Preparation And Sodium Storage Performance Of Iron-based Prussian Blue And Its Composites

In recent years,secondary clean energy has been rapidly developed,and electrochemical energy storage devices have also made tremendous progress.The sodium-ion battery is rich in resources and environment-friendly,and has a broad space for development,especially in large-scale electrochemical energy storage applications.The ion radius of sodium is larger than that of lithium,and therefore sodium ion batteries require electrode materials with more stable structures and properties to achieve high capacity and long charge-discharge cycle life.Prussian blue and its analogues A_aM'_b[M?_c?CN?₆]·xH₂O?A:alkaline cations,M:transition metal ions?have an open framework structure,allowing Na⁺to be rapidly embedded and released,which is considered as promising electrode materials in sodium-ion batteries.Although Prussian blue with a high specific capacity can theoretically allow two Na⁺deintercalations,defects such as vacancies and coordination water in the structure may make cycle stability poor;and the side reactions between the electrode and the electrolyte may also lead to a decrease in the cycle performance.This article mainly embarks from the synthesis of Prussian blue materials via changing the morphology of Prussian blue and surface modification to explore electrochemical properties as a cathode material for sodium ion batteries through related characterization.?1?The hydrothermal method was used to systematically study the role of acid in the growth of Prussian blue materials.The reaction temperature and surfactant are the key parameters for preparing different morphological features.The acid not only played an etching role in the reaction process,but also played a role in the catalyst,making the reaction proceed smoothly.Prussian blue materials with different morphological were prepared via varying the amount of acid added.The Prussian blue nanoparticles with concave centers exhibited good cycle stability when used as cathode materials for sodium ion batteries,and presented long-term cycling performance with a stable capacity of 77.8 mA h g^–1 after 500 cycles at 0.2 A g^–1,and even at 5 A g^–1,the specific capacity of 82 mA h g^–1 can be achieved.In addition,a full battery was assembled and also showed a capacity of 70 mA h g^–1 at 0.1 A g^–1.?2?Polypyrrole coating was performed on the prepared nano Prussian blue surface by chemical oxidation polymerization to stabilize the structure of Prussian blue and improve its electrochemical stability.Polypyrrole-coated Prussian blue composites exhibited excellent cycling stability when used as a cathode material for sodium-ion batteries,and can maintain 83.4 mA h g^–1 after 500 cycles at a current density of 0.2 A g^–1.At high current densities of 8 A g^–1 and 10 A g^–1,the specific capacity can be maintained at 69 mA h g^–1 and 61.2 mA h g^–1.The prepared electrode was soaked in the electrolyte for one month,and after testing,good cycle stability was still maintained.At a current density of 0.2 A g^–1,400cycles were performed,and the discharge specific capacity was maintained at 86.8 mA h g^–1.The results showed that the surface-coated polypyrrole reduces the side reaction between the electrolyte and the electrode material,and the structure of the Prussian blue material is more stable,improving the electrochemical performance of the electrode material.?3?Prussian blue composites coated with nano-Zn O particles were successfully synthesized by low-temperature calcination.The composite material coated with zinc oxide was used as positive electrode of sodium ion battery,and had more stable cycle performance and excellent rate performance compared to PB without coating.At a current density of 0.2 A g^–1,the specific discharge capacity remained 88.1 mA h g^–1 after 1000 cycles,and even at current densities up to 10 A g^–1,the specific capacity can still reach 83.4mA h g^–1.The results showed that the structural stability of Prussian blue composites coated with nano-ZnO is good,and the surface coating can reduce the side reactions between the electrolyte and the electrode materials,improving the electrochemical performance of the battery materials.