Electrochemistry of Magnesium Electrolytes in Ionic Liquids for Secondary Batteries

摘要

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~-), trifluoromethane-sulfonate (TfO~-), and bis(trifluoromethanesulfonyl)imide (Tf2N~-) salts of Mg were investigated. Three ILs were considered: 1-H-butyl-3-methylimidazolium (BMIM)-Tf2N, N-methyl-N-propyrpiperidi-nium (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.