Characterization of Electrochemical Cycling-Induced New Products of NaCuO2 Cathode Material for Sodium Secondary Batteries

Abstract

Using a Na/NaCuO 2 cell, we investigate the conversion of NaCuO 2 during charge and discharge reactions and the new products formed by the conversion. In the voltage range of 0.75 to 3.0 V, the results of ex-situ XRD analysis indicate that Na 2 CuO 2 , an unstable amorphous discharge product, converted into CuO and Cu 2 O. Moreover, an XPS analysis reveals Na 2 O is formed on the surface of a NaCuO 2 electrode. From 1.7 to 4.2 V, on the other hand, the first charge product, Na 1-x CuO 2 , should partially form CuO. This behavior is similar to the reaction in which the charge of a Li/LiCuO 2 cell forms CuO. Then, after the discharge, CuO and Cu 2 O are observed as the main components in XRD patterns of the electrode. NaCuO 2 phase appeared again after the subsequent charge. NaCuO 2 is gradually converted into CuO as the main component as the cycles proceed. The cycling-induced new products of NaCuO 2 change, depends on the voltage ranges.