Scalable production of freestanding few-layer β12-borophene single crystalline sheets as efficient electrocatalysts for lithium

H.J. Lin, H.D. Shi, Z. Wang, Y.W. Mu, S.D. Li, J.J. Zhao, J.W. Guo, B. Yang, Z.-S. Wu,* and F. Liu*

ACS Nano, 2021, 15, 11, 17327–17336.

Two-dimensional (2D) borophene is predicted as an idealelectrode materialfor lithium sulfur (Li-S) batteries because of its low-density, metallic conductivity, high Li-ion surface mobility and strong interface bonding energy to polysulfide. But until now, 2D borophene-based Li-S batteries have not yet been achieved due to the absence of large-scale synthetic method of freestanding borophene nanostructures withnicestructural stability and uniformity for practical use. Herein, we developed a novel low-temperature liquid exfoliation (LTLE) method to synthesize freestanding few-layerβ₁₂-borophene single crystalline sheets with asymmetryin tens of milligram scale. The as-synthesized 2D sheets were used as the polysulfide immobilizers and electrocatalysts of Li-S batteries for the first time. The resulting Li-S cells using borophene sheets delivered a strikingly large areal capacity of 5.2 mAh cm^-2at a high sulfur loading of 7.8 mg cm^-2, an very excellent rate performance of 8 C(@721 mAh g^-1)as well as an ultralow capacity fading rate of 0.039% in1000 cycles, which was much better than commercial Li-ion batteries and many other 2D material-based Li-S batteries. Based on density functional theory (DFT) model, their high-activity behaviors are believed to originate from the significant enhancement of both the Li-ion’s surface migration and the adsorption energy for Li₂S_nclusters under the help of few-layerβ₁₂-borophene. Our research reveals great potential of freestandingβ₁₂-borophene single crystalline sheets in future high-performance Li-S batteries.