Insights into the reactive sintering and separated specific grain/grain boundary conductivities of Li1.3Al0.3Ti1.7(PO4)3

Li1.3Al0.3Ti1.7(PO4)3 (LATP) is a promising candidate as solid electrolyte and Li+ conductive component in the composite electrodes of all-solid-state Li-ion batteries. For both applications, reducing the sintering temperature of LATP while preserving its electrochemical properties is highly desired. This work is dedicated to reducing the sintering temperature of LATP from conventionally around 1000 °C to a low temperature of 775 °C with adding an extra 10 wt % of Li2CO3 to the precursors by a reactive sintering process. Comparative investigations with the stoichiometric LATP prepared by the same sintering method indicate that the combination effect of reactive sintering and Li2CO3-excess promotes the liquid phase sintering within LATP yielding a high relative density of 95.3%, whereas the stoichiometric LATP can only achieve a comparable relative density at 875 °C. Furthermore, the reactive sintering assisted Li2CO3-excess LATP exhibits a significantly higher ionic conductivity of 0.65 mS cm−1 at 25 °C and lower total activation energy of 0.334 eV compared with that of the stoichiometric LATP. Correlative studies on the microstructure and the separated specific grain/grain boundary conductivities for the two samples reveal that the improvement of Li+ conductivity for Li-excess LATP is attributed to its smaller total grain boundary thickness.