(322c) Challenges and Current Development of Sulfur Cathode in Lithium-Sulfur Battery
Rechargeable lithium-sulfur (Li-S) batteries have exceptional theoretical capacity; however, the practical applications are still elusive to date due to many critical challenges. This presentation summarizes the technical issues of the sulfur cathode and the state of the art strategies in recent years to address these issues from the aspects of lithium polysulfides sequestration, new concepts of sulfur cathode materials, functionality of binders, and the roles of the electrolytes. With regard to conventional sulfur cathodes, liquid-phase reactions involving polysulfides are inevitable. Therefore, the cycle stability is essentially dependent on the affinity of the cathode with lithium polysulfides. Cathode components, including the sulfur host, additive, and binder, should all be active to attract lithium polysulfides. Because polysulfide anions are the electrochemically active species, the sequestration functionality of the cathode components should be specifically designed to attract polysulfide anions. Metal oxides and heteroatoms show promising properties in attracting polysulfides, but the electrochemical â??inactiveâ? mass associated with their use needs to be minimized. Polycation binders also seem effective in their ability to attract polysulfide anions due to the electrostatic attraction, but systematic investigation on binders is lacking. In addition to the polysulfide affinity, other properties of polymer binders, including mechanical strength (molecular weight), solubility, and long-term stability in specific electrolytes, are all important to the optimization of the binder system. Moreover, the electrolyte/sulfur weight ratio needs to be watched carefully since almost all studies in open literature used a ratio too high to ever achieve full cell capacity to surpass state of the art Li-ion batteries. It is clear that the development of practical high capacity Li-S batteries still has a long winding road ahead to travel.