P2-phase impurity effeet to structure stability and performance of solid solution NaFe02-NaCo02

NaFeOrNaCo02 solid solution or NaFeo.5Co0.5O2 hereafter exhibited high capacity and high average voltage over cathode materials for sodium-ion batteries. This work aims at exploring the effect of P2 impurity to the structure stability and cycling performance of solid solution NaFe0.5C0.5O2 (NFC). The crystalline structure and surface morphology of the synthesized material was studied by X-ray diffraction and Scanning Electron Microscopy (SEM). Cyclic voltammogram of the as-prepared sample exhibits peaks belonged to O3 solid solutions as well as the P2 phase impurity. In sodium half-cell, the sample showed the well-defined charge-discharge profile of NFC but less pronounced. The structure disruption could be the reason for capacity fading. XRD ex-situ results revealed that P2 impurity disappeared after the material was charged to 3.1 V and the presence of P2 phase seem to have no effect on the evolution of structure during first charging.