| Lithium-sulfur(Li-S)batteriy,as a new type of secondary battery,has been widely concerned at home and abroad for its high specific capacity,environment-friendly,natural abundance,low cost and so on.It is an ideal choice for the next generation of energy storage devices.However,the commercialization of Li-S batteriy faces some bottlenecks,such as the insulation of sulfur,the“volume effect”of sulfur after lithiation,the“shuttle effect”of the reaction intermediate products and the growth of lithium dendrites.In view of the above problems,it is an effective method to modify the separator of lithium sulfur battery.Metal organic frameworks(MOFs),as a new type of nano porous materials,have been widely used in energy storage and conversion systems due to their large specific surface area,ordered pore structure,adjustable pore size and surface chemical properties.In this paper,we designed and prepared a modified coating of derived porous materials based on ZIF-8 precursor to suppress the“shuttle effect”and efficiently improve the electrochemical performance of the battery.The specific work is as follows:(1)Using industrial-grade carbon nanotubes(CNT)as a carrier,ZIF-8 particles are generated in situ on CNT by the normal temperature aqueous solution method and carbonized at high temperatures to obtain N-C@CNT composite materials,which is coated on the side of separator polyethylene(PE)to study the effect on the electrochemical performance of the battery.The results show that when sulfur loading of 3.3 mg cm-2 and the initial discharge capacity of N-C@CNT modified separator is852.9 m Ah g-1 at 0.5 C.Even after 500 cycles,a steady reversible capacity of 424.4m Ah g-1can be obtained.This is mainly attributed to the high conductivity of long linear CNT,which provides an effective path for electronic and Li ion transport,the abundant mesopores alleviate the“volume effect”before and after the reaction,cooperate with MOF micropores to block polysulfides efficiently,and N atom doping promotes the redox reaction.(2)ZIF-8 particles and Mn-MOF were generated in situ on CNT by the normal temperature aqueous solution method and carbonized at high temperature to obtain the Mn O/N-C@CNT modified material,which was coated on the side of separator polyethylene(PE)to assemble the battery for electrochemical performance test.The test results show that the performance of the Mn O/N-C@CNT modified coating continues to improve on the basis of N-C@CNT,and the initial discharge capacity reaches 920.3 m Ah g-1at the sulfur loading of of 3.3 mg cm-2at the rate of 0.5 C.After500 cycles,the capacity is maintaining at 500.2 m Ah g-1.This is attributed to the strong chemisorption formed by the polarity surface anchoring polysulfide of nano-Mn O.At the same time,the metal oxygen bond and oxygen vacancy are also conducive to the dissociation of S-S bond,which accelerates the transformation of polysulfide lithium and catalyzes the redox reaction inside the battery.(3)Mn3[Fe(CN)6]2·n H2O precursor was prepared by co-precipitation method as template and Mn source.Nano-sheet Mn S was prepared by the solvothermal method and loaded on the N-C@CNT composite prepared in the research(1)to obtain Mn S/N-C@CNT.And coated it on the separator polyethylene(PE)and assembles into a battery to study the influence of the modified coating on the electrochemical performance of the battery.The results show that the first discharge specific capacity is 923.9 m Ah g-1at sulfur content of 3.3 mg cm-2 at the rate of 0.5 C,and after 500 cycles the capacity maintain 500.8 m Ah g-1;the discharge capacity at high rate of 2 C is 498 m Ah g-1,and it shows the good reversibility.It is owing to the strong affinity of Mn S particles for polysulfide-containing sulfur,the promotion of polysulfide nucleation growth improves the oxidation-reduction kinetics and has a better catalytic effect on electrochemical reactions. |
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