Self-Templated Formation of P2-type K_0.6CoO₂ 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 K_0.6CoO₂ microspheres that consist of aggregated primary nanoplates as PIB cathodes. The unique K_0.6CoO₂ microspheres with aggregated structure significantly enhanced the kinetics of the K⁺ intercalation/deintercation and also minimized the parasitic reactions between the electrolyte and K_0.6CoO₂. The P2-K_0.6CoO₂ microspheres demonstrated a high reversible capacity of 82 mAh g^-1 at 10 mA g^-1, high rate capability of 65 mAh g^-1 at 100 mA g^-1, and long cycle life (87% capacity retention over 300 cycles). The high reversibility of the P2-K_0.6CoO₂ 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 K_0.6CoO₂ cathodes and microspheres K_0.6CoO₂∥hard carbon full cells, but also provides new insights into the exploration of other layered metal oxides for PIBs.