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Connection between lithium coordination and lithium diffusion in [Pyr12O1][FTFSI] ionic liquid electrolytes

: Giffin, Guinevere A.; Moretti, Arianna; Jeong, Sangsik; Pilar, Kartik; Brinkkötter, Marc; Greenbaum, Steven G.; Schönhoff, Monika; Passerini, Stefano


ChemSusChem. Chemistry & sustainability, energy & materials 11 (2018), Nr.12, S.1981-1989
ISSN: 1864-5631
ISSN: 1864-564X
Fraunhofer ISC ()
ionische Flüssigkeit; Elektrolyte; flüssige Elektrolyte; lithium

The use of highly concentrated ionic liquid-based electrolytes results in improved rate capability and capacity retention at 20 °C compared to Li+-dilute systems in Li-metal and Li-ion cells. This work explores the connection between the bulk electrolyte properties and the molecular organization to provide insight into the concentration dependence of the Li+ transport mechanisms. Below 30 mol %, the Li+-containing species are primarily smaller complexes (one Li+ cation) and the Li+ ion transport is mostly derived from the vehicular transport. Above 30 mol %, where the viscosity is substantially higher and the conductivity lower, the Li+-containing species are a mix of small and large complexes (one and more than one Li+ cation, respectively). The overall conduction mechanism likely changes to favor structural diffusion through the exchange of anions in the first Li+ solvation shell. The good rate performance is likely directly influenced by the presence of larger Li+ complexes, which promote Li+-ion transport (as opposed to Li+-complex transport) and increase the Li+ availability at the electrode.