Biomass-Derived Graphitic Carbon/Co₃O₄ Nanocomposites with Pseudocapacitance for Lithium Storage

The reuse of waste biomass resources has recently become one of the most popular themes in the sustainable development of human society. To this end, waste scallion root was used as a biotemplate and carbon source to synthesize graphitic carbon-doped mesoporous Co₃O₄ nanocomposites (Co₃O₄/C) through a simple cobalt salt impregnation, carbonization, and low-temperature oxidation method. The effect of different carbon contents on the nanostructure and electrochemical performance is investigated. The hierarchical microtubes with a ribs-shaped inner wall in the product oxidized at 320 °C (Co₃O₄/C-2) are formed by the cross-linking of uniform small Co₃O₄ nanoparticles and 39.9% biomass-derived carbon. The Co₃O₄/C-2 nanocomposite has a large specific surface area of 360.2 m²·g^–1, uniform mesopore size of 2.35 nm, and abundant oxygen vacancy defects. Such a unique nanostructure can exhibit a good pseudocapacitance behavior during the charge/discharge process, thereby effectively enhancing the lithium storage performance. The Co₃O₄/C-2 nanocomposite exhibits a high capacity and good rate capability. Even at 1.0 A g^–1, it can still retain a capacity of 620 mA h g^–1 after 1500 cycles. The superior capacity retention and long-cycling stability can be assigned to the synergistic effect of the unique nanostructure of the Co₃O₄/C-2 material (a uniform mesopore and large specific surface area), appropriate graphitic carbon doping, and pseudocapacitance contribution. Therefore, the reuse strategy of the waste scallion root biomass resource conforms to the concept of sustainable development and also provides a useful reference for the synthesis of other nanostructured anode materials with excellent performance.