Sustainable Performance of Li-S Battery Using Ultramicroporous Carbon-Sulphur Composite Electrode in Carbonate Based Electrolyte

Lithium-sulphur (Li-S) batteries are being considered for high-energy storage applications due to the high theoretical specific capacity (1672 mAh g^-1) and energy density (2600 Wh kg^‑1) of sulphur.^1-3 However, the Li-S battery technology suffers from poor cycle life.^4,5 The electrochemical reaction of lithium with cyclic octa sulphur (S₈) leads to the formation of higher order polysulphides (Li₂S_x, x=4-8). These higher order polysulphides are highly soluble in liquid electrolytes and lead to the continuous depletion of the active material and trigger unwanted side reactions. Development of a sustainable cathode is the key factor for the advancement of Li-S batteries. Many efforts were put into the improvement of the Li-S batteries. One promising approach is microporous carbon confined sulphur, which eliminates the formation of higher order polysulphides.⁶

Herein, we report an easily scalable, inexpensive ultramicroporous carbon confined sulphur composite cathode and its sustainable performance in Li-S cell using commercial carbonate based electrolyte. The ultramicroporous carbon sulphur (UC-S) composite with a sulphur loading of 46 % exhibits a reversible capacity of 700 mAh g^-1 at C/5 (335 mA g^-1) even after 100 cycles (Figure 1). The observed cycling stability was attributed to the direct formation of low order polysulphides (Li₂S₂/ Li₂S) during the discharge process of UC-S cathode. For the first time we have examined and validated the lithiation/delithiation mechanism and the mechanism of capacity fading over cycling for sulphur confined in microporous carbon cathode by analysing the subsurface using XPS.

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