SEI chemistry enlightened by liquid Madelung potential analysis and MLFF-MD simulation.

Lithium metal batteries offer exceptionally high energy density but their use is fundamentally limited by the high reactivity of lithium metal, which induces continuous electrolyte decomposition. Stabilisation of the lithium metal surface therefore relies on the formation of a solid electrolyte interphase (SEI) that electronically passivates the interface while maintaining ionic transport; yet how electrolyte composition governs SEI formation remains incompletely understood. Here, we investigate SEI chemistry on lithium metal across a range of electrolytes containing different anion species by electrode potential analyses based on liquid Madelung potential calculations, which capture the electrostatic stabilization of Li+ in the liquid phase, as well as machine-learning force field molecular dynamics (MLFF-MD) simulations that resolve interfacial decomposition reactions. Under highly concentrated electrolyte conditions, more electronically delocalised anions exhibit weak coordination to Li+, destabilising the liquid Madelung potential and inducing larger positive shifts in the Li/Li+ redox potential, thereby reducing the kinetic burden on the SEI. Moreover, these anions are preferentially reduced at the lithium metal surface, promoting the formation of structurally dense, inorganic-rich initial SEI layers. This computational framework provides a rational basis for electrolyte design strategies that simultaneously regulate lithium metal reactivity and the formation of stable SEI structures.