Stack pressure on lithium-ion pouch cells: A comparative study of constant pressure and fixed displacement devices

This study addresses the effects of stack pressure on lithium-ion pouch cells by comparing different fixture designs and their impact on variation of stack pressure with time. While previous research has examined pouch cell performance under varying stack pressures, a comprehensive comparison of fixture types and their influence on pressure variation has been lacking. This research provides insights for researchers in selecting appropriate fixture designs for their specific investigations. Two categories of fixtures were investigated: constant pressure fixtures (utilizing springs and a passive pneumatic system) and fixed displacement fixtures (employing bolted plates). The experiments evaluated the pressure loss from an initial static pressure of 90 kPa over a 48h resting period, in addition to the pressure changes under dynamic load profiles. Our findings reveal that, under dynamic loading, the fixed displacement fixture exhibited a pressure variation five times higher than the constant pressure device using springs, and 3.7 higher than the pneumatic device. Additionally, the results demonstrated that the fixed displacement device is unable to mitigate the pressure loss due to relaxation effects of the cell and the bolted connections. In contrast, the spring-based fixture offered a simple and effective solution to hold pressure during experiments. • Stack pressure variation is significantly different among the fixtures tested. • Spring-based fixtures offer a robust solution to apply stack pressure. • Fixed displacement devices fail to mitigate cell relaxation effects. • Pneumatic devices are best explored with active pressure control.