Electrification of systems previously dominated by internal combustion engines presents many challenges to the automotive, aerospace, machinery, and other industries.Disciplines affected include the following:
Noise, vibration, and harshness – e.g. noise quality (whines, etc)
Durability – e.g. motors, driveline durability impacted by electric motor torque profiles
Electric motor design - weight reduction, efficiency, E-M emission?
Thermal management – batteries, control units, motors
Battery technology – charge time, thermal, weight, crash safety, etc
CAE already plays a major role in addressing these disciplines with traditional powerunits, and will no doubt enable engineers to identify solutions to the problems that arise with electrification. Existing CAE methods and processes will require adaption and innovation to support design, development, and manufacture in a timely and effective manner.
The influence of temperature on the impedance of batteries is more important than any other effect, and dominates their behavior , and very high and low temperatures are also deleterious to the cycle life of batteries. While absolute heat removal is important, our recent research  suggests that the thermal gradients caused by thermal management systems also contribute to performance degradation. This is because of current inhomogeneities caused by the thermal gradients. Equivalent Circuit Network (ECN) models using a network of resistors, capacitors and voltage sources have been widely adopted in the battery industry to simulate battery behavior and heat generation. However, these models typically model only the ‘lumped’ behavior of a cell without accounting for the thru-thickness variation of temperature on the SOC, current and impedance.
Zhao et al.  have developed a multi-layered ECN model that captures this behavior, and that can predict the internal temperature gradients, inhomogeneities in current and SoC and predict the significant differences in useable capacity at high C rates for different types of thermal management systems, as shown in the figure below, adapted from . A ‘lumped’ thermal model would not predict any of these effects. The model also identified that the most significant thermal bottleneck for tab cooling of one particular cell was the limited cross-sectional area of the tab and current collector to tab weld, and that optimising this region of the cell for better thermal conductivity would increase the benefits of tab cooling.
In this work, we will test this model (with modifications) on Xalt Energy cells for different cooling rates and current profiles. Results from a ‘lumped’ ECN model will also be presented and the difference in results discussed. We will compare the results with experiment and present the conclusions. Future areas of research will also be identified.
|Date||4th June 2019|