Layered P2-Type K0.65Fe0.5Mn0.5O2 Microspheres as Superior Cathode for High-Energy Potassium-Ion Batteries

Potassium-ion batteries have been regarded as the potential alternatives to lithium-ion batteries (LIBs) due to the low cost, earth abundance, and low potential of K (-2.936 vs standard hydrogen electrode (SHE)). However, the lack of low-cost cathodes with high energy density and long cycle life always limits its application. In this work, high-energy layered P2-type hierarchical K0.65Fe0.5Mn0.5O2 (P2-KFMO) microspheres, assembled by the primary nanoparticles, are fabricated via a modified solvent-thermal method. Benefiting from the unique microspheres with primary nanoparticles, the K+ intercalation/deintercalation kinetics of P2-KFMO is greatly enhanced with a stabilized cathodic electrolyte interphase on the cathode. The P2-KFMO microsphere presents a highly reversible potassium storage capacity of 151 mAh g(-1) at 20 mA g(-1), fast rate capability of 103 mAh g(-1) at 100 mA g(-1), and long cycling stability with 78% capacity retention after 350 cycles. A full cell with P2-KFMO microspheres as cathode and hard carbon as anode is constructed, which exhibits long-term cycling stability (>80% of retention after 100 cycles). The present high-performance P2-KFMO microsphere cathode synthesized using earth-abundant elements provides a new cost-effective alternative to LIBs for large-scale energy storage.