Expanded K_0.37Fe_0.04Al_0.07Mn_0.89O₂ Layered Material as a High-Performance Cathode in Sodium-Ion Batteries

Due to a high operating voltage and theoretical capacity, P2-type layered Mn-based metal oxides are considered to be promising cathodes in sodium-ion batteries, but their poor structural stability in the process of Na⁺ insertion/deinsertion severely hinders their practical application. Here, an interesting K⁺ pre-intercalation is used to expand the interlayer distance and enhance the electrochemical reversibility of K_sFe_xAl_yMn_zO₂. With a suitable K⁺ content, the optimized electrode shows a high specific capacity of 135 mAh g⁻¹ at 0.1 C, a good rate capability of 80 mAh g⁻¹ at 5 C and an excellent cycling performance of 76.4% capacity retention after 200 cycles at a high rate of 5 C. This work proves the feasibility of a K⁺ pre-intercalation strategy in a P2-type layered cathode.