Differentiating allotropic LiCoO₂/Li₂Co ₂O₄: A structural and electrochemical study

In situ high-energy X-ray diffraction was carried out to investigate the structural transformation of lithium cobalt oxides during the solid-state synthesis. Two allotropic phases were observed during the synthesis process; Li₂Co₂O₄ with a spinel structure was formed within the temperature window between 450 °C and 650 °C, beyond which Li₂Co₂O₄ was converted to its hexagonal counterpart, layered LiCoO₂, through a cation exchange between Li and Co. In electrochemical tests, the Li₂Co₂O₄ was estimated to have a very low reversible capacity, ∼20 mAh g^-1, and a high initial irreversible capacity loss of about 80 mAh g^-1. An interfacial phase between layered LiCoO₂ domain and spinel Li ₂Co₂O₄ domain was also identified by ex situ high-resolution X-ray diffraction. © 2014 Published by Elsevier B.V.