Synthesis Of Three-dimensional Aligned Carbon Nanotube Arrays/Sulfide And Lithium Storage Performance

Three dimensional aligned carbon nanotube arrays possess highly ordered morphology,which can shorten the electron/ion transport path and accelerate the permeation of the electrolyte to the active materials.Molybdenum disulfide(MoS2)has high specific capacity and excellent conductivity,which is one of the hot spots in the research field.However,there are some problems that stop their practical use,such as low conductivity and rapid capacity-fading.To overcome these problems,recent signicant investigation drives hot-concern on the MoS2/C based nanocomposites.For selenium sulfide(SexSy),it combines the high capacity of sulfur and high stability of selenium,but there are still some problems,such as low conductivity and shuttle effect,and one of the effective solutions to solve this kind of problem is to load the selenium sulfide to porous conductive material.In summary,based on 3D aligned carbon nanotube arrays by spray pyrolysis method and melt impregnation method,CNT/MoS2 and CNT/SexSy composite electrode material were prepared and studied on its lithium storage performance.The main results and new findings in this work are summarized as follows:(1)Molybdenum disulfide nanosheet embedded three-dimensional vertically aligned carbon nanotube arrays for lithium-ion anodes:Molybdenum disulfide(MoS2)nanosheets embedded in three-dimensional(3D)vertically aligned carbon nanotube arrays(VACNTs)have been fabricated via a simple nebulization-assisted hydrothermal method.The MoS2/VACNTs possess a highly ordered and uniformly oriented 3D structure with MoS2 nanosheets adhering strictly to the surface of VACNTs.When evaluated as lithium-ion anode materials,so-obtained MoS2/VACNTs composites containing 52 wt%MoS2 exhibit superb electrochemical performances,including high capacity(1078 mAh g-1 at 100 mA g-1 after 1st cycle),good rate capability(789 mAh g-1 at 2000 mA g'1 after 20 cycles),and extremely-excellent cycling stability,for the MoS2/VACNTs electrode can still deliver a discharge capacity of 512 mAh g-1 after 1000 cycles at 5000 mA g-1,compared with pristine MoS2(negligible discharge capacity at the 70th cycle).Such high electrical properties can mainly be attributed to the unique well-directed pore-morphology which provides low-resistant shortest diffusion pathways upon the high-conductive VACNTs to accelerate ion/electron movement.Moreover,the elastic spare-space inside/outside VACNTs as a buffer factor effectively restrains large volumetric change from MoS2 during the charge/discharge process.(2)SexSy encapsulated in three-dimensional(3D)nitrogen-doped vertically aligned carbon nanotube arrays for high performance lithium-sulfur batteries:3D nitrogen-doped vertically aligned carbon nanotube arrays(NVACNTs)with well-directed pore-morphology are used as a conducting matrix to encapsulate SexSy(SexSy/NVACNTs)as a cathode for for high performance lithium-sulfur batteries.In this composite architecture,the NVACNTs not only acted as effective SexSy carriers by confining the polysulfides and buffering volume changes during the charge-discharge processes but also provided an effective 3D conductive network to improve the electronic conductivity of the SexSy cathode.As results,compared with the S/NVACNTs cathode,the composite SexSy/NVACNTs as cathode material for Li-S batteries shows an excellent performance with up to 1110 mAh g-1 discharge capacity at 0.5 A/g while the S/VACNTs hold 1180 mAh g"1.However,when the electric current attain up to 2 A/g,the SexSy/NVACNTs still keep a high level of discharge capacity with 937 mAh g-1,whilest the S/VACNTs has just 550 mAh g-1.Furthermore,various kinds of conductive carbon structure with SexSy are compared in this paper.As results,the composite SexSy/NVACNTs perform a better electric chemical property:at 0.5 A/g,its discharge capacity is up to 1110 mAh g-1 discharge capacity while the S/VACNTs hold 1180 mAh g-1 up to 844 mAh g-1,hybrids exhibited a high and stable discharge capacity of up to 844 mAh g-1 over 150 cycles with capacitiy of 988 mAh g-1 for the first cycle.