Synthesis Of Carbon Based Materials Derived From ZIF-67 And Application For Lithium-Sulfuer Batteries

Lithium-sulfur?Li-S?battery is recognized as one of most promising energy storage system owing to their overwhelming theoretical energy density and ultrahigh theoretical specific capacity.Nevertheless,the practical application of Li-S batteries still remains many challenges,such as low discharge capacity,poor cycle stability and poor rate capability,which were mainly originated from the insulating nature of sulfur,drastic volume exoansion under cycling and so called“shuttle effect”.Notably,the reasonable design and preparation of sulfur cathode is recognized as an efficient strategy to address these issues.At present,utilizing metal-organic frameworks?MOFs?as template to prepare carbon/inorganic composite nano materials with complex pore structure and heteratomic doping is one of the most popular strategies.In this work,three kinds of carbon/inorganic composite materials?Co-NC,CoS₂-NC and Co₉S₈-NC?derived from ZIF-67 were prepared,and then applied them as sulfur hosts for cathode materials of Li-S batteries.Systematic study the influences of nanostructure of carbon hosts,N-doping and polar nano inorganic materials on electrochemical performances of Li-S battery.Besides,this work focused on the suppression mechanism between CoS₂-NC,Co₉S₈-NC and LiPSs to improving the electrochemical performance of Li-S batteries.?1?Co-NC porous carbon materials were prepared by optimize the aging times and reactant molar ratio of ZIF-67 precursor,and then,the effects of annealing temperature and HCl etching time on the structure and electrochemical properties of Co-NC materials were systematically studied.The S/Co-NC?24 h?electrode showed enhanced cycle performance and rate capability,after 200 cycles at 0.2 C curreng density,a high capacity of 725.2 mAh?g^-1 was still obtained,and even at a high current rate of 5.0 C,the cathode still possess a promising capacity of 718 mAh?g^-1.The enhanced electrochemical performances mainly originated from the physical absorption between N-doped porous carbon host and LiPSs.?2?CoS₂-NC porous carbon material was successfully prepared by directly sulfidizing the Co-NC,and then applied CoS₂-NC as sulfur host for cathode caterials of Li-S battery.The S/CoS₂-NC electrode exhibited enhanced cycle stability and rate performance,when cycled at 0.2 C current density,a high initial discharge capacity of1264 mAh?g^-1 was obtained,and possessed a low capacity decay rate of 0.064%per cycles after 500 cycles at 1.0 C current density.Natably,even at a high current rate of5.0 C,a promising discharge capacity of 845 mAh?g^-1.Experimental results reveal that the improvement in electrochemical performances mainly originated from the strong chemsorption between S/CoS₂-NC electrode and LiPSs and catalysis effect of polar CoS₂ nanoarticles on redox reaction.?3?A hollow carbon composite material Co₉S₈-NC was prepared by h hydro-thermal treatment of ZIF-67 precursor,and then applies as sulfur host for Li-S battery.The S/Co₉S₈-NC electrode exhibited a high initial discharge capacity of 1176.9mAh?g^-1,and a low capacity decay rate of 0.11%per cycle after 400 cycles at 0.5 C current density,even cycled at a high current rate of 5.0 C,the electrode still possess a promising discharge capacity of 745.8 mAh?g^-1.Experimental results reveal that the strong chemsorption between S/Co₉S₈-NC and LiPSs and catalysis effect on redox reaction attributed to Co₉S₈ nanoparticles acted as key role for improving the electrochemical performances of Li-S battery.