Oxygen-rich lithium oxides for lithium-air battery electrode

Figure caption: Crystal structures of five lithium oxide and ε-O<sub>8</sub> phases. a) Li<sub>2</sub>O<sub>2</sub> (P63/mmc), b) LiO<sub>2</sub> (Pnnm), c) LiO<sub>2</sub> (P4/mbm), d) LiO<sub>4</sub> (Ibam), e) high pressure Li<sub>2</sub>O<sub>3</sub> (Im-3m), f) ε-O<sub>8</sub> (C2/m) phase. Red and green spheres represent oxygen and lithium atoms, respectively.
Figure caption: Crystal structures of five lithium oxide and ε-O8 phases. a) Li2O2 (P63/mmc), b) LiO2 (Pnnm), c) LiO2 (P4/mbm), d) LiO4 (Ibam), e) high pressure Li2O3 (Im-3m), f) ε-O8 (C2/m) phase. Red and green spheres represent oxygen and lithium atoms, respectively.

Lithium–air (Li–O2) batteries may possess energy densities close to that of gasoline. It is commonly known that the Li–O2 battery often forms insoluble discharge products, mainly oxides, which accelerate the degradation of the electrode and electrolyte, thus reducing the cycle stability and efficiency. Lithium superoxide has been considered as an alternative cathode based on reduced graphene oxide. The major problem is that the lithium superoxide is unstable at ambient condition. Investigation of the stability of oxygen-rich lithium oxides would greatly extend our knowledge on improving the capability and lifetime of lithium–air batteries. Based on the theoretical predictions, a research team has used the HPCAT facility in successfully synthesizing several new stable oxygen-rich lithium oxides under high pressure. Three new high pressure oxide phases that form at high temperature and pressure are identified: Li2O3, LiO2, and LiO4. The LiO2 and LiO4 consist of a lithium layer sandwiched by an oxygen ring structure inherited from high pressure ε-O8 phase, while Li2O3 inherits the local arrangements from ambient LiO2 and Li2O2 phases. These novel lithium oxides beyond the ambient Li2O, Li2O2, and LiO2 phases show great potential in improving battery design and performance in large battery applications under extreme conditions. More in W. Yang et al. Advanced Science, 4, 1600453, 2017.