Partial boronization of transition metal within double heterostructure nanosheet achieves high-rate and long-cycling lithium-sulfur batteries

Lithium-sulfur batteries (LSBs) have emerged as highly promising next-generation chemical power sources, characterized by their elevated specific energy. Their exceptionally high theoretical energy density has attracted considerable attention in both academic research and industrial application. Nonetheless, the shuttle effect and sluggish redox kinetics significantly hinder their advancement, resulting in the rapid deterioration of battery capacity and substantially limiting their practical application. To address this issue, this work reports a molten salt-assisted strategy. Using ZnCo-ZIF as a precursor, a novel dual heterostructure nanosheet (Co/CoB/NBC) composed of nitrogen and boron co-doped carbon (NBC), transition metal boride (CoB), and metallic element (Co) is successfully constructed and applied to modify the polypropylene (PP) separator in LSBs. The lithium-sulfur (Li-S) battery utilizing the Co/CoB/NBC-PP separator demonstrates remarkable cycle stability, successfully completing 800 cycles at a high rate of 8 C, with an initial discharge capacity reaching to 757 mAh g^-1 and a capacity retention of 80%. At 2 C, the initial discharge capacity is recorded at 1013 mAh g^-1, and following 1000 cycles, the average capacity degradation and capacity retention rate are measured at 0.025% and 75%, respectively. Furthermore, when subjected to cycling at a low current density of 0.5 C over the course of 100 cycles, the capacity retention rate is 81.3%. It is worth noting that when the sulfur loading of the electrode is as high as 5.2 mg cm^-2 and electrolyte-to-sulfur (E/S) ratio is 2.88 μL mg^-1, the first discharge capacity at 0.2 C is 825 mAh g^-1. This study provides a novel and highly valuable method for designing dual heterostructure nanosheet among metallic element, metal boride and carbon, aimed at enhancing the energy density and longevity of LSBs. This work also establishes a robust foundation for the continued advancement and practical implementation of LSBs technology.