuming and labor-intensive. Therefore, it is necessary to provide a simple and efficient method for preparing a high-purity 3.5-valent vanadium electrolyte. Summary of the invention

[0006] The purpose of the present invention is to provide a method for preparing an all-vanadium flow battery electrolyte based on vanadium pentoxide and formic acid, aiming to overcome the high cost, low efficiency and complex process problems in traditional preparation methods. The method uses vanadium pentoxide (V2O5) as a vanadium source and introduces formic acid (HCOOH) as a reducing agent. By optimizing the reaction conditions and process flow, a one-step direct preparation of a high-purity 3.5-valent vanadium electrolyte is achieved. The method not only reduces production costs and energy consumption, but also improves the purity and electrochemical stability of the electrolyte, and is suitable for large-scale commercial applications.

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

[0008] A method for preparing an all-vanadium liquid flow battery electrolyte based on vanadium pentoxide and formic acid in one step, comprising the following steps:

[0009] (1) calculating the amount of vanadium pentoxide according to the vanadium ion concentration of the target electrolyte, and then adding the vanadium pentoxide into a dilute sulfuric acid solution to dissolve the vanadium pentoxide;

[0010] (2) adding a reducing agent, formic acid, to the solution obtained in step (1);

[0011] (3) adding a formic acid oxidation catalyst to the solution obtained in step (2), and then continuously heating and stirring;

[0012] (4) sampling and testing the valence and concentration of the electrolyte prepared in step (4); if the valence of the electrolyte does not reach the target valence of 3.5, then continue to slowly add formic acid to adjust the valence according to the test results until the desired valence is reached;

[0013] (5) After the reaction is completed, the electrolyte is cooled to room temperature and undissolved solid residues are removed by filtration to ensure the cleanliness and purity of the electrolyte.

[0014] Preferably, the concentration of the dilute sulfuric acid solution in step (1) is 0.1-5 mol / L, and the vanadium ion concentration in the target electrolyte is 0.1-3 mol / L. The present invention uses deionized water to dilute concentrated sulfuric acid (98% H2SO4) to prepare a dilute sulfuric acid solution of the required concentration, and the concentration of the dilute sulfuric acid solution is usually 0.1-5 mol / L, depending on the acid concentration requirement of the final target electrolyte; according to the vanadium ion concentration of the target electrolyte (usually in the range of 0.01-4 mol / L, preferably 0.1-3 mol / L in the present invention) and the volume of the electrolyte, the mass of the required vanadium pentoxide (V2O5) is calculated.

[0015]

[0016] Preferably, after adding vanadium pentoxide in step (1), the solution is heated to 40-80° C. and continuously stirred to promote the dissolution of V 2 O 5 .

[0017] Preferably, the amount of formic acid added in step (2) is calculated based on the vanadium ion concentration, with 1 to 2 moles of formic acid added per mole of vanadium pentoxide, and most preferably 1.5 moles of formic acid added per mole of vanadium pentoxide.

[0018] During the dissolution of V2O5, formic acid (HCOOH) is slowly added. Formic acid acts as a reducing agent to participate in the reduction reaction and reduce V2O5 to the target 3.5-valent vanadium state (VO 2+ With V 3+ The amount of formic acid added is adjusted according to the amount of V2O5 used and the reaction requirements. The theoretical molar ratio of formic acid to V2O5 should be 3:2. According to the average result of sampling and detection, formic acid exceeding 3:2 can be added in this step. Preferably, the molar amount of formic acid added is 1 to 2 times that of V2O5 (corresponding to the theoretical value of reduction to tetravalent and trivalent) to ensure that the reduction process is fully carried out.

[0019] Preferably, the amount of formic acid oxidation catalyst added in step (3) is: 0.1g formic acid oxidation catalyst is added per 100mL target electrolyte. The addition of the catalyst helps to improve the efficiency of the reduction reaction and accelerate the conversion of the valence state of the vanadium ion. As a reducing organic acid, formic acid can thermodynamically spontaneously undergo redox reactions with high-valent vanadium oxides and high-valent vanadium electrolytes. However, in actual operation, due to the high reaction energy barrier limitation, the reaction rate and reaction depth are poor, resulting in a low formic acid conversion rate, which is far from theory. The introduction of the catalyst and the regulation of temperature can solve this problem well and complete the rapid one-step preparation of vanadium electrolytes.

[0020] Preferably, the formic acid oxidation catalyst in step (3) is a platinum-carbon (Pt / C) catalyst.

[0021] Preferably, the time of continuous heating and stirring in step (3) is 0.5 to 10 hours, and the temperature is 40 to 80° C. In the presence of formic acid and a catalyst, the solution is continued to be heated and stirred to ensure that the reaction is complete and reaches equilibrium. Continuous stirring can prevent the formation of precipitation and ensure the uniformity of the electrolyte.

[0022] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0023] 1. The method of the present invention can prepare high-purity 3.5-valent vanadium electrolyte efficiently and at low cost, solving many problems in traditional methods and significantly improving the application prospects and commercial potential of all-vanadium liquid flow batteries.

[0024] 2. The one-step method for preparing commercial 3.5-valent electrolyte in the method of the present invention has good operability and adaptability, can be adjusted according to different application scenarios, and provide high-quality vanadium electrolyte products that meet different needs; in addition, it also has the advantages of simple process, low cost, high product purity, etc., and is suitable for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is the X-ray diffraction pattern of the vanadium pentoxide raw material (V2O5) used in the examples and comparative examples of the present invention.

[0026] Figure 2 The cyclic voltammetry curves of the 3.5-valent electrolyte prepared in Example 1 at different scanning speeds are shown in the figure. It can be seen from the figure that the peak current increases with the increase of the scanning speed.

[0027] Figure 3 The peak current-scan rate relationship in the cyclic voltammetry curve of the 3.5-valent electrolyte prepared in Example 1 is a linear relationship between the peak current and the square root of the scan rate, which proves that the redox of the vanadium electrolyte is a diffusion-controlled process.

[0028] Figure 4 This is the UV-visible absorption spectrum of the 3.5-valent electrolyte prepared in Example 1.

[0029] Figure 5 The voltage-capacity curve of the all-vanadium liquid flow battery charge-discharge test composed of the 3.5-valent electrolyte prepared in Example 1.

[0030] Figure 6 This is the UV-visible absorption spectrum of the quadrivalent electrolyte prepared using oxalic acid in Comparative Example 1.

[0031] Figure 7The UV-visible absorption spectra of the 3.5-valent electrolyte prepared by using formic acid in Example 1 and the 4-valent electrolyte prepared by using oxalic acid in Comparative Example 1 are compared.

[0032] Figure 8 This is the UV-visible absorption spectrum of the electrolyte prepared in Comparative Example 2 using formic acid but without a catalyst.

[0033] Fig. 9 The UV-visible absorption spectra of the 3.5-valent electrolyte prepared by using formic acid in Example 1 and the electrolyte prepared by using formic acid but without a catalyst in Comparative Example 2 are compared. DETAILED DESCRIPTION

[0034] The present invention is further described in detail below in conjunction with the examples, but the embodiments of the present invention are not limited thereto. The raw materials involved in the present invention can be directly purchased from the market. For process parameters not particularly noted, conventional techniques can be used.

[0035] Example 1

[0036] The 3.5-valent vanadium electrolyte was prepared according to the following steps:

[0037] (1) Preparation of dilute sulfuric acid solution: Add 60 L of deionized water to a reaction kettle, then slowly add 21.739 L of concentrated sulfuric acid (98% H2SO4), stir evenly, and obtain a 4 mol / L dilute sulfuric acid solution.

[0038] (2) Calculate the amount of vanadium pentoxide: The target electrolyte volume is 100 L, the vanadium ion concentration is 1.5 mol / L, and the required V2O5 mass is 13.641 kg.

[0039] (3) Dissolving V2O5: Add 13.641 kg of weighed V2O5 into the 4 mol / L dilute sulfuric acid solution prepared in step (1), heat to 70°C and stir to dissolve.

[0040] (4) Adding reducing agent formic acid: Slowly add 5.1784 kg formic acid (96% HCOOH) to promote the dissolution and reduction reaction of V2O5.

[0041] (5) Adding Pt / C catalyst: Add 100 g of Pt / C catalyst (0.1 g / 100 mL target electrolyte).

[0042] (6) Continue heating and stirring: Continue heating at 70°C and stirring for 4 hours to ensure complete reaction.

[0043] (7) Sampling and testing: Use a potentiometric titrator or UV-visible absorption spectrometer to determine the valence and concentration of the electrolyte. If the valence is higher than 3.5, continue to add formic acid to adjust.

[0044] (8) Cooling and Filtration: After the reaction is completed, cool to room temperature, filter out the solid residue, and collect the filtrate.

[0045] (9) Sampling, testing and storage: Test the composition and concentration of the electrolyte, transfer it to a clean storage container and seal it for storage.

[0046] Comparative Example 1

[0047] The electrolyte was prepared by referring to steps (1) to (6) of Example 1, except that formic acid was replaced by oxalic acid in Comparative Example 1. The valence and concentration of the electrolyte were measured by potentiometric titrator or UV-visible absorption spectroscopy. If the valence was higher than 3.5, the electrolyte could only be reduced to 4 valences by continuing to add excess oxalic acid and could not be further reduced.

[0048] It can be seen that oxalic acid and formic acid are both commonly used reducing agents, but in the actual electrolyte preparation process, the specific reaction conditions such as the strength of the reducing property, reaction kinetics, and reaction depth are involved. Between the two, oxalic acid is not substitutable for formic acid. When oxalic acid is used as a reducing agent, the electrolyte can still only be reduced to a valence of four when oxalic acid is in excess. That is, the reducing property of oxalic acid can only reduce a valence of five to a valence of four and cannot be further reduced to a valence of three.

[0049] Comparative Example 2

[0050] The electrolyte was prepared by referring to the steps of Example 1, except that the catalyst added in step (5) was omitted in Comparative Example 2. The valence and concentration of the electrolyte were measured by a potentiometric titrator or UV-visible absorption spectrometry. If the valence was higher than 3.5, the electrolyte could not be reduced to 3.5 or even completely reduced to 4 even if excess formic acid was added.

[0051] It can be seen that although formic acid is also considered to be a commonly used reducing agent, in the actual electrolyte preparation process, it involves specific reaction conditions such as reaction kinetics, reaction depth, reaction energy barrier, etc. between the high-valent vanadium electrolyte and vanadium oxide. For the system that actually uses formic acid as a reducing agent to prepare vanadium battery electrolyte, there are still many problems that need to be studied and overcome.

[0052] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A method for preparing an electrolyte for an all-vanadium redox flow battery based on vanadium pentoxide and formic acid in one step, characterized in that: The following steps are involved: (1) calculating the amount of vanadium pentoxide according to the vanadium ion concentration of the target electrolyte, and then adding the vanadium pentoxide into a dilute sulfuric acid solution to dissolve the vanadium pentoxide; (2) adding a reducing agent, formic acid, to the solution obtained in step (1); (3) adding a formic acid oxidation catalyst to the solution obtained in step (2), and then continuously heating and stirring; (4) sampling and testing the valence and concentration of the electrolyte prepared in step (4); if the valence of the electrolyte does not reach the target valence of 3.5, then continue to slowly add formic acid to adjust the valence according to the test results until the desired valence is reached; (5) After the reaction is completed, the electrolyte is cooled to room temperature and undissolved solid residues are removed by filtration to ensure the cleanliness and purity of the electrolyte.

2. The method according to claim 1, characterized in that: The concentration of the dilute sulfuric acid solution in step (1) is 0.1 to 5 mol / L, and the concentration of vanadium ions in the target electrolyte is 0.1 to 3 mol / L.

3. The method according to claim 1, characterized in that After adding vanadium pentoxide in step (1), the solution is heated to 40-80° C. and stirred continuously.

4. The method according to claim 1, characterized in that: The amount of formic acid added in step (2) is calculated based on the vanadium ion concentration, and 1 to 2 moles of formic acid are added per mole of vanadium pentoxide.

5. The method according to claim 1, characterized in that The amount of formic acid oxidation catalyst added in step (3) is: 0.01 to 0.5 g of formic acid oxidation catalyst is added per 100 mL of target electrolyte.

6. The method according to claim 1, characterized in that The formic acid oxidation catalyst in step (3) is a platinum-carbon catalyst.

7. The method according to claim 1, characterized in that The continuous heating and stirring time in step (3) is 0.5 to 10 hours, and the temperature is 40 to 80°C.

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