A Potential Cathode Material for Rechargeable Potassium-Ion Batteries Inducing Manganese Cation and Oxygen Anion Redox Chemistry: Potassium-Deficient ${\mathrm{K}}_{0.4}\mathrm{F}{\mathrm{e}}_{0.5}\mathrm{M}{\mathrm{n}}_{0.5}{\mathrm{O}}_2$

Abstract

Potassium-ion ($\mathrm{K}$-ion) rechargeable batteries; considered to be lucrative low-cost battery options for large-scale and capacious energy storage systems, have been garnering tremendous attention in recent years. However, due to the scarcity of cathode materials that can condone the reversible re-insertion of the large $\mathrm{K}$-ions at feasible capacities, the viability of $\mathrm{K}$-ion batteries has been greatly undercut. In this paper, we explore a potential cathode material in the ${\mathrm{K}}_2\mathrm{O}$-$\mathrm{F}{\mathrm{e}}_2{\mathrm{O}}_3$-$\mathrm{Mn}{\mathrm{O}}_2$ ternary phase system, that not only demonstrates reversible $\mathrm{K}$-ion reinsertion but also manifests relatively fast rate capabilities. The titled cathode compound, ${\mathrm{K}}_{0.4}\mathrm{F}{\mathrm{e}}_{0.5}\mathrm{M}{\mathrm{n}}_{0.5}{\mathrm{O}}_2$, demonstrates a reversible capacity of approximately $120$ mAh g${}^{-1}$ at $10$ hours of (dis)charge ($viz.$, $C/10$ rate) with $ca.$ $85$% of the capacity being retained at a $1$ hour of (dis)charge ($1C$ rate) which is considered to be good capacity retention. Additionally, both hard and soft X-rays have been employed to unravel the mechanism by which $\mathrm{K}$-ion is reversibly inserted into ${\mathrm{K}}_{0.4}\mathrm{F}{\mathrm{e}}_{0.5}\mathrm{M}{\mathrm{n}}_{0.5}{\mathrm{O}}_2$. The results revealed a cumulative participation of both manganese cations and oxygen anions in ${\mathrm{K}}_{0.4}\mathrm{F}{\mathrm{e}}_{0.5}\mathrm{M}{\mathrm{n}}_{0.5}{\mathrm{O}}_2$ illustrating its potential as a high-capacity $\mathrm{K}$-ion battery cathode material that relies on both anion and cation redox. Further development of related high-capacity cathode compositions can be anticipated.

17 pages, 4 figures, 1 cover art