Layered P2-Type K0.44Ni0.22Mn0.78O2 as a High-Performance Cathode for Potassium-Ion Batteries

Potassium-ion batteries (KIBs) are emerging as one of the most promising candidates for large-scale energy storage owing to the natural abundance of the materials required for their fabrication and the fact that their intercalation mechanism is identical to that of lithium-ion batteries. However, the larger ionic radius of K+ is likely to induce larger volume expansion and sluggish kinetics, resulting in low specific capacity and unsatisfactory cycle stability. A new Ni/Mn-based layered oxide, P2-type K0.44Ni0.22Mn0.78O2, is designed and synthesized. A cathode designed using this material delivers a high specific capacity of 125.5 mAh g(-1) at 10 mA g(-1), good cycle stability with capacity retention of 67% over 500 cycles and fast kinetic properties. In situ X-ray diffraction recorded for the initial two cycles reveals single solid-solution processes under P2-type framework with small volume change of 1.5%. Moreover, a cathode electrolyte interphase layer is observed on the surface of the electrode after cycling with possible components of K2CO3, RCO2K, KOR, KF, etc. A full cell using K0.44Ni0.22Mn0.78O2 as the cathode and soft carbon as the anode also exhibits exceptional performance, with capacity retention of 90% over 500 cycles as well as superior rate performance. These findings suggest P2-K0.44Ni0.22Mn0.78O2 is a promising candidate as a high-performance cathode for KIBs.