Ex-situ TEM Analysis of ZnMn2O4 Nanowires as Anode Materials for Lithium Ion Batteries

Abstract

Nanoslrllctllred 3d-transition metal oxides have received attention as possible anodic alternatives for Li-ion batteries. These transition metal oxides have no free interstitial sites w ithin their clystallographic structure to host lithium and do not forn alloys with lithium. However, they can react reversibly with lithium according to a process tenned conversion reaction. This electrode reaction leads to form composite materials consisting of metallic nanograins dispersed into amorphous Li2O matrix . Owing to the nanometric nature of this composite, such reactions are highly reversible. Thus，they are potential to provide high and constant lithium storage capacities upon cycling. One-dimensional ZnMn2O4 nanowires have been prepared and investigated as anode materials in Li rechargeable batteries. The highly crystalline ZnMn2O4 nanowires about 15 nm in width and 500 nm in length showed a high specific capacity of about 650 mAhg-1 at a current rate of 100 mAg-1 after 40 cycles. They also exhibited high power capability at elevated current rates, i.e. , 450 and 350 mAh'g-1 at current rates of 500 and 1000 mA'g-1, respectively. Formation of Mn3O4 and ZnO phases was identified by ex-situ X-ray diffraction (XRD) and transmission electron microscopy (TEM) studies after the initial discharge-charge cycle, which indicates that the ZnMn2O4 phase was converted to a nanocomposite of Mn3O4 and ZnO phases immediately after the electrochemical conversion reaction.