Preparation Of Azine-based Frameworks And Their Performance In Lithium-sulfur Batteries

Lithium-sulfur(Li-S)batteries with a high energy density,high power density and the abundant resources have been widely concerned as the next generation energy storage system.At present,there are still some issues of cathode investigation of Li-S batteries:(1)The insulating property of sulfur and the reduction products(Li₂S_x,1?x?2),(2)The large volume expansion up to 80%at cycling,(3)Shuttle effect of lithium polysulfide(Li₂S_n,n>2).Covalent triazine frameworks is one kind of porous organic polymers,considering the good conductivity,designable composition and structure,and abundant in pores,several CTFs have been applied as host materials to lithium sulfur batteries.With these regards,we prepared two kinds of covalent organic frameworks(CTFs)through Friedel–Crafts Alkylation for the sulfur loading materials.Then,we synthesis the sulfur/carbon composites by traditional melting-diffusion as the cathode of Li-S batteries.The thesis mainly contains all the results as follow:(1)The nitrogen rich covalent triazine framework(TTPB)was synthesized by connectingbetweenN,N,N',N'-Tetraphenylbenzidine(TPB)and2,4,6-Triphenoxy-s-triazine.S@CTFO cathode exhibits initial discharge capacities of653 m Ah·g^-1at 1 C,and retains 586.3 m Ah·g^-1after 100 cycles with a low capacity attenuation rate of 0.10%.The good cycling stability due to the regular arrangement of functional groups and rich in nitrogen atoms.(2)The covalent triazine framework rich in nitrogen and oxygen was successfully synthesized by a connection between 2,4,6-Triphenoxy-s-triazine and2,4,6-trichloro-1,3,5-triazine via Friedel–Crafts Alkylation.The S@CTFO cathode with abundant nitrogen and oxygen atoms exhibits good capturing ability of polysulfide,resulting in a better Coulombic efficiency and cycling stability of the batteries.The cell has initial discharge capacities of 791 m Ah·g^-1at 1 C,and still retains 512 m Ah·g^-1after 300 cycles with a low capacity attenuation rate of 0.117%,revealing that the S@CTFO/Li cell possesses good long cycle stability.Therefore,the covalent triazine framework rich in nitrogen and oxygen shows a great potential as a cathode material for lithium-sulfur batteries.