Controllable synthesis and morphology evolution of hierarchical LiFePO4 cathode materials for Li-ion batteries

Abstract

Hierarchical LiFePO4 crystals self-assembled with subunits were successfully synthesized via a simple hydrothermal method. The X-ray diffraction (XRD) curve indicates the highly crystalline nature of the prepared samples. The field-emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) images reveal that with increased KOH concentrations, the LiFePO4 products evoluted from microspheres self-assembled with microwires to spindle-like structures self-assembled with micro-needles and eventually to flower-like hierarchical nanostructures self-assembled with nanorods. The crystal growth mechanism could be explained by the synergetic effect of pH value and the surface-adsorbed K+ ions. The OH– anions represent pH value dominate the hierarchical morphology under both low and high KOH concentration, while K+ ions play the major role in synthesizing monodispersed LiFePO4 nanorods under medium KOH concentration. Moreover, charge–discharge curves and CV measurements demonstrated good reversible capacities and stable cycle performances of the LFP/C samples.