Few-layer δ-MnO2 nanosheets grown on three-dimensional N-doped hierarchically porous carbon networks for long-life aqueous zinc ion batteries

Manganese dioxide (MnO2) is typically used as aqueous zinc-ion batteries (AZIBs) cathode material because of its ideal theoretical capacity, but low rate performance and short cycle life are some challenges for commercial applications. Herein, we report few-layer δ-MnO2 nanosheets anchored in situ on three-dimensional (3D) N-doped hierarchically porous carbon networks (NCM) by using the green template method and simple hydrothermal process. The synthesized NCM possess the characteristics, such as excellent electric conductivity and abundant active sites, which can enhance the electron/ion transfer kinetics and buffer the volume changes of δ-MnO2 nanosheets. Owing to the structural properties, the specific capacity can deliver 335 mAh g−1 at a current density of 0.1 A g−1 and exhibits superior cycle stability (92.5% capacity retention after 1000 cycles at 1 A g−1 and 88% capacity retention after 5000 cycles at 2 A g−1). First-principles calculations also show that the introduction of NC improves the number of electrons near the Fermi level of δ-MnO2 and reduces the diffusion barriers of Zn2+ ions. This work develops a promising strategy for designing high-performance and low-cost AZIBs.