All-surface-state potassium storage enabled ultra-stable potassium cathode

Potassium-ion batteries are gaining interest as grid-scale energy storage devices due to their abundant potassium sources and low cost. However, the large size K + ions (1.3 Å) cause severe structural damage to the host materials, leading to limited lifespan. Here, an ultra-stable potassium cathode composed of single-bilayer V 2 O 5 is prepared, exhibiting high capacity (132 mAh g −1 ), excellent rate capability (8 A g −1 ) and durable lifetime of over 9000 cycles. Our kinetics and theoretical analyses revealed that the all-surface-state K storage capability of single-bilayer V 2 O 5 is responsible for such exceptional cathode performance. It enables easy access for K + ions to redox sites and permits rapid redox kinetics with negligible effect on the crystal structure. By pairing the cathode with pre-potassiated graphite, the full cell achieved a capacity retention of up to 83% after 400 cycles. The study establishes a new insight into host design for durable potassium cathode.