Espeon's Ability only negates the additional effects of Attacks, not Damage.
For instance, if your pokemon with energy was hit by Cobalion's Iron Breaker, it would be able to attack next turn, although it would still take 80 damage. As a rule of thumb, Espeon's ability lets you pretend that all the attacks on your opponents pokemon have no text, just an energy cost and damage.
A caveat to that, attacks that have effects reliant on circumstance (such as Scizor Prime's Metal Scissors) still have that aspect of their effect, despite Espeon's ability. So, Metal Scissors would still do 30+20*Metal Energy, even though Espeon's Ability makes your pokemon immune to effects, because that "effect" is just a qualifier for how much damage is being done.
If in doubt, check out the rulings on Unown G.