Suppressed Layered-to-Spinel Phase Transition in δ-MnO 2 via van der Waals Interaction for Highly Stable Zn/MnO 2 Batteries.

Although birnessite-type manganese dioxide (δ-MnO ₂ ) with a large interlayer spacing (≈7 Å) is a promising cathode candidate for aqueous Zn/MnO ₂ batteries, the poor structural stability associated with Zn ²⁺ intercalation/deintercalation limits its further practical application. Herein, δ-MnO ₂ 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-MnO ₂ and rGO can effectively suppress the layered-to-spinel phase transition in δ-MnO ₂ during cycling. As a result, the coupled δ-MnO ₂ /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-MnO ₂ and rGO results in improved electron transfer and strengthened layered structure for δ-MnO ₂ . This work establishes a viable strategy to mitigate the adverse layered-to-spinel phase transition in layered manganese oxide in aqueous energy storage systems.
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