Preparation and application of gradient carbonized filter paper diaphragm based on femtosecond laser induction

Abstract

The application relates to the field of zinc ion batteries, and discloses a preparation and application of a filter paper diaphragm based on femtosecond laser-induced gradient carbonization. In view of the technical bottlenecks of the existing zinc ion batteries, such as zinc negative electrode dendrite growth, serious hydrogen evolution side reaction and insufficient performance of traditional diaphragms, the application selects a cellulose-based qualitative filter paper with a specific gray scale, utilizes the high-energy instantaneity and controllability characteristics of a femtosecond laser, constructs a porous carbon film in the shallow layer of the filter paper film to form a gradient carbonized filter paper diaphragm. The diaphragm can accurately control the carbonization degree and the porous structure by regulating the laser parameters, realize uniform distribution of the electric field on the electrode surface, directional deposition of zinc ions, and simultaneously enhance the mechanical stability and corrosion resistance, thereby significantly improving the cycle life, coulomb efficiency and ion transmission efficiency of the battery. The preparation process is controllable, and the raw material cost is low, which provides key technical support for the low-cost, high-safety and large-scale energy storage application of the zinc ion battery.

Description

Technical Field

[0001] This invention belongs to the field of zinc-ion battery technology, specifically relating to a method for preparing a filter paper separator based on femtosecond laser-induced gradient carbonization, the separator product and its application in zinc-ion batteries, especially suitable for high-performance zinc-ion batteries in large-scale energy storage scenarios. Background Technology

[0002] Against the backdrop of surging global demand for energy storage and the scarcity and safety concerns surrounding lithium-ion batteries, zinc-ion batteries have become a core focus of new energy storage technologies. Their core advantages are significant: zinc is abundant in the Earth's crust, its cost is only 1 / 50th that of lithium, and the aqueous electrolyte used poses no risk of combustion or explosion. Theoretically, their specific capacity can reach 820 mAh / g, making them well-suited for large-scale energy storage scenarios. However, the development of zinc-ion batteries is currently constrained by three major bottlenecks: zinc anodes are prone to dendrite growth during charging and discharging, and dendrites piercing the separator can cause short circuits, resulting in a cycle life often less than 500 cycles; hydrogen evolution side reactions and anode corrosion continuously consume the electrolyte, reducing coulombic efficiency to below 80%; traditional separators (such as glass fiber) have poor mechanical strength and uneven ion conduction, further exacerbating performance degradation and severely hindering commercialization.

[0003] Carbonization of filter paper separators can improve the performance of zinc-ion batteries in multiple ways. After carbonization, a carbon nanolayer forms on the filter paper surface. This carbon layer can regulate the uniform distribution of the electric field on the electrode surface, preventing localized accumulation of zinc ions. Simultaneously, its porous structure provides numerous nucleation sites, inducing directional and uniform deposition of zinc ions, inhibiting dendrite growth and side reactions, and significantly improving the battery's electrochemical performance. At the same time, the carbonization process introduces a graphite structure into the filter paper, greatly enhancing its mechanical stability and effectively withstanding the stress generated by changes in electrode volume during charge and discharge. Furthermore, the carbon layer possesses excellent resistance to acid and alkali corrosion, fundamentally preventing short-circuit risks caused by separator damage. The carbonization process also forms micropores with a pore size of 20-50 nm inside the filter paper. Combined with the hydroxyl functional groups on the carbon surface, this creates highly efficient zinc ion transport channels. Compared to traditional filter paper, this significantly improves ionic conductivity while intercepting dissolved positive electrode active materials in the electrolyte, reducing capacity decay, and maintaining a coulombic efficiency of over 95%. Overall, filter paper membrane carbonization precisely addresses the core pain points of zinc-ion batteries through the synergistic effects of dendrite suppression, structural strengthening, and improved conductivity, providing key technological support for their low-cost and high-safety energy storage applications. However, existing carbonization methods, such as high-temperature calcination and plasma treatment, have two major drawbacks: 1) the degree of carbonization is uncontrollable, easily leading to complete carbonization and embrittlement of the filter paper or insufficient carbonization; 2) it cannot form a gradient carbonization structure, resulting in poor adhesion between the carbon layer and the substrate, making it prone to detachment during charging and discharging. Therefore, there is an urgent need to develop a filter paper membrane preparation technology with strong controllability and the ability to form a gradient carbonization structure. Summary of the Invention

[0004] The purpose of this invention is to overcome the dual defects of existing zinc-ion battery separators, such as poor dendrite suppression, severe side reactions, insufficient mechanical strength and ion conduction performance, and poor controllability and inability to form gradient structures in traditional carbonization methods. This invention provides a method, product and application for preparing filter paper separators based on femtosecond laser-induced gradient carbonization. By leveraging the high energy instantaneity and parameter controllability of femtosecond lasers, precise gradient carbonization of filter paper separators can be achieved, while optimizing the structure and performance of the separator to meet the needs of high-performance zinc-ion batteries.

[0005] To achieve the above objectives, this invention provides a method for preparing a femtosecond laser-induced gradient carbonization filter paper diaphragm, comprising the following steps: selecting a qualitative filter paper with a gray level of 0.05-0.13%; utilizing the high-energy transient characteristics of a femtosecond laser to scan the shallow layer of the membrane of the qualitative filter paper; constructing a porous carbon membrane in the shallow layer of the cellulose filter paper membrane; thereby forming a gradient carbonization structure on the surface of the filter paper; and finally obtaining a femtosecond laser-induced gradient carbonization filter paper diaphragm; wherein the intensity of the femtosecond laser is 50-200 W / cm². 2 The prepared gradient carbonized filter paper diaphragm has a carbonized layer thickness of 10-30 μm and a porous carbon pore size of 5-15 μm. The ash content of qualitative filter paper essentially refers to the percentage of ash mass remaining after complete combustion, directly reflecting the content of impurities (such as metal oxides, inorganic salts, and residual lignin) in the filter paper. Lower ash content indicates fewer impurities and higher cellulose purity; higher ash content indicates higher impurity content and lower cellulose purity. The core purpose of selecting a ash content range of 0.05-0.13% is to balance the controllability of laser carbonization with the integrity of the diaphragm function. The core advantage of femtosecond lasers is their high-energy instantaneous nature, acting only on the shallow layer (10-30 μm) of the filter paper to form a gradient carbonized layer. If the gray content of the filter paper exceeds the standard (>0.13%), impurities will interfere with the uniform absorption and conduction of laser energy, resulting in local over-carbonization or under-carbonization, and failing to form a porous carbon film with uniform thickness and consistent pore size; if the gray content is too low (<0.05%), although the purity of the filter paper fiber is high, the fiber density is too large, making it difficult for laser energy to penetrate to the shallow layer to form a porous structure, which can easily lead to the carbonization layer being too thin or broken.

[0006] Furthermore, the qualitative filter paper is cellulose-based qualitative filter paper, and the diameter of the qualitative filter paper is 10-15 cm.

[0007] Furthermore, the degree of carbonization of the filter paper membrane and the pore size of the porous carbon are controlled by adjusting the intensity of the femtosecond laser and the number of laser scans; wherein the number of laser scans is 1-5 times.

[0008] Furthermore, the qualitative filter paper has a gray level of 0.08% and a diameter of 12.5 cm.

[0009] Furthermore, the intensity of the femtosecond laser is 150 W / cm².2 The prepared gradient carbonized filter paper membrane has a carbonized layer thickness of 20 μm and a porous carbon pore size of 10 μm.

[0010] Furthermore, the pulse width of the femtosecond laser is 100-500 fs, and the laser scanning speed is 10-50 mm / s.

[0011] The present invention also provides a femtosecond laser-induced gradient carbonization filter paper diaphragm, which is prepared by the above-mentioned preparation method; the diaphragm uses cellulose-based qualitative filter paper as a substrate, and a gradient-distributed porous carbon membrane is formed in the shallow layer of the substrate. The porosity of the porous carbon membrane is 50%-70%, and there is a gradual structural transition between the carbonization layer and the substrate.

[0012] Furthermore, after the diaphragm is immersed in an acidic or alkaline environment with pH = 1-14 for 72 hours, the carbonized layer does not peel off and the substrate is not damaged, maintaining structural integrity.

[0013] The present invention also provides an application of the femtosecond laser-induced gradient carbonization filter paper membrane described above in a zinc-ion battery, characterized in that the membrane is assembled between the positive and negative electrode plates of the zinc-ion battery as an electrolyte membrane; the zinc-ion battery uses an aqueous zinc salt electrolyte, wherein the aqueous zinc salt electrolyte is an aqueous solution of ZnSO4, Zn(NO3)2, or ZnCl2.

[0014] Furthermore, the positive electrode material of the zinc-ion battery is a vanadium-based oxide, a manganese-based oxide, or a Prussian blue analogue, and the negative electrode material is zinc foil.

[0015] The beneficial effects of this invention are:

[0016] The gradient carbonized filter paper membrane material prepared by the method provided in this invention exhibits a porous structure in SEM characterization tests. This porous structure allows for the regulation of the uniform distribution of the electric field on the electrode surface, promoting uniform zinc ion deposition and preventing localized zinc ion aggregation. Simultaneously, the porous structure provides numerous nucleation sites, inducing directional and uniform zinc ion deposition, inhibiting dendrite growth and side reactions, thus improving the ion transport efficiency of the zinc-ion battery and effectively suppressing the transport of the electrolyte cathode material. The femtosecond laser carbonization of the filter paper surface significantly improves the corrosion resistance of the filter paper and extends the service life of the filter paper membrane. Introducing a protective layer on the zinc foil surface can indirectly regulate the electrode / electrolyte interface, promoting uniform zinc ion deposition while reducing side reactions, demonstrating excellent cycle stability, superior coulombic efficiency, battery storage performance, and reversibility. This invention provides a membrane based on cellulose filter paper, where the degree of carbonization and the porous carbon pore size of the filter paper membrane are adjusted by changing the femtosecond laser intensity and the number of laser scans, thereby achieving the optimal modification effect. By utilizing the high-energy transient characteristics of femtosecond lasers, porous carbon membranes are constructed in the shallow layer of cellulose filter paper membranes, thereby carbonizing the surface of the filter paper and forming a femtosecond laser-induced gradient carbonization filter paper membrane material. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the femtosecond laser scanning of cellulose filter paper according to the present invention.

[0018] Figure 2 This is a comparison of the microstructure of the gradient carbonized filter paper diaphragm before and after treatment according to the present invention.

[0019] Figure 3 This is a schematic diagram of the structure of the aqueous zinc-ion battery involved in this invention.

[0020] Figure 4 The voltage-time cycling stability curves of the gradient carbonized filter paper diaphragm (LCFS-ZB) described in this invention, the traditional glass fiber diaphragm (GFS-ZB), and the uncarbonized filter paper diaphragm (CFS-ZB) are shown.

[0021] Figure 5 This is a comparison chart of the battery coulombic efficiency of the gradient carbonized filter paper membrane (LCFS-ZB) described in this invention, compared with that of the traditional glass fiber membrane (GFS-ZB) and the uncarbonized filter paper membrane (CFS-ZB).

[0022] Figure 6 This is a comparison chart of the battery cycle performance of the gradient carbonized filter paper separator (LCFS-ZB) described in this invention, the traditional glass fiber separator (GFS-ZB), and the uncarbonized filter paper separator (CFS-ZB). Detailed Implementation

[0023] The specific embodiments of the present invention will be described in further detail below with reference to specific examples. These examples are used to illustrate the present invention, but are not intended to limit the scope of the invention.

[0024] To keep the embodiments concise, only the parts related to the present invention are schematically shown in the embodiments, and they do not represent the actual structure of the product. In addition, to make the embodiments concise and easy to understand, only one of the components with the same structure or function in the embodiments is schematically drawn, or only one of them is marked.

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, specific implementation methods of the present invention will be described below. Obviously, those skilled in the art can obtain other similar structural products and other implementation methods based on this embodiment without any creative effort.

[0026] Example 1

[0027] Raw material preparation: Select cellulose-based qualitative filter paper with an ash content of 0.08%, cut it into circular pieces with a diameter of 12.5 cm using a circular cutter, and place it in a vacuum drying oven at 60℃ for 4 hours to remove surface moisture;

[0028] Femtosecond laser processing: Fix the dried filter paper onto the laser processing platform and set the femtosecond laser parameters: laser intensity 150W / cm². 2 The pulse width is 300 fs, the number of scans is 2, and the scanning speed is 30 mm / s to perform a shallow scan on the filter paper surface; during the scanning process, the processing environment is kept in an inert gas (argon) atmosphere to avoid carbon layer oxidation;

[0029] Post-processing of the product: After laser treatment, the filter paper is placed in a vacuum drying oven and dried at 80°C for 6 hours to obtain a femtosecond laser-induced gradient carbonized filter paper diaphragm.

[0030] Comparative Example 1: GFS-ZB Preparation

[0031] Purchase commercially available conventional glass fiber diaphragms (model: Whatman GF / F, thickness 200μm, average pore size 1.2μm), cut them into 13mm diameter discs, and vacuum dry them at 60℃ for 4 hours for later use.

[0032] (3) Comparative Example 2: CFS-ZB Preparation

[0033] Cellulose qualitative filter paper of the same batch and specifications as the experimental group (0.08% grayness, 12.5cm diameter) was selected, and without femtosecond laser carbonization treatment, it was directly cut into 13mm diameter discs and vacuum dried at 60℃ for 4 hours for later use.

[0034] Battery assembly: The separator prepared in the examples and comparative examples was used as the electrolyte separator, zinc foil (0.1 mm thick) was used as the negative electrode, V2O5 / carbon composite material was used as the positive electrode, and 2 mol / L ZnSO4 aqueous solution was used as the electrolyte; CR2032 coin cells were assembled in the following order: negative electrode shell, zinc foil, separator, positive electrode sheet, gasket, spring sheet, and positive electrode shell. The assembly process was carried out in an argon glove box (water oxygen content < 0.1 ppm).

[0035] Performance testing: The assembled battery is placed in the battery testing system and its electrochemical performance is tested at 25°C.

[0036] Figure 2 These are scanning electron microscope (SEM) images of the filter paper septum before and after femtosecond laser treatment. Figure a shows the planar morphology of the original qualitative filter paper before treatment, which is composed of slender, curved cellulose fibers randomly interwoven. The pores are irregular gaps formed by fiber stacking, resulting in an irregular pore structure. This loose fiber structure has low mechanical strength and large fluctuations in pore size. Figure b shows the cross-section before treatment, displaying the thickness direction structure of the original filter paper. The fibers are loosely stacked without obvious layering, and the overall structure is chaotic. Figure c shows the planar morphology after treatment, where the original fiber structure disappears, transforming into a uniformly distributed porous carbon membrane with regular circular / quasi-circular pores. This porous structure can provide uniform transport channels and nucleation sites for zinc ions, while simultaneously intercepting active substances in the electrolyte. Figure d shows the cross-section after treatment, clearly revealing a gradient carbonization structure. A porous carbon layer of uniform thickness is formed on the surface, while the supporting structure of cellulose fibers is still retained in the deeper layers. The carbon layer and the substrate have a gradual transition, which not only ensures the dendrite suppression and high conductivity of the surface layer, but also retains the mechanical support of the deeper layers, thus solving the defects of traditional carbonized membranes where the carbon layer is easy to fall off and the structure is easy to become brittle.

[0037] Figure 4 These are the voltage-time cycle stability curves of the battery, used to test the effect of different separators on the zinc anode. Initially, the voltage is generally stable, but the voltage fluctuations of GFS-ZB and CFS-ZB gradually increase, indicating that these two separators cannot effectively regulate zinc ion distribution, and local dendrite growth has begun to appear on the zinc anode. In the mid-term, the curve shows a sharp voltage jump, which is characteristic of the short circuit caused by dendrite piercing the separator in the batteries corresponding to GFS-ZB and CFS-ZB. The structural defects of traditional separators (such as uneven porosity and low mechanical strength) cannot prevent dendrite growth, leading to premature battery failure. In the later stages, only the curve corresponding to LCFS-ZB remains stable, and it remains stable even after switching to high areal capacity, indicating that the gradient carbonization separator of this invention can continuously regulate the uniform deposition of zinc ions, effectively suppress dendrite growth, and enable the zinc anode to achieve ultra-long cycle stability.

[0038] Figure 5This chart compares the coulombic efficiency of batteries using a gradient carbonized filter paper separator (LCFS-ZB), a traditional glass fiber separator (GFS-ZB), and an uncarbonized filter paper separator (CFS-ZB). For the traditional separators (GFS-ZB and CFS-ZB), the coulombic efficiency drops rapidly in the initial cycling phase (within only a few hundred cycles), indicating that these two separators cannot suppress the side reactions of the zinc anode. The structural defects of the traditional separators (uniform porosity and lack of carbonization layer regulation) lead to localized zinc ion aggregation, which initiates dendrite growth and accelerates side reactions such as hydrogen evolution and zinc corrosion, resulting in ineffective zinc consumption and a sharp decline in coulombic efficiency. In contrast, the LCFS-ZB maintains a stable coulombic efficiency close to 100% from the initial cycle to 4000 cycles; even when the areal capacity is switched from high to low load, the efficiency shows no significant fluctuation. This demonstrates that the gradient carbonized separator of this invention, through uniform pore regulation of zinc ion distribution and carbon layer suppression of side reaction sites, significantly reduces ineffective reactions such as hydrogen evolution and corrosion, making the zinc deposition-stripping process highly reversible.

[0039] Figure 6 This chart compares the battery cycle performance of the gradient carbonized filter paper separator (LCFS-ZB) described in this invention with that of traditional glass fiber separators (GFS-ZB) and uncarbonized filter paper separators (CFS-ZB). The traditional separator groups (GFS-ZB and CFS-ZB) exhibit rapid capacity decay in the initial stage of cycling (within hundreds of cycles), eventually dropping to extremely low levels and failing to maintain effective energy output. In contrast, the LCFS-ZB group maintains a consistently high specific capacity close to 400 mAh / g, with only slight fluctuations in the later stages, indicating that this separator effectively suppresses battery capacity decay and maintains continuous high energy output. Compared to traditional separators, it maintains both high battery specific capacity and high coulombic efficiency, solving the dual defects of rapid capacity decay and continuous efficiency reduction inherent in traditional separators. This provides crucial support for the high-performance and long-cycle practical application of zinc-ion batteries.

[0040] The embodiments described above are some, but not all, embodiments of the present invention. The detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A method for preparing a zinc-ion battery based on femtosecond laser-induced gradient carbonization filter paper membrane, characterized in that, Includes the following steps: A qualitative filter paper with a grayscale of 0.05-0.13% is selected, wherein the qualitative filter paper is cellulose-based. The shallow layer of the membrane layer of the qualitative filter paper is scanned using the high-energy transient characteristics of a femtosecond laser, and a gradient-distributed porous carbon membrane is constructed in the shallow layer of the qualitative filter paper, ultimately obtaining the femtosecond laser-induced gradient carbonized filter paper diaphragm; wherein the intensity of the femtosecond laser is 50-200 W / cm². 2 The carbonized layer thickness in the prepared gradient carbonized filter paper membrane is 10-30 μm, and the pore size of the porous carbon is 5-15 μm.

2. The preparation method according to claim 1, characterized in that... The diameter of the qualitative filter paper is 10-15 cm.

3. The preparation method according to claim 1, characterized in that, The degree of carbonization of the filter paper membrane and the pore size of the porous carbon are controlled by adjusting the intensity of the femtosecond laser and the number of laser scans; wherein the number of laser scans is 1-5.

4. The preparation method according to claim 2, characterized in that, The qualitative filter paper has a gray level of 0.08% and a diameter of 12.5 cm.

5. The preparation method according to claim 1, characterized in that, The intensity of the femtosecond laser is 150 W / cm². 2 The prepared gradient carbonized filter paper membrane has a carbonized layer thickness of 20 μm and a porous carbon pore size of 10 μm.

6. The preparation method according to claim 1, characterized in that, The femtosecond laser has a pulse width of 100-500 fs and a laser scanning speed of 10-50 mm / s.

7. A femtosecond laser-induced gradient carbonization filter paper diaphragm, characterized in that, The membrane is prepared by any one of the preparation methods described in claims 1-6; the membrane is based on cellulose-based qualitative filter paper, and a porous carbon membrane with a gradient distribution is formed in the shallow layer of the substrate. The porosity of the porous carbon membrane is 50%-70%, and there is a gradual structural transition between the carbonized layer and the substrate.

8. The femtosecond laser-induced gradient carbonization filter paper diaphragm according to claim 7, characterized in that, After being immersed in an acidic or alkaline environment with pH = 1-14 for 72 hours, the carbonized layer of the diaphragm did not peel off and the substrate remained intact, maintaining its structural integrity.

9. The application of the femtosecond laser-induced gradient carbonization filter paper membrane according to claim 7 or 8 in a zinc-ion battery, characterized in that, The separator, serving as the electrolyte separator of the zinc-ion battery, is assembled between the positive and negative electrode plates of the battery; the zinc-ion battery uses an aqueous zinc salt electrolyte, which is an aqueous solution of ZnSO4, Zn(NO3)2, or ZnCl2.

10. The application according to claim 9, characterized in that, The positive electrode material of the zinc-ion battery is vanadium-based oxide, manganese-based oxide, or a Prussian blue analogue, and the negative electrode material is zinc foil.

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