Fluoroethylene carbonate (FEC) has emerged as a critical electrolyte additive in lithium-ion batteries (LIBs), significantly enhancing electrochemical stability and extending cycle life. Recent studies reveal that FEC forms a robust solid-electrolyte interphase (SEI) layer on the anode surface, particularly in silicon-based anodes, which are prone to severe volume expansion. For instance, a 2023 study demonstrated that adding 10 wt% FEC to a conventional electrolyte increased the capacity retention of Si-graphite composite anodes from 62% to 92% after 500 cycles at 1C. The SEI layer formed by FEC is rich in LiF, which exhibits high ionic conductivity and mechanical stability, reducing irreversible capacity loss. Experimental data also show that FEC reduces the SEI thickness by ~30%, from 12 nm to 8.5 nm, minimizing impedance growth.
FEC's role in mitigating cathode degradation has also been extensively investigated. In high-voltage LIBs (>4.5 V), FEC suppresses oxidative decomposition of the electrolyte, preventing transition metal dissolution and cathode surface reconstruction. A 2022 study on LiNi0.8Mn0.1Co0.1O2 (NMC811) cathodes revealed that 5 wt% FEC addition reduced capacity fade from 25% to 8% after 300 cycles at 4.6 V. Furthermore, X-ray photoelectron spectroscopy (XPS) analysis confirmed that FEC-derived species form a protective cathode-electrolyte interphase (CEI), reducing Ni oxidation state changes by ~40%. This stabilization mechanism is critical for achieving energy densities exceeding 300 Wh/kg in next-generation LIBs.
The thermal stability of LIBs is another area where FEC excels. Accelerating rate calorimetry (ARC) tests have shown that FEC-containing electrolytes exhibit higher onset temperatures for thermal runaway, increasing from 180°C to 220°C in graphite/LiCoO2 cells. This improvement is attributed to FEC's ability to scavenge reactive radicals and form thermally stable SEI components. Additionally, differential scanning calorimetry (DSC) measurements indicate that FEC reduces heat generation during SEI decomposition by ~50%, from 450 J/g to 225 J/g, enhancing safety in high-energy-density applications.
Recent advances have also explored FEC's compatibility with emerging battery chemistries, such as lithium-metal and solid-state batteries. In lithium-metal batteries, FEC suppresses dendritic growth by promoting uniform Li deposition, as evidenced by a ~60% reduction in dendrite density observed via scanning electron microscopy (SEM). For solid-state batteries with sulfide electrolytes, FEC improves interfacial contact and reduces interfacial resistance by ~70%, from 500 Ω·cm² to 150 Ω·cm², enabling stable cycling at room temperature.
Despite its benefits, challenges remain in optimizing FEC concentration and understanding its long-term degradation mechanisms. Excessive FEC (>15 wt%) can lead to increased gas evolution and reduced Coulombic efficiency due to excessive polymerization reactions. However, advanced machine learning models are now being employed to predict optimal FEC formulations for specific battery chemistries, paving the way for tailored electrolyte designs.
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