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

The objective of the present study is to investigate the interaction between immersion cooling and lithium plating as a degradation mechanism in high-charge-rate Li-ion batteries. Commercial 5Ah cylindrical cells (graphite/NMC) were subjected to aggressive charge cycling (1.3C) under different thermal boundary conditions: air-cooling (reference) and immersion liquid cooling with flow rates between zero 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 SOC region, on the transition impedance obtained via pseudo-EIS. The signature was then used as a non-destructive diagnostic for plating in the immersion-cooled cells. Counterintuitively, the immersion-cooled cells, particularly those with higher coolant flow rates 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 flow rates. This suggested that, while immersion cooling effectively reduced bulk temperature, the intensive cooling at high flow rates lowered the cell's temperature, thereby increasing internal resistance and overpotential. This drove anode potential below 0.0V vs 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.