Lithium metal batteries with in situ copolymerized fluorinated polyether electrolytes

Abstract

Ether electrolytes are an important component of lithium metal batteries. However, the safety hazards from liquid solvent leakage and combustion, as well as the relatively narrow electrochemical stabilization window, are challenges for ether electrolytes. Although polyether electrolytes avoid the risk of leakage, they have a low room temperature ionic conductivity. Herein, a series of fluorinated gel polyether electrolytes were prepared via the in situ copolymerization of the monomer 3-(2,2,3,3-tetrafluoropropoxy)-1,2-propylene oxide (TFPO) and 1,3-dioxolane (DOL) in different volume mixtures initiated by tris(pentafluorophenyl)borane (TB). Among them, the fluorinated copolyether electrolyte 0.03TB-TFPO/9DOL (TB concentration of 0.03 M, TFPO/DOL volume ratio of 1/9) demonstrated excellent overall performance with high oxidative stability (>4.5 V) and ionic conductivity (1.7 × 10⁻³ S cm⁻¹ at 25 °C). The electrolyte was compatible with lithium metal and its cycling stability was significantly improved in Li–LiFeO₄ batteries. Moreover, this non-flammable and non-leakage fluorinated copolyether electrolyte provides an important guarantee for the safety of lithium metal batteries.