Cinnamon-Derived Hierarchically Porous Carbon as an Effective Lithium Polysulfide Reservoir in Lithium-Sulfur Batteries.

Ranjith Thangavel,Dong-Won Kim,Aravindaraj G Kannan,Won-Sub Yoon,Karthikeyan Kaliyappan,Yun-Sung Lee,Rubha Ponraj

doi:10.3390/nano10061220

Ranjith Thangavel, Dong-Won Kim + Show 5 more

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https://doi.org/10.3390/nano10061220

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Abstract

Lithium–sulfur batteries are attractive candidates for next generation high energy applications, but more research works are needed to overcome their current challenges, namely: (a) the poor electronic conductivity of sulfur, and (b) the dissolution and migration of long-chain polysulfides. Inspired by eco-friendly and bio-derived materials, we synthesized highly porous carbon from cinnamon sticks. The bio-carbon had an ultra-high surface area and large pore volume, which serves the dual functions of making sulfur particles highly conductive and acting as a polysulfide reservoir. Sulfur was predominantly impregnated into pores of the carbon, and the inter-connected hierarchical pore structure facilitated a faster ionic transport. The strong carbon framework maintained structural integrity upon volume expansion, and the unoccupied pores served as polysulfide trapping sites, thereby retaining the polysulfide within the cathode and preventing sulfur loss. These mechanisms contributed to the superior performance of the lithium-sulfur cell, which delivered a discharge capacity of 1020 mAh g−1 at a 0.2C rate. Furthermore, the cell exhibited improved kinetics, with an excellent cycling stability for 150 cycles with a very low capacity decay of 0.10% per cycle. This strategy of combining all types of pores (micro, meso and macro) with a high pore volume and ultra-high surface area had a synergistic effect on improving the performance of the sulfur cathode.

Highlights

The ever increasing energy demands for portable electronic devices and electric vehicles, along with the demands of grid-scale energy storage devices for the back-up and load-leveling of intermittent renewable energy sources such as solar cells and wind mills, have shifted the focus of battery research to high energy density storage devices such as lithium–sulfur (Li–S) batteries [1,2]
The sulfur cathode design has been reconfigured by embedding sulfur into highly conductive porous carbons [8,9,10], encapsulating sulfur using conductive polymer coatings [11,12,13], utilizing Li2S as an initial active material [14] and utilizing lithium polysulfide adsorbents to trap the lithium polysulfides within the cathode to enhance the cycling performance of Li–S cells [15,16,17]
Strategies such as protecting the lithium metal surface [18,19,20], utilizing non-lithium metal anodes [21], modifying the electrolyte composition through a rational selection of solvents and electrolyte additives [22,23] and modifying the separator to block the migration of lithium polysulfides to the anode side have been adopted to mitigate the capacity-fading observed upon cycling [24,25,26]

Summary

Introduction

The ever increasing energy demands for portable electronic devices and electric vehicles, along with the demands of grid-scale energy storage devices for the back-up and load-leveling of intermittent renewable energy sources such as solar cells and wind mills, have shifted the focus of battery research to high energy density storage devices such as lithium–sulfur (Li–S) batteries [1,2]. The inherent disadvantages of these batteries, including (a) the highly insulating nature (both electronically and ionically) of sulfur and its discharge products, (b) the dissolution of intermediate lithium polysulfides (Li2Sn, where 4 < n < 8) in the electrolyte, (c) the migration and poisoning of lithium metal anodes by lithium polysulfides and (d) the volume expansion of the sulfur cathode upon lithiation, result in a low coulombic efficiency, poor sulfur utilization and poor cycle life, which renders them unsuitable for practical applications in the current state [5,6,7] To address these issues, the sulfur cathode design has been reconfigured by embedding sulfur into highly conductive porous carbons [8,9,10], encapsulating sulfur using conductive polymer coatings [11,12,13], utilizing Li2S as an initial active material [14] and utilizing lithium polysulfide adsorbents to trap the lithium polysulfides within the cathode to enhance the cycling performance of Li–S cells [15,16,17]. Conventional porous carbons can be obtained from the activation of fossil fuels such as coke and coal, which are environmentally harmful and unsustainable

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