Charging electric vehicles involves more than pure energy supply. Communication before and during the charging operation needs to be taken into consideration, as well as all kinds of requirements. These include aspirations regarding safety, suitability for daily use and user-friendliness, which, in turn, create a basis for customer acceptance. Therefore, FKFS is conducting in-depth research into inductive charging of electric vehicles, preferring to take a holistic approach.

Electro-mobility is a key element of a future-proof mobility concept. Lithium-ion technology is used for the traction batteries in today's electric vehicles, and has proven to be reliable, stable and efficient. Despite its capability for high energy and power densities, as it ages, this technology represents a great challenge for the operation and monetary evaluation of electric vehicles.

In our electro-mobility activities at FKFS, to start with we are intensively investigating the state-of-the-art for lithium-ion cells, as well as diagnostic options in general – and specifically regarding use in hybrid and electric vehicles. This includes visualization of measurements on the battery test bench for analyzing the general behavior of cells under different boundary conditions. The results from the measurements on the battery test bench help estimate the state of health of traction batteries in hybrid and electric vehicles, without having to use additional sensors.

Other battery evaluation activities at FKFS are the development of a battery tester and remote battery diagnosis, including representation of the central link between cloud IT and the vehicle. The battery tester also acts as a user interface for battery diagnostics, both in the workshop and in the test environment.

For automotive applications, large battery packs with multiple cells are assembled in series to extend the range of electric vehicles. The individual cells in such battery packs differ from each other due to manufacturing variations, temperature differences and aging effects. We are also investigating and developing different active and passive balancing approaches, demonstrating the advantages and disadvantages of the respective approaches.

Currently, electric and hybrid vehicles primarily use lithium-ion batteries, since these types of batteries have a high energy density, can withstand a high number of charging cycles and have almost no memory effect. In addition, predictions that energy content will double in the years to come make lithium-ion batteries increasingly attractive for use in electro-mobility, since the range of electric vehicles is directly related to the charging capacity of the battery. But as batteries age, their performance capability also decreases. This can be clearly specified by the ratio of the actual maximum usable capacity to the rated capacity. This ratio is known as the state of health (SoH) and reflects the aging state of a battery. In electric vehicles, batteries are generally used up to an SoH of 80% and are then redeployed in "second life" applications where less capacity is required, for example, in photovoltaic systems. To predict when a battery reaches the end of its life, it is important to be able to determine the residual capacity. However, this is very difficult to specify as it cannot be measured directly and the aging process is influenced by many factors.

Currently, complex procedures are often used to determine the residual capacity of batteries. These deliver unreliable predictions and are too complicated for quickly checking a used vehicle. So, in cooperation with DEKRA Automobil GmbH, FKFS has developed a new accelerated procedure to evaluate the batteries of used electric vehicles.

This diagnostic procedure determines the battery state during a short test drive which loads the battery. The battery state is evaluated by comparing the acquired data with the reference values for a new vehicle of the same type. This enables an evaluation of the aging state. So the accelerated procedure developed by DEKRA and FKFS delivers a result after just a few minutes.