The mechanism of NaFePO4 (de)sodiation determined by in situ X-ray diffraction

Abstract

The reaction mechanism occurring during the (de)intercalation of sodium into the host olivine FePO₄ structure is thoroughly analysed through a combination of structural and electrochemical methods. In situ XRD experiments have confirmed that the charge and discharge reaction mechanisms are different and have revealed the existence of a solid solution domain from 1 < x < 2/3 in Na_xFePO₄ upon charge. The second part of the charge proceeds through a 2-phase reaction between Na_2/3FePO₄ and FePO₄ with strongly varying solubility limits. The strong cell mismatch between Na_2/3FePO₄ and FePO₄ enhances the effects of the diffuse interface and therefore varying solubility limits are first observed here in micrometric materials.