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Interfused Hollow Nitrogen-doped Carbon Developed as Sulfur Hosts for High-energy-density Lithium-Sulfur Batteries

Sep 17, 2019

Lithium-sulfur (Li-S) batteries are considered as one of promising energy storage systems owing to their high theoretical specific capacity and high energy density. 

Hollow heteroatom-doped carbon materials have been utilized as sulfur hosts for improving specific capacity and cycling life due to their large voids for relieving volume expansion and enhancing confinement towards polysulfides. But most of them are discrete and are lack of interfacial connectivity and conductivity, which increases the interface resistance and reduces the volumetric energy density.  

In a study published in Advanced Functional Materials, Prof. WANG Ruihu and his colleagues from Fujian Institute of Research on the Structure of Matter from the Chinese Academy of Sciences reported one type of new interfused hollow nitrogen-doped carbon (HNPC) materials derived from imidazolium-based ionic polymer (ImIP)-encapsulated zeolitic imidazolate framework-8 (ZIF-8).  

The researchers found that when HNPC was used as sulfur host, the unique structure merits greatly decrease the interfacial resistance and promote the redox kinetics of sulfur species, which endows the resultant electrodes with remarkable cycling stability, high rate capability and large volumetric energy density. The electrochemical performance is greatly superior to those in the traditional porous heteroatom-doped carbon-based cathode materials.  

In addition, they proposed a general method for the fabrication of the interfused HNPC. 

In the core-shell ZIF-8@ImIP materials, the low thermal stability of ImIP will allow the released volatile molecules to be adsorbed into the intrinsic pores of ZIF-8, resulting in gradual disassembly of internal ZIF-8 core during pyrolysis, which not only avoids the additional procedures for the removal of cores, but also enriches porous properties of the resultant carbon materials.

Meanwhile, the thermal polymerization of dicyandiamide (DCA) anions in the ImIP shell could form triazine-based intermediates, which sustains the collapse of the outer shell during pyrolysis, resulting in the formation of HNPC. 

The proposed methodology can be extended to a large family of core-shell materials based on various metal–organic frameworks (MOFs) and ionic polymers, which not only opens a new avenue for the design of a broad range of hollow-structured architectures with target functionalities, but also holds great promise for the development of various high-performance energy storage and conversion systems. 

 

Schematic illustration for the synthesis of HNPC, Nitrogen-doped porous carbon (NPC), and Nitrogen/Sulfur-codoped porous (NSPC) (Image by Prof. WANG’s group) 

Contact

WANG Ruihu

Fujian Institute of Research on the Structure of Matter

E-mail:

Engineered Interfusion of Hollow Nitrogen‐Doped Carbon Nanospheres for Improving Electrochemical Behavior and Energy Density of Lithium–Sulfur Batteries

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