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(Fe ₃C) _x with Fe ₃ C 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/Fe ₃ C@SSe and improved electrochemical performances are obtained. The influence of Fe ₃C content on the structure and properties of the composites is investigated. It has been observed that an increase in Fe ₃ C content leads to a reduction in specific surface area, thereby enhancing chemical adsorption while simultaneously weakening physical adsorption. When the Fe ₃C content reached 2.7%, the composite achieved a specific surface area of 1150.0 m² g ⁻¹. The synergistic effect of Fe ₃ C quantum dots, N-doped carbon, and selenium resulted in outstanding electrochemical properties exhibited by the composite. At 1 C, GC/(Fe ₃C) _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.