| Lithium-air battery has been considered a promising alternative energy storagedevice in recent years because of its compelling advantage of high gravimetric energy,low cost and friendly to environment. However, the practical applications of lithium-airbattery encounter many significant challenges including high overpotnetial, poor round-trip efficiency and undesirable rate capacity. In order to solve these problems, thisreaearch is devoted to the optimization of the structure of the air electrode andpreparation of high dispersed cathodic catalyst.Firstly, the Co3O4catalyst with four different morphologies namely sphere, cube,octahedron and nanorod were synthesized through hydrothermal method and was usedas cathodic active material to prepare the Co3O4/C air electrode by in situ carbonizedsucrose method. The galvanostatic charge and discharge results of lithium-air batteryindicated that the Co3O4catalyst with smaller particle size showed better activity owingto the perfect combination with carbon black XC-72. The lithium-air battery employingthe Co3O4/C (Co3O4:10wt.%, sphere) air electrode exhibited good cycling performancethat the capacity retention was as high as61.3%after5cycles with an initial dischargespecific capacity of462mAh·g-1catalystand charge plateau of3.75V when working at0.10mA·cm-2.Secondly, the Pd/C catalyst was synthesized by microwave-assisted polyol processand the carbon riveted Pd/C air electrode was prepared based it. The TEM resultsshowed that the Pd particles were highly dispersed on the XC-72carbon black withmean size of2.6nm and2.8nm respectively before and after the riveting process. Theair electrode was improved with a more porous structure. The palladium nanoparticlesand Pd/C catalyst were adhered to the carbon black XC-72and substrate respectively bythe layer of carbonized sucrose as―binder‖. The impedance of the carbon riveted Pd/Cair electrode was greatly decreased because the carbonized sucrose was moreconductive than the Kynar binder (PVdF). Therefore, the charge plateau of the batteryemploying the prepared electrode effectively fell into3.60V. Moreover, the improvedporous structure created by the carbonized sucrose provided more space for oxygendiffusion and products deposition, and the high dispersion of the palladium particles onthe surface of the air electrode provided more active sites for electrochemical reactions, both of which resulted in a longer initial discharge lifespan. Finally, a specific capacityof986mAh g-1catalystwas obtained from the lithium-air battery with the carbon rivetedPd/C air electrode. In addition, the Pd/C catalyst could effectively decrease theoverpotential in discharging and increase the discharge plateau, when working at thecurrent density of0.02mA·cm-2, the discharge plateau was as high as2.91V, closed tothe theoretical value (2.96V).Finally, the Pd/Co3O4/C air electrode was prepared by in situ carbonized sucrosemethod with the prepared Co3O4and Pd/C catalyst. The SEM images showed that animproved porous structure was formed on the air electrode. The lithium-oxgen batterydelivered a high specific capacity of7167mAh·g-1catalystat the current density of0.05mA·cm-2when the content of Pd and Co3O4were20wt.%and10wt.%respectively.The initial discharge specific capacity and discharge plateau decreased with theincreasing of the current density, however, the rate of decrease turned much smaller thanthat batteries employing the Co3O4/C and Pd/C air electrode. |
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