Abstract
Ion transport behaviour of halogen-free hybrid electrolytes for lithium-ion batteries based on phosphonium bis(salicylato)borate [P4,4,4,8][BScB] ionic liquid mixed with diethylene glycol dibutyl ether (DEGDBE) is investigated. The Li[BScB] salt is dissolved at different concentrations in the range from 0.15 mol kg−1 to 1.0 mol kg−1 in a mixture of [P4,4,4,8][BScB] and DEGDBE in 1:5 molar ratio. The ion transport properties of the resulting electrolytes are investigated using viscosity, electrical impedance spectroscopy and pulsed-Field Gradient (PFG) NMR. The apparent transfer numbers of ions are calculated from the diffusion coefficients measured by using PFG NMR. PFG NMR data suggested ion association upon addition of Li salt to the [P4,4,4,8][BScB] in DEGDBE solution. This is further confirmed by liquid state 7Li and 11B NMR, and FTIR spectroscopic techniques, which suggest strong interactions between the lithium cation and oxygen atoms of the [BScB]− anion in the hybrid electrolytes.
Highlights
Extensive research efforts are being made to identify electrolytes that can perfectly meet the requirements of lithium-ion batteries
The ion transport behaviour of halogen-free hybrid electrolytes based on [P4,4,4,8][BScB] Ionic liquids (ILs) mixed with diethylene glycol dibutyl ether (DEGDBE) in a 1:5 molar ratio was thoroughly investigated
An increase in the ionic conductivity is observed with increase in temperature and a decrease is found with the addition of Li[BScB] salt to the mixture [P4,4,4,8][BScB] and DEGDBE
Summary
Ion transport behaviour of halogen-free hybrid electrolytes for lithium-ion batteries based on phosphonium bis(salicylato)borate [P4,4,4,8][BScB] ionic liquid mixed with diethylene glycol dibutyl ether (DEGDBE) is investigated. An appropriate organic solvent is critically important for the dissolution of lithium orthoborate salt and for oxidative stability, thermally stability, satisfactory conductivity, cell performance and life cycle[28].Ether based organic solvents ( known as glymes) are gaining attentions in lithium ion batteries due to a number of advantages such as low viscosity, high thermal stability and safety[29,30]. A number of studies have demonstrated that mixtures of ionic liquids and glymes possess excellent electrolyte properties and are promising solvents for lithium-ion batteries[31,32,33,34,35]. The physical and transport properties are investigated using ionic conductivity, viscosity, thermal analysis, multinuclear 13C,31P, 11B and 7Li NMR spectroscopy, FTIR spectroscopy and NMR diffusometry
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