Manufacturing defects in lithium-ion batteries are a major cause of thermal runaway, with copper foreign matter being one of the most common defects on battery production lines. Such defects can induce internal short circuits (ISCs) that may trigger thermal runaway, posing significant safety risks. The occurrence of ISCs in copper defect batteries is closely associated with the charging stages during formation and cycling processes. However, the abnormal characteristics during these processes are not yet fully understood, and existing methods for detecting copper matter in batteries primarily rely on offline self-discharge measurements. In this study, a detailed analysis of abnormal current and voltage characteristics in copper defect batteries during formation and cycling is conducted, a multi-stage defect detection method is proposed. The proposed method achieves detection rates of 84.2% in the formation stage, 84.2% in the single-cycle stage, and 68.4% in the multi-cycle stage. Using this multi-stage detection method, all copper defect batteries, including those prone to sudden ISCs, are successfully identified. Furthermore, the proposed method requires no complex calculations or additional equipment and relies only on standard current and voltage data collected during formation and cycling. This provides an efficient and practical solution for detecting copper foreign matter defects in lithium-ion batteries, thereby enhancing overall battery safety.

Lithium-ion batteries are currently the most widely used energy storage devices due to their superior energy density, long lifespan, and high efficiency. However, the manufacturing defects, caused by production flaws and raw material impurities can accelerate battery degradation. In extreme cases, these defects may result in severe safety incidents, such as thermal runaway. Metal foreign matter is one of the main types of manufacturing defects, frequently causing internal short circuits in lithium-ion batteries. Among these, copper particles are the most common contaminants.

This paper addresses the safety risks posed by manufacturing defects in lithium-ion batteries, analyzes their classification and associated hazards, and reviews the research on metal foreign matter defects, with a focus on copper particle contamination. Furthermore, we summarize the detection methods to identify defective batteries and propose future research directions to address metal foreign matter defects.