In the recent years, the intercalation based lithium-ion batteries (LIBs) are considered as the potential candidate for portable electronic devices. However, development of low cost electrode materials with improved energy density and long cycle stability are the great challenges to meet the increasing demands of upcoming electric vehicle technology [1]. Among the rechargeable LIB electrode materials, sulfur cathode offers high theoretical specific capacity of 1672 mAh g^-1 (energy density of 2600 Wh kg^-1), which is ~ 3-5 times higher than the conventionally used LIB cathode materials. Moreover, the elemental sulfur is abundantly available in nature, eco-friendly and hence the fabricated cells using sulfur cathode is expected to deliver high electrochemical performance with low cost. However, the commercialization of this system is hampered largely owing to low electrical conductivity of elemental sulfur, polysulfide dissolution into the electrolyte and large volume expansion during charge/discharge process resulted in poor electrochemical performance of the cell [2,3].

To mitigate these issues, various strategies including designing of unique cathode structure comprising of carbon based materials (micro & mesoporous carbons, MWCNTs, graphene and graphene oxide), metal oxide composites, conductive polymers, etc have been tried so far. Particularly carbon materials are of interest, because micro and mesoporous carbon materials are known for efficient trapping of dissolved polysulfides during redox process to enhance the performance of lithium-sulfur (Li-S) battery [2]. In the present study, we synthesized a biomass derived high surface area activated carbon (AC) with narrow pore size distribution and high graphitic content and used it as host for sulfur cathode in Li-S battery. FE-SEM and HR-TEM images (Figure 1a and 1b) of as prepared AC reveals the presence of carbon with graphene sheet like structure (inset of Figure 1a and 1b). The elemental mapping of sulfur infused AC confirms homogenous distribution of elemental sulfur throughout the carbon matrix indicating uniform dispersion after melt diffusion process (155 ºC).

The schematic representation of Li-S cell with modified separator is shown in Figure 1c. The use of modified separator is expected to inhibit the migration of dissolved polysulfide into electrolyte solution to the anode surface during redox process. The AC/S composite with modified separator displays impressive electrochemical performance in terms of specific capacity, rate capability and cyclic stability due to efficient trapping of polysulfide species and improved ionic and electronic conductivities. Figure 1d shows the long term cycle performance curve measured at 1 C rate with in-set of CV profile for the initial 10 cycles. The detailed physico-chemical and electrochemical measurements will be discussed during the presentation.

Figure 1 (a) FE-SEM and (b) TEM images of as prepared AC sample, (c) schematic representation of Li-S cell with modified separator and (d) Electrochemical cyclic stability data’s of AC/S cathode (in-set CV curve) measured in the voltage range of 1.5-2.8 V at current rate of 1C with pristine separator and modified separator.

References:

[1] P. G. Bruce, S. A. Freunberger, L. J. Hardwick, J. M. Tarascon, Nature Materials, 11 (2012) 19-29.

[2] H. Sohn, M. L. Gordin, T. Xu, S. Chen, A. Manivannan, D. Wang, ACS Appl. Mater. Interfaces, 6 (2014) 7596-7606.

[3] E. Hari Mohan, B. V. Sarada, R. V. R. Naidu, G. Salian, A. K. Haridas, B. V. Appa Rao, T. N.Rao, Electrochimica Acta, 219 (2016) 701-710.