Unveiling the Role of Local Atomic Configurations of Tin on Enhanced Na Storage for Carbon Anode Materials

Elucidating the interplay between Na⁺ electrochemical behavior and the local atomic configurations of sub-nano metal species in carbon-based anodes remains pivotal for advancing sodium-ion battery technology. Here, nitrogen-fluorine co-doped carbon matrices (NFC) embedded with abundant Sn single atoms (SnSAs) and slight clusters (Sn─Clu) are engineered via a one-pot synthesis. Precise modulation of SnCl₂ precursor content enables tailored Sn─NFC architectures with optimized specific surface areas (SSA: 208.1 m² g^-1 for 17% Sn─NFC), tunable Sn─Clu sizes, and SnSA/Sn─Clu ratios. Synchrotron spectroscopy and density functional theory reveal that coexisting SnSAs and Sn─Clu synergistically enhance Na⁺ adsorption (ΔE = -2.56 to -2.64 eV) and electronic conductivity through coordinated Sn─N bonding and cluster-mediated charge redistribution. The 17% Sn─NFC anode achieves exceptional sodium storage performance, delivering 362.2 mAh g^-1 at 0.05 A g^-1 and 140.1 mAh g^-1 at 20 A g^-1 with 87.4% capacity retention over 500 cycles in ester-electrolyte, surpassing most carbon-based counterparts. Ether-electrolyte optimization further amplifies kinetics, yielding 366.7 mAh g^-1 (0.05 A g^-1) and 206.3 mAh g^-1 (20 A g^-1). This work establishes a multi-scale design framework, bridging atomic-scale Sn configurations to macroscopic electrode performance, and propels high-power sodium-ion battery development.