Neutron Scattering Studies of Glassy Solid-State Lithium Ion Based Electrolytes

Abstract

We present neutron diffraction results on superionic materials that are good candidates for use as solid-state electrolytes in next generation Li⁺ ion batteries. Lithium ion conducting glasses of the compositions xLi₂SO₄-(1-x) [0.5Li₂O-0.5(2NH₄H₂PO₂)] ; x=0 and 0.1 were synthesized by conventional melt-quenching. The transparent homogeneous glassy flakes were thus obtained and used for the characterization. The materials are glassy in nature and composed of a complex network of the following sub-units: Li₂O, Li₂SO₄, and 2NH₄H₂PO₂. This disordered structure is integral to its function in that it promotes Li⁺ ion conduction while suppressing electronic conduction, the necessary qualities of a good Li⁺ electrolyte. We used neutron diffraction to study the formation of crystallites upon heating of the material above 400°C. The crystallite formation is understood to be detrimental to the Li⁺ ion mobility and, hence, is identified with a diminished performance in devices that require heating in their fabrication processs. Here, we report the changes in the material, as observed by neutron diffraction, as a function of annealing temperature and temperature history.