Hysteresis during Cycling of Nickel Hydroxide Active Material

Abstract

The nickel hydroxide electrode is known to exhibit a stable hysteresis loop, with the potential on charge being higher than that on discharge at every state-of-charge ͑SOC͒. What we show here is that this loop created during a complete charge and discharge ͑i.e., boundary curves͒ is not sufficient to define the state of the system. Rather, internal paths within the boundary curves ͑i.e., scanning curves͒ can be generated that access potentials between the boundary curves. The potential obtained at any SOC, as well as how the material charges and discharges from that point, depends on the cycling history of the material. The implication of this phenomenon is that the potential of nickel-based batteries cannot be used as an indication of the SOC of the cell. Analysis of the boundary and scanning curves suggest that the electrode consists of a number of individual units or domains, each of which exhibits two or more metastable states. The cycling behavior of the nickel hydroxide electrode is discussed within the context of previously developed theoretical arguments regarding domain theory. Although the specific cause for the metastability in each domain is not understood, considerable insights are provided into the history-dependent behavior of the nickel hydroxide electrode. Finally, an empirical procedure is developed to predict the scanning curves based on the boundary curves.

Modeling Battery Behavior for Accurate State-of-Charge Indication

“…Taking the average of the charge and discharge voltage has the scope of eliminating to the greatest extent possible the presence of the overpotential and hysteresis in the EMF function. [13][14][15][16] In this paper, the EMF has been determined by means of the linear interpolation method described as follows. First, the battery has been fully charged until 4.2 V at a constant 0.05 C rate.…”

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

“…This quantity was evaluated by correcting for the oxygen evolution reaction as described previously [25].…”

“…They also assumed that the discharged material contained one proton per nickel vacancy (i.e., n 1 =1, y 1 =0, x 1 =0. 25), and that on charge this proton was replaced with a potassium ion (i.e., y 2 =x 2 =0.25). The limitation of their assumptions is that changes in mass and capacity were linked through a single parameter, z.…”

Battery Aging and Its Influence on the Electromotive Force

“…The emf measurements were obtained by means of galvanostatic intermittent titration technique ͑GITT͒ for both fresh and aged batteries. New measurements regarding the emf hysteresis, 11,[14][15][16] as a function of battery aging are presented below.…”