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

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.