The design and synthesis of spinel one-dimensional multi-shelled nanostructures for Li-ion batteries

The rational design, synthesis, and massive production of one-dimensional (1D) spinel composite oxides with multi-shelled nanostructures are critical for the realization of highly efficient energy conversion and storage. However, owing to the limitations of the synthetic methods, the 1D multi-shelled nanostructures, especially for multi-element oxides and binary-metal oxides, have been rarely fabricated. Herein, we design a facile and general method to fabricate 1D spinel composite oxides with complex architectures. It is found that the concentration of the precursor polymer PAN can control the structures of the products at optimal heating rate, including hollow nanofibers, wire-in-tube nanofibers, and tube-in-tube nanofibers. This technique could be extended to various inorganic multi-element oxides and binary-metal oxides. Moreover, numerous twin boundaries (TBs) are found to form in the Co_0.5Ni_0.5Fe₂O₄ tube-in-tube nanofibers. Benefiting from both large porosity and TBs structures, the tube-in-tube hollow nanostructures are measured to possess superior electrochemical performances with high energy and stability in lithium-ion storage.