Pressure-induced capillary encapsulation protocol for ultrahigh loading of sulfur and selenium inside carbon nanotubes: application as high performance cathode in Li–S/Se rechargeable batteries

Abstract

There has been a paradigm shift in research foci toward elemental electrodes from the conventional intercalation compound-based electrochemical storage. Replacing intercalation transition metal (oxide) compounds with elemental cathodes (e.g., sulfur, oxygen) theoretically raises the storage capacities by more than one order in magnitude. The insulating nature and complexities of the redox reaction associated with electroactive elements necessitates their housing inside an electronic conductor, which has been mainly carbon. Efficiency of the electrochemical storage using such elemental electrodes, besides depending on factors related to the electrolyte, solid-state diffusion, mainly depends on characteristics of the carbon host. We report here a novel, simple, and efficient pressure-induced capillary encapsulation protocol for the confinement of chalcogens, sulfur (S) and selenium (Se), inside carbon nanotubes (CNTs). Confinement led to lowering of the surface tension of molten S/Se, resulting in superior wetting and ultrahigh loading of the CNTs. Higher than 95% of the CNTs is loaded, and very high loading, nearly 85% of S/Se inside the CNTs, is achieved. When assembled at a very high areal loading (∼10 mg cm^–2) in the Li–S/Se battery, the S/Se-CNT cathodes exhibited very stable cyclability and high values of specific capacity at widely varying operating current densities (0.1–10 C-rates).