Fabrication of a Cyanide-Bridged Coordination Polymer Electrode for Enhanced Electrochemical Ion Storage Ability

Abstract

Host frameworks with the ability to store guest ions are very important in a wide range of applications including electrode materials for Li-ion batteries. In this report, we demonstrate that the ion storage ability of the cyanide-bridged coordination polymer (Prussian blue analogue, PBA) can be enhanced by suppressing vacancy formation. K-ions in the vacancy-suppressed PBA framework K1.72Mn[Mn(CN)6]0.93·□0.07·0.65H2O (□: a [Mn(CN)6]4– defect) were electrochemically extracted. The open circuit voltages (OCVs) during K-ion extraction exhibited two specific plateaus at 3.0 and 3.7 V vs Li/Li+. Ex situ X-ray diffraction and IR spectroscopy revealed drastic structural and electronic changes during K-ion extraction. Furthermore, after K-ion extraction, the vacancy-suppressed PBA framework was applied to the cathode material for a Li-ion battery. The charge/discharge experiments revealed that the framework can accommodate a large amount of Li-ions.