(719c) Reversible Aluminum Intercalation in Transition Metal Sulfides

Rechargeable aluminum batteries are promising technologies for large scale energy storage. One of the main obstacles hindering the development of rechargeable aluminum batteries is the lacking of understanding of cathode materials. We hereby demonstrate Chevrel phase molybdenum sulfide (Mo₆S₈) as the intercalation-type of cathode material with aluminum chloride/1-butyl-3-methyimidazolium chloride (AlCl₃-[BmIm]Cl) ionic liquid as the electrolyte. Electrochemical characterizations including cyclic voltammetry and galvanostatic charge-discharge demonstrate unambiguous Al intercalation-extraction in the Mo₆S₈. The X-ray diffraction analysis further indicates the crystal structure change of Mo₆S₈ after Al intercalation. In addition, we report the synthesis and electrochemical properties of layered TiS₂ and cubic Ti₂S₄ as intercalation-type cathode materials for rechargeable aluminum battery at both room temperature and 50 °C. We further confirmed the aluminum intercalation in the TiS₂ and Ti₂S₄ crystal structure using combined electrochemical analysis and ex-situ XRD. The proposed titanium sulfide cathode materials showed decent reversible capacity and a higher working potential than Mo₆S₈. Furthermore, our study suggests the low Al ion diffusivity in the titanium sulfide framework induced by strong coulombic intercalation is the key obstacle for fast discharge-charge. This finding could provide guideline for design and synthesis of future titanium sulfides electrode materials.