In Situ Assembled Carboxyl‐Functionalized Hexaazatrinaphthylene Enables Accelerated Li + Transport and Localized FEC Enrichment in Silicon Anodes

ABSTRACT Rational interfacial regulation is critical to resolving the structural instability of high‐performance silicon (Si) anodes for lithium‐ion batteries (LIBs). Here, a molecular interphase engineering strategy based on hexaazatrinaphthylene tricarboxylic acid (HATNTA), a carboxyl‐functionalized derivative of hexaazatrinaphthylene (HATN), is proposed to regulate the interfacial chemistry of Si anodes. The π‐conjugated framework provides abundant polar nitrogen sites (C═N) that may facilitate Li + coordination. The carboxyl groups incorporated into HATNTA enable localized fluoroethylene carbonate (FEC) enrichment, thereby steering the interfacial reaction pathway toward the formation of a LiF‐rich solid electrolyte interphase (SEI). The resulting interphase suppresses excessive electrolyte decomposition and mitigates electrode swelling and structural degradation during prolonged cycling. The Si‐HATNTA anode achieves an initial Coulombic efficiency (ICE) of 92.56%. It exhibits a rate capability of 1122 mAh g −1 at 5 A g −1 and maintains 1341 mAh g −1 after 200 cycles at 1.0 A g −1 . The NCM811//Si‐HATNTA full cell retains 70.49% of its initial capacity after 100 cycles at 0.2 C. This work provides a molecular design strategy for stabilizing Si anodes through interfacial chemistry regulation.