Development of Na2FePO4F/Conducting-Polymer composite as an exceptionally high performance cathode material for Na-ion batteries

Na2FePO4F encircled by a nanolayer composed of a conductive polymer, poly(3,4-ethylenedioxythiophene) (PEDOT), is prepared using a simple low-temperature process, and X-ray diffraction analysis indicates that the Na2FePO4F–PEDOT composite is the pure phase without any impurities. The existence and uniform encapsulation of PEDOT on the surface of the Na2FePO4F particles are clearly confirmed through Fourier-transform infrared spectroscopy and transmission electron microscopy. The PEDOT coating results in remarkably enhanced electrochemical performance compared with that of pristine Na2FePO4F. At C/5 (1C = 124 mA g−1), the Na2FePO4F–PEDOT composite retains a specific capacity of ∼123.1 mAh g−1, which is close to its theoretical capacity. Even at 10C, the Na2FePO4F–PEDOT composite delivers a capacity of ∼76.1 mAh g−1, which is ∼10 times higher than that of pristine Na2FePO4F under the same conditions. Furthermore, the Na2FePO4F–PEDOT composite maintains ∼70% of its initial discharge capacity over 700 cycles at 1C.