Fabrication of PANI-coated ZnFe₂O₄ nanofibers with enhanced electrochemical performance for energy storage

We successfully combined electrospinning with in situ polymerization methods to synthesize the PANI-coated ZnFe₂O₄ nanofibers which possess the abundant pore structure. The lithium storage properties of PANI-coated ZnFe₂O₄ nanofibers as anode materials for lithium-ion batteries have been discussed for the first time. PANI nanoparticles were directly coated on the surface of the ZnFe₂O₄ nanofibers, increasing the electrical conductivity, and also acting as the protect shell to enhance the mechanical strength of material. The electrochemical performance showed that 15% PANI incorporated ZnFe₂O₄ composite nanofibers (ZP-15) exhibited the highest reversible capacity of 1142 mAhg⁻¹ after 50 cycles, which was much higher than that of pure ZnFe₂O₄ nanofibers (628 mAhg⁻¹), 10% PANI incorporated ZnFe₂O₄ composite nanofibers (ZP-10, 975 mAhg⁻¹), and 20% PANI incorporated ZnFe₂O₄ composite nanofibers (ZP-20, 536 mAhg⁻¹). Additionally, the ZP-15 composite nanofibers achieved outstanding cycling rate capacity of 852, 738, 609 and 539 mAhg⁻¹ with current densities range from 500 to 5000 mA g⁻¹, and exhibited a specific capacity of 1082 mAhg⁻¹ when the current reverted to 50 mA g⁻¹ from the high rate charge-discharge cycles. The enhanced electrochemical performance of PANI-coated ZnFe₂O₄ nanofibers can be attributed to the PANI providing a highly electrical conductive medium, which can promote electron transfer and facilitate the Li⁺ transport in the lithiation/delithiation process, also can reduce self-discharge; moreover, the PANI layer covered on the surface of ZnFe₂O₄ nanofibers can be as buffer matrix to restrain the stress of volume expansion to get stable structure.