Preparation method and application of porous carbon and flower-shaped NiS composite electrode material

Abstract

The invention is applicable to the technical field of new energy materials and devices, and provides a preparation method and application of a porous carbon and flower-shaped NiS composite electrode material, and the method prepares a high-performance BIC and NiS composite electrode material through in-situ deposition of flower-shaped NiS on the surface of a biomass derived carbon material with a hierarchical pore structure. And multi-scale structure regulation and interface optimization of the material are realized. The introduced carbon material with a hierarchical pore structure can effectively inhibit agglomeration of flower-like NiS nanocrystals, so that the composite material has a relatively high specific surface area and a rich pore structure, more electrochemical active sites are provided for oxidation-reduction reaction, and the theoretical specific capacity and rate capability of the composite material are improved. The BIC coated NiS-1 electrode shows high specific capacitance and long cycle stability, and a feasible method is provided for efficient integration of an electroactive material and a carbon material.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of new energy materials and devices, and particularly relates to a preparation method and application of a porous carbon@flower-like NiS composite electrode material. BACKGROUND

[0002] As a kind of efficient electrochemical energy storage device, supercapacitors have important application potential in the fields of renewable energy smoothing output, power grid peak shaving and electric vehicle power assistance, due to their high power density, fast charge and discharge capability and excellent cycle stability. Among various electrode materials, biomass-derived carbon materials are considered as one of the ideal choices for constructing high-performance supercapacitor electrodes, due to their wide sources, low cost, adjustable structure and environmental friendliness.

[0003] At present, a variety of biomass precursors (such as wood, fruit shells, crop straw, etc.) have been used to prepare porous carbon materials. By reasonably designing the carbonization process, selecting the type of activator and optimizing the process parameters, the specific surface area, pore structure and surface chemical properties of the derived carbon materials can be effectively controlled. Generally speaking, a higher pyrolysis temperature helps to form a graphitized structure, which improves the electrical conductivity of the material; and chemical activation (such as using KOH, NaOH and other alkaline activators) can significantly increase the proportion of micropores and mesopores, and expand the effective specific surface area, thereby providing more active sites for charge storage. In addition, the electronic structure and surface wettability of carbon materials can be further adjusted by heteroatom doping (such as nitrogen, oxygen, etc.), which enhances their electrochemical performance.

[0004] However, pure biomass carbon materials still face certain challenges in practical applications, mainly due to their low bulk density and limited specific capacity, which restricts the further improvement of the energy density of the device. To overcome the above limitations, researchers propose a strategy of compounding biomass carbon with transition metal compounds (such as oxides, sulfides, etc.). Such composite materials not only can combine the double-layer capacitance and pseudo-capacitance two energy storage mechanisms to achieve capacity improvement, but also can optimize the overall electrochemical behavior through the synergistic effect between them. Among them, the carbon skeleton as a conductive substrate not only provides support for the nucleation and growth of metal compounds, promotes the rapid transmission of electric charge, but also effectively alleviates the volume change of the metal compounds during the cycle process, maintaining the structural integrity of the electrode. The metal compounds contribute considerable additional capacitance through highly reversible Faraday reactions, significantly prolonging the discharge time and improving the energy output of the device.

[0005] Therefore, reasonably designing and preparing transition metal-based biomass carbon composite materials with controllable structure and good interface coupling has become an important way to promote the development of high-performance supercapacitors. SUMMARY

[0006] The embodiment of the application aims to provide a preparation method and application of a porous carbon@flower-like NiS composite electrode material, and aims to solve the problems in the background art.

[0007] The embodiment of the application is implemented as follows: a preparation method of a porous carbon@flower-like NiS composite electrode material, comprising the following steps: Step 1: after the water spinach stems are pretreated, pre-carbonization is performed under a nitrogen atmosphere, and then KOH and NaOH mixed alkali are used for activation at 600 DEG C at a mass ratio of 1:5; after acid washing and drying, a porous biomass carbon (BIC) is obtained; Step 2: by one-step hydrothermal method, Ni (NO3) 2·6H2O, thiourea and BIC are reacted at 180 DEG C for 12 hours; after centrifugation, washing and drying, the BIC@NiS composite material is finally prepared.

[0008] Further technical solutions, in the step 1, the pretreatment of the water spinach stems comprises: The water spinach stems are first cut into pieces, and the surface impurities and insoluble substances are removed with ultrapure water and anhydrous ethanol solution, and then they are placed in an electric heating air drying oven at 60 DEG C for drying for 24 hours for standby.

[0009] Further technical solutions, in the step 1, the pre-carbonization comprises the following specific steps: After the drying of the water spinach stems is completed, the water spinach stems are pre-carbonized at 800 DEG C under N2 atmosphere at a speed of 5 DEG C / minute, and the temperature is kept for 2 hours; the cooling speed is also kept at 5 DEG C / minute; after cooling, the product (IC) is ground into powder, washed with ultrapure water, and dried at 60 DEG C for 24 hours.

[0010] Further technical solutions, in the step 1, the activation operation comprises the following specific steps: In ultrapure water, NaOH and KOH are uniformly mixed, and then the product and NaOH / KOH are mixed at a mass ratio of 1:5, and then placed in an electric heating air oven for drying at 80 DEG C for 24 hours; then the mixture is placed in a crucible and heated to 600 DEG C at a speed of 5 DEG C / minute for secondary carbonization, and the temperature is kept for 2 hours, and then cooled to room temperature at a speed of 5 DEG C / minute.

[0011] Further technical solutions, in the step 1, the black solid after activation is collected, ground into powder, washed with 1M HCl and ultrapure water until neutral, and then dried at 60 DEG C overnight to obtain the final sample BIC.

[0012] Further technical solutions, the step 2 comprises the following specific steps: Step 2.1: 0.6 mmol of Ni(NO3)2·6H2O was dissolved in a DMF mixed solvent, 2.4 mmol of thiourea was added, and the mixture was stirred and mixed; Step 2.2: BIC was added, magnetically stirred and ultrasonicated; the mixture was transferred to a 50 ml PPL high-pressure reaction kettle, and reacted in an electric heating drying oven; after cooling to room temperature, the precipitate was centrifuged with ultrapure water and anhydrous ethanol for several times, and impurities were removed; Step 2.3: The precipitate was placed in a vacuum drying oven for drying, and the BIC@NiS composite material was obtained.

[0013] Further technical solutions, in the step 2.1, the volume ratio V DMF :V 水 =1:2 in the DMF mixed solvent.

[0014] Further technical solutions, in the step 2.1, the stirring and mixing time is 10 minutes; Further technical solutions, in the step 2.2, the ultrasonic time is 10 minutes; Further technical solutions, in the step 2.2, the reaction time in the electric heating drying oven is 12 hours, and the reaction temperature is 180℃.

[0015] Further technical solutions, in the step 2.3, the drying time in the vacuum oven is 12 hours, and the drying temperature is 80℃.

[0016] Further technical solutions, in the step 2.2, the addition amount (mass fraction) of BIC is 1.0 wt%, 3.0 wt%, 4.0 wt% and 5.0 wt% respectively, and the products are marked as BIC@NiS-1, BIC@NiS-3, BIC@NiS-4 and BIC@NiS-5 respectively, and the best ratio is 1.0 wt%, that is, the product BIC@NiS-1.

[0017] Another purpose of the embodiment of the application is the application of the porous carbon@flower-like NiS composite electrode material, the BIC@NiS composite material prepared based on the above method is used as an electrode material in a supercapacitor.

[0018] The application embodiment provides a preparation method and application of a porous carbon@flower-like NiS composite electrode material, the method is used for preparing a BIC@NiS composite electrode material with high performance by in-situ depositing flower-like NiS on the surface of a biomass-derived carbon material with a multi-level pore structure, and multi-scale structure regulation and interface optimization of the material are realized. The carbon material with the multi-level pore structure introduced can effectively inhibit agglomeration of flower-like NiS nanocrystals, so that the composite material has a higher specific surface area and rich pore structure, more electrochemical active sites are provided for redox reactions, and the theoretical specific capacity and rate performance of the composite material are improved. The BIC@NiS-1 electrode exhibits high specific capacitance (1157.76 F / g at 1 A / g) and long cycle stability (94.32% retention rate after 10000 cycles). The BIC@NiS-1 / / BIC assembled can realize an energy density of 85.12 Wh / kg at 1494 W / kg, and the stability is 73.88% after 10000 cycles. In addition, the porous structure of the BIC helps to relieve the large mechanical stress caused by the volume change in the NiS charging / discharging process, ensures the good cycle stability of the electrode material, and provides a feasible method for efficient integration of electroactive materials and carbon materials. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 A flowchart of the preparation method of the porous carbon@flower-like NiS composite electrode material provided by the application embodiment is shown in the figure; Figure 2 Scanning electron microscope images of the BIC@NiS composite material (wherein a-b is IA, c-d is IC, e-f is BIC, g-h is NiS, a1-a2 is BIC@NiS-1, b1-b2 is BIC@NiS-3, c1-c2 is BIC@NiS-4, d1-d2 is BIC@NiS-5, and i is an element distribution map of BIC@NiS-1); Figure 3 Chemical composition analysis maps of the BIC@NiS composite material (wherein a is an XRD map, and b is a Raman map) and a microstructure TEM map of BIC@NiS-1 (wherein c-d is BIC, e-f is NiS, and g is BIC@NiS-1); Figure 4 XPS maps of chemical element composition and structure analysis of the BIC@NiS-1 composite material (wherein a is a fine spectrum map of C 1s, b is a fine spectrum map of O 1s, c is a fine spectrum map of Ni 2p, and d is a fine spectrum map of S 2p); Figure 5 Specific surface area and pore size analysis maps of the BIC@NiS-1 composite material (wherein a is a N2 adsorption-desorption isotherm, and b is a pore size distribution curve); Figure 6 Electrochemical performance of NiS and BIC@NiS electrodes with different carbon doping amounts (where a is the CV curve at 5 mV / s, b is the GCD curve at 1 A / g) and electrochemical performance of BIC@NiS-1 (c is the CV curve at different scan rates, d is the GCD curve at different current densities, e is the comparison of rate performance, f is the comparison of electrochemical impedance, g is the specific capacitance retention and coulombic efficiency after 10,000 cycles at a current density of 10 A / g, and h is the pseudocapacitance contribution rate). Figure 7 Electrochemical performance tests were conducted on BIC@NiS-1 / / BIC asymmetric supercapacitors assembled using BIC@NiS-1 and BIC as positive and negative electrode materials, respectively (where a is the CV curve at different scan rates, b is the GCD curve at different current densities, c is the rate performance, d is the electrochemical impedance, e is the 10,000-cycle test at 5 A / g, and f is the power density versus energy density graph). Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0021] The specific implementation of the present invention will be described in detail below with reference to specific embodiments.

[0022] like Figure 1 As shown, an embodiment of the present invention provides a method for preparing a porous carbon@flower-like NiS composite electrode material, comprising the following steps: Step 1: After pre-treating the water spinach stems, pre-carbonize them under a nitrogen atmosphere, then activate them at 600℃ using a mixed alkali of KOH and NaOH at a mass ratio of 1:5. After acid washing and drying, BIC is obtained. Step 2: Ni(NO3)2·6H2O, thiourea and BIC were reacted at 180℃ for 12 hours by a one-step hydrothermal method. After centrifugation, washing and drying, the BIC@NiS composite material was finally obtained.

[0023] In a preferred embodiment of the present invention, the pretreatment of water spinach stems in step 1 includes: First, cut the water spinach stems into small pieces, and remove surface impurities and insoluble substances with ultrapure water and anhydrous ethanol solution. Then, place them in an electric heating drying oven at 60℃ and dry for 24 hours for later use.

[0024] In a preferred embodiment of the present invention, step 1, pre-carbonization includes the following specific steps: After the drying is completed, the hollow stem is pre-carbonized at 800℃ at a speed of 5℃ / min under N2 atmosphere, and the temperature is kept for 2 hours, and the cooling speed is also kept at 5℃ / min; after cooling, the IC is ground into powder, and then washed with ultrapure water, and dried at 60℃ for 24 hours.

[0025] As a preferred embodiment of the present application, in the step 1, the activation operation comprises the following specific steps: In ultrapure water, NaOH and KOH are uniformly mixed, and then the product is mixed with NaOH / KOH at a mass ratio of 1:5, and then placed in an electric heating air oven for drying at 80℃ for 24 hours; then the mixture is placed in a crucible and heated to 600℃ at a speed of 5℃ / min for secondary carbonization, and kept for 2 hours, and then cooled to room temperature at a speed of 5℃ / min.

[0026] As a preferred embodiment of the present application, in the step 1, the activated black solid is collected, ground into powder, washed with 1M HCl and ultrapure water until neutral, and then dried at 60℃ overnight to obtain the final sample BIC.

[0027] As a preferred embodiment of the present application, the step 2 comprises the following specific steps: Step 2.1: 0.6 mmol of Ni(NO3)2·6H2O is dissolved in a DMF mixed solvent, 2.4 mmol of thiourea is added, and the mixture is stirred and mixed; Step 2.2: BIC is added, and magnetic stirring and ultrasonic are performed; the mixture is transferred to a 50ml PPL high-pressure reaction kettle, and placed in an electric heating air drying oven for reaction; after cooling to room temperature, the precipitate is centrifuged and washed with ultrapure water and anhydrous ethanol several times to remove impurities; Step 2.3: The precipitate is placed in a vacuum drying oven for drying, and the BIC@NiS composite material is obtained.

[0028] As a preferred embodiment of the present application, in the step 2.1, the volume ratio V DMF :V 水 of DMF to water in the DMF mixed solvent is 1:2.

[0029] As a preferred embodiment of the present application, in the step 2.1, the stirring and mixing time is 10 minutes; As a preferred embodiment of the present application, in the step 2.2, the ultrasonic time is 10 minutes; As a preferred embodiment of the present application, in the step 2.2, the reaction time in the electric heating air drying oven is 12 hours, and the reaction temperature is 180℃.

[0030] As a preferred embodiment of the present application, in the step 2.3, the drying time in the vacuum oven is 12 hours, and the drying temperature is 80°C.

[0031] As a preferred embodiment of the present application, in the step 2.2, the BIC is added in an amount (mass fraction) of 1.0 wt%, 3.0 wt%, 4.0 wt% and 5.0 wt%, respectively, and the optimal ratio is 1.0 wt%.

[0032] The following provides several specific examples to verify the effectiveness of the present method.

[0033] The capacitance detection method of the composite electrode material is as follows: The CHI660E electrochemical workstation is used for electrochemical performance test of the electrode, and the three-electrode system is working electrode, Pt sheet as counter electrode, Hg / HgO as reference electrode, and the electrolyte is 6 M KOH. The scan rate of cyclic voltammetry (CV) is 5-200 mV / s. Galvanostatic charge / discharge (GCD) is used to test the charge / discharge time of the electrode at different current densities. The electrochemical impedance spectroscopy (EIS) test frequency is 0.01 Hz-100 kHz.

[0034] The BIC@NiS / / BIC asymmetric supercapacitor is assembled by using CR2016 type button cell shell and 6 M KOH as electrolyte, and the electrode sheet should be fully wetted in the electrolyte before assembly. First, place the negative shell at the bottom end, put in the gasket and negative electrode sheet, use a pipette to inject 70 µL of electrolyte and put in the cellulose separator. Then put in the positive electrode sheet, inject 70 µL of electrolyte again, and then put in the gasket and spring in turn, cover the positive shell. The assembled supercapacitor is transferred to the hydraulic machine for compaction and sealing, and finally the surface stains are removed and left for a period of time before electrochemical test by electrochemical workstation.

[0035] Example 1: (1) Preparation of double-base activated water spinach stem derived porous carbon: The water spinach stems were first cut into small pieces and cleaned with ultrapure water and anhydrous ethanol solution to remove surface impurities and insoluble substances, and then placed in an oven at 60°C for drying for 24 hours. After drying, the IC was pre-carbonized at 800°C at a rate of 5°C / min under N2 atmosphere, and the temperature was kept for 2 hours. The cooling rate was also kept at 5°C / min. After cooling, the IC was ground into powder and washed with ultrapure water and dried at 60°C for 24 hours. In the subsequent chemical activation step, NaOH and KOH were first uniformly mixed in ultrapure water, and then the product was mixed with NaOH / KOH at a mass ratio of 1:5, and then placed in an oven at 80°C for drying for 24 hours. Then the mixture was placed in a crucible and carbonized at 600°C at a rate of 5°C / min for 2 hours, and then cooled to room temperature at a rate of 5°C / min. The black solid was collected, ground into powder, washed with 1M HCl and ultrapure water until neutral, and then dried at 60°C overnight to obtain the final sample BIC.

[0036] (2) Preparation of BIC@NiS composite material: 0.6 mmol of Ni(NO3)2·6H2O was dissolved in a DMF mixed solvent (V DMF :V 水 =1:2), 2.4 mmol of thiourea was added, and the mixture was magnetically stirred for 10 minutes. Then 1.0 wt% of BIC was added, magnetically stirred for 10 minutes and ultrasonically stirred for 10 minutes. The mixture was transferred to a 50 ml PPL high-pressure reaction kettle, and placed in an electric heating drying oven at 180°C for 12 hours. After cooling to room temperature, the precipitate was washed several times with ultrapure water and anhydrous ethanol by centrifugation to remove impurities. The precipitate was placed in a vacuum drying oven at 80°C for 12 hours to obtain BIC@NiS, and the sample was labeled as BIC@NiS-1.

[0037] It was detected that the specific capacitance of the synthesized BIC@NiS-1 electrode material was 1157.76 F / g at a current density of 1 A / g, and the capacitance retention rate was as high as 94.32% after 10000 cycles at a current density of 10 A / g. At a scan rate of 50 mV / s, the capacitance contribution accounted for 79.68% of the total capacitance contribution. The high capacitance contribution is conducive to the stable storage of ions in the electrode, which also makes the energy storage performance of the BIC@NiS-1 electrode better than most of the currently reported electrode materials.

[0038] Example 2: (1) Preparation of double-alkali activated water spinach stem derived porous carbon: The water spinach stems were first cut into small pieces and cleaned with ultrapure water and anhydrous ethanol solution to remove surface impurities and insoluble substances, and then placed in an oven at 60°C for drying for 24 hours. After drying, the water spinach stems were pre-carbonized at 800°C at a rate of 5°C / min under N2 atmosphere, and the temperature was kept for 2 hours. The cooling rate was also kept at 5°C / min. After cooling, the IC was ground into powder and washed with ultrapure water and dried at 60°C for 24 hours. In the subsequent chemical activation step, NaOH and KOH were first uniformly mixed in ultrapure water, and then the product was mixed with NaOH / KOH at a mass ratio of 1:5, and then placed in an oven at 80°C for drying for 24 hours. Then the mixture was placed in a crucible and heated to 600°C at a rate of 5°C / min for secondary carbonization, and the temperature was kept for 2 hours, and then cooled to room temperature at a rate of 5°C / min. The black solid was collected, ground into powder, washed with 1M HCl and ultrapure water until neutral, and then dried at 60°C overnight to obtain the final sample BIC.

[0039] (2) Preparation of BIC@NiS composite material: 0.6 mmol of Ni(NO3)2·6H2O was dissolved in a DMF mixed solvent (V DMF :V 水 =1:2), 2.4 mmol of thiourea was added, and the mixture was magnetically stirred for 10 minutes. Then 3.0 wt% of BIC was added, magnetically stirred for 10 minutes and ultrasonically treated for 10 minutes. The mixture was transferred to a 50 ml PPL high-pressure reaction kettle, placed in an electric heating drying oven at 180°C for 12 hours. After cooling to room temperature, the precipitate was washed several times with ultrapure water and anhydrous ethanol by centrifugation to remove impurities. The precipitate was placed in a vacuum drying oven at 80°C for 12 hours to obtain BIC@NiS. The sample was labeled as BIC@NiS-3.

[0040] It was detected that the specific capacitance of the synthesized BIC@NiS-3 electrode material was 1157.76 F / g at a current density of 1 A / g.

[0041] Example 3: (1) Preparation of double-base activated water spinach stem derived porous carbon: The water spinach stems were first cut into small pieces and treated with ultrapure water and anhydrous ethanol solution to remove surface impurities and insoluble substances. Then, they were dried in an oven at 60°C for 24 hours. After drying, the water spinach stems were pre-carbonized at 800°C under a nitrogen atmosphere at a rate of 5°C / min, held at this temperature for 2 hours, and then cooled at a rate of 5°C / min. After cooling, the IC was ground into powder, washed with ultrapure water, and dried at 60°C for 24 hours. In the subsequent chemical activation step, NaOH and KOH were uniformly mixed in ultrapure water, and then the product was mixed with NaOH / KOH at a mass ratio of 1:5 and dried in an oven at 80°C for 24 hours. The mixture was then placed in a crucible and heated to 600°C at a rate of 5°C / min for secondary carbonization, held at this temperature for 2 hours, and then cooled to room temperature at a rate of 5°C / min. The black solid was collected, ground into powder, washed with 1M HCl and ultrapure water until neutral, and then dried at 60°C overnight to obtain the final sample BIC.

[0042] (2) Preparation of BIC@NiS composite material: 0.6 mmol of Ni(NO 3 )2·6H2O dissolved in DMF mixed solvent (V DMF :V 水 Add 2.4 mmol of thiourea (ratio 1:2) to the mixture and stir magnetically for 10 minutes. Then add 4.0 wt% BIC, stir magnetically for 10 minutes, and sonicate for 10 minutes. Transfer the mixture to a 50 ml PPL autoclave and place it in an electrically heated drying oven at 180°C for 12 hours. After cooling to room temperature, wash the precipitate several times with ultrapure water and anhydrous ethanol to remove impurities. Place the precipitate in a vacuum drying oven at 80°C for 12 hours to obtain BIC@NiS. Label the sample as BIC@NiS-4.

[0043] The synthesized BIC@NiS-4 electrode material was tested and found to have a specific capacitance of 876.6 F / g at a current density of 1 A / g.

[0044] Example 4: (1) Preparation of porous carbon derived from water spinach stems by double alkali activation: The water spinach stems were first cut into small pieces and treated with ultrapure water and anhydrous ethanol solution to remove surface impurities and insoluble substances. Then, they were dried in an oven at 60°C for 24 hours. After drying, the water spinach stems were pre-carbonized at 800°C under a nitrogen atmosphere at a rate of 5°C / min, held at this temperature for 2 hours, and then cooled at a rate of 5°C / min. After cooling, the IC was ground into powder, washed with ultrapure water, and dried at 60°C for 24 hours. In the subsequent chemical activation step, NaOH and KOH were uniformly mixed in ultrapure water, and then the product was mixed with NaOH / KOH at a mass ratio of 1:5 and dried in an oven at 80°C for 24 hours. The mixture was then placed in a crucible and heated to 600°C at a rate of 5°C / min for secondary carbonization, held at this temperature for 2 hours, and then cooled to room temperature at a rate of 5°C / min. The black solid was collected, ground into powder, washed with 1M HCl and ultrapure water until neutral, and then dried at 60°C overnight to obtain the final sample BIC.

[0045] (2) Preparation of BIC@NiS composite material: 0.6 mmol of Ni(NO3)2·6H2O was dissolved in a DMF mixed solvent (V DMF :V 水 Add 2.4 mmol of thiourea (ratio 1:2) to the mixture and stir magnetically for 10 minutes. Then add 5.0 wt% BIC, stir magnetically for 10 minutes, and sonicate for 10 minutes. Transfer the mixture to a 50 ml PPL autoclave and place it in an electrically heated drying oven at 180°C for 12 hours. After cooling to room temperature, wash the precipitate several times with ultrapure water and anhydrous ethanol to remove impurities. Place the precipitate in a vacuum drying oven at 80°C for 12 hours to obtain BIC@NiS. Label the sample as BIC@NiS-5.

[0046] The synthesized BIC@NiS-5 electrode material was tested and found to have a specific capacitance of 754.2 F / g at a current density of 1 A / g.

[0047] Example 5: A BIC@NiS-1 / / BIC asymmetric supercapacitor was assembled using a CR2016 button cell casing and 6 M KOH as the electrolyte. Before assembly, the electrode plates were thoroughly wetted in the electrolyte. The negative electrode casing was placed at the bottom, followed by the gasket and negative electrode plate. 70 µL of electrolyte was injected using a pipette, and a cellulose membrane was then placed in the middle. The positive electrode plate was then added, followed by another 70 µL of electrolyte, and then the gasket and spring were placed in sequence. The positive electrode casing was then replaced. The assembled supercapacitor was transferred to a hydraulic press for compaction and sealing. Finally, surface contaminants were removed, and the capacitor was allowed to stand for a period of time before electrochemical testing was performed using an electrochemical workstation.

[0048] Testing revealed that the assembled BIC@NiS-1 / / BIC asymmetric supercapacitor has a specific capacitance of 94.58 F / g at a current density of 5 A / g, achieves an energy density of 85.12 Wh / kg at 1494 W / kg, and retains a capacitance of 73.88% after 10,000 cycles at a current density of 10 A / g.

[0049] Comparative Example 1: Preparation of porous carbon derived from water spinach stems activated by dual alkalis: Water spinach stems were first cut into small pieces and surface impurities and insoluble substances were removed with ultrapure water and anhydrous ethanol solution. Then, they were dried in an oven at 60°C for 24 hours. After drying, the water spinach stems were pre-carbonized at 800°C under a N2 atmosphere at a rate of 5°C / min, held at this temperature for 2 hours, and then cooled at a rate of 5°C / min. After cooling, the IC was ground into powder, washed with ultrapure water, and dried at 60°C for 24 hours. In the subsequent chemical activation step, NaOH and KOH were uniformly mixed in ultrapure water, and then the product was mixed with NaOH / KOH at a mass ratio of 1:5 and dried in an oven at 80°C for 24 hours. Next, the mixture was placed in a crucible and heated to 600°C at a rate of 5°C / min for secondary carbonization, held at this temperature for 2 hours, and then cooled to room temperature at a rate of 5°C / min. The black solid was collected, ground into powder, washed with 1M HCl and ultrapure water until neutral, and then dried at 60°C overnight to obtain the final sample BIC.

[0050] The synthesized IC electrode material was found to have a specific capacitance of 146.25 F / g at a current density of 1 A / g, while the BIC electrode material had a specific capacitance of 560.82 F / g at a current density of 1 A / g.

[0051] Comparative Example 2: 0.6 mmol of Ni(NO3)2·6H2O was dissolved in a DMF mixed solvent (V DMF :V 水 Add 2.4 mmol of thiourea (ratio 1:2), stir the mixture magnetically for 10 minutes, transfer it to a 50 ml PPL high-pressure reactor, and place it in an electrically heated drying oven at 180°C for 12 hours. After cooling to room temperature, wash the precipitate several times with ultrapure water and anhydrous ethanol to remove impurities. Place the precipitate in a vacuum drying oven at 80°C for 12 hours to obtain NiS.

[0052] The synthesized NiS electrode material was tested and found to have a specific capacitance of 1071.55 F / g at a current density of 1 A / g.

[0053] Figure 1This is a flowchart illustrating the preparation method of porous carbon@flower-like NiS composite electrode material. Using green water spinach stalks as a precursor, a porous carbon framework (BIC) rich in oxygen-containing functional groups is formed through the depolymerization and ring-opening reactions of cellulose, hemicellulose, and lignin during pyrolysis. Simultaneously, nitrogen-containing species released by the pyrolysis of amino acids retain nitrogen in the carbon matrix through Maillard reactions, forming stable heterocyclic structures such as pyridine nitrogen and pyrrole nitrogen. Acid washing and alkali metal vapor etching further construct hierarchical channels, enhancing ion diffusion and electrochemical accessibility. The introduced NiS, guided by O / N functional groups, grows directionally into a flower-like nanostructure and forms a strong interfacial coupling with the carbon matrix, achieving a synergistic energy storage mechanism of double-layer capacitance and pseudocapacitance, significantly improving the electrochemical performance of the composite material.

[0054] Figure 2 This is a scanning electron microscope image. Figure 2 a-2b shows that the original water spinach stems have a layered structure with indistinct pores. After carbonization at 800℃, as shown... Figure 2 c-2d, the thermal decomposition of lignocellulose releases volatiles, causing the layered structure to collapse and form a continuous porous carbon skeleton. Its surface roughness increases, transforming it into isotropic amorphous carbon, which not only increases the specific surface area but also forms macroporous channels that are conducive to electrolyte transport. Figure 2 As shown in e-2f, during the KOH / NaOH activation process, a synergistic etching effect is significant when the alkali-to-carbon ratio is 1:5, constructing a rich and interconnected open channel system. The pores exhibit honeycomb-like depressions and ridge-like protrusions, with localized longitudinal cracks formed by gas release stress. The material contact angle is 39.25°, demonstrating good hydrophilicity. Further combining NiS with BIC during the hydrothermal process… Figure 2 The NiS nanosheets shown in g-2h form three-dimensional flower-like clusters through Ostwald ripening and self-assembly. The O / N functional groups on the BIC surface guide the directional growth of NiS and form chemical bonds. Figure 2 Observations in a1-d2 show that when the BIC content is 1 wt%, the composite material retains the flower-like morphology of NiS and the porous structure of the carbon skeleton, while the contact angle decreases to 6.34°, significantly improving electrolyte wettability and active site utilization. As the BIC content increases to 3–5 wt%, the confinement effect of the carbon skeleton strengthens, and the NiS nanoflower structure tends to disperse, forming a "carbon framework-nanosheet" composite system. However, excessive carbon coverage may cause interfacial stress and structural defects, affecting cycle and rate performance. This composite structure effectively combines double-layer capacitance and pseudocapacitance, achieving a synergistic improvement in energy storage performance. Furthermore, through… Figure 2 EDS energy dispersive spectroscopy analysis of i confirmed that the elements from NiS and BIC were uniformly distributed.

[0055] Figure 3 Chemical composition analysis and microstructure diagram of BIC@NiS composite material. Figure 3XRD analysis of the water spinach stem raw material revealed two broad diffraction peaks with 2θ values ​​of approximately 15° and 23°, which are diffraction peaks of cellulose and hemicellulose, respectively. Observation of the XRD curves of IC and BIC showed that BIC with different carbon-base ratios exhibited diffraction peaks at approximately 23° and 43°, which are related to the (002) and (100) crystal planes of graphite carbon, respectively. Compared to IC, the (002) crystal plane of the electrode material shifted to the left and the (100) peak intensity increased after activation treatment. The diffraction peaks of the prepared NiS are consistent with those of standard β-NiS (JCPDS 12-41). 2θ = 18.66°, 30.33°, 32.17°, 35.70°, 37.27°, 40.61°, 48.80°, 50.13°, 52.73°, 56.11°, 57.34°, and 59.56° correspond to the (110), (101), (300), (021), (220), (211), (131), (410), (401), (321), (330), and (012) crystal planes, respectively. Furthermore, there are no other impurities, indicating that β-NiS has a very high degree of crystallinity and is very pure. However, the characteristic diffraction peaks of the BIC@NiS composite material only showed the characteristic peaks of β-NiS, and the (002) characteristic peak of BIC was very weak and not clearly observed, indicating that the uniform coating of the carbon network did not destroy the crystallinity of nickel sulfide.

[0056] Figure 3 The two characteristic peaks in the Raman spectrum in b represent the D band (1350 cm⁻¹). −1 ) and G-band (1580 cm) −1 The D band is caused by structural defects and impurities, while the G band is the in-plane stretching vibration of sp2 hybridized carbon in graphite crystals. With increasing carbon-base ratio, the I band... D / I G As the ratio gradually increases (from 0.93 to 0.99), the graphitization degree of the material decreases and the defect density increases, which is consistent with the XRD results. When BIC and NiS are combined with different contents, characteristic peaks belonging to NiS and BIC, respectively, can be clearly observed. In BIC@NiS, as the amount of BIC added increases from 1 wt% to 5 wt%, I... D / I G The ratio gradually increased (1.3→1.8), indicating that the introduction of NiS promoted the graphitization of the carbon skeleton, possibly due to the high temperature and high pressure induced carbon structure rearrangement during the hydrothermal process. Figure 3 c-3D analysis shows that the activated BIC exhibits a three-dimensional interconnected porous network structure, with an amorphous carbon matrix on the carbon skeleton surface and graphite microcrystals visible in local areas. This indicates that the alkaline activator (such as K / Na salt) induced the graphitization of carbon or the defect structure formed during the carbonization process. Figure 3In e-3f, NiS is formed by interwoven curved nanosheets that create flower-like clusters. Figure 3 The g-type BIC@NiS-1 uses a porous carbon network of BIC as a substrate, with NiS nanosheets growing vertically on the carbon surface. Close contact without significant gaps is visible at the interface, indicating that functional groups (such as -OH and -COOH) on the carbon surface chemically bond with the NiS precursor during in-situ hydrothermal processing, promoting heterogeneous nucleation. High-resolution TEM shows that the lattice fringes at the interface between the NiS nanosheets (100) and the carbon framework (002) coexist continuously, indicating that they are bonded by van der Waals forces or weak chemical bonds.

[0057] Figure 4 This is a diagram showing the chemical elemental composition and structural analysis of the BIC@NiS-1 composite material. Figure 4 In the composite BIC@NiS-1, the high-resolution C 1s spectrum was decomposed into four peaks at 284.8 eV, 286.3 eV, 286.9 eV, and 288.9 eV, belonging to CC / C=C, CO, C=O, and OC=O, respectively. After recombination, the intensity of the CC / C=C peak in BIC@NiS-1 may be slightly reduced, indicating that the introduction of NiS may partially cover the carbon surface or affect the electronic structure of the graphitized region. The CO peak weakened, while the C=O and OC=O peaks relatively strengthened, suggesting that NiS may have undergone oxidation during hydrothermal processes, oxidizing some hydroxyl groups (C-OH) or ether groups (COC) to carbonyl groups (C=O) or carboxyl groups (OC=O), leading to a redistribution of oxygen-containing functional groups. Figure 4 The high-resolution 1s spectrum of BIC shown in b exhibits peaks at 531.8 eV, 531.2 eV, and 533.3 eV, belonging to C-OH / COC, C=O, and CO, respectively. After recombination, due to the hydrothermal reaction process, Ni... 2+ Ions may coordinate or chemically react with oxygen-containing functional groups (such as C-OH and C=O) on the surface of carbon materials to form Ni-O bonds. This bonding enhances the interfacial bonding between BIC carbon materials and NiS, which is beneficial for charge transport and structural stability. However, some oxygen-containing functional groups (such as C=O and C-OH) are consumed during the reaction to form Ni-O bonds or other intermediate products, resulting in a decrease in their peak intensity. Changes in oxygen-containing functional groups may affect the charge distribution on the surface of carbon materials, thereby altering the electrochemical properties of the composite material.

[0058] Figure 4 In c, Ni 2p 3 / 2 Located at 853.5 eV, Ni 2p 1 / 2 Located at 871.0 eV, corresponding to Ni 2+ The chemical state of β-NiS. Located at 859 eV (Ni 2p). 3 / 2 (satellite peak) and 876 eV (Ni 2p)1 / 2 Satellite peaks are formed by Ni 2+ The multi-electron excitations were triggered, verifying the integrity of the electronic structure of NiS. The Ni 2p phase of the composite BIC@NiS-1 was [further details needed]. 3 / 2 The peak position shifted slightly to 854.0 eV, Ni 2p 1 / 2 The shift to 871.5 eV indicates a change in the chemical environment of Ni, possibly due to carbon doping leading to polarization of the Ni-S bonds or changes in the local coordination structure, forming Ni-OC bonds at the interface, thus altering the Ni coordination environment and causing Ni to... 2+ Peak shift. Localized oxidation state of nickel (Ni 3 + The formation of Ni may be related to the oxidation of carbon by hydroxyl groups (-OH) or dissolved oxygen on the carbon surface. The decrease in satellite peak intensity reflects the presence of Ni. 2+ The electronic structure is affected by the carbon interface, and charge transfer suppresses the multi-electron excitation process.

[0059] exist Figure 4 In d, the high-resolution S 2p spectrum of NiS shows that it is located at 161.5 eV (S 2p). 3 / 2 ) and 162.7 eV (S2p 1 / 2 ) Corresponding to S in NiS 2- The typical binding energy indicates that sulfur exists in the form of sulfides. The absence of a significant peak at 168-170 eV indicates that sulfur in pure NiS has not undergone significant oxidation. The S 2p... 3 / 2 and S 2p 1 / 2 The peaks shift slightly towards higher binding energies (~161.8 eV and ~163.0 eV), indicating a decrease in the electron cloud density of sulfur, possibly due to electron extraction from the carbon skeleton. A weak peak appears at 168.5 eV, corresponding to sulfate (SO4). 2- ) or sulfites (SO3) 2- The presence of SO bonds indicates that some sulfur was oxidized during the recombination process, possibly due to the intervention of oxygen in the hydrothermal reaction or the oxidation of oxygen-containing functional groups on the carbon surface.

[0060] Figure 5 The specific surface area and pore size analysis diagrams for the BIC@NiS-1 composite material are shown. BIC@NiS-1 exhibits a type IV adsorption isotherm with a typical hysteresis loop, indicating a microporous structure within the material. BIC@NiS-1 (149.54 m...) 2 The specific surface area of ​​( / g) is greater than that of BIC (1200 m²). 2The significant decrease in adsorption capacity ( / g) is mainly due to the aggregation of NiS nanoparticles during the hydrothermal reaction, which occupy or cover the microporous surface of the biochar, potentially creating new pores in the 2–50 nm range (manifested as an increase in adsorption capacity in the medium-pressure region or the appearance of H3-type hysteresis loops). NiS particles may clog micropores, leading to a reduction in adsorption capacity in the low-pressure region. While a decrease in specific surface area may reduce adsorption capacity, the increase in mesopores and NiS active sites may enhance additional redox active sites, increasing the pseudocapacitive contribution of the composite material.

[0061] Figure 6 The electrochemical performance of the electrodes was assessed. The BIC material, after carbonization and activation treatment, exhibited redox peaks of double-layer capacitance and pseudocapacitance originating from N heteroatoms; while NiS and its composites (BIC@NiS-1 to BIC@NiS-5) all showed significant redox peaks. Among them, BIC@NiS-1 had the largest CV area and the longest GCD charge-discharge time, with a specific capacitance of 1157.76 F / g at a current density of 1 A / g, significantly higher than IC (142.65 F / g), BIC (560.82 F / g), and NiS (1071.55 F / g). Simultaneously, BIC@NiS-1 exhibited a smaller contact resistance (R0) in the high-frequency region. s =0.87 Ω) and charge transfer resistance (R ct =0.56Ω), and the low-frequency curve is closer to the Y-axis, indicating low ion diffusion resistance and superior conductivity. After 10,000 cycles at 10 A / g, BIC@NiS-1 still maintains a specific capacitance of 94.32% and good coulombic efficiency. Kinetic analysis shows that at a scan rate of 5 mV / s, diffusion control contributes 58.13% of the total capacitance; as the scan rate increases to 50 mV / s, the capacitive contribution rises to 79.68%, indicating that at high scan rates, electrode energy storage is mainly dominated by surface control mechanisms, giving it superior rate performance and ion storage stability.

[0062] Figure 7The electrochemical performance of the asymmetric supercapacitor (ASC) was evaluated. The optimal operating voltage window for the ASC was determined to be 0–1.8 V using CV testing. At a current density of 5 A / g, the specific capacitance of the ASC reached 94.58 F / g, and it maintained 4.0 F / g at 10 A / g. Cyclic stability testing showed that after 10,000 charge-discharge cycles at 10 A / g, the capacitance retention was still 73.88%. This ASC achieved an energy density of 85.12 Wh / kg at a power density of 1494 W / kg; even with a power density increased to 8400 W / kg, the energy density remained at 42 Wh / kg. These results demonstrate that the BIC@NiS-1 / / BIC ASC possesses high energy density, good rate performance, and cycle stability, showing great promise for practical energy storage applications.

[0063] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements 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 preparing a porous carbon@flower-like NiS composite electrode material, characterized in that, Comprising the following steps: Step 1: After the water spinach stem is pretreated, it is pre-carbonized under a nitrogen atmosphere, and then activated at 600 DEG C using a mixed alkali of KOH and NaOH at a mass ratio of 1:5, and after acid washing and drying, BIC is obtained; Step 2: By a one-step hydrothermal method, nickel nitrate, thiourea and BIC are reacted at 180 DEG C for 12 hours, and after centrifugation, washing and drying, the BIC@NiS composite material is finally prepared.

2. The preparation method of the porous carbon@flower-like NiS composite electrode material according to claim 1, characterized in that, In the step 1, the pretreatment of the water spinach stem comprises: The water spinach stem is first cut into pieces, and the surface impurities and insoluble substances are removed with ultrapure water and anhydrous ethanol solution, and then it is placed in a 60 DEG C electric heating air drying oven for drying for 24 hours for standby.

3. The method for preparing the porous carbon@flower-like NiS composite electrode material according to claim 1, characterized in that, In the step 1, the pre-carbonization comprises the following specific steps: After the drying of the water spinach stem is completed, it is pre-carbonized at 800 DEG C under N2 atmosphere at a speed of 5 DEG C / minute, and the temperature is kept for 2 hours, and the cooling speed is also kept at 5 DEG C / minute; after cooling, the IC is ground into powder, washed with ultrapure water, and dried at 60 DEG C for 24 hours.

4. The preparation method of the porous carbon@flower-like NiS composite electrode material according to claim 1, characterized in that, In the step 1, the activation operation comprises the following specific steps: In ultrapure water, NaOH and KOH are uniformly mixed, and then the product is mixed with NaOH / KOH at a mass ratio of 1:5, and then placed in an electric heating air oven for drying at 80 DEG C for 24 hours; then the mixture is placed in a crucible and heated to 600 DEG C at a speed of 5 DEG C / minute for secondary carbonization, and kept for 2 hours, and then cooled to room temperature at a speed of 5 DEG C / minute.

5. The method for preparing the porous carbon@flower-like NiS composite electrode material according to claim 4, characterized in that, In the step 1, the activated black solid is collected, ground into powder, washed with 1M HCl and ultrapure water until neutral, and then dried at 60 DEG C overnight to obtain the final sample BIC.

6. The method of claim 1, wherein the porous carbon@flower-like NiS composite electrode material is prepared by the following steps: (1) preparing a porous carbon material; (2) preparing a flower-like NiS material; and (3) mixing the porous carbon material and the flower-like NiS material. The step 2 comprises the following specific steps: Step 2.1: 0.6 mmol of Ni(NO3)2·6H2O is dissolved in a DMF mixed solvent, 2.4 mmol of thiourea is added, and the mixture is stirred and mixed; Step 2.2: BIC is added, magnetically stirred and ultrasonicated; the mixture is transferred to a 50 ml PPL high-pressure reaction kettle, and placed in an electric heating air drying oven for reaction; after cooling to room temperature, the precipitate is centrifuged and washed with ultrapure water and anhydrous ethanol several times to remove impurities; Step 2.3: The precipitate is placed in a vacuum drying oven for drying, and the BIC@NiS composite material is obtained.

7. The method for preparing the porous carbon@flower-like NiS composite electrode material according to claim 6, characterized in that, In the step 2.2, the addition amount of BIC is 1.0 wt%, 3.0 wt%, 4.0 wt% and 5.0 wt% respectively. 8.The method for preparing the porous carbon@flower-like NiS composite electrode material according to claim 7, characterized in that, The addition amount of BIC is 1.0 wt%.

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