Lithium salt-regulated dual-stabilized elastomeric quasi-solid electrolyte for high-voltage lithium metal batteries

Elastomeric electrolytes exhibit attractive benefits in lithium-metal batteries due to the accommodation of volume changes during the lithium metal plating and stripping processes. However, their narrow oxidation potential restricts their application in high-energy batteries. Herein, an improved high-voltage elastomeric quasi-solid electrolyte (QSE) was fabricated through in situ polymerization by incorporating lithium difluoro(oxalate)borate (LiDFOB). LiDFOB could preferentially react at the cathode side to form an enhanced LiF-rich cathode electrolyte interphase (CEI) before the decomposition of the bulk electrolyte. Moreover, the crosslinked oligomeric borates (B-O), LiF and B-F-containing solid electrolyte interphase (SEI) possibly guide the formation of a uniform morphology after lithium deposition. Benefitting from the dual-stabilized effect of LiDFOB, the as-designed QSE exhibited a significantly improved electrochemical window of 5.36 V compared with the initial 4.6 V, as revealed by the linear sweep voltammetry (LSV) results. In particular, the Li/LiVPO₄F cell with a high cut-off voltage of 4.7 V displayed a discharge capacity of 121.5 mA h g⁻¹ with a capacity retention of ∼84.03% after 100 cycles. Density functional theory (DFT) calculations further reveal that LiDFOB is critical to fabricating LiF-rich CEI and uniform lithium deposition. The compatible modification strategy employed in this work for the in situ formed elastomeric QSE gives new insights into improving the performance of elastomeric electrolytes.