Abstract
<jats:p> Garnet-phase Li <jats:sub>7</jats:sub> La <jats:sub>3</jats:sub> Zr <jats:sub>2</jats:sub> O <jats:sub>12</jats:sub> (LLZO) is a promising solid-state electrolyte in lithium metal batteries but suffers from contaminant formation upon exposure to ambient conditions. We use a suite of analytical methods to quantify this contamination and the resulting protonation of LLZO’s crystal structure, and their removal via heat treatment under argon. We quantify contaminant removal in 3 unique temperature regimes, one where LiOH is removed at lower temperatures (<350 <jats:sup>o</jats:sup> C) and two where Li <jats:sub>2</jats:sub> CO <jats:sub>3</jats:sub> is removed at intermediate (350-550 <jats:sup>o</jats:sup> C) and high (>550 <jats:sup>o</jats:sup> C) temperatures. Removal of LiOH and Li <jats:sub>2</jats:sub> CO <jats:sub>3</jats:sub> in the intermediate regime proceeds through a mechanism involving beneficial H <jats:sup>+</jats:sup> /Li <jats:sup>+</jats:sup> exchange with the LLZO lattice, whereas high temperature Li <jats:sub>2</jats:sub> CO <jats:sub>3</jats:sub> removal proceeds through the thermal decomposition mechanism of Li <jats:sub>2</jats:sub> CO <jats:sub>3</jats:sub> to evolve CO <jats:sub>2</jats:sub> and deposit solid Li <jats:sub>2</jats:sub> O. Through these quantification methods, we show that most, but not all, contaminants are removed upon heating to 800 ˚C, with 97% of the Li <jats:sub>2</jats:sub> CO <jats:sub>3</jats:sub> and 85% of the LiOH present in the as-given materials being removed. We show that heat treatment in a stagnant atmosphere is less effective than treatment under active gas flow. Relithiation of the LLZO lattice is also found to improve Li <jats:sup>+</jats:sup> transport across the LLZO particle interface when immersed in a Li <jats:sup>+</jats:sup> -bearing organic electrolyte, and the protonation of LLZO contributes more to slowing interfacial Li <jats:sup>+</jats:sup> transport than the presence of interfacial contaminants. </jats:p>