Removal and Reoccurrence of LLZTO Surface Contaminants under Glovebox Conditions

The reactivity of Li_6.4La₃Zr_1.4Ta_0.6O₁₂ (LLZTO) solid electrolytes to form lithio-phobic species such as Li₂CO₃ on their surface when exposed to trace amounts of H₂O and CO₂ limits the progress of LLZTO-based solid-state batteries. Various treatments, such as annealing LLZTO within a glovebox or acid etching, aim at removing the surface contaminants, but a comprehensive understanding of the evolving LLZTO surface chemistry during and after these treatments is lacking. Here, glovebox-like H₂O and CO₂ conditions were recreated in a near ambient pressure X-ray photoelectron spectroscopy chamber to analyze the LLZTO surface under realistic conditions. We find that annealing LLZTO at 600 °C in this atmosphere effectively removes the surface contaminants, but a significant level of contamination reappears upon cooling down. In contrast, HCl_(aq) acid etching demonstrates superior Li₂CO₃ removal and stable surface chemistry post treatment. To avoid air exposure during the acid treatment, an anhydrous HCl solution in diethyl ether was used directly within the glovebox. This novel acid etching strategy delivers the lowest lithium/LLZTO interfacial resistance and the highest critical current density.