Vacancy‐Suppressed Garnet Electrolytes for Durable Solid‐State Batteries

ABSTRACT Cubic‐garnet‐type solid electrolytes (SEs) are promising candidates for all‐solid‐state batteries (ASSBs) due to their high ionic conductivity and stability against lithium metal. However, intrinsic lithium and oxygen vacancies formed during high‐temperature sintering can lead to interfacial metal reduction and phase transitions, ultimately causing short circuits. In this study, we quantified these intrinsic vacancies in Li 6.5 La 3 Zr 1.5 Ta 0.5 O 12 (LLZTO) and proposed a strategy to achieve vacancy‐suppressed, lithium‐stuffed garnet SEs by simply tuning the lithium content in both the green pellet and bedding powder during sintering. The optimized Li‐stuffed LLZTO exhibited lithium occupancy exceeding 6.5 per formula unit (pfu) and oxygen‐vacancy concentrations below 0.02 pfu, resulting in improved chemical stability at the electrolyte–electrode interface and enhanced air stability. The garnet electrolyte demonstrated a critical current density of 1.00 mA cm −2 at 30°C and 1.75 mA cm −2 at 60°C, along with stable cycling performance over 3000 h in lithium symmetric cells and 2000 cycles in hybrid full‐cells, demonstrating 90% capacity retention. These findings highlight the pivotal role of intrinsic vacancy control in enhancing the structural and electrochemical integrity of garnet electrolytes, thereby promoting their practical application in ASSBs.