(Invited) Low-Temperature Electrolytes for G/NMC811 Cells

Abstract

We report and validate an electrolyte design strategy based on a group of soft solvents that strikes a balance between weak Li+–solvent interactions, sufficient salt dissociation and desired electrochemistry to fulfill all the aforementioned requirements. Remarkably, the 4.5-volt NMC811||graphite coin cells with areal capacities of more than 2.5 milliampere hours per square centimeter retain 75 percent (54 percent) of their room-temperature capacity when these cells are charged and discharged at −50 degrees Celsius (−60 degrees Celsius) at a C rate of 0.1C, and the NMC811||graphite pouch cells with lean electrolyte (2.5 grams per ampere hour) achieve stable cycling with an average Coulombic efficiency of more than 99.9 percent at −30 degrees Celsius. The comprehensive analysis further reveals an impedance matching between the NMC811 cathode and the graphite anode owing to the formation of similar lithium-fluoride-rich interphases, thus effectively avoiding lithium plating at low temperatures. This electrolyte design principle can be extended to other alkali-metal-ion batteries operating under extreme conditions.