The Carbon Nanotubes Reactor For Lithium-sulfur Batteries

Due to its highest charge capacity,low cost and non-toxicity in all known cathode materials,elemental sulfur is a promising cathode material for the next generation of high-performance lirhium batteriers. However,previous Li/S batteries encounter many serious problems,such as poor rechargeability and very low active material utilization,which inhibit the commercialization of rechargeable Li/S batteries.In this study, a variety different sizes of carbon nanotubes/sulfur composites were prepared as cathode materials for Li/S batteries. The structures and components of the composites were characterized by TEM,Raman,XPS and TGA.The charge and diacharge capacities,reversibilities and the cycle performance of the above-mentioned composites were systematically studied in lithium batteries.We found the states of active substances in the composites have a great influence on the performance of the composite by studying the S-in-SCNTs and S-on-SCNTs composite.The S-on-SCNTs composite have an initial discharge capacity of 421.7mAh/g which much higher than the S-in-SCNTs composite. But the capacity fade is very quickly and after the first discharge,its nearly impossible to recharge.Although the capacity of the S-in-SCNTs composite is very low, but it's very stable and it maintains a reversible capacity of 115.3 mAh/g after 100 cycles.The different performance of S-in-SCNTs and S-on-SCNTs mainly lie on the states of elemental sulfur in the composite. If the elemental sulfur out of the nanotubes,the elemental and high soluble polysulfides very easily dissolve into the electrolyte between the charge-discharge process and led to the low charge-discharge capacity and poor cycle performance.But if the elemental sulfur was filled in the pore channels of the carbon nanotubes,the carbon nanotubes acted as the nanoreactor which can inhibit the elemental sulfur and polysulfides dissolve into the electrolyte by the confinement effect of the carbon nanotubes and improve the performance of the battery. Through designing the nanoreactor in the cathode structure can greatly improve the performance of the Li/S battery. In view of the unique structure of the carbon nanotubes, their cavities in nanotubes can limit the reaction process. The nanoreactor can effectively prevent the ploysulfides dissolve in the electrolyte,so that the utilization of the elemental sulfur can be greatly improved and improve the cycle performance of the Li/S battery.Designing the nanoreactor in the carbon nanotubes/sulfur composites can greatly improve the level of the performance of lithium-sulfur battery,and the size of the carbon nanotubes is crucial for the performance.The S-in-MWCNT1020 composite has the first discharge/charge capacity of 1071.9/759.1mAh/g,and remintains 538.5mAh/g after 50 cycles,which is the best in all composites.The S-in-MWCNT1030 can't compare with the S-in-MWCNT1020,its discharge/charge capacity is stable at 320mAh/g after 50 cycles. The S-in-SCNTs and S-in-MWCNT10 composites have a very bad performance.