RESUMO
Acetonitrile (AN) electrolyte solutions display uniquely high ionic conductivities, of which the rationale remains a long-standing puzzle. This research delves into the solution species and ion conduction behavior of 0.1 and 3.0 M LiTFSI AN and propylene carbonate (PC) solutions via Raman and dielectric relaxation spectroscopies. Notably, LiTFSI-AN contains a higher fraction of free solvent uncoordinated to Li ions than LiTFSI-PC, resulting in a lower viscosity of LiTFSI-AN and facilitating a higher level of ion conduction. The abundant free solvent in LiTFSI-AN is attributed to the lower Li-solvation power of AN, but despite this lower Li-solvation power, LiTFSI-AN exhibits a level of salt dissociation comparable to that of LiTFSI-PC, which is found to be enabled by TFSI anions loosely bound to Li ions. This work challenges the conventional notion that high solvating power is a prerequisite for high-conductivity solvents, suggesting an avenue to explore optimal solvents for high-power energy storage devices.
RESUMO
As the applications of lithium-ion batteries (LIBs) have expanded, battery safety has emerged as a major concern because of the thermal runaway of LIBs arising from the use of flammable liquid electrolytes (LEs). Gel polymer electrolytes (GPEs) have been considered as potential candidates to replace LEs and improve the thermal safety of LIBs. In our study, a chemically cross-linked nonflammable GPE was synthesized and used in an LIB. A cross-linking agent, spirocyclic pentaerythritol diphosphate perfluorinated ether acrylate, comprising a phosphorus moiety and a fluoroether chain, was designed and synthesized to prepare a nonflammable cross-linked GPE. The obtained GPE effectively suppressed the deleterious reactions of the LE and imparted nonflammable characteristics. The pouch-type graphite/LiNi0.6Co0.2Mn0.2O2 cell with a nonflammable GPE delivered an initial discharge capacity of 146.7 mAh g-1 with a capacity retention of 71.1% after 300 cycles at 0.5 C and 55 °C. Moreover, the chemically cross-linked GPE exhibited excellent dimensional and thermal stability, which allowed for the safer operation of LIBs even under harsh conditions. This work provides guidelines for designing nonflammable electrolyte systems for advanced LIBs with high safety, enhanced thermal stability, and good cycling characteristics at elevated temperatures.