Preparation and performance of highly-conductive dual-doped Li7La3Zr2O12 solid electrolytes for thermal batteries

Garnet LiLaZrO (LLZO) electrolytes have been recognized as a promising candidate to replace liquid/molten-state electrolytes in battery applications due to their exceptional performance, particularly Ga-doped LLZO (LLZGO), which exhibits high ionic conductivity. However, the limited size of the Li transport bottleneck restricts its high-current discharging performance. The present study focuses on the synthesis of Ga and Ba co-doped LLZO (LLZGBO) and investigates the influence of doping contents on the morphology, crystal structure, Li transport bottleneck size, and ionic conductivity. In particular, GaBa exhibits the highest ionic conductivity (6.11E-2 S cm at 550 °C) in comparison with other compositions, which can be attributed to its higher-energy morphology, larger bottleneck and unique Li transport channel. In addition to Ba, Sr and Ca have been co-doped with Ga into LLZO, respectively, to study the effect of doping ion radius on crystal structures and the properties of electrolytes. The characterization results demonstrate that the easier Li transport and higher ionic conductivity can be obtained when the electrolyte is doped with larger-radius ions. As a result, the assembled thermal battery with GaBa-LLZO electrolyte exhibits a remarkable voltage platform of 1.81 V and a high specific capacity of 455.65 mA h g at an elevated temperature of 525 °C. The discharge specific capacity of the thermal cell at 500 mA amounts to 63% of that at 100 mA, showcasing exceptional high-current discharging performance. When assembled as prototypes with fourteen single cells connected in series, the thermal batteries deliver an activation time of 38 ms and a discharge time of 32 s with the current density of 100 mA cm. These findings suggest that Ga, Ba co-doped LLZO solid-state electrolytes with high ionic conductivities holds great potential for high-capacity, quick-initiating and high-current discharging thermal batteries.