Boosting electrochemical performances of lithium sulfur battery via rational design and fabrication engineering of cobalt boride-based core-shell structure composite as a multifunctional sulfur host

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 2C, 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 5C, 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. The CoB/NCCS composite with a cobalt boride core and a nitrogen-doped carbon shell is designed and fabricated by four technological steps, co-precipitation synthesis of ZIF-67, dopamine polymerization on ZIF-67, boronization process and pyrolysis treatment . When the core-shell structure is applied as a sulfur host, it can not only provide internal volume buffering but also accelerate electron transport and sulfur conversion, displaying an excellent cycling stability at a high current density of 5C. • CoB/NCCS composite integrates a cobalt boride core with a nitrogen-doped shell. • The core-shell structure accommodates volume expansion with its internal cavity. • Sulfur conversion facilitated by the Co and B dual active sites of CoB/NCCS. • Li-S battery with CoB/NCCS host demonstrates high capacity and stability.