Controlling Dendrite Formation for Long-Term Cyclability and Fast Li⁺ Diffusion Kinetics in Solid-State Electrolyte Li₇La₃Zr₂O₁₂

Ga-doped Li 7 La 3 Zr 2 O 12 (Ga-LLZO) solid-state electrolyte is a promising material for advanced batteries due to its superior ionic conductivity and mechanical properties. However, Ga-LLZO is challenged by high grain boundary (GB) resistance and dendrite propagation. Therefore, in this study, we suggest the two-step sintering (TSS) method for controlling the microstructure, resulting in lower GB resistance and achieving superior dendrite resistance. To elucidate the cycling performance, a critical current density (CCD) test was performed on a Ga-LLZO sample fabricated with TSS. As a result, the Ga-LLZO sample fabricated with TSS demonstrates a superior CCD value of 0.32 mA cm –2 as well as shows stable cycling at a current density of 0.2 mA cm –2 . According to the impedance analysis, the sample fabricated with TSS demonstrates a significant increase in ionic conductivity compared to the sample fabricated with the conventional sintering (CS) method. This phenomenon implies that the enhanced sintering technique of TSS can reduce the GB resistance and dendrite formation by achieving the densification and tight GB. Extensive investigation into the dendrite formation mechanism has provided compelling evidence that dendrites are not solely composed of pure Li but rather consist of a compound containing both C and O elements. This finding significantly contributes to the understanding of the composition and nature of dendrites in Ga-LLZO, shedding light on their role in the acceleration of the phase decomposition process.