Liu Jintao, Xiao Shu Hao, Zhang Zheye, Chen Yuan, Xiang Yong, Liu Xingquan, Chen Jun Song, Chen Peng
School of Materials and Energy, University of Electronic Science and Technology of China, Chengdu, 610054, China.
School of Chemical and Biomedical Engineering Nanyang Technological University 70 Nanyang Drive, Singapore 637457, Singapore.
Nanoscale. 2020 Feb 27;12(8):5114-5124. doi: 10.1039/c9nr10419d.
Even though lithium-sulfur batteries have appealing advantages including a high theoretical capacity and energy density, their commercial implementation has been seriously hindered by some notorious reasons, particularly the severe shuttling effect, the insulating nature of sulfur, the large volumetric variation during cycling and the sluggish redox reaction kinetics. To tackle these issues, a biomass (ginkgo-nut) derived N,S-codoped porous carbon (GC) with an interconnected honeycomb-like hierarchical structure is synthesized by a templated carbonization method, followed by hydrothermal growth of transition metal sulfide MS2 (M = Co, Ni) nanocrystals, giving rise to a hybrid 3D electrocatalyst. The unique structure constructed by N,S-codoping can expose more active sites and polar surfaces to physically confine and chemically adsorb polysulfides. Meanwhile, the embedded MS2 polyhedral-like nanoparticles further enhance the interaction with polysulfides and improve conversion and redox kinetics of polysulfides. Remarkably, with 80 wt% sulfur loading (∼2.5 mg cm-2), GC-CoS2 exhibits a reversible capacity of 988.8 mA h g-1 after 500 cycles at 0.1 C and an excellent capacity of 610.3 mA h g-1 after 1000 cycles at 2 C, outperforming bare GC and GC-NiS2. Compared with the electrochemical performances of the representative reported biomass-derived sulfur host for Li-S batteries, evidently, both the discharge capacity and cycling stability of our GC-CoS2 sample are superior. Density functional theory (DFT) calculation results suggest that CoS2 exhibits a higher binding energy towards lithium polysulfides and a lower energy barrier for Li+ diffusion on the surface compared to the NiS2 counterpart, suggesting that CoS2 is a better choice for lithium-sulfur batteries than NiS2. This work provides a new avenue to rationally design a carbonaceous catalyst host for high-performance lithium-sulfur batteries.
尽管锂硫电池具有诸如高理论容量和能量密度等吸引人的优点，但其商业化应用却因一些众所周知的原因而受到严重阻碍，特别是严重的穿梭效应、硫的绝缘性质、循环过程中的大体积变化以及缓慢的氧化还原反应动力学。为了解决这些问题，通过模板碳化法合成了具有相互连接的蜂窝状分级结构的生物质（银杏果）衍生的氮、硫共掺杂多孔碳（GC），随后通过水热生长过渡金属硫化物MS2（M = Co、Ni）纳米晶体，得到一种混合三维电催化剂。通过氮、硫共掺杂构建的独特结构可以暴露出更多活性位点和极性表面，从而物理限制和化学吸附多硫化物。同时，嵌入的MS2多面体状纳米颗粒进一步增强了与多硫化物的相互作用，并改善了多硫化物的转化和氧化还原动力学。值得注意的是，在硫负载量为80 wt%（约2.5 mg cm-2）时，GC-CoS2在0.1 C下500次循环后表现出988.8 mA h g-1的可逆容量，在2 C下1000次循环后表现出610.3 mA h g-1的优异容量，优于裸GC和GC-NiS2。与报道的用于锂硫电池的代表性生物质衍生硫宿主的电化学性能相比，显然，我们的GC-CoS2样品的放电容量和循环稳定性都更优异。密度泛函理论（DFT）计算结果表明，与NiS2相比，CoS2对多硫化锂表现出更高的结合能，并且在表面上Li+扩散的能垒更低，这表明CoS2比NiS2更适合用于锂硫电池。这项工作为合理设计用于高性能锂硫电池的碳质催化剂宿主提供了一条新途径。
