Sparingly Soluble Nitrate as an Interfacial Chemistry Director for Constructing Mechanically Compliant Interphases in High‐Energy SiC/NCM811 Batteries

ABSTRACT The development of high‐energy‐density lithium‐ion batteries coupling silicon‐carbon (SiC) anodes with high‐nickel cathodes is hindered by interfacial mechanical and chemical instability. Herein, we report an interfacial regulation strategy that employs sparingly soluble lithium nitrate as an interfacial chemistry director in a carbonate/carboxylate‐based electrolyte. Unlike conventional sacrificial additives that merely decompose, the strongly coordinating NO 3 ‒ anion associates with Li + and redirects the interfacial decomposition pathway from deep anion defluorination toward moderate organic polymerization. This interfacial regulation yields an organic‐rich composite solid electrolyte interphase (SEI), wherein flexible polymeric domains confer viscoelastic compliance to accommodate volume fluctuations, and dispersed inorganic grains provide mechanical rigidity. This SEI is thinner, smoother, and more mechanically uniform than that formed in the LiNO 3 ‐free baseline electrolyte. Simultaneously, a robust cathode electrolyte interphase enriched with Li 2 CO 3 /Li 2 O effectively suppresses transition‐metal dissolution and electrolyte oxidation. Electrolyte change experiments demonstrate that the enhanced cyclability originates from the interfacial rather than bulk electrolyte. The resulting SiC/NCM811 full‐cells deliver exceptional capacity retention of 90.27% after 500 cycles in pouch‐cell configuration and reliable operation from ‒40°C to 45°C. This work challenges the prevailing LiF‐centric interphase design paradigm and underscores the pivotal role of balanced organic‐inorganic architectures in enabling durable high‐energy batteries.