In search of widening the electrochemical window of solid electrolytes for Li-batteries: the La0.29Li0.12+xM1−xZrxO3 (M = Nb, Ta) perovskite-type systems†

All solid-state batteries (ASSBs) are required to address challenges of the last generation of Li-batteries such as advances in safety performance, energy density and battery life. Progress of Li-ASSBs requires the development of solid electrolytes with high Li-conductivity and wide electrochemical window. The La_(2/3)−xLi_3xTiO₃ (LLTO) oxides present the highest “bulk” Li-conductivity among the electrolytes with perovskite structure but present significant grain boundary effects that decrease the total conductivity and confer poor electrochemical stability. The oxides of the La_(1/3)−xLi_3xNbO₃ system (LLNO) present slightly lower reduction voltages than the LLTO-oxides and similar values of total conductivity. We have studied the La_0.29Li_0.12+xNb_1−xZr_xO₃ (LLNZO) and La_0.29Li_0.12+xTa_1−xZr_xO₃ (LLTaZO) systems with the aim of increasing the Li-conductivity and electrochemical stability of perovskite-based electrolyte oxides. Conductivity values as high as in LLNO are found in the LLNZO system but somewhat lower in the LLTaZO system. However, the electrochemical window of these new solid electrolytes is remarkably wide, in particular in the La_0.29Li_0.17Ta_0.95Zr_0.05O₃ compound, which is stable between 1.35 and 4.8 V vs. Li⁺/Li.