Rational Design of Statically and Dynamically Stable Lithium–Sulfur Batteries with High Sulfur Loading and Low Electrolyte/Sulfur Ratio

Abstract

The primary challenge with lithium–sulfur battery research is the design of sulfur cathodes that exhibit high electrochemical efficiency and stability while keeping the sulfur content and loading high and the electrolyte/sulfur ratio low. With a systematic investigation, a novel graphene/cotton-carbon cathode is presented here that enables sulfur loading and content as high as 46 mg cm⁻² and 70 wt% with an electrolyte/sulfur ratio of as low as only 5. The graphene/cotton-carbon cathodes deliver peak capacities of 926 and 765 mA h g⁻¹, respectively, at C/10 and C/5 rates, which translate into high areal, gravimetric, and volumetric capacities of, respectively, 43 and 35 mA h cm⁻², 648 and 536 mA h g⁻¹, and 1067 and 881 mA h cm⁻³ with a stable cyclability. They also exhibit superior cell-storage capability with 95% capacity-retention, a low self-discharge constant of just 0.0012 per day, and stable poststorage cyclability after storing over a long period of six months. This work demonstrates a viable approach to develop lithium–sulfur batteries with practical energy densities exceeding that of lithium-ion batteries.

Use of a graphene/cotton-carbon cathode with a high sulfur loading (46 mg cm⁻²), a high sulfur content (70 wt%), and a low electrolyte/sulfur ratio of 5 enables synchronous improvements in the cyclability of lithium–sulfur batteries with high areal, volumetric, and gravimetric capacities as well as long shelf-life of half a year with a low self-discharge.

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