Multi‐Factor Influence Mechanism of Mechanical Stress Distribution During the Service Life of Large Commercial Soft‐Pack Batteries

ABSTRACT

Lithium‐ion pouch batteries are widely used in electric vehicles and energy storage systems due to their high energy density. However, irreversible expansion and nonuniform stress distribution during the cycling process severely limit battery lifespan and safety performance. In this study, a distributed stress monitoring system for battery surfaces was developed to investigate the influence of various factors on surface mechanical stress under actual operating conditions of battery modules and to reveal the expansion mechanism of batteries. The results indicated that the evolution of mechanical stress exhibited a three‐stage characteristic: charging increase, stable standby and discharge recovery. Spatial distribution shows significant gradients, with maximum stress values at the centre, intermediate stress near the tabs and minimal stress at the edge constraint zone. Regarding influencing factors, within the studied range, both charging/discharging rates and pre‐tensioning force generally correlate positively with mechanical stress. Moderate pre‐tensioning enhances discharge capacity. Temperature effects exhibited differentiated characteristics: Mechanical stress significantly increased under high‐temperature conditions, whereas high stress levels persisted at low temperatures due to lithium ion surface accumulation. This research provides a theoretical foundation for selecting buffer materials for battery casings, optimising module structures and implementing pressure‐adaptive control in battery management systems.