Microstructure and ionic conductivities of NASICON-type Li₁.₃A1₀.₃Ti₁.₇(PO₄)₃ solid electrolytes produced by cold sintering assisted process

Li1.3Al0.3Ti1.7(PO4)3 (LATP) is a promising solid electrolyte for lithium-ion batteries. However, it is challenging to densify LATP ceramics at reduced sintering temperature while preserving their electrical properties. Herein, LATP ceramics were pre-densified via cold sintering process (CSP) at 250 °C for 1 h and exhibited room temperature ionic conductivity of 2.01 × 10−6 S/cm. Subsequent post-annealing at as low as 900 °C for 1 h resulted in two orders of magnitude improvement in both grain boundary conductivity and total conductivity, compared to those of as-CSPed LATP. The optimal total conductivity (4.29 × 10−4 S/cm) obtained from post-annealed material is among the best reported values so far. It is also 5 times greater than the conductivity (8.51 × 10−5 S/cm) of the conventionally sintered LATP. We propose that post-annealing effectively eliminates amorphous insulating phases generated during CSP and promotes crack-free microstructure with moderate grain growth, which collectively contributes to dramatically enhanced conductivity. This work unambiguously demonstrates that CSP-assisted process can avoid the detrimental effects of high temperature associated with conventional sintering on microstructure and conductivity, and thus is a cost-effective processing route for fabrication of solid-state electrolytes for battery applications.