Decoupling Li+ Desolvation from Potential-Driven Reduction for Solid Electrolyte Interphase Formation at Battery Anodes

Abstract The solid electrolyte interphase (SEI) critically governs the reversibility and kinetics of lithium-ion batteries, yet its formation has long been viewed as a potential-driven electrolyte reduction process, with the role of Li+ desolvation largely overlooked. Here, we reveal the decisive role of Li+ desolvation in SEI formation by employing tailored electrolyte–electrode pairs. By using a TiNb2O7 anode with a high working potential that substantially suppresses direct solvent reduction, the desolvation-regulated contribution to SEI chemistry becomes experimentally resolvable. Along this solvent-engineered desolvation gradient, faster desolvation suppresses solvent reduction, shifts interfacial decomposition toward anion-derived pathways, and leads to an inorganic-rich SEI. This principle is further validated on graphite anodes, where Li+ desolvation and potential-driven reduction coexist and jointly govern SEI formation. This work establishes a kinetic framework for SEI formation and provides a guideline for interphase design in advanced batteries.