Li4Ti5O12 is a highly promising anode material for use in Li-ion batteries. Herein, Li4Ti5O12 samples are prepared by sintering Li2CO3 and anatase TiO2 with varying Li molar excess. Characterization by AC impedance spectroscopy, X-ray diffraction spectroscopy and scanning electron microscopy is performed. The electrochemical performance, crystal structure and surface morphology are found to be dependent on the Li content. The effect of TiO2 and Li2TiO3 impurities in Li4Ti5O12 on electrochemical characteristics including charge–discharge cycling and the AC impedance spectra is also investigated. These two impurities are found to have different effects on the electrochemical properties of Li4Ti5O12. At a 2% molar Li excess, a high capacity and Li ion diffusion coefficient are achieved.