ABSTRACT
Lithium-ion batteries (LIBs) have attracted increasing attention because of their promising applications for the next generation of energy storage devices and hybrid/electric vehicles. 1–4 The commercially available electrolytes used for LIBs are conventionally composed of volatile and flammable organic carbonates, such 198as ethylene carbonate (EC), diethyl carbonate (DEC), and propylene carbonate (PC), and thermally unstable lithium salt such as LiPF6, causing LIBs to carry the risks of leakage and related fire hazards. 5–7 The safety concern posted by these commercial electrolytes has deterred the practical application of LIBs in a large scale. It is for this reason that there is an urgent demand to develop alternative electrolytes that are electrochemical stable, nonflammable, and nonvolatile. Room temperature ionic liquids (RTILs), which are low-temperature molten salts, have recently emerged as a new class of electrolyte due to their wide electrochemical window, nonflammability, and high thermal stability, 8–12 which are the key properties required by stable and safe electrolytes. 13–15 However, the simple replacement of carbonates with ILs in LIBs results in poor cycling performance for LIBs. 16 , 17 Several studies have shown that the liquid electrolytes containing mixtures of IL and carbonate solvent using LiPF6 or lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) as a salt exhibited good physical properties and battery performance at optimized compositions. 14 , 18–23 However, the ratio of the carbonate solvent in the mixtures is still quite high, most of which are above 20 wt%, and there are some issues, including the evaporation of carbonates and electrolyte leakage for this type of liquid electrolytes, 19 , 22 which may cause volatile carbonates to accumulate inside batteries or leak out upon short circuit, overheating, or abuse. One way to circumvent the drawback is to incorporate both RTILs and carbonates into organic or inorganic matrix. 24 , 25
