The study demonstrates that the introduction of the electrochemically inactive dielectric additive Li2TiO3 to LTO results in a strong decrease in the grain boundary resistance of LTO-Li2TiO3 (LTC) composites at a low concentration of Li2TiO3. With the increase in the concentration of Li2TiO3 in LTC composites, the grain boundary resistance goes through a minimum and increases again due to the growth of the insulation layer of small Li2TiO3 particles around LTO grains. For LTO-TiO2 (LTT) composites, a similar effect was observed, albeit not as strong. It was found that LTC composites at low concentration of Li2TiO3 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 Li2TiO3 in the vicinity of the interfaces between LTO and Li2TiO3. 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 TiO2 preventing the formation of coherent interfaces.
Keywords: Li4Ti5O12-Li2TiO3; Li4Ti5O12-TiO2 composites; excess charge capacity; grain boundary resistance; ionic conductivity; solid-state synthesis.