THE MANGANESE-DIOXIDE ELECTRODE .11. AN X-RAY-DIFFRACTION STUDY OF MATERIALS PRODUCED BY H-INSERTION INTO AN EMD

Thirty-one samples of composition MnOOH(r), where 0.1 < r < 1.0, were prepared under mild conditions by reacting a commercial electrodeposited manganese dioxide (EMD) with xylene, acetone, cinnamyl alcohol or combinations thereof. Although the X-ray pattern reflected the expected dilation of the crystal structure in the region 0.1 < r < 0.8 the attainment of an H insertion level of MnOOH0.8 without the emergence of additional peaks is a new finding. The expansion was nearly isotropic and careful examination of peak positions and intensities indicated changes in behaviour at about r = 0.25 and 0.45. Another finding was the ability of inserted H to migrate across the boundaries of nominally dry powders in the region 0.1 < r < 0.8. In the region r > 0.8 expansion was clearly anisotropic and as a consequence new diffraction peaks emerged and some of the peaks present at lower H insertion levels were substantially reduced in intensity. A particularly important observation was the restricted mobility shown by inserted H in the end-product MnOOH as this has implications for the performance of EMD in batteries. The X-ray diffraction pattern of the end-product was dissimilar to alpha-and gamma-MnOOH in important respects and a previous suggestion that it is called delta-MnOOH seems preferable.