Application of electrochemical kinetics to predict the failure modes of nickle cadmium cells

Abstract

A critical review of the literature on nondestructive techniques to predict failure modes of sealed rechargeable battery-cells, such as nickel-cadmium cells, has been made. It is thus concluded that a.c. impedance measurements which are usually considered in this regard are alone inadequate, and data from d.c. and transient techniques are also required for the purpose.

A theoretical treatment has been developed in this work to analyse the transient response to a constant-voltage charge of a positive-limited nickel-cadmium battery-cell from an initially discharged state to a small, finite state-of-charge. The theory takes into account the double layer charging process, polarisation due to mass transfer, charge transfer and ohmic resistances in the cell, as well as self-discharge due to any internal electronic short.

It has been shown that the complexity of porous electrode structure in the battery-cell under test is immaterial for the above theoretical treatment provided that the transient response is examined under near-equilibrium conditions.

Experimental precautions required to obtain such transient response data for nickel-cadmium battery-cells have been identified.

Experimental data of transient response to a constant voltage charge have thus been obtained for several nickel-cadmium battery-cells with and without any internal electronic short.

A comparison of the above data with theory has been made which indicates that charge transfer step is not rate-controlling in these cells but mass transfer step could be rate-controlling.

As a corollary to the theory developed above, a new method has been evolved to detect in an accelerated and nondestructive manner the presence of any internal electronic short in a rechargeable battery-cell. The method involves mainly a measurement of the quiescent current through an initially discharged battery-cell subjected to charge by a constant-voltage source up to a predetermined final voltage.

A quantitative expression has been derived to determine the magnitude of any internal electronic short by the above method.

An experimental verification of the proposed method has been carried out successfully with vented nickel-cadmium battery-cells of both positive-limited and negative-limited types.

Experimental precautions required to evaluate the magnitude of any internal electronic short quickly (for example, within a few hours) and accurately (for example, within about 8%) have been identified for nickel-cadmium battery-cells.

A phenomenological model has been proposed for the open-circuit voltage recovery transient of positive-limited nickel-cadmium battery-cells.

A theoretical analysis has been made of this model for the open-circuit voltage recovery transient of a positive-limited nickel-cadmium battery-cell from an initially discharged state, taking into account polarisation phenomena due to slow charge or mass transfer, double layer charging process, and the presence, if any, of an internal electronic short.

Analytical results have been deduced from the above theory for limiting cases with and without an internal electronic short.

The theoretical expressions for open-circuit voltage recovery transient have been compared with experimental data obtained with nickel-cadmium battery-cells without any internal electronic short.

Experimental conditions most favourable for a failure-mode analysis of nickel-cadmium battery-cells by open-circuit voltage recovery transient studies have been identified, as for example, maintenance of a fixed but sufficiently long ‘dead-short’ period prior to the open-circuit test.

A comparison of theory with experiment shows that mass transfer step is rate-controlling in such cases. It follows that failure-modes of nickel-cadmium battery-cells governed by mass-transfer limitations become predictable by this method, in principle.