Proton Intercalation Hysteresis in Charging and Discharging Nickel Hydroxide Electrodes

A reproducible hysteresis in charge‐discharge cycling of thin‐film (10–40 nm thickness) electroprecipitated nickel hydroxide electrodes was quantified. Thin‐film electrodes were prepared both with and without coprecipitated cobalt hydroxide, a common additive to nickel hydroxide electrodes. The ascending and descending branches of the hysteretic loop were determined. Experimental data were gathered using commonly employed techniques to capture electrode behavior on short‐ and long‐time scales. Cyclic voltammetry and galvanostatic discharge experiments were performed, and a macroscopic model of the nickel hydroxide solid material was constructed and used to interpret the simultaneous mass‐transfer, kinetic, and thermodynamic phenomena occurring at the nickel hydroxide intercalation electrode. The persistent hysteresis exhibited by these thin‐film electrodes cannot be due only to solid‐state mass‐transfer limitations. Agreement between calculated and experimental results is achieved with treatment of the hysteresis effect as a permanent, thermodynamic quantity. The numerical model may be applied to most rechargeable cells and is especially suited for systems which exhibit a permanent hysteretic loop or in which side reactions are prevalent. Model results agree with current and potential waveforms gathered from experiments performed with nickel hydroxide thin‐film electrodes. © 1999 The Electrochemical Society. All rights reserved.