Electric cars: Cost-effective alternative to battery replacement

Intelligent cell of the Fraunhofer IPA: A microcontroller records physical parameters such as temperature and state of charge. If a cell is empty, it switches itself off automatically (Fraunhofer IPA)

Developing (cost-)effective batteries is still a central challenge of electromobility. Liquid fuel for conventional combustion engines has a higher energy density. Furthermore, it is more economical for the end user – without consideration of external effects like pollution and its impacts on the climate. But things are changing rapidly. Drops in prices for batteries and regular innovations like the very large 2nd-use battery storage in Germany, Smartscooter from Taiwan or the energy management system which incorporates electric vehicles into the household are examples for the movement in the whole sector.

Normally a complete battery replacement is needed in case of one damaged cell

Scientists at the Fraunhofer Institute for Manufacturing Engineering and Automation IPA in Germany are researching on more efficient batteries too. They recently announced the development of a new type of battery cell which is much more cost-effective over the whole life cycle compared with previous models.

Cell replacement instead of an entire battery replacement

A battery of an electric car is usually made of more than a hundred battery cells. They are housed in a monolithic block together with other important technology. Theoretically, each cell should store the same amount of energy. Practically, they do not. It is not possible to produce hundred percent identical battery cells. It happens that their capacities vary. Because they are connected in series, the entire battery is only as strong as its weakest cell. And in case of one broken cell, a complete battery replacement is needed. If that is not enough, the electric car has to be recharged if only one cell is discharged. The remaining energy of the other cells would not help to continue driving. If manufacturer presort and install cells of similar capacities, the prices increase.

The researchers at Fraunhofer in Stuttgart (Germany) created an alternative. “Our modular battery system solves these problems,” says Dr. Kai Pfeiffer, Group Manager at the IPA. The team modified the battery. Information like charging status and temperature are recorded now by a built-in microcontroller in each cell. It enables to control the status of each cell.

In case of one discharged cell, the driver has not to stop driving like before. The empty cell simply decouples from the cluster, acting like a current by-pass. The remaining cells power the electric motor. “Depending on the cell quality, we can therefore increase the range by at least four percent,” explains Pfeiffer. “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”.

A prototype of the battery cell is already existing – Entire battery replacement soon a thing of the past?

Under these circumstances, manufacturers do not need to presort cells anymore. The lower manufacturing costs compensate the more complex battery with its new microcontrollers. Additionally, the capacities of the cells adapt to each other over time. Cells with a higher capacity run longer and their capacity decreases faster than earlier switched off cells with a lower capacity.

A broken battery cell is maybe no reason for an entire battery replacement in the garage anymore. The remaining cells are able to power the engine. The electric car is not dependent on an individual cell. And if desired, the owner can replace a single cell instead of the whole battery.

A prototype of the battery cell is already existing. The challenge is now to minimize the electronics and embed them into cells. “We want it to cost less than a Euro,” Pfeiffer says. Part of the development process is being conducted in the EU project “3Ccar”.