Biological phytic acid guided formation of monodisperse large-sized carbon@LiFePO4/graphene composite microspheres for high-performance lithium-ion battery cathodes

Large-sized porous glucose-derived carbon (C) and graphene (G) co-modified LiFePO4 (LFP) composite microspheres (C@LFP/G) have been successfully in situ synthesized by one-pot solvothermal and followed annealing process using biological phytic acid (PhyA) as phosphorus source. The loose and porous microspheres with diameters in the range of 5–12 μm are self-assembled by carbon coated LFP nano particles along with randomly embedded/distributed graphene sheets. The effect of PhyA dosage and carbon modification on morphology and electrochemical properties were investigated. The results indicated that PhyA dosage plays an important role in construction of the self-assembled three-dimensional spherical microstructures during hydrothermal process. A reasonable assembly process elucidating the formation of the different structure is provided based on the experimental results. Additionally, the effects of carbon modification were also investigated, which reflected that the graphene and glucose-derived carbon personate a synergistic effect in regulating the size of LFP primary nanoparticles. The typical large-sized C@LFP/G microspheres composite exhibited the best electrochemical properties with the discharge specific capacity of 163.7 mA h g−1 at 0.1 C, excellent rate capability and cycling performance. This method may be extended to prepare other spherical olivine structured materials with large size as cathode materials for lithium-ion batteries.