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Enhanced Cycling Stability of Sulfur Electrodes Through Effective Binding of Pyridine-Functionalized Polymer Yu-Chi Tsao, Zheng Chen, Simon Rondeau-Gagne, Qianfan Zhang, HongBin Yao, Shucheng Chen, Guangmin Zhou, Chenxi Zu, Yi Cui, and Zhenan Bao ACS Energy Lett., Just Accepted Manuscript • DOI: 10.1021/acsenergylett.7b00772 • Publication Date (Web): 20 Sep 2017 Downloaded from http://pubs.acs.org on September 20, 2017
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ACS Energy Letters
Enhanced Cycling Stability of Sulfur Electrodes Through Effective Binding of Pyridine-Functionalized Polymer Yuchi Tsao,a, ‡ Zheng Chen,b,‡, § Simon Rondeau-Gagné,b,‡,◊ Qianfan Zhang,c Hongbin Yao,d Shucheng Chenb, Guangmin Zhoue, Chenxi Zue, Yi Cuie,f* and Zhenan Baob,* a b
c
d
Department of Chemistry, Stanford University, Stanford, CA 94305, USA
Department of Chemical Engineering, Stanford University, Stanford, CA 94305, USA
School of Materials Science and Engineering, Beihang University, Beijing, P.R. China
School of Chemistry and Material Science, University of Science and Technology of China, Hefei, P.R. China e
Department of Materials Science and Engineering, Stanford University, Stanford, CA 94305, USA
f
Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, CA 94025, USA
§
Current address: Department of NanoEngineering, University of California, San Diego, La Jolla, CA 92093 ◊
Current address: Department of Chemistry and Biochemistry, University of Windsor, 401 Sunset Avenue, Windsor, Ontario, Canada, N9B 3P4 *Correspondence:
[email protected];
[email protected] ‡
These authors contributed equally to this work
Abstract Porous carbons have previously been widely used as host materials for sulfur (S) electrodes because of their high conductivity and high surface area. But they generally lack strong chemical affinity stabilize polysulphide species. Therefore, conducting polymers have been employed to stabilize S electrodes. Integrating conducting polymers with high-surface-area carbons can create a new materials platform and synergize their functions. However, the previously used conducting polymers were often insoluble and coating them uniformly from solution onto non-polar carbon substrate is a challenge. Here, we report that solution processable isoindigo-based polymers incorporating polar substituents provide critical features: 1) conjugated backbone provides good conductivity; 2) functional pyridine groups provides high affinity to polysulphide species and 3) high solubility in organic solvents. These lead to effective coating on various carbonaceous substrates to provide highly stable sulfur electrodes. Importantly, the
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electrodes exhibit good capacity retention (80 % over 300 cycles) at sulfur mass loading of 3.2 mg/cm2, which significantly surpass performance of other reported in polymer-enabled sulfur cathodes.
Rapid evolution of modern electronics, electric vehicles and electric grids calls for rechargeable batteries with significantly improved energy storage performance compared with current lithium-ion batteries (LIBs). Lithium-sulfur (Li-S) battery represents one of the most promising candidates for nextgeneration energy storage due to its ~5 times higher theoretical energy density than today’s LIBs (2500 vs. 400 Wh/kg).1 However, cell performance remain far below this potential because of several fundamental issues: 1) charged (S) and discharged (Li2S) species are highly insulating for both electrons and ions, resulting in large charge transfer resistance, 2) dissolution and deposition of S and Li2S are inhomogeneous inside electrode, causing loss of active materials; 3) various lithium polysulfide species (LiPSs) are mobile in electrodes and can diffuse to react with anode, resulting in shuttling effect. These problems often cause low sulfur utilization, poor cycling stability and low Coulombic efficiency (CE), making it difficult to fabricate high-performance sulfur electrodes. Tremendous efforts have been made to address the above challenges by designing functional structures and compositions for sulfur electrodes. Various porous, conductive scaffolds with high surface area were designed to support sulfur with intimate electrical contact, physical trapping, short diffusion length and large interface for facile charge transfer and redox reactions. Common examples are mesoporous carbons,2 carbon nanotubes/nanofibers,3 and graphene-porous carbons.4 While these nanostructured carbon materials can often provide high utilization of sulfur active materials and thus increased charge capacity, their electrode cycling stability still needs improvement.
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ACS Energy Letters
Systematic studies using in situ transmission electron microscope (TEM) together with first-principle calculations revealed that capacity fading of sulfur cathodes is often associated with the detachment of Li2Sx (0
