Investigation Of Defective Metal-organic Frameworks Applied In High-cycling Lithium-sulfur Batteries

Lithium-sulfur?Li-S?batteries have been deemed to be one of the most promising energy storage systems due to their superior theoretical energy density,low cost,and environmental friendliness.However,commercial applications of Li-S batteries were still greatly constrained by a series of obstacles,In particular,dissolution and shuttle of the polysulfides?LiPSs?have not been effectively solved,causing that the Li-S batteries still have serious capacity degradation problems.In this work,a novel Uio-66/carbon nanotubes?UC?composite was initially synthesized via a facile solvothermal method,in which abundant linker-missing defects were caused by an introduced competitive coordination,meanwhile,flexible and interlaced carbon nanotubes?CNT?throughout mechanically stable Uio-66nanoparticles constructed a reliable conductive network.UC composite not only inherited the high mechanical stability,high specific surface,and microporosity of Uio-66,but also exhibited good conductivity due to implantation of CNT networks.Furthermore,abundant linker-missing defects display a strong chemisorption for the LiPSs.As a new type of polar material,we have investigated the influence on the electrochemical performance of the Li-S battery in two aspects of the sulfur host and separator modification.As the sulfur host,Because of superior structural stability,high electronic conductivity and strong polysulfides chemisorptivity,the as-prepared S@UC-3cathode shows an excellent cycling stability,delivering an initial capacity of 925mAh·g^-1 and a very low fading rates of 300 cycles for 0.055%per cycle at 0.5 A·g^-1.In addition,strong chemical affinity between coordination defects and LiPSs was revealed by first principle calculations,which provides a powerful theoretical support for improving the cycle performance of the battery.On application of the separator modification,the prepared sandwich-like CNT/UC/CNT composite layer?SCL?on the surface of PP separator displayed a very strong restriction for LiPSs with physically and chemically.Electrochemical test results show that the Li-S cells using SCL separators exhibited excellent electrochemical properties,including high capacity,high cycling stability,superior rate performance and extremely low self-discharge.Especially,the initial capacity was up to 1244 mAh·g^-1 and still maintained 920 mAh·g^-1 after 300 cycles at 0.5C.Moreover,at the high current density of 1C and 2C,the maximum capacity reached1020 mAh·g^-1 and 782 mAh·g^-1,respectively,and the decay rate of each cycle was as low as 0.052%and 0.029%after 1000 cycles,respectively.Even matching with the cathode containing high sulfur content and high sulfur loading,the SCL separator still enables the battery to exhibit excellent capacity performance and cycling stability.