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Battery aging is a main concern within hybrid and electrical cars. Determining the current state-of-health (SOH) of the battery on board of a vehicle is still a challenging task. Electrochemical Impedance Spectroscopy (EIS) is an established laboratory method for the characterization of electrochemical energy storages such as Lithium-Ion (Li-Ion) cells. EIS provides a lot of information about electrochemical processes and their change due to aging. Therefore it can be used to estimate the current SOH of a cell. Standard EIS methods require the excitation of the cell with a certain waveform for obtaining the impedance spectrum. This waveform can be a series of monofrequent sinusoidal signals or a time-domain current pulse with a dedicated Fourier spectrum. However, any form of dedicated perturbation is not generally applicable on board of an electric vehicle. This work presents a new passive spectroscopy method, which obtains the impedance spectrum directly out of real driving data.

Lithium-ion batteries are the most favored energy storage technology for high-efficiency hybrid and electrical vehicles. Online State-of-Charge (SOC) estimation is required for this application to estimate the remaining cruising distance. However, variation of battery parameters with temperature and cycle life has to be taken into account in order to achieve high accuracy. In this work electrical tests on lithium-ion cells in different States-of-Health are performed and used to extract model parameters such as open-circuit-voltage and impedance. High precision test equipment has been developed to accurately track the true SOC of the cell during measurements. A strong influence of cycle-life on electrical battery behavior is observed. A dynamic cell model based on the measurement results including temperature and aging effects is generated and subsequently used for SOC estimation with an Extended-Kalman-Filter.

Plug-In Hybrid Electric Vehicles (PHEV) are becoming increasingly important as an intermediate step on the roadmap to Battery Electric Vehicles (BEV). Li-Ion is the most important battery technology for future hybrid and electrical vehicles. Cycle life of batteries for automotive applications is a major concern of design and development on vehicles with electrified powertrain. Cell manufacturers present various cell chemistries based on Li-Ion technology. For choosing cells with the best cycle life performance appropriate test methods and criteria must be obtained. Cells must be stressed with accelerated aging methods, which correlate with real life conditions. There is always a conflict between high accelerating factors for fast results on the one hand and best accordance with reality on the other hand. Investigations are done on three different Li-Ion cell types which are applicable in the use of PHEVs.