Synergistic effect of small-size MnO2 nanodots and conductive reduced graphene oxide boosting cathode materials for high-performance aqueous zinc-based energy storage

Manganese dioxides (MnO2), featuring significant theoretical capacity and low cost, are widely used as superior cathode materials for aqueous Zn-ion batteries/capacitors (ZIBs/ZICs). However, the MnO2 cathode still suffers from sluggish electrochemical kinetics and poor cycle life, impeding the further application of aqueous ZIBs/ZICs. Herein, the novel MnO2 nanodots/reduced graphene oxide (MnO2 NDs/rGO) composite is prepared via hydrothermal approach followed by ultrasonic treatment, and applied to aqueous ZIBs/ZICs cathode materials for the first time. Benefiting from the synergistic effect of small-size MnO2 nanodots and conductive rGO, the MnO2 NDs/rGO composite as a cathode for ZIBs exhibits enhanced specific capacity (294 mAh g−1 at 0.1 A g−1), rate performance (124 mAh g−1 at 2.0 A g−1) and cycling stability (90.1% capacity retention after 1000 cycles at 1.0 A g−1) compared with pure MnO2. Electrochemical kinetics analyses and density functional theory (DFT) calculations elucidate the improved diffusion kinetics and charge transfer ability, and ex-situ tests verify the reversible H+/Zn2+ co-insertion mechanism of MnO2 NDs/rGO cathode. Additionally, the new ZICs with MnO2 NDs/rGO cathode deliver a large energy density and an excellent cycling stability. This impressive work can offer a good strategy for boosting cathode materials for high-performance aqueous ZIBs/ZICs.