Journal
ACS NANO
Volume 10, Issue 1, Pages 1050-1059Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acsnano.5b06373
Keywords
lithium-sulfur batteries; molecular sorbents; lithium-nitrile interactions; sequestering lithium polysulfide
Categories
Funding
- National Science Foundation [IIP-1237622]
- Texas Advanced Computing Center [TG-DMR050028N, TG-DMR140067]
- NSF [DMR-1120296]
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The rechargeable lithium sulfur (Li-S) battery is an attractive platform for high-energy, low-cost electrochemical energy storage. Practical Li-S cells are limited by several fundamental issues, including the low conductivity of sulfur and its reduction compounds with Li and the dissolution of long-chain lithium polysulfides (LiPS) into the electrolyte. We report on an approach that allows high-performance sulfur carbon cathodes to be designed based on tethering polyethylenimine (PEI) polymers bearing large numbers of amine groups in every molecular unit to hydroxyl- and carboxyl-functionalized multiwall carbon nanotubes. Significantly, for the first time we show by means of direct dissolution kinetics measurements that the incorporation of CNT-PEI hybrids in a sulfur cathode stabilizes the cathode by both kinetic and thermodynamic processes. Composite sulfur cathodes based the CNT-PEI hybrids display high capacity at both low and high current rates, with capacity retention rates exceeding 90%. The attractive electrochemical performance of the materials is shown by means of DFT calculations and physical analysis to originate from three principal sources: (i) specific and strong interaction between sulfur species and amine groups in PEI; (ii) an interconnected conductive CNT substrate; and (iii) the combination of physical and thermal sequestration of UPS provided by the CNT=PEI composite.
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