Graphite-Like Carbon-Decorated δ -MnO 2 Nanoparticles as a High-Performance Cathode for Rechargeable Zinc-Ion Batteries

For rechargeable aqueous Zn-ion batteries (ZIBs), MnO 2 is a desirable cathode material because of its structural diversity and high theoretical capacity of ~308 mA h g −1 . MnO 2 materials’ poor cycle life and inferior conductivity, however, continue to be key obstacles to their application in ZIBs. These problems are anticipated to be resolved by developing a nanocomposite system consisting of MnO 2 and a carbon-based matrix. Herein, a series of graphite carbon-coated δ -MnO 2 nanoparticles (denoted as GC- δ -MnO 2 -X; X = 1, 2, and 3) for ZIB cathode materials is prepared via a feasible redox route and varying the amount of KMnO 4 (7, 8, and 9 mmol). Benefiting from the abundant active sites and boosted Zn 2+ ion diffusion rate, the GC- δ -MnO 2 -2 nanoparticles (8 mmol KMnO 4 ) display excellent capacity of 299.6 mA h g −1 at 0.3 A g −1 with good cycle stability (62% capacity retention after 1500 cycles at 2 A g −1 ), surpassing that of the GC- δ -MnO 2 -1 (7 mmol KMnO 4 ) and GC- δ -MnO 2 -3 (9 mmol KMnO 4 ) samples. Moreover, the constructed quasi-solid-state ZIBs based on the GC- δ -MnO 2 -2 cathode show respectable capacity of 194.3 mA h g −1 at 0.3 A g −1 , as well as outstanding safe properties.