Core/shell-structured nickel cobaltite/onion-like carbon nanocapsules as improved anode material for lithium-ion batteries

Core/shell-structured nanocapsules consisting of a nickel cobaltite (NiCo2O4) nanoparticle core encapsulated in an onion-like carbon (C) shell are synthesized by arc-discharge and air-annealing methods. Void spaces between NiCo2O4core and the carbon shell are observed in the NiCo2O4/C nanocapsules. Lithium-ion batteries fabricated using the nanocapsules as the anode material exhibit enhanced initial coulombic efficiency of 82.3% and specific capacity of 1197.2 mA h/g after 300 cycles at 0.2 A g-1current density. Varying the rate of charge/discharge current from 0.2 to 4 A/g does not show negative effects on the recycling stability of the nanocapsules and a recoverable specific capacity as high as 1270.4 mA h/g is obtained. The introduction of the onion-like C shell and the presence of the void spaces are found to increase the contact areas between the electrolyte and the nanocapsules for improved electrolyte diffusion, to enhance the electronic conductivity and ionic mobility of the NiCo2O4nanoparticle cores, and to accommodate the change in volume during the lithium-ion insertion/extraction process.