Synthesis And Sodium Storage Properties Of Transition Metal Chalcogenides Nanocomposites

In recent years,the high demand for clean and renewable energy in the development of society has greatly promoted the exploration process of advanced energy storage systems.As potential replacement devices for lithium-ion batteries,sodium-ion batteries(SIBs)have attracted great attention due to their low cost and high efficiency and are becoming potential candidates for energy storage.Recent studies have demonstrated that metal sulfides(MS)are considered to be promising electrode candidates for sodium storage devices due to their excellent redox reversibility and relatively high capacity.However,the problem of persulfide and volume expansion during charge and discharge process severely restrict its practical application.In order to overcome the above problems,the composites of metal sulfides and carbons with unique nanostructures were rationally designed and synthesized in this paper.The morphology and composition of the composite were investigated by electron microscopy and X-ray diffraction techniques.In addition,we have conducted an in-depth analysis of the effects of the introduction of carbon materials on their electrochemical properties.As a rich mineral in the earth’s crust,iron sulfide not only has a high theoretical capacity but also is environmentally friendly.Therefore,it has great potential application in battery anode materials.In this paper,we successfully prepared a 500 nm Fe7S8/C composite by a simple hydrothermal method.A large number of cubes of 200 nm size are dispersed on the surface of the composite,and a 10 nm thick carbon nanolayer is coated on the surface of the particle.The introduction of thin carbon not only increases the conductivity of Fe7S8,but also provide more available paths for the transport of electrons and ions.When it was used as the sodium anode electrode,its reversible capacity was 497 mAh g-1 after 100 cycles.Compared with the performance of pure Fe7Ss electrode material,Fe7Ss/C composite material has great improvement in cycle life and rate performance.In order to further improve the electrochemical performance of metal sulfides,we successfully prepared three-dimensional(3D)carbon structure embedded nickel sulfide composites(NiSx@PCM)based on hydrothermal and freeze-drying techniques.The composites consists of a 3D carbon structure and embedded nano-nickel sulfide particles.The presence of 3D carbon material provides a large specific surface area for the electrode material,and the mesoporous and micropores can effectively alleviate the volume expansion effect caused by intercalation of sodium ions,and effectively improve the cycle performance.Relying on its unique properties,the NiSx@PCM electrode for SIBs delivered a high specific capacity(680 mAh g-1 at 0.2 A g-1)and the remarkable cycling stability(more than 300 mAh g-1 retained after 800 cycles at 1 A g-1).The as-configured sodium ion hybrid capacitor(SIHC)also presented obviously enhanced energy and power densities.