Facile Solvothermal Synthesis of Phase-Pure Cu₄O₃ Microspheres and Their Lithium Storage Properties

Phase-pure Cu₄O₃ microspheres were synthesized for the first time via a facile solvothermal method, using Cu­(NO₃)₂·3H₂O as the precursor. A formation mechanism was proposed based on the observation of a series of reaction intermediates. The samples were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, thermogravimetric analysis, temperature-programmed reduction and oxidation, X-ray photoelectron spectroscopy, and nitrogen adsorption. It was found that the composition of the prepared products were highly dependent on the synthesis conditions, particularly the hydrate water content in the copper precursor of Cu­(NO₃)₂. Pure Cu₄O₃ microspheres with a diameter of 2–10 μm could be obtained via the symproportionation reaction (2CuO + Cu₂O → Cu₄O₃), which was regarded not being feasible in aqueous media under mild synthesis conditions. The electrochemical properties of the Cu₄O₃ microspheres as anode materials for Li-ion batteries were also investigated. Compared to the simple physical mixture of CuO and Cu₂O with an equivalent atomic ratio of 2:1, the as-prepared Cu₄O₃ exhibited unique lithium storage behaviors at a low voltage range and superior electrochemical performances as an anode material for Li-ion batteries. The successful preparation of pure Cu₄O₃ material could provide opportunities to further explore its physicochemical properties and potential applications