NaF–FeF2 nanocomposite: New type of Na-ion battery cathode material

Na-ion batteries (NIBs) are considered one of the most attractive alternatives for Li-ion batteries (LIBs) because of the natural abundance of Na and the similarities between the NIB technology and the well-established LIB technology. However, the discovery of high-performance electrode materials remains a key factor in the success of NIBs. Herein, we propose a new type of cathode material for NIBs based on a nanocomposite of an alkali metal fluoride (NaF) and a transition metal fluoride (FeF 2 ). Although neither of these components is electrochemically active with Na, the nanoscale mixture of the two can deliver a reversible capacity of ∼125 mAh/g in the voltage range of 1.2–4.8 V vs. Na/Na + via an Fe 2+ /Fe 3+ redox couple. X-ray absorption spectroscopy reveals that the reversible Na storage is aided by the F–ions due to the decomposition of NaF, which are absorbed on the surface of …