La2O3 precursor purification for enhanced LLZTO solid electrolytes

Garnet-type Li 6.4 La 3 Zr 1.4 Ta 0.6 O 12 (LLZTO) is a promising solid electrolyte, but Li dendrite penetration remains a critical challenge. Since pores and grain boundaries are often regarded as preferential sites for Li deposition, the local structure and chemistry of these regions were investigated. Zr enrichment was observed near pores and grain boundaries, and focused ion beam (FIB)-transmission electron microscopy (TEM) analysis identified the grain boundary impurity phase as Li 2 ZrO 3 , indicating that local chemical heterogeneity is closely associated with failure-sensitive regions in LLZTO. To trace the origin of this impurity phase, the precursor was further examined. La 2 O 3 was found to undergo hydration during storage, forming La(OH) 3 and introducing an effective stoichiometric deviation during synthesis, which promotes Li 2 ZrO 3 formation. After pre-annealing purification of La 2 O 3 , the impurity phase was significantly suppressed, while the relative density and critical current density (CCD) of LLZTO were both markedly improved. These results demonstrate that precursor purification is an effective strategy for improving the phase purity, relative density, and current tolerance of LLZTO. Graphical abstract Online Figure: La 2 O 3 precursor purification improves LLZTO relative density and current tolerance. Pre-annealing commercial La 2 O 3 at 900 °C for 10 h reduces hydroxide/oxycarbonate-related impurities, suppresses Li 2 ZrO 3 formation, and yields denser LLZTO ceramics with enhanced CCD.