Garnet-based all-solid-state Li-metal batteries (ASSLBs) have garnered considerable attention due to their potential for high energy density. However, they remain severely plagued by short-circuit failures caused by Li dendrites penetration. Reducing voids that provide growth sites for Li dendrites within garnet-type solid-state electrolytes (SSEs, Li_6.4La₃Zr_1.4Ta_0.6O₁₂ (LLZTO)) is one promising strategy. Furthermore, the sacrificial powder with identical composition required in conventional sintering processes contains La and necessitates synthesis, resulting in resource wastage. To overcome this limitation, we propose using Li₂O as a sacrificial powder to enhance the densification of garnet-type SSEs, without containing La or requiring synthesis. With an appropriate Li₂O dosage, the garnet-type SSEs can attain a relative density of up to 98.6% and a critical current density of 0.9 mA cm⁻². LiFePO₄/LLZTO/Li cells showcase an average discharge capacity of 145.4 mAh g^–1 at 0.5 C and a capacity retention of 103.4% after 100 cycles at 0.2 C.