Coordination-Driven Transport in Chloroaluminate Electrolytes

Abstract

Transport in electrolytes reflects both the stability of coordination complexes and their dynamic reorganization through chemical bond association and dissociation. Establishing an atomistic description of how the dynamic coordination governs equilibrium speciation and transport remains a central challenge in electrolyte science, as classical molecular dynamics (MD) simulations often neglect such reactive bond association and dissociation in replicating experimental information. Here, we apply machine-learning force field molecular dynamics (MLFF-MD) simulations to chloroaluminate NaCl–AlCl3 melts, a plausible model system for dynamic reorganization where tetrahedral coordination species of AlxCly reacts with one another to form and break Al–Cl bonds. MLFF-MD enables statistically robust sampling of coordination dynamics beyond the limitations of ab initio simulations. Starting from fully randomized atomic configurations without predefined complexes, a series of reactive AlxCly coordination complexes emerge spontaneously, forming a dynamic coordination ensemble. Within this ensemble, equilibrium distributions and rapid Al–Cl bond association/dissociation processes are directly resolved. As a consequence, transport emerges from coordination stability and ligand exchange within dynamic ensembles, with chloride (Cl–) ions exhibiting enhanced mobility relative to Al-containing complexes at equimolar composition, whereas under Lewis-acidic conditions, neutral AlCl3-like motifs and Al2Cl6 species exhibit fast mass transport. The findings further suggest that electrochemically active [AlnCl3n+1]– species can be regenerated near interfaces through rapid Al–Cl bond association. By enabling direct identification of dynamically evolving coordination complexes without imposing predefined species models, this work connects reactive coordination speciation, ligand-exchange-mediated reorganization, and mass transport in an atomistic framework.