Study On The Electrochemical Performance Of The Sulfur Loaded On Carbon Nanotube Sponges

Carbon nanotubes?CNTs?have been widely studied in lithium-sulfur batteries for their theoretically high electrical conductivity.However,the current method cannot achieve the uniform dispersion of sulfur on the CNTs.Furthermore,the flexibility of the substrate would be decreased sharply for high mass of sulfur loading.Therefore,it is urgent to explore a simple method to obtain dispersed sulfur particles on support with high mass loading and flexibility for their practical applications.?1?In this thesis,fluffy and porous CNT sponges?CNTF?were prepared from CNT continuums.The sponges show high viscosity that can be used for absorption of sulfur.The integrated electrode with sulfur that dispersed uniformly on the surface of the CNT sponge can be obtained after sulfur evaporated.The electrode can be prepared on a large scale with simple method.In addition,the discharge specific capacity of the obtained electrode with 50wt%sulfur loading is as high as 1288 mAh g^-11 at the current density of 1.58 A g^-1,and the value is also as high as 823 mAh g^-11 at current density of 1.58 A g^-1.The results indicated high utilization rate of sulfur in the electrode.The high mass loading of 77 wt%sulfur in the electrode also can be obtained after absorbing sulfur on the sponges then heated.The specific capacity of the electrode is about 500 mAh g^-11 after 200 cycles at a current density of 0.2 C,indicating potential applications in batteries.?2?The transparent soft lithium-sulfur battery was assembled to directly observe the electrochemical reaction during charging/discharging processes based on the color of the electrolyte.The UV based on electrolyte with different color was used to characterize the electrochemical reactions in lithium-sulfur battery.In addition,XRD and Raman spectra were also used to identify the intermediate products in the battery.And thereby different polysulfides in different reaction process can be demonstrated.?3?The diffusivity of the polysulfide was demonstrated through the transparent soft lithium-sulfur battery.The polysulfide is considered to be high electrochemical activity in sulfur products.After discharge the lithium-sulfur battery to a potential of 2.1 V,the obtained polysulfide in electrolyte can be wetted by CNTF for sulfur electrode.The electrode indicates homogenous sulfur distribution and high discharge specific capacity of 1346 mAh g^-11 at current density of 0.1 C.And the specific capacity of the electrode is still as high as 880 mAh g^-11 at current density of 5 C.The results suggest excellent coulomb efficiency of 99%in charging/discharging process.The SEM images also indicate that the obtained active polysulfide with high electrochemistry distributes homogenously in the CNT sponges,thereby shuttle effect in the lithium-sulfur battery can be restrained.