Hierarchical hollow porous structures of nickel-doped λ-MnO₂ anodes for Li-ion energy storage systems

Metal oxides with hollow porous structures are attractive and promising anode candidates for Li-ion batteries due to their high surface area, high loading capacity, and low density. In this work, hierarchical hollow porous structures of nickel (Ni)-doped λ-MnO₂ were prepared via a facile, and cost-effective approach, where different amounts of Ni were introduced into MnO₂ structures to tailor their physical and chemical properties. When the prepared Ni-doped MnO₂ hollow structures were studied as anode materials for Li-ion batteries, the electrode showed excellent electrochemical properties, such as stable cyclability and admirable rate capability. Moreover, Ni doping significantly enhances the diffusion properties of the active materials. The material was also investigated as an anode in another high power and energy Li-ion storage device, namely, a Li-ion hybrid capacitor, which exhibited excellent comprehensive electrochemical performance in terms of good specific cell capacity of 25 mA h g^-1 at a high current density of 5 A g^-1 and achieved a maximum power density of 29 W kg^-1 (with energy density of 30 W h kg^-1) with a long cycle life. These results indicate that the Ni-doped MnO₂ is suitable for application as an anode material and give considerable insight into future Li-energy storage applications.