Cold sintering of oxide-based llto and llzo solid-stateelectrolytes and their integration into lithium metalbatteries

Oxide-based solid electrolytes such as perovskite-type Li₃ₓLa₂⁄₃₋ₓTiO₃ (LLTO) and garnet-type Li₇La₃Zr₂O₁₂ (LLZO) are promising candidates for next-generation solid-state lithium batteries due to their high ionic conductivities and stability. However, the practical application of these materials is limited by the requirement for high-temperature sintering and challenges in electrode–electrolyte integration. In this thesis, the cold sintering process was investigated as a low-temperature fabrication method for LLTO and LLZO composites; densification was achieved below 150 °C within 30 minutes by using transient solvents and moderate pressure. By optimizing sintering parameters such as solvent type, particle size, and binder–salt content, ionic conductivities greater than 10⁻⁴ S/cm were attained. Co-sintering of LLTO with LiFePO₄ (LFP) and LLZO with LiCoO₂ (LCO) cathodes at approximately 100 °C was successfully demonstrated without any structural or chemical degradation. To prevent instability between LLTO and lithium metal, a PVDF membrane wetted with a small amount of LiPF₆-based electrolyte was employed, effectively suppressing Ti⁴⁺ reduction and stabilizing the interfacial resistance. The fabricated Li/PVDF/LLTO/LFP full cells exhibited discharge capacities of 151 mAh/g and 135 mAh/g at current rates of 0.1 C and 0.2 C, respectively. Similarly, Li/PPC-LiFSI/LLZO/LCO cells demonstrated discharge capacities of 158 mAh/g and 141 mAh/g at 0.1 C and 0.2 C, respectively. Furthermore, the recyclability of LLTO composites through multiple reprocessing cycles was confirmed. Even after ten cycles, LLTO maintained its high crystallinity and phase purity, exhibiting a high ionic conductivity of approximately 2 × 10⁻⁴ S/cm.