Enhancements of Interfacial Properties via Organic Sulfonyl Fluoride Electrolyte Additives for High-Nickel Lithium...

High-nickel lithium nickel cobalt manganese oxide (NCM) cathodes suffer interfacial instability that impairs initial efficiency and long-term cycling. To overcome those problems, we evaluate a series of five sulfonyl fluoride (-SO₂F) electrolyte additives-Ethenesulfonyl fluoride (A), 2-(Benzylthio)-2-phenylethane-1-sulfonyl fluoride (B), 2-Chloroethane-1-sulfonyl fluoride (C), Methyl 2-(fluorosulfonyl)acetate (D), Methanesulfonyl fluoride (E) for high-nickel NCM cells. Additives C and E yielded the highest initial Coulombic efficiencies (ICE) (∼90%), markedly higher than other additives. Additives B and E showed higher specific discharge capacity (∼230 mAh/g). X-ray photoelectron spectroscopy (XPS) revealed that the effective additives E form F-rich and S-containing interfacial layers (e.g., LiF and organosulfur species), in contrast to a negligible S signal without additives. These findings demonstrate that -SO₂F functional additives can significantly enhance the initial efficiency and interphase stability of Ni-rich cathodes. The results correlate the molecular structure of additives to their film-forming behavior: proper small alkyl-SO₂F (E) effectively form protective interphases. This study qualitatively evaluated the influence of SO₂F moieties on high-energy lithium battery performance depending on the surrounding materials and provides material-function-performance insights for the design of functional electrolyte additives to enhance battery performance.