Detection of jelly roll pressure evolution in large-format Li-ion batteries via in situ thin film flexible pressure sensors

Mechanical pressure develops in Li-ion batteries (LIBs) during operation and is critical to battery performance and safety. Detecting pressures in situ is essential to elucidate the operating mechanisms. However, the feasibility and scalability of the current methods face challenges in practical in-situ measurements given the harsh battery internal environment and shell obstruction, especially for large-format LIBs. This study develops an in-situ measurement method for the mechanical pressure of electrode stacks, referred to as jelly rolls, by using embedded thin-film flexible pressure sensors. Pressure sensors are placed inside a prismatic power LIB, and the pressure behaviors are detected. The experiments demonstrate that this method can be used to inspect the mechanical behavior of the jelly roll over a long operation time. The mechanical pressure generated by the volume expansion of the jelly roll is related to the lithiation and delithiation of the graphite cathode. Both reversible and irreversible pressures can be observed using this method, their evolution characteristics are related to spatial location, charging/discharging rate, external pressure, and electrode stack assembly. The proposed method is promising in detecting the pressure state of LIBs and assisting in the evaluation of battery engineering design, manufacturing, and operation monitoring.