Bamboo fiber / nickel-based composite electrode material, preparation method thereof and supercapacitor

Abstract

The invention belongs to the field of energy storage materials, and discloses a preparation method of a bamboo fiber / nickel-based composite electrode material, which comprises the following steps of: adding a bamboo block or a bamboo bundle into an alkaline solution for hydrothermal reaction, and cleaning and drying the bamboo block or the bamboo bundle after the hydrothermal reaction is finished; adding the bamboo blocks or the bamboo bundles into a strong oxidizing solution for hydrothermal reaction, taking out the bamboo blocks or the bamboo bundles after the reaction is completed, and cleaning and drying the bamboo blocks or the bamboo bundles; nickel salt, C6H12N4, water and polyethylene glycol are prepared into a reaction solution, a dried sample is immersed into the reaction solution for a hydrothermal reaction, after the reaction is finished, the dried sample is taken out, washed, aired and subjected to high-temperature heat treatment, and the bamboo fiber / nickel-based composite electrode material is obtained. According to the preparation method, a series of pretreatment and in-situ growth technologies are carried out on bamboo bundles or bamboo blocks, the nickel / nickel oxide nano material with high pseudocapacitance activity is successfully, uniformly and stably loaded on a carbon fiber skeleton derived from bamboo fibers, and the obtained composite electrode material is of an independent fiber structure; in an electrolyte, the material has good ion transmission and electron conduction efficiency and excellent electrochemical performance and cycling stability.

Description

Technical Field

[0001] This invention belongs to the field of energy storage materials, and particularly relates to a method for preparing a bamboo fiber / nickel-based composite electrode material with excellent electrochemical performance. Background Technology

[0002] With rapid economic development, the consumption of traditional energy sources is accelerating, accompanied by severe environmental pollution. Therefore, it is essential to rationally develop and utilize limited resources to achieve sustainable development and reform the energy structure. Supercapacitors have attracted much attention due to their long lifespan and high power density, but their electrochemical performance depends on the electrode materials. In recent years, nickel and its oxides or hydroxides have become a research hotspot in the energy storage field both domestically and internationally. However, the low conductivity and easy aggregation of nickel and its oxides or hydroxides affect the electron migration rate, thereby hindering the normal progress of redox reactions and reducing the electrochemical performance of the electrode materials.

[0003] In order to improve the problems of easy agglomeration and low electrochemical performance of nickel and its oxides or hydroxides as electrode materials, researchers need to treat them during the preparation of electrode materials to improve their electrochemical performance. However, the following problems still exist in the field of using modified nickel and its oxides or hydroxides as electrode materials for supercapacitors: (1) The weak conductivity of nickel and its oxides or hydroxides themselves makes their electron transport rate slow, resulting in a decrease in electrochemical performance; (2) In practical applications, nickel and its oxides or hydroxides and conductive agents are usually mixed with binders to prepare electrode materials. This not only increases the complexity of the preparation process, but the binder will also affect the electrochemical performance of the electrode materials; (3) After agglomeration, nickel and its oxides or hydroxides have a small specific surface area, which reduces the electrochemical performance of the electrode materials. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the deficiencies and defects mentioned in the background art above, and to provide a bamboo fiber / nickel-based composite electrode material, its preparation method and a supercapacitor.

[0005] To solve the above-mentioned technical problems, the technical solution proposed by this invention is as follows: A method for preparing a bamboo fiber / nickel-based composite electrode material includes the following steps: (1) Add bamboo blocks or bamboo bundles to an alkaline solution for hydrothermal reaction. After the hydrothermal reaction is completed, clean and dry the bamboo bundles or bamboo blocks. (2) Add the bamboo blocks or bundles after step (1) to a strong oxidizing solution for hydrothermal reaction. The bamboo blocks or bundles are broken down into single fibers by delignin treatment. After the reaction is completed, they are taken out and cleaned. (3) Add nickel salt and C6H 12N4, water and polyethylene glycol are used to prepare a reaction solution, and the sample obtained in step (2) is immersed in the reaction solution for hydrothermal reaction. Metallic nickel nanoparticles are grown in situ on bamboo fiber through hydrothermal reaction. After the reaction is completed, the sample is taken out, cleaned and dried. (4) The material obtained in step (3) is heat-treated at high temperature and carbonized at high temperature to prepare a bamboo fiber / nickel-based composite electrode material with high electrochemical activity and cycle stability.

[0006] Nickel, being a transition metal, often exhibits multiple valence states. It possesses good redox properties, a stable crystal structure, and abundant redox reaction sites. Therefore, nickel and its oxides or hydroxides are used in clean energy materials such as lithium batteries, gas adsorption, and supercapacitors. Bamboo fiber (also known as bamboo bast fiber or natural bamboo fiber) is the bast fiber obtained from the stem of bamboo. It possesses advantages such as abundant surface functional groups and flexibility. Carbonizing bamboo fiber yields carbon materials that provide a large surface area, high conductivity, strong connectivity, and toughness. These carbon fibers can be directly used as carbon electrode materials, providing convenient channels for ion transport in the electrolyte, thereby improving the electrochemical performance of the electrode material and meeting the requirement for high conductivity. Therefore, this invention loads nickel / nickel oxide onto bamboo fiber using in-situ growth and redox reactions, obtains a bamboo fiber / nickel-based composite material through freeze-drying, and then obtains a bamboo fiber / nickel-based composite electrode material after high-temperature carbonization in a tube furnace. Nickel / nickel oxide provides the composite electrode material with high energy density and chemical stability, while bamboo fiber provides a convenient channel for electron transport and ion conduction during charge and discharge. This invention cleverly combines bamboo fiber carbon material with nickel-based material exhibiting Faraday pseudocapacitive properties, achieving complementary advantages of two energy storage mechanisms. The resulting composite electrode material possesses both high energy density and high power density. Furthermore, its unique flexible integrated structure effectively buffers the stress generated by the volume change of the nickel-based material during charge and discharge, preventing active material shedding and structural collapse. In addition, the in-situ bonding method of this application ensures a strong bonding interface and good electrical contact during cycling, resulting in an electrode exhibiting ultra-long cycle life and excellent capacity retention.

[0007] In the above preparation method, preferably, in step (1), the alkaline solution is a NaOH solution with a mass concentration of 10%~15%.

[0008] In the above preparation method, preferably, in step (1), the hydrothermal reaction temperature is 80~120℃ and the hydrothermal reaction time is 10~20h. If the reaction temperature and reaction time are too low, the bamboo fiber cannot be separated from the bamboo block or bamboo bundle and cannot form a single bamboo fiber; if the reaction temperature and reaction time are too high, the morphological structure of the bamboo fiber will be damaged to a certain extent.

[0009] In the preferred embodiment of the above preparation method, step (1) involves drying the bamboo fiber by freezing it in a vacuum freeze dryer for 8-20 hours and then vacuum drying it at 10-40°C for 12-24 hours, wherein the freezing temperature in the vacuum freeze dryer is -40°C to -60°C. If the vacuum drying time is too short, the moisture in the bamboo fiber cannot be effectively removed, affecting the subsequent in-situ growth of nickel / nickel oxide; if the drying time is too long, the bamboo fiber will exhibit wrinkles, bends, and other phenomena. This invention first uses freeze drying to quickly remove a large amount of water, and then uses vacuum drying to remove a small amount of water that is difficult to remove. The total time consumed is much less than the time required to achieve the same low moisture content by simply relying on freeze drying; at the same time, it avoids the huge energy consumption of maintaining high vacuum and low temperature for a long time in the later stage of freeze drying to remove a small amount of bound water, making the overall energy utilization more reasonable and reducing production costs.

[0010] In the above preparation method, preferably, in step (2), the strong oxidizing solution is a NaClO2 solution with a mass fraction of 2% to 10%. If the mass fraction of the NaClO2 solution is too low, the lignin removal rate in the bamboo fiber is low, and the bamboo fiber toughness is insufficient, causing the carbonized material to break easily. If the mass fraction of the NaClO2 solution is too high, the morphology of the bamboo fiber will be damaged to a certain extent. The hydrothermal reaction temperature is 100℃ to 150℃, and the reaction time is 5 to 20 hours. In the above preparation method, preferably, in step (3), the nickel salt includes at least one of nickel nitrate, nickel chloride, and nickel sulfate; in the reaction solution, for every 20 mL of water added, the molar amount of nickel salt is 1-100 mmol, and the nickel salt reacts with C6H... 12 The molar ratio of N4 is (1.9-2.5):1, and the molar ratio of nickel salt to polyethylene glycol is (0.9-1.2):1.

[0011] In the above preparation method, preferably, in step (3), the ratio of the amount of the reaction solution to the amount of the dried sample (i.e., bamboo fiber) from step (2) is 20 mL: (20-50) mg.

[0012] If the molar mass of the nickel salt is too small, it will be impossible to form a uniformly distributed nickel / nickel oxide on the bamboo fiber, affecting the electrochemical performance of the electrode material; if the molar mass of the nickel salt is too large, the nickel / nickel oxide will form agglomerates on the bamboo fiber, affecting the electrochemical performance of the electrode material.

[0013] In the above preparation method, preferably, in step (3), the hydrothermal reaction temperature is 100~140℃ and the hydrothermal reaction time is 5~20h.

[0014] In the above preparation method, preferably, in step (4), the high-temperature heat treatment is carried out in nitrogen gas, the temperature of the high-temperature heat treatment is 700℃~1000℃, the heating rate is 3~5℃ / min, and the heat treatment time is 4~10h. If the heat treatment temperature is too low, the bamboo fiber will not be completely carbonized, affecting the conductivity of the composite electrode material; if the temperature is too high, the shrinkage rate of the bamboo fiber will be too large, and the composite material will be fragile when preparing the electrode material, affecting the electrochemical performance.

[0015] Based on a general inventive concept, the present invention also provides a bamboo fiber / nickel-based composite electrode material, which is prepared by the above-described preparation method. The bamboo fiber composite electrode material includes bamboo fibers with a rich pore structure and an active substance loaded on the bamboo fibers. The active substance includes nickel and its oxides or hydroxides.

[0016] The bamboo fiber composite electrode material of the present invention first increases the internal pores and fluid permeation paths of bamboo bundles or blocks through an alkaline solution, which facilitates the subsequent penetration of a strong oxidizing solution to remove the lignin components of the bamboo bundles or blocks, thereby obtaining single bamboo fibers. Then, a uniform layer of nickel and its oxide or hydroxide nanoparticles is generated in the pores and on the surface of the bamboo fibers. Finally, the bamboo fiber-based composite electrode material with high capacitance performance and cycle stability is obtained by high-temperature calcination.

[0017] Based on a general inventive concept, the present invention also provides a supercapacitor comprising the above-mentioned bamboo fiber / nickel-based composite electrode material.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) By performing a series of pretreatments and in-situ growth techniques on bamboo bundles or bamboo blocks, the present invention successfully loads nickel / nickel oxide nanomaterials with high pseudocapacitive activity uniformly and stably onto a carbon fiber skeleton derived from bamboo fiber. The resulting composite electrode material is an independent fiber structure, which has good ion transport and electronic conduction efficiency in the electrolyte, and has excellent electrochemical performance and cycle stability.

[0019] (2) The bamboo fiber / nickel-based composite electrode material prepared by the present invention is an independent electrode material. It does not require the addition of non-active substances such as conductive agents and binders. It can be directly assembled into a supercapacitor without being prepared into a slurry. This effectively avoids the problems of increased interface resistance and reduced active sites caused by the use of insulating binders in traditional electrode preparation, and provides a seamless and fast channel for electron transport and ion diffusion.

[0020] (3) The preparation method of the present invention has a clear process flow, is simple and convenient to operate, does not require complex and expensive equipment, and the main raw material bamboo fiber is widely available, renewable and extremely low in cost. Nickel salt is also a common chemical raw material, which greatly reduces the production cost. The entire preparation process is mild and controllable, which meets the requirements of green chemistry and sustainable development strategy.

[0021] (4) The bamboo fiber / nickel-based composite electrode material prepared by the present invention has good mechanical strength and can be used as a self-supporting electrode, and its electrochemical performance remains stable. This characteristic enables it to be directly assembled with gel electrolytes and the like into flexible supercapacitors, which has great application potential in the field of flexible and wearable electronic devices. Attached Figure Description

[0022] 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 some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a SEM image of the bamboo fiber / nickel-based composite electrode material obtained in Example 1 of the present invention.

[0024] Figure 2 This is a SEM image of the bamboo fiber / nickel-based composite electrode material obtained in Example 2 of the present invention.

[0025] Figure 3 This is a physical image of the bamboo fiber / nickel-based composite electrode material obtained in Example 3 of the present invention.

[0026] Figure 4 The graph shows the specific capacitance data of the bamboo fiber / nickel-based composite electrode materials obtained in comparative examples and Examples 1, 2, and 3 of this invention. Detailed Implementation

[0027] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0028] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0029] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0030] The experimental material used in this invention is moso bamboo (Phyllostachys pubescens), purchased from Hunan Taohuajiang Bamboo Technology Co., Ltd., with a size of 20 mm × 20 mm × 5 mm.

[0031] Example 1: A method for preparing a bamboo fiber / nickel-based composite electrode material according to the present invention includes the following steps: (1) After washing the bamboo blocks with deionized water, place them in a reaction vessel containing 15% NaOH solution for hydrothermal reaction. React at 80°C for 20 hours. After the reaction is complete, remove and wash them. (2) Place the sample from step (1) into a vacuum freeze dryer, freeze at -40℃ for 8 hours, and then vacuum dry at 10℃ for 24 hours. After drying, take out the sample for later use. (3) The sample obtained after step (2) is placed in a reaction vessel containing a 2% NaClO2 solution for hydrothermal reaction at a reaction temperature of 140℃ for 10h. After the reaction is completed, the sample is taken out, cleaned, and dried. (4) Add 1 mmol of Ni(NO3)2·6H2O and 0.5 mmol of C6H 12 N4, 20 mL of H2O and 1 mmol of PEG-2000 were used to prepare a reaction solution. 30 mg of the sample obtained in step (3) was immersed in the above solution and placed in a hydrothermal reactor for hydrothermal reaction. The reaction temperature was 120℃ and the reaction time was 5 h. After the reaction was completed, the sample was taken out, cleaned and air-dried. (5) The material obtained in step (4) is placed in a tube furnace and subjected to high-temperature thermal decomposition under nitrogen atmosphere protection. The heating temperature for thermal decomposition is 700℃, the heating rate is 4℃ / min, and the holding time is 4h to obtain bamboo fiber / nickel-based composite electrode material. The SEM image of the bamboo fiber / nickel-based composite electrode material obtained in this embodiment is as follows: Figure 1 As shown. Figure 1 A layer of nanoparticles was loaded onto the bamboo fiber, and the number of nanoparticles was large and the size varied. Among them, the active material particles with larger particle sizes were about 200~500 nm, which proved that nickel and its oxide or hydroxide nanoparticles were successfully loaded into the pores and surface of the bamboo fiber / nickel-based composite electrode material.

[0032] The bamboo fiber / nickel-based composite electrode material used in this example was directly used as the positive electrode, and its capacitance performance was tested in a three-electrode system with a voltage window of 0 to 0.6 V. At a current density of 0.25 A / g, the specific capacitance of the bamboo fiber / nickel-based composite electrode material was 74.18 F / g, and its specific capacitance did not decrease significantly with increasing current density, indicating that the bamboo fiber / nickel-based composite electrode material is relatively stable. After 1000 cycles of testing, the capacitance performance still maintained 98% of the initial specific capacitance.

[0033] Example 2: A method for preparing a bamboo fiber / nickel-based composite electrode material according to the present invention includes the following steps: (1) After washing the bamboo blocks with deionized water, place them in a reaction vessel containing 15% NaOH solution for hydrothermal reaction. React at 100℃ for 16 hours. After the reaction is completed, remove and wash them. (2) Place the sample from step (1) into a vacuum freeze dryer, freeze at -40℃ for 16 hours, and then vacuum dry at 25℃ for 24 hours. After drying, take out the sample for later use. (3) The sample obtained after step (2) is placed in a reaction vessel containing a 5% NaClO2 solution for hydrothermal reaction at a reaction temperature of 120°C for 15 hours. After the reaction is completed, the sample is taken out, cleaned and dried. (4) Add 2 mmol of Ni(NO3)2·6H2O and 1 mmol of C6H 12 N4, 20 mL of H2O and 2 mmol of PEG-2000 were used to prepare a reaction solution. 30 mg of the sample obtained in step (3) was immersed in the above solution and placed in a hydrothermal reactor for hydrothermal reaction. The reaction temperature was 120℃ and the reaction time was 10 h. After the reaction was completed, the sample was taken out, cleaned and air-dried. (5) The material obtained in step (4) is placed in a tube furnace and subjected to high-temperature thermal decomposition under nitrogen atmosphere protection. The heating temperature for thermal decomposition is 800℃, the heating rate is 3℃ / min, and the holding time is 4 h to obtain bamboo fiber / nickel-based composite electrode material.

[0034] The SEM image of the bamboo fiber / nickel-based composite electrode material obtained in this embodiment is as follows: Figure 2 As shown. Compared to Example 1, due to the increased concentration of metallic nickel, the surface of the bamboo fiber / nickel-based composite electrode material is densely lamellar, with nickel particles tightly loaded in the lamellar structure. The nickel particles are very uniformly distributed and relatively large, which may result in outstanding electrochemical performance of the material.

[0035] The bamboo fiber / nickel-based composite electrode material used in this example was directly used as the positive electrode, and its capacitance performance was tested in a three-electrode system with a voltage window of 0 to 0.6 V. At a current density of 0.25 A / g, the specific capacitance of the bamboo fiber / nickel-based composite electrode material was 108.50 F / g, maintaining a high specific capacitance and excellent rate performance. After 1000 cycles, the capacitance performance still retained 95% of the initial specific capacitance.

[0036] Example 3: A method for preparing a bamboo fiber / nickel-based composite electrode material according to the present invention includes the following steps: (1) After washing the bamboo blocks with deionized water, place them in a reaction vessel containing 15% NaOH solution for hydrothermal reaction. React at 120℃ for 10 hours. After the reaction is completed, take them out and wash them. (2) Place the sample from step (1) into a vacuum freeze dryer, freeze at -40℃ for 20h, and then vacuum dry at 40℃ for 20h. After drying, take out the sample for later use. (3) The sample obtained after step (2) is placed in a reaction vessel containing a 10% NaClO2 solution for hydrothermal reaction at a reaction temperature of 100℃ for 20h. After the reaction is completed, the sample is taken out, cleaned and dried. (4) Add 1 mmol of Ni(NO3)2·6H2O and 0.5 mmol of C6H 12 N4, 20 mL of H2O and 1 mmol of PEG-2000 were used to prepare a reaction solution. 30 mg of the sample obtained in step (3) was immersed in the above solution and placed in a hydrothermal reactor for hydrothermal reaction. The reaction temperature was 120℃ and the reaction time was 20 h. After the reaction was completed, the sample was taken out, cleaned and air-dried. (5) The material obtained in step (4) is placed in a tube furnace and subjected to high-temperature thermal decomposition under nitrogen atmosphere protection. The heating temperature for thermal decomposition is 1000℃, the heating rate is 5℃ / min, and the temperature is held for 4 h to obtain bamboo fiber / nickel-based composite electrode material.

[0037] A physical image of the bamboo fiber / nickel-based composite electrode material obtained in this embodiment is shown below. Figure 3 As shown in the figure. Observation revealed that the bamboo fiber / nickel-based composite electrode material retained the straight structure of bamboo fiber even after hydrothermal reaction, freeze-drying, loading with metal active materials, and high-temperature calcination. This demonstrates that the prepared bamboo fiber / nickel-based composite electrode material possesses good flexibility and mechanical strength, and its electrochemical performance remains stable. Capacitance performance was tested in a three-electrode system with a voltage window of 0 to 0.6 V. Under a current density of 0.25 A / g, the specific capacitance of the bamboo fiber / nickel-based composite electrode material was 76.02 F / g, exhibiting superior capacitance performance. After 1000 cycles, the capacitance performance still maintained 98% of the initial specific capacitance.

[0038] Comparative Example 1: The preparation method of the bamboo fiber-based electrode material in this comparative example includes the following steps: (1) After washing the bamboo blocks with deionized water, place them in a reaction vessel containing 15% NaOH solution for hydrothermal reaction. React at 80°C for 20 hours. After the reaction is complete, remove and wash them. (2) Place the sample from step (1) into a vacuum freeze dryer, freeze at -40℃ for 8 hours, and then vacuum dry at 10℃ for 24 hours. After drying, take out the sample for later use. (3) The sample obtained after step (2) is placed in a reaction vessel containing a 2% NaClO2 solution for hydrothermal reaction at a reaction temperature of 140℃ for 10h. After the reaction is completed, the sample is taken out, cleaned and dried. (4) The material obtained in step (3) is placed in a tube furnace and subjected to high-temperature thermal decomposition under nitrogen atmosphere protection. The heating temperature for thermal decomposition is 700℃, the heating rate is 4℃ / min, and the temperature is maintained for 4h to obtain bamboo fiber electrode material.

[0039] The electrochemical performance of the electrode materials of Examples and Comparative Example 1 was tested in a three-electrode system using an electrochemical workstation (CHI660E). The electrode materials were held in place by platinum electrode clips as the working electrode, a graphite rod as the counter electrode, and an Hg / HgO electrode as the reference electrode. The electrolyte was a 6M KOH aqueous solution. Capacitance performance was tested in a three-electrode system with a voltage window of -1 to 0 V. The specific capacitance of the bamboo fiber / nickel-based composite electrode materials obtained in the comparative examples and three examples at a current density of 0.25 A / g is shown in the figure below. Figure 4 As shown, under a current density of 0.25 A / g, the capacitance performance of Comparative Example 1 without nickel loading was poor, with a specific capacitance of only 15.2 F / g. However, after loading nickel onto the bamboo fiber in the three examples, the capacitance performance was significantly improved. The capacitance performances of the three examples were 74.18 F / g, 108.50 F / g, and 76.02 F / g, respectively. It can be seen that the composite electrode materials obtained in the three examples have significantly improved electrochemical performance compared with the pure bamboo fiber electrode material. The electrochemical performance of Example 2 was the best, leading to the conclusion that the electrochemical performance of the bamboo fiber-based composite electrode material improves with increasing nickel salt concentration.

[0040] Comparative Example 2: The preparation method of the bamboo fiber / nickel-based composite electrode material in this comparative example includes the following steps: (1) After washing the bamboo blocks with deionized water, place them in a reaction vessel containing 15% NaOH solution for hydrothermal reaction. React at 80°C for 20 hours. After the reaction is complete, remove and wash them. (2) Place the sample from step (1) into a vacuum freeze dryer, freeze at -40℃ for 8 hours, and then vacuum dry at 10℃ for 24 hours. After drying, take out the sample for later use. (3) The sample obtained after step (2) is placed in a reaction vessel containing a 2% NaClO2 solution for hydrothermal reaction at a reaction temperature of 140℃ for 10h. After the reaction is completed, the sample is taken out, cleaned and dried. (4) 1 mmol of Ni(NO3)2·6H2O and 30 mg of the sample obtained in step (3) were directly mixed and placed in a tube furnace for high-temperature thermal decomposition treatment. The heating temperature for thermal decomposition was 700℃, the heating rate was 4℃ / min, and the temperature was held for 4h to obtain bamboo fiber / nickel-based composite electrode material.

[0041] The capacitance performance of Comparative Example 2 electrode was tested in a three-electrode system with a voltage window of 0 to 0.6 V using an electrochemical workstation (CHI660E). At a current density of 0.25 A / g, the capacitance performance of Comparative Example 2 electrode, which directly mixes bamboo fiber with nickel-based electrode material, was poor, with a specific capacitance of only 36.30 F / g. After 1000 cycles, the capacitance performance still maintained 65% of the initial specific capacitance. Compared to the method of hydrothermally growing nickel-based electrode material onto bamboo fiber, the electrode material directly mixed with bamboo fiber has fewer metal particles, less stable anchoring, and is more prone to detachment at high current densities, resulting in the poorer electrochemical performance of Comparative Example 2 electrode material.

[0042] Comparative Example 3: The preparation method of the wood nanofiber aerogel / nickel-based composite electrode material of this comparative example includes the following steps: (1) Pour the poplar nanofiber (diameter 100nm) dispersion into a glass beaker, dilute it with deionized water to a concentration of 0.5wt%, stir vigorously at high speed for 6 h, and place it in a refrigerator to stand to remove air bubbles.

[0043] (2) Place the sample prepared in step (1) into a vacuum freeze dryer, freeze at -40℃ for 8 hours, and then vacuum dry at 10℃ for 24 hours. After drying, take out the sample for later use. (3) Add 1 mmol of Ni(NO3)2·6H2O and 0.5 mmol of C6H 12 N4, 20 mL of H2O and 1 mmol of PEG-2000 were used to prepare a reaction solution. 30 mg of the sample obtained in step (3) was immersed in the above solution and placed in a hydrothermal reactor for hydrothermal reaction. The reaction temperature was 120℃ and the reaction time was 5 h. After the reaction was completed, the sample was taken out, cleaned and air-dried. (4) The material obtained in step (3) is placed in a tube furnace and subjected to high-temperature thermal decomposition under nitrogen atmosphere protection. The heating temperature for thermal decomposition is 700℃, the heating rate is 4℃ / min, and the temperature is held for 4 h to obtain wood nanofiber aerogel / nickel-based composite electrode material.

[0044] The capacitance performance of the electrode material of Comparative Example 3 was tested in a three-electrode system with a voltage window of 0 to 0.6 V using an electrochemical workstation (CHI660E). At a current density of 0.25 A / g, the specific capacitance of the wood-based nanofiber hydrogel / nickel-based composite electrode material of Comparative Example 3 was 62.20 F / g, indicating poor capacitance performance. Furthermore, compared to the bamboo fiber / nickel-based composite electrode material, the preparation of the wood-based nanofiber hydrogel precursor is more complex. The bamboo fiber / nickel-based composite electrode material uses bamboo fiber directly as the substrate for growing metallic nickel, offering the advantage of a simpler preparation process.

[0045] Comparative Example 4: The preparation method of the bamboo fiber / nickel-based composite electrode material in this comparative example includes the following steps: (1) After washing the bamboo blocks with deionized water, place them in a reaction vessel containing 15% NaOH solution for hydrothermal reaction. React at 80°C for 20 hours. After the reaction is complete, remove and wash them. (2) Place the sample from step (1) into a vacuum freeze dryer, freeze at -40℃ for 8 hours, and then vacuum dry at 10℃ for 24 hours. After drying, take out the sample for later use. (3) Add 1 mmol of Ni(NO3)2·6H2O and 0.5 mmol of C6H 12 N4, 20 mL of H2O and 1 mmol of PEG-2000 were used to prepare a reaction solution. 30 mg of the sample obtained in step (2) was immersed in the above solution and placed in a hydrothermal reactor for hydrothermal reaction. The reaction temperature was 120℃ and the reaction time was 5 h. After the reaction was completed, the sample was taken out, cleaned and air-dried. (4) The material obtained in step (3) is placed in a tube furnace for high-temperature thermal decomposition treatment. The heating temperature for thermal decomposition is 700℃, the heating rate is 4℃ / min, and the temperature is held for 4h to obtain bamboo fiber / nickel-based composite electrode material.

[0046] The capacitance performance of Comparative Example 3 electrode was tested in a three-electrode system with a voltage window of 0 to 0.6 V using an electrochemical workstation (CHI660E). Under a current density of 0.25 A / g, the specific capacitance of the bamboo fiber / nickel-based composite electrode material in Comparative Example 4 was 67.06 F / g. The electrochemical performance of the bamboo fiber / nickel-based composite electrode material in Example 1 remained superior. This indicates that removing lignin from bamboo fiber in a strongly oxidizing solution effectively improves the electrochemical activity of bamboo fiber-based electrode materials. This is because removing lignin increases the specific surface area and porosity of bamboo fiber, exposing more active functional groups, providing more active sites for the growth of metallic nickel, increasing the loading rate of metallic nickel, and thus improving the electrochemical performance of the bamboo fiber / nickel-based composite electrode material.

[0047] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a bamboo fiber / nickel-based composite electrode material, characterized in that, The method comprises the following steps: (1) adding bamboo pieces or bamboo bundles into an alkaline solution for hydrothermal reaction, and cleaning and drying the bamboo pieces or bamboo bundles after the hydrothermal reaction; (2) adding the bamboo pieces or bamboo bundles after step (1) into a strong oxidizing solution for hydrothermal reaction, and cleaning and drying the bamboo pieces or bamboo bundles after the reaction; (3) preparing a reaction solution with nickel salt, C6H 12 N4, water and polyethylene glycol, and immersing the sample obtained in step (2) in the reaction solution for hydrothermal reaction, and taking out, cleaning and air-drying after the reaction. (4) performing high-temperature heat treatment on the material obtained in step (3) to obtain a bamboo fiber / nickel-based composite electrode material.

2. The production method according to claim 1, wherein In step (1), the alkaline solution is a NaOH solution with a mass concentration of 10-15%.

3. The production method according to claim 1, wherein In step (1), the temperature of the hydrothermal reaction is 80-120℃, and the hydrothermal reaction time is 10-20h.

4. The production method according to claim 1, wherein In step (1), the drying comprises first freezing in a vacuum freeze dryer for 8-20h, and then vacuum drying at 10-40℃ for 12-24h, wherein the freezing temperature in the vacuum freeze dryer is -40℃--60℃.

5. The production method according to claim 1, wherein In step (2), the strong oxidizing solution is a NaClO2 solution with a mass fraction of 2-10%, the temperature of the hydrothermal reaction is 100-150℃, and the reaction time is 5-20h.

6. The production method according to claim 1, wherein In step (3), the nickel salt includes at least one of nickel nitrate, nickel chloride, and nickel sulfate; and in the reaction solution, the molar ratio of the nickel salt to C6H 12 The molar ratio of N4 to N is (1.9-2.5):1, and the molar ratio of the nickel salt to polyethylene glycol is (0.9-1.2):

1.

7. The production method according to claim 1, wherein In step (3), the temperature of the hydrothermal reaction is 100-140℃, and the hydrothermal reaction time is 5-20h.

8. The production method according to claim 1, wherein In step (4), the high-temperature heat treatment is performed in nitrogen, the temperature of the high-temperature heat treatment is 700-1000℃, the heating rate is 3-5℃ / min, and the heat treatment time is 4-10h.

9. A bamboo fiber / nickel-based composite electrode material, characterized in that, The bamboo fiber / nickel-based composite electrode material prepared by the preparation method of any one of claims 1-8.

10. An ultracapacitor, characterized by, The bamboo fiber / nickel-based composite electrode material of claim 9.

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