Layered K0.54Mn0.78Mg0.22O2 as a high-performance cathode material for potassium-ion batteries

Layered Mn-based oxides are one of the promising cathode materials for potassium-ion batteries (KIBs) owing to their high theoretical capacities, abundant material supply, and simple synthesis method. However, the structural deterioration resulting from the Jahn-Teller effect of Mn ions hinders their further development in KIBs. Herein, a novel Mn-based layered oxide, K0.54Mn0.78Mg0.22O2, is successfully designed and fabricated as KIBs cathode for the first time. It delivers smooth charging/discharging curves with high specific capacity of 132.4 mA·g−1 at 20 mA·g−1 and good high-rate cycling stability with a capacity retention of 84% over 100 cycles at 200 mA·g−1. Combining in-situ X-ray diffraction (XRD) and ex-situ X-ray photoelectron spectroscopy (XPS) analysis, the storage of K-ions by K0.54Mn0.78Mg0.22O2 is revealed to be a solid-solution processes with reversible slip of the crystal lattice. The studies suggest that the rational doping of inactive Mg2+ can effectively suppress the Jahn-Teller effect and provide outstanding structure stability. This work deepens the understanding of the structural evolution of Mn-based layered materials doped with inactive materials during de/potassiation processes.