Garnet-type Li₇La₃Zr₂O₁₂ (LLZO) is a promising electrolyte for solid-state lithium metal batteries owing to its high ionic conductivity and chemical stability towards lithium metal. High-temperature sintering (over 1100 °C) is essential for the fabrication and production of LLZO, which is often challenged by elemental loss (i.e. lithium volatilization) during sintering and thus causes product reliability issues. Here, we propose a simple and scalable coating strategy to enable LLZO to be sintered efficiently without sacrificial mother powder. We reveal that multifunctional Li-Al-O compounds coated on LLZO electrolytes effectively promote sintering process while mitigating lithium loss upon conventional high-temperature sintering, rendering a highly dense (98.2%) sintered pellet with high ionic conductivity (8.82 × 10⁻⁴ S cm^-1) and low electronic conductivity (7.59 × 10⁻¹⁰ S cm^-1). The fabricated pellets exhibit a significantly enhanced critical current density along with low charge-transfer resistance at the interface with lithium metals, attributable to the lithophilic Li-Al-O compound that is uniformly distributed across the particles/grain boundaries. Furthermore, we demonstrate the practical viability of the strategy by showcasing the fabrication of high-quality supersized pellets with arial size up to 16 cm² (after sintering). We expect that this simple yet effective strategy involving multifunctional agents to simultaneously design materials and their fabrication process expedites the technological advancement of sintering for solid-state oxide electrolytes towards commercialization.