In Situ Mg/MgO-Embedded Mesoporous Carbon Derived from Magnesium 1,4-Benzenedicarboxylate Metal Organic Framework as Sustainable Li–S Battery Cathode Support

Abstract

Development of advanced carbon cathode support with the ability to accommodate high sulfur (S) content as well as effective confinement of the sulfur species during charge–discharge is of great importance for sustenance of Li–S battery. A facile poly(vinylpyrrolidone)-assisted solvothermal method is reported here to prepare Mg–1,4-benzenedicarboxylate metal organic framework (MOF) from which mesoporous carbon is derived by thermal treatment, where the hexagonal sheetlike morphology of the parent MOF is retained. Existence of abundant pores of size 4 and 9 nm extended in three dimensions with zigzag mazelike channels helps trapping of S in the carbon matrix through capillary effect, resulting in high S loading. When tested as a cathode for lithium–sulfur battery, a reversible specific capacity of 1184 mAh g –1 could be achieved at 0.02 C. As evidenced by X-ray photoelectron spectroscopy, in situ generated Mg in the carbon structure enhances the conductivity, whereas MgO provides support to S immobilization through chemical interactions between Mg and sulfur species for surface polarity compensation, restricting the dissolution of polysulfide into the electrolyte, the main cause for the “shuttle phenomenon” and consequent capacity fading. The developed cathode shows good electrochemical stability with reversible capacities of 602 and 328 mAh g –1 at 0.5 and 1.0 C, respectively, with retentions of 64 and 67% after 200 cycles. The simple MOF-derived strategy adopted here would help design new carbon materials for Li–S cathode support.

In situ assembly of MnO2 nanosheets on sulfur-embedded multichannel carbon nanofiber composites as cathodes for lithium-sulfur batteries

“…The overlap has been observed in many carbon/S composite cathodes reported previously, which might be attributed to the fast reaction kinetics of oxidation of polysulfides to sulfur [39,40]. The reduction peaks in the second cathodic scan shift to higher potential side relative to these in the first scan, which could be attributed to the electrode activation process [41]. The last fourth CV curves are almost overlapped, suggesting relatively high stability, which benefits from the MnO 2 nanosheet shell offering chemical and physical adsorption of long chain polysulfides.…”

Influence of C–S interactions on the electrochemical performance of –COOH functionalized MWCNT/S composites as lithium-sulfur battery cathode

“…Essentially, all the composites show very similar cathodic behaviour with two clear peaks at ∼2.3 V and 2.0 V indicating a multistep reduction of sulfur. 56,73,74 The first peak can be assigned to the formation of Li 2 S 8 whereas the second peak is a signature for deep reduction of higher order polysulfides (Li 2 S x ; 4 < x < 8) to lower order polysulfides (Li 2 S x ; x ≤ 2). However, the anodic scans show a markedly different behaviour for CSCH compared to CSM and CSC.…”

Applications of Metal–Organic‐Framework‐Derived Carbon Materials

“…After cycling for 200 cycles, the capacity maintained 1220 mA h g −1 at 0.10 C, and after an ultralong 1000 cycles, it could remain 727 mA h g −1 at 2 C with a capacity loss of only 0.02% every cycle. The average discharge capacities are displayed in Figure f, with 1261, 1200, 1117, 900, and 759 mA h g −1 at 0.10, 0.20, 0.50, 2, and 5 C, respectively, and restored to 1254 mA h g −1 as the C‐rate switched from 5 C back to 0.10 C. Nevertheless, there are also many other Li–S batteries with a carbon material derived from different kinds of MOFs as their electrodes, and all of them performed ideal electrochemical performances …”