Conversion and displacement reaction types of transition metal compounds for sodium ion battery

Abstract Transition metal compounds of FeSe and CuWO 4 thin films have been successfully fabricated by using R.F. sputtering method. Although two kinds of transition metal compounds of FeSe and CuWO 4 thin films can react with sodium electrochemically, they exhibit different electrochemical features. The nanosized metal Fe is highly dispersed into Na 2 Se matrix and metal Cu is extruded from Na 2 WO 4 mixture after the FeSe/Na and CuWO 4 /Na cells are discharged, respectively. The conversion reaction mechanism between FeSe and Na 2 Se is proposed for the FeSe/Na cell. While the displacement reaction mechanism for CuWO 4 /Na cell is proposed for the first time based on the transmission electron microscopy (TEM) and selected area electron diffraction (SAED) data. These various mechanisms make transition metal compounds interesting materials for rechargeable sodium ion batteries.