Mechanism and suppression of accelerated winding collapse in mechanically deformed lithium-ion batteries during cycling

Minor mechanical deformation can significantly accelerate performance degradation in lithium-ion batteries during subsequent cycling. However, the underlying mechanisms remain poorly understood. In this study, we investigate commercial 21700 cells using integrated experiments and coupled electrochemical–mechanical modeling to elucidate how mechanically induced defects evolve into catastrophic winding collapse during charge–discharge cycling. Controlled compressive deformations (1-4 mm) introduce non-fatal jellyroll flattening, which acts as a latent stress concentrator. During cycling, intercalation-induced volume changes amplify these defects via progressive stress accumulation, driving a coupled electrochemo-mechanical degradation pathway that hastens structural collapse. Consequently, cells subjected to 4 mm deformation exhibit rapid impedance growth (a 2.39-fold increase) and accelerated capacity decay, dropping to a 90% state of health within 100 cycles. Guided by simulation, we demonstrate that an electrode-thickening strategy (Δ t = 0.24-0.28 mm) suppresses collapse by enhancing jellyroll stiffness and mitigating stress concentration, though this effect has a clear saturation limit. Ultimately, these findings identify cycling-driven electrochemo-mechanical amplification as the primary mechanism governing winding collapse in deformed cells, providing quantitative design guidelines for safer, mechanically robust battery architectures.