First Principles Study of the Li10GeP2S12 Lithium Super Ionic Conductor Material

In this paper, we investigate the diffusivity, stability, and electrochemical window of the Li10GeP2S12 (LGPS) lithium super ionic conductor using a variety of first principles techniques. LGPS was recently reported by Kamaya et al. as having the highest conductivity ever achieved among solid lithium electrolytes of 12 mS/cm at room temperature and outstanding electrochemical performance in Li batteries. We find that LGPS is a metastable phase in the calculated phase diagram and that LGPS is not stable against reduction by lithium at low voltage or extraction of Li with decomposition at high voltage. Our calculated lithium grand potential phase diagrams suggest that the observed wide electrochemical window of LGPS could be the result of the formation of passivation layers at the electrode-electrolyte that are nonetheless still high conducting and do not impede Li transport. We also identified the diffusion pathways and calculated the corresponding activation energies and diffusion coefficient using ab initio molecular dynamics simulations. Our simulations show that LGPS is in fact a three-dimensional ion conductor rather than a one-dimensional ion conductor. Our calculated overall activation barrier of 0.21 eV and conductivity of 9 mS/cm at room temperature are in remarkable agreement with the experimental results. In this paper, we investigate the diffusivity, stability, and electrochemical window of the Li10GeP2S12 (LGPS) lithium super ionic conductor using a variety of first principles techniques. LGPS was recently reported by Kamaya et al. as having the highest conductivity ever achieved among solid lithium electrolytes of 12 mS/cm at room temperature and outstanding electrochemical performance in Li batteries. We find that LGPS is a metastable phase in the calculated phase diagram and that LGPS is not stable against reduction by lithium at low voltage or extraction of Li with decomposition at high voltage. Our calculated lithium grand potential phase diagrams suggest that the observed wide electrochemical window of LGPS could be the result of the formation of passivation layers at the electrode-electrolyte that are nonetheless still high conducting and do not impede Li transport. We also identified the diffusion pathways and calculated the corresponding activation energies and diffusion coefficient using ab initio molecular dynamics simulations. Our simulations show that LGPS is in fact a three-dimensional ion conductor rather than a one-dimensional ion conductor. Our calculated overall activation barrier of 0.21 eV and conductivity of 9 mS/cm at room temperature are in remarkable agreement with the experimental results.