A method for preparing a modified diaphragm for all-vanadium liquid flow battery

Abstract

The invention relates to the technical field of diaphragms for all-vanadium liquid flow batteries, and discloses a method for preparing a modified diaphragm for all-vanadium liquid flow batteries, comprising the following steps: preparing a precursor solution from thiazolidinone substances, olefin cyanide substances, and an organic solvent; preparing a crosslinker solution from a crosslinker and an organic solvent; adding the crosslinker solution to the precursor solution for reaction, filtering, washing the precipitate with an eluent, and drying to obtain a modifier; preparing a membrane-making liquid from a polymer resin, a modifier, a surfactant, and a membrane solvent; preparing a pre-modified diaphragm from the membrane-making liquid; soaking the pre-modified membrane in a thiazolidinone substance solution, and drying to obtain a modified diaphragm for all-vanadium liquid flow batteries. The thiazole ring and ketone group present in the thiazolidinone substances can enhance the repulsion of the diaphragm to vanadium ions, thereby reducing the transmembrane diffusion of vanadium ions, reducing the cross-contamination of the positive and negative electrolytes of the all-vanadium liquid flow battery, and improving the coulombic efficiency, energy efficiency, and capacity retention rate of the battery.

Description

Technical Field

[0001] The invention relates to the technical field of all-vanadium redox flow battery diaphragms, and in particular to a method for preparing a modified diaphragm for an all-vanadium redox flow battery. Background Art

[0002] All-vanadium flow batteries (vanadium batteries) achieve the conversion of electrical energy and chemical energy through the redox reaction of vanadium ions of different valence states in the positive and negative electrolytes. The diaphragm is the core component of all-vanadium flow batteries. It organizes the mixing of positive and negative active materials and conducts protons to form the circuit inside the battery.

[0003] The requirements of all-vanadium liquid flow batteries for diaphragms are: (1) high proton conductivity to reduce the internal resistance and ohmic polarization of the battery and improve the voltage efficiency of the battery; (2) high proton selectivity, that is, high vanadium resistance, to reduce cross-contamination of positive and negative electrode active materials, reduce self-discharge, and improve the coulombic efficiency and capacity retention rate of the battery; (3) excellent physical and chemical stability to ensure the long-term stable operation of the battery; (4) low price to facilitate large-scale commercial promotion.

[0004] At present, the vanadium liquid flow battery membrane has problems of insufficient proton conductivity and poor vanadium resistance, which directly affects the efficiency and capacity retention rate of the all-vanadium liquid flow battery, and further causes an increase in construction cost, use cost and maintenance cost. Summary of the invention

[0005] The purpose of the present invention is to provide a method for preparing a modified diaphragm for an all-vanadium liquid flow battery, so as to solve the problems of insufficient proton conductivity and poor vanadium resistance of the all-vanadium liquid flow battery diaphragm, and to improve the coulombic efficiency, energy efficiency, voltage efficiency and capacity retention rate of the battery.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] A method for preparing a modified diaphragm for an all-vanadium liquid flow battery comprises the following steps:

[0008] S1, dissolving a thiazolidinone substance and an olefin cyanide substance in an organic solvent to obtain a precursor solution; dissolving a cross-linking agent in an organic solvent to obtain a cross-linking agent solution;

[0009] S2. Under ice bath stirring conditions, add 1 volume part of the cross-linking agent solution dropwise to 10-50 volume parts of the precursor solution at a rate of 1-5 mL / min, ultrasonicate for 20-60 min under the protection of an inert gas, let stand for 5-20 h after the ultrasonicate is completed, filter, wash the precipitate with an eluent, and vacuum dry to obtain a modifier;

[0010] S3, uniformly dispersing the polymer resin, the modifier, and the surfactant in the membrane solvent to obtain a membrane-making solution;

[0011] S4, evenly coating the membrane-making solution on a flat plate, and vacuum drying to obtain a pre-modified membrane;

[0012] S5. Soak the pre-modified membrane in a thiazolidinone substance solution, control the concentration, soaking temperature and soaking time of the thiazolidinone substance solution, take out and dry after soaking, and obtain a modified diaphragm for all-vanadium liquid flow battery.

[0013] Preferably, the thiazolidinone substance in step S1 is one of 2-mercapto-5-thiazolidinone, 2-thiazolidinone, 2,4-thiazolidinedione, and 3-ethyl-2-thio-4-thiazolidinedione; and the concentration of the thiazolidinone substance in the precursor solution is 0.01-0.1 mol / L.

[0014] Preferably, the olefin cyanide substance in step S1 is a substance in which the olefin double bond is located at the end of the carbon chain, specifically one of 4-pentenenitrile, 5-hexenenitrile, 2-chloroacrylonitrile, and 3-hydroxypent-4-enenitrile; the concentration of the olefin cyanide substance in the precursor solution is 0.2~0.5 mol / L.

[0015] Preferably, the organic solvent in step S1 is one of dimethyl sulfoxide, acetone and N,N-dimethylformamide.

[0016] Preferably, in step S1, the crosslinking agent is one of divinylbenzene and ethylene glycol dimethacrylate; and the concentration of the crosslinking agent in the crosslinking agent solution is 0.1-1 mol / L.

[0017] Preferably, the inert gas in step S2 is one of nitrogen and argon.

[0018] Preferably, the eluent in step S2 is one of methanol, ethanol and acetone.

[0019] Preferably, in step S3, the mass ratio of polymer resin: modifier: surfactant: membrane solvent is (30-100):1:(0.01-0.1):(500-1500).

[0020] Preferably, in step S3, the polymer resin is one of perfluorosulfonic acid resin and sulfonated polyetheretherketone resin, the surfactant is one of benzalkonium chloride, benzalkonium chloride and benzalkonium bromide, and the membrane solvent is one of N,N-dimethylformamide, N-methylpyrrolidone and N,N-dimethylacetamide.

[0021] Preferably, the concentration of the thiazolidinone substance solution in step S5 is 1-20 mmol / L, the immersion temperature is 5-20° C., the immersion time is 1-20 min, and the thiazolidinone substance in the thiazolidinone substance solution is the same compound as the thiazolidinone substance in the precursor solution in step S1.

[0022] Beneficial effects of the present invention:

[0023] 1. The present invention loads thiazolidinone substances onto the diaphragm. The thiazole ring and ketone group in the thiazolidinone substances can enhance the repulsion of the diaphragm to vanadium ions, thereby reducing the transmembrane diffusion of vanadium ions, reducing the cross-contamination of the positive and negative electrolytes of the all-vanadium liquid flow battery, and improving the coulombic efficiency, energy efficiency and capacity retention rate of the battery;

[0024] 2. In the present invention, the cyanide substances are cross-linked in the presence of thiazolidinone substances and the action of a cross-linking agent to form a polymer compound containing thiazolidinone substances. The thiazolidinone substances are removed from the polymer compound by further elution to form a molecular imprinting material of the thiazolidinone substances, and in the subsequent film-making process, the molecular imprinting material is evenly distributed on the diaphragm. Before use, the diaphragm is immersed in a solution of thiazolidinone substances to complete the modification of the diaphragm, thereby increasing the uniformity of the distribution of thiazole rings and keto groups on the diaphragm, and further improving the coulombic efficiency, energy efficiency and capacity retention rate of the battery;

[0025] 3. The -CN group present after cross-linking of cyanide substances can be hydrolyzed into amide or carboxylic acid during the use of the diaphragm, promoting the transmission of protons and improving the voltage efficiency of the battery;

[0026] 4. By adjusting the concentration, immersion time and immersion temperature of the immersion solution, the number of modified groups on the diaphragm can be accurately controlled, which not only makes the diaphragm more universal, but also enables the vanadium resistance and proton transport of the diaphragm to reach the optimal balance, thereby improving the voltage efficiency of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 A schematic diagram of a method for preparing a modified diaphragm for an all-vanadium redox flow battery according to the present invention;

[0028] Figure 2 Comparison of vanadium barrier performance of the diaphragm of Example 1 of the present invention and Comparative Example 3. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention is further described in detail below through the accompanying drawings and embodiments. However, it should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the scope of the present invention. In addition, in the following description, the description of known structures and technologies is omitted to avoid unnecessary confusion of the concept of the present invention.

[0030] like Figure 1 As shown, a method for preparing a modified diaphragm for an all-vanadium liquid flow battery comprises the following steps:

[0031] S1. Dissolve thiazolidinone substances and enocyanide substances in an organic solvent to obtain precursor solutions with concentrations of thiazolidinone substances and enocyanide substances of 0.01-0.1 mol / L and 0.2-0.5 mol / L, respectively; dissolve a crosslinker in an organic solvent to obtain a crosslinker solution with a crosslinker concentration of 0.1-1 mol / L; the thiazolidinone substance is one of 2-mercapto-5-thiazolidinone, 2-thiazolidinone, 2,4-thiazolidinedione, and 3-ethyl-2-thio-4-thiazolidinedione; the enocyanide substance is a substance in which the olefin double bond is located at the end of the carbon chain, specifically one of 4-pentenenitrile, 5-hexenenitrile, 2-chloroacrylonitrile, and 3-hydroxypent-4-enenitrile; the organic solvent is one of dimethyl sulfoxide, acetone, and N,N-dimethylformamide; the crosslinker is one of divinylbenzene and ethylene glycol dimethacrylate;

[0032] S2. Under ice bath stirring conditions, add 1 volume part of the cross-linking agent solution dropwise to 10-50 volume parts of the precursor solution at a rate of 0.2-1 volume part / min, and perform ultrasonic treatment for 20-60 min under the protection of an inert gas. After the ultrasonic treatment, let the solution stand for 5-20 h, filter, wash the precipitate with an eluent, and dry it in vacuum to obtain a modifier; the inert gas is one of nitrogen and argon; the eluent is one of methanol, ethanol, and acetone;

[0033] S3, uniformly dispersing polymer resin, modifier, and surfactant in a membrane solvent to obtain a membrane solution; the mass ratio of polymer resin: modifier: surfactant: membrane solvent is (30-100):1:(0.01-0.1):(500-1500); the polymer resin is one of perfluorosulfonic acid resin and sulfonated polyetheretherketone resin, the surfactant is one of benzalkonium chloride, benzalkonium chloride, and benzalkonium bromide, and the membrane solvent is one of N,N-dimethylformamide, N-methylpyrrolidone, and N,N-dimethylacetamide;

[0034] S4, evenly coating the membrane-making solution on a flat plate, and vacuum drying to obtain a pre-modified membrane;

[0035] S5. Soak the pre-modified membrane in a thiazolidinone substance solution, control the concentration, soaking temperature and soaking time of the thiazolidinone substance solution, take out and dry after soaking to obtain a modified diaphragm for all-vanadium liquid flow battery; the concentration of the thiazolidinone substance solution is 1~20mmol / L, the soaking temperature is 5~20℃, and the soaking time is 1~20min. The thiazolidinone substance in the thiazolidinone substance solution is the same compound as the thiazolidinone substance in the precursor solution in step S1.

[0036] Embodiment 1: This embodiment specifically includes the following steps;

[0037] S1, dissolving 2-mercapto-5-thiazolidinone and 4-pentenenitrile in dimethyl sulfoxide to obtain a precursor solution in which the concentrations of thiazolidinone and cyanide are 0.05 mol / L and 0.2, respectively; dissolving divinylbenzene in acetone to obtain a crosslinking agent solution in which the concentration of the crosslinking agent is 0.3 mol / L;

[0038] S2. Under ice bath stirring, add 1 mL of the cross-linking agent solution dropwise to 10 mL of the precursor solution at a rate of 0.2 mL / min, and perform ultrasonication for 20 min under the protection of nitrogen. After the ultrasonication, let it stand for 5 h, filter, wash the precipitate with methanol, and vacuum dry to obtain a modifier;

[0039] S3, 100g of perfluorosulfonic acid resin, 1g of benzalkonium chloride, and 0.1g of surfactant are uniformly dispersed in 1500g of N,N-dimethylformamide to obtain a membrane-making solution;

[0040] S4, evenly coating the membrane-making solution on a flat plate, and vacuum drying to obtain a pre-modified membrane;

[0041] S5. Soak the pre-modified membrane in a 20 mmol / L 2-mercapto-5-thiazolidinone solution at 5°C for 1 min, take it out and dry it to obtain a modified diaphragm for all-vanadium redox flow battery.

[0042] Embodiment 2: This embodiment specifically includes the following steps:

[0043] S1, dissolving 2-thiazolidinone and 5-hexenonitrile in dimethyl sulfoxide to obtain a precursor solution in which the concentrations of thiazolidinone and cyanide are 0.1 mol / L and 0.5 mol / L, respectively; dissolving divinylbenzene in dimethyl sulfoxide to obtain a crosslinking agent solution in which the concentration of the crosslinking agent is 0.7 mol / L;

[0044] S2. Under ice bath stirring, add 1 mL of the cross-linking agent solution dropwise to 50 mL of the precursor solution at a rate of 1 mL / min, perform ultrasound for 50 min under the protection of argon, let stand for 10 h after the ultrasound, filter, wash the precipitate with methanol, and vacuum dry to obtain a modifier;

[0045] S3, 30g of sulfonated polyetheretherketone resin, 1g of modifier, and 0.08g of benzalkonium chloride are uniformly dispersed in 500g of N-methylpyrrolidone to obtain a film-forming solution;

[0046] S4, evenly coating the membrane-making solution on a flat plate, and vacuum drying to obtain a pre-modified membrane;

[0047] S5. Soak the pre-modified membrane in a 10 mmol / L thiazolidinone solution at 15°C for 10 min, take it out and dry it to obtain a modified diaphragm for all-vanadium redox flow battery.

[0048] Embodiment 3: This embodiment specifically includes the following steps:

[0049] S1, dissolving 2-mercapto-5-thiazolidinone and 2-chloroacrylonitrile in N,N-dimethylformamide to obtain a precursor solution in which the concentrations of thiazolidinone and cyanide are 0.07 mol / L and 0.3 mol / L, respectively; dissolving ethylene glycol dimethacrylate in acetone to obtain a crosslinking agent solution in which the concentration of the crosslinking agent is 0.1 mol / L;

[0050] S2. Under ice bath stirring, add 1 mL of the cross-linking agent solution dropwise to 20 mL of the precursor solution at a rate of 0.5 mL / min, perform ultrasonication for 60 min under the protection of nitrogen, let stand for 20 h after the ultrasonication, filter, wash the precipitate with ethanol, and vacuum dry to obtain a modifier;

[0051] S3, 50g of perfluorosulfonic acid resin, 1g of modifier, and 0.01g of benzalkonium chloride are uniformly dispersed in 800g of N,N-dimethylacetamide to obtain a membrane-making solution;

[0052] S4, evenly coating the membrane-making solution on a flat plate, and vacuum drying to obtain a pre-modified membrane;

[0053] S5. Soak the pre-modified membrane in a 1 mmol / L thiazolidinone solution at 10°C for 15 min, take it out and dry it to obtain a modified diaphragm for all-vanadium redox flow battery.

[0054] Embodiment 4: This embodiment specifically includes the following steps;

[0055] S1, dissolving 3-ethyl-2-thio-4-thiazolidinedione and 5-hexenonitrile in acetone to obtain a precursor solution with a concentration of 0.01 mol / L of thiazolidinone and 0.2 mol / L of cyanide; dissolving divinylbenzene in an organic solvent to obtain a crosslinking agent solution with a crosslinking agent concentration of 0.5 mol / L;

[0056] S2. Under ice bath stirring, add 1 mL of the cross-linking agent solution dropwise to 30 mL of the precursor solution at a rate of 0.4 mL / min, perform ultrasonication for 40 min under the protection of nitrogen, let stand for 15 h after the ultrasonication, filter, wash the precipitate with acetone, and vacuum dry to obtain a modifier;

[0057] S3, 70g of sulfonated polyetheretherketone resin, 1g of modifier, and 0.05g of benzalkonium bromide are uniformly dispersed in 1000g of N,N-dimethylacetamide to obtain a membrane-making solution;

[0058] S4, evenly coating the membrane-making solution on a flat plate, and vacuum drying to obtain a pre-modified membrane;

[0059] S5. Soak the pre-modified membrane in a 5 mmol / L thiazolidinone solution at 10°C for 20 min, take it out and dry it to obtain a modified diaphragm for all-vanadium redox flow battery.

[0060] Embodiment 5: This embodiment specifically includes the following steps:

[0061] S1. Dissolve 2,4-thiazolidinedione and 3-hydroxypent-4-enenitrile in N,N-dimethylformamide to obtain a precursor solution in which the concentrations of thiazolidinone and ene cyanide are 0.03 mol / L and 0.4 mol / L, respectively; dissolve ethylene glycol dimethacrylate in an organic solvent to obtain a crosslinker solution in which the concentration of the crosslinker is 1 mol / L;

[0062] S2. Under ice bath stirring conditions, 1 mL of the cross-linking agent solution was added dropwise to 40 mL of the precursor solution at a rate of 0.7 mL / min, and ultrasonicated for 30 min under the protection of argon. After the ultrasonication, the mixture was allowed to stand for 10 h, filtered, and the precipitate was washed with ethanol and dried in vacuo to obtain a modifier.

[0063] S3, 100g of perfluorosulfonic acid resin, 1g of modifier, and 0.02g of benzalkonium bromide are uniformly dispersed in 1200g of N,N-dimethylformamide to obtain a membrane-making solution;

[0064] S4, evenly coating the membrane-making solution on a flat plate, and vacuum drying to obtain a pre-modified membrane;

[0065] S5. Soak the pre-modified membrane in a 15 mmol / L thiazolidinone solution at 5°C for 10 min, take it out and dry it to obtain a modified diaphragm for all-vanadium redox flow battery.

[0066] Comparative Example 1: This comparative example differs from Example 1 in that step S5 is not performed.

[0067] Comparative Example 2: The difference between this comparative example and Example 1 is that no modifier is added in step S3.

[0068] Comparative Example 3: A blank film prepared using the polymer resin in Example 1.

[0069] Diaphragm vanadium barrier performance test: The diaphragms obtained in Example 1 and Comparative Example 3 were assembled into a vanadium battery stack. Under the same operating conditions, the battery was first charged to 95% SOC, and then the electrolyte circulation pump was kept turned on to test the battery open circuit voltage value. The open circuit voltage value can directly reflect the battery self-discharge rate. The test results are as follows: Figure 2 As shown, it can be seen that the vanadium barrier performance of the diaphragm prepared in Example 1 is significantly better than that of the blank diaphragm in Comparative Example 3.

[0070] Vanadium battery performance test: The diaphragms obtained in Examples 1-5 and Comparative Examples 1-3 were assembled into vanadium battery stacks, and charge and discharge cycle tests were performed under the same operating conditions. The battery efficiency and capacity retention rate after 100 cycles are summarized in Table 1.

[0071] Table 1 Summary of vanadium battery stack results

[0072]

[0073] The battery test results are shown in Table 1. It can be seen that compared with Comparative Examples 1 and 3, Examples 1-5 have higher coulombic efficiency, energy efficiency, voltage efficiency and capacity retention rate, indicating that by loading thiazolidinone substances onto the diaphragm, the thiazole ring and ketone group present in the thiazolidinone substances can enhance the diaphragm's repulsion to vanadium ions, thereby reducing the transmembrane diffusion of vanadium ions, reducing the cross-contamination of the positive and negative electrolytes of the all-vanadium liquid flow battery, and improving the battery's coulombic efficiency, energy efficiency and capacity retention rate. At the same time, by regulating the concentration, immersion time and immersion temperature of the immersion solution, it is also possible to accurately control the number of modified groups on the diaphragm, which not only makes the diaphragm more universal, but also enables the diaphragm's vanadium resistance and proton transport to reach an optimal balance, thereby improving the battery's voltage efficiency. Compared with Comparative Examples 2 and 3, Examples 1-5 have higher coulombic efficiency, energy efficiency, voltage efficiency and capacity retention rate, indicating that the cyanide substances in the present invention are cross-linked in the presence of thiazolidinone substances and under the action of a cross-linking agent to form a polymer compound containing thiazolidinone substances, and the thiazolidinone substances are removed from the polymer compound by further elution to form a molecular imprinting material of the thiazolidinone substances, and in the subsequent film making process, the molecular imprinting material is evenly distributed on the diaphragm. Before use, the diaphragm is immersed in a solution of thiazolidinone substances to complete the modification of the diaphragm, thereby increasing the uniformity of the distribution of thiazole rings and keto groups on the diaphragm, and further improving the coulombic efficiency, energy efficiency and capacity retention rate of the battery; the -CN group present after the cross-linking of the cyanide substances can be hydrolyzed into amides or carboxylic acids during the use of the diaphragm, thereby promoting the transmission of protons and improving the voltage efficiency of the battery.

[0074] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modification, equivalent substitution or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a modified diaphragm for an all-vanadium redox flow battery, characterized in that: The steps include: S1, dissolving a thiazolidinone substance and an olefin cyanide substance in an organic solvent to obtain a precursor solution; dissolving a cross-linking agent in an organic solvent to obtain a cross-linking agent solution; S2. Under ice bath stirring conditions, add 1 volume part of the cross-linking agent solution dropwise to 10-50 volume parts of the precursor solution at a rate of 1-5 mL / min, ultrasonicate for 20-60 min under the protection of an inert gas, let stand for 5-20 h after the ultrasonicate is completed, filter, wash the precipitate with an eluent, and vacuum dry to obtain a modifier; S3, uniformly dispersing the polymer resin, the modifier, and the surfactant in the membrane solvent to obtain a membrane-making solution; S4, evenly coating the membrane-making solution on a flat plate, and vacuum drying to obtain a pre-modified membrane; S5. Soak the pre-modified membrane in a thiazolidinone substance solution, control the concentration, soaking temperature and soaking time of the thiazolidinone substance solution, take out and dry after soaking, and obtain a modified diaphragm for all-vanadium liquid flow battery.

2. The method for preparing a modified diaphragm for an all-vanadium redox flow battery according to claim 1, characterized in that: In step S1, the thiazolidinone substance is one of 2-mercapto-5-thiazolidinone, 2-thiazolidinone, 2,4-thiazolidinedione, and 3-ethyl-2-thio-4-thiazolidinedione; and the concentration of the thiazolidinone substance in the precursor solution is 0.01-0.1 mol / L.

3. The method for preparing a modified diaphragm for an all-vanadium redox flow battery according to claim 1, characterized in that: In step S1, the olefin cyanide substance is a type of substance in which the olefin double bond is located at the end of the carbon chain, specifically one of 4-pentenenitrile, 5-hexenenitrile, 2-chloroacrylonitrile, and 3-hydroxypent-4-enenitrile; the concentration of the olefin cyanide substance in the precursor solution is 0.2~0.5mol / L.

4. The method for preparing a modified diaphragm for an all-vanadium redox flow battery according to claim 1, characterized in that: In step S1, the organic solvent is one of dimethyl sulfoxide, acetone, and N,N-dimethylformamide.

5. The method for preparing a modified diaphragm for an all-vanadium redox flow battery according to claim 1, characterized in that: In step S1, the crosslinking agent is one of divinylbenzene and ethylene glycol dimethacrylate; the concentration of the crosslinking agent in the crosslinking agent solution is 0.1-1 mol / L.

6. The method for preparing a modified diaphragm for an all-vanadium redox flow battery according to claim 1, characterized in that: In step S2, the inert gas is argon.

7. The method for preparing a modified diaphragm for an all-vanadium redox flow battery according to claim 1, characterized in that: In step S2, the eluent is one of methanol, ethanol and acetone.

8. The method for preparing a modified diaphragm for an all-vanadium redox flow battery according to claim 1, characterized in that: In step S3, the mass ratio of polymer resin: modifier: surfactant: membrane solvent is (30~100):1:(0.01~0.1):(500~1500).

9. The method for preparing a modified diaphragm for an all-vanadium redox flow battery according to claim 1, characterized in that: In step S3, the polymer resin is one of perfluorosulfonic acid resin and sulfonated polyetheretherketone resin, the surfactant is one of benzalkonium chloride, benzalkonium chloride and benzalkonium bromide, and the membrane solvent is one of N,N-dimethylformamide, N-methylpyrrolidone and N,N-dimethylacetamide.

10. The method for preparing a modified diaphragm for an all-vanadium redox flow battery according to claim 1, characterized in that: The concentration of the thiazolidinone substance solution in step S5 is 1-20 mmol / L, the soaking temperature is 5-20° C., and the soaking time is 1-20 min. The thiazolidinone substance in the thiazolidinone substance solution is the same compound as the thiazolidinone substance in the precursor solution in step S1.

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