Neutron Scattering Studies of Lithium-Ion Diffusion in Ternary Phosphate Glasses

Abstract

We have studied the diffusion mechanism of lithium ions in glassy oxide-based solid state electrolytes using elastic and quasielastic neutron scattering. Samples of xLi₂SO₄-(1-x)(Li₂O-P₂O₅) were prepared using conventional melt techniques. Elastic and inelastic scattering measurements were performed using the triple-axis spectrometer (TRIAX) at Missouri University Research Reactor at University of Missouri and High Flux Backscattering Spectrometer (HFBS) at NIST Center for Neutron Research, respectively. These compounds have a base glass compound of P₂O₅ which is modified with Li₂O. Addition of Li₂SO₄ leads to the modification of the structure and to an increase lithium ion (Li⁺) conduction. We find that an increase of Li₂SO₄ in the compounds leads to an increase in the Lorentzian width of the fit for the quasielastic data, which corresponds to an increase in Li⁺ diffusion until an over-saturation point is reached (< 60% Li₂SO₄). We find that the hopping mechanism is best described by the vacancy mediated Chudley-Elliot model. A fundamental understanding of the diffusion process for these glassy compounds can help lead to the development of a highly efficient solid electrolyte and improve the viability of clean energy technologies.