Preparation method of modified zinc-bromine flow battery carbon felt negative electrode and carbon felt negative electrode prepared by method

Abstract

The invention discloses a preparation method of a modified zinc-bromine flow battery carbon felt negative electrode and the carbon felt negative electrode prepared by the method, and belongs to the field of zinc-bromine flow batteries. A copper organic matter precursor is heated and gasified in a double-temperature-zone tubular furnace, molecules of the partially gasified copper organic matter precursor are loaded to the position where a carbon felt is located by hydrogen and adsorbed on the carbon felt, the copper organic matter precursor reacts with the hydrogen to form a copper elementary substance, and the copper elementary substance is attached to the surface of the carbon felt to form a load. Therefore, the purpose of modifying the carbon felt by loading the copper elementary substance is achieved. According to the method, the obstruction of low conductivity of the loaded oxide on electron transfer in the zinc deposition / stripping process is overcome; inactivation caused by reaction of loaded metal active sites and electrolyte acidic components is avoided; and the problem that the internal fibers of the carbon felt are difficult to uniformly load metal elementary substances or oxide particles due to high surface tension between the metal salt solution and the carbon felt is solved, efficient and uniform loading of the copper elementary substances on the carbon felt is realized, and the negative electrode performance of the zinc-bromine flow battery is remarkably improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of zinc-bromine flow battery, and particularly relates to a preparation method of a modified carbon felt negative electrode of zinc-bromine flow battery and the carbon felt negative electrode prepared by the method. BACKGROUND

[0002] Zinc-bromine flow battery is expected to become a large-scale energy storage system technology route for promoting efficient use of renewable energy due to its low cost, high energy density, safety features and long cycle life. When zinc-bromine flow battery operates as a hybrid flow battery system, it stores energy in the form of metal zinc at the negative electrode and bromine / polybromine phase at the positive electrode. Like other flow batteries, zinc-bromine flow battery is mainly composed of electrolyte, positive and negative electrodes, separator, external storage tank and the like. As one of the key materials of flow battery, electrode provides a reaction site for the oxidation-reduction reaction in the charging and discharging process and provides a channel for the transmission of internal active substances. The performance of electrode material directly affects the electrochemical reaction rate, internal resistance of the battery and electrolyte transmission process, so electrode material is of great significance to improve the energy efficiency, power density, operation efficiency and service life of flow battery and reduce the system cost. At present, the electrode material used in flow battery is mainly carbon felt, which has the characteristics of low cost, adjustable structure and good stability, but also has problems such as incompatibility of solid-liquid interface, few active sites and large mass transfer resistance, which will cause mass transfer polarization and uneven mass transfer, and further cause zinc dendrite growth. Zinc dendrites will puncture the separator and reduce the coulombic efficiency, increase the risk of self-discharge, short circuit and battery polarization of flow battery, thereby limiting the improvement of battery energy density. Since the physicochemical properties of carbon felt electrode directly affect the rate and reversibility of the oxidation-reduction reaction of active substances in the charging and discharging process, therefore, modification of the negative carbon felt electrode is of great importance to promote the industrialization of zinc-bromine flow battery.

[0003] In order to improve the compatibility of the solid-liquid interface between the electrolyte and the carbon felt electrode, increase the active sites of zinc deposition on the carbon felt, and form a uniform zinc deposition layer on the carbon felt, and inhibit the formation of zinc dendrites, researchers have adopted the modification method of loading metal elements or oxides on the carbon felt. The Chinese patent document with publication number CN117832517A discloses a method of loading nickel, tin, cobalt and other metal oxides on the surface of carbon felt through high-temperature heat treatment. By modifying the carbon felt electrode with metal oxides, the electrochemical performance, power density, energy efficiency and cycle stability of the zinc-bromine flow battery are significantly improved. However, the conductivity of the loaded metal oxides is low, and as the electrochemical reaction active site, it is not conducive to the transfer of electrons during the zinc deposition / peeling process between the carbon felt and the zinc deposition layer. The Chinese patent document with publication number CN106159286A discloses a method of depositing tin on the surface of carbon felt using a slightly alkaline electrolyte. Through the electroplating process, tin is uniformly plated on the surface of carbon fiber, which not only reduces the nucleation overpotential of Zn, but also increases the hydrogen evolution overpotential. This helps to prevent the formation of zinc dendrites under high surface capacity conditions, thereby improving the cycle life and reliability of the battery. However, the tin deposited on the surface of the carbon felt has relatively active chemical reaction activity. During the charging and discharging process of the battery, the acidic substances in the electrolyte will react with the tin, causing the tin active site of zinc deposition to fail. In addition, the implementation process of such technical solutions requires soaking the carbon felt in the corresponding metal salt solution. Due to the relatively poor hydrophilicity of the carbon felt, there is a large surface tension between the metal salt solution and the carbon felt, so the internal pores of the carbon felt are not completely infiltrated, which will cause the internal fibers of the carbon felt to not load the corresponding metal element or oxide particles. SUMMARY

[0004] The purpose of the present application is to provide a preparation method for modifying the carbon felt negative electrode of a zinc-bromine flow battery, which can solve the problem of low conductivity of the oxide loaded on the surface of the carbon felt, affecting the electron transfer during the zinc deposition / peeling process; solve the problem of reaction between the loaded metal active sites and the acidic substances in the electrolyte, causing the active sites to fail; solve the problem of the internal fibers of the carbon felt not loading the corresponding metal element or oxide particles due to the large surface tension between the metal salt solution and the carbon felt.

[0005] To solve the above technical problems, the present application provides a preparation method for modifying the carbon felt negative electrode of a zinc-bromine flow battery, which comprises the following steps: (1) vacuum drying the cleaned carbon felt to obtain carbon felt A; (2) placing the copper organic precursor in the temperature zone A of the gas inlet of the double-temperature-zone tube furnace, placing the carbon felt A in the temperature zone B of the gas outlet, introducing hydrogen, raising the temperature zone A to 50-350 DEG C at a rate of 3-9 DEG C / min, raising the temperature zone B to 400-900 DEG C at the same rate, and keeping the temperature for 5-15 h to carry out the vapor deposition reaction, and then naturally reducing to room temperature to obtain the carbon felt B; the copper organic precursor can form copper atoms under the high-temperature hydrogen atmosphere; (3) washing and vacuum drying the carbon felt B to obtain the carbon felt negative electrode of the copper single-element modified zinc-bromine flow battery.

[0006] Preferably, in step (1), the temperature of the vacuum drying is 60-190 DEG C, and the time is 8-22 h.

[0007] Preferably, in step (2), the copper organic precursor is one of bis(hexafluoroacetylacetone) copper (II), copper acetylacetonate and bis(dimethylamino-2-propoxy) copper (II); the mass ratio of the copper organic precursor to the carbon felt A is 1-10:1.

[0008] Preferably, in step (2), the hydrogen flow rate is 50-200 ml / min.

[0009] Preferably, in step (3), the temperature of the vacuum drying is 100-200 DEG C, and the time is 12-24 h.

[0010] The application further provides a carbon felt negative electrode of a copper single-element modified zinc-bromine flow battery, which is prepared by the above method; the carbon felt negative electrode comprises a carbon felt matrix and copper single-element particles loaded on the carbon felt.

[0011] Compared with the prior art, the application has the following beneficial effects: (1) The technical scheme of the present application loads copper elemental particles on the carbon felt negative electrode through a vapor deposition process. In this process, the gaseous copper organic precursor is not affected by the surface tension between solid and liquid, and can fill all the pores of the carbon felt, thereby ensuring the loading of copper elemental particles on the surface and internal fibers of the carbon felt. The loaded copper element has good chemical stability and is not prone to chemical reaction with acidic substances in the electrolyte. This feature effectively avoids the problem of active sites being disabled due to side reactions during charging and discharging. At the same time, copper has good electrical conductivity. During the electrochemical reaction, the copper elemental particles loaded on the carbon felt act as active sites for zinc deposition, which can quickly transfer electrons between the carbon felt and the zinc deposition layer, facilitating the rapid transfer of electrons during zinc deposition / peeling, effectively reducing the interfacial charge transfer resistance and facilitating the electrochemical reaction. In addition, due to the strong electronic coupling between copper atoms and zinc lattices, copper has a zinc affinity. The copper elemental particles loaded on the surface of the carbon felt can significantly reduce the activation energy required for zinc ion reduction nucleation and form active sites for electrochemical reaction on the surface of the carbon felt. The good zinc affinity of copper atoms allows zinc to preferentially deposit on the active sites formed by copper rather than on the deposited zinc sites, thereby inhibiting the further development of zinc deposition unevenness during charging and ultimately achieving the inhibition of zinc dendrite growth. The zinc-bromine flow battery using the copper elemental modified carbon felt prepared by the technical scheme of embodiment 1 as the negative electrode has an energy efficiency and coulombic efficiency retention rate of 95.7% and 94.5% after 1600 cycles, respectively, showing excellent cycle performance. This indicates that the copper elemental loading on the carbon felt has been playing the role of zinc deposition active site during the cycle of the battery.

[0012] (2) The copper organic precursor used in the technical scheme of the present application has a low evaporation temperature and a high saturated vapor pressure, which can ensure that sufficient copper organic precursor can be carried to the carbon felt position and reduced to form copper elemental loading, i.e. copper atoms are formed under a high-temperature hydrogen atmosphere, thereby forming copper elemental particles on the carbon felt. The organic ligand by-product formed in the reaction has good volatility and can be easily removed from the double-zone tube furnace, effectively avoiding the impact of the by-product on the deposited copper elemental particles.

[0013] (3) The technical scheme of the present application significantly improves the performance of zinc-bromine flow battery by precisely regulating key process parameters. First, the mass ratio of copper organic precursor to carbon felt A needs to be controlled, which affects the number of copper single particle loaded on the carbon felt. The inventor found that if the ratio is too small, the number of copper single particles loaded on the carbon felt is too small, which cannot effectively increase the active sites for zinc deposition; if the ratio is too large, the number of copper single particles loaded on the carbon felt is too large, which blocks the pore structure of the carbon felt, affects the transmission of electrolyte inside the carbon felt, and reduces the available space position for zinc deposition; therefore, a suitable mass ratio of copper organic precursor to carbon felt A can not only introduce enough copper single zinc deposition active sites on the carbon felt, but also avoid the blockage of the pore structure of the carbon felt by copper single. Second, the hydrogen flow rate plays a key role in reaction equilibrium and product discharge. The inventor found that too fast hydrogen flow rate will blow out more copper organic precursor and hydrogen gas reaction to form copper single from the double-temperature zone tube furnace, which is not conducive to the loading of copper single on the carbon felt, causing waste of copper organic precursor; too slow hydrogen flow rate cannot take out volatile organic ligand formed by the reaction of copper organic precursor and hydrogen gas from the double-temperature zone tube furnace, which interferes with the copper deposition process; therefore, a suitable hydrogen flow rate can achieve efficient delivery of the precursor and timely discharge of by-products. Third, the temperature and holding time of each temperature zone also need to be controlled well. The inventor found that a suitable temperature in temperature zone A can ensure that the copper organic precursor can be vaporized and gasified without decomposition; a suitable temperature in temperature zone B can ensure that the copper deposited on the carbon felt has high crystallinity and high bonding strength between the carbon felt, avoiding the falling off of the copper loading; a suitable holding time in the two temperature zones can ensure that the reaction is completely carried out, while controlling the particle size of copper particles, further improving the crystallinity of copper single and the bonding strength between copper loading and carbon felt. In summary, due to the synergistic optimization of the above parameters, efficient and uniform loading of copper single is achieved, which lays the foundation for the improvement of battery performance.

[0014] (4) The present application significantly improves the performance of zinc-bromine flow battery by loading copper single particles on the carbon felt negative electrode through the vapor deposition process. Experimental results show that under the conditions of current density of 60 mA / cm 2 , specific capacity of 40 mAh / cm 2 , the zinc-bromine flow battery with the copper single modified carbon felt prepared by the present technical scheme as the negative electrode can achieve a coulombic efficiency of up to 95.0-97.4%, a voltage efficiency of 82.6-85.3%, and an energy efficiency of 78.5-83.1%. The zinc-bromine flow battery with the copper single modified carbon felt prepared in Example 1 as the negative electrode has a retention rate of energy efficiency and coulombic efficiency of 95.7% and 94.5% respectively after 1600 cycles, showing excellent cycle performance. The negative electrode material has good chemical and electrochemical stability, and has wide application prospect, which will make the zinc-bromine flow battery have better electrochemical performance and longer service life in practical application. Attached Figure Description

[0015] Figure 1 The constant current charge-discharge curves are used to test the electrochemical performance of the copper-modified carbon felt prepared in Example 1 of this invention and the carbon felt in Comparative Example 1, respectively, as the negative electrodes of the zinc-bromine flow battery. Figure 2 Cyclic curves for electrochemical performance testing of the copper-modified carbon felt prepared in Example 1 of this invention as the negative electrode of a zinc-bromine flow battery. Figure 3 Cyclic curves for electrochemical performance testing using carbon felt as the negative electrode of a zinc-bromine flow battery (Comparative Example 1). Figure 4 X-ray diffraction (XRD) patterns of copper-modified carbon felt and unmodified carbon felt prepared in Example 1 of this invention; Figure 5 This is a scanning electron microscope (SEM) image of the copper-modified carbon felt prepared in Example 1 of the present invention. Figure 6 This is a scanning electron microscope (SEM) image of carbon felt, Comparative Example 1 of the present invention; Figure 7 This is an electron image collected during energy-dispersive X-ray spectroscopy analysis of the copper-modified carbon felt prepared in Example 1 of this invention; Figure 8 for Figure 7 Energy dispersive X-ray spectra (EDS) of selected regions. Detailed Implementation

[0016] To make the present invention more apparent and understandable, the technical solution of the present invention will be further described and illustrated below through embodiments and in conjunction with the accompanying drawings, but this is not intended to limit the scope of protection of the present invention.

[0017] The dual-temperature zone tube furnace used in this invention is model OTF-1200X-II, purchased from Hefei Kejing Materials Technology Co., Ltd.; the three copper organic precursors, namely bis(hexafluoroacetylacetone)copper(II), copper acetylacetonate, and bis(dimethylamino-2-propoxy)copper(II), were purchased from Gaide Chemicals website; other pharmaceuticals and reagents were purchased from Aladdin website or Guoyao Reagents website. Example 1

[0018] The carbon felt is cleaned to remove impurities on the surface of the carbon felt, and the cleaned carbon felt is placed in a vacuum oven and dried at 125°C for 15h to obtain carbon felt A; the copper organic precursor bis(hexafluoroacetylacetone) copper (II) is placed in temperature zone A close to the gas inlet of the double temperature zone tube furnace, and the carbon felt A is placed in temperature zone B close to the gas outlet of the double temperature zone tube furnace, and the mass ratio of the copper organic precursor to the carbon felt A is 5:1, hydrogen is introduced to replace the air in the double temperature zone tube furnace, and then the flow rate of the hydrogen is adjusted to 125ml / min, temperature zone A is heated to 200°C at a rate of 6°C / min, and temperature zone B is heated to 650°C at the same heating rate, and after the temperature of the two temperature zones reaches the set temperature, the gas phase deposition reaction is carried out for 10h, and after the heat preservation is completed, the double temperature zone tube furnace is naturally cooled to room temperature, and hydrogen is introduced at the same flow rate as the heating stage during the heat preservation and cooling stage, and then the carbon felt is taken out to obtain carbon felt B; the obtained carbon felt B is washed with deionized water and ethanol, and the washed carbon felt is vacuum dried at 150°C for 18h to obtain the carbon felt negative electrode of the copper element modified zinc-bromine flow battery.

[0019] During the reaction process, the copper organic precursor bis(hexafluoroacetylacetone) copper (II) placed in temperature zone A is gasified during heating, and part of the gasified bis(hexafluoroacetylacetone) copper (II) molecules are carried by hydrogen to temperature zone B and adsorbed on the carbon felt, and bis(hexafluoroacetylacetone) copper (II) reacts with hydrogen to form copper single element and organic ligand byproduct. The organic ligand byproduct is discharged from the double temperature zone tube furnace with the gas after the reaction. The copper single element adheres to the surface of the carbon felt to form a load, thereby achieving the purpose of loading modification of the carbon felt by copper single element.

[0020] Compared with other liquid-phase processes, the gas-phase deposition process is not affected by the surface tension between solid and liquid, and the vaporized copper organic precursor can fill all pores of the carbon felt, which is conducive to loading copper particles on the surface and internal fibers of the carbon felt. The copper particles loaded on the surface of the carbon felt are chemically stable and not prone to chemical reaction with acid. This can avoid the reaction with acidic substances in the electrolyte during the charging and discharging process, thereby avoiding the inactivation of the active sites for zinc deposition. Copper has good electrical conductivity, and during the electrochemical reaction, the copper particles loaded on the carbon felt can quickly transfer electrons between the carbon felt and the zinc deposition layer as active sites for zinc deposition, which is conducive to the rapid transfer of electrons during the zinc deposition and stripping process, effectively reduces the interfacial charge transfer resistance, and thus facilitates the electrochemical reaction. In addition, due to the strong electronic coupling between copper atoms and zinc lattices, copper has a zinc affinity, and the copper particles loaded on the surface of the carbon felt can significantly reduce the activation energy required for the reduction of zinc ions to nucleate and form active sites for electrochemical reaction on the surface of the carbon felt. The good zinc affinity of copper atoms can make zinc preferentially deposit on the active sites formed by copper rather than the deposited zinc sites, thereby inhibiting the further development of uneven zinc deposition during the charging process, and ultimately achieving the inhibition of zinc dendrite growth. Example 2

[0021] The carbon felt was cleaned to remove impurities on the surface of the carbon felt, and the cleaned carbon felt was placed in a vacuum oven at 100°C for 18h to obtain carbon felt A; the copper organic precursor copper acetylacetonate was placed in temperature zone A close to the gas inlet of the double-temperature zone tube furnace, and the carbon felt A was placed in temperature zone B close to the gas outlet of the double-temperature zone tube furnace, and the mass ratio of the copper organic precursor to the carbon felt A was 6:1; hydrogen was introduced to replace the air in the double-temperature zone tube furnace, and then the flow rate of hydrogen was adjusted to 150ml / min; temperature zone A was heated to 220°C at a rate of 7°C / min, and temperature zone B was heated to 660°C at the same heating rate; after the temperature of both temperature zones reached the set temperature, the gas-phase deposition reaction was carried out for 9h; after the heat preservation was completed, the double-temperature zone tube furnace was naturally cooled to room temperature; during the heat preservation and cooling stages, hydrogen was introduced at the same flow rate as the heating stage; then the carbon felt was taken out to obtain carbon felt B; the obtained carbon felt B was washed with deionized water and ethanol, and then the washed carbon felt was vacuum dried at 140°C for 19h to obtain the copper-modified carbon felt negative electrode for zinc-bromine flow battery. Example 3

[0022] The carbon felt was cleaned to remove impurities on the surface of the carbon felt, and the cleaned carbon felt was placed in a vacuum oven and dried at 150°C for 12h to obtain carbon felt A; the copper organic precursor bis(dimethylamino-2-propoxy) copper (II) was placed in temperature zone A close to the gas inlet of the double-temperature zone tube furnace, and the carbon felt A was placed in temperature zone B close to the gas outlet of the double-temperature zone tube furnace, the mass ratio of the copper organic precursor to the carbon felt A was 4:1, hydrogen was introduced to replace the air in the double-temperature zone tube furnace, then the flow rate of hydrogen was adjusted to 100ml / min, temperature zone A was heated to 180°C at a rate of 5°C / min, and temperature zone B was heated to 640°C at the same heating rate, after the temperature of both temperature zones reached the set temperature, the gas phase deposition reaction was carried out for 11h, after the heat preservation was completed, the double-temperature zone tube furnace was naturally cooled to room temperature, hydrogen was introduced at the same flow rate as the heating stage during the heat preservation and cooling stage, then the carbon felt was taken out to obtain carbon felt B; the obtained carbon felt B was washed with deionized water and ethanol, and the washed carbon felt was vacuum dried at 160°C for 17h to obtain the carbon felt negative electrode of the copper elemental modified zinc-bromine flow battery. Example 4

[0023] The carbon felt was cleaned to remove impurities on the surface of the carbon felt, and the cleaned carbon felt was placed in a vacuum oven and dried at 80°C for 20h to obtain carbon felt A; the copper organic precursor bis(hexafluoroacetylacetone) copper (II) was placed in temperature zone A close to the gas inlet of the double-temperature zone tube furnace, and the carbon felt A was placed in temperature zone B close to the gas outlet of the double-temperature zone tube furnace, the mass ratio of the copper organic precursor to the carbon felt A was 3:1, hydrogen was introduced to replace the air in the double-temperature zone tube furnace, then the flow rate of hydrogen was adjusted to 80ml / min, temperature zone A was heated to 100°C at a rate of 4°C / min, and temperature zone B was heated to 500°C at the same heating rate, after the temperature of both temperature zones reached the set temperature, the gas phase deposition reaction was carried out for 13h, after the heat preservation was completed, the double-temperature zone tube furnace was naturally cooled to room temperature, hydrogen was introduced at the same flow rate as the heating stage during the heat preservation and cooling stage, then the carbon felt was taken out to obtain carbon felt B; the obtained carbon felt B was washed with deionized water and ethanol, and the washed carbon felt was vacuum dried at 120°C for 21h to obtain the carbon felt negative electrode of the copper elemental modified zinc-bromine flow battery. Example 5

[0024] The carbon felt was cleaned to remove impurities on the surface of the carbon felt, and the cleaned carbon felt was placed in a vacuum oven and dried at 170°C for 10h to obtain carbon felt A; the copper organic precursor bis(hexafluoroacetylacetone)copper(II) was placed in temperature zone A close to the gas inlet of the double-temperature zone tube furnace, and the carbon felt A was placed in temperature zone B close to the gas outlet of the double-temperature zone tube furnace, the mass ratio of the copper organic precursor to the carbon felt A was 8:1, hydrogen was introduced to replace the air in the double-temperature zone tube furnace, then the flow rate of hydrogen was adjusted to 180ml / min, temperature zone A was heated to 300°C at a rate of 8°C / min, and temperature zone B was heated to 800°C at the same heating rate, after the temperature of the two temperature zones reached the set temperature, the gas phase deposition reaction was carried out for 7h, after the heat preservation was completed, the double-temperature zone tube furnace was naturally cooled to room temperature, hydrogen was introduced at the same flow rate as the heating stage during the heat preservation and cooling stage, then the carbon felt was taken out to obtain carbon felt B; the obtained carbon felt B was washed with deionized water and ethanol, and the washed carbon felt was vacuum dried at 180°C for 15h to obtain the carbon felt negative electrode of the zinc-bromine flow battery modified by copper element. Example 6

[0025] The carbon felt was cleaned to remove impurities on the surface of the carbon felt, and the cleaned carbon felt was placed in a vacuum oven and dried at 60°C for 22h to obtain carbon felt A; the copper organic precursor bis(hexafluoroacetylacetone)copper(II) was placed in temperature zone A close to the gas inlet of the double-temperature zone tube furnace, and the carbon felt A was placed in temperature zone B close to the gas outlet of the double-temperature zone tube furnace, the mass ratio of the copper organic precursor to the carbon felt A was 1:1, hydrogen was introduced to replace the air in the double-temperature zone tube furnace, then the flow rate of hydrogen was adjusted to 50ml / min, temperature zone A was heated to 50°C at a rate of 3°C / min, and temperature zone B was heated to 400°C at the same heating rate, after the temperature of the two temperature zones reached the set temperature, the gas phase deposition reaction was carried out for 15h, after the heat preservation was completed, the double-temperature zone tube furnace was naturally cooled to room temperature, hydrogen was introduced at the same flow rate as the heating stage during the heat preservation and cooling stage, then the carbon felt was taken out to obtain carbon felt B; the obtained carbon felt B was washed with deionized water and ethanol, and the washed carbon felt was vacuum dried at 200°C for 12h to obtain the carbon felt negative electrode of the zinc-bromine flow battery modified by copper element. Example 7

[0026] The carbon felt was washed to remove impurities on the surface of the carbon felt, and the washed carbon felt was placed in a vacuum oven and dried at 190°C for 8h to obtain carbon felt A; the copper organic precursor bis(hexafluoroacetylacetone) copper (II) was placed in temperature zone A close to the gas inlet of the double temperature zone tube furnace, and the carbon felt A was placed in temperature zone B close to the gas outlet of the double temperature zone tube furnace, and the mass ratio of the copper organic precursor to the carbon felt A was 10:1; hydrogen was introduced to replace the air in the double temperature zone tube furnace, and then the flow rate of hydrogen was adjusted to 200ml / min; temperature zone A was heated to 350°C at a rate of 9°C / min, and temperature zone B was heated to 900°C at the same heating rate; after the temperature of the two temperature zones reached the set temperature, the gas phase deposition reaction was carried out for 5h; after the heat preservation was completed, the double temperature zone tube furnace was naturally cooled to room temperature; hydrogen was introduced at the same flow rate as the heating stage during the heat preservation and cooling stage; then the carbon felt was taken out to obtain carbon felt B; the obtained carbon felt B was washed with deionized water and ethanol, and then vacuum dried at 100°C for 24h to obtain the carbon felt negative electrode of the zinc-bromine flow battery modified by copper single element. Comparative Example 1

[0027] The carbon felt was washed to remove impurities on the surface of the carbon felt, and the washed carbon felt was placed in a vacuum oven and dried at 125°C for 15h to obtain carbon felt A; the carbon felt A was placed in temperature zone B close to the gas outlet of the double temperature zone tube furnace, and hydrogen was introduced to replace the air in the double temperature zone tube furnace; then the flow rate of hydrogen was adjusted to 125ml / min; temperature zone A close to the gas inlet was heated to 200°C at a rate of 6°C / min, and temperature zone B was heated to 650°C at the same heating rate; after the temperature of the two temperature zones reached the set temperature, the heat preservation was carried out for 10h; after the heat preservation was completed, the double temperature zone tube furnace was naturally cooled to room temperature; hydrogen was introduced at the same flow rate as the heating stage during the heat preservation and cooling stage; then the carbon felt was taken out to obtain carbon felt B; the obtained carbon felt B was washed with deionized water and ethanol, and then vacuum dried at 150°C for 18h to obtain the carbon felt negative electrode of the zinc-bromine flow battery.

[0028] The difference between Example 1 and Comparative Example 1 is that no copper organic precursor was placed in the double temperature zone tube furnace during the implementation process of Comparative Example 1, and only the carbon felt was simply heat treated, without loading copper single element on the carbon felt. Comparative Example 2

[0029] The carbon felt was washed to remove impurities on the surface of the carbon felt, and the washed carbon felt was placed in a vacuum oven at 125°C for 15h to obtain carbon felt A; the copper organic precursor bis(hexafluoroacetylacetone) copper (II) was placed in temperature zone A close to the gas inlet of the double temperature zone tube furnace, and the carbon felt A was placed in temperature zone B close to the gas outlet of the double temperature zone tube furnace, the mass ratio of the copper organic precursor to the carbon felt A was 15:1, hydrogen was introduced to replace the air in the double temperature zone tube furnace, then the flow rate of hydrogen was adjusted to 125ml / min, temperature zone A was heated to 200°C at a rate of 6°C / min, and temperature zone B was heated to 650°C at the same heating rate, after the temperature of the two temperature zones reached the set temperature, the gas phase deposition reaction was carried out for 10h, after the heat preservation was completed, the double temperature zone tube furnace was naturally cooled to room temperature, hydrogen was introduced at the same flow rate as the heating stage during the heat preservation and cooling stage, then the carbon felt was taken out to obtain carbon felt B; the obtained carbon felt B was washed with deionized water and ethanol, and the washed carbon felt was vacuum dried at 150°C for 18h to obtain the carbon felt negative electrode of the copper element modified zinc-bromine flow battery.

[0030] The difference from Example 1 is that the mass ratio of the copper organic precursor to the carbon felt A in Comparative Example 2 is 15:1, which is higher than the value of this process parameter in all examples. Comparative Example 3

[0031] The carbon felt was washed to remove impurities on the surface of the carbon felt, and the washed carbon felt was placed in a vacuum oven at 125°C for 15h to obtain carbon felt A; the copper organic precursor bis(hexafluoroacetylacetone) copper (II) was placed in temperature zone A close to the gas inlet of the double temperature zone tube furnace, and the carbon felt A was placed in temperature zone B close to the gas outlet of the double temperature zone tube furnace, the mass ratio of the copper organic precursor to the carbon felt A was 15:1, hydrogen was introduced to replace the air in the double temperature zone tube furnace, then the flow rate of hydrogen was adjusted to 125ml / min, temperature zone A was heated to 200°C at a rate of 6°C / min, and temperature zone B was heated to 650°C at the same heating rate, after the temperature of the two temperature zones reached the set temperature, the gas phase deposition reaction was carried out for 10h, after the heat preservation was completed, the double temperature zone tube furnace was naturally cooled to room temperature, hydrogen was introduced at the same flow rate as the heating stage during the heat preservation and cooling stage, then the carbon felt was taken out to obtain carbon felt B; the obtained carbon felt B was washed with deionized water and ethanol, and the washed carbon felt was vacuum dried at 150°C for 18h to obtain the carbon felt negative electrode of the copper element modified zinc-bromine flow battery.

[0032] The difference from Example 1 is that the mass ratio of the copper organic precursor to the carbon felt A in Comparative Example 3 is 0.2:1, which is lower than the value of this process parameter in all examples. Comparative Example 4

[0033] The carbon felt was washed to remove impurities on the surface of the carbon felt, and the washed carbon felt was placed in a vacuum oven at 125°C for 15h to obtain carbon felt A; the copper organic precursor bis(hexafluoroacetylacetone) copper (II) was placed in temperature zone A close to the gas inlet of the double temperature zone tube furnace, and the carbon felt A was placed in temperature zone B close to the gas outlet of the double temperature zone tube furnace, the mass ratio of the copper organic precursor to the carbon felt A was 5:1, hydrogen was introduced to replace the air in the double temperature zone tube furnace, then the flow rate of hydrogen was adjusted to 10ml / min, temperature zone A was heated to 200°C at a rate of 6°C / min, and temperature zone B was heated to 650°C at the same heating rate, after the temperature of the two temperature zones reached the set temperature, the gas phase deposition reaction was carried out for 10h, after the heat preservation was completed, the double temperature zone tube furnace was naturally cooled to room temperature, hydrogen was introduced at the same flow rate as the heating stage during the heat preservation and cooling stage, then the carbon felt was taken out to obtain carbon felt B; the obtained carbon felt B was washed with deionized water and ethanol, and the washed carbon felt was vacuum dried at 150°C for 18h to obtain the carbon felt negative electrode of the zinc-bromine flow battery modified by copper element.

[0034] The difference from Example 1 is that the flow rate of hydrogen in Comparative Example 4 is 10ml / min, which is lower than the value of this process parameter in all examples. Comparative Example 5

[0035] The carbon felt was washed to remove impurities on the surface of the carbon felt, and the washed carbon felt was placed in a vacuum oven at 125°C for 15h to obtain carbon felt A; the copper organic precursor bis(hexafluoroacetylacetone) copper (II) was placed in temperature zone A close to the gas inlet of the double temperature zone tube furnace, and the carbon felt A was placed in temperature zone B close to the gas outlet of the double temperature zone tube furnace, the mass ratio of the copper organic precursor to the carbon felt A was 5:1, hydrogen was introduced to replace the air in the double temperature zone tube furnace, then the flow rate of hydrogen was adjusted to 300ml / min, temperature zone A was heated to 200°C at a rate of 6°C / min, and temperature zone B was heated to 650°C at the same heating rate, after the temperature of the two temperature zones reached the set temperature, the gas phase deposition reaction was carried out for 10h, after the heat preservation was completed, the double temperature zone tube furnace was naturally cooled to room temperature, hydrogen was introduced at the same flow rate as the heating stage during the heat preservation and cooling stage, then the carbon felt was taken out to obtain carbon felt B; the obtained carbon felt B was washed with deionized water and ethanol, and the washed carbon felt was vacuum dried at 150°C for 18h to obtain the carbon felt negative electrode of the zinc-bromine flow battery modified by copper element.

[0036] The difference from Example 1 is that the flow rate of hydrogen in Comparative Example 5 is 300ml / min, which is higher than the value of this process parameter in all examples. Comparative Example 6

[0037] The carbon felt was washed to remove impurities on the surface of the carbon felt, and the washed carbon felt was placed in a vacuum oven at 125°C for 15h to obtain carbon felt A; the copper organic precursor bis(hexafluoroacetylacetone) copper (II) was placed in temperature zone A close to the gas inlet of the double temperature zone tube furnace, and the carbon felt A was placed in temperature zone B close to the gas outlet of the double temperature zone tube furnace, the mass ratio of the copper organic precursor to the carbon felt A was 5:1, hydrogen was introduced to replace the air in the double temperature zone tube furnace, then the flow rate of hydrogen was adjusted to 125ml / min, temperature zone A was heated to 30°C at a rate of 6°C / min, and temperature zone B was heated to 360°C at the same heating rate, after the temperature of the two temperature zones reached the set temperature, the gas phase deposition reaction was carried out for 10h, after the heat preservation was completed, the double temperature zone tube furnace was naturally cooled to room temperature, hydrogen was introduced at the same flow rate as the heating stage during the heat preservation and cooling stage, then the carbon felt was taken out to obtain carbon felt B; the obtained carbon felt B was washed with deionized water and ethanol, and the washed carbon felt was vacuum dried at 150°C for 18h to obtain the carbon felt negative electrode of the copper element modified zinc-bromine flow battery.

[0038] The difference from Example 1 is that the heat preservation temperature of temperature zone A of Comparative Example 6 is 30°C, and the heat preservation temperature of temperature zone B is 360°C, which is lower than the value of this process parameter in all examples. Comparative Example 7

[0039] The carbon felt was washed to remove impurities on the surface of the carbon felt, and the washed carbon felt was placed in a vacuum oven at 125°C for 15h to obtain carbon felt A; the copper organic precursor bis(hexafluoroacetylacetone) copper (II) was placed in temperature zone A close to the gas inlet of the double temperature zone tube furnace, and the carbon felt A was placed in temperature zone B close to the gas outlet of the double temperature zone tube furnace, the mass ratio of the copper organic precursor to the carbon felt A was 5:1, hydrogen was introduced to replace the air in the double temperature zone tube furnace, then the flow rate of hydrogen was adjusted to 125ml / min, temperature zone A was heated to 400°C at a rate of 6°C / min, and temperature zone B was heated to 1000°C at the same heating rate, after the temperature of the two temperature zones reached the set temperature, the gas phase deposition reaction was carried out for 10h, after the heat preservation was completed, the double temperature zone tube furnace was naturally cooled to room temperature, hydrogen was introduced at the same flow rate as the heating stage during the heat preservation and cooling stage, then the carbon felt was taken out to obtain carbon felt B; the obtained carbon felt B was washed with deionized water and ethanol, and the washed carbon felt was vacuum dried at 150°C for 18h to obtain the carbon felt negative electrode of the copper element modified zinc-bromine flow battery.

[0040] The difference from Example 1 is that the heat preservation temperature of temperature zone A of Comparative Example 7 is 400°C, and the heat preservation temperature of temperature zone B is 1000°C, which is higher than the value of this process parameter in all examples. Comparative Example 8

[0041] The carbon felt was washed to remove impurities on the surface of the carbon felt, and the washed carbon felt was placed in a vacuum oven at 125°C for 15h to obtain carbon felt A; the copper organic precursor bis(hexafluoroacetylacetone) copper (II) was placed in temperature zone A close to the gas inlet of the double temperature zone tube furnace, and the carbon felt A was placed in temperature zone B close to the gas outlet of the double temperature zone tube furnace, the mass ratio of the copper organic precursor to the carbon felt A was 5:1, hydrogen was introduced to replace the air in the double temperature zone tube furnace, then the flow rate of hydrogen was adjusted to 125ml / min, temperature zone A was heated to 200°C at a rate of 6°C / min, and temperature zone B was heated to 650°C at the same heating rate, after the temperature of the two temperature zones reached the set temperature, the gas phase deposition reaction was carried out for 1h, after the heat preservation was completed, the double temperature zone tube furnace was naturally cooled to room temperature, hydrogen was introduced at the same flow rate as the heating stage during the heat preservation and cooling stage, then the carbon felt was taken out to obtain carbon felt B; the obtained carbon felt B was washed with deionized water and ethanol, and the washed carbon felt was vacuum dried at 150°C for 18h to obtain the carbon felt negative electrode of the zinc-bromine flow battery modified by copper element.

[0042] The difference from Example 1 is that the holding time of Comparative Example 8 is 1h, which is lower than the value of this process parameter in all examples. Comparative Example 9

[0043] The carbon felt was washed to remove impurities on the surface of the carbon felt, and the washed carbon felt was placed in a vacuum oven at 125°C for 15h to obtain carbon felt A; the copper organic precursor bis(hexafluoroacetylacetone) copper (II) was placed in temperature zone A close to the gas inlet of the double temperature zone tube furnace, and the carbon felt A was placed in temperature zone B close to the gas outlet of the double temperature zone tube furnace, the mass ratio of the copper organic precursor to the carbon felt A was 5:1, hydrogen was introduced to replace the air in the double temperature zone tube furnace, then the flow rate of hydrogen was adjusted to 125ml / min, temperature zone A was heated to 200°C at a rate of 6°C / min, and temperature zone B was heated to 650°C at the same heating rate, after the temperature of the two temperature zones reached the set temperature, the gas phase deposition reaction was carried out for 20h, after the heat preservation was completed, the double temperature zone tube furnace was naturally cooled to room temperature, hydrogen was introduced at the same flow rate as the heating stage during the heat preservation and cooling stage, then the carbon felt was taken out to obtain carbon felt B; the obtained carbon felt B was washed with deionized water and ethanol, and the washed carbon felt was vacuum dried at 150°C for 18h to obtain the carbon felt negative electrode of the zinc-bromine flow battery modified by copper element.

[0044] The difference from Example 1 is that the holding time of Comparative Example 9 is 20h, which is higher than the value of this process parameter in all examples. Comparative Example 10

[0045] The carbon felt was washed to remove impurities on the surface of the carbon felt, and the washed carbon felt was placed in a vacuum oven at 125°C for drying for 15h to obtain carbon felt A; the copper organic precursor bis(hexafluoroacetylacetone) copper (II) was placed in temperature zone A close to the gas inlet of the double temperature zone tube furnace, and the carbon felt A was placed in temperature zone B close to the gas outlet of the double temperature zone tube furnace, the mass ratio of the copper organic precursor to the carbon felt A was 5:1, hydrogen was introduced to replace the air in the double temperature zone tube furnace, then the flow rate of hydrogen was adjusted to 125ml / min, temperature zone A was heated to 200°C at a rate of 6°C / min, and temperature zone B was heated to 650°C at the same heating rate, after the temperature of the two temperature zones reached the set temperature, the temperature was kept for 9h, then the hydrogen was replaced by air and the flow rate was kept at 125ml / min, and the gas phase deposition reaction was continued at 650°C for 1h, after the temperature keeping ended, the double temperature zone tube furnace was naturally cooled to room temperature, air was introduced at the same flow rate as the heating stage during the temperature keeping and cooling stages, then the carbon felt was taken out to obtain carbon felt B; the obtained carbon felt B was washed with deionized water and ethanol, and the washed carbon felt was vacuum dried at 150°C for 18h to obtain the carbon felt negative electrode of the zinc-bromine flow battery modified by copper and copper oxide composite.

[0046] The difference from example 1 is that in the gas phase deposition reaction stage of keeping at 650°C, the gas passed in the first nine hours of the comparative example 10 is hydrogen, and the hydrogen is replaced by air in the tenth hour, and part of the copper loaded on the carbon felt is oxidized to copper oxide. Comparative example 11

[0047] The carbon felt was washed to remove impurities on the surface of the carbon felt, and the washed carbon felt was placed in a vacuum oven at 125°C for drying for 15h to obtain carbon felt A; the copper organic precursor bis(hexafluoroacetylacetone) copper (II) was placed in temperature zone A close to the gas inlet of the double temperature zone tube furnace, and the carbon felt A was placed in temperature zone B close to the gas outlet of the double temperature zone tube furnace, the mass ratio of the copper organic precursor to the carbon felt A was 5:1, the flow rate of air was adjusted to 125ml / min, temperature zone A was heated to 200°C at a rate of 6°C / min, and temperature zone B was heated to 650°C at the same heating rate, after the temperature of the two temperature zones reached the set temperature, the temperature was kept for 10h for the gas phase deposition reaction, after the temperature keeping ended, the double temperature zone tube furnace was naturally cooled to room temperature, air was introduced at the same flow rate as the heating stage during the temperature keeping and cooling stages, then the carbon felt was taken out to obtain carbon felt B; the obtained carbon felt B was washed with deionized water and ethanol, and the washed carbon felt was vacuum dried at 150°C for 18h to obtain the carbon felt negative electrode of the zinc-bromine flow battery modified by copper oxide.

[0048] The difference from example 1 is that in the gas phase deposition reaction stage of keeping at 650°C for 10h, the gas passed in the comparative example 11 is air, and the copper loaded on the carbon felt is oxidized to copper oxide. Comparative example 12

[0049] The carbon felt was cleaned to remove impurities on the surface of the carbon felt, and the cleaned carbon felt was placed in a vacuum oven at 125°C for 15h to obtain carbon felt A; the carbon felt A was immersed in a 3% nickel acetate aqueous solution for 5h to obtain carbon felt B, and the mass ratio of nickel acetate in the solution to the carbon felt A was controlled to be 5:1; the carbon felt B was placed in a vacuum oven at 150°C for 18h to obtain carbon felt C; the carbon felt C was placed in an atmosphere tube furnace, hydrogen was introduced to replace the air in the atmosphere tube furnace, then the flow rate of hydrogen was adjusted to 125ml / min, the atmosphere tube furnace was heated to 650°C at a rate of 6°C / min and kept for 10h, after the heat preservation was completed, the atmosphere tube furnace was naturally cooled to room temperature, and hydrogen was introduced at the same flow rate as the heating stage during the heat preservation and cooling stage, then the carbon felt was taken out to obtain carbon felt D; the obtained carbon felt D was washed with deionized water and ethanol, and the washed carbon felt was vacuum dried at 150°C for 18h to obtain the carbon felt negative electrode of the zinc-bromine flow battery modified by nickel element.

[0050] The difference from Example 1 is that Comparative Example 12 uses a liquid phase immersion process to load nickel element on the carbon felt.

[0051] The zinc-bromine flow battery was assembled for electrochemical performance test. The carbon felt prepared from the examples and comparative examples was used as the negative electrode, the unmodified carbon felt was used as the positive electrode, the microporous filter membrane was used as the separator, and the electrolyte of the positive electrode and the negative electrode was composed of 2mol / L zinc bromide, 3mol / L potassium chloride, 0.2M tetramethylammonium bromide and 0.2M tetrabutylammonium bromide. The effective area of the positive and negative carbon felt electrodes was 3cm×3cm.

[0052] The electrochemical performance of the zinc-bromine flow battery was tested by using the constant current charge and discharge mode. During the test, the positive and negative electrolytes flowed at 35mL / min, and first charged at a current of 60mA / cm 2 According to the battery charge and discharge curve, the electrochemical performance indexes such as coulombic efficiency (CE), voltage efficiency (VE) and energy efficiency (EE) were calculated.

[0053] The results of the first cycle charge and discharge test of the electrochemical performance of each material are shown in Table 1.

[0054]

[0055] The electrochemical performance data of Table 1 shows that when the copper-loaded modified carbon felt prepared by Examples 1-7 is used as the negative electrode material of the zinc-bromine flow battery, the zinc-bromine flow battery is significantly superior to the zinc-bromine flow battery using the carbon felt of Comparative Examples 1-12 in terms of three key indicators, namely, coulombic efficiency, voltage efficiency and energy efficiency. This result confirms that loading copper elemental particles on the surface of the carbon felt can effectively improve the electrochemical performance of the carbon felt as the negative electrode of the zinc-bromine flow battery. It is worth noting that among the modified materials of Examples 1-7, Example 1 developed with the optimal process parameters exhibits the best overall performance, with the three efficiency parameters reaching the highest level. As the process parameter range gradually increases, the three key indicators, namely, coulombic efficiency, voltage efficiency and energy efficiency of Examples 2-7 have a decreasing trend. The coulombic efficiency, voltage efficiency and energy efficiency of Example 1 are 97.4%, 85.3% and 83.1%, respectively; while the coulombic efficiency, voltage efficiency and energy efficiency of Example 7 are 95.0%, 82.6% and 78.5%, respectively. This can indicate that the copper organic precursor type, the mass ratio of the copper organic precursor to carbon felt A, the hydrogen flow rate, the holding temperature and the holding time of the two temperature zones and other process parameters need to be optimized and combined to significantly improve the electrochemical performance of the zinc-bromine flow battery.

[0056] Under the condition of constant charging capacity, higher coulombic efficiency directly reflects that the zinc-bromine flow battery can release more effective discharge capacity. The experimental data (Table 1) show that the coulombic efficiency of Examples 1-7 is not less than 95%, which is higher than the numerical level of Comparative Examples 1-12 (<87%). This result verifies that the copper-loaded modified carbon felt can significantly improve the reversible release capacity of electric charge, and the mechanism mainly reflects the following aspects: first, the copper nanoparticles loaded on the surface of the carbon felt have excellent zinc affinity, effectively reducing the activation energy of zinc deposition nucleation, and at the same time, increasing the number of surface active sites to improve the electrochemical activity of the carbon felt; second, the strong interaction force between copper-zinc interface can guide the uniform deposition / stripping of zinc ions on the electrode surface, and inhibit the formation of zinc dendrites.

[0057] Voltage efficiency reflects the ratio of average discharge voltage to average charge voltage during the charging and discharging process of the battery, and the size of this parameter is directly affected by the polarization during the charging and discharging process of the battery. In terms of voltage efficiency, the values of the batteries of Examples 1-7 are stable at more than 82%, which shows a certain advantage over Comparative Examples 1-12 (≤81%). The improvement of voltage efficiency is mainly due to the high conductivity of copper, which as an electrochemical active site can quickly transfer electrons between the carbon felt and the zinc deposition layer, effectively reducing the interface charge transfer resistance, thereby effectively reducing the voltage loss during the charging and discharging process.

[0058] Energy efficiency, as a result of the synergy of coulombic efficiency and voltage efficiency, is an evaluation index for evaluating the electric energy conversion efficiency of the battery in the charging and discharging process. The energy efficiency of Examples 1-7 reaches a high level of more than 78%, while that of Comparative Examples 1-12 does not exceed 70%. The performance improvement of the energy efficiency of the examples is due to the triple optimization effect of the copper-modified carbon felt: the zinc nucleation barrier is reduced by the zincophilic property of copper particles; the interface charge transfer resistance is reduced by the high electrical conductivity of copper particles, reducing polarization; and the uniform deposition / stripping of zinc is achieved by the strong interfacial interaction between copper and zinc. The synergistic effect of these beneficial effects significantly improves the energy conversion efficiency of the examples.

[0059] As can be seen from Comparative Example 1 and Comparative Example 1, the performance indicators of Example 1 are much better than those of Comparative Example 1. This can indicate that simple heat treatment of carbon felt without loading copper single substance cannot achieve the purpose of improving the electrochemical performance of carbon felt.

[0060] As can be seen from Comparative Example 1 and Comparative Examples 2 and 3, the mass ratio of copper organic precursor to carbon felt A affects the number of copper single substance particles loaded on the carbon felt. If the ratio is too large, too many copper single substance particles are loaded on the carbon felt, blocking the pore structure of the carbon felt, affecting the transport of electrolyte inside the carbon felt, and reducing the available space for zinc deposition; if the ratio is too small, too few copper single substance particles are loaded on the carbon felt, which cannot effectively increase the active sites for zinc deposition; therefore, a suitable mass ratio of copper organic precursor to carbon felt A not only introduces enough copper single substance zinc deposition active sites on the carbon felt, but also avoids the blockage of the pore structure of the carbon felt by copper single substance.

[0061] As can be seen from Comparative Example 1 and Comparative Examples 4 and 5, the hydrogen flow rate plays a key role in the reaction equilibrium and product discharge. If the hydrogen flow rate is too slow, the volatile organic ligand formed by the reaction of the copper organic precursor with hydrogen cannot be carried out of the double-temperature zone tube furnace, interfering with the copper deposition process; if the hydrogen flow rate is too fast, more copper organic precursors will react with hydrogen to form copper single substance and be blown out of the double-temperature zone tube furnace, which is not conducive to the loading of copper single substance on the carbon felt, resulting in waste of copper organic precursors; therefore, a suitable hydrogen flow rate can achieve efficient delivery of the precursors and timely discharge of by-products.

[0062] As can be seen from Comparative Example 1 and Comparative Examples 6 and 7, a suitable temperature in temperature zone A can ensure that the copper organic precursor is vaporized and not decomposed; a suitable temperature in temperature zone B can ensure that the copper deposited on the carbon felt has high crystallinity and high bonding force with the carbon felt, avoiding the shedding of the copper load; a suitable holding time in the two temperature zones can ensure that the loading process is complete, control the particle size of the loaded copper single substance particles, and improve the crystallinity of the copper load and the bonding force between the copper load and the carbon felt.

[0063] As can be seen from Comparative Example 1 and Comparative Examples 8 and 9, the appropriate holding time can ensure that the reaction is completely carried out, while controlling the particle size of the copper particles, further improving the crystallinity of the copper element and the bonding strength between the copper-loaded material and the carbon felt.

[0064] In summary, through the synergistic optimization of the above parameters, efficient and uniform loading of copper element is achieved, which lays a foundation for performance improvement of zinc-bromine flow batteries.

[0065] In Comparative Example 10, the gas used in the gas-phase deposition reaction stage at 650°C is hydrogen for the first nine hours, and air is used instead of hydrogen in the tenth hour. Part of the copper element loaded on the carbon felt is oxidized to copper oxide, and the loaded material is a composite of copper and copper oxide. In Comparative Example 11, the gas used in the gas-phase deposition reaction is air, which makes the loaded material on the carbon felt copper oxide. As can be seen from Comparative Example 1 and Comparative Examples 10 and 11, the material loaded on the carbon felt according to the technical solution of the present application is only copper element particles, and its performance indicators are much better than those of Comparative Example 10 loaded with a composite of copper and copper oxide and Comparative Example 11 loaded with copper oxide. Compared with the composite of copper and copper oxide and copper oxide, the copper element loaded on the carbon felt has extremely high electrical conductivity, which can quickly transfer electrons between the carbon felt and the zinc deposition layer, is conducive to the rapid transfer of electrons during the zinc deposition / peeling process, and can effectively reduce the interface charge transfer resistance.

[0066] As can be seen from Comparative Example 1 and Comparative Example 12, the performance indicators of Example 1 are much better than those of Comparative Example 12. This is because when the carbon felt is soaked in the nickel acetate solution, the nickel acetate solution cannot completely fill all the pores of the carbon felt due to the influence of the surface tension between the solid and the liquid, and the nickel particles cannot be loaded on the surface and internal carbon fibers of the carbon felt. In addition, after 600 cycles, the Coulomb efficiency, voltage efficiency and energy efficiency of Comparative Example 12 are reduced to 65.2%, 67.8% and 44.2%, respectively. This is because the nickel element loaded on the carbon felt has a relatively active chemical property, which is easy to react with acidic substances in the electrolyte, thereby causing the nickel active site for zinc deposition to be ineffective.

[0067] Figure 1Figure 1 shows the galvanostatic charge-discharge curves of the zinc-bromine flow battery using the carbon felt prepared in Example 1 and the carbon felt of Comparative Example 1 as the negative electrode, respectively. The difference between Example 1 and Comparative Example 1 is that the copper organic precursor is not placed in the double-temperature zone tube furnace during the implementation process of Comparative Example 1, and only the carbon felt is subjected to simple heat treatment, without loading copper element on the carbon felt. In the galvanostatic charge-discharge test, the electrolyte flow rate is controlled at 35 mL / min, and the battery is subjected to constant current charging at a current density of 60 mA / cm2for 40 minutes, and then discharged at the same current density to the terminal voltage of 0.6 V. As can be seen from the figure, the specific discharge area capacity of the copper element modified carbon felt negative electrode obtained in Example 1 is 38.96 mAh / cm2, which is 5.28 mAh / cm2higher than that of Comparative Example 1. 2 , which is 5.28 mAh / cm 2 2 higher than that of Comparative Example 1. Benefiting from the improvement of the specific discharge area capacity, the coulombic efficiency of the carbon felt obtained in Example 1 reaches 97.4%, which is about 13.2% higher than that of Comparative Example 1. In the constant current charging stage, the voltage platform curves of Example 1 and Comparative Example 1 show high consistency, but the discharge voltage of the copper element modified carbon felt negative electrode is about 1.69 V, which is about 130 mV higher than that of Comparative Example 1. Benefiting from the improvement of the discharge voltage, the voltage efficiency of the carbon felt obtained in Example 1 is 85.3%, which is about 6% higher than that of Comparative Example 1. Benefiting from the comprehensive effect of the coulombic efficiency and the voltage efficiency, the energy efficiency of the carbon felt obtained in Example 1 is 83.1%, which is 16.5% higher than that of Comparative Example 1. Through the above comparison, it can be shown that the copper loaded on the surface of the carbon felt has a synergistic effect through multiple mechanisms such as reducing the activation energy required for zinc nucleation, increasing the active sites on the surface of the carbon felt, and reducing the polarization, etc., which ultimately significantly improves the three key indicators of the zinc-bromine flow battery, i.e., the coulombic efficiency, the voltage efficiency and the energy efficiency.

[0068] Figure 2 With Figure 3 Figure 2 shows the cycle performance test results of the zinc-bromine flow battery using the copper element modified carbon felt of Example 1 and the carbon felt of Comparative Example 1 as the negative electrode under the same test conditions. After 1600 cycles, the coulombic efficiency and the energy efficiency of the copper element modified carbon felt negative electrode obtained in Example 1 are 93.2% and 78.5%, respectively, and the retention rates of the coulombic efficiency and the energy efficiency are 95.7% and 94.5%, respectively. The carbon felt negative electrode of Comparative Example 1 fluctuates greatly during the cycle process, and after only 130 cycles, the coulombic efficiency and the energy efficiency are attenuated to 58.4% and 46.4%, respectively, and the retention rates of the coulombic efficiency and the energy efficiency are 69.4% and 69.7%, respectively. The index fluctuation of the coulombic efficiency and the energy efficiency during the cycle process and the retention rate index are related to zinc dendrites. Through comparison, the beneficial effect of the copper element modified carbon felt prepared by the technical solution of the present application in inhibiting zinc dendrites is obvious.

[0069] Figure 4X-ray diffraction (XRD) patterns of the copper elemental modified carbon felt prepared in Example 1 and the unmodified carbon felt are shown for comparison. By X-ray diffraction (XRD) analysis, the modified carbon felt obtained in Example 1 is detected to have copper elemental (111), (200) and (220) characteristic diffraction peaks at diffraction angle positions of 43.5°, 50.6° and 74.3°, respectively. This observation clearly indicates that under the process conditions of Example 1, copper elemental has been successfully loaded on the surface of the carbon felt substrate material. The presence of each diffraction peak not only verifies the existence of copper crystals, but also reflects the integrity of its crystal structure. Further by comparing the X-ray diffraction patterns of the copper modified carbon felt prepared in Example 1 and the unmodified carbon felt, it can be known that except for the copper elemental characteristic peaks, the remaining diffraction peak positions and intensities of the two samples are basically consistent. This can first indicate that the loading material introduced on the carbon felt by the modification process of Example 1 is only copper elemental, without copper oxide, cuprous oxide and other copper compounds; secondly, it can be indicated that the modification process adopted in Example 1 does not significantly affect the crystal structure of the carbon felt, and the modification method better retains the original crystal phase characteristics of the carbon felt while loading copper elemental particles on the surface of the carbon felt.

[0070] Figure 5 and Figure 6 are scanning electron microscope (SEM) images of the copper elemental modified carbon felt prepared in Example 1 and the carbon felt of Comparative Example 1, respectively. By comparing the microstructures of Figure 5 and Figure 6 , it can be found that the surface of the copper elemental modified carbon felt prepared in Example 1 is uniformly distributed with a large number of nanoparticles Figure 5 , while the surface of the carbon fiber of the carbon felt of Comparative Example 1 Figure 6 is smooth and no obvious particles are observed. This difference can directly prove that the gas phase deposition process adopted in Example 1 loads nanoparticles on the surface of the carbon fiber of the carbon felt.

[0071] Figure 7 is an electron map collected when energy dispersive X-ray spectroscopy analysis is performed on the copper elemental modified carbon felt prepared in Example 1. Figure 8 shows Figure 7 the energy dispersive X-ray spectroscopy data of the selected area. In addition to observing the characteristic signals of carbon (C) and oxygen (O), the characteristic peak of copper (Cu) element is clearly detected, indicating the presence of copper element distribution in the area. Combined with the X-ray diffraction (XRD) patterns of Figure 7 , Figure 8 and Figure 4 , it can be clearly determined that the nanoparticles attached to the surface of the carbon fiber of the carbon felt in Figure 5 are copper elemental. This can further indicate that copper elemental particles are loaded on the carbon felt by the technical solution of Example 1.

[0072] The above detailed description does not limit the present application. Instead, any modification, equivalent substitution or improvement made without departing from the spirit and principle of the present application should be included within the scope of the present application.

Claims

1. A method for preparing a modified carbon felt negative electrode for a zinc-bromine flow battery, characterized in that, Includes the following steps: (1) The cleaned carbon felt is vacuum dried to obtain carbon felt A; (2) Place the copper organic precursor in temperature zone A at the gas inlet of the dual-temperature zone tube furnace, place the carbon felt A in temperature zone B at the gas outlet, introduce hydrogen gas, raise the temperature zone A to 50 to 350°C at 3 to 9°C / min, raise the temperature zone B to 400 to 900°C at the same rate, hold for 5 to 15 hours for vapor deposition reaction, and then let it cool naturally to room temperature to obtain carbon felt B. (3) Wash and vacuum dry carbon felt B to obtain copper element modified zinc bromine flow battery carbon felt negative electrode; In step (2), the copper organic precursor is one of bis(hexafluoroacetylacetone)copper(II), copper acetylacetonate, or bis(dimethylamino-2-propoxy)copper(II); the mass ratio of the copper organic precursor to carbon felt A is 1 to 10:

1.

2. The method for preparing the modified zinc-bromine flow battery carbon felt negative electrode according to claim 1, characterized in that, In step (1), the vacuum drying temperature is 60-190℃ and the time is 8-22h.

3. The method for preparing the modified zinc-bromine flow battery carbon felt negative electrode according to claim 1, characterized in that, In step (2), the hydrogen flow rate is 50-200 ml / min.

4. The method for preparing the modified zinc-bromine flow battery carbon felt negative electrode according to claim 1, characterized in that, In step (3), the vacuum drying temperature is 100-200℃ and the time is 12-24h.

5. A modified zinc-bromine flow battery carbon felt negative electrode, characterized in that, The modified zinc-bromine flow battery carbon felt anode is prepared by any one of claims 1 to 4, and the carbon felt anode comprises a carbon felt matrix and copper elemental particles loaded on the carbon felt.

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