In‐Plane versus Through‐Plane Thermal Gradients during Cyclic Aging of Lithium‐Ion Batteries: An Experimental Study

During application, lithium-ion battery cells can be exposed to inhomogeneous temperature distributions which has been argued to accelerate aging. A through-plane thermal gradient with respect to the cell stack is suggested to accelerate aging even further. In this work, in-plane and through-plane inhomogeneous temperature boundary conditions on a 20 Ah pouch cell are applied during cyclic aging and the capacity loss is compared to a reference scenario. Both directions of temperature gradients from 10 to 40 °C accelerate the linear capacity loss trajectory by 25% ± 4% in comparison to an equivalent homogeneous aging temperature of 25 °C. Postmortem analyses reveal locally increased solid-electrolyte interface growth as a probable reason for the globally observed aging acceleration. This significant aging acceleration is still 6 times lower than by increasing the homogeneous aging temperature from 25 to 40 °C for the investigated cell. An increase in average temperature with thermal gradient leads to a higher capacity loss acceleration for through-plane than an in-plane thermal gradient. Additional aging mechanisms are found for through-plane thermal gradients whose origins are open for future research.