Study On The Synthesis Of Metal Organic Framework And The Lithium Storage Properties Of Its Derivatives

Recently,with the gradual depletion of fossil energy,as well as more and more seriously haze and other environmental problems caused by the use of fossil energy,the development of high performance energy storage technology to make clean energy usable for people’s daily life has become one of the hottest research fields.Lithium-ion batteries because of its environment-friendly,easy access to raw materials and other advantages caused by people’s attention,but because the volume effect in the process of charging and discharging its specific capacity is relatively low.Lithium-sulfur batteries,due to their high theoretical specific capacity,theoretical specific energy and environmental benign nature,have gained intensive concerns from the scientific community and industry.However,the poor conductivity of sulfur cathode and the shuttle effect of lithium polysulfide generated during the charging and discharging process led to the rapid capacity degradation of lithium sulfur batteries.In order to solve the key scientific problems of lithium-sulfur batteries mentioned above,the research works done in this dissertation attempt to comprehensive utilize the positive effects of the high capacity of cheap manganese oxide,high specific surface area and porosity,excellent electrical conductivity of metal organic framework（MOF）derivatives,the strong chemical and physical absorption to polysulfide.MOFs derivative coated MnO nanowires are successfully developed as high capacity,high rate composite anode materials and high sulfur content inhibitors for obtaining annealed MOF-MnO₂/S composite cathode material for high performance lithium-sulfur batteries,respectively.The detailed research works are summarized as follows:（1）100 nm MOF（ZIF-67）particles are uniformly grown on the surface of the MnO₂ nanowires modified by polyvinylpyrrolidone（PVP）through solution method at room temperature.The scanning electron microscope（SEM）images indicate an interesting structure like Chinese candied hawthorn fruit on a stick of the ZIF-67 on MnO₂ nanowire（ZIF-67-MnO₂ NWs）.（2）The obtained ZIF-67-MnO₂ NWs are used as precursor to develop high performance anode materials.Being annealed at 550 oC in argon gas atmosphere,ZIF-67 carbonized derivative evenly coated MnO nanowires（C/Co-MnO）composite materials finally obtained.Due to the synergistic effect of highly conductive MOF-derived carbon coating and high capacity MnO nanowires,the composite anode materials deliver much high capacity,rate capability and cyclic stability than the original MnO₂ NWs,higher capacity and much larger energy density than single MOF derived carbon,respectively.The capacities still maintain at 848,836,834 and 718 mAhg-1 after 40 cycles of charging and discharging cycles at current densities of 500,1000,2000 and 5000 mAg-1,respectively.（3）In addition,a novel sulfur inhibitor,namely ZIF-67-MnO₂ derivative,is obtained by annealing ZIF-67-MnO₂ at 300 oC in argon gas.Benefitted from the strong chemical and physical absorption to sulfur and its compound,annealed ZIF-67-MnO₂/S composite materials with a high sulfur content of 60 wt.% is eventually developed.As cathode material for lithium-sulfur batteries,it can retain 612.7 and 365.8 mAhg-1 after 100 charge and discharge cycles at 335 and 1675 mAg-1,respectively.As a conclusion,above research results indicate that the research scheme proposed in this dissertation is reasonable and feasible.Furthermore,C/Co-MnO NWs composites and annealed ZIF-67-MnO₂ NWs/S composites are excellent candidate anode and cathode materials,respectively,for developing next generation high capacity,high power and high safety of lithium-sulfur batteries.