Improved electrochemical performances of MOF-derived Ni-Co layered double hydroxide complexes using distinctive hollow-in-hollow structures

Metal-organic framework (MOF)-derived electroactive materials have drawn great attention due to their diverse design and high electrochemical activity. Herein, a unique hybrid structure consisting of Ni-Co layered double hydroxides (LDHs) and hollow carbon spheres (HCSs) is first synthesized using HCS@ZIF-67 as a precursor. Particularly, when the ZIF-67 content in the precursor is optimized, a novel hybrid with a hollow-in-hollow structure can be obtained by distributing ZIF-67-derived hollow Ni-Co LDHs on a HCS shell. Owing to their distinctive structural characteristics, the as-prepared architectures deliver a high specific capacity (156.4 mA h g(-1) at 5 A g(-1)) and excellent cycle stability (73.4% capacity retention after 10 000 cycles). Notably, during the charge storage process, the dual hollow system of the composite effectively decreases the ion diffusion path, resulting in drastically improved rate performance (70% retention of its highest capacity at 80 A g(-1)). Furthermore, an all-solid-state hybrid supercapacitor is assembled using the as-fabricated hybrid as the positive material and mesoporous plasma-reduced graphene oxide as the negative material, and exhibits a maximum energy density of 34.5 W h kg(-1) and a peak power density of 55 kW kg(-1).