Flexible self-supporting fiber membranes and methods of making, and their use in electrode materials
The preparation of core-shell structured flexible self-supporting fiber membranes by coaxial electrospinning solves the problems of weight and flexibility of traditional sodium-ion battery electrode materials, improves the electrochemical performance and cycle stability of the electrodes, and is suitable for sodium-ion batteries and flexible electronic devices.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- JIANGXI COPPER TECHNOLOGY RESEARCH INSTITUTE CO LTD
- Filing Date
- 2025-11-14
- Publication Date
- 2026-07-24
AI Technical Summary
Traditional sodium-ion battery electrode materials suffer from problems such as increased weight and cost due to metal current collectors, as well as limitations in flexibility and electrochemical performance. When using single-walled carbon nanotubes alone, sodium ion insertion is slow and the structure is unstable, affecting battery capacity and cycle life.
A flexible, self-supporting fiber membrane with a core-shell structure was prepared by coaxial electrospinning. The inner layer consists of a network structure formed by single-walled carbon nanotubes and sodium supplementation agents, while the outer layer is a carbon skeleton. The conductivity and mechanical strength were improved by pre-oxidation and carbonization treatments, which also promoted sodium ion transport.
It achieves a lightweight design that eliminates the need for current collectors, improves electrode capacity, rate performance, and cycle stability, and is suitable for flexible electronic devices, while reducing battery weight and cost.
Smart Images
Figure CN121366864B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of electrode material technology, specifically relating to a flexible self-supporting fiber membrane and its preparation method, as well as its application in electrode materials. Background Technology
[0002] With the continued growth of global demand for clean energy storage, sodium-ion batteries, due to their abundant sodium resources and low cost, are considered a highly promising next-generation energy storage technology, especially showing broad application prospects in emerging fields such as large-scale energy storage systems and flexible electronic devices. As a key component of sodium-ion batteries, the performance of electrode materials directly determines key performance indicators such as energy density, power density, and cycle life. Traditional sodium-ion battery electrodes are typically prepared by coating a mixture of active materials, conductive agents, and binders onto a metal current collector. However, this preparation method has inherent limitations. First, the introduction of the metal current collector increases the overall weight and manufacturing cost of the battery, hindering lightweight design. Second, in applications of flexible electronic devices, the presence of the metal current collector severely limits the flexibility and integration of the device. Furthermore, the use of binders may impede the efficient transport of ions and electrons within the electrode, thus negatively impacting the battery's electrochemical performance.
[0003] To overcome these problems, researchers have gradually shifted towards developing self-supporting electrodes that do not require metal current collectors. Single-walled carbon nanotubes (SWCNTs) have become an ideal substrate for constructing high-performance self-supporting electrodes due to their excellent conductivity, high specific surface area, lightweight properties, and superior mechanical flexibility. However, when using SWCNTs alone, problems such as slow sodium ion insertion and structural instability during charge and discharge often occur, limiting the battery's capacity and cycle life. Summary of the Invention
[0004] To solve all or part of the above-mentioned technical problems, the present invention provides the following technical solutions: A first aspect of the present invention provides a method for preparing a flexible self-supporting fiber membrane, comprising: An inner spinning solution and an outer spinning solution are provided, wherein the inner spinning solution comprises single-walled carbon nanotubes, a dispersant, and a sodium supplementer, and the outer spinning solution comprises a carbon precursor; The precursor membrane was obtained by coaxial electrospinning using the inner and outer spinning solutions described above. The precursor membrane is subjected to pre-oxidation and carbonization treatments in sequence to obtain a flexible self-supporting fiber membrane composed of core-shell structured fibers.
[0005] This invention utilizes coaxial electrospinning to fabricate a flexible self-supporting fiber membrane composed of core-shell structured fibers. The inner layer of the core-shell fibers includes carbon nanotubes and a sodium supplement. The carbon nanotubes form a network structure, and the sodium supplement is uniformly distributed within the network structure. The synergistic effect between the two gives the flexible self-supporting fiber membrane excellent electrochemical performance. Simultaneously, after pre-oxidation and carbonization treatment, the outer shell forms a carbon skeleton coating layer, exhibiting good conductivity and mechanical strength. Based on the synergistic effect between the outer shell and the inner layer at the interface, sodium ion transport is promoted, making this flexible self-supporting fiber membrane suitable as an electrode material, improving electrode capacity, rate performance, and cycle stability. Furthermore, due to the good mechanical strength of this flexible self-supporting fiber membrane, no current collector is required, reducing battery weight and cost, making it suitable for flexible electronic devices.
[0006] In some embodiments, the content of single-walled carbon nanotubes in the inner spinning solution is 0.2wt%~0.5wt% to ensure the effective construction of the conductive network.
[0007] In some embodiments, the sodium supplement is present in an amount of 5 wt% to 20 wt% of the mass of the single-walled carbon nanotubes.
[0008] In some embodiments, the sodium supplement includes sodium phosphate. The added sodium supplement, particularly sodium sources such as sodium phosphate, chemically reacts with carbon nanotubes (SWCNTs) during carbonization to form stable sodium sources. These sources provide more sodium ion storage sites during charge and discharge, promoting efficient sodium ion insertion and extraction reactions. The sodium supplement enhances the network structure of the carbon nanotubes and improves the ionic conductivity and stability of the electrode, thereby improving the battery's capacity, rate performance, and cycle stability. The synergistic effect of the sodium supplement and carbon nanotubes ensures high electrode efficiency and long-term cycle stability, especially under high-rate charge and discharge conditions.
[0009] In some embodiments, the dispersant includes polyoxyethylene sorbitan fatty acid ester and sodium polyacrylate. The amount of polyoxyethylene sorbitan fatty acid ester is 150wt%~200wt% of the mass of the single-walled carbon nanotubes to achieve sufficient wetting and dispersion of the single-walled carbon nanotubes. The amount of sodium polyacrylate is 25wt%~100wt% of the mass of the single-walled carbon nanotubes to further stabilize the dispersion of the single-walled carbon nanotubes in the aqueous solvent through electrostatic repulsion.
[0010] In some embodiments, the molecular weight of the sodium polyacrylate is 2000 g / mol to 5000 g / mol.
[0011] In some embodiments, the polyoxyethylene sorbitan fatty acid ester includes Tween 20 and / or Tween 80.
[0012] In some embodiments, the inner spinning solution further includes 0.1 wt% to 5 wt% of auxiliaries, including one or more combinations of polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), polyacrylamide (PAM), hydroxypropyl methylcellulose (HPMC), sodium carboxymethyl cellulose (CMC-Na), polyethylene glycol (PEG), and sodium alginate (SA). These auxiliaries can act as viscosity modifiers and fiber-forming aids in aqueous systems, helping to improve the rheological properties and fiber formation continuity of the electrospinning solution, and improve droplet stability and fiber uniformity during spinning. By adding appropriate amounts of these auxiliaries, the viscosity and conductivity balance of the spinning solution can be effectively adjusted, thereby obtaining a more stable jet stream and a dense fiber membrane structure. Furthermore, these materials also have good hydrophilicity and high molecular chain flexibility, which can play a role in thickening, improving fiber formation and dispersion stability in aqueous electrospinning solutions, thereby ensuring the uniform distribution of components in the inner spinning solution and the stability of the jetting process.
[0013] Preferably, the auxiliary agent is 0.5wt% to 5wt% polyvinyl alcohol; or, when polyvinylpyrrolidone (PVP) is used, its dosage range is 0.3wt% to 3wt%; when polyacrylamide (PAM) is used, its dosage range is 0.1wt% to 2wt%; when sodium alginate and / or sodium carboxymethyl cellulose are used, their dosage should be controlled within the range of 0.2wt% to 1wt% to avoid excessively high system viscosity affecting spinning flowability.
[0014] In some embodiments, the preparation method of the inner layer spinning solution specifically includes: dispersing the single-walled carbon nanotubes, dispersant, and optional auxiliary agent in an aqueous solvent, emulsifying at high speed of 500 rpm to 2000 rpm for 10 min to 20 min, then adding the sodium supplement agent, and then emulsifying at high speed of 1000 rpm to 3000 rpm for 10 min to 30 min, and then performing high-pressure homogenization dispersion under high pressure of 500 bar to 900 bar to obtain a uniformly dispersed inner layer spinning solution.
[0015] In some embodiments, the total concentration of carbon precursor in the outer spinning solution is 15wt%~20wt%.
[0016] In some embodiments, the carbon precursor includes one or more of polyacrylonitrile, lignin, polyvinyl alcohol, phenolic resin, polyaniline, polypyrrole, and cellulose, but is not limited thereto.
[0017] In some preferred embodiments, the carbon precursor in the outer spinning solution includes lignin and polyacrylonitrile, wherein the mass percentage of polyacrylonitrile is 30wt%~40wt%. Lignin, as a natural high-molecular carbon source, contains abundant aromatic structures and hydroxyl functional groups. During carbonization, it can generate an amorphous carbon phase with a porous structure, effectively increasing the specific surface area and the number of ion diffusion channels, and also improving the ion conductivity of the fiber membrane. Furthermore, the introduction of lignin can partially reduce the shrinkage effect of PAN, making the composite carbon skeleton formed after carbonization more flexible and stable. If only polyacrylonitrile is used, the resulting fiber membrane has a relatively dense structure and low porosity. Although it has good mechanical strength and conductivity, the sodium ion diffusion path is limited, resulting in a decrease in the capacity retention rate of the battery under long-cycle or high-rate conditions. If only lignin is used, although the fiber membrane structure is relatively porous and has a certain specific capacity advantage, the poor fiber-forming properties of lignin slightly reduce the continuity and mechanical strength of the membrane, making it prone to structural collapse during carbonization, leading to a slight decrease in the integrity of the conductive network and a reduction in cycle stability. In contrast, the composite system of lignin and polyacrylonitrile combines the advantages of both: lignin provides an abundant carbon source and porous structure, which helps to form a high specific surface area and excellent ion conductivity; polyacrylonitrile provides structural support and continuous fiber-forming ability, ensuring the compactness and mechanical toughness of the membrane. The synergistic effect of the two enables the carbonized fiber membrane to achieve a balanced optimization in terms of conductivity, mechanical stability and electrochemical performance, exhibiting excellent flexibility, self-support and high specific capacity, thus making it a more preferred solution.
[0018] In some embodiments, the solvent of the outer spinning solution includes N,N-dimethylformamide (DMF), but is not limited thereto.
[0019] In some embodiments, the process conditions for coaxial electrospinning include: a spinning voltage of 22kV~24kV to provide a stable electric field force for driving the spinning solution injection; a flow rate of 0.5mL / h~0.8mL / h for the inner layer spinning solution to adjust the uniform supply of the inner layer material; a flow rate of 0.6mL / h~0.8mL / h for the outer layer spinning solution to ensure the thickness and uniformity of the outer layer coating; and a receiving distance of 12cm~15cm to ensure stable fiber formation on the receiving roller.
[0020] In some embodiments, the pre-oxidation treatment includes subjecting the precursor film to pre-oxidation at 280°C to 350°C under an oxygen-containing atmosphere. This pre-oxidation treatment introduces cross-linked structures within the fiber, effectively maintaining the fiber's morphology and structural integrity during subsequent high-temperature carbonization, and reducing the risk of melting or breakage during the carbonization process.
[0021] Furthermore, the oxygen-containing atmosphere is air.
[0022] Furthermore, the temperature is increased to 280℃~350℃ at a heating rate of 0.8℃ / min~1.5℃ / min and held for 1h~2h to carry out the pre-oxidation treatment.
[0023] In some embodiments, the carbonization treatment includes: holding at 900℃~1100℃ for 1~2 hours under an inert atmosphere. The carbonization treatment can transform the carbon precursor in the outer layer into a carbon framework with good conductivity and mechanical strength, providing the electrode with an efficient electron transport network and stable structural support. Simultaneously, the uniformly distributed single-walled carbon nanotube network in the inner layer undergoes an interfacial reaction with the sodium supplement under the high-temperature conditions of carbonization, producing a synergistic effect to improve the electrode's sodium ion storage capacity, excellent rate performance, and good cycle stability, among other electrochemical properties.
[0024] A second aspect of the present invention provides a flexible self-supporting fiber membrane, which is prepared by the preparation method described in any of the above technical solutions.
[0025] The flexible self-supporting fiber membrane is composed of fibers with a core-shell structure. The outer layer of the core-shell structured fiber is a carbon skeleton coating layer, and the inner layer includes single-walled carbon nanotubes and a sodium supplement. The single-walled carbon nanotubes form a network structure, and the sodium supplement is uniformly distributed in the network structure.
[0026] A third aspect of the present invention provides the application of the aforementioned flexible self-supporting fiber membrane in the fabrication of sodium-ion battery electrodes, sodium-ion batteries, wearable devices, or flexible electronics.
[0027] A fourth aspect of this invention provides a flexible self-supporting sodium-ion battery electrode, comprising the flexible self-supporting fiber membrane described in any of the technical solutions. The fiber membrane obtained by this invention possesses good mechanical strength and good conductivity, and can be directly used as an electrode material for sodium-ion batteries without the need for an additional metal current collector.
[0028] A fifth aspect of the present invention provides a sodium-ion battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the negative electrode is the flexible self-supporting sodium-ion battery electrode described above.
[0029] Compared with the prior art, the present invention has at least the following technical effects: (1) The flexible self-supporting fiber membrane prepared by this invention has good electrochemical performance and excellent sodium ion transport performance, making it suitable as an electrode material for sodium-ion batteries; moreover, it has good flexibility and mechanical strength, requires no current collector, and can reduce battery weight and cost, making it suitable for flexible electronic devices. Sodium-ion batteries using it as an electrode material have good sodium ion storage capacity, excellent rate performance, and good cycle stability.
[0030] (2) The preparation method provided by this invention introduces a cross-linked structure into the fiber through pre-oxidation treatment, which effectively maintains the integrity of the fiber's morphology and structure during the subsequent high-temperature carbonization process, reducing the risk of melting or breakage of the fiber during high-temperature carbonization. At the same time, the carbonization treatment enables the carbon precursor to form a carbon skeleton with good conductivity and mechanical strength, providing an efficient electron transport network and stable structural support for the electrode. The inner single-walled carbon nanotubes and sodium supplementation agent work synergistically with the carbon skeleton shell to improve the overall electrochemical performance of the electrode.
[0031] (3) The present invention uses coaxial electrospinning process to prepare core-shell structure flexible self-supporting fiber membrane. Compared with multi-step coating process, the preparation method is simpler and more conducive to industrial production. Attached Figure Description
[0032] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0033] Figure 1a This is a photograph of the inner spinning solution prepared in Example 1; Figure 1b This is a photograph of the outer spinning solution prepared in Example 1; Figure 1c This is a diagram showing the dispersion effect of the inner layer spinning solution prepared in Example 1 in water; Figure 1d This is a state diagram of the inner layer spinning solution prepared in Example 1 during the electrospinning process; Figure 2 This is a schematic diagram of the structure of the flexible self-supporting fiber membrane prepared in Example 1; Figure 3 These are electrochemical performance curves of the half-cells assembled in Example 1 and Comparative Example 1. Figure 4 This is a cycle performance diagram of the half-cell assembled in Example 2; Figure 5 These are room temperature diagrams and flexibility test state diagrams of the flexible self-supporting fiber membranes prepared in Example 3 and Comparative Example 3. Detailed Implementation
[0034] The technical solutions of the present invention will be described in detail below with reference to specific embodiments, so that those skilled in the art can better understand and implement the technical solutions of the present invention. The specific functional details disclosed herein should not be construed as limiting, but are merely intended to form the basis of the claims and to teach those skilled in the art to employ the representative basis of the invention in different ways in any suitable detailed embodiment.
[0035] In addition, unless otherwise specified, all raw materials used in the following embodiments can be purchased from the market or other sources, and all production and testing equipment used are known in the art.
[0036] Unless otherwise specified, the "%" used in the specific embodiments of the present invention refers to mass percentages.
[0037] Example 1 This embodiment provides a flexible self-supporting sodium-ion battery electrode and its preparation method, specifically including the following steps: (1) Preparation of inner layer spinning solution: 0.3% by mass of single-walled carbon nanotubes (SWCNTs), 0.48% by mass of Tween 80, 0.1% by mass of sodium polyacrylate (PAA, molecular weight 3000 g / mol), 1% by mass of polyvinyl alcohol (PVA), and the balance of deionized water were uniformly mixed and then subjected to high-speed shear emulsification for 10 min. Then, sodium phosphate (Na3PO4) with a mass fraction of 10% relative to SWCNTs was added, and high-speed shear emulsification was performed again for 10 min to obtain a preliminarily uniformly mixed dispersion. Then, a completely uniformly dispersed aqueous slurry was obtained by high-pressure homogenization dispersion.
[0038] (2) Preparation of outer spinning solution: 9 wt% lignin and 6 wt% polyacrylonitrile (PAN, Mw≈150,000) were added to the remaining DMF and stirred magnetically at 60 ℃ for 12 h to completely dissolve and form a uniform, particle-free solution.
[0039] (3) Coaxial electrospinning: Using a dual-channel nozzle, the flow rates of the outer spinning solution and the inner spinning solution are set to 0.8 mL / h and 0.5 mL / h, respectively. A voltage of 23 kV is applied, and the receiving distance is 13 cm. The electrospinning process is completed under the condition that the ambient humidity is less than 45%, and the precursor membrane is obtained.
[0040] (4) Pre-oxidation treatment: The precursor film prepared above is placed in an air atmosphere and heated to 300 °C at a heating rate of 2 °C / min for 1 h for pre-oxidation.
[0041] (5) Carbonization treatment: After stabilizing the carbon skeleton structure, the carbon is heated to 1000 ℃ for 1 h under argon protection at a heating rate of 5 ℃ / min to obtain a flexible self-supporting fiber membrane composed of core-shell structured fibers.
[0042] Figure 1a This is a picture of the inner spinning solution. Figure 1b This is a photograph of the outer spinning solution, based on... Figure 1a , Figure 1b It can be seen that they all present as a uniform black dispersion system, and no agglomeration or sedimentation occurs after 72 hours of standing. Figure 1c This is a diagram showing the dispersion effect of the inner spinning solution in water. Figure 1d This is a diagram showing the state of the inner spinning solution during the electrospinning process.
[0043] Figure 2 This is a schematic diagram of the structure of the flexible self-supporting fiber membrane after carbonization in this embodiment, as shown. Figure 2 As shown, it has a complete core-shell framework structure. The outer shell is a lignin / PAN carbon framework, and the inner layer is a uniformly distributed single-walled carbon nanotube and sodium phosphate. The single-walled carbon nanotubes form a network structure, and the sodium phosphate is distributed in the network structure, which gives the flexible self-supporting fiber membrane a good electronic / ion conduction path.
[0044] The present invention also tested the electrode performance of the prepared flexible self-supporting fiber membrane. The obtained flexible self-supporting fiber membrane was cut into 14 mm circular electrodes and assembled into a coin cell sodium-ion battery for testing. The initial specific capacity of the coin cell sodium-ion battery in this embodiment was measured to be 350 mAh g⁻¹. -1 After 100 cycles at a current density of 50 mA / g, the capacity retention is 95.3%. This structure requires no current collector support and exhibits excellent flexibility and stability.
[0045] Example 2 Example 2 is basically the same as Example 1, except that the PAA content in the inner spinning solution of Example 2 is increased to 0.3 wt% to enhance the dispersibility of carbon nanotubes and the stability of aqueous slurry. The rest is the same as Example 1.
[0046] A coin-type sodium-ion battery was prepared and tested using the same method as in Example 1. It was found that the cycle performance of the battery in Example 2 was further improved compared to that in Example 1, with an initial specific capacity of 365 mAh g⁻¹. -1 The retention rate after 100 cycles was 97.5%. Figure 4 The graph shows the cycle performance of the battery in Example 2, demonstrating that this example is superior in both cycle stability and capacity retention.
[0047] Example 3 Example 3 is basically the same as Example 1, except that the amount of sodium phosphate (Na3PO4) supplementing sodium in the inner spinning solution of Example 3 is 20 wt.% of the mass of SWCNT, in order to explore its compatibility in the aqueous slurry system and its effect on improving the performance of sodium-ion batteries. The rest of the implementation is the same as in Example 1, and will not be repeated here.
[0048] The flexible self-supporting fiber membrane prepared in Example 3 was assembled into a coin cell sodium-ion battery using the same method as in Example 1, and tested. The battery was tested at 50 mA g. -1 The initial specific capacity at current density is 362 mAh g. -1 After 100 cycles, the capacity retention rate was 97.6%, indicating good cycling stability.
[0049] This embodiment maintains good specific capacity output even with a high Na3PO4 doping ratio, indicating that an appropriate amount of sodium supplement can effectively increase the number of sodium ion intercalation sites, thereby increasing capacity without compromising slurry dispersion stability and spinning continuity.
[0050] Example 4 (1) Preparation of inner layer spinning solution: 0.2% by mass of single-walled carbon nanotubes (SWCNTs), 0.3% by mass of Tween 20, 0.05% by mass of sodium polyacrylate (PAA, molecular weight 3000 g / mol), 1% by mass of polyvinyl alcohol (PVA), and the balance of deionized water were uniformly mixed and then subjected to high-speed shear emulsification for 10 min. Then, sodium phosphate (Na3PO4) with a mass fraction of 5% relative to SWCNTs was added, and high-speed shear emulsification was performed again for 10 min to obtain a preliminary uniformly mixed dispersion. Then, a completely uniformly dispersed aqueous slurry was obtained by high-pressure homogenization dispersion.
[0051] (2) Preparation of outer spinning solution: 12 wt% lignin and 8 wt% polyacrylonitrile (PAN, Mw≈150,000) were added to the remaining DMF and stirred magnetically at 60 ℃ for 12 h to completely dissolve and form a uniform, particle-free solution.
[0052] (3) Coaxial electrospinning: Using a dual-channel nozzle, the flow rates of the outer spinning solution and the inner spinning solution are set to 0.6 mL / h and 0.8 mL / h, respectively. A voltage of 22 kV is applied, and the receiving distance is 12 cm. The electrospinning process is completed under the condition that the ambient humidity is less than 45%, and a precursor membrane with a core-shell structure is obtained.
[0053] (4) Pre-oxidation treatment: The precursor film prepared above is placed in an air atmosphere and heated to 280 °C at a heating rate of 0.8 °C / min for 1.5 h pre-oxidation.
[0054] (5) Carbonization treatment: After stabilizing the carbon skeleton structure, the temperature is increased to 900 ℃ for 1 h under argon protection at a heating rate of 5 ℃ / min to obtain a flexible self-supporting fiber membrane with a core-shell structure.
[0055] Example 5 (2) Preparation of inner layer spinning solution: 0.5% by mass of single-walled carbon nanotubes (SWCNTs), 1% of Tween 20, 0.5% of sodium polyacrylate (PAA, molecular weight 3000 g / mol), 5% of polyvinyl alcohol (PVA), and the balance of deionized water were uniformly mixed and then subjected to high-speed shear emulsification for 10 min. Then, sodium phosphate (Na3PO4) with a mass fraction of 20% relative to SWCNTs was added, and high-speed shear emulsification was performed again for 10 min to obtain a preliminarily uniformly mixed dispersion. Then, a completely uniformly dispersed aqueous slurry was obtained by high-pressure homogenization dispersion.
[0056] (2) Preparation of outer spinning solution: 9 wt% lignin and 6 wt% polyacrylonitrile (PAN, Mw≈150,000) were added to the remaining DMF and stirred magnetically at 60 ℃ for 12 h to completely dissolve and form a uniform, particle-free solution.
[0057] (3) Coaxial electrospinning: Using a dual-channel nozzle, the flow rates of the outer spinning solution and the inner spinning solution are set to 0.7 mL / h and 0.7 mL / h, respectively. A voltage of 24 kV is applied, and the receiving distance is 15 cm. The electrospinning process is completed under the condition that the ambient humidity is less than 45%, and a precursor membrane with a core-shell structure is obtained.
[0058] (4) Pre-oxidation treatment: The precursor film prepared above is placed in an air atmosphere and heated to 350 °C at a heating rate of 1.5 °C / min for 2 h of pre-oxidation.
[0059] (5) Carbonization treatment: After stabilizing the carbon skeleton structure, the carbon is heated to 1100 ℃ for 2 h under argon protection at a heating rate of 5 ℃ / min to obtain a flexible self-supporting fiber membrane with a core-shell structure.
[0060] Example 6 The only difference between Example 6 and Example 1 is that in step (2) of Example 6, the composite system of lignin and polyacrylonitrile is replaced with polyaniline. The rest is the same as in Example 1, and will not be repeated here.
[0061] Comparing Examples 1 and 6, it was found that while using polyaniline as a carbon precursor can improve the conductivity of the membrane to some extent, the uniformity of the fiber structure is reduced, the spinning process is less stable, and the fiber diameter distribution in the resulting precursor membrane is uneven, with adhesion and breakage in some areas. After carbonization, the overall flexibility of the fiber membrane decreases, and the electrode exhibits high polarization during cyclic charge-discharge. Test results after assembling a sodium-ion battery show that the initial specific capacity of Example 6 is 328 mAh g⁻¹. -1 After 100 cycles, the capacity retention was 90.8%, significantly lower than that of Example 1 (350 mAh g). -1 (95.3% retention rate). This indicates that it is difficult to maintain good structural integrity while forming stable fibers using only polyaniline. The lignin / PAN composite system can better balance fiber-forming properties and mechanical strength after carbonization.
[0062] Therefore, in some embodiments where higher requirements are placed on fiber-forming properties and mechanical strength, the carbon precursor is preferably a composite system of lignin and polyacrylonitrile, with excellent results when the mass percentage of polyacrylonitrile is 30wt%~40wt%. However, when other materials such as polyvinyl alcohol, phenolic resin, polyaniline, polypyrrole, and cellulose are used as the carbon precursor, a carbon skeleton coating layer can also be formed to achieve certain effects.
[0063] Example 7 The only difference between Example 7 and Example 1 is that Example 7 uses only polyacrylonitrile instead of lignin, and the amount of polyacrylonitrile used is the same as the total amount of polyacrylonitrile and lignin used in Example 1. The rest of the procedures are the same as in Example 1 and will not be repeated here.
[0064] The resulting flexible fiber membrane, obtained through electrospinning and carbonization under the same conditions, exhibits a dense structure with uniform fiber diameter and a smooth overall surface, but with few surface pores. When used as the anode material for a sodium-ion battery, the initial specific capacity of the battery was 325 mAh g⁻¹. -1 After 100 cycles, the capacity retention rate was 91.5%. Although it exhibited high conductivity and structural integrity, due to its low porosity, sodium ion insertion / extraction was restricted, resulting in rapid capacity decay at high charge-discharge rates and a slight decrease in rate performance.
[0065] The results indicate that while using PAN alone is beneficial for fiber forming and carbonized skeleton construction, it lacks porous carbon structure support and is inferior to Example 1 in terms of balancing electrochemical activity and ion transport performance.
[0066] Example 8 The only difference between Example 8 and Example 1 is that Example 8 uses only lignin instead of polyacrylonitrile, and the amount of lignin used is the same as the total amount of polyacrylonitrile and lignin used in Example 1. The rest of the procedures are the same as in Example 1 and will not be repeated here.
[0067] The obtained precursor membrane exhibited slight fiber breakage and localized aggregation during electrospinning, resulting in poor fiber formation and uneven membrane thickness. After pre-oxidation and carbonization treatment, the resulting membrane structure was relatively loose, with numerous pores but insufficient continuity. When used as an electrode material, the initial specific capacity of the battery was 340 mAh g⁻¹. -1 However, after 100 cycles, the capacity retention rate was only 86.2%, showing a significant capacity decay. This phenomenon is mainly attributed to the fact that while the porous structure generated during the carbonization of lignin increases the ion diffusion rate, it leads to a decrease in the mechanical strength and electrical continuity of the membrane.
[0068] Therefore, while using lignin alone is beneficial for increasing specific capacity, it is inferior to Example 1 in ensuring the structural integrity and cycle stability of the fiber membrane.
[0069] Example 9 The only difference between Example 9 and Example 1 is that in step (1) of Example 9, polyvinyl alcohol is not added, that is, the inner spinning solution of Example 9 does not contain polyvinyl alcohol. The rest is the same as that of Example 1, and will not be repeated here.
[0070] Comparing Examples 1 and 9, it was found that without PVA, the viscosity of the inner spinning solution decreased, resulting in insufficient rheological properties, unstable jet flow during electrospinning, a wider fiber diameter distribution, and the appearance of fractures and beaded structures in some areas. After carbonization treatment, the surface smoothness of the resulting flexible self-supporting fiber membrane decreased, with localized pores and microcracks, leading to a reduction in the membrane's mechanical strength and conductive continuity. The initial specific capacity of the coin cell sodium-ion battery assembled from this membrane was only 310 mAhg. -1 After 100 cycles, the capacity retention was approximately 89.6%, significantly lower than the 350 mAh g⁻¹ in Example 1. -1 With a retention rate of 95.3%, this indicates that polyvinyl alcohol (PVA) in this system not only improves the viscosity and stability of the electrospinning solution but also forms a microporous support structure of the carbon skeleton after carbonization, promoting ion diffusion and electrode structure stability. Appropriate addition of PVA can significantly improve the fiber-forming properties, flexibility, and electrochemical performance of the fiber membrane.
[0071] Furthermore, this invention also uses auxiliaries such as polyvinylpyrrolidone, polyacrylamide, hydroxypropyl methylcellulose, sodium carboxymethyl cellulose, polyethylene glycol, and sodium alginate to replace polyvinyl alcohol, and found that these materials have similar effects to polyvinyl alcohol. Therefore, in some embodiments where higher requirements are placed on spinning stability and the microporous support structure of the carbon skeleton, it is preferable to add the above-mentioned auxiliaries to the inner spinning solution.
[0072] Comparative Example 1 The only difference between Comparative Example 1 and Example 1 is that no dispersant was added to the inner spinning solution of Comparative Example 1, i.e., no Tween 80 and PAA were added. All other conditions were kept the same to verify the role of dispersant in slurry stability and fiber forming performance.
[0073] Comparing the inner layer spinning solutions prepared in Example 1 and Comparative Example 1, it was found that the inner layer spinning solution without dispersant had a lower viscosity and agglomerated and settled within 24 hours after standing. Furthermore, during electrospinning, it was clearly observed that single-walled carbon nanotubes agglomerated and settled without dispersant, further leading to clogging of the pinholes in the spinning solution. Therefore, the inner layer spinning solution needs to be constantly replaced during the spinning process. However, even with this, the final spinning result still showed significant aggregation, leading to discontinuous fiber film structure. After pre-oxidation treatment, some areas exhibited pores and fractures, resulting in poor interfacial stability.
[0074] Selected areas without holes or fractures were used to prepare battery electrodes and assemble half-cells using the same process as in Example 1, and their battery characteristics were tested. Figure 3 The graphs show the electrochemical performance of Example 1 and Comparative Example 1. Figure 3 The results show that the electrochemical performance of the sample in Comparative Example 1 is significantly worse than that in Example 1. Under the same test conditions, the initial specific capacity of the half-cell assembled in Comparative Example 1 is 250 mAh g⁻¹. -1 After 100 cycles, the retention rate was only 84%.
[0075] Comparative Example 2 The only difference between Comparative Example 2 and Example 2 is that the PAA content in the inner spinning solution was increased to 0.8 wt% to investigate the effect of excessively high viscosity on spinning stability. The rest of the procedures were the same as in Example 2 and will not be repeated here.
[0076] Compared with Example 2, it was found that the inner spinning solution of Comparative Example 2 had a higher viscosity, which caused the nozzle to be blocked multiple times during the spinning process, resulting in discontinuous fiber film formation and making the preparation more difficult, making it basically impossible to complete the spinning and subsequent processes.
[0077] Comparative Example 3 The only difference between Comparative Example 3 and Example 3 is that the carbonization temperature in the preparation method of Comparative Example 3 is 1200°C, which is used to evaluate the effect of excessively high carbonization temperature on fiber structure and properties. The rest of the procedures are the same as in Example 3, and will not be repeated here.
[0078] While increasing the carbonization temperature can enhance the crystallinity of carbon materials, it also introduces significant structural problems. Specifically, after carbonization at 1200℃, the fiber membrane surface exhibited slight shrinkage and brittleness, with structural collapse occurring in some areas. This phenomenon is caused by excessive dehydrogenation of carbon precursors (such as lignin and PAN) due to the excessively high carbonization temperature. This compromises the membrane's stability, resulting in excessively large porosity and an uneven surface structure, thereby affecting its electrochemical performance.
[0079] From an electrochemical performance perspective, the battery prepared in Comparative Example 3 showed a significant decrease in performance compared to Example 3. Test results showed an initial specific capacity of 315 mAh / g, but after 100 charge-discharge cycles, the capacity retention was only 91.3%, significantly lower than the 97.6% of Example 3. Furthermore, the rate performance decreased, and the electrode flexibility also weakened. This indicates that the excessively high carbonization temperature led to over-crystallization of the carbon skeleton, resulting in a decrease in the electrode's ion storage capacity and conductivity.
[0080] In summary, excessively high carbonization temperatures lead to battery capacity decay and reduced rate performance, while excessive carbonization also reduces electrode flexibility, affecting the long-term stability of the battery.
[0081] Comparative Example 4 The main difference between Comparative Example 4 and Example 3 is that Comparative Example 4 did not undergo carbonization treatment, but instead directly used a pre-oxidized fiber membrane. The rest of the procedures were the same as in Example 3, and will not be repeated here.
[0082] While this treatment method can enhance the thermal stability of the membrane to some extent, the lack of a carbonization process prevents the formation of a stable carbon framework, significantly impacting the membrane's conductivity and mechanical strength. Compared to Example 3, the uncarbonized membrane exhibits significantly poorer mechanical properties and conductivity, leading to a substantial decrease in the battery's electrochemical performance.
[0083] In the tests, the initial specific capacity of the battery in Comparative Example 4 was significantly lower than that in Example 3, and both the capacity retention and rate performance of the battery decreased significantly during high-rate charge and discharge. Due to the lack of a stable carbon skeleton and poor conductivity, the battery could not maintain stable electrochemical performance during long-term use. The electrode film without carbonization treatment, due to its loose structure, was difficult to maintain stable battery capacity and cycle performance during charge and discharge.
[0084] Therefore, the performance of uncarbonized electrode films in batteries is far inferior to that of carbonized electrode films. The capacity decay, rate performance reduction, and reduced flexibility of the battery all indicate that the carbonization process is crucial to battery performance.
[0085] Comparative Example 5 The main difference between Comparative Example 5 and Example 3 is that Comparative Example 5 did not undergo pre-oxidation treatment during the preparation process; instead, the precursor film obtained from spinning was directly carbonized. The rest of the procedures were the same as in Example 3 and will not be repeated here.
[0086] Pre-oxidation treatment introduces cross-linked structures into the fiber membrane, enhancing its stability during subsequent carbonization and improving its conductivity and structural integrity. Membranes without pre-oxidation lack this step, resulting in less uniform carbon skeleton formation and significant structural instability.
[0087] In the comparative tests, the battery performance of Comparative Example 5 was poor. Even under the same carbonization conditions, the unoxidized film failed to effectively maintain the battery's high performance. Compared to Example 3, the unoxidized film showed poorer results in terms of capacity retention, rate performance, and cycle stability. This indicates that pre-oxidation treatment plays an important role in the formation of the electrode film, providing better structural support and stability for the subsequent carbonization process.
[0088] Therefore, the untreated film, especially in terms of long-term battery stability and rate performance, is far inferior to the pre-oxidized electrode film in Example 3.
[0089] Comparative Example 6 The main difference between Comparative Example 6 and Example 1 is that Comparative Example 6 mixes all raw materials (including single-walled carbon nanotubes, Tween 80, sodium polyacrylate, polyvinyl alcohol, sodium phosphate, lignin and PAN) together and performs electrospinning to obtain a non-core-shell structured monolayer membrane.
[0090] The non-core-shell membrane, lacking a stable structure separating the inner and outer layers, cannot provide a good electron / ion conduction pathway like in Example 1, resulting in significant differences in electrode performance. During charge and discharge, the battery's specific capacity and rate performance decrease significantly, and due to the absence of a stable carbon framework, the electrode's mechanical strength and flexibility are poor, leading to a much lower cycle stability than in Example 1.
[0091] Therefore, compared with core-shell structured electrode films, non-core-shell structured single-layer films have significant disadvantages in terms of battery electrochemical performance, rate performance and long-cycle stability, especially in high-rate charge and discharge applications, where they perform poorly.
[0092] In summary, this invention utilizes coaxial electrospinning technology, employing an aqueous slurry of single-walled carbon nanotubes containing a sodium supplement as the inner spinning solution and a mixed solution of lignin and polyacrylonitrile as the outer spinning solution. By precisely controlling the electrospinning process parameters and subsequent pre-oxidation and high-temperature carbonization treatments, a flexible self-supporting electrode composed of core-shell structured fibers was successfully prepared. The carbonization of the outer layer of the core-shell structured fibers forms a continuous carbon skeleton coating layer with good conductivity and mechanical strength. The synergistic effect between the inner carbon nanotubes and the sodium supplement significantly improves the electrochemical performance of the electrode. The development of this novel flexible self-supporting electrode addresses the problems of heavy weight, high cost, poor flexibility, and unstable conductivity in existing electrode materials, particularly for high-performance sodium-ion batteries and flexible energy storage applications.
[0093] In addition, the inventors of this case also conducted experiments with other raw materials, process operations, and process conditions described in this specification, referring to the aforementioned embodiments, and obtained relatively ideal results in all cases.
[0094] All aspects, embodiments, features, and examples of this invention should be considered illustrative and used to explain and illustrate the invention, but not to limit the invention. The scope of the invention is defined only by the claims.
[0095] Although the invention has been described with reference to illustrative embodiments, those skilled in the art will understand that various other changes, omissions, and / or additions can be made without departing from the spirit and scope of the invention, and that elements in the described embodiments can be substituted with substantially equivalents. Furthermore, many modifications can be made without departing from the scope of the invention to adapt particular situations or materials to the teachings of the invention. Therefore, this invention is not intended to be limited to the specific embodiments disclosed, but rather to encompass all embodiments falling within the scope of the appended claims. Moreover, unless specifically stated otherwise, any use of the terms first, second, etc., does not indicate any order or importance, but is used to distinguish one element from another.
Claims
1. A method for preparing a flexible self-supporting fiber membrane, characterized in that, include: An inner spinning solution and an outer spinning solution are provided. The inner spinning solution comprises single-walled carbon nanotubes, a dispersant, and a sodium supplement, wherein the sodium supplement comprises sodium phosphate. The outer spinning solution comprises a carbon precursor, wherein the carbon precursor comprises polyacrylonitrile and lignin, wherein the mass percentage of polyacrylonitrile is 30wt% to 40wt% of the total mass of the two. The precursor membrane was obtained by coaxial electrospinning using the inner and outer spinning solutions described above. The precursor membrane is subjected to pre-oxidation and carbonization treatments in sequence to obtain a flexible self-supporting fiber membrane composed of core-shell structured fibers; wherein, the pre-oxidation treatment includes: pre-oxidizing the precursor membrane at 280℃~350℃ under an oxygen-containing atmosphere.
2. The preparation method according to claim 1, characterized in that: The content of single-walled carbon nanotubes in the inner spinning solution is 0.2wt%~0.5wt%.
3. The preparation method according to claim 1, characterized in that: The sodium supplement contains 5 wt% to 20 wt% of the mass of the single-walled carbon nanotubes.
4. The preparation method according to claim 1, characterized in that: The inner spinning solution also includes 0.1wt% to 5wt% of auxiliaries, which include one or more of the following: polyvinyl alcohol, polyvinylpyrrolidone, polyacrylamide, hydroxypropyl methylcellulose, sodium carboxymethyl cellulose, polyethylene glycol, and sodium alginate.
5. The preparation method according to claim 4, characterized in that: The additives are 0.5wt%~5wt% of polyvinyl alcohol, 0.3wt%~3wt% of polyvinylpyrrolidone, 0.1wt%~2wt% of polyacrylamide, or 0.2wt%~1wt% of sodium alginate and / or sodium carboxymethyl cellulose.
6. The preparation method according to claim 1, characterized in that: The dispersant comprises polyoxyethylene sorbitan fatty acid ester and sodium polyacrylate, wherein the amount of polyoxyethylene sorbitan fatty acid ester is 150wt% to 200wt% of the mass of the single-walled carbon nanotubes, and the amount of sodium polyacrylate is 25wt% to 100wt% of the mass of the single-walled carbon nanotubes.
7. The preparation method according to claim 1, characterized in that, Specifically, it includes: The single-walled carbon nanotubes and dispersant are dispersed in an aqueous solvent and emulsified at a high speed of 500 rpm to 2000 rpm for 10 min to 20 min. Then, the sodium supplement is added, and the emulsification is carried out at a high speed of 1000 rpm to 3000 rpm for 10 min to 30 min. Finally, the mixture is subjected to high-pressure homogenization dispersion under a pressure of 500 bar to 900 bar to obtain a uniformly dispersed inner layer spinning solution.
8. The preparation method according to claim 1, characterized in that: The total concentration of carbon precursor in the outer spinning solution is 15wt%~20wt%.
9. The preparation method according to claim 1, characterized in that, The process conditions for coaxial electrospinning include: a spinning voltage of 22kV~24kV, a flow rate of 0.5mL / h~0.8mL / h for the inner spinning solution, a flow rate of 0.6mL / h~0.8mL / h for the outer spinning solution, and a receiving distance of 12cm~15cm.
10. The preparation method according to claim 1, characterized in that, The carbonization process includes: holding at 900℃~1100℃ for 1h~2h under an inert atmosphere.
11. A flexible self-supporting fiber membrane, characterized in that, It is prepared by any one of claims 1 to 10.
12. The flexible self-supporting fiber membrane according to claim 11, characterized in that, The flexible self-supporting fiber membrane is composed of fibers with a core-shell structure. The outer layer of the core-shell structured fiber is a carbon skeleton coating layer, and the inner layer includes single-walled carbon nanotubes and a sodium supplement. The single-walled carbon nanotubes form a network structure, and the sodium supplement is uniformly distributed in the network structure.
13. The use of the flexible self-supporting fiber membrane according to claim 11 or 12 in the preparation of electrodes for sodium-ion batteries, sodium-ion batteries, wearable devices or flexible electronics.
14. A flexible self-supporting sodium-ion battery electrode, characterized in that, Includes the flexible self-supporting fiber membrane as described in claim 11 or 12.
15. A sodium-ion battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, characterized in that, The negative electrode is the flexible self-supporting sodium-ion battery electrode according to claim 14.