Fully integrated hierarchical double-shelled Co9S8@CNT nanostructures with unprecedented performance for Li–S batteries

Abstract

The insulating and dissoluble features of sulfur and polysulfide intermediates significantly hinder the cycling performance and coulombic efficiency of Li–S batteries. We herein design fully integrated hierarchical double-shelled Co₉S₈@CNT hollow nanospheres as a sulfur host, where each shell owns a tri-layer sandwich structure and six functional layers are constructed in total. Uniquely, the hierarchical structures integrate the beneficial functions of electrical conductivity, ion diffusion, polysulfide immobilization and polysulfide redox kinetics. The Co₉S₈@CNT/S delivers a reversible specific capacity of 1415 mA h g⁻¹ at 0.2C, which is very close to the theoretical capacity of sulfur. Moreover, even at a high rate of 10C, an unprecedented capacity of 676.7 mA h g⁻¹ can still be achieved, which represents the best rate capability among the ever-reported sulfur cathodes with similar sulfur content. More importantly, the Co₉S₈@CNT/S also displays a high coulombic efficiency of nearly 100% and an excellent cycling performance for up to 1000 cycles with a capacity fading rate of only 0.0448% per cycle. Even at the loading amount of 5.5 mg cm⁻², the areal capacity can still reach 4.3 mA h cm⁻². The concept to rationally integrate distinct components into fully functional units could provide valuable insights for the development of Li–S batteries and beyond.