Study On Modification Of Prussian Blue Cathode Materials For Sodium Ion Batteries

Among the many energy storage technologies available today,lithium-ion batteries have become the mainstream choice due to their high energy density,high charge/discharge rate,long cycle life and mature key technologies.However,given the cost,lithium-ion batteries are hardly the ideal choice for large-scale energy storage.On the one hand,sodium and lithium physical and chemical properties are similar,sodium ion batteries have similar working principles as lithium ion batteries,and can be a good alternative to lithium ion batteries;on the other hand,sodium ion batteries are abundant in the earth’s crust,evenly distributed,low cost and low mining difficulty,which is sufficient to support the huge demand for continued growth of electrochemical energy storage.Therefore,sodium-ion batteries have become one of the important new energy storage system technology routes.In order to further improve the performance of sodium ion energy storage batteries,the development of sodium ion battery cathode materials with high specific capacity,high energy density and long life becomes an inevitable choice.Prussian blue compounds have the advantages of low price,good stability,high theoretical specific capacity,high reversibility and good tunability,and are a very promising cathode material for sodium ion batteries.Therefore,the modification of Prussian blue cathode material can be studied to further improve its electrochemical performance,extend its cycle life and increase its energy density and power density,which is of great significance for realizing the commercial application of sodium ion batteries.This paper addresses the problems of poor electrical conductivity,high crystalline water and poor cycling stability of conventional sodium ion battery Prussian blue cathode materials by modifying:(1)The iron-based Prussian blue exhibits poor electronic conductivity,susceptibility to side reactions with the electrolyte,and severe polarization during long cycling.In this study,high-crystallinity and well-shaped Prussian blue nanoparticles were synthesized using a single iron source crack method,and further enhancing the conductivity of the composite material by tightly coating it with PEDOT.This reduced the electrochemical impedance,improved the diffusion performance of sodium ions within the material,avoided side reactions caused by direct contact between the active material and the electrolyte,and enhanced the reversibility of the material during the cycling process.After the coating treatment,the material exhibits a high specific capacity of 101.14 mA h/g at a current density of 0.25C(1C=100 mA h/g)and maintains a specific capacity of 66.42 mA h/g after 1000 cycles at 1C(68.34%capacity retention),which greatly improves its cycling performance.The material exhibits a specific capacity of 81.68 mA h/g at a rate of 20C,with an improved sodium ion diffusion coefficient of 9.49 ×10-14 cm2/s and improved rate capability.Furthermore,even at a low temperature of10℃,the material maintains discharge specific capacity of 80.2 mA h/g after 200 cycles at a current density of 2C,with a capacity retention rate of 98.16%,demonstrates good low temperature performance.(2)The synthesis of Prussian blue is prone to crystalline water and Fe(CN)6 defects,which can seriously hinder the diffusion of sodium ions and the conduction of electrons,thus leading to its poor rate performance.In this paper,graphene oxide(GO)was used as a chelating agent to control the release of Fe3+ and retard the nucleation rate of Prussian blue during the crystallisation process,which not only effectively reduced the crystalline water and Fe(CN)6 defects of Prussian blue,but also enhanced the electrical conductivity of the composite material after the poorly conductive Prussian blue was compounded with the conductive carbon material graphene oxide.In addition,the composite material exhibits a high discharge rate capacity of 111.18 mA h/g at a current density of 0.25C and maintains a discharge rate capacity of 86.66 mA h/g even at high current densities of 20C.The sodium ion diffusion coefficient is increased to 4.80×10-14 cm2/s and the rate capability is greatly improved.