Doping Implications of Li Solid State Electrolyte Li7La3Zr2O12

Solid-state electrolytes, like Li7La3Zr2O12 (LLZO), can enable safer, more energy dense and longer lasting batteries. However, there are still challenges concerning dendrite formation and poor Li-ion conductivity. Here we investigate the effect of Al, Ga, Nb, Ta, and Y doping of LLZO using hybrid density functional theory calculations. The inferred site preferences of Al, Ga, Nb, and Ta result in donor defects that stabilise additional Li vacancies. More Li vacancies lead to increased disorder on the Li sublattice, thus predicting a stabilisation of the more ionic conducting cubic phase. Furthermore, our calculations indicate that the effect of the dopants on the sintering process is even more important than the ability to induce more ionic charge carriers. Finally, differences in Li vacancy formation energies suggest a new possible explanation for the two orders of magnitude increase in ionic conductivity upon stabilising the cubic phase.