Suppressed Layered‐to‐Spinel Phase Transition in δ‐MnO2 via van der Waals Interaction for Highly Stable Zn/MnO2 Batteries.

Although birnessite‐type manganese dioxide (δ‐MnO2) with a large interlayer spacing (≈7 Å) is a promising cathode candidate for aqueous Zn/MnO2 batteries, the poor structural stability associated with Zn2+ intercalation/deintercalation limits its further practical application. Herein, δ‐MnO2 ultrathin nanosheets are coupled with reduced graphene oxide (rGO) via van der Waals (vdW) self‐assembly in a vacuum freeze‐drying process. It is interesting to find that the presence of vdW interaction between δ‐MnO2 and rGO can effectively suppress the layered‐to‐spinel phase transition in δ‐MnO2 during cycling. As a result, the coupled δ‐MnO2/rGO hybrid cathode with a sandwich‐like heterostructure exhibits remarkable cycle performance with 80.1% capacity retained after 3000 cycles at 2.0 A g−1. The first principle calculations demonstrate that the strong interfacial interaction between δ‐MnO2 and rGO results in improved electron transfer and strengthened layered structure for δ‐MnO2. This work establishes a viable strategy to mitigate the adverse layered‐to‐spinel phase transition in layered manganese oxide in aqueous energy storage systems. [ABSTRACT FROM AUTHOR]