HKUST-2 And MOF-5 Derived Porous Carbon And Their Application As Cathode Materials In Lithium-Sulfur Batteries

In recent years,the research on energy storage and power batteries become hot topics.Lithium-sulfur batteries use elemental sulfur as the positive electrode material with the specific capacity(1675 mAh/g)and energy density(2600 Wh/kg),which is regarded as one of the most promising next generation rechargeable devices.This paper is based on the above-mentioned two methods of MOF materials applied in lithium-sulfur batteries.On the one hand,we used the bimetallic MOF material HKUST-2 as the basic raw material to synthesize the HKUST-2/S composite materials successfully,and the conductivity of the HKUST-2 was improved by adding appropriate carbon nano-tube(CNT).On the other hand,we prepared porous carbon/sulfur(MPC/S)composites by using MOF-5 as the pore-forming agent,and heated under vacuum with sulfur.Finally,the structure and morphology of the above three kinds of composites were analyzed,their electrochemical properties were tested.The main results are summarized as follows:1.We successfully synthesized a bimetallic MOF material HKUST-2 with large specific surface area and rich microporous structure by using solvothermal method.Then the HKUST-2/S composite cathode material was obtained by simple vacuum heat treatment method.Electrochemical test results showed that the first discharge capacity of the HKUST-2/S is about 900 mAh/g at the discharge rate of 0.5 C,the discharge capacity remains only about 300 mAh/g after 150 cycles,and the coulombic efficiency is around 88%.The results show that the capacity of the battery decrease fast relatively.2.In view of the poor conductivity of the HKUST-2 material,the HKUST-2@CNT/S composite material was synthesized by using appropriate carbon nanotube(CNT)to improve the electrical conductivity of the composite material.The performance test shows that the initial discharge specific capacity of composite HKUST-2@CNT/S near 1200 mAh/g at 0.5 C rate.After 200 cycles,the discharge specific capacity remains at 600 mAh/g,and the coulombic efficiency is in the range of 93%to 96%.The conductivity of HKUST-2/S is improved effectively and then enhanced the cycling stability of the battery.3.Based on MOF-derived porous carbon materials can improve the performance of lithium-sulfur batteries,porous carbon material(MPC)was synthesized by solvothermal method and high-temperature carbonization method by using the organic framework material MOF-5 as a pore-forming agent and glucose(C6H12O6)as the carbon source,which has good conductivity,high specific surface area,and microporous structure.The porous carbon/sulfur composites(MPC/S)as cathode material of lithium-sulfur battery was synthesized by compounding sulfur with porous carbon through heat treatment method.Electrochemical performance tests show that the initial discharge specific capacity of MPC/S material is 1200 mAh/g at 0.5 C charge/discharge rate,the capacity remains 500 mAh/g after 600 cycles,and the coulombic efficiency remains around 99%.At a large charge/discharge rate of 2 C,the capacity remains above 500 mAh/g after 100 cycles,the corresponding capacity retention rate is up to 80%and coulombic efficiency is around 98%,which indicates that the MPC/S material exhibits good rate capability of charge and discharge.The adsorption capacity test of polysulfide for MPC porous carbon material shows that MPC has a strong adsorption capacity for polysulfide.