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 (delta-MnO2) with a large interlayer spacing (approximate to 7 angstrom) 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, delta-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 delta-MnO2 and rGO can effectively suppress the layered-to-spinel phase transition in delta-MnO2 during cycling. As a result, the coupled delta-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 delta-MnO2 and rGO results in improved electron transfer and strengthened layered structure for delta-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.

Automated summary

Coupling delta-MnO2 nanosheets with reduced graphene oxide (rGO) through vdW self-assembly can effectively suppress the phase transition issue and achieve excellent cycling performance in the hybrid cathode.