소듐-공기 배터리 방전산화물 생성 및 충방전 메커니즘 연구

Abstract

Recently, metal–air batteries, such as lithium–air and zinc–air systems, have been studied extensively as potential candidates for ultra–high energy density storage devices because of their exceptionally high capacities. Na–O2 batteries have been regarded as the most promising candidates because of their lower charge overpotential compared with that of the Li–O2 system, regarding it is abundant and inexpensive. However, conflicting observations with several different discharge products have inhibited the understanding of the precise reactions in the battery. Firstly in Chapter 2, two types of sodium–oxygen batteries were introduced and studied, i.e., with carbonate and non–carbonate electrolytes. Both types could deliver specific capacities (2800 and 6000 mAh/g) comparable to that of lithium–oxygen batteries but with slightly lower discharge voltages (2.3 V and 2.0 V). The reaction mechanisms of sodium–oxygen batteries in carbonate and non–carbonate electrolytes were investigated and compared with those of lithium–oxygen batteries. In Chapter 3, we demonstrate that the competition between the electrochemical and chemical reactions in Na–O2 batteries leads to the dissolution and ionization of NaO2, liberating O2– and triggering the formation of Na2O2•2H2O. Upon the formation of phases other than NaO2, the charge overpotential of Na–O2 cells significantly increases. This report is the first verification addressing the origin of the different discharge products and conflicting overpotentials observed in Na–O2 systems. Our proposed model provides guidelines to help direct the reactions in Na–O2 batteries to achieve high efficiency and rechargeability.