Simplify the text.
Known methods of producing antimatter from energy also produce an equal amount of normal matter, so the theoretical limit is that half of the input energy is converted to antimatter. Counterbalancing this, when antimatter annihilates with ordinary matter, energy equal to twice the mass of the antimatter is liberated a '' so energy storage in the form of antimatter could (in theory) be 100% efficient.
The reason this is important to understand antimatter is because scientists found that when matter and antimatter touch each other, the amount of energy that is released comes very close to the amount of energy says should be all together in those two pieces.