Y. Shaohorn et al., STRUCTURAL CHARACTERIZATION OF HEAT-TREATED ELECTROLYTIC MANGANESE-DIOXIDE AND TOPOTACTIC TRANSFORMATION OF DISCHARGE PRODUCTS IN THE LI-MNO2 CELLS, Journal of the Electrochemical Society, 144(9), 1997, pp. 3147-3153
The crystal structures of heat-treated electrolytic manganese dioxide
(HEMD) and the discharge products are characterized by high-spatial-re
solution convergent-beam electron diffraction (CBED) and lattice imagi
ng. In this paper, CBED results are used to clarify the ambiguity in t
he x-ray diffraction (XRD) patterns of these materials. The CBED resul
ts of KEMD used as the positive electrode material confirms that the m
ajor phase has the pyrolusite space group, P4(2)/mnm, but with a range
of cia ratios. The experimentally observed variability of the lattice
parameters from grain to grain is found to coincide with broadening o
n the low-angle sides of the XRD peaks. Both XRD and CBED analyses ind
icate that the unit cell volume of the pyrolusite-type phase increases
during discharge, which is consistent with previous work by Ohzuku et
al. CBED patterns of the discharge products suggest that a second dis
charge phase is formed by a topotactic phase transformation during dis
charge and has a specific orientation relationship with the expanded p
yrolusite-type phase. The symmetry and lattice parameters obtained fro
m the single-crystal diffraction patterns of the second discharge phas
e are consistent with an intermediate structure in the mechanism propo
sed by David ct al.(1) for the formation of the spinel structure upon
chemical lithiation of beta-MnO2.