Synergistic effect of Fe3C quantum dots, N-doped carbon and selenium on high conductive stable host for lithium sulfur batteries

Lithium-sulfur batteries are considered as one of the most promising energy storage devices. However, their development is still hindered by significant obstacles, particularly the well-known "shuttle effect". To overcome the issues, a three-dimensional porous biochar composite GC(Fe3C)x with Fe3C quantum dots/ C heterostructure is prepared by a simple one-stage chemical activation method as a sulfur host. A small amount of selenium is also added to form GC/Fe3C@SSe and improved electrochemical performances are obtained. The influence of Fe3C content on the structure and properties of the composites is investigated. It has been observed that an increase in Fe3C content leads to a reduction in specific surface area, thereby enhancing chemical adsorption while simultaneously weakening physical adsorption. When the Fe3C content reached 2.7%, the composite achieved a specific surface area of 1150.0 m² g−1. The synergistic effect of Fe3C quantum dots, N-doped carbon, and selenium resulted in outstanding electrochemical properties exhibited by the composite. At 1 C, GC/(Fe3C)2.7@SSe provides an initial specific discharge capacity of 803.7 mAh g−1. After 1000 long cycles, the specific discharge capacity is maintained at 363.1 mAh g−1, and the per-cycle capacity loss rate is 0.055%. Even at the current density of 5 C, the initial discharge capacity is 424.5 mAh g−1, and the capacity after 500 cycles is 322.9 mAh g−1, with a single cycle capacity decay rate of 0.048%. This work provides guidance for the design of lithium-sulfur battery cathode materials with synergetic physisorption and chemisorption for inhibiting shuttle effect.