Microstructural engineering for Ta-doped Li-garnet solid electrolyte toward enhancing performance

Solid-state lithium batteries (SSLBs) based on Li-garnet solid electrolytes have received tremendous attention owning to their strong safety and high energy density. However, poor ionic conductivity at room temperature and low relative density of Li-garnet solid electrolytes hinder their widespread applications. Herein, microstructural engineering enabled by further Yb-doping strategy is adopted to enhance the performance of Li-garnet solid electrolyte Li6.5La3Zr1.5Ta0.5O12 (LLZTO). The introduction of Yb exerts dual regulation of intragrain and grain boundary, enlarging the bottleneck size for Li+ migration and suppressing abnormal grain growth (AGG), which enhance ion conductivity and fabricate homogeneous dense electrolyte. First principles calculation demonstrates Yb into electrolyte can reduce Gibbs free energy change (ΔG) of electrolyte reaction, making sintering process easier to complete. A dense microstructure is obtained when 0.1 Yb is doped LLZTO, and the maximum ion conductivity achieves 7.67 × 10−4 S·cm−1 with relative density of 96.2 %. The critical current density (CCD) of Li symmetric cell composed of 0.1Yb-LLZTO reaches 1.30 mA cm−2 and provides stable cycling performance for 4000 h at 0.1 mA cm−2. Additionally, SSLB matched with 0.1Yb-LLZTO and LiFePO4 delivers a remarkable cycling performance with a discharge capacity of 125.4 mAh g−1 and capacity retention of 83.2 % after 300 cycles (0.5 C). The findings of this study provide important implications for understanding microstructural engineering in electrolyte preparation and developing high-performance Li-garnet-based SSLBs.