Effect of Mechanical Activation and Carbon Coating on Electrochemistry of TiNb2O7 Anodes for Lithium-Ion Batteries

TiNb2O7 anode material with a Wadsley-Roth crystallographic shear structure was prepared by solid-state synthesis at a relatively low temperature (1000 degrees C) and a short calcination time (4 h) using preliminary mechanical activation of the reagent mixture. The as-prepared final product was then ball milled in a planetary mill with and without carbon black. The crystal structure and morphology of the samples were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Electrochemical performance was studied in a galvanostatic mode in varied voltage intervals and at different cycling rates in combination with in situ electrochemical impedance spectroscopy (EIS) measurements. The resistance measured using in situ EIS had the highest values at the end of the discharge and the lowest when charging. The lithium diffusion coefficient, determined by galvanostatic intermittent titration technique (GITT), in samples milled with and without carbon black was an order of magnitude higher than that for the pristine sample. It was shown that improved electrochemical performance of the carbon composite TiNb2O7/C (reversible capacity of 250 mAh g(-1) at C/10 with Coulomb efficiency of similar to 99%) was associated with improved conductivity due to the formation of a conductive carbon matrix and uniform distribution of submicron particles by size.