From High-Capacity to Practical: Lean-Tin Alloying Strategy in Borophene-Encased Hard Carbon Hosts as Anodes for...

Inspired by the "lean-silicon" strategy used in practical high-capacity lithium-ion anodes, we report, for the first time, a sodium-ion battery (SIB)-compatible lean-tin alloying-type anode built on a borophene-encased hard carbon (B/HC) framework. A series of B/HC hosts with varying borophene loadings was systematically screened, after which Sn nanoparticles were introduced through NaBH₄-assisted wet-chemical reduction to obtain a "lean-tin" architecture. Electrochemical analysis shows that 15 wt% Sn loaded on a 10 wt% borophene-hard carbon host (15Sn@10B/HC) exhibits a strongly diffusion-dominated charge-storage mechanism, with Na⁺ diffusion coefficients nearly double that of pristine B/HC. The 15Sn@10B/HC anode delivers 399.8 mAh g-¹ and sustains long-term cycling for up to 500 cycles at 0.25 C (∼167 days test duration) with 93.9% retention. In full-pouch cell configuration with Na₃V₂(PO₄)₃ cathode, the 15Sn@10B/HC anode delivers a nominal discharge voltage of 3.0 V with 235.8 mAh g-¹ _ANODE (61.5 mAh g^‒1 _COMBINED) reversible discharge capacity and 707.4 Wh kg^-1 _ANODE (184.5 Wh kg^‒1 _COMBINED) energy density at 0.25 C rate. DFT calculations further confirm the superior Na⁺ adsorption behavior linked to this proposed "lean-tin" architecture. Overall, this work demonstrates that lean-tin loading on a borophene-hard carbon scaffold provides a practical, scalable, and industry-relevant pathway for developing high-capacity SIB anodes.