Synthesis, structural and electrochemical characterizations of the sol-gel birnessite MnO1.84•0.6H2O

The electrochemical features of the sol-gel birnessite MnO1.84.0.6H(2)O are reported here in terms of OCV data, cycling behavior kinetics of Li transport in the oxide. We have confirmed that the sol-gel birnessite remains one of the best manganese oxides as rechargeable cathodic materials with an initial specific capacity of 270 mAh g(-1) due to the high amount of Mn(IV). However, from a practical viewpoint, this hydrated compound has been proved to exhibit an important and constant capacity fading in the potential window 4.2-2 V associated with a strong disordering process. The ac impedance measurements have proved this behavior was mainly due to an increase of the cathode impedance and a strong decrease in kinetics of Li transport in the oxide. Such a phenomenon can be overcome when the Co-doped form Co0.15Mn0.85O1.84.0.6H(2)O is used. In that case, a constant capacity as high as 170 mAh g(-1) can be maintained over more than 50 cycles with no change in the electrochemical behavior of the Co-doped sample. This clearly shows that stable capacity can be expected even from a hydrated oxide network. (C) 2002 Elsevier Science B.V. All rights reserved.