Highly Ordered Complex Framework Materials (CFMs) As Sulfur Hosts for Li-S Batteries
Authors: Murugavel Shanthi Pavithra , Jampani Hanumantha Prashanth , Gattu Bharat , Velikokhatnyi Oleg I , Kumta Prashant N 
Published: February 2020

In recent years, there is a near exponential increase in the number of plug – in hybrid vehicles and portable energy storage devices. This results in an increased demand for portable energy storage devices with greater efficiency. The commercial Li – ion batteries based on lithiation chemistry has a maximum theoretical capacity of 372 mAh/g could not meet this ever increasing demand. Thus the need of the hour is to find new materials and hybrids with improved energy storage capacity.

Sulfur with a theoretical specific capacity of 1672 mAh/g1
,
2 is a promising candidate for high energy density lithium batteries. Sulfur being one of the abundant elements on the Earth’s crust adds advantages as a low cost and environmentally benign promising technology3. Despite these advantages, sulfur has very low conductivity (- 10-30 S/cm) which restricts the complete utilization of the active material. Sulfur forms non – intercalation based polysulfide intermediates (Li2Sn ; n = 2 – 8)4which are soluble in liquid electrolyte resulting in active material loss. In addition, the dissolved polysulfide gets coated onto the anode resulting in cell failure. These problems prevents the technology from being commercialized.

Utilizing mesoporous5 and hollow carbonaceous materials6
,
7as sulfur hosts has shown to reduce polysulfide dissolution by avoiding direct contact with the liquid electrolyte. However, the pore size of these materials are in the order of µm and hence the problem of polysulfide dissolution has not been completely addressed. Porous materials with pore size comparable or less than the size of the polysulfide is required to completely overcome this problem.

In this work, highly ordered complex framework materials (CFM) were used as hosts for sulfur. These nano porous hosts trap the polysulfides formed during lithiation of sulfur and thus prevent active material loss with cycling. Two variants of the host were synthesized at room temperature and sulfur was infiltrated into them using infiltration techniques. These sulfur impregnated CFM cathodes showed a stable electrochemical performance with an initial discharge capacity of 1476 mAh/g which stabilized at 609 mAh/g for over 200 cycles (Figure 1). Results of these studies are presented and discussed.

References

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4.         C.-N. Lin, W.-C. Chen, Y.-F. Song, C.-C. Wang, L.-D. Tsai and N.-L. Wu, Journal of Power Sources, 2014, 263, 98-103.

5.         S.-R. Chen, Y.-P. Zhai, G.-L. Xu, Y.-X. Jiang, D.-Y. Zhao, J.-T. Li, L. Huang and S.-G. Sun, Electrochimica Acta, 2011, 56, 9549-9555.

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7.         J. Guo, Y. Xu and C. Wang, Nano Letters, 2011, 11, 4288-4294.

Figure 1