Efficient boron-based electrolytes constructed by anionic and interfacial co-regulation for rechargeable magnesium batteries

Rechargeable magnesium batteries (RMBs) based on two-electron transfer chemistry offer great opportunities for realizing high energy density storage technology. However, the lack of magnesium-compatible electrolytes is still the biggest research and development challenge. Boron-based electrolytes, as a viable solution, have always been plagued by complex synthesis processes and high costs. In this work, an efficient boron-based electrolyte was present by a facile one-step mixed reaction of MgCl2, triphenyl borate [B(OPh)3], and tris(pentafluorophenyl)boron (TPFPB) in tetrahydrofuran (THF). By adjusting the composition and ratio of boron-based salts in the electrolyte, a modified anion structure with lower HOMO states was obtained. Besides, the as-prepared electrolyte also contributes to the formation of MgF2-rich solid electrolyte interphase (SEI) layer, which significantly inhibits the electrolyte decomposition, enhance the cycling stability of Mg anodes. Eventually, the electrolyte exhibits a wide electrochemical window (>3 V vs Mg/Mg2+), low polarization voltage (150 mV) and an average Coulombic efficiency above 98 %. Finally, the successful assembly of the Mg/CuS and Mg/Mo6S8 full batteries confirms the practicability of this electrolyte in RMBs. More importantly, the dual regulation strategy of anions and interfaces offers a novel idea for designing efficient electrolytes in RMBs.