Electrochemical Modeling of Linear and Nonlinear Aging of Lithium-Ion Cells

We present an electrochemical aging model with solid electrolyte interphase (SEI) formation, SEI re-formation due to cracking of the layer during graphite expansion, lithium plating when the potential of the negative electrode becomes negative vs Li/Li+, and subsequent lithium stripping once the potential becomes positive again. The model considers the transition from an early stage, linear to a later stage, nonlinear capacity fade. While SEI re-/formation define linear aging, the onset and slope of nonlinear aging is simulated based on the ratio of reversibly and irreversibly plated lithium. With ongoing aging, more lithium is plated irreversibly so that less lithium is stripped. The simulation data agree very well with experimental data on commercial 18 650-type lithium-nickel-cobalt-manganese-oxide vs graphite (NCM/C) cells.