High-pressure low-temperature densification of NASICON-based LATP electrolytes for solid-state lithium batteries

Ceramic oxides are promising solid electrolytes for Lithium metal solid-state batteries (SSBs) because of their high ionic conductivity and stability under ambient conditions. Nonetheless, the need for high-temperature densification approaches challenges their processability towards upscaling and their implementation into practical SSB devices. Here, we investigate a High-Pressure Low-Temperature (HPLT) processing technique for the densification of NASICON-based Li_1+xAl_xTi_2-x(PO4)₃ (LATP) solid electrolyte, providing an understanding of several key parameters such as temperature, pressure and time. Our results show that nanometric LATP can be densified using the HPLT technique at 200°C within 2 min delivering an ionic conductivity of 6.15×10⁻⁵ Scm⁻¹, which is the highest reported value at this temperature without the addition of solvents. On the other hand, by combining HPLT with a short post-heat treatment at 700 or 800 °C for 1 hour, highly dense pellets with an ionic conductivity of 10⁻⁴ Scm⁻¹ can be obtained. This represents a reduction of the densification temperature of 400°C compared to conventional high-temperature sintering and shows the potential of HPLT to overcome current densification constraints derived from the use of very high temperatures.