Preparation And Properties Investigation Of Prussian Blue Cathode Material For Sodium Ion Batteries

Aqueous sodium ion batteries are considered to be one of the most promising batteries due to their low cost,safety and high energy density.It is crucial to find suitable high-capacity electrode materials.In this project,Prussian blue is used as the research object.In view of the structural defects of the current Prussian blue materials,the poor cycling stability of the materials due to crystalline water,Moreover,the frequent dissolution of active substances in aqueous batteries leading to poor battery performance.This project proposes two strategies for the synthesis and design of cathode materials and highly concentrated electrolytes.By combining the above solutions,various aqueous sodium ion battery systems with high specific capacity and excellent cycling stability are constructed.High performance cobalt-based Prussian blue cathode material for sodium ion battery was synthesized by coprecipitate method.By adjusting the amount of the chelating agent sodium citrate and drying temperature,so as to control the precipitation rate and crystal water content,high capacity and low defect cobalt Prussian blue material was obtained.The characterization of the synthesized material revealed a rhomboid structure with good electrochemical properties,which showed high initial coulomb efficiency,excellent rate performance and cycling performance,showing a high reversible capacity of 105.1 m Ah/g and long cycling performance,with a capacity retention rate of 80%after 100 cycles.In order to solve the problem of poor cycling stability of cobalt-Prussian blue,Prussian blue with different Co/Ni ratio was designed and synthesized as the cathode material of water-based sodium ion battery and its performance was studied.The Prussian blue compound based on Co-Ni doping was prepared by co-precipitation method,and the best ratio of Ni and Co was explored,so as to obtain the material with high capacity and high stability.The incorporation of Co increases the specific capacity of the material,the addition of Ni stabilizes the structure,and then improves the cyclic stability of the material.Determining an optimal Co/Ni ratio can make the material maintain a large capacity at the same time,still has good cyclic stability.The optimum ratio of Co:Ni=7:3 was determined,and the specific discharge capacity of the compound reached 105.7 m Ah/g,After 100 cycles,there is still 85%capacity retention rate.Using Na₂Ni_0.3Co_0.7[Fe（CN）₆]as cathode material for aqueous sodium ion batteries,the effects of different aqueous electrolytes and concentrated electrolytes on the electrochemical performance of sodium ion batteries were studied.Firstly,the effects of four electrolytes on the properties of Prussian blue were compared by electrochemical tests,and it was found that the type of electrolyte anions had a significant effect on the electrochemical properties.Furthermore,the influence of sodium perchlorate electrolyte concentration on the electrochemical performance of Prussian blue was explored.It was found that high concentration of sodium perchlorate electrolyte could not only improve the activity of Na⁺,thus improving the working potential,but also inhibit side reactions,thus improving the initial coulomb efficiency.The cells assembled with the optimized electrolyte showed excellent cycling stability（83.3%capacity retention rate after 2000 cycles）.