Contiguous High-Mobility Interphase Surrounding Nano-Precipitates in Polymer Matrix Solid Electrolyte.

We establish that an interfacial region develops around amorphous Li1.3Al0.3Ti1.7(PO4)3 (LATP) nanoparticles in a poly(ethylene oxide) (PEO), which exhibits a 30 times higher Li+ mobility than the polymer matrix. To take advantage of this gain throughout the material, nanoparticles must be uniformly dispersed across the matrix, so that the interphase formation is minimally blocked by LATP particle agglomeration. This is achieved using a water-based in situ precipitation method, carefully controlling the temperature schedule during processing. A maximum conductivity of 3.80 × 10-4 S cm-1 at 20 °C for an ethylene oxide to Li ratio of 10 is observed at 25 wt % (12.5 vol %) particle loading, as predicted by our tri-phase model. Comparative infrared spectroscopy reveals softening and broadening of the C-O-C stretching modes, reflecting increased disorder in the polymer backbone that is consistent with opening passageways for cation migration. A transition state theory-based approach for analyzing the temperature dependence of the ionic conductivity reveals that thermally activated processes within the interphase benefit more from higher activation entropy than from the decrease in activation enthalpy. The lithium infusion from LATP particles is small, and the charge carriers tend to concentrate in a space-charge configuration near the particle/polymer interface.