Alkaline flow battery based on carbon felt surface functionalization and electrolyte additive collaborative optimization

Abstract

The invention relates to the technical field of alkaline zinc-manganese flow batteries, in particular to an alkaline flow battery based on carbon felt surface functionalization and electrolyte additive collaborative optimization. The surface functionalization of the carbon felt is that the carbon felt is modified by nitrogen-doped carbon dots, so that the pore size of the carbon felt is increased, the pore volume, the specific surface area and the hydrophilicity of the carbon felt are improved, the wettability of an electrolyte and the adsorption capacity to zinc atoms can be enhanced, and more zinc deposition sites are provided. Sodium gluconate is selected as an additive and is coordinated with zinc ions in the negative electrode electrolyte, so that the solvation structure of the zinc ions is changed. Through cooperative regulation and control of carbon felt modification and sodium gluconate, the zinc deposition morphology is changed, the zinc deposition is compact and uniform, the performance of the battery is improved, and the cycle life of the battery is prolonged. The invention has the advantages of outstanding performance, safety, environmental protection, low price and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of alkaline flow batteries, and specifically to an alkaline flow battery based on the synergistic optimization of carbon felt surface functionalization and electrolyte additives. Background Art

[0002] Developing energy storage and conversion devices with high energy density, long cycle life, low cost, and high safety is crucial for the full utilization of intermittent renewable energy such as solar energy, wind energy, and hydropower. Among them, zinc-based flow batteries in electrochemical energy storage technology have good application prospects in fields such as user-side energy storage and distributed energy due to their advantages of good safety, low cost, and high energy density. Alkaline zinc-manganese flow batteries are a new type of low-cost flow battery with a relatively high open-circuit voltage and have shown good prospects in large-scale applications.

[0003] For example, in existing alkaline zinc-manganese flow batteries, the positive electrolyte uses an alkaline solution of sodium permanganate, the negative electrolyte uses a strong base, the negative electrode uses a composite electrode composed of a zinc sheet and carbon felt, and the positive electrode uses carbon felt as the electrode. Since the negative electrode is a zinc deposition and dissolution reaction, when operating at a high current density, serious zinc dendrites or dead zinc will be generated due to uneven zinc deposition. The continuously growing dendrites will pierce the diaphragm, causing battery short-circuit. Dead zinc will cause pipeline blockage, resulting in a decrease in battery efficiency and capacity. At the same time, side reactions such as hydrogen evolution and self-corrosion will also occur when zinc is in a strong base condition.

[0004] Chinese Patent CN119764506A discloses a negative electrolyte of a zinc-iron flow battery and a zinc-iron flow battery. The negative electrolyte provided by this invention adds a quinone molecular additive, which can convert the "dead zinc" that has lost electrical contact back into electrochemically active zinc, realizing capacity recovery and greatly improving the cycle life of the zinc-based flow battery. However, in the cyclic voltammetry test of the battery in the examples, for the batteries using anthraquinone derivatives (1,5-DHAQ, 2,6-DHAQ, 1,8-DHAQ), at a current density of 50 mA / cm 2 , the highest number of cycle loops is 285, and this performance needs to be optimized. Summary of the Invention

[0005] In view of the above-mentioned problems of zinc dendrites, dead zinc, hydrogen evolution, and self-corrosion at the negative electrode of the alkaline zinc-manganese flow battery, it is particularly important to develop a safe, reliable, low-cost, and superior-performance alkaline zinc-manganese flow battery.

[0006] To achieve the above object, the following specific technical solutions are adopted:

[0007] The present invention provides an alkaline flow battery based on the synergistic optimization of carbon felt surface functionalization and electrolyte additives, including a negative electrolyte storage tank, a positive electrolyte storage tank, a negative chamber, a positive chamber, a separator, a negative electrode, a positive electrode, a negative peristaltic pump, and a positive peristaltic pump. The preparation raw materials of the negative electrolyte include a zinc-based redox active substance, a supporting electrolyte, an additive, and a solvent; the additive is sodium gluconate; the negative electrode material is a composite electrode composed of a zinc sheet and a carbon felt, and the carbon felt of the negative electrode is loaded with nitrogen-doped carbon dots.

[0008] Further, the zinc-based redox active substance is at least one of zinc oxide, zinc chloride, zinc iodide, zinc bromide, and zinc sulfate.

[0009] Further, the supporting electrolyte is at least one of sodium hydroxide, potassium hydroxide, and lithium hydroxide.

[0010] Further, the concentration of the additive in the negative electrolyte is 0.01 - 0.1 mol / L, the concentration of the zinc-based redox active substance in the negative electrolyte is 0.1 - 1 mol / L, and the concentration of the supporting electrolyte in the negative electrolyte is 2 - 6 mol / L.

[0011] Further, the mass of the nitrogen-doped carbon dots loaded on the carbon felt of the negative electrode is 0.3 - 3 mg, the diameter of the carbon dots is 2.89 ± 0.78 nm, and after the carbon felt of the negative electrode is loaded with nitrogen-doped carbon dots, the pore diameter of the carbon felt increases.

[0012] The present invention also provides a modification method for the carbon felt of the negative electrode of an alkaline flow battery based on the synergistic optimization of carbon felt surface functionalization and electrolyte additives. The specific preparation steps are as follows:

[0013] Step 1: Mix a biomass-based carbon source and an organic nitrogen source in a mass ratio of 2:1, and prepare a crude product of nitrogen-doped carbon dots through a hydrothermal reaction.

[0014] Step 2: Purify the crude product of nitrogen-doped carbon dots in Step 1 through dialysis to obtain nitrogen-doped carbon dots.

[0015] Step 3: Configure the nitrogen-doped carbon dots after dialysis treatment in Step 2 into a solution with a concentration of 0.1 - 1 mg / mL, immerse the carbon felt in the solution, and after hydrothermal reaction, perform drying treatment to obtain a surface-functionalized carbon felt.

[0016] Further, the biomass-based carbon source in Step 1 is coffee grounds, and the organic nitrogen source is polyaspartic acid.

[0017] Further, the specific steps of Step 1 include fully dissolving the dried coffee grounds in deionized water, filtering to obtain a filtrate; adding polyaspartic acid to the filtrate, then performing a hydrothermal reaction, pouring the well-mixed solution into a reaction kettle, and reacting in an electrothermal blast drying oven at 160 °C for 4 h; after the hydrothermal reaction, centrifuging is performed, and the centrifuge parameters are set to 10,000 r / min for 20 min.

[0018] Further, the specific steps of dialysis in Step 2 are as follows.

[0019] The solution obtained after centrifugation in Step 2 is placed in a filtration membrane with a pore size of 0.45 μm for dialysis. An MD77 dialysis bag is used, and the deionized water is changed every 4 h during the dialysis process until the deionized water does not turn yellow, at which point the dialysis ends; after dialysis, distillation is performed, and the distillation is stopped when the evaporated solution is approximately one-third of the original solution. The distilled solution is sealed and freeze-dried at a low temperature to obtain purified nitrogen-doped carbon dots.

[0020] Further, the specific steps of dialysis in Step 3 are as follows.

[0021] The nitrogen-doped carbon dots obtained in Step 2 are dissolved in deionized water to form a solution with a concentration of 0.1 - 1 mg / mL. The carbon felt is completely immersed in the solution, and ultrasonic treatment is performed for 30 min. Then, a hydrothermal reaction is carried out. The solution and the carbon felt are poured into a reaction kettle and reacted in an electrothermal blast drying oven at 180 °C for 12 h; after the reaction, it is placed in a vacuum drying oven for drying treatment to obtain a surface-functionalized carbon felt.

[0022] Advantages of the present invention:

[0023] (1) By utilizing the coordination of divalent zinc ions with additives and the adsorption of the zinc deposition layer with additives, not only the occurrence of the hydrogen evolution side reaction is inhibited, the generation of by-products is reduced, but also the growth of zinc dendrites is inhibited, improving the performance and cycle life of the battery. Sodium gluconate can effectively change the solvation structure of divalent zinc ions, form a stable complex, inhibit the hydrogen evolution side reaction caused by free water, reduce the probability of by-product generation, and adsorb on the zinc deposition layer to change the double-layer structure, forming a protective layer to avoid the growth of zinc dendrites, improving the battery performance and cycle life, and laying a foundation for its further application.

[0024] (2) By modifying the carbon felt with nitrogen-doped carbon dots, the pore size of the carbon felt can be increased, the pore volume, specific surface area, and hydrophilicity of the carbon felt can be improved, the electrolyte wettability and the adsorption capacity for zinc atoms can be enhanced, and more zinc deposition sites can be provided. Description of the drawings

[0025] Figure 1 It is a working mechanism diagram of the novel alkaline zinc-manganese flow battery prepared in Examples 1 - 4;

[0026] Figure 2 Flow chart for the modification treatment of carbon felt in the negative electrode of Example 3 and Example 4;

[0027] Figure 3 TEM image of the prepared nitrogen-doped carbon quantum dots;

[0028] Figure 4 SEM images of the unmodified carbon felt in Example 1 and 2 and the modified carbon felt in Example 3 and 4;

[0029] Figure 5 Diagram of the three efficiencies (Coulomb efficiency, voltage efficiency, energy efficiency) of the alkaline zinc-based flow battery in Example 1;

[0030] Figure 6 Diagram of the three efficiencies (Coulomb efficiency, voltage efficiency, energy efficiency) of the alkaline zinc-based flow battery in Example 2;

[0031] Figure 7 Diagram of the three efficiencies (Coulomb efficiency, voltage efficiency, energy efficiency) of the alkaline zinc-based flow battery in Example 3;

[0032] Figure 8 Diagram of the three efficiencies (Coulomb efficiency, voltage efficiency, energy efficiency) of the alkaline zinc-based flow battery in Example 4;

[0033] Figure 9 SEM images of zinc deposition after charge-discharge cycling in Example 1 - 4. Specific implementation

[0034] To better illustrate the object, technical solution and advantages of the present invention, the present invention will be further described through specific examples below.

[0035] The alkaline zinc-manganese flow battery of the present invention mainly includes: a negative electrode electrolyte storage tank, a positive electrode electrolyte storage tank, a negative electrode chamber, a positive electrode chamber, a diaphragm, a negative electrode, a positive electrode, a negative peristaltic pump, and a positive peristaltic pump. The structure is as follows:

[0036] The negative electrode electrolyte in the negative electrode electrolyte storage tank enters the negative electrode chamber through the negative peristaltic pump. When the negative electrode electrolyte flows through the negative electrode, the active substance undergoes an electrochemical reaction on the surface of the negative electrode. Then, the negative electrode electrolyte flows out of the negative electrode chamber and re-enters the negative electrode electrolyte storage tank. The positive electrode electrolyte in the positive electrode electrolyte storage tank enters the positive electrode chamber through the positive peristaltic pump. When the positive electrode electrolyte flows through the positive electrode, the active substance undergoes an electrochemical reaction on the surface of the positive electrode. Then, the positive electrode electrolyte flows out of the positive electrode chamber and re-enters the positive electrode electrolyte storage tank. Due to the presence of the diaphragm, the negative electrode chamber and the negative electrode electrolyte therein, and the positive electrode chamber and the positive electrode electrolyte therein are independent of each other and can only transport potassium ions. Figure 1It is a mechanism diagram of a novel alkaline zinc-manganese flow battery.

[0037] Example 1

[0038] In this example, an alkaline zinc-manganese flow battery is prepared, and the electrolyte solution of the battery is configured as follows:

[0039] Configuration process of the positive electrode electrolyte: The manganese-based redox active substance is sodium permanganate, and its dosage concentration in the solvent is 0.1 mol / L. The supporting electrolyte is NaOH with a concentration of 6 mol / L, and the solvent is deionized water. Dissolve NaOH in deionized water, and after complete dissolution, obtain the positive electrode electrolyte, which is sealed in the positive electrode storage tank.

[0040] Configuration process of the negative electrode electrolyte: The zinc-based redox active substance is zinc oxide, and its dosage concentration in the solvent is 0.1 mol / L. The supporting electrolyte is NaOH with a concentration of 6 mol / L, the solvent is deionized water, and the additive is sodium gluconate with a concentration of 0.1 mol / L. Obtain the negative electrode electrolyte, which is sealed in the negative electrode storage tank and used as the negative electrode electrolyte of the battery.

[0041] The single cell includes: the positive electrode is composed of a positive end plate, a positive graphite plate, a positive electrode frame, and carbon felt; the ion exchange membrane is a perfluorosulfonic acid membrane; the negative electrode is composed of carbon felt, a zinc sheet, a negative electrode frame, a negative graphite plate, and a negative end plate. The sizes of the positive electrode, negative electrode, and ion exchange membrane are all 3×3 cm. 2 。

[0042] Assemble the above alkaline zinc-based flow battery, and assemble the above positive electrode, the positive electrode storage tank filled with the positive electrode electrolyte, the negative electrode, and the negative electrode storage tank filled with the negative electrode electrolyte into an alkaline zinc-manganese flow battery.

[0043] Cyclic voltammetry test of the single cell: At a charge-discharge current density of 60 mA / cm 2 , the charge-discharge voltage range is 1.7 - 2.2 V. Perform constant current charge and discharge on the above single cell using a mixed solution of 6 mol / L sodium hydroxide solution and 0.1 mol / L sodium gluconate concentration as the negative electrode electrolyte, and the carbon felt of the negative electrode in the battery is not modified. Analyze the changes in the Coulomb efficiency, voltage efficiency, energy efficiency, and discharge capacity of the battery during long-term cycling.

[0044] The test results are as Figure 5 shown. The Coulomb efficiency of the battery is 95.35%, and the three efficiencies (Coulomb efficiency CE, voltage efficiency VE, and energy efficiency EE) remain stable during 600 cycles.

[0045] In this example, 0.1 mol / L sodium gluconate is used as an additive to coordinate with zinc ions in the negative electrode electrolyte, and the carbon felt is not modified.

[0046] Example 2

[0047] In this example, an alkaline zinc-manganese flow battery was prepared by referring to the method of Example 1, except that there was no additive in the negative electrolyte.

[0048] Configuration process of the positive electrolyte: The manganese-based redox active substance is sodium permanganate, and its concentration in the solvent is 0.1 mol / L. The supporting electrolyte is NaOH with a concentration of 6 mol / L, and the solvent is deionized water. Dissolve NaOH in deionized water, and after complete dissolution, obtain the positive electrolyte, which is sealed in the positive liquid storage tank.

[0049] Configuration process of the negative electrolyte: The zinc-based redox active substance is zinc oxide, and its concentration in the solvent is 0.1 mol / L. The supporting electrolyte is NaOH with a concentration of 6 mol / L, and the solvent is deionized water. Obtain the negative electrolyte, which is sealed in the negative liquid storage tank and used as the negative electrolyte of the battery.

[0050] The single cell includes: the positive electrode is composed of a positive end plate, a positive graphite plate, a positive electrode frame, and carbon felt; the ion exchange membrane is a perfluorosulfonic acid ion membrane; the negative electrode is composed of carbon felt, a zinc sheet, a negative electrode frame, a negative graphite plate, and a negative end plate. The sizes of the positive electrode, negative electrode, and ion exchange membrane are all 3×3 cm 2 。

[0051] Assemble the above alkaline zinc-based flow battery by assembling the above positive electrode, the positive liquid storage tank filled with the positive electrolyte, the negative electrode, and the negative liquid storage tank filled with the negative electrolyte into an alkaline zinc-manganese flow battery.

[0052] Cyclic test of the single cell: At a charge-discharge current density of 60 mA / cm 2 , the charge-discharge voltage range is 1.7 - 2.2 V. Perform constant current charge-discharge on the single cell based on the electrolyte of the above 6 mol / L sodium hydroxide solution, and analyze the changes in the Coulomb efficiency, voltage efficiency, energy efficiency, and discharge capacity of the battery during long-term cycling.

[0053] The test results are as Figure 6 shown. The Coulomb efficiency of the battery is 94.28%, and the capacity starts to decrease rapidly after 150 cycles, and the three efficiencies (Coulomb efficiency CE, voltage efficiency VE, and energy efficiency EE) gradually decrease.

[0054] In this example, as a blank control group, the negative electrolyte of the battery is 6 mol / L NaOH, without additives and the negative carbon felt is not modified. The Coulomb efficiency of this battery is 94.28%, and it only stably cycles 150 times.

[0055] Example 3

[0056] In this example, an alkaline zinc-manganese flow battery was prepared by referring to the method of Example 1. The difference is that the negative electrolyte contains additives and the negative carbon felt was modified.

[0057] The preparation process of the positive electrolyte: The manganese-based redox active substance is sodium permanganate, and its concentration in the solvent is 0.1 mol / L. The supporting electrolyte is NaOH with a concentration of 6 mol / L, and the solvent is deionized water. Dissolve NaOH in deionized water, and after complete dissolution, obtain the positive electrolyte, which is sealed in the positive electrolyte storage tank.

[0058] The preparation process of the negative electrolyte: The zinc-based redox active substance is zinc oxide, and its concentration in the solvent is 0.2 mol / L. The supporting electrolyte is NaOH with a concentration of 6 mol / L, and the solvent is deionized water. The additive is sodium gluconate with a concentration of 0.1 mol / L, obtaining the negative electrolyte, which is sealed in the negative electrolyte storage tank and used as the negative electrolyte of the battery.

[0059] The single cell includes: the positive electrode is composed of a positive end plate, a positive graphite plate, a positive electrode frame, and a carbon felt; the ion exchange membrane is a perfluorosulfonic acid ion membrane; the negative electrode is composed of a carbon felt, a zinc sheet, a negative electrode frame, a negative graphite plate, and a negative end plate. The sizes of the positive electrode, negative electrode, and ion exchange membrane are all 3×3 cm. 2 The carbon felt in the negative electrode was modified with 0.5 mg / mL carbon dots.

[0060] In this example, the modification steps of the carbon felt are as Figure 2 shown.

[0061] Step 1: Prepare the crude product of nitrogen-doped carbon dots.

[0062] First, weigh 8 g of dried coffee grounds, add them to 200 mL of deionized water, stir on a magnetic stirrer for 2 h, perform ultrasonic treatment for 10 min, and then filter to obtain the filtrate; add 4 g of polyaspartic acid to the filtrate, and then carry out a hydrothermal reaction. Pour the uniformly mixed solution into a reaction kettle and react in an electrothermal blast drying oven at 160 °C for 4 h. After the hydrothermal reaction, centrifuge, and the centrifuge parameters are set to 10000 r / min for 20 min.

[0063] Step 2: Filtration and purification of the crude product of nitrogen-doped carbon dots.

[0064] After centrifugation, the solution is placed in a filtration membrane with a pore size of 0.45 μm for dialysis using an MD77 dialysis bag. In this step, the dialysis bag is cut to a certain length according to the volume of the solution. First, clamp the bottom with a clip, then pour in the solution and clamp the top. Then it is placed in a beaker filled with deionized water for dialysis. During dialysis, the deionized water is changed approximately every 4 hours. During this period, the water will turn yellow. When the water no longer turns yellow, dialysis is completed, which takes about 48 hours. After dialysis, distillation is carried out. This step is completed when the evaporated solution is about one-third of the original solution. The distilled solution is placed in a petri dish, sealed with plastic wrap, and stored in the refrigerator for about 2 to 3 days. The sample is freeze-dried, which takes about 3 days to complete. After drying, nitrogen-doped carbon quantum dots with a diameter of 2.89 ± 0.78 nm ( Figure 3 ) can be obtained.

[0065] Step 3: Modification treatment of carbon felt.

[0066] Weigh a certain mass of the nitrogen-doped carbon quantum dots prepared in Step 2 and dissolve them in 70 mL of deionized water to obtain a solution with a nitrogen-doped carbon quantum dot concentration of 0.1 - 1 mg / mL. After dissolution, add a 3×3 cm carbon felt to completely immerse it in the solution and ultrasonically treat it for 30 minutes. Then, a hydrothermal reaction is carried out. Pour the solution and the carbon felt into a reaction kettle and react at 180 °C for 12 hours in an electrothermal blast drying oven. After the reaction, place it in a vacuum drying oven to evacuate, at 80 °C for 2 hours. After drying, take it out to obtain a carbon felt modified with nitrogen-doped carbon dots. The mass of nitrogen-doped carbon quantum dots contained in the modified carbon felt is 0.3 - 3 mg. As Figure 4 shown, the deposition of nitrogen-doped carbon quantum dots on the carbon felt increases the pore size of the carbon felt.

[0067] Assemble the above alkaline zinc-based flow battery by assembling the above positive electrode, the positive electrode storage tank filled with the positive electrode electrolyte, the negative electrode, and the negative electrode storage tank filled with the negative electrode electrolyte into a zinc-manganese flow battery.

[0068] Cyclic test of a single cell: At a charge-discharge current density of 60 mA / cm 2 , the charge-discharge voltage range is 1.7 - 2.2 V. Perform constant current charge-discharge on a single cell based on the above-mentioned mixed solution of 6 mol / L sodium hydroxide solution and 0.1 mol / L sodium gluconate concentration as the negative electrode electrolyte and with the negative electrode modified, and analyze the changes in the Coulomb efficiency, voltage efficiency, energy efficiency, and discharge capacity of the battery during long-term cycling.

[0069] The test results are as Figure 7 shown. The Coulomb efficiency of the battery is 95.28%, and the three efficiencies (Coulomb efficiency CE, voltage efficiency VE, and energy efficiency EE) remain stable during 750 cycles.

[0070] In this embodiment, compared with Embodiment 1 and Embodiment 2, the Coulombic efficiency stability of the zinc-manganese flow battery is better. On the one hand, sodium gluconate is used as an additive in the negative electrolyte to coordinate with zinc ions in the electrolyte, changing the zinc ion solvation structure, and synergistically regulating to promote the uniform deposition of zinc ions. This not only inhibits the occurrence of the hydrogen evolution side reaction, reduces the generation of by-products, but also inhibits the growth of zinc dendrites. On the other hand, the carbon felt is modified by nitrogen-doped carbon dots, which increases the pore size of the carbon felt, improves the pore volume, specific surface area and hydrophilicity of the carbon felt, enhances the electrolyte wettability and the adsorption ability of zinc atoms, and provides more zinc deposition sites. This makes the zinc deposition more uniform and further inhibits the growth of zinc dendrites. As Figure 9 shown, after multiple charge-discharge cycles, there are a small amount of zinc crystal branches on the surface of the negative zinc sheet in Embodiment 1 (electrolyte containing additives) and Embodiment 3 (electrolyte containing additives and negative carbon felt modified), while there are a large number of zinc crystal branches on the surface of the negative zinc sheet in Embodiment 4 (only negative carbon felt modified) and Embodiment 2 (electrolyte without additives and negative carbon felt unmodified). The deposition uniformity on the surface of the zinc sheet in Embodiment 3 is better than that in Embodiment 1, indicating that after the carbon felt is modified, the zinc ions in the electrolyte can be deposited more uniformly. Therefore, after maintaining a high Coulombic efficiency, the battery cycle life of Embodiment 3 is further improved, from 600 times to 750 times.

[0071] Embodiment 4

[0072] In this embodiment, an alkaline zinc-manganese flow battery is prepared by referring to the method of Embodiment 3, except that there is no additive in the negative electrolyte.

[0073] Configuration process of the positive electrolyte: The manganese-based redox active substance is sodium permanganate, and its concentration in the solvent is 0.1 mol / L. The supporting electrolyte is NaOH with a concentration of 6 mol / L, and the solvent is deionized water. Dissolve NaOH in deionized water, and after complete dissolution, obtain the positive electrolyte, which is sealed in the positive electrolyte storage tank.

[0074] Configuration process of the negative electrolyte: The zinc-based redox active substance is zinc oxide, and its concentration in the solvent is 0.1 mol / L. The supporting electrolyte is NaOH with a concentration of 6 mol / L, and the solvent is deionized water. Obtain the negative electrolyte, which is sealed in the negative electrolyte storage tank and used as the negative electrolyte of the battery.

[0075] The single cell includes: the positive electrode is composed of a positive end plate, a positive graphite plate, a positive electrode frame, and a carbon felt; the ion exchange membrane is a perfluorosulfonic acid ion membrane; the negative electrode is composed of a carbon felt, a zinc sheet, a negative electrode frame, a negative graphite plate, and a negative end plate. The sizes of the positive electrode, negative electrode, and ion exchange membrane are all 3×3 cm 2。The carbon felt in the negative electrode is modified by carbon dots at a concentration of 0.5 mg / ml.

[0076] In this embodiment, the modification steps of the carbon felt are as Figure 2 shown, and the specific steps refer to the content of Example 3.

[0077] Assemble the above alkaline zinc-based flow battery by assembling the above positive electrode, the positive electrode storage tank filled with the positive electrode electrolyte, the negative electrode, and the negative electrode storage tank filled with the negative electrode electrolyte into an alkaline zinc-manganese flow battery.

[0078] Cyclic test of a single cell: At a charge-discharge current density of 60 mA / cm 2 , the charge-discharge voltage range is 1.7 - 2.2 V. For the single cell based on this embodiment, with 6 mol / L sodium hydroxide solution as the negative electrolyte and the negative electrode being modified, perform constant current charge-discharge, and analyze the changes in the Coulombic efficiency, voltage efficiency, energy efficiency, and discharge capacity during long-term cycling of the battery.

[0079] The test results are as Figure 8 shown. The Coulombic efficiency of the battery is 94.37%, and it only stably cycles 250 times.

Claims

1. An alkaline flow battery based on the synergistic optimization of carbon felt surface functionalization and electrolyte additives, comprising a negative electrolyte storage tank, a positive electrolyte storage tank, a negative electrode chamber, a positive electrode chamber, a separator, a negative electrode, a positive electrode, a negative peristaltic pump, and a positive peristaltic pump; characterized in that, The preparation raw materials of the negative electrode electrolyte include a zinc-based redox active substance, a supporting electrolyte, an additive, and a solvent; the additive is sodium gluconate; the negative electrode material is a composite electrode composed of a zinc sheet and a carbon felt, and the carbon felt of the negative electrode is loaded with nitrogen-doped carbon dots.

2. The alkaline flow battery based on the synergistic optimization of carbon felt surface functionalization and electrolyte additives according to claim 1, wherein, The zinc-based redox active substance is at least one of zinc oxide, zinc chloride, zinc iodide, zinc bromide, and zinc sulfate.

3. The alkaline flow battery based on the synergistic optimization of carbon felt surface functionalization and electrolyte additives according to claim 1, characterized in that The supporting electrolyte is at least one of sodium hydroxide, potassium hydroxide, and lithium hydroxide.

4. The alkaline flow battery based on the synergistic optimization of carbon felt surface functionalization and electrolyte additives according to claim 1, wherein The concentration of the additive in the negative electrode electrolyte is 0.01 - 0.1 mol / L, the concentration of the zinc-based redox active substance in the negative electrode electrolyte is 0.1 - 1 mol / L, and the concentration of the supporting electrolyte in the negative electrode electrolyte is 2 - 6 mol / L.

5. The alkaline flow battery based on the synergistic optimization of carbon felt surface functionalization and electrolyte additives according to claim 1, characterized in that The mass of the nitrogen-doped carbon dots loaded on the carbon felt of the negative electrode is 0.3 - 3 mg, the diameter of the carbon dots is 2.89 ± 0.78 nm, and after the carbon felt of the negative electrode is loaded with nitrogen-doped carbon dots, the pore diameter of the carbon felt increases.

6. A method for modifying the negative electrode carbon felt of an alkaline flow battery based on the synergistic optimization of carbon felt surface functionalization and electrolyte additives as described in claim 1, characterized in that It includes the following steps Step 1: Mix the biomass-based carbon source and the organic nitrogen source in a mass ratio of 2:1, and prepare a crude product of nitrogen-doped carbon dots through a hydrothermal reaction. Step 2: Purify the crude product of nitrogen-doped carbon dots in Step 1 through dialysis to obtain nitrogen-doped carbon dots. Step 3: Configure the nitrogen-doped carbon dots after dialysis treatment in Step 2 into a solution with a concentration of 0.1 - 1 mg / mL, immerse the carbon felt in the solution, after a hydrothermal reaction, and then through a drying process to obtain a surface-functionalized carbon felt.

7. The modification method of the negative electrode carbon felt of the alkaline flow battery based on the synergistic optimization of carbon felt surface functionalization and electrolyte additives according to claim 6, characterized in that The biomass-based carbon source in Step 1 is coffee grounds, and the organic nitrogen source is polyaspartic acid.

8. The modification method of the negative electrode carbon felt of the alkaline flow battery based on the synergistic optimization of carbon felt surface functionalization and electrolyte additives according to claim 7, characterized in that, The specific steps of Step 1 include: fully dissolve the dried coffee grounds in deionized water, filter to obtain a filtrate; add polyaspartic acid to the filtrate, then conduct a hydrothermal reaction, pour the well-mixed solution into a reaction kettle, and react in an electrothermal blast drying oven at 160 °C for 4 h; after the hydrothermal reaction, conduct centrifugation, and the centrifuge parameters are set at 10000 r / min for 20 min.

9. The alkaline zinc-manganese flow battery based on the synergistic optimization of carbon felt surface functionalization and electrolyte additives according to claim 6, characterized in that, The specific steps of dialysis in Step 2 are as follows Put the solution obtained after centrifugation in Step 2 into a filtration membrane with a pore size of 0.45 μm for dialysis, use an MD77 dialysis bag, change the deionized water every 4 h during the dialysis process until the deionized water does not turn yellow, then the dialysis ends; after dialysis, conduct distillation, and when the evaporated solution is about one-third of the original solution, seal the distilled solution and conduct freeze-drying treatment at a low temperature to obtain the purified nitrogen-doped carbon dots.

10. The alkaline flow battery based on the synergistic optimization of carbon felt surface functionalization and electrolyte additives according to claim 6, wherein, The specific steps of dialysis in Step 3 are as follows Dissolve the nitrogen-doped carbon dots obtained in Step 2 in deionized water to form a solution with a concentration of 0.1 - 1 mg / mL, completely immerse the carbon felt in the solution, ultrasonically treat for 30 min, then conduct a hydrothermal reaction, pour the solution and the carbon felt into a reaction kettle, and react in an electrothermal blast drying oven at 180 °C for 12 h; after the reaction, put it into a vacuum drying oven for drying treatment to obtain the surface-functionalized carbon felt.

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