Engineering the interplanar spacing of K-birnessite for ultra-long cycle Zn-ion battery through “hydrothermal potassium insertion” strategy

To satisfy the growing need for safe and sustainable energy storage technologies, rechargeable aqueous zinc-ion batteries (ZIBs) are highly attractive for large-scale energy storage. Birnessite-MnO2 is more suitable as cathode for ion storage than other manganese-based materials due to its layered structure. However, electrochemical performance of birnessite-MnO2 is greatly undermined by the frustrating structural degradation during charge − discharge process. Here, K-birnessite (K0.29MnO2·0.67H2O) was prepared through a “hydrothermal potassium insertion” strategy, with ultra-large interplanar spacing (7.4 Å) and fast ion diffusion kinetics, ascribed to the introduction of adequate K+ and crystal water to expand the interlayer distance. Furthermore, the K/O electrostatic interaction between the introduced K+ and MnO6 octahedra increases the structural stability. As cathode, it exhibited a excellent reversible capacity of 300 mAh g−1 at 200 mA g−1 and the capacity remains at 158 mAh g−1 after 12,000 times ultra-long cycles at a high current density of 2000 mA g−1. More importantly, the pouch battery with K-birnessite as cathode also exhibited superior electrochemical performance in terms of reversible capacity and cycle life. The “hydrothermal potassium insertion” strategy is expected to provide new insights for development of advanced cathode materials for high-performance aqueous ZIBs.