The Effect of Heat-Treatment on Electrolytic Manganese Dioxide: A #2#1 and #2#1 Magic Angle Spinning NMR Study

Abstract

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 . Three types of protons in EMD were detected by 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. NMR and TGA data indicate that the molecular water desorbs below 150°C, Ruetschi protons between 150 and 250°C, and Coleman protons between 150 and 350°C, but there is no clear-cut boundary between the heat-treatment temperatures required for removing each type of structural water. ion-exchanged EMD (LiEMD) was studied by XRD and and MAS NMR spectroscopy. and NMR data suggest that 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 “γ−” phase to the “β-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.