A flexible self-supporting electrode and a method of manufacturing the same

Abstract

This invention relates to the field of battery materials technology, and proposes a flexible self-supporting electrode and its preparation method. The preparation method includes the following steps: S1, plant fibers are dispersed in water after TEMPO oxidation treatment to obtain a cellulose dispersion; S2, conductive materials are dispersed in an organic solvent, and then aminoanthraquinone monomers and aldehyde monomers are added. The reaction is carried out under inert gas protection, and the product is washed and dried to obtain a polyimide-anthraquinone composite material; S3, the polyimide-anthraquinone composite material is added to the cellulose dispersion, a crosslinking agent is added, and the mixture is stirred to obtain a homogeneous slurry; S4, the slurry is injected into a mold and directionally freeze-dried to form a porous membrane with vertical channels; S5, the porous membrane is hot-pressed to obtain a flexible self-supporting electrode. The flexible self-supporting electrode of this invention not only utilizes the energy storage function of polyimide-anthraquinone, but also leverages the softness of cellulose as a supporting material, making it suitable as an electrode material for supercapacitors.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, and in particular to a flexible self-supporting electrode and its preparation method. Background Technology

[0002] With the rise of the Internet of Things (IoT), wearable devices, medical and health monitoring, flexible displays, electronic skin, and other fields, there is an urgent need for electronic devices to possess characteristics such as lightweight, flexibility, stretchability, and biocompatibility. However, traditional electronic devices are based on silicon materials, which have high rigidity and brittleness, making them difficult to adapt to application scenarios involving bending, stretching, or dynamic deformation (such as wearable devices and biomedical implants).

[0003] Flexible self-supporting electrodes for lithium-ion batteries are core components of flexible electronic devices, requiring a combination of high conductivity, mechanical flexibility, and structural stability. Traditional flexible electrodes typically use polymer substrates (such as polyethylene terephthalate (PET) or polyimide (PI)) coated with active materials, but this approach suffers from several drawbacks: the substrate material is non-degradable and environmentally unfriendly; the active material has weak adhesion to the substrate and is prone to detachment; and the fabrication process is complex.

[0004] Cellulose is a widely available and biodegradable natural polymer material, among which nanofibers (CNFs) possess high specific surface area, high mechanical strength, and film-forming properties. However, the current application of CNFs as conductive substrates for self-supporting electrodes still faces challenges, requiring solutions to address their poor conductivity. Summary of the Invention

[0005] In view of this, the present invention proposes a flexible self-supporting electrode with high conductivity and its preparation method.

[0006] The technical solution of the present invention is implemented as follows: In a first aspect, the present invention provides a method for preparing a flexible self-supporting electrode, comprising the following steps: S1, Plant fibers are dispersed in water after TEMPO oxidation treatment to obtain a cellulose dispersion; S2, the conductive material is dispersed in an organic solvent, and then aminoanthraquinone monomer and aldehyde monomer are added. The reaction is carried out under the protection of an inert gas (aminoanthraquinone monomer and aldehyde monomer on the surface of the conductive material are polycondensed to generate polyimide anthraquinone, which coats the conductive material to form a composite material with a coating structure). After the reaction is completed, the product is washed and dried to obtain the polyimide anthraquinone composite material. S3, add the polyimide anthraquinone composite material from step S2 to the cellulose dispersion from step S1, add a crosslinking agent, and stir to obtain a homogeneous slurry. S4, the slurry from step S3 is injected into a mold and freeze-dried in a directional manner to form a porous membrane with vertical channels; S5, after hot pressing the porous membrane from step S4, a flexible self-supporting electrode is obtained.

[0007] Specifically, this invention uses cellulose nanofibers as a framework to form a three-dimensional conductive network through directional freeze-drying and hot-pressing processes. The cellulose nanofibers and conductive materials form an interpenetrating network via hydrogen bonds and π-π interactions, eliminating the need for additional binders; freeze-drying creates vertical channels that promote rapid ion transport. The -C=O double bonds and -COH in polyimide anthraquinone provide redox active sites for energy storage, offering a new approach for supercapacitor material development. This invention combines the energy storage characteristics of active sites in polyimide anthraquinone polymers with the self-supporting properties of cellulose, enabling the synthesized composite material to be directly used as an energy storage material for supercapacitors.

[0008] Based on the above technical solutions, preferably, in step S2, the aminoanthraquinone monomer includes one or more of 1,5-diaminoanthraquinone, 2,6-diaminoanthraquinone, and 1,5-diamino-4,8-dihydroxy-9,10-anthradinone; the aldehyde monomer includes one or two of terephthalaldehyde and 2,5-dihydroxyterephthalaldehyde.

[0009] Based on the above technical solutions, preferably, in step S2, the molar ratio of the aminoanthraquinone monomer and the aldehyde monomer is 1:1.05-1.05:1.

[0010] Based on the above technical solutions, preferably, in step S2, the conductive material is at least one of carbon nanotubes and graphene oxide, and the amount of the conductive material is 5%-30% of the total solute mass.

[0011] Based on the above technical solutions, preferably, in step S3, the mass ratio of the composite material, cellulose dispersion and crosslinking agent is 10-30:70-90:0.1-0.3, and the solid content of the cellulose dispersion is 0.5wt%-3wt%.

[0012] Based on the above technical solutions, preferably, in step S3, the crosslinking agent is glutaraldehyde or citric acid.

[0013] Based on the above technical solutions, preferably, in step S5, hot pressing is performed at 80-120℃ and 5-10 MPa, and the film thickness after hot pressing is 50-200 μm.

[0014] Based on the above technical solutions, preferably, in step S1, the TEMPO oxidation treatment method is as follows: plant fibers are placed in a reactor, water, TEMPO, NaBr and NaClO are added, the mixture is stirred evenly, and the pH value is adjusted to 10.0-10.5 for reaction. After the reaction is completed, ethanol is added, followed by centrifugation and washing.

[0015] Based on the above technical solutions, preferably, in step S1, the mass molar ratio of plant fiber, water, TEMPO, NaBr and NaClO is 1-2g:100-200g:0.1-0.2mmol:1-2mmol:5-10mmol.

[0016] Secondly, the present invention provides a flexible self-supporting electrode, which is prepared by the above-described preparation method.

[0017] The flexible self-supporting electrode and its preparation method of the present invention have the following advantages over the prior art: This invention provides a simple and environmentally friendly method for preparing flexible self-supporting electrodes. Using cellulose nanofibers as a framework, conductive materials (such as carbon nanotubes and graphene oxide) and the active substance polyimide anthraquinone are combined in situ to form a three-dimensional porous structure. Among the active substances, polyimide anthraquinone can achieve energy storage through redox reactions with cations in the electrolyte due to the -C-OH and C=O bonds on its polymer molecular chain, making it an excellent electrode material for supercapacitors. Combining cellulose nanofibers with conductive materials and polyimide anthraquinone yields a self-supporting composite material. This material not only utilizes the energy storage function of polyimide anthraquinone but also leverages the flexibility of cellulose as a supporting material. This composite material can be directly used as an electrode material for supercapacitors without the need for an additional substrate or current collector. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention 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 of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a diagram illustrating the energy storage mechanism of the polyimide anthraquinone (AQP) of this invention. Detailed Implementation

[0020] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0021] The TEMPO used in this invention is 2,2,6,6-tetramethylpiperidine oxide, CAS number 2564-83-2. The graphene oxide is sheet-like graphene prepared from artificial graphite using the Hummers method, with a sheet diameter of 5-10 μm. The carbon nanotubes are purchased from Shenzhen Jinbaina Nanotechnology Co., Ltd., and are multi-walled carbon nanotubes with a diameter of 5-12 nm.

[0022] Example 1 This embodiment provides a method for fabricating a flexible self-supporting electrode, including the following steps: S1. Take 10g of plant fiber (wood pulp) into a beaker, then add 1L of deionized water, 1mmol TEMPO, 10mmol NaBr, and 50mmol NaClO. Place the beaker on a magnetic stirrer and start stirring. Insert a pH meter into the reactor to detect the pH value of the reaction liquid. Slowly add NaOH to maintain the pH value at 10.2. After reacting for 3 hours, add ethanol, followed by centrifugation and washing. Then disperse the treated cellulose in water to form a nanocellulose (CNF) dispersion with a solid content of 3wt%.

[0023] S2, take 0.2 mol of 1,5-diamino-4,8-dihydroxy-9,10-anthraquinone (54 g) and 0.2 mol of p-2,5-dihydroxy-terephthalaldehyde (33.23 g), and weigh 9.7 g of graphene oxide (10% of the total mass of aminoanthraquinone monomer, aldehyde monomer, and graphene oxide). Disperse the graphene oxide in 400 ml of DMSO solvent, and then dissolve the monomers (aminoanthraquinone monomer and aldehyde monomer) in the graphene oxide dispersion. Under a protective atmosphere (Ar), stir the reaction at 180 °C for 24 h. After the reaction is complete, wash away the residual monomers with N,N-dimethylacetamide, then wash repeatedly with ethanol, and then dry in an oven at 120 °C for 12 h to obtain the composite material Gr / AQP-1.

[0024] S3, the composite material Gr / AQP-1 prepared in step S2 and citric acid are added to the CNF dispersion in step S1. The mass ratio of Gr / AQP-1:CNF dispersion:citric acid is 20:79.8:0.2. The mixture is ultrasonically stirred for 2 hours. The slurry is then injected into a polytetrafluoroethylene mold, frozen in liquid nitrogen, and freeze-dried for 36 hours. It is then hot-pressed at 100℃ and 8 MPa for 5 minutes to obtain a flexible electrode with a thickness of 120 μm. The electrode is symmetrically placed on a flexible conductive substrate (such as an Au sheet), with a diaphragm placed in the middle. 1M H2SO4 is added as the electrolyte, and the substrate is then sealed with a PET flexible film. After the electrode is fabricated into a supercapacitor, a charge-discharge current of 0.5 A / g is used to perform cyclic testing on an electrochemical workstation to obtain the capacitance value of the composite material.

[0025] Example 2 The difference between Example 2 and Example 1 is that the solid content of CNF dispersion in step S1 is 1.5 wt%, and the rest is the same as in Example 1.

[0026] Example 3 The difference between Example 3 and Example 1 is that the amount of graphene oxide used is 30% of the total solute mass, resulting in the composite material Gr / AQP-2. The rest of the contents are the same as in Example 1.

[0027] Example 4 The difference between Example 4 and Example 3 is that in step S3, the ratio of Gr / AQP-2: CNF dispersion: citric acid is 10:89.9:0.1, and the rest is the same as in Example 3.

[0028] Example 5 The difference between Example 5 and Example 3 is that carbon nanotubes are used to replace graphene oxide to obtain the composite material CNT / AQP-1. The rest of the contents are the same as in Example 3.

[0029] Example 6 The difference between Example 6 and Example 3 is that 1,5-diamino-4,8-dihydroxy-9,10-anthraquinone is replaced with 2,6-diaminoanthraquinone to obtain the composite material Gr / AQP-3. The rest of the contents are the same as in Example 3.

[0030] Example 7 This embodiment provides a method for fabricating a flexible self-supporting electrode, including the following steps: S1. Take 15g of plant fiber (wood pulp) into a beaker, then add 1.5L of deionized water, 1.5mmol TEMPO, 15mmol NaBr, and 80mmol NaClO. Place the beaker on a magnetic stirrer and start stirring. Insert a pH meter into the reactor to detect the pH value of the reaction liquid. Slowly add NaOH dropwise to maintain the pH value at 10.0. After reacting for 3 hours, add ethanol, followed by centrifugation and washing. Then disperse the treated cellulose in water to form a nanocellulose (CNF) dispersion with a solid content of 0.5wt%.

[0031] S2, take 0.2 mol of 1,5-diaminoanthraquinone (47.65 g) and 0.2 mol of terephthalaldehyde (26.83 g), and weigh 3.92 g of graphene oxide (5% of the total mass of aminoanthraquinone monomer, aldehyde monomer, and graphene oxide). Disperse the graphene oxide in 400 ml of DMSO solvent, and then dissolve the monomers (aminoanthraquinone monomer and aldehyde monomer) in the graphene oxide dispersion. Under a protective atmosphere (Ar), stir the reaction at 180 °C for 24 h. After the reaction is complete, wash away the residual monomers with N,N-dimethylacetamide, then wash repeatedly with ethanol, and then dry in an oven at 120 °C for 12 h to obtain the composite material Gr / AQP-4.

[0032] S3, the composite material Gr / AQP-4 prepared in step S2 and glutaraldehyde are added to the CNF dispersion prepared in step S1. The mass ratio of Gr / AQP-4:CNF dispersion:glutaraldehyde is 30:69.7:0.3. The mixture is ultrasonically stirred for 2 hours. The slurry is injected into a polytetrafluoroethylene mold, frozen with liquid nitrogen, and then freeze-dried for 36 hours. Then, it is hot-pressed at 80°C and 10 MPa for 5 minutes to obtain a flexible electrode with a thickness of 50 μm. The electrode is symmetrically placed on a flexible conductive substrate (such as an Au sheet), with a diaphragm placed in the middle. 1M H2SO4 is added as an electrolyte, and then sealed with a PET flexible film. After the electrode is made into a supercapacitor, a charge-discharge current of 0.5 A / g is used to perform a cyclic test on an electrochemical workstation to obtain the capacitance value of the composite material.

[0033] Example 8 This embodiment provides a method for fabricating a flexible self-supporting electrode, including the following steps: S1. Take 20g of plant fiber (wood pulp) into a beaker, then add 2L of deionized water, 2mmol / L TEMPO, 20mmol / L NaBr, and 100mmol / L NaClO. Place the beaker on a magnetic stirrer and start stirring. Insert a pH meter into the reactor to detect the pH value of the reaction liquid. Slowly add NaOH to maintain the pH value at 10.5. After reacting for 3 hours, add ethanol, followed by centrifugation and washing. Then disperse the treated cellulose in water to form a nanocellulose (CNF) dispersion with a solid content of 2wt%.

[0034] S2, take 0.2 mol of 2,6-diaminoanthraquinone (47.65 g) and 0.2 mol of p-2,5-dihydroxyterephthalaldehyde (33.23 g), and weigh 20.22 g of graphene oxide (20% of the total mass of aminoanthraquinone monomer, aldehyde monomer, and graphene oxide). Disperse the graphene oxide in 400 ml of DMSO solvent, and then dissolve the monomers (aminoanthraquinone monomer and aldehyde monomer) in the graphene oxide dispersion. Under a protective atmosphere (Ar), stir the reaction at 180 °C for 24 h. After the reaction is complete, wash away the residual monomers with N,N-dimethylacetamide, then wash repeatedly with ethanol, and then dry in an oven at 120 °C for 12 h to obtain the composite material Gr / AQP-5.

[0035] S3, the composite material Gr / AQP-5 prepared in step S2 and citric acid are added to the CNF dispersion prepared in step S1. The mass ratio of Gr / AQP-5:CNF dispersion:citric acid is 25:74.8:0.2. The mixture is ultrasonically stirred for 2 hours. The slurry is then injected into a polytetrafluoroethylene mold, frozen in liquid nitrogen, and freeze-dried for 36 hours. It is then hot-pressed at 120°C and 5 MPa for 5 minutes to obtain a flexible electrode with a thickness of 200 μm. The electrode is symmetrically placed on a flexible conductive substrate (such as an Au sheet), with a diaphragm placed in the middle. 1M H2SO4 is added as the electrolyte, and the electrode is then sealed with a PET flexible film. After the electrode is fabricated into a supercapacitor, a charge-discharge current of 0.5 A / g is used to perform cyclic testing on an electrochemical workstation to obtain the capacitance value of the composite material.

[0036] Comparative Example 1 Graphene composite material Gr / AQP-1 was prepared according to the method in Example 1. 9g of Gr / AQP-1 was added to a 60wt% PTFE solution, with a Gr / AQP-1 to PTFE ratio of 9:1. After the slurry was stirred evenly, it was rolled into an electrode sheet with a thickness of 120μm and then dried at 120℃ to obtain the electrode. The electrode was symmetrically placed on a flexible conductive substrate (such as an Au sheet), with a separator placed in the middle. 1M H2SO4 was added as the electrolyte, and the electrode was then sealed with a PET flexible film. After the electrode was fabricated into a supercapacitor, a charge-discharge current of 0.5A / g was used to perform cyclic testing on an electrochemical workstation to obtain the capacitance value of the composite material.

[0037] Comparative Example 2 9g of polyimide, 12g of polyaniline, and 9g of carbon nanotubes were dissolved in NMP to form a polymer solution. Then, under the influence of a high-voltage electrostatic field in an electrospinning machine, the droplets were charged and overcame surface tension to form a high-speed jet. During the jetting process, the solvent evaporated and was ejected into fibers. These fibers were deposited on a metal plate collector to form a 120μm nonwoven flexible fiber membrane. The fiber membrane electrodes were assembled into a supercapacitor, and cyclic testing was conducted on an electrochemical workstation using a charge-discharge current of 0.5A / g.

[0038] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that the amount of conductive material graphene oxide used is 2% of the total solute mass, and the rest is the same as in Example 1.

[0039] Comparative Example 4 The difference between Comparative Example 4 and Example 1 is that the amount of conductive material graphene oxide used is 35% of the total solute mass, and the rest is the same as in Example 1.

[0040] Comparative Example 5 The difference between Comparative Example 5 and Example 1 is that the mass ratio of the composite material, cellulose dispersion and crosslinking agent is 35:64.8:0.2, and the rest is the same as in Example 1.

[0041] Comparative Example 6 The difference between Comparative Example 6 and Example 1 is that the mass ratio of the composite material, cellulose dispersion and crosslinking agent is 5:94.8:0.2, and the rest is the same as in Example 1.

[0042] Table 1 Results of Bending Cycle Test

[0043] Specific capacitance (F / g) test: Electrochemical tests were performed using a Chenhua 660E electrochemical workstation. The material was charged and discharged under a current density of 0.5 A / g in a flat state. The measured capacitance is the specific capacitance of the material.

[0044] Capacitance retention rate (%) test after 1000 cycles: The charge and discharge capacitance of the material is repeatedly tested by bending the flexible device to a radius of curvature of 10 mm until 1000 cycles are completed, and the cycle retention rate is calculated.

[0045] As can be seen from the data in Table 1, the flexible self-supporting electrode prepared in the embodiments of the present invention exhibits significant advantages in both specific capacitance and cycle stability. The specific capacitance range of Examples 1–8 is 205-336 F / g, and the capacitance retention rate after 1000 cycles is all above 80%, with most maintaining 93%-95%. In contrast, although Comparative Example 3 has a specific capacitance of 340 F / g, its capacitance retention rate is only 70%. Comparative Examples 1 and 5 have higher specific capacitances (315 F / g and 325 F / g, respectively), but their retention rates after cycling are only 75% and 88%, respectively, all lower than most of the embodiments. This indicates that the present invention, through in-situ composite of a cellulose skeleton and polyimide anthraquinone / conductive material, significantly improves the mechanical flexibility and structural stability of the electrode while ensuring a high specific capacitance.

[0046] When the amount of graphene oxide is 5%-30% of the total solute mass, the electrode exhibits both high specific capacitance and high cycle retention. However, Comparative Example 3 (2%), due to its incomplete conductive network, while showing a slightly higher specific capacitance, suffers from structural collapse and a sharp drop in cycle stability. Comparative Example 4 (35%), on the other hand, experiences a decrease in specific capacitance due to excessive agglomeration. When the ratio of composite material to cellulose is within the range of 10-30:70-90, the cellulose skeleton effectively supports the conductive network, preventing the active material from detaching. However, Comparative Examples 5 (35:64.8) and 6 (5:94.8), due to imbalanced ratios, exhibit insufficient flexibility or weak mechanical support, resulting in a decrease in both specific capacitance and cycle stability. Furthermore, replacing graphene oxide with carbon nanotubes (Example 5) or replacing the aminoanthraquinone monomer (Example 6) still maintains a 94%-95% capacitance retention rate, demonstrating the universality and stability of the formulation of this invention.

[0047] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for fabricating a flexible self-supporting electrode, characterized in that, Includes the following steps: S1, Plant fibers are dispersed in water after TEMPO oxidation treatment to obtain a cellulose dispersion; S2, the conductive material is dispersed in an organic solvent, and then aminoanthraquinone monomer and aldehyde monomer are added. The reaction is carried out under inert gas protection. After the reaction is completed, the product is washed and dried to obtain polyimide anthraquinone composite material. S3, add the polyimide anthraquinone composite material from step S2 to the cellulose dispersion from step S1, add a crosslinking agent, and stir to obtain a homogeneous slurry. S4, the slurry from step S3 is injected into a mold and freeze-dried in a directional manner to form a porous membrane with vertical channels; S5, after hot pressing the porous membrane from step S4, a flexible self-supporting electrode is obtained.

2. The method for preparing a flexible self-supporting electrode as described in claim 1, characterized in that, In step S2, the aminoanthraquinone monomer includes one or more of 1,5-diaminoanthraquinone, 2,6-diaminoanthraquinone, and 1,5-diamino-4,8-dihydroxy-9,10-anthradinone; the aldehyde monomer includes one or both of terephthalaldehyde and 2,5-dihydroxyterephthalaldehyde.

3. The method for preparing a flexible self-supporting electrode as described in claim 2, characterized in that, In step S2, the molar ratio of the aminoanthraquinone monomer to the aldehyde monomer is 1:1.05-1.05:

1.

4. The method for preparing a flexible self-supporting electrode as described in claim 3, characterized in that, In step S2, the conductive material is at least one of carbon nanotubes and graphene oxide, and the amount of the conductive material is 5%-30% of the total solute mass.

5. The method for preparing a flexible self-supporting electrode as described in claim 1, characterized in that, In step S3, the mass ratio of the composite material, cellulose dispersion and crosslinking agent is 10-30:70-90:0.1-0.3, and the solid content of the cellulose dispersion is 0.5wt%-3wt%.

6. The method for preparing a flexible self-supporting electrode as described in claim 5, characterized in that, In step S3, the crosslinking agent is glutaraldehyde or citric acid.

7. The method for preparing a flexible self-supporting electrode as described in claim 1, characterized in that, In step S5, hot pressing is performed at 80-120℃ and 5-10 MPa, resulting in a film thickness of 50-200 μm after hot pressing.

8. The method for preparing a flexible self-supporting electrode as described in claim 1, characterized in that, In step S1, the TEMPO oxidation treatment method is as follows: plant fibers are placed in a reactor, water, TEMPO, NaBr and NaClO are added, the mixture is stirred evenly, and the pH value is adjusted to 10.0-10.5 for reaction. After the reaction is completed, ethanol is added, followed by centrifugation and washing.

9. The method for preparing a flexible self-supporting electrode as described in claim 8, characterized in that, In step S1, the molar ratio of plant fiber, water, TEMPO, NaBr and NaClO is 1-2g: 100-200g: 0.1-0.2 mmol: 1-2 mmol: 5-10 mmol.

10. A flexible self-supporting electrode, characterized in that, It is prepared by the preparation method according to any one of claims 1-9.

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