Stress relief principles milestoning the industrial application of lithium metal battery systems.

Stress critically influences the cycling and safety of lithium metal batteries, especially in pouch cell or pack configurations. However, intrinsic coupling between stress and swelling persistently obscures the fundamental understanding of stress-strain effects. Herein, through real-time stress control, we identify that electro-chemo-mechanical responses of industrial-level cells are directly linked to stress relief principles of Li negative electrode. Li dendrites can hardly penetrate separators due to the plastic collapse of porous Li deposits. While densification of collapsed deposits occurs at 0.1 ~ 0.2 MPa, the dense architecture necessitates stress relief through creep or plastic deformation. Crucially, the separator penetration-induced short circuit originates from plastic deformation of densified Li, under stress exceeding its bulk yield strength (~1 MPa). These stress relief principles enlighten us achieving the stress-optimized 27 Ah, 402 Wh kg-1 module with nondeteriorative cycling performance compared to single cell, providing a scalable framework for addressing key challenges in high-energy battery systems.