A vanadium redox flow battery anode material and its preparation method

Abstract

This application belongs to the technical field of energy storage battery electrode materials, specifically relating to a vanadium redox flow battery anode material and its preparation method. The preparation method of the vanadium redox flow battery anode material includes the following steps: mixing agricultural and forestry waste, phosphoric acid, and a nitrogen source, and performing microwave pretreatment to obtain a biomass precursor; mixing the biomass precursor, carbon felt, cobalt source, and solvent and performing a hydrothermal reaction to obtain an electrode precursor; and sequentially subjecting the electrode precursor to pyrolysis and activation treatments to obtain the flow battery anode material. The beneficial effects of this application include: the vanadium redox flow battery anode material modified with a biomass nitrogen-doped porous carbon coupled with a Co3O4 catalyst effectively improves the electrode's conductivity; improves the Co3O4 modification and loading effect; enhances the electrode's hydrophilicity and stability; and achieves better electrochemical activity and redox performance.

Description

Technical Field

[0001] This application belongs to the field of energy storage battery electrode material technology, specifically relating to a vanadium redox flow battery negative electrode material and its preparation method. Background Technology

[0002] Vanadium redox flow batteries offer advantages such as flexible design of output power and capacity to meet specific needs, long cycle life, corrosion-resistant electrodes, short response time, high energy conversion efficiency, low cost, and safety and environmental friendliness. Therefore, they are widely used in energy storage devices and grid peak-valley regulation. However, compared to other energy storage devices, vanadium redox flow batteries also have some unresolved issues, such as low energy density, large size, and poor electrode electrochemical activity.

[0003] Electrodes are the core components of vanadium redox flow batteries, directly affecting the overall performance of the battery. Carbon materials (such as carbon felt, graphite felt, and carbon paper) are commonly used as electrode materials. However, these carbon materials lack electrochemical activity and have poor hydrophilicity, requiring appropriate modification before use, such as surface oxidation activation, surface etching, heteroatom doping, and catalyst introduction. Biomass porous carbon raw materials, typically using coconut shells, bamboo, and agricultural waste, offer advantages such as low development costs, easy activation and pore formation, and diversified resource utilization pathways, reducing environmental pollution while creating economic value. Furthermore, transition metal oxide catalysts possess the core advantages of variable oxidation states, abundant active sites, high stability, and cost-effectiveness, combining redox activity with structural tunability. Therefore, utilizing biomass as a raw material to prepare high-performance porous carbon coupled with transition metal oxide catalysts to modify vanadium redox flow battery anode materials, thereby improving the energy storage performance and economic benefits of vanadium redox flow batteries, is of great significance. Summary of the Invention

[0004] This application provides a vanadium redox flow battery anode material and its preparation method. The in-situ hydrothermal preparation technology solves the problems of cumbersome preparation process, poor loading or modification effect, and poor stability in the current modification strategies of carbon anode materials for vanadium redox flow batteries, thereby improving the electrochemical activity and hydrophilicity of carbon material electrodes.

[0005] The first aspect of this application provides a method for preparing a negative electrode material for a flow battery, comprising the following steps: (1) Mix agricultural and forestry waste, phosphoric acid and nitrogen source, and perform microwave pretreatment to obtain biomass precursor; (2) The biomass precursor, carbon felt, cobalt source and solvent are mixed and subjected to hydrothermal reaction to obtain the electrode precursor; (3) The electrode precursor is subjected to pyrolysis and activation treatment in sequence to obtain the negative electrode material of the flow battery.

[0006] The second aspect of this application provides a vanadium redox flow battery anode material, which is prepared by the preparation method described in the first aspect of this application.

[0007] The beneficial effects of this application include: the vanadium redox flow battery anode material modified by biomass nitrogen-doped porous carbon coupled with Co3O4 catalyst effectively improves the conductivity of the electrode; improves the Co3O4 modification and loading effect; improves the hydrophilicity and stability of the electrode, and obtains better electrochemical activity and redox performance. Attached Figure Description

[0008] Figure 1 The N2 adsorption-desorption curves are shown for the battery negative electrode materials described in Example 1 and Comparative Examples 1-3 of this application. Figure 2 This is a pore size distribution diagram of the battery negative electrode material described in Embodiment 1 and Comparative Examples 1-3 of this application; Figure 3 The X-ray diffraction patterns are those of the battery anode materials described in Example 1 and Comparative Examples 1-3 of this application. Figure 4 The images show the Raman spectra of the battery anode materials described in Example 1 and Comparative Examples 1-3 of this application. Figure 5 This is a thermogravimetric analysis curve of the battery negative electrode material described in Example 1 of this application; Figure 6 This is a diagram showing the water contact angle of the battery negative electrode material described in Embodiment 2 of this application; Figure 7 This is a scanning electron microscope image of the battery negative electrode material described in Embodiment 3 of this application; Figure 8 This is an EDS elemental mapping diagram of the battery negative electrode material described in Embodiment 4 of this application; Figure 9 This is a high-magnification transmission electron microscope image of the battery negative electrode material described in Embodiment 1 of this application; Figure 10 The battery negative electrode material described in Embodiment 1 and Comparative Example 1 of this application is at 100 mA / cm 2 Charge-discharge curves at current density; Figure 11 The electrochemical impedance spectroscopy diagrams are shown for the battery negative electrode materials described in Example 1 and Comparative Example 2 of this application. Figure 12 The polarization curves are shown for the battery negative electrode materials described in Embodiment 1 and Comparative Example 3 of this application. Figure 13 The energy efficiency diagrams are for the battery anode materials described in Embodiment 1 and Comparative Examples 1-3 of this application. Figure 14 The coulombic efficiency diagrams are for the battery anode materials described in Example 1 and Comparative Examples 1-3 of this application. Detailed Implementation

[0009] The embodiments of the present invention are described in detail below. These embodiments are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0010] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0011] This application provides a method for preparing a negative electrode material for a flow battery, including the following steps: (1) Mix agricultural and forestry waste, phosphoric acid and nitrogen source, and perform microwave pretreatment to obtain biomass precursor; (2) The biomass precursor, carbon felt, cobalt source and solvent are mixed and subjected to hydrothermal reaction to obtain the electrode precursor; (3) The electrode precursor is subjected to pyrolysis and activation treatment in sequence to obtain the negative electrode material of the flow battery.

[0012] The negative electrode material for a vanadium redox flow battery described in this application is a biomass porous carbon-coupled Co3O4 modified negative electrode material prepared from agricultural and forestry waste. It utilizes a low-cost Co3O4 catalyst to reduce costs and employs in-situ preparation technology to address issues such as cumbersome preparation processes, poor loading or modification effects, and poor stability inherent in modification strategies. Nitrogen source additives are added during the preparation process to assist in pore formation and incorporate heteroatoms, thereby improving conductivity. The staged pyrolysis of the nitrogen source additives forms a specific porous structure, and air is used as an activator, making it environmentally friendly and reducing energy consumption.

[0013] The negative electrode material of the flow battery described in this application is prepared in situ using a hydrothermal reaction method to form uniform active sites, prevent catalyst agglomeration, and solve the problem of uneven distribution of electrocatalytic active sites in the negative electrode material.

[0014] In some embodiments of this application, the agricultural and forestry waste includes one or more of cotton stalks, corn stalks, fruit pits, rice husks, and peanut shells.

[0015] In some embodiments of this application, the nitrogen source includes one or more of dicyandiamide, urea, melamine, and carbamide; microwave treatment can improve the effect of phosphoric acid leaching on agricultural waste and promote the effective blending of nitrogen source and leaching material, thereby facilitating subsequent nitrogen source-assisted pore formation and improving the pore structure parameters of porous carbon.

[0016] In some embodiments of this application, the mass-to-volume ratio of the agricultural and forestry waste to the phosphoric acid is 10g:(20-30)mL; for example, 10g:20mL, 10g:24mL, 10g:26mL, 10g:28mL, 10g:30mL, etc. As a preferred embodiment, the mass concentration of phosphoric acid is 48%-55%.

[0017] In some embodiments of this application, the mass ratio of the agricultural and forestry waste to the nitrogen source is 100:(1-5); for example, 100:1, 100:2, 100:3, 100:5, etc.

[0018] In some embodiments of this application, the power of the microwave pretreatment is 200-500W and the time is 15-45min; for example, 15min, 20min, 25min, 30min, 40min, 45min, etc.

[0019] In some embodiments of this application, the mass ratio of the biomass precursor to the carbon felt is 1:(5-20); for example, 1:5, 1:6, 1:8, 1:10, 1:15, 1:20, etc. If the biomass precursor content is too low, the prepared porous carbon content is small, resulting in a weak modification effect on the carbon felt, which is detrimental to obtaining higher electrochemical performance of the vanadium redox flow battery anode material. If the biomass precursor content is too high, the porous carbon content is high, leading to excessive modification of the carbon felt, an increase in specific surface area, and a decrease in electrode stability and hydrophilicity, thereby inhibiting the electrochemical performance of the flow battery anode material.

[0020] In some embodiments of this application, the mass ratio of the biomass precursor to the cobalt source is 1:(1-5); for example, 1:1, 1:2, 1:3, 1:5, etc. If the cobalt source content is too low, the synthesized Co3O4 content is low, resulting in an insignificant modification effect on the carbon felt, which is detrimental to improving the electrochemical performance of the carbon felt anode. If the cobalt source content is too high, the synthesized Co3O4 content is high, leading to excessive modification of the carbon felt, reducing the electrode's qualitative properties, hydrophilicity, and specific surface area, thereby inhibiting the redox performance of the carbon felt electrode.

[0021] In some embodiments of this application, the cobalt source is selected from one or more of cobalt acetylacetonate, cobalt nitrate hexahydrate, cobalt sulfate heptahydrate, and cobalt chloride hexahydrate; In some embodiments of this application, the solvent is water; In some embodiments of this application, the pH of the reaction solution formed in step (2) is 7.5-8.5, such as 7.5, 7.8, 8, 8.1, 8.5, etc. Within this pH range, the synthesis of the Co3O4 precursor Co2N is favorable.

[0022] In some embodiments of this application, pyridine is used to adjust the pH of the reaction solution in step (2).

[0023] In some embodiments of this application, in step (2), the temperature at which the mixture reacts is 160-200℃, for example, 160℃, 170℃, 180℃, 190℃, 200℃, etc., and the time is 8-12h, for example, 8h, 9h, 10h, 12h, etc. A hydrothermal reaction temperature that is too low is not conducive to the full reaction of the cobalt source to synthesize the Co3O4 precursor Co2N, nor to the effective coupling with the biomass porous carbon precursor; a hydrothermal reaction temperature that is too low will lead to excessive oxidation of the biomass porous carbon precursor, reducing the specific surface area and other pore structure parameters of the final porous carbon product, thus affecting the modification effect.

[0024] In some embodiments of this application, in step (3), the pyrolysis temperature is 700-1000℃, such as 700℃, 800℃, 900℃, 1000℃, etc., and the time is 1-3h, such as 1h, 2h, 3h, etc.

[0025] In some embodiments of this application, the atmosphere for pyrolysis is an inert atmosphere.

[0026] In some embodiments of this application, the heating rate of the pyrolysis is 8-12℃ / min; for example, 8℃ / min, 9℃ / min, 10℃ / min, 12℃ / min, etc.

[0027] In some embodiments of this application, in step (3), the activation treatment temperature is 250-400℃, such as 250℃, 300℃, 380℃, 400℃, etc., and the time is 2-6h; such as 2h, 3h, 4h, 6h, etc.

[0028] In some embodiments of this application, the activation atmosphere is an air atmosphere.

[0029] This application also provides a vanadium redox flow battery anode material, prepared by the method described in the first aspect of this application. The vanadium redox flow battery anode material described in this application, after modification with a biomass nitrogen-doped porous carbon coupled with a Co3O4 catalyst, effectively improves electrode conductivity; enhances the Co3O4 modification and loading effect; improves electrode hydrophilicity and stability; and achieves better electrochemical activity and redox performance.

[0030] The technical solution of this application will be further described below with reference to specific embodiments.

[0031] Example 1 A method for preparing a negative electrode material for a flow battery includes the following steps: (1) Wash the cotton stalks with distilled water to remove inorganic impurities, then dry them in a forced-air oven at 100℃ for 24 hours, and then pulverize the cotton stalks with a high-speed ball mill to obtain raw material powder with a particle size >300 mesh; (2) Weigh 10g of raw material powder, add 25mL of 50% phosphoric acid and 3% dicyandiamide by mass of raw material powder, and pretreat the raw material powder in a microwave pressure reactor at 350W power for 30min to obtain biomass precursor. (3) Add biomass precursor and carbon felt (mass ratio 1:10) to the hydrothermal reactor, add 250 mL of cobalt acetylacetone aqueous solution (biomass precursor and cobalt acetylacetone mass ratio 1:3), add 10 mL of pyridine to adjust the pH value to 8.0, seal the hydrothermal reactor and heat to 180°C, react for 10 h, wash with deionized water and dry after the reaction to obtain the electrode precursor; (4) The above electrode precursor was placed in a tube furnace for high-temperature pyrolysis / activation: inert gas atmosphere, gas flow rate controlled at 35 mL / min, heating rate at 10 °C / min, heated to 900 °C, and pyrolyzed for 2 h under these conditions; then the atmosphere was adjusted to air, gas flow rate at 45 mL / min, cooled to 350 °C, and activated for 4 h under these conditions to obtain the flow battery negative electrode material, denoted as NC@Co3O4 / CF.

[0032] Example 2 The only difference between the preparation method of the negative electrode material of the flow battery in Example 2 and that in Example 1 is that peanut shells are used instead of cotton stalks in the preparation process of the negative electrode material of the flow battery in Example 2.

[0033] Example 3 The only difference between the preparation method of the flow battery negative electrode material in Example 3 and that in Example 1 is that the mass ratio of the biological precursor to the carbon felt is 1:1 during the preparation of the flow battery negative electrode material in Example 3.

[0034] Example 4 The only difference between the preparation method of the flow battery negative electrode material in Example 4 and that in Example 1 is that the mass ratio of the biological precursor to the carbon felt is 1:15 during the preparation of the flow battery negative electrode material in Example 4.

[0035] Example 5 The only difference between the preparation method of the flow battery negative electrode material in Example 5 and that in Example 1 is that the mass ratio of the biological precursor to the carbon felt is 1:30 during the preparation of the flow battery negative electrode material in Example 5.

[0036] Example 6 The only difference between the preparation method of the flow battery negative electrode material in Example 6 and that in Example 1 is that the mass ratio of the biological precursor and cobalt acetylacetone in the preparation process of the flow battery negative electrode material in Example 6 is 1:0.5.

[0037] Example 7 The only difference between the preparation method of the flow battery anode material in Example 7 and that in Example 1 is that the mass ratio of the biological precursor to cobalt acetylacetone in the preparation process of the flow battery anode material in Example 7 is 1:2.

[0038] Example 8 The only difference between the preparation method of the flow battery anode material in Example 8 and that in Example 1 is that the mass ratio of the biological precursor to cobalt acetylacetone in the preparation process of the flow battery anode material in Example 8 is 1:10.

[0039] Example 9 The only difference between the preparation method of the flow battery negative electrode material in Example 9 and Example 1 is that the hydrothermal reaction temperature of the biomass precursor, carbon felt and cobalt acetylacetone aqueous solution in the preparation process of the flow battery negative electrode material in Example 9 is 120°C.

[0040] Example 10 The only difference between the preparation method of the flow battery negative electrode material in Example 10 and Example 1 is that the hydrothermal reaction temperature of the biomass precursor, carbon felt and cobalt acetylacetone aqueous solution in the preparation process of the flow battery negative electrode material in Example 10 is 170°C.

[0041] Example 11 The only difference between the preparation method of the flow battery negative electrode material in Example 11 and Example 1 is that the hydrothermal reaction temperature of the biomass precursor, carbon felt and cobalt acetylacetone aqueous solution in the preparation process of the flow battery negative electrode material in Example 11 is 250°C.

[0042] Comparative Example 1 The only difference between the preparation method of the flow battery negative electrode material in Comparative Example 1 and Example 1 is that the raw material powder, phosphoric acid and dicyandiamide are directly mixed in the preparation process of the flow battery negative electrode material in Comparative Example 1 without microwave pretreatment. The remaining operation steps are the same as in Example 1.

[0043] Comparative Example 2 The only difference between the preparation method of the flow battery negative electrode material in Comparative Example 2 and Example 1 is that dicyandiamide was not added during the preparation of the flow battery negative electrode material in Comparative Example 2, while the other operation steps were the same as in Example 1.

[0044] Comparative Example 3 The only difference between the preparation method of the flow battery negative electrode material in Comparative Example 3 and Example 1 is that the electrode precursor was not activated during the preparation process of the flow battery negative electrode material in Comparative Example 3.

[0045] 1. The pore structure and conductivity properties of the flow battery negative electrode materials described in Examples 1-11 and Comparative Examples 1-3 of this application are shown in Table 1.

[0046] Table 1

[0047] As can be seen from Table 1, the specific surface area of ​​the negative electrode material of the flow battery described in Example 1 of this application is 854.5 m². 2 / g, with high pore volume and small average pore size. Microwave acid leaching pretreatment of biomass can effectively decompose lignin and cellulose components in biomass raw materials, which is beneficial for subsequent high-temperature pyrolysis and activation pore formation, thereby improving the dispersion of electrode catalyst and increasing active sites.

[0048] Compared with Examples 3-5, in Example 1, the ratio of biomass porous carbon to carbon felt was 1:10. In Example 1, porous carbon showed the best modification effect on carbon felt, and a suitable specific surface area was beneficial to improving the stability of the electrode and reducing hydrophilicity. Compared with Examples 6-8, in Example 1, the ratio of biomass porous carbon to cobalt source was 1:3. In Example 1, Co3O4 showed the best modification effect on carbon felt. Excessive modification would reduce the stability and specific surface area of ​​the electrode, thereby inhibiting the redox performance of the carbon felt electrode. Compared with Examples 9-11, in Example 1, the hydrothermal reaction temperature was 180℃, which was conducive to the full reaction of the cobalt source to synthesize Co2N and to achieve effective coupling with the biomass porous carbon precursor, preventing excessive oxidation of the biomass porous carbon precursor.

[0049] The negative electrode material of the battery described in Comparative Example 1 was not subjected to microwave treatment, resulting in a decrease in specific surface area to 725.7 m². 2 / g, with an average pore size of 14.7nm. During the hydrothermal reaction of the carbon felt, the pyrolysis and foaming effect of dicyandiamide was utilized to generate numerous cracks and channels while loading biochar onto the carbon felt. This facilitates subsequent air activation, producing microporous and mesoporous structures and increasing the specific surface area of ​​the biochar. Comparative Example 2 did not contain dicyandiamide, and therefore did not play an auxiliary pore-forming role during pyrolysis and activation, resulting in a decrease in the sample's specific surface area to 689.6nm. 2 / g, pore volume only 1.21cm 3 / g. The high-temperature pyrolysis process generates a Co3O4 catalyst, which is then in-situ modified onto the carbon felt, simultaneously carbonizing the biomass to form a graphite microcrystalline structure. During air activation, numerous micropores and mesopores are formed, further improving the pore structure parameters such as the specific surface area of ​​the biomass carbon and the electrode. Comparative Example 3 did not undergo air activation, resulting in a sample specific surface area of ​​only 243.4 m². 2 / g, dicyandiamide also served as a nitrogen dopant source, achieving nitrogen doping in the sample, improving conductivity, and enhancing battery electrode performance. Comparative Example 2, which did not include dicyandiamide, resulted in lower conductivity and subsequent catalytic performance in its electrode sample.

[0050] 2. The N2 adsorption-desorption curves and pore size distribution diagrams obtained based on DFT calculations of the battery negative electrode materials described in Example 1 and Comparative Examples 1-3 of this application are shown below. Figure 1 and Figure 2 As shown.

[0051] from Figure 1 and Figure 2 As can be seen from the data, the adsorption-desorption curves of the battery negative electrode materials described in Example 1 and Comparative Examples 1-3 of this application belong to type IV, indicating that the carbon material is mainly composed of microporous and mesoporous structures, and that the adsorption-desorption curves are suitable for P / P applications. 0 The presence of a distinct H1-type hysteresis loop at 0.6-0.9 μm indicates that the sample possesses a uniform and regular mesoporous structure with a relatively uniform pore size distribution. Microwave treatment can improve the effect of phosphoric acid leaching and promote effective blending of the nitrogen source and the leaching material, which is beneficial for subsequent nitrogen-assisted pore formation. Comparative Example 1 did not undergo microwave treatment, resulting in a decrease in specific surface area. The hydrothermal reaction process utilizes the pyrolysis and foaming effect of dicyandiamide, generating numerous cracks and pore structures while loading biochar onto the carbon felt, which is beneficial for subsequent air activation, producing microporous and mesoporous structures. Comparative Example 2 did not add dicyandiamide, thus failing to play an auxiliary pore-forming role during pyrolysis and activation, resulting in a low specific surface area. During air activation, a large number of microporous and mesoporous structures are formed, further improving the pore structure parameters such as the specific surface area of ​​the biochar and electrode. The specific surface area of ​​the sample in Comparative Example 3, which did not undergo air activation, was only 243.4 m². 2 / g.

[0052] 3. X-ray diffraction patterns of the battery anode materials described in Embodiment 1 and Comparative Examples 1-3 of this application, as shown below. Figure 3 As shown.

[0053] from Figure 3As can be seen, the electrode samples all exhibit characteristic diffraction peaks of carbon materials at 22° and 43°, namely (002) and (100). The peaks at 36.8° and 44.8° correspond to the (311) and (400) crystal planes of Co3O4, respectively, and the XRD results confirm the presence of Co3O4. The different preparation processes of Example 1 and Comparative Examples 1-3 did not have a significant impact on the crystal structure of the electrodes.

[0054] 4. Raman spectra of the battery anode materials described in Example 1 and Comparative Examples 1-3 of this application, as shown below. Figure 4 As shown.

[0055] from Figure 4 It can be seen from this that the electrode samples are all at 1350 cm⁻¹ -1 and 1590cm -1 Two carbon characteristic peaks appear nearby, corresponding to the D peak of the defect structure and the G peak of the ordered structure, respectively. The area ratio of these two peaks indicates the degree of graphitization. Comparative Examples 1-3 did not undergo the relevant processing, therefore their I... D / I G The values ​​are all below 1.13, indicating a relatively high degree of graphitization and a low specific surface area.

[0056] 5. Thermogravimetric analysis curve of the battery negative electrode material described in Example 1 of this application, as shown in the figure. Figure 5 As shown.

[0057] from Figure 5 As can be seen from the data, the electrode of Example 1 has a thermal decomposition temperature greater than 800℃, exhibiting good thermal stability and good cycle stability as a negative electrode material for vanadium redox flow batteries.

[0058] 6. The water contact angle diagram of the battery negative electrode material described in Embodiment 1 of this application, as shown below. Figure 6 As shown.

[0059] from Figure 6 As can be seen from this, the outer contact angle of the battery negative electrode material described in Example 1 of this application is >120°, indicating good hydrophilicity.

[0060] 7. Scanning electron microscope image of the battery negative electrode material described in Embodiment 1 of this application, as shown below. Figure 7 As shown.

[0061] from Figure 7 As can be seen from the above, the electrode of Example 1 has been successfully modified by biomass porous carbon coupled with Co3O4 catalyst. The biomass porous carbon exhibits a sheet-like morphology, and the nanorod-shaped Co3O4 catalyst is also uniformly loaded onto the carbon felt electrode.

[0062] 8. The EDS elemental mapping diagram of the battery negative electrode material described in Embodiment 1 of this application, as shown below. Figure 8 As shown.

[0063] from Figure 8 As can be seen from this, the battery negative electrode material described in Example 4 of this application contains C, N, O and Co elements, that is, N element was successfully incorporated by adding a nitrogen-containing dopant during the preparation process.

[0064] 9. A high-magnification transmission electron microscope image of the battery negative electrode material described in Embodiment 1 of this application, as shown below. Figure 9 As shown.

[0065] from Figure 9 As can be seen from the high-magnification transmission electron microscope image of the electrode sample in Example 1, the (002) graphite microcrystalline structure of porous carbon and the (311) and (400) crystal planes of the Co3O4 catalyst are visible, which confirms that the biomass porous carbon coupled with the Co3O4 catalyst has successfully modified the carbon felt electrode.

[0066] 10. The battery negative electrode material described in Embodiment 1 and Comparative Example 1 of this application operates at 100 mA / cm². 2 Charge-discharge curves at current density, such as Figure 10 As shown.

[0067] Note: The battery negative electrode material samples were used as negative electrodes, heat-treated carbon felt as positive electrodes, Nafion 115 type as ion exchange membrane separators, and 30 mL of 2 mol / L VO2+ electrolyte as the positive electrode electrolyte. 2+ And 2 mol / L H2SO4 solution, the negative electrode electrolyte is 30 mL of 2 mol / L H2SO4 solution. 3+ Electrochemical performance tests, including electrochemical impedance spectroscopy, cyclic voltammetry, and charge-discharge, were performed using a 2 mol / L H2SO4 solution to calculate coulombic efficiency, energy efficiency, and voltage efficiency.

[0068] from Figure 10 As can be seen, the specific capacitance of the battery negative electrode material described in Comparative Example 1 is significantly lower than that of the battery negative electrode material described in Example 1. The main reason is that Comparative Example 1 has lower conductivity and poorer pore structure.

[0069] 11. Electrochemical impedance spectroscopy diagrams of the battery negative electrode materials described in Example 1 and Comparative Example 2 of this application, as shown... Figure 11 As shown.

[0070] from Figure 11 As can be seen from this, since dicyandiamide was not added to the negative electrode material of the battery described in Comparative Example 2, the electrode sample has a high interfacial resistance.

[0071] 12. Polarization curves of the battery negative electrode materials described in Embodiment 1 and Comparative Example 3 of this application, as shown... Figure 12 As shown.

[0072] from Figure 12As can be seen, since the negative electrode material of the battery described in Comparative Example 3 was not air-activated, the electrode sample had a poor pore structure, resulting in a significant decrease in current density in the flow battery.

[0073] 13. The energy efficiency and coulombic efficiency of the battery anode materials described in Embodiment 1 and Comparative Examples 1-3 of this application are respectively as follows: Figure 13 and Figure 14 As shown.

[0074] from Figure 13 and Figure 14 As can be seen, Comparative Example 1 was not microwave-treated, Comparative Example 2 did not contain dicyandiamide, and Comparative Example 3 was not air-activated. The porous carbons in Comparative Examples 1-3 did not form a good pore structure and specific surface area, resulting in poor conductivity (electrochemical impedance) and mass transfer performance (current density) of the battery negative electrode material. Therefore, their energy efficiency and coulombic efficiency were lower than those of the electrode in Example 1.

[0075] Although the above embodiments have been shown and described, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Any changes, modifications, substitutions and variations made to the above embodiments by those skilled in the art are within the protection scope of the present invention.

Claims

1. A method for preparing a negative electrode material for a vanadium redox flow battery, characterized in that, Includes the following steps: (1) Mix agricultural and forestry waste, phosphoric acid and nitrogen source, and perform microwave pretreatment to obtain biomass precursor; (2) The biomass precursor, carbon felt, cobalt source and solvent are mixed and subjected to hydrothermal reaction to obtain the electrode precursor; (3) The electrode precursor is subjected to pyrolysis and activation treatment in sequence to obtain the negative electrode material of the flow battery.

2. The method for preparing the vanadium redox flow battery negative electrode material according to claim 1, characterized in that, The agricultural and forestry waste includes one or more of cotton stalks, corn stalks, fruit pits, rice husks, and peanut shells; And / or, the nitrogen source includes one or more of dicyandiamide, urea, melamine, and carbamide; And / or, the mass-to-volume ratio of the agricultural and forestry waste to the phosphoric acid is 10 g: (20-30) mL; the mass concentration of the phosphoric acid is 48%-55%; And / or, the mass ratio of the agricultural and forestry waste to the nitrogen source is 100:(1-5).

3. The method for preparing the vanadium redox flow battery negative electrode material according to claim 1, characterized in that, The microwave pretreatment power is 200-500W, and the time is 15-45min.

4. The method for preparing the vanadium redox flow battery negative electrode material according to claim 1, characterized in that, The mass ratio of the biomass precursor to the carbon felt is 1:(5-20). And / or, the mass ratio of the biomass precursor to the cobalt source is 1:(1-5).

5. The method for preparing the vanadium redox flow battery negative electrode material according to claim 1, characterized in that, The cobalt source is selected from one or more of cobalt acetylacetonate, cobalt nitrate hexahydrate, cobalt sulfate heptahydrate, and cobalt chloride hexahydrate; And / or, the solvent is water; And / or, the pH of the reaction solution formed in step (2) is 7.5-8.

5.

6. The method for preparing the vanadium redox flow battery negative electrode material according to claim 5, characterized in that, In step (2), pyridine is used to adjust the pH of the reaction solution.

7. The method for preparing the vanadium redox flow battery negative electrode material according to claim 1, characterized in that, In step (2), the temperature for mixing and reaction is 160-200℃ and the time is 8-12h.

8. The method for preparing the vanadium redox flow battery negative electrode material according to claim 1, characterized in that, In step (3), the pyrolysis temperature is 700-1000℃ and the time is 1-3h; And / or, the atmosphere for the pyrolysis is an inert atmosphere; And / or, the heating rate of the pyrolysis is 8-12 °C / min.

9. The method for preparing the vanadium redox flow battery negative electrode material according to claim 1, characterized in that, In step (3), the activation treatment is performed at a temperature of 250-400℃ for 2-6 hours. And / or, the activation atmosphere is an air atmosphere.

10. A vanadium redox flow battery anode material, characterized in that, It is prepared by the preparation method according to any one of claims 1-9.

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