Self-healing polymer electrolytes with nitrogen‑boron coordinated boroxine for all-solid-state lithium metal batteries

Abstract

Polymer networks with dynamic covalent cross-linked boroxine have received a great deal of attention as recyclable and self-healing materials, but their application was rarely mentioned in all-solid-state polymer electrolytes. In this work, the boroxine-based self-healing solid polymer electrolytes (ONBSPE-x) with nitrogen‑boron (NB) coordination were prepared by the amidation reaction between different molecular weight NH2-PEG-NH2 and ortho-triphenylboroxine with the plasticization of lithium salt. To highlight the effect of NB coordination on the self-healing ability of the polymer electrolytes, PNBSPE-2000 with para-triphenylboroxine structure was prepared for comparison. It was proved that the ortho-triphenylboroxine is conducive to the formation of NB coordination and the NB coordination can accelerate the equilibrium of boroxine, further speeding the self-healing ability of ONBSPE-x without external stimulation at room temperature. More importantly, given the strong electron-withdrawing effect of boroxines groups, the ONBSPE-2000 membranes show an ionic conductivity value up to 0.168 mS cm−1 and comparatively high lithium-ion transference number (0.60) at 25 °C, which will minimize concentration polarization between electrolytes and lithium metal anode, then inhibiting lithium dendrite generation. The NB coordination and the interaction between boroxine groups and anions in ONBSPE-2000 were further studied with density functional theory (DFT). The Li|ONBSPE-2000|LiFePO4 coin cell performs excellent cycling stability with an initial discharge capacity of 130.9 mAh g−1 at 0.1C and coulombic efficiency of 94.8 %. Thus, the self-healing solid polymer electrolytes with nitrogen‑boron coordinated boroxine provide a prospective application for high-performance lithium metal batteries.