Flow battery diaphragm, modification method and flow battery

Abstract

The invention provides a flow battery diaphragm, a modification method and a zinc-bromine flow battery. The method comprises the following steps: mixing and stirring a conductive material, a binder and an organic solvent to obtain a modified coating solution; coating an ion exchange membrane with the modified coating solution; carrying out evaporation treatment on the ion exchange membrane to obtain a modified ion exchange membrane; the modified ion exchange membrane is subjected to direct-current pulse heating treatment, and the modified diaphragm is obtained.According to the technical scheme, the pulse heating method is adopted for increasing the coating temperature of the ion exchange membrane in a short time, dendritic crystals are eliminated, and a high-concentration zinc ion solution caused by concentration polarization possibly generating the dendritic crystals is interfered; and the ion selectivity and the ion penetrability of the ion exchange membrane are not influenced, the function of removing existing and potential zinc dendrites is added, and the ion exchange membrane has good mechanical properties, relatively high flow battery efficiency, excellent durability, corrosion resistance and the like, can replace the existing ion exchange membrane, and has wide application prospects. The method is applied to the field of flow battery energy storage.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of zinc-bromine flow battery, and particularly relates to a flow battery separator, a modification method and a flow battery. BACKGROUND

[0002] Zinc-bromine flow battery is a kind of flow battery technology with the same positive and negative electrolyte. It uses polyolefin porous membrane as a separator, and the price is relatively cheap. Zinc-bromine flow battery has high energy density, about 430 Wh / kg and 300 Wh / L, which can provide long-lasting high energy output. It has a long service life and can be charged and discharged about 3000 times, and the conversion efficiency can reach about 70%. The working temperature range of zinc-bromine flow battery is-20℃ to 60℃. According to the cost estimate, the price is about 0.8 yuan to 1 yuan / Wh. Overall, zinc-bromine flow battery has the advantages of high energy storage, cost-effectiveness and reliability, and is suitable for various energy storage needs.

[0003] However, in the cyclic reaction process of zinc-bromine flow battery, the problem of zinc dendrite formation on the separator will seriously affect its performance and service life. Current technical means include separator selection and modification, addition of dendrite inhibitor, temperature control strategy, research and development of new materials, etc. But they are only symptomatic treatment, not the root cause. These means can only inhibit and slow down the generation of zinc dendrites, but cannot eliminate the existing accumulated zinc dendrites in the middle of the separator. Only inhibiting the generation of zinc dendrites cannot solve the root problem from the source. SUMMARY

[0004] In view of this, it is necessary to provide a flow battery separator, a modification method and a zinc-bromine flow battery capable of eliminating zinc dendrites in the middle of the flow battery separator, thereby improving the service life and performance of the zinc-bromine flow battery, in view of the defects of the current flow battery separator in zinc-bromine flow battery affected by dendrites.

[0005] To solve the above problems, the technical scheme adopted by the present application is as follows:

[0006] One of the purposes of the present application is to provide a modification method of flow battery separator, comprising the following steps:

[0007] Mixing and stirring conductive material, adhesive and organic solvent in a mass ratio of 1:1:100-200 to obtain a modified coating solution;

[0008] Coating the modified coating solution on the ion exchange membrane;

[0009] Evaporating the ion exchange membrane to obtain a modified ion exchange membrane;

[0010] Direct current pulse heating treatment is performed on the modified ion exchange membrane to obtain a modified separator.

[0011] In some embodiments, in the step of mixing and stirring the conductive material, binder and organic solvent to obtain a modified coating solution, the conductive material includes at least one of carbon nanotubes, graphene, carbon paste, carbon dots, carbon powder, nano-silver, nano-gold or titanium mesh.

[0012] In some embodiments, in the step of mixing and stirring the conductive material, binder and organic solvent to obtain a modified coating solution, the binder is at least one of styrene-butadiene rubber, polyurethane, cellulose nitrate or polyvinyl acetate.

[0013] In some embodiments, in the step of mixing and stirring the conductive material, binder and organic solvent to obtain a modified coating solution, the organic solvent includes at least one of N-methylpyrrolidone, benzene, toluene, ethanol, diethyl ether, dichloromethane, tetrachloromethane or chloroform.

[0014] In some embodiments, the ion exchange membrane comprising a commercially available Dynamic Alpha membrane or a flow battery membrane is used in the step of coating the modified coating solution onto the ion exchange membrane.

[0015] In some embodiments, in the step of evaporating the ion exchange membrane to obtain a modified ion exchange membrane, the evaporation temperature is 50-90°C.

[0016] In some embodiments, the step of subjecting the modified ion exchange membrane to DC pulse heating to obtain the modified membrane specifically includes the following steps:

[0017] The modified ion exchange membrane is loaded into a zinc-bromine flow battery fixture, with the modified coating surface of the modified ion exchange membrane facing the zinc negative electrode direction.

[0018] The modified ion exchange membrane is treated with DC pulse heating technology to remove zinc dendrites from the modified ion exchange membrane.

[0019] In some embodiments, the DC voltage range in the DC pulse heating technology is 10-220V, and the number of pulses in the DC pulse heating technology is 2-1000.

[0020] A second objective of this application is to provide a modified flow battery separator, prepared by any of the modification methods described in the present application.

[0021] A third objective of this application is to provide a zinc-bromine flow battery, including the modified flow battery separator described above.

[0022] The present application adopts the above technical solution, and its beneficial effects are as follows:

[0023] The flow battery separator, modification method, and zinc-bromine flow battery provided in this application involve mixing and stirring conductive materials, binders, and organic solvents to obtain a modified coating solution; coating the modified coating solution onto an ion exchange membrane; evaporating the ion exchange membrane to obtain a modified ion exchange membrane; and subjecting the modified ion exchange membrane to DC pulse heating to obtain a modified separator. The above technical solution of this application uses pulse heating to briefly raise the temperature of the ion exchange membrane coating, eliminating dendrites and high-concentration zinc ion solutions caused by concentration polarization that may lead to dendrite formation, without affecting the ion selectivity and ion permeability of the ion exchange membrane itself. It increases the function of removing existing and potential zinc dendrites, possesses good mechanical properties, high flow battery efficiency, and excellent durability and corrosion resistance, and can replace existing ion exchange membranes for application in the field of flow battery energy storage. Attached Figure Description

[0024] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the description of the embodiments of this application or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 The flowchart illustrates the steps of the method for modifying the flow battery separator provided in Example 1, which is an embodiment of this application.

[0026] Figure 2 The image provided in Example 1 is a scanning electron microscope (SEM) image of the modified coating solution uniformly coated on an ion exchange membrane.

[0027] Figure 3 The pulse heating device provided in Example 1 includes a flow battery clamp and a DC power supply.

[0028] Figure 4 The modified ion exchange membrane provided in Example 1 is compared with the scanning electron microscope (SEM) images before and after pulse heating.

[0029] Figure 5 This is a schematic diagram of the device for eliminating dendrites using pulse heating in Example 1.

[0030] Figure 6 The relationship between the amount of modified solution coating and surface resistivity provided in Example 1 and the temperature rise over 30 seconds.

[0031] Figure 7 The relationship between the coating amount and energy efficiency of the modified solution provided in Example 1.

[0032] Combination Figure 5Figure 6 The optimal coating amount was found to be 1.5 mg / cm², which yielded the highest overall efficiency in terms of energy efficiency and temperature rise.

[0033] Figure 8 The voltage efficiency improvement curve after pulse heating provided in Example 1.

[0034] Figure 9 Dendrite elimination voltage curve after pulse heating provided in Example 1.

[0035] Figure 10 Battery cycle diagram of the implementation results provided for Comparative Example 1. Detailed Implementation

[0036] The embodiments of this application are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this application, and should not be construed as limiting this application.

[0037] In the description of this application, it should be understood that the terms "upper", "lower", "horizontal", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.

[0038] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0039] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments.

[0040] Please see Figure 1 The following is a flowchart of the modification method for the flow battery separator provided in the embodiments of this application, including the following steps S110 to S140. The implementation of each step is described in detail below.

[0041] Step S110: Mix and stir the conductive material, binder and organic solvent in a mass ratio of 1:1:100-200 to obtain a modified coating solution.

[0042] In this embodiment, the conductive material includes at least one of carbon nanotubes, graphene, carbon paste, carbon dots, carbon powder, nano-silver, nano-gold, or titanium mesh.

[0043] It is understood that this embodiment uses conductive materials such as carbon nanotubes, graphene, carbon paste, carbon dots, carbon powder, nano-silver, nano-gold, and titanium mesh. The above conductive materials can exist stably in the flow electrolyte. Moreover, the mass percentage of the conductive material in the conductive coating modification solution is controlled to be below 5%. When the mass percentage exceeds 5%, it will lead to a decrease in ion permeability and affect the voltage efficiency of the flow battery.

[0044] In this embodiment, the adhesive is at least one of styrene-butadiene rubber, polyurethane, nitrocellulose, or polyvinyl acetate.

[0045] It is understood that the binders used in this embodiment, such as styrene-butadiene rubber, polyurethane, nitrocellulose and polyvinyl acetate, can exist stably in the electrolyte of zinc-bromine flow batteries.

[0046] In this embodiment, the organic solvent includes at least one of N-methylpyrrolidone, benzene, toluene, ethanol, diethyl ether, dichloromethane, tetrachloromethane, or chloroform.

[0047] It is understood that this embodiment uses stable organic solvents that do not react with carbon materials, such as N-methylpyrrolidone, benzene, toluene, ethanol, diethyl ether, dichloromethane, tetrachloromethane, and chloroform.

[0048] Step S120: Apply the modified coating solution onto the ion exchange membrane.

[0049] In this embodiment, the ion exchange membrane includes a commercially available Dynamic alpha membrane or a flow battery membrane. The flow battery membrane includes a zinc-bromine flow battery membrane or other flow battery system membranes.

[0050] Furthermore, the coating amount of the modified coating solution is 0.5 mL / cm². -2

[0051] Step S130: Evaporate the ion exchange membrane to obtain a modified ion exchange membrane.

[0052] It is understood that in this embodiment, the ion exchange membrane is subjected to evaporation treatment to evaporate the solvent in the coating, thereby obtaining a pre-made modified ion exchange membrane.

[0053] Furthermore, the evaporation temperature range is 50-90℃. This temperature range is required because below 50℃, the modified ion-selective membrane is difficult to dry; while above 90℃, the modified ion-selective membrane begins to melt, affecting the pore size and ion conductivity.

[0054] Step S140: The modified ion exchange membrane is subjected to DC pulse heating treatment to obtain the modified membrane.

[0055] In this embodiment, the step of subjecting the modified ion exchange membrane to DC pulse heating to obtain the modified membrane specifically includes the following steps:

[0056] The modified ion exchange membrane is loaded into a zinc-bromine flow battery fixture, with the modified coating surface of the ion exchange membrane facing the zinc negative electrode direction; the modified ion exchange membrane is treated with DC pulse heating technology to remove zinc dendrites on the modified ion exchange membrane.

[0057] Furthermore, the DC voltage range in the DC pulse heating technology is 10-220V, and the number of pulses in the DC pulse heating technology is 2-1000.

[0058] It should be noted that the instantaneous temperature achievable by the DC pulse heating technology in this embodiment should be below 55°C to avoid high-temperature melting of the modified ion-selective membrane.

[0059] By coating an ion exchange membrane with a 5% carbon nanotube solution from step S110, a 150Ωcm ion exchange membrane can be modified. -2 The surface resistance is such that a 10V DC voltage generates a temperature of 52°C within 30 seconds, which can eliminate dendrites already formed on the surface of the ion-selective membrane. Pulse current and time can be adjusted according to actual conditions. While maintaining the energy efficiency of the zinc-bromine flow battery without degradation, it can still maintain over 80% energy efficiency after 500 cycles.

[0060] The modified flow battery separator provided in this application uses pulse heating to briefly raise the temperature of the ion exchange membrane coating, eliminating dendrites and high-concentration zinc ion solution caused by concentration polarization that may lead to dendrite formation. This does not affect the ion selectivity and ion permeability of the ion exchange membrane itself, but increases the function of removing existing and potential zinc dendrites. It has good mechanical properties, high flow battery efficiency, and excellent durability and corrosion resistance, and can replace existing ion exchange membranes for application in the field of flow battery energy storage.

[0061] The modification method for the modified flow battery separator provided in this application utilizes widely available and inexpensive raw materials, effectively controlling costs. The preparation process is relatively simple, with mild conditions, making it suitable for large-scale industrial production. The prepared ion exchange membrane exhibits enhanced dendrite removal capabilities, along with good mechanical properties, high zinc-bromine flow battery efficiency, and excellent durability and corrosion resistance. This membrane can replace existing ion exchange membranes and be applied in the field of flow battery energy storage.

[0062] The technical solutions described above in this application will be explained in detail below with reference to specific embodiments.

[0063] The Dynamic Alpha power membrane used in this invention can be purchased directly, or it can be replaced with other zinc-bromine flow battery separators.

[0064] Performance testing conditions for zinc-bromine redox flow batteries with ion exchange membranes: at a current density of 20 mA / cm² -2 Charge-discharge experiments were conducted under the following conditions: charging to 80mAh and discharging to 0.01V. Commercially available carbon felt was used as the reaction electrode, with an effective working area of ​​4cm². 2 The positive and negative electrode electrolytes are both aqueous solutions of ZnBr2, and the battery operates at room temperature.

[0065] Example 1

[0066] (1) Dissolve 100 mg of carbon nanotubes and 100 mg of polyvinylidene fluoride (PVDF) in 10 mL of N-methylpyrrolidone and stir at 60 °C for 2 hours to obtain a modified coating solution.

[0067] (2) The modified solution was prepared at a concentration of 0.5 mL / cm². 2 Uniformly coated onto a commercially available Dynamic Alpha membrane. See also... Figure 2 The image shown is a scanning electron microscope (SEM) image of the modified coating solution uniformly coated on an ion exchange membrane, as provided in this embodiment.

[0068] (3) The solvent in the coating is evaporated at 60°C for four hours to obtain the pre-made modified ion exchange membrane.

[0069] (4) Load the pre-made modified ion exchange membrane into the zinc-bromine flow battery fixture, with the modified coating facing the zinc negative electrode, and leave a wire to directly connect to the conductive coating.

[0070] Please see Figure 3 This embodiment provides a flow battery clamp and a DC power supply for a pulse heating device. Conductive copper plates on both sides of the clamp are connected to the positive and negative terminals of the DC power supply, respectively.

[0071] (5) Every 100 cycles, use 10V DC pulse heating technology for 30 seconds to remove zinc dendrites on the zinc-bromine flow battery separator.

[0072] Please see Figure 4 SEM images of the modified ion exchange membrane before and after pulse heating are shown.

[0073] In the images, a and e are side scans before and after 100 cycles of pulse heating. b, c, and d are scans before 100, 200, and 300 cycles of pulse heating, respectively. f, g, and h are scans after 100, 200, and 300 cycles of pulse heating, respectively. As the number of cycles increases, the number, volume, and sharpness of dendrites increase, while pulse heating technology can significantly alleviate the severity of dendrite formation.

[0074] Please see Figure 5 In Embodiment 1 of this application, a pulse heating dendrite elimination device was used to achieve 300 cycles, or 600 hours of cycle time. It is worth noting that the efficiency decreased twice at cycles 110 and 195, but the pulse heating technique successfully reactivated the efficiency. In the figure, CE represents coulombic efficiency, VE represents voltage efficiency, and EE represents energy efficiency.

[0075] Please see Figure 6 This represents the relationship between the amount of modified solution coated and the surface resistivity provided in Example 1, and the temperature rise over 30 seconds.

[0076] Please see Figure 7 This represents the relationship between the amount of the modified coating solution applied and the energy efficiency provided in Example 1.

[0077] Combination Figure 6 Figure 7 The optimal coating amount was found to be 1.5 mg / cm². 2 This yields the highest overall efficiency in terms of energy efficiency and temperature rise.

[0078] Please see Figure 8 The voltage curve showing the improvement in voltage efficiency after pulse heating provided in this embodiment 1.

[0079] Please see Figure 9 The above is the dendrite elimination voltage curve after pulse heating provided in Example 1.

[0080] As can be seen from the above, the modified flow battery separator provided in this embodiment can maintain an energy efficiency of over 80% after 500 hours of operation without reducing the energy efficiency of the zinc-bromine flow battery.

[0081] It is worth noting that the modified coating does not react with the base film; therefore, the physical and mechanical properties of the modified ion-selective membrane depend on the physical and mechanical properties of the base film.

[0082] Example 2

[0083] The difference between this embodiment and Embodiment 1 is that carbon nanotubes are replaced with graphene. Everything else remains the same as in Embodiment 1. Battery life performance is largely the same as in Embodiment 1.

[0084] Example 3

[0085] The difference between this embodiment and Embodiment 1 is that: every 200 cycles, a 20V DC pulse heating technique is used for 30 seconds to remove zinc dendrites from the zinc-bromine flow battery separator. Everything else remains the same as in Embodiment 1. It is not significantly different from Embodiment 1.

[0086] Comparative Example 1

[0087] The difference between this comparative example and Example 1 is that pulse heating is not used to process the battery device in a timely manner. The battery efficiency begins to decline after 110 cycles.

[0088] Please see Figure 10 The battery cycle diagram is for Comparative Example 1. The battery efficiency began to decrease after 110 cycles.

[0089] Comparative Example 2

[0090] The difference between this comparative example and Example 1 is that a 25V voltage pulse heating for 30 seconds was used, which burned through the separator and caused the battery to short-circuit.

[0091] It is understood that the technical features of the above embodiments can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0092] The above are merely preferred embodiments of this application, and only specifically describe the technical principles of this application. These descriptions are only for explaining the principles of this application and should not be construed as limiting the scope of protection of this application in any way. Based on this explanation, any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application, as well as other specific embodiments of this application that can be conceived by those skilled in the art without creative effort, should be included within the scope of protection of this application.

Claims

1. A method of modifying a flow battery separator membrane, characterized by, The method comprises the following steps: a conductive material, a binder and an organic solvent are mixed and stirred in a mass ratio of 1:1:100-200 to obtain a modified coating solution; the modified coating solution is coated on an ion exchange membrane; the ion exchange membrane is subjected to evaporation treatment to obtain a modified ion exchange membrane; the modified ion exchange membrane is subjected to direct current pulse heating treatment to obtain a modified separator.

2. The method of modifying a flow battery separator of claim 1, wherein, In the step of mixing and stirring the conductive material, the binder and the organic solvent to obtain the modified coating solution, the conductive material comprises at least one of carbon nanotubes, graphene, carbon paste, carbon dots, carbon powder, nano-silver, nano-gold or titanium mesh.

3. The method of modifying a flow battery separator of claim 1, wherein, In the step of mixing and stirring the conductive material, the binder and the organic solvent to obtain the modified coating solution, the binder is at least one of butadiene rubber, polyurethane, nitrocellulose or polyvinyl acetate.

4. The method of modifying a flow battery separator of claim 1, wherein, In the step of mixing and stirring the conductive material, the binder and the organic solvent to obtain the modified coating solution, the organic solvent comprises at least one of N-methyl pyrrolidone, benzene, toluene, ethanol, diethyl ether, dichloromethane, tetrachloromethane or chloroform.

5. The method of modifying a flow battery separator of claim 1, wherein, In the step of coating the modified coating solution on the ion exchange membrane, the ion exchange membrane includes a commercial Dynamic Alpha membrane or a flow battery separator, and the coating amount of the modified coating solution is 0.5 mL cm -2 .

6. The method of modifying a flow battery separator of claim 1, wherein, In the step of subjecting the ion exchange membrane to evaporation treatment to obtain the modified ion exchange membrane, the temperature of the evaporation is 50-90°C.

7. The method of modifying a flow battery separator of claim 1, wherein, In the step of subjecting the modified ion exchange membrane to direct current pulse heating treatment to obtain the modified separator, the step specifically comprises the following steps: the modified ion exchange membrane is loaded in a flow battery clamp, and the modified coating surface of the modified ion exchange membrane faces the direction of the zinc negative electrode; the modified ion exchange membrane is treated by using a direct current pulse heating technology to remove zinc dendrites on the modified ion exchange membrane.

8. The method of modifying a flow battery separator of claim 7, wherein, In the direct current pulse heating technology, the range of direct current is 10-220V, and the number of interval turns in the direct current pulse heating technology is 2-1000.

9. A modified flow battery separator, characterized in that, The modified method is prepared by any one of claims 1-8.

10. A zinc-bromine flow battery characterized by, The modified flow battery separator comprises the modified method of claim 8.

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