Study on micro-structure and transport properties of KF-NaF-AlF3-Al2O3 system by first-principles molecular dynamics simulation

[Display omitted] •The ionic micro-structure and transport properties of the system are studied by FPMD.•Complex ion groups in KF-NaF-AlF3-Al2O3 system are mainly [AlF4]−, [AlF5]2− and [AlF6]3−.•The diffusion ability of ions in the system is Na > K > F > O > Al. It has always been a challenging problem to conduct research on low temperature aluminum electrolyte KF-NaF-AlF3-Al2O3 because of high temperature and strong corrosiveness in aluminum electrolysis industry. Fortunately, the rapid advancement of computational materials science provides us with a good tool to study it. In this paper, the ionic micro-structure and transport properties of KF-NaF-AlF3-Al2O3 system are studied by adopting first-principles molecular dynamics simulation directly. The calculated results show that the complex ion groups in KF-NaF-AlF3-Al2O3 system are mainly [AlF4]−, [AlF5]2− and [AlF6]3−, meantime, with the increasing concentration of Al2O3, [AlF4] − decreases but the coordination number of Al-F complex ion groups increases gradually. Intricate complex ion groups of Al-F-Al, Al-O-Al and Al-O-F are formed on account of the presence of bridge F and bridge O ions. Besides, the proportion of bridge F and Bridge O ions increases with the increasing concentration of Al2O3, and the ionic micro-structure of the system becomes more intricate than before, reducing the ionic conductivity and increasing the viscosity of the system. This study can provide a useful guide for designing suitable low temperature electrolyte system in aluminum electrolysis production.