Hierarchically designed ZIF-8-derived Ni@ZnO/carbon nanofiber freestanding composite for stable Li storage

We present a uniform rhombohedral Ni@ZnO bimetallic oxide host over carbon nanofibers (CNF) as an anode material for Li-ion batteries. Ni@ZnO was produced by annealing a Ni@zeolitic imidazolate framework (ZIF-8) hierarchically decorated over CNFs. The rationally-designed freestanding composite exhibited promising stability in electrochemical performance. A first reversible capacity of 1051 mA·h·g⁻¹ was measured at a current density of 100 mA·g⁻¹, and 88% of this capacity was retained after 100 cycles. We attribute this high capacity retention to the hierarchical structure of the Ni@ZnO-enwrapped carbon framework encapsulating the conductive CNFs, as demonstrated by scanning and transmission electron microscopy. The composite electrode also showed a high specific capacity of ∼497 mA·h·g⁻¹ in high-rate testing at 1000 mA·g⁻¹, because the cage-like framework of the material allowed rapid charge transfer and Li-ion diffusion in the anode.