Inhomogeneous Aging in Lithium‐Ion Batteries Caused by Temperature Effects

Abstract

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.

Thermal Transients to Accelerate Cyclic Aging of Lithium‐Ion Batteries

“…[46,47] Another influence might be locally changing kinetics due to changing temperatures. [16] Additionally, a higher temperature than 25 °C enhances a passivation of the deposited lithium with electrolyte. [20,21] All in all, thermal transients triggered different additional aging mechanisms compared to the steady-state reference cases and can thus not be considered for aging acceleration of steady-state lab conditions.…”

“…As summarized by Waldmann et al, [48] plating happens during cycling due to a combination of low temperature, high current or high SoC. In the study of Werner et al [2,12] and Paarmann et al, [16] the low temperature presumably was decisive. Their findings in combination with this work also explain, why thermal transients -including a high temperature -lead to a stronger capacity decrease in comparison to steady-state inhomogeneous temperature fields.…”

“…This is in line with the findings from Werner et al [2,12] In the same study, [2,12] plating did not occur in the regions of higher temperature, but in the regions of 0 °C for an inhomogeneous steady-state temperature condition. [16] However, one has to note that the cell under investigation was a high power cell, [2] which is not as sensitive to high currents. As summarized by Waldmann et al, [48] plating happens during cycling due to a combination of low temperature, high current or high SoC.…”

“…[21] The change to a higher temperature is also suspected to be of importance by Paarmann et al [16] They suggested, that increasing the temperature from 0 °C to 50 °C during charging influences the reaction rates of all occurring processes slightly different enabling lithium plating. [16] These findings clearly show that temperature changes with certain combinations of higher and lower temperatures during cycling can accelerate the capacity loss. Generally, different charging and discharging temperatures affect the capacity loss even with thermal equilibration between charging and discharging steps.…”

“…Werner et al [12] have seen a significantly increased capacity loss for cells, that cycled while constantly changing the temperature between 0 °C and 50 °C. Both Paarmann et al [16] and Carter et al [17] detected lithium plating for cells subjected to a temperature change.…”