Effect of Functional Groups on Polysulfide Trapping Properties of Complex Framework Materials (CFM) Serving As Effective Sulfur Hosts for Li – S Batteries
Authors: Murugavel Shanthi Pavithra , Jampani Prashanth , Ramalinga Bandi , Gattu Bharat , Datta Moni Kanchan , Velikokhatnyi Oleg I , Kumta Prashant Nagesh 
Published: February 2020

Increased demand for efficient portable energy storage systems has promoted researches to focus on identifying better alternatives to the conventional insertion-based lithium-ion battery cathodes. With a theoretical specific capacity of 1672 mAh/g, sulfur has emerged as a promising candidate for high energy density lithium battery cathodes1
,
2. Favorable economics, abundance and ease of availability are additional arguments favoring the use of sulfur cathodes in comparison to transition metal – based cathodes. However, elemental sulfur has poor electronic conductivity (~10-15 S/cm)3 at room temperature which restricts the active material utilization in Li-S batteries. The formation of soluble non-intercalation based polysulfide intermediates (Li2Sn; n=2-8)4 during electrochemical cycling further leads to active material loss by coating onto the anode leading to eventual battery failure.

Numerous sulfur encapsulation strategies have been reported in the literature of which, utilizing a mesoporous5 and hollow carbonaceous materials6, 7 as 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 on microns and hence the problem of polysulfide dissolution has not been completely addressed. Porous materials with pore sizes comparable or less than the size of polysulfide species (PSS) need to devised in order to completely overcome this problem.

In this work, several highly ordered nanoporous complex framework materials (CFM) were synthesized and engineered for use as effective hosts for sulfur. These nanoporous CFM architectures act as effective hosts to bind and trap the polysulfide species (PSS) serving to effectively prevent their dissolution into the electrolyte during cycling. The CFMs with three different functional groups were effectively crafted and synthesized. The resulting materials were then infiltrated with sulfur using vapor-phase infiltration techniques. The surface structure of the CFMs play a major role in efficiently trapping the polysulfide species and controlling their dissolution. The effects of functional groups created on these CFMs specifically on their polysulfide (PS) trapping properties and the corresponding electrochemical cycling performance of the sulfur impregnated CFM based cathodes were studied in detail and the results will be presented and discussed.

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