Three-dimensional macroporous CNTs microspheres highly loaded with NiCo2O4 hollow nanospheres showing excellent lithium-ion storage performances

Abstract

Three-dimensional macroporous carbon nanotubes microspheres highly loaded with phase-pure NiCo2O4 hollow nanospheres are synthesized by the spray pyrolysis process and are characterized for potential use in lithium-ion batteries. Polystyrene nanobead template and the nanoscale Kirkendall diffusion process are first combined and are applied to the spray pyrolysis process to form macroporous NiCo2O4/carbon nanotubes composite microspheres with extremely high rate performance as anode materials for lithium-ion batteries. Metallic NiCo2/carbon nanotubes composite microspheres—formed as intermediate products—are transformed into composite microspheres of phase-pure NiCo2O4 hollow nanospheres and carbon nanotubes by the nanoscale Kirkendall diffusion process. The mean size of the hollow NiCo2O4 nanospheres decorated on the carbon nanotubes backbone is 28 nm. The macroporous NiCo2O4/carbon nanotubes composite microspheres have discharge capacities of 840, 748, 677, 591, 514, 451, 391, 337, and 289 mA h g−1 at current densities of 0.5, 1, 2, 5, 10, 15, 20, 25, and 30 A g−1, respectively. The discharge capacity of the macroporous NiCo2O4/carbon nanotubes microspheres for the 500th cycle at a current density of 3 A g−1 is 572 mA h g−1. The uniquely structured hollow NiCo2O4 nanosphere/carbon nanotubes composite microspheres have superior cycling and rate performances for lithium-ion storage.