Battery technology is rapidly evolving and continuously improves costumer experience of battery electric vehicles in terms of driving range, charging time, lifetime, and vehicle cost. Connecting high energy and high-performance properties results in new requirements for the battery thermal management. An optimal thermal management is essential to keep the battery cells within their ideal temperature operation range to guarantee the availability of power and energy under all environmental conditions and load cases over lifetime.

One of the technologies contributing to the improvement of cells are anode active materials with high silicon content. Unique properties of silicon in heat generation, heat transfer and swelling behavior make it necessary to establish optimized cell operation strategies and enhance thermal management performance. Based on experimental results with automotive cells and battery modules, heat generation, heat transfer and swelling behavior is assessed for anode configurations with different percentages of silicon content.

Comprehensive cell tests were conducted to analyze the generated heat with and without open circuit voltage (OCV) hysteresis. For classic graphite anodes the OCV can be used as voltage baseline and main part of the generated heat can be calculated using overpotential and current. Due to OCV-hysteresis of silicon for charge and discharge there is an additional energy amount which is not covered using the overpotential. In this study the quantitative effects of OCV-hysteresis on heat generation are demonstrated as function of state of charge SOC and silicon content and correlated with the load case.

Two immersion cooled modules were tested, one of them containing cells with graphite anodes and the other one cells with high silicon content. For fast charging scenarios the difference in heat dissipation and thermal management was highlighted. The influence of specific swelling and breathing of the cells on thermal contact resistances in the cell module were analyzed as well. Eventually, a thermally optimized fast charging profile depending on the silicon content was derived.