Three-dimensional graphene network-supported Co, N-codoped porous carbon nanocages as free-standing polysulfides mediator for lithium-sulfur batteries

Abstract

Construction of sulfur host with high immobilization ability and catalytic effect towards polysulfide intermediates is of great significance to boost the electrochemical performance of lithium-sulfur (Li-S) batteries. Herein, for the first time, a free-standing sulfur host consisting of cobalt and nitrogen co-doped porous carbon nanocages supported by reduced graphene oxide (Co/N-PCN@rGO) is synthesized via a calcination of graphene-supported cobalt-based zeolitic imidazolate framework precursor and, followed by etching treatment. After a melt infiltration process, the sulfur can be uniformly confined within the Co/N-PCN@rGO host (Co/N-PCN@rGO@S). When employed as the free-standing cathode material for Li-S batteries, the achieved Co/N-PCN@rGO@S not only shows an exceptional initial discharge capacity of 1290 mA h g−1 at 0.2 C, but also keeps a capacity of 640 mA h g−1 over 500 cycles at 1.0 C with a fading rate of only 0.066% per cycle. In addition, the high rate test also confirms its superior rate capability with a high capacity of 880 mA h g−1 at 2 C. Such outstanding performance can be attributed to the synergism of the integrated conductive network, the favorable surface structures of carbon framework as well as its strong charge coupling with Co and N species, ensuring an enhanced electron transfer kinetics, increased sulfur utilization, and improved immobilization and catalytic ability towards polysulfide intermediates.