Contribution of silicon alloy and graphite in blended lithium-ion battery anode were demonstrated and discussed through electrochemical characterization and modeling. Pure and composite materials with varied ratio were evaluated with galvanostatic intermittent titration technique (GITT) and rate tests during delithiation process, followed by model analysis. The large difference between open circuit potential (OCP) of the two material suggested participation of silicon alloy was in later stage of delithiation under slow c-rate condition. A greater diffusion overpotential was also introduced as diffusion coefficients of silicon alloy was smaller by one to two orders of magnitude than that of graphite. Thus, contribution of silicon alloy with greater specific capacity was limited by both higher OCP and slower diffusion kinetics, in agreement of exchange current density obtained from Multi-Scale Multi-Dimensional modeling.