Low‐Cost Layered K0.45Mn0.9Mg0.1O2 as a High‐Performance Cathode Material for K‐Ion Batteries

Abstract Novel, potassium‐deficient, layered P3‐K 0.45 Mn 0.9 Mg 0.1 O 2 is successfully prepared through a simple solid‐state reaction method; its electrochemical performance as a cathode material for K‐ion batteries is explored for the first time. The as‐prepared K 0.45 Mn 0.9 Mg 0.1 O 2 delivers a high reversible capacity of 108 mAh g −1 at a current density of 20 mA g −1 in the potential region from 1.5 to 4.0 V. Moreover, the cyclability is enhanced by Mg substitution. After 100 cycles, the capacity of K 0.45 Mn 0.9 Mg 0.1 O 2 can remain at about 80.8 mAh g −1 at 20 mA g −1 . It also presents an excellent rate performance of 69.8 mAh g −1 even at a high current density of 200 mA g −1 . Furthermore, the potassium storage mechanism is studied by using the ex situ XRD technique. These results contribute to the development of rechargeable K‐ion batteries based on earth‐abundant elements.