Experimental and Model-based Investigations of the electrochemical performance effects of non-uniform temperature distributions on Lithium-ion batteries
By: Matt Klein Advisors: Professor Jae Wan Park
This work focuses on deepening our understanding of the electrochemical performance effects that non-uniform temperature profiles have on Lithium-ion batteries. The internal resistance of Li-ion batteries has a high temperature sensitivity. Therefore, non-uniform temperatures occurring within and/or among interconnected cells within battery packs causes current distribution non-uniformity. This generally leads to reduced useable capacity in the short-term and accelerated degradation in the long-term. Hence, we are motivated to study this further, in order to understand what levels of thermal non-uniformity are tolerable design limits for battery packs in automotive applications.
We have organized this work into three main studies. In our first study, we experimentally investigated the bulk effects that non-uniform temperature profiles had on a single automotive style Li-ion pouch cell. In our second experimental study, we developed a system that allowed for us to measure the current distribution among five cells that were connected in parallel, and operated under varying degrees of controlled thermal non-uniformity. Finally, we conclude our work with the development and validation of a physics-based, spatially-distributed, and temperature-dependent electrochemical model.
The single pouch cell study indicated that the cell resistance under short electrical pulse conditions was reduced in the presence of increasing temperature non-uniformity. However, when this cell was operated under a two-hour long automotive dynamic power profile, it became clear that the useable capacity was effectively reduced with increasing levels of temperature non-uniformity. The multi-cell study developed our understanding of the controlling factors for the non-uniform current distribution that evolves among parallel-connected cells. At short time scales, upon the initial application of a constant current pulse, the non-uniform temperature induced resistance distribution dictates the current distribution. However, under sustained discharge, non-uniform capacity evolves among the cells due to the non-uniform current distribution. The non-uniform capacity induces a secondary effect whereby the equilibrium potential difference generated among the cells can provide a corrective action to re-unify the current distribution among the cells. Finally, our model is capable of predicting the current distributions, and the state of several important internal variables. This tool will be useful for aiding in design optimization of lithium-ion cells, from a thermal perspective, and battery pack thermal management systems in vehicle applications.
Date(s) - 06/09/2017
2:15 pm - 3:15 pm
2130 Bainer - MAE Conference Room