Supramolecular “flame-retardant” electrolyte enables safe and stable cycling of lithium-ion batteries

Although energy densities of lithium-ion batteries (LIBs) continue to increase, safety problems such as fires and explosions have significantly hindered their large-scale applications. Conventional wisdom tells us the fire of LIBs largely originated from the flammable liquid carbonate solvents, and thus the research on additives with properties of suppressing “liquid-type fire” is the way to fabricate nonflammable batteries. However, the outcome has been proven to be inferior. Here, we carefully examined the evolution of battery fire under thermal abuse condition and found that the “jet fire” caused by flammable gases inside batteries is critical for the fire hazard, and the research effort should be redirected to search proper additives with “gaseous-type fire” suppressing properties. Unfortunately, conventional “gaseous-type fire suppressant” shows poor compatibility with battery electrolytes. Thus, we rationally designed a new kind of supramolecular electrolyte, where the molecules of “gaseous-type fire suppressant” and “SEI&CEI improver” are self-assembled together by intermolecular interactions. Due to this design, the supramolecular electrolyte produces improved cycling stability of Li metal anode and high voltage LiCoO2 cathode (up to 4.4 V). More importantly, it sharply decreases the self-extinguish time of carbonate-based electrolyte from ∼100 s/g to ∼0 s/g, which is unprecedented and can effectively suppress the “jet fire”, thus preventing the further combustion of commercial pouch cell during thermal runaway. Our work is providing the criteria required to overcome this challenge via supramolecular engineering of the electrolyte, which provides a new way to tune electrolyte functions and may bring numerous new possibilities.