Speaker
Description
Lithium-ion pouch cells are one of three cell geometries frequently employed in electric vehicles due to their high energy density and flexible design [1,2], enabling high gravimetric and volumetric energy density. However, their performance and degradation are highly sensitive to external mechanical stabilisation, where stack pressure strongly influences lifetime and safety [3]. In this study, the electrochemical ageing of large-format pouch cells was systematically investigated under different pressure conditions using long-term cycling and synchrotron powder diffraction radiography. Unconstrained cells delivered the highest initial depth of discharge but suffered from rapid capacity fade, fast resistance growth, elevated temperature, and shortened lifetime. Constrained cells, in contrast, exhibited reduced accessible capacity but significantly improved cycle life, stabilised resistances, and lower thermal stress. At high pressure, transport limitations were dominating, while moderate pressure balanced cell stability and performance. Diffraction results revealed homogeneous lithiation in fresh cells, but ageing induced strong inhomogeneities. High pressure led to doughnut-shaped lithium profiles with central depletion and edge enrichment, attributed to reduced porosity, increased tortuosity, and electrolyte redistribution. The results establish a direct link between mechanical pressure, degradation, and lithiation heterogeneity, highlighting moderate pressure as the optimal regime for long-term pouch cell operation.
References:
[1] Yoshino, A., Angewandte Chemie International Edition, 51(24), 2012 (DOI: 10.1002/anie.201105006).
[2] Gröger, O., et al., Journal of The Electrochemical Society, 162(14), 2015 (DOI: 10.1149/2.0211514jes).
[3] Schommer, A., et al., Journal of Power Sources, 629, 2025 (DOI: 10.1016/j.jpowsour.2025.236019).
