An ethyl bromofluoroacetate redox mediator enables a robust LiF-rich solid electrolyte interphase for advanced lithium–oxygen batteries

Abstract

The high charging overpotential and poor stability of the lithium anode severely restrict the development of non-aqueous Li–O₂ batteries. Herein, to overcome both intractable challenges, ethyl bromofluoroacetate (EBFA) is introduced into Li–O₂ batteries as an innovative bifunctional redox mediator (RM). Through a particular electrochemical pretreatment method in an argon-filled atmosphere, EBFA reacts on the surface of the lithium anode, leading to the dissociation of Br⁻ and F⁻ from EBFA molecules. The generated Br⁻ acts as the effective component of the RM, considerably reducing the charging overpotential of the Li–O₂ battery. At the same time, a robust LiF-rich solid electrolyte interphase (SEI) is in situ formed on the surface of the lithium anode. The formed SEI film, with high lithium-ion conductivity and outstanding stability, significantly protects the lithium anode from the growth of lithium dendrites. Hence, the addition of EBFA in a TEGDME-based non-aqueous electrolyte solution enables a stable Li–O₂ coin battery operation up to 265 cycles.