DYNAMIC MONITORING OF STRUCTURAL CHANGES IN POROUS NICKEL HYDROXIDE ELECTRODES EMPLOYED IN BATTERIES.

M.G. ORTIZ, S. G. REAL, D. BECKER, G. GARAVENTTA, A. VISINTIN, E. B. CASTRO

Algarve

Simposio; -8th International Symposium on Electrochemical Impedance Spectroscopy; 2010

A common feature of rechargeable batteries such as Ni/Cd, Ni/MH and Ni/H2 is the nickel hydroxide active material used as positive electrode. The nickel hydroxide electrode is the essential limiting factor in the overall battery energy density. The electrochemical energy storage in the nickel hydroxide electrodes is related to the reversible insertion of H into the nickel hydroxide/oxihydroxide. The goal in the present work is to explore the use of the electrochemical impedance spectroscopy technique as a tool to characterize the dynamic behavior of porous nickel hydroxide electrodes obtained with different preparation methods and accordingly to compare their performances. In this study two types of nickel and cobalt hydroxide electrodes were prepared on sintered nickel sheet plates, type using in positive plate of batteries for space application, nickel hydroxide electrodeposited employing constant currents and pulse currents. The electrochemical behavior of the prepared samples was studied using electrochemical charge-discharge cycling, Electrochemical Impedance Spectroscopy (EIS) and Scanning Electron Microscopy (SEM). The results obtained by EIS for different state of discharge of nickel electrode are presented and discussed according to physicochemical models developed at the laboratory. The model, from which the impedance function of the system is derived, takes into account the porous nature of the materials, the charge transfer processes at the active area/electrolyte interface, the diffusion of hydrogen in the active material and the charge transport processes in the electrolyte and solid phases. The parameter identification procedure allows the estimating of the active area per unite volume, the solution conductivity as well as diffusion and kinetic constants related to the process. These results show important differences according to the preparation method of the active material.