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Aninda Bhattacharyya1 Subhra Gope1

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 electrodes in rechargeable batteries. This strategy enhances the energy density by nearly one order of magnitude. The concept of sulfur as a positive electrode material was highlighted as early as 1962 by Herbet and Ulam. Sulfur delivers a high theoretical capacity of 1672 mAh g-1, nearly one order higher compared to the intercalation oxide cathodes (IOC) used in conventional Li/Na-ion batteries. The high theoretical capacity originates from the possibility of two exchangeable Li-ions/S-atom as compared to only one Li+-ion/formula unit of IOC. In addition to high storage, 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 Li-S battery pose a formidable challenge mainly due to the various intermediate polysulfides formed during the reversible conversion of elemental S8 to Li2S. Bulk of the work related to Li-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. This strategy however, 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 various hosts for the sulfur cathodes for rechargeable Li-S battery. Recently, usage of interlayers between conventional S|C composite cathode and separator has been demonstrated in Li-S batteries. This interlayer, mostly carbon or doped carbon, has been used to trap the polysulfides in between the interlayer and S-cathode. Instead of carbon, we demonstrate here an alternative and novel interlayer of metal oxide nanoparticles between cathode and separator to efficiently trap and arrest the polysulfides at the S-cathode. Oxide-based compounds exhibit superior ability to hold the lower order polysulfides towards the S-cathode by bonding interactions thereby, enhancing anode protection. In the presence of metal-oxide nanoparticle interlayer, an alternative pathway for S-reduction and oxidation takes place which simultaneously lead to a phenomenal reduction in the polysulfide shuttle effect, even at extremely high loadings of sulfur (up to 15 mg cm-2). The inhibition of the shuttle effect is studied by probing the battery separator and interlayer ex situ (cycled at various depths of discharge and charge). The conventional Li-S cell with S/C composite cathodes and metal oxide interlayers exhibits a remarkable improvement in cycliability and rate capability vis a vis the cell without any interlayer. The talk will also discuss some of our explorations in to other metal-sulfur chemistries viz. Na-S and Mg-S.

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