Activity-structure relationship of electrocatalysts derived from lithium cobalt oxides for metal-air batteries

Abstract

Lithium cobalt oxides are widely investigated as promising bifunctional catalysts for metal-air batteries in recent years. Generally, the promotion of catalytic activity of LiCoO2-based materials is mainly due to the ultra-thin layer structure with thickness of several atomic layers. Herein, a series of nanosheets are obtained from layered LiCoO2 material treated by nitric acid. More unexpectedly, although the specific surface area of the samples increases dramatically due to ultrathin nanosheets, the catalytic activities almost are not improved compared with that of bulk LiCoO2 material. After annealing process, these samples exhibit superior catalytic performance in alkaline solutions. Based on X-ray diffraction spectra, raman spectra, X-ray photoelectron spectroscopy, and O2 temperature-programmed desorption analysis, the results indicate that metastable Li1-x-yHyCoO2 nanosheets are obtained from bulk LiCoO2 material treated by acid. They transform into main phase of spinel-type Li1-xCoO2-δ material with more oxygen vacancies after annealing process. The great difference in electrochemical performances between the two-type materials is attributed to the crystal structures, the exposure of Co–O octahedral sites in the plane of spinel-type Li1-xCoO2-δ, the coexistence of valence state of Con+ and oxygen vacancy.