From waste to wealth: Cd-adsorbed rapeseed meal towards CdS-decorated nanocarbons for high-performance sodium metal batteries

Sodium metal batteries (SMBs) are considered one of the most promising energy storage technologies due to the low cost, low redox potential, and high capacity of sodium (Na) anodes. However, dendrite growth caused by uneven Na deposition hinders its practical application. Herein, a green strategy is proposed to synthesize CdS-decorated nanocarbons (RM/CdS) for Na anode modification using Cd-adsorbed rapeseed meal (RM/Cd) as precursor. As biomass waste, rapeseed meal (RM) can efficiently purify Cd²⁺-containing wastewater due to its S,N,O-enriched functional groups. By following pyrolysis, the RM/Cd is directly transformed into RM/CdS with controllable structural composition. As RM/CdS is used to modify the current collector for Na anode, the sodiophilic CdS nanoparticles and derivates enable easy Na⁺ desolvation, low Na⁺ diffusion barrier, and rich nucleation sites, thus reducing the Na nucleation overpotential of the anode and facilitating dendrite-free Na deposition. Consequently, a high average Coulombic efficiency of 99.87 % over 900 cycles and a long lifetime over 1400 h with low overpotential are achieved in asymmetric and symmetric half cells, respectively. The modified Na anodes are further used to assemble full cells with a Na₃V₂(PO₄)₃ cathode, which exhibited excellent capacity retention of 91 % even after 1500 cycles at 1C, demonstrating a promising application in SMBs.