Preparation And Investigation Of Prussian Blue Cathode Material Na₂MnFe（CN）₆@PPy In Aqueous Hybrid Ion Battery

With the excessive consumption of traditional fossil fuels and the increasing demand for energy by human beings,current research aims at the ways to efficiently utilize traditional energy and develop new energy.New energy sources such as solar and wind energy are intermittent,which need to be combined with an energy storage battery system to ensure continuous energy supply.Among current energy storage batteries,rechargeable zinc-ion batteries have excellent characteristics such as high safety,low cost,and good environmental protection.However,there are still some problems yet to be solved urgently in rechargeable zinc-ion batteries,such as the difficulty of cathode materials in meeting the needs of commercial applications.Prussian blue is a promising cathode material in aqueous zinc-ion batteries,but its specific capacity and cycling stability still remain to be further improved.It is an effective improvement scheme to optimize the electrochemical performance of Prussian blue cathode materials in the aspects of electrolyte and structural modification.In this work,a study on the electrochemical performance of Na₂MnFe（CN）₆@PPy as cathode material is conducted.Firstly,Na₂MnFe（CN）₆@PPy nanosheets were synthesized by co-precipitation and ice-coating methods,and.The specific capacity and cycling stability of the composites were improved compared to those before modification.This work also synthesized K₂MnFe（CN）₆@PPy nanosheets by a similar method to compare the performance of the two composite electrode materials and investigate the pattern between the structure and the performance of the materials,and the relevant research results can help to promote the development of aqueous hybrid ion battery cathode materials with high capacity.The main research contents and results are as follows:（1）Na₂MnFe（CN）₆ and K₂MnFe（CN）₆ nanosheets were synthesized by a simple co-precipitation reaction,and the surface of the material was coated with PPy in ice bath to obtain Na₂MnFe（CN）₆@PPy nanosheets The materials were systematically characterized by XRD and other phase characterization methods,proving that PPy is successfully coated on the surface of the materials.（2）The hybrid electrolyte was adjusted,while the electrochemical performance test results of the electrode materials before and after PPy modification were also analyzed.Experiment results show the cycle performance and rate performance of the Na₂MnFe（CN）₆@PPy nanosheet electrode material are significantly improved,and the battery capacity remains at 50.1 m Ah g^-1 after 150 cycles.While the uncoated electrode material showed a obvious capacity drop in the first 30 cycles,and the capacity was only 25.1 m Ah g^-1 after 150 cycles.The impedance of the coated electrode material is reduced,indicating that the coating of PPy can improve the electrochemical kinetics of the electrode material.In addition,in the Na-Zn hybrid electrolyte,the electrode material exhibits better electrochemical performance than other hybrid ion electrolyte,indicating that the intercalation of Na-Zn hybrid ions is of great benefit to improving ion diffusion kinetics and electrochemical performance.The results show that the K₂MnFe（CN）₆@PPy nanosheet electrode material exhibits best performance in Li-Zn hybrid electrolyte,due to the lower ionic radius of Li⁺,which can be carried out in the framework of the material during relatively smooth deintercalation reaction,and the effect of K⁺in K₂MnFe（CN）₆@PPy nanosheet material is not as stable as Na⁺in the framework of the material,resulting in the overall lower electrochemical performance of electrode material in three different hybrid electrolytes than those of Na₂MnFe（CN）₆@PPy.（3）By means of ex-situ XRD and ex-situ XPS tests,the electrochemical reaction mechanism of the coated Na₂MnFe（CN）₆@PPy nanosheets was analyzed,and the deintercalation of the hybrid ions during the charging and discharging process in the hybrid electrolyte was explored.This work also characterized and analyzed the electromechanical kinetics after coating with PPy,and then calculated the ratio of pseudocapacitance through multi-sweep speed CV test.