AUTHOR=Kim Yunsung , Yoo Aeri , Schmidt Robert , Sharafi Asma , Lee Heechul , Wolfenstine Jeff , Sakamoto Jeff 

TITLE=Electrochemical Stability of Li6.5La3Zr1.5M0.5O12 (M = Nb or Ta) against Metallic Lithium

JOURNAL=Frontiers in Energy Research

VOLUME=Volume 4 - 2016

YEAR=2016

URL=https://www.frontiersin.org/journals/energy-research/articles/10.3389/fenrg.2016.00020

DOI=10.3389/fenrg.2016.00020

ISSN=2296-598X

ABSTRACT=The electrochemical stability of Li6.5La3Zr1.5Nb0.5O12 (LLZNO) and Li6.5La3Zr1.5Ta0.5O12 (LLZTO) against metallic Li was studied using direct current (DC) and electrochemical impedance spectroscopy (EIS).  Dense polycrystalline LLZNO (ρ=97 %) and LLZTO (ρ=92 %) were made using sol-gel synthesis and rapid induction hot-pressing at 1100 °C and 15.8 MPa.  During DC cycling tests at room temperature (±0.01 mA/cm2 for 36 cycles), LLZNO exhibited an increase in Li-LLZNO interface resistance and eventually short-circuiting while the LLZTO was stable.  After DC cycling, LLZNO appeared severely discolored while the LLZTO did not change in appearance.  We believe the increase in Li-LLZNO interfacial resistance and discoloration are due to reduction of Nb5+ to Nb4+.  The negligible change in interfacial resistance and no color change in LLZTO suggest that Ta5+ may be more stable against reduction than Nb5+ in cubic garnet versus Li during cycling.