Synthesis of Tetrahedral LiFeO2 and Its Behavior as a Cathode in Rechargeable Lithium Batteries

Abstract

Synthesis and structural characterization of the first LiFeO₂ compound with tetrahedrally coordinated Fe³⁺ is reported. When used as a positive intercalation electrode in a lithium cell, it can store charge of up to 120 mAhg^-1 at a rate of 100 mAg^-1. However, it converts to the defect spinel LiFe₅O₈ on cycling. By combining results from powder X-ray diffraction, differential electrochemical mass spectrometry, electrochemical cycling, and TG-MS, it is shown that such conversion, which involved oxygen loss, is not associated with direct O₂ gas evolution but instead reaction with the electrolyte. We suggest that intercalation/deintercalation is accompanied by the exchange of Li⁺ by H⁺ in the material and subsequent loss of H₂O, thus converting LiFeO₂ to the defect spinel LiFe₅O₈ on cycling.