A Sol-Gel Derived Sodium Iron Pyrophosphate Sulfate Cathode Material for High-Performance Sodium-Ion Batteries

Sodium-ion batteries (SIBs) have shown significant potential for application in large-scale energy storage systems due to their abundance of sodium resources, cost-effectiveness, and environmental compatibility. Polyanionic cathode materials, with their unique crystal structure and high theoretical specific capacity, have become a focus of research in SIBs. In this study, we develop a novel pyrophosphate- and sulfate-containing Na_2+2xFe_2-xP₂O₇SO₄ (NFPS) polyanionic chemical material featuring a three-dimensional open-framework structure for the first time via the sol-gel method. The diffraction peaks are successfully indexed to the Pna2₁ orthorhombic system for NFPS. In situ carbon-coated NFPS cathode materials are prepared successfully with a lower-cost biomass carbon source. The cathode material delivers an initial specific capacity of up to 101.46 mAh g^-1 at 0.05 C and retains 83.56% of its capacity after 500 cycles at 5 C, demonstrating its feasibility for application in SIBs. This study provides an innovative NFPS polyanionic material and methods for developing high-performance cathode materials for SIBs, which are expected to promote the application of SIBs in large-scale energy storage.