Dynamic Monitoring of Structural Changes in Porous Nickel Hydroxide Electrodes Employed in Batteries

E. B. CASTRO; M. ORTIZ; A, VISINTIN; S. G. REAL

Foz de Iguaçú, Brasil

Congreso; ISE 2008 Spring Meeting; 2008

International Society of Electrochemistry

The high power density, very good cyclability and high specific energy nickel hydroxide electrode make them very competitive for extended range of applications such as electrode material for Nickel /Hydrogen and Nickel /metal hydride batteries.  The electrochemical energy storage in the nickel hydroxide electrodes is related to the reversible characteristics of the redox couple nickel hydroxide/oxihydroxide. The process reversibility is an important property of electrode materials for batteries. The nickel electrode has being study for many researchers, however there are still many factors not well understood, as the “sudden death” of the batteries, that are dependent on many factors:  the concentration of the alkaline solution, the preparation method and the global kinetics of the process.  In the case of nickel hydroxide electrode the insertion of hydrogen takes place during discharge, while the inverse process occurs during charge.  In this study two types of nickel hydroxide electrodes were prepared by electrodeposition on sintered and foam nickel substrates.  Into these matrix, nickel hydroxide was electrodeposited using 1,8 M Ni(NO3 )2+ y M X(NO3) solution, X being Na, and Co.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           The Experiments were curried out using electrochemical charge-discharge cycling and electrochemical impedance spectroscopy (EIS). The results obtained by EIS for different state of discharge (SOD) of nickel hydroxide electrode are presented and discussed according to physicochemical models developed at the laboratory. The models account for the charge/discharge process, the diffusion of hydrogen in the solid matrix and the transport processes in the electrolyte phase added to the porous nature of the electrode . The impedance function derived from the model takes into account the finite conductivity of both the solid and liquid phases. The parameter identification procedure allows estimating characteristic structural parameters such as, double layer capacity per volume unit (Cdlxae), the active area per unit volume ae, porosity (Vl) and thickness (L) of the active material as a function SOD. These changes are discussed considering the volume expansion taking place during discharge