A zinc-bromine flow battery carbon plastic bipolar plate and a preparation method and application thereof

Abstract

This invention discloses a carbon-plastic bipolar plate for a zinc-bromine flow battery, its preparation method, and its application, belonging to the field of electrochemical energy storage technology. The method includes: dispersing nitrogen-doped hollow carbon nanotubes and spraying them onto the positive electrode side of a carbon-plastic bipolar plate; after drying, a nitrogen-doped hollow carbon nanotube-modified positive electrode carbon-plastic bipolar plate is obtained; dispersing boron-nitrogen co-doped carbon and spraying it onto the negative electrode side of a pretreated carbon-plastic bipolar plate, after drying again, a boron-nitrogen co-doped carbon-plastic negative electrode carbon-plastic bipolar plate is obtained. On the positive electrode side, the nitrogen-doped hollow carbon nanotubes catalyze the bromine reaction through nitrogen doping, reducing the overpotential; the hollow structure adsorbs bromine species and uses charge action to inhibit bromine permeation, reducing self-discharge. On the negative electrode side, the boron-nitrogen co-doped carbon uses B-N zinc-loving sites to guide uniform and dense zinc deposition, inhibiting dendrite formation; and inhibits hydrogen evolution through charge regulation. Both methods synergistically improve the bromine barrier performance, reaction kinetics, and dendrite suppression ability of the carbon-plastic bipolar plate.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical energy storage technology, specifically relating to a carbon-plastic bipolar plate for a zinc-bromine flow battery, its preparation method, and its application. Background Technology

[0002] Zinc-bromine flow batteries, as an important electrochemical energy storage technology, have broad application prospects in large-scale energy storage due to their advantages such as high energy density, low cost, and long cycle life. However, their industrialization has long been limited by the following core bottlenecks: the active bromine species in the positive electrode (Br3). - The bromine / bromine compound (Br2 / Br2) penetrates the membrane, triggering self-discharge and causing a sharp drop in coulombic efficiency and continuous capacity decay. - The conversion reaction is slow, involves multiple steps, and requires high activation energy. Typically, a complexing agent is added to the positive electrode to complex Br2 and improve its solubility, but this further complicates the Br2 reaction pathway. The slow Br2 reaction becomes a bottleneck in overall battery performance, resulting in high polarization voltage, significantly reducing voltage efficiency and power density, leading to low energy efficiency, limited power density, and low coulombic efficiency. The uneven electric field distribution at the negative electrode makes it easy for dendrites to form during zinc deposition, which can easily puncture the separator, causing a short circuit, threatening safety, and limiting cycle life (<500 cycles). These bottlenecks directly lead to the industrialization dilemma of zinc-bromine flow batteries.

[0003] Traditional zinc-bromine flow battery bipolar plates suffer from several drawbacks. First, they lack sufficient resistance to bromine corrosion; bromine and polybrominates in the electrolyte corrode the graphite matrix, leading to material pulverization, increased resistance, and shortened battery life. Second, they exhibit high interfacial resistance; the contact resistance between the bipolar plate and the electrodes results in high internal resistance, reducing voltage and energy efficiency. Finally, they are inert to bromine reactions; traditional bipolar plates lack catalytic activity, failing to promote bromine / bromine conversion reactions, limiting the battery's power density, and potentially exacerbating bromine side reactions. These defects collectively restrict the battery's long-term cycle stability and power performance. Chinese patent application CN120978108A discloses a composite bipolar plate for zinc-bromine flow batteries and its preparation method. By constructing a "point-line-surface" interpenetrating conductive network using carbon fiber, Ketjen black, and graphene, the overall conductivity of the bipolar plate is significantly improved. Simultaneously, by spraying nitrogen-doped porous carbon material onto the substrate surface, its large specific surface area and mesoporous structure provide Br2 adsorption sites, thereby enhancing bromine reaction kinetics and suppressing bromine shuttle. However, the modified layer of this scheme has a single function, using the same nitrogen-doped porous carbon material on both the positive and negative electrode sides, and does not provide a specific solution for special problems such as zinc dendrite growth and hydrogen evolution side reactions on the negative electrode side. Chinese patent application CN121307076A further proposes a technical approach of partitioned modification of the positive and negative electrodes, disclosing a multifunctional bipolar plate for a zinc-bromine flow battery and its preparation method. This scheme loads polyaniline on the positive electrode side, utilizing its benzene ring structure for physical coverage and its reversible adsorption through a complex structure to achieve a combination of bromine barrier and catalytic functions; and loads a cyclodextrin polymer / Nafion composite coating on the negative electrode side, using cyclodextrin nanochannels to restrict Zn 2+ The diffusion direction and the sulfonic acid groups of Nafion form directional ion channels, synergistically regulating the uniform deposition of zinc and stabilizing the interfacial pH to suppress hydrogen evolution. While this scheme achieves functional partitioning of the positive and negative electrodes, its negative electrode modification material is an organic polymer system with limited electronic conductivity, and the regulation of zinc deposition mainly relies on physical confinement and ion conduction, lacking specific control over Zn. 2+ There is still room for improvement in the active sites with strong chemisorption properties in guiding uniform zinc nucleation and fundamentally inhibiting dendrite growth.

[0004] Therefore, there is an urgent need to develop novel bipolar plate materials that combine high selectivity, high catalytic performance, high ion conduction, and strong mechanical / chemical stability, which is of great significance for improving the performance of zinc-bromine flow batteries and promoting their practical application. Summary of the Invention

[0005] In order to overcome the shortcomings of the prior art, the present invention aims to provide a carbon-plastic bipolar plate for zinc-bromine flow batteries, its preparation method and application, so as to solve the technical problems of bromine permeation, slow bromine kinetic reaction and zinc dendrite growth in zinc-bromine flow batteries.

[0006] To achieve the above objectives, the present invention employs the following technical solution:

[0007] This invention discloses a method for preparing a carbon-plastic bipolar plate for a zinc-bromine flow battery, comprising:

[0008] Zinc nitrate hexahydrate and 2-methylimidazole were dissolved in methanol and mixed. The mixture was then subjected to static reaction, centrifugation, washing, drying and high-temperature pyrolysis to obtain nitrogen-doped hollow carbon nanotubes. The nitrogen-doped hollow carbon nanotubes were dispersed and sprayed onto the positive electrode side of a carbon-plastic bipolar plate. After drying again, a positive carbon-plastic bipolar plate modified with nitrogen-doped hollow carbon nanotubes was obtained.

[0009] Chitosan powder was dissolved in dilute acetic acid, boric acid was added and stirred until uniform, dried and ground into fine powder, and then subjected to high-temperature pyrolysis. After grinding again, boron-nitrogen co-doped carbon was obtained. The boron-nitrogen co-doped carbon was dispersed and sprayed onto the negative electrode side of a pretreated carbon-plastic bipolar plate. After drying again, a negative carbon-plastic bipolar plate modified with boron-nitrogen co-doped carbon was obtained.

[0010] Preferably, the ratio of zinc nitrate hexahydrate, 2-methylimidazole and methanol is (15-25) g: (8-15) g: (1.0-1.5) L.

[0011] Preferably, in the preparation process of nitrogen-doped hollow carbon nanotubes, the static reaction time is 20-24 h; the centrifugation speed is 8000-10000 rpm and the centrifugation time is 10-15 min; the drying temperature is 50-60℃ and the drying time is 10-12 h.

[0012] The dispersion conditions for nitrogen-doped hollow carbon nanotubes include: dispersing nitrogen-doped hollow carbon nanotubes in deionized water to obtain a nitrogen-doped hollow carbon nanotube dispersion with a mass concentration of 5-30 mg / mL; dispersing by ultrasound with a power of 300-400 W for 10-60 min; spraying with a spray velocity of 5-10 mL / min for 5-10 min; and drying at a temperature of 40-60℃ for 8-10 h.

[0013] Preferably, the high-temperature pyrolysis conditions during the preparation of nitrogen-doped hollow carbon nanotubes include: a heating rate of 3-5℃ / min, a pyrolysis temperature of 800-1000℃, a pyrolysis time of 2-2.5h, and a nitrogen flow rate of 50-200ml / min.

[0014] Preferably, the ratio of chitosan, dilute acetic acid and boric acid is (5-10) g: (300-600) ml: (5-10) g.

[0015] Preferably, during the preparation of boron-nitrogen co-doped carbon, the stirring rate is 300-500 rpm and the stirring time is 2-4 hours; the drying temperature is 60-80℃ and the drying time is 12-24 hours.

[0016] The conditions for dispersing boron-nitrogen co-doped carbon include: dispersing boron-nitrogen co-doped carbon in deionized water to obtain a boron-nitrogen co-doped carbon dispersion with a mass concentration of 5-25 mg / mL; dispersing by ultrasonication with a power of 300-400 W for 10-60 min; spraying with a spray velocity of 5-10 mL / min for 5-10 min; and drying at a temperature of 40-60℃ for 8-10 h.

[0017] Preferably, the conditions for high-temperature pyrolysis during the preparation of boron-nitrogen co-doped carbon include: a heating rate of 2-5℃ / min, a pyrolysis temperature of 800-1000℃, a holding time of 1-3h, and a nitrogen flow rate of 50-200ml / min.

[0018] Preferably, the carbon-plastic bipolar plates are all pretreated carbon-plastic bipolar plates. The pretreatment conditions include: ultrasonically cleaning the carbon-plastic bipolar plates with ethanol or deionized water for 15-30 minutes, and then drying them in a vacuum drying oven at 40-60°C for 12-24 hours.

[0019] This invention discloses a carbon-plastic bipolar plate for a zinc-bromine flow battery, which is prepared using the above-mentioned method for preparing a carbon-plastic bipolar plate for a zinc-bromine flow battery.

[0020] This invention discloses the application of carbon-plastic bipolar plates in the preparation of zinc-bromine flow batteries, with the coulombic efficiency of the zinc-bromine flow batteries being 94.3%-96.1%, the voltage efficiency being 85.3%-86.1%, and the energy efficiency being 80.44%-83.03%.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] This invention discloses a method for preparing a carbon-plastic bipolar plate for a zinc-bromine flow battery. Zinc nitrate hexahydrate and 2-methylimidazolium are used as raw materials to prepare a zeolitic imidazolate framework-8 (ZIF-8). Using ZIF-8 as a precursor, nitrogen-doped carbon hollow nanoboxes (NC-HNBs) are prepared by high-temperature pyrolysis. The internal cavity of NC-HNBs provides a structural basis for the subsequent physical confinement of bromine species. Simultaneously, nitrogen atoms from 2-methylimidazolium are in situ doped into the carbon framework, forming catalytically active sites such as pyridine nitrogen and pyrrole nitrogen, creating conditions for accelerating the redox reaction of bromine. The carbon framework formed by pyrolysis also endows the material with excellent conductivity, providing channels for rapid electron transport. NC-HNBs are dispersed and sprayed onto the positive electrode side. The continuous and dense coating formed by the spraying process constructs a highly conductive interconnect network on the surface of the bipolar plate, ensuring that electrons can be rapidly transferred from the bipolar plate to the reaction sites, reducing ohmic resistance and polarization loss. The hollow cavities of NC-HNBs can physically encapsulate the generated Br2 and polybrominates, while nitrogen-doped sites chemically adsorb negatively charged polybrominates through electrostatic interactions. Together, they anchor bromine species on the positive electrode side, effectively suppressing bromine permeation and self-discharge. At the same time, the dense coating acts as a chemically inert barrier, protecting the bipolar plate substrate from corrosion by the highly oxidizing bromine environment. Boron and Nitrogen Co-doped Carbon (BNC) is prepared by solution composite and high-temperature pyrolysis using chitosan as the carbon and nitrogen source and boric acid as the boron source. The amino groups of chitosan are uniformly complexed with boric acid at the molecular level, ensuring that B and N atoms form a proximity doping structure in the carbon lattice after pyrolysis. Because the electronegativity of B atoms is lower than that of C and N atoms, the co-doping of B and N produces strong local charge polarization, forming a large number of Zn atoms. 2+ Zinc-loving sites with strong adsorption capacity can reduce Zn 2+The nucleation overpotential guides uniform nucleation; charge redistribution alters the electronic state of the material surface, increasing the hydrogen evolution reaction overpotential and thermodynamically suppressing side reactions; the carbon framework also ensures high conductivity. This achieves a material-level integration of guided deposition and hydrogen evolution suppression. Dispersed BNC is sprayed onto the negative electrode side. The uniform BNC coating ensures a highly uniform electric field distribution on the bipolar plate surface, avoiding preferential zinc ion deposition caused by localized charge concentration; the synergistic zincophilic sites formed by exposed B and N co-doping guide zinc atoms to preferentially nucleate at these uniformly distributed sites, achieving two-dimensional layered dense deposition and fundamentally suppressing dendrite growth; simultaneously, high conductivity provides an efficient electron transport path for zinc deposition and dissolution reactions, promoting reaction kinetics; the carbon framework of BNC is highly stable in acidic environments and at negative potentials, protecting the underlying bipolar plate from corrosion. The intrinsic properties of BNC are transformed into interface control capabilities. Through independent synthesis and partitioned loading of positive and negative electrode materials, a synergistic system of positive electrode catalysis and bromine fixation, and negative electrode zincophilicity and hydrogen suppression is constructed. The positive electrode NC-HNBs inhibit bromine permeation, reducing interference from the negative electrode side reactions. The negative electrode BNC inhibits dendrite growth, reducing the irreversible consumption of bromine in the positive electrode. The two form a virtuous cycle, which improves the battery's coulombic efficiency, voltage efficiency, energy efficiency, and cycle life.

[0023] This invention discloses a carbon-plastic bipolar plate for a zinc-bromine flow battery, featuring a functionally partitioned bipolar plate with an NC-HNBs modification layer on the positive electrode side and a BNC modification layer on the negative electrode side. This bipolar plate is not a simple superposition of positive and negative electrode modification layers, but rather, through synergistic design, it creates a virtuous cycle between the rapid bromine reaction at the positive electrode and the uniform zinc deposition at the negative electrode. The positive electrode side inhibits bromine permeation, reducing side reaction interference at the negative electrode, while the negative electrode side inhibits dendrite growth, reducing irreversible bromine consumption at the positive electrode, thereby achieving performance improvement.

[0024] This invention discloses the application of a carbon-plastic bipolar plate for zinc-bromine flow batteries in the fabrication of zinc-bromine flow batteries. Through the synergistic effect of functional partitioning modification of the positive and negative electrodes, a systematic improvement in electrochemical performance is achieved. On the positive electrode side, the nitrogen-doped sites of NC-HNBs significantly accelerate the redox reaction kinetics of bromine to reduce overpotential. Its hollow structure anchors bromine species on the positive electrode side through physical confinement and electrostatic adsorption to inhibit bromine permeation. Simultaneously, its highly conductive network reduces interfacial resistance and protects the bipolar plate substrate from bromine corrosion. On the negative electrode side, in boron-nitrogen co-doped carbon, the synergistic zinc-loving sites formed by B and N co-doping guide the uniform nucleation and dense deposition of zinc ions to inhibit dendrite growth. Its charge polarization effect increases the hydrogen evolution overpotential to reduce side reactions, while high conductivity promotes the kinetics of zinc deposition and dissolution reactions. The synergistic effect of the positive and negative electrode modification layers forms a virtuous cycle: the positive electrode inhibits bromine permeation, reducing interference from negative electrode side reactions; and the negative electrode inhibits dendrite growth, reducing irreversible bromine consumption at the positive electrode. In Comparative Example 1, the coulombic efficiency of the unmodified bipolar plate was only 91.2% and the energy efficiency was only 76.06%. However, in Example 4, with NC-HNBs concentration of 25 mg / mL and BNC concentration of 20 mg / mL, the efficiency was increased to 96.1% and 83.03%, respectively. This directly demonstrates the significant effect of the positive and negative electrode partitioning modification strategy in suppressing bromine shuttle, reducing polarization, and reducing energy loss. This improved the battery coulombic efficiency to 94.3%-96.1%, voltage efficiency to 85.3%-86.1%, and energy efficiency to 80.44%-83.03%, comprehensively improving the battery's cycle life, energy efficiency, and safety. Detailed Implementation

[0025] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] Unless otherwise specified, all embodiments and preferred embodiments mentioned herein can be combined to form new technical solutions.

[0027] Unless otherwise specified, all the technical features and preferred features mentioned herein can be combined to form new technical solutions.

[0028] In this invention, unless otherwise specified, percentage (%) or parts refer to weight percentage or parts relative to the composition.

[0029] In this invention, unless otherwise specified, the components involved or their preferred components can be combined to form new technical solutions.

[0030] In this invention, unless otherwise specified, the numerical range "a~b" is an abbreviation for any combination of real numbers between a and b, where a and b are both real numbers.

[0031] The "scope" disclosed in this invention can be in the form of a lower limit and an upper limit, and can be one or more lower limits and one or more upper limits, respectively.

[0032] In this invention, the term "and / or" as used herein refers to any combination of one or more of the associated listed items, as well as all possible combinations, and includes such combinations.

[0033] Unless otherwise stated, the technical and scientific terms used herein have the same meanings as those familiar to those skilled in the art. Furthermore, any methods or materials similar to or equivalent to those described herein may also be used in this invention.

[0034] This invention discloses a method for preparing a carbon-plastic bipolar plate for a zinc-bromine flow battery, comprising the following steps:

[0035] 1) Synthesis of NC-HNBs

[0036] Dissolve 15-25 g of zinc nitrate hexahydrate and 8-15 g of 2-methylimidazole separately in 1.0-1.5 L of methanol at room temperature. Mix rapidly and allow to stand for 20-24 h. After the reaction is complete, centrifuge at 8000-10000 rpm for 10-15 min to collect the white precipitate. Wash the precipitate 2-3 times with methanol by centrifugation to remove residual reactants. Dry the washed precipitate in a vacuum drying oven at 50-60 °C for 10-12 h to obtain ZIF-8 precursor powder. Pyrolyze the obtained ZIF-8 precursor powder at high temperature under a nitrogen atmosphere at a heating rate of 3-5 °C / min, a pyrolysis temperature of 800-1000 °C, and a pyrolysis time of 2-2.5 h. After pyrolysis, allow the furnace to cool naturally to room temperature under a nitrogen atmosphere at a gas flow rate of 50-200 ml / min. The resulting black powder is NC-HNBs.

[0037] 2) Synthesis of BNC

[0038] Dissolve 5-10g of chitosan powder in 300-600ml of dilute acetic acid, mechanically stirring until completely dissolved. Stir at 300-500rpm for 2-4 hours at room temperature. Then, add 5-10g of boric acid and continue stirring at room temperature for 2-4 hours to ensure thorough mixing. Dry the homogeneous solution in an oven at 60-80℃ for 12-24 hours to obtain the precursor, which is then ground into a fine powder. Place the ground powder in a tube furnace for high-temperature pyrolysis under a nitrogen inert gas atmosphere at a flow rate of 50-200ml / min to completely remove oxygen. Proceed to the target temperature from room temperature at a slow heating rate of 2-5℃ / min. Set the final pyrolysis temperature to 800-1000℃ and maintain this temperature for 1-3 hours to ensure complete carbonization and doping. After pyrolysis, allow to cool naturally to room temperature under a protective atmosphere. The resulting black powder product, after grinding, is BNC.

[0039] 3) Pretreatment of positive and negative carbon-plastic bipolar plates

[0040] The carbon-plastic bipolar plate was ultrasonically cleaned with ethanol or deionized water for 15-30 minutes to remove impurities and contaminants from the surface. After cleaning, it was placed in a vacuum drying oven at 40-60℃ and dried for 12-24 hours to obtain the pretreated carbon-plastic bipolar plate.

[0041] 4) Preparation of NC-HNBs modified positive carbon-plastic bipolar plate material

[0042] The prepared NC-HNBs powder was dispersed in deionized water as a suitable dispersant to form an NC-HNBs dispersion with a concentration of 5-30 mg / mL. Ultrasonic dispersion was then performed at a power of 300-400 W for 10-60 min.

[0043] Take 50 mL of the above mixed solution and spray the suspension evenly onto the positive carbon-plastic bipolar plate using a spray gun. The spraying speed is 5-10 mL / min and the spraying time is 5-10 min. Place the sprayed positive carbon-plastic bipolar plate in a vacuum drying oven and dry it at 40-60℃ for 8-10 h to complete the modification of the positive carbon-plastic bipolar plate with NC-HNBs, and obtain the positive carbon-plastic bipolar plate modified with nitrogen-doped hollow carbon nanotubes.

[0044] 5) Preparation of BNC-modified carbon-plastic bipolar plate material for negative electrode

[0045] The prepared BNC powder was dispersed in deionized water as a suitable dispersant to form a BNC dispersion with a concentration of 5-25 mg / mL. Ultrasonic dispersion was then performed at a power of 300-400 W for 10-60 min.

[0046] Take 50 mL of the above mixed solution and spray the suspension evenly onto the negative carbon-plastic bipolar plate using a spray gun. The spraying speed is 5-10 mL / min and the spraying time is 5-10 min. Place the sprayed negative carbon-plastic bipolar plate in a vacuum drying oven and dry it at 40-60℃ for 8-10 h to complete the modification of the negative carbon-plastic bipolar plate with BNC, and obtain the negative carbon-plastic bipolar plate modified with boron and nitrogen co-doped carbon.

[0047] The present invention also discloses a zinc-bromine flow battery comprising the carbon-plastic bipolar plate of the zinc-bromine flow battery described above, wherein the coulombic efficiency of the zinc-bromine flow battery is 94.3%-96.1%; the voltage efficiency is 85.3%-86.1%; and the energy efficiency is 80.44%-83.03%.

[0048] This invention loads NC-HNBs onto a carbon-plastic bipolar plate at the positive electrode of a zinc-bromine flow battery. NC-HNBs, through nitrogen atom doping, effectively regulate the charge distribution on the surface of the carbon material, thereby altering the charge distribution on the bipolar plate and facilitating the redox reaction of bromine (Br₂). - The presence of Br2 / Br2 creates numerous highly catalytically active sites, significantly reducing the reaction overpotential and thus accelerating the bromine reaction kinetics. NC-HNBs, with their large specific surface area, load more active sites, increasing the reaction interface for the bromine redox reaction and further accelerating the bromine reaction kinetics. The internal cavities of NC-HNBs confine the generated Br2 and polybrominates within their cavities or adsorb them onto the pore walls, effectively reducing the free diffusion of bromine. On the other hand, nitrogen-doped sites have a strong chemisorption effect on polybrominates, especially the electrostatic interaction between positively charged carbon atoms and negatively charged polybrominates, further anchoring them to the positive electrode side, thereby mitigating bromine permeation, reducing self-discharge and capacity decay, and significantly improving the battery's coulombic efficiency and cycle capacity retention. NC-HNBs form a highly conductive interconnect network on the bipolar plate surface, ensuring rapid electron transport from the bipolar plate to the reaction sites, and their excellent conductivity and catalytic properties jointly accelerate the Br2 / ... - The increased electron transfer rate of the redox couple significantly reduces the resistance between them, directly lowering the ohmic internal resistance and polarization losses during battery operation, thereby improving the battery's voltage efficiency and energy efficiency. In highly oxidizing and corrosive bromine environments, the NC-HNBs coating acts as a robust chemically inert barrier, directly covering and protecting the metal bipolar plate substrate, preventing corrosion and passivation. This not only maintains the long-term conductivity and structural integrity of the bipolar plates but also avoids performance degradation caused by corrosion products contaminating the electrolyte, providing crucial protection for extending the overall battery lifespan.

[0049] This invention loads BNC onto a carbon-plastic bipolar plate as the negative electrode of a zinc-bromine flow battery. On one hand, the extremely high conductivity of the BNC coating ensures a highly uniform electric field distribution on the bipolar plate surface, avoiding localized charge concentration and thus preventing uneven zinc ion deposition and reducing zinc dendrite formation. On the other hand, the co-doping of B and N produces a unique electronic structure and localized charge distribution, forming a large number of Zn atoms. 2+ Zinc-loving sites with strong adsorption capacity. These zinc-loving sites can reduce Zn... 2+ The initial nucleation overpotential guides zinc atoms to preferentially nucleate at these uniformly distributed sites, rather than randomly growing at protrusions, thereby achieving two-dimensional layered dense deposition of zinc. This further effectively suppresses dendrites and improves the cycle life and safety of the battery. Boolean atoms have lower electronegativity than C and N atoms. Co-doping of B and N creates strong local charge polarization in the carbon lattice. This charge redistribution significantly alters the electronic state of the material surface, shifting the Fermi level upwards and adjusting the d-band center position, thus making the material surface more responsive to H. + The adsorption energy weakens, thereby increasing the onset overpotential of HER, making H... + The reduction reaction is thermodynamically less likely to occur, thus inhibiting the hydrogen evolution reaction and improving the battery's coulombic efficiency. The high conductivity of BNC material provides an efficient electron transport path for the zinc deposition and dissolution reactions, ensuring rapid zinc deposition / dissolution, promoting reaction kinetics, and facilitating high-power charging and discharging of the battery. This reduces voltage loss on the negative electrode side during charging and discharging, improving energy efficiency. Although the oxidizing environment on the negative electrode side is not as strong as the bromine environment on the positive electrode side, the electrolyte is acidic, still posing a challenge of electrode corrosion. The carbon skeleton of BNC material is very stable in acidic environments and at negative potentials, resisting acid corrosion and protecting the underlying bipolar plate material.

[0050] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. The components of the embodiments of the present invention shown herein can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0051] Example 1

[0052] A method for preparing a carbon-plastic bipolar plate for a zinc-bromine flow battery includes the following steps:

[0053] 1) Synthesis of NC-HNBs

[0054] 15 g of zinc nitrate hexahydrate and 8 g of 2-methylimidazole were dissolved separately in 1.0 L of methanol at room temperature. After rapid mixing, the mixture was allowed to stand for 20 h. After the reaction was complete, the white precipitate was collected by centrifugation at 8000 rpm for 10 min. The precipitate was then washed three times with methanol by centrifugation to remove residual reactants. The washed precipitate was dried in a vacuum drying oven at 50 °C for 10 h to obtain ZIF-8 precursor powder. The obtained ZIF-8 precursor powder was then subjected to high-temperature pyrolysis under a nitrogen atmosphere at a heating rate of 3 °C / min, a pyrolysis temperature of 900 °C, and a pyrolysis time of 2 h. After pyrolysis, the furnace was allowed to cool naturally to room temperature under a nitrogen atmosphere at a gas flow rate of 100 ml / min. The resulting black powder was the final NC-HNBs.

[0055] 2) Pretreatment of the positive carbon-plastic bipolar plate

[0056] The carbon-plastic bipolar plate was ultrasonically cleaned with deionized water for 30 minutes to remove impurities and contaminants from the surface. After cleaning, it was placed in a vacuum drying oven at 50°C for 16 hours.

[0057] 3) Preparation of NC-HNBs modified positive carbon-plastic bipolar plate material

[0058] 1250 mg of NC-HNBs powder was slowly added to 50 ml of deionized water and dispersed by ultrasonication at a power of 300 W for 30 min to form an NC-HNBs dispersion with a concentration of 25 mg / mL.

[0059] The above 50 mL mixed solution was evenly sprayed onto the positive carbon-plastic bipolar plate using a spray gun at a spray rate of 5 mL / min for 10 min. The sprayed positive carbon-plastic bipolar plate was then placed in a vacuum drying oven and dried at 50 °C for 10 h to complete the modification of the positive carbon-plastic bipolar plate by NC-HNBs.

[0060] 4) BNC synthesis steps:

[0061] 5g of chitosan powder was dissolved in 300ml of dilute acetic acid and mechanically stirred until completely dissolved. The mixture was stirred at 400rpm for 3 hours at room temperature. Then, 5g of boric acid was added, and stirring continued for another 3 hours at room temperature to ensure thorough mixing. The homogeneous solution was dried in an oven at 60℃ for 12 hours to obtain the precursor, which was then ground into a fine powder. The ground powder was then subjected to high-temperature pyrolysis in a tube furnace under a nitrogen inert gas atmosphere at a flow rate of 100ml / min to completely eliminate oxygen. The temperature was programmed to increase from room temperature to the target temperature at a slow rate of 3℃ / min. The final pyrolysis temperature was set at 800℃ and held at this temperature for 2 hours to ensure complete carbonization and doping. After pyrolysis, the mixture was allowed to cool naturally to room temperature under a protective atmosphere. The resulting black powder product was then ground to obtain the BNC material.

[0062] 5) Pretreatment of negative carbon-plastic bipolar plates

[0063] The carbon-plastic bipolar plate was ultrasonically cleaned with ethanol or deionized water for 30 minutes to remove impurities and contaminants from the surface. After cleaning, it was placed in a vacuum drying oven at 50°C and dried for 16 hours.

[0064] 6) Preparation of BNC-modified carbon-plastic bipolar plate material for negative electrode

[0065] 250 mg of BNC powder was slowly added to 50 ml of deionized water and dispersed by ultrasonication at a power of 300 W for 30 min to form a BNC dispersion with a concentration of 5 mg / mL.

[0066] The above 50 mL mixed solution was evenly sprayed onto the negative carbon plastic bipolar plate using a spray gun at a spray speed of 5 mL / min for 10 min. The sprayed negative carbon plastic bipolar plate was then placed in a vacuum drying oven and dried at 50 °C for 10 h to complete the BNC modification of the negative carbon plastic bipolar plate.

[0067] Example 2

[0068] The difference from Example 1 is as follows:

[0069] In step 6), the BNC powder is prepared into a BNC dispersion with a concentration of 10 mg / mL.

[0070] Example 3

[0071] The difference from Example 1 is as follows:

[0072] In step 6), the BNC powder is prepared into a BNC dispersion with a concentration of 15 mg / mL.

[0073] Example 4

[0074] The difference from Example 1 is as follows:

[0075] In step 6), the BNC powder is prepared into a BNC dispersion with a concentration of 20 mg / mL.

[0076] Example 5

[0077] The difference from Example 1 is as follows:

[0078] In step 6), the BNC powder is prepared into a BNC dispersion with a concentration of 25 mg / mL.

[0079] Example 6

[0080] The difference from Example 1 is as follows:

[0081] In step 6), the BNC powder is prepared into a BNC dispersion with a concentration of 20 mg / mL; the spraying speed is 7 mL / min, and the spraying time is 7 min.

[0082] Example 7

[0083] The difference from Example 1 is as follows:

[0084] In step 6), the BNC powder is prepared into a BNC dispersion with a concentration of 20 mg / mL; the spraying speed is 10 mL / min, and the spraying time is 5 min.

[0085] Example 8

[0086] A method for preparing a carbon-plastic bipolar plate for a zinc-bromine flow battery includes the following steps:

[0087] 1) Synthesis of NC-HNBs

[0088] 15 g of zinc nitrate hexahydrate and 8 g of 2-methylimidazole were dissolved separately in 1.0 L of methanol at room temperature, rapidly mixed, and allowed to stand for 20 h. After the reaction was complete, the white precipitate was collected by centrifugation at 8000 rpm for 10 min, and then washed three times with methanol by centrifugation. The washed precipitate was dried in a vacuum drying oven at 50 °C for 10 h to obtain ZIF-8 precursor powder. The obtained ZIF-8 precursor powder was subjected to high-temperature pyrolysis under a nitrogen atmosphere at a heating rate of 3 °C / min, a pyrolysis temperature of 800 °C, and a pyrolysis time of 2 h. After pyrolysis, the furnace was allowed to cool naturally to room temperature under a nitrogen atmosphere at a gas flow rate of 50 ml / min. The resulting black powder was NC-HNBs.

[0089] 2) Pretreatment of the positive carbon-plastic bipolar plate

[0090] The carbon-plastic bipolar plate was ultrasonically cleaned with deionized water for 15 minutes to remove impurities and contaminants from the surface. After cleaning, it was placed in a vacuum drying oven at 40°C for 12 hours.

[0091] 3) Preparation of NC-HNBs modified positive carbon-plastic bipolar plate material

[0092] 250 mg of NC-HNBs powder was slowly added to 50 ml of deionized water and dispersed by ultrasonication at a power of 300 W for 10 min to form a NC-HNBs dispersion with a concentration of 5 mg / mL.

[0093] The above 50 mL mixed solution was uniformly sprayed onto the positive carbon-plastic bipolar plate using a spray gun at a spray rate of 5 mL / min for 10 min. The sprayed positive carbon-plastic bipolar plate was then placed in a vacuum drying oven and dried at 40 °C for 8 h to complete the modification of the positive carbon-plastic bipolar plate by NC-HNBs.

[0094] 4) Synthesis of BNC

[0095] 5g of chitosan powder was dissolved in 300ml of dilute acetic acid and mechanically stirred until completely dissolved. The mixture was stirred at 300rpm for 2 hours at room temperature. Then, 5g of boric acid was added, and stirring was continued at room temperature for another 2 hours to ensure thorough mixing. The homogeneous solution was dried in an oven at 60℃ for 12 hours to obtain the precursor, which was then ground into a fine powder. The ground powder was then subjected to high-temperature pyrolysis in a tube furnace under nitrogen inert gas at a flow rate of 50ml / min. The temperature was programmed to rise from room temperature to 800℃ at a rate of 2℃ / min and held at that temperature for 1 hour. After pyrolysis, the mixture was allowed to cool naturally to room temperature under a protective atmosphere. The resulting black powder product was then ground to obtain BNC material.

[0096] 5) Pretreatment of negative carbon-plastic bipolar plates

[0097] The carbon-plastic bipolar plate was ultrasonically cleaned with ethanol or deionized water for 15 minutes to remove impurities and contaminants from the surface. After cleaning, it was placed in a vacuum drying oven at 40°C and dried for 12 hours.

[0098] 6) Preparation of BNC-modified carbon-plastic bipolar plate material for negative electrode

[0099] 250 mg of BNC powder was slowly added to 50 ml of deionized water and dispersed by ultrasonication at a power of 300 W for 10 min to form a BNC dispersion with a concentration of 5 mg / mL.

[0100] The above 50 mL mixed solution was evenly sprayed onto the negative carbon-plastic bipolar plate using a spray gun at a spray rate of 5 mL / min for 10 min. The sprayed negative carbon-plastic bipolar plate was then placed in a vacuum drying oven and dried at 40 °C for 8 h to complete the BNC modification of the negative carbon-plastic bipolar plate.

[0101] Example 9

[0102] A method for preparing a carbon-plastic bipolar plate for a zinc-bromine flow battery includes the following steps:

[0103] 1) Synthesis of NC-HNBs

[0104] 18 g of zinc nitrate hexahydrate and 11 g of 2-methylimidazole were dissolved separately in 1.2 L of methanol at room temperature, rapidly mixed, and allowed to stand for 21 h. After the reaction was complete, the white precipitate was collected by centrifugation at 8500 rpm for 12 min, and then washed three times with methanol by centrifugation. The washed precipitate was dried in a vacuum drying oven at 53 °C for 10.5 h to obtain ZIF-8 precursor powder. The obtained ZIF-8 precursor powder was subjected to high-temperature pyrolysis under a nitrogen atmosphere at a heating rate of 3.5 °C / min, a pyrolysis temperature of 850 °C, and a pyrolysis time of 2.2 h. After pyrolysis, the furnace was allowed to cool naturally to room temperature under a nitrogen atmosphere at a gas flow rate of 100 ml / min. The resulting black powder was NC-HNBs.

[0105] 2) Pretreatment of the positive carbon-plastic bipolar plate

[0106] The carbon-plastic bipolar plate was ultrasonically cleaned with deionized water for 20 minutes to remove impurities and contaminants from the surface. After cleaning, it was placed in a vacuum drying oven at 45°C for 16 hours.

[0107] 3) Preparation of NC-HNBs modified positive carbon-plastic bipolar plate material

[0108] 500 mg of NC-HNBs powder was slowly added to 50 ml of deionized water and dispersed by ultrasonication at a power of 320 W for 30 min to form a NC-HNBs dispersion with a concentration of 10 mg / mL.

[0109] The above 50 mL mixed solution was uniformly sprayed onto the positive carbon-plastic bipolar plate using a spray gun at a flow rate of 6.2 mL / min for 8 min. The sprayed positive carbon-plastic bipolar plate was then placed in a vacuum drying oven and dried at 45 °C for 8.5 h to complete the modification of the positive carbon-plastic bipolar plate by NC-HNBs.

[0110] 4) Synthesis of BNC

[0111] 6.5 g of chitosan powder was dissolved in 400 ml of dilute acetic acid and mechanically stirred until completely dissolved. The mixture was stirred at 360 rpm for 2.5 h at room temperature. Then, 6.5 g of boric acid was added, and stirring was continued at room temperature for another 2.5 h to ensure thorough mixing. The homogeneous solution was dried in an oven at 65 °C for 16 h to obtain the precursor, which was then ground into a fine powder. The ground powder was then subjected to high-temperature pyrolysis in a tube furnace under a nitrogen inert gas atmosphere at a flow rate of 100 ml / min. The temperature was programmed to rise from room temperature to 850 °C at a rate of 3 °C / min and held at that temperature for 1.5 h. After pyrolysis, the mixture was allowed to cool naturally to room temperature under a protective atmosphere. The resulting black powder product was then ground to obtain the BNC material.

[0112] 5) Pretreatment of negative carbon-plastic bipolar plates

[0113] The carbon-plastic bipolar plate was ultrasonically cleaned with ethanol or deionized water for 20 minutes to remove impurities and contaminants from the surface. After cleaning, it was placed in a vacuum drying oven at 45°C and dried for 16 hours.

[0114] 6) Preparation of BNC-modified carbon-plastic bipolar plate material for negative electrode

[0115] 500 mg of BNC powder was slowly added to 50 ml of deionized water and dispersed by ultrasonication at a power of 320 W for 30 min to form a BNC dispersion with a concentration of 10 mg / mL.

[0116] The above 50 mL mixed solution was uniformly sprayed onto the negative carbon-plastic bipolar plate using a spray gun at a spray rate of 6.2 mL / min for 8 min. The sprayed negative carbon-plastic bipolar plate was then placed in a vacuum drying oven and dried at 45 °C for 8.5 h to complete the BNC modification of the negative carbon-plastic bipolar plate.

[0117] Example 10

[0118] A method for preparing a carbon-plastic bipolar plate for a zinc-bromine flow battery includes the following steps:

[0119] 1) Synthesis of NC-HNBs

[0120] 22 g of zinc nitrate hexahydrate and 13 g of 2-methylimidazole were dissolved separately in 1.4 L of methanol at room temperature, rapidly mixed, and allowed to stand for 23 h. After the reaction was complete, the white precipitate was collected by centrifugation at 9500 rpm for 14 min, and then washed three times with methanol by centrifugation. The washed precipitate was dried in a vacuum drying oven at 57 °C for 11.5 h to obtain ZIF-8 precursor powder. The obtained ZIF-8 precursor powder was subjected to high-temperature pyrolysis under a nitrogen atmosphere at a heating rate of 4.5 °C / min, a pyrolysis temperature of 950 °C, and a pyrolysis time of 2.3 h. After pyrolysis, the furnace was allowed to cool naturally to room temperature under a nitrogen atmosphere at a gas flow rate of 150 ml / min. The resulting black powder was NC-HNBs.

[0121] 2) Pretreatment of the positive carbon-plastic bipolar plate

[0122] The carbon-plastic bipolar plate was ultrasonically cleaned with deionized water for 25 minutes to remove impurities and contaminants from the surface. After cleaning, it was placed in a vacuum drying oven at 53°C for 20 hours.

[0123] 3) Preparation of NC-HNBs modified positive carbon-plastic bipolar plate material

[0124] 1000 mg of NC-HNBs powder was slowly added to 50 ml of deionized water and dispersed by ultrasonication at a power of 360 W for 50 min to form an NC-HNBs dispersion with a concentration of 20 mg / mL.

[0125] The above 50 mL mixed solution was uniformly sprayed onto the positive carbon-plastic bipolar plate using a spray gun at a spray rate of 8 mL / min for 6.2 min. The sprayed positive carbon-plastic bipolar plate was then placed in a vacuum drying oven and dried at 53 °C for 9.5 h to complete the modification of the positive carbon-plastic bipolar plate by NC-HNBs.

[0126] 4) Synthesis of BNC

[0127] 8.5g of chitosan powder was dissolved in 500ml of dilute acetic acid and mechanically stirred until completely dissolved. The mixture was stirred at 400rpm for 3.5h at room temperature. Then, 8.5g of boric acid was added, and stirring was continued at room temperature for another 3.5h to ensure thorough mixing. The homogeneous solution was dried in an oven at 75℃ for 20h to obtain the precursor, which was then ground into a fine powder. The ground powder was then subjected to high-temperature pyrolysis in a tube furnace under nitrogen inert gas at a flow rate of 150ml / min. The temperature was programmed to rise from room temperature to 950℃ at a rate of 4℃ / min and held at that temperature for 2.5h. After pyrolysis, the mixture was allowed to cool naturally to room temperature under a protective atmosphere. The resulting black powder product was then ground to obtain BNC material.

[0128] 5) Pretreatment of negative carbon-plastic bipolar plates

[0129] The carbon-plastic bipolar plates were ultrasonically cleaned with ethanol or deionized water for 25 minutes to remove impurities and contaminants from the surface. After cleaning, they were placed in a vacuum drying oven at 53°C for 20 hours.

[0130] 6) Preparation of BNC-modified carbon-plastic bipolar plate material for negative electrode

[0131] 1000 mg of BNC powder was slowly added to 50 ml of deionized water and dispersed by ultrasonication at a power of 360 W for 50 min to form a BNC dispersion with a concentration of 20 mg / mL.

[0132] The above 50 mL mixed solution was uniformly sprayed onto the negative carbon-plastic bipolar plate using a spray gun at a spray rate of 8 mL / min for 6.2 min. The sprayed negative carbon-plastic bipolar plate was then placed in a vacuum drying oven and dried at 53 °C for 9.5 h to complete the BNC modification of the negative carbon-plastic bipolar plate.

[0133] Example 11

[0134] A method for preparing a carbon-plastic bipolar plate for a zinc-bromine flow battery includes the following steps:

[0135] 1) Synthesis of NC-HNBs

[0136] 25 g of zinc nitrate hexahydrate and 15 g of 2-methylimidazole were dissolved separately in 1.5 L of methanol at room temperature, rapidly mixed, and allowed to stand for 24 h. After the reaction was complete, the white precipitate was collected by centrifugation at 10000 rpm for 15 min, and then washed three times with methanol by centrifugation. The washed precipitate was dried in a vacuum drying oven at 60 °C for 12 h to obtain ZIF-8 precursor powder. The obtained ZIF-8 precursor powder was subjected to high-temperature pyrolysis under a nitrogen atmosphere at a heating rate of 5 °C / min, a pyrolysis temperature of 1000 °C, and a pyrolysis time of 2.5 h. After pyrolysis, the furnace was allowed to cool naturally to room temperature under a nitrogen atmosphere at a gas flow rate of 200 ml / min. The resulting black powder was NC-HNBs.

[0137] 2) Pretreatment of the positive carbon-plastic bipolar plate

[0138] The carbon-plastic bipolar plate was ultrasonically cleaned with deionized water for 30 minutes to remove impurities and contaminants from the surface. After cleaning, it was placed in a vacuum drying oven at 60°C for 24 hours.

[0139] 3) Preparation of NC-HNBs modified positive carbon-plastic bipolar plate material

[0140] 1500 mg of NC-HNBs powder was slowly added to 50 ml of deionized water and dispersed by ultrasonication at a power of 400 W for 60 min to form an NC-HNBs dispersion with a concentration of 30 mg / mL.

[0141] The above 50 mL mixed solution was uniformly sprayed onto the positive carbon-plastic bipolar plate using a spray gun at a spray rate of 10 mL / min for 5 min. The sprayed positive carbon-plastic bipolar plate was then placed in a vacuum drying oven and dried at 60 °C for 10 h to complete the modification of the positive carbon-plastic bipolar plate by NC-HNBs.

[0142] 4) Synthesis of BNC

[0143] 10g of chitosan powder was dissolved in 600ml of dilute acetic acid and mechanically stirred until completely dissolved. The mixture was stirred at 500rpm for 4 hours at room temperature. Then, 10g of boric acid was added, and stirring was continued at room temperature for another 4 hours to ensure thorough mixing. The homogeneous solution was dried in an oven at 80℃ for 24 hours to obtain the precursor, which was then ground into a fine powder. The ground powder was then subjected to high-temperature pyrolysis in a tube furnace under nitrogen inert gas at a flow rate of 200ml / min. The temperature was programmed to rise from room temperature to 1000℃ at a rate of 5℃ / min and held at that temperature for 3 hours. After pyrolysis, the mixture was allowed to cool naturally to room temperature under a protective atmosphere. The resulting black powder product was then ground to obtain BNC material.

[0144] 5) Pretreatment of negative carbon-plastic bipolar plates

[0145] The carbon-plastic bipolar plate was ultrasonically cleaned with ethanol or deionized water for 30 minutes to remove impurities and contaminants from the surface. After cleaning, it was placed in a vacuum drying oven at 60°C and dried for 24 hours.

[0146] 6) Preparation of BNC-modified carbon-plastic bipolar plate material for negative electrode

[0147] 1250 mg of BNC powder was slowly added to 50 ml of deionized water and dispersed by ultrasonication at a power of 400 W for 60 min to form a BNC dispersion with a concentration of 25 mg / mL.

[0148] The above 50 mL mixed solution was evenly sprayed onto the negative carbon-plastic bipolar plate using a spray gun at a spray rate of 10 mL / min for 5 min. The sprayed negative carbon-plastic bipolar plate was then placed in a vacuum drying oven and dried at 60 °C for 10 h to complete the BNC modification of the negative carbon-plastic bipolar plate.

[0149] Comparative Example 1

[0150] A method for preparing a carbon-plastic bipolar plate for a zinc-bromine flow battery includes the following steps:

[0151] Both the positive and negative electrodes used unmodified carbon-plastic bipolar plates for battery performance testing, and the pretreatment of the carbon-plastic bipolar plates was the same as in the above embodiment.

[0152] Comparative Example 2

[0153] The difference from Example 1 is as follows:

[0154] In step 3), the NC-HNBs powder is prepared into a 5 mg / mL NC-HNBs dispersion.

[0155] (Steps 4 to 6 are omitted) and unmodified negative carbon-plastic bipolar plates are used directly.

[0156] Comparative Example 3

[0157] The difference from Example 1 is as follows:

[0158] In step 3), the NC-HNBs powder is prepared into a 10 mg / mL NC-HNBs dispersion.

[0159] (Steps 4 to 6 are omitted) and unmodified negative carbon-plastic bipolar plates are used directly.

[0160] Comparative Example 4

[0161] The difference from Example 1 is as follows:

[0162] In step 3), the NC-HNBs powder is prepared into a 15 mg / mL NC-HNBs dispersion.

[0163] (Steps 4 to 6 are omitted) and unmodified negative carbon-plastic bipolar plates are used directly.

[0164] Comparative Example 5

[0165] The difference from Example 1 is as follows:

[0166] In step 3), the NC-HNBs powder is prepared into a 20 mg / mL NC-HNBs dispersion.

[0167] (Steps 4 to 6 are omitted) and unmodified carbon-plastic bipolar plates are used directly.

[0168] Comparative Example 6

[0169] The difference from Example 1 is as follows:

[0170] In step 3), the NC-HNBs powder is prepared into a 25 mg / mL NC-HNBs dispersion.

[0171] (Steps 4 to 6 are omitted) and unmodified carbon-plastic bipolar plates are used directly.

[0172] Comparative Example 7

[0173] The difference from Example 1 is as follows:

[0174] In step 3), the NC-HNBs powder is prepared into a 30 mg / mL NC-HNBs dispersion.

[0175] (Steps 4 to 6 are omitted) and unmodified carbon-plastic bipolar plates are used directly.

[0176] Comparative Example 8

[0177] The difference from Example 1 is as follows:

[0178] In step 3), the spray velocity is 7 mL / min and the spraying time is 7 min.

[0179] (Steps 4 to 6 are omitted) and unmodified carbon-plastic bipolar plates are used directly.

[0180] Comparative Example 9

[0181] The difference from Example 1 is as follows:

[0182] In step 3), the spray velocity is 10 mL / min and the spraying time is 5 min.

[0183] (Steps 4 to 6 are omitted) and unmodified carbon-plastic bipolar plates are used directly.

[0184] Comparative Example 10

[0185] The difference from Example 1 is as follows:

[0186] (Steps 1) to 3) are skipped, and unmodified positive carbon-plastic bipolar plates are used directly.

[0187] Comparative Example 11

[0188] The difference from Comparative Example 10 is:

[0189] In step 6), the BNC powder is prepared into a BNC dispersion with a concentration of 15 mg / mL.

[0190] Comparative Example 12

[0191] The difference from Comparative Example 10 is:

[0192] In step 6), the BNC powder is prepared into a BNC dispersion with a concentration of 25 mg / mL.

[0193] To test the performance of the carbon-plastic bipolar plates in the flow batteries of Examples 1-11 and Comparative Examples 1-12, batteries were assembled using conventional electrode materials and electrolyte systems for zinc-bromine flow batteries. The separator was a commercially available microporous membrane, and the electrode area was 9 cm². 2 The electrolyte is ZnBr2. Charge-discharge tests were performed on a battery testing system at a charge-discharge rate of 20 mA / cm². 2 The charging time was 2 hours, and the test temperature was 25℃.

[0194] Table 1. Synthesis conditions of carbon-plastic bipolar plates for zinc-bromine flow batteries in different embodiments and comparative examples.

[0195]

[0196] Table 2 Comparison of electrochemical performance of zinc-bromine flow batteries under different embodiment and comparative conditions

[0197]

[0198] Table 1 shows the synthesis conditions of carbon-plastic bipolar plates for zinc-bromine flow batteries in different embodiments and comparative examples; Table 2 shows the comparison of electrochemical performance of zinc-bromine flow batteries under different embodiments and comparative examples. As can be seen from Table 2, Examples 1-11 all showed better electrochemical performance data than Comparative Example 1, indicating that the carbon-plastic bipolar plates modified with NC-HNBs and BNC have better electrochemical performance than the unmodified carbon-plastic bipolar plates used in zinc-bromine flow batteries. NC-HNBs and BNC help improve the energy efficiency, coulombic efficiency, and voltage efficiency of zinc-bromine flow batteries. The carbon-plastic bipolar plates modified with NC-HNBs and BNC have a significant impact on improving bromine barrier capacity, accelerating bromine reaction capacity, and inhibiting zinc dendrite formation.

[0199] Comparing the data from Examples 1-11 and Comparative Examples 2-12, it is evident that the electrochemical performance of Examples 1-11 is superior to that of Comparative Examples 2-12. This indicates that when the positive and negative electrodes of the carbon-plastic bipolar plate in a zinc-bromine flow battery are modified with NC-HNBs and BNC, respectively, their overall electrochemical performance is superior to that of carbon-plastic bipolar plates modified with only NC-HNBs or BNC. This demonstrates that modifying both the positive and negative electrodes of the carbon-plastic bipolar plate with NC-HNBs and BNC can simultaneously address key issues such as bromine corrosion, bromine permeation, slow reaction kinetics, zinc dendrite formation, and hydrogen evolution side reactions, comprehensively improving the battery's cycle life, energy efficiency, coulombic efficiency, voltage efficiency, and safety. As can be seen from Comparative Examples 2-11, within the test concentration range, the NC-HNBs concentration (25 mg / mL) corresponding to Comparative Example 6 exhibits better electrochemical performance data. This indicates that within a certain concentration range, carbon-plastic bipolar plates modified with higher concentrations of NC-HNBs solution have higher coulombic efficiency, voltage efficiency, and energy efficiency. Within a certain concentration range, increasing the concentration of NC-HNBs solution has a significant impact on improving bromine inhibition and accelerating bromine reaction.

[0200] NC-HNBs can effectively modulate the charge distribution on the surface of carbon materials through nitrogen atom doping, thereby changing the charge distribution on the bipolar plates and facilitating the redox reaction of bromine (Br₂). - The Br2 / Br2 combination creates numerous highly catalytically active sites, significantly reducing the reaction overpotential and thus accelerating the bromine reaction kinetics. Furthermore, the hollow nanoboxes of NC-HNBs possess a large specific surface area, loading even more active sites, increasing the reaction interface for the bromine redox reaction, and further accelerating the bromine reaction kinetics.

[0201] Furthermore, the internal cavity of the hollow nanobox in NC-HNBs can confine the generated Br2 and polybrominates within the cavity or adsorb them onto the pore walls, effectively reducing the free diffusion of bromine. On the other hand, nitrogen-doped sites have a strong chemisorption effect on polybrominates, especially the electrostatic interaction between positively charged carbon atoms and negatively charged polybrominates, which further anchors them to the positive electrode side, thereby alleviating bromine permeation, reducing self-discharge and capacity decay, and significantly improving the coulombic efficiency and cycle capacity retention of the battery.

[0202] NC-HNBs can also form a highly conductive interconnect network on the surface of the bipolar plate, ensuring that electrons can be rapidly transported from the bipolar plate to the reaction site. Furthermore, their excellent conductivity and catalytic properties together accelerate the Br2 / Br2 reaction. - The electron transfer rate of the redox couple greatly reduces the resistance between them, which directly reduces the ohmic internal resistance and polarization loss of the battery during operation, thereby improving the battery's voltage efficiency and energy efficiency.

[0203] However, when the concentration of NC-HNBs solution is too high, the coulombic efficiency, voltage efficiency, and energy efficiency will decrease. This is mainly because the core advantage of NC-HNBs lies in the high specific surface area and abundant nitrogen-doped active sites brought about by its hollow and porous structure. When the concentration of NC-HNBs solution is too high, the NC-HNBs will aggregate and block the pores, preventing the internal surface and active sites from contacting the electrolyte, resulting in a decrease in performance.

[0204] As can be seen from Comparative Examples 6, 8, and 9, Comparative Example 6 achieved relatively better overall electrochemical performance, proving that reducing the spraying rate and extending the spraying time can improve the coulombic efficiency, voltage efficiency, and energy efficiency of zinc-bromine flow batteries. This indicates that different spraying rates and times have a profound impact on the performance of the prepared NC-HNBs-modified carbon-plastic bipolar plates.

[0205] Compared with Examples 1-5, within the test concentration range, the BNC concentration (20 mg / mL) corresponding to Example 4 showed better electrochemical performance data, indicating that within a certain concentration range, the carbon-plastic bipolar plate modified with higher concentrations of BNC solution has higher coulombic efficiency, voltage efficiency, and energy efficiency. This also indicates that within a certain concentration range, increasing the concentration of BNC solution has a significant impact on the ability to suppress zinc dendrites and the ability to suppress hydrogen evolution reaction.

[0206] The extremely high conductivity of the BNC coating ensures a highly uniform electric field distribution on the bipolar plate surface, preventing localized charge concentration and thus preventing zinc ion deposition, thereby reducing zinc dendrite formation. On the other hand, the co-doping of B and N produces a unique electronic structure and localized charge distribution, forming a large number of Zn atoms. 2+ Zinc-loving sites with strong adsorption capacity. These zinc-loving sites can reduce Zn... 2+ The initial nucleation overpotential guides zinc atoms to preferentially nucleate at these uniformly distributed sites, rather than growing randomly at protrusions, thereby achieving two-dimensional layered dense deposition of zinc, further effectively suppressing dendrites and improving the cycle life and safety of the battery.

[0207] Furthermore, the electronegativity of boron (B) atoms is lower than that of carbon (C) and nitrogen (N). Co-doping of B with N will create strong local charge polarization in the carbon lattice. This charge redistribution will significantly change the electronic state of the material surface, shifting the Fermi level upwards and adjusting the d-band center position, thus making the material surface more susceptible to hydrogen. + The adsorption energy weakens, thereby increasing the onset overpotential of HER, making H... + The reduction reaction is thermodynamically less likely to occur, thus inhibiting the hydrogen evolution reaction and improving the battery coulombic efficiency.

[0208] The high conductivity of BNC materials also provides an efficient electron transport path for the zinc deposition and dissolution reactions, ensuring that the zinc deposition / dissolution reactions can proceed rapidly, promoting reaction kinetics, which is beneficial for high-power charging and discharging of the battery, thereby reducing voltage loss on the negative electrode side during charging and discharging and improving energy efficiency.

[0209] In summary, this invention provides a carbon-plastic bipolar plate for a zinc-bromine flow battery, its preparation method, and its application. By loading NC-HNBs and BNC onto the positive and negative bipolar plates of the zinc-bromine flow battery, respectively, a systematic improvement in battery performance is achieved. On the positive electrode side, NC-HNBs, through nitrogen atom doping, create abundant catalytic sites, significantly accelerating the redox reaction kinetics of bromine and reducing overpotential. Furthermore, its hollow structure can adsorb bromine species, and combined with surface charge, inhibits bromine permeation, thereby reducing self-discharge and improving coulombic efficiency and capacity retention. Simultaneously, its highly conductive network reduces interfacial resistance, improves energy efficiency, and the dense coating can block bromine corrosion, protect the bipolar plate substrate, and extend its lifespan. On the negative electrode side, the BNC coating utilizes its uniform conductivity and unique B... The N-type zinc-loving sites guide uniform nucleation and dense deposition of zinc ions, effectively inhibiting dendrite growth; and by suppressing hydrogen evolution side reactions through charge regulation, they improve coulombic efficiency. Their high conductivity promotes zinc deposition / dissolution kinetics, enhancing power and energy efficiency, while their acid corrosion resistance protects the negative electrode bipolar plate. Through synergistic modification of both positive and negative electrodes, key issues such as bromine corrosion, bromine permeation, slow reaction kinetics, zinc dendrites, and hydrogen evolution side reactions are simultaneously addressed, comprehensively improving the battery's cycle life, energy efficiency, coulombic efficiency, voltage efficiency, and safety. The synergistic effect of both materials results in a comprehensive improvement in the carbon-plastic bipolar plate's bromine barrier performance, reaction kinetics, and dendrite suppression.

[0210] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a carbon-plastic bipolar plate for a zinc-bromine flow battery, characterized in that, include: Zinc nitrate hexahydrate and 2-methylimidazole were dissolved in methanol and mixed. The mixture was then subjected to static reaction, centrifugation, washing, drying and high-temperature pyrolysis to obtain nitrogen-doped hollow carbon nanotubes. The nitrogen-doped hollow carbon nanotubes were dispersed and sprayed onto the positive electrode side of a carbon-plastic bipolar plate. After drying again, a positive carbon-plastic bipolar plate modified with nitrogen-doped hollow carbon nanotubes was obtained. Chitosan powder was dissolved in dilute acetic acid, boric acid was added and stirred until uniform, dried and ground into fine powder, and then subjected to high-temperature pyrolysis. After grinding again, boron-nitrogen co-doped carbon was obtained. The boron-nitrogen co-doped carbon was dispersed and sprayed onto the negative electrode side of a pretreated carbon-plastic bipolar plate. After drying again, a negative carbon-plastic bipolar plate modified with boron-nitrogen co-doped carbon was obtained.

2. The method for preparing the carbon-plastic bipolar plate of the zinc-bromine flow battery according to claim 1, characterized in that, The ratio of zinc nitrate hexahydrate, 2-methylimidazole and methanol is (15-25) g: (8-15) g: (1.0-1.5) L.

3. The method for preparing the carbon-plastic bipolar plate for the zinc-bromine flow battery according to claim 1, characterized in that, In the preparation process of the nitrogen-doped hollow carbon nanotubes, the static reaction time is 20-24 h; the centrifugation speed is 8000-10000 rpm and the centrifugation time is 10-15 min; the drying temperature is 50-60℃ and the drying time is 10-12 h. The conditions for dispersing the nitrogen-doped hollow carbon nanotubes include: dispersing the nitrogen-doped hollow carbon nanotubes in deionized water to obtain a nitrogen-doped hollow carbon nanotube dispersion with a mass concentration of 5-30 mg / mL; dispersing by ultrasound with a power of 300-400 W for 10-60 min; spraying with a spray velocity of 5-10 mL / min for 5-10 min; and drying at a temperature of 40-60℃ for 8-10 h.

4. The method for preparing the carbon-plastic bipolar plate of the zinc-bromine flow battery according to claim 1, characterized in that, During the preparation of the nitrogen-doped hollow carbon nanotubes, the high-temperature pyrolysis conditions include: a heating rate of 3-5℃ / min, a pyrolysis temperature of 800-1000℃, a pyrolysis time of 2-2.5h, and a nitrogen flow rate of 50-200ml / min.

5. The method for preparing the carbon-plastic bipolar plate of the zinc-bromine flow battery according to claim 1, characterized in that, The ratio of chitosan, dilute acetic acid and boric acid is (5-10) g: (300-600) ml: (5-10) g.

6. The method for preparing the carbon-plastic bipolar plate of the zinc-bromine flow battery according to claim 1, characterized in that, During the preparation of the boron-nitrogen co-doped carbon, the stirring rate is 300-500 rpm and the stirring time is 2-4 hours; the drying temperature is 60-80℃ and the drying time is 12-24 hours. The conditions for dispersing boron-nitrogen co-doped carbon include: dispersing boron-nitrogen co-doped carbon in deionized water to obtain a boron-nitrogen co-doped carbon dispersion with a mass concentration of 5-25 mg / mL; dispersing by ultrasound with a power of 300-400 W for 10-60 min; spraying with a spray velocity of 5-10 mL / min for 5-10 min; and drying at a temperature of 40-60℃ for 8-10 h.

7. The method for preparing the carbon-plastic bipolar plate of the zinc-bromine flow battery according to claim 1, characterized in that, In the preparation process of the boron-nitrogen co-doped carbon, the high-temperature pyrolysis conditions include: a heating rate of 2-5℃ / min, a pyrolysis temperature of 800-1000℃, a holding time of 1-3h, and a nitrogen flow rate of 50-200ml / min.

8. The method for preparing the carbon-plastic bipolar plate of the zinc-bromine flow battery according to claim 1, characterized in that, All carbon-plastic bipolar plates are pretreated carbon-plastic bipolar plates. The pretreatment conditions include: ultrasonically cleaning the carbon-plastic bipolar plates with ethanol or deionized water for 15-30 minutes, and then drying them in a vacuum drying oven at 40-60℃ for 12-24 hours.

9. A carbon-plastic bipolar plate for a zinc-bromine flow battery, characterized in that, The carbon-plastic bipolar plate for zinc-bromine flow batteries as described in any one of claims 1-8 is prepared using this method.

10. The application of the carbon-plastic bipolar plate of the zinc-bromine flow battery according to claim 9 in the preparation of a zinc-bromine flow battery, characterized in that, The zinc-bromine flow battery has a coulombic efficiency of 94.3%-96.1%, a voltage efficiency of 85.3%-86.1%, and an energy efficiency of 80.44%-83.03%.

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