Low-Temperature Lithium Plating/Corrosion Hazard in Lithium-Ion Batteries: Electrode Rippling, Variable States of Charge, and Thermal and Nonthermal Runaway

Spatially dependent low-temperature to room- temperature degradation mechanisms for Li(Ni0.5Mn0.3Co0.2)O-2/LixC6 (NMC532/graphite) large format 50Ah Li-ion batteries were investigated. First, highly stressed regions of the cathode/anode are found to be exacerbated by extreme conditions (i.e., low-temperature cycling). The severe electrochemical polarization of large 50Ah electrodes at low temperature leads to substantial Li-0 deposition and severe gassing at the regions of high stress (i.e., high curvature, edges, and electrode ripples). A series of analytical techniques (e.g., SEM, XPS, GC-MS, and Raman spectroscopy) found that Li-0 plating (charge) or corrosion (storage) leads to severe gassing and decomposition products (including carbides). The expansion/contraction and extreme polarization during low-temperature cycling, was found to cause a ripple-type Li-0 deposition on the electrode. Multilocation liquid nitrogen (N-2) Raman spectroscopy of electrodes indicates significant quantities of Li-0 deposition reside at ripple peaks (high-stress region) and are found negligible at ripple troughs. Postmortem analysis discovered two failure scenarios that originate from low-temperature cycling, either nonthermal runaway venting or an internally shorted thermal runaway. It was found in the first case (storage) that LiC6-Li-0 undergoes severe corrosion and gassing during storage conditions (i.e., no movement, current, and temperature) and proceeds to trigger thermal runaway and ejection of materials (similar to 2 weeks). The second case (RT cycling after low temperature) resulted in nonthermal runaway overpressurized venting of the cell and release of detectable quantities of flammable/toxic gases (e.g., CO2, CO, CH4, and C2H2). The second event was found to be caused by competing reactions (i.e., Li-0 stripping, Li-0 corrosion, and severe gassing). This study finds that low-temperature Li-0 plating and LiC6-Li-0 corrosion results in severe gassing, which exacerbates highly stressed regions (i.e., electrode buckling) and greatly compromises safety of the application-via nonthermal runaway venting when cycled (e.g., stripping of Li-0 and gassing) and catastrophic thermal runaway when resting under storage (e.g., larger quantities of LixC6-Li-0 corrosion).