Hierarchical assemblies of conjugated ultrathin COF nanosheets for high-sulfur-loading and long-lifespan lithium-sulfur batteries: Fully-exposed porphyrin matters
Hierarchical assemblies of conjugated ultrathin COF nanosheets for high-sulfur-loading and long-lifespan lithium-sulfur batteries: Fully-exposed porphyrin matters
复制标题
用于高硫载量和长寿命锂硫电池的共轭超薄COF纳米片的分层组装：完全暴露的卟啉物质
DOI：
10.1016/j.ensm.2018.12.021
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发表时间：
2019-11-01
影响因子：
20.4
通讯作者：
Yu, Dingshan
中科院分区：
文献类型：
--
作者：
Hu, Xuanhe;Jian, Junhua;Yu, Dingshan
共价有机骨架（COF）是用于下一代能量存储装置如Li-S电池的有前途的电极材料。然而，大多数现有的COF材料被生产为具有密集堆积结构和微孔纹理的微晶粉末，这导致缓慢的离子扩散、活性位点利用不足或活性材料负载有限，限制了实际实施。在本文中，我们报告了第一个自下而上合成的3D分层COF超结构，包括富含卟啉的共轭碳纳米片，作为一个多尺度的工程解决方案，以充分展示COF在锂硫电池中的潜力，上述障碍。制备的超结构具有最小的纳米片重堆叠，大的可及表面积和独特的宏观-介观-微观孔隙率，这不仅将传统COF中以扩散为主的氧化还原动力学转变为电荷转移控制的过程，而且还充分利用了固有的丰富活性位点，以最大化多硫化物的化学吸附并提高硫的利用率。重要的是，COF超结构可以作为一个理想的模型来探测活性官能团的特定作用，并揭示了完全暴露的卟啉作为独特的锚定位点与多硫化物的强化学结合。因此，COF超结构作为一种新的聚合物主体，赋予Li-S电池大容量，优异的倍率性能和优异的循环稳定性，特别是在高硫含量或负载下。
Covalent organic frameworks (COFs) are promising electrode materials for next-generation energy storage devices such as Li-S batteries. However, most existing COF materials are produced as microcrystalline powders with densely packed structure and microporous texture, which leads to sluggish ion diffusion, insufficient active site utilization or limited active material loading, constraining practical implementation. Herein, we report the first bottom-up synthesis of 3D hierarchical COF superstructures comprising porphyrin-rich conjugated ultrathin nanosheets, as a multiscale engineering solution to the above obstacles for fully demonstrating the potential of COFs in Li-S batteries. As-made superstructure features minimum nanosheet restacking, large accessible surface area with unique macro-meso-micro-porosity, which not only turns diffusion-dominated redox kinetics in conventional COFs into charge-transfer controlled process, but also renders sufficient utilization of inherent abundant active sites for maximizing the chemisorptions of polysulfides and boosting sulfur utilization. Importantly, COF superstructure can be used as an idea model to probe the specific role of active functional groups and fully exposed porphyrin is revealed to act as unique anchoring sites with strong chemical binding to polysulfides. Thus, COF superstructures, as a new polymeric host, endow Li-S battery with large capacity, excellent rate capability and superb cycling stability particularly at high sulfur content or loading.