Enhanced ionic conductivity and excellent lithium stability of garnet-type Li6.55Ga0.15La3Zr2O12 solid-state electrolytes by magnesium doping

Abstract

Li7La3Zr2O12 (LLZO) garnet solid electrolyte has garnered significant attention as a highly promising material owing to its exceptional electrochemical properties. Nevertheless, it encounters challenges such as low ionic conductivity and inadequate interfacial properties compared to liquid electrolytes. In this study, we employed simultaneous doping of Mg2+ and Ga3+ to obtain a dense LLZO material with enhanced Li+ conductivity. By utilizing the conventional solid-state reaction method, garnet-structured oxides with a chemical composition of Li6.55+2xGa0.15La3Zr2-xMgxO12 (x = 0, 0.05, 0.1, 0.15) were synthesized. The phase composition, morphology, and lithium-ion conductivity were characterized to investigate the synergistic effects of two dopants on solid electrolytes. The density of Ga and Mg co-doped garnet pellets reached as high as 96 % - 97 %, and the peak lithium-ion conductivity of Li6.65Ga0.15La3Zr1.95Mg0.05O12 electrolyte at room temperature was obtained to be 1.13 mS cm−1. Additionally, when employed in a symmetrical Li/LLZO/Li cell, this Ga and Mg co-doped garnet electrolyte exhibited excellent electrochemical stability to lithium metal and demonstrated good performance for more than 200 h in the lithium plating/stripping cycle at a current density of 0.1 mA cm−2. The LiFePO4/Ga0.15Mg0.05/Au/Li cell delivers an initial discharge capacity of 153 mAh g−1 and retains a good capacity of 143.8 mAh g−1 after 30 charge-discharge cycles.