| Summary: | Conversion reactions of SnO2-based anode materials have recently been confirmed reversible by using well-designed nanostructures, while the detailed mechanism during charging and discharging is still ambiguous. Unwrapping the real mechanism is helpful to design high-performance SnO2-based anode materials. In this work, we designed and fabricated a nanoarchitecture of ultrafine SnO2 (3–5 nm) anchored on the surfaces of carbon nanofibers (denoted as u-TOCNFs). The u-TOCNFs electrode exhibits high reversible capacity of 1006.4 mAh·g−1, high initial Coulombic efficiency of 71.3% and good cycle stability mainly due to good dispersion of ultrafine SnO2 on the conductive carbon nanofibers. The structure evolution is investigated by TEM observations that confirm the presence of amorphous SnO2 on the delithiated nanoanode at 1.28 V after 100 cycles. Charge/discharge induced amorphization of SnO2 nanocrystals is firstly observed that readily explain the capacity increasing around 100 cycles. In particular, we propose the mechanism of reversible conversion reactions of SnO2 and Sn induced by the amorphization of ultrafine SnO2 during lithiation/delithiation. We believe that it is a new direction to study SnO2-based anode materials to improve the electrochemical performance for lithium ion batteries. Keywords: Ultrafine SnO2, Reversible conversion, Amorphization, Lithium ion battery
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