VRLA battery with AGM-gel hybrid for superior performance

The need to improve the stability and performance of VRLA (valve-regulated lead-acid) battery has been the subject of considerable debate ever since its deployment became commonplace in standby applications. These VRLA batteries predominantly utilize an ´absorbent glass mat´ (AGM) to immobilize the electrolyte, but that component is often identified as the weak link - AGM loses compression as the cells mature, affecting the electrical performance. Gel is the other common means to immobilize the free electrolyte-it has been promoted as a superior technology in some applications. Known problems include the shrinkage (of gel) with age and loss of contact with the active mass in the plate as dry-out occurs, which affects performance. There is also the inherently lower efficiency for oxygen recombination of gel cells when compared to VRLA cells made with the AGM technology. Hence, in spite of the known problems with AGM, it has been the preferred material for immobilizing the battery electrolyte in VRLA cells. A test method has been developed by us to assess and screen AGM separators - those that exhibit enhanced stability are then used for building superior VRLA cells. A proven approach used by C&D to further improve the performance of such VRLA batteries in cycling applications has been that of utilizing our patented colloidal poly-silica gel technology in combination with the AGM technology, giving rise to the ´hybrid gel technology.´ Gel provides electrolyte reservoir while AGM ensures retention of plate contact for efficient ion transfer, as seen from the more stable end of discharge voltage for cells with hybrid gel under an aggressive cycle domain. Superior thermal properties have also been demonstrated that extends the long-term reliability in cycle service and in adverse environmental conditions. An update on this technology and the available data on float and cycle service are discussed.