Sodium di-vacancy patterns and staging onset in layered
TM-oxides
Masoud Aryanpour and Young-Gyoon Ryu
Advanced Materials Lab, SAIT-America
1st Cambridge Center, Cambridge, MA-02142
In recent years, electrode materials for Na-ion batteries have been the focus of extensive research. If successful, that would potentially lower the price of advanced batteries in a wide range of applications from mobile devices up to electric vehicles.
Designing Na-based electrode materials cannot be achieved by simply replacing Li with Na in known materials for lithium-ion batteries. Experiment and theory point to the requirement of redesign and re-optimization endeavors to reach similar or better performances.
An important class of materials is layered compounds containing alkaline atoms intercalated in between layers of transition metal oxides (NaMO2). These compounds have been the topic of research for a few decades [2,3], yet their complex electrochemical behavior remains much to be fully understood.
De-intercalation of sodium as the cathode material being charged is often accompanied by several phase changes that in turn prevent reaching high capacity and energy density that are offered theoretically by layered materials. In a previous work, we studied the effect of Na mono- vacancy in electrode materials [4]. In this work, we consider the effect of two atomic vacancies in one or two sodium layers the first few transition metal compounds NaMO2 (M=Sc, Ti, V, Cr, Mn). This study can elucidate dominant vacancy superstructures, as well as the inclination of these materials toward staging as the charging proceeds.
[1] BL Ellis and LF Nazar. “Sodium and sodium-ion energy storage batteries”, Current Opinion in Solid State and Materials Science, 16(4):168-177, 2012.
[2] C. Didier, M. Guignard, C. Denage, O. Szajwaj, S. Ito, I. Saadoune, J. Darriet, and C. Delmas, “Electrochemical Na-Deintercalation from NaVO2”, Electrochemical Solid- State Letters, 14(5), A75-A78, 2011
[3] M.M. Doeff, M.Y. Peng, Y. Ma, and L.C. De Jonghe, “Orthorhombic NaxMnO2 as Cathode Material for Secondary Sodium and Lithium Polymer Batteries”, Journal of Electrochemical Society, 141 (11), L145-L147
[4] M. Aryanpour, H.-S Lee, “Atomic Re-arrangements and Energetics of Selected TM-oxides Caused by an Na- vacancy”, 223rd Electrochemical Society Meeting,
May2013

Figure 1 Crystal structure of layered NaMO2 materials used in Na-ion batteries