Preparation And Electrochemical Performance Of Prussian Blue Analogue/Carbon As Cathode Material For Sodium Ion Batteries

As one of the most promising energy storage systems,sodium-ion battery(SIB)has been widely concerned and studied by researchers.Nowadays,prussian blue analogue(PBA)is regarded as an ideal cathode for SIB due to its open frame structure,which enables the rapid migration of alkali metal ions.However,the poor conductivity and agglomeration of PBA restrict its cycle stability and rate performance.In this work,Na/ K alkali metal-manganese hexacyanoferrate(NaK-MnHCF)was prepared by chemical co-precipitation.Two kinds of composites were prepared by growing NaK-MnHCF on carbon nanotubes(CNTs)and three-dimensional ultra-thin carbon networks(3DNC),indicated as NaK-MnHCF@CNTs and NaK-MnHCF@3DNC respectively.The electrochemical properties of the two composites as cathode for SIB were studied.The mechanism of sodium storage and the characteristics of reaction kinetics were investigated.The results show that replacing part of sodium with potassium can facilitate the reversible extracton/ insertion of sodium ions into/ from PBA,avoid the phase transformation,and improve the structural stability of the materials.When the PBA is compounded with carbon nanotubes,the large number active sites of carbon materials can effectively avoid the aggregation of PBA,and the constructed conductive network can improve the rate performance of the materials.Through experimental analysis and first principle calculation,it is verified that the combination of NaK-MnHCF and 3DNC changes the reaction mechanism of PBA,and the sodium storage mechanism is transfered from the diffusion-controlled to the capacitive process,which leads to faster ions transfer and better reaction kinetics in NaK-MnHCF@3DNC electrode.In addition,there is a synergistic effect at the interface between NaK-MnHCF and 3DNC which can provide extra sodium storage in the composite through adsorption/desorption.Therefore,NaK-MnHCF@3DNC composite has high reversible specific capacity,good rate performance and long cycle life,delivering a reversible capacity of 220 mAh/g at 20 mA/g,and when the current density increased to 500 mA/g,the specific capacity after 1000 cycles is 99 mAh/g.This research provides a new idea for the preparation of high-performance cathode materials for SIB.