Electrochemical Effects of Proton Exchange and Contamination Formation on LLZO Solid Electrolytes

Cubic Lithium Lanthanum Zirconium Oxide (LLZO) and its aliovalently doped counterparts are amongst the most promising solid electrolyte candidates due to their high bulk ionic conductivity and stability with Lithium metal. However, its performance as a solid electrolyte is significantly hindered by detrimental side reactions. LLZO readily undergoes Li+/H+ exchange in the presence of protic solvents such as water. In air, the exchanged Li+ can subsequently undergo surface reactions that result in the formation of lithophobic contaminants such as Lithium carbonate. These surface reactions detrimentally affect the electrochemical performance of LLZO by removing Li+ from the bulk electrolyte and exasperating current constriction phenomena at the Lithium metal interface.<br/><br/>In this work the surface chemistry of LLZO under different treatment conditions is systematically examined and correlated to the interfacial electrochemistry. The impact of surface contaminants and proton exchange on Lithium plating dynamics, bulk ionic conductivity, constriction impedance and charge transfer are discussed.