Ion Transport Kinetics and Energy Barrier in Polymer Nanocomposite with Superionic Ceramic Nanorods*

Incorporating superionic ceramic electrolyte fillers into a polymer electrolyte matrix may result in composites with increased ionic conductivity, enhanced electrochemical stability, and favorable device performance. In such a composite electrolyte, the ionic conductivity enhancement mainly originates from two proposed mechanisms: 1) through a fast ion-transport interface layer along the ceramic particle-polymer interface, and 2) through percolated, highly conductive ceramic fillers. It is important to understand the enhancement mechanism, as the electrolyte design principles for these two mechanisms may vary.

In this work, we investigate the ion transport and energy barrier controlling this transport in composites made with a single-ion-conducting (SIC) polymer electrolyte with lithium lanthanum titanate (LLTO) nanorods. We use broadband dielectric spectroscopy (BDS) and pulsed-filed gradient nuclear magnetic resonance (PFG-NMR) to understand the ion transport mechanisms in the composite. The results show that the incorporation of 50 wt% of LLTO nanorod resulted in a two-fold enhancement of the ionic conductivity. The enhancement originates from the interface layer near the LLTO nanorod surface, through enhanced Li ion diffusion and restricted polyanion diffusion. The interfacial zone’s connectivity and thickness are examined. The ion transport energy barrier in the composites is analyzed and quantified as a function of temperature through BDS analysis. Small-angle X-ray scattering (SAXS) is used to investigate the spatial distribution/dispersion/percolation of LLTO in SIC polymer electrolyte matrix. This work sheds light on how to design composite electrolytes to maximize favorable ion transport paths and minimize barriers.