Research Of Cathode Materials For Li-S Batteries And Device

Recent years,lithium sulfur batteries have attracted extensive attention due to its high theoretical specific capacity and high energy density.However,the traditional lithium sulfur batteries have the following main defects:（1）Low conductivity of sulfur and its discharge product.The insulating nature of sulfur and lithium sulfide（Li₂S/Li₂S₂）results in poor utilization of active material.As a result,low discharge capacities and rapid capacity decay are often observed during cycling.（2）Dissolution of intermediate lithium polysulfides into the electrolyte.During the cycling process,long-chain lithium polysulfides（Li₂S₄ to Li₂S₈）will shuttle between the lithium anode and sulfur cathode,which leads to continuous loss of active material into the electrolyte.Therefore,it is particularly important to improve the conductivity of the cathode materials and the utilization of active materials.In this theis,two kinds of new composite materials were designed based on Tp Pa-COF applied to lithium sulfur battery.The specific work content is divided into the following two parts:（1）A porous Tp Pa-COF@MWCNTs with core-shell structure was prepared by hydrothermal method.The composite showed large surface area and abundant microporous pores,as well as excellent electrochemical properties.At the current density of 0.05 C,the initial discharge capacity is 1242.2 m Ah·g^-1.When the current density increased to 0.5 C,the discharge capacity remained 525.6 m Ah·g^-1 after 450 cycles,each circle attenuation rate was low to 0.099% and the coulombic efficiency was stable at 100%.（2）Tp Pa-COF was used as precursor to be carbonated at high temperature in nitrogen atmosphere and the resultant material with high porosity,high conductivity and rich in nitrogen were obtained.The electrochemical performance results showed that: The initial discharge capacity of 869 m Ah? g^-1 was obtained at 1 C and the discharge capacity was 670 m Ah?g^-1 after 200 cycles;At 0.5 C,the discharge capacity remained 547 m Ah?g^-1 after 500 cycles and each circle attenuation rate was low to 0.08%.We improved the electrochemical performance of Tp Pa-COF through carbonization and it opened up an effective way for the study of energy storage device based on COFs.