Sodium-ion batteries are on the verge of mass production, due to their cost effectiveness and special performances. Within this context, sodium iron pyrophosphate (NFP) has emerged as a promising cathode material for practical applications, owing to its facile synthesis and consistent product quality. In this work, two NFP variants with different sodium-to-iron ratios were synthesized via a ball-milling-assisted high-temperature solid-state reaction. To address the inherently poor electronic and ionic conductivity of these materials, carbon nanofibers were introduced to bridge the active material particles. The electrochemical performance and sodium storage mechanisms of both NFP variants were systematically investigated. Notably, the carbon-modified low-sodium iron pyrophosphate, denoted as N3.12FP/C, delivered a high specific capacity of 119.5 mAh·g−1 and exhibited excellent cycling stability and rate capability, retaining 89.3% of its initial capacity after 4000 cycles at a high current density of 20 C. Kinetic analyses via the galvanostatic intermittent titration technique (GITT) and electrochemical impedance spectroscopy (EIS) further reveal enhanced Na+ diffusion coefficients and suppressed charge transfer resistance, corroborating the improved reaction kinetics. Moreover, ex situ X-ray diffraction (XRD) and cyclic voltammetry (CV) elucidate the underlying sodium storage mechanism. These results suggest that N3.12FP/C is a promising cathode material for future sodium-ion batteries.
Ma et al. (Wed,) studied this question.