Department of Materials Science & Engineering and ‡Department of Chemical and Biomolecular Engineering, Cornell University , Ithaca, New York 14853, United States.
ACS Nano. 2016 Jan 26;10(1):1050-9. doi: 10.1021/acsnano.5b06373. Epub 2015 Dec 11.
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 LiPS provided by the CNT=PEI composite.
可充电锂硫（Li-S）电池是一种很有吸引力的高能、低成本电化学储能平台。实用的 Li-S 电池受到几个基本问题的限制，包括硫及其与 Li 反应的还原化合物的导电性低，以及长链多硫化物（LiPS）溶解在电解质中。我们报告了一种方法，可以根据将大量伯胺基团固定在每个分子单元中的聚亚乙基亚胺（PEI）聚合物与羟基和羧基功能化多壁碳纳米管结合，设计高性能的硫-碳阴极。重要的是，我们首次通过直接溶解动力学测量表明，将 CNT-PEI 杂化物掺入硫阴极中通过动力学和热力学过程稳定了阴极。基于 CNT-PEI 杂化物的复合硫阴极在低电流和高电流速率下均表现出高容量，容量保持率超过 90%。通过 DFT 计算和物理分析表明，材料具有吸引力的电化学性能源于三个主要来源：（i）硫物种与 PEI 中的胺基团之间的特定和强相互作用；（ii）相互连接的导电 CNT 基底；以及（iii）由 CNT-PEI 复合材料提供的 LiPS 的物理和热隔离的组合。
