Failure Mechanisms in the Valve Regulated Lead/acid Battery

Abstract

Recent advances in lead/acid battery technology have resulted in the development and widespread use of the valve regulated lead acid (VRLA) battery. The major differences between the VRLA, and traditional flooded design, is the use of an immobilised electrolyte and inclusion of a gas release valve. These features allow the oxygen recombination reaction to occur. Advantages of this battery type include low maintenance and the ability to operate in any orientation. Typical applications include, standby power supplies, SLI (starting, lighting and ignition) and electric vehicle power.

This programme of work has investigated a number of design and operational features that determine VRLA battery performance. These include grid alloy composition, positive active material composition and separator paper type. Specimen batteries were cycled using a C5 cycling regime until the failure point, at 80% of original capacity, was reached. Following cycling batteries were dismantled and the cells exhibiting the most and least reduction in voltage
during a constant current discharge extracted. Removed cells were subsequently examined using a range of analytical techniques to establish the cause of failure and determine the relative operational characteristics of battery variants.

The main analytical techniques used to examine positive and negative electrodes were, light and electron microscopy, electron probe microanalysis, x-ray diffraction and metallographic techniques. This involved examination of both active materials and positive grid corrosion layers. Correlation between current density and corrosion layer thickness on the positive electrode grid was established using a numerical modelling technique. Finally, a number of
different separator paper types were examined using electron microscopy. The diffusive and compressive properties of the sample separator papers were characterised at varying saturation levels using specifically designed equipment.

Date of Award	22 Nov 2000
Original language	English
Awarding Institution	University of Bath
Supervisor	Ronald Stevens (Supervisor)