It's called SM-102.
Verifying that it is in the Moderna COVID vaccine, I find a 12/30/20 CDC document titled: "COVID-19 Vaccines: Update on Allergic Reactions, Contraindications, and Precautions." 
If you scroll down halfway through the document, you'll see a chart titled, "Ingredients Included in mRNA COVID vaccines." (pg 20)The right-hand side of the chart shows ingredients in the Moderna vaccine. The fifth ingredient down is "SM-102: heptadecan-9-yl 8-((2-hydroxyethyl) (6-oxo-6-(undecyloxy) hexyl) amino) octanoate."
Now we go to a document published by the Cayman Chemical Company of Ann Arbor, Michigan: "Safety Data Sheet acc. to OSHA HCS." (04/11/2021) 
This data sheet lists the effects of SM-102. Here is the opening note: "For research use only, not for human or veterinary use."