An unique lithium salt for the improved electrolyte of Li-ion battery

Abstract

Lithium oxalyldifluoroborate (LiODFB) is first reported as the salt for improved electrolyte of Li-ion battery. This salt was found to have the combined advantages of lithium bis(oxalato)borate (LiBOB) and LiBF 4 due to its chemical structure comprising the half molecular moieties of LiBOB and LiBF 4. Compared with LiBOB, the salt is more soluble in linear carbonates and the resulting solution is less viscous, which results in the battery better low temperature and high rate performance. Unlike LiBF 4, the salt is highly capable of stabilizing solid electrolyte interface (SEI) on the surface of graphite anode, which enables Li-ion cell to be operated stably at high temperature. For example, a graphite/LiNi 1− x− y M x N y O 2 (M and N are metal atoms) Li-ion cell suffered only about 10% capacity loss after 200 cycles at 60 °C. On the other hand, graphite can be cycled reversibly with LiODFB even in a solution containing high concentration (50 wt%) of propylene carbonate (PC), which makes it possible to formulate the low freezing temperature electrolyte by using PC as the co-solvent. Other merits of the LiODFB-based electrolytes include (1) the ability to support metallic lithium cycling reversibly on the surface of copper anode current collector, (2) the ability to passivate aluminum cathode current collector at high potentials, (3) the ability to participate in formation of the SEI and support Li-ion battery operating stably at high temperatures, and (4) the ability to increase battery safety protection and overcharge tolerance.