Metal Particle Foreign Matter as a Hidden Driver of Battery Aging: A Defect-Informed Modeling Study

Metal particle foreign matter (MPFM), inadvertently introduced during electrode fabrication, calendaring, or cell assembly, represents a critical manufacturing defect that can compromise lithium-ion battery reliability and lifetime consistency. However, the degradation pathways associated with MPFM contamination remain insufficiently resolved, limiting the development of defect-informed process control and quality assurance strategies. In this work, a microstructure-resolved electrochemo-mechanical model is developed to quantify MPFM-induced aging by explicitly accounting for solid-electrolyte interphase (SEI) formation and lithium plating on both graphite (Gr) and metallic inclusion surfaces. The results show that MPFM contamination produces negligible signatures in cell-level voltage responses yet significantly perturbs internal electrochemical fields by amplifying local electrolyte concentration and potential gradients from the earliest cycles, while also slightly increasing mechanical heterogeneity within electrode particles. While initial SEI growth and lithium deposition on the MPFM surface are limited, the metal-electrolyte interface promotes a faster reduction in interfacial overpotential during cycling, accelerating the transition to plating-dominated degradation. Parametric analysis reveals strong sensitivities to MPFM type, spatial distribution, through-thickness location and size, with degradation severity following the trend Al > Ni > Fe > Cu. MPFM located near the separator further intensifies capacity loss by facilitating preferential plating initiation at the anode-separator interface, with smaller MPFM particles exacerbating degradation via a surface-area-controlled increase in cumulative lithium plating, underscoring the need for contamination-aware manufacturing and reliability assessment.