Eco-Friendly Hydrothermal synthesis of LiFePO4/rGO nanocomposites: How Graphene Oxide Chemistry Shapes Structure and Conductivity?

LiFePO4 is a widely used lithium-ion battery cathode material owing to its environmental benignity, low cost, safe ~3.45 V operating voltage, and thermal stability. However, its low electronic conductivity and limited lithium-ion diffusion restrict its electrochemical performance. In this work, an eco-friendly hydrothermal route was developed to synthesize LiFePO4/rGO nanocomposites at 140 °C for 20 h using an aqueous three-reagent system. Unlike most reported studies, where graphene derivatives are added after LiFePO4 formation, this method enables in situ interaction between GO and the precursor system during composite formation, promoting effective interfacial coupling. To assess the role of GO chemistry, composites from the conventional Hummer's method were compared with those from an eco-friendly, NaNO3-free oxidation route. Materials were characterized by Rietveld-refined XRD, Raman spectroscopy, XPS, SEM, and electrical measurements. Raman analysis showed a lower ID/IG ratio for the eco-friendly composite (0.52 vs. 1.03), indicating higher graphitization and fewer defects. XRD confirmed phase-pure olivine LiFePO4 in all samples, with the eco-friendly LiFePO4/rGOFR composite showing enhanced crystallinity without compromising the olivine structure. Electrical measurements revealed conductivities of ~10⁻⁴ S/cm, a five-order-of-magnitude improvement over pristine LiFePO4. These findings highlight the importance of GO chemistry in producing highly conductive LiFePO4/rGO composites for advanced energy storage.