Study of sodium containing layered oxides for battery applications*

Sodium ion batteries have been studied since the 1970s, but with the success that lithium ion batteries gained, studies on sodium ion batteries were diminished until recently. Na2Ni2TeO6 has shown much promise for use in sodium ion batteries. Crystalline Na2Ni2TeO6 was synthesized experimentally and characterized using X-ray diffraction (XRD) measurements. In order to understand the position of Na atoms that is very intriguing, we carried out density-functional theory (DFT) calculations for three different Na sites (i.e., Na1, Na2, and Na3) in Na2Ni2TeO6. Our result indicates that Na atoms in the Na1 site are energetically more favorable than the ones either in Na2 or in Na3 sites. This finding agrees well with the measured XRD data. Structural and magnetic properties were also investigated. The relationship between ionic diffusion and concentrations of sodium and/or nickel based on the total energy of the system will be discussed in this talk.