A cyclic phosphate-based battery electrolyte for high voltage and safe operation

The traditional electrolyte for lithium-ion batteries is a combination of 1 M LiPF6 with a cyclic carbonate-based solvent (for example, ethylene carbonate). The lack of a suitable alternative solvent has hindered further exploration of new functional electrolytes. Here we design and synthesize a fluorinated cyclic phosphate solvent, 2-(2,2,2-trifluoroethoxy)-1,3,2-dioxaphospholane 2-oxide (TFEP), for use in lithium-ion batteries. Our design rationale is that this solvent molecule has a fused chemical structure of cyclic carbonates that can form a stable solid electrolyte interphase and organic phosphates that can trap hydrogen radicals and prevent combustion. An electrolyte formula composed of 0.95 M LiN(SO2F)2 in TFEP/2,2,2-trifluoroethyl methyl carbonate shows excellent non-flammability with zero self-extinguishing time and enables the highly stable operation of graphite anodes (~0.1 V versus lithium) and high-voltage LiNi0.5Mn1.5O4 cathodes (~4.7 V versus lithium), and thereby outperforms traditional electrolytes. This work opens up new frontiers in electrolyte developments towards safe lithium-ion batteries with higher energy densities.