Unlike lithium peroxide, lithium superoxide can easily dissociate into lithium and oxygen, leading to high efficiency and good cycle life. In addition, theoretical calculations have indicated that some forms of LiO₂ may have a long lifetime.

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 form because it is thermodynamically unstable with respect to disproportionation, giving Li₂O₂.

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).

—Lu et al.

The major advantage of a battery based on lithium superoxide, Argonne battery scientists Larry Curtiss and Khalil Amine explained, is that it allows, at least in theory, for the creation of a lithium-air battery that consists of a closed system. Open systems require the consistent intake of extra oxygen from the environment, while closed systems do not—making them safer and more efficient.

The stabilization of the superoxide phase could lead to developing a new closed battery system based on lithium superoxide, which has the potential of offering truly five times the energy density of lithium ion.

—Khalil Amine

The researchers attributed the growth of the lithium superoxide to the spacing of iridium atoms in the electrode used in the experiment.

However, this is just an intermediate step. We have to learn how to design catalysts to understand exactly what’s involved in lithium-air batteries.

—Jun Lu, lead author

The researchers confirmed the lack of lithium peroxide by using X-ray diffraction provided by the Advanced Photon Source, a DOE Office of Science User Facility located at Argonne. They also received allocations of time on the Mira supercomputer at the Argonne Leadership Computing Facility, which is also a DOE Office of Science User Facility. The researchers also performed some of the work at Argonne’s Center for Nanoscale Materials, which is also a DOE Office of Science User Facility.

This discovery really opens a pathway for the potential development of a new kind of battery. Although a lot more research is needed, the cycle life of the battery is what we were looking for.

—Larry Curtiss

The work was funded by the DOE’s Office of Energy Efficiency and Renewable Energy and Office of Science.

Resources

• Jun Lu, Yun Jung Lee, Xiangyi Luo, Kah Chun Lau, Mohammad Asadi, Hsien-Hau Wang, Scott Brombosz, Jianguo Wen, Dengyun Zhai, Zonghai Chen, Dean J. Miller, Yo Sub Jeong, Jin-Bum Park, Zhigang Zak Fang, Bijandra Kumar, Amin Salehi-Khojin, Yang-Kook Sun, Larry A. Curtiss & Khalil Amine (2016) “A lithium–oxygen battery based on lithium superoxide” Nature doi: 10.1038/nature16484

• Ujjal Das, Kah Chun Lau, Paul C. Redfern, and Larry A. Curtiss (2014) “Structure and Stability of Lithium Superoxide Clusters and Relevance to Li–O₂ Batteries” The Journal of Physical Chemistry Letters 5 (5), 813-819 doi: 10.1021/jz500084e