The solid state structure of the nickel electrode controls the electrochemical properties. properties which critically depend upon the structure. Undesirable phases can cause battery failure. If we can define the critical structural components (including nonstoichiometry and disorder in fine particle size materials), it is possible to control the empirical variables to optimize the electrochemical Proton diffusion and electron conduction are examples of properties. properties and how the structure can be controlled during electrode preparation, including deposition and formation. Definition of structure allows one to sort out the complex property-preparation relationship. Th third side of the triangle, which provides control of electrochemical properties, is defined if we know the other two sides, structure-property structure-preparation.To do this we must know both how the structure controlsIn this paper we shall summarize our previous Raman spectroscopic results discuss imDortant structural differences in the various Dhases of active phases, and allow one to distinguish each phase, even when the compound is amorphous to x-rays (i.e. does not scatter x-rays because of a lack of order and/or smal 1 particle size). The structural changes incurred during formation, charge and discharge, cobalt addition, and aging will be discussed and related to electrode properties.Raman spectra provide unique signatures for these Important structural differences include Ni02 layer stacking, nonstoichiometry (especially cation-deficit nonstoichiometry), disorder, dopant content, and water content. Our results indicate that optimal nickel active mass is non-close packed and nonstoi chiometric. The formation process transforms precursor phases into this structure. Therefore, the precursor disorder, or lack thereof, influences this final active mass structure and the rate of formation. Aging processes induce structural change which is believed to be detrimental. The role of cobalt addition can be appreciated in terms of structures favored or stabilized by the dopant.In recent work, we have developed the in s i t u Raman technique to characterize the critical structural parameters. An i n s i t u method is necessary if one wishes to relate structure, electrochemistry, and preparation. We collect i n s i t u Raman spectra of cells during charge and discharge, either during cyclic voltammetry or under constant current conditions. With the structure-preparation knowledge now on-hand, and the new i n s i t u Raman tool, it will be possible to define the structure-property-preparation relations in more detail. This instrumentation has application to a variety of electrode systems. 28https://ntrs.nasa.gov/search.jsp?R=19890013630 2018-05-10T15:58:30+00:00Z

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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, P4,/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.' for the formation of the spinel structure upon chemical lithiation of j-MnO 2 .

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