Efficient Mutual-Compensating Li-Loss Strategy toward Highly Conductive Garnet Ceramics for Li-Metal Solid-State Batteries

Garnet-type Li₇La₃Zr₂O₁₂ (LLZO) is a promising solid-state electrolyte (SSE) due to its high Li⁺ conductivity and stability against lithium metal. However, wide research and application of LLZO are hampered by the difficulty in sintering highly conductive LLZO ceramics, which is mainly attributed to its poor sinterability and the hardship of controlling the Li₂O atmosphere at a high sintering temperature (∼1200 °C). Herein, an efficient mutual-compensating Li-loss (MCLL) method is proposed to effectively control the Li₂O atmosphere during the sintering process for highly conductive LLZO ceramics. The Li_6.5La₃Zr_1.5Ta_0.5O₁₂ (LLZTO) ceramic SSEs sintered by the MCLL method own high relative density (96%), high Li content (5.54%), high conductivity (7.19 × 10^-4 S cm^-1), and large critical current density (0.85 mA cm^-2), equating those sintered by a hot-pressing technique. The assembled Li-Li symmetric battery and a Li-metal solid-state battery (LMSSB) show that the as-prepared LLZTO can achieve a small interfacial resistance (17 Ω cm²) with Li metal, exhibits high electrochemical stability against Li metal, and has broad potential in the application of LMSSBs. In addition, this method can also improve the sintering efficiency, avoid the use of mother powder, and reduce raw-material cost, and thus it may promote the large-scale preparation and wide application of LLZO ceramic SSE.