Graphite-Like Carbon-Decorated δ-MnO₂ Nanoparticles as a High-Performance Cathode for Rechargeable Zinc-Ion Batteries

For rechargeable aqueous Zn-ion batteries (ZIBs), MnO₂ is a desirable cathode material because of its structural diversity and high theoretical capacity of ~308 mA h g⁻¹. MnO₂ 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 MnO₂ and a carbon-based matrix. Herein, a series of graphite carbon-coated δ-MnO₂ nanoparticles (denoted as GC-δ-MnO₂-X; X = 1, 2, and 3) for ZIB cathode materials is prepared via a feasible redox route and varying the amount of KMnO₄ (7, 8, and 9 mmol). Benefiting from the abundant active sites and boosted Zn²⁺ ion diffusion rate, the GC-δ-MnO₂-2 nanoparticles (8 mmol KMnO₄) 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-MnO₂-1 (7 mmol KMnO₄) and GC-δ-MnO₂-3 (9 mmol KMnO₄) samples. Moreover, the constructed quasi-solid-state ZIBs based on the GC-δ-MnO₂-2 cathode show respectable capacity of 194.3 mA h g⁻¹ at 0.3 A g⁻¹, as well as outstanding safe properties.