CATHODE MATERIALS OF ROCK SALT DERIVATIVE STRUCTURES FOR SODIUM-ION SECONDARY POWER SOURCES

The rechargeable lithium-ion batteries have been dominating the portable electronic market for the past two decades with high energy density and long cycle-life. However, applications of lithium-ion batteries in large-scale stationary energy storage are likely to be limited by the high cost and availability of lithium resources. The room temperature Na-ion secondary battery have received extensive investigations for large-scale energy storage systems (EESs) and smart grids lately due to similar chemistry of “rocking-chair” sodium storage mechanism, lower price and huge abundance. They are considered as an alternative to lithium-ion batteries for large-scale applications, bringing an increasing research interests in materials for sodium-ion batteries. Although there are many obstacles to overcome before the Na-ion battery becomes commercially available, recent research discoveries corroborate that some of the cathode materials for the Na-ion battery have indeed advantages over its Li-ion competitors. Layered oxides are promising cathode materials for sodium ion batteries because of their high theoretical capacities. In this publication, a review of layered oxides (NaxMO2, M = V, Cr, Mn, Fe, Co, Ni, and a mixture of 2 or 3 elements) as a Na-ion battery cathode is presented. O3 and P2 layered sodium transition metal oxides NaxMO2 are a promising class of cathode materials for Na secondary battery applications. These materials, however, all suffer from capacity decline when the extraction of Na exceeds certain capacity limits. Understanding the causes of this capacity decay is critical to unlocking the potential of these materials for battery applications. Single layered oxide systems are well characterized not only for their electrochemical performance, but also for their structural transitions during the cycle. Binary oxides systems are investigated in order to address issues regarding low reversible capacity, capacity retention, operating voltage, and structural stability. Some materials already have reached high energy density, which is comparable to that of LiFePO4. On the other hand, the carefully chosen elements in the electrodes also largely determine the cost of SIBs. Therefore, earth abundant-based compounds are ideal candidates for reducing the cost of electrodes. Among all low-cost metal elements, cathodes containing iron, chromium and manganese are the most representative ones. The aim of the article is to present the development of Na layered oxide materials in the past as well as the state of the art today.