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.