Does a lid that is only used when storing food ever require tevilah?
Yes, the lid requires tevillah if it is made of an obligated material.
See also sources, below.
In principle a lid of a pot requires tevillah (Rema, Yoreh De’ah 120:5).
However, this is because the lid is integral to the pot, for a pot without a lid is flawed.
In the case of a storage utensil, it appears that the lid is likewise part of the utensil, since without a lid the utensil is flawed as a storage container. Because this is the case, it follows that the lid needs tevilah, even if it is rarely used.
However, there are types of vessels and utensils (such as salad bowl and others) for which the lid is generally not used, and it is only provided for special circumstances. In this case, the status of the lid will be more questionable.
Certainly, it is best to tovel the lid together with the new vessel, and not to make a beracha on the lid alone.