A nanocarbon fiber film electrode for flexible solid-state supercapacitors and a preparation method thereof

Abstract

The application discloses a kind of nanometer carbon fiber membrane electrode for flexible solid-state supercapacitor and preparation method thereof, belong to nanometer material preparation and application technical field.The present application uses kelp processing industry solid waste kelp residue as raw material, through pickling, alkali washing, bleaching treatment extraction kelp residue cellulose, then acryloyl chloride graft modification is obtained acrylated cellulose;Acrylated cellulose is mixed with photosensitive resin, photoinitiator and active diluent to prepare photocuring slurry, after forming by DLP photocuring 3D printing, nanometer carbon fiber membrane is obtained by carbonization process.The nanometer carbon fiber membrane prepared by the present application has a conductivity higher than 230S / m, a breaking strength exceeding 2100MPa, an elongation at break higher than 12%, a specific capacitance reaching 320F / g, and a capacity retention rate of 93% after 10,000 cycles, realizing the high-value conversion of kelp residue and having a broad application prospect in the field of flexible supercapacitors.

Description

Technical Field

[0001] This invention belongs to the field of supercapacitor electrode material technology, and relates to a flexible solid-state supercapacitor nanofiber membrane electrode and its preparation method. Background Technology

[0002] Kelp residue is a major solid waste generated by the kelp processing industry. Its treatment primarily involves landfilling, incineration, or low-value utilization. This not only occupies land resources, but its high salt and organic matter content can also cause environmental problems such as soil salinization and eutrophication. Therefore, developing high-value transformation pathways for kelp residue and realizing its resource utilization has significant environmental and economic benefits. The compositional characteristics of kelp residue provide a material basis for its high-value utilization. Analysis shows that the crude fiber content of kelp residue exceeds 45%, mainly derived from cellulose and alginic acid residue in the kelp cell walls, exhibiting a natural porous fiber network structure. Simultaneously, kelp residue contains abundant metal ions and proteins.

[0003] In recent years, with the rapid development of energy storage technology, the preparation of supercapacitor electrode materials using biomass waste has become a research hotspot. Supercapacitors, as a novel energy storage device between traditional capacitors and secondary batteries, possess advantages such as high power density, long cycle life, and fast charge / discharge speed, and have broad application prospects in portable electronic devices, new energy vehicles, and smart grids. Electrode materials are the core factor determining the performance of supercapacitors, among which carbon materials are the most widely used due to their high specific surface area, good conductivity, and strong chemical stability. Against this backdrop, utilizing the characteristics of kelp residue—rich in crude fiber, protein, and metal ions—to convert it into carbon electrode materials for supercapacitors represents a high-value conversion path that combines environmental and economic benefits.

[0004] However, the application of kelp residue in supercapacitors still faces a series of technical challenges. First, the coarse fibers in kelp residue are large and unevenly distributed, making it difficult to precisely control the pore structure of the carbon material formed after direct carbonization, resulting in insufficient specific surface area and ion transport performance. Second, the metal ions in kelp residue are complex, and various inorganic salts may remain during carbonization; some of these salts may clog pores or affect the cycling stability of the electrode material. Finally, the intrinsic conductivity of carbon materials derived from kelp residue is relatively insufficient, leading to significant limitations in ion transport when preparing high-load electrodes. Furthermore, the energy density of the devices is generally low due to the operating voltage window of aqueous electrolytes, making it difficult to meet the demands of high-energy-density applications. Summary of the Invention

[0005] To address the problems and deficiencies in existing technologies, this invention provides a flexible solid-state supercapacitor nanofiber membrane electrode and its preparation method.

[0006] In a first aspect, the present invention provides a method for preparing a flexible solid-state supercapacitor carbon nanofiber membrane electrode, comprising: using kelp residue as raw material, and obtaining kelp residue cellulose through acid washing, alkali washing and bleaching treatment; obtaining acryloyl cellulose by grafting acryloyl chloride onto acryloyl chloride; mixing acryloyl cellulose, photosensitive resin, photoinitiator and reactive diluent to obtain a slurry, printing it into shape by digital light processing technology, and obtaining a carbon nanofiber membrane after carbonization.

[0007] The photosensitive resin is polydimethylsiloxane-poly(hydroxyethyl acrylate);

[0008] The photoinitiator is 2,4,6-trimethylbenzoyl-diphenylphosphine oxide;

[0009] The active diluent is hydroxyethyl acrylate.

[0010] Furthermore, in the preparation method of the flexible solid-state supercapacitor nanofiber membrane electrode provided by the present invention, the preparation of acryloyl cellulose includes: ultrasonically dispersing kelp residue cellulose in N,N-dimethylacetamide solvent containing lithium chloride, sequentially adding triethylamine and acryloyl chloride, reacting under nitrogen protection, and after the reaction is completed, precipitating the product with anhydrous ethanol; after washing and drying the product, acryloyl cellulose is obtained.

[0011] Furthermore, in the preparation method of the flexible solid-state supercapacitor nanofiber membrane electrode provided by the present invention, the mass ratio of kelp residue cellulose, acryloyl chloride and triethylamine is 1:1.5~3:1.68~3.36;

[0012] The reaction time is 4-6 hours and the temperature is 25-30℃.

[0013] Furthermore, in the preparation method of the flexible solid-state supercapacitor nanofiber membrane electrode provided by the present invention, based on the total mass of solids, the slurry includes: 2wt%~4wt% acryloyl cellulose, 2wt%~3wt% 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, 2wt%~3wt% hydroxyethyl acrylate, and the balance is polydimethylsiloxane-poly(hydroxyethyl acrylate).

[0014] Furthermore, in the preparation method of the flexible solid-state supercapacitor nanofiber membrane electrode provided by the present invention, the digital light processing technology includes: a photocuring wavelength of 405 nm, a layer thickness of 50 μm, an exposure time of 30-40 s for the bottom layer, and an exposure time of 10-20 s for the single layer.

[0015] Furthermore, in the preparation method of the flexible solid-state supercapacitor nanofiber membrane electrode provided by the present invention, the carbonization includes: heating to 200°C at a rate of 2°C / min and holding for 0.5h under an argon atmosphere; heating to 350°C at a rate of 1°C / min and holding for 1h; heating to 600°C at a rate of 2°C / min and holding for 0.5h; heating to 1000°C at a rate of 5°C / min and holding for 2h; and naturally cooling to room temperature.

[0016] Furthermore, in the preparation method of the flexible solid-state supercapacitor nanofiber membrane electrode provided by the present invention, the acid washing solution is a 2% hydrochloric acid solution.

[0017] The alkaline washing solution is a 2% sodium hydroxide solution;

[0018] The bleaching solution is a 5% sodium chlorite solution.

[0019] Secondly, the present invention provides a carbon nanofiber membrane electrode for a flexible solid-state supercapacitor, which is prepared by the above-mentioned method for preparing a carbon nanofiber membrane electrode for a flexible solid-state supercapacitor.

[0020] Thirdly, the present invention provides a flexible solid-state supercapacitor, comprising the above-mentioned flexible solid-state supercapacitor nanofiber membrane electrode, current collector and gel electrolyte;

[0021] The gel electrolyte is disposed between two nanofiber membrane electrodes, and the current collector is disposed on the outside of the two nanofiber membrane electrodes.

[0022] Furthermore, in the flexible solid-state supercapacitor provided by the present invention, the current collector is nickel foam;

[0023] The gel electrolyte is a polyvinyl alcohol-phosphate hydrogel electrolyte.

[0024] Compared with the prior art, the technical solution provided by the present invention has at least the following beneficial effects or advantages:

[0025] (1) This invention introduces acrylyl groups into kelp residue cellulose through acrylation grafting modification, endowing it with photocurable reactivity. The macroscopic structure of the fiber membrane is precisely controlled by DLP photocuring 3D printing technology, combined with a carbonization process, to prepare nanofiber membranes. The nanofiber membranes prepared in Examples 1-3 all exhibit conductivity higher than 230 S / m and tensile strength exceeding 2100 MPa, indicating that the technical solution provided by this invention effectively improves the graphitization degree and conductivity of carbon materials, solving the problems of uncontrollable pore structure and insufficient conductivity in traditional direct carbonization methods.

[0026] (2) In the cellulose extraction step, the present invention uses hydrochloric acid solution to remove calcium salts and minerals, sodium hydroxide solution to remove lignin and soluble impurities, and sodium chlorite to bleach and purify the cellulose. After multiple water washings to neutrality, high-purity kelp residue cellulose is obtained.

[0027] (3) This invention introduces nitrogen-containing functional groups through acrylation grafting, thereby introducing an additional nitrogen source into the carbon framework. The low-temperature pre-carbonization stage (200~350℃) in the carbonization process slows down the rapid escape of nitrogen, which is beneficial to increasing the nitrogen doping content in the carbon material. In Example 1, without the addition of an external nitrogen source, a synergistic effect of high conductivity and good electrochemical performance was achieved, with a specific capacitance of 320 F / g and an energy density of 44.44 Wh / kg.

[0028] (4) This invention modifies cellulose by acrylyl grafting, introducing acryloyl groups that can participate in photocuring onto the cellulose surface, forming a covalent bond interface with the PDMS-PHEA resin matrix during photocuring. Comparative Example 1 uses unmodified kelp residue cellulose, which, due to the lack of covalent bonding, suffers from severe cracking due to mismatched thermal shrinkage during carbonization, resulting in a conductivity of only 49.62 S / m and a tensile strength of only 605.85 MPa. Comparative Example 2 also exhibits microcracks when the grafting rate is insufficient, leading to a deterioration in overall performance.

[0029] (5) The carbon nanofiber membrane prepared in Example 1 at 5 mA / cm 2 At current density, the specific capacitance reaches 320 F / g, and the energy density reaches 44.44 Wh / kg. After 10,000 cycles, the capacity retention rate is 93%. Although Comparative Example 3 has a slightly higher specific capacitance (340 F / g) and energy density (47.22 Wh / kg), its cycle stability is poor (only 76% retention rate after 10,000 cycles), and its mechanical properties cannot meet the requirements of flexible applications. Detailed Implementation

[0030] The technical solution of the present invention will be described below with reference to embodiments. However, the present invention is not limited to the following embodiments. Unless otherwise specified, the experimental methods and detection methods described in each embodiment are conventional methods; unless otherwise specified, the reagents and materials can be purchased commercially.

[0031] The kelp residue used in the following examples is from Qingdao Haixingyuan Biotechnology Co., Ltd.

[0032] Example 1

[0033] This embodiment provides a method for preparing carbon nanofiber membranes.

[0034] The preparation method described in this embodiment is as follows:

[0035] (1) Extraction of cellulose from kelp residue: Kelp residue was washed with deionized water until the effluent was clear. Then, a 2% hydrochloric acid solution was added to the washed kelp residue at a solid-liquid ratio of 1:10, and the mixture was stirred for 1 hour to remove residual calcium salts and minerals. The residue was then filtered and washed with water until neutral. The treated kelp residue was added to a 2% sodium hydroxide (NaOH) solution at a solid-liquid ratio of 1:10, stirred at 60°C for 4 hours, filtered, washed with water until neutral, and the process was repeated once. The filtered residue was collected. The filtered residue was bleached overnight with a 5% sodium chlorite (NaClO2) solution at a solid-liquid ratio of 1:10, filtered, washed, dried at 50°C for 24 hours, and pulverized through a 100-mesh sieve to obtain kelp residue cellulose (KC).

[0036] (2) Preparation of acryloyl cellulose (ACL-KC): 2 g of KC was added to 50 mL of N,N-dimethylacetamide (DMAC) solvent containing 5% lithium chloride (LiCl). The mixture was ultrasonically dispersed at 500 W for 5 min. The dispersed KC was then transferred to a 100 mL three-necked flask, and 6.71 g of triethylamine (TEA) was added. The mixture was placed in a 30 °C constant temperature water bath for reaction, with a stirring speed of 100 r / min. Acryloyl chloride (6 g, ACL) was added in small amounts several times, and the reaction was carried out for 5 h under nitrogen protection. After the reaction was completed, the product was precipitated with anhydrous ethanol, washed three times with anhydrous ethanol and deionized water, and then dried under vacuum at 40 °C and stored in the dark to obtain acryloyl cellulose (ACL-KC).

[0037] (3) Preparation of slurry: Based on the total mass of solids, 4wt% ACL-KC, 91wt% polydimethylsiloxane-poly(hydroxyethyl acrylate) (PDMS-PHEA), 2wt% 2,4,6-trimethylbenzoyl-diphenylphosphine oxide (TPO) and 3wt% hydroxyethyl acrylate (HEMA) were mixed evenly to obtain the slurry.

[0038] (4) Preparation of carbon nanofiber membrane: A 1mm×10mm×30mm fiber membrane was printed using a DLP photopolymerization 3D printer. The photopolymerization wavelength was 405nm, the layer thickness was 50μm, the bottom layer exposure time was 30s, and the single layer exposure time was 10s. After printing, the surface of the fiber membrane was cleaned with anhydrous ethanol to remove residual slurry, and after air drying, it was vacuum dried at 60℃ for 12h. The fiber membrane was transferred to a tube furnace and heated to 200℃ at a rate of 2℃ / min and held for 0.5h under an argon atmosphere; then heated to 350℃ at a rate of 1℃ / min and held for 1h; then heated to 600℃ at a rate of 2℃ / min and held for 0.5h; then heated to 1000℃ at a rate of 5℃ / min and held for 2h; finally, it was naturally cooled to room temperature to obtain the carbon nanofiber membrane.

[0039] Example 2

[0040] The preparation method of the carbon nanofiber membrane in this embodiment is the same as that in Example 1, except that the mass ratio of KC, ACL and TEA is 1:2:2.24 during the preparation of ACL-KC; and the composition of the slurry based on the total solid mass is 3wt% ACL-KC, 91wt% PDMS-PHEA, 3wt% TPO and 3wt% HEMA.

[0041] Example 3

[0042] The preparation method of the carbon nanofiber membrane in this embodiment is the same as that in Example 1, except that the mass ratio of KC, ACL and TEA is 1:1.5:1.68 during the preparation of ACL-KC; and the composition of the slurry based on the total solid mass is 2wt% ACL-KC, 94wt% PDMS-PHEA, 2wt% TPO and 2wt% HEMA.

[0043] Comparative Example 1

[0044] The preparation method of the comparative example carbon nanofiber membrane is the same as that in Example 1, except that, based on the total mass of solids, the composition of the slurry is 4wt% KC, 91wt% PDMS-PHEA, 2wt% TPO and 3wt% HEMA.

[0045] Comparative Example 2

[0046] The preparation method of the comparative carbon nanofiber membrane is the same as that in Example 1, except that the mass ratio of KC, ACL and TEA is 1:1:1.12 during the preparation of ACL-KC.

[0047] Comparative Example 3

[0048] The preparation method of the comparative example carbon nanofiber membrane is the same as that in Example 1, except that, based on the total mass of solids, the composition of the slurry is 5wt% ACL-KC, 90wt% PDMS-PHEA, 2wt% TPO and 3wt% HEMA.

[0049] Comparative Example 4

[0050] The preparation method of the comparative example carbon nanofiber membrane is the same as that in Example 1, except that, based on the total mass of solids, the composition of the slurry is 4wt% ACL-KC, 94wt% PDMS-PHEA and 2wt% TPO.

[0051] The conductivity of the carbon nanofiber membrane was measured using the four-probe method. The breaking strength and elongation at break were measured using a universal testing machine at a tensile rate of 5 mm / min and a clamp spacing of 20 mm. Each sample was tested three times and the average value was taken.

[0052] Table 1. Conductivity, tensile strength and elongation at break of carbon nanofiber membranes.

[0053]

[0054] As shown in Table 1, the carbon nanofiber membranes prepared in Examples 1-3 have intact surfaces without cracks and exhibit excellent comprehensive properties. Their conductivity is all higher than 230 S / m, their tensile strength exceeds 2100 MPa, and their elongation at break is higher than 12%. This indicates that by acrylamide grafting modification of kelp residue cellulose (ACL-KC) and controlling the ACL-KC content within the range of 2-4 wt%, a synergistic effect of high conductivity and high mechanical properties can be achieved in the material.

[0055] Comparative Example 1 used unmodified kelp residue cellulose (KC). Due to the lack of chemical grafting, there was no covalent bond between KC and PDMS-PHEA. The mismatch in thermal shrinkage during carbonization led to severe cracking, and the conductivity and mechanical properties were significantly deteriorated. In Comparative Example 2, the amount of acryloyl chloride added was insufficient, resulting in a low grafting rate and weak interfacial bonding strength. Microcracks appeared after carbonization, and the overall performance was lower than that of Examples 1-3. In Comparative Example 3, the ACL-KC content was increased to 5wt%. Although the conductivity was the highest (247.53 S / m), the excessive KC led to a significant increase in brittleness after carbonization. The breaking strength (1206.65 MPa) and elongation at break (3.78%) both decreased significantly, failing to meet the requirements for flexible applications. Comparative Example 4 did not add the reactive diluent HEMA. The crosslinking density of the system was too high, and the network stiffness was too large after carbonization, resulting in microcracks and reduced flexibility.

[0056] Example 4

[0057] This embodiment provides a method for fabricating a flexible solid-state supercapacitor.

[0058] The preparation method described in this embodiment is as follows:

[0059] (1) Preparation of PVA-H3PO4 gel electrolyte: 1g of polyvinyl alcohol (PVA) was added to 10mL of water and stirred at 90℃ until PVA was completely dissolved. When the dissolved PVA gel was cooled to 60℃, 1g of phosphoric acid (H3PO4) was added and stirred thoroughly to prepare PVA-H3PO4 gel electrolyte.

[0060] (2) Assembly of flexible solid-state supercapacitor: The flexible supercapacitor is assembled with nano-carbon fiber membrane as the electrode, nickel foam as the current collector, and PVA-H3PO4 gel electrolyte in the middle, which also acts as a diaphragm to prevent the two electrodes from contacting each other and causing a short circuit in the flexible supercapacitor. It is connected to the workstation fixture at both ends, and then the flexible supercapacitor is assembled in the order of top to bottom: nickel foam, electrode, gel electrolyte, electrode, nickel foam and outer packaging.

[0061] Performance testing was conducted using an electrochemical workstation. Cyclic voltammetry was performed with a voltage window of 0–1 V and scan rates of 5, 10, 20, 50, 100, and 200 mV / s. Current densities were 1, 2, 5, 10, and 20 mA / cm². 2 A constant current charge-discharge test was conducted with a voltage window of 0-1V. Based on the above test results, the specific capacitance, power density, and energy density were calculated. At 5mA / cm²... 2 The specific capacitance retention rate was calculated after 10,000 constant current charge-discharge cycles at the current density.

[0062] Table 2. Electrochemical performance test results of carbon fiber nanofilms

[0063]

[0064] As shown in Table 2, the carbon nanofiber membrane prepared in Example 1 has a performance of 5 mA / cm². 2 At the specified current density, the specific capacitance is 320 F / g, with a capacity retention of 93% after 10,000 cycles. The power density is 1000 W / kg, and the energy density is 44.44 Wh / kg. Comparative Example 3, while possessing slightly higher specific capacitance (340 F / g) and energy density (47.22 Wh / kg), exhibits poor cycle stability (only 76% retention after 10,000 cycles) and its mechanical properties (elongation at break of only 3.78%) fail to meet the requirements for flexible applications.

[0065] This invention constructs a covalent interface through acrylation grafting modification and controls the ACL-KC content within the range of 2~4wt%, successfully preparing a carbon nanofiber membrane with high conductivity, high mechanical properties, excellent electrochemical performance and good cycling stability.

[0066] The embodiments described above are some, but not all, of the 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 of the invention. All other embodiments obtained by those skilled in the art through related deductions and substitutions based on the inventive concept, without inventive effort, are within the scope of protection of the present invention.

Claims

1. A method for preparing a nanofiber membrane electrode for a flexible solid-state supercapacitor, characterized in that, include: Kelp residue was used as raw material, and cellulose was obtained from kelp residue through acid washing, alkali washing and bleaching. Acrylamide cellulose was obtained by grafting cellulose from kelp residue with acrylamide chloride. Acrylamide cellulose, photosensitive resin, photoinitiator and reactive diluent are mixed to obtain a slurry, which is then printed using digital light processing technology and carbonized to obtain a carbon nanofiber membrane. The photosensitive resin is polydimethylsiloxane-poly(hydroxyethyl acrylate); The photoinitiator is 2,4,6-trimethylbenzoyl-diphenylphosphine oxide; The reactive diluent is hydroxyethyl acrylate; Kelp residue cellulose was ultrasonically dispersed in N,N-dimethylacetamide solvent containing lithium chloride, and triethylamine and acryloyl chloride were added sequentially. The reaction was carried out under nitrogen protection. After the reaction was completed, the product was precipitated with anhydrous ethanol. The product was washed and dried to obtain the acryloyl cellulose.

2. The method for preparing the nanofiber membrane electrode for flexible solid-state supercapacitors according to claim 1, characterized in that, The mass ratio of cellulose, acryloyl chloride, and triethylamine in kelp residue is 1:1.5~3:1.68~3.36; The reaction time is 4-6 hours and the temperature is 25-30℃.

3. The method for preparing a flexible solid-state supercapacitor nanofiber membrane electrode according to claim 1, characterized in that, Based on the total solid mass, the slurry comprises: 2wt%~4wt% acryloyl cellulose, 2wt%~3wt% 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, 2wt%~3wt% hydroxyethyl acrylate, and the balance being polydimethylsiloxane-poly(hydroxyethyl acrylate).

4. The method for preparing the nanofiber membrane electrode for flexible solid-state supercapacitors according to claim 1, characterized in that, The digital light processing technology includes: a photocuring wavelength of 405nm, a layer thickness of 50μm, an exposure time of 30~40s for the bottom layer, and an exposure time of 10~20s for the single layer.

5. The method for preparing a flexible solid-state supercapacitor nanofiber membrane electrode according to claim 1, characterized in that, The carbonization process includes: heating to 200°C at a rate of 2°C / min and holding for 0.5 h under an argon atmosphere; heating to 350°C at a rate of 1°C / min and holding for 1 h; heating to 600°C at a rate of 2°C / min and holding for 0.5 h; heating to 1000°C at a rate of 5°C / min and holding for 2 h; and then naturally cooling to room temperature.

6. The method for preparing a flexible solid-state supercapacitor nanofiber membrane electrode according to claim 1, characterized in that, The pickling solution is a 2% hydrochloric acid solution; The alkaline washing solution is a 2% sodium hydroxide solution; The bleaching solution is a 5% sodium chlorite solution.

7. A nanofiber membrane electrode for a flexible solid-state supercapacitor, characterized in that, It is prepared by the method for preparing the flexible solid-state supercapacitor nanofiber membrane electrode according to any one of claims 1 to 6.

8. A flexible solid-state supercapacitor, characterized in that, Includes the nanofiber membrane electrode, current collector, and gel electrolyte for flexible solid-state supercapacitors as described in claim 7; The gel electrolyte is disposed between two nanofiber membrane electrodes, and the current collector is disposed on the outside of the two nanofiber membrane electrodes.

9. The flexible solid-state supercapacitor according to claim 8, characterized in that, The current collector is nickel foam; The gel electrolyte is a polyvinyl alcohol-phosphate hydrogel electrolyte.

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