Structural and electrochemical properties of a K2FeO4 cathode for rechargeable Li ion batteries

Ferrate is considered to be a potential cathode material for high-energy batteries, due to its high capacity based on three-electron transfer in electrochemical reactions. In this work, high-purity potassium ferrate (K2FeO4) was synthesized by a direct hypochlorite oxidation method. X-ray diffraction (XRD) and a charge-coupled device (CCD) were used to characterize the structure of the K2FeO4 as well as the channels for intercalation–deintercalation of Li ions. The one-dimension channel was observed in the direction of the a and b axes in the unit cell, with a radius 0.93 Å, which is beneficial for Li ion (radius = 0.76 Å) intercalation and deintercalation in K2FeO4. The experimental super-iron Li ion battery was assembled with 1 M LiPF6 organic electrolyte (PC:EC:DMC = 1:3:6, v/v), a K2FeO4 cathode, and a metal lithium anode. The electrochemical performance of the K2FeO4 cathode was evaluated by a galvanostatic method and cyclic voltammetry (CV) in the potential range of 4.3–0.5 V at room temperature. It was demonstrated that one Li ion intercalates into the lattice of the K2FeO4 cathode along the channels of the a and b axes of the K2FeO4 unit cell, followed by a two-Li ion intercalation of isotropy in the initial discharge process. Amorphization of the K2FeO4 cathode is the main cause of its electrochemical performance decay.