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

Abstract

Experimental capacities and mass changes are recorded using an electrochemical quartz crystal microbalance during the first 9 charge and discharge cycles of nickel hydroxide thin films cycled in 3.0 weight percent (wt%) potassium hydroxide electrolyte.For the first time, the film capacities have been corrected for the oxygen evolution side reaction, and the data used as input into the point defect-containing structural model to track the changes that occur during short-term cycling. Variations in capacity and mass during formation and charge/discharge cycling are related to changes in the point defect parameters, thus providing a structural origin for the unique experimental variations observed here and often reported in the literature, but previously unexplained. Proton-, potassium-, and water-content vary in the active material during charge/discharge cycling. The observed capacity loss, or "capacity fade," is explained by incomplete incorporation of potassium ions in (or near) the nickel vacancy during charge, as additional protons are then allowed to occupy the vacant lattice site. The increase in water content during reduction parallels the expansion of the electrode that is well known during cycling. This result confirms the origin of the swelling phenomenon as being caused by water incorporation. The model and methodology developed in this paper can be used to correlate electrochemical signatures with material chemical structure.

Definition of the aging process parameters for nickel hydroxide in the alkaline medium

“…These changes can be summarized in a diagram presented in Fig. 1 [16,17]. Transformation in the base is also called "aging" process [18].…”

Effect of Crystallinity of β- and βbc-Nickel Hydroxide Samples on Chemical Cycling

“…During the charge-discharge process, redox reaction occurs inducing structural changes in the positive and negative electrode materials. The electrochemical performances of -nickel hydroxide are lower than that of bc -nickel hydroxide [7], even though there are several reports on the structural changes which occur during the electrochemical cycling ofnickel hydroxide [8][9][10][11]. It is difficult to separate the oxidized and reduced phases of the active materials used in the battery or electrochemical cell; thus, attracting different methods adopted towards characterization provides information in the local environment [10,12,13].…”

The oxygen evolution kinetics in sealed rechargeable NiMH batteries

“…The impact of the electrode structural and morphological on the reaction kinetics has hardly been quantified in the literature. The following references are useful to obtain more qualitative information [12,13,24,26,30,39,79,[85][86][87][88][89][90][91][92][93][94][95].…”