Abstract
Phase boundaries facilitate the charge transportation and alleviate the intrinsic stress upon cycles. Therefore, how to achieve regular phase boundaries is very attractive. Herein, dimer-like Sn-Bi@C nanostructures, where is a well-defined phase boundary between Sn and Bi, have been prepared by a two-step process for the first time. The phase boundary not only provides additional and fast transportation for Na+, but also mitigates the structure stress/strain upon cycling. Therefore, Sn-Bi@C exhibits a high capacity (472.1 mA h g−1 at 2 A g−1 for 200 cycles), an ultra-long cyclic life (355.6 mA h g−1 at 5 A g−1 for 4500 cycles) and an excellent rate performance (372 mA h g−1 at 10 A g−1) for sodium storage, much higher than those of Sn@C, Bi@C, and Sn@C + Bi@C. Notably, the full cells of Sn-Bi@C//Na3V2(PO4)3/rGO (Sn-Bi@C//NVP/rGO) demonstrate impressive performance (323 mA h g−1 at 2 A g−1 for 300 cycles). The underlying mechanism for such an excellent performance is elucidated by in-situ X-ray diffraction, ex-situ scanning electron microscopy /high-resolution transmission electron microscopy and atomic force microscopy, revealing the good electrode stability and improved mechanical properties of Sn-Bi@C. The synthetic method is extended to dimer-like Sn-Pb@C and Sn-Ag@C heterostructures, which also exhibit the good cycle stability for sodium storage.
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