Low-temperature charging of lithium-ion cells part I: Electrochemical modeling and experimental investigation of degradation behavior

Fast charge of Li-ion cells is one of the main challenges in automotive battery application. As a particular problem at low temperatures and high charging rates, lithium deposits as metal on the anode surface (so-called lithium plating) instead of intercalation. Electrochemical models help to understand internal processes and predict aging effects, which finally lead to optimized charging strategies. In this work, a 1D + 1D (pseudo-2D) electrochemical model is developed, applied over a wide range of temperature (T = −25 °C to 40 °C) and current (I = 0.1 C to 6 C), and coupled with a 0D thermal model. The model is parameterized with measurement data in frequency domain using electrochemical impedance spectroscopy (EIS) and validated with time-domain data. In experiments cells are charged under different operating conditions. Capacity fade is measured after a significant number of cycles and compared to the simulated anode potential. A qualitative correlation is found between the degradation in experiment and the anode potential dropping below 0 V vs. Li/Li+ at the separator-anode boundary in the simulation. Furthermore a semi-quantitative expression for degradation is introduced. The transformation of the model into an on-board applicable form is presented in the companion contribution (part II).