Rational Electrolyte Design for Elevated-Temperature and Thermally Stable Lithium-Ion Batteries with Nickel-Rich Cathodes

As the energy density of lithium-ion batteries (LIBs) increases, the shortened cycle life and the increased safety hazards of LIBs are drawing increasing concerns. To address such challenges, a series of localized high-concentration electrolytes (LHCEs) based on a solvating-solvent mixture of tetramethylene sulfone and trimethyl phosphate and a high flash-point diluent 1H,1H,5H-octafluoropentyl 1,1,2,2-tetrafluoroethyl ether were designed. The LHCEs exhibited nonflammability and greatly suppressed heat release at elevated temperatures, which would potentially improve the safety performance of the LIBs. Moreover, the optimal LHCE achieved capacity retentions of 87.1% and 81.7% in graphite||LiNi0.8Mn0.1Co0.1O2 cells after 500 cycles at 25 and 45 °C, respectively, which were significantly higher than the conventional electrolyte, whose capacity retentions were only 75.2% and 38.5% under the same conditions. Mechanistic studies revealed that the LHCE not only formed a more robust solid electrolyte interphase but also exhibited improved anodic stability, compared with the conventional electrolyte. This work sheds light on rational electrolyte design for high-energy density LIBs with high battery performance and low safety concerns.