In this work, different promising electrolyte salts, solvents and additives have been evaluated for nanosilicon (nano-Si) negative-electrode materials. For a wide range of solvents and salts used to formulate electrolytes, we found that fluoroethylene carbonate (FEC) is important for good Si electrode performance. The combination of FEC with dimethyl carbonate (DMC) gives the best electrochemical performance. We provide arguments to support our perspective that the superior solubility of the salts and FEC decomposition products in DMC leads to a more protective solidelectrolyte interphase (SEI). Consistent with this view, some SEI-forming precursors such as VC, LiBOB, LiODFB, if added in relatively large quantities (>2wt%), have deleterious effects on Si electrode performance due to competitive reactions with FEC decomposition, which, in the absence of such precursors, can form a more robust SEI on Si.