The Air Stability of Sodium Layered Oxide Cathodes

Sodium-ion batteries (NIBs) are listed as one of the ideal alternatives for lithium-ion batteries (LIBs), due to the abundant sodium resources, cost-effective electrode materials of NIBs, and same architecture of NIBs to LIBs. To enable the practical implementation of NIBs, advanced cathodes with higher energy/power densities, better safety and cycle life, as well as lower cost are required. Layered lithium transition metal oxides (LiTMO2) are one of the most successful cathode materials for commercial LIBs. Similarly, layered sodium transition metal oxides (NaxTMO2, also termed as sodium layered oxides) are of particular interest for commercial NIBs owing to their high specific capacity, a wide variety of redox-active elements, and the possibility for the manufacturers to employ established synthesis processes as their lithium counterparts. Sodium layered oxides are built up by ordered stacking of alternate alkali-metal (Na+) layers and transition metal layers (TmO2). The two-dimensional structure makes them the natural hosts for alkali-metal ions and other ions or small molecules, such as H2O. Therefore, when exposed to moist atmospheres, layered oxide materials tend to react with H2O which adsorbed on their surface and thus deteriorate their structure and electrochemical performances. Accordingly, the air-sensitive sodium layered oxides should be well protected from the moist atmospheres, rendering a higher manufacturing and preservation cost. Here, based on the reaction mechanisms, critical influencing factors, and modification methods of layered oxides in moisture, we try to reach a comprehensive understanding of the air-stability of sodium layered oxides. Moreover, future efforts to resolve the air-stability of sodium layered oxides from Argonne National Laboratory will be also presented. References 1. Han, M. H.; Gonzalo, E.; Singh, G.; Rojo, T. A comprehensive review of sodium layered oxides: powerful cathodes for Na-ion batteries. Energy Environ. Sci. 2015, 8, 81-102. 2. Zuo, W.; Qiu, J.; Liu, X.; Ren, F.; Liu, H.; He, H.; Luo, C.; Li, J.; Ortiz, G. F.; Duan, H.; Liu, J.; Wang, M. S.; Li, Y.; Fu, R.; Yang, Y. The stability of P2-layered sodium transition metal oxides in ambient atmospheres. Commun. 2020, 11, 3544. 3. Xu, G. L.; Liu, X.; Zhou, X.; Zhao, C.; Hwang, I.; Daali, A.; Yang, Z.; Ren, Y.; Sun, C. J.; Chen, Z.; Liu, Y.; Amine, K. Native lattice strain induced structural earthquake in sodium layered oxide cathodes. Commun. 2022, 13, 436. 4. Zuo, W.; Xiao, Z.; Zarrabeitia, M.; Xue, X.; Yang, Y.; Passerini, S. Guidelines for Air-Stable Lithium/Sodium Layered Oxide Cathodes. ACS Materials Letters 2022, 4, 1074-1086. 5. Fu, F.; Liu, X.; Fu, X.; Chen, H.; Huang, L.; Fan, J.; Le, J.; Wang, Q.; Yang, W.; Ren, Y.; Amine, K.; Sun, S. G.; Xu, G. L. Entropy and crystal-facet modulation of P2-type layered cathodes for long-lasting sodium-based batteries. Commun. 2022, 13, 2826.