Phosphite as Polyanion-Based Cathode for Li-Ion Battery: Synthesis, Structure, and Electrochemistry of LiFe(HPO₃)₂

A new lithium containing iron­(III) phosphite, LiFe­(HPO₃)₂, has been synthesized via a solvent-free, low temperature, solid-state synthesis route. The crystal structure of this material has been determined employing single-crystal X-ray diffraction, which indicates that the compound has a three-dimensional structure formed by isolated FeO₆ octahedral units joined together via bridging HPO₃ pseudopyramidal moieties. This arrangement leads to the formation of channels along all the three crystallographic directions, where channels along the <i>a-</i> and <i>b</i>-axes host Li⁺ ions. The compound was further characterized by TGA, IR, and Mössbauer spectroscopic techniques. Additionally, it has been demonstrated that this phase is electrochemically active toward reversible intercalation of Li⁺ ions and thus can be used as a cathode material in Li-ion cells. An average discharge potential of 2.8 V and a practical capacity of 70 mAh·g^–1 has been achieved as indicated by the results of cyclic voltammetry and galvanostatic charge–discharge tests