Anthozoan-like porous nanocages with nano-cobalt-armed CNT multifunctional layers as a cathode material for highly stable Na–S batteries

Abstract

The capacity decay of room temperature Na–S batteries is mainly caused by the poor electronic conductivity, shuttle effect, and volume expansion of sulfur/polysulfides (NaPSs). Herein, anthozoan-like nitrogen-doped porous carbon nanocages with a nano-Co-armed carbon nanotube (CNT) multifunctional layer are proposed to improve the stability of Na–S batteries effectively. In this unique structure, the nano-Co-armed CNT functional layer not only enhances the adsorption of soluble NaPSs through Co–S bonding but also efficiently catalyzes their conversion to Na₂S_x (2 ≤ x ≤ 6). The hollow and porous nanocages provide a buffer space for volume expansion of the electrode material during the cycle. The nitrogen-doped highly graphitized carbon has high electronic conductivity. As the cathode material in room temperature (RT) Na–S batteries, the proposed material with a nano-Co-armed CNT functional layer delivered an improved stable electrochemical performance and achieved 314.8 mA h g⁻¹ at 0.5 C with a 0.025% decay rate per cycle for 1000 cycles, high coulombic efficiency (∼100%), and excellent capacity rate (426.1 mA h g⁻¹ at 0.1 C, 351.8 mA h g⁻¹ at 0.5 C, and 411.9 mA h g⁻¹ when back to 0.1 C).