Impact of Different Amounts of Lithium Plating on the Thermal Safety of Lithium Ion Cells

Safety tests are usually conducted on fresh cells. However, occurring lithium plating for example due to harsh aging conditions or electrode inhomogeneities can negatively affect the thermal properties of cells over their lifespan. Recent literature studies showed serious deterioration of the thermal cell properties due to lithium plating while other studies showed no impact at all. These differences are at least partly explained by different amounts of metallic lithium. Here, the impact of the amount of lithium plating on the thermal cell properties was investigated. 1 Ah LiNi0.8Co0.1Mn0.1O2 (NMC811) || artificial graphite pouch cells were aged at 0 °C between zero and ten cycles. The amount of lithium plating was found to influence the self-heating-rates reached during the initial phase of a thermal safety experiment, but did not have a major impact on the safety at higher temperatures. Despite the presence of lithium plating of up to 15% of the initial capacity, none of the cells showed exothermic self-heating for more than three consecutive measuring points below 85 °C. An impact on the onset temperature of first permanent exothermic reactions could only be reliably detected if a cell had already suffered from 10 % capacity loss due to lithium plating.