Lithium-ion cell requirements in a real-world 48 V system and implications for an extensive aging analysis

Mild hybrid vehicles with a 48 V vehicle electrical system are regarded as a great contribution for achieving the fleet-wide CO2 targets of many car manufacturers. For minimizing the fuel consumption the utilization of the 48 V battery has to be optimized. Knowledge about realistic load profiles of the lithium-ion battery in a mild hybrid application is essential to improve the component design and to avoid serious durability issues. In this paper, we investigate battery data of over 60 test drives with mild hybrid development vehicles, covering an accumulated driving distance of more than 7,000 km. Here, the electrical and thermal load of the high-power lithium-ion battery is characterized and critical operating conditions with regard to cell aging are identified. Differences with respect to the cycling conditions of batteries in fully electrified vehicles are highlighted. Application-oriented aging matrices are defined, which allow an evaluation of the lifetime and a detailed parametrization of an aging model. Our research helps to optimize and minimize testing effort based on insights from real world data. Moreover, it enables a better evaluation of new cell candidates in early development stages and proofs the conformity of lifetime requirements of early cell sample phases within vehicle development cycles.