Synergistic enhancement of Li 2 FeSiO 4 cathode material via Sn (IV) and nitrogen-doped rGO co-doping strategy for lithium-ion batteries

Abstract

To address the intrinsic limitations of Li₂FeSiO₄ (LFS) cathode materials, including low electronic and ionic conductivity, a synergistic co-doping strategy was employed. This approach combined Sn(IV) substitution at the Si sites with nitrogen-doped reduced graphene oxide (N-rGO) nanosheets to simultaneously improve multiple electrochemical parameters. While single dopants or additives typically only improve a specific aspect of cathode performance, this dual-doping design enabled a comprehensive improvement in both charge transfer and lithium-ion diffusion kinetics. N-rGO was synthesized using a microwave-assisted method, followed by the incorporation of Sn(IV) using a solid-state method. Band gap was evaluated using diffuse reflectance spectroscopy (DRS). Structural, morphological, and chemical properties were characterized using powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Raman analysis, field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET) spectroscopy, and X-ray photoelectron spectroscopy (XPS). Electrochemical investigations, including cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), demonstrated significantly reduced charge transfer resistance and improved redox kinetics. The 4Sn-LFS/NG sample (1% Sn and 5 wt% N-rGO) delivered a high initial discharge capacity of 266.9 mAhg⁻¹, significantly exceeding the original LFS (143.6 mAhg⁻¹). These improvements are due to the synergistic effects of double doping, which reduced the band gap and improved both ionic and electronic pathways. The results demonstrate that the 4Sn-LFS/NG nanocomposite is a promising cathode candidate for next-generation lithium-ion batteries with superior electrochemical performance.

Graphical Abstract