Structural characterization of heat-treated electrolytic manganese dioxide and topotactic transformation of discharge products in the Li-MnO < inf> 2 cells

Document Type

Article

Publication Date

1-1-1997

Abstract

The crystal structures of heat-treated electrolytic manganese dioxide (HEMD) and the discharge products are characterized by high-spatial-resolution convergent-beam electron diffraction (CBED) and lattice imaging. In this paper, CBED results are used to clarify the ambiguity in the x-ray diffraction (XRD) patterns of these materials. The CBED results of HEMD used as the positive electrode material confirms that the major phase has the pyrolusite space group, P42/mnm, but with a range of c/a ratios. The experimentally observed variability of the lattice parameters from grain to grain is found to coincide with broadening on the low-angle sides of the XRD peaks. Both XRD and CBED analyses indicate 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 discharge phase is formed by a topotactic phase transformation during discharge and has a specific orientation relationship with the expanded pyrolusite-type phase. The symmetry and lattice parameters obtained from the single-crystal diffraction patterns of the second discharge phase are consistent with an intermediate structure in the mechanism proposed by David et al.1 for the formation of the-spinel structure upon chemical lithiation of β-MnO2.

Publication Title

Journal of the Electrochemical Society

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