Structural Changes and Electrochemical Properties of Chemically oxidized Na_xFeO₂

Abstract

Na_xFeO₂ was obtained by chemical oxidization method using NO₂BF₄ and Br₂ which shows the redox potential of ca. 5.1 V and ca. 4.1 V vs Li/Li⁺, respectively. The oxidized products showed different X-ray diffraction patterns depending on the oxidizing species. In case of NO₂BF₄, as soaking time progressed, new phase increased with decreasing of NaFeO₂ as stating material. The oxidized Na_xFeO₂ was possible to be inserted the Li ion electrochemically, and resulted in the crystal structure similar to the layered LiFeO₂ synthesized by the Li-ion-exchange method from NaFeO₂. Reversible discharge-charge reactions were progressed for Na_xFeO₂ // Li cell, and ac. 150-200 mAh/g of initial capacities were achieved although the capacities decreased with cycle numbers.