Aninda Bhattacharyya1

1, Indian Institute of Science, Bengaluru, , India

Over the last decade, there has been a paradigm shift towards usage of earth abundant and cost effective materials in rechargeable batteries. A prominent example in this context, is sulfur. Sulfur delivers a high theoretical capacity of 1672 mAh g-1, nearly one order higher compared to the best known intercalation cathodes (IOCs) used in Li/Na-ion batteries. The high theoretical capacity originates from the possibility of higher than one exchangeable Li-ion per S-atom (theoretically two exchangeable Li-ions per S-atom) as compared to only one Li-ion/formula unit of IOC. Additionally, S is cheap, highly abundant and non-toxic in nature. Despite these advantages, the chemical reactions determining the mechanism and quantum of electrical energy storage in a liquid electrolyte based Li-S battery pose several challenges. The main challenge is due to the various intermediate polysulfides formed during the reversible conversion of elemental S8 to metal-sulfide. Bulk of the work related to metal-S rechargeable battery revolves around materials design strategies of a suitable carbon(/non-carbon)-host matrix targeted towards the entrapment of S and prevention of leaching out of polysulfides into the electrolyte. However, this limits the extent of S-loading and depending on the host may simultaneously increase the un-utilizable mass of S in the electrode. The presentation will discuss some of our important recent results in the context of M-S (M: Li, Na, Mg) highlighting the critical role of materials design and in operando monitoring studies for the development of highly stable metal-S bateries. The talk will discuss at length various ways for efficient anchoring of sulfur and the polysulfides at the S-cathode for various rechargeable metal-S batteries. Strategies will include (a) design of novel S-scaffolds based on molecular systems such as covalent organic frameworks (COFs), conducting carbon-based scaffolds, (b) additives and (c) interlayers based on non-carbonaceous nanoparticles. Our studies reveal several interesting fundamental insights related to the mechanism of storage which eventually have strong bearing on the metal-sulfur battery performance.