Synthesis And Electrochemical Performance Of Nanocarbon-based Composite Lithium-sulfur Battery Electrode

Lithium sulfur battery has become one of the most promising energy storage systems due to its high theoretical energy density,environmental friendliness and low price.However,the problems of poor conductivity of sulfur,the drastic volume change in the redox process,and the“shuttle effect”caused by polysulfide limited the further development of lithium sulfur battery.In view of the above problems,this paper is carried out from the following three aspects to improve the performance of lithium sulfur battery:First.Carbon material is used as the matrix to construct a stable three-dimensional conductive network,which can improve conductivity of sulfur and alleviate the volume change;what's more,Mitigate the“shuttle effect”through ingenious structural/molecular design,physical restriction or chemical anchoring of polysulfide;Finally,explore and analyze the intrinsic characteristics of electrode capacity attenuation with the help of atomic force microscope,so as to provide supports for subsequent studies.?1?Three-dimensional carbon fiber-reduced graphene oxide?CNF-RGO?was prepared by electrospinning combined with heat treatment and used as carrier of inorganic sulfur in lithium sulfur batteries.Adsorption experiments show that the cross-linked porous CNF-RGO materials have a strong adsorption effect on the high-order lithium polysulfide?Li₂S₆?.Electrochemical tests showed that the CNF-RGO/S electrode maintained a discharge capacity of 227 m Ah/g after 100 cycles at a large current of 5 C,and there was almost no capacity attenuation in the following 300 cycles.It shows that the CNF-RGO matrix provides stable mechanical structure,shortenes the diffusion path of Li⁺,effectively alleviates the“shuttle effect”,and improves the performance of CNF-RGO/S electrode.?2?In view of the shortcomings of CNF-RGO/S materials such as low sulfur content and performance to be further improved,dendritic cp?TTCA-CNTs?composite organosulfur materials were prepared by hydrothermal method.The experimental results showed that the sulfur content of cp?S-TTCA-CNTs?-1?4:1?composite material was up to 78wt%,the initial discharge capacity at 1 C was 698 m Ah/g,and it remained553 m Ah/g after 1000 cycles,which was significantly improved compared with the CNF-RGO/S electrode.It is shown that organosulfur can be distributed in large quantities and uniformly on the cp?TTCA-CNTs?matrix,and the matrix can anchor the polysulfide by chemical bond to inhibit the“shuttle effect”.On the other hand,the TTCA-modified CNTs network can be used as a flexible conductive additive to enhance the redox kinetics and alleviate the sulfur volume changes.Therefore,the performance of cp?S-TTCA-CNTs?-1?4:1?was significantly improved compared with CNF-RGO/S electrode.?3?Capacity attenuation is still a problem whether inorganic sulfur/organic sulfur is used as the active material.Therefore,the intrinsic characteristics of sulfur capacity attenuation are explored and analyzed from the micro-nano scale with the help of atomic force microscope.The results show that with the increase of cycle times,the diffusion coefficient of Li⁺in the sulfur matrix decreases sharply and the diffusion resistance gradually increases,indicating that the diffusion is more and more difficult.By scanning the same area several times,it was found that the surface of sulfur tended to be flat in the cycling process,and the volume change of a single sulfur particle in the charging and discharging process was observed.The match of microcosmic analysis and macroscopic experimental phenomena provides a strong support for the design of better host materials in the future.