(Keynote) Transition Metal Sulfides As Intercalation Cathode Materials for Rechargeable Aluminum Batteries

Wednesday, 4 October 2017: 11:00
Chesapeake K (Gaylord National Resort and Convention Center)
L. Geng and J. Guo (University of California, Riverside)
Rechargeable aluminum (Al) batteries are promising technologies for large scale energy storage applications. One of the main challenges hindering the development of rechargeable aluminum batteries is the lacking of understanding of cathode materials. In this study, we investigate a number of transition metal sulfides as the intercalation-type cathode materials for rechargeable Al batteries. Our selection of metal sulfides instead of oxides as Al-ion cathode materials is crucial: Due to the strong coulombic effect, the energy barrier for multivalent ion transport in the oxide crystal structure is very high. Thus, a more polarizable (softer) anionic framework is needed for facile Al-ion intercalation-extraction. The sulfide anion is more polarizable than the oxide anion due to the larger size, making transition metal sulfides promising candidates as Al-ion cathode materials. We hereby demonstrate Chevrel phase molybdenum sulfide (Mo6S8) as the intercalation-type 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.