State-of-electrode (SOE) analytics of lithium-ion cells under overdischarge extremes

Overdischarge is an electrical abuse that may arise in a Li-ion battery module when a voltage imbalance occurs between series-connected cells. Although a wide range of studies has investigated overdischarge-induced aging at the full cell scale, the role of each electrode in degradation mechanisms and impacts of C-rates still require fundamental understanding. While most previous studies focus on copper dissolution, the inter-electrode crosstalk which occurs under an overdischarge scenario remains an open question. To fill these gaps, we deconvolute anode and cathode characteristics from the full cell performance during overdischarge abuses by fabricating Li-ion cells with a reference electrode configuration. Electrode potentials vs. Li/Li+ are measured and interpreted for increasingly severe overdischarge cycles under various C-rates. Deterioration of state of health is tracked by monitoring cell surface temperature, internal resistance, volumetric expansion, capacity retention, and impedance evolution. Surface microscopic characterizations are implemented to explore morphological changes and chemical state variations of electrodeposition with particle deformation. This study reveals the dual effect of the C-rate on explicit anode-centric failure mechanisms and implicit cathode-centric degradation pathways, providing new insights on overdischarge abuse fundamentals and effective mitigation strategies.