Improvement of Short-Circuit Tolerance of Garnet Type Solid Electrolyte Li_6.4La₃Zr_1.4Ta_0.6O₁₂ by Li₂WO₄ and Al₂O₃ Sintering Aids and La Deficiency (Supporting Information)

Garnet-type Li_6.4La₃Zr_1.4Ta_0.6O₁₂ (LLZT) is one of the most promising solid electrolytes for all solid-state batteries due to its relatively high Li-ion conductivity and electrochemical stability against Li metal anode. However, the presence of pores and voids in the electrolyte causes short circuit due to lithium dendrites growth. In the present study, the effects of Li₂WO₄ (LWO) and Al₂O₃ sintering aids on the densification of LLZT were investigated to decrease the pores and voids and thereby to improve the tolerance for Li dendrite growth. Both sintering aids were effective for improving the densification; however, their effects were totally different. While 2 wt% Al₂O₃ significantly enhanced the grain growth, 4 wt% LWO gave smaller grains of uniform size distribution (3–5 µm). Simultaneous addition of 4 wt% LWO and 2 wt% Al₂O₃ gave relatively larger grains (5–20 µm) with very few voids, and a very high relative density of 99.3 % was obtained. The critical current density (CCD) was improved from 0.2 to 0.4 mA cm⁻². Reducing the amount of lanthanum in LLZT led to the formation of lithium zirconate as a self-forming sintering aid and achieved a higher relative density (99.7 %) for La-deficient (6 %) LLZT with 4 wt% LWO and 2 wt% Al₂O₃. The CCD was further improved to 0.6 mA cm⁻².