Temperature has a significant influence on the behavior of batteries and their lifetime. There are several studies in literature that investigate the aging behavior under electrical load, but are limited to homogeneous, constant temperatures. This article presents an approach to quantifying cyclic aging of lithium-ion cells that takes into account complex thermal boundary conditions. It not only considers different temperature levels but also spatial and transient temperature gradients that can occur despite-or even due to-the use of thermal management systems. Capacity fade and impedance rise are used as measured quantities for degradation and correlated with the temperature boundary conditions during the aging process. The concept and definition of an equivalent aging temperature (EAT) is introduced to relate the degradation caused by spatial and temporal temperature inhomogeneities to similar degradation caused by a homogeneous steady temperature during electrical cycling. The results show an increased degradation at both lower and higher temperatures, which can be very well described by two superimposed exponential functions. These correlations also apply to cells that are cycled under the influence of spatial temperature gradients, both steady and transient. Only cells that are exposed to transient, but spatially homogeneous temperature conditions show a significantly different aging behavior. The concluding result is a correlation between temperature and aging rate, which is expressed as degradation per equivalent full cycle (EFC). This enables both temperature-dependent modeling of the aging behavior and its prediction.

Alongside electrical loads, it is known that temperature has a strong influence on battery behavior and lifetime. Investigations have mainly been performed at homogeneous temperatures and non-homogeneous conditions in single cells have at best been simulated. This publication presents the development of a methodology and experimental setup to investigate the influence of thermal boundary conditions during the operation of lithium-ion cells. In particular, spatially inhomogeneous and transient thermal boundary conditions and periodical electrical cycles were superimposed in different combinations. This required a thorough design of the thermal boundary conditions applied to the cells. Unlike in other contributions that rely on placing cells in a climatic chamber to control ambient air temperature, here the cell surfaces and tabs were directly connected to individual cooling and heating plates. This improves the control of the cells' internal temperature, even with high currents accompanied by strong internal heat dissipation. The aging process over a large number of electrical cycles is presented by means of discharge capacity and impedance spectra determined in repeated intermediate characterizations. The influence of spatial temperature gradients and temporal temperature changes on the cyclic degradation is revealed. It appears that the overall temperature level is indeed a decisive parameter for capacity fade during cyclic aging, while the intensity of a temperature gradient is not as essential. Furthermore, temperature changes can have a substantial impact and potentially lead to stronger degradation than spatial inhomogeneities.

Lithium‐ion batteries (LIBs) are widely used as electrochemical energy storage devices due to their advantages in energy and power density as well as their reliability. One research focus is the cyclic lifetime of LIB, where the influence of thermal conditions during cycling is not yet completely understood. In previous publications, investigations on the cyclic aging behavior of LIB under various thermal boundary conditions are presented, including defined temperature gradients and temperature transients. Thereupon, herein, the results of cell openings and an extensive postmortem study with analyses of scanning electron micrographs, electrode thickness, X‐ray diffraction, and inductively coupled plasma optical emission spectroscopy are presented, evaluated, and correlated with the thermal conditions. The results reveal significant variations on the electrode and atomic scale for the different thermal boundary conditions during cycling. The electrodes exposed to a temperature gradient exhibit an inhomogeneous distribution of aging behavior that directly correlates with the local temperature. Cycling with superimposed transient temperatures reveals fundamentally different aging effects. With this knowledge, critical temperature conditions can be avoided in applications to prolong cyclic lifetime.

The lifetime of the battery significantly influences the acceptance of electric vehicles. Calendar aging contributes to the limited operating lifetime of lithium-ion batteries. Therefore, its consideration in addition to cyclical aging is essential to understand battery degradation. This study consequently examines the same graphite/NCA pouch cell that was the subject of previously published cyclic aging tests. The cells were aged at different temperatures and states of charge. The self-discharge was continuously monitored, and after each storage period, the remaining capacity and the impedance were measured. The focus of this publication is on the correlation of the measurements. An aging correlation is obtained that is valid for a wide range of temperatures and states of charge. The results show an accelerated capacity fade and impedance rise with increasing temperature, following the law of Arrhenius. However, the obtained data do also indicate that there is no path dependency, i.e., earlier periods at different temperature levels do not affect the present degradation rate. A large impact of the storage state of charge at 100% is evident, whereas the influence is small below 80%. Instead of the commonly applied square root of the time function, our results are in excellent agreement with an exponential function.

Herein, a comprehensive experimental studies on the interdependence of temperature and current distribution in lithium‐ion batteries is presented. Initially, a method for measuring the current distribution on a single cell is presented and verified by comparison with measurements on a parallel circuit. The presented method is straightforward and robust. It provides accurate quantitative and reproducible results. They are consistent with literature and show a higher current with increasing temperature. This temperature dependency is more pronounced at lower temperatures. Furthermore, it offers the opportunity to determine the influence of the temperature on the current distribution more precisely. Finally, this publication correlates the normalized current with temperature quantitatively using an Arrhenius‐like approach according to I∼exp(−1T).