Phosphoric acid fuel cell electrolyte membrane and method of making same

Abstract

The application provides a phosphoric acid fuel cell electrolyte diaphragm and a preparation method thereof. The preparation method comprises the following steps: mixing: ceramic powder, a binder and a pore-forming agent are stirred and mixed to form a first mixture; wherein the binder is a fluorine-containing polymer; dispersion and pre-fibrillation: the first mixture is subjected to high-speed shearing treatment, the rotating speed is controlled to be 500 r / min-10000 r / min, the ceramic powder is uniformly dispersed, the binder is pre-fibrillated to form a three-dimensional fiber network, and a second mixture is obtained; hot calendering: the second mixture is subjected to hot calendering treatment at 40 DEG C-180 DEG C, the three-dimensional fiber network wraps the ceramic powder and the pore-forming agent, and a green film is prepared; pore-forming agent removal: an extracting agent is used to remove the pore-forming agent in the green film, and an electrolyte diaphragm is formed. The application realizes controllable preparation of the diaphragm performance and improvement of the battery performance by innovating the diaphragm preparation method through microstructure design, and has an important promoting effect on commercialization of the phosphoric acid fuel cell.

Description

Technical Field

[0001] This application relates to the field of phosphoric acid fuel cell technology, specifically to an electrolyte membrane for a phosphoric acid fuel cell and its preparation method. Background Technology

[0002] Phosphoric acid fuel cells, due to their high operating temperature, exhibit good tolerance to impurities in the fuel gas, eliminating the need for high-purity hydrogen and broadening fuel sources. They are also compatible with existing fossil fuel-based infrastructure systems, thus providing a feasible technological path to reduce the high costs and risks associated with hydrogen storage and transportation. Currently, research and development in this field mainly focuses on stack structure design, system integration optimization, and the development of novel catalysts.

[0003] In phosphoric acid fuel cells, the electrolyte membrane, as the core component of the membrane electrode assembly (MEA), directly affects the proton conduction efficiency, the barrier effect on reactant gases, and the long-term operational stability of the cell, thus determining the overall output performance and lifespan of the battery. Traditional processes often employ methods such as screen printing and spraying to directly coat a mixture of materials like silicon carbide and polytetrafluoroethylene (PTFE) onto the electrode substrate surface. However, the resulting coating typically lacks density, requiring subsequent high-temperature sintering to improve its density and mechanical strength. This leads to cumbersome process steps and high requirements for the uniformity of the substrate material and process, hindering production efficiency and large-scale manufacturing.

[0004] Furthermore, current research and industrial practice still focus on the macroscopic forming and mechanical properties of the separator. From the perspective of fundamental innovation in materials design and manufacturing processes, there is still a lack of innovative technologies to systematically optimize the adsorption, storage, and proton conduction behavior of phosphoric acid electrolyte by actively controlling the microstructure of the separator (such as porosity, pore size distribution, and pore connectivity), thereby directly improving the battery's output power, operational stability, and cycle life.

[0005] In view of this, there is an urgent need for a new preparation method that can simultaneously ensure the stability of the membrane structure and the reliability of its performance, while taking into account the process efficiency and ease of operation, in order to meet the needs of large-scale manufacturing and commercialization of phosphoric acid fuel cells. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides an electrolyte membrane for a phosphoric acid fuel cell and its preparation method. The method involves high-speed shearing of ceramic powder, a fluoropolymer binder, and a pore-forming agent. This process achieves uniform dispersion of the ceramic powder and pre-fiberization of the binder to form a three-dimensional fiber network. Simultaneously, subsequent extraction of the pore-forming agent enables controllable preparation of the membrane's porosity and pore size. This invention innovates the membrane preparation method by focusing on microstructure design, achieving not only controllable preparation of key membrane properties and significantly improving battery performance, but also demonstrating significant advantages in process simplification, cost control, and large-scale production. This has significant value in promoting the commercial application of phosphoric acid fuel cells.

[0007] To achieve the above objectives, the present invention provides a method for preparing an electrolyte membrane for a phosphoric acid fuel cell, comprising the following steps: Mixing: Ceramic powder, binder and pore-forming agent are stirred and mixed to form a first mixture; wherein the binder is a fluoropolymer; Dispersion and prefiberization: The first mixture is subjected to high-speed shearing treatment, with the rotation speed controlled at 500 r / min-10000 r / min, so that the ceramic powder is uniformly dispersed and the binder is prefiberized to form a three-dimensional fiber network, thus obtaining the second mixture; Hot calendering: The second mixture is hot calendered at 40℃-180℃, and the three-dimensional fiber network encapsulates the ceramic powder and the pore-forming agent to obtain a green film; Pore-forming agent removal: The pore-forming agent in the green film is removed by an extractant to form an electrolyte membrane.

[0008] Optionally, the ceramic powder is 50-99 parts by weight, the binder is 1-50 parts, and the pore-forming agent is 1-25 parts.

[0009] Optionally, the particle size of the ceramic powder is ≤20μm.

[0010] Optionally, the fluoropolymer is selected from fluoropolymers.

[0011] Optionally, the ceramic powder includes one or more of silicon carbide, silicon nitride, boron carbide, and boron nitride; and / or The fluoropolymer is polytetrafluoroethylene (PTFE), or a mixture of PTFE and other fluoropolymers; the other fluoropolymers are selected from one or more of polyvinylidene fluoride (PVDF), fusible PTFE, and polychlorotrifluoroethylene (PTFE); and when the fluoropolymer is a mixture of PTFE and other fluoropolymers, the PTFE content is 75%-100% by mass of the total mass of the mixture; and / or The pore-forming agent includes one or more of the following: paraffin wax, sodium chloride, starch, polyvinyl alcohol, ammonium carbonate, and ammonium bicarbonate; and / or The extractant includes one or more of water, ethanol, hexane, acetone, petroleum ether, and chloroform.

[0012] Optionally, the high-speed shearing process includes at least three sequential rotational speed stages, wherein the shearing speed is gradually increased from 500 r / min to 10000 r / min.

[0013] Optionally, the high-speed shearing process includes three sequential rotational speed stages, wherein: In the first rotational speed stage, the shearing speed is 500 r / min-2000 r / min, and the processing time is 2 min-25 min; In the second rotational speed stage, the shearing speed is 2001 r / min-7000 r / min, and the processing time is 2 min-25 min; In the third rotational speed stage, the shearing speed is 7001 r / min-10000 r / min, and the processing time is 2 min-25 min.

[0014] Optionally, the hot calendering process includes at least three sequentially performed stages, wherein the roll gap is gradually reduced from 1.0 mm to 0.05 mm.

[0015] Optionally, the hot rolling process includes three sequentially performed stages, wherein: In the first hot rolling stage, the roll gap is 0.80mm-1.00mm; In the second hot rolling stage, the roll gap is 0.20mm-0.79mm; In the third hot rolling stage, the roll gap is 0.05mm-0.19mm.

[0016] On the other hand, the present invention also provides an electrolyte membrane for a phosphoric acid fuel cell prepared by any of the above preparation methods.

[0017] Optionally, the thickness of the electrolyte membrane is 50-300 μm; and / or The porosity of the electrolyte membrane is 40%-65%.

[0018] Compared with the prior art, the present invention has the following beneficial effects: (1) In terms of microstructure control, the present invention achieves the regulation of porosity and pore size distribution through the synergistic process of "high-speed shear prefiberization-pore-forming agent extraction", which solves the key problem that existing technologies cannot optimize microstructure to improve electrolyte conductivity.

[0019] (2) In terms of overall performance, the prepared separator exhibits excellent phosphoric acid electrolyte adsorption, storage and proton conduction capabilities due to its optimized microstructure, thereby directly improving the battery's output power, operating stability and cycle life, overcoming the bottleneck of low performance of existing batteries.

[0020] (3) In terms of process efficiency, the method has a low molding temperature (40℃-180℃), does not require high-temperature sintering, has simple process steps, low energy consumption, convenient operation, and is easy to scale up for continuous production, thus meeting commercial needs.

[0021] (4) In terms of structural reliability, the three-dimensional fiber network formed by prefiberization effectively wraps and fixes the ceramic powder and pore-forming agent in hot calendering. The self-supporting diaphragm obtained still maintains a complete skeleton after the pore-forming agent is removed, and has good mechanical strength and structural stability. Detailed Implementation

[0022] To make the technical problems solved, the technical solutions, and the beneficial effects of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0023] As used herein, the term "green film" refers to a film-like preform that has a final shape and size after a forming process (hot rolling) and whose structure is mainly maintained by a binder before the removal of the pore-forming agent; wherein the removal of the pore-forming agent does not change the macroscopic geometry of the green film.

[0024] This invention provides a phosphoric acid fuel cell separator and its preparation method. The preparation method of the electrolyte separator includes the following steps: S100 Mixing: Ceramic powder, binder and pore-forming agent are stirred and mixed to form a first mixture; wherein the binder is a fluoropolymer.

[0025] In this embodiment of the invention, the initial uniform mixing state achieved in the mixing step provides a foundation for the pre-fiberization of the binder, the formation of the three-dimensional network, and the further uniform dispersion of ceramic powder and pore-forming agent during the subsequent high-speed shearing process.

[0026] In some embodiments, during the mixing step, the ceramic powder, binder, and pore-forming agent are mixed by mechanical stirring to form a first mixture. The mechanical stirring can be performed using at least one of the following: a planetary centrifuge, a twin-shaft paddle mixer, a two-dimensional / three-dimensional motion mixer, a vacuum mixer, a V-type mixer, a horizontal ribbon mixer, or a plow mixer. The stirring speed is controlled at 50-480 r / min, the mixing time is 1-120 min, and the temperature during the mixing process is maintained within the range of 0-30°C to ensure thorough mixing of the components.

[0027] In some embodiments, the mixing step employs a segmented variable-speed stirring process, including at least two sequentially performed speed stages. The stirring speed is gradually increased from a lower initial value (e.g., about 50 r / min) to a higher final value (e.g., about 480 r / min). By setting the gradient of speed and time, ceramic powders, binders, and pore-forming agents with large differences in density and polarity are mixed uniformly in stages, avoiding agglomeration or segregation caused by a single speed.

[0028] In some embodiments, the mixing step includes two rotational speed stages: During the first stage of mixing, the stirring speed is 50 r / min-200 r / min, and the stirring time is 2 min-30 min. During the second stage of mixing, the stirring speed is 201r / min-480r / min, and the stirring time is 2min-30min.

[0029] It is understood that parameters such as the number of rotation speed stages, the stirring speed of each stage, and the duration of each stage in the mixing process can all be adjusted by those skilled in the art based on the actual mixing system under the "segmented variable speed mixing" concept provided by this invention. For example, for more complex mixing systems, the number of rotation speed stages can be increased accordingly (e.g., three to five stages), and the rotation speed and time of each stage can be optimized for matching, so that the best mixing effect can be obtained through a limited number of conventional experiments.

[0030] In some embodiments, the ceramic powder comprises 50-99 parts by weight, the binder comprises 1-50 parts by weight, and the pore-forming agent comprises 1-25 parts by weight.

[0031] In a preferred embodiment, the ceramic powder is 70-97 parts by weight. In an exemplary embodiment, the ceramic powder can be 70, 75, 78, 80, 85, 90, or 97 parts.

[0032] In a preferred embodiment, the adhesive is 1-20 parts by weight. In an exemplary embodiment, the adhesive may be 1 part, 5 parts, 10 parts, 15 parts, or 20 parts.

[0033] In a preferred embodiment, the pore-forming agent is 5-15 parts by weight. In an exemplary embodiment, the pore-forming agent may be 5 parts, 9 parts, 12 parts, or 15 parts.

[0034] In some embodiments, the particle size of the ceramic powder is ≤20μm. In exemplary embodiments, the particle size of the ceramic powder can be 1μm, 5μm, 8μm, 10μm, 12μm, 15μm, 18μm, or 20μm.

[0035] In some embodiments, the ceramic powder includes one or more of silicon carbide, silicon nitride, boron carbide, and boron nitride. Silicon carbide exhibits near-inert corrosion resistance in concentrated phosphoric acid media, effectively adsorbing and retaining the phosphoric acid electrolyte to form a stable proton-conducting layer. Its excellent thermal conductivity also contributes to the heat dissipation management of the battery system. Silicon nitride has superior mechanical strength and toughness compared to silicon carbide, making it suitable for battery configurations with higher requirements for the mechanical strength and crush resistance of the separator. Boron carbide is characterized by its extremely high hardness and wear resistance. Boron nitride exhibits superior thermal conductivity compared to silicon carbide, significantly improving the heat uniformity and heat dissipation efficiency during battery operation. By selecting or combining the above-mentioned ceramic powders, the proton conduction performance, mechanical support performance, and thermal management performance of the electrolyte separator can be specifically controlled and optimized.

[0036] In some embodiments, the fluoropolymer is selected from fluoropolymers, which are not only simple binders but also the "structural framework" of the membrane. Fluoropolymers ensure the long lifespan of the membrane through their acid resistance and achieve low-temperature composite with ceramic powder through their fibrillation properties, ultimately constructing a porous electrolyte membrane with both good proton conductivity and excellent mechanical strength.

[0037] In some embodiments, the fluoropolymer is polytetrafluoroethylene (PTFE), or a mixture of PTFE and other fluoropolymers; the other fluoropolymers are selected from one or more of polyvinylidene fluoride (PVDF), fusible PTFE, and polychlorotrifluoroethylene (PTFE); and when the fluoropolymer is a mixture of PTFE and other fluoropolymers, the PTFE content is 75%-100% by mass of the total mass of the mixture.

[0038] In this embodiment of the invention, the fluoropolymer must contain polytetrafluoroethylene (PTFE). Specifically, when the fluoropolymer is composed of PTFE and other fluoropolymers (e.g., one or more of polyvinylidene fluoride, fusible PTFE, and polychlorotrifluoroethylene), the PTFE content is 75% or more by mass of the total fluoropolymer to ensure the stability of the membrane structure and the film-forming processing performance.

[0039] In this embodiment of the invention, the pore-forming agent is selected from materials that can be removed by liquid-phase elution or low-temperature thermal decomposition.

[0040] In some embodiments, the pore-forming agent includes one or more of beeswax, sodium chloride, starch, polyvinyl alcohol, ammonium carbonate, and ammonium bicarbonate. Ammonium carbonate and ammonium bicarbonate can completely decompose into gases at relatively low temperatures (<100°C) without producing solid residues, thus avoiding negative impacts of impurity ions on battery performance. Sodium chloride can be dissolved and removed by washing with water, and its particle size can be controlled to precisely regulate the pore distribution in the separator, which is beneficial for uniform impregnation of the phosphoric acid electrolyte. Starch and polyvinyl alcohol are widely available and environmentally friendly. Beeswax helps to form a uniformly distributed pore structure.

[0041] S200 Dispersion and Prefiberization: The first mixture is subjected to high-speed shearing treatment, with the rotation speed controlled at 500-10000 r / min, so that the ceramic powder is uniformly dispersed and the binder is prefiberized to form a three-dimensional fiber network, thus obtaining the second mixture.

[0042] In this embodiment of the invention, the dispersion and pre-fiberization steps are key pretreatment steps for constructing the three-dimensional framework structure of the "ceramic-polymer" composite membrane. Their core function is to simultaneously achieve uniform dispersion of the ceramic powder and pre-fiberization of the binder under high-speed shearing, causing the binder to form an entangled three-dimensional fiber network. This three-dimensional fiber network structure encapsulates and fixes the ceramic powder and the pore-forming agent, forming a self-supporting second mixture, providing a structural basis for subsequent hot-calendering.

[0043] In some embodiments, during the dispersion and prefiberization steps, a high-speed pulverizer, a high-intensity mixer, a planetary ball mill, an air jet mill, or other equipment is used to perform high-speed shearing treatment on the first mixture to simultaneously achieve homogeneous dispersion of the ceramic powder and prefiberization of the binder.

[0044] The process parameters for high-speed shearing are adapted to the composition of the first mixture. In some embodiments, the high-speed shearing process includes at least three sequentially performed rotational speed stages, wherein the shearing speed is gradually increased from 500 r / min to 10000 r / min to achieve a transition of the first mixture from initial dispersion to full prefiberization.

[0045] In some embodiments, the high-speed shearing process includes three to six sequential rotational speed stages, wherein the shearing speed is gradually increased from 500 r / min to 10000 r / min.

[0046] In some embodiments, the high-speed shearing process includes three sequentially performed rotational speed stages, wherein: In the first rotational speed stage (for initial dispersion), the shearing speed is 500 r / min-2000 r / min, and the processing time is 2 min-25 min; In the second rotational speed stage (for deep homogenization), the shearing speed is 2001 r / min-7000 r / min, and the processing time is 2 min-25 min. In the third rotational speed stage (used for high-speed shear-induced prefiberization), the shearing speed is 7001 r / min-10000 r / min, and the processing time is 2 min-25 min.

[0047] In some embodiments, the first rotational speed stage of the high-speed shearing process can be 500 r / min, 1000 r / min, 1500 r / min, or 2000 r / min, and the processing time can be 2 min, 5 min, 10 min, 15 min, 20 min, or 25 min.

[0048] In some embodiments, the second rotational speed stage of the high-speed shearing process can be a shearing speed of 2001 r / min, 2500 r / min, 3000 r / min, 3500 r / min, 4000 r / min, 4500 r / min, 5000 r / min, 5500 r / min, 6000 r / min, 6500 r / min, or 7000 r / min, and the processing time can be 2 min, 5 min, 10 min, 15 min, 20 min, or 25 min.

[0049] In some embodiments, the third rotational speed stage of the high-speed shearing process can be 7001 r / min, 7500 r / min, 8000 r / min, 8500 r / min, 9000 r / min, 9500 r / min, or 10000 r / min, and the processing time can be 2 min, 5 min, 10 min, 15 min, 20 min, or 25 min.

[0050] In some embodiments, after the dispersion and prefiberization steps and before the hot calendering step, an auxiliary treatment is further included to perform secondary fiberization and densification on the second mixture. The auxiliary treatment includes at least one selected from grinding and refining in a mill, kneading in a kneader, and hot refining and plasticizing in a hot mill; wherein the duration of the auxiliary treatment is 5-60 minutes. Those skilled in the art can determine the specific treatment duration within this time range through conventional experiments, depending on the type of equipment selected.

[0051] In some embodiments, the mixing, dispersion and prefiberization and auxiliary treatment steps can be repeated as required by the formulation and process.

[0052] In a preferred embodiment, a process of adding the adhesive in stages can be employed. Exemplarily, the required total adhesive dosage is added in two stages, specifically including the following steps: The first stage of processing involves mixing ceramic powder, pore-forming agent, and a first-part binder accounting for 40%-70% of the total binder dosage, followed by dispersion and pre-fiberization treatment to obtain an intermediate mixture.

[0053] Second stage processing: Add the remaining binder to the intermediate mixture, mix evenly, and then perform dispersion and pre-fiberization treatment again to obtain the second mixture.

[0054] In some embodiments, in the first stage of processing, an auxiliary process may be performed after the dispersion and prefiberization treatment to obtain an intermediate mixture. In some embodiments, in the second stage of processing, an auxiliary process may be performed after the dispersion and prefiberization treatment to obtain a second mixture.

[0055] S300 hot calendering: The second mixture is hot calendered at 40℃-180℃, and the three-dimensional fiber network encapsulates the ceramic powder and the pore-forming agent to obtain a green film.

[0056] In this embodiment of the invention, the hot calendering step is a physical shaping process that transforms the second mixture with a three-dimensional fiber network into a self-supporting green film. This step is a continuation and reinforcement of the dispersion and pre-fiberization steps. Its core is not to rebuild the fiber network, but to further compact and entangle the already formed three-dimensional fiber network under the synergistic effect of temperature and pressure at 40℃-180℃, so that it more firmly wraps and locks the ceramic powder and the pore-forming agent, thereby constructing the mechanical skeleton of the membrane and realizing the key transformation from a loose mixture to a green film with a specific thickness and structural integrity.

[0057] In some embodiments, the hot calendering is a dry rolling process. Traditional wet membrane processes require the use of large amounts of organic solvents to dissolve the polymer, resulting in complex processes, high energy consumption, and environmental and safety risks. In contrast, the dry process used in this application eliminates the need for pulping, coating, and prolonged drying, making it simple, low-cost, and environmentally friendly. More importantly, the three-dimensional fiber network skeleton constructed through dry rolling results in a membrane that exhibits excellent performance in terms of thermal stability, mechanical strength, wettability to phosphoric acid electrolyte, and ionic conductivity.

[0058] In some embodiments, the hot calendering step uses a two-roll, three-roll, four-roll, or multi-roll calender to press the second mixture into the green film.

[0059] In some embodiments, the temperature of the hot calendering step is 40°C-120°C. In exemplary cases, the temperature of the hot calendering step can be 40°C, 50°C, 70°C, 90°C, 110°C, or 120°C. This temperature range is suitable for the plasticizing and stretching of various fluoropolymer binders, enabling effective compaction of the three-dimensional fiber network while preventing the binder from over-melting and damaging the network's supporting structure.

[0060] In some embodiments, the hot calendering process includes at least three sequentially performed stages, wherein the roll gap is gradually reduced from 1.0 mm to 0.05 mm.

[0061] In other embodiments, the hot rolling process includes three to six sequentially performed stages.

[0062] In some embodiments, the hot rolling process includes three sequentially performed stages, wherein: In the first hot rolling stage, the roll gap is 0.80mm-1.00mm; In the second hot rolling stage, the roll gap is 0.20mm-0.79mm; In the third hot rolling stage, the roll gap is 0.05mm-0.19mm.

[0063] In some embodiments, the roll gap in the first hot calendering stage can be 0.80 mm, 0.85 mm, 0.90 mm, 0.95 mm, or 1.00 mm.

[0064] In some embodiments, the roll gap in the second hot calendering stage can be 0.20mm, 0.25mm, 0.30mm, 0.35mm, 0.40mm, 0.45mm, 0.50mm, 0.55mm, 0.60mm, 0.65mm, 0.70mm, 0.75mm, or 0.79mm.

[0065] In some embodiments, the roll gap in the third hot calendering stage can be 0.05 mm, 0.10 mm, 0.15 mm, or 0.19 mm.

[0066] In another specific embodiment, the hot calendering process includes six sequentially performed stages, wherein the roll gaps are, in sequence: 1.0 mm, 0.7 mm, 0.4 mm, 0.2 mm, 0.1 mm, and 0.05 mm.

[0067] In this embodiment of the invention, the number of rolls in each hot calendering stage can be adaptively adjusted according to the required degree of densification of the green film. Those skilled in the art can determine this through conventional experiments, and the present invention does not impose specific limitations on this.

[0068] S400 Pore-forming agent removal: The pore-forming agent in the green film is removed by an extractant to form an electrolyte diaphragm.

[0069] In this embodiment of the invention, in order to remove the pore-forming agent while avoiding damage to the green film structure, an extractant is used to remove the pore-forming agent from the green film to form a porous framework.

[0070] In some embodiments, the extractant includes one or more of water, ethanol, hexane, acetone, petroleum ether, and chloroform.

[0071] In this embodiment of the invention, a matching extractant is used to precisely remove pore-forming agents with different chemical properties from the green film. Water effectively removes sodium chloride, ammonium carbonate, and ammonium bicarbonate, and can also swell starch for removal. Ethanol assists in dissolving or swelling polar components such as polyvinyl alcohol and starch. Acetone dissolves polyvinyl alcohol and some low-melting-point waxes. Non-polar solvents such as hexane and petroleum ether, or chloroform with stronger dissolving power, are mainly used to dissolve non-polar pore-forming agents, such as paraffin wax. Through this targeted solvent matching, the pore-forming agents can be removed gently and directionally under low-temperature conditions, thereby constructing a uniform porous structure while avoiding structural stress damage and defect formation that may result from traditional high-temperature thermal decomposition processes.

[0072] In embodiments of the present invention, the specific amount of extractant is not limited, as long as the amount of extractant used is sufficient to extract and remove the pore-forming agent from the green film. For example, an excess of extractant can be used to soak or perform Soxhlet extraction on the green film to ensure complete extraction. Those skilled in the art can determine the specific amount of extractant based on the content of the pore-forming agent in the green film through conventional experiments.

[0073] In some embodiments, the water is deionized water.

[0074] In some embodiments, to improve the removal efficiency and thoroughness of the pore-forming agent, physical enhancement methods can be employed during the solvent extraction process. For example, ultrasonic treatment can be used to promote solvent penetration and diffusion, moderate heating can be used to reduce solvent viscosity and increase solubility, or centrifugation can be performed after the removal step to ensure that the dissolved pore-forming agent is effectively removed.

[0075] In addition, embodiments of this application also provide an electrolyte membrane for a phosphoric acid fuel cell prepared by any of the above-described preparation methods.

[0076] In some embodiments, the thickness of the electrolyte membrane is 50-300 μm. In exemplary embodiments, the thickness of the electrolyte membrane can be 50 μm, 80 μm, 110 μm, 140 μm, 170 μm, 200 μm, 230 μm, 260 μm, 280 μm, or 300 μm.

[0077] In some embodiments, the porosity of the electrolyte membrane is 40%-65%, and in exemplary embodiments, the porosity of the electrolyte membrane can be 40%, 45%, 50%, 55%, 60%, or 65%.

[0078] To further illustrate the technical effects of the present invention, the following specific embodiments are also provided.

[0079] Example 1 Example 1 provides an electrolyte membrane for a phosphoric acid fuel cell. The preparation method of the electrolyte membrane includes the following steps: The specific steps for mixing S101 are as follows: Weigh out 78 parts by weight of ceramic powder (silicon carbide), 3 parts by weight of binder (polytetrafluoroethylene), and 11 parts by weight of pore-forming agent (polyvinyl alcohol) according to the specified ratio. Place the weighed raw materials in a mixing device and mix them at 25°C using a segmented variable speed process: the first stage is mixed at a speed of 200 r / min for 3 min; then, the second stage is mixed at a speed of 480 r / min for 3 min.

[0080] The specific steps for S201 dispersion and prefiberization are as follows: The material obtained in step S101 is subjected to high-speed shearing, which includes three sequential speed stages: In the first rotational speed stage (for initial dispersion), the shearing speed is 2000 r / min and the processing time is 5 min; In the second rotational speed stage (for deep homogenization), the shearing speed is 6000 r / min and the processing time is 2 min; In the third rotational speed stage (used for high-speed shear-induced prefiberization), the shearing speed is 8000 r / min and the processing time is 2 min.

[0081] S301 auxiliary processing, the specific steps are as follows: The material processed in step S201 is transferred into a grinding mill and ground for 30 minutes to obtain an intermediate mixture.

[0082] The second stage of S401 adhesive addition involves the following steps: Add 3 parts by mass of binder (polytetrafluoroethylene) to the intermediate mixture obtained in step S301 and mix thoroughly. Then, repeat all operations of step S201 (dispersion and prefiberization) and step S301 (auxiliary treatment) to obtain a second mixture.

[0083] The specific steps for hot rolling S501 are as follows: At 80°C, the second mixture obtained in step S401 is subjected to a six-stage hot calendering process using a twin-roll calender to obtain a green film; wherein the roll gaps of the six stages are set sequentially as follows: 1.0 mm, 0.7 mm, 0.4 mm, 0.2 mm, 0.1 mm, and 0.05 mm.

[0084] S601 removes the pore-forming agent. The specific steps are as follows: The green membrane obtained in step S501 is immersed in the extractant (deionized water), and the water-soluble pore-forming agent (polyvinyl alcohol) is removed using an ultrasonic-assisted extraction process. Specifically, the membrane is ultrasonically treated at 40°C for 45 minutes, then the deionized water is replaced, and the above process is repeated a total of 3 times. Finally, a porous electrolyte membrane is obtained.

[0085] Example 2 Example 2 provides an electrolyte membrane for a phosphoric acid fuel cell. The preparation method of the electrolyte membrane includes the following steps: The specific steps for mixing S102 are as follows: Weigh out 80 parts by weight of ceramic powder (silicon nitride), 6 parts by weight of binder (polytetrafluoroethylene), and 10 parts by weight of pore-forming agent (sodium chloride). Place the above raw materials in a mixing device and mix them at 20°C using a segmented variable speed process: in the first stage, mix at a speed of 200 r / min for 5 min; then, in the second stage, increase the speed to 480 r / min and mix for another 7 min to obtain the first mixture.

[0086] The specific steps for S202 dispersion and prefiberization are as follows: The first mixture obtained in step S102 is subjected to high-speed shearing to obtain a second mixture. This high-speed shearing process includes three sequentially occurring rotational speed stages: In the first rotational speed stage (for initial dispersion), the shearing speed is 1000 r / min and the processing time is 10 min; In the second rotational speed stage (for deep homogenization), the shearing speed was 4000 r / min and the processing time was 15 min; In the third rotational speed stage (used for high-speed shear-induced prefiberization), the shearing speed was 9000 r / min and the processing time was 10 min.

[0087] The specific steps for hot rolling S302 are as follows: At 60°C, the second mixture obtained in step S202 is subjected to a three-stage hot calendering process using a twin-roll calender to obtain a green film; wherein the roll gaps of the three stages are set to 1.00 mm, 0.50 mm, and 0.10 mm respectively.

[0088] S402 removes the pore-forming agent. The specific steps are as follows: The green membrane obtained in step S302 is immersed in the extractant (deionized water), and the water-soluble pore-forming agent (sodium chloride) is removed using an ultrasonic-assisted extraction process. Specifically, the membrane is ultrasonically treated at 30°C for 10 minutes, then the deionized water is replaced, and the above process is repeated a total of 3 times. Finally, a porous electrolyte membrane is obtained.

[0089] Example 3 Example 3 provides an electrolyte membrane for a phosphoric acid fuel cell. The preparation method of the electrolyte membrane includes the following steps: The specific steps for mixing S103 are as follows: Weigh out 80 parts by weight of ceramic powder (silicon nitride), 6 parts by weight of binder (5.4 parts by weight of polytetrafluoroethylene and 0.6 parts by weight of fusible polytetrafluoroethylene), and 10 parts by weight of pore-forming agent (sodium chloride). Place the above raw materials in a mixing device and mix them at 20°C using a segmented variable speed process: in the first stage, mix at a speed of 200 r / min for 5 min; then, in the second stage, increase the speed to 480 r / min and mix for another 7 min to obtain the first mixture.

[0090] The specific steps for S203 dispersion and prefiberization are as follows: The first mixture obtained in step S103 is subjected to high-speed shearing to obtain the second mixture. This high-speed shearing process includes three sequentially occurring rotational speed stages: In the first rotational speed stage (for initial dispersion), the shearing speed is 1000 r / min and the processing time is 10 min; In the second rotational speed stage (for deep homogenization), the shearing speed was 4000 r / min and the processing time was 15 min; In the third rotational speed stage (used for high-speed shear-induced prefiberization), the shearing speed was 9000 r / min and the processing time was 10 min.

[0091] The specific steps for hot rolling S303 are as follows: At 60°C, the second mixture obtained in step S203 is subjected to a five-stage hot calendering process using a twin-roll calender to obtain a green film; wherein the roll gaps of the five stages are set sequentially as follows: 1.00mm, 0.80mm, 0.60mm, 0.40mm, and 0.10mm.

[0092] S403 removes the pore-forming agent. The specific steps are as follows: The green membrane obtained in step S303 is immersed in the extractant (deionized water), and the water-soluble pore-forming agent (sodium chloride) is removed using an ultrasonic-assisted extraction process. Specifically, the membrane is ultrasonically treated at 30°C for 10 minutes, then replaced with fresh deionized water, and the above process is repeated a total of 3 times. Finally, a porous electrolyte membrane is obtained.

[0093] Example 4 Example 4 provides an electrolyte membrane for a phosphoric acid fuel cell. The preparation method of Example 4 is basically the same as that of Example 3, except that: The ceramic powder used was boron carbide, and the binder consisted of polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), with PTFE accounting for 80% of the total binder mass. The pore-forming agent was ammonium bicarbonate, and the hot-calendering step was performed at 40°C. The extractant was deionized water, and the ultrasonic conditions for removing the pore-forming agent were as follows: ultrasonic treatment at room temperature for 40 minutes, followed by replacement with fresh deionized water, and the process was repeated three times.

[0094] Example 5 Example 5 provides an electrolyte membrane for a phosphoric acid fuel cell. The preparation method of Example 5 is basically the same as that of Example 4, except that: The ceramic powder used is boron nitride, the binder is composed of polytetrafluoroethylene and polychlorotrifluoroethylene, of which polytetrafluoroethylene accounts for 75% of the total mass of the binder, the pore-forming agent is starch, and the temperature of the hot pressing step is 50°C.

[0095] Comparative Example 1 Comparative Example 1 provides an electrolyte membrane for a phosphoric acid fuel cell. The preparation method of Comparative Example 1 is basically the same as that of Example 3, except that: Comparative Example 1 did not use a pore-forming agent (polyvinyl alcohol).

[0096] Comparative Example 2 Comparative Example 2 provides an electrolyte membrane for a phosphoric acid fuel cell. The preparation method of Comparative Example 2 is basically the same as that of Example 3, except that: Comparative Example 2 omitted the "dispersion and prefiberization" step after completing the mixing step and directly carried out hot calendering.

[0097] Results of Comparative Example 2: During the hot calendering process, because the binder did not undergo high-speed shearing treatment, it was unable to form a three-dimensional fiber network that could uniformly encapsulate and bridge the ceramic powder particles. The material exhibited a loose, cohesive granular aggregate. Therefore, it was impossible to obtain a continuous green film with structural integrity, uniform thickness, and self-supporting properties through conventional single-pass or limited-pass hot calendering processes.

[0098] To verify the progressiveness of the embodiments of the present invention, the electrolyte membranes of the phosphoric acid fuel cells prepared in Examples 1-5 and Comparative Examples 1-2 were tested for bubble pressure, porosity, phosphoric acid absorption rate, and resistance. The specific performance test results are shown in Table 1.

[0099] Table 1. Electrolyte membrane performance test of phosphoric acid fuel cells

[0100] Based on the data analysis of Examples 1-5 and Comparative Examples 1-2 in Table 1, the results are as follows: Compared with Comparative Example 1, the electrolyte membranes prepared in Examples 1, 3, 4, and 5 of this invention exhibit significantly improved bubble pressure, moderately increased porosity, and improved acid absorption rate. These structural characteristics collectively contribute to a significant reduction in electrical resistance, indicating stronger proton conductivity. This invention innovates the membrane preparation method by starting with microstructural design, not only achieving controllable preparation of key membrane properties and significantly improving battery performance, but also demonstrating significant advantages in process simplification, cost control, and large-scale production, which is of great value in promoting the commercial application of phosphoric acid fuel cells.

[0101] Compared with the prior art, the present invention has the following beneficial effects: (1) In terms of microstructure control, the present invention achieves the regulation of porosity and pore size distribution through the synergistic process of "high-speed shear prefiberization-pore-forming agent extraction", which solves the key problem that existing technologies cannot optimize microstructure to improve electrolyte conductivity.

[0102] (2) In terms of overall performance, the prepared separator exhibits excellent phosphoric acid electrolyte adsorption, storage and proton conduction capabilities due to its optimized microstructure, thereby directly improving the battery's output power, operating stability and cycle life, overcoming the bottleneck of low performance of existing batteries.

[0103] (3) In terms of process efficiency, the method has a low molding temperature (40℃-180℃), does not require high-temperature sintering, has simple process steps, low energy consumption, convenient operation, and is easy to scale up for continuous production, thus meeting commercial needs.

[0104] (4) In terms of structural reliability, the three-dimensional fiber network formed by prefiberization effectively wraps and fixes the ceramic powder and pore-forming agent in hot calendering. The self-supporting diaphragm obtained still maintains a complete skeleton after the pore-forming agent is removed, and has good mechanical strength and structural stability.

[0105] The specific embodiments of the present invention have been described above. It should be understood that the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention fall within the scope of protection and disclosure of the present invention.

Claims

1. A method for preparing an electrolyte membrane for a phosphoric acid fuel cell, characterized in that, Includes the following steps: Mixing: Ceramic powder, binder and pore-forming agent are stirred and mixed to form a first mixture; wherein the binder is a fluoropolymer; Dispersion and prefiberization: The first mixture is subjected to high-speed shearing treatment, with the rotation speed controlled at 500 r / min-10000 r / min, so that the ceramic powder is uniformly dispersed and the binder is prefiberized to form a three-dimensional fiber network, thus obtaining the second mixture; Hot calendering: The second mixture is hot calendered at 40℃-180℃, and the three-dimensional fiber network encapsulates the ceramic powder and the pore-forming agent to obtain a green film; Pore-forming agent removal: The pore-forming agent in the green film is removed by an extractant to form an electrolyte membrane.

2. The preparation method according to claim 1, characterized in that, The ceramic powder comprises 50-99 parts by weight, the binder comprises 1-50 parts, and the pore-forming agent comprises 1-25 parts.

3. The preparation method according to claim 1, characterized in that, The particle size of the ceramic powder is ≤20μm.

4. The preparation method according to claim 1, characterized in that, The fluoropolymer is selected from fluoropolymers.

5. The preparation method according to claim 1, characterized in that, The ceramic powder includes one or more of silicon carbide, silicon nitride, boron carbide, and boron nitride; and / or The fluoropolymer is polytetrafluoroethylene (PTFE), or a mixture of PTFE and other fluoropolymers; the other fluoropolymers are selected from one or more of polyvinylidene fluoride (PVDF), fusible PTFE, and polychlorotrifluoroethylene (PTFE); and when the fluoropolymer is a mixture of PTFE and other fluoropolymers, the PTFE content is 75%-100% by mass of the total mass of the mixture; and / or The pore-forming agent includes one or more of the following: paraffin wax, sodium chloride, starch, polyvinyl alcohol, ammonium carbonate, and ammonium bicarbonate; and / or The extractant includes one or more of water, ethanol, hexane, acetone, petroleum ether, and chloroform.

6. The preparation method according to claim 1, characterized in that, The high-speed shearing process includes at least three sequential rotational speed stages, wherein the shearing speed is gradually increased from 500 r / min to 10000 r / min.

7. The preparation method according to claim 6, characterized in that, The high-speed shearing process includes three sequential rotational speed stages, wherein: In the first rotational speed stage, the shearing speed is 500 r / min-2000 r / min, and the processing time is 2 min-25 min; In the second rotational speed stage, the shearing speed is 2001 r / min-7000 r / min, and the processing time is 2 min-25 min; In the third rotational speed stage, the shearing speed is 7001 r / min-10000 r / min, and the processing time is 2 min-25 min.

8. The preparation method according to claim 1, characterized in that, The hot rolling process includes at least three sequentially performed stages, wherein the roll gap is gradually reduced from 1.0 mm to 0.05 mm.

9. The preparation method according to claim 8, characterized in that, The hot rolling process includes three sequentially performed stages, wherein: In the first hot rolling stage, the roll gap is 0.80mm-1.00mm; In the second hot rolling stage, the roll gap is 0.20mm-0.79mm; In the third hot rolling stage, the roll gap is 0.05mm-0.19mm.

10. An electrolyte membrane for a phosphoric acid fuel cell, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 9.

11. The electrolyte membrane according to claim 10, characterized in that, The thickness of the electrolyte membrane is 50-300 μm; and / or The porosity of the electrolyte membrane is 40%-65%.

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