KOH Activated CNTs/sputtered FeS₂ Composites As Sulfur Host For Lithium-sulfur Batteries

Lithium-sulfur batteries?LSBs?,due to their extremely high theoretical specific capacities and energy densities as well as their low cost and environmental friendliness,have been regarded as one of the most promising alternative to lithium-ion batteries as the next generation of new secondary batteries.However,LSBs often suffered from the dissolution and shuttle effect of lithium polysulfides?LPSs?during the charging/discharging processes,the non-conductivity of sulfur and LPSs,which greatly restricts the progresses in the commercial application of LSBs.In view of the above problems,this dissertation has introduced polar oxygen-containing groups into carbon nanotubes by KOH activation and sputtered a layer of FeS₂ on self-supporting sulfur positive electrode,so as to enhance the chemisorption of LPSs,to improve the utilization efficiency of electrodes'active materials,and accordingly to improve the performances of LSBs.The main results and conclusions of this dissertation have been summarized as follows:?1?Utilizing the defects and polar oxygen-containing functional groups?OFGs,such as C-O,C=O,-OH and O-C=O?created by KOH activation on CNTs to effectively adsorb and confine the LPSs.In this work,KOH activation treatments were systematically conducted on chemical-vapor-deposition-grown multi-walled carbon nanotubes?CNTs?to introduce polar OFGs on their surface,and to explore the role of each OFG on the electrochemical performances of LSB cathodes.Results showed that the capacity of activated-CNT-sulfur?a-CNT-S?cathodes is 33%higher than that of the pristine CNT-S cathodes,and their rate capability and cycling stability were also enhanced.Furthermore,the analyses combining with X-ray photoelectron spectroscopy?XPS?and Fourier transform infrared spectrum indicated that the enhanced electrochemical performances of a-CNT-S cathodes show a linear correlation with the numbers of the formed C-O bonds on CNTs.In addition,the optimal activation conditions on CNT-based Li-S battery cathodes were explored to be 10 min at700°C.?2?Introducing the polar ferrous disulfide to enhance the chemisorption of LPSs and to effectively depress the shuttle of LPSs during the charging/discharging processes.In this work,a thin layer of FeS₂ was successfully incorporated into CNT/s cathodes via simple and effective sputtering combining with post ambient annealing treatments,and a type of CNT/FeS₂/S cathodes was well designed.Results showed,the specific capacity of the CNT/FeS₂/S cathodes is twice as much as that of CNT/S ones,and the CNT/FeS₂/S cathodes also showed an excellent rate capability and a good cycling stability.Furthermore,combining electrochemical galvanostatic intermittent titration technique?GITT?and quasi in-situ XPS analysis during the discharging processes,we found that,FeS₂ can not only show an excellent adsorption effect on the LPS during the discharging processes,but also effectively catalyze the redox reaction on the electrodes during the charging/discharging processes,making the redox reaction faster and more thoroughly,improving the utilization efficiency of the active materials,and accordingly effectively improving the electrochemical performances of the electrodes.