Quantitative and Spatially Resolved Evaluation of Lithium Plating in Lithium Ion Batteries with Manufacturing Defects

Small manufacturing defects within a lithium ion battery (LIB) might not be detected by typical end-of-line tests, but they might impact cell safety, which should be investigated. Therefore, this work experimentally simulates three possible manufacturing defects and analyze their influence on cell aging behavior. The defects include a loss of active material by missing coating, a non-conductive object within the cell, and a separator fold. Their impacts are qualitatively examined by spatially resolved techniques like laser ablation, inductively coupled plasma, and scanning electron microscopy. Quantitative spatially resolved data were obtained with a newly developed gas chromatography mapping method which uses the reaction between inactive reductive lithium and water to form hydrogen gas. A non-uniform lithium distribution was demonstrated and the enhanced plating of lithium at the defects or defect edge could be detected. Transition metal (TM) did not show enhanced deposition at the defect site. Therefore, no co-deposition of lithium with TMs were detected which indicates the defect to trigger lithium plating. In addition, lithium was shown to be locally concentrated in the separator which might indicate an enhanced probability of penetrating the separator, leading to short circuits causing a severe safety hazard.