Electrochemical examination of core–shell mediated Li+ transport in Li4Ti5O12 anodes of lithium ion batteries

Lithium titanium oxide (LTO) particles of < 100 nm average size are used as the active material for a Li ion battery anode, and the electrochemical features of (core–shell type) structural phase transition in these particles are probed in a LiClO4 electrolyte of ethylene and diethyl carbonates. The experiments involve a combination of galvanostatic cycling, slow scan cyclic voltammetry and electrochemical impedance spectroscopy (EIS). Experimentally generated Ragone plots show that, specific energies measured during fast charging of LTO are higher than those obtained during similarly paced discharge steps. The electronic conductivity of the LTO shell plays a key role in supporting this particular effect. EIS results illustrate the kinetics of Li transport in LTO as well as in the solid-electrolyte interphase. EIS also shows certain marks of anomalous Li+ diffusion within the spatially heterogeneous, core–shell structured LTO particles. Voltage dependent values of the charge transfer resistance, intercalation capacitance and chemical diffusion coefficient of Li+ in LTO are measured using EIS. Detailed potential profiles of these impedance parameters elucidate how charge transport in LTO is affected by the biphasic behavior of this material.