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.  

In this paper*, glovebox-like H₂O and CO₂ conditions were recreated in a near ambient pressure X-ray photoelectron spectroscopy chamber to analyse the LLZTO surface under realistic conditions.  The authors, made up a team from this department, the University of Edinburgh, Diamond Light Source and The Faraday Institution, found that annealing LLZTO at 600^oC in this atmosphere effectively removed the surface contaminants, but a significant level of contamination reappeared on cooling down.  

In contrast, HCl_(aq) acid etching demonstrated 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 delivered the lowest lithium/LLZTO interfacial resistance and the highest critical current density.

*ACS Applied Materials Interfaces: 'Removal and reoccurrence of LLZTO surface contaminants under glovebox conditions'.