Grain boundary microstructure engineering of Li1.3Al0.3Ti1.7(PO4)3 electrolytes with a low-temperature-prepared nanopowder and Bi2O3 additive

All-solid-state lithium batteries have great potential applying to the fields of transportation and portable devices because of their high safety and energy density as the power source. As a critical component of device, solid-state electrolyte has been paid much attention. Given the excellent physical and chemical stability, Li1+xAlxTi2-x(PO4)3 (LATP)-based electrolyte has been considered as one of the most promising electrolytes for the next generation batteries. However, a further promotion of its ionic conductivity becomes extremely difficult, originating mainly from the poor connection of grains and a low relative density of LATP. Here, the nanosized and homogenous LATP (x=0.3) powders were synthesized through reducing the agglomeration of precursor powders and preparing at low temperatures. It is revealed that uniformly superfine LATP powders are able to improve the microstructure of grain boundaries during the pellet sintering process, thereby reducing the grain boundary resistance. Furthermore, as-synthesized nanosized powders mixed with Bi2O3 additive present a better enhancement on the connection of grains and the relative density in LATP. On the basis of this understanding, we prepared LATP electrolytes with 0.5 wt% Bi2O3 exhibiting a high ionic conductivity of 8.56×10-4 S/cm, a high relative density of 94.4% and a low activation energy of 0.27 eV, which is demonstrated as a prospective electrolyte in all-solid-state lithium battery LiFePO4/PEO/LATP/PEO/Li.