Preparation and electrochemical characterization of cobalt-manganese oxide as electrode materials for electrochemical capacitors

Cobalt-manganese oxide materials (CMOs) were prepared by chemical method and heat treated at 150, 400, 600, 800 and 1000 degrees C, respectively. The physical and electrochemical properties of the materials were characterized. The heat treatment process leads to the removal of water molecules adsorbed on the surface of CMO particles (below 400 degrees C) and the progressive reduction of Mn and Co ions from Mn4+ and Co3+ to Mn3+/Mn2+ and Co2+, respectively (440-1000 degrees C). CMOs obtained by treatment below 800 degrees C have poor crystallinity and a. highly crystallized tetragonal phase by treatment at 1000 degrees C. The ratio of Mn and Co in CMOs is found by EDX analysis to be about 2:1. The electrochemical testing results indicate that the high crystallization of CMO is disadvantageous for the energy storage as electrode material of electrochemical capacitors. However, for CMOs with poor crystallinity, relatively high specific capacitances can be obtained. The incorporation of protons and ions into the CMO's lattice during electrochemical charge/discharge process leads to the distortion of crystal lattice and improvement of crystallinity of CMO. The XRD patterns show that negative electrode (NE) and positive electrode (PE) have tetragonal (Co, Mn)(Mn, CO)204 phase. (C) 2008 Elsevier Ltd. All rights reserved.