Self-Assembled Molecular Interfaces in Batteries: From Surface Passivation to Programmable Interphase Engineering.

As secondary batteries pursue higher energy density, faster charging, improved safety, and longer lifetime, electrode/electrolyte interfaces govern transport, reaction pathways, and failure. Self-assembled monolayers offer molecular-scale thickness, negligible mass penalty, and programmable chemistry for controlling these interfaces. This Perspective classifies their functions into four mechanisms. Interfacial energy regulation improves wetting, dispersion, and adhesion. Interfacial passivation limits exposure to reactive species. Microenvironment regulation controls electric fields, ion distributions, and solvation structures. Interphase film construction uses molecular layers as precursors for solid electrolyte interphase (SEI)/cathode electrolyte interphase (CEI) formation. Representative applications across battery components and systems illustrate their evolution from passive protection to programmable interphase engineering. Future molecular design, manufacturing compatibility, and application-specific strategies are discussed to guide their development as broadly applicable battery interface platforms.