Interconnected\nCoFe₂O₄–Polypyrrole Nanotubes as Anode\nMaterials for High Performance Sodium Ion Batteries

Abstract

CoFe₂O₄-coated polypyrrole (PPy) nanotubes (CFO-PPy-NTs) with three-dimensional\n(3-D) interconnected networks have been prepared through a simple\nhydrothermal method. The application has been also studied for sodium\nion batteries (SIBs). The finely crystallized CoFe₂O₄ nanoparticles (around 5 nm in size) are uniformly grown on\nthe PPy nanotubes. When tested as anode materials for SIBs, the CFO-PPy-NT\nelectrode maintains a discharge capacity of 400 mA h g^–1 and a stable Coulombic efficiency of 98% after 200 cycles at 100\nmA g^–1. Even at a higher current density of 1000\nmA g^–1, the composite can still retain a discharge\ncapacity of 220 mA h g^–1 after 2000 cycles. The\nsuperior electrochemical performance could be mainly ascribed to the\nuniform distribution of CoFe₂O₄ on the 3-D matrix\nof PPy interconnected nanotubes, which favors the diffusion of sodium\nions and electronic transportation and also buffers the large volumetric\nexpansion during charge/discharge. Thereby our study suggests that\nsuch CFO-PPy-NTs have great potential as an anode material for SIBs.