FAILURE MODES OF VALVE-REGULATED LEAD ACID BATTERIES/

The decline in the cycle-life performance of lead/acid batteries is of ten caused by deterioration of the positive plates. When batteries are used in electric vehicles, however, the decline in performance is due not only to positive-plate degradation, but also to serious problems with the negative plates. This is because electric-vehicle batteries a re used in the form of a pack and their temperature rises excessively (especially during the hot weather) which, in turn, causes decompositi on of the lignin additive in the negative plates. Deterioration of the negative plates limits vehicle-running performance even in hybrid ele ctric vehicles (HEV). When batteries are used in this way, charging is achieved during travel via regenerative current and the generator. Th us, the batteries are charged by large currents, and charging is irreg ular. This causes the accumulation of lead sulfate in the negative pla tes. Such behaviour can be suppressed by increasing the amount of carb on, one of the negative-plate additives. As a consequence, cycle-life performance is improved significantly. On the other hand, in small val ve-regulated lead/acid batteries for trickle use, contact between the plates and separators is impaired and this results in a decline in the high-rate discharge performance. This occurs because transmission of water vapour from the battery container lowers the amount of electroly te in the separators, which then contract.