Electrode Potential in Ionic Liquid Enlightened by Liquid Madelung Theory

Abstract

Electrode potentials in electrolytes vary systematically with salt concentration, yet establishing a quantitative connection between electrolyte structure and electrode potential remains a longstanding challenge. Here, we demonstrate that the liquid Madelung energyan atomistically resolved Coulombic descriptor obtained from simulations of all constituent molecules and ionsquantitatively accounts for electrode-potential shifts observed for the solvent-based and ionic liquid electrolytes investigated in the present study, the latter representing the concentrated limit. Decomposition of the Li+ electrostatic energy into contributions from surrounding species reveals two key electrostatic factors governing the potential shift: reduced electrostatic stabilization arising from Li+–anion coordination in the first coordination shell and enhanced Li+–Li+ repulsion emerging in the second coordination shell at high concentrations. This atomistic framework captures structural fluctuations inaccessible to classical Debye–Hückel and pseudo-lattice theories, and can be applied to ionic liquids exhibiting apparent nanoscale heterogeneity. These results demonstrate that the liquid Madelung framework can be extended from conventional solvent-based to ionic liquid electrolytes and provide an atomistic electrostatic perspective for the rational design of next-generation electrolytes composed of complex polyatomic species.