A novel low-cost and environment-friendly cathode with large channels and high structure stability for potassium-ion storage

Abstract

Potassium-ion batteries (KIBs) are promising candidates for large-scale energy storage due to the abundance of potassium and its chemical similarity to lithium. Nevertheless, the performances of KIBs are still unsatisfactory for practical applications, mainly hindered by the lack of suitable cathode materials. Herein, combining the strong inductive effect of sulphate and the feasible preparation of Fe2+-containing compounds in oxalate system, a compound with novel architecture, K4Fe3(C2O4)3(SO4)2, has been identified as a low-cost and environmentally friendly cathode for stable potassium-ion storage. Its unique crystal structure possesses an unprecedented two-dimensional framework of triple layers, with 3.379 A interlayer distance and large intralayer rings in the size of 4.576×6.846 A. According to first-principles simulations, such a configuration is favorable for reversible K-ion migration with a very low volume change of 6.4%. Synchrotron X-ray absorption spectra and X-ray diffraction characterizations at different charging/discharging states and electrochemical performances based on its half and full cells further verify its excellent reversibility and structural stability. Although its performance needs to be improved via further composition tuning with multi-valent transition metals, doping, structural optimization, etc., this study clearly presents a stable structural model for K-ion cathodes with merits of low cost and environmental friendliness.