On the synergistic interplay between synthetic and processing approaches for enhanced grain boundary conductivity of LATP solid electrolyte

Abstract

NASICON-type Li1.3Al0.3Ti1.7(PO4)3 (LATP) solid-state electrolyte (SSE) is regarded as a promising candidate for all-solid-state lithium-ion batteries owing to its high bulk ionic conductivity, air stability, and low cost. However, the grain boundary resistance limits its overall ionic conductivity limiting its practical application. Herein, LATP has been successfully prepared using sol-gel synthetic procedure. The synthesis conditions – annealing temperature and pH-controlled sol-gel process, as well as the processing approaches – sintering temperature and impact of LiPO3 glass addition have been systematically monitored. Their impact on the structure, microstructure of the LATP powdered product and on the densification behavior of pelletized LATP SSE have been thoroughly investigated. The key for successful combination is to design a porosity-free LATP SSE with reduced grain boundary resistance and enhanced mechanical integrity at lower sintering temperatures. With the respective annealing and sintering temperatures of 850 °C and 950 °C and the suitable pH value of 5, a high grain boundary conductivity of 1.8 × 10−4 S/cm has been achieved. Thereafter, the addition of a small amount of LiPO3 (2 wt%) has been found to effectively reduce the sintering temperature by 100 °C, resulting in improved grain boundary conductivity of 2.1 × 10−4 S/cm, compared to 5.07 × 10−5 S/cm for the bare LATP SSE. This work highlights the role of microstructural engineering strategy to design LATP SSE with high ionic conductivity and mechanical strength.