Mesoporous hollow carbon capsules as sulfur hosts for highly stable lithium–sulfur batteries

Abstract

Lithium–sulfur (Li–S) batteries have been becoming one of the most promising candidates for energy storage devices due to their large theoretical specific energy density (2600 Wh kg−1) and theoretical specific capacity (1675 mAh g−1). However, there are still several obstacles that restrict their commercial applications such as the insulating nature of sulfur, large volumetric expansion of sulfur cathodes and the shuttle effect of the soluble lithium polysulfide (Li2Sx, 4 ≤ x ≤ 8) intermediates, leading to the low sulfur utilization, fast capacity fading and low coulombic efficiency. Herein, we develop a simple, low-cost and high-yield method to synthesize mesoporous hollow carbon capsules (MHCCs) as sulfur cathode hosts for Li–S batteries. There are numerous worm-like mesopores with a size of 3.8 nm on the capsule’s wall (about 10 nm in thickness). As the sulfur hosts, the 3.8 nm mesopores on the walls of MHCCs can dramatically prevent polysulfides inside or adsorbed on the surface of the MHCCs to effuse from cathode to anode. As a consequence, the sulfur cathodes that utilizing unique MHCCs as the sulfur hosts (MHCCs/S cathodes) can significantly improve the long-term cycle performance (72% capacity retention after 600 cycles) of Li–S batteries.