| The rapid development of micro-electronics, communication and new energytechnics is in great demand of high energy density power sources. The advent of Li-airbattery featuring ultra-high theoretical energy density, low material cost andenvironmental friendliness opens up a new possibility to satisfy this increasing demand ofhigh-performance power sources. Oxygen, as the cathode reactant, can be directlyacquired from air, which effectively lowers the costs. The Li-air battery is based on theformation and decomposition of Li2O2, its theoretical energy density is estimated to be3600Wh/kg, even when the whole battery package is included, a high energy density upto600Wh/kg can still be obtained which is close to the energy density (700Wh/kg) ofgasoline combustion in internal combustion engines. Given the advantage in energydensity, Li-air battery has been considered as a next energy storage and conversion sourceto replace combustion engine. However, Li-air battery technology is at its infancy, varioustechnical issues needed to be resolved before large-scale commercialization. For instance,there is a lack of systemic understanding of the reaction mechanisms, the improper designof cathode porosity can lead to hindered energy density, the parasitic reactions caused bythe instability of electrolyte and carbon electrode resulting in poor cycling stability, andhigh overpotentials during charge and discharge owing to the lack of efficientelectrocatalysts.In this thesis, several transition metal oxide electrocatalysts with particularcompositions and constructions are reported, those electrocatalysts are found toeffectively lower the overpotentials, and their tailored microstructure enabled the Li-airbatteries with high energy density and cycling performance.First，Fe2O3nanowires (Fe2O3NWs) were prepared by electrospinning method andused as cathode catalyst for Li-O2battery. Surprisingly, the corresponding Li-O2batterydemonstrated a relatively high capacity and good cycling stability. The enhancement inperformance can be ascribed to the synergy of the good catalytic activity and uniquehierarchical structure of the Fe2O3NWs, which can tailor the cathode structure,highlighting the significance of cathode structure on battery performance. Despite therelatively low conductivity of Fe2O3NWs which had a negative effect on the ratecapability, the hierarchical structure can effectively promote the transportation of oxygenand electrolyte as well as provide sufficient space for the deposition of discharge products. Owing to the good catalytic activity and porous structure of Fe2O3NWs, the Li-O2batteryexhibited much higher capacity and better cycling performance than that based on pureSP cathode.Secondly, perovskites have good catalytic activity toward oxygen reduction reaction(ORR) and evolution reaction (OER). A three-dimensional ordered macroporous LaFeO3(3DOM-LFO) is prepared by a template method, and is used as bifunctionalelectrocatalyst for Li-air battery. The unique porous structure can provide effectivetransport pathways for oxygen and electrolyte. In addition, the macropores can providesufficient void space for the deposition of discharge products. Experimental results showthat the3DOM-LFO can actively catalyze the ORR and OER process, the Li-air batterybased on3DOM-LFO catalyst exhibits higher specific capacity, better rate capacity andcycling performance than that based on carbon electrode. This enhancement inperformance can be attributed to the synergy of the porous structure and excellentcatalytic activity of the3DOM-LFO.In summary, this thesis is based on two research of the application and performanceof transition metal oxides in Li-O2battry. Symetic investigation was conducted on theimpact of catalytic activity and structure on the performance of Li-O2battry such asdischarge/charge potietials, capacity and cycling performance. This thesis is believed toprovide important experimental data and experience for the further development of Li-O2battry. |
PDF Full Text Request