P2‐K<sub>0.75</sub>[Ni<sub>1/3</sub>Mn<sub>2/3</sub>]O<sub>2</sub> Cathode Material for High Power and Long Life Potassium‐Ion Batteries
Jae Hyeon Jo, Ji Ung Choi, Yun Ji Park, Young Hwa Jung, Docheon Ahn, Tae‐Yeol Jeon, Hyungsub Kim, Jongsoon Kim, Seung‐Taek Myung
Abstract
Abstract Rationally designed P2‐K 0.75 [Ni 1/3 Mn 2/3 ]O 2 is introduced as a novel cathode material for potassium‐ion batteries (KIBs). P2‐K 0.75 [Ni 1/3 Mn 2/3 ]O 2 cathode material designed through electrochemical ion‐exchange from P2‐Na 2/3 [Ni 1/3 Mn 2/3 ]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 [Ni 1/3 Mn 2/3 ]O 2 is revealed to be a single‐phase reaction with small lattice change upon charge and discharge, presenting the Ni 4+/2+ redox couple reaction. Such high power capability is possible through the facile K + migration in the K 0.75 [Ni 1/3 Mn 2/3 ]O 2 structure with a low activation barrier energy of ≈210 meV. These findings indicate that P2‐K 0.75 [Ni 1/3 Mn 2/3 ]O 2 is a promising candidate cathode material for high‐rate and long‐life KIBs.