FSI-Bound Interfacial Treatment for Fast-Charging Silicon-Based Lithium-Ion Batteries

A lithium fluoride (LiF)-rich solid electrolyte interphase (SEI) in lithium-ion batteries (LIBs) is useful for stabilizing the interface with the silicon (Si) anode, which undergoes large volume changes during cycling. Efforts have focused on increasing the fluorine content of the SEI layer, yet its uniformity has received less attention. Here, we propose an interfacial engineering strategy to promote uniform LiF-rich SEI formation by introducing fluorosulfonylimide (FSI) anions onto the Si surface using a 1,3-diallylimidazolium bis(fluorosulfonyl)imide ionic liquid (DFIL). The DFIL uniformly covers the Si surface and facilitates the in situ formation of a mechanically robust, LiF-rich SEI layer. This SEI improves the fast-charging (3C) performance and extends the calendar life (4 weeks at 60 °C). Full-cell evaluations with LiNi0.8Co0.1Mn0.1O2 cathodes under lean electrolyte (3.0 g Ah–1) and high-voltage (∼4.3 V) conditions demonstrate the practical feasibility of this strategy, highlighting the importance of uniform LiF-rich SEI formation for Si anode-based LIBs.