P2‐K0.75[Ni1/3Mn2/3]O2 Cathode Material for High Power and Long Life Potassium‐Ion Batteries

Abstract

AbstractRationally designed P2‐K0.75[Ni1/3Mn2/3]O2 is introduced as a novel cathode material for potassium‐ion batteries (KIBs). P2‐K0.75[Ni1/3Mn2/3]O2 cathode material designed through electrochemical ion‐exchange from P2‐Na2/3[Ni1/3Mn2/3]O2 exhibits satisfactory electrode performances; 110 mAh g−1 (20 mA g−1) retaining 86% of capacity for 300 cycles and unexpectedly high reversible capacity of about 91 mAh g−1 (1400 mA g−1) with excellent capacity retention of 83% over 500 cycles. According to theoretical and experimental investigations, the overall potassium storage mechanism of P2‐K0.75[Ni1/3Mn2/3]O2 is revealed to be a single‐phase reaction with small lattice change upon charge and discharge, presenting the Ni4+/2+ redox couple reaction. Such high power capability is possible through the facile K+ migration in the K0.75[Ni1/3Mn2/3]O2 structure with a low activation barrier energy of ≈210 meV. These findings indicate that P2‐K0.75[Ni1/3Mn2/3]O2 is a promising candidate cathode material for high‐rate and long‐life KIBs.