Spray-drying synthesis of Na2FePO4F/carbon powders for lithium-ion batteries

• Pure Na2FePO4F/carbon powders were prepared by spray-drying.
• As-sprayed powders were calcined at 600 °C in argon for 12 h.
• Mössbauer spectroscopy detects 98% Fe (II) and 2% Fe (III) in the calcined powder.
• Particles in as-sprayed and calcined powders are hollow spheres with thin shells.
• The Na2FePO4F/C powder exhibits a discharge capacity of 110 mAh/g at C/15 rate.

Sodium iron fluorophosphate Na2FePO4F is a candidate positive electrode material for both lithium-ion batteries and sodium-ion batteries. We report the synthesis of Na2FePO4F/carbon powders by the simple and easily up-scalable technique of spray-drying. An aqueous solution containing citric acid as a carbon source was sprayed in a pilot-scale spray-dryer. Heat treatment at 600 °C in argon for 12 h was found appropriate to obtain single-phase Na2FePO4F; only 1.8% of Fe (III) was detected by iron-57 Mössbauer spectroscopy. When cycled against lithium, the discharge capacity reached 110 mA h/g at C/15 rate.