Modeling of SEI Formation Based on a Electrochemical Reduced Order Model for Li(MnNiCo)O2/Carbon Polymer Battery

Experimental investigations conducted on a large format lithium ion polymer battery have revealed that one of the major factors causing capacity and power fade is the formation and growth of solid electrolyte interphase (SEI), particularly at anode during charging, which consumes lithium ions and electrolytes. As a result, internal resistance increases. The SEI formed at the graphite anode surface protects the electrode from being decomposed by electrolyte solvent initially, but its growth leads to a gradual capacity and power fade. This phenomenon is described by Butler- Volmer equation that is incorporated into an electrochemical reduced order model. The model consists of coupled physics-based partial differential equations that mimic the lithium ion intercalation reactions and the solvent reduction reactions that produce SEI. The developed reduced order model is validated experimentally at different current rates. Simulation results of the SEI resistance with respect to cycle numbers, as well as the changes of the corresponding electrochemical parameters, are presented.