Hierarchical Co₃O₄@N-Doped Carbon Composite as an Advanced Anode Material for Ultrastable Potassium Storage

Cobalt oxide (Co₃O₄) delivers a poor capacity when applied in large-sized alkali metal-ion systems such as potassium-ion batteries (KIBs). Our density functional theory calculation suggests that this is due to poor conductivity, high diffusion barrier, and weak potassium interaction. N-doped carbon can effectively attract potassium ions, improve conductivity, and reduce diffusion barriers. Through interface engineering, the properties of Co₃O₄ can be tuned via composite design. Herein, a Co₃O₄@N-doped carbon composite was designed as an advanced anode for KIBs. Due to the interfacial design of the composite, K⁺ were effectively transported through the Co₃O₄@N-C composite via multiple ionic pathways. The structural design of the composite facilitated increased Co₃O₄ spacing, a nitrogen-doped carbon layer reduced K-ion diffusion barrier, and improved conductivity and protected the electrode from damage. Based on the entire composite, a superior capacity of 448.7 mAh/g was delivered at 50 mA/g after 40 cycles, and moreover, 213 mAh/g was retained after 740 cycles when cycled at 500 mA/g. This performance exceeds that of most metal-oxide-based KIB anodes reported in literature.