Highly stable lithium–sulfur batteries based on p–n heterojunctions embedded on hollow sheath carbon propelling polysulfides conversion

Abstract

Newly-developed lithium–sulfur batteries (LSBs) have been supposed to be extremely promising devices as they deliver a high theoretical energy of 2600 W h kg⁻¹. Utilizing sulfur as the cathode material is advantageous due to its low price, non-toxicity, and abundant resources. The main bottleneck hindering the practical application of LSBs is their poor cycling performance due to the shuttling of soluble lithium polysulfides (LiPSs), poor conductivity, and sluggish redox reaction. Herein, we prepared a new type of p–n heterostructure embedded into carbon hollow nanosheet arrays grown on carbon cloth by subsequent sulfidation and nitridation. The hollow heterostructures can sufficiently restrict the dissolution of LiPSs due to the polar chemisorption and physical confinement, and facilitate polysulfide redox kinetics (Li₂S_x → Li₂S, 2 ≤ x ≤ 8). The abundant active sites and boundary defects constructed by the Co₉S₈–Co₄N heterostructures improve the nucleation/conversion redox kinetics of Li₂S. Also, the hollow structure can increase the sulfur loading and supply enough space for relieving the volume expansion during the whole cycling process. After melting the diffused sulfur of the nanocomposites, the resulting free-standing S/CC@Co₉S₈–Co₄N electrode exhibits a highly stable cycling rate with an ultralow capacity fading rate of 0.027% per cycle at 5.0C over 1000 cycles. Our work provides a potential avenue for constructing heterostructured materials for LSBs with high performance.