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

Rationally designed P2-K-0.75[Ni1/3Mn2/3]O-2 is introduced as a novel cathode material for potassium-ion batteries (KIBs). P2-K-0.75[Ni1/3Mn2/3]O-2 cathode material designed through electrochemical ion-exchange from P2-Na-2/3[Ni1/3Mn2/3]O-2 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-K-0.75[Ni1/3Mn2/3]O-2 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 K-0.75[Ni1/3Mn2/3]O-2 structure with a low activation barrier energy of approximate to 210 meV. These findings indicate that P2-K-0.75[Ni1/3Mn2/3]O-2 is a promising candidate cathode material for high-rate and long-life KIBs.