Establishing the Field-Flow Competition Model to Decipher the Nonmonotonic Interfacial Li + Dynamic Process for Stabilizing the High-Voltage Cathode–Electrolyte Interface

Deciphering the evolution of the interfacial solvation structure represents a critical frontier in unlocking high-performance lithium-ion batteries. While the solvation chemistry of bulk electrolytes has been extensively characterized, the dynamic behavior of interfacial species under electric and concentration fields, as well as its governing role in cathode-electrolyte interphase (CEI) formation, remains elusive. Here, we employ in situ electrochemical spectroscopy to uncover a multistage nonmonotonic evolution of the interfacial Li⁺ population, which exhibits an "enrichment-depletion-re-enrichment" trend. We introduce a field-flow competitive regulation model wherein the interfacial electric field drives Li⁺ migration away from the interface, while the delithiation-induced Li⁺ inflow replenishes the interfacial concentration. This mechanistic framework correlates interfacial solvation configurations with operational parameters (field strength, current density, solvent polarity) and ultimately dictates CEI composition through a phase-controlled solvation stage. Leveraging these insights, we developed a potential-modulated activation protocol to bypass the deleterious Li⁺/anion-depletion phase, enabling the construction of a mechanically robust CEI. This approach significantly enhances the cycling stability of high-voltage cathodes. By uncovering the principles of dynamic interfacial solvation engineering, this work provides a foundation for the rational design of electrode/electrolyte interfaces in advanced energy storage systems.