High-performing mesoporous iron oxalate anodes for lithium-ion batteries

Mesoporous iron oxalate (FeC₂O₄) with two distinct morphologies, i.e., cocoon and rod, has been synthesized via a simple, scalable chimie douce precipitation method. The solvent plays a key role in determining the morphology and microstructure of iron oxalate, which are studied by field-emission scanning electron microscopy and high-resolution transmission electron microscopy. Crystallographic characterization of the materials has been carried out by X-ray diffraction and confirmed phase-pure FeC₂O ₄·2H₂O formation. The critical dehydration process of FeC₂O₄·2H₂O resulted in anhydrous FeC₂O₄, and its thermal properties are studied by thermogravimetric analysis. The electrochemical properties of anhydrous FeC ₂O₄ in Li/FeC₂O₄ cells are evaluated by cyclic voltammetry, galvanostatic charge-discharge cycling, and electrochemical impedance spectroscopy. The studies showed that the initial discharge capacities of anhydrous FeC₂O₄ cocoons and rods are 1288 and 1326 mA h g^-1, respectively, at 1C rate. Anhydrous FeC₂O₄ cocoons exhibited stable capacity even at high C rates (11C). The electrochemical performance of anhydrous FeC₂O ₄ is found to be greatly influenced by the number of accessible reaction sites, morphology, and size effects.