A nanocomposite membrane for flow batteries and a method of making the same

Abstract

The application relates to the field of electrochemical energy storage, in particular to a nano-composite membrane for a flow battery and a preparation method thereof. The nano-composite membrane comprises polybenzimidazole as a membrane matrix and nanoparticles as a dopant. The polybenzimidazole as the membrane matrix can effectively prevent the penetration of active substances between the positive and negative electrode electrolytes; the nanoparticles doped in the matrix have strong hydrophilicity, improve the water and acid content of the membrane, and promote the cross-membrane transmission of carriers. The preparation method mainly comprises the following steps: firstly, preparing a polybenzimidazole solution with a proper concentration; then uniformly dispersing the nanoparticles in the polybenzimidazole solution; then coating the obtained casting solution on a flat plate; finally, evaporating the solvent and solidifying to form the nano-composite membrane. The nano-composite membrane has the advantages of strong ion selectivity, high proton conductivity, good chemical stability, strong mechanical performance, low cost, high repeatability, easy mass production and application in the field of flow batteries.

Description

Technical Field

[0001] This invention relates to the field of electrochemical energy storage, specifically to a nanocomposite membrane for flow batteries and its preparation method. Background Technology

[0002] Developing grid-scale energy storage systems is a primary task in addressing the intermittency of renewable energy sources and ensuring a stable power supply. Redox flow batteries (RFBs) store energy in a liquid electrolyte and offer advantages such as power and capacity independence, high reliability, environmental friendliness, and long cycle life, making them one of the most promising large-scale energy storage technologies. Among them, vanadium redox flow batteries (VRFBs) utilize vanadium ions in different valence states as the positive and negative electrode active materials, fundamentally avoiding the cross-contamination problem of electrolytes in traditional flow batteries, and are at the forefront in both technological innovation and commercial application. However, the high cost of these batteries poses a significant challenge to the further commercialization of vanadium redox flow batteries.

[0003] As a key component of vanadium redox flow batteries, the separator has a significant impact on the battery's cost and performance. Currently, the most widely used separator in vanadium redox flow batteries is the Nafion series produced by DuPont. While Nafion membranes possess high proton conductivity and excellent chemical stability, their poor ion selectivity and high price not only reduce battery energy efficiency and capacity but also significantly increase battery costs. Therefore, developing battery separators with high proton conductivity, strong ion selectivity, chemical and mechanical stability, and low cost has become crucial for the further development of flow batteries.

[0004] Due to their high ion selectivity and outstanding chemical stability, polybenzimidazole (PBI)-based membranes have attracted considerable attention and extensive research in recent years. However, the tight packing of their rigid backbone results in low proton conductivity in PBI membranes, thus limiting improvements in battery performance. Even widening the ion transport channels through acid treatment (e.g., sulfuric acid, phosphoric acid) has limited effect on improving the membrane's proton conductivity. Some studies have found that introducing hydrophilic organic compounds into the PBI matrix to prepare blended membranes can increase the membrane's acid and water content, thereby promoting proton transport. However, the addition of hydrophilic organic compounds can easily lead to membrane swelling, causing dimensional, mechanical, and chemical instability, which severely reduces battery life. Therefore, to address the critical issue of low proton conductivity in PBI-based membranes, more sophisticated and appropriate modifications are needed to improve membrane performance while ensuring a longer lifespan. Summary of the Invention

[0005] The purpose of this invention is to provide a nanocomposite membrane for flow batteries and its preparation method. By uniformly dispersing hydrophilic inorganic materials within a polybenzimidazole matrix, the acid and water content of the membrane is increased, promoting proton transport in this inorganic-organic composite membrane. Simultaneously, the inherent vanadium-blocking ability and anti-swelling properties of the inorganic nanoparticles ensure the composite membrane's ultra-high ion selectivity and excellent long-cycle stability. Furthermore, the preparation process is simple, applicable to a wide range of inorganic materials, exhibits good reproducibility, and is easily scaled up industrially.

[0006] The technical solution of this invention is:

[0007] A nanocomposite membrane for flow batteries is disclosed, wherein the composite membrane uses polybenzimidazole as the membrane matrix and inorganic nanoparticles as the doping phase, wherein: the polybenzimidazole matrix mainly plays an ion selection role; the inorganic nanoparticles uniformly dispersed in the membrane have strong hydrophilicity, which increases the water and acid content of the membrane, thereby enhancing the proton conduction capability of the membrane.

[0008] Furthermore, in the aforementioned nanocomposite membrane for flow batteries, the polybenzimidazole refers to a polymer material whose main chain contains benzimidazole groups; the inorganic nanoparticles include zero-dimensional, one-dimensional, and two-dimensional nanoparticles with intrinsic hydrophilicity or hydrophilic treatment, specifically including hydrophilic carbon nanotubes containing hydroxyl, amino, and sulfonic acid groups, boron phosphate, montmorillonite, lithium saponite, and zwitterionic modified silica microspheres.

[0009] Furthermore, in the aforementioned nanocomposite membrane for flow batteries, the amount of inorganic nanoparticles added accounts for 0.1 to 80 wt% of the total mass of the casting solution.

[0010] A method for preparing a nanocomposite film for a flow battery specifically includes the following steps:

[0011] (1) Weigh a certain amount of polybenzimidazole powder, dissolve it in an organic solvent, and prepare a polybenzimidazole solution;

[0012] (2) Weigh a certain mass of inorganic nanoparticles and disperse them uniformly in the polybenzimidazole solution obtained in step (1) by ultrasonication and stirring to obtain casting solution;

[0013] (3) The casting liquid obtained in step (2) is coated onto a plate using a solvent casting method;

[0014] (4) The membrane solution coated on the plate obtained in step (3) is heated and solidified by evaporation solvent method, and the nanocomposite membrane is obtained after cooling.

[0015] (5) Before use, the nanocomposite membrane obtained in step (4) is immersed in sulfuric acid or phosphoric acid solution for acid treatment.

[0016] Furthermore, in the above-mentioned method for preparing nanocomposite membranes for flow batteries, the organic solvent used in step (1) can be one or a combination of N-methylpyrrolidone (NMP), N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), and dimethyl sulfoxide (DMSO).

[0017] Furthermore, in the above-mentioned method for preparing nanocomposite membranes for flow batteries, the mass percentage of the polybenzimidazole solution in step (1) is 1-20 wt%.

[0018] Furthermore, in the above-mentioned method for preparing nanocomposite films for flow batteries, the inorganic nanoparticles used in step (2) have a size of 0.01 to 10 μm.

[0019] Furthermore, in the above-mentioned method for preparing nanocomposite films for flow batteries, the thickness of the nanocomposite film obtained in step (4) is 1 to 500 μm.

[0020] The present invention has the following advantages and beneficial effects:

[0021] The nanocomposite membrane prepared by this invention has advantages such as high water and acid content, good mechanical and chemical stability, strong ion selectivity, and high proton conductivity, making it suitable for use in flow batteries.

[0022] (1) By uniformly dispersing hydrophilic inorganic materials in the polybenzimidazole matrix, the acid and water content of the membrane is increased, thereby promoting proton transport in the inorganic-organic composite membrane. At the same time, the natural vanadium-blocking ability and anti-swelling properties of the inorganic nanoparticles ensure the ultra-high ion selectivity and excellent long-term cycling stability of the composite membrane;

[0023] (2) By adjusting the geometry, hydrophilicity, and amount of inorganic nanoparticles, this invention can flexibly control the ion selectivity and proton conductivity of the composite membrane, thereby preparing ion exchange membranes suitable for different battery systems and operating conditions. The preparation process is simple, applicable to a wide range of inorganic materials, has good repeatability, and is easy to scale up industrially. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the nanocomposite film in Example 1;

[0025] Figure 2 The diagram shows the structure (a), scanning electron microscope (SEM) image (b), and FTIR image (c) of the nanoparticles (hydrophilic mesoporous silica microspheres, AMS) used in Example 1.

[0026] Figure 3 The images show scanning electron microscope (SEM) images of the surface (a) and cross-section (b) of the nanocomposite film prepared in Example 1.

[0027] Figure 4 A comparison graph (c) shows the acid and water content (a), proton conductivity (b), and vanadium ion permeability of the nanocomposite membrane prepared in Example 1, the experimental control group PBI membrane, and the commercial control group Nafion 212 membrane.

[0028] Figure 5 This is a comparison chart of the battery performance of the nanocomposite membrane prepared in Example 1, the experimental control group PBI membrane, and the commercial control group Nafion212 membrane. Detailed Implementation

[0029] To facilitate understanding of the present invention, a more comprehensive description will be given below. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the present invention.

[0030] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0031] The present invention will be further described in detail below with reference to embodiments and accompanying drawings.

[0032] Example 1:

[0033] The specific preparation process of the nanocomposite film for the flow battery in this embodiment is as follows:

[0034] (1) Weigh 1g of polybenzimidazole powder, dissolve it in the organic solvent DMAc, and prepare a 10wt% polybenzimidazole solution.

[0035] (2) Weigh 0.4g of AMS with a particle size of about 120nm, and use ultrasound and stirring to uniformly disperse it in the polybenzimidazole solution obtained in step (1) to obtain a casting solution with an inorganic nanoparticle addition of 4wt%.

[0036] (3) The casting liquid obtained in step (2) is coated onto a plate using the solvent casting method.

[0037] (4) The membrane solution obtained in step (3) is coated on the plate by evaporation solvent method. After heating and solidification, the nanocomposite membrane is obtained after cooling. The thickness of the nanocomposite membrane is about 25 μm.

[0038] (5) Before use, immerse the nanocomposite membrane obtained in step (4) in 3M sulfuric acid solution for acid treatment at room temperature for 3 days.

[0039] The structure and properties of the nanocomposite membrane in this embodiment will be characterized below:

[0040] like Figure 1 The diagram shown is a schematic of the nanocomposite membrane in this embodiment. It can be seen that the hydrophilic mesoporous silica particles are uniformly dispersed in the polybenzimidazole matrix.

[0041] like Figure 2 The diagram shows the structure (a), SEM image (b), and FTIR image (c) of the nanoparticles used (hydrophilic mesoporous silica microspheres, AMS). In this embodiment, dahlia-shaped mesoporous silica microspheres (with a particle size of approximately 120 nm) were used as inorganic particles, which, due to their large surface area, allow for extensive modification with hydrophilic groups. Subsequently, to enhance the hydrophilicity of the inorganic particles, hydrophilic polymers polyethyleneimine (PEI) and phytic acid (PA) were deposited on the microspheres through layer-by-layer self-assembly.

[0042] like Figure 3 The images show SEM images of the surface (a) and cross-section (b) of the prepared nanocomposite membrane. It can be seen that the AMS particles are uniformly dispersed in the PBI membrane matrix, which ensures the high ion selectivity and mechanical dimensional stability of the membrane.

[0043] like Figure 4 The figure shows a comparison (c) of acid and water content (a), proton conductivity (b), and vanadium ion permeability of the prepared nanocomposite membrane, the experimental control group PBI membrane, and the commercial control group Nafion 212 membrane. Figure 4 (a) It can be seen that the addition of inorganic nanoparticles greatly increases the acid and water content of the composite membrane. Therefore, the proton conductivity of this composite membrane (57.7 mS / cm) is significantly improved. -1 It is nearly 7 times that of pure PBI membrane (8.7 mS / cm) -1 It is even superior to commercial Nafion membranes. Figure 4 (b)). By Figure 4 (c) It can be seen that the vanadium ion permeability of this composite membrane is 10.5 × 10⁻⁶. -7 cm 2 h -1 (This is) far lower than that of commercial Nafion 212 membranes (168×10). -7 cm 2 h -1 The presence of 100 indicates that it has excellent vanadium blocking ability.

[0044] like Figure 5The figure shows a comparison of battery performance between the nanocomposite membrane, the experimental control group PBI membrane, and the commercial control group Nafion 212 membrane. Due to its significantly improved proton conductivity compared to the PBI membrane and its higher vanadium blocking capability compared to the Nafion 212 membrane, this composite membrane exhibits higher coulombic efficiency, voltage efficiency, and energy efficiency in vanadium redox flow battery tests. Even at 240 mA cm⁻¹... -2 At high current densities, its energy efficiency remains above 80% (80.4%), which is 10.4% higher than that of pure PBI film and 6.1% higher than that of commercial Nafion 212 film.

[0045] Example 2:

[0046] The method is the same as in Example 1, except that the concentration of the PBI solution prepared in step (1) is 5 wt%.

[0047] Example 3:

[0048] The method is the same as in Example 1, except that DMF is used as the solvent in step (1).

[0049] Example 4:

[0050] The method is the same as in Example 1, except that the inorganic nanoparticles used in step (2) are hydrophilic carbon nanotubes.

[0051] Example 5:

[0052] The method is the same as in Example 1, except that the amount of inorganic nanoparticles added in step (2) is 6 wt%.

[0053] Example 6:

[0054] The method is the same as in Example 1, except that the thickness of the composite film prepared in step (4) is 35 μm.

Claims

1. A method for preparing a nanocomposite film for a flow battery, characterized in that, include: The composite membrane uses polybenzimidazole as the membrane matrix and inorganic nanoparticles as the doping phase. The polybenzimidazole matrix mainly plays an ion selection role. The inorganic nanoparticles uniformly dispersed in the membrane have strong hydrophilicity, which increases the water and acid content of the membrane, thereby enhancing the proton conduction capacity of the membrane. Specifically, the following steps are included: (1) Weigh a certain amount of polybenzimidazole powder, dissolve it in an organic solvent, and prepare a polybenzimidazole solution; (2) Weigh a certain mass of inorganic nanoparticles and disperse them uniformly in the polybenzimidazole solution obtained in step (1) by ultrasonication and stirring to obtain casting solution; (3) The casting solution obtained in step (2) is coated onto a plate using a solvent casting method; (4) The membrane solution coated on the plate obtained in step (3) is heated and solidified by evaporation solvent method, and then cooled to obtain nanocomposite membrane; (5) Before use, the nanocomposite membrane obtained in step (4) is immersed in sulfuric acid or phosphoric acid solution for acid treatment. Specifically, before use, the nanocomposite membrane obtained in step (4) is immersed in 3M sulfuric acid solution for acid treatment at room temperature for 3 days. To enhance the hydrophilicity of inorganic nanoparticles, hydrophilic polymers polyethyleneimine and phytic acid were deposited on microspheres through a layer-by-layer self-assembly process. The inorganic nanoparticles are dahlia-shaped hydrophilic mesoporous silica microspheres with a particle size of 120 nm.

2. The method for preparing a nanocomposite film for a flow battery according to claim 1, characterized in that, The polybenzimidazole refers to a polymer material whose main chain contains benzimidazole groups.

3. The method for preparing a nanocomposite film for a flow battery according to claim 2, characterized in that, The amount of inorganic nanoparticles added accounts for 4 wt% of the total mass of the casting solution.

4. The method for preparing the nanocomposite film for flow batteries according to claim 1, characterized in that, The organic solvent used in step (1) is one or a combination of N-methylpyrrolidone, N,N-dimethylacetamide, N,N-dimethylformamide and dimethyl sulfoxide.

5. The method for preparing the nanocomposite film for flow batteries according to claim 1, characterized in that, The mass percentage of the polybenzimidazole solution in step (1) is 1~20 wt%.

6. The method for preparing the nanocomposite film for flow batteries according to claim 1, characterized in that, The thickness of the nanocomposite film obtained in step (4) is 25 μm.

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