Researchers at the Fraunhofer Institute for Manufacturing Engineering and Automation IPA in Stuttgart have developed a prototype intelligent battery cell that they say could lower the cost of automotive battery packs and extend the range.
Each battery cell has its own built-in microcontroller that records relevant physical parameters, such as the temperature and the state of charge of the cell—i.e., each cell knows its own condition. The cells communicate via the existing power wiring between battery cells; they can also communicate with other devices, such as the on-board controller, which uses the data from the cells to calculate the state of charge.
|Prototype cell. Click to enlarge.|
The potential benefits of this come in to play when considering the current state of pack assembly. So far, these have been monolithic blocks in which the individual battery cells as well as the necessary supporting technology have been housed.
All individual cells should theoretically have the same energy capacity. In practice, though, this is somewhat different: due to production reasons, capacities vary. This is problematic, since the cells are connected in series. The entire battery is therefore only as strong as its weakest cell.
If the charge in this cell is depleted, the remaining energy in the other battery cells does not help—the car has to be recharged. For that reason, manufacturers presort and install cells of a similar capacity into a battery. Since some cells are sorted out as a result of this process, this pushes up the price of the battery packs.
Another shortcoming is that when a cell is defective, the vehicle stops functioning.
With the new Fraunhofer approach, if a cell is empty, but the others still have energy stored, the car does not have to stop like it did before. Rather, the empty battery cell simply decouples from the cluster, acting like a current by-pass. The others continue to deliver energy.
Depending on the cell quality, we can therefore increase the range by at least four percent. Over time, this effect is amplified: in the case of an old battery, and if the empty cells are replaced, it is conceivable that a range up to ten percent higher can be achieved.—Dr. Kai Pfeiffer, Group Manager at Fraunhofer IPA
Since one cell with lower capacity hardly affects the overall range of a car, the manufacturers would no longer need to pre-sort. This could significantly reduce costs. In addition, the capacities of the cells adapt to each other over time—the ones that can store less energy are switched off earlier. The cells therefore run longer and, as a result, faster: their capacity decreases.
If a battery cell malfunctions, it is not necessary to bring the vehicle to the workshop. Since the car has more than one hundred cells, it does not depend on any individual one. If the driver decides in favor of a repair, it is sufficient to merely replace the single cell instead of the entire battery.
The researchers have already developed a prototype of the battery cell. The challenge is now to miniaturize the electronics and embed them into cells. “We want it to cost less than a euro,” Pfeiffer says.
3Ccar. Part of the development process is being conducted in the EU project “3Ccar”. 3Ccar is a European collaborative project funded by the ECSEL (Electronic Components and Systems for European Leadership) Joint Undertaking. Launched in June 2015, 3Ccar aims to address the vehicle control architecture and its subsystems in order to achieve the next level of efficiency.
3Ccar is working on advanced system designs with high local intelligence (computing power, sensing abilities, modularity) and extended network bandwidth to enable smart system partitioning. The goal is a reduction in the system complexity of EVs, with positive effects on costs as well as maintenance, monitoring and update functionalities.
The total project consists of 10 supply chains—one of which is smart battery cells, led by Fraunhofer—developing the major project breakthroughs, structured in 8 work packages generating more than 100 deliverables with around a €54-million research and innovation budget distributed over 3 years.