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.

Abstract Conventional lithium (Li) ion batteries (LIBs) are approaching the limit imposed by their theoretical energy density, and they urgently require advanced strategies to transcend this boundary. Li‐ion/Li metal hybrid systems, which leverage reversible Li metal deposition within void spaces in the anode during charging, offer a significant leap forward for capacity enhancement without the need for complex structural modifications. However, the uncontrolled growth of Li dendrites at the electrode surfaces remains a critical barrier to practical adoption. Here, a protection strategy based on a lithio‐amphiphilic bilayer for graphite (Gr) anodes is proposed, engineered via the sequential deposition of silver (Ag) and chromium (Cr) thin films. The lithiophilic Ag layer functions as a nucleation template for homogenized Li plating across the electrode surface, whereas the lithiophobic Cr layer forms a robust barrier to suppress dendrite propagation. This Gr‐AgCr architecture enabled stable cycling at an ultralow negative‐to‐positive electrode capacity ratio (N/P ratio) of 0.4 and an electrolyte‐to‐capacity ratio (E/C ratio) of 1.1 g Ah −1 , achieving a 49% increase in energy density compared to conventional LIBs. This design provides a scalable pathway toward high‐energy‐density hybrid battery systems within existing LIB manufacturing frameworks, bridging the gap between Li metal and conventional intercalation chemistries.