CN102453262B - Electrolyte diaphragm for vanadium cell and preparation method thereof - Google Patents

Abstract

The invention discloses an electrolyte diaphragm for a vanadium battery and a preparation method thereof. The method comprises the following steps: 1) immersing the porous polytetrafluoroethylene membrane in a mixed solution composed of methanol and water to obtain mixed solution I; 2) mixing the mixed solution composed of methanol and tetraethyl orthosilicate with the mixture obtained in step 1). The mixed liquid I is mixed and reacted. After the reaction, the obtained porous polytetrafluoroethylene membrane is taken out, vacuum-dried and soaked in a proton-conducting polymer solution to obtain the electrolyte diaphragm for the vanadium battery. The electrolyte membrane for vanadium batteries provided by the invention reduces the consumption of expensive proton-conducting polymers on the whole, that is, reduces the cost of the electrolyte membrane; the addition of nano-silica can effectively control the pore structure of the ion membrane, Reducing the permeation of vanadium ions is beneficial to the maintenance of battery capacity.

Description

Electrolyte diaphragm for vanadium battery and preparation method thereof

technical field

The invention belongs to the technical field of vanadium batteries, in particular to an electrolyte diaphragm for a vanadium battery and a preparation method thereof.

Background technique

The use of renewable energy for power generation is a sustainable development path. Due to the unstable characteristics of the power generation system, large-scale energy storage devices are required to improve the quality of electric energy. All-vanadium redox flow battery has the characteristics of high efficiency, low cost, long life, adjustable capacity and power, and convenient operation. It is a relatively mature large-scale energy storage technology.

Among the various components of the all-vanadium redox flow battery, the electrolyte separator plays the role of separating the positive and negative electrolytes and conducting the ionic current inside the battery, and is one of the most critical materials. At present, in the field of vanadium batteries, commonly used ion separators mainly include DuPont's Nafion series of cation membranes and Asahi Glass's Selemion series of anion membranes. These separators have high ion conductivity, long life, and good chemical and electrochemical stability, but they are expensive and have poor barrier properties to vanadium ions, which affects the cycle capacity of the battery.

my country has not yet commercially produced ion separators suitable for vanadium batteries, and can only rely on imports. However, commercial separators still face a major problem, that is, the penetration of vanadium ions. In actual use, the diaphragm cannot completely prevent the penetration of vanadium ions in the positive and negative electrolytic cells, so that the vanadium ions in the positive and negative electrolytic cells penetrate each other, resulting in a decrease in battery capacity; at the same time, the migration of vanadium ions in the diaphragm will also drive water The migration of molecules will cause the water imbalance of the positive and negative electrolytes, resulting in changes in the concentration of the electrolyte, which may cause unstable precipitation of the electrolyte and affect the battery life.

Contents of the invention

The object of the present invention is to provide an electrolyte diaphragm for a vanadium battery and a preparation method thereof.

The method for preparing the electrolyte membrane for vanadium batteries provided by the invention comprises the following steps:

1) Soak the porous polytetrafluoroethylene membrane in a mixed solution composed of methanol and water to obtain a mixed solution I;

2) mixing the mixed solution composed of methanol and tetraethyl orthosilicate with the mixed solution I obtained in step 1) for reaction, taking out the obtained porous polytetrafluoroethylene membrane after the reaction, vacuum drying and soaking in the proton conductive polymer solution, The electrolyte separator for the vanadium battery is obtained.

In step 1) of the above method, the thickness of the porous polytetrafluoroethylene membrane is 0.05-0.5mm, preferably 0.1-0.2mm, the porosity is 50-90%, preferably 70-80%, and the pore diameter is 20-500nm, Preferably 100-200nm, the number average molecular weight is 100,000-300,000, preferably 200,000; in the mixed solution composed of methanol and water, the volume ratio of methanol and water is 1-10:1, preferably 1- 5:1; the mass ratio of the porous polytetrafluoroethylene membrane to the mixed solution composed of methanol and water is 1:100-1000, preferably 1:500-700; in the soaking step, the temperature is 0-50°C , preferably at 25°C, for 10-24 hours, preferably 12-16 hours.

In this step, the commercially produced porous polytetrafluoroethylene membrane is selected as the basic membrane structure material. On the one hand, the production and manufacturing costs of the membrane can be greatly reduced. At the same time, the polytetrafluoroethylene membrane has excellent chemical stability. And electrochemical stability, it can be well adapted to the operating environment of vanadium batteries, and can maintain long-term stability in strong acid and strong oxidizing media. The porous polytetrafluoroethylene membrane is soaked in the mixed solution of methanol and water, so that the methanol solution can be adsorbed in the holes of the polytetrafluoroethylene, so that the hydrolysis reaction of tetraethyl orthosilicate in the next step can be Occurs in the pores of tetrafluoroethylene, and generates nano-silica on the walls of the pores.

In the step 2), in the proton conductive polymer solution, the solute is selected from perfluorosulfonic acid, sulfonated polyethersulfone, sulfonated polyimide, sulfonated polyetheretherketone and modified polybenzimidazole At least one of them, (the number average molecular weight is between 50,000 and 100,000, preferably 60,000), preferably perfluorosulfonic acid, and the solvent is selected from at least one of methanol, ethanol, dimethylformamide and methylpyrrolidone, preferably Dimethylformamide; in the mixed solution composed of methanol and ethyl orthosilicate, the molar ratio of methanol to ethyl orthosilicate is 2-10:1, preferably 3-6:1; the proton conductive polymerization The mass percent concentration of the product solution is 1-10%, preferably 2-5%; in the vacuum drying step, the temperature is 50-80°C, preferably 70°C, the time is 10-20 hours, preferably 12 hours, and the pressure is 0.02- 0.08MPa, preferably 0.05MPa; in the reaction step, the temperature is 0-30°C, preferably 10-20°C, and the time is 3-30 minutes, specifically 3-15 minutes or 15-30 minutes, preferably 10-20 minutes; In the soaking step, the temperature is 0-40°C, specifically 0-20°C or 20-40°C, preferably 25°C, and the time is 5-30 minutes, specifically 5-30 minutes, 5-10 minutes or 10-30 minutes, preferably 15 minutes.

In this step, described reaction is the hydrolysis reaction of orthoethyl silicate (TEOS), and its reaction equation is as follows:

(Si(OC ₂ H ₅ ) ₄ +xH ₂ O ＝Si(OH) _x (OC ₂ H ₅ ) _nx +x C ₂ H ₅ OH(1≤x≤4))

The nano-scale silicon dioxide produced in porous PTFE enhances the mechanical properties of the porous PTFE membrane, changing from the original soft and deformable membrane to a self-supporting membrane, which is more convenient for battery assembly; Silicon oxide exhibits a certain ion conductivity in the aqueous solution system; at the same time, it is an inorganic material with very stable chemical properties, similar to polytetrafluoroethylene materials, and can be stable for a long time in the operating environment of vanadium batteries. exist.

The nano-silica generated on the pore wall of porous PTFE can further reduce the pore size of the porous PTFE membrane. It is selective and effectively inhibits the migration of vanadium ions; at the same time, the silicon dioxide generated on the porous PTFE membrane hole wall changes the hydrophobicity of the initial PTFE membrane, making the PTFE membrane composed of The transition from the hygroscopic membrane to the hydrophilic membrane is more conducive to the loading of the polymer proton membrane in the next step.

The final loaded proton conductive polymer is selectively filled in the pores of the silica, rather than on the surface of the PTFE membrane, because in the second step, the nano-silica is grown on the porous PTFE membrane. In the pores of ethylene, rather than on the surface of the membrane, the hydrophilic property in the pores is much better than that of the surface of the membrane. Therefore, the hydrophilic ion-conducting polymer is more convenient to form in the pores of the membrane. The proton conductive polymer can further improve the proton conductivity of the membrane, and at the same time, the usage amount of the proton conductive polymer is greatly reduced, and it is only used in the effective point of the ion conductor, and the manufacturing cost of the whole membrane is greatly reduced.

The electrolyte separator for vanadium batteries prepared by the above method also belongs to the protection scope of the present invention.

The present invention takes the porous polytetrafluoroethylene membrane as the basic skeleton, utilizes its unique chemical and electrochemical stability to form the basic framework of the electrolyte membrane, and then fills the pores of the porous polytetrafluoroethylene with nano-silica, and its effect makes PTFE changed from a hydrophobic film to a hydrophilic film, which also improved the pore structure of the porous PTFE, making it more orderly and regular; then the porous PTFE filled with nano-silica On the membrane of ethylene, a polymer with proton conductivity is loaded, forming an organic and inorganic composite ion-conducting membrane. The matching of porous polytetrafluoroethylene membrane and nano-silica enhances the mechanical properties of the base membrane, and can artificially control the pore structure, so that hydrogen ions and vanadium ions in the vanadium battery electrolyte can pass through selectively; at the same time, the two The addition of silicon oxide improves the hydrophilic property of the porous polytetrafluoroethylene membrane, so that the polymer ion conductor can be effectively incorporated into the matrix membrane. Since the basic materials constituting the ion conductor membrane have good chemical stability and electrochemical stability, it can ensure its long-term stable operation in the vanadium battery.

The electrolyte membrane for vanadium batteries provided by the invention reduces the consumption of expensive proton-conducting polymers on the whole, that is, reduces the cost of the electrolyte membrane; the addition of nano-silica can effectively control the pore structure of the ion membrane, Reducing the permeation of vanadium ions is beneficial to the maintenance of battery capacity.

Description of drawings

Figure 1 is the contrast curve of permeability between Nafion membrane and PTFE/SiO ₂ /Nafion composite membrane.

Fig. 2 is the permeability comparison curve of PTFE/SiO ₂ /Nafion composite membrane, PTFE/SiO ₂ /SPEEK composite membrane and PTFE/SiO ₂ /OPBI composite membrane.

Detailed ways

The present invention will be further described below in conjunction with specific examples, but the present invention is not limited to the following examples. The methods described in the following examples are conventional methods unless otherwise specified. The Nafion solution used in the following examples was purchased from DuPont, USA, wherein the solute was perfluorosulfonic acid resin, the product number was DE-421, and the solvent was ethanol. The porous polytetrafluoroethylene membrane used in the following examples was purchased from Shanghai Dagong New Material Co., Ltd.

Example 1

1) 0.5 g of a porous polytetrafluoroethylene film with a thickness of 0.05 mm, a porosity of 50%, a pore diameter of 20 nm, and a number average molecular weight of 200,000 is immersed in 50 g of a solution with a volume ratio of methanol and water of 1:1, Stir and soak at 0°C for 10 hours to obtain a mixed solution I.

2) Pour the mixed solution of methanol and ethyl orthosilicate in the molar ratio of 2:1 into the above mixed solution I at 0°C, continue to stir, take the film out of the solution after 10 minutes, and dry it naturally Vacuum dry at 50° C. under a pressure of 0.02 MPa for 10 hours. Then, put the obtained porous polytetrafluoroethylene membrane into a Nafion solution with a mass percent concentration of 1%, soak it for 5 minutes at 0°C, take it out and dry it in the air to obtain a PTFE/SiO ₂ /Nafion composite membrane, which is the present invention Provided is an electrolyte separator for a vanadium battery.

Figure 1 is a comparison of the permeability of VOSO ₄ in the untreated Nafion117 membrane and the PTFE/SiO ₂ /SPEEK composite membrane. From the calculation results, the permeability in the composite membrane is nearly 25 times lower than that in the Nafion117 membrane .

Example 2

1) 0.5 g of a porous polytetrafluoroethylene membrane with a thickness of 0.5 mm, a porosity of 90%, a pore diameter of 500 nm, and a number average molecular weight of 200,000 is immersed in 500 g of a solution with a volume ratio of methanol and water of 10:1, Stir and soak at 50° C. for 24 hours to obtain a mixed solution I.

2) Pour the mixed solution of methanol and ethyl orthosilicate in a molar ratio of 10:1 into the above mixed solution I at 30°C, continue to stir, take the film out of the solution after 30 minutes, and dry it naturally Vacuum dry at 80° C. under a pressure of 0.08 MPa for 20 hours. Next, put the obtained porous polytetrafluoroethylene membrane into a Nafion solution with a mass percent concentration of 10%, soak it for 30 minutes at 40°C, take it out and dry it in the air to obtain a PTFE/SiO ₂ /Nafion composite membrane, which is the present invention Provided is an electrolyte separator for a vanadium battery.

Example 3

1) 0.5 g of a porous polytetrafluoroethylene film with a thickness of 0.1 mm, a porosity of 70%, a pore diameter of 100 nm, and a number average molecular weight of 200,000 is immersed in 250 g of a solution with a volume ratio of methanol and water of 5: 1, Stir and soak at 25°C for 15 hours to obtain a mixed solution I.

2) Pour the mixed solution of methanol and ethyl orthosilicate in a molar ratio of 3:1 into the above mixed solution I at 20°C, continue to stir, take the film out of the solution after 15 minutes, and dry it naturally Vacuum dry at 70° C. and 0.05 MPa pressure for 10 hours. Next, put the obtained porous polytetrafluoroethylene membrane into a Nafion solution with a mass percent concentration of 5%, soak it for 10 minutes at 20°C, take it out and dry it in the air to obtain a PTFE/SiO ₂ /Nafion composite membrane, which is the present invention. Provided is an electrolyte separator for a vanadium battery.

Example 4

1) 0.5 g of a porous polytetrafluoroethylene film with a thickness of 0.05 mm, a porosity of 50%, a pore diameter of 20 nm, and a number average molecular weight of 200,000 is immersed in 50 g of a solution with a volume ratio of methanol and water of 1:1, Stir and soak at 0°C for 10 hours to obtain a mixed solution I.

2) Pour the mixed solution of methanol and ethyl orthosilicate in the molar ratio of 2:1 into the above mixed solution I at 0°C, continue to stir, take the film out of the solution after 10 minutes, and dry it naturally Vacuum dry at 50° C. under a pressure of 0.02 MPa for 10 hours. Then, put the obtained porous polytetrafluoroethylene membrane into a sulfonated polyetheretherketone (SPEEK) (number average molecular weight 50000) solution (solvent is dimethylformamide) with a mass percent concentration of 1% at 0 Soak for 5 minutes at ℃, take it out and dry it in the air to obtain a PTFE/SiO ₂ /SPEEK composite membrane, which is the electrolyte separator for a vanadium battery provided by the present invention.

Example 5

1) 0.5 g of a porous polytetrafluoroethylene membrane with a thickness of 0.5 mm, a porosity of 90%, a pore diameter of 500 nm, and a number average molecular weight of 200,000 is immersed in 500 g of a solution with a volume ratio of methanol and water of 10:1, Stir and soak at 50° C. for 24 hours to obtain a mixed solution I.

2) Pour the mixed solution of methanol and ethyl orthosilicate in a molar ratio of 10:1 into the above mixed solution I at 30°C, continue to stir, take the film out of the solution after 30 minutes, and dry it naturally Vacuum dry at 80° C. under a pressure of 0.08 MPa for 20 hours. Then, put the obtained porous polytetrafluoroethylene membrane into a sulfonated polyetheretherketone (SPEEK (number-average molecular weight: 100,000)) solution (solvent is dimethylformamide) with a concentration of 10% by mass at 40 Soak for 30 minutes at ℃, take it out and dry it in the air to obtain a PTFE/SiO ₂ /SPEEK composite membrane, which is the electrolyte diaphragm for a vanadium battery provided by the present invention.

Example 6

1) 0.5 g of a porous polytetrafluoroethylene film with a thickness of 0.1 mm, a porosity of 70%, a pore diameter of 100 nm, and a number average molecular weight of 200,000 is immersed in 250 g of a solution with a volume ratio of methanol and water of 5: 1, Stir and soak at 25°C for 15 hours to obtain a mixed solution I.

2) Pour the mixed solution of methanol and ethyl orthosilicate in a molar ratio of 3:1 into the above mixed solution I at 20°C, continue to stir, take the film out of the solution after 15 minutes, and dry it naturally Vacuum dry at 70° C. and 0.05 MPa pressure for 10 hours. Then, put the obtained porous polytetrafluoroethylene membrane into a sulfonated polyether ether ketone (SPEEK (number average molecular weight: 60,000)) solution (solvent is dimethylformamide) with a mass percent concentration of 5% at 20 Soak for 10 minutes at ℃, take it out and dry it in the air to obtain a PTFE/SiO ₂ /SPEEK composite membrane, which is the electrolyte separator for vanadium battery provided by the present invention.

Example 7

1) 0.5 g of a porous polytetrafluoroethylene film with a thickness of 0.05 mm, a porosity of 50%, a pore diameter of 20 nm, and a number average molecular weight of 200,000 is immersed in 50 g of a solution with a volume ratio of methanol and water of 1:1, Stir and soak at 0°C for 10 hours to obtain a mixed solution I.

2) Pour the mixed solution of methanol and ethyl orthosilicate in the molar ratio of 2:1 into the above mixed solution I at 0°C, continue to stir, take the film out of the solution after 10 minutes, and dry it naturally Vacuum dry at 50° C. under a pressure of 0.02 MPa for 10 hours. Then, put the obtained porous polytetrafluoroethylene membrane into the modified polybenzimidazole (OPBI (number average molecular weight 50000)) solution (solvent is methylpyrrolidone) with a mass percent concentration of 1% and soak at 0 ° C. After 5 minutes, take it out and dry it in the air to obtain a PTFE/SiO ₂ /OPBI composite membrane, which is the electrolyte diaphragm for a vanadium battery provided by the present invention.

Example 8

1) 0.5 g of a porous polytetrafluoroethylene membrane with a thickness of 0.5 mm, a porosity of 90%, a pore diameter of 500 nm, and a number average molecular weight of 200,000 is immersed in 500 g of a solution with a volume ratio of methanol and water of 10:1, Stir and soak at 50° C. for 24 hours to obtain a mixed solution I.

2) Pour the mixed solution of methanol and ethyl orthosilicate in a molar ratio of 10:1 into the above mixed solution I at 30°C, continue to stir, take the film out of the solution after 30 minutes, and dry it naturally Vacuum dry at 80° C. under a pressure of 0.08 MPa for 20 hours. Then, put the obtained porous polytetrafluoroethylene membrane into the modified polybenzimidazole (OPBI (number average molecular weight 100000)) solution (solvent is methylpyrrolidone) with a mass percent concentration of 10% and soak at 40 ° C. After 30 minutes, take it out and dry it in the air to obtain a PTFE/SiO ₂ /OPBI composite membrane, which is the electrolyte diaphragm for a vanadium battery provided by the present invention.

Example 9

1) 0.5 g of a porous polytetrafluoroethylene film with a thickness of 0.1 mm, a porosity of 70%, a pore diameter of 100 nm, and a number average molecular weight of 200,000 is immersed in 250 g of a solution with a volume ratio of methanol and water of 5: 1, Stir and soak at 25°C for 15 hours to obtain a mixed solution I.

2) Pour the mixed solution of methanol and ethyl orthosilicate in a molar ratio of 3:1 into the above mixed solution I at 20°C, continue to stir, and take the film out of the solution after reacting for 15 minutes, and let it dry naturally Afterwards, vacuum-dry at 70° C. and a pressure of 0.05 MPa for 10 hours. Then, put the obtained porous polytetrafluoroethylene membrane into the modified polybenzimidazole (OPBI (number average molecular weight 60000)) solution (solvent is methylpyrrolidone) with a mass percent concentration of 5% and soak at 20 ° C. After 10 minutes, take it out and dry it in the air to obtain a PTFE/SiO ₂ /OPBI composite membrane, which is the electrolyte diaphragm for a vanadium battery provided by the present invention.

Figure 2 is a comparison of the permeability of VOSO ₄ in PTFE/SiO ₂ /Nafion composite membrane, PTFE/SiO ₂ /SPEEK composite membrane, PTFE/SiO ₂ /OPBI composite membrane, in which vanadium ions are in PTFE/SiO ₂ /SPEEK composite membrane The medium permeability is one time lower than that in PTFE/SiO ₂ /Nafion composite membrane, but there is basically no permeability in PTFE/SiO ₂ /OPBI composite membrane.

Claims (14)

1. one kind prepares vanadium cell with the membranous method of ionogen, comprises the steps:

1) voided polytetrafluoroethylene film is soaked in the mixed solution of being made up of methyl alcohol and water, obtains mixed liquor I; The thickness of described voided polytetrafluoroethylene film is 0.05-0.5mm, and porosity is 50-90%, and the aperture is 20-500nm;

2) will react by mixed solution and the step 1) gained mixed liquor I mixing that methyl alcohol and tetraethoxy are formed, after finishing, reaction takes out the gained voided polytetrafluoroethylene film, be soaked in after the vacuum-drying in the proton conductive polymer solution, obtain described vanadium cell electrolyte membrance.

2. method according to claim 1 is characterized in that: in the described step 1), the number-average molecular weight of described voided polytetrafluoroethylene film is 100,000 to 300,000, and thickness is 0.1-0.2mm, and porosity is 70-80%, and the aperture is 100-200nm; In the described mixed solution of being made up of the first alcohol and water, the volume ratio of described first alcohol and water is 1～10:1; The mass ratio of described voided polytetrafluoroethylene film and the described mixed solution of being made up of methyl alcohol and water is 1:100-1000.

3. method according to claim 2 is characterized in that: in the described step 1), the number-average molecular weight of described voided polytetrafluoroethylene film is 200,000; In the described mixed solution of being made up of the first alcohol and water, the volume ratio of described first alcohol and water is 1-5:1; The mass ratio of described voided polytetrafluoroethylene film and the described mixed solution of being made up of methyl alcohol and water is 1:500-700.

4. according to claim 1 or 2 or 3 described methods, it is characterized in that: in the described step 1) soaking step, temperature is 0-50 ℃, and the time is 10-24 hour.

5. method according to claim 4 is characterized in that: in the described step 1) soaking step, temperature is 25 ℃, and the time is 12-16 hour.

6. according to claim 1 or 2 or 3 described methods, it is characterized in that: described step 2), in the described proton conductive polymer solution, solute is selected from least a in perfluorinated sulfonic acid, sulfonated polyether sulfone, sulfonated polyimide, sulfonated polyether-ether-ketone and modified polyphenyl and the imidazoles; Solvent is selected from least a in methyl alcohol, ethanol, dimethyl formamide and the methyl-2-pyrrolidone.

7. method according to claim 6, it is characterized in that: described step 2), the number-average molecular weight of described sulfonated polyether sulfone is 50000-100000, the number-average molecular weight of described sulfonated polyimide is 50000-100000, the number-average molecular weight of described sulfonated polyether-ether-ketone is 50000-100000, and the number-average molecular weight of described modified polyphenyl and imidazoles is 50000-100000.

8. according to claim 1 or 2 or 3 described methods, it is characterized in that: described step 2), in the described mixed solution of being made up of methyl alcohol and tetraethoxy, the mol ratio of methyl alcohol and tetraethoxy is 2～10:1; The mass percentage concentration of described proton conductive polymer solution is 1-10%.

9. method according to claim 8 is characterized in that: described step 2), in the described mixed solution of being made up of methyl alcohol and tetraethoxy, the mol ratio of methyl alcohol and tetraethoxy is 3-6:1; The mass percentage concentration of described proton conductive polymer solution is 2-5%.

10. according to claim 1 or 2 or 3 described methods, it is characterized in that: described step 2) in the vacuum drying step, temperature is 50～80 ℃, and the time is 10-20 hour, and pressure is 0.02-0.08MPa.

11. method according to claim 10 is characterized in that: described step 2) in the vacuum drying step, temperature is 70 ℃, and the time is 12 hours, and pressure is 0.05MPa.

12. according to claim 1 or 2 or 3 described methods, it is characterized in that: described step 2) in the reactions steps, temperature is 0～30 ℃, and the time is 3～30 minutes; In the described soaking step, temperature is 0-40 ℃, and the time is 3-30 minute.

13. method according to claim 12 is characterized in that: described step 2) in the reactions steps, temperature is 10-20 ℃, and the time is 10-20 minute; In the described soaking step, temperature is 25 ℃, and the time is 10-20 minute.

14. the arbitrary described method of claim 1-13 prepares gained vanadium cell electrolyte membrance.