Superfluous means unnecessary, not needed. Redundant means the thing's purpose has been fulfilled by something else. A difference in nuance is that redundant implies there is something else with the same function, but superfluous just means not needed, whether it's because of something else, or simply because it's irrelevant.

Synonym for superfluous They essentially mean the same thing. The only minor difference is that "redundant" can refer to something that is unnecessary because it's repetitive, for example "the shirt was torn, ripped and shredded" is redundant because "torn, ripped and shredded" mean essentially the same thing and so all three aren't needed.