An electrochemical impedance spectroscopy study of new lithiated manganese oxides for 3 V application in rechargeable Li-batteries

The main electrochemical properties of 3 V manganese oxides Li(0.45)MnO(2.1) and Li(0.45)Mn(0.85)CO(0.15)O(2.3) synthesized via a solution technique are reported. These materials are characterized by an attractive cycle life with a stable specific capacity in the voltage range 4.2-2 V between 165 and 195 mAh g(-1) depending the C rate and the compound. Impedance spectroscopy is used to evaluate the chemical diffusion coefficient of lithium in both cathodic materials. D(Li) is found to be twofold higher in the Co-doped compound and little affected by Li concentration in the composition range 0.45 < x < 0.85. Analysis of impedance diagrams supports the existence of a passivating layer (Li(+)-ion conducting layer) onto the electrode when propylene carbonate is used as solvent or cosolvent. The presence of cobalt promotes the formation of this surface layer. (C) 2002 Elsevier Science Ltd. All rights reserved.