Evaluation Of Electrochemical Stability And Li-Ion Interactions In Ether Functionalized Pyrrolidinium And Phospholanium Ionic Liquids

Potential electrolytes for lithium ion batteries (LIB) depicting high electrochemical stability and ionic conductivity still represents a great challenge. Herein, we investigate the reduction stability and Li+ cation interactions with substituted cyclic phospholanium (CylP(5)(+)) and pyrrolidinium (Pyr(+)) ionic liquids (ILs) with bis(trifluoromethanesulfonyl)imide (TFSI-) anion. The cations CylP(5)(+) and Pyr(+) are functionalized with varying chain lengths of alkyl and alkoxy substituents and their reduction potentials evaluated with respect to Li+/Li. CylP(5)(+) cations, in general have better stability than Pyr(+) based ILs, while the alkoxy substitution is found to lower the reduction stability compared to alkyl substituents in both ILs. Furthermore, the interaction energies between the substituent modified-cations (C), Li+ cation and the anion (A) were evaluated. The ion-pair (C-A) interaction energies on addition of Li+ cation is shown to decrease for both Pyr(+) and CylP(5)(+) cations with shorter alkoxy chain lengths, thereby implying faster diffusion of ions due to weaker interactions. Similarly, among the two cations, lowest Delta E were noted between alkoxy substituted [Li(CylP(5))](2+) cation and TFSI-, signifying faster diffusion of ions in CylP(5)(+) based electrolytes than that of Pyr(+) based ILs. These results govern the synthesis of novel ILs with promising base cation and functionalization for LIB. (c) 2020 The Electrochemical Society ("ECS"). Published on behalf of ECS by IOP Publishing Limited. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.