Behavior of Li defects in solid electrolyte lithium thiophosphate Li7P3S11: A first principles study

We investigate the impact of interstitial Li and Li vacancy on the electronic structure of Li7P3S11 and the mechanism of Li ion migration in Li7P3S11 through first principles calculations. We find that Li7P3S11 is a good insulator with a wide band gap of 3.5 eV. We find that both Li vacancy and interstitial Li+ ion do not introduce states in the band gap hence they do not deteriorate the electronic properties of Li7P3S11. The calculated formation energy of Li vacancy is much larger than that of Li interstitial. The interstitial Li are found to be stable at many sites in Li7P3S11. More importantly, the lowest energy barrier for interstitial Li+ ion diffusion in Li7P3S11 is found to be 0.24 eV. Our calculations suggest that interstitial Li ions play a very important role on the Li7P3S11 ionic conductivity.