Achieving highly electrochemically active maricite NaFePO4 with ultrafine NaFePO4@C subunits for high rate and low temperature sodium-ion batteries

Maricite NaFePO4 (NFP) as cathode for sodium-ion batteries has attracted much attention because of the high theoretical capacity (155 mA h g(-1)) and simple synthetic process. However, electrochemically active maricite NFP is greatly dependent on the design of the nanostructure. Highly dispersed maricite NFP nanoclusters (NFPNCs) with ultrafine NFP@C subunits (3 nm) are designed and synthesized by a facile method. The unique ultrafine NFPNCs nanostructure makes electrochemically inactive maricite NFP change to highly active amorphous phase due to the ultrafine nanosize effect. The NFPNCs based cathode displays ultrahigh capacity (149.2 mA h g(-1) at 0.2C), excellent rate performance (75.7 mA h g(-1) at 5 degrees C) and superior cycling performance (91.3 mA h g(-1) at 10C after 5000 cycles with 95.0% retention). Even at low temperature (-10 and -20 degrees C), the NFPNCs still exhibit 85.5% and 75.8% capacity retention at -10 and -20 degrees C, respectively, in comparison to that of 25 degrees C. Furthermore, when coupled with hard carbon anode, the fabricated sodium-ion full batteries also exhibit high capacity, splendid cycling and rate properties. The ultrafine NFP@C subunits shorten Na+/electron diffusion pathways and provide high electrical conductivity, leading to high rate property and outstanding low temperature application.