Impact of Negative Charge Delocalization on the Properties of Solid Polymer Electrolytes

The nature of salt anion is of particular relevance in determining the features of solid polymer electrolytes (SPEs). Here, lithium salt containing an extremely delocalized anion (Li[CF3SO(=NSO2CF3)(2)], LisTFSI) is introduced into SPEs utilizing poly(ethylene oxide) (PEO) as a matrix, aiming to elucidate the role of negative charge delocalization on the properties of SPEs. In comparison with the reference Li[N(SO2CF3)(2)] (LiTFSI)/PEO electrolyte, LisTFSI/PEO shows higher lithium-ion transference number and lithium-ion-only conductivity (i. e., the ionic conductivity contributed only by the lithium ions), owing to the improved flexibility and super-delocalized negative charge of the -SO2N(-)-SO(=NSO2CF3)- structure in sTFSI(-) (vs. TFSI-). Moreover, the interphases of lithium metal electrode|SPE formed in LisTFSI/PEO show superior stability upon storage. These interesting properties of the LisTFSI/PEO system suggest that extending negative charge delocalization in sulfonimide anions is a powerful tool to improve the properties of SPEs.

Automated summary

The study explores the impact of introducing anion with extremely delocalized negative charge into solid polymer electrolytes, and finds that the Li[CF3SO(=NSO2CF3)2] (LisTFSI)/PEO system exhibits superior properties in terms of lithium-ion transference number, lithium-ion-only conductivity, and stability at the lithium metal electrode|SPE interface. This suggests that extending negative charge delocalization in sulfonimide anions is an effective strategy to improve the performance of SPEs.