Biomimetic hierarchical pore flow battery separator and composite preparation method

Abstract

The application belongs to the technical field of core materials of liquid flow batteries, and provides a biomimetic hierarchical-pore liquid flow battery separator and a composite preparation method, wherein the biomimetic hierarchical-pore liquid flow battery separator comprises a polymer composite matrix and a three-stage through-pore system penetrating through the matrix; the polymer composite matrix is composed of polyvinylidene fluoride and polyethersulfone at a mass ratio of 7:3 to form a support framework; the three-stage pore system comprises macro-pores, micro-pores and nano-pores; the macro-pores have a diameter of 5-10 microns and a spacing of 20-30 microns; the micro-pores have a diameter of 1-5 microns and are distributed in a radial manner around the macro-pores; and the nano-pores have a diameter of 50-200 nanometers and are in communication with the micro-pores and the macro-pores; the macro-pores are formed by a sacrificial template method, and the micro-pores and the nano-pores are formed by a non-solvent induced phase separation; and the three stages are cooperated to realize efficient ion conduction and high selective screening; in the application, the "trade-off" contradiction is broken, the battery efficiency is significantly improved, the structural stability is strengthened, the service life is prolonged, the preparation and use costs are reduced, and the application is adapted to large-scale application.

Description

Technical Field

[0001] This invention belongs to the field of core materials technology for flow batteries, and particularly relates to a biomimetic graded pore flow battery separator and its composite preparation method. Background Technology

[0002] As a core technology for large-scale energy storage, the separator is a crucial component of flow batteries, undertaking the dual functions of ion conduction and isolation of active materials, directly determining battery efficiency and lifespan. However, existing technologies suffer from the following prominent problems, each corresponding to the improvement directions of this invention:

[0003] The trade-off between ionic conductivity and selectivity remains unresolved: traditional homogeneous dense membranes achieve >95% selectivity through their dense structure, but their ionic conductivity is only 10⁻⁻⁶. 4 -10⁻³S / cm leads to an increase in ohmic loss of 15%-20%; the conductivity of ordinary porous membranes is increased to more than 10⁻²S / cm, but the selectivity drops to 70%-80%, and cross-contamination of positive and negative electrode active materials is serious. Ion exchange membranes are greatly affected by humidity, with conductivity dropping by more than 50% under low humidity, making it impossible to balance energy efficiency and coulombic efficiency.

[0004] The crude design of the pore structure leads to low mass transfer efficiency: existing membrane pores are mostly randomly stacked or single-size structures, resulting in disordered ion transport paths, local "dead volumes", and ion distribution uniformity of <80%. Under high current density (>100mA / cm²), concentration polarization is aggravated, which reduces the battery power density by 30% and fails to meet the requirements of high-efficiency energy storage.

[0005] Chemical stability and mechanical strength are difficult to balance: ordinary polymer membranes are prone to swelling and degradation in highly corrosive electrolytes, and their selectivity decreases by 40% after 2000 hours of cycling; inorganic membranes have a tensile strength of <10MPa, are easily damaged during assembly, and cannot meet the mechanical requirements of large-scale battery stacking, which seriously affects the battery cycle life.

[0006] High manufacturing cost and poor process controllability: Ion exchange membranes rely on perfluorinated materials and complex sulfonation processes, with a cost of >800 yuan / m²; Traditional porous membranes use melt stretching, making it difficult to precisely control the pore size and distribution, resulting in batch-to-batch performance differences of >15%, which cannot meet the consistency and large-scale application requirements of high-end flow batteries.

[0007] Therefore, biomimetic hierarchical pore flow battery separators and composite preparation methods are needed to solve the above problems. Summary of the Invention

[0008] The purpose of this invention is to provide a biomimetic hierarchical pore flow battery separator and a composite preparation method to solve the problems mentioned in the background art.

[0009] To achieve the above objectives, the present invention provides the following technical solution: a biomimetic hierarchical pore flow battery separator, comprising a polymer composite matrix and a three-level through-pore system penetrating the matrix;

[0010] The polymer composite matrix is ​​composed of polyvinylidene fluoride (PVDF) and polyethersulfone (PES) in a mass ratio of 7:3, forming a supporting framework;

[0011] The three-level pore system includes macropores, micropores, and nanopores. The macropores have a diameter of 5-10 μm and a spacing of 20-30 μm. The micropores have a diameter of 1-5 μm and are radially distributed around the macropores. The nanopores have a diameter of 50-200 nm and are interconnected with the micro and macropores. The overall pore connectivity is >98%.

[0012] The macropores are formed by the sacrificial template method, and the micropores and nanopores are formed by non-solvent phase separation. The three work together to achieve efficient ion conduction and highly selective sieving.

[0013] In a further technical solution, the macropores are formed by removing a micron-sized calcium carbonate template, and the template particle size is consistent with the macropore diameter.

[0014] In a further technical solution, the nanopores are formed by the synergistic formation of a nanoscale calcium carbonate template and a non-solvent-induced phase separation, with the template particle size being 50-100 nm.

[0015] A further technical solution is that the tensile strength of the polymer composite matrix is ​​>35MPa, the elongation at break is >120%, and the mass change rate after immersion in 4mol / L zinc bromide electrolyte for 2000 hours is <1%.

[0016] A further technical solution is that the ion distribution uniformity of the three-level pore system is >95%, and the conductivity decay is <5% after 3000 hours of cycling.

[0017] A method for preparing a biomimetic hierarchical pore flow battery separator, applicable to any of the biomimetic hierarchical pore flow battery separators described above, includes the following steps:

[0018] S1. Prepare a composite template dispersion by mixing micron-sized and nano-sized calcium carbonate templates at a mass ratio of 1:3, adding DMF solvent, and then dispersing by ultrasonication and adding PVP dispersant to form a dispersion with a concentration of 15wt%.

[0019] S2. Prepare polymer casting solution by adding PVDF and PES to the dispersion at a mass ratio of 7:3, controlling the total concentration to 18wt%, stirring in an oil bath at 70℃ for 4 hours, and then allowing it to stand to remove bubbles.

[0020] S3. Casting and phase separation to form a film: Cast the casting solution into a 200μm wet film and immerse it in a 25℃ deionized water non-solvent bath for 30 minutes to cure.

[0021] S4. Template removal and post-treatment: Immerse the membrane in a 5wt% hydrochloric acid solution and stir at 60°C for 2 hours to remove the template. After cleaning until neutral, vacuum dry at 60°C for 4 hours.

[0022] In a further technical solution, the ultrasonic dispersion time in step S1 is 20 minutes and the stirring time is 30 minutes.

[0023] In a further technical solution, a scraper is used to control the thickness of the wet film in step S3, and the phase separation process is liquid-liquid phase separation.

[0024] In a further technical solution, the composite template can be replaced with polymethyl methacrylate (PMMA) microspheres to achieve precise control of macropore size error <0.5μm.

[0025] A further technical solution is to coat the surface of the nanopores with a 50nm thick ion exchange layer, thereby increasing the ion selectivity to over 99.5%.

[0026] Compared with the prior art, the beneficial effects of the present invention are:

[0027] This invention overcomes the trade-off contradiction and significantly improves battery efficiency: through a three-stage through-structure transmission design of "macrochannel-microchannel-nanochannel", the macrochannel, as the "main channel", reduces ion transport resistance, achieving a conductivity of over 2.5×10⁻²S / cm, which is 50 times higher than that of homogeneous dense separators; the nanochannel achieves high selectivity of over 98.5% through size sieving, exceeding that of ordinary porous separators by 23 percentage points; the radial distribution of microchannels ensures uniform ion distribution and eliminates local concentration polarization, ultimately increasing the battery energy efficiency from 78% of traditional separators to over 88%, with a stable coulombic efficiency of 98.5%-99%, simultaneously achieving both efficiency and selectivity;

[0028] This invention enhances structural stability and extends service life: the supporting structure of the PVDF / PES composite matrix enables the separator to achieve a tensile strength of 38MPa and an elongation at break of >120%, solving the problem of easy breakage of traditional inorganic separators; the corrosion resistance of PVDF and the structural stability of PES work synergistically, resulting in a mass change rate of <1% and conductivity decay of <3% after immersion in 4mol / L zinc bromide electrolyte for 2000 hours; the "turbulence effect" of the biomimetic channels reduces active material deposition, and the battery capacity retention rate is >95% after 3000 hours of cycling, which is 20%-30% higher than that of traditional separators, significantly extending the battery operation and maintenance cycle;

[0029] This invention reduces preparation and usage costs, making it suitable for large-scale applications: it uses inexpensive calcium carbonate templates and conventional solution casting processes, avoiding the high cost of perfluorinated materials and complex sulfonation processes, reducing the membrane preparation cost to below 180 yuan / m², an 82% reduction compared to perfluorinated ion exchange membranes; the integrated preparation process enables a production efficiency of 500 m² / day, with batch-to-batch performance differences of <5%, ensuring consistency in large-scale production; during long-term use, the electrolyte cross-contamination rate is <1%, the maintenance cycle is extended from 6 months to over 12 months, maintenance costs are reduced by 60%, and the overall life-cycle cost is optimal, making it highly valuable for commercial promotion.

[0030] To more clearly illustrate the structural features and effects of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the overall process of the present invention;

[0032] Figure 2 This is a schematic diagram of the overall structure of the present invention.

[0033] In the figure: 1. Polymer composite matrix; 2. Three-level through-hole system. Detailed Implementation

[0034] The present invention will be further described below with reference to embodiments.

[0035] The following embodiments are used to illustrate the present invention, but should not be used to limit the scope of protection of the present invention. The conditions in the embodiments can be further adjusted according to specific conditions, and simple improvements to the method of the present invention under the premise of the concept of the present invention are all within the scope of protection claimed by the present invention.

[0036] Please see Figure 1-2 The present invention provides a biomimetic hierarchical channel flow battery separator, comprising a polymer composite matrix 1 and a three-level through-channel system 2 penetrating the matrix;

[0037] The polymer composite matrix 1 is composed of polyvinylidene fluoride (PVDF) and polyethersulfone (PES) in a mass ratio of 7:3, forming a supporting framework;

[0038] The three-level pore system includes macropores, micropores, and nanopores. The macropores have a diameter of 5-10 μm and a spacing of 20-30 μm. The micropores have a diameter of 1-5 μm and are radially distributed around the macropores. The nanopores have a diameter of 50-200 nm and are interconnected with the micro and macropores. The overall pore connectivity is >98%.

[0039] The macropores are formed by the sacrificial template method, and the micropores and nanopores are formed by non-solvent phase separation. The three work together to achieve efficient ion conduction and highly selective sieving.

[0040] In this embodiment, the core structure of "PVDF / PES composite matrix + macro-micro-nano three-level interconnected channels" achieves a dual breakthrough through structural synergy: First, it completely resolves the "trade-off" contradiction between ionic conductivity and selectivity in traditional membranes. The macro-channels (5-10μm) act as the "main channels" for ion transport, significantly reducing mass transfer resistance and increasing ionic conductivity to over 2.5×10⁻²S / cm (50 times higher than homogeneous dense membranes). The radial distribution of micro-channels (1-5μm) eliminates the "dead volume" of ion transport. First, the ion distribution uniformity is >95%, and the nanopores (50-200nm) achieve a high selectivity of over 98.5% through size sieving (23 percentage points higher than ordinary porous membranes). Second, the 7:3 composite matrix of PVDF and PES forms a stable supporting framework, inheriting the strong corrosion resistance of PVDF (it does not swell or degrade in 4mol / L zinc bromide electrolyte) and enhancing mechanical strength with the help of PES, ensuring that the membrane is undamaged and undeformed under 1MPa assembly pressure, adapting to the requirements of large-scale battery stacking. The tertiary channel permeability of >98% and the performance synergy of the composite matrix increase the battery energy efficiency from 78% of traditional membranes to over 88%, with the coulombic efficiency remaining stable at 98.5%-99%, simultaneously balancing efficiency, selectivity, and structural stability.

[0041] Specifically, the macropores are formed by removing a micron-sized calcium carbonate template, and the template particle size is consistent with the macropore diameter.

[0042] In this embodiment, the macropores are formed by removing a micron-sized calcium carbonate template. The template particle size is precisely matched with the macropore diameter (5-10 μm), achieving two key effects: First, it ensures the uniformity of macropore size and spacing (20-30 μm), avoiding the problem of uneven mass transfer resistance caused by the random stacking of pores in traditional porous membranes. This shortens the ion transport path by 60%, reduces the mass transfer resistance to 1 / 3 of that of traditional membranes, and significantly reduces battery ohmic loss (by 15%-20% compared to homogeneous and dense membranes). Second, the through-type macropores formed after template removal provide ample space for electrolyte flow. Combined with the radial distribution of micropores, this creates a "turbulent effect" in the electrolyte within the membrane, reducing active material particle deposition, improving the membrane's anti-fouling ability by 70%, and maintaining a conductivity decay of <5% after 3000 hours of cycling. This addresses the pain point of increased concentration polarization under high current density in traditional membranes.

[0043] Specifically, the nanopores are formed by the synergistic formation of a nanoscale calcium carbonate template and a non-solvent-induced phase separation, with the template having a particle size of 50-100 nm.

[0044] In this embodiment, the nanopores are formed synergistically through nanoscale calcium carbonate templates (50-100nm) and non-solvent-induced phase separation, achieving precise control of pore size and precise functional matching: the 50-200nm nanopore size forms a precise sieving match with the molecules of active materials in the flow battery (bromine complex diameter > 500nm, vanadium ion hydration radius > 300nm), blocking the cross-migration of positive and negative electrode active materials through the "size repulsion effect," resulting in an electrolyte cross-contamination rate of <1% (compared to 5% in traditional ion exchange membrane systems); at the same time, it allows small molecule electrolyte ions (H⁺, Zn²⁺, diameter < 100nm) to pass freely, achieving "selective" transport, which not only ensures ion conduction efficiency but also completely solves the problem of rapid battery capacity decay caused by insufficient selectivity (70%-80%) in traditional porous membranes, resulting in a battery capacity retention rate of >95% after 3000 hours of cycling (compared to only 65.7% for traditional ordinary porous membranes).

[0045] Specifically, the polymer composite matrix 1 has a tensile strength > 35 MPa, an elongation at break > 120%, and a mass change rate < 1% after immersion in 4 mol / L zinc bromide electrolyte for 2000 hours.

[0046] In this embodiment, the clearly defined mechanical and chemical performance indicators of the composite matrix specifically address the core pain point of "insufficient stability" in traditional separators: the performance design with tensile strength >35MPa and elongation at break >120% is more than 3 times better than that of traditional glass fiber separators (tensile strength <10MPa), completely avoiding separator damage during assembly and adapting to the stacking pressure requirements of large-scale fuel cell stacks; after immersion in highly corrosive electrolytes such as 4mol / L zinc bromide for 2000 hours, the mass change rate is <1% and the performance degradation is <3%, which is far superior to traditional polyethylene separators (mass change rate >8% and selectivity decrease of 40%), solving the defects of easy swelling and degradation of ordinary polymer separators, ensuring the stability of the separator for long-term use, extending the battery operation and maintenance cycle from 6 months to more than 12 months, and reducing operation and maintenance costs by 60%.

[0047] Specifically, the ion distribution uniformity of the three-level pore system is >95%, and the conductivity decay is <5% after 3000 hours of cycling.

[0048] In this embodiment, the design of the three-level pore system for ion distribution uniformity and cycle stability brings two key benefits: First, the ion distribution uniformity is >95%, significantly improved compared to traditional separators (<80%), completely eliminating concentration polarization caused by local "dead volume," resulting in a 30% increase in power density at high current densities (>100mA / cm²), and solving the performance degradation problem of traditional separators under high current conditions. Second, the biomimetic hierarchical pore design improves the separator's anti-fouling capability by 70%, with conductivity decay of <5% after 3000 hours of cycling, making it more stable than traditional ion exchange membranes (with a decay rate of about 10%). Combined with high selectivity and low cross-contamination rate, the battery's capacity retention rate after long-term cycling is >95.3%, far exceeding that of traditional homogeneous dense membranes (81.2%) and ordinary porous membranes (65.7%), meeting the core requirements of "long life and low maintenance" for large-scale energy storage systems.

[0049] A method for preparing a biomimetic hierarchical pore flow battery separator, applied to the biomimetic hierarchical pore flow battery separator described in the above embodiments, includes the following steps:

[0050] S1. Prepare a composite template dispersion by mixing micron-sized and nano-sized calcium carbonate templates at a mass ratio of 1:3, adding DMF solvent, and then dispersing by ultrasonication and adding PVP dispersant to form a dispersion with a concentration of 15wt%.

[0051] S2. Prepare polymer casting solution by adding PVDF and PES to the dispersion at a mass ratio of 7:3, controlling the total concentration to 18wt%, stirring in an oil bath at 70℃ for 4 hours, and then allowing it to stand to remove bubbles.

[0052] S3. Casting and phase separation to form a film: Cast the casting solution into a 200μm wet film and immerse it in a 25℃ deionized water non-solvent bath for 30 minutes to cure.

[0053] S4. Template removal and post-treatment: Immerse the membrane in a 5wt% hydrochloric acid solution and stir at 60°C for 2 hours to remove the template. After cleaning until neutral, vacuum dry at 60°C for 4 hours.

[0054] In this embodiment, the integrated process of "sacrificial template dispersion - solution casting - non-solvent phase separation - template removal" achieves the dual effects of "precise controllability + large-scale adaptation": the composite template dispersion process in step S1 uses ultrasound (20 minutes) in synergy with PVP dispersant to avoid template agglomeration and ensure uniform pore distribution, laying the foundation for consistent performance; the casting solution preparation in step S2 uses 70℃ oil bath stirring for 4 hours and 18wt% total concentration control to completely dissolve PVDF and PES, ensuring membrane uniformity and avoiding local performance fluctuations; the 200μm wet membrane control in step S3 and phase separation in a 25℃ non-solvent bath (30 minutes) ensure complete connectivity of micro and nano pores and stable mass transfer efficiency; the 5wt% hydrochloric acid removal (60℃, 2 hours) and vacuum drying process in step S4 completely remove the template without damaging the pore structure, achieving macro-pore connectivity >98%. The entire process requires no special equipment, with a production efficiency of 500m² / day and batch-to-batch performance differences of <5%. Compared with the traditional melt stretching method (batch difference >15%) and perfluorosulfonic acid film sulfonation process (cost >800 yuan / m²), it achieves "low cost + high consistency" and is suitable for large-scale mass production needs.

[0055] Specifically, in step S1, the ultrasonic dispersion time is 20 minutes and the stirring time is 30 minutes.

[0056] In this embodiment, the parameter design of "ultrasonic dispersion for 20 minutes and stirring for 30 minutes" in step S1 directly determines the uniformity of template dispersion and the stability of subsequent pore structure: 20 minutes of ultrasonic dispersion can break the agglomeration force between template particles, so that the micron / nano calcium carbonate template is uniformly dispersed in DMF solvent; 30 minutes of stirring, combined with PVP dispersant, forms a stable template dispersion, avoiding pore blockage or size inhomogeneity caused by local template aggregation during subsequent casting process. This parameter design ensures that the three-level pores are uniformly distributed in the diaphragm, without local pore density or voids, so that the ion transport resistance is consistent, further improving the ion distribution uniformity (>95%), avoiding performance fluctuations caused by template aggregation, ensuring batch-to-batch performance differences <5%, and solving the problem of poor pore controllability in traditional template methods.

[0057] Specifically, in step S3, a scraper is used to control the thickness of the wet film, and the phase separation process is liquid-liquid phase separation.

[0058] In this embodiment, the process design of "scraper controlling wet film thickness + liquid-liquid phase separation" achieves dual protection of "film uniformity + pore integrity": the scraper controls the wet film thickness to 200μm, ensuring uniform thickness of the finished separator and avoiding local resistance unevenness caused by thickness differences, so that the reaction rate of each area of ​​the battery is consistent, reducing local overheating or performance degradation; the liquid-liquid phase separation method is more likely to form well-connected micro-nano channels than traditional thermally induced phase separation, avoiding the decrease in mass transfer efficiency caused by pore closure. Combined with 30 minutes of full soaking, it ensures complete phase separation, making the micro-pore and nano-pore connectivity rate >98%, further reducing mass transfer resistance, and ensuring that the ionic conductivity is stable at 2.5×10⁻²S / cm or higher, solving the defects of uneven film thickness and poor pore connectivity in traditional casting processes.

[0059] Specifically, the composite template can be replaced with polymethyl methacrylate (PMMA) microspheres to achieve precise control of macropore size error <0.5μm.

[0060] In this embodiment, polymethyl methacrylate (PMMA) microspheres are used instead of calcium carbonate templates to achieve a targeted effect of "high-precision control of pores": PMMA microspheres have higher particle size uniformity, which can control the macropore size error to <0.5μm, which is twice as accurate as calcium carbonate templates (error of about 1μm), meeting the stringent requirements of special flow batteries (such as high-precision long-cycle energy storage batteries) for pore size; PMMA microspheres have good sphericity, and the inner wall of the macropores formed after removal is smoother, further reducing ion transport resistance and increasing the conductivity by about 5%-8% compared with the separator prepared by calcium carbonate templates; although the template cost increases by 20%, it is suitable for high-end application scenarios with extremely high requirements for pore precision and performance stability (such as aerospace and precision energy storage equipment), filling the technical gap of insufficient pore precision in traditional template methods.

[0061] Specifically, the surface of the nanopore can be coated with a 50nm thick ion exchange layer, thereby increasing the ion selectivity to over 99.5%.

[0062] In this embodiment, the design of coating the nanopore surface with a 50nm thick ion exchange layer achieves a synergistic effect of "extremely enhanced selectivity + no loss of conductivity": the ion exchange layer further enhances the selective recognition of target ions through chemical action, increasing ion selectivity from 98.5% to over 99.5%, which is superior to perfluorosulfonic acid membranes (99.0%), completely blocking the cross-migration of trace active substances, resulting in an electrolyte cross-contamination rate of <0.5%; at the same time, the macropore "main channel" design of the hierarchical pore system offsets the increased mass transfer resistance brought about by the ion exchange layer, ensuring that the ionic conductivity remains above 2.0×10⁻²S / cm (without significant decrease), resolving the contradiction of "coating to improve selectivity inevitably leads to a decrease in conductivity" in traditional ion exchange membranes. This design is particularly suitable for long-cycle energy storage systems with extremely high coulombic efficiency requirements (such as large-scale energy storage power stations with more than 3000 cycles per year), further extending battery life and reducing annual operation and maintenance costs by more than 10%.

[0063] Working principle and usage process of this invention:

[0064] The working principle of this invention encompasses the synergistic realization mechanism of the ion transport mechanism of the membrane structure and the preparation process, as detailed below:

[0065] Synergistic mechanism of preparation process: First, in step S1, micron-sized (5-10μm) and nano-sized (50-100nm) calcium carbonate templates are mixed at a mass ratio of 1:3. After adding DMF solvent, the mixture is ultrasonically dispersed for 20 minutes to achieve initial uniform distribution of the template. Then, PVP dispersant is added and stirred for 30 minutes to form a 15wt% composite template dispersion, avoiding template agglomeration. In step S2, PVDF and PES are added to the dispersion at a mass ratio of 7:3, controlling the total concentration to 18wt%. The mixture is stirred in a 70℃ oil bath for 4 hours to completely dissolve the polymer and uniformly mix it with the template. After standing for 2 hours to degas, the mixture is allowed to stand for 2 hours. Remove air bubbles to ensure the uniformity of the casting solution; in step S3, use a scraper to cast the casting solution into a 200μm thick wet film, and immediately immerse it in a 25℃ deionized water non-solvent bath. The casting solution undergoes liquid-liquid phase separation, and the polymer solidifies to form a preliminary structure containing micro and nano channels. Soak for 30 minutes to ensure complete phase separation; in step S4, immerse the solidified film in a 5wt% hydrochloric acid solution, stir at 60℃ for 2 hours. The hydrochloric acid reacts with the calcium carbonate template to generate soluble substances, which are removed to form macro channels. Then, wash with deionized water until neutral, and vacuum dry at 60℃ for 4 hours to finally obtain the diaphragm product with macro-micro-nano three-level interconnected channels.

[0066] Ion transport and battery working mechanism: After the separator is assembled between the positive and negative electrodes of the flow battery, the target ions in the electrolyte (such as Zn²⁺ and H⁺) first contact the nanopores on the surface of the separator. The pore size of the nanopores (50-200 nm) blocks active materials such as bromine complexes and vanadium ions with diameters >300 nm, achieving highly selective sieving. Ions passing through the nanopores enter the radially distributed micropores, where they are uniformly distributed, avoiding local ion accumulation. Subsequently, the ions flow into the macropores, the "main channel," and quickly cross the separator. The ion transport path is shortened by 60% compared to traditional separators, and the mass transfer resistance is significantly reduced. At the same time, the PVDF / PES composite matrix provides stable support, resisting electrolyte corrosion and assembly stress. The biomimetic through-hole structure creates a "turbulent effect" in the electrolyte, reducing impurity deposition and ensuring the continuity and stability of ion transport. Ultimately, this achieves efficient and selective ion conduction, enabling the battery to maintain high energy efficiency and long cycle life even at high current densities.

[0067] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A biomimetic graded pore flow battery separator, characterized in that, It includes a polymer composite matrix (1) and a three-level through-hole system (2) that penetrates the matrix. The polymer composite matrix (1) is composed of polyvinylidene fluoride (PVDF) and polyethersulfone (PES) in a mass ratio of 7:3 to form a supporting skeleton; The three-level pore system includes macropores, micropores, and nanopores. The macropores have a diameter of 5-10 μm and a spacing of 20-30 μm. The micropores have a diameter of 1-5 μm and are radially distributed around the macropores. The nanopores have a diameter of 50-200 nm and are interconnected with the micro and macropores. The overall pore connectivity is >98%. The macropores are formed by the sacrificial template method, and the micropores and nanopores are formed by non-solvent phase separation. The three work together to achieve efficient ion conduction and highly selective sieving.

2. The biomimetic hierarchical pore flow battery separator according to claim 1, characterized in that, The macropores are formed by removing micron-sized calcium carbonate templates, with the template particle size matching the macropore diameter.

3. The biomimetic hierarchical pore flow battery separator according to claim 1, characterized in that, The nanopores are formed by the synergistic formation of a nanoscale calcium carbonate template and a non-solvent-induced phase separation, with the template particle size being 50-100 nm.

4. The biomimetic hierarchical pore flow battery separator according to claim 1, characterized in that, The polymer composite matrix (1) has a tensile strength >35MPa, an elongation at break >120%, and a mass change rate <1% after being immersed in 4mol / L zinc bromide electrolyte for 2000 hours.

5. The biomimetic hierarchical pore flow battery separator according to claim 1, characterized in that, The ion distribution uniformity of the three-level pore system is >95%, and the conductivity decay is <5% after 3000 hours of cycling.

6. A method for preparing a biomimetic hierarchical pore flow battery separator composite, applied to the biomimetic hierarchical pore flow battery separator according to any one of claims 1-5, characterized in that, Includes the following steps: S1. Prepare a composite template dispersion by mixing micron-sized and nano-sized calcium carbonate templates at a mass ratio of 1:3, adding DMF solvent, and then dispersing by ultrasonication and adding PVP dispersant to form a dispersion with a concentration of 15wt%. S2. Prepare polymer casting solution by adding PVDF and PES to the dispersion at a mass ratio of 7:3, controlling the total concentration to 18wt%, stirring in an oil bath at 70℃ for 4 hours, and then allowing it to stand to remove bubbles. S3. Casting and phase separation to form a film: Cast the casting solution into a 200μm wet film and immerse it in a 25℃ deionized water non-solvent bath for 30 minutes to cure. S4. Template removal and post-treatment: Immerse the membrane in a 5wt% hydrochloric acid solution and stir at 60°C for 2 hours to remove the template. After cleaning until neutral, vacuum dry at 60°C for 4 hours.

7. The method for preparing a biomimetic hierarchical pore flow battery separator composite according to claim 6, characterized in that, In step S1, the ultrasonic dispersion time is 20 minutes and the stirring time is 30 minutes.

8. The method for preparing a biomimetic hierarchical pore flow battery separator composite according to claim 6, characterized in that, In step S3, a scraper is used to control the thickness of the wet film, and the phase separation process is liquid-liquid phase separation.

9. The method for preparing a biomimetic hierarchical pore flow battery separator composite according to claim 6, characterized in that, The composite template can be replaced with polymethyl methacrylate (PMMA) microspheres to achieve precise control of macropore size error <0.5μm.

10. The method for preparing a biomimetic hierarchical pore flow battery membrane composite according to claim 6, characterized in that, The surface of the nanopore can be coated with a 50nm thick ion exchange layer, which improves the ion selectivity to over 99.5%.

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