A polymer-coated sodium hexafluoroferrate composite electrode material, its preparation method and application

Abstract

The present invention discloses a composite electrode material of polymer-coated sodium hexafluoroferrate, a preparation method thereof and applications. The preparation method is to control the synthesis conditions, use ferric sulfate or ferrous sulfate or polyferric as the iron source, sodium carbonate or sodium hydroxide as the sodium source, and hydrofluoric acid as the fluorine source to successfully prepare sodium hexafluoroferrate, and then in-situ grow a conductive polymer on its surface. The conductive polymer is polyaniline or polypyrrole, and finally a composite electrode material of polymer-coated sodium hexafluoroferrate is obtained. The synthesis method of the present invention is simple, with low cost, and the composite electrode material has good electrochemical performance and has certain application potential in energy storage such as zinc-ion batteries.

Description

Technical Field

[0001] The present invention belongs to the field of electrode materials, and particularly relates to a polymer-coated sodium hexafluoroferrate composite electrode material, a preparation method thereof, and an application thereof. Background Art

[0002] With the rapid development of portable electronic devices, people have put forward higher requirements for energy storage devices. In the electrochemical energy storage system, aqueous zinc-ion batteries with high power density, long cycle life, safety and environmental protection have received more and more attention. However, compared with lead-acid batteries, fuel cells, and lithium-ion batteries, there is still a certain gap in the energy density of zinc-ion batteries. Therefore, effectively improving the energy density of the device while maintaining a high power density is the breakthrough point for the wide application of aqueous zinc-ion batteries. In energy storage devices, as the main component, the electrode material directly affects important performance indicators such as the capacitance, energy, power density, and cycle stability of the device. To break through the bottleneck of low energy density, preparing stable and efficient electrode materials is considered to be one of the effective ways to maintain a high power density and achieve a high energy density.

[0003] In 2012, Kisuk Kang, Jang Wook Choi, etc. proposed using carbon-coated sodium hexafluoroferrate (Na3FeF6) as the positive electrode material for ion batteries, but its electrochemical performance was not high and the cycle stability was poor. After analysis, they believed that the main reasons for the poor electrochemical performance were that the material contained more impurities, had serious agglomeration phenomena, and the conductivity of the material itself was not good. In 2017, Liu Wanmin, etc. proposed using carbon-coated sodium hexafluoroferrate synthesized by a low-temperature liquid-phase method. The sodium hexafluoroferrate synthesized by this method had good crystallinity, regular morphology, uniform and controllable particle size, and had a relatively high specific capacity and good stability. After research, it was found that conductive polymers, as pseudocapacitive materials, not only helped to maintain the stability of the material structure, but also had higher electrochemical performance than carbon materials. Therefore, using conductive polymers to wrap active materials might further improve the electrochemical performance of the materials. In addition, zinc-ion batteries can be stably charged and discharged in aqueous electrolytes, have lower costs compared to lithium and sodium-ion batteries, and are safer and more environmentally friendly. An aqueous zinc-ion battery assembled using a polymer-coated sodium hexafluoroferrate composite electrode material as the positive electrode not only has a simple synthesis method, is easy to operate, has low costs, but also can exhibit high electrochemical performance. Summary of the Invention

[0004] The purpose of the present invention is to provide a polymer-coated sodium hexafluoroferrate composite electrode material suitable for zinc-ion batteries, with a simple synthesis method, low costs, and excellent electrochemical performance, and a preparation method thereof. At the same time, the application performance of the material in zinc batteries is tested.

[0005] The present invention is realized through the following technical solutions:

[0006] A preparation method of a polymer-coated sodium hexafluoroferrate composite electrode material, comprising the following steps:

[0007] Disperse sodium hexafluoroferrate uniformly in water to obtain solution A, disperse aniline or pyrrole monomer in concentrated hydrochloric acid to obtain solution B, disperse ammonium persulfate in water to obtain solution C, mix solution A, solution B and solution C, stir and react at room temperature. After the reaction is completed, wash and dry to obtain the polymer-coated sodium hexafluoroferrate composite electrode material. Wash with water, and the water used for washing is 1-2 times the mass of the filtered product; the drying temperature is 50-100 °C, and the drying time is 2-10 h.

[0008] The sodium hexafluoroferrate is obtained through the following process:

[0009] Under room temperature stirring, add hydrofluoric acid and a sodium source aqueous solution to an iron source aqueous solution, stir and react. The reaction time is 2-5 h. After the reaction is completed, filter, wash and dry to obtain sodium hexafluoroferrate powder. The iron source is ferric sulfate or ferrous sulfate or polyiron, and the sodium source is sodium carbonate or sodium hydroxide. The atomic molar ratio of Na, Fe, and F is (3-6):1:6. When the iron source is ferrous sulfate, hydrogen peroxide needs to be added to oxidize Fe 2+ to Fe 3+ ; Wash with water, and the water used for washing is 1-2 times the mass of the filtered ointment. The drying temperature is 50-100 °C, and the drying time is 2-10 h. The rotation speed of mechanical stirring is 100-400 rpm.

[0010] The concentration of the iron source aqueous solution is 15-25 wt%, the concentration of hydrofluoric acid is 15-25 wt%, the concentration of the sodium source aqueous solution is 15-25 wt%, and the concentrations of the iron source aqueous solution, hydrofluoric acid and sodium source aqueous solution are the same; the molar ratio of ferrous sulfate to hydrogen peroxide is 2:1.

[0011] Specifically, the concentrations of the iron source aqueous solution, hydrofluoric acid and sodium source aqueous solution are all 20 wt%.

[0012] Preferably, the mass fraction of solution A is (5-15) wt%, the mass ratio of the monomer to concentrated hydrochloric acid in solution B is 1:1-10, and the concentration of ammonium persulfate in solution C is 0.1 mol / L-2 mol / L.

[0013] Preferably, the mass ratio of aniline or pyrrole monomer to sodium hexafluoroferrate is (1-8):1, and the mass ratio of aniline or pyrrole monomer to ammonium persulfate is (1-5):1.

[0014] The polymer-coated sodium hexafluoroferrate composite electrode material prepared by the above preparation method.

[0015] The application of the above polymer-coated sodium hexafluoroferrate composite electrode material in a zinc battery involves mixing the polymer-coated sodium hexafluoroferrate composite electrode material, carbon black, and PVDF in a mass ratio of 8:1:1, grinding, adding N-methylpyrrolidone, grinding again, coating the resulting slurry on conductive carbon paper, drying, and preparing a positive electrode sheet. Using a zinc sheet as the negative electrode and zinc sulfate as the electrolyte, a battery is assembled.

[0016] Preferably, the loading amount of the polymer-coated sodium hexafluoroferrate composite electrode material on the conductive carbon paper is 1.5 mg / cm 2 ~1.6 mg / cm 2 , and the concentration of zinc sulfate is 1 mol / L to 3 mol / L.

[0017] The advantages of the present invention are as follows:

[0018] 1. The synthesis method involved in the present invention is simple and easy to operate. All are liquid-phase reactions and can be carried out at room temperature conditions, with relatively low energy consumption.

[0019] 2. The sodium hexafluoroferrate synthesized by the method of the present invention has good crystallinity and fewer impurities. After in-situ growth coating with a polymer, the aggregation and adhesion of the polymer can be avoided.

[0020] 3. The polymer-coated sodium hexafluoroferrate composite material prepared by the present invention, as the positive electrode of a zinc-ion battery, exhibits good electrochemical performance and good stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 XRD pattern of the polyaniline-coated sodium hexafluoroferrate composite electrode material prepared in Example 1;

[0022] Figure 2 XRD pattern of the polyaniline-coated sodium hexafluoroferrate composite electrode material prepared in Example 2;

[0023] Figure 3 XRD pattern of the polypyrrole-coated sodium hexafluoroferrate composite electrode material prepared in Example 3;

[0024] Figure 4 Charge-discharge curve of a zinc-ion battery assembled using the polypyrrole-coated sodium hexafluoroferrate composite electrode material prepared in Example 3 as the positive electrode material;

[0025] Figure 5 Charge-discharge curve of a zinc-ion battery assembled using the polypyrrole-coated sodium hexafluoroferrate composite electrode material prepared in Example 3 as the positive electrode;

[0026] Figure 6Cyclic stability test diagrams of zinc-ion batteries assembled with the composite electrode material of sodium hexafluoroferrate wrapped with polypyrrole prepared in Example 3 (Curve A) and sodium hexafluoroferrate (Curve B) as the positive electrode respectively;

[0027] Figure 7 Charge and discharge curve diagram of a zinc-ion battery assembled with the composite electrode material of sodium hexafluoroferrate wrapped with polyaniline prepared in Example 4 as the positive electrode. Specific implementation mode

[0028] The present invention will be further described below in conjunction with specific embodiments:

[0029] Example 1

[0030] A preparation method of a composite electrode material of polyaniline-coated sodium hexafluoroferrate is as follows:

[0031] Take 60 g of polyiron (the iron content in the polyiron in this example is 18 wt% - 19 wt%) and dissolve it in 240 g of water to prepare a 20 wt% iron solution. Take 60 g of 39 wt% hydrofluoric acid and disperse it in 60 g of water to prepare a 20 wt% fluorine solution. Take 24 g of sodium hydroxide and dissolve it in 106 g of water to prepare a 20 wt% sodium solution. The feeding molar ratio of sodium, iron and fluorine is Na:Fe:F = 3:1:6. Under the condition of mechanical stirring at room temperature, add the hydrofluoric acid solution to the iron solution, with a rotation speed of 250 rpm. After uniform dispersion, add the sodium solution and stir for 3 h, then filter to obtain a solid ointment of sodium hexafluoroferrate. Disperse the ointment in 51 g of deionized water for the first washing. After filtration, dry the ointment at 80 °C for 5 h to obtain 20 g of sodium hexafluoroferrate powder.

[0032] Weigh 15 g of sodium hexafluoroferrate powder and disperse it in 135 g of water to obtain solution A. Take 100 g of aniline monomer and disperse it in 200 g of concentrated hydrochloric acid (36 wt%, the same below) to obtain solution B. Take 60 g of ammonium persulfate and disperse it in 200 g of water to obtain solution C. Add solution B to solution A, stir evenly, then add solution C and stir at room temperature for 5 h. After the reaction, filter to obtain a composite material ointment. Disperse the ointment in 90 g of deionized water for the first washing. After filtration, dry the ointment at 80 °C for 5 h to obtain 36 g of the composite electrode material of polyaniline-wrapped sodium hexafluoroferrate.

[0033] Figure 1 XRD pattern of the composite electrode material of polyaniline-wrapped sodium hexafluoroferrate, from Figure 1 It can be seen that the sodium hexafluoroferrate synthesized under the feeding ratio of Na:Fe:F = 3:1:6 contains iron trifluoride impurities, and the crystallinity of polyaniline is weak, so its characteristic peaks cannot be shown. In addition, the yield of sodium hexafluoroferrate synthesized under this ratio is relatively low, only 42%.

[0034] Example 2

[0035] A preparation method of a composite electrode material of sodium hexafluoroferrate coated with polyaniline is as follows:

[0036] Take 30 g of ferrous sulfate and dissolve it in 120 g of water to prepare a 20wt% ferrous solution. Take 60 g of 39wt% hydrofluoric acid and disperse it in 60 g of water to prepare a 20wt% fluorine solution. Take 32 g of sodium hydroxide and dissolve it in 128 g of water to prepare a 20wt% sodium solution. The feeding molar ratio of sodium, iron and fluorine is Na:Fe:F = 4:1:6. Under the condition of mechanical stirring at room temperature, 12 g of 30wt% hydrogen peroxide is added dropwise to the ferrous sulfate solution. After stirring and reacting at a rotation speed of 270 rpm for 2 h, the 20% fluorine solution is added to the iron solution. After uniform dispersion, the sodium solution is added and stirred and reacted for 3 h. After filtration, a sodium hexafluoroferrate solid ointment is obtained. The ointment is dispersed in 83 g of deionized water for primary washing. After filtration, the ointment is dried at 80°C for 5 h to obtain 38 g of sodium hexafluoroferrate powder.

[0037] Weigh 15 g of sodium hexafluoroferrate powder and disperse it in 135 g of water to obtain solution A. Take 50 g of aniline monomer and disperse it in 200 g of concentrated hydrochloric acid to obtain solution B. Take 30 g of ammonium persulfate and disperse it in 100 g of water to obtain solution C. Add solution B to solution A, stir evenly, then add solution C and stir and react at room temperature for 5 h. After the reaction is completed, filter to obtain a composite material ointment. The ointment is dispersed in 117 g of deionized water for primary washing. After filtration, the ointment is dried at 80°C for 5 h to obtain 47 g of a composite electrode material of polyaniline-coated sodium hexafluoroferrate.

[0038] Figure 2 XRD pattern of the composite electrode material of polyaniline-coated sodium hexafluoroferrate, from Figure 2 it can be seen that the sodium hexafluoroferrate synthesized at the feeding ratio of Na:Fe:F = 4:1:6 also contains iron trifluoride impurities. In addition, the yield of sodium hexafluoroferrate synthesized at this ratio is higher than that at the feeding ratio of Na:Fe:F = 3:1:6, which is 79%.

[0039] Example 3

[0040] A preparation method of a composite electrode material of sodium hexafluoroferrate coated with polypyrrole is as follows:

[0041] Take 40 g of ferric sulfate and dissolve it in 160 g of water to prepare a 20wt% iron solution, take 60 g of 39wt% hydrofluoric acid and disperse it in 60 g of water to prepare a 20wt% fluorine solution, take 40 g of sodium hydroxide and dissolve it in 160 g of water to prepare a 20wt% sodium solution, and the molar ratio of sodium, iron and fluorine is Na:Fe:F=5:1:6. Under room temperature mechanical stirring conditions, add the 20wt% fluorine solution to the iron solution at a speed of 230 rpm, add the sodium solution after uniform dispersion, stir and react for 3 h, filter to obtain sodium hexafluoroferrate ointment, disperse the ointment in 98 g of deionized water for one wash, filter and dry the ointment at 80°C for 5 h to obtain 40g of sodium hexafluoroferrate powder.

[0042] Weigh 15 g of sodium hexafluoroferrate powder and disperse it in 135 g of water to obtain solution A, take 30 g of pyrrole monomer and disperse it in 200 g of concentrated hydrochloric acid to obtain solution B, and take 15 g of ammonium persulfate and disperse it in 60 g of water to obtain solution C. Add solution B to solution A, stir evenly, then add solution C and stir and react at room temperature for 5 h. After the reaction is completed, filter to obtain a composite material ointment, disperse the ointment in 120 g of deionized water for washing once, filter and dry the ointment at 80°C for 5 h to obtain 48 g of a composite electrode material of polypyrrole-wrapped sodium hexafluoroferrate.

[0043] Figure 3 This is the XRD pattern of polypyrrole-coated sodium hexafluoroferrate composite electrode material. Figure 3 It can be seen that the sodium hexafluoroferrate synthesized at the feed ratio of Na:Fe:F=5:1:6 is relatively pure, and its XRD does not characterize other impurities. Among them, the crystallinity of polypyrrole is weak, so its characteristic peak cannot be shown. In addition, the yield of sodium hexafluoroferrate synthesized at this ratio is relatively high, which can reach 84%.

[0044] The sodium hexafluoroferrate and polypyrrole-coated sodium hexafluoroferrate composite electrode materials, conductive agent (carbon black) and binder (PVDF) were mixed in a mass ratio of 8:1:1 and fully ground until a uniform fine powder was formed. Then, an appropriate amount of N-methylpyrrolidone (NMP) was dropped and fully ground again. Finally, the mixture slurry was evenly coated on a cleaned conductive carbon paper substrate (with a diameter of about 1.2 cm). After vacuum drying at 60°C for 6 h, the positive electrode was obtained. The loading amounts of the sodium hexafluoroferrate positive electrode and the polypyrrole-coated sodium hexafluoroferrate composite electrode material on the carbon paper were 1.6 mg cm -2 and 1.5 mg cm -2Using a zinc sheet as the negative electrode material, Whatman glass fiber membrane as the separator (model: 1822 - 047), and 2M ZnSO4 as the electrolyte (soak the separator until there are no bubbles, about 0.3 mL), assemble a zinc-ion battery (button battery model CR2025) for electrochemical testing. The results are shown in Figures 4 to 6 . It can be seen from Figure 4 that the discharge specific capacity of the device with sodium hexafluoride ferrate as the positive electrode is 62 mA h g -1 at a current density of 1 Ag -1 , and the charge specific capacity is 65 mA h g -1 . It can be seen from Figure 6 that after cycling 400 times at a current density of 1 Ag -1 , only 41% of the original capacity remains; it can be seen from Figure 5 that the battery with a composite electrode material of polypyrrole-coated sodium hexafluoride ferrate as the positive electrode has a discharge specific capacity of 160 mA h g -1 at a current density of 1 A g -1 , and the charge specific capacity is 171 mA h g -1 . It can be seen from Figure 6 that after cycling 500 times at a current density of 1 A g -1 , 86% of the original capacity can be retained.

[0045] Example 4

[0046] A preparation method of a composite electrode material of polyaniline-coated sodium hexafluoride ferrate is as follows:

[0047] Dissolve 40 g of ferric sulfate in 160 g of water to prepare a 20% iron solution, disperse 60 g of 39% hydrofluoric acid in 60 g of water to prepare a 20% fluorine solution, dissolve 40 g of sodium hydroxide in 160 g of water to prepare a 20% sodium solution, and the feeding molar ratio of sodium, iron, and fluorine is Na:Fe:F = 5:1:6. Under the condition of mechanical stirring at room temperature, add the 20% fluorine solution to the iron solution at a rotation speed of 230 rpm. After uniform dispersion, add the sodium solution and stir for 3 h, then filter to obtain a sodium hexafluoride ferrate solid ointment. Disperse the ointment in 93 g of deionized water for the first washing. After filtration, dry the ointment at 80 °C for 5 h to obtain 38 g of sodium hexafluoride ferrate powder.

[0048] Weigh 15 g of sodium hexafluoroferrate powder and disperse it in 135 g of water to obtain solution A, take 30 g of aniline monomer and disperse it in 200 g of concentrated hydrochloric acid to obtain solution B, and take 15 g of ammonium persulfate and disperse it in 60 g of water to obtain solution C. Add solution B to solution A, stir evenly, then add solution C and stir and react at room temperature for 5 h. After the reaction is completed, filter to obtain a composite material ointment, disperse the ointment in 112 g of deionized water for washing once, filter and dry the ointment at 80°C for 5 h to obtain 45 g of a composite electrode material of polyaniline-wrapped sodium hexafluoroferrate.

[0049] The polyaniline-wrapped sodium hexafluoroferrate composite electrode material, conductive agent (carbon black) and binder (PVDF) were mixed in a mass ratio of 8:1:1 and fully ground until a uniform fine powder was formed. Then, an appropriate amount of N-methylpyrrolidone (NMP) was dropped and fully ground again. Finally, the mixture slurry was evenly coated on a cleaned conductive carbon paper substrate (with a diameter of about 1.2 cm). After vacuum drying at 60 °C for 6 h, the positive electrode was obtained. The loading amount of the polyaniline-wrapped sodium hexafluoroferrate composite electrode material on the carbon paper was 1.5 mg cm -2 The zinc sheet was used as the negative electrode material, the Whatman glass fiber film was used as the separator, and 2M ZnSO4 was used as the electrolyte (about 0.3 mL, which can soak the separator without bubbles). The electrochemical test results are shown in Figure 7 .and Figure 4 Compared with the device with sodium hexafluoroferrate as the positive electrode at 1 A g -1 The specific capacity at the current density is 62 mA h g -1 ); Figure 7 The results show that the battery with polyaniline-wrapped sodium hexafluoroferrate composite electrode material as the positive electrode has a high performance at 1 A g -1 The discharge capacity at the current density is 145 mA h g -1 , the charge capacity is 152 mA hg -1 .

[0050] Figure 4 and Figure 5 , Figure 7 By comparison, it is found that the specific capacity of sodium hexafluoroferrate is greatly improved after being coated with polypyrrole or polyaniline. Figure 6 It can be seen that the cycle stability of the polypyrrole-coated sodium hexafluoroferrate composite electrode material is significantly better than that of pure sodium hexafluoroferrate. This shows that the polymer-coated sodium hexafluoroferrate composite electrode material has a positive effect on improving specific capacity and enhancing cycle stability.

[0051] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the specific implementation of the invention rather than to limit it. Those of ordinary skill in the art should understand that any equivalent substitution or obvious modification of the implementation manner of the present invention without changing its performance or use should be covered within the scope of protection claimed by the present invention on the premise of not violating the purpose of the present invention.

Claims

1. A preparation method of a polymer-coated sodium hexafluoroferrate composite electrode material for zinc ion batteries, characterized in that, It includes the following steps: Sodium hexafluoroferrate is uniformly dispersed in water to obtain solution A, aniline or pyrrole monomer is dispersed in concentrated hydrochloric acid to obtain solution B, ammonium persulfate is dispersed in water to obtain solution C, solution A, solution B and solution C are mixed, and stirred at room temperature for reaction. After the reaction is completed, it is washed and dried to obtain a polymer-coated sodium hexafluoroferrate composite electrode material; the mass ratio of aniline or pyrrole monomer to sodium hexafluoroferrate is (1~8):1, and the mass ratio of aniline or pyrrole monomer to ammonium persulfate is (1~5):1; The sodium hexafluoroferrate is obtained through the following process: Under stirring at room temperature, hydrofluoric acid and an aqueous solution of a sodium source are added to an aqueous solution of an iron source, and the mixture is stirred and reacted for 2 to 5 h. After the reaction is completed, the mixture is filtered, washed, and dried to obtain sodium hexafluoroferrate powder. The iron source is ferric sulfate, ferrous sulfate, or polyiron, and the sodium source is sodium carbonate or sodium hydroxide. The atomic molar ratio of Na, Fe, and F is (4 to 6):1:

6. When the iron source is ferrous sulfate, hydrogen peroxide needs to be added to oxidize Fe 2+ to Fe 3+ .

2. The preparation method of the polymer-coated sodium hexafluoroferrate composite electrode material for zinc ion batteries according to claim 1, wherein The mass fraction of solution A is (5~15) wt%, the mass ratio of monomer to concentrated hydrochloric acid in solution B is 1:1~10, and the concentration of ammonium persulfate in solution C is 0.1 mol / L~2 mol / L.

3. The preparation method of the polymer-coated sodium hexafluoroferrate composite electrode material for zinc ion batteries according to claim 1, wherein, The concentration of the iron source aqueous solution is 15~25 wt%, the concentration of hydrofluoric acid is 15~25 wt%, the concentration of the sodium source aqueous solution is 15~25 wt%, and the concentrations of the iron source aqueous solution, hydrofluoric acid and sodium source aqueous solution are the same; the molar ratio of ferrous sulfate to hydrogen peroxide is 2:

1.

4. The preparation method of the polymer-coated sodium hexafluoroferrate composite electrode material for zinc ion batteries according to claim 1, wherein The washing refers to washing with water, and the water used for washing is 1~2 times the mass of the filtered product; the drying temperature is 50~100 °C, and the drying time is 2~10 h.

6. A polymer-coated sodium hexafluoroferrate composite electrode material for zinc ion batteries prepared by the preparation method according to any one of claims 1 to 4.

7. Application of the polymer-coated sodium hexafluoroferrate composite electrode material according to claim 5 in a zinc ion battery.

7. The application according to claim 6, characterized in that, The polymer-coated sodium hexafluoroferrate composite electrode material, carbon black and PVDF are mixed in a mass ratio of 8:1:1, ground, N-methylpyrrolidone is added, and ground. The obtained slurry is coated on a conductive carbon paper and dried to prepare a positive electrode sheet. A zinc sheet is used as the negative electrode and zinc sulfate is used as the electrolyte to assemble a battery.

8. The application according to claim 7, wherein The loading amount of the polymer-coated sodium hexafluoroferrate composite electrode material on the conductive carbon paper is 1.5 mg / cm 2 ~1.6 mg / cm 2 , and the concentration of zinc sulfate is 1 mol / L to 3 mol / L.

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