Revealing the Ion Dynamics in Li10GeP2S12 by Quasi-Elastic Neutron Scattering Measurements

초록

Understanding Li-ion conduction in superionic conductors accelerates the development of new solid electrolytes to enhance the charge–discharge performances of all-solid-state batteries. We performed a quasi-elastic neutron scattering study on a model superionic conductor (Li10+xGe1+xP2–xS12, LGPS), to reveal its ion dynamics on an angstrom-scale spatial range and a pico-to-nanosecond temporal range. The observation of spectra at 298 K confirmed the high lithium diffusivity. The obtained diffusion coefficient was in the order of 10–6 cm2 s–1 at temperatures >338 K and was higher than the reported diffusion coefficient over a longer time scale, as determined by the pulse-field gradient nuclear magnetic resonance method. This difference indicates that there are impediments to ionic motion over a longer time scale. The dynamic behavior of the Li ions was compared with that observed for the Li9P3S9O3 phase, which possesses the same crystal structure type, but a lower ionic conductivity. The LGPS phase possessed a high lithium mobility over a distance of ∼10 Å, as well as a larger fraction of mobile Li ions, thereby indicating that these features enhance lithium conduction over a longer spatial scale, which is important in all-solid-state batteries.