Regulated electrochemical performance of manganese oxide cathode for potassium-ion batteries: A combined experimental and first-principles density functional theory (DFT) investigation

Potassium-ion batteries (KIBs) are promising energy storage devices owing to their low cost, environmental-friendly, and excellent K⁺ diffusion properties as a consequence of the small Stoke's radius. The evaluation of cathode materials for KIBs, which are perhaps the most favorable substitutes to lithium-ion batteries, is of exceptional importance. Manganese dioxide (α-MnO₂) is distinguished by its tunnel structures and plenty of electroactive sites, which can host cations without causing fundamental structural breakdown. As a result of the satisfactory redox kinetics and diffusion pathways of K⁺ in the structure, α-MnO₂ nanorods cathode prepared through hydrothermal method, reversibly stores K⁺ at a fast rate with a high capacity and stability. It has a first discharge capacity of 142 mAh/g at C/20, excellent rate execution up to 5C, and a long cycling performance with a demonstration of moderate capacity retention up to 100 cycles. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) simulations confirm that the K⁺ intercalation/deintercalation occurs through 0.46 K movement between Mn^IV/Mn^III redox pairs. First-principles density functional theory (DFT) calculations predict a diffusion barrier of 0.31 eV for K⁺ through the 1D tunnel of α-MnO₂ electrode, which is low enough to promote faster electrochemical kinetics. The nanorod structure of α-MnO₂ facilitates electron conductive connection and provides a strong electrode–electrolyte interface for the cathode, resulting in a very consistent and prevalent execution cathode material for KIBs.