Pilot-Scale Synthesis Sodium Iron Fluorophosphate Cathode with High Tap Density for a Sodium Pouch Cell

Sodium-ion batteries (SIBs) have attracted wide interest for energy storage because of the sufficient sodium element reserve on the earth; however, the electrochemical performance of SIBs cannot achieve the requirements so far, especially, the limitation of cathode materials. Here, a kilogram-scale route to synthesize Na₂ FePO₄ F/carbon/multi-walled carbon nanotubes microspheres (NFPF@C@MCNTs) composite with a high tap density of 1.2 g cm^-3 is reported. The NFPF@C@MCNTs cathode exhibits a reversible specific capacity of 118.4 mAh g^-1 at 0.1 C. Even under 5 C with high mass loading (10 mg cm^-2 ), the specific capacity still maintains at 56.4 mAh g^-1 with a capacity retention rate of 97% after 700 cycles. In addition, a hard carbon||NFPF@C@MCNTs pouch cell is assembled and tested, which exhibits a volumetric energy density of 325 Wh L^-1 and gravimetrical energy density of 210 Wh kg^-1 (base on electrode massing), and it provides more than 200 cycles with a capacity retention rate of 92%. Furthermore, the pouch cell can operate in an all-climate environment ranging from -40 to 80 °C. These results demonstrate that the NFPF@C@MCNTs microspheres are a promising candidate cathode for SIBs and facilitate its practical application in sodium cells.