Decoupled Interface Passivation Enabled by Directional Ion Migration in Lithium-Ion Batteries

Long-term cycleability of lithium-ion batteries is limited by interfacial degradation and irreversible lithium loss from parasitic electrolyte decomposition after solid electrolyte interphase formation. In this study, an ionic molecule with individually functionalized cation and anion components is designed to enable the decoupling of interfacial passivation in graphite/NCM811 cells based on directional ion migration. The additive consists of a cation and anion bearing complementary film-forming functionalities; these two components migrate under electrochemical polarization and selectively decompose at opposite electrodes, leading to the formation of a nitrogen-rich interphase on the negative electrode and a sulfur-containing film on the positive electrode. This enables simultaneous stabilization of both interfaces using a single additive. The resulting decoupled passivation suppresses electrolyte decomposition, salt degradation, and continuous film growth, thereby reducing irreversible lithium consumption and impedance growth. Evaluation of 1.2 A h pouch cells demonstrates improved capacity retention, higher Coulombic efficiency, and suppressed resistance growth over 600 cycles at elevated temperatures for the additive-added cells. This study establishes directional ion migration as a design principle for electrolyte additives and offers a unified strategy for interfacial stabilization in high-energy-density lithium-ion batteries.