Mesoporous cobalt oxalate nanostructures as high-performance anode materials for lithium-ion batteries: Ex situ electrochemical mechanistic study

Two distinct mesoporous nanostructures, that is, rod and sheet cobalt oxalate (CoC₂O₄), have been synthesized via facile chimie douce precipitation technique. The selective interaction between solvent type and crystallographic planes of the metal ion is the key factor in morphological variations. The morphology and microstructure are studied by high-resolution transmission electron microscopy. Structural characterization of the materials has been carried out by X-ray diffraction and confirmed phase pure CoC ₂O₄·2H₂O formation. The critical dehydration process of CoC₂O₄·2H₂O led to anhydrous CoC₂O₄, and its thermal properties are investigated by thermogravimetric analysis. Electrochemical properties of anhydrous CoC₂O₄ in half-cells are studied by cyclic voltammetry, galvanostatic charge-discharge cycling, and electrochemical impedance spectroscopy. The studies showed that initial discharge capacity of anhydrous CoC₂O₄ nanorods and sheets is 1599 and 1518 mA h g^-1, respectively, at 1C-rate. Anhydrous CoC₂O ₄ nanostructures fabricated by this chimie douce process achieved higher reversible capacity, more stable cycling, and better rate capabilities than reported. The electrochemical performances of anhydrous CoC ₂O₄ nanostructures are found to be significantly influenced by morphology and porosity. In addition, the interfacial electrochemical mechanism related to the transitional metal oxidation states, phase structural changes, and distribution during cycling are validated.