| The room-temperature sodium-sulfur battery system has become a research hotspot in the sodium battery due to its high specific capacity,good safety,low cost and environmental friendliness.However,there are a series of problems such as the poor conductivity of sulfur and polysulfide in the sulfur cathode,the pulverization caused by the volume change during the charging and discharging process,and the"shuttle effect",which seriously hinder the practical application of the room temperature sodium sulfur battery.In order to solve the above problems,this topic will focus on the sulfur cathode,by constructing a cobalt modified nitrogen-doped carbon matrix material and compounding with sulfur,it can solve the problems of poor conductivity,serious volume change and slow electrochemical reaction kinetics of the room temperature sodium-sulfur battery cathode.In addition,by constructing a theoretical interface model of the material and studying its energy storage mechanism,the microporous structure of the material and the role of the Co element are analyzed to provide a basis for the subsequent development of room temperature sodium-sulfur batteries.Two different Co-modified ZIF-8 precursors were synthesized by impregnation method and eutectic method respectively,and S@Co/NC cathode material was obtained by high-temperature carbonization and combination with sulfur.The morphology of the matrix material after high temperature carbonization is intact,and it has a relatively high specific surface area and micropore volume.Among the sulfur-loaded composite materials prepared by the impregnation method and high-temperature carbonization,S@0.5h-Co/NC-1 synthesied with an impregnation time of 0.5 h has excellent cyclic and rate performance.The as-prepared S@0.5h-Co/NC-1 electrode has an initial specific capacity of 1271 m Ah g-1 at 0.1 C,a reversible specific capacity of 691 m Ah g-1 at a high rate of 3.0 C.Meanwhile,the capacity retention rate are 90.9%at 0.2 C after 100 cycles and 84.0%at 1.0 C after 150 cycles.In the S@Co/NC-2 electrode prepared by eutectic method and high-temperature carbonization,the cyclic and rate performance of the material is excellent when the ratio of zinc to cobalt is 9:1,which has an initial specific capacity of 1336 m Ah g-1 at 0.1 C,a reversible specific capacity of 835 m Ah g-1 at a high rate of 3.0 C.Meanwhile,the capacity retention rate are 93.8%at 0.2 C after 100 cycles and 84.7%at 1.0 C after 200 cycles..Based on TEM,XRD and other test analysis,it is found that the existence form of Co element in the matrix material is related to its content.When the content of Co element is small,it exists in the form of small clusters.With the increase of Co content,the Co of small clusters spontaneously agglomerate to form Co particles.Theoretical calculations show that the monodisperse Co and N elements will improve the conductivity of the carbon matrix interface,and improve the adsorption capacity and electrochemical performance of the interface for sulfur and polysulfides.It was verified by GITT that Co element can improve the diffusion rate of Na+,and through CV curves of different sweep speeds and EIS curves at different potentials,it was confirmed that Co element played an accelerating role in the electrochemical reaction process.At the same time,the construction of different sizes of micropore interface models proved that a certain size of micropore structure will have a confinement effect on sulfur and polysulfides. |
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