Failure modes of lead/acid batteries

Abstract

The delivery and storage of electrical energy in lead/acid batteries via the conversion of lead dioxide and lead to, and from, lead sulphate is deceptively simple. In fact, battery performance depends upon the cell design, the materials of construction, a complex interplay between the multitudinous parameters involved in plate preparation, the chemical composition/structure of the active materials, and the duty/conditions of battery operation. It is not surprising, therefore, that the factors responsible for the degradation of battery performance, and eventual failure, are many and varied. Apart from occasional field surveys of automotive batteries in the U.S.A., comprehensive failure analyses of units removed from service are rarely published. In general, the information is kept proprietary, or appears as a post mortem report that is subsidiary to some other topic of interest. By contrast, the literature abounds with detailed laboratory investigations of phenomena that are likely to contribute, wholly or in part, to the demise of batteries. In broad terms, this review draws together the fragmented and scattered data presently available on the failure mechanisms of lead/acid batteries in order to provide a platform for further exploration of the phenomena, and for the planning of remedial strategies. The approach taken is to classify, first, the different lead/acid technologies in terms of required duty (i.e., float, cycling and automotive applications), unit design (i.e., flat or tubular plate, flooded or immobilized electrolyte), and grid alloy (i.e., leadantimony or leadcalcium system). A distinction is then made between catastrophic failure, as characterized by a sudden inability of the battery to function, and progressive failure, as demonstrated by some more subtle deviation from optimum performance. Catastrophic failure is attributed to incorrect cell design, poor manufacturing practice, abuse, or misuse. These problems are obvious and, accordingly, have been afforded little discussion. Progressive life-limiting factors encountered with flooded-electrolyte batteries are discussed in detail. These are mainly associated with degradation of the positive plate, the negative plate and the separator. The technology of valve-regulated (i.e., immobilized-electrolyte) batteries is still at an early stage compared with that of flooded designs and, consequently, published information on failure modes is very limited. Nevertheless, based on the reports that are available and the authors' own knowledge, it is possible to make estimates of the major and minor causes of failure (note, these will also occur in flooded systems, but with shifted emphasis). Grid corrosion and growth are generally considered to be of major importance. Both negative-plate sulphation and water loss are also of concern, particularly in cycling applications. By contrast, the traditional problems associated mossing and dendritic growth of the active material should be reduced in valve-regulated batteries.