Enhancing the diffusion of lithium ions to propel sulfur redox for lithium-sulfur batteries

Abstract

Lithium-sulfur batteries are considered one of the most promising energy carriers due to their ultra-high theoretical energy density and low manufacturing cost. However, the limited diffusion of lithium ions at the electrode interface and the slow redox kinetics of the sulfur cathode easily led to frequent shuttle effects, affecting the electrochemical performance of the battery. In this paper, sulfur electrode materials with different structures of one-dimensional carbon as the carrier and MoS₂ as the catalytic active material are designed by exploring the lithium ions diffusion and electrode reaction behaviors on the cathode surface. Among them, it is found that compared with carbon nanofibers and large-diameter carbon nanotubes, small-diameter carbon nanotubes (SD-CNT) have uniform hollow tubular morphology, abundant micropores, mesopores, and specific surface area, which is not only conducive to containing more active substances but also help the lithium ions diffusion inside the electrode material. Better electrochemical performance is obtained by constructing an interface environment that matches the ionic reaction and diffusion processes. It shows that the first discharge capacity of the obtained SD-CNT@MoS₂-S cathode is as high as 1144 mAh g⁻¹. The capacity retention rate reached more than 92.9% after 100 cycles at 0.5 C rate, further proving that SD-CNT@MoS₂-S can promote the diffusion of lithium ions and the redox kinetics of sulfur. This study provides a new strategy for developing lithium-sulfur batteries with high electrochemical performance.