Study On Performance Of G-C₃N₄@S Cathode And Modification Of Lithium Anode

Lithium-sulfur batteries are most likely to be a candidate for high energy density power batteries because of their high theoretical specific capacity of sulfur cathode?1675 mAh/g?and high specific energy?2600 Wh/Kg?.However,the application of lithium-sulfur batteries is hindered due to the insulation of sulfur,the volume expansion caused by the redox reaction of sulfur cathode during charging and discharging of lithium-sulfur batteries,the shuttle effect caused by the dissolution of polysulfides in electrolyte,and the lithium dendrite growth caused by the redox process of lithium cathode.It is urgent to solve the problems of lithium sulfur batteries.The purpose of this paper is to solve the shuttle effect of lithium-sulfur battery,the volume expansion of sulfur positive electrode and the lithium dendrite growth of lithium negative electrode.The sulfur cathode and lithium anode of lithium-sulfur battery were modified by us.Firstly,2 dimension g-C₃N₄ nanosheets?2D g-C₃N₄?was prepared by different methods.And then 2D g-C₃N₄ and 3 dimension g-C₃N₄ nanomesh?3D g-C₃N₄?were used to modify the cathode of lithium-sulfur batteries.Finally,nitrogen-doped graphene and iron-doped monoatomic graphene were used to modify the surface of lithium anode and copper collector.The main research contents and experimental results are as follows:?1?We prepared 2D g-C₃N₄ and 3D g-C₃N₄ electrodes by doping with S as cathode active material of lithium-sulfur batteries.Through the electrochemical tests and visualization experiments,it is proved that the optimum performance is achieved in the charging and discharging process of lithium sulfur batteries.The 3D g-C₃N₄@S cathode exhibit better performance than 2D g-C₃N₄@S cathode.It shows the initial discharge specific capacity of 715 mAh/g at 0.2 C.After several activation processes,the discharge specific capacity of the 3D g-C₃N₄@S cathode can reach 731 mAh/g.After 180 charging and discharging cycles,the cycle retention rate is 73.9%,and the capacity of each cycle decreases by 0.14%.?2?Nitrogen-doped graphene and Fe-doped graphene were used to modify the surface of lithium anode and copper collector.In conclusion,we found that Fe monoatomic doped graphene has a better effect on regulating Li nucleation and inhibiting dendrite growth.In the electrochemical test of asymmetric lithium-copper batteries,the Coulomb efficiency of the Cu-G@Fe electrode increased from 92.8%?the first deposition cycle?to 97.9%?the tenth deposition cycle?,and the high average Coulomb efficiency of 98.4%was achieved after 250 cycles.This can be attributed to the increase of Li-affinity on the surface of the electrode with the doping of Fe single atoms.More importantly,the stability of the atomic structure of Li is improved.Thus,the Coulomb efficiency and cycle life can be greatly improved.