Pulse microwave deposition of cobalt oxide nanoparticles on graphene nanosheets as anode materials for lithium ion batteries

We report the high capacity, superior rate capability, and excellent cyclic stability of graphene nanosheets (GNs) decorated with Co ₃O ₄ nanoparticles as anodes in Li-ion batteries. A pulse microwave-assisted (MA) polyol method (total period: 30 min) is adopted to deposit cobalt oxides onto the GNs in water and ethylene glycol (EG), forming two types of Co ₃O ₄@GN hybrids. The selection of solvent in the MA process plays a central role in affecting the crystallinity, dispersion, and particle size of cobalt oxide particles. The resulting Co ₃O ₄@GN hybrid, prepared by the MA method in EG, shows a homogeneous dispersion of Co ₃O ₄ nanocrystals with an average size of 10 nm. The Co ₃O ₄@GN hybrid displays advantages of high reversible capacity, excellent cycleability, and high rate capability. This improved cyclic performance can be attributed to the formation of a three-dimensional GN framework decorated with Co ₃O ₄ nanocrystals, leading to fast diffusion of Li ions (diffusion coefficient: 5.82 × 10 ^-12 cm ² s ^-1) and low internal resistance (equivalent series resistance: 92.2 Ω) determined by electrochemical impedance spectroscopy. With its ease of MA fabrication and good performance, the Co ₃O ₄@GN hybrid will hold promise in practical Li-ion batteries.