The effect of heat-treatment on electrolytic manganese dioxide: A H-2 and Li-6 magic angle spinning NMR study

Deuterium magic angle spinning (MAS) NMR techniques, in conjunction with X-ray diffraction (XRD) and thermogravimetric analysis (TGA), were used to study the effects of heat treatment on the structure and water content of electrolytic manganese dioxide (EMD), a battery grade gamma-MnO2. Three types of protons in EMD were detected by H-2 MAS NMR: surface and Ruetschi protons (i.e., vacancy protons) at 100 ppm, Coleman protons (i.e., protons in MnOOH type local environments) at 350 ppm, and molecular water loosely bound to the surface or trapped inside the micropores at 5 ppm. H-2 NMR and TGA data indicate that the molecular water desorbs below 150 degrees C, Ruetschi protons between 150 and 250 degrees C, and Coleman protons between 150 and 350 degrees C, but there is no clear-cut boundary between the heat-treatment temperatures required for removing each type of structural water. Li+ ion-exchanged EMD (LiEMD) was studied by XRD and H-2 and Li-6 MAS NMR spectroscopy. H-2 and Li-6 NMR data suggest that Li+ ions replace the Ruetschi and surface protons at room temperature, but progressively replace the more inaccessible Coleman protons upon heat treatment. The change of the XRD patterns of EMD upon heat treatment is consistent with the structural transformation of the gamma- MnO2 phase to the beta-like phase of a heat-treated EMD. In contrast, this structural transformation does not occur for the LiEMD material, but instead an ordered intergrowth phase is formed. Variable temperature MAS NMR techniques were used to investigate the dynamics of the different deuterium and Li species as a function of temperature. (c) 2005 The Electrochemical Society. [DOI: 10.1149/1.1943607] All rights reserved.