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 similar to 30 nm thicked porous carbon walls inlaid homogenously with similar to 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-CoO/C hollow microspheres with complex microstructures after annealing at 450 degrees 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. (C) 2017 Elsevier B.V. All rights reserved.