Freestanding cellulose paper-derived carbon/Fe/Fe3C with enhanced electrochemical kinetics for high-performance lithium-sulfur batteries

Abstract

The loss and sluggish kinetics of intermediate polysulfides in electrochemical processes seriously reduce electrochemical activity of sulfur in lithium-sulfur batteries (LSBs). Herein, we design and synthesize freestanding graphitized carbon interlayers decorated with Fe/Fe3C nanocatalysts by thermal treatment of cellulose paper with adsorbed ferric nitrate at 1000 °C, during which the freestanding carbon network derives from the cellulose paper while the Fe results from the reduction of Fe3+ with a carbothermal reduction process; simultaneously, the in situ formed Fe boosts graphitization of carbon to enhance electrical conductivity of the interlayer, and the carbon network effectively helps confine and accommodate Fe/Fe3C nanoparticles. Therefore, the well dispersed Fe/Fe3C nanoparticles catalytically accelerate electrochemical conversion of polysulfides, while the enhanced conductive network of carbon benefits the electron transfer during the electrocatalytic process. The cell with an optimal carbon/Fe/Fe3C interlayer delivers excellent cyclability and rate performances. At current densities of 0.2C and 2C, the specific capacities are close to 1000 and 735 mA h g−1, respectively. Even after 200 cycles at 1C, the reversible specific capacity is still 772 mA h g−1. Such a synergistic catalytic interlayer with an enhanced conversion kinetic towards polysulfides provides a new approach for improving electrochemical performances of LSBs.