 A series of potassium transition metal oxide such as K0.3MnO2, K0.55CoO2 have been demonstrated as cathode material with a layered structure.Polyanionic compounds with inductive defects could provide the highest working voltage among other types of cathode for potassium-ion batteries.During the electrochemical cycling process, its crystal structure will be distorted to created more induced defects upon the insertion of potassium ion .