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Study On The Preparation And Performance Of 3D Self-supporting Carbon Nanotube-based Li-S Battery Cathode Materials

Posted on:2021-01-07Degree:MasterType:Thesis
Country:ChinaCandidate:L Z GuoFull Text:PDF
GTID:2381330605974594Subject:Physics
Abstract/Summary:PDF Full Text Request
Lithium-sulfur batteries have ultra-high specific capacity and energy density.The elemental sulfur has the advantages of low cost and eco-friendly,thus has attracted widespread attention from researchers.At present,there are many problems still need to be solved for lithium-sulfur batteries:Firstly,the poor conductivity of elemental sulfur and its discharge products lead to inefficient utilization of active materials and low electrochemical activity.Secondly,the formation of soluble polysulfide in the discharge process will cause shuttle effect,which will lead to the continuous loss of active substances,thus reducing the specific capacity of the device.In addition,the volume change of the electrode material during the charge and discharge process will destroy the electrode structure,seriously reducing the cycle stability of the battery.In view of the above problems,the cathode materials based on carbon nanotube arrays/sulfur and carbon nanotube sponges/sulfur composites(CNTA/S,CNTS/S)with 3D self-supporting porous structure has been prepared for Li-S battery Compared with the random carbon nanotubes/sulfur composites(RCNT/S)prepared under the same conditions,we investigated the effects of sulfur content,loading method as well as different pore structures of carbon nanotube electrodes on the electrochemical capacity,ion migration efficiency and cycle stability of Li-S battery It provides a necessary experimental reference for the further design and development of high-performance Li-S battery cathode materials.In this paper we find that both CNTA and CNTS materials with 3D self-supporting structure have three-dimensional conductive network and pore structure,which can effectively improve the utilization and electrochemical activity of sulfur,depress the shuttle effect of polysulfide,and buffer the volume change during charging and discharging process.They exhibit lower internal resistance,higher specific capacity,and longer cycle life than RCNT/S composites under the same conditions.Compared with the solution-based method,the molten-based method is easier to obtain crystalline sulfur and own a higher capacity.The CNTA has highly aligned pore structures,which is more conducive to the penetration of electrolyte and the transmission of electrons and ions.Hence the CNTA/S samples have smaller resistance and better rate performance.The CNTS has a three-dimensional interconnected network structure with larger porosity and can obtain higher sulfur loadings.At the same time,its elastic network structure is of a great benefit to buffering the volume change in the process of charging and discharging,thus greatly improves the cycle stability.The first discharge specific capacity of M-CNTS/S composites with sulfur loading up to 60%(wt.%)was measured to be 1285.5,1029.6 and 899.7 mAh g-1 at the current density of 0.5,1 and 3 C,respectively.After 100 cycles at the current density of 3 C,the retention of discharge specific capacity was still 88%.
Keywords/Search Tags:Lithium-sulfur batteries, carbon nanotube arrays, carbon nanotube sponges
PDF Full Text Request
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