Fluorine-doped K0.39Mn0.77Ni0.23O1.9F0.1 microspheres with highly reversible oxygen redox reaction for potassium-ion battery cathode

Mn-rich layered oxides are appealing cathodes for potassium ion batteries (PIBs) in view of their comprehensive virtues such as low cost, high energy density and mature craftsmanship. However, the insufficient covalency between transition metal (TM) and O usually induces irreversible structural evolution and cation migration during repeated insertion and extraction of K+, resulting in capacity loss, voltage fading and sluggish kinetics. Herein, an anion substitution strategy is proposed for a stable operation of layered oxide cathode by adjusting the valence electron layer structure between TM and O. The resultant strong TM−O skeleton can inhibit the occurrence of side effects derive from Ni4+ during the deep potassium process, so as to achieve a gentle structural transition. Consequently, stable cycling performance of K0.39Mn0.77Ni0.23O1.9F0.1 (KMNOF) cathode is achieved with 77% capacity retention over 350 cycles at 100 mA/g, yielding high discharge capacity 93.5 mAh/g at 20 mA/g and significantly improved rate capability of 50.1 mAh/g at 500 mA/g, whereas irreversible structural evolution and rapid capacity fade with KMNO cathode. Finally, in situ/ex situ characterizations and theoretical computations sheds light on the charge transfer and structure evolution mechanisms of KMNOF.