Template assisted lithium superoxide growth for lithium–oxygen batteries

Abstract

Developing batteries with energy densities comparable to internal combustion technology is essential for a worldwide transition to electrified transportation. Li–O₂ batteries are seen as the ‘holy grail’ of battery technologies since they have the highest theoretical energy density of all battery technologies. Current lithium–oxygen (Li–O₂) batteries suffer from large charge overpotentials related to the electronic resistivity of the insulating lithium peroxide (Li₂O₂) discharge product. One potential solution is the formation and stabilization of a lithium superoxide (LiO₂) discharge intermediate that exhibits good electronic conductivity. However, LiO₂ is reported to be unstable at ambient temperature despite its favorable formation energy at −1.0 eV per atom. In this paper – based on our recent work on the development of cathode materials for aprotic lithium oxygen batteries including two intermetallic compounds, LiIr₃ and LiIr, that are found to form good template interfaces with LiO₂ – a simple goodness of fit R factor to gauge how well a template surface structure can support LiO₂ growth, is developed. The R factor is a quantitative measurement to calculate the geometric difference in the unit cells of specific Miller Index 2D planes of the template surface and LiO₂. Using this as a guide, the R factors for LiIr₃, LiIr, and La₂NiO_4+δ, are found to be good. This guide is attested by simple extension to other noble metal intermetallics with electrochemical cycling data including LiRh₃, LiRh, and Li₂Pd. Finally, the template concept is extended to main group elements and the R factors for LiO₂ (111) and Li₂Ca suggest that Li₂Ca is a possible candidate for the template assisted LiO₂ growth strategy.