One of the challenges associated with silicon as an anode material for Li-ion batteries is the formation of an unstable solid-electrolyte interphase which, forms continuously while consuming lithium and other components; and consequently contributes to irreversible capacity. To elucidate some of the details of the formation and subsequent dissolution of species formed during lithiation of silicon anodes we have produced thin film silicon electrodes and analyzed them during lithiation and delithiation using an electrochemical quartz microbalance with in-situ dissipation (EQCM-D). Measurements were conducted on electrodes with silicon alone and silicon with a silicon dioxide coating, and in EC:EMC and EC:DEC:FEC based electrolytes. Mass loss during lithiation was observed in both solvents systems when an oxide layer was present on the surface of the electrode. Solid state and solution NMR measurements indicate that the formation and dissolution of Li2O is the most likely cause of mass loss. (C) 2015 Elsevier B.V. All rights reserved.