Two-Dimensional Metal-fr ee Compounds of BC4N and BC6N2 with Boron Atoms as Highly Efficient Catalytic Centers toward Sulfur Redox in Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries are considered as ideal next-generation energy storage devices, the commercial applications of them are hindered by their inherent drawbacks of shuttle effect and sluggish conversion among lithium polysulfides (LiPs). To tackle these issues, significant research efforts have been devoted to designing high-performance metal-based catalysts implemented in the sulfur cathodes, which however face the challenges of source scarcity and cycling instability. Here, based on first-principles calculations, we investigated our previously predicted two-dimensional (2D) metal-free boron-containing catalysts of BC4N and BC6N2 and found that they possess strong trapping capability for LiPs adsorption energy as low as-6.41 eV beneficial for suppressing shuttle effect. Moreover, BC4N exhibits even superior catalytic performances toward the redox of sulfur, which can be evidenced by the low free energy change of the rate determining step of reduction reaction and small energy barrier of 0.80 eV for Li2S decomposition, outperforming most previously reported metal-based catalysts. Our research can pave a new way for designing new 2D metal-free catalysts in Li-S batteries, which highlights the importance of boron atoms in suppressing shuttle effect and catalyzing sulfur redox.