The thin solid-electrolyte-interface (SEI) films that grow around electrode particles play important roles in Li–ion battery performance. The objective of the present paper is to develop and apply models of SEI behavior that incorporate detailed chemical kinetics and multicomponent species transport. Species- and charge-conservation equations are derived and solved within the SEI film. The SEI model is coupled at its boundaries with an intercalation model within the electrode particles and with Li–ion transport and chemistry at the interface between the SEI and the electrolyte solution. The results of the model provide new insights concerning the influences of the intercalation fraction and cycling rate on SEI growth rates. The model also provides new insight concerning the influence of the SEI film on reversible potential and interfacial resistance.