| The development of renewable energy and energy storage technologies that can replace fossil fuels is of great significance to achieve "carbon peaking" and"carbon neutrality".Lithium-oxygen batteries have received increasing attention due to their clean,low-carbon,environmentally friendly and ultra-high energy density(～3505 Wh kg-1).In this thesis,aiming at the problems of high oxygen evolution overpotential,overexpansion and difficult decomposition of electrode caused by insulating discharge products of lithium-oxygen battery,by tuning the micro-morphology and catalytic active center of MOF/nanofiber derivatives,the synergistic mechanism between porous,beaded and macroporous interconnected carbon nanofiber structure and catalytic active site was realized,then three novel high-performance cathode materials for lithium-oxygen battery were fabricated.MOF/porous carbon nanofiber composite electrode materials were employed as the research object.According to the key points of electrode conductivity,porous structure and catalytic active sites,three kinds of MOF/porous carbon nanofiber composite electrode materials were constructed as self-supporting positive electrodes of lithiumoxygen batteries.Firstly,the hollow Co-Nx nanocubes/porous carbon nanofiber electrode was prepared by electrospinning technology and pyrolysis process;secondly,by further micro morphology construction,the size of ZIF-8 nanocubes particles and electrospinning parameters were further precisely controlled to prepare a beaded hollow Co-Nx nanocubes/porous carbon nanofiber electrode with a different structure from the former;thirdly,since the porous structures presented by the electrodes with the first two morphologies lack interconnected channels,they couldn’t perform better ion/electron transfer and storage and conversion of discharge products.Based on this,Co/Co3O4Ni/NiO doped macroporous interconnected hollow carbon nanofiber electrodes were fabricated by coaxial electrospinning technology and self-sacrificial template method.Attributing to porous structure and high specific surface area,Zn/CoNC@CPCFs electrode could accommodate more discharge products and increased the oxygen concentration per unit volume and the exposure of catalytic active centers,exhibiting good long-cycle performance(57 circle)under a current density of 0.02 mA cm-2(20.6 mA g-1)with a cut-off capacity of 0.2 mAh cm-2(206 mAh g-1).Because the porous structure on the Zn/CoNC@CPCFs electrode was easy to be blocked,which leaded to the inactivation of the Co-Nx catalytic active site and the lack of advantage in long cycle performance,a stable three-phase reaction interface was constructed by further adjusting the pore morphology.The obtained BH/PCNFs electrode materials had a more stable framework and more intuitive catalytic active centers,achieving better cycle performance(145 cycles)under a current density of 200 mAh g-1 with a cut-off capacity of 500 mAh g-1;The electrode material was further evolved into a macroporous interconnected hollow pipe structure,and the obtained Co/Co3O4-Ni/NiO@MHCNFs electrode was attributed to its excellent flexibility,electrical conductivity,hierarchical porosity,and abundant catalytic active sites.The as-prepared electrodes exhibited remarkable electrocatalytic performance in lithium-oxygen batteries,achieving the best long-cycle performance(163 cycles)under a current density of 200 mA g-1 with a cut-off capacity of 500 mAh g-1 and maximum capacity(16623 mAh g-1)under a current density of 100 mA g-1.In this thesis,three kinds of self-supporting electrodes with different microscopic morphologies were prepared for the purpose of optimizing the conductivity,porous structure and catalytic active center of the cathode material,enabling fast electronic and ionic conductivities and mass/charge storage/transport.Meanwhile,the synergistic mechanism of microscopic morphology and catalytic active centers in improving the performance of lithium-oxygen batteries was revealed. |
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