Advanced Energy Materials

It has been widely assumed that the flammability of the liquid electrolyte is one of the most influential factors that determine the safety of lithium-ion batteries (LIBs). Following this consideration, a completely nonflammable electrolyte is designed and adopted for graphite||LiFePO4 (Gr||LFP) batteries. Contrary to the conventional understanding, the completely nonflammable electrolyte with phosphorus-containing solvents exhibits inferior safety performance in commercial Gr||LFP batteries, in comparison to the flammable conventional LiPF6-organocarbonate electrolyte. Mechanistic studies identify the exothermic reactions between the electrolyte (especially the salt LiFSI) and the charged electrodes as the "culprit" behind this counterintuitive phenomenon. The discovery emphasizes the importance of reducing the electrolyte reactivity when designing safe electrolytes, as well as the necessity of evaluating safety performance of electrolytes on a battery level. Laboratory Directed Research and Development (LDRD) Program of Pacific Northwest National Laboratory (PNNL); Vehicle Technologies Office of the U.S. Department of Energy (DOE) under the Advanced Cathode Materials Program [DE-LC-000L053]; Washington State Department of Commerce's Clean Energy Fund; DOE's Office of Biological and Environmental Research and located at PNNL; DOE [DE-AC05-76RL01830]; Science Undergraduate Laboratory Internships (SULI) Program under DOE's Office of Science Published version H.J. and Z.Y. contributed equally to this work. This work was supported by the Laboratory Directed Research and Development (LDRD) Program of Pacific Northwest National Laboratory (PNNL). The TEM characterization was supported by the Vehicle Technologies Office of the U.S. Department of Energy (DOE) under the Advanced Cathode Materials Program (Award No. DE-LC-000L053). The XPS measurement was supported under a partial grant from the Washington State Department of Commerce's Clean Energy Fund. The microscopic and spectroscopic characterizations were conducted in the William R. Wiley Environmental Molecular Sciences Laboratory (EMSL), a national scientific user facility sponsored by DOE's Office of Biological and Environmental Research and located at PNNL. PNNL is operated by Battelle for the DOE under Contract No. DE-AC05-76RL01830. The electrode sheets were kindly provided by Dr. Bryant Polzin of Cell Analysis, Modeling, and Prototyping (CAMP) facility of ANL. The LiFSI salt was kindly supplied by Dr. Kazuhiko Murata and Dr. Kazuhisa Hirata of Nippon Shokubai Co., Ltd. Benjamin Broekhuis acknowledged the support by the Science Undergraduate Laboratory Internships (SULI) Program under DOE's Office of Science.