Lithium-sulfur (Li/S) batteries are considered as one of the promising rechargeable battery technology due to their low cost, ecofriendly and high theoretical energy density (~2500 Wh kg-1)[1, 2]. The high theoretical specific capacity (~1672 mAh g-1) of Li/S battery is the result of reversible two electron conversion reactions between sulfur and lithium (S8 + 16Li+ + 16e- ----> 8Li2S) at an average voltage of 2.1 V with respect to Li/Li+ and finally form solid lithium sulfide (Li2S) through a series of intermediate liquid polysulfides . The physiochemical properties of the carbon host matrix and their sulfur loadings at the cathode side play a major role in the electrochemical performance of lithium-sulfur (Li/S) batteries. In this work, we have designed a highly sulfur loaded (~ 75 wt. %) carbon matrix (S/NGC), with hierarchically organized micro/meso pore structures and containing nitrogen and oxygen functional groups, using metal oxide nano templates. The S/NGC electrodes give the reversible capacities of 868 and 666 mAh g-1 in C/5 current rates, at the sulfur loadings of 2.2 and 3.4 mgSulfur cm-2, respectively. Based on the advantages of the hierarchical porous structure and nitrogen doping, S/NGC electrode gives a long cycling stability (0.03% capacity decay per cycle up to 1000 cycles) and very good coulombic and voltage efficiencies (Fig. 1). Further, the charge/discharge mechanism of the cell is investigated in detail by Raman spectroscopy and ex-situ XPS. The presence of nitrogen on carbon support is found to enhance the bonding between sulfur and oxygen functional groups present in the carbon support, which is supposed to take a major role in the prevention of sulfur/polysulfides species dissolution to anode side.
1. Mikhaylik YV, Kovalev I, Schock R, Kumaresan K, Xu J, Affinito J. High Energy Rechargeable Li-S Cells for EV Application: Status, Remaining Problems and Solutions. ECS Transactions. 2010;25(35):23-34.
2. Nazar LF, Cuisinier M, Pang Q. Lithium-sulfur batteries. MRS Bulletin. 2014;39(05):436-42.