The Performance Effects of Edge-Based Heat Transfer on Lithium-Ion Pouch Cells Compared to Face-Based Systems 2014-01-1866

Optimizing the hardware design and control strategies of thermal management systems (TMS) in battery packs using large format pouch cells is a difficult but important problem due to the limited understanding of how internal temperature distributions impact the performance and lifetime of the pack. Understanding these impacts is difficult due to the greatly varying length and time scales between the coupled phenomena, causing the need for complex and computationally expensive models. Here, an experimental investigation is performed in which a set of fixed one-dimensional temperature distributions are applied across the face of a Nickel-Cobalt-Manganese (NCM) cathode lithium ion pouch cell in order to study the performance impacts. Effects on the open circuit voltage (OCV), Ohmic resistance, bulk discharge and charge resistance and instantaneous power are investigated. It is observed that temperature gradients have a negative impact on the bulk performance by lowering the OCV and also increasing the bulk discharge resistance. These negative effects are particularly apparent at lower average temperatures. The implications may be that higher TMS heat transfer rates are possible at higher average cell temperatures, where the gradients have a reduced effect on performance. These results are preliminary and ongoing work is being pursued to develop an understanding of the particular physical phenomena that are affected as well as the lifetime impacts.