Engineering topics

Cornilsen, Bahne C.

Publications and source records attributed to Cornilsen, Bahne C..

6 records

NASA NTRS1994

Raman structural studies of the nickel electrode

The objectives of this investigation have been to define the structures of charged active mass, discharged active mass, and related precursor materials (alpha-phases), with the purpose of better understanding the chemical and electrochemical reactions, including failure mechanisms and cobalt incorporation, so that the nickel electrode may be improved. Although our primary tool has been Raman spectroscopy, the structural conclusions drawn from the Raman data have been supported and augmented by three other analysis methods: infrared spectroscopy, powder X-ray Diffraction (XRD), and x-ray absorption spectroscopy (in particular EXAFS, Extended X-ray Absorption Fine Structure spectroscopy).

Cornilsen, Bahne C.↗

NASA NTRS1990

Structural comparison of nickel electrodes and precursor phases

In this paper the previous Raman spectroscopic results are summarized and important structural differences in the various phases of active mass and active mass precursors are discussed. Raman spectra provide unique signatures for these 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 small particle size). The structural changes incurred during formation, charge and discharge, cobalt addition, and aging wil be discussed. The oxidation states and dopant contents are explained in terms of the nonstoichiometric structures.

Cornilsen, Bahne C.↗

NASA NTRS1989

Structural comparison of nickel electrodes and precursor phases

Researchers summarize previous Raman spectroscopic results and discuss important structural differences in the various phases of active mass and active mass precursors. Raman spectra provide unique signatures for these 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 small particle size). The structural changes incurred during formation, charge and discharge, cobalt addition, and aging are discussed. The oxidation states and dopant contents are explained in terms of the nonstoichiometric structures.

Cornilsen, Bahne C.↗

NASA NTRS1989

Structural comparison of nickel electrodes and precursor phases

A summary of previous Raman spectroscopic results and a discussion of important structural differences in the various phases of active mass and active mass precurors are presented. Raman spectra provide unique signatures for these 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 small particle size). The structural changes incurred during formation, charge and discharge, cobalt addition, and aging will be discussed and related to electrode properties. Important structural differences include NiO2 layer stacking, nonstoichiometry (especially cation-deficit nonstoichiometry), disorder, dopant content, and water content. The results indicate that optimal nickel active mass is non-close packed and nonstoichiometric. 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, the in situ Raman technique to characterize the critical structural parameters was developed. An in situ method relates structure, electrochemistry, and preparation. In situ Raman spectra of cells during charge and discharge, either during cyclic voltammetry or under constant current conditions were collected. With the structure-preparation knowledge and the in situ 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.

Cornilsen, Bahne C.↗

NASA NTRS1987

Structural models for nickel electrode active mass

Raman spectroscopic data allow one to distinguish nickel electrode active mass, alpha and beta phase materials. Discharges active mass is not isostructural with beta-Ni(OH)2. This is contrary to the generally accepted model for the discharged beta phase of active mass. It is concluded that charged active mass displays a disordered and nonstoichiometric, nonclose packed structure of the R3 bar m, NiOOH structure type. Raman spectral data and x ray diffraction data are analyzed and shown to be consistent with this structural model.

Cornilsen, Bahne C.↗

NASA NTRS1986

A point defect model for nickel electrode structures

The Raman spectra for nickel electrode active mass indicate a single formula-unit crystallographic unit cell of the layered NiOOH-type. Empirical stoichiometric formulas require that extensive point defects, cation dopants and nickel vacancies, be incorporated on nickel sites. Structural differences between the alpha/gamma and beta/beta cycles, and the influence of cobalt addition on the structure will be discussed in terms of the point defect model. Other empirical data supporting the point defect model will be considered.

Loyselle, Patricia L.↗