3-D structured SnO₂-polypyrrole nanotubes applied in Na-ion batteries

SnO₂-coated polypyrrole (PPy) with a three-dimensional (3-D) structured nanotube network has been prepared via a facile hydrothermal method and tested as an anode material for Na-ion batteries. The crystalline SnO₂ nanoparticles (less than 25 nm in size) are distributed uniformly on the surfaces of the PPy tubes. When it is used as an anode material for sodium-ion batteries (SIBs), the composite electrode can deliver a good reversible capacity of nearly 288 mA h g^-1 when discharging at 100 mA g^-1, with more than 69.1% capacity retention and stable coulombic efficiency of 99.6% after 150 cycles. The good electrochemical performance compared to the 151 mA h g^-1 achieved by bare SnO₂, which was fabricated by the same method in the absence of PPy, could be mainly attributed to the good dispersion of SnO₂ on the 3-D matrix of PPy tubes, which facilitates the diffusion of Na⁺ ions and buffers the large volumetric changes during charge/discharge. Our results suggest that such SnO₂/carbonaceous composites would be good anode candidates for SIBs.