Electrochemical Insertion of Li and Na Ions into Nanocrystalline Fe[sub 3]O[sub 4] and α-Fe[sub 2]O[sub 3] for Rechargeable Batteries

Abstract

powders with different particle sizes on average (400, 100, and ) were prepared and characterized by X-ray diffraction, transmission electron microscopy, Mössbauer spectroscopy, and electrochemical methods. To examine the electrochemical activity of in relation to the particle size effect, galvanostatic cycling tests in aprotic electrolytes containing lithium or sodium ions were conducted. The electrochemical activity was significantly enhanced as the mean particle size decreased. The nanocrystallized prepared by precipitation method delivered of the rechargeable capacity in the voltage range of in a lithium-ion containing electrolyte, whereas the 400 and powders showed 10 and of the rechargeable capacity, respectively. An ex situ X-ray diffraction study for the electrochemically cycled samples suggested the partly reversible Fe ion migration from the tetrahedral sites to the octahedral sites with a retained spinel framework structure. The nanocrystallized as well as were highly electrochemically active in the sodium salt electrolyte. The rechargeable capacity of 160 or with excellent capacity retention was obtained for nanocrystalline or , respectively.