title: Ionic liquids and oligomer electrolytes based on the B(CN)4(-) anion; ion association, physical and electrochemical properties.
abstract: The role of B(CN)(4)(-) (Bison) as a component of battery electrolytes is addressed by investigating the ionic conductivity and phase behaviour of ionic liquids (ILs), ion association mechanisms, and the electrochemical stability and cycling properties of LiBison based electrochemical cells. For C(4)mpyrBison and C(2)mimBison ILs, and mixtures thereof, high ionic conductivities (3.4 ≤σ(ion)≤ 18 mS cm(-1)) are measured, which together with the glass transition temperatures (-80 ≤T(g)≤-76 °C) are found to shift systematically for most compositions. Unfortunately, poor solubility of LiBison in these ILs hinders their use as solvents for lithium salts, although good NaBison solubility offers an alternative application in Na(+) conducting electrolytes. The poor IL solubility of LiBison is predicted to be a result of a preferred monodentate ion association, according to first principles modelling, supported by Raman spectroscopy. The solubility is much improved in strongly Li(+) coordinating oligomers, for example polyethylene glycol dimethyl ether (PEGDME), with the practical performance tested in electrochemical cells. The electrolyte is found to be stable in Li/LiFePO(4) coin cells up to 4 V vs. Li and shows promising cycling performance, with a capacity retention of 99% over 22 cycles.
authors.affiliation: Department of Applied Physics, Chalmers University of Technology, SE-412 96 Gothenburg, Sweden. johan.scheers@chalmers.se
authors.forename: Johan
authors.initials: J
authors.lastname: Scheers
authors.forename: Jagath
authors.initials: J
authors.lastname: Pitawala
authors.forename: Frederic
authors.initials: F
authors.lastname: Thebault
authors.forename: Jae-Kwang
authors.initials: JK
authors.lastname: Kim
authors.forename: Jou-Hyeon
authors.initials: JH
authors.lastname: Ahn
authors.forename: Aleksandar
authors.initials: A
authors.lastname: Matic
authors.forename: Patrik
authors.initials: P
authors.lastname: Johansson
authors.forename: Per
authors.initials: P
authors.lastname: Jacobsson
mesh_terms: D000838:Anions / Q000737:chemistry; D001881:Borates / Q000737:chemistry*; D004553:Electric Conductivity; D004563:Electrochemistry; D004573:Electrolytes / Q000737:chemistry; D052578:Ionic Liquids / Q000737:chemistry*; D008094:Lithium / Q000737:chemistry; D012995:Solubility; D013059:Spectrum Analysis, Raman
chemical_list: D000838:Anions; D001881:Borates; D004573:Electrolytes; D052578:Ionic Liquids; D008094:Lithium