Aging investigations and consideration for automotive high power lithium-ion batteries in a 48 V mild hybrid operating strategy

This paper focuses on the battery aging of automotive high power lithium-ion batteries intended for 48 V mild hybrid systems. Due to a long vehicle lifetime, battery aging is of high importance, and its consideration within a hybrid system is crucial to ensure a sufficient lifetime for the battery. At the moment, only a few aging investigations and models specifically for automotive high power cells are available. Consequently, all present aging consideration methods are based on the few published aging models focusing on consumer cells. This paper describes the development of an aging model for automotive high power cells and the integration into a mild hybrid operating strategy to actively control the battery aging process during its operation. The underlying aging investigations of high-power battery cells are shown to analyze the main influences of temperature, state of charge, and C-rate. These tests are used to develop the aging model, capable of considering the main influences on the aging process. Based on this model and all gained insights, different methods for considering battery aging in a mild hybrid system are investigated. The goal is to control the aging process during operation and consequently decrease the negative influence. Two active intervention methods are developed and integrated into a 48 V mild hybrid operating strategy to validate their potential. It is possible to control the aging process and at the same time to use the insights for improving the basic hybrid powertrain design regarding reduced aging and battery costs.