Interface-modulated fabrication of hierarchical yolk-shell Co₃O₄/C dodecahedrons as stable anodes for lithium and sodium storage

Transition-metal oxides (TMOs) have gradually attracted attention from researchers as anode materials for lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs) because of their high theoretical capacity. However, their poor cycling stability and inferior rate capability resulting from the large volume variation during the lithiation/sodiation process and their low intrinsic electronic conductivity limit their applications. To solve the problems of TMOs, carbon-based metal-oxide composites with complex structures derived from metal-organic frameworks (MOFs) have emerged as promising electrode materials for LIBs and SIBs. In this study, we adopted a facile interface-modulated method to synthesize yolk-shell carbon-based Co₃O₄ dodecahedrons derived from ZIF-67 zeolitic imidazolate frameworks. This strategy is based on the interface separation between the ZIF-67 core and the carbon-based shell during the pyrolysis process. The unique yolk-shell structure effectively accommodates the volume expansion during lithiation or sodiation, and the carbon matrix improves the electrical conductivity of the electrode. As an anode for LIBs, the yolk-shell Co₃O₄/C dodecahedrons exhibit a high specific capacity and excellent cycling stability (1, 100 mAh·g^-1 after 120 cycles at 200 mA·g^-1). As an anode for SIBs, the composites exhibit an outstanding rate capability (307 mAh·g^-1 at 1, 000 mA·g^-1 and 269 mAh·g^-1 at 2, 000 mA·g^-1). Detailed electrochemical kinetic analysis indicates that the energy storage for Li⁺ and Na⁺ in yolk-shell Co₃O₄/C dodecahedrons shows a dominant capacitive behavior. This work introduces an effective approach for fabricating carbon- based metal-oxide composites by using MOFs as ideal precursors and as electrode materials to enhance the electrochemical performance of LIBs and SIBs.