During the discharge of the battery, the oxygen from the air is reduced at the cathode and combines with a Li ion to form solid Li 2 O 2 . During the recharge, the reverse decomposition of Li 2 O 2 occurs. The overpotential needed to recharge the battery determines its efficiency and depends on several factors that can have different origin. The source of the energy barriers originates in the intrinsic reversible reaction but also is affected by the morphology of the discharge product or the presence of side-reaction secondary phases. A profound knowledge of the electronic and transport properties of Li 2 O 2 both in bulk and at the surface is crucial to understand the reversible reaction of Eq. 1 and to propose new routes to circumvent the above mentioned difficulties.