Preparation method of zinc-bromine static battery positive electrode material and application thereof

Abstract

The application discloses a preparation method of a zinc-bromine static battery positive electrode material and application thereof, and relates to the technical field of battery energy storage. The preparation steps are as follows: (1) a multi-walled carbon nanotube is subjected to calcination treatment under an ammonia atmosphere, and is naturally cooled to obtain a nitrogen-doped multi-walled carbon nanotube; (2) a strong oxidant is added to the nitrogen-doped multi-walled carbon nanotube, ultrasonic dispersion is carried out, condensation reflux is carried out, filtration is carried out, then the nitrogen-doped multi-walled carbon nanotube is washed to be neutral with a sodium hydroxide solution, and then is washed with deionized water, and is dried to obtain a carboxylated nitrogen-doped multi-walled carbon nanotube; (3) a cyclodextrin is added to the carboxylated nitrogen-doped multi-walled carbon nanotube, ultrasonic dispersion is carried out, stirring is carried out, filtration is carried out, washing is carried out with ultrapure water, and drying is carried out to obtain a cyclodextrin-nitrogen-doped multi-walled carbon nanotube, which is the positive electrode material. The prepared positive electrode material has a structure of enriching Brˉ and Br3ˉ and high-efficiency catalytic sites, and effectively solves the problems of large charging polarization and self-discharge of a zinc-bromine static battery.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of battery energy storage, in particular to a preparation method of a zinc-bromine static battery positive electrode material and application thereof. BACKGROUND

[0002] Zn 2+ Zinc-bromine flow batteries based on Zn / Zn (negative electrode) and Br2 / Br- (positive electrode) redox couples have been a strong contender in the large-scale energy storage market due to their high safety and theoretical energy density. On this basis, zinc-bromine static batteries, which eliminate the need for expensive ion exchange membranes and circulating separation liquid systems, have attracted widespread attention and interest in the market due to their breakthrough cost advantage. Such batteries generally use carbon-based materials as the positive electrode and ZnBr2 aqueous solution as the electrolyte.

[0003] However, zinc-bromine static batteries face great challenges in practical applications: during charging, the electrochemical oxidation reaction of Br- on the carbon-based material is slow, causing increased charging polarization and reducing the energy efficiency of the system; during storage, Br- and the charging product Br2 of the positive electrode form Br3-, which is easily soluble in water and diffuses to the negative electrode under the driving of the concentration gradient, causing a serious self-discharge behavior. Therefore, introducing structures that can enrich Br- and Br3- and high-efficiency catalytic sites into the positive electrode of the battery to address the problems of large charging polarization and self-discharge behavior is of great significance to promote the practical application of zinc-bromine static batteries.

[0004] In the prior art, patent CN 116742092 A discloses a zinc-bromine flow battery positive electrode homogeneous electrolyte. The patent uses cyclodextrin derivatives (methylated cyclodextrin, hydroxyethyl cyclodextrin, hydroxypropyl cyclodextrin, carboxymethyl cyclodextrin, sulfate cyclodextrin, sulfonate cyclodextrin, phosphate cyclodextrin) as bromine complexes to obtain a zinc-bromine flow battery with excellent CE, VE and EE. Patent CN 118431529 A discloses the application of a bromine capturing agent based on supramolecular assembly in a zinc-bromine flow battery. The patent uses cyclodextrin and its derivatives as bromine capturing agents to effectively improve the coulombic efficiency of the battery. The above patents all use the technology of dissolving cyclodextrin in the electrolyte to improve the performance of the zinc-bromine flow battery. In zinc-bromine static batteries, if the same technology is used, cyclodextrin complexed with Br3- will still diffuse to the negative electrode under the driving of the concentration gradient, causing self-discharge to occur. Therefore, further improvements are needed for the method of enriching Br- and Br3- in view of the practical application of zinc-bromine static batteries. SUMMARY

[0005] In view of the above deficiencies, the application provides a preparation method of a zinc-bromine static battery positive electrode material and application thereof, the positive electrode material has a structure rich in Br- and Br3-, and high-efficiency catalytic sites, effectively solving the problems of large charging polarization and self-discharge of the zinc-bromine static battery, and the specific technical solutions are as follows.

[0006] A preparation method of a zinc-bromine static battery positive electrode material, comprising the following steps:

[0007] (1) calcining multi-walled carbon nanotubes (CNTs) under an ammonia atmosphere for 6-10 hours, with a calcination temperature of 300-450 DEG C, and naturally cooling to obtain nitrogen-doped multi-walled carbon nanotubes (NCNTs);

[0008] (2) adding a strong oxidizing agent to the NCNTs, ultrasonic dispersion for 30-40 minutes, condensation reflux at a speed of 1000-1200 rpm and a temperature of 40-80 DEG C for 6-12 hours, filtration, then washing with a sodium hydroxide solution until neutral, washing with deionized water, and drying at 70-85 DEG C for 8-10 hours to obtain carboxylated nitrogen-doped multi-walled carbon nanotubes (NCNTs-COOH);

[0009] (3) adding cyclodextrin (CD) to the NCNTs-COOH, ultrasonic dispersion for 30-60 minutes, stirring, filtration, washing with ultrapure water, and drying at 60-80 DEG C for 8-12 hours to obtain cyclodextrin-nitrogen-doped multi-walled carbon nanotubes (CD-NCNTs), which is the positive electrode material.

[0010] Further, before the calcination treatment in step (1), ammonia gas is introduced for 15-30 minutes, the gas flow rate of ammonia gas during the calcination process is 20-25 mL / min, argon gas is introduced to remove residual ammonia gas after the calcination is completed, and the argon gas introduction time is not less than 15 minutes.

[0011] Further, in step (2), the oxidizing agent is potassium permanganate, concentrated nitric acid, or a mixture of concentrated sulfuric acid and concentrated nitric acid.

[0012] Further, in the mixture of concentrated sulfuric acid and concentrated nitric acid, the volume ratio of concentrated sulfuric acid to concentrated nitric acid is 3-4:1.

[0013] Further, in step (2), the concentration of the sodium hydroxide solution is 0.1-0.5 mol / L.

[0014] Further, in step (2), the cyclodextrin is one or more of alpha-cyclodextrin, beta-cyclodextrin, gamma-cyclodextrin, hydroxypropyl-alpha-cyclodextrin, hydroxyethyl-beta-cyclodextrin, and hydroxypropyl-gamma-cyclodextrin.

[0015] Further, in step (3), the stirring is normal temperature stirring, and when the stirring is normal temperature stirring, the preparation method of the CD-NCNTs is as follows: 0.2-0.5 g of the NCNTs-COOH and 20-40 mL of a saturated CD solution are placed in a 100 mL flask, ultrasonic dispersion is carried out for 30-60 min, stirring is carried out at normal temperature for 8-10 h, then filtration is carried out, washing is carried out with ultrapure water for 5-7 times, and drying is carried out at 60-80 DEG C for 8-12 h to obtain the CD-NCNTs.

[0016] Further, in step (3), the stirring is heating stirring, and when the stirring is heating stirring, the preparation method of the CD-NCNTs is as follows: 0.2-0.5 g of the NCNTs-COOH and 10 times the mass of CD powder are placed in a 100 mL flask, 30-40 mL of water is added, ultrasonic dispersion is carried out for 30-60 min, heating is carried out to 60-80 DEG C, and stirring is carried out for 18-20 h, then filtration is carried out, washing is carried out with ultrapure water for 5-7 times, and drying is carried out at 60-80 DEG C for 8-12 h to obtain the CD-NCNTs.

[0017] The application further provides a preparation method of a battery positive electrode, which is prepared by using the above positive electrode material, and the specific preparation method is as follows: CD-NCNTs, XC-72 conductive carbon and polytetrafluoroethylene are uniformly mixed according to a mass ratio of 90:5:5, isopropyl alcohol is added for slurry preparation, then the slurry is pressed into a sheet by a stainless steel film rolling machine and is vacuum dried at 120 DEG C, and finally the sheet is cut into a proper size to obtain the battery positive electrode.

[0018] The application further provides a zinc-bromine static battery, which is composed of a positive electrode, a negative electrode, a diaphragm and an electrolyte, wherein the positive electrode is the battery positive electrode prepared by the above method, the negative electrode is a commercially available zinc foil, the diaphragm is a commercially available microporous diaphragm, and the electrolyte formula is a 1-3 mol / L ZnBr2 aqueous solution.

[0019] Compared with the prior art, the application has the following beneficial effects:

[0020] 1. The application first proposes a zinc-bromine static battery positive electrode material, which has a structure rich in Brˉ and Br3ˉ and high-efficiency catalytic sites.

[0021] 2. The zinc-bromine static battery positive electrode material prepared by the application introduces pyridine nitrogen as a high-efficiency catalytic site and fixes cyclodextrin as a structure for enriching Br- and Br3-, effectively solving the problems of large charging polarization and self-discharge of the zinc-bromine static battery. Specifically, in the charging process, the fixed cyclodextrin structural units and the introduced pyridine nitrogen in the material respectively play the roles of enriching Br- and catalyzing the oxidation of Br-, successively improving the mass transfer capacity and reaction activity, promoting the rapid progress of the electrochemical oxidation reaction, thereby effectively reducing the charging polarization; in the storage process, the fixed cyclodextrin structural units in the material efficiently enrich Br3-, play the role of a material reserve, and inhibit the diffusion behavior of Br3-, i.e., hinder the diffusion of the charging product of the positive electrode to the negative electrode, thereby significantly improving the self-discharge performance.

[0022] 3. The pyridine nitrogen can be generated by calcining the multi-walled carbon nanotubes under an ammonia atmosphere, and the introduction of the pyridine nitrogen on the multi-walled carbon nanotubes can make the material have high-efficiency catalytic sites.

[0023] 4. The strong oxidant is added to oxidize the NCNTs during the reaction, so that the surface of the NCNTs is activated, and then oxygen-containing groups such as carboxyl groups are introduced, which can provide reaction sites for the subsequent connection and fixation of cyclodextrin. BRIEF DESCRIPTION OF DRAWINGS

[0024] In order to more clearly illustrate the technical solutions of the embodiments of the application, the following will briefly introduce the drawings needed to be used in the embodiment description.

[0025] Figure 1 XPS data of the NCNTs prepared by the application;

[0026] Figure 2 Infrared spectrum of the material prepared by the application: (A) NCNTs, (B) NCNTs-COOH, (C) β-CD, (D) β-CD-NCNTs;

[0027] Figure 3 SEM image of the material prepared by the application: (A) NCNTs, (B) NCNTs-COOH, (C) β-CD-NCNTs. DETAILED DESCRIPTION

[0028] The specific embodiments of the application will be described in detail below, but it should be understood that the protection scope of the application is not limited by the specific embodiments.

[0029] The CD used in the following examples and comparative examples was purchased from Aladdin Chemical Reagent Co., Ltd., and the CNTs was purchased from Chengdu Institute of Organic Chemistry, Chinese Academy of Sciences.

[0030] Example 1

[0031] The embodiment of the application discloses a preparation method of a zinc-bromine static battery positive electrode material.

[0032] (1) Preparation of NCNTs: 0.5 g of CNTs powder was placed in a 30 mL magnetic boat, the magnetic boat was placed in a tube furnace, ammonia gas was introduced for 15 min, the reaction environment was ensured to be filled with ammonia gas, the material was heated to 300 DEG C at a temperature increasing rate of 15 DEG C / min, and the target temperature was kept for 8 h, the gas flow rate of ammonia gas during the calcination process was 20 mL / min, argon gas was introduced after the heat preservation was finished, the excess ammonia gas was removed, and natural cooling was performed to room temperature, and NCNTs was obtained.

[0033] (2) Preparation of NCNTs-COOH: 1 g of NCNTs powder was placed in a 150 mL round-bottom flask, 100 mL of concentrated nitric acid solution was added, and the solution was dispersed under ultrasonic conditions for 30 min; the dispersed solution was condensed and refluxed at 80 DEG C and 1200 rpm for 6 h; after the reaction was finished, the product was filtered, and neutralized to neutral with 0.1 mol / L sodium hydroxide solution; then the product was washed with deionized water for 5 times to remove residual acidic substances, and the washed product was dried at 80 DEG C for 8 h to obtain NCNTs-COOH.

[0034] (3) Preparation of β-CD-NCNTs: 0.5 g of NCNTs-COOH and 30 mL of saturated β-cyclodextrin (β-CD) solution were placed in a 100 mL flask, ultrasonic treatment was performed for 30 min to ensure uniform dispersion, and stirring was performed at room temperature overnight; after the stirring was stopped, the product was filtered and washed with ultrapure water to remove excess β-CD; and the final product was dried at 80 DEG C for 8 h to obtain β-CD-NCNTs.

[0035] XPS data of the NCNTs prepared in the embodiment is shown in Figure 1 The nitrogen characteristic peak appears in the material, and the peak value is 398.3 eV, which indicates that pyridine nitrogen is successfully introduced into the CNTs to prepare the NCNTs.

[0036] The infrared spectrum of the material prepared in the embodiment is shown in Figure 2 After the NCNTs (substance A) is treated by oxidation, a -C-O- bond appears at 1100 cmˉ 1 , which indicates that the carboxyl group (-COOH) is successfully introduced into the surface of the NCNTs (substance B). In the subsequent esterification reaction of the cyclodextrin, the infrared spectrum of the material appears signals at 1600 cmˉ 1 (-C=O-), 1750 cmˉ 1 (-C=C-), and 1100 cmˉ 1The positive shift of -C-O- vibration indicates that the esterification reaction between the carboxyl group and β-CD occurs, and β-CD-NCNTs (material D) is formed.

[0037] The SEM image of the material prepared in this example is shown in FIG. A, and compared with NCNTs (FIG. A), the obtained NCNTs-COOH does not change obviously (FIG. B) after surface activation and access to carboxyl. Further esterification reaction and fixation of β-CD result in the occurrence of adhesion phenomenon of β-CD-NCNTs (FIG. C), which may be due to the rich hydrogen bonding of β-CD inducing the aggregation of the material. Figure 3

[0038] Example 2

[0039] The preparation method of the zinc-bromine static battery positive electrode material in this example includes the following steps:

[0040] (1) Preparation of NCNTs: 1 g of CNTs powder was placed in a 30 mL magnetic boat, the magnetic boat was placed in a tube furnace, and ammonia gas was introduced for 15 min to ensure that the reaction environment was filled with ammonia gas. The material was heated to 350℃ at a heating rate of 20℃ / min, and the target temperature was maintained for 8 h. The gas flow rate of ammonia during calcination was 25 mL / min. After heat preservation, argon was introduced to remove excess ammonia gas, and the material was naturally cooled to room temperature to obtain NCNTs.

[0041] (2) Preparation of NCNTs-COOH: 1 g of NCNTs powder was placed in a 150 mL round-bottom flask, 100 mL of potassium permanganate solution was added, and ultrasonic dispersion was performed for 40 min. Condensation reflux was performed at 80℃ and 1200 rpm for 8 h. After filtering the product, it was washed with 0.1 mol / L sodium hydroxide solution until neutral, and then washed with a large amount of deionized water. The washed product was dried at 80℃ for 8 h to obtain NCNTs-COOH.

[0042] (3) Preparation of β-CD-NCNTs: 0.5 g of NCNTs-COOH and 30 mL of saturated β-CD solution were placed in a 100 mL flask, ultrasonic treatment was performed for 30 min to ensure uniform dispersion, and stirring was performed at room temperature overnight. After stopping stirring, the product was filtered and washed with ultrapure water to remove excess β-CD. The final product was dried at 80℃ for 8 h to obtain β-CD-NCNTs.

[0043] Example 3

[0044] The preparation method of the zinc-bromine static battery positive electrode material in this example includes the following steps:

[0045] ​(1) Preparation of NCNTs: 1 g of CNTs powder was placed in a 30 mL magnetic boat, the magnetic boat was placed in a tube furnace, and ammonia gas was introduced for 20 min to ensure that the reaction environment was filled with ammonia gas. The material was heated to 400°C at a heating rate of 20°C / min, and the target temperature was maintained for 10 h. During the calcination process, the gas flow rate of ammonia was 20 mL / min. After the heat preservation was completed, argon was introduced to remove excess ammonia gas, and the system was naturally cooled to room temperature to obtain NCNTs.

[0046] (2) Preparation of NCNTs-COOH: 1 g of NCNTs powder was placed in a 150 mL round-bottom flask, and 90 mL of a mixed solution prepared by mixing concentrated sulfuric acid and concentrated nitric acid at a ratio of 3:1 was added. The mixture was dispersed under ultrasonic conditions for 30 min, and then condensed and refluxed at 80°C and 1200 rpm for 6 h. After filtering the product, it was washed with 0.1 mol / L sodium hydroxide solution until it was neutral, and then washed with a large amount of deionized water. The washed product was dried at 80°C for 8 h to obtain NCNTs-COOH.

[0047] (3) Preparation of β-CD-NCNTs: 0.5 g of NCNTs-COOH and 30 mL of saturated β-CD solution were placed in a 100 mL flask, and ultrasonic treatment was performed for 30 min to ensure uniform dispersion. The mixture was stirred at room temperature overnight, and then filtered. The product was washed with ultrapure water to remove excess β-CD, and then dried at 80°C for 8 h to obtain β-CD-NCNTs.

[0048] Example 4

[0049] The present embodiment is a method for preparing a zinc-bromine static battery anode material, which comprises the following steps:

[0050] (1) Preparation of NCNTs: 0.5 g of CNTs powder was placed in a 30 mL magnetic boat, the magnetic boat was placed in a tube furnace, and ammonia gas was introduced for 15 min to ensure that the reaction environment was filled with ammonia gas. The material was heated to 300°C at a heating rate of 15°C / min, and the target temperature was maintained for 8 h. During the calcination process, the gas flow rate of ammonia was 20 mL / min. After the heat preservation was completed, argon was introduced to remove excess ammonia gas, and the system was naturally cooled to room temperature to obtain NCNTs.

[0051] (2) Preparation of NCNTs-COOH: Take 1 g of NCNTs powder and place it in a 150 mL round-bottom flask. Add 100 mL of concentrated nitric acid solution and disperse it under ultrasonic conditions for 30 min. Condense the solution at 80°C and 1200 rpm for 6 h under reflux. After the reaction is complete, filter the product and neutralize it with 0.1 mol / L sodium hydroxide solution to neutral. Then wash it thoroughly with deionized water for 5 times to remove residual acidic substances. Dry the washed product at 80°C for 8 h to obtain NCNTs-COOH.

[0052] (3) Preparation of β-CD-NCNTs: Take 0.2 g of NCNTs-COOH and 1 g of β-CD powder and place them in a 100 mL flask. Add 30 mL of deionized water and ultrasonically disperse for 30 min to ensure uniform mixing. Heat the mixture to 60°C and stir at this temperature for 20 h to promote the esterification reaction to proceed fully. After stopping the stirring, filter the product and wash it with ultrapure water. Wash it with ultrapure water for 7 times to remove excess β-CD. Dry the washed product at 80°C for 8 h to obtain β-CD-NCNTs.

[0053] Example 5

[0054] The preparation method of the zinc-bromine static battery anode material of this embodiment is the same as that of Example 4, except that the ultrasonic dispersion time in step (3) is 60 minutes.

[0055] Example 6

[0056] The preparation method of the zinc-bromine static battery anode material of this embodiment is the same as that of Example 4, except that the stirring time in step (3) is 20 hours.

[0057] Example 7

[0058] The preparation method of the zinc-bromine static battery anode material of this embodiment is the same as that of Example 1, except that step (3) uses α-cyclodextrin (α-CD) for preparation. Specifically, take 0.2 g of NCNTs-COOH and 2 g of α-CD powder and place them in a 100 mL flask. Add an appropriate amount of deionized water and ultrasonically treat for 30 min to ensure uniform mixing. Heat the mixture to 60°C and stir under reflux for 20 h to promote the esterification reaction to proceed fully. After stopping the stirring, filter the product and wash it with ultrapure water. Wash it with ultrapure water for 5 times to remove excess α-CD. Dry the washed product at 80°C for 8 h to obtain α-CD-NCNTs.

[0059] Example 8

[0060] The preparation method of the positive material of the zinc-bromine static battery in this embodiment is as follows: steps (1) and (2) are the same as those in embodiment 1, and step (3) is prepared by using γ-cyclodextrin (γ-CD). Specifically, 0.2 g of NCNTs-COOH and 2 g of γ-CD powder are placed in a 100 mL flask, an appropriate amount of deionized water is added, ultrasonic treatment is performed for 30 min, and the mixture is heated to 60°C and refluxed and stirred for 20 h to promote the esterification reaction to proceed fully. After stopping stirring, filtration is performed, and ultrapure water is used for washing, and the mixture is washed with ultrapure water for 5 times to remove excess γ-CD. Drying is performed at 80°C for 8 h to obtain γ-CD-NCNTs.

[0061] Embodiment 9

[0062] The preparation method of the positive material of the zinc-bromine static battery in this embodiment is as follows: steps (1) and (2) are the same as those in embodiment 1, and step (3) is prepared by using hydroxyethyl-β-cyclodextrin (HE-β-CD). Specifically, 0.2 g of NCNTs-COOH and 2 g of HE-β-CD powder are placed in a 100 mL flask, an appropriate amount of deionized water is added, ultrasonic treatment is performed for 30 min, and the mixture is heated to 60°C and refluxed and stirred for 15 h. After stopping stirring, filtration is performed, and ultrapure water is used for washing, and the mixture is washed with ultrapure water for 5 times to remove excess HE-β-CD. Drying is performed at 80°C for 8 h to obtain HE-β-CD-NCNTs material.

[0063] Embodiment 10

[0064] The preparation method of the positive material of the zinc-bromine static battery in this embodiment is as follows: steps (1) and (2) are the same as those in embodiment 1, and step (3) is prepared by using hydroxyethyl-β-cyclodextrin (HE-β-CD). Specifically, 0.2 g of NCNTs-COOH and 2 g of HE-β-CD powder are placed in a 100 mL flask, an appropriate amount of deionized water is added, ultrasonic treatment is performed for 30 min, and the mixture is heated to 60°C and refluxed and stirred for 15 h. After stopping stirring, filtration is performed, and ultrapure water is used for washing, and the mixture is washed with ultrapure water for 5 times to remove excess HE-β-CD. Drying is performed at 80°C for 8 h to obtain HE-β-CD-NCNTs material.

[0065] Embodiment 11

[0066] The preparation method of the positive electrode material of the zinc-bromine static battery in this embodiment is as follows: steps (1) and (2) are the same as those in embodiment 1, and step (3) is prepared using hydroxypropyl-γ-cyclodextrin (HP-γ-CD). Specifically, 0.2 g of NCNTs-COOH and 1 g of HP-γ-CD powder are placed in a 100 mL flask, an appropriate amount of deionized water is added, and ultrasonic treatment is performed for 30 min. The mixture is heated to 65°C and stirred for 18 h to promote the esterification reaction to proceed fully. After stopping stirring, filtration is performed, washing is performed using ultrapure water, and washing is performed 7 times using ultrapure water to remove excess HP-γ-CD. Drying is performed at 80°C for 8 h to obtain HP-γ-CD-NCNTs material.

[0067] Preparation of the battery positive electrode: The CD-NCNTs positive electrode material synthesized in each embodiment is used for preparation. The specific preparation method is as follows: first, CD-NCNTs, XC-72 conductive carbon, and polytetrafluoroethylene are uniformly mixed according to a mass ratio of 90:5:5, isopropyl alcohol is added for slurry preparation, then the slurry is pressed into a thin sheet by a stainless steel film rolling machine and vacuum dried at 120°C, and finally the thin sheet is cut into an appropriate size to obtain the battery positive electrode.

[0068] Preparation of the zinc-bromine static battery: The zinc-bromine static battery of each embodiment is composed of a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the positive electrode is the battery positive electrode prepared by the above method, the negative electrode is a commercially available zinc foil, the separator is a commercially available microporous separator, and the electrolyte formula is 2 mol / L ZnBr2 aqueous solution.

[0069] Comparative Example 1

[0070] The preparation method of the positive electrode in this comparative example is as follows: first, CNTs, XC-72 conductive carbon, and polytetrafluoroethylene are uniformly mixed according to a mass ratio of 90:5:5, isopropyl alcohol is added for slurry preparation, then the slurry is pressed into a thin sheet by a stainless steel film rolling machine and vacuum dried at 120°C, and finally the thin sheet is cut into an appropriate size to obtain the battery positive electrode.

[0071] The zinc-bromine static battery of this comparative example is composed of a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the positive electrode is the battery positive electrode prepared by the above method, the negative electrode is a commercially available zinc foil, the separator is a commercially available microporous separator, and the electrolyte formula is 2 mol / L ZnBr2 aqueous solution.

[0072] Comparative Example 2

[0073] The preparation method of the positive electrode in this comparative example is the same as that in comparative example 1.

[0074] The zinc-bromine static battery of this comparative example is composed of a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the positive electrode is the battery positive electrode prepared by the above method, the negative electrode is a commercially available zinc foil, the separator is a commercially available microporous separator, and the electrolyte formula is 2 mol / L ZnBr2 aqueous solution + 0.2 mol / L HP-α-CD.

[0075] Comparative Example 3

[0076] The positive electrode of the present comparative example was prepared by the same method as Comparative Example 1.

[0077] The zinc-bromine static battery of the present comparative example was composed of a positive electrode, a negative electrode, a separator and an electrolyte, wherein the positive electrode was the battery positive electrode prepared by the above method, the negative electrode was a commercially available zinc foil, the separator was a commercially available microporous separator, and the electrolyte formula was 2 mol / L ZnBr2 aqueous solution + 0.2 mol / L HE-β-CD.

[0078] Performance test:

[0079] (1) Electrochemical tests were performed on the zinc-bromine static batteries of each example and each comparative example to investigate the charge polarization and self-discharge performance, and the experimental conditions were as follows:

[0080] The test temperature was 25°C; the current density for charging and discharging was the same, and two current densities were selected: 10 and 40 mA / cm 2 ; the charging cutoff voltage was 1.8 V, and the discharging cutoff voltage was 0.6 V. The severity of the battery charge polarization was evaluated by the voltage difference between the charging platform and the discharging platform. For the investigation of self-discharge performance, the discharge energy retention rate of the battery after standing for 4 days after charging to the cutoff voltage was used for comparison.

[0081] (2) The battery performance test results are shown in Table 1:

[0082] Table 1: Battery performance test results of examples and comparative examples

[0083]

[0084]

[0085] (3) The results show that the difference between the examples and Comparative Example 1 is that the positive electrode of the examples uses CD-NCNTs prepared by the present application, and the positive electrode of Comparative Example 1 uses CNTs, and the electrolyte of both is 2 mol / L ZnBr2 aqueous solution. Under different current densities, the charge-discharge voltage difference of the examples is smaller than that of Comparative Example 1, and the standing discharge energy retention rate is much greater than that of Comparative Example 1, indicating that the examples have smaller charge polarization and lower self-discharge than Comparative Example 1. This means that by introducing pyridine nitrogen as a high-efficiency catalytic site and fixing cyclodextrin as a structure for enriching Brˉ and Br3ˉ, the problems of large charge polarization and self-discharge of zinc-bromine static batteries are effectively solved.

[0086] In addition, in order to evaluate the effect of the technology of dissolving cyclodextrin into electrolyte adopted by patents CN 116742092 A and CN 118431529 A on the self-discharge performance of zinc-bromine static battery, we made Comparative Example 2 and Comparative Example 3. The results of the static discharge energy retention rate of the battery showed that the technology of dissolving cyclodextrin into electrolyte could not improve the self-discharge performance of zinc-bromine static battery.

[0087] In summary: the present application is by first introducing pyridine nitrogen on the multi-walled carbon nanotube, then surface activation, access to carboxyl, finally through the esterification reaction of carboxyl and hydroxyl in cyclodextrin molecules, the cyclodextrin is fixed on the nitrogen-doped multi-walled carbon nanotube, so as to prepare the positive electrode material (CD-NCNTs) with the structure of enriching Brˉ and Br3ˉ and high-efficiency catalytic site, which is used to make zinc-bromine static battery positive electrode. In the charging process, the fixed cyclodextrin structure unit and the introduced pyridine nitrogen in the material respectively play the roles of enriching Brˉ and catalyzing Brˉ oxidation, relay to improve the mass transfer capacity and reaction activity, promote the rapid progress of electrochemical oxidation reaction, thereby effectively reducing the charging polarization; in the storage process, the fixed cyclodextrin structure unit in the material efficiently enriches Br3ˉ, plays the role of material storage, inhibits the diffusion behavior of Br3ˉ, that is, hinders the diffusion of the charging product of the positive electrode to the negative electrode, thereby significantly improving the self-discharge performance, effectively solving the problems of large charging polarization and self-discharge of zinc-bromine static battery.

[0088] The foregoing description of specific exemplary embodiments of the application is intended to be illustrative only and is not intended to limit the application to the precise forms described. Many modifications and variations are possible in light of the above teachings without departing from the spirit or essential characteristics of the application. The exemplary embodiments were chosen and described in order to explain the principles of the application and its practical application and to allow others skilled in the art to understand the application for various exemplary embodiments with various modifications being suited to the particular use contemplated. The scope of the application is to be defined by the claims and their equivalents.

Claims

1. A method for preparing a positive electrode of a zinc-bromine static battery, characterized in that: First, cyclodextrin-nitrogen-doped multi-walled carbon nanotubes, XC-72 conductive carbon, and polytetrafluoroethylene are uniformly mixed in a mass ratio of 90:5:5, and isopropyl alcohol is added to prepare a slurry. The slurry is then pressed into a thin sheet using a stainless steel rolling machine, and vacuum-dried at 120°C. Finally, the sheet is cut into a suitable size to obtain the zinc-bromine static battery positive electrode; The preparation method of cyclodextrin-nitrogen-doped multi-walled carbon nanotubes comprises the following steps: (1) calcining multi-walled carbon nanotubes in an ammonia atmosphere for 6-10 h at a calcination temperature of 300-450 °C and cooling naturally to obtain nitrogen-doped multi-walled carbon nanotubes; Before the calcination treatment, ammonia is first introduced for 15-30 minutes. The gas flow rate of ammonia during the calcination process is 20-25 mL / min. After the calcination is completed, argon is introduced to remove residual ammonia. The argon introduction time is not less than 15 minutes. (2) adding a mixture of concentrated sulfuric acid and concentrated nitric acid in a volume ratio of (3-4):1 to the nitrogen-doped multi-walled carbon nanotubes, ultrasonically dispersing for 30-40 min, condensing and refluxing at a speed of 1000-1200 rpm and a temperature of 40-80 ° C for 6-12 h, filtering, and then washing with a sodium hydroxide solution with a concentration of 0.1-0.5 mol / L until neutral, and then washing with deionized water, and drying at 70-85 ° C for 8-10 h to obtain carboxylated nitrogen-doped multi-walled carbon nanotubes; (3) adding cyclodextrin to the carboxylated nitrogen-doped multi-walled carbon nanotubes, ultrasonically dispersing for 30-60 min, stirring, filtering, washing with ultrapure water, and drying at 60-80 °C for 8-12 h to obtain cyclodextrin-nitrogen-doped multi-walled carbon nanotubes; The cyclodextrin is one or more of α-cyclodextrin, β-cyclodextrin, γ-cyclodextrin, hydroxypropyl-α-cyclodextrin, hydroxyethyl-β-cyclodextrin and hydroxypropyl-γ-cyclodextrin.

2. The method for preparing a zinc-bromine static battery positive electrode according to claim 1, wherein: In step (3), the stirring is stirring at room temperature. When stirring at room temperature, the preparation method of the cyclodextrin-nitrogen-doped multi-walled carbon nanotubes is as follows: adding saturated cyclodextrin to the carboxylated nitrogen-doped multi-walled carbon nanotubes, ultrasonically dispersing for 30-60 min, stirring at room temperature for 8-10 h, filtering, washing with ultrapure water, and drying at 60-80 ° C for 8-12 h to obtain cyclodextrin-nitrogen-doped multi-walled carbon nanotubes.

3. The method for preparing a zinc-bromine static battery positive electrode according to claim 1, wherein: In step (3), the stirring is heating stirring. During the heating stirring, the preparation method of the cyclodextrin-nitrogen-doped multi-walled carbon nanotubes is as follows: adding cyclodextrin powder and water to the carboxylated nitrogen-doped multi-walled carbon nanotubes, ultrasonically dispersing for 30-60 min, heating to 60-80 ° C and stirring for 18-20 h, filtering, washing with ultrapure water, and drying at 60-80 ° C for 8-12 h to obtain cyclodextrin-nitrogen-doped multi-walled carbon nanotubes.

4. A zinc-bromine static battery, characterized in that The battery uses the zinc-bromine static battery positive electrode prepared by the method according to any one of claims 1 to 3 as the positive electrode.

Images