Layered P2-NaxCoO2 and NaxFeO2 as Cathode Materials for Potassium-Ion Batteries

Abstract

Electrochemical intercalation of sodium and potassium-ion in NaxCoO2 and NaxFeO2 was successfully studied in this work. The Na0.84CoO2 and NaxFeO2 were synthesized by solution combustion synthesis technique using urea as fuel. The as-prepared Na0.84CoO2 assumed a hexagonal structure with P 63/mmc space group built from slabs of edge-sharing CoO6 octahedra accommodating Na in prismatic sites. Hexagonal platelet-like morphology was observed by SEM and TEM micrography. Firstly, the Na-ion intercalation in P2-type Na0.84CoO2 layered material was examined. The P2-type Na0.84CoO2 exhibited a reversible capacity of 148 mA h g-1 in Na-ion cell. Following, the K-ion (de)intercalation behavior of the material was investigated for the first time. The reversible K-ion (de)intercalation was observed with the high capacity of 71 mA h g-1 at C/10 current rate. Na0.84CoO2 cathode act as a suitable host for K+ intercalation delivering robust cycling, rate capability and Coulombic efficiency. In contrast, NaxFeO2 was found to be electrochemically inactive for K-ion insertion.