Synthesis and electrochemical performance of carbon-coated three-dimensional porous carbon nanoflowers derived from walnut shells for lithium-ion battery applications

In this study, a novel lithium-ion battery material, carbon-coated three-dimensional porous carbon nanoflowers derived from walnut shells (C@WS), was successfully synthesized by utilizing molten salt as a reaction medium to promote the activation of pore-forming agents. The resulting C@WS retains the disordered carbon honeycomb structure inherent in the original walnut shell (WS), with an enhanced specific surface area (930.9 m²g⁻¹ for WS and 1227.1 m²g⁻¹ for C@WS). Moreover, a unique CC core/shell architecture is formed between the carbon coating and the WS substrate. Electrochemical analysis demonstrates that C@WS exhibits excellent lithium storage capacity, delivering a specific capacity of 569.41 mAhg⁻¹ at a current density of 0.1C (40.7 mA g⁻¹). It also shows superior rate capability, maintaining a capacity of 381.45 mAhg⁻¹ at 0.5C, as well as excellent cycling stability and remarkable capacity recovery, retaining 99.3 % of its initial capacity after 900 cycles at 3C. Furthermore, the carbon coating significantly enhances both the initial Coulombic efficiency (by 11.93 %) and the lithium-ion diffusion kinetics, with the diffusion coefficient (DLi⁺) of C@WS (2.52 × 10⁻⁷ cm² s⁻¹) being notably higher than that of WS (1.86 × 10⁻⁷ cm² s⁻¹).