Materials issues affecting vrla battery life

Towards the end of the twentieth century the lead-acid battery underwent a significant functional revision. For most of its long history the battery had operated with its plates immersed in a mobile electrolyte and provision had been made for gas produced during overcharge to be freely released into the atmosphere. The gases allowed to escape in this way represented a loss of water from the electrolyte which needed to be replaced in a regular maintenance operation. The modem, valve-regulated, lead-acid battery has been designed to operate an internal gas cycle in which oxygen evolved during overcharge of the positive electrode transfers through a gas space to the negative electrode where it is reduced. The oxygen cycle depolarizes the negative electrode and reduces hydrogen evolution to very low levels. A pressure release valve is provided to ensure that even the residual low level of hydrogen produced does not generate high pressure. The changes made to the construction of the battery in the move to the valve regulated design have brought new challenges for the materials scientist seeking to overcome the traditional life-limiting mechanisms of the lead-acid battery: paste softening, electrolyte stratification, incomplete charging and grid corrosion. The reward for a complete resolution of these issues is a battery that requires virtually no maintenance, presents no acid spill threat, and can be deployed with a minimal footprint.