Structural comparison of nickel electrodes and precursor phases

Abstract

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

A nonstoichiometric structural model to characterize changes in the nickel hydroxide electrode during cycling

“…However, Raman spectroscopic studies on electrode active mass have indicated that these four electrochemically active materials actually share a common, nonclosepacked crystal structure (with …ABBCCA… stacking). This common structure is indicated by the Raman spectral selection rules; these do not change during cycling [11,12]. Only the peak positions vary.…”

“…This structure should be called the γ structure (after the structure of the charged phase in the α−γ cycle [10]), and was confirmed by reanalysis of the γ phase powder XRD pattern [11]. This structure contrasts with the closepacked, β−phase structure (with …ABAB… stacking), which is electrochemically unstable under normal cycling conditions [5,11,12]. "Aging" active mass in concentrated Conversion in KOH Overcharge alkali transform it into the β−phase structure [5,11,12].…”

“…Two electrochemical cycles were identified in 1969, and four phases were proposed to explain the voltage differences in 1980 [5,10]. In 1988 and 1990 these four phases were shown to exhibit the same layer-type structure, and variations in empirical formulae were directly correlated with the nonstoichiometry and point defect structure [11,12].…”

Electrodeposition of Nickel Hydroxide Nanoparticles on Carbon Nanotube Electrodes: Correlation of Particle Crystallography with Electrocatalytic Properties

“…The improved performance of the -phase over the -phase could be due to several factors including: (i) the more disordered structure of -Ni(OH) 2 /-NiOOH which enables more facile ion-solvent intercalation, to maintain charge neutrality during electrocatalysis; 75 (ii) -NiOOH has a higher oxidation state than -NiOOH and, in principle, could act as a more effective electro-oxidation catalyst. [70][71][72] This revealed typical NP crystallites of sizes 10 nm and 5 nm for the direct and indirect approaches, respectively. The latter data supported the idea that the larger nanostructured material, as observed by AFM, was produced by the aggregation of smaller NPs.…”

``In-situ'' spectro-electrochemical studies of radionuclide-contaminated surface films on metals

“…As the peak at ~3.10 Å is relatively weak we find that this interaction can also be represented as a Cr-Cr correlation at 3.44 (5) There has been a number of studies designed to understand the local atomic and electronic structure of iron and other metal ions incorporated into α-Ni(OH) 2 [23][24][25][26][27][28][29]. For brevity, we omit discussion of previous works here.…”