Lithium plating is known to be a central safety and performance issue of lithium-ion cells. Especially for electric vehicles (EVs), lithium plating has become one of the main challenges to tackle to improve longevity, performance and safety of the battery pack. At its onset, lithium plating leads to an accelerated loss of capacity of the cell, meaning direct cell ageing and decreased performance. Furthermore, there is also a risk of metallic lithium forming dendrites and penetrating through the cell’s separator, causing an internal short circuit. This can cause a significantly increased self-discharge or even thermal runaway on the cell. Therefore, understanding the factors that promote the occurrence of lithium plating is of utmost importance to improve safety and overall performance of battery packs.
The aim of this study is to decouple the influences of temperature and current charging rate on lithium plating, and, consequently, develop and index to grade the susceptibility of a specific cell type to this effect. For that, a quick electrical test was designed to provoke lithium plating under different temperatures and charging current rates. To be able to analyse both conditions separately, a special test setup was prepared to achieve a constant temperature during the whole test, controlling this way not only the ambient temperature but the temperature of the cell itself. As a result, high charging currents had a negligible influence on the cell’s temperature. The test data was then evaluated using differential voltage analysis (DVA) to confirm the presence of reversible lithium plating and to quantify it. Additionally, the capacity loss caused by irreversible lithium plating was calculated.
One of the initial findings of this work is the significant influence of the cell’s self-heating on plating tests without a constant temperature setup, as the temperature rise would hinder the occurrence of lithium plating even at low temperatures. Whereas with the special setup, the cell would show plating at the same ambient conditions. Furthermore, the dependence of the magnitude of reverse plating on the cell’s temperature was observed, while the influence of the current rate was minimal at subzero temperatures.