Template-free synthesis of a yolk-shell Co3O4/nitrogen-doped carbon microstructure for excellent lithium ion storage

Developing novel composite materials with delicate micro or nanoscale structures that enable fast lithium transport is crucial for high performance anode materials for lithium batteries. Herein, we developed a novel template-free synthesis method for a Co-based metal composite (amCoC) with a unique open yolk-shell structure, which uses an ionic liquid (IL) as a new structure-directing agent. Subsequently, the amCoC can be converted into a Co3O4/nitrogen-doped carbon composite (Co3O4/NDC) by thermal treatment. The morphology and phase transformation processes were investigated by in situ transmission electron microscopy (in situ TEM). Atomic scale probe aberration-corrected STEM confirms that the cobalt content in the open yolk-shell Co3O4/NDC is in the form of spinel Co3O4. Density functional theory calculations indicate that the carbon can optimize the band structure and improve the lithium ion diffusion ability. When applied in lithium ion batteries, the open yolk-shell Co3O4/NDC shows excellent electrochemical performance with a reversible capacity of 1220 mA h g(-1) at 0.5C after 100 cycles. This template-free synthesis method for yolk-shell Co3O4/NDC microstructures paves new paths for design of high performance energy storage materials.