Electrochemical studies on Li+/K+ ion exchange behaviour in K4Fe(CN)6 cathode material for Li, K-ion battery

Abstract

The electrochemical studies of anhydrous K4Fe(CN)6 is reported. Anhydrous material was produced after dehydrating K4Fe(CN)6.3H2O crystal at 200°C in an open atmosphere. The material, as obtained, was characterized by various spectroscopic techniques, such as UV-Visible, FTIR, powder X-ray diffraction and FESEM-EDX. Electrochemical and Li+/K+ ion exchange behaviour of the synthesized material were studied by cyclic voltametry (CV), chronoamperometry (CA) and galvanostatic charge-discharge method after preparing a laboratory model cell against lithium anode instead of potassium. During anodic scan in the 1st cycle, peak maximum was observed at 3.93 V vs. Li+/Li due to removal of K+ ions from the ferrocyanide matrix, whereas, in the reverse scan (cathodic sweep) as well as in consequent cycles, peak maxima due to Li+ ion insertion and extraction were observed at 2.46 V and 3.23 V vs. Li+/Li, respectively. Cell, assembled using ferrocyanide cathode and lithium anode, shows an open circuit potential of 3.08 V and delivers a maximum capacity of 61 mAh g−1 (theoretical capacity 72 mAh g−1) at a rate of 0.2 C at room temperature. Highly dispersed crystalline K4Fe(CN)6 has been synthesized by simple cost effective route. The material was charge-discharged using lithium-salt electrolyte against Li metal. The redox peak current increment, shift of peak position in CV and capacity enhancement during charge-discharge cycles were explained in terms of faster exchange rate of K+ by Li+ ion.