The Effective Design of a Polysulfide-Trapped Separator at the Molecular Level for High Energy Density Li–S Batteries

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• 作者：Chao-Ying Fan ; Hai-Yan Yuan ; Huan-Huan Li ; Hai-Feng Wang ; Wen-Liang Li ; Hai-Zhu Sun ; Xing-Long Wu ; Jing-Ping Zhang
• 刊名：ACS Applied Materials & Interfaces
• 出版年：2016
• 出版时间：June 29, 2016
• 年：2016
• 卷：8
• 期：25
• 页码：16108-16115
• 全文大小：492K
• 年卷期：0
• ISSN：1944-8252

文摘

In this work, the lightweight and scalable organic macromolecule graphitic carbon nitride (g-C₃N₄) with enriched polysulfide adsorption sites of pyridinic-N was introduced to achieve the effective functionalization of separator at the molecular level. This simple method overcomes the difficulty of low doping content as well as the existence of an uncontrolled form of nitrogen heteroatom in the final product. Besides the conventional pyridinic–N-Li bond formed in the vacancies of g-C₃N₄, the C–S bond was interestingly observed between g-C₃N₄ and Li₂S, which endowed g-C₃N₄ with an inherent adsorption capacity for polysulfides. In addition, the microsized g-C₃N₄ provided the coating layer with good mechanical strength to guarantee its restriction function for polysulfides during long cycling. As a result, an excellent reversible capacity of 840 mA h g^–1 was retained at 0.5 C after 400 cycles for a pure sulfur electrode, much better than that of the cell with an innocent carbon-coated separator. Even at a current density of 1 C, the cell still delivered a stable capacity of 732.7 mA h g^–1 after 500 cycles. Moreover, when further increasing the sulfur loading to 5 mg cm^–2, an excellent specific capacity of 1134.7 mA h g^–1 was acquired with the stable cycle stability, ensuring a high areal capacity of 5.11 mA h cm^–2. Besides the intrinsic adsorption ability for polysulfides, g-C₃N₄ is nontoxic and mass produced. Therefore, a scalable separator decorated with g-C₃N₄ and a commercial sulfur cathode promises high energy density for the practical application of Li–S batteries.