Effect of Proton Diffusion, Electron Conductivity, and Charge‐Transfer Resistance on Nickel Hydroxide Discharge Curves

Abstract

Constant-current discharge curves for the nickel hydroxide electrode are simulated assuming resistances due to diffusion of protons and conduction of electrons through the nickel hydroxide film, and charge-transfer resistance at the film/electrolyte interface contribute to the polarization losses of the electrode. Good qualitative agreement is observed between the model predictions and experimental discharge curves. The results suggest that polarization losses due to diffusional limitations of protons is a critical factor in determining the characteristics of the discharge curve. Ohmic resistance has a significant effect on the discharge curves at the end of discharge, and charge-transfer resistance is a minor contributor to the polarization losses. These findings indicate that accurately measuring the diffusion coefficient of protons, the thickness of the hydroxide film, the initial state-of-charge, and the electronic conductivity as a function of state-of-charge towards the end of discharge are critical in accurately predicting the discharge characteristics of nickel hydroxide. Physical constants which were shown to have minor influence on the discharge curves are the film conductivity at the beginning of discharge, and the exchange current density and cathodic transfer coefficient for the reaction. The time-dependent, one-dimensional diffusion equation has been solved analytically which should provide a computationally efficient means of accounting for proton diffusion and variable electronic conductivity in a macrohomogeneous battery model without sacrificing accuracy.

Ultra-small, size-controlled Ni(OH)2 nanoparticles: elucidating the relationship between particle size and electrochemical performance for advanced energy storage devices

“…In contrast, a reverse trend in R ct and D is observed as the size of the Ni(OH) 2 nanoparticles further decreases below 7.9 nm, and a decrease in the capacity occurs. It should be noted that this reverse trend in R ct and D is synchronized with the rapidly decreasing trend in σ caused by the quantum confinement effect, which is consistent with other reports 10,13,[30][31][32][33][34][35] and confirms the underlying relationship between σ, R ct and D. As a result, 3.3-nm Ni(OH) 2 nanoparticles have a minimum capacity value because of their low conductivity, large charge transfer resistance and small proton diffusion coefficient.…”

“…Weidner et al suggested that the rapid decrease in conductivity causes a significant polarization loss via the theoretical simulation of the discharge character of Ni(OH) 2 . [30][31][32] In our study, at a particle size that is less than the critical value (7.9 nm), there is a decrease in capacity as the particle size decreases, which corresponds to a rapid decrease in conductivity; this result demonstrates the role of conductivity in the electrochemical performance. Moreover, many works have proven that the conductivity of electrode materials is closely related to the diffusion of protons through the nanoparticle and the redox reaction rate on the surface.…”

“…Moreover, many works have proven that the conductivity of electrode materials is closely related to the diffusion of protons through the nanoparticle and the redox reaction rate on the surface. 10,13,[30][31][32][33][34][35] This result leads us to hypothesize that the charge transfer resistance (R ct ) and proton diffusion coefficient (D) in the electrodes and electrolytes could change and differ from the traditional understanding because the particle size of Ni(OH) 2 is less than the critical size.…”

Discharge Model for the Lithium Iron-Phosphate Electrode

“…However, simulations based on the transport parameters estimated above do not give us the necessary slope. In addition, we attempted adjusting the transfer coefficient in the kinetic expression to see if the discharge curves can be made more sloped, 44 but this was also not useful in achieving the needed fits. Finally, we are left with an ohmic effect, with an increasing ohmic drop with SOD.…”

A Review of Approaches for the Design of Li-Ion BMS Estimation Functions

“…Simplified 1D electrochemical models versions of this approach have also been presented, either by removing the radial dimension, [40], or by neglecting the x-dimension variations with an averaging procedure in [2,[41][42][43].…”