Phase transition in lithium garnet oxide ionic conductors Li7La3Zr2O12: The role of Ta substitution and H2O/CO2 exposure

• Published in: Journal of power sources Vol. 275; pp. 612 - 620
• Main Authors: Wang, Yuxing, Lai, Wei
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.02.2015
• Subjects: Garnet oxide; Li ion conductor; Phase transition; Proton exchange; Ta substitution; Transport property; Transport property; Li ion conductor; Proton exchange; Garnet oxide; Ta substitution; Phase transition
• ISSN: 0378-7753; 1873-2755
• DOI: 10.1016/j.jpowsour.2014.11.062

High Li-content lithium garnet oxides are promising solid electrolyte materials for lithium batteries. Being the highest Li-content lithium garnet oxides, Li7La3Zr2O12 has been reported to crystallize in either the tetragonal or cubic phase with no consensus on the exact conditions under which these two phases are formed, which may be due to unintentional Al contamination and air exposure. In this work, the effects of Ta substitution and H2O/CO2 exposure have been studied under Al-contamination free conditions with minimal air exposure. We showed that 1) the Ta-substitution induced phase transition occurred through a two-phase mechanism and a minimum 0.6 mol of Ta substitution to Zr is needed to stabilize the cubic phase; 2) H2O and CO2 can individually induce the tetragonal-cubic phase transition in Li7La3Zr2O12 through proton exchange and Li extraction, respectively, which can have great influence on the transport properties of Li7La3Zr2O12. •Measures were taken to eliminate/minimize Al-contamination and air exposure.•In-situ impedance measurement to probe phase transition temperature of LLZ.•A minimum of 0.6 mol of Ta is needed to stabilize the cubic phase LLZ.•H2O interacts with LLZ through a proton exchange mechanism.•CO2 interaction with LLZ worsens the grain boundary conduction.