Submicron ultra-thin self-supporting ion-conducting membrane, and preparation method therefor and use thereof

Abstract

Disclosed in the present application are a submicron ultra-thin self-supporting ion-conducting membrane, and a preparation method therefor and the use thereof. The ion-conducting membrane is obtained by reacting an organic polymer resin with a cross-linking agent, and has a fully cross-linked structure; and there is no interface impedance between a separation layer and a support layer. The organic polymer resin is selected from polybenzimidazole polymers; and the cross-linking agent is selected from 4,4'-bis(chloromethyl)biphenyl and / or p-chloromethylbenzene. A reaction and diffusionless phase transformation method is used, and a portion that is not cross-linked or has a low degree of cross-linking is dissolved after the reaction, so as to prepare a submicron-sized ion-conducting membrane for flow batteries. A cross-linking reaction results in a more tightly packed polymer structure and a reduced membrane pore size, thereby mitigating the crossover of active materials in a flow battery and improving the coulombic efficiency of the battery; moreover, the reduced thickness of the membrane can effectively shorten the transport path of ions in the membrane, thereby improving the voltage efficiency of the battery.

Description

Sub-micron ultra-thin self-supporting ion-conducting membrane, preparation method and application thereof TECHNICAL FIELD

[0001] The present application relates to a sub-micron ultra-thin self-supporting ion-conducting membrane, preparation method and application thereof, and belongs to the field of ion-conducting membrane materials. BACKGROUND

[0002] At present, clean energy represented by solar energy and wind energy is developing rapidly, but its intermittency and instability limit its further application. Large-scale energy storage technology can solve the above problems to a certain extent, and among many energy storage technologies, aqueous flow battery is considered to be one of the most promising energy storage technologies due to its advantages of independent design of power density and storage capacity, high safety, etc.

[0003] As one of the key materials of the flow battery, the performance and cost of the ion-conducting membrane significantly affect the overall performance and cost of the battery. The main role of the ion-conducting membrane is to block the positive and negative active materials and conduct carriers to form a closed loop for the battery. The ideal ion-conducting membrane should have high ion selectivity, high ion conductivity, high chemical stability, high mechanical stability, and low manufacturing cost, etc. Traditional ion-conducting membranes include ion exchange membranes and porous ion-conducting membranes. Ion exchange membranes conduct ions through ion exchange groups. In order to have high ion selectivity, the membrane requires more ion exchange groups, which will make the membrane have high swelling rate and low chemical stability. Porous membranes do not contain ion exchange groups and have higher stability than ion exchange membranes. However, in order to improve its ion selectivity, the membrane requires a more dense structure, which will lower its ion conductivity. In summary, both of them are difficult to break the trade-off effect between ion selectivity and conductivity. Preparing an ion-conducting membrane with high ion selectivity and high ion conductivity is of great significance for the further application of the flow battery. Composite membranes are composed of two parts, the separation layer and the support layer, which can be independently controlled. However, there are usually problems such as large interface impedance between the two parts, poor combination between the separation layer and the support layer, easy separation of the separation layer, etc.

[0004] Reducing the thickness of the ion-conducting membrane is an effective method to improve the ion conductivity. Reducing the thickness of the membrane can effectively shorten the transmission path of ions in the membrane and thus improve the ion conductivity. However, in general, reducing the thickness of the membrane will greatly reduce the mechanical properties of the membrane. Therefore, it is of great significance to develop an ion-conducting membrane that can improve the ion conductivity without sacrificing the ion selectivity and has high mechanical properties to meet the use requirements of the flow battery. SUMMARY

[0005] The application aims to provide a sub-micron self-supporting ion-conducting membrane and a preparation method thereof, and application thereof in the fields of all-vanadium redox flow batteries, alkaline zinc-iron redox flow batteries and the like. The self-supporting membrane is prepared by a reaction-non-diffusion phase inversion method, and then the unreacted or less-reacted part is dissolved. The prepared membrane has a low thickness, can shorten the ion transmission path to improve the ion conductivity, and can make the membrane structure more compact by using a cross-linking reaction, and improve the mechanical properties of the ultra-thin membrane to meet the use requirements of the redox flow battery. The all-vanadium redox flow battery and the alkaline zinc-iron redox flow battery assembled using the membrane have high battery performance and cycle stability.

[0006] According to one aspect of the application, a sub-micron ultra-thin self-supporting ion-conducting membrane is provided, which is obtained by cross-linking reaction of polybenzimidazole and a cross-linking agent, has a full cross-linking structure, and has no interface impedance between a separation layer and a support layer.

[0007] The cross-linking agent is selected from 4,4'-bis(chloromethyl) biphenyl (CM) and / or p-chloromethyl benzene.

[0008] The thickness of the sub-micron ultra-thin self-supporting ion-conducting membrane is 0.3-11 μm.

[0009] Optionally, the thickness of the sub-micron ultra-thin self-supporting ion-conducting membrane is 0.5-11 μm.

[0010] According to another aspect of the application, a preparation method of a sub-micron ultra-thin self-supporting ion-conducting membrane is provided, which adopts a reaction-non-diffusion phase inversion method, and the unreacted or less-reacted part is dissolved after reaction to obtain a sub-micron ion-conducting membrane for a redox flow battery.

[0011] The method comprises the following steps:

[0012] The solution I containing the organic high molecular resin and the solvent A is coated on a substrate, and then the whole is immersed in the solution II containing the cross-linking agent and the solvent B, and after reaction, the cross-linked membrane is obtained by placing in water, and then the sub-micron ultra-thin self-supporting ion-conducting membrane is obtained by sequentially immersing in the solvent A and the solvent C.

[0013] The organic high molecular resin is selected from polybenzimidazole.

[0014] The cross-linking agent is selected from 4,4'-bis(chloromethyl) biphenyl (CM) and / or p-chloromethyl benzene.

[0015] The solvent A is a polar organic solvent, and is at least one selected from dimethyl sulfoxide (DMSO), N,N-dimethylacetamide (DMAc), N-methyl pyrrolidone (NMP), N,N-dimethylformamide (DMF) and tetrahydrofuran (THF).

[0016] The solvent B is selected from at least one of n-pentane, n-heptane, n-hexane, n-decane, cyclohexane;

[0017] The solvent C is selected from at least one of water, ethanol, isopropanol, acetone, flow battery electrolyte.

[0018] The content of the organic polymer resin in the solution I containing the organic polymer resin and the solvent A is 8-20wt%;

[0019] Optionally, the content of the organic polymer resin in the solution I containing the organic polymer resin and the solvent A is any value of 8wt%, 10wt%, 12wt%, 14wt%, 15wt%, 16wt%, 18wt%, 20wt% or a range value between any two of them.

[0020] The content of the crosslinking agent in the solution II containing the crosslinking agent and the solvent B is 0.5-2g / L.

[0021] Optionally, the content of the crosslinking agent in the solution II containing the crosslinking agent and the solvent B is any value of 0.5g / L, 1g / L, 1.5g / L, 2g / L or a range value between any two of them.

[0022] The reaction time is 30-60min.

[0023] Optionally, the reaction time is any value of 30min, 40min, 50min, 60min or a range value between any two of them.

[0024] The coating method includes blade coating, spin coating, casting or spraying, preferably blade coating.

[0025] The coating thickness is 10-50μm.

[0026] Optionally, the blade coating thickness is any value of 10μm, 20μm, 30μm, 40μm, 50μm or a range value between any two of them.

[0027] Optionally, the following steps are included:

[0028] (1) Dissolve the organic polymer resin in the solvent A, and fully stir at a temperature of 20-40℃ for 12-24h to obtain a uniform polymer solution, and then stand the polymer solution for 12-48h to remove bubbles, wherein the solid content of the organic polymer resin is 8-20wt%;

[0029] (2) Dissolve the crosslinking agent in the solvent B, and fully stir or ultrasonically dissolve for 1-5h to form a uniform crosslinking agent solution, wherein the concentration of the crosslinking agent is 0.5-2g / L;

[0030] (3) The polymer solution prepared in step (1) is coated on a clean and flat glass sheet with a thickness of 10-50 μm, and the glass sheet is placed in the crosslinking agent solution obtained in step (2) for reaction for 30-60 min;

[0031] (4) The glass sheet in step (3) is taken out and placed in solvent C to obtain an ion-conducting membrane with a crosslinked structure.

[0032] (5) The crosslinked membrane prepared in step (4) is wiped dry;

[0033] (6) The crosslinked membrane in step (5) is placed in solvent A for immersion for 1-48 h;

[0034] (7) The membrane treated in step (6) is taken out and placed in solvent C to obtain a sub-micron self-supporting ion-conducting membrane.

[0035] According to another aspect of the present application, there is provided an application of the above-mentioned sub-micron ultra-thin self-supporting ion-conducting membrane to a full vanadium redox flow battery or an alkaline zinc-iron redox flow battery.

[0036] The full vanadium redox flow battery comprises a positive electrolyte and a negative electrolyte, the positive electrolyte is a VOSO4 and sulfuric acid aqueous solution, and the negative electrolyte is a V2(SO4)3 and sulfuric acid aqueous solution.

[0037] Optionally, the concentration of VOSO4 and V2(SO4)3 is between 0.5-1.65 mol / L, and the concentration of the sulfuric acid aqueous solution is between 1-5 mol / L.

[0038] Optionally, the positive electrolyte is 1.65 mol / L VOSO4 and 3 mol / L sulfuric acid aqueous solution, and the negative electrolyte is 1.65 mol / L V2(SO4)3 and 3 mol / L sulfuric acid aqueous solution.

[0039] The alkaline Zn-Fe redox flow battery also comprises a positive electrolyte and a negative electrolyte.

[0040] Optionally, the positive electrolyte comprises a ferric salt, a base and water, the ferric salt is selected from at least one of K2Fe(CN)6 and Na2Fe(CN)6, the concentration is between 0.2-1 mol / L, the base is selected from at least one of KOH, NaOH and Ca(OH)2, and the concentration is between 0.5-4 mol / L.

[0041] Optionally, the negative electrolyte comprises a zinc salt or zinc oxide, a base and water, the zinc salt or zinc oxide is at least one of ZnCl2, ZnBr2, ZnSO4, Zn(NO3)2 and ZnO, and the concentration is between 0.2 and 1 mol / L, the base is at least one of KOH, NaOH and Ca(OH)2, and the concentration is between 0.5 and 4 mol / L;

[0042] Optionally, the positive electrolyte is 0.8 mol / L of K2Fe(CN)6 and 3 mol / L of KOH, and the negative electrolyte is 0.4 mol / L of ZnO and 3.8 mol / L of NaOH.

[0043] The application can produce beneficial effects, including:

[0044] (1) The application adopts a reaction-non-diffusion phase inversion method, and the part not crosslinked or with low crosslinking degree is dissolved after the reaction, so that a sub-micron ion conductive membrane for a flow battery is prepared. The crosslinking reaction makes the polymer packing more compact, the membrane pore size is reduced, the mutual diffusion of active substances in the flow battery is slowed down, the coulombic efficiency of the battery is improved, and the reduced membrane thickness can effectively shorten the ion transmission path in the membrane, thereby improving the voltage efficiency of the battery;

[0045] (2) The crosslinking reaction adopted in the application can improve the mechanical properties and chemical stability of the membrane, meet the requirements of the working conditions of the flow battery, and make the battery have higher cycle stability;

[0046] (3) The membrane prepared in the application can realize effective control of the membrane pore size by selecting the crosslinking agent and changing the crosslinking time, and the performance of the battery can be controllably adjusted;

[0047] (4) The membrane prepared in the application has a simple preparation process, is environmentally friendly, and has a low cost;

[0048] (5) The membrane prepared in the application has a stable crosslinking structure and has the advantage of resisting organic solvents, can be used in organic solvents, and can further expand its application range;

[0049] (6) The application proposes a new membrane preparation method, which can change organic high molecular materials, crosslinking agent molecules and the like to obtain different types of membranes, and is applied to different flow battery systems, thereby expanding the types of membrane materials. BRIEF DESCRIPTION OF DRAWINGS

[0050] Fig. 1 is the membrane thickness and AFM diagram of the ion conductive membrane prepared in Example 1;

[0051] Fig. 2 is the membrane thickness and AFM diagram of the ion conductive membrane prepared in Example 2;

[0052] Figure 3 is a comparison of the area resistance of ion-conducting membranes prepared in Examples 1-2 and Comparative Examples 1-3 under acidic conditions;

[0053] Figure 4 is a comparison of the rate capability of a full vanadium redox flow battery equipped with ion-conducting membranes prepared in Examples 1-2 and Comparative Example 1;

[0054] Figure 5 is a comparison of the cycle performance of a full vanadium redox flow battery equipped with ion-conducting membranes prepared in Example 1 and Comparative Example 6;

[0055] Figure 6 is the rate capability of an alkaline zinc-iron redox flow battery equipped with ion-conducting membranes prepared in Examples 1-2;

[0056] Figure 7 is a comparison of the area resistance of ion-conducting membranes prepared in Examples 1-2 and Comparative Example 1 under alkaline conditions. DETAILED DESCRIPTION

[0057] The present application will be described in detail below with reference to examples, but the present application is not limited to these examples.

[0058] Unless otherwise specified, the raw materials in the examples of the present application are purchased through commercial channels.

[0059] The instrument used in the charge-discharge test system in the examples of the present application is Arbin BT2000.

[0060] Example 1

[0061] 3 g of polybenzimidazole was dissolved in 17 g of DMAc, and stirred at 25°C under conditions of less than 30% humidity for 12 h to make it fully dissolved, forming a polymer solution with a polybenzimidazole solid content of 15 wt%. 0.2 g of 4,4'-bis(chloromethyl) biphenyl (CM) was dissolved in 200 ml of n-heptane and ultrasonically treated for 30 min to make it fully dissolved, obtaining a crosslinking agent solution of 1 g / L. Under conditions of a temperature of 25°C and less than 20% humidity, the polymer solution was blade-coated on a smooth and clean glass sheet with a doctor blade thickness of 10 μm, and the polymer solution and glass sheet were quickly placed in 200 ml of n-heptane solution of CM, reacted for 30 min, and then quickly placed in water, obtaining a crosslinked membrane.

[0062] The obtained crosslinked membrane was wiped to remove surface moisture, placed in 20 ml of DMAc for one hour to make the uncrosslinked or less crosslinked parts of the polymer membrane fully dissolved, and then placed in water (such as 200 ml) to obtain a self-supporting crosslinked membrane.

[0063] Figure 1 is the membrane thickness and AFM image of the ion-conducting membrane prepared in Example 1; it can be seen that a 0.880 μm thick membrane with a dense full crosslinked structure was obtained.

[0064] A full vanadium redox flow battery was assembled using the prepared self- supporting crosslinked membrane, in which the electrode was carbon felt, the current collector was graphite plate, and the effective area of the membrane was 9 cm 2 The positive and negative electrolyte had the same volume and was composed of 1.65 mol / L VOSO4 and 3 mol / L aqueous sulfuric acid solution, 1.65 mol / L V2(SO4)3 and 3 mol / L aqueous sulfuric acid solution, and the volume of each was 40 ml. A magnetic pump was used to make the electrolyte flow into the battery for charge and discharge test.

[0065] A basic Zn-Fe redox flow battery was assembled using the prepared self- supporting crosslinked membrane, in which the electrode was carbon felt, the current collector was graphite plate, and the effective area of the membrane was 9 cm 2 The positive electrolyte was 0.8 mol / L K2Fe(CN)6 and 3 mol / L KOH, and the negative electrolyte was 0.4 mol / L ZnO and 3.8 mol / L NaOH, and the volume of each was 40 ml. A magnetic pump was used to make the electrolyte flow into the battery for charge and discharge test.

[0066] Example 2

[0067] 3 g of polybenzimidazole was dissolved in 17 g of DMAc, and was stirred at 25°C under the condition that the humidity was less than 30% for 12 h to make it fully dissolved, forming a polymer solution with a polybenzimidazole solid content of 15 wt%. 0.2 g of 4,4'-bis(chloromethyl) biphenyl (CM) was dissolved in 200 ml of n-heptane and was ultrasonically treated for 30 min to make it completely dissolved, obtaining a crosslinking agent solution of 1 g / L. The polymer solution was blade-coated on a smooth and clean glass sheet at a temperature of 25°C under the condition that the humidity was less than 20%, and the thickness of the blade was 10 μm. The polymer solution and the glass sheet were quickly put into 200 ml of n-heptane solution of CM, and were reacted for 60 min. Then, they were quickly put into water (such as 200 ml), obtaining a crosslinked membrane.

[0068] The obtained crosslinked membrane was wiped to remove surface moisture, was immersed in 20 ml of DMAc for one hour to make the uncrosslinked part or the part with lower crosslinking degree of the polymer membrane fully dissolved, and then was put into water (such as 200 ml), obtaining a self-supporting crosslinked membrane.

[0069] Figure 2 is the membrane thickness and AFM diagram of the ion-conducting membrane prepared in Example 2. It can be seen that a 1.316 μm thick membrane was obtained, which had a dense and fully crosslinked structure.

[0070] The full vanadium redox flow battery and the basic Zn-Fe redox flow battery were assembled as in Example 1.

[0071] Example 3

[0072] 3g of polybenzimidazole was dissolved in 17g of DMAc and stirred at 25°C for 12h under humidity less than 30% to make sure it was fully dissolved, forming a polymer solution with 15wt% of polybenzimidazole solid content. 0.1g of 4,4'-bis(chloromethyl)diphenyl (CM) was dissolved in 200ml of n-heptane and sonicated for 30min to make sure it was fully dissolved, forming a 0.5g / L crosslinker solution. The polymer solution was cast on a clean glass plate at 25°C under humidity less than 20% with a doctor blade thickness of 10μm. The polymer solution and the glass plate were quickly put into 200ml of n-heptane solution of CM and reacted for 30min. Then they were quickly put into water to get the crosslinked membrane.

[0073] The obtained crosslinked membrane was wiped to remove the surface water and then immersed in 20ml of DMAc for one hour to make sure the uncrosslinked or less crosslinked part of the polymer membrane was fully dissolved. Then it was put into water (e.g. 200ml) to get a self-standing dense crosslinked membrane.

[0074] The all-vanadium redox flow battery and the alkaline Zn-Fe redox flow battery were assembled as in Example 1.

[0075] Example 4

[0076] 3g of polybenzimidazole was dissolved in 17g of DMAc and stirred at 25°C for 12h under humidity less than 30% to make sure it was fully dissolved, forming a polymer solution with 15wt% of polybenzimidazole solid content. 0.1g of 4,4'-bis(chloromethyl)diphenyl (CM) was dissolved in 200ml of n-heptane and sonicated for 30min to make sure it was fully dissolved, forming a 0.5g / L crosslinker solution. The polymer solution was cast on a clean glass plate at 25°C under humidity less than 20% with a doctor blade thickness of 10μm. The polymer solution and the glass plate were quickly put into 200ml of n-heptane solution of CM and reacted for 30min. Then they were quickly put into water to get the crosslinked membrane.

[0077] The obtained crosslinked membrane was wiped to remove the surface water and then immersed in 20ml of DMAc for one hour to make sure the uncrosslinked or less crosslinked part of the polymer membrane was fully dissolved. Then it was put into water (e.g. 200ml) to get a self-standing dense crosslinked membrane.

[0078] The all-vanadium redox flow battery and the alkaline Zn-Fe redox flow battery were assembled as in Example 1.

[0079] Example 5

[0080] 3g of polybenzimidazole was dissolved in 17g of DMAc and stirred at 25°C for 12h under the condition of humidity less than 30% to make it fully dissolved, forming a polymer solution with polybenzimidazole solid content of 15wt%. 0.2g of p-chloromethyl benzene was dissolved in 200ml of n-heptane and ultrasonicated for 30min to make it fully dissolved, forming a 1g / L crosslinking agent solution. The polymer solution was casted on a smooth and clean glass sheet at 25°C under the condition of humidity less than 20%, with the doctor blade thickness of 10μm. The polymer solution and the glass sheet were quickly put into 200ml of n-heptane solution of p-chloromethyl benzene, reacted for 30min, and then quickly put into water to obtain a crosslinked membrane.

[0081] The obtained crosslinked membrane was wiped to remove surface moisture, immersed in 20ml of DMAc for one hour to make the uncrosslinked or less crosslinked part of the polymer membrane fully dissolved, and then put into water (such as 200ml) to obtain a self-supporting dense crosslinked membrane.

[0082] The all-vanadium redox flow battery and the alkaline Zn-Fe redox flow battery were assembled as in Example 1.

[0083] Example 6

[0084] 3g of polybenzimidazole was dissolved in 17g of DMAc and stirred at 25°C for 12h under the condition of humidity less than 30% to make it fully dissolved, forming a polymer solution with polybenzimidazole solid content of 15wt%. 0.2g of 4,4'-bis(chloromethyl) biphenyl (CM) was dissolved in 200ml of n-heptane and ultrasonicated for 30min to make it fully dissolved, forming a 1g / L crosslinking agent solution. The polymer solution was casted on a smooth and clean glass sheet at 25°C under the condition of humidity less than 20%, with the doctor blade thickness of 50μm. The polymer solution and the glass sheet were quickly put into 200ml of n-heptane solution of CM, reacted for 30min, and then quickly put into water to obtain a crosslinked membrane.

[0085] The obtained crosslinked membrane was wiped to remove surface moisture, immersed in 20ml of DMAc for one hour to make the uncrosslinked or less crosslinked part of the polymer membrane fully dissolved, and then put into water (such as 200ml) to obtain a self-supporting dense crosslinked membrane.

[0086] The all-vanadium redox flow battery and the alkaline Zn-Fe redox flow battery were assembled as in Example 1.

[0087] Example 7

[0088] 1.6 g of polybenzimidazole was dissolved in 18.4 g of DMAc and stirred at 25 °C for 12 h under the condition of humidity less than 30% to make it fully dissolved, forming a polymer solution with a polybenzimidazole solid content of 8 wt%. 0.2 g of 4,4'-bis(chloromethyl)diphenyl (CM) was dissolved in 200 ml of n-heptane and ultrasonicated for 30 min to make it fully dissolved, obtaining a 1 g / L crosslinking agent solution. The polymer solution was cast on a smooth and clean glass sheet at a temperature of 25 °C under the condition of humidity less than 20%, with a doctor blade thickness of 10 μιη. The polymer solution and the glass sheet were quickly put into 200 ml of n-heptane solution of CM, reacted for 30 min, and then quickly put into water to obtain a crosslinked membrane.

[0089] The obtained crosslinked membrane was wiped to remove surface moisture, immersed in 20 ml of DMAc for one hour to make the uncrosslinked or less crosslinked part of the polymer membrane fully dissolved, and then put into water (such as 200 ml) to obtain a self-supporting dense crosslinked membrane.

[0090] The all-vanadium redox flow battery and the alkaline Zn-Fe redox flow battery were assembled as in Example 1.

[0091] Example 8

[0092] 4 g of polybenzimidazole was dissolved in 16 g of DMAc and stirred at 25 °C for 12 h under the condition of humidity less than 30% to make it fully dissolved, forming a polymer solution with a polybenzimidazole solid content of 20 wt%. 0.2 g of 4,4'-bis(chloromethyl)diphenyl (CM) was dissolved in 200 ml of n-heptane and ultrasonicated for 30 min to make it fully dissolved, obtaining a 1 g / L crosslinking agent solution. The polymer solution was cast on a smooth and clean glass sheet at a temperature of 25 °C under the condition of humidity less than 20%, with a doctor blade thickness of 10 μιη. The polymer solution and the glass sheet were quickly put into 200 ml of n-heptane solution of CM, reacted for 30 min, and then quickly put into water to obtain a crosslinked membrane.

[0093] The obtained crosslinked membrane was wiped to remove surface moisture, immersed in 20 ml of DMAc for one hour to make the uncrosslinked or less crosslinked part of the polymer membrane fully dissolved, and then put into water (such as 200 ml) to obtain a self-supporting dense crosslinked membrane.

[0094] The all-vanadium redox flow battery and the alkaline Zn-Fe redox flow battery were assembled as in Example 1.

[0095] Comparative Example 1

[0096] Commercial Nafion 212 membrane.

[0097] Comparative Example 2

[0098] 3g of polybenzimidazole was dissolved in 17g of DMAc, and stirred at 25°C for 12h under the condition of humidity less than 30% to make it fully dissolved, forming a polymer solution (polymer solution) with polybenzimidazole solid content of 15wt%. 0.2g of 4,4'-bis(chloromethyl)diphenyl (CM) was dissolved in 200ml of n-heptane and ultrasonically treated for 30min to make it fully dissolved, obtaining a crosslinking agent solution of 1g / L. The polymer solution was blade-coated on a smooth and clean glass sheet at 25°C under the condition of humidity less than 20%, with the thickness of the blade being 10μm, and the polymer solution and the glass sheet were quickly put into 200ml of n-heptane solution of CM, reacted for 30min, and then quickly put into water, obtaining a crosslinked membrane.

[0099] The all-vanadium redox flow battery and the alkaline Zn-Fe redox flow battery were assembled as in Example 1.

[0100] Comparative Example 3

[0101] 3g of polybenzimidazole was dissolved in 17g of DMAc, and stirred at 25°C for 12h under the condition of humidity less than 30% to make it fully dissolved, forming a polymer solution (polymer solution) with polybenzimidazole solid content of 15wt%. 0.2g of 4,4'-bis(chloromethyl)diphenyl (CM) was dissolved in 200ml of n-heptane and ultrasonically treated for 30min to make it fully dissolved, obtaining a crosslinking agent solution of 1g / L. The polymer solution was blade-coated on a smooth and clean glass sheet at 25°C under the condition of humidity less than 20%, with the thickness of the blade being 10μm, and the polymer solution and the glass sheet were quickly put into 200ml of n-heptane solution of CM, reacted for 60min, and then quickly put into water, obtaining a crosslinked membrane.

[0102] The all-vanadium redox flow battery and the alkaline Zn-Fe redox flow battery were assembled as in Example 1.

[0103] Comparative Example 4

[0104] 3g of polybenzimidazole was dissolved in 17g of DMAc, and stirred at 25°C for 12h under the condition of humidity less than 30% to make it fully dissolved, forming a polymer solution (polymer solution) with polybenzimidazole solid content of 15wt%. 0.2g of 4,4'-bis(chloromethyl)diphenyl (CM) was dissolved in 200ml of n-heptane and ultrasonically treated for 30min to make it fully dissolved, obtaining a crosslinking agent solution of 1g / L. The polymer solution was blade-coated on a smooth and clean glass sheet at 25°C under the condition of humidity less than 20%, with the thickness of the blade being 10μm, and the polymer solution and the glass sheet were quickly put into 200ml of n-heptane solution of CM, reacted for 10min, and then quickly put into water, obtaining a crosslinked membrane.

[0105] The crosslinked membrane was obtained by immersing the crosslinked membrane in 20 ml of DMAc for 1 hour to remove the surface water, and then immersing the crosslinked membrane in 200 ml of water. The polymer membrane was damaged and could not be obtained as a complete self-supporting polymer film.

[0106] Comparative Example 5

[0107] 3 g of polybenzimidazole was dissolved in 17 g of DMAc, and the solution was stirred at 25°C and a humidity of less than 30% for 12 hours to form a polymer solution (polymer solution) having a solid content of 15 wt% of polybenzimidazole. 0.2 g of 4,4'-dichloromethyl biphenyl (CM) was dissolved in 200 ml of n-heptane and ultrasonically treated for 30 minutes to form a crosslinking agent solution having a concentration of 1 g / L. The polymer solution was coated on a smooth and clean glass sheet at a temperature of 25°C and a humidity of less than 20% using a doctor blade having a thickness of 5 μm. The polymer solution and the glass sheet were quickly immersed in 200 ml of a n-heptane solution of CM, and then quickly immersed in water. Since the thickness of the membrane was too thin, a crosslinked membrane having no defects could not be obtained.

[0108] Comparative Example 6

[0109] 3 g of polybenzimidazole was dissolved in 17 g of DMAc, and the solution was stirred at 25°C and a humidity of less than 30% for 12 hours to form a polymer solution (polymer solution) having a solid content of 15 wt% of polybenzimidazole. 0.2 g of 4,4'-dichloromethyl biphenyl (CM) was dissolved in 200 ml of n-heptane and ultrasonically treated for 30 minutes to form a crosslinking agent solution having a concentration of 1 g / L. The polymer solution was coated on a smooth and clean glass sheet at a temperature of 25°C and a humidity of less than 20% using a doctor blade having a thickness of 5 μm. The polymer solution and the glass sheet were quickly immersed in 200 ml of a n-heptane solution of CM, and then quickly immersed in water. Since the thickness of the membrane was too thin, a crosslinked membrane having no defects could not be obtained.

[0110] A full vanadium redox flow battery and an alkaline Zn-Fe redox flow battery were assembled in the same manner as in Example 1.

[0111] The amide bond formed by the reaction of 1,3,5-benzene tricarbonyl chloride as a crosslinking agent with polybenzimidazole is unstable and is easily hydrolyzed in the acidic system of the full vanadium redox flow battery. The original crosslinking structure is destroyed, resulting in poor cycle stability of the full vanadium redox flow battery.

[0112] Comparative Example 7

[0113] 3g of polybenzimidazole was dissolved in 17g of DMAc, and stirred at 25°C for 12h under the condition of humidity less than 30% to make it fully dissolved, forming a polymer solution with polybenzimidazole solid content of 15wt%. 0.2g of 1,3,5-benzene tricarbonyl chloride was dissolved in 200ml of n-heptane and ultrasonically treated for 30min to make it fully dissolved, obtaining a 1g / L crosslinking agent solution. Under the condition of temperature 25°C and humidity less than 20%, the polymer solution was blade-coated on a smooth and clean glass sheet with a blade thickness of 10μm, and the polymer solution and glass sheet were quickly put into 200ml of 1,3,5-benzene tricarbonyl chloride n-heptane solution for reaction for 30min, and then quickly put into water to obtain a crosslinked membrane.

[0114] The obtained crosslinked membrane was wiped to remove surface moisture and soaked in 20ml of DMAc for one hour. Because the reaction rate of 1,3,5-benzene tricarbonyl chloride with polybenzimidazole is fast and the formed dense layer is more dense, it is difficult for 1,3,5-benzene tricarbonyl chloride to further diffuse downward, so that the formed crosslinked layer is thinner. The polymer membrane is prone to breakage when taken out of DMAc due to being too thin, and a complete self-supporting polymer thin film cannot be obtained.

[0115] Comparative Example 8

[0116] 3g of polybenzimidazole was dissolved in 17g of DMAc, and stirred at 25°C for 12h under the condition of humidity less than 30% to make it fully dissolved, forming a polymer solution with polybenzimidazole solid content of 15wt%. 0.2g of 1,3,5-benzene tricarbonyl chloride was dissolved in 200ml of n-heptane and ultrasonically treated for 30min to make it fully dissolved, obtaining a 1g / L crosslinking agent solution. Under the condition of temperature 25°C and humidity less than 20%, the polymer solution was blade-coated on a smooth and clean glass sheet with a blade thickness of 10μm, and the polymer solution and glass sheet were quickly put into 200ml of 1,3,5-benzene tricarbonyl chloride n-heptane solution for reaction for 30min, and then quickly put into water to obtain a crosslinked membrane.

[0117] The obtained crosslinked membrane was wiped to remove surface moisture and soaked in 20ml of DMAc for one hour. Because the reaction rate of 1,3,5-benzene tricarbonyl chloride with polybenzimidazole is fast and the formed dense layer is more dense, it is difficult for 1,3,5-benzene tricarbonyl chloride to further diffuse downward, so that the formed crosslinked layer is thinner. The polymer membrane is prone to breakage when taken out of DMAc due to being too thin, and a complete self-supporting polymer thin film cannot be obtained.

[0118] Comparative Example 9

[0119] 3g of polybenzimidazole was dissolved in 17g of DMAc and stirred at 25°C for 12h under the condition of humidity less than 30% to make it fully dissolved, forming a polymer solution with polybenzimidazole solid content of 15wt%. 0.2g of isophthaloyl dichloride was dissolved in 200ml of n-heptane by ultrasonic for 30min to make it fully dissolved, forming a crosslinking agent solution of 1g / L. The polymer solution was coated on a smooth and clean glass sheet by doctor blade with a thickness of 10μm at 25°C under the condition of humidity less than 20%, and the polymer solution and the glass sheet were quickly put into 200ml of n-heptane solution of isophthaloyl dichloride, reacted for 30min, and then quickly put into water to obtain a crosslinked membrane.

[0120] The obtained crosslinked membrane was dried to remove surface moisture, soaked in 20ml of DMAc for one hour, and then put into 200ml of water. The polymer membrane was damaged and a complete self-supporting polymer film could not be obtained.

[0121] Comparative Example 10

[0122] 3g of polybenzimidazole was dissolved in 17g of DMAc and stirred at 25°C for 12h under the condition of humidity less than 30% to make it fully dissolved, forming a polymer solution with polybenzimidazole solid content of 15wt%. 0.2g of terephthaloyl dichloride was dissolved in 200ml of n-heptane by ultrasonic for 30min to make it fully dissolved, forming a crosslinking agent solution of 1g / L. The polymer solution was coated on a smooth and clean glass sheet by doctor blade with a thickness of 10μm at 25°C under the condition of humidity less than 20%, and the polymer solution and the glass sheet were quickly put into 200ml of n-heptane solution of terephthaloyl dichloride, reacted for 30min, and then quickly put into water to obtain a crosslinked membrane.

[0123] The obtained crosslinked membrane was dried to remove surface moisture, soaked in 20ml of DMAc for one hour, and then put into 200ml of water. The polymer membrane was damaged and a complete self-supporting polymer film could not be obtained.

[0124] Comparative Example 11

[0125] 3g of polybenzimidazole was dissolved in 17g of DMAc and stirred at 25°C for 12h under the condition of humidity less than 30% to make it fully dissolved, forming a polymer solution with polybenzimidazole solid content of 15wt%. 0.04g of 4,4'-bis(chloromethyl) biphenyl (CM) was dissolved in 200ml of n-heptane by ultrasonic for 30min to make it fully dissolved, forming a crosslinking agent solution of 0.2g / L. The polymer solution was coated on a smooth and clean glass sheet by doctor blade with a thickness of 10μm at 25°C under the condition of humidity less than 20%, and the polymer solution and the glass sheet were quickly put into 200ml of n-heptane solution of CM, reacted for 30min, and then quickly put into water to obtain a crosslinked membrane.

[0126] The crosslinked membrane was then immersed in 20 ml of DMAc for 1 h to dissolve the uncrosslinked or less crosslinked parts of the polymer film. The crosslinked membrane was then immersed in 200 ml of water to obtain a self-supporting crosslinked membrane.

[0127] Comparative Example 12

[0128] 3 g of polybenzimidazole was dissolved in 17 g of DMAc and stirred at 25 °C for 12 h under a humidity of less than 30% to form a polymer solution (polymer solution) with a solid content of 15 wt% of polybenzimidazole. 0.5 g of 4,4'-bis(chloromethyl)diphenyl (CM) was dissolved in 200 ml of n-heptane and ultrasonically treated for 30 min to form a crosslinking agent solution with a concentration of 2.5 g / L. The polymer solution was coated on a smooth and clean glass sheet at a temperature of 25 °C and a humidity of less than 20% using a doctor blade with a thickness of 10 μm. The polymer solution and the glass sheet were quickly immersed in 200 ml of the n-heptane solution of CM and reacted for 30 min. The crosslinked membrane was then quickly immersed in water to obtain a crosslinked membrane.

[0129] The crosslinked membrane was then immersed in 20 ml of DMAc for 1 h to dissolve the uncrosslinked or less crosslinked parts of the polymer film. The crosslinked membrane was then immersed in 200 ml of water to obtain a self-supporting crosslinked membrane.

[0130] The all-vanadium redox flow battery and the alkaline Zn-Fe redox flow battery were assembled in the same manner as in Example 1.

[0131] Comparative Example 13

[0132] 3 g of polybenzimidazole was dissolved in 17 g of DMAc and stirred at 25 °C for 12 h under a humidity of less than 30% to form a polymer solution (polymer solution) with a solid content of 15 wt% of polybenzimidazole. 0.5 g of 4,4'-bis(chloromethyl)diphenyl (CM) was dissolved in 200 ml of n-heptane and ultrasonically treated for 30 min to form a crosslinking agent solution with a concentration of 2.5 g / L. The polymer solution was coated on a smooth and clean glass sheet at a temperature of 25 °C and a humidity of less than 20% using a doctor blade with a thickness of 10 μm. The polymer solution and the glass sheet were quickly immersed in 200 ml of the n-heptane solution of CM and reacted for 30 min. The crosslinked membrane was then quickly immersed in water to obtain a crosslinked membrane.

[0133] The crosslinked membrane was then immersed in 20 ml of DMAc for 1 h to dissolve the uncrosslinked or less crosslinked parts of the polymer film. The crosslinked membrane was then immersed in 200 ml of water to obtain a self-supporting crosslinked membrane.

[0134] The all-vanadium redox flow battery and the alkaline Zn-Fe redox flow battery were assembled in the same manner as in Example 1.

[0135] Comparative Example 14

[0136] 3 g of polybenzimidazole was dissolved in 17 g of DMAc and stirred at 25 °C for 12 h under the condition of humidity less than 30% to make it fully dissolved, forming a polymer solution (polymer solution) with a polybenzimidazole solid content of 15 wt%. 0.2 g of 4,4'-bis(chloromethyl)diphenyl (CM) was dissolved in 200 ml of n-heptane and ultrasonically treated for 30 min to make it fully dissolved, obtaining a crosslinking agent solution of 1 g / L. The polymer solution was blade-coated on a smooth and clean glass sheet at a temperature of 25 °C under the condition of humidity less than 20%, with a doctor blade thickness of 10 μm. The polymer solution and the glass sheet were quickly put into 200 ml of n-heptane solution of CM, reacted for 70 min, and then quickly put into water, obtaining a crosslinked membrane.

[0137] The obtained crosslinked membrane was wiped to remove surface moisture and immersed in 20 ml of DMAc for one hour to make the uncrosslinked or less crosslinked part of the polymer membrane fully dissolved, and then put into 200 ml of water to obtain a self-supporting crosslinked membrane.

[0138] The all-vanadium redox flow battery and the alkaline Zn-Fe redox flow battery were assembled as in Example 1.

[0139] Comparative Example 15

[0140] 1 g of polybenzimidazole was dissolved in 19 g of DMAc and stirred at 25 °C for 12 h under the condition of humidity less than 30% to make it fully dissolved, forming a polymer solution with a polybenzimidazole solid content of 5 wt%. 0.2 g of 4,4'-bis(chloromethyl)diphenyl (CM) was dissolved in 200 ml of n-heptane and ultrasonically treated for 30 min to make it fully dissolved, obtaining a crosslinking agent solution of 1 g / L. The polymer solution was blade-coated on a smooth and clean glass sheet at a temperature of 25 °C under the condition of humidity less than 20%, with a doctor blade thickness of 10 μm. The polymer solution and the glass sheet were quickly put into 200 ml of n-heptane solution of CM, reacted for 30 min, and then quickly put into water. However, due to the too low solid content of the polymer solution, the finally formed membrane was too thin and cracked, and a complete crosslinked membrane could not be obtained.

[0141] Comparative Example 16

[0142] 4.4 g of polybenzimidazole was dissolved in 15.6 g of DMAc and stirred at 25 °C for 12 h under the condition of humidity less than 30% to make it fully dissolved, forming a polymer solution with a solid content of 22 wt%. 0.2 g of 4,4'-bis(chloromethyl)diphenyl (CM) was dissolved in 200 ml of n-heptane and ultrasonically treated for 30 min to make it fully dissolved, obtaining a 1 g / L crosslinking agent solution. The polymer solution was cast on a smooth and clean glass sheet at a temperature of 25 °C and humidity less than 20%, with a doctor blade thickness of 10 μm. The polymer solution and the glass sheet were quickly put into 200 ml of n-heptane solution of CM, and reacted for 30 min, and then quickly put into water. However, due to the too high solid content of the polymer solution, the polybenzimidazole was not fully dissolved, and the crosslinked membrane obtained had obvious defects on the surface.

[0143] Table 1: Membrane preparation parameters of self-supporting ion-conducting membranes

[0144] Comparative Examples 2 and 3 had thicker polymer membranes due to the absence of re- soaking in DMAc, and the uncrosslinked or lowly crosslinked portions of the polymer membranes still existed.

[0145] Comparative Example 4 had a too thin crosslinked layer due to the short reaction time, and it was not possible to obtain a complete self-supporting polymer membrane after the support layer was dissolved. Comparative Example 5 had a broken membrane due to the thin cast thickness, and it was difficult to obtain a complete polymer membrane. Comparative Example 15 had a too thin and broken membrane due to the too low solid content of the polymer solution, and it was difficult to obtain a complete polymer membrane. Comparative Example 16 had obvious defects on the surface of the obtained membrane due to the too high solid content of the polymer solution, and the polymer was not fully dissolved.

[0146] Table 2: Performance parameters of liquid flow batteries equipped with self-supporting ion-conducting membranes

[0147] Comparative Example 13 had a too thin thickness, and it was not possible to assemble a liquid flow battery.

[0148] Figure 3 is a comparison of the area resistance of the ion-conducting membranes prepared in Examples 1-2 and Comparative Examples 1-3 under acidic conditions. It can be seen that after the support layer was dissolved and the thickness of the membrane was reduced, the area resistance of the membrane was significantly reduced, and was superior to that of the commercial Nafion 212.

[0149] Figure 4 is a comparison of the rate capability of the all-vanadium redox flow batteries prepared with the ion-conducting membranes of Examples 1-2 and Comparative Example 1; it can be seen that the performance of Examples 1 and 2 at different current densities is better than that of the commercial Nafion 212, and because Examples 1 and 2 have low area resistance, they can be operated at high current densities, in which Example 1 can be operated at a current density of 300 mA cm -2 with an EE greater than 80%.

[0150] Figure 5 is a comparison of the cycle performance of the all-vanadium redox flow batteries prepared with the ion-conducting membranes of Example 1 and Comparative Example 6; it can be seen that Example 1 has better cycle stability than Comparative Example 6 of the prior work, which benefits from the more stable crosslinking structure of Example 1 that can exist stably in an acidic environment.

[0151] Figure 6 is a comparison of the area resistance of the ion-conducting membranes prepared in Examples 1-2 and Comparative Example 1 under alkaline conditions; it can be seen that Examples 1 and 2 have low area resistance under alkaline conditions, which is significantly lower than that of the commercial Nafion 212, proving that the membranes of the examples are suitable for use under both acidic and alkaline conditions.

[0152] Figure 7 is the rate capability of the alkaline zinc-iron redox flow batteries prepared with the ion-conducting membranes of Examples 1-2; it can be seen that Examples 1 and 2 have low area resistance and can be operated at high current densities, in which they can be operated at a current density of 260 mA cm -2 with an EE greater than 80%.

[0153] The above is only a few embodiments of the present application, and does not limit the present application in any form. Although the above describes the preferred embodiments of the present application, it is not intended to limit the present application. Any skilled person in the art can make some changes or modifications to the above disclosed technical content without departing from the scope of the technical solutions of the present application, and such changes or modifications are equivalent to equivalent embodiments, and are within the scope of the technical solutions.

Claims

1. A sub-micron ultra-thin self-supporting ion-conducting membrane, characterized in that, the sub-micron ultra-thin self-supporting ion-conducting membrane is obtained by cross-linking reaction of polybenzimidazole and a cross-linking agent, and has a full cross-linking structure; the cross-linking agent is selected from 4,4'-bis(chloromethyl) biphenyl and / or p-chloromethyl benzene.

2. The sub-micron ultra-thin self-supporting ion-conducting membrane according to claim 1, characterized in that, the thickness of the sub-micron ultra-thin self-supporting ion-conducting membrane is 0.3-11 μm; preferably, the thickness of the sub-micron ultra-thin self-supporting ion-conducting membrane is 0.5-11 μm.

3. A method for preparing a sub-micron ultra-thin self-supporting ion-conducting membrane, characterized in that, the method comprises the following steps: coating a solution I containing an organic high molecular resin and a solvent A on a substrate, then immersing the whole in a solution II containing a cross-linking agent and a solvent B, after reaction, placing in water to obtain a cross-linked membrane, and then immersing in a solvent A and a solvent C in sequence to obtain the sub-micron ultra-thin self-supporting ion-conducting membrane.

4. The method according to claim 3, characterized in that, the organic high molecular resin is selected from polybenzimidazole; the cross-linking agent is selected from 4,4'-bis(chloromethyl) biphenyl and / or p-chloromethyl benzene.

5. The method according to claim 3, characterized in that, the solvent A is selected from at least one of dimethyl sulfoxide, N,N-dimethylacetamide, N-methyl pyrrolidone, N,N-dimethylformamide, and tetrahydrofuran; the solvent B is selected from at least one of n-pentane, n-heptane, n-hexane, n-decane, and cyclohexane; the solvent C is selected from at least one of water, ethanol, isopropanol, and acetone.

6. The method according to claim 3, characterized in that, in the solution I containing the organic high molecular resin and the solvent A, the content of the organic high molecular resin is 8-20 wt%; in the solution II containing the cross-linking agent and the solvent B, the content of the cross-linking agent is 0.5-2 g / L.

7. The method according to claim 3, characterized in that, the reaction time is 30-60 min.

8. The method according to claim 3, characterized in that, the coating thickness is 10-50 μm.

9. Use of the sub-micron ultra-thin self-supporting ion-conducting membrane according to any one of claims 1 or 2 or the membrane prepared by the method according to any one of claims 3-8, characterized in that, for a full vanadium redox flow battery.

10. Use of the sub-micron ultra-thin self-supporting ion-conducting membrane according to any one of claims 1 or 2 or the membrane prepared by the method according to any one of claims 3-8, characterized in that, for an alkaline zinc-iron redox flow battery.

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