Energy storage Hybrid storage has a longer lifespan

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Supercapacitors and lithium-ion batteries are highly compatible, especially in hybrid systems where they can reduce aging. A research project is developing a degradation model to predict battery aging, which could extend the lifespan of hybrid systems by 20%.

Supercapacitors, also known as supercaps, can absorb and supply a great deal of power in a very short time without suffering life span degradation. However, their energy density is low, so their capacity is quickly exhausted. In contrast, lithium-ion batteries have high capacity, but do not handle short-term load peaks well. This creates heat stress, which causes them to age faster.

In many applications, it can make sense to combine both storage techniques: the batteries for continuous operation, the super capacitors for peak loads such as recuperation, i.e. the recovery of braking energy. However, up until now it has been difficult to reliably predict how coupling with a super capacitor will affect the battery's lifespan—making the decision for such a system and its design more complex.

Exact predictions of battery aging

"We have now eliminated this deficit with our joint research project: our toolbox provides meaningful data that potential users can use to make their decision for or against coupling the two battery technologies on a secure basis," says project leader Dr. Wei Wei Shan at the Fraunhofer IEE. The leadership of the SuKoBa consortium is held by super capacitor manufacturer Skeleton Technologies. The research project was funded by the Federal Ministry for Economic Affairs and Climate Protection.

The degradation model developed in the project enables analysis of different configurations and control algorithms to find the best combination of super capacitors and batteries for a specific system design and different operating scenarios with regard to lifespan and cost.

To do this, the model simulates, among other things, the behavior of the battery in a hybrid system under realistic operating conditions. It takes into account both the electrochemical processes in the battery as well as the thermal effects and the dynamics of the load profiles. These simulations allow for accurate prediction of battery aging. Thanks to these features, the hybrid system can be designed and the battery life is maximized.

A software dimensions the battery

Another advantage of this model is the ability to optimize the sizing of the battery. By using super capacitors, peak loads can be intercepted, thus relieving the battery. The model can calculate to what extent the size of the battery can be reduced without affecting system performance. This leads to a reduction in costs while simultaneously improving the overall system's economy.

The degradation model is based on the BaSiS (Battery Simulation Studio) software developed by Fraunhofer IEE, a highly precise simulation environment for dynamic processes and aging effects of electrochemical energy storage systems. This software has established itself in the industry as a reliable tool for the development, testing and optimization of battery cells, packs, components and management systems in both mobile and stationary applications.

Simulate the aging process of the battery

A key aspect of the BaSiS software is its ability to be adapted and parameterized for different battery technologies. This is necessary in order to make precise and reliable predictions about the behavior and aging of the batteries in different application scenarios. The parameters needed for the battery model are derived by the researchers at Fraunhofer IEE from constructive data and experimental measurements of the battery cells. This approach ensures that the model delivers reliable results, independent of the specific battery type or manufacturer.

The precise parameterization of the BaSiS model allows detailing the electrochemical processes within the battery and simulating their response to different operating conditions. This allows for the prediction of aging processes and enables the design of hybrid systems to be optimized to protect the battery and maximize its life span. This is especially beneficial in applications with variable load profiles, such as in electromobility or in the integration of renewable energies.

Combine super capacitors and lithium-ion batteries

Furthermore, the research partners developed control algorithms within the scope of SuKoBa, allowing optimal distribution of the performances of the two storage techniques. Finally, the experts tested both the methods for the design of the hybrid storage and the control algorithms for various applications and verified them with a scaled demonstrator.

The tests show that hybrid storage is particularly advantageous when peaks in charging power of high amplitude and short duration occur, especially in larger systems with high requirements in the peak load area.

An example are trucks used in mining, so-called mining trucks: The tests show that the battery life in an optimally designed hybrid system is extended by twenty percent compared to its sole use—at competitive system costs. At the same time, the electrical losses of the battery are reduced by six and the thermal losses by ten percent. The battery accounts for 95 percent of the storage capacity of the hybrid system.

In a passenger car, a battery also achieves 20 percent longer life when coupled with a super capacitor. However, when considering investment costs, hybrid systems are far less economical here than in mining trucks, as the super capacitors make up 70 percent of the total costs in this use case. In mining trucks, the supercaps account for only ten percent of the costs. (heh)

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Link: Research Project SuKoBa – Super capacitors for lifespan optimization of battery hybrid systems.