title: Electrochemistry of magnesium electrolytes in ionic liquids for secondary batteries.
abstract: The electrochemistry of Mg salts in room-temperature ionic liquids (ILs) was studied using plating/stripping voltammetry to assess the viability of IL solvents for applications in secondary Mg batteries. Borohydride (BH4(-)), trifluoromethanesulfonate (TfO(-)), and bis(trifluoromethanesulfonyl)imide (Tf2N(-)) salts of Mg were investigated. Three ILs were considered: l-n-butyl-3-methylimidazolium (BMIM)-Tf2N, N-methyl-N-propylpiperidinium (PP13)-Tf2N, and N,N-diethyl-N-methyl(2-methoxyethyl)ammonium (DEME(+)) tetrafluoroborate (BF4(-)). Salts and ILs were combined to produce binary solutions in which the anions were structurally similar or identical, if possible. Contrary to some prior reports, no salt/IL combination appeared to facilitate reversible Mg plating. In solutions containing BMIM(+), oxidative activity near 0.8 V vs Mg/Mg(2+) is likely associated with the BMIM cation, rather than Mg stripping. The absence of voltammetric signatures of Mg plating from ILs with Tf2N(-) and BF4(-) suggests that strong Mg/anion Coulombic attraction inhibits electrodeposition. Cosolvent additions to Mg(Tf2N)2/PP13-Tf2N were explored but did not result in enhanced plating/stripping activity. The results highlight the need for IL solvents or cosolvent systems that promote Mg(2+) dissociation.
authors.affiliation: Materials Science and Engineering Department, and ‡Chemical Engineering Department, University of Michigan , 2300 Hayward Street, Ann Arbor, Michigan 48109, United States.
authors.forename: Gulin
authors.initials: G
authors.lastname: Vardar
authors.forename: Alice E S
authors.initials: AE
authors.lastname: Sleightholme
authors.forename: Junichi
authors.initials: J
authors.lastname: Naruse
authors.forename: Hidehiko
authors.initials: H
authors.lastname: Hiramatsu
authors.forename: Donald J
authors.initials: DJ
authors.lastname: Siegel
authors.forename: Charles W
authors.initials: CW
authors.lastname: Monroe
keywords: Mg deposition from ionic-liquid solvents; deposition and dissolution of simple Mg salts; magnesium electrolytes; rechargeable Mg battery