Boosting Electrochemical Performances of Lithium Sulfur Battery Via Rational Design and Fabrication Engineering of Cobalt Boride-Base Core-Shell Structure Composite as a Multifunctional Sulfur Host

Abstract

Lithium-sulfur (Li-S) batteries possess high theoretical energy density (2600 Wh kg-1), but face some issues such as polysulfide shuttle and lithium dendrite growth. Transition metal borides (TMBs) are promising materials in which both metal and boron atoms act as active sites, enhancing the binding with lithium polysulfides (LiPSs) and facilitating LiPSs conversion reactions. Here, we ingeniously integrate carbon materials with polar TMBs to synthesize a CoB/NCCS composite which features a nitrogen-doped conductive carbon shell (NCCS) and a cobalt boride (CoB) core, via co-precipitation synthesis of ZIF-67, dopamine polymerization on ZIF-67, boronization process and pyrolysis treatment. As a result, the Li-S battery with CoB/NCCS as the sulfur host achieves impressive discharge specific capacities of 1606.3, 1143.0, 1001.8, 946.2, and 727.0 mAh g-1 at 0.1, 0.2, 0.5, 1 and 2 C, respectively. Additionally, the electrode also exhibits a remarkably low capacity decay rate of 0.05% per cycle over 1000 cycles at a high current density of 5 C, supporting the stable cycling characteristic. This work not only demonstrates that the CoB/NCCS composite is an extraordinary sulfur host material, but also provides an effective strategy to improve the electrochemical performances of metal borides by rational design and fabrication engineering.

Keywords: Lithium-sulfur batteries, Transition metal borides, Polysulfide shuttle, Core-shell structure