Lattice softening enables highly reversible sodium storage in anti-pulverization Bi-Sb alloy/carbon nanofibers

The high theoretical capacity of Sb-based intermetallic alloys makes them attractive potential anode materials for sodium-ion batteries (SIBs) with high energy density. However, their cycling stability is greatly restricted by the huge volumetric variations resulted from the intrinsic (de-)alloying mechanism. Herein, we demonstrate a unique lattice softening mechanism, which enables highly reversible sodium storage and stable cycling of the as-prepared Bi-Sb alloy/carbon nanofibers electrodes. Theoretical analyses show that the elastic modulus of Bi-Sb alloys is reduced whereas the toughness is enhanced by tuning the lattice chemistry of rhombohedral Bi-Sb alloys, which is of great importance in relieving the concentrated stress during the continuous (de-)sodiation processes. In-situ characterization and electrochemical evaluations demonstrate that the electrodes made of BiSb3/C nanofibers exhibit high anti-pulverization capability upon Na-cycling and extraordinary long-life cyclability. Specifically, a highly reversible capacity of 233.2 mAh g(-1) at 2 A g(-1) is achieved over 2500 cycles. Moreover, a full cell assembled with the pre-sodiated BiSb3/C anode and a Na3V2(PO4)(3)/C cathode delivers a high reversible capacity of 333.2 mAh g(-1) at 0.2 A g(-1) over 200 cycles. This present work provides further understandings and new solution for developing high-performance alloying-based anodes for SIBs.