Flame-retardant electrolytes with electrochemically-inert and weakly coordinating dichloroalkane diluents for practical lithium metal batteries.

The next-generation of lithium metal batteries urgently require electrolytes that simultaneously possess low-cost, high-safety, wide-temperature operating range, high electrochemical stability and good electrode-electrolyte interphases formation ability. Here we present a flame-retardant electrolyte by introducing electrochemically-inert and weakly coordinating dichloroalkane diluents in triethyl phosphate-based high-concentration electrolyte. We systematically investigate the effects of dichloroalkane diluents with diverse carbon chain lengths on the Li+ solvation structure, redox behavior, and lithium metal interfacial chemistry in the electrolyte. Consequently, 1,3-dichloropropane, which shows the favorable electrochemical inertness, weakly coordinating ability and wide liquid temperature range (-99 to +120 °C), is chosen as an ideal diluent in electrolyte to form robust anions-derived inorganic-rich electrode-electrolyte interphases on electrodes and improve the Li+ transport/de-solvation capability. The developed electrolyte exhibits significant improvement in safety, cycling stability, rate capability and wide temperature operation capability of high-voltage lithium metal batteries. Particularly, the practical Li (50 μm)||LiNi0.83Co0.12Mn0.05O2 (NCM83, 5.6 mAh cm-2) pouch cells exhibit stable cycling performance over 100 cycles with a high capacity retention rate of 94.1% at 0.1 C charge/0.2 C discharge under 25 °C, and deliver a promising application potential within a broad temperature range of -60 to +60 °C.