A cellulose-based supercapacitor separator with a multi-level heterogeneous structure and a preparation method and application thereof

Abstract

The application discloses a cellulose-based supercapacitor diaphragm with a multi-level heterogeneous structure and a preparation method and application thereof, and relates to the technical field of supercapacitor diaphragm material preparation. The diaphragm is prepared by using natural heterogeneous hard vascular plant fibers as raw materials; the diaphragm comprises skeleton blocks and interwoven sheet layers, the interwoven sheet layers are connected into an integrated multi-level composite network structure in a winding, coating and bridging manner, the skeleton blocks are fiber bundles or fiber segments which are not completely dissociated in the plant fibers, and the interwoven sheet layers are micro / nano fiber filaments, sheet layer structures or two-dimensional nanosheets which are formed by peeling, filaments or sheet layering of the plant fibers from the cell walls in the dissociation process. The application actively utilizes the inherent tissue heterogeneity of the plant raw materials by segmental beating, constructs a multi-level structure of'skeleton blocks and interwoven sheet layers' in situ in the same system, and prepares the diaphragm with excellent performance, so that the problems of complex preparation and poor performance of the existing supercapacitor diaphragm are solved.

Description

Technical Field

[0001] This invention relates to the field of supercapacitor membrane material preparation technology, specifically to a cellulose-based supercapacitor membrane with a multi-level heterogeneous structure, its preparation method, and its application. Background Technology

[0002] With the rapid development of renewable energy and smart grids, supercapacitors, as high-power-density energy storage devices, are playing an increasingly important role in electric vehicles, smart grid frequency regulation, and rail transit energy recovery. The separator, as one of the core components of a supercapacitor, undertakes the crucial functions of isolating the positive and negative electrodes, preventing short circuits, storing electrolyte, and providing ion transport channels. Currently, commercially available supercapacitor separators mainly include three types: polyolefin (PP / PE) porous membranes, glass fiber membranes, and cellulose paper-based membranes. Polyolefin membranes have poor hydrophilicity, insufficient temperature resistance, and are not biodegradable; glass fiber membranes, although hydrophilic, are thick, brittle, and have uneven pore sizes, which are detrimental to device miniaturization and long-cycle stability; cellulose paper-based membranes are mostly prepared from softwood pulp or dissolving pulp through papermaking processes. Although the prepared membranes have good performance, these raw materials undergo high chemical purification and regeneration, resulting in the complete destruction of the natural heterogeneity of the fiber structure. Furthermore, their production is cumbersome, energy-intensive, and expensive.

[0003] In recent years, nanocellulose-based membranes have attracted widespread attention due to their renewability, biodegradability, high specific surface area, and good electrolyte affinity. Existing technologies have reported the preparation of lignin-cellulose nanofiber (LCNF) membranes using bamboo powder, the construction of three-dimensional interconnected porous biomass membranes using beech wood, and the preparation of CNF membranes using rice straw. However, most existing nanocellulose membranes are single-morphology fiber networks or pure two-dimensional sheet stacked structures. While all-fiber networks offer some mechanical flexibility, their dense structure and tortuous ion transport paths make them problematic. Pure two-dimensional sheet stacked membranes, although exhibiting fast ion transport, are brittle, lack self-support, and are prone to cracking, leading to short-circuit risks. Achieving a unified balance of high porosity, high self-supporting strength, rapid ion conduction, and excellent flexibility within a single membrane remains a technological bottleneck hindering the practical application of biomass membranes. Therefore, there is an urgent need to develop a novel membrane technology that requires no complex chemical modification and can fully utilize the natural structural characteristics of plant fibers to construct membranes with both high strength and efficient ion channels. Summary of the Invention

[0004] To address the aforementioned technical problems, the present invention aims to provide a cellulose-based supercapacitor membrane with a multi-level heterogeneous structure, its preparation method, and its application, thereby solving the problems of complex preparation and poor performance of existing supercapacitor membranes.

[0005] The technical solution of the present invention to solve the above-mentioned technical problems is as follows: a cellulose-based supercapacitor separator with a multi-level heterogeneous structure is provided. The separator is made from natural heterogeneous rigid vascular plant fibers. The separator includes a skeleton block and interwoven sheets. The interwoven sheets connect the skeleton block into an integrated multi-level composite network structure by winding, covering and bridging. The skeleton block is a fiber bundle or fiber fragment that has not been completely dissociated in the plant fiber. The interwoven sheets are micro / nanofiber filaments, sheet-like structures or two-dimensional nanosheets formed by cell wall peeling, splitting or lamination of natural heterogeneous rigid vascular plant fibers during the dissociation process.

[0006] Based on the above technical solution, the present invention can be further improved as follows: Furthermore, the cell wall is the cell wall of fibroblasts and parenchyma cells.

[0007] Furthermore, the length of the skeleton block is 50-200μm and the diameter is 5-20μm, and the skeleton block constitutes the mechanical support framework of the diaphragm; the thickness of the interwoven sheet is 5-50nm and the lateral dimension is 1-10μm.

[0008] Furthermore, the membrane has a porosity of 60%-80%, an average pore size of 500-1000 nm, a thickness of 30-50 μm, a tensile strength of ≥40 MPa, a contact angle with electrolyte of <2°, and a liquid absorption rate of ≥120%.

[0009] Furthermore, the interwoven layers originate from skeletal segments, rather than being introduced from external sources.

[0010] The beneficial effects of adopting the above-mentioned further technical solutions are as follows: the skeleton block retains the high crystallinity and mechanical integrity of the fibers, forming the main support framework of the membrane, and endowing the membrane with excellent tensile strength, flexibility and thermal stability. The interwoven layers effectively cut the large pores between the skeleton into micro-nano-scale through-pores, reducing the non-uniformity of pore size distribution, suppressing self-discharge, and at the same time providing a short, straight and efficient ion transport channel in a two-dimensional plane.

[0011] Furthermore, the raw material cellulose of natural heterogeneous hard vascular plant fibers has a cellulose content of ≥30wt%, and the cross-sectional microstructure shows that there are two or more morphological cell regions with an average wall thickness ratio of ≥1.5.

[0012] Furthermore, the natural heterogeneous hard vascular plant fibers are derived from at least one of the following: grasses, bananas, and woody plants.

[0013] Furthermore, the grasses include plants of the Bambusoideae subfamily, Miscanthus sinensis, reeds, straw, or sugarcane bagasse.

[0014] Furthermore, the Bambusoideae subfamily includes at least one of the following: Phyllostachys pubescens, Phyllostachys aurea, Phyllostachys nigra, Phyllostachys pubescens, and Phyllostachys nigra.

[0015] The present invention also provides a method for preparing the above-mentioned cellulose-based supercapacitor membrane with a multi-level heterostructure, comprising the following steps: (1) The raw material of natural heterogeneous hard vascular plant fiber is pretreated to obtain natural heterogeneous hard vascular plant fiber, and then chemically treated to remove lignin and hemicellulose to obtain purified plant fiber. (2) The purified plant fiber obtained in step (1) is mixed with water to obtain a pulp, and the first pulping stage and the second pulping stage are performed in sequence to obtain a mixed pulp; wherein, the first pulping stage is performed to a pulping degree of 30-50°SR, and the second pulping stage is performed to a pulping degree of 60-80°SR. (3) The mixed slurry obtained in step (2) is film-formed and dried to obtain a cellulose-based supercapacitor membrane with a multi-level heterogeneous structure.

[0016] Furthermore, in step (1), the pretreatment includes washing and crushing.

[0017] Furthermore, in step (1), the chemical treatment is achieved by the following method: first, solution one is used for treatment, followed by filtration and washing until neutral; then solution two is used for treatment, followed by filtration and washing until neutral; solution one is a solution containing sodium hydroxide, sodium sulfide and anthraquinone, and solution two is a solution containing chelating agent, magnesium sulfate, hydrogen peroxide and sodium hydroxide.

[0018] The beneficial effects of adopting the above-mentioned further technical solution are as follows: by removing some matrix components through chemical treatment, the natural mechanical difference interface between fibroblasts and thin-walled tissues is fully exposed, creating conditions for subsequent differential dissociation.

[0019] Furthermore, the chelating agent is ethylenediaminetetraacetic acid.

[0020] Furthermore, in solution one, the content of sodium hydroxide is 15-18 wt% of natural heterogeneous hard vascular plant fiber, the content of sodium sulfide is 2-5 wt% of natural heterogeneous hard vascular plant fiber, the content of anthraquinone is 0.1-0.3 wt% of natural heterogeneous hard vascular plant fiber, and the mass ratio of water to natural heterogeneous hard vascular plant fiber is 15-25:1.

[0021] Furthermore, in solution one, the content of sodium hydroxide is 15-18 wt% of natural heterogeneous hard vascular plant fiber, the content of sodium sulfide is 2-5 wt% of natural heterogeneous hard vascular plant fiber, the content of anthraquinone is 0.1-0.2 wt% of natural heterogeneous hard vascular plant fiber, and the mass ratio of water to natural heterogeneous hard vascular plant fiber is 15-25:1.

[0022] Furthermore, in solution two, the content of the chelating agent is 0.2-0.5 wt% of the natural heterogeneous hard vascular plant fiber, the content of magnesium sulfate is 0.5 wt% of the natural heterogeneous hard vascular plant fiber, the content of hydrogen peroxide is 4-5 wt% of the natural heterogeneous hard vascular plant fiber, the content of sodium hydroxide is 1.2 wt% of the natural heterogeneous hard vascular plant fiber, and the mass ratio of water to natural heterogeneous hard vascular plant fiber is 10-15:1.

[0023] Furthermore, when using mixed solution one, soak and stir at 145-165 ℃ for 3-4 hours; when using mixed solution two, soak and stir at 60 ℃ for 2-5 hours.

[0024] Furthermore, in step (2), the slurry concentration is 3-5 wt%.

[0025] Furthermore, in step (2), the first stage of pulping is performed to a pulping degree of 40-45°SR, and the second stage of pulping is performed to a pulping degree of 70-75°SR.

[0026] Furthermore, in step (2), the first stage of pulping is pulped to a pulping degree of 45°SR, and the second stage of pulping is pulped to a pulping degree of 75°SR.

[0027] Furthermore, in step (2), the first stage of pulping blade pressure is 3-4 kgf and the pulping time is 15-20 min; the second stage of pulping blade pressure is 1-2 kgf and the pulping time is 20-40 min.

[0028] The beneficial effects of adopting the above-mentioned further technical solution are as follows: the first stage of pulping uses high shear force to loosen and moderately cut the fibers, and the fibers selectively break along weak interfaces such as thin-walled cell junctions to form a skeleton block prototype with a length of 50-200μm; the second stage of pulping reduces the shear force and continues pulping under low energy input. The low shear force selectively acts on the surface area of ​​the fiber segment, causing the cell walls in the natural heterogeneous hard vascular plant fibers to undergo interlayer peeling, lamellarization, or broom-like filament splitting, forming nanosheets, lamellar peels and / or micro-nanofibers, while the core of the fiber segment is preserved due to high crystallinity, resulting in a mixed pulp in which the skeleton block and interwoven lamellars coexist uniformly.

[0029] Furthermore, in step (2), the pulping power of the first stage is 1500-1600W; the pulping power of the second stage is 500-600W.

[0030] Furthermore, in step (2), after performing the first stage of pulping and the second stage of pulping in sequence, ultrasonic treatment is performed to obtain a mixed slurry.

[0031] The beneficial effect of adopting the above-mentioned further technical solution is that it enables the skeleton blocks and interwoven layers to form a uniform and stable suspension system in water.

[0032] Furthermore, in step (3), dehydration filtration is used to form a film. Furthermore, in step (3), vacuum drying is carried out at 50-70℃.

[0033] The present invention also provides the application of the above-mentioned cellulose-based supercapacitor separator with multi-level heterostructure in the fabrication of supercapacitors.

[0034] Furthermore, supercapacitors include flexible supercapacitors, wearable supercapacitors, or high-operating-voltage supercapacitors.

[0035] The present invention has the following beneficial effects: 1. This invention provides a cellulose-based supercapacitor membrane formed in situ through stepwise differential brooming of natural heterogeneous vascular plant fibers. This membrane utilizes the natural differences in the cell tissues and cell wall hierarchical structures within the fiber raw material to form a multi-level network structure composed of "skeleton blocks" and "interwoven sheets" in the same aqueous pulping system. The skeleton blocks, composed of incompletely dissociated fiber bundles or thick-walled fiber cells, possess high crystallinity and mechanical stability, providing support and a porous framework. The interwoven sheets, formed by peeling and splitting thin-walled tissues or the outer layer of cell walls, connect the skeleton blocks through winding, coating, and bridging, and control macropores into continuous micro-nano pores.

[0036] 2. The core of this invention lies in utilizing the structural heterogeneity of vascular plant fibers. In plant fibers from families such as Poaceae, Musaceae, and Urticaceae, thick-walled fiber cells have a dense and strong structure, while thin-walled cells and the outer layer of the cell wall have a loose structure and are easily disintegrated. This difference provides a basis for hierarchical disintegration and structural construction.

[0037] 3. Unlike traditional homogenization methods, this invention employs segmented pulping to control the dissociation process. The first stage uses high blade pressure and power to crush and open fibers, causing them to break along weak interfaces and form skeleton blocks. The second stage reduces energy, causing the fiber surface to peel and filaments to separate, while preserving the internal structure. This results in the formation of skeleton blocks and interwoven sheets within the same system, and the construction of an integrated network through physical entanglement and hydrogen bonding.

[0038] 4. Based on this structure, this invention achieves multi-scale control without the addition of external nanomaterials. The resulting membrane exhibits high porosity, good liquid absorption, low equivalent series resistance, and excellent stability. The preparation process is primarily aqueous, simple, environmentally friendly, and suitable for various natural vascular plant fiber raw materials.

[0039] Compared with the prior art, the present invention has the following beneficial effects: 1. For the first time, by segmented pulping, the inherent tissue heterogeneity of plant raw materials is actively utilized to construct a multi-level structure of "skeleton blocks and interwoven lamellae" in situ within the same system, without the need to add additional nanomaterials or carry out complex physical mixing and post-assembly.

[0040] 2. Significant synergistic mechanical effects. The framework blocks and interwoven sheets form an integrated network through in-situ connections and hydrogen bonding, avoiding interface defects caused by physical mixing. The framework blocks provide high porosity and flexibility, while the interwoven sheets fill micron-level defects and prevent short circuits. Together, they resolve the contradiction between strength and ion conduction in traditional biomass membranes.

[0041] 3. Precise pore size control. The two-dimensional morphology of the interwoven layers effectively divides the large pores between the framework into micro-nano-level through-holes, making the pore size distribution more concentrated and suppressing the self-discharge phenomenon caused by excessively large through-holes.

[0042] 4. Excellent electrochemical performance. This membrane exhibits super affinity for electrolytes (contact angle <2°) and rapid wetting ability, with low ion transport tortuosity and a significantly reduced equivalent series resistance (ESR). Compared with continuously prepared membranes, the ionic conductivity is increased by more than 18.9 times, and the capacity retention is improved by 36% after 10,000 charge-discharge cycles.

[0043] 5. Wide range of raw material sources and highly universal methods. Applicable to a variety of plant fiber raw materials with natural heterogeneous structures, such as those from the Poaceae, Musaceae, and Urticaceae families, without relying on a single scarce raw material variety.

[0044] 6. Green and environmentally friendly. The entire process uses an aqueous medium, avoiding the use of toxic organic solvents, which meets the requirements of green chemistry and sustainable development. At the same time, the segmented pulping method effectively reduces energy consumption. Attached Figure Description

[0045] Figure 1 This is a low-magnification scanning electron microscope image of the diaphragm prepared in Example 1; Figure 2 for Figure 1 High-magnification scanning electron microscope images; Figure 3 The mechanical property curves of the diaphragm prepared in Example 1 are shown. Figure 4 The Nyquist curve of the diaphragm prepared in Example 1; Figure 5 This is an SEM image of the diaphragm obtained in Example 2.

[0046] Figure 6 This is a SEM image of the diaphragm prepared in Comparative Example 1. Detailed Implementation

[0047] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are for illustrative purposes only and are not intended to limit the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer should be followed. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0048] Example 1: A cellulose-based supercapacitor separator with a multi-level heterogeneous structure is prepared by the following steps: (1) The raw material of natural heterogeneous hard vascular plant fiber (4-year-old bamboo pole) is pretreated. The pretreatment includes peeling, washing and crushing to obtain bamboo powder (natural heterogeneous hard vascular plant fiber). Then, chemical treatment is used to remove lignin and hemicellulose to obtain purified plant fiber. The chemical treatment is as follows: bamboo powder is added to solution one and stirred at 165 ℃ for 4 hours, filtered, and repeatedly washed with deionized water until the filtrate is neutral to obtain partially lignin-free alkalized bamboo fiber; then it is added to solution two and stirred at 60 ℃ for 5 hours to further purify the bamboo fiber, and washed with deionized water until neutral. Solution 1 is a solution containing sodium hydroxide, sodium sulfide and anthraquinone. The contents of sodium hydroxide, sodium sulfide and anthraquinone are 15wt%, 3wt% and 0.2wt% of natural heterogeneous hard vascular plant fibers, respectively, and the mass ratio of water to natural heterogeneous hard vascular plant fibers is 20:1. Solution 2 is a solution containing a chelating agent, magnesium sulfate, hydrogen peroxide, and sodium hydroxide. The contents of the chelating agent (ethylenediaminetetraacetic acid), magnesium sulfate, hydrogen peroxide, and sodium hydroxide are 0.5 wt%, 0.5 wt%, 5 wt%, and 1.2 wt% of the natural heterogeneous hard vascular plant fiber, respectively. The mass ratio of water to natural heterogeneous hard vascular plant fiber is 10:1. (2) The purified plant fiber obtained in step (1) is mixed with water to obtain a pulp (concentration of 2wt%), which is placed in a Wali pulper and subjected to the first stage pulping and the second stage pulping treatment in sequence to obtain a mixed pulp. The pulping process is as follows: In the first stage of pulping, the load on the cutter roller is adjusted to 3 kgf, and the operating power of the equipment is stabilized at 1500W. Pulping is carried out for 20 minutes, and the freeness is measured to be 45°SR. At this time, the fibers are mainly loosened and moderately cut, thus forming a skeleton block. In the second stage of pulping, the load on the cutter roller is adjusted to 2 kgf, and the operating power of the equipment is stabilized at 600W. Pulping is carried out for 40 minutes, and the freeness is measured to be 75°SR. During the pulping process, it can be observed that the pulp gradually changes from coarse particles to a milky suspension. (3) The mixed slurry obtained in step (2) was vacuum filtered on a PTFE filter membrane with a pore size of 74 μm to form a membrane. Then the membrane was peeled off and vacuum dried at 60°C for 6 hours to obtain a cellulose-based supercapacitor membrane with a multi-level heterogeneous structure (thickness of about 30 μm).

[0049] Example 2: A cellulose-based supercapacitor separator with a multi-level heterogeneous structure is prepared by the following steps: (1) The raw material of natural heterogeneous hard vascular plant fiber (commercially available abaca fiber, natural average length >5mm, slender fiber and obvious cell wall layer structure) is pretreated. The pretreatment includes cutting it to about 20mm to obtain pretreated abaca fiber (natural heterogeneous hard vascular plant fiber). Then, chemical treatment is used to remove lignin and hemicellulose to obtain purified plant fiber. The chemical treatment is as follows: the pretreated abaca fiber is added to solution one, stirred at 160 ℃ for 3 hours, filtered, and repeatedly washed with deionized water until the filtrate is neutral to obtain partially lignin-free alkalized abaca fiber; then it is added to solution two and stirred at 60 ℃ for 3 hours to further purify the abaca fiber, and washed with deionized water until neutral. Solution 1 is a solution containing sodium hydroxide, sodium sulfide and anthraquinone. The contents of sodium hydroxide, sodium sulfide and anthraquinone are 18wt%, 3wt% and 0.2wt% of natural heterogeneous hard vascular plant fibers, respectively, and the mass ratio of water to natural heterogeneous hard vascular plant fibers is 15:1. Solution 2 is a solution containing a chelating agent, magnesium sulfate, hydrogen peroxide, and sodium hydroxide. The contents of the chelating agent (ethylenediaminetetraacetic acid), magnesium sulfate, hydrogen peroxide, and sodium hydroxide are 0.5 wt%, 0.5 wt%, 3 wt%, and 1.2 wt% of the natural heterogeneous hard vascular plant fiber, respectively. The mass ratio of water to natural heterogeneous hard vascular plant fiber is 15:1. (2) The purified plant fiber obtained in step (1) is mixed with water to obtain a pulp (concentration of 3wt%). The pulp is placed in a Wali pulper and subjected to the first and second stages of pulping in sequence. The pulp is ultrasonically treated for 30 minutes to fully homogenize it and obtain a mixed pulp. The pulping process is as follows: In the first stage of pulping, the load on the cutter roller is adjusted to 3 kgf, and the operating power of the equipment is stabilized at 1500W. Pulping is carried out for 20 minutes, and the freeness is measured to be 45°SR. At this time, the fibers are mainly loosened and moderately cut. In the second stage of pulping, the load on the cutter roller is adjusted to 2 kgf, and the operating power of the equipment is stabilized at 600W. Pulping is carried out for 30 minutes, and the freeness is measured to be 75°SR. During the pulping process, it can be observed that the pulp gradually changes from coarse particles to a milky suspension. (3) The mixed slurry obtained in step (2) was vacuum filtered on a PTFE filter membrane with a pore size of 74 μm to form a membrane. Then the membrane was peeled off and vacuum dried at 50°C for 6 h to obtain a cellulose-based supercapacitor membrane with a multi-level heterogeneous structure (thickness of about 35 μm).

[0050] Example 3: A cellulose-based supercapacitor separator with a multi-level heterogeneous structure is prepared by the following steps: (1) The raw material of natural heterogeneous hard vascular plant fiber (reed stalk) is pretreated. The pretreatment includes removing leaves and nodes, crushing, and obtaining reed powder (natural heterogeneous hard vascular plant fiber). Then, chemical treatment is used to remove lignin and hemicellulose to obtain purified plant fiber. The chemical treatment is as follows: Reed powder is added to solution one, stirred at 145℃ for 3 hours, filtered, and repeatedly washed with deionized water until the filtrate is neutral to obtain partially lignin-free alkalized reed fiber; then added to solution two, stirred at 60℃ for 2 hours to further purify the reed fiber, and washed with deionized water until neutral. Solution 1 is a solution containing sodium hydroxide, sodium sulfide and anthraquinone. The contents of sodium hydroxide, sodium sulfide and anthraquinone are 15wt%, 3wt% and 0.1wt% of natural heterogeneous hard vascular plant fibers, respectively, and the mass ratio of water to natural heterogeneous hard vascular plant fibers is 25:1. Solution 2 is a solution containing a chelating agent, magnesium sulfate, hydrogen peroxide, and sodium hydroxide. The contents of the chelating agent (ethylenediaminetetraacetic acid), magnesium sulfate, hydrogen peroxide, and sodium hydroxide are 0.2 wt%, 0.5 wt%, 4 wt%, and 1.2 wt% of the natural heterogeneous hard vascular plant fiber, respectively. The mass ratio of water to natural heterogeneous hard vascular plant fiber is 15:1. (2) The purified plant fiber obtained in step (1) is mixed with water to obtain a pulp (concentration of 4wt%), which is placed in a Wali pulper and subjected to the first stage pulping and the second stage pulping treatment in sequence to obtain a mixed pulp. The pulping process is as follows: In the first stage of pulping, the load on the cutter roller is adjusted to 3 kgf, and the operating power of the equipment is stabilized at 1500W. Pulping is carried out for 15 minutes, and the freeness is measured to be 45°SR. At this time, the fibers are mainly loosened and moderately cut. In the second stage of pulping, the load on the cutter roller is adjusted to 2 kgf, and the operating power of the equipment is stabilized at 600W. Pulping is carried out for 20 minutes, and the freeness is measured to be 75°SR. During the pulping process, it can be observed that the pulp gradually changes from coarse particles to a milky suspension. (3) The mixed slurry obtained in step (2) is vacuum filtered on a PTFE filter membrane with a pore size of 74 μm to form a membrane. Then the membrane is peeled off and vacuum dried at 70°C for 6 h to obtain a cellulose-based supercapacitor membrane with a multi-level heterostructure.

[0051] Example 4: A cellulose-based supercapacitor separator with a multi-level heterogeneous structure is prepared by the following steps: (1) The raw material of natural heterogeneous hard vascular plant fiber (sugarcane bagasse) is pretreated. The pretreatment includes removing leaves and nodes, crushing, and obtaining sugarcane powder (natural heterogeneous hard vascular plant fiber). Then, chemical treatment is used to remove lignin and hemicellulose to obtain purified plant fiber. The chemical treatment is as follows: sugarcane powder is added to solution one, stirred at 145°C for 3 hours, filtered, and repeatedly washed with deionized water until the filtrate is neutral to obtain partially lignin-free alkalized sugarcane fiber; then added to solution two, stirred at 60°C for 2 hours to further purify the sugarcane fiber, and washed with deionized water until neutral. Solution 1 is a solution containing sodium hydroxide, sodium sulfide and anthraquinone. The contents of sodium hydroxide, sodium sulfide and anthraquinone are 15wt%, 3wt% and 0.1wt% of natural heterogeneous hard vascular plant fibers, respectively, and the mass ratio of water to natural heterogeneous hard vascular plant fibers is 25:1. Solution 2 is a solution containing a chelating agent, magnesium sulfate, hydrogen peroxide, and sodium hydroxide. The contents of the chelating agent (ethylenediaminetetraacetic acid), magnesium sulfate, hydrogen peroxide, and sodium hydroxide are 0.2 wt%, 0.5 wt%, 4 wt%, and 1.2 wt% of the natural heterogeneous hard vascular plant fiber, respectively. The mass ratio of water to natural heterogeneous hard vascular plant fiber is 15:1. (2) The purified plant fiber obtained in step (1) is mixed with water to obtain a pulp (concentration of 2wt%), which is then placed in a Wali pulper and subjected to the first and second stages of pulping in sequence to obtain a mixed pulp. The pulping process is as follows: In the first stage of pulping, the load on the cutter roller is adjusted to 4 kgf, and the operating power of the equipment is stabilized at 1600 W. Pulping is carried out for 15 minutes, and the freeness is measured to be 40°SR. At this time, the fibers are mainly loosened and moderately cut. In the second stage of pulping, the load on the cutter roller is adjusted to 1 kgf, and the operating power of the equipment is stabilized at 500 W. Pulping is carried out for 30 minutes, and the freeness is measured to be 70°SR. During the pulping process, it can be observed that the pulp gradually changes from coarse particles to a milky suspension. (3) The mixed slurry obtained in step (2) is vacuum filtered on a PTFE filter membrane with a pore size of 74 μm to form a membrane. Then the membrane is peeled off and vacuum dried at 60°C for 6 hours to obtain a cellulose-based supercapacitor membrane with a multi-level heterogeneous structure.

[0052] Comparative Example 1: A plant cellulose-based supercapacitor separator, the preparation method of which includes the following steps: In step (2), without segmentation, the pulp is directly beaten to 75°SR at a power of 1500W, and the rest is the same as in Example 1.

[0053] Comparative Example 2: A plant cellulose-based supercapacitor separator, the preparation method of which includes the following steps: In step (1), commercially available acetic acid-grade dissolving slurry (α-cellulose content > 95%) was used as raw material, and its cellular heterogeneous structure had been largely eliminated during the highly chemical purification process. The rest is the same as in Example 1.

[0054] Test case I. Example 1: Diaphragm Testing 1. The diaphragm prepared in Example 1 was examined by scanning electron microscopy, and the results are shown in the figure. Figures 1-2 .

[0055] Depend on Figures 1-2 It can be seen that the membrane exhibits a typical "skeleton block-interwoven sheet" structure. Under low magnification SEM, a large number of fiber segments with lengths of 50-200 μm and diameters of 5-20 μm can be seen forming a loose supporting skeleton; under high magnification SEM, a large number of wing-shaped two-dimensional nanosheets with a thickness of about 5-50 nm and a lateral size of 1-10 μm can be clearly seen. These sheets are wrapped around the surface of the skeleton fibers and interwoven to fill the gaps in the skeleton, dividing the macroscopic pores into micro-nano-level through-pores, forming an integrated multi-level network.

[0056] 2. The mechanical properties of the diaphragm prepared in Example 1 were tested using the national standard test method GB / T36363-2018. The results are shown in [Figure 1]. Figure 3 .

[0057] Depend on Figure 3 It can be seen that the diaphragm has a high tensile strength of 73.76 MPa.

[0058] 3. The membrane prepared in Example 1 was tested using the liquid absorption method, and its porosity was 72%, liquid absorption rate was 180%, and ionic conductivity was 5.62 × 10⁻⁶. -4 S / cm. The contact angle of the diaphragm with the TEAFB electrolyte was determined to be 1.5° using a contact angle measuring instrument.

[0059] 4. The electrochemical performance of the diaphragm was measured at room temperature (25℃) using an electrochemical workstation and a Xinwei testing instrument. Specifically, a symmetrical supercapacitor was assembled using activated carbon as the electrode material and 1M TEAFB electrolyte for testing. The results are shown below. Figure 4 .

[0060] Depend on Figure 4The equivalent series resistance (ESR) is 3.4Ω. After 10,000 constant current charge-discharge cycles at a current density of 1A / g, the capacity retention is 96.4%, the coulombic efficiency is 99.2%, and the specific capacitance reaches 23.1 F / g.

[0061] Under the same conditions, the device using a traditional one-piece pulped bamboo fiber diaphragm has an ESR of 37.5 Ω and a capacity retention of 60.3%.

[0062] II. Example 2: Diaphragm Detection 1. The diaphragm prepared in Example 2 was examined by scanning electron microscopy, and the results are shown in the figure. Figure 5 .

[0063] Depend on Figure 5 It is known that the skeletal blocks formed by abaca fibers are more slender (250-500μm in length and 5-12μm in diameter), the area of ​​the interwoven sheets is larger, and the sheet thickness is about 10-20nm.

[0064] 2. Using the same method described above, its physicochemical properties were tested. The results showed that the membrane porosity was 68%, the tensile strength was 60.32 MPa, the liquid absorption rate was 130%, and the ionic conductivity was 4.36 × 10⁻⁶. -4 S / cm. The contact angle of the diaphragm with the TEAFB electrolyte was determined to be 1.1° using a contact angle measuring instrument.

[0065] 3. The electrochemical performance of the diaphragm was determined using an electrochemical workstation and a Xinwei testing instrument at room temperature (25℃). A symmetrical supercapacitor was assembled using activated carbon as the electrode material and 1M TEAFB electrolyte for testing.

[0066] The results show that at a current density of 1 A / g, the specific capacitance reaches 20.6 F / g, and the equivalent series resistance is 2.4 Ω. After 10,000 constant current charge-discharge cycles, the capacity retention is 92.4%, and the coulombic efficiency is 99.6%.

[0067] III. Example 3: Diaphragm Detection 1. Using the same method described above, its physicochemical properties were tested. The results showed that the membrane porosity was 71%, the tensile strength was 45.3 MPa, the liquid absorption rate was 218%, the electrolyte contact angle was 1.3°, and the ionic conductivity was 5.74 × 10⁻⁶. -4 S / cm.

[0068] 2. The electrochemical performance of the diaphragm was determined using an electrochemical workstation and a Xinwei tester at room temperature of 25°C.

[0069] The results show that at a current density of 1 A / g, the specific capacitance reaches 23.1 F / g, and the equivalent series resistance is 1.52 Ω. After 5000 constant current charge-discharge cycles, the capacity retention is 95.7%, and the coulombic efficiency is 99.33%.

[0070] IV. Example 4: Diaphragm Detection 1. The diaphragm also has a skeleton block-interwoven lamellar layer structure.

[0071] 2. Using the same method described above, its physicochemical properties were tested. The results showed: porosity 69%, tensile strength 32.1 MPa, liquid absorption rate 192%, electrolyte contact angle 1.2°, and ionic conductivity 6.31 × 10⁻⁶. -4 S / cm.

[0072] 3. The electrochemical performance of the diaphragm was measured at room temperature (25°C) using an electrochemical workstation and a Xinwei tester.

[0073] The results show that at a current density of 1 A / g, the specific capacitance reaches 24.3 F / g, and the equivalent series resistance is 1.14 Ω. After 5000 constant current charge-discharge cycles, the capacitance retention is 94.8%, and the coulombic efficiency is 99.46%. Both the mechanical and electrochemical properties meet the requirements for supercapacitor applications.

[0074] V. Diaphragm Testing in Comparative Example 1 1. The diaphragm prepared in Comparative Example 1 was examined by scanning electron microscopy, and the results are shown in the figure. Figure 6 .

[0075] Depend on Figure 6 It can be seen that the membrane of Comparative Example 1 exhibits a uniform nanofiber / sheet hybrid network under SEM, and fails to form a clear hierarchical differentiation of skeletal blocks and interwoven sheets.

[0076] 2. Using the same method described above, its physicochemical properties were tested. The results showed that the membrane porosity was only 35%, the tensile strength was only 41.2 MPa, the liquid absorption rate was 89%, the electrolyte contact angle was 17.6°, and the ionic conductivity was 2.82 × 10⁻⁶. -5 S / cm.

[0077] 3. Electrochemical tests showed that the ESR was as high as 37.5Ω, and the capacity retention rate dropped to 60.3% after 10,000 cycles.

[0078] This indicates that achieving the same degree of beating without segmented differentiated energy input is insufficient to construct the required skeletal block-interwoven multi-level structure, leading to a significant decrease in the overall performance of the membrane.

[0079] VI. Diaphragm Testing in Comparative Example 2 Even using the exact same segmented pulping process as in Example 1, only a chaotic network of microfibers was observed under electron microscopy, with no framework block-interwoven lamellar structure formed. This diaphragm is brittle, has poor mechanical strength, and a liquid absorption rate of only 105%, making it unable to self-support and failing to meet the basic requirements of supercapacitors for flexibility and high liquid capacity.

[0080] In summary: 1. Although bamboo, abaca, reed stalks, and sugarcane bagasse belong to different subfamilies such as Poaceae, Musaceae, and Urticaceae, their fiber raw materials all possess a natural heterogeneous structure where thick-walled fiber cells and thin-walled cells coexist. Under segmented pulping conditions, these raw materials can successfully construct a multi-level heterogeneous structure of "skeleton block-interwoven lamellar structure" and exhibit excellent diaphragmatic properties. This fully demonstrates the broad applicability of the method described in this invention to vascular plants of different families and genera.

[0081] 2. The dissolving pulp of Comparative Example 2, due to its high degree of purification, had its natural heterogeneous structure of the fibers eliminated, making it impossible to form the aforementioned multi-level structure. This demonstrates, conversely, that the inherent multi-level heterogeneous structure of the raw materials is a necessary condition for forming the "skeleton block-interwoven lamellar" structure described in this invention. Simultaneously, the one-stage pulping results of Comparative Example 1 show that even with raw material heterogeneity, differential dissociation cannot be achieved without a staged pulping process. Therefore, the inherent heterogeneity of the raw materials and the staged pulping process are two indispensable core conditions; their synergistic effect is necessary to obtain the multi-level heterogeneous structure membrane described in this invention.

[0082] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A cellulose-based supercapacitor separator with a multi-level heterogeneous structure, characterized in that, The diaphragm is made from natural heterogeneous rigid vascular plant fibers. The diaphragm includes a skeleton block and interwoven sheets. The interwoven sheets connect the skeleton block into an integrated multi-level composite network structure by winding, covering and bridging. The skeleton block is a fiber bundle or fiber fragment that has not been completely dissociated in the plant fiber. The interwoven sheets are micro / nanofibers, sheet-like structures or two-dimensional nanosheets formed by cell wall peeling, splitting or lamination of plant fibers during the dissociation process.

2. The cellulose-based supercapacitor separator with a multi-level heterogeneous structure according to claim 1, characterized in that, The skeleton segment has a length of 50-200μm and a diameter of 5-20μm, and the skeleton segment constitutes the mechanical support framework of the diaphragm; the interwoven sheet has a thickness of 5-50nm and a lateral dimension of 1-10μm.

3. The cellulose-based supercapacitor separator with a multi-level heterogeneous structure according to claim 1, characterized in that, The raw material of the natural heterogeneous hard vascular plant fiber has a cellulose content of ≥30wt%, and the cross-sectional microstructure shows that there are two or more morphological cell regions with an average wall thickness ratio of ≥1.

5.

4. The method for preparing a cellulose-based supercapacitor separator with a multi-level heterogeneous structure according to any one of claims 1-3, characterized in that, Includes the following steps: (1) The raw material of natural heterogeneous hard vascular plant fiber is pretreated to obtain natural heterogeneous hard vascular plant fiber, and then chemically treated to remove lignin and hemicellulose to obtain purified plant fiber. (2) The purified plant fiber obtained in step (1) is mixed with water to obtain a pulp, and the first pulping stage and the second pulping stage are performed in sequence to obtain a mixed pulp; wherein, the first pulping stage is performed to a pulping degree of 30-50°SR, and the second pulping stage is performed to a pulping degree of 60-80°SR. (3) The mixed slurry obtained in step (2) is film-formed and dried to obtain a cellulose-based supercapacitor membrane with a multi-level heterogeneous structure.

5. The method for preparing a cellulose-based supercapacitor separator with a multi-level heterogeneous structure according to claim 4, characterized in that, In step (1), the pretreatment includes washing and crushing.

6. The method for preparing a cellulose-based supercapacitor separator with a multi-level heterogeneous structure according to claim 4, characterized in that, In step (1), the chemical treatment is achieved by the following method: first, solution one is used for treatment, followed by filtration and washing until neutral; then solution two is used for treatment, followed by filtration and washing until neutral; solution one is a solution containing sodium hydroxide, sodium sulfide and anthraquinone, and solution two is a solution containing chelating agent, magnesium sulfate, hydrogen peroxide and sodium hydroxide.

7. The method for preparing a cellulose-based supercapacitor separator with a multi-level heterogeneous structure according to claim 4, characterized in that, In step (2), the slurry concentration is 3-5 wt%.

8. The method for preparing a cellulose-based supercapacitor separator with a multi-level heterogeneous structure according to claim 4, characterized in that, In step (2), the first stage of pulping is performed until the freeness is 40-45°SR, and the second stage of pulping is performed until the freeness is 70-75°SR.

9. The application of the cellulose-based supercapacitor separator with a multi-level heterogeneous structure according to any one of claims 1-3 in the fabrication of supercapacitors.

10. The application according to claim 9, characterized in that, Supercapacitors include flexible supercapacitors, wearable supercapacitors, or high-operating-voltage supercapacitors.

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