Weiping Diao1, Bin Xu1,2 and Michael G. Pecht1
1 Center for Advanced Life Cycle Engineering, University of Maryland, College Park, MD 20742, USA
2 School of Mechanical Engineering, Xi'an Jiaotong University, Xi'an, Shaanxi 710049, China
Lithium-ion batteries are considered fully charged when they are charged to the battery manufacturer's specified cut-off voltage using the specified cut-off C-rate. To assess the consequences of going beyond this charged state, four types of 18650 lithium-ion battery cells were charged from 100% state of charge until the cells' internal safety mechanisms were triggered, or thermal runaway occurred. The electrical, thermal, and mechanical behavior of the cells was monitored and compared using X-ray computed tomography, visual inspection, cross-sectional analysis, and scanning electron microscopy/energy dispersive X-ray spectroscopy analysis. In some samples, a unique degradation mechanism — electrode layer fracturing is identified, which is shown and discussed.