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

Abstract

Spatially dependent low-temperature to room-temperature degradation mechanisms for Li­(Ni0.5Mn0.3Co0.2)­O2/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 Li0 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 Li0 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 Li0 deposition on the electrode. Multilocation liquid nitrogen (N2) Raman spectroscopy of electrodes indicates significant quantities of Li0 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–Li0 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 (∼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., Li0 stripping, Li0 corrosion, and severe gassing). This study finds that low-temperature Li0 plating and LiC6–Li0 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 Li0 and gassing) and catastrophic thermal runaway when resting under storage (e.g., larger quantities of LixC6–Li0 corrosion)