Electrochemical Window of the Li-Ion Solid Electrolyte Li₇La₃Zr₂O₁₂

The recent discovery of fast ion-conducting solid electrolytes could enable solid-state and other advanced battery chemistries with higher energy densities and enhanced safety. In addition to high ionic conductivity, a viable electrolyte should also exhibit an electrochemical window that is wide enough to suppress undesirable electronic transport (i.e., self-discharge and/or short circuiting) arising from charge injection or extraction from the electrodes. Here, direct current chronoamperometry, alternating current electrochemical impedance spectroscopy, and optical absorption band gap measurements are combined with first-principles calculations to systematically characterize the electrochemical window of the promising superionic conductor Li 7 La 3 Zr 2 O 12 (LLZO). Negligible electronic current was measured within LLZO for a wide range of voltages relevant for high-voltage cathodes. This auspicious behavior is consistent with both the large band gap (∼6 eV) predicted for LLZO and the absolute positions of its band edges. These features imply that a wide electrochemical window is an intrinsic property of LLZO, facilitating its use in next-generation batteries.