Application Research Of Lithium Selenium Batteries Based On Covalent Organic Frameworks

Lithium-selenium batteries are a new type of energy storage devices in recent years.Because of the characteristics of selenium as positive electrode,lithium-selenium batteries have high conductivity and volume specific capacity,so they have attracted extensive attention of researchers.Covalent organic frameworks(COFs)are a kind of porous materials with periodic crystallinity.They are mainly connected by light elements through covalent bonds,so they have the characteristics of low density,high porosity and large specific surface area.In this paper,covalent organic frameworks,which have attracted much attention in recent years,are applied to lithium-selenium batteries.The main contents are as follows:(1)TpPa-COF@MWCNTs core-shell composite,synthesized by solvothermal condition,was fused with selenium to form TpPa-COF@MWCNTs/Se,then TpPa-COF@MWCNTs/Se is used as cathode of lithium-selenium batteries with 50 wt%selenium.The TpPa-COF@MWCNTs/Se showed a high initial discharge capacity of463.5 mAh·g^-1 at a high current density of 3 C,and the coulombic efficiency was almost 99%during cycling.(2)Selenium nanorods were synthesized by hydrothermal method,thin layered covalent organic nanosheets were derived from COFs by the simple ultrasonic exfoliation method,and G-TpPa@Se composite was obtained by adding graphene into both of them.According to characterization,the covalent organic frameworks have been successfully peeled into thin layers about 4 nm thick and the obtained selenium nanorods have a diameter of several hundred nanometers and a length of several microns.The G-TpPa@Se can provide initial discharge capacity of435.2 mAh·g^-1 at 2 C,and the coulombic efficiency is stable at 100%in100 cycles,indicating that the lithium-selenium batteries based on covalent organic frameworks have good cycle stability and coulombic efficiency.