Elucidating the Impact of Cobalt Doping on the Lithium Storage Mechanism in Conversion/Alloying-Type Zinc Oxide Anodes

Herein, an in-depth investigation of the influence of transition-metal doping on the structural and electrochemical characteristics of a hybrid conversion/alloying-type lithium-ion anode material is presented. Therefore, pure zinc oxide (ZnO) and cobalt-doped ZnO (Zn0.9Co0.1O) were investigated comparatively. Characterization by using X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) confirmed the successful incorporation of the cobalt (Co) dopant into the wurtzite ZnO structure, which led to a decreased particle size for the doped compound. The insitu electrochemical XRD analysis of the first de-/lithiation of ZnO and Zn0.9Co0.1O revealed the highly beneficial impact of the transition-metal dopant on the reversible degradation of lithium oxide (Li2O) and suppression of zinc crystallite growth upon lithiation; both effects are essential for greatly improved electrochemical performance. As a result, Co doping leads to a substantially increased specific capacity from 326mAhg(-1) for pure ZnO to 789mAhg(-1) for Zn0.9Co0.1O after 75 full charge-discharge cycles.