A cobalt cyanide solid energy storage material applied to a liquid flow battery and a preparation method thereof

Abstract

The application discloses a cobalt ferrocyanide solid energy storage material applied to a liquid flow battery and a preparation method thereof, and belongs to the technical field of electrochemical energy storage. The application solves the problem of poor potential matching between the existing solid energy storage material and a water-based TEMPO positive electrode system. The application provides a cobalt ferrocyanide redox targeting material with a redox potential matched with a TEMPO electrolyte, and applies the material as a solid energy storage material to a liquid flow battery with a TEMPO aqueous solution as a positive electrode electrolyte. The solid energy storage material has high matching degree with the TEMPO positive electrode of the water-based liquid flow battery, can significantly improve the energy density of the water-based TEMPO positive electrode, and will not reduce the electrolyte flowability.

Description

Technical Field

[0001] This invention relates to a cobalt ferricyanide solid energy storage material for use in flow batteries and its preparation method. Specifically, it relates to the preparation of a cobalt ferricyanide redox-targeting material and its application as a solid energy storage material for redox-targeting reactions in an aqueous flow battery with 2,2,6,6-tetramethylpiperidine 1-hydroxyl oxide (TEMPO) as the positive electrode, belonging to the field of electrochemical energy storage technology. Background Technology

[0002] Due to the non-renewable nature of traditional energy sources such as fossil fuels, the development and utilization of new energy sources such as wind and solar power has become an inevitable choice for human sustainable development. Aqueous flow batteries, as an electrochemical energy storage technology, possess advantages such as simple structure, high stability, flexible design, and high safety, making them one of the effective ways to solve the problems of strong randomness, poor stability, and poor continuity in renewable energy power generation. In aqueous flow battery systems, 2,2,6,6-tetramethylpiperidine-1-hydroxyl oxide (TEMPO) has become a strong candidate to replace the currently defective vanadium redox flow battery's positive electrode active material due to its high redox potential, excellent reversibility, and environmental friendliness. However, the limited solubility of the active material TEMPO in water leads to insufficient energy density in conventional flow batteries. To improve the battery's energy density, semi-solid flow batteries with higher active material concentrations can be used, but the suspension generally has high viscosity and poor electrolyte flowability, posing a risk of poor electrolyte circulation or even blockage in practical applications, making it difficult to meet practical application requirements.

[0003] Therefore, flow batteries based on redox-targeted reactions have become an effective way to solve the problems of low energy density in conventional aqueous flow batteries and the practical application difficulties of semi-solid flow batteries. These batteries incorporate solid energy storage materials into the electrolyte storage tank, utilizing the redox-targeted reaction between the solid energy storage material and the redox medium to store electrical energy, thereby improving the energy density of the flow battery. This type of flow battery combines the advantages of traditional aqueous and semi-solid flow batteries and has high application potential. However, the redox-targeted reaction in flow batteries requires the redox potential of the solid energy storage material to match that of the redox medium. Currently reported solid energy storage materials for redox-targeted flow batteries include Prussian blue and its derivatives, polyanionic compounds (mainly phosphates such as LiFePO4, Na3V2(PO4)3, etc.), Ni(OH)2-based materials, and organic electrode materials (such as polyimide). These materials have poor potential matching with the aqueous TEMPO cathode system, resulting in very limited improvement in battery energy density. Therefore, developing targeted materials for redox flow batteries with high energy density, low cost, and redox potential matching that of TEMPO active materials is an urgent problem to be solved. Summary of the Invention

[0004] The purpose of this invention is to provide a cobalt ferricyanide redox targeting material whose redox potential matches that of TEMPO electrolyte, and to apply it as a solid energy storage material in a flow battery with TEMPO aqueous solution as the positive electrode electrolyte.

[0005] The technical solution of this invention:

[0006] One objective of this invention is to provide a method for preparing cobalt ferricyanide solid energy storage material, the method comprising the following steps:

[0007] (1) Add ferricyanide aqueous solution and cobalt salt aqueous solution dropwise to deionized water at a certain concentration ratio, stir, and obtain a uniform mixed solution;

[0008] (2) The mixed solution obtained in (1) was allowed to stand for a certain period of time to age, then filtered, the filter residue was washed with deionized water and dried to obtain cobalt ferricyanide powder.

[0009] (3) Mix the cobalt ferricyanide powder, carbon black and PVDF obtained in (2) and granulate them to obtain cobalt ferricyanide solid energy storage material.

[0010] Further specifying, (1) the ferricyanide is one or a mixture of potassium ferricyanide, sodium ferrohydride, lithium ferricyanide, and ammonium ferricyanide.

[0011] Further specifying, (1) the cobalt salt is one or a mixture of cobalt nitrate, cobalt sulfate, cobalt chloride, and cobalt bromide.

[0012] Further specified, the concentration ratio of ferricyanide to cobalt salt in the mixed solution in (1) is 1:2.

[0013] Further specified, (1) a peristaltic pump is used to control the dripping rate of ferricyanide aqueous solution and cobalt salt aqueous solution, and the rotation speed of the peristaltic pump is 30-100 r / min.

[0014] Furthermore, the peristaltic pump speed is specified as 30 r / min, 40 r / min, 50 r / min, 60 r / min, 70 r / min, 80 r / min, 90 r / min or 100 r / min.

[0015] Further, the static aging time in (2) is 12-24h.

[0016] Furthermore, the aging time is specified as 12h, 14h, 16h, 18h, 20h, 22h or 24h.

[0017] Further specified, (2) the drying temperature is 40-80℃ and the time is 12-24h.

[0018] Furthermore, the drying temperature is specified as 40℃, 50℃, 60℃, 70℃, or 80℃.

[0019] Furthermore, the drying time is specified as 12h, 14h, 16h, 18h, 20h, 22h or 24h.

[0020] Further specified, (3) the mass ratio of cobalt ferrocyanide powder, carbon black and PVDF is (60-80): (10-20): (10-20).

[0021] Furthermore, the cobalt ferricyanide content in the cobalt ferricyanide solid energy storage material is specified to be 60 wt%, 65 wt%, 70 wt%, 75 wt%, or 80 wt%.

[0022] Furthermore, the carbon black content in the cobalt ferricyanide solid energy storage material is specified to be 10 wt%, 12 wt%, 14 wt%, 16 wt%, 18 wt%, or 20 wt%.

[0023] Furthermore, the PVDF content in the cobalt ferricyanide solid energy storage material is specified to be 10wt%-20wt%, for example, 10wt%, 12wt%, 14wt%, 16wt%, 18wt%, or 20wt%.

[0024] The second objective of this invention is to provide an application of the cobalt ferricyanide solid energy storage material prepared by the above method, specifically as a solid energy storage material applied in a flow battery using TEMPO aqueous solution as the positive electrode electrolyte.

[0025] Further specified, the concentration of the positive electrode TEMPO electrolyte is 0.01-0.2M.

[0026] Furthermore, the concentration of the positive electrode TEMPO electrolyte is specified as 0.01M, 0.05M, 0.1M, 0.15M, or 0.2M.

[0027] Beneficial effects:

[0028] The cobalt ferricyanide solid energy storage material prepared by this invention has a high degree of matching with the TEMPO cathode of aqueous flow batteries. It significantly improves the energy density of aqueous TEMPO cathodes without reducing the fluidity of the electrolyte. Attached Figure Description

[0029] Figure 1 The Raman spectrum of cobalt ferrocyanide prepared in Example 1;

[0030] Figure 2 The X-ray diffraction pattern of cobalt ferrocyanide prepared in Example 1;

[0031] Figure 3 The infrared spectrum of cobalt ferrocyanide prepared in Example 1;

[0032] Figure 4 This is a scanning electron microscope image of cobalt ferrocyanide prepared in Example 2;

[0033] Figure 5 Transmission electron microscope image of cobalt ferrocyanide prepared in Example 2;

[0034] Figure 6 Cyclic voltammetry curves of cobalt ferricyanide prepared in Example 3 in aqueous solution;

[0035] Figure 7 The results of charge-discharge tests on the symmetrical battery assembled in Example 4;

[0036] Figure 8 The graph shows the variation of capacity and efficiency of the symmetrical battery assembled in Example 4 with the number of cycles. Detailed Implementation

[0037] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0038] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0039] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0040] Example 1

[0041] Step I: Add 0.06M potassium ferricyanide aqueous solution and 0.12M cobalt sulfate aqueous solution at a concentration ratio of 1:2 to 1180mL of deionized water using a peristaltic pump at a rate of 50r / min and stir to mix.

[0042] Step II: Let the solution obtained in Step I stand for 24 hours to age, filter it, wash the filter residue with deionized water, and dry it at 60°C for 16 hours to obtain the cobalt ferricyanide product.

[0043] The product prepared in this embodiment was analyzed and tested, and the results are shown in the figure. Figures 1-3 . Figure 1 The image shows the Raman spectrum of cobalt ferrocyanide prepared in this embodiment. Figure 2 The X-ray diffraction pattern of cobalt ferrocyanide prepared in this embodiment is shown below. Figure 3 The image shows the infrared spectrum of cobalt ferricyanide prepared in Example 1. As can be seen from the figure, the substance prepared in this example is pure cobalt ferricyanide, and it is in the form of cobalt ferricyanide crystals.

[0044] Example 2

[0045] Step I: Add 0.05M potassium ferricyanide aqueous solution and 0.1M cobalt sulfate aqueous solution at a concentration ratio of 1:2 to 980mL of deionized water using a peristaltic pump at a rate of 60r / min and stir to mix.

[0046] Step II: Let the solution obtained in Step I stand for 18 hours to age, filter it, wash the filter residue with deionized water, and dry it at 40°C for 24 hours to obtain the cobalt ferricyanide product.

[0047] The product prepared in this embodiment was analyzed and tested. The scanning electron microscope (SEM) image and transmission electron microscope (TEM) image of the cobalt ferricyanide prepared in this embodiment are shown below. Figure 4 and Figure 5 As shown.

[0048] Example 3

[0049] Step I: Add 0.02M potassium ferricyanide aqueous solution and 0.04M cobalt sulfate aqueous solution at a concentration ratio of 1:2 to 380mL of deionized water using a peristaltic pump at a rate of 80r / min and stir to mix.

[0050] Step II: Let the solution obtained in Step I stand for 20 hours to age, filter it, wash the filter residue with deionized water, and dry it at 50°C for 20 hours to obtain the cobalt ferricyanide product.

[0051] The product prepared in this embodiment was subjected to cyclic voltammetry testing in an aqueous solution (1 M KCl). The results... Figure 6 As shown in the figure, the redox potential of the substance prepared by this invention in aqueous solution is similar to that of TEMPO, and it can be used as a redox-targeting material to match it.

[0052] Example 4

[0053] Step I: Add 0.03M potassium ferricyanide aqueous solution and 0.06M cobalt sulfate aqueous solution at a concentration ratio of 1:2 to 580mL of deionized water using a peristaltic pump at a rate of 90r / min and stir to mix.

[0054] Step II: Let the solution obtained in Step I stand for 22 hours to age, filter it, wash the filter residue with deionized water, and dry it at 70°C for 16 hours to obtain the cobalt ferricyanide product.

[0055] Step III: The cobalt ferricyanide powder obtained in this embodiment is mixed with carbon black and PVDF binder at a mass ratio of 7:2:1, and then granulated into cobalt ferricyanide solid energy storage material particles using a granulation mechanism.

[0056] Step IV: Assemble a symmetrical flow battery with a 0.2M TEMPO aqueous electrolyte, wherein the electrodes are graphite felt with an area of ​​13.5 cm². 2 The bipolar plate is a graphite plate, and the ion exchange membrane is a Nafion 117 cation exchange membrane manufactured by DuPont. The cobalt ferricyanide solid energy storage material obtained above was added to the battery's storage tank. The charge-discharge test results of the symmetrical battery are shown below. Figure 7 As shown in the figure, the substance prepared by this invention can effectively increase the capacity of batteries using TEMPO aqueous solution as the electrolyte, up to 244 mAh.

[0057] Example 5

[0058] Step I: Add 0.08M potassium ferricyanide aqueous solution and 0.16M cobalt sulfate aqueous solution at a concentration ratio of 1:2 to 1580mL of deionized water using a peristaltic pump at a rate of 90r / min and stir to mix.

[0059] Step II: Let the solution obtained in Step I stand for 22 hours to age, filter it, wash the filter residue with deionized water, and dry it at 70°C for 16 hours to obtain the cobalt ferricyanide product.

[0060] Step III: The cobalt ferricyanide powder obtained in this embodiment is mixed with carbon black and PVDF binder at a mass ratio of 6:2:2, and then granulated into cobalt ferricyanide solid energy storage material particles using a granulation mechanism.

[0061] Step IV: Assemble a flow battery with a positive electrode of 0.2M TEMPO aqueous solution and a negative electrode of metallic zinc. The electrode is made of graphite felt with an area of ​​13.5 cm². 2 The bipolar plate is a graphite plate, and the ion exchange membrane is a Nafion 117 cation exchange membrane manufactured by DuPont. The cobalt ferricyanide solid energy storage material obtained above is added to the storage tank of the positive electrode of the flow battery. The changes in the flow battery capacity, efficiency, etc., with the number of cycles are shown in [the table / document / reference needed]. Figure 8 As shown in the figure, the substance prepared in this invention has a relatively stable effect on improving the capacity of batteries using TEMPO aqueous solution as the electrolyte.

[0062] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Anyone skilled in the art can make various modifications and alterations without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be determined by the claims.

Claims

1. An application of a cobalt ferrocyanide solid energy storage material, characterized in that, It can be used as a solid energy storage material in flow batteries with TEMPO aqueous solution as the positive electrode electrolyte; The preparation methods of cobalt ferricyanide solid energy storage materials include: (1) Add the ferricyanide aqueous solution and the cobalt salt aqueous solution dropwise to deionized water at a certain concentration ratio, stir, and obtain a uniform mixed solution; (2) The mixed solution obtained in (1) was allowed to stand for a certain period of time and then filtered. The filter residue was washed with deionized water and dried to obtain cobalt ferricyanide powder. (3) Mix the cobalt ferricyanide powder, carbon black and PVDF obtained in (2) and granulate to obtain cobalt ferricyanide solid energy storage material.

2. The application of the cobalt ferrocyanide solid energy storage material according to claim 1, characterized in that, (1) The ferricyanide is one or a mixture of potassium ferricyanide, sodium ferrohydride, lithium ferricyanide and ammonium ferricyanide.

3. The application of the cobalt ferrocyanide solid energy storage material according to claim 1, characterized in that, (1) The cobalt salt is one or a mixture of cobalt nitrate, cobalt sulfate, cobalt chloride, and cobalt bromide.

4. The application of the cobalt ferrocyanide solid energy storage material according to claim 1, characterized in that, (1) The concentration ratio of ferricyanide to cobalt salt in the mixed solution is 1:

2.

5. The application of the cobalt ferrocyanide solid energy storage material according to claim 1, characterized in that, (1) A peristaltic pump is used to control the dripping rate of ferricyanide aqueous solution and cobalt salt aqueous solution. The speed of the peristaltic pump is 30-100 r / min.

6. The application of the cobalt ferrocyanide solid energy storage material according to claim 1, characterized in that, (2) The static aging time is 12-24 h.

7. The application of the cobalt ferrocyanide solid energy storage material according to claim 1, characterized in that, (2) The drying temperature is 40-80 ℃ and the time is 12-24 h.

8. The application of the cobalt ferrocyanide solid energy storage material according to claim 1, characterized in that, (3) The mass ratio of cobalt ferrocyanide powder, carbon black and PVDF is (60-80): (10-20): (10-20).

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