3. Chemistry and Operation of Li-S Batteries

Lithium-sulfur (Li-S) batteries are promising high-energy-density energy storage systems. It is generally agreed that shuttle of the polysulfides in a functional battery is slowed by intense anchoring of the intermediates. However, there is still a lack of knowledge regarding the chemistry involved. Here, using advanced quantum chemical computations, we examine the Li bond chemistry in Li-S batteries with concept of hydrogen bond. The Li bond, a strong dipole-dipole connection between Li-S cathode materials and Li polysulfides, is facilitated by electron-rich donors like pyridinic nitrogen (pN), and is further strengthened by the conjugative and inductive effect of scaffold materials having π-electrons like graphene. This research elucidates the importance of Li bond chemistry in Li-S cells and provides a comprehensive knowledge, which is helpful for rational choice of cathode materials and implementation of Li-S batteries in the practical applications.

Because of sulfur’s natural insulation, substantial volume expansion, shuttling of the soluble polysulfides, and, most critically, slow conversion of polysulfide intermediates, Li-S battery performance is still far from theoretical prediction. The electrochemical performance of Li-S batteries (e.g., lifespan, rate capability, cyclability, etc.) can be influenced by manipulating the architectures and functions of polymer materials; hence, they play an essential role in solving these problems. In this chapter a brief introduction of Li-S battery followed by its fundamental electrochemistry and challenges has been given. The mechanisms of operation of the Li-S batteries are then considered, with special emphasis on the uses of several polymers in all components.