Aging can drastically reduce the performance of lithium-ion batteries. Hence, the aging behavior needs to be tested which is mostly done on the laboratory scale. These tests are usually performed in a climate chamber, ensuring a constant ambient temperature. In application, however, the temperature conditions can differ greatly. Due to the heat generation of the battery cell itself and the cooling system, the internal temperature can both be inhomogeneous and transient. An example are different temperature fields due to tab versus single sided cooling of pouch cells[1]. Some simulative investigations of the effect of such inhomogeneous temperature fields on the aging behavior exist[2]. However, the experimental aging data basis on commercial cells with specifically applied temperature profiles in comparison to homogeneously aged cells is rather small[3].

To remedy this shortage, multiple aging test series on different lithium-ion batteries ensuring an accurate temperature control including reference test conditions were performed. The reference aging tests at homogenous temperature served as baseline to understand the aging behavior of the investigated cell. The temperature control was achieved with thermal plates supplied by cryostats. Temperature changes were realized with valves and inhomogeneous temperatures perpendicular and parallel to the electrode stack were applied with the thermal plates. These conditions were chosen in a temperature range from 5 °C to 45 °C to mimic extreme temperature changes and inhomogeneous temperatures resulting from an automotive battery management system. The investigated cells ranged from 3.4 Ah high energy cells with NMC532 / graphite chemistry over 1 Ah cells with nickel-rich NMC and a silicon containing graphite anode to a high power 20 Ah cell with an NMC111/LMO blend cathode and a graphite anode. The global aging behavior was evaluated via nominal capacity and resistance measurements and differential voltage analysis during the checkups at a constant temperature of 25 °C. The local aging behavior was analyzed after cell opening. The goal of this work is to highlight the key messages regarding the effect of thermal transients and thermal gradients on the global and local aging behavior which was shown across the different investigated cells. Cycling with temperature changes can accelerate the capacity loss much more powerful than an inhomogeneous temperature. Reasons for the global behavior can be found in the inhomogeneous aging behavior on electrode scale. [4,5]

(1) Hunt, I. A.; Zhao, Y.; Patel, Y.; Offer, J. Surface Cooling Causes Accelerated Degradation Compared to Tab Cooling for Lithium-Ion Pouch Cells. J. Electrochem. Soc. 2016, 163 (9), 1846–1852. https://doi.org/10.1149/2.0361609jes.
(2) Li, S.; Zhang, C.; Zhao, Y.; Offer, G. J.; Marinescu, M. Effect of Thermal Gradients on Inhomogeneous Degradation in Lithium-Ion Batteries. Commun Eng 2023, 2 (1), 74. https://doi.org/10.1038/s44172-023-00124-w.
(3) Werner, D.; Paarmann, S.; Wiebelt, A.; Wetzel, T. Inhomogeneous Temperature Distribution Affecting the Cyclic Aging of Li-Ion Cells. Part I: Experimental Investigation. Batteries 2020, 6 (1), 13. https://doi.org/10.3390/batteries6010013.
(4) Cloos, L.; Queisser, O.; Chahbaz, A.; Paarmann, S.; Sauer, D. U.; Wetzel, T. Thermal Transients to Accelerate Cyclic Aging of Lithium‐Ion Batteries. Batteries & Supercaps 2024, 7 (3), e202300445. https://doi.org/10.1002/batt.202300445.
(5) Cloos, L.; Langer, J.; Schiffler, M.; Weber, A.; Wetzel, Th. Challenges of Predicting Temperature Dependent Capacity Loss Using the Example of NMC-LMO Lithium-Ion Battery Cells. J. Electrochem. Soc. 2024, 171 (4), 040538. https://doi.org/10.1149/1945-7111/ad3ec3.