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Abstract
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 (3.16x10-5 S cm-1) at polymer-in-salt concentration (100 mol%) compared to those with lithium bis(fluorosulfonyl)imide (LiFSI, 1.01x10-5 S cm-1) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI, 1.72x10-7 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 behaviour 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 Li2>SCN
Supplementary materials
Title
Enhanced Charge Transport Through Ion Networks in Highly Concentrated LiSCN-polyethylene Carbonate Solid Polymer Electrolytes
Description
Supporting Information contains experimental methods, dielectric relaxation spectroscopic analysis details, molecular dynamics simulation methodology, analyses protocols of simulated ion translation characteristics, ion diffusion coefficients and binding energy calculations in LiFSI-PEC and LiTFSI-PEC SPEs, activation energy determination, molar ionic conductivity calculation, simulated monomer MSD and relaxation kinetics around O-C-C-O dihedral of a polymer chain, CN number calculation protocols, C≡N stretch band analysis in organic carbonate solutions of LiSCN, protocols of SCN- vibrational spectra simulation, pump-probe IR results, Supporting Tables 1 to 9 and Supporting Scheme for chemical structure of LiSCN, PEC and monomer, Supporting Figures 1 to 18, additional references.
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