High-Capacity Sb/Fe2S3 Sodium-Ion Battery Anodes Fabricated by a One-Step Redox Reaction, Followed by Ball Milling with Graphite

Antimony (Sb) has been considered a promising anode for sodium-ion batteries (SIBs) owing to its high theoretical capacity (660 mA h g^-1) and low redox voltage (0.2-0.9 V vs Na⁺/Na). However, the capacity degradation caused by the volumetric variation during battery discharge/charge hinders the practical application. Herein, guided by the DFT calculation, Sb/Fe₂S₃ was fabricated by annealing Fe and Sb₂S₃ mixed powder. Next, Sb/Fe₂S₃ was blended with 15 wt % graphite by ball milling, yielding nano-Sb/Fe₂S₃ anchored on an exfoliated graphite composite (denoted as Sb/Fe₂S₃-15%). When applied as an anode of SIBs, Sb/Fe₂S₃-15% delivered reversible capacities of 565, 542, 467, 366, 285, and 236 mA h g^-1 at current rates of 1, 2, 4, 6, 8, and 10 A g^-1, respectively, surpassing most of the Sb-based anodes. The co-existence of highly conductive Fe₂S₃ and Sb minimizes the polarization of the anode. Our experiments proved that the Sb and Fe₂S₃ phases were reversible during discharge/charge cycling, and the exfoliated graphite can accelerate the Na⁺ diffusion and e^- conduction. The proposed synthesis method of this work can also be applicable to synthesize various antimony/transition metal sulfide heterostructures (Sb/M_1-xS), which may be applied in a series of fields.