A method for preparing a surface passivated prussian blue analogue and an energy storage device

Abstract

The application belongs to the technical field of sodium ion battery positive electrode materials, and particularly relates to a preparation method of surface passivated Prussian blue analogues and an energy storage device. A simple co-precipitation method is used to introduce surface passivated metal ions into Prussian blue analogues to control the surface morphology. The surface passivated iron-based Prussian blue analogues exhibit good air stability and excellent electrochemical performance under high surface loading. The process flow of the application is simple, the cost is low, the designed high surface loading electrode material meets the actual industrial production in the sodium ion battery energy storage system, and has strong commercial practicability.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery cathode materials technology, specifically to a method for preparing a surface-passivated Prussian blue analogue and its energy storage device. Background Technology

[0002] The growing demand in portable electronics, grid-scale energy storage, and electric vehicles has driven the development of rechargeable batteries. Compared to lithium-ion batteries, sodium-ion batteries have the advantages of abundant and inexpensive sodium resources, making them ideal for low-cost energy storage applications. Currently, the mainstream cathode materials for sodium batteries include polyanionic compounds, Prussian blue, and layered transition metal oxides. Prussian blue analogues, due to their unique open-frame structure, abundant sodium storage sites, and large ion migration channels, have gradually become a research hotspot in academia and industry. However, to reduce the cost of raw material protection during the industrialization of sodium-ion batteries and to improve the energy density and power density of the batteries, it is necessary to improve the air stability and electrode surface loading of the materials to achieve the practical application of high-energy batteries. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings and deficiencies of existing technologies and provide a method for preparing surface-passivated Prussian blue analogues. By surface-passivating the Prussian blue analogues, the air stability of the Prussian blue analogues is improved, and simultaneously, the cycle stability of high-area-load cathode materials is enhanced.

[0004] A first aspect of the present invention provides a method for preparing a surface-passivated and air-stabilized Prussian blue analogue, comprising the following steps:

[0005] S1. Dissolve a certain amount of chelating agent in 100 mL of deionized water. Then, add ferrous salt, zinc salt and ascorbic acid, stir to dissolve, and record as solution A.

[0006] S2, a certain amount of sodium ferrocyanide is dissolved in 100 mL of deionized water, and this solution is denoted as solution B.

[0007] S3. Slowly add the solutions prepared in steps S1 and S2 dropwise into solution C containing 50 mL of deionized water at a certain dropping rate, and stir for a period of time at a certain temperature and stirring speed.

[0008] S4. Let the mixed solution from step S3 stand and age for a period of time at a certain temperature.

[0009] S5, after the reaction is complete, the product is washed repeatedly by centrifugation with deionized water and anhydrous ethanol, and then freeze-dried under vacuum for a period of time. Finally, a blue powder is obtained, which is the surface-passivated Prussian blue analogue.

[0010] The chelating agent in step S1 is one or more of citric acid, sodium citrate, disodium ethylenediaminetetraacetate, and sodium pyrophosphate, with sodium citrate being the preferred chelating agent.

[0011] The zinc salt in step S1 is one or more of zinc sulfate, zinc chloride, zinc phosphate, and zinc nitrate, with zinc sulfate being the preferred zinc salt.

[0012] The ferrous salt in step S1 is one or more of ferrous sulfate, ferrous chloride, ferrous nitrate, and ferrous acetate, with ferrous sulfate being the preferred ferrous salt.

[0013] Preferably, the concentration of the chelating agent is 0-2 mol / L. -1 The concentration of zinc salt is 0-0.1 mol L. -1 The concentration of ascorbic acid is 0-0.2 mol / L. -1 The concentration of ferrous salt is 0-0.5 mol / L. -1 More preferably, the concentration of the chelating agent is 1.8 mol L. -1 The concentration of zinc salt is 0.045 mol L. -1 The concentration of ascorbic acid was 0.085 mol / L. -1 The concentration of ferrous salt is 0.405 mol / L. -1 .

[0014] Preferably, the concentration of sodium ferrocyanide is 0-0.5 mol / L. -1 More preferably, the concentration of sodium ferrocyanide is 0.45 mol / L. -1 .

[0015] Preferably, the drip rate in step S3 is 10 mL / h. -1 -20 mL h -1 The stirring speed is 400-500 rpm, the stirring time is 0.5-3 h, and the stirring temperature is 35-45 ℃. More preferably, the dropping rate in step S3 is 15 mL / h. -1 The stirring speed was 500 rpm, the stirring time was 3 h, and the stirring temperature was 45 ℃.

[0016] Preferably, the aging temperature in step S4 is 35-45 ℃ and the aging time is 3-24 h. More preferably, the aging temperature in step S4 is 45 ℃ and the aging time is 12 h.

[0017] Preferably, the freeze-drying temperature in step S5 is -30 to -60 ℃ and the freeze-drying time is 12-24 h. More preferably, the freeze-drying temperature in step S5 is -60 ℃ and the freeze-drying time is 12 h.

[0018] In a second aspect, the present invention provides a high surface-load sodium-ion battery electrode, wherein the battery electrode comprises the surface-passivated and air-stable Prussian blue analogue prepared as described above.

[0019] The preparation method of the above-mentioned high surface load sodium-ion battery electrode is as follows: a surface passivated and air-stable Prussian blue analog, a conductive agent and a binder are mixed in a ratio of 90:5:5 (wt%). The resulting mixture is transferred to a 2 mL slurry tube, several 3 mm zirconium dioxide beads are added, and the mixture is shaken thoroughly to obtain a uniform slurry. The slurry is coated on aluminum foil and placed in an 80 ℃ vacuum drying oven for 12 h to allow the solvent to evaporate completely. After the solvent is completely evaporated, the electrode is rolled by a roller press to obtain a sodium-ion battery high surface load electrode with a certain compaction density. The electrode is then cut, weighed and the surface load mass and active material loading are calculated.

[0020] In the preparation method of high surface area sodium-ion battery electrode, the compaction density is 1.4 g cm⁻¹. -3 -1.8 g cm -3 The preferred compaction density is 1.4 g / cm³. -3 .

[0021] In the preparation method of high areal load sodium-ion battery electrode, the areal load calculated by weighing is 14 mg / cm³. -2 -22 mg cm -2 The preferred weighing calculation surface load is 14 mg cm. -2 .

[0022] The conductive agent used in the preparation method of high surface area sodium-ion battery electrode can be a commonly used conductive agent raw material for battery electrodes, such as carbon black, acetylene black, Ketjen black, Super-P and carbon nanotubes, with Ketjen black being the preferred conductive agent.

[0023] The adhesive used in the preparation method of high surface area sodium-ion battery electrode can specifically adopt commonly used adhesive raw materials for battery electrodes, such as polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose, starch, hydroxypropyl cellulose, water-based adhesive, N-methyl-2-pyrrolidone, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer, pump rubber, fluororubber and various copolymers, with water-based adhesive being preferred.

[0024] The beneficial effects of this invention are as follows:

[0025] The Prussian blue analogue was prepared by co-precipitation, using readily available raw materials, inexpensive metals, a simple process, and low production costs, thus possessing the potential for large-scale production.

[0026] Prussian blue analogues with passivated surfaces exhibit good structural stability in air and are not prone to phase transitions. Furthermore, they can stabilize the interface during cycling, reduce side reactions, and improve cycling stability.

[0027] The prepared surface-passivated Prussian blue analogues exhibit good cycle capacity retention and rate performance in high-area-load positive electrode sheets, which is beneficial for industrial applications. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, obtaining other drawings based on these drawings without creative effort still falls within the scope of the present invention.

[0029] Figure 1 The thermogravimetric (TG) comparison diagrams of FHCF and PFHCF-2 prepared in Examples 1-2 of this invention are shown.

[0030] Figure 2 The images shown are cross-sectional views of the high-area electrode sheets prepared in Examples 1-2 of this invention, obtained using a scanning electron microscope (SEM).

[0031] Figure 3 The electrode sheets of FHCF and PFHCF-2 prepared in Examples 1-2 of this invention were subjected to a 100 mA g test. -1 Comparison of cycling performance at current density.

[0032] Figure 4 This is a comparison chart of the rate performance of the FHCF and PFHCF-2 electrode sheets prepared in Examples 1-2 of the present invention.

[0033] Figure 5 The electrode sheets of FHCF and PFHCF-2 prepared in Example 3 of this invention were subjected to a 100 mA g test. -1 Comparison of cycling performance at current density.

[0034] Figure 6 This is a comparison of the Fourier transform infrared (FT-IR) spectra of the air stability of FHCF and PFHCF-2 prepared in Example 4 of this invention.

[0035] Figure 7 This is a comparison of X-ray powder diffraction (XRD) images of the air stability of FHCF and PFHCF-2 prepared in Example 4 of this invention.

[0036] Figure 8This is a comparison of the Raman spectra of the air stability of FHCF and PFHCF-2 prepared in Example 4 of the present invention.

[0037] Figure 9 The air stability of the electrode sheet for FHCF and PFHCF-2 prepared in Example 4 of this invention was tested at 100 mAg. -1 Comparison of cycling performance at current density. Detailed Implementation

[0038] The present invention will be further described below with reference to embodiments, but these embodiments are not intended to limit the invention in any way. Any simple modifications, equivalent changes, and alterations made to the following examples based on the technical essence of the present invention shall still fall within the scope of the present invention.

[0039] Example 1, S1: Sodium citrate (180 mmol) was dissolved in 100 mL of pure water. Then, ferrous sulfate (40.5 mmol), zinc sulfate (4.5 mmol) and ascorbic acid (8.2 mmol) were dissolved in the above solution. The solution was stirred on a constant temperature magnetic stirrer for 3 h and denoted as solution A.

[0040] S2, dissolve sodium ferrocyanide (45 mmol) in 100 mL of pure water and stir on a constant temperature magnetic stirrer for 3 h. This solution is denoted as solution B. The beaker containing 50 mL of pure water is denoted as solution C.

[0041] S3, dissolve solutions A and B separately at 15 mL h -1 The solution was added dropwise to a C solution at a constant temperature of 45 °C, stirred for 2 h, and aged for 12 h. The lower precipitate was then washed several times with water and ethanol, and then freeze-dried in a vacuum freeze dryer at -60 °C for 12 h. The surface-passivated Prussian blue analogue (denoted as PFHCF-2) was collected.

[0042] S4, Electrode Preparation: The PFHCF-2 material, Ketjen Black (conductive agent), and water-based adhesive (binder) from step S3 were mixed in a 90:5:5 (wt%) ratio. The resulting mixture was transferred to a vibrating tube, and six 3 mm zirconium dioxide beads were added and vibrated thoroughly to obtain a uniform slurry. This slurry was then uniformly coated onto aluminum foil using a coating machine (MSK-AFA-I). The foil was then vacuum-dried in a 100 ℃ vacuum drying oven for 12 h to allow complete solvent evaporation. Finally, the electrode was compacted using a roller press to achieve a density of 1.4 g / cm³. -3 The electrode was cut into circular pieces with a diameter of 10 mm using a cutting machine (MSK-T10), and the surface load was measured to be 14 mg cm⁻¹. -2 .

[0043] S5, Electrochemical Performance Testing: All battery assembly was performed in an inert atmosphere (O2 wt% ≤ 0.01%, H2O wt% ≤ 0.01%) within a glove box. Constant current charge-discharge and long-cycle tests of the CR2032 coin cells were conducted using a Neware CT4000. The test voltage window was 2-4.0 V, and the current density was 1C = 100 mA g. -1 For comparison, FHCF was prepared under the same conditions.

[0044] Example 2 differs from Example 1 in that zinc sulfate is removed in step ①, while the ferrous sulfate content is increased to 45 mmol. All other conditions remain the same as in Example 1. The resulting product (denoted as FHCF) was then tested for its electrochemical performance.

[0045] Example 3 differs from Examples 1 and 2 in that the weighing surface load of the 10 mm diameter circular electrode is 22 mg cm. -2 All other conditions are exactly the same as in Examples 1 and 2.

[0046] Example 4: In this example, the Prussian blue analogues FHCF and PHCCF-2 prepared in Examples 1 and 3 were placed in the air for one month, and other conditions were completely consistent with steps S4 and S5 in Example 1.

[0047] Figure 1 The TG comparison charts of FHCF and PFHCF-2 prepared in Examples 1-2 of this invention show that PFHCF-2 contains less water of crystallization.

[0048] Figure 2 The images shown are cross-sectional SEM images of the high-area electrode sheets prepared in Examples 1-2 of this invention. It can be seen that at 1.4 g / cm³... -3 At a compaction density of 14 mg / cm³ -2 and 22 mg cm -2 The mass-loaded electrodes exhibit thicknesses of 78 μm and 136 μm, respectively.

[0049] Figure 3 The electrode sheets of FHCF and PFHCF-2 prepared in Examples 1-2 of this invention were subjected to a 100 mA g test. -1 The comparison chart of cycling performance under current density shows that PFHCF-2 has a high capacity retention rate after 400 cycles.

[0050] Figure 4 This is a comparison chart of the rate performance of the FHCF and PFHCF-2 electrode sheets prepared in Examples 1-2 of this invention. It can be seen that PFHCF-2 achieves a rate performance of 750 mA g. -1At a current density, it still maintains 115 mAh g. -1 The capacity.

[0051] Figure 5 The electrode sheets of FHCF and PFHCF-2 prepared in Example 3 of this invention were subjected to a 100 mA g test. -1 The comparison chart of cycling performance at current density shows that PFHCF-2 has high capacity and high cycle retention.

[0052] Figure 6 The FTIR comparison diagrams of the air stability of FHCF and PFHCF-2 prepared in Example 4 of this invention show that after the samples were placed for one month, the C≡N peak of FHCF showed a red shift, indicating that the structure had changed, while PFHCF-2 showed a stable structure.

[0053] Figure 7 The XRD comparison diagrams of the air stability of FHCF and PFHCF-2 prepared in Example 4 of this invention show that after the samples were placed for one month, the XRD peak of FHCF showed a phase transition and the byproduct Na4Fe(CN)6 was derived, indicating that the structure changed, while PFHCF-2 showed a stable phase structure.

[0054] Figure 8 The image shows a Raman comparison of the air stability of FHCF and PFHCF-2 prepared in Example 4 of this invention. It can be seen that after one month of storage, the Raman peak of FHCF shifts to a higher wavelength range, and the Fe content in the product... 3+ Content higher than Fe 2 + PFHCF-2 exhibits a relatively stable structure, and the product is mainly Fe. 2+ Mostly.

[0055] Figure 9 The air stability of the electrode sheet for FHCF and PFHCF-2 prepared in Example 4 of this invention was measured at 100 mA g. -1 The comparison chart of cycling performance under current density shows that after one month of storage, the capacity of FHCF decreased and the cycling stability was poor, while the capacity of PFHCF-2 hardly changed and the cycling stability was good.

[0056] The above description is merely a preferred embodiment of the present invention and should not be construed as limiting the scope of the invention. Therefore, any equivalent changes made in accordance with the claims of the present invention are still within the scope of the present invention.

Claims

1. A method for preparing a surface-passivated and air-stabilized Prussian blue analogue, characterized in that, Includes the following steps: S1, dissolve sodium citrate in 100 mL of pure water, then add ferrous sulfate, zinc sulfate and ascorbic acid to the solution, wherein sodium citrate is 180 mmol, zinc sulfate is 4.5 mmol, ascorbic acid is 8.2 mmol and ferrous sulfate is 40.5 mmol; S2, dissolve sodium ferrocyanide in 100 mL of pure water, wherein the amount of sodium ferrocyanide is 45 mmol; S3, simultaneously dissolve the solutions prepared in steps S1 and S2 at a rate of 10 mL / h. -1 -20 mL h -1 The solution was added dropwise to a beaker containing 50 mL of pure water at a constant rate of 400-500 rpm for 0.5-3 h at a temperature of 35-45 ℃. S4, let the mixed solution from step S3 stand for aging, wherein the aging temperature is 35-45 ℃ and the aging time is 3-24 h; S5. After the reaction is complete, the product is washed repeatedly by centrifugation with deionized water and anhydrous ethanol, and then freeze-dried under vacuum at a temperature of -30 to -60 °C for 12 to 24 h to finally obtain a powdered Prussian blue analogue.

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