A lithium–oxygen battery based on lithium superoxide

Abstract

Batteries based on sodium superoxide and on potassium superoxide have recently been reported^1,2,3. However, there have been no reports of a battery based on lithium superoxide (LiO₂), despite much research^4,5,6,7,8 into the lithium–oxygen (Li–O₂) battery because of its potential high energy density. Several studies^{9,10,11,12,13,14,15,16} of Li–O₂ batteries have found evidence of LiO₂ being formed as one component of the discharge product along with lithium peroxide (Li₂O₂). In addition, theoretical calculations have indicated that some forms of LiO₂ may have a long lifetime¹⁷. These studies also suggest that it might be possible to form LiO₂ alone for use in a battery. However, solid LiO₂ has been difficult to synthesize in pure form¹⁸ because it is thermodynamically unstable with respect to disproportionation, giving Li₂O₂ (refs 19, 20). Here we show that crystalline LiO₂ can be stabilized in a Li–O₂ battery by using a suitable graphene-based cathode. Various characterization techniques reveal no evidence for the presence of Li₂O₂. A novel templating growth mechanism involving the use of iridium nanoparticles on the cathode surface may be responsible for the growth of crystalline LiO₂. Our results demonstrate that the LiO₂ formed in the Li–O₂ battery is stable enough for the battery to be repeatedly charged and discharged with a very low charge potential (about 3.2 volts). We anticipate that this discovery will lead to methods of synthesizing and stabilizing LiO₂, which could open the way to high-energy-density batteries based on LiO₂ as well as to other possible uses of this compound, such as oxygen storage.