Wednesday, 4 October 2017
Prince George's Exhibit Hall D/E (Gaylord National Resort and Convention Center)
Sodium ion batteries (NIBs) have attracted much attention as promising alternatives of lithium ion batteries (LIBs) for large scale energy storage systems. This is because sodium is cheap and abundant throughout the world contrary to lithium. However, low gravimetric/volumetric energy density of NIBs hinders its practical use. For sodium layered oxide, Na+/vacancy ordering appears at certain Na concentration, which is caused by energy minimization of electrostatic interactions between cations. This ordering leads to first-order transition that acts as kinetic barrier in battery application. In order to investigate how Na+/vacancy ordering affects battery performance, we report P2-type Na0.67Co1-xTixO2 (x≤0.2) cathode with different ordering characters. The Ti-substituted cathode utilize more Na+ ions through expanded cut-off potential, whereas Na0.67CoO2 suffers a severe capacity loss at the same condition. Also, as the ordering is mitigated, rate capability of the sample is improved. In this study, we will discuss the detailed mechanism of the improvement through TEM, in-situ XRD, and electrochemical methods.