The Preparation And Electrochemical Performance Of Cathode Composite Materials With Graphene For Lithium-sulfur Battery

With the rapid development of society,higher requirements are put forward for the performance of power storage system,especially for the higher energy density of secondary battery system.Lithium-sulfur batteries have attracted more attention because of their excellent properties such as high specific capacity and high energy density.However,the electrochemical performance of the battery is too weak,because of the large volume changes and“shuttle effect”in the process of charging and discharging for limiting the development of lithium-sulfur batteries.Therefore,graphene matrix with special morphology,structure and composition was prepared as the framework of cathode materials for lithium-sulfur batteries and flexible lithium-sulfur batteries,which can effectively improve the electrochemical performance of cathode materials for lithium-sulfur batteries.The main research contents are as follows:A very simple and low-cost one-step hydrothermal reaction was used to reduce the graphene oxide solution and obtain cylindrical hydrogel graphene.After freezing and drying,the graphene aerogels/sulfur composites were obtained by liquid-phase infiltration method.The graphene aerogels with three dimensional porous structure were prepared and the sulfur content was 70 wt%.After activation in the first cycle,the specific discharge capacity is about 620 mAh·g^-1 at 0.1 C current density.After 200 cycles,the specific discharge capacity is 359.7 mAh·g^-1,and the coulomb efficiency was 95.29%.Based on the prepared three-dimensional porous graphene,in order to further improve the electrochemical performance of the cathode materials for lithium-sulfur batteries,a three-dimensional porous nitrogen-doped graphene conductive matrix was fabricated by hollow cathode plasma discharge.The three-dimensional nitrogen-doped graphene/sulfur composite material?3D rNGO/S?was prepared by liquid-phase infiltration method.The composite material was used as the cathode of lithium-sulfur battery at 0.1 C current density,The initial discharge specific capacity was 1186 mAh·g^-1,After 200 cycles,the Coulomb efficiency was 96%.At 1.0 C current density,after 1000 cycles,the discharge specific capacity remained 578 mAh·g^-1.Based on the successful preparation of reduced graphene oxide with special structure and morphology,in this paper,two kinds of non-binder flexible graphene paper were prepared by filtration.One is the non-porous graphene paper?rGP?obtained by direct filtration of graphene oxide solution followed by reduction of HI acid,the other is porous graphene paper?HGP?obtained by a series of chemical reactions followed by filtration.The graphene paper/sulfur composite cathode was prepared by liquid phase infiltration of two kinds of graphene paper,and the flexible battery was assembled for comparison.The prepared HGP behaves better than rGP.The first discharge capacity of HGP/S composite cathode was 840.8 mAh·g^-1 at 0.05 C.After 200 cycles,the discharge specific capacity remained 320 mAh·g^-1.