Core-double shell sulfur@carbon black nanosphere@oxidized carbon nanosheet composites as the cathode materials for Li-S batteries

Although lithium-sulfur batteries (LSBs) have rather high capacity and specific energy, they are facing many drawbacks, e.g. low electrical conductivity of sulfur (S₈) and lithium sulfide (Li₂S), low capacity retention, large volume expansion of lithium sulfide in full lithiation state and dissolution of intermediate lithium polysulfides into the electrolytes. In order to address some drawbacks of the LSBs, here, sulfur was encapsulated by carbon black nanospheres (CN) and oxidized carbon nanosheet (OCN) with a sheet-like morphology by a mechanofusion and a colloidal coating techniques, respectively. Core-double shell S@CN@OCN composites were used as the cathode materials for Li-S batteries. The first CN shell can reduce the volume expansion of the sulfur during the charging process and also enhance the electrical conductivity. The second OCN shell can accommodate the volume expansion of the sulfur and decrease the "redox shuttle effect". The LSB using the core-double shell S@CN@OCN cathode can provide the first and second discharge specific capacities of 1,313 and 1,279 mAh g⁻¹ at 0.1C, respectively. In addition, the stability of this LIB tested at 1C over 400 cycles provides 77% capacity retention and 98% coulombic efficiency. This newly designed core-double shell S@CN@OCN structure may be the promising cathode of LSBs leading to the practical applications.