Enhanced Li S Batteries Using Amine Functionalized Carbon Nanotubes in the Cathode.
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.
ACS nano