I know of no scientific reason to suppose that "dark energy" is anything more than the cosmological curvature constant identified by Einstein in 1917 as occurring naturally in the GR equation for spacetime curvature. It might eventually turn out to be related to some type of energy. That's possible. But so far there seems to be no reason to imagine that it is is connected with anything we'd normally consider an energy---it is simply the universe's baseline curvature in the absence of matter. The phrase "dark energy" tends to get newcomers confused because they try to understand something much simpler (a small pervasive constant baseline curvature) in terms of energy. The phrase should probably be replaced by something less misleading.