Detection of Copper Foreign Matter Defects in Lithium-ion Batteries through Abnormal Characteristic during Formation and Cycling Processes

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.