Coating lithium titanate anodes with a mixed ionic-electronic conductor for high-rate lithium-ion batteries

Lithium titanate (Li4Ti5O12; LTO) is a promising anode material for fast (dis)charging Li-ion batteries (LIBs). However, its low Li diffusion coefficient and electronic conductivity limit its applications. Here, we uniformly coat the LTO surface with a 1.6 nm layer of partially lithiated titania (LixTiO2, x ≈ 0.5), which is found to be a mixed ionic-electronic conductor (MIEC), using a simple solid-state method. The MIEC layer simultaneously transfers electrons and Li-ions, facilitating efficient charge transfer to (de)lithiate LTO over the entire particle surface. MIEC-nanocoated LTO exhibits highly improved capacity retention and rate capability than pristine LTO; based on electrochemical simulations, MIEC nanocoating causes performance enhancement by maximum surface-area utilization for charge transfer. Furthermore, electrochemical impedance spectroscopy and density functional theory calculations confirm facile ionic transport and high electronic conductivity of LixTiO2 nanolayer. This general strategy of MIEC nanocoating can boost the electrochemical performances of various insulating electrodes, maximizing the materials utilization.