Transport and Electrochemical Properties of Li[sub.4]Ti[sub.5]O[sub.12]-Li[sub.2]TiO[sub.3] and Li[sub.4]Ti[sub.5]O[sub.12]-TiO[sub.2] Composites

The study demonstrates that the introduction of the electrochemically inactive dielectric additive Li[sub.2]TiO[sub.3] to LTO results in a strong decrease in the grain boundary resistance of LTO-Li[sub.2]TiO[sub.3] (LTC) composites at a low concentration of Li[sub.2]TiO[sub.3]. With the increase in the concentration of Li[sub.2]TiO[sub.3] in LTC composites, the grain boundary resistance goes through a minimum and increases again due to the growth of the insulation layer of small Li[sub.2]TiO[sub.3] particles around LTO grains. For LTO-TiO[sub.2] (LTT) composites, a similar effect was observed, albeit not as strong. It was found that LTC composites at low concentration of Li[sub.2]TiO[sub.3] have unusually high charge-discharge capacity exceeding the theoretical value for pure LTO. This effect is likely to be caused by the occurrence of the electrochemical activity of Li[sub.2]TiO[sub.3] in the vicinity of the interfaces between LTO and Li[sub.2]TiO[sub.3]. The increase in the capacity may be qualitatively described in terms of the model of two-phase composite in which there is the interface layer with a high capacity. Contrasting with LTC composites, in LTT composites, no capacity enhancement was observed, which was likely due to a noticeable difference in crystal structures of LTO and TiO[sub.2] preventing the formation of coherent interfaces.