Active material blended electrodes, comprised of physical mixtures of two or more lithium insertion compounds, can have superior balanced performance compared to electrodes with an individual active compound. Due to their high complexity, a good understanding of blended electrodes is still lacking, including their electrolyte/electrode interfacial kinetics, which is a key factor for determining battery service life, safety, and power performance. In this paper, a comprehensive study of the interfacial impedance in Si-alloy/graphite blended electrodes is presented through experiment and theory. Experiments were conducted by the characterization of symmetric cells by electrochemical impedance spectroscopy. An inhomogeneous transmission line model (ITLM) was developed to investigate this binary system on a large scale. Both experimental and theoretical results show that adding a small proportion of low interfacial impedance particles can suppress interfacial impedance growth in blended electrodes.