Effects of synthesis temperature and precursor composition on the crystal structure, morphology, and electrode activity of 1D nanostructured manganese oxides

1D nanostructured manganese oxides are prepared by oxidation reaction of precursor LiMn2-xCrxO4 microcrystals under hydrothermal condition. The crystal structure and morphology of the obtained manganese oxides are strongly dependent on the reaction condition and the chemical composition of the precursors. The alpha-MnO2 nanowires are prepared by reaction at 120 degrees C, and their aspect ratios decrease with the Cr content in the precursor. Treating precursors with persulfate ions at 160-180 C yields the beta-MnO2 nanorods for the precursors LiMn2-xCrxO4 with lower Cr content and the alpha-MnO2 nanowires for the precursors with higher Cr content. The structure dependence of the products on the Cr content in the precursors is related to the high octahedral site stabilization energy of Cr3+ ions and/or to the increase of Mn valence state upon Cr substitution. The increase of Cr content in the precursors degrades the electrode performance for the manganates prepared at 160 degrees C but improves electrode activity for those prepared at 180 degrees C. This observation can be explained by the structural variation and chromium substitution of the hydrothermally treated manganates. We conclude that the use of spinel LiMn2-xCrxO4 as precursors provides an effective way to synthesize 1D nanostructured manganate with tailored crystal structure and morphology. (C) 2009 Elsevier B.V. All rights reserved.