Co₃O₄/C nanocapsules with onion-like carbon shells as anode material for lithium ion batteries

The synthesis and characterization of core/shell-type Co₃O ₄/C nanocapsules for application as anode material in lithium ion batteries are reported in this paper. The synthesis process involves the preparation of Co/C nanocapsules using a modified arc-discharge method and the annealing of the Co/C nanocapsules at 300 C for 2 h in air. The as-synthesized products show a spherical shape and a core/shell-type structure in which a Co₃O₄ nanoparticle core of diameter 10-30 nm is encapsulated by an onion-like carbon shell of thickness approximately 1 nm. The Co/C nanocapsules can be stable below 130 C, and be oxidized above 205 C in air. The Co₃O₄/C nanocapsules deliver an initial discharge capacity of 1467.6 mAh g^-1 at 0.5 C and maintain a high reversible capacity of 1026.9 mAh g^-1 after 50 charge-discharge cycles, much higher than the Co₃O₄ nanoparticles (471.5 mAh g ^-1). A postmortem analysis of the Co₃O₄ and Co₃O₄/C anodes subjected to prolonged cycling reveals the existence of a lower degree of surface cracking and particle breakage in the Co₃O₄/C anode than the Co₃O₄ anode. The improved electrochemical performance and structural stability in the Co ₃O₄/C nanocapsules are attributed to the enhanced electrical conductivity and structural buffering provided by the onion-like carbon shell.