<p>Electrolysis of Al₂S₃ in molten fluorides is an effective low-carbon strategy for the production of aluminum. In the present study, Raman spectroscopy and quantum chemical calculations were employed to investigate the types of complex ions in Na₃AlF₆-LiF-Al₂S₃ molten salts and the dissolution mechanism of Al₂S₃ in the molten salts. The results showed that five types of complex ions existed in the Na₃AlF₆-LiF-Al₂S₃ molten salts: AlF₅²⁻, Al₂SF₇³⁻, AlF₆³⁻, Al₂S₂F₄²⁻, and Al₂S₂F₃⁻. As the temperature increased, three different reactions occurred: the reaction between AlF₅²⁻ and F⁻ to generate AlF₆³⁻, the reaction of AlF₅²⁻ with Al₂S₂F₃⁻ and S²⁻ to generate Al₂S₂F₄²⁻, and F⁻, and the reaction between Al₂SF₇³⁻ and S²⁻ to generate Al₂S₂F₄²⁻ and F⁻. With increasing Al₂S₃ content, four reactions occurred: the reaction between AlF₅²⁻ and F⁻ to generate AlF₆³⁻, the reaction of Al₂S₃ with AlF₅²⁻ and F⁻ to generate Al₂SF₇³⁻, the reaction of Al₂S₃ with AlF₅²⁻ and F⁻ to generate Al₂S₂F₄²⁻, and the reaction between Al₂S₂F₃⁻ and F⁻ to form Al₂S₂F₄²⁻. The Al³⁺ ion in AlF₅²⁻ was the easiest to be reduced at the cathode, while the non-bridging S²⁻ ion in Al₂S₂F₄²⁻ was the easiest to be oxidized at the anode.</p> Graphical abstract <p></p>