Enhanced Conductivity <i>via</i> Homopolymer-Rich Pathways in Block Polymer Composite Electrolytes

The BP electrolyte polystyrene-block-poly(oligo-oxyethylene methacrylate) [PS-b-POEM] was blended with POEM homopolymers of varying molecular weights to explore the impact of polymer additives on ion conductivity. The incorporation of a higher molecular weight homopolymer additive promoted a ‘dry brush-like’ homopolymer distribution within the BP self-assembly and led to higher lithium salt concentrations in the more mobile homopolymer-rich region, increasing overall ionic conductivity relative to the ‘wet brush-like’ and unblended composites. Furthermore, using ⁷Li solid-state nuclear magnetic resonance spectroscopy, we found a temperature corresponding to a transition in lithium mobility (T_{Li mobility}) that was a function of blend-type. T_{Li mobility} was found to be 39 °C above T_g in all cases. Interestingly, the ionic conductivity of the blended BPs was highest in the ‘dry brush-like’ composites even though these composites had higher T_gs than the ‘wet brush-like’ composites, suggesting that homopolymer-rich conducting pathways formed in the ‘dry brush-like’ assemblies had a larger influence on conductivity than the greater lithium ion mobility in the ‘wet brush-like’ blends.