Structural analysis of NaCuO2 cathode at various charged/discharged stages and its reaction mechanism

Abstract

We investigated NaCuO2 as a positive electrode material for sodium-ion energy storage batteries. Its charge/discharge properties in a Na/NaCuO2 cell were evaluated in voltage ranges of 0.75-3.0, 1.7-4.2, and 0.75-4.2V. It was found that the charge/discharge properties and cycling-induced new products depended on the voltage range. In the range of 0.75-4.2V, NaCuO2 showed a reversible capacity of 190mAh/g after ten cycles, with an average voltage of 2.5V versus Na/Na+. The results of an ex-situ XRD analysis of NaCuO2 electrode at various charged/discharged stages revealed that NaCuO2 is converted to NaCuO after the second cycle, and then, reversible structural changes occur between NaCuO and CuO.