Study On The Preparation Of Waste Materials Derived Carbon And Application In Lithium-sulfur Batteries

Lithium-sulfur batteries have become one of the research hotspots in the field of automotive power batteries because of their advantages,such as high specific capacity and easy availability of cathode sulfur.However,the conductivity of sulfur and discharge products is poor,and the volume change is obvious.Besides,its intermediate product Li₂S_n（4≤n≤8）is easily dissolved in the electrolyte,causing a shuttle effect,resulting in the loss of active material and affecting the electrochemical performance.In order to overcome the above-mentioned shortcomings,improve the cycle stability of the battery,and respond to the call of the national waste recycling policy to expand the application field of waste.In this thesis,two carbon-based materials were designed and prepared as a cathode or interlayer materials for lithium-sulfur batteries using waste corn silks and non-woven fabrics as carbon precursors to enhance the electrochemical performance of the batteries,and the mechanisms of the different materials in the batteries were explored.The relevant studies are as follows:（1）Porous carbon materials（CS-XNHP-C）were prepared using waste corn silks as carbon precursors and ammonium dihydrogen phosphate in different mass ratios as activators and used as sulfur cathode carriers.It is shown that the proper amount of activator can help the carbon material to make pores,but too high a content will destroy the formed pore structure and affect the electrochemical performance of the battery.At a mass ratio of 1.5,the CS-1.5NHP-C material with abundant mesoporous structures exhibited relatively optimal electrochemical performance.The S@CS-1.5NHP-C shows good performance in the multiplier tests at 0.1 C,0.5 C,1 C,and 2 C corresponding to average specific capacities of 1057.3,766.5,642.1,and 501.5 m Ah g^-1.It can be stably cycled for 500 cycles at 1 C,showing good cycling stability.（2）To synthesize Co particle-catalyzed growth of nitrogen-doped carbon nanotube-modified carbonized nonwoven materials（NCN-Co）,waste nonwoven fabric was used as precursors with melamine as carbon and nitrogen sources.The free-standing composites can be used as an interlayer for lithium-sulfur batteries directly.The 3D structured interlayer with nitrogen atom doping can act as a barrier to provide sufficient storage space and chemisorption sites for lithium polysulfide to suppress the shuttle effect.In addition,electrochemical tests and theoretical calculations show that the encapsulated Co nanoparticles can improve the catalytic activity of lithium polysulfide,lower the reaction energy barrier and enhance the redox kinetics.The initial discharge specific capacity of the lithium-sulfur battery with the addition of NCN-Co was 1092 m Ah g^-1 at 2 C.Even after 600 cycles of charging and discharging,it still exhibited high-capacity retention capability and the electrochemical performance of the battery was significantly improved.