Study of Segmental Dynamics in Polymer-Ceramic Composite Electrolytes using Quasi-elastic Neutron Scattering*

Composite solid electrolytes consisting of a polymer electrolyte and an ion-conducting ceramic electrolyte have potential in achieving high ionic conductivity, high mechanical modulus and good processability to enable higher energy density technologies. In this work we fabricated composite electrolyte consisting of poly(ethylene oxide) (PEO), lithium trifluoromethanesulfonate (LiTf), and a lithium-conducting glass ceramic (LICGC) from Ohara corporation. We discovered that thermal history has a profound impact on the PEO segmental dynamics, resulting in drastically different conductivities below the melting point of PEO in the first heating and cooling cycles. The average relaxation time of PEO chains decreased with the presence of LICGC. However, the enhanced segmental motion contradicts the decrease in the ionic conductivity of the composite electrolyte. The relationship between ionic conductivity, segmental motion, crystallinity and tortuosity in the composite electrolyte will be discussed.