In addition to these well-known species, there are also a number of novel products that have not previously been proposed to participate in SEI formation. Among these are six additional alkyl carbonates (Fig. dotted light green) which are each very similar to known products in molecular size, composition, bonding, and contained functional groups. Due to the extreme difficulty of experimentally characterizing the SEI and the resulting limited ability to resolve small signal to noise, the likely spectroscopic similarity of these species to the known products means that they may be present in the SEI in small quantities but that they could not easily be positively identified.