Large-scale low temperature fabrication of SnO2 hollow/nanoporous nanostructures: the template-engaged replacement reaction mechanism and high-rate lithium storage

Abstract

The morphology-controlled synthesis of SnO₂ hollow/nanoporous nanostructures (nanotubes, urchin-like morphologies and nanospheres) was achieved via a template-engaged replacement reaction at a mild temperature (lower than 80 °C). The formation mechanism of hollow interior and nanoporous walls for the obtained SnO₂ nanostructures (SnO₂ nanotubes were used as an example) was investigated based on TEM and HRTEM observations during different reaction stages. It is found that bridge voids firstly form at the MnO₂/SnO₂ interface, followed by the inward development of voids before the MnO₂ core is completely consumed. Two types of short-circuited galvanic cells, MnO₂/Mn²⁺∣SnO₂/Sn²⁺ and concentration cell-SnO₂/Sn²⁺ (interior)∣SnO₂/Sn²⁺ (exterior), are probably responsible for the formation of SnO₂ nanotubes and outward growth of SnO₂ along MnO₂. Moreover, the calculation result of the outer diameter of SnO₂ nanotubes is in good agreement with the observation results by SEM and TEM. When evaluated as anodes for lithium ion batteries (LIBs), the three SnO₂ nanostructures exhibit superior rate capability and cycling performance. Especially, SnO₂ nanotubes present the best rate capability: specific capacities of above 800 mA h g⁻¹ at 200 mA g⁻¹ and about 500 mA h g⁻¹ at 4000 mA g⁻¹ were achieved, respectively. Importantly, the 1D morphology of SnO₂ nanotubes can be well preserved after prolonged cycling at a relatively high current density, indicating good structural stability of the resulting nanotubes during the Li⁺ insertion/extraction process. These results indicate that the obtained SnO₂ hollow/nanoporous nanostructures would be promising anode materials for next-generation LIBs.