Page 121 - Handbook of Battery Materials

89

3
Structural Chemistry of Manganese Dioxide
and Related Compounds

J¨ org H. Albering

3.1
Introduction

In this section the structural properties of the most common manganese diox-
ide modifications and closely related compounds will be presented and briefly
compared. A huge number of compounds are designated as ‘Braunstein’ (i.e., man-
ganese dioxide). This term includes all natural and synthetic manganese oxides
of composition MnO 1.4 –MnO 2.0 , regardless of the presence of foreign cations,
hydroxide anions, or water molecules in the structure. All the known – and more
or less structurally characterized – materials of that composition cannot be re-
viewed here. The main purpose is to give an overview of the variety of features
in the chemistry of manganese oxides and to point out the structural correlations
of various modifications within the large family of manganese oxide minerals
and synthetic compounds. The occurrence of MnO 2 in natural ores and some
methods of synthesizing the different modifications in the laboratory will be briefly
described. Details of its electrochemical behavior in Leclanch´ e cells and alkaline
Zn/MnO 2 cells, and of its use as a lithium storage material in lithium-ion cells are
given in Part II Chapter 4 and Part III Chapter 1, respectively.
In general, it is very difficult to obtain well-developed single crystals of any
modification of MnO 2 in the laboratory [1]. Hence most of the structural data
on manganese dioxide are obtained either from single crystals selected from
natural ores (e.g., crystals up to 30 cm in length are reported for α-MnO 2 [2])
or by X-ray diffraction (XRD) or neutron powder techniques combined with
Rietveld refinements [3]. Most manganese oxides are usually fine-grained and
the crystallites may contain many defects, twin domains, superstructures, and
partially occupied crystallographic sites. Therefore the XRD technique – although
it is the most commonly used and successful method for the determination
of the structural properties – is often limited by the poor crystallinity of the
materials. Consequently, the effects of structural disorder (e.g., selective reflex
broadening, preferred orientation, and the presence of indistinct, overlapping
Bragg reflections) on the X-ray powder diffraction patterns can lead to incomplete or
false interpretations of the diffraction data and subsequently to incorrect structural

Handbook of Battery Materials, Second Edition. Edited by Claus Daniel and J¨ urgen O. Besenhard.
 2011 Wiley-VCH Verlag GmbH & Co. KGaA. Published 2011 by Wiley-VCH Verlag GmbH & Co. KGaA.