The unique interconnected structure of hollow carbon skeleton doped by F and N facilitating rapid Li ions diffusion in lithium-sulfur batteries

Abstract

Hollow carbons are considered as one of promising host materials applied in lithium-sulfur batteries because sulfur can be well encapsulated in these hollow units. However, the ineffective contact among these discrete units tends to cause high lithium ions diffusion barrier and interunit resistance, thus reducing sulfur conversion kinetics and utilization. Herein, a hollow carbon skeleton (NFHC) with interconnected tubular cavity is fabricated by successfully replicating the nanostructure complementary to attapulgite fiber bundle templates. The unique interconnected structure and introduction of polar F and N sites facilitate lithium ions diffusion and inhibit the shuttle effect of polysulfides through chemisorption. The NFHC/S cathode delivers a reversible capacity of 675.3 mAh g−1 at 0.5 C after 500 cycles with a low capacity decay rate of 0.05% per cycle. Its lithium ions diffusion rate is 2–3 times as that of dispersed carbon nanotubes. Therefore, NFHC/S delivers an improved capacity with 546.8 mAh g−1 at 4 C. Further increasing the sulfur loading to 4.7 mg cm−2, the NFHC/S cathode exhibits a reversible capacity of 530.0 mAh g−1 with a low E/S ratio of 6 μL mg−1 after 300 cyles. This work provides new insights into the structural optimization of hollow functional materials.