Combining cold sintering and Bi 2 O 3 -Activated liquid-phase sintering to fabricate high-conductivity Mg-doped NASICON at reduced temperatures

The cold sintering process (CSP) and Bi 2 O 3 -activated liquid-phase sintering (LPS) are combined to densify Mg-doped NASICON (Na 3.256 Mg 0.128 Zr 1.872 Si 2 PO 12 ) to achieve high densities and conductivities at reduced temperatures. As an example, a cold-sintered specimen with the addition of 1.1 wt % Bi 2 O 3 sintering additive achieved a high conductivity of 0.91 mS/cm (with ∼96% relative density) after annealing at 1000 °C; this conductivity is >70% higher than that of a cold-sintered specimen without adding the Bi 2 O 3 sintering additive, and it is >700% of the conductivity of a dry-pressed counterpart with the same amount of Bi 2 O 3 added, all of which are subjected to the same heating profile. The highest conductivity achieved in this study via combining CSP and Bi 2 O 3 -activated LSP is  > 1.5 mS/cm. This study suggests an opportunity to combine the new CSP with the traditional LPS to sinter solid electrolytes to achieve high densities and conductivities at reduced temperatures. This combined CSP-LPS approach can be extended to a broad range of other materials to fabricate the “thermally fragile” solid electrolytes or solid-state battery systems, where reducing the processing temperature is often desirable.