Structural Design,Controllable Synthesis And Sodium-storage Performance Of Prussian Blue Analogs

In recent years,sodium ion batteries(SIBs)are drawing more and more attentions in the fields of energy storage due to the earth-abundant and inexpensive sodium resources.The development of cathode materials is critical for the promotion of performance and the application of SIBs.Among the cathode materials for SIBs,Prussian blue analogs(PBAs)featured by large sodium ion diffusion paths and sufficient sodium storage sites are attracting increasing interests.However,shortages in cycle stability and/or rate capability still hinder the application of SIBs.Therefore,based on the structural characteristics and growth mechanism of PBAs,the thesis focuses on the promotion of cycle stability and rate performance and a systematic research work has been carried out,in order to promote its application.In chapter 1,an evaluation of the applications of different types of PBAs for rechargeable batteries,especially SIBs are given.After a generalized summization of the challenges that PBAs face,thouths and methods of modifications are proposed.In chapter 2,the experimental reagents,equipment and methods used in this dissertation are introduced,followed by a detailed description of the material characterization methods and electrochemical test technologies.The growting condition of PBAs evidently affects their constituent and structure,and further affects the electrochemical performance of PBA-electrods.In chapter 3,we studied the synthesis condition on the basis of the growth mechanism of PBAs,verifying the impact of temperature on constituent,structure and electrochemical performances of PBA-cathodes.This work provides theoretical and experimental basis for the modifications afterward.In chapter 4,we proposed the idea of concentration-gradient nickel substitution based on the layer-by-layer growth of PBAs in order to satisfy the requirement of cycle stability.We prepared gradient-nickel-substituted Prussian blue featured by high-stable nickel-rich outer layer and high-capacity iron-rich inner layer,which significantly improves cycle stability without lowering its high capacity.In order to improve the rate performance of PBAs,establishing intercalation pseudocapacitance which can eliminate the rate limitation of diffusion in the bulk phase in PBAs is proposed in chapter 5.Herein,a low-vacancy copper hexacyanoferrate with intercalation pseudocapacitive is successfully synthesized,achieving excellent high-rate and low-temperature performance.In chapter 6,copper Prussian blue and iron Prussian blue obtained in previous work with excellent electrochemical performances are chosen as the cathode and anode to construct an all-Prussian-blue aqueous sodium ion battery.Electrochemical tests shows that the battery can deliver a capacity of 50 mAh g-1 with an average working potential of 0.70 V,and a stable cycling performance.Finally,in chapter 7,an overview and the deficiency of the dissertation are summarized.Some prospects and suggestions on the possible future research are presented.