Nano-assembled Na2FePO4F/carbon nanotube multi-layered cathodes for Na-ion batteries

The electrochemical performance of multi-layered cathodes containing alternately arranged Na2FePO4F nanopartides and amino-functionalized carbon nanotubes (CNTs) for Na-ion batteries has been investigated. The Na2FePO4F/CNT multi-layered cathodes are fabricated using a layer-by-layer (LbL) nano-assembly technique, which leads to a three-dimensional porous structure that may contribute to fast Na-ion transport. The highly intertwined CNT layers serve as an electrical conductive network and the abundant pores serve as ionic conductive pathways. Evidences of enhanced electric and ionic transport are provided by impedance spectroscopy data, which show a significantly decreased resistance compared to traditional batteries. The unique multi-layered Na-ion cathodes are found to deliver 100 mA hg(-1) reversible capacity at a rate of 0.4 C and 80 mA hg(-1) at 0.8 C, and to maintain 60% of capacity at 2 C. After 400 cycles at 0.4 C, the cells still provide 77.8 mA hg(-1) capacity, corresponding to 74% capacity retention. (C) 2015 Elsevier B.V. All rights reserved.