Comparative in-operando analysis of lithium-ion cell swelling in pouch cells: Constant force versus foam-buffered quasi-constant force

Accurate monitoring of thickness changes in lithium-ion batteries during operation is critical for understanding swelling behavior and its impact on performance and longevity. With the increasing focus on high energy density materials such as silicon-rich anodes, early-stage evaluation of cell swelling has become particularly important. In this study, we present a comparative analysis of two in-operando swelling measurement setups for small format pouch cells: (1) state-of-the-art pneumatic cell presses operating under constant-force conditions, and (2) a printed circuit board (PCB)-based eddy-current displacement sensors applying a quasi-constant preload force via compression pads. While pneumatic presses can be employed for in-operando swelling measurements under variable force, their size, cost, and complexity limit their widespread adoption. The PCB-based setup provides a compact, cost-effective alternative that enables long-term, high-resolution thickness measurements without the need for bulky equipment. Building on earlier work, we optimized the latter setup for long-term cycling with an emphasis on understanding the relaxation behavior of the compression pads and how it affects the thickness change measurements. Beyond serving as a mechanical fixture, the compression pad was found to beneficially influence electrochemical performance, highlighting its dual role as a functional component in cell testing. The results validate the PCB-based setup as a practical substitute for pneumatic presses and emphasize the performance advantages of incorporating a compression pad in in-operando measurements. • In-operando quantification of cell swelling using PCB-embedded eddy-current sensors for high-resolution monitoring. • Calibration curve and foam relaxation behavior combined with a structured data analysis workflow for PCB-based tests. • Adjustable bracing pressure achieved by changing the initial compression of the foam in the PCB-based setup. • Validation of sensor-based swelling measurements using pneumatic press reference under constant force load. • Improving long-term electrochemical performance of silicon-containing lithium-ion cells by using compression foams.