title: Two-cation competition in ionic-liquid-modified electrolytes for lithium ion batteries.
abstract: It is a common observation that when ionic liquids are added to electrolytes the performances of lithium ion cells become poor, while the thermal safeties of the electrolytes might be improved. In this study, this behavior is investigated based on the kinetics of ionic diffusion. As a model ionic liquid, we chose butyldimethylimidazolium hexafluorophosphate (BDMIPF(6)). The common solvent was propylene carbonate (PC), and lithium hexafluorophosphate (LiPF(6)) was selected as the lithium conducting salt. Ionic diffusion coefficients are estimated by using a pulsed field gradient NMR technique. From a basic study on the model electrolytes (BDMIPF(6) in PC, LiPF(6) in PC, and BDMIPF(6) + LiPF(6) in PC), it was found that the BDMI(+) from BDMIPF(6) shows larger diffusion coefficients than the Li(+) from LiPF(6). However, the anionic (PF(6)(-)) diffusion coefficients present little difference between the model electrolytes. The higher diffusion coefficient of BDMI(+) than that of Li(+) suggests that the poor C-rate performance of lithium ion cells containing ionic liquids as an electrolyte component can be attributed to the two-cation competition between Li(+) and BDMI(+).
authors.affiliation: Batteries R and D and Corporate R and D, LG Chem, 104-1, Moonji-dong, Yusong-gu, Daejon 305-380, South Korea. syleeq@lgchem.com
authors.forename: Sang-Young
authors.initials: SY
authors.lastname: Lee
authors.forename: Hyun Hang
authors.initials: HH
authors.lastname: Yong
authors.forename: Young Joo
authors.initials: YJ
authors.lastname: Lee
authors.forename: Seok Koo
authors.initials: SK
authors.lastname: Kim
authors.forename: Soonho
authors.initials: S
authors.lastname: Ahn