Doping Li₇La₃Zr₂O₁₂ (LLZO)—Implications for Charge Carrier Concentration and Processing

The solid-state Li ion electrolyte Li₇La₃Zr₂O₁₂ (LLZO) is investigated by hybrid density functional theory (DFT) calculations with respect to doping with Al, Ga, Nb, Ta and Y [1]. Point defect models are assessed and the results from hybrid DFT calculations are compared with experimental literature reports. The calculated site preferences of Al, Ga, Nb and Ta imply that they act as donor defects which favour more Li vacancies and thus a more disordered Li substructure. This also contributes to stabilize the more disordered and more conducting cubic LLZO polymorph at the expense of the tetragonal ground state structure. Equilibrium dopant concentrations from DFT are discussed with respect to the important distinction between closed and open synthesis conditions where the nominal stoichiometry of a sample during processing is preserved or not, respectively. Following this, we infer that the effect of dopants on the sintering process can be even more important than inducing more ionic charge carriers.
[1] K. Eggestad, S. M. Selbach, and B. A. D. Williamson, “Doping implications of Li solid state electrolyte Li₇La₃Zr₂O₁₂” J. Mater. Chem. A 12 (2024) 15666.