Stabilizing the NASICON Solid Electrolyte in an Inert Atmosphere as a Function of Physical Properties and Sintering Conditions for Solid- State Battery Fabrication

The interfacial contact between a solid electrolyte and cathode materials is one of the challenges for the solid-state battery (SSB) industry. The cosintering of a solid electrolyte and cathode materials could be a possible solution. Considering the future scope of solid-state battery fabrication by the cosintering process of phosphate-based solid electrolytes and phosphate-based cathodes (LiFePO4, Li3V2(PO4)3, etc.), the present study focuses on stabilizing the NASICON structured Li1.4Al0.4Ti1.6(PO4)3 (LATP) solid electrolyte in an inert atmosphere as proposed cathode materials are not stable in air at high temperatures. The results show a high influence of particle size and heating rate along with sintering temperature on achieving a pure phase and fully dense pellets in an argon atmosphere. Cracks/voids, secondary phases, and reduction of Ti were observed in pellets prepared with a powder of bigger size under argon gas sintering. The present work not only successfully solves these issues by decreasing the particle size and reducing the heating rate but also produces highly dense pellets with more than 98% density at 800 degrees C. We have also achieved a high conductivity of 8.77 x 10-4 S cm-1 at room temperature for the pellet sintered at just 800 degrees C in argon, which is 3-4 times higher than the conductivity of samples sintered at higher than 800 degrees C. Therefore, we succeeded in obtaining for the first time a high conductivity, pure phase, and high density of the LATP solid electrolyte at a relatively low temperature of 800 degrees C in an argon atmosphere, which is an important solution for solid-state battery fabrication by cosintering process. Furthermore, the stabilized NASICON electrolyte in an argon atmosphere also shows superior electrochemical performance when tested with Li metal in a symmetric battery cell.