High-Yield Preparation of ZnO Nanoparticles on Exfoliated Graphite as Anode Material for Lithium Ion Batteries and the Effect of Particle Size as well as of Conductivity on the Electrochemical Performance of Such Composites

The combination of zinc oxide (ZnO) nanoparticles (NP) and graphite provides a promising approach for applications in the field of anode materials for lithium ion batteries. Here, we report a facile and environmentally friendly method yielding uniformly dispersed ZnO particles with a controllable particle size between 5 and 80 nm, supported by exfoliated graphite (EG) sheets. A thermal post-treatment (420 to 800 °C, N2) of ZnO@EG composite results in high yield with the opportunity for industrial scale-up. The post-treatment leads to growing ZnO particles on the EG sheets, while oxygen is disincorporated from ZnO by the associated carbothermal reduction of ZnO@EG composites above 600 °C and the conductivity is increased. ZnO@EG composite anodes, reduced at 600 °C, show improved Li storage capacity (+25%) and good cycle stability, compared to the EG anode. This can be attributed to the increased conductivity, despite the particle size increased up to 80 nm. Furthermore, we suggest that the mechanism for the reaction of Li+ ions with ZnO@EG-composites including ZnO-particles with an average particle size below 20 nm differs from the classical Li+ ions insertion/de-insertion or alloying process.