Synergistic Effect of Covalent Bonding and Physical Encapsulation of Sulfur in the Pores of a Microporous COF to Improve Cycling Performance in Li-S Batteries
Abstract
Lithium-sulfur batteries stands out as a promising technology for energy storage owing to a combination of favorable characteristics including a high theoretical gravimetric capacity, energy density, inexpensive character, and environmental benignity. Covalent organic frameworks (COFs) are a rapidly developing family of functional nanostructures which combine porosity and crystallinity, and which have been already used in these kinds of batteries to build sulfur electrodes, by embedding sulfur into porous COFs in order to enhance cycle lifetimes. In this contribution, this is taken one step forward and a COF endowed with vinyl groups is used, in order to graft sulfur to the COF skeleton through inverse vulcanization. The main aim of the article is to show the synergistic effect of covalent bonding and physical encapsulation of sulfur in the pores of the COF in order to alleviate the fatal redox shuttling process, to improve the cycling performance, and to provide faster ion diffusion pathways. In addition, it is shown how the material with covalently-bound S provides better electrochemical performance under demanding and/or changeable charge conditions than a parent analogue material with sulfur physically confined, but without covalent linkage
Description
Financial support from Spanish Government (Projects MAT2016‐77608‐C3‐1‐P, MAT2016‐77608‐C3‐2‐P, FIS2017‐82415‐R, ENE2016‐77055‐C3‐1‐R), the “María de Maeztu” Programme for Units of Excellence in R&D (MDM‐2014‐0377) and the UCM (INV.GR.00.1819.10759) is acknowledged. We thank the BACH beamline team at Elettra for technical assistance with XPS measurements. The research leading to these results has received funding from the European Community's Horizon 2020 Framework Programme under grant agreement No 730872
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