Thermal Testing of Batteries

CamMotive’s battery testing facility includes an environmental chamber, allowing data to be captured at extreme ambient temperatures.? Battery characterisation and testing at extreme temperatures is critical to understanding their performance under all anticipated operating conditions. Furthermore, understanding the nature of electrochemical cell behaviour in response to high and low ambient temperatures is vital to ensuring the battery management system can act appropriately, efficiently, safely and maintain good lifetime characteristics. Our chambers allow ambient conditions to be controlled within the range: -35°C to 175°C.

For batteries which have an indirect liquid thermal management, the chamber has access ports to allow coolant of any temperature to be circulated. A process chiller unit allows the coolant and ambient temperature to operate at different setpoints to better recreate real-world operating conditions. Coolant and ambient chamber temperature can be dynamically controlled to emulate scenarios such as drive-cycles, warm-up and fast charging, including pre-conditioning.

Electrochemical Impedance Spectroscopy (EIS) thermal sensitivity

Following on from our recent investigation into the effect of SOC on battery impedance, further data has been collected on impedance variation with temperature.

Data below shows impedance vs. temperature for a Panasonic 18650 cell, across a frequency range of 0.1Hz to 100Hz. At -10°C, the impedance at low frequencies is an order of magnitude higher than at 25°C or 45°C. Lower frequencies are indicative of the slower chemical processes in the cell, such as those responsible for Li+ interfacial diffusion and graphite intercalation. Higher frequencies, where the impedance change is relatively low, are more indicative of the resistive portion of impedance.

These results show that the charge transfer kinetics are largely responsible for the increased impedance at cold temperatures.

The Nyquist plot below shows the frequency at the peak of the second semicircle. Shown as Rct, this portion of the diagram is related to charge transfer kinetics. The reducing peak frequency is another indication that lithium ion charge transfer becomes the limiting factor at cold temperatures.

Example application - EV fast charging

As fast charging becomes more important for the wider acceptance of EV’s, managing impedance in the battery holds the key to unlocking higher charging rates. Whilst thermal management can keep the battery pack able to perform as designed, discovering where Li+ transfer is limited and how to speed up those kinetics are essential for reducing EV charge times.

Each product and application are different, connect to one of our experts to learn how CamMotive can help with your development and testing requirements.