Doping behavior of Br in Li4Ti5O12 anode materials and their electrochemical performance for Li-ion batteries

Br-doped Li4Ti5O12-xBrx ("x" = 0, 01, 0.3, 0.5 and 0.7) anode materials were synthesized by a conventional solid-state reaction technique using precursors of Li2CO3, TiO2 and LiBr, and the doping behavior and related electrochemical properties of these materials were studied. In our investigation, quantitative instrumental analyses revealed that most of the Br ions are situated on the surfaces/interfaces of agglomerated particles rather than in the bulk lattice. Narrow conduction paths of electron and Li-ion were, thus, formed on their surfaces/ interfaces. During charging/discharging process, the presence of these narrow surface electrical conduits increased the rate-capability of the LTOBr samples. The LTOBr0.5 sample showed the highest capacity of 125 mAh/g at 1C compared to 115 mAh/g for pure LTO. A highly Br-doped sample (LTOBr0.7), however, showed a slight reduction in capacity. This was explained with the formation of fine precipitations (Br-containing second phase) on the surfaces of the LTO particles due to high Br addition.