V Maybe it's because the lead acid battery has been around for more than 160 years Years ago: Indispensable and largely reliable, it leads the shadowy existence of a seemingly mature component in our cars. Research funds, complains Dominik Schulte from RWTH Aachen University, therefore only flow into new technologies, even though there is ample need for development in the existing one. Because to this day not all processes are really understood.
Lead-acid batteries still indispensable
The fact that lead-acid batteries are still considered indispensable for the power supply in cars is due to some of their undisputed advantages. Their material costs - especially lead and sulfuric acid - are extremely cheap. Self-discharge is low and, unlike lithium-ion or nickel-metal hydride batteries, it can be used at temperatures between -40 and +70 ° C without any problems. Last but not least, the cost-effective industrial production process and efficient recycling speak in favor of lead batteries.
The high material weight of lead and the associated relatively modest energy density are physically unchangeable: modern lithium-ion batteries are around 200 Wh /kg is four to five times superior to conventional lead batteries. Another shortcoming are the poorer performance values and the low cycle stability, but so far this has been sufficient for the classic starter battery function.
Electronic permanent consumers are a challenge
However, the requirements have increased significantly recently. In the past, an on-board battery only had to provide the starter current, nowadays high loads have to be covered at idle speed and electronic permanent consumers have to be safely supplied - now even when the engine is switched off.
Eckhard Karden from the Ford Research Center in Aachen sees this stop-start operation as a technology that will be used across the board by 2020 and thus as the greatest challenge for lead batteries. The cycle stability required for this is severely limited in conventional lead batteries due to the destruction of the active electrode masses ('sulfation'). In addition, the phenomenon of acid stratification affects the lead battery. It has therefore been further developed into the EFB (Enhanced Flooded Battery) especially for this application. In this type, the positive electrode plate is covered with a special braid called aPolyester scrim coated to stabilize the active material. This practically doubles the cycle stability.
Ultra battery combines lead-acid battery and super capacitor
Another one The development with the AGM battery (Absorbent Glass Mat), in which the acid is completely bound in a fleece made of micro glass fibers, is now going one step further. This prevents the harmful acid stratification. In addition, the high pressure stabilizes the electrode set and minimizes the loss of the active material. This further doubling of the cycle stability makes AGM batteries around twice as expensive as conventional wet batteries, which is mainly due to the far greater precision in production, says Manfred Gelbke, Head of Development at Moll Batteries.
Even for use In micro-hybrid applications, where braking energy often has to be fed back, he sees himself well equipped with the AGM battery. That does not mean, however, that the lead-battery faction is not already thinking ahead: For example, the ultra-battery, an integrated combination of lead-acid battery and super-capacitor, is emerging on the horizon. That would further increase the charging dynamics and thus the possible uses for hybrids.