Synergistic Engineering of Template-Guided Densification and Dopant-Induced Pore Filling for Pressureless Sintering of Li₇La₃Zr₂O₁₂ Solid Electrolyte at 1000 °C

Li₇La₃Zr₂O₁₂ (LLZO) is a leading candidate for solid-state batteries due to its high ionic conductivity and lithium metal compatibility, but its application is limited by the need for high-temperature or pressure-assisted sintering. Herein, a strategy combining Ga/Si co-addition with a La_2.4Zr_1.2Ta_0.4O₇ (LZT) template-assisted approach to enable dense LLZO sintering at 1000 °C without external pressure is proposed. The LZT template facilitates early cubic phase crystallization and fine particle formation, lowering the activation barrier for sintering. Concurrently, Ga and Si additives generate transient Li–Ga–O and Li–Si–O phases that promote pore filling and grain connectivity. Notably, Li–Si–O suppresses Ga segregation and stabilizes the cubic phase, offsetting its low ionic conductivity through improved densification. The synthesized LLZO achieves a relative density of 95.38% and an ionic conductivity of 5.05 × 10⁻⁴ S cm⁻¹ under conventional sintering at 1000 °C. Symmetric cells exhibit stable long-term cycling without any liquid electrolytes, while full cells demonstrate 89.1% rate retention (1C/0.1C) and maintain 99.0% of their capacity after 300 cycles. This study offers a scalable route to high-performance garnet electrolytes and highlights the synergistic effects of precursor crystallinity and grain boundary chemistry in enabling low-temperature sintering.