ABSTRACT A major challenge in garnet‐type Li 7 La 3 Zr 2 O 12 (LLZO) system all‐solid‐state electrolytes is the high porosity that typically remains after sintering, which compromises ionic conductivity and degrades battery cycling performance. To address this, we propose an innovative strategy to achieve uniform lithium enrichment on the surface of electrolyte powder particles by controlling the calcination atmosphere. The resulting garnet‐type solid‐state electrolyte powder features a thin, uniform Li 2 O‐based lithium‐rich coating layer that effectively eliminates sintering‐induced porosity without introducing impurities (or the second phase) while simultaneously promoting grain fusion and moderate structural amorphization. This synergistic function enhances both ionic conductivity and resistance to lithium filament growth. At 25°C, the Ta‐doped LLZO (Ta‐LLZO) exhibits an ionic conductivity of 1.12 × 10 −3 S cm −1 and supports a critical current density of 1.4 mA cm −2 in symmetric lithium cells. The assembled Li/Ta‐LLZO/NCM811 all‐solid‐state battery achieves a discharge capacity of 163.5 mAh g −1 with 91.4% capacity retention over 120 cycles at 0.3C, along with excellent rate performance. These results significantly outperform those of garnet electrolytes lacking surface treatment or exhibiting nonuniform lithium deposition. This scalable and controllable in situ surface engineering approach effectively addresses the long‐standing challenges of porosity and interfacial properties in garnet electrolytes, offering a promising pathway toward the commercial deployment of advanced solid‐state batteries.
Xiao et al. (Sun,) studied this question.