Self-Templated Formation of P2-type KCoO Microspheres for High Reversible Potassium-Ion Batteries.

Layered metal oxides have been widely used as the best cathode materials for commercial lithium-ion batteries and are being intensively explored for sodium-ion batteries. However, their application to potassium-ion batteries (PIBs) is hampered because of the poor cycling stability and low rate capability due to the larger ionic size of K than of Li or Na. Herein, a facile self-templated strategy was used to synthesize unique P2-type KCoO microspheres that consist of aggregated primary nanoplates as PIB cathodes. The unique KCoO microspheres with aggregated structure significantly enhanced the kinetics of the K intercalation/deintercation and also minimized the parasitic reactions between the electrolyte and KCoO. The P2-KCoO microspheres demonstrated a high reversible capacity of 82 mAh g at 10 mA g, high rate capability of 65 mAh g at 100 mA g, and long cycle life (87% capacity retention over 300 cycles). The high reversibility of the P2-KCoO full cell paired with a hard carbon anode further demonstrated the feasibility of PIBs. This work not only successfully demonstrates exceptional performance of P2-type KCoO cathodes and microspheres KCoO∥hard carbon full cells, but also provides new insights into the exploration of other layered metal oxides for PIBs.