Designing Hollow Carbon Sphere with Hierarchal Porous for Na-S Systems with Ultra-Long Cycling Stabilities.

Captured by the low-cost and high theoretical specific capacity, Na-S systems have garnered much attention. However, their intermediate products (dissolved polysulfide) are always out of control. Considering the excellent space confinements and conductivity, they have been regarded as promising candidates. Herein, the hollow spheres with suitable thickness shell (~20 nm) are designed as hosting materials, accompanied by in-depth complexing. Benefitting from the abundant micro-pores (mainly about conical-type and slits-type pores < 1.0 nm), the active S4 molecules are successfully filled in the pores through vacuum tube sealing technology, effectively avoiding the process from solid S8 to liquid Na2S6. As cathode for Na-S systems, their capacity could remain at 920 mAh g−1 at 0.1 C after 100 cycles. Even at 10.0 C, the capacity still remained at about 310 mAh g−1 after 7000 cycles. Supported by the detailed kinetic behaviors, the improvement of ions diffusion behaviors is noted, bringing about the effective thorough redox reactions. Moreover, the enhanced surface-controlling behaviors further induces the evolution of rate properties. Therefore, their stable phase changing is further confirmed through in situ resistances. Thus, the work is anticipated to offer significant design for hosting carbon materials and complexing manners.