Improved capacity and cycling stability of SnO₂ nanoanode induced by amorphization during cycling for lithium ion batteries

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.