Preparation And Application Research Of Function-based MOFs In Lithium-sulfur Battery Separators

People's demand for energy is gradually increasing with the rapid development of the times.While the fossil energy is continuously depleting,and the development of traditional lithium-ion batteries and lead-acid batteries has fallen into a bottleneck.Therefore,exploring new energy storage devices is pretty critical.Among them,lithium-sulfur(Li-S)batteries is one of the most potential next generation energy storage batteries due to its high theoretical specific capacity(1675 mAh g-1),high energy density(2600 Wh kg-1)and the sulfur used as positive electrode active material has the advantages of natural abundance and environmental friendliness.However,the practical application process of Li-S batteries has been greatly affected due to some serious issues,such as sulfur insulation,low ionic conductivity and polysulfide shuttle effect,etc.By blocking the migration of polysulfides to the anode,the loss of active sulfur can be effectively reduced and the electrochemical performance of the batteries can be improved,which is one of the effective means to improve the lithium sulfur batteries.In this paper,we designed and synthesized two functional-based MOFs,then using the two MOFs designed and prepared high-performance interlayers in hope of suppressing the shuttle of polysulfide during the charging and discharging of lithium-sulfur batteries and improving the electrochemical performance of lithium-sulfur batteries.The Specific research contents are listed as follows:1.Spherical Ce-MOFs with amino groups were designed and synthesized using cerium ammonium nitrate and 2-aminoterephthalic acid as raw materials under atmospheric pressure.The composition and structure of Ce-MOFs were characterized,and then adsorption effect of the prepared Ce-MOFs on polysulfide anions was investigated to effectively suppress the shuttle effect of polysulfides.The prepared Ce-MOFs and conductive carbon(Super-P)were combined to design a functional barrier for lithium-sulfur batteries.By he adsorption and catalytic conversion effect of Ce-MOFs on poly sulfide ions and the conductivity of Super-P,the shuttle effect of polysulfides effectively was inhibited and the ? electrochemical performance of lithium-sulfur batteries was improved.The research result showed that the battery with Ce-MOFs/Super-P coated separator delivered an initial specific capacity 1366.3 mAh g-1 at a rate of 0.2 C.And at a high rate of 2 C,the capacity of the battery can reach to 653.3 mAh g-1.When the sulfur content of the cathode in this system was increased to 3.5mg cm-2,the capacity still could maintain at 627.5 mAh g-1 after 300 cycles,and the average capacity decay rate at each cycle is just 0.09%.This provides a new material for improving the performance of lithium-sulfur batteries.2.Under normal pressure and temperature conditions,nickel acetate,4,4-bipyridine and sodium 2-amino-1,4-benzenedisulfonate reacted quickly,then Ni-MOFs with two functional groups of amino and sulfonic acid groups was designed and synthesized.By characterizing the structure and performance of the material,it was revealed that the prepared Ni-MOFs exhibited a sheet structure and had a chemical adsorption effect on polysulfides,thereby blocking the diffusion of polysulfides to the anode side.Based on the adsorption of Ni-MOFs on polysulfides and the good conductivity of Super-P,functional coating layer for lithium-sulfur batteries were designed and prepared.The addition of carbon materials can improve the conductivity,and at the same time,it could be used as a secondary current collector in the system to improve the utilization of active material sulfur in the cathode of lithium-sulfur batteries.The influence of Ni-MOFs content on the battery performance was investigated,and the rules of its function were revealed.The research results show that the lithium-sulfur battery using the Ni-MOFs/Super-P coating layer exhibits excellent cycle performance and rate performance when the mass ratio of Ni-MOFs and Super-P was 1.After 300 cycles at a current density of 1 C,the capacity decay is only 0.059%per cycle and the cycle efficiency remained above 98.5%in the whole cycles.This provides a new method for improving the performance of lithium-sulfur batteries.