Nonflammable organic electrolytes for high-safety lithium-ion batteries

Lithium-ion batteries (LIBs) have been widely applied in electronic devices and electric vehicles. Nevertheless, safety of LIBs still remains a challenge. Conventional LIBs consist of highly flammable liquid electrolytes (LEs). LEs can be ignited under abuse conditions, leading to thermal runaways, fires and explosions of LIBs. It is essential to develop electrolytes with good flame retardance. Incorporating appropriate flame-retardant additives or nonflammable solvents into LEs and gel polymer electrolytes (GPEs) can reduce their flammability, achieving nonflammable LEs and nonflammable GPEs. Nonflammable LEs and nonflammable GPEs can reduce the fire risk of LIBs, significantly enhancing the safety of LIBs. LIBs assembled with optimal nonflammable LEs and nonflammable GPEs even showed better performances than the LIBs assembled with conventional LEs. In this paper, we review nonflammable LEs and nonflammable GPEs for LIBs in terms of flame retardant mechanism, characterization methods of flammability limits, flame-retardant additives, nonflammable solvents, preparation methods, flame retardant properties and electrochemical performances. The challenges and future perspectives of nonflammable LEs and nonflammable GPEs are presented.