Tandem Carbon Hollow Spheres with Tailored Inner Structure as Sulfur Immobilization for Superior Lithium-Sulfur Batteries

The construction of lithium-sulfur battery cathode materials while simultaneously achieving high areal sulfur-loading, adequate sulfur utilization, efficient polysulfides inhibition, rapid ion diffusion, etc. remains a major challenge. Herein, an internal regulatory strategy to fabricate the unique walnut-like yolk-shell carbon flower@carbon nanospheres is presented (WSYCS) as sulfur hosts. The internal carbon flower, suitable cavity, and external carbon layer effectively disperse the insulate sulfur, accommodate volumetric expansion, and confine polysulfides, thus improving the performance of lithium-sulfur batteries. The finite element simulation method also deduces the enhanced Li+ diffusion and lithium-sulfur reaction kinetics. More importantly, WSYCS2 is grafted onto carbon fiber (CF) by electro-spinning method to form a tandem WSYCS2@CF 3D film as a sulfur host for the free-standing electrode. The corresponding battery exhibits an extremely high areal capacity of 15.5 mAh cm-2 with a sulfur loading of 13.4 mg cm-2. Particularly, the flexible lithium-sulfur pouch cell delivers a high capacity of 8.1 mAh cm-2 and excellent capacity retention of 65% over 800 cycles at a relatively high rate of 1C, corresponding to a calculated energy density of 539 Wh kg-1 and 591 Wh L-1. This work not only provides guidance for tailoring thick carbon/sulfur electrodes but also boosts the development of practical lithium-sulfur batteries. The rationally designed carbon hollow sphere internal structure of carbon fiber tandem as the sulfur cathode of flexible self-supporting lithium-sulfur batteries significantly optimizes the dispersion of sulfur/lithium sulfide, the diffusion of Li+, and the kinetics of the lithium-sulfur reaction, which leads to a significant enhancement of the energy density of the batteries.image