The Study Of Ball Milling Synthesis Of Ultrafine Prussian Blue And Its Sodium Storage Performance

Growing energy demand and environmental pressure require the sustainable energy alternatives,including renewable energy sources and sustainable energy storage technologies.Due to the abundant reserves and low price,sodium-ion battery is considered to be the next-generation technology for large-scale electric energy storage applications.Among the cathode materials for sodium ion battery,Prussian blue analogs appear to be the attractive candidates due to their open framework structure,abundant redox sites,and excellent structural stability.However,the practical applications of Prussian blue analogs are still hindered due to some drawbacks,such as low synthetic productivity and poor conductivity.In this thesis,Sodium iron hexacyanoferrate?Fe-PBA?,Sodium manganese hexacyanoferrate?Mn-PBA?and MnFe-PBA were prepared by the facile ball milling method,and their sodium storage properties were studied.Firstly,Fe-PBA was obtained by ball-milling the ferrous dichloride and sodium ferrocyanide.The ball milling method is simple,non-toxic,and suitable for large-scale production.Fe-PBA/16 was obtained by ball-milling the hydrous iron dichloride and sodium ferrocyanide,which exhibits excellent sodium storage performance,delivering a capacity of 128 mAh g^-1 at 35 mA g^-1 and 106 mAh g^-1 at 5100 mA g^-1.When cycled at170 mA g^-1,the electrode delivers an initial discharge capacity of 120 mAh g^-1 and shows a capacity retention of 72%after 500 cycles.Further investigations show that the enhanced sodium storage performance of Fe-PBA/16 results from its better crystallinity and less[Fe?CN?₆]vacancies in the crystal frameworks.In addition,the excellent rate performance of ultrafine Fe-PBA/16 can be mainly ascribed to the size effect.Secondly,Mn-PBA was obtained by the ball-milling method and shows higher sodium content and energy density.Through partial substitution of Fe for Mn in Mn-PBA,MnFe-PBA was obtained.Among them,MnFe-PBA/0.4 shows a significantly improved cycling and rate performance compared with Mn-PBA.At 170 mAh g^-1,the MnFe-PBA/0.4 electrode delivers a discharge capacity of 118 mAh g^-1 in the first cycle and exhibits a capacity retention of 65%after 350 cycles.When the current density is3400 and 5100 mA g^-1,the electrode still maintains a capacity of 86 and 85 mAh g^-1,respectively.Ex-situ XRD and EIS analysis show that after partial substitution of Fe for Mn,the crystal structure of MnFe-PBA/0.4 is more stable during charge/discharge process and its electronic conductivity,sodium ion diffusion coefficient also improve,which result in the better cycling and rate performance.