Calendar Aging of Li-Ion Cells—Experimental Investigation and Empirical Correlation

Abstract

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.

Inhomogeneous Aging in Lithium‐Ion Batteries Caused by Temperature Effects

“…The calendar aging of this cell type is considered elsewhere. [69] In this work, the electrodes of the cycled cells are investigated separately in a postmortem analysis considering electrode, particle, and atomic level. To reveal potential inhomogeneities, methods are chosen that can resolve the properties locally and samples are taken from different locations of the electrodes.…”

A Review of Modeling, Management, and Applications of Grid-Connected Li-Ion Battery Storage Systems

“…A basic equation to represent the capacity fade due to calendric aging would be as defined in ( 5) [122]. The model formulates the degradation as a function of time, SOC, and temperature.…”

Growth of the Solid-Electrolyte Interphase: Electron Diffusion Versus Solvent Diffusion

“…Under storage conditions, the literature reports two important observations. The first one is the dependence of capacity loss on the state-of-charge (SOC) [36,37,38,39], and the second one is the square-root behavior in time [40,41,42,43].…”