Protecting elemental Li from the atmosphere
Industrially, this has been done by coating with Parylene.

The Rubber and Plastics Age, Volume 46 says:


  Parylene coated lithium metal granules on the left exhibit no reaction with water on which they float


and  New linear polymers says:


  Encapsulation of reactive chemicals in thin parylene C coatings provides protection. Parylene-coated lithium metal granules at left exhibit no reaction with water on which they float Unprotected granules at right react instantly and violently with water. 


However, I don't know on what timescale this protection lasts.  As others are saying, lithium metal is an extreme fire hazard.  What if the coating is scratched or peels? Be careful!