High cycling stability enabled by Li vacancy regulation in Ta-doped garnet-type solid-state electrolyte

Ta-doped solid-state electrolyte (SSE) is employed to reveal Li vacancy regulation process and densification mechanism through thermodynamic analysis. The vacancy concentration has an optimal value corresponding to the lowest free energy of the Ta-doped SSE system. Low system free energy accelerates grain growth and promotes grain fusion for SSE densification, which is consistent with microstructure evolution. The relative density and Li-ion conductivity reach 96.1 % and 6.47 × 10^?4 S cm^?1 at 0.5 of Ta doping. Symmetric Li battery exhibits stable cycling at a high current density of 1.41 mA cm^?2 and cycles 250 h without polarization at 0.2 mA cm^?2. Full battery with LiFePO₄ cathode keeps stability with high Coulombic efficiency of ～99 % after 150 cycles at 0.5 C. This work provides theoretical insights into the Li vacancy regulation of Ta-doped SSE, constituting a significant step toward practical applications.