The Effect of Immersion Cooling on Lithium Plating Degradation in Lithium-Ion Batteries

Abstract The objective of this study is to investigate the interaction between immersion cooling and lithium plating as a degradation mechanism in high charge rate Li-ion batteries. Commercial 5 Ah cylindrical cells (graphite/lithium nickel manganese cobalt oxide (NMC)) were subjected to aggressive charge cycling (1.3C) under different thermal boundary conditions: air cooling (reference) and immersion liquid cooling with flowrates between 0 and 4 lpm. The reference cell aged in air was confirmed to have significant lithium plating by performing a destructive physical analysis and subsequent electrode analysis. The plated cell validated the characteristic impedance drop signature, in the high state of charge (SOC) region, on the transition impedance obtained via pseudo-electrochemical impedance spectroscopy (EIS). The signature was then used as a nondestructive diagnostic for plating in the immersion-cooled cells. Counterintuitively, the immersion-cooled cells, particularly those with higher coolant flowrates, exhibited faster capacity fade, higher internal resistance, and higher transition impedance after only 70 equivalent cycles compared to the air-cooled cells. Pseudo-EIS corroborated this, showing a more pronounced impedance drop at high SOC (signature of lithium plating) in the cells cooled with higher flowrates. This suggested that, while immersion cooling effectively reduced bulk temperature, the intensive cooling at high flowrates lowered the cell's operating temperature, thereby increasing internal resistance and overpotential. This drove the anode potential below 0.0 V versus Li/Li+, promoting lithium plating and degradation and highlighting the need for dynamic thermal management strategies during fast charging, especially in conjunction with effective thermal management capabilities such as immersion cooling.