Thermal management of 4680 battery cells during fast charging: Mitigating degradation and revealing major reversible capacity recovery

To improve energy density while reducing costs, large-format cylindrical cells with a diameter of 46 mm are more frequently used in current and future battery-electric vehicles. As cylindrical cells increase in size, their thermal behavior deserves more attention. This study examines the impact of the thermal management concept on degradation during fast charging. For this purpose, 4680-type cells are cycled at various temperatures using a thermal battery test bench with mantle surface, side, and bottom cooling. Results show that side cooling is superior to bottom cooling at similar peak temperatures, due to reduced thermal gradients. Furthermore, a higher absolute temperature is beneficial for prolonging battery lifetime under fast-charging conditions. For all cells, a strong inhomogenization of the negative electrode is observed, which decreases significantly after a three-month rest period, accompanied by a capacity recovery of up to 50 %. Differential voltage analysis indicates that loss of lithium inventory is the primary degradation mode, with different root causes depending on the thermal boundary conditions. These findings demonstrate the crucial role of the thermal management concept in mitigating cell degradation, underscoring the need to adapt it to balance temperature uniformity and the average operating temperature. Given the significant role of reversible degradation, the relevant real-world operating conditions should be critically examined.