First-principles investigation of transition metal-substituted layered oxides KMn2/3TM1/3O2 (TM = Cr, Nb, Ag) as promising cathode materials for potassium-ion batteries

Extensive research is currently in progress on Potassium-ion batteries (PIBs) as a viable substitute for lithium-ion batteries (LIBs) due to the necessity of high-performance and reasonably priced energy storage devices. Manganese-based layered oxides have gained attention as possible cathodes due to their low cost, high theoretical capacity, and natural availability. In this work, to minimize the distortion that compromises structural performance and stability, a series of transition metal-substituted Manganese-based layered oxides KMn_2/3TM_1/3O₂ (where TM = Cr, Nb, Ag),are explored for their structural, electronic, magnetic, thermoelectric, and electrochemical, properties as potential cathodes for PIBs using first-principles calculations. Our DFT analysis shows that Mn-3d orbitals are the primary cause of states close to the Fermi level, with O-2p orbitals playing a significant role. KMn_2/3Ag_1/3O₂ has the highest theoretical voltage of 3.96 V among the studied compounds but lacks structural stability. With a theoretical voltage of 3.0 V and a reversible 214 mAh g⁻¹ capacity, KMn_2/3Cr_1/3O₂ exhibits the most stable and excellent electrochemical performance among the studied compositions. The results have suggested that KMn_2/3TM_1/3O₂ (where TM = Cr, Nb, Ag) are promising cathode materials for high-rate PIBs applications by combining theoretical capacity, voltage, and stability evaluations.