Influence of temperature on expander stability and on the cycle life of negative plates

The influence of temperature and the type of expander on the cycle life of negative lead-acid battery plates set to cycling tests following the requirements of the ECE-15 test protocol has been investigated. The plates prepared with the currently used expanders Vanisperse (Vs) or Indulin (In) alone have a considerably shorter cycle life than negative plates produced with a blend of the two expanders. The new experimental products UP-393 and UP-414 of Borregaard LignoTech (Norway) ensure much better cycle life performance when used for EV battery applications. Investigations on the influence of temperature on battery cycle life have evidenced that with increase of temperature the cycle life of the battery features a maximum at 40 degreesC (UP-393, Indulin + Vanisperse). At 60 degreesC almost all expanders disintegrate and the cycle life of the batteries decreases, though the plates with UP-393 and UP-414 have better cycle life performance than those with other expanders. A gradual degradation of the NAM structure is observed with batteries set to EV cycling. The energetic structure of NAM, which is built up of small crystals with large surface area, is converted into skeleton structure at the end of battery life, which comprises large crystals with small surface area yielding low battery capacity. On cycling at temperature about 60 degreesC, the NAM is converted into a well-developed network of thin lead branches with large pores in between. On discharge, some of these branches are oxidized more quickly, thus, excluding part of NAM from the current generation process, which consequently reduces the capacity of the negative plates. (C) 2002 Elsevier Science B.V. All rights reserved.