       Despite ubiquitous applications of lithium-ion (Li-ion) batteries in consumer electronics, electric vehicles and energy storage systems, several challenges, such as high safety risks and poor lifetime still need fundamental understanding and better amelioration. Overdischarge phenomenon is one of the most common electrical abuses during operations of Li-ion battery packs especially when the management system fails to identify defective cells leading to imbalances in voltage between cells. Although several studies have revealed that the overdischarge of a single cell is relatively benign due to the mild temperature rise and in some cases, mild swelling, safety threats are no more a trivial matter within the module since local hotspots induced by certain overdischarged aging cells are more likely to propagate heat and even cause catastrophic thermal runaway in severe cases. Besides, the side reaction of copper dissolution and deposition on the electrodes and separator and the failure mechanism of internal short circuits due to other subsequent reactions were also introduced in previous research efforts to characterize the physical nature of the overdischarge phenomenon. Majority of the investigations, however, merely focus on studying the overdischarge scenarios while ignoring the individual electrode potential behavior, recharge capability, electrolyte degradation, and gas generation after overdischarge extremes. In this work, a reference-electrode configuration based on the Li-ion pouch cell is proposed to decouple anode and cathode potentials from full cell voltage for a comprehensive understanding of electrochemical performance during the overdischarge-recharge stage. A copper wire coated with lithium titanium oxide (LTO) is charged to a stable voltage plateau and fabricated in a commercial pouch cell to function as the reference electrode. Anode and cathode potentials are separately measured and interpreted to determine the transient electrode kinetics and the onset of copper dissolution using differential voltage analysis at multiple overdischarge cutoff limits, operating C-rates, and ambient temperatures. Internal resistance, volume expansion, recharge capacity, and recharge time duration are monitored in each case to evaluate the state of health (SOH) after multistep overdischarge degradation. Post-mortem inspections, including destructive physical analysis and surface microscopic characterizations (scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy), are implemented to investigate morphological changes and chemical elementdistributions on electrode surfaces while providing insights on the chemical state and electrical conductivity of copper electrodeposition. Furthermore, compositional variations in the electrolyte and generated gas are discussed based on gas chromatography-mass spectroscopy techniques to shed light on the mechanism of degenerative electrolyte transformation, swelling deformation, as well as the decomposition and reformation of the solid electrolyte interphase (SEI) layer that interacts with the organic carbonates at multilevel depths of overdischarge.


Investigating Overdischarge Characteristics of Li-Ion Cells Using Reference Electrode Configurations

Division / Sponsors: 
Aerospace, Bioengineering, Applied Mechanics, Design Engineering Division, Advanced Energy Systems, Manufacturing Engineering Division, Noise Control and Acoustics, Nondestructive Evaluation, Diagnosis, and Prognosis (NDPD), Nuclear Engineering Division, Process Industries Division, Fluids Engineering, Heat Transfer, Materials, Microelectromechanical Systems, Safety Engineering and Risk Analysis, Computers & Information in Engineering


Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2020/volume/84478

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