A cover-band concert is like a drag queen: The show is familiar, predictable and includes the performer’s personal flair. But a tribute-band gig is more like a transgendered person, in that it’s trying to “pass” and mimic the features that would identify it as the band it’s honoring. In all cases, the illusion usually works best when seen across a smoky bar. Lithium: A Tribute to Nirvana plays convincing covers that span the length of Nirvana’s career — from the sludge of Bleach to the glorious chaos of In Utero. The band members themselves don’t much look like Nirvana, but their clothing, stage setup and attempts to stay in character more than make up for it. Lithium’s bassist bounds around barefoot, and the singer sports Cobain’s shoulder-length blond bob and iconic green grandpa sweater.