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Preparation And Electrochemical Performance Of Nitrogen Containing Based Mesoporous Materials As Cathode Matrix For High Performance Lithium/Sulfur Batteries

Posted on:2017-03-22Degree:MasterType:Thesis
Country:ChinaCandidate:C S XuFull Text:PDF
GTID:2271330485456279Subject:Chemical engineering
Abstract/Summary:PDF Full Text Request
Lithium sulfur (Li/S) batteries have attracted researchers’attention due to its high specific capacity and large energy density. It is considered as one of the most promising next-generation secondary batteries. In spite of the above advantages, it still faces with several challenges to develop the Li/S batteries, including the low conductivity of sulfur and discharge products (Li2S/Li2S2), the shuttle effect and the volume change at charge/dischargr process. It needs to solve these problems for the application of Li/S batteries. In order to solve the above mentioned issues, the template method was adopted to prepare carbon nitride (CN) materials as hosts for Li/S batteries. The morphologies, structures and electrochemical performance of materials were characterized using BET, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) measurement, transmission electron microscopy (TEM), and a series of electrochemical test systems.A facile silica template nanocasting method was adopted to effectively synthesize mesoporous carbon nitride (MCN) based materials as cathode matrixes for advanced lithium/sulfur (Li/S) batteries. The materials were characterized by BET, XRD, XPS, scanning electron microscopy and transmission electron microscopy. After removing SBA-15 templates, the MCN sample showed a very high specific surface area of 770.5 m2 g-1 and a large total pore volume of 1.19 cm3 g-1, providing an excellent potential for high sulfur loading. As a result, the MCN/S composite cathode displays excellent electrochemical performance with initial discharge capacities of 1284.5 and 1107.1 mA h g-1 for 66.7 wt% active material at 0.1 and 0.5 C, respectively. And it presents good rate performance and stability with remaining discharge capacity of 828.4 mA h g-1 after 100 cycles at 0.5 C.In our work, the three-dimensional interconnected mesoporous carbon nitride (3D-MCN) materials were prepared using SiO2 nanoparticles as the template, and used by cathode matrixes materials for advanced Li/S batteries. They presented three-dimensional interconnected structure were beneficial to the transport of ions and electrons, and restraining the shuttle effect of polysulfides. The materials were characterized by BET, XRD, XPS, SEM and TEM. After removing SiO2 templates, the 3D-MCN sample presented a very high specific surface area of 836.6 m2 g-1 and a large total pore volume of 1.60 cm3 g-1, providing the excellent potential for high sulfur loading. Additionally,3D-MCN shows three-dimensional interconnected mesoporous structure and nano-capsules by SEM and TEM. As a result, the 3dMCN/S composite cathode displays excellent electrochemical performance with initial discharge capacities of 1382 mA h g-1 for 72.6 wt% active material at 0.1 C. And it presents discharge capacity of 849.6 mA h g-1 after 100 cycles at 0.5 C. it attains good rate performance and stability with remaining discharge capacity of 679.7 mAh g-1 after 200 cycles at higher 1 C. The excellent performances are mainly attributed to three-dimensional interconnected structure and the strong chemical interaction between sulfur and carbon-nitrogen framework, which not only can provide polysulfides reservoirs and transport channels for the transportation of ions and electrons within 3D-MCN/S, but also is beneficial to restrain polysulfides migration.
Keywords/Search Tags:lithium sulfur batteries, cathode materials, carbon nitride, hard-template method, electrochemical performance
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