The solid electrolyte interphase (SEI) is a passivation layer formed on an electrode surface that can enhance long-term electrode stability. The inorganic components formed in SEI layer, including lithium carbonate and lithium fluoride, play a critical role in terms of providing both mechanical and chemical protection as well as accommodating lithium ion transport. Although lithium carbonate and lithium fluoride have relatively low ionic conductivities, surprisingly, we find that a synthetic composite coating made of both components creates a defect-intensive interface, which significantly improves lithium transport. The synergetic effect of both inorganic components leads yields higher current efficiencies and cycling stability. We envision that the defect-intensive composite coating is a promising artificial SEI layer for the suppression of undesirable side reactions and improvement in the life of lithium ion batteries employing silicon negative electrodes.