Development of High-Performance Iron-Based Phosphate Cathodes toward Practical Na-Ion Batteries.

Iron-based phosphate cathode of NaFe(PO)(PO) has been regarded as a low-cost and structurally stable cathode material for Na-ion batteries (NIBs). However, their practical application is greatly hindered by the insufficient electrochemical performance and limited energy density. Here, we report a new iron-based phosphate cathode of NaFe(PO)(PO) with the intergrown heterostructure of the maricite-type NaFePO and orthorhombic NaFe(PO)(PO) phases at a mole ratio of 0.5:1. Benefited from the increased composition ratio and the spontaneous activation of the maricite-type NaFePO phase, the as-prepared NaFe(PO)(PO) composites deliver a reversible capacity over 130 mA h g and energy density close to 400 W h kg, which is far beyond that of the single-phase NaFe(PO)(PO) cathode (∼120 mA h g and ∼350 W h kg). Moreover, the kg-level products from the scale-up synthesis demonstrate a stable cycling performance over 2000 times at 3 C in pouch cells. We believe that our findings could show the way forward the practical application of the iron-based phosphate cathodes for NIBs.