Lithium Oxalyldifluoroborate as a Salt for the Improved Electrolytes of Li-Ion Batteries

Abstract

This paper introduces lithium oxalyldifluoroborate (LiODFB) as a salt and an additive, respectively, for the improved electrolytes of Li-ion batteries. Due to its unique chemical structure consisting of the same molecular species of lithium bis(oxalato)borate (LiBOB) and lithium tetrafluoroborate (LiBF4), LiODFB has the combined advantages of LiBOB and LiBF4 salts. Compared with LiBOB, LiODFB has higher solubility in alkyl carbonate solvents and is able to provide the battery with much better rate capability and low temperature cycling performance. Compared with LiBF4, LiODFB is more powerful in facilitating the formation of solid electrolyte interface (SEI) on the surface of graphite anode and is able to offer better high temperature cycleability. It is shown that the Li-ion bat- tery with LiODFB electrolyte can be stably and safely operated in a wide temperature range. Meanwhile, LiODFB can be served as an electrolyte additive to stabilize the SEI. Other unique properties of the LiODFB electrolytes include: (1) the optimized ionic con-ductivity over a wide temperature range, (2) the ability to support reversible cycling of metallic Li on copper anode current collector, and (3) the ability to passivate aluminum cathode current collector.