Revisiting Liquid Electrolyte Structures: The Overlooked Role of Anion–Anion Interactions

Anion–anion interactions in liquid electrolytes have long been overlooked compared to those of cation-centered solvation structures. Recent small-angle X-ray scattering (SAXS) studies reveal that, especially in highly concentrated electrolytes, anion–anion correlations give rise to nanoscale network structures that directly influence electrolyte properties. Here, we summarize our recent efforts to quantify anion network formation across multiple electrolyte systems. In water-in-salt electrolytes, increasing salt concentration drives the development of anion-rich domains, as evidenced by distinct low-q scattering features. Beyond concentration effects, variations in anion molecular structure, such as asymmetry and size, systematically modulate network dimensions and dynamics. Solvent environments further reshape anion correlations by altering the cation solvation and imposing spatial constraints. Recognizing anion–anion correlations as a critical structural motif introduces a new dimension for electrolyte design. Incorporating these nanoscale interactions enables more effective control over ion transport and interfacial stability, offering opportunities to advance next-generation electrochemical systems.