Research On Modified Prussian Blue Materials As Cathode Materials For Sodium Ion Batteries

Lithium ion batteries have appeared in every area of human society,but because of the shortage of lithium,their use in large energy storage systems（EESs）is limited.Sodium ion batteries（SIBs）as sodium is the same host of lithium,are applied to（ESSs）due to abundant resources and low cost.However,the larger volume of Na⁺makes the choices of electrode materials much more difficult.Prussian blue and its analogues（PBAs）are ideal cathode materials for sodium ion batteries.The three-dimensional framework structure brought broad channels for migration of Na⁺.The Prussian blue（PB）materials exhibit high theoretical discharge capacity of 170mAh g^-1 and good electrochemical stability.Although PB has many advantages,the long cycle life and high rate performance are not enough for practical application.These defects occurred because of the existence of vacancies and coordination water.These can lead to the collapse of crystal structure and low electron conductivity of PB materials.Combining with the current research of the Prussian blue material as the cathode material of sodium ion batteries,a plan was made of using three kind of methods of carbon coating,ion doping and morphology modification to improve the electrochemical performance of Prussian blue material.Firstly,in this work,we describe the hydrothermal synthesis PB@rGO compounds which the PB particles were in situ growing on the graphene and used hydrazine to reduce the oxide graphene oxide.The coated graphene can optimize the crystallinity of the material and reduce the water content in the material.The initial discharge capacity of PB@rGO is 120mAh g^-1 at current density of 50mA g^-1,and maintained nearly 85.8%after 200 cycles.Then we also choose Cu²⁺to ion exchange of Fe²⁺by a facile hydrothermal process at the surface of PB materials and get the binary PBAs materials ex-PBHCF.Ion exchange reaction is verified by the EDS mapping.The product ex-PBHCF delivered an initial discharge capacity of 89mAh g^-1 and the capacity retention was among 90%after 1000 cycles.Ex-PBHCF showed a good rate performance as well.Finally,the BR-FeHCF sample was synthesized by a simple aqueous precipitation method and exhibited rich borders.The BR-FeHCF electrode delivered a high initial capacity of 120mAh g^-1 and the capacity retention was over 80%after 280 cycles.BR-FeHCF also exhibited high rate performance,which can delivered a capacity of 60mAh g^-1 at the rate of 10C.