Ultra-fast sintering of garnet-type electrolyte enabled by in-situ formed liquid phase for high-performance solid-state batteries

Garnet-type solid-state electrolytes are promising for high-safety solid-state lithium metal batteries, owing to their high ionic conductivity and excellent stability against lithium metal anodes. However, conventional multi-hour high-temperature sintering causes severe lithium volatilization, unwanted impurities, and low production efficiency. Herein, an ultra-fast sintering strategy is developed to fabricate dense Li_6.5La₃Zr_1.5Ta_0.5O₁₂ (LLZTO) electrolytes via only 1 min of sintering. During high-temperature sintering, volatilized lithium originating from the LLZTO green body reacts with oxygen to form a sintering-active liquid in situ. This liquid phase greatly boosts mass transport, thereby drastically accelerating the densification process. By raising the sintering temperature to 1300 °C, the thermodynamic conditions for liquid phase formation are turned, and lithium volatilization from the green body is promoted simultaneously, enabling full densification of LLZTO within just 1 min. The optimized LLZTO electrolyte delivers a room-temperature ionic conductivity up to 1.02 mS cm⁻¹ coupled with an ultralow electronic conductivity. Li||LLZTO||Li cells assembled with this electrolyte exhibit a critical current density of 0.7 mA cm⁻² and maintain stable cycling for over 500 h at 0.2 mA cm⁻². This work deepens the understanding of in-situ liquid-phase sintering and provides guidance for ultra-fast fabrication of garnet-type electrolytes.