Development of Safe Electrolytes for Lithium Ion Batteries

With the pursuit of high energy density of lithium ion batteries (LIBs), the safety of LIBs is raising intensive concerns. The high flammability of the liquid electrolytes used in state-of-the-art LIBs is one critical link of the overall safety property of LIBs. The conventional approach to reduce the flammability of the liquid electrolytes is to introduce a certain amount of a miscible flame retardant (FR) as additive or co-solvent into the LiPF₆/carbonates electrolytes. However, the added FRs, normally organic phosphate compounds, are incompatible with the graphite electrodes, hence they actually induce severe deterioration in battery performance. Meanwhile, the continuous consumption of FR molecules at the electrode/electrolyte interfaces by the parasitic reactions, the flame retarding effectiveness of the FR gradually decreases. In response to these challenges, new safe electrolytes based on the concept of localized high-concentration electrolyte (LHCE) were developed by using common FRs, organic phosphorus-containing solvents. The incompatibility issue between phosphorus-containing solvents and graphite has been successfully resolved by the unique solvation structure of LHCEs and the incorporation of a small amount of electrolyte additives. Ignition tests show that these LHCEs are much less flammable than the conventional LiPF₆/carbonate electrolyte. Moreover, the graphite-based LIBs using such phosphorus-solvent-based LHCEs can achieve long cycle life, similar to or much better than those of conventional LiPF₆/carbonate electrolyte depending on cell chemistries. More details will be reported during the presentation.