Using confined carbonate crystals for the fabrication of nanosized metal oxide@carbon with superior lithium storage capacity

Abstract

Carbon coating of metal oxides is an effective approach to prepare anode materials for LIBs. However, during high-temperature pyrolysis, metal oxides can be easily converted to their metallic phase by carbothermal reduction and tend to form big particles. A new method proposed for the preparation of meso-oxide@carbon is the pyrolysis of polydopamine-encapsulated carbonate crystals. The confined carbonate splits into nanosized particles and the generated CO₂ gases not only create interconnected mesopores throughout the particle and abundant micropores in the carbon layer, but also provide a soft oxidizing atmosphere, which can effectively promise a pure oxide phase by preventing the formation of the metallic phase arising from carbothermal reduction during the pyrolysis of polydopamine. Taking MnCO₃ as an example, the MnO@C hybrid consists of nanosized MnO (∼15 nm) with carbon shells (∼18 nm thick) and developed mesopores, which delivers an excellent reversible capacity of 886 mA h g⁻¹ over 200 cycles at 0.2 A g⁻¹. Even at a high current density of 2 A g⁻¹, a superior capacity of 770 mA h g⁻¹ is retained after 300 cycles. This novel approach also offers an effective preparation of other materials such as CoO/Co₃O₄@C and Fe₃O₄/γ-Fe₂O₃@C, which respectively show reversible capacities of 1058 and 770 mA h g⁻¹ at 0.2 A g⁻¹, with good cycling stability.