Easy approach of highly electrochemical-active maricite NaFePO4 cathode for low cost and high rate sodium-ion batteries

Well-crystallized maricite NaFePO4 is thermodynamically stable but electrochemically inactive toward sodium owing to the close packed framework. An efficient activation-approach is to construct amorphous composites with carbon by the complex and energy-intensive synthetic process. Here, a facile approach was proposed by the combination of low-temperature sintering and ball milling, which is environmentally friendly and suitable for scalable synthesis. Quasi-amorphous maricite NaFePO4 was first prepared via reducing the calcination temperature to 350 °C. Amorphous composite NaFePO4/C was further obtained by ball milling of NaFePO4-350 °C with super P, which delivers a reversible capacity of 134 mAh g−1, closing to its theoretical capacity. More impressively, the NaFePO4/C electrode still demonstrates decent capacity-retention of ∼75.4% over 1000 cycles, which is encouraging for future research. Pairing with hard carbon anode, the (+)NaFePO4/C//HC(−) sodium-ion full cell delivers outstanding power density (169.9 Wh kg−1 calculated based on the total mass of positive and negative electrodes) and excellent cycling stability (84.5% capacity retention after 500 cycles at 5C), exhibiting powerful competitiveness compared with previously reported NaFePO4 based sodium-ion full cells. These results demonstrate the practical potential of maricite NaFePO4 cathode through low-temperature sintering.