Decomposition of Trace Li<sub>2</sub>CO<sub>3</sub> During Charging Leads to Cathode Interface Degradation with the Solid Electrolyte LLZO
Alexander A. Delluva, Jonas Kulberg‐Savercool, Adam Holewinski
Abstract
Abstract A major challenge for lithium‐containing electrochemical systems is the formation of lithium carbonates. Solid‐state electrolytes circumvent the use of organic liquids that can generate these species, but they are still susceptible to Li 2 CO 3 formation from exposure to water vapor and carbon dioxide. It is reported here that trace quantities of Li 2 CO 3 , which are re‐formed following standard mitigation and handling procedures, can decompose at high charging potentials and degrade the electrolyte–cathode interface. Operando electrochemical mass spectrometry (EC–MS) is employed to monitor the outgassing of solid‐state batteries containing the garnet electrolyte Li 7 La 3 Zr 2 O 12 (LLZO) and using appropriate controls CO 2 and O 2 are identified to emanate from the electrolyte–cathode interface at charging potentials > 3.8 V (vs Li/Li + ). The gas evolution is correlated with a large increase in cathode interfacial resistance observed by potential‐resolved impedance spectroscopy. This is the first evidence of electrochemical decomposition of interfacial Li 2 CO 3 in garnet cells and suggests a need to report “time‐to‐assembly” for cell preparation methods.