In this work, we find that the strong electrostatic repulsion between K ions due to the short K+-K+ distance destabilizes the layered structure in a stoichiometric composition of KTMO2. However, a stoichiometric KCrO2 is thermodynamically stable in the layered structure despite short K+-K+ distance unlike other KTMO2 compounds that form non-layered structures. The unique stability of layered KCrO2 is attributable to the unusual ligand field preference of Cr3+ in octahedral sites that can compensate for the energy penalty from the short K+-K+ distance. Therefore, we develop the stoichiometric layered KCrO2 cathode material for KIBs and investigate its K-storage properties. In K-half cells, the KCrO2 cathode delivers a reversible specific capacity of ~90 mAh/g with an average voltage of ~2.73 V (vs. K/K+). In-situ diffraction and electrochemical characterization further demonstrate multiple phase transitions via reversible topotatic reactions occurring as the K content changes.
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