| With the rapid development of electric vehicles and miniaturised electronic devices,the driving range of electric vehicles is increasing with the improved performance of lithium-ion batteries.However,due to the limitation of the specific capacity of electrode materials,the energy density of current commercial lithium-ion batteries is difficult to increase significantly.Therefore,electrochemical energy storage systems with high energy density have attracted widespread attention.Lithium-oxygen(Li-O2)batteries with lithium metal as anode and oxygen as active material for the cathode reaction,present an energy density of up to 3505 Wh g-1.Recent research on Li-O2 batteries has advanced the development of Li-O2 batteries to a large extent.However,there are still many challenges for Li-O2 batteries,including excessive polarization voltage,low Coulomb efficiency,short cycle life,and corrosion of lithium metal anode.In view of the above existing problems,the research in this thesis is carried out from the following two aspects:(1)The microstructure of carbon nanotubes was regulated by KOH to improve the pore structure of carbon nanotubes,which enhanced the ability of Li-O2 cells to store discharge products.After KOH etching,a large number of defect sites were created on the surface of the carbon nanotubes,which reduced the wall thickness of the multiwalled carbon nanotubes and enhanced the mass transfer at the three-phase interface of the cathode catalyst.In addition,the presence of defect sites ensured the uniform attachment of Ru nanoparticles,improving the efficiency of precious metals.The LiO2 cell with Ru@(CNTs:KOH=2:1)catalyst as the cathode was able to cycle 194 cycles stably at a limited capacity of 1000 mAh g-1 and a current density of 300 mA g-1.Comparing the SEM images of the carbon nanotubes with different degrees of etching after loading Ru,Ru@(CNTs:KOH=2:1)material showed a more uniform distribution of Ru,and the polarization voltage of the Li-O2 cell was 0.99 V.(2)The lithium metal anode also largely limits the cycling performance of Li-O2 batteries.Due to the Li-O2 cell is an open system,oxygen from the cathode,by-products carbon dioxide,and oxygen reduction intermediates can all shuttle to the cathode causing severe corrosion of the lithium metal.A composite protective layer on the surface of lithium metal was generated by reacting triethyl phosphate and lithium metal,which enhanced the cycling stability of lithium metal in Li-O2 batteries The Li-Li symmetric cell with treated lithium plates was able to cycle stably for 760 h in an oxygen atmosphere at a limited capacity of 0.5 mAh cm-2 and a current density of 0.25 mA cm-2,whereas the cell without treated lithium plates was only able to cycle for approximately 260 h.In addition,the Li-O2 cells with treated lithium plates were able to cycle for 149 and 89 cycles at a current density of 300 mA g-1 with a cut-off capacity of 500 mAh g-1 and a current density of 300 mA g-1 with a cut-off capacity of 1000 mAh g-1,respectively,which was significantly outperforming the untreated lithium paltes.In this thesis,the performance of Li-O2 batteries was improved by modulating the structure and composition of the electrodes.The effect of the microstructure of the cathode catalyst on the performance of the Li-O2 battery was analysed.Meanwhile,an artificial SEI layer is formed by a simple treatment to protect the lithium anode,mitigating the corrosion of the lithium metal. |
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