Enhanced Charge Transport through Ion Networks in Highly Concentrated LiSCN-Polyethylene Carbonate Solid Polymer Electrolytes.

Challenging the preference for bulky anions due to low binding energy with Li(+) ion, the lithium thiocyanate-polyethylene carbonate (LiSCN-PEC) solid polymer electrolyte (SPE) demonstrates higher ionic conductivities (3.16 × 10(-5) S cm(-1)) at polymer-in-salt concentration (100 mol%) compared to those with lithium bis(fluorosulfonyl)imide (LiFSI, 1.01 × 10(-5) S cm(-1)) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI, 1.72 × 10(-7) S cm(-1)). Through the careful selection of PEC and LiSCN as components of SPE, the carbonyl stretching of PEC and the SCN(-) stretching band as vibrational reporters provide detailed structural insights into the Li(+) ion transport channel. Spectroscopic investigations reveal that enhanced ion aggregation alters the solvation structure around the Li(+) and diminishes the interaction between Li(+) and polymer (PEC) with increasing LiSCN concentrations, promoting faster segmental motion as a major transport mechanism. However, the transition observed from subionic to superionic behavior in the Walden plot indicates the onset of segmental motion decoupled charge transport pathway. The SCN(-) vibrational spectrum elucidates the evolution from a Li-SCN-Li type chain-like structure to a Li(2) > SCN < Li(2) type extended ion network with increasing LiSCN concentration, revealing that the ion network provides an alternative channel for Li(+) ion transfer at higher concentrations, enhancing conductivity.