Fluoroethylene carbonate (FEC), as a key electrolyte component, has been extensively employed across diverse electrolyte systems owing to its excellent compatibility with different anode materials. However, its mechanistic role on the cathode side remains under debate due to the strong electron-withdrawing nature of the fluorine incorporation. Here, we demonstrate that lithium difluoro(oxalate)borate (LiDFOB) can effectively trigger the latent cathode-side functionality of FEC through a rationally designed dual-additive electrolyte. At the LiNi0.9Co0.05Mn0.05O2 cathode, oxidative cleavage of LiDFOB generates BOF2 intermediates that activate FEC and direct its decomposition toward LiF and B-O/B-F-rich inorganic species, constructing a compact and resilient cathode-electrolyte interphase (CEI). Simultaneously, the coupled reduction of FEC and DFOB- at the lithium metal anode yields a boron-rich, LiF-enriched solid electrolyte interphase (SEI) that enhances interfacial compatibility and suppresses dendrite growth. These LiDFOB-enabled, FEC-mediated interfacial pathways significantly improve ion transport and durability, delivering 73.4% capacity retention of Li||NCM9055 full cells after 1000 cycles at 4.7 V, versus 55.1% for the base electrolyte.
Wu et al. (Sat,) studied this question.
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