Effect of Temperature on the Morphology and Anode Performance of Binder-Free Carbon Nanofiber/Nickel Cobalt Hydroxide and Carbon Nanofiber/Nickel Cobalt Oxide for Lithium-Ion Batteries

摘要

Hierarchical composite materials composed of electrospun carbon nanofibers and binary nickel cobalt hydroxide (Ni-Co(OH)(2)) nanoflakes were synthesized for use as anodes for lithium-ion batteries. To clarify the effect of temperature on the structure and electrochemical performance of the composites, the ternary composite fibers were annealed at various temperatures. When the annealing temperature increased, the interconnected Ni-Co(OH)(2) nanoflakes on the carbon surface gradually converted to Ni-Co(OH)(2) nanoneedles. Subsequently, the chemical structure of Ni-Co(OH)(2) was transformed into binary nickel cobalt oxide (Ni-CoO) at 300 degrees C. Further annealing at 400 degrees C caused the aggregation of nanoneedles, forming flowerlike particles. The incorporation of Ni-Co(OH)(2) nanoflakes into carbon nanofibers resulted in a substantial increase in the specific capacity compared with that of the pure carbon nanofibers. The increased specific capacity was because of the synergistic effects of the high theoretical capacity of Ni-Co(OH)(2) and easily accessible charge transport in the carbon nanofiber network. The specific capacity of the composite fibers increased with the annealing temperature and reached a maximum of 64S mAh/g at a current density of 150 mA/g at 300 degrees C. The increased specific capacity was mainly attributed to the change in the specific surface area, mesopore volume, and electrical conductivity of the composite fibers with temperature.