Hierarchically porous Zn-Co-O NCs-in-carbon hollow microspheres with high rate-capacity and cycle stability as anode materials for lithium-ion batteries

Zn-Co-O/C hollow microspheres composed of center hole with an average size of 400 nm and ∼30 nm thicked porous carbon walls inlaid homogenously with ∼5.2 nm Zn-Co-O nanocrystals are successfully prepared for the first time via a Na-citrate mediated solvothermal method and a subsequent annealing process of Zn-Co-ethylene glycolate (Zn-Co-EG) precursor. The obtained powders were systematically characterized by XRD, IR, FESEM, TEM, BET and Raman techniques. The data indicate that the polymerization reaction of Zn-Co-EG crystals confined by Na-citrate should be responsible for the formation of the hollow microspherical precursors, which are then converted into the hierarchically porous Zn-Co-O/C hollow microspheres with complex microstructures after annealing at 450 °C for 3 h. These porous Zn-Co-O/C hollow microspheres used as an anode material for lithium-ion batteries exhibit a high reversible capacity of 991.7 mAh g−1, 81.6% of the second cycle discharge capacity after 200 cycles at 1 A g−1, and a high-rate delivery of 823.4 mAh g−1 after 1000 cycles at 4 A g−1. The superior performance of Zn-Co-O/C hollow microspheres is mainly attributed to the local dynamic confinement of tiny Zn-Co-O nanoparticles in the ultrathin porous carbon matrix. Na-citrate as surfactants is effectively adopted to mediate the growth of Zn-Co-EG into hollow microspheres, which are then transformed by annealing in N2 at 450 °C into porous Zn-Co-O/C hollow microspheres with Zn-Co-O NCs confined-in-carbon microstructures and extremely high rate capacity and cycling stability as anode materials for lithium-ion batteries. [Display omitted] •Na-citrate directed growth of Zn-Co-EG hollow microspheres.•Novel Zn-Co-O/C composites with excellent microstructure.•High-rate anode materials for LIBs.•A distinguished synergistic effect between C and nanosized Zn-Co-O.