A Reversible Solid-State Crystalline Transformation in a Metal Phosphide Induced by Redox Chemistry

Abstract

We demonstrate low-potential intercalation of lithium in a solid-state metal phosphide. A topotactic first-order transition between different but related crystal structures at room temperature takes place by an electrochemical redox process: MnP ₄ ↔ Li ₇ MnP ₄ . The P-P bonds in the MnP ₄ structure are cleaved at the time of Li insertion (reduction) to produce crystalline Li ₇ MnP ₄ and are reformed after reoxidation to MnP ₄ , thereby acting as an electron storage reservoir. This is an unusual example of facile covalent bond breaking within the crystalline solid state that can be reversed by the input of electrochemical energy.