Probing Lithiation Kinetics of Carbon-Coated ZnFe2O4 Nanoparticle Battery Anodes

The investigation of the lithiation-delithiation kinetics of anodes comprising carbon-coated ZnFe2O4 nanoparticles is reported in here. The study confirmed that, as occurring with other conversion electrodes, lithiation of ZnFe2O4 nanoparticles is a multistep process involving the presence of intermediate Li-Zn-Fe-O phases as precursors for the formation of amorphous Li2O. A detailed knowledge on the reaction kinetics of the involved electrochemical mechanisms has been achieved by using impedance spectroscopy. It has been observed that lithiation reactions introduce a long delay that limits the electrode charging, not related to diffusion mechanisms. The sloping curve following the conversion plateau of the galvanostatic discharge is connected to a retardation effect in the reaction kinetics. This limitation is seen as an additional resistive process originated by the specific lithiation microscopic features. It is concluded that capacitance spectra allow distinguishing two separate processes: formation of kinetically favored intermediate Li-Zn-Fe-O phases and subsequent reaction to produce highly dispersed LiZn and Fe-0 in an amorphous Li2O matrix. A detailed electrical model is provided accounting for the overall electrode lithiation process.