Solvothermal synthesis of monodisperse LiFePO₄ micro hollow spheres as high performance cathode material for lithium ion batteries

A microspherical, hollow LiFePO₄ (LFP) cathode material with polycrystal structure was simply synthesized by a solvothermal method using spherical Li₃PO₄ as the self-sacrificed template and FeCl₂·4H₂O as the Fe²⁺ source. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) show that the LFP micro hollow spheres have a quite uniform size of ∼1 μm consisting of aggregated nanoparticles. The influences of solvent and Fe ²⁺ source on the phase and morphology of the final product were chiefly investigated, and a direct ion exchange reaction between spherical Li₃PO₄ templates and Fe²⁺ ions was firstly proposed on the basis of the X-ray powder diffraction (XRD) transformation of the products. The LFP nanoparticles in the micro hollow spheres could finely coat a uniform carbon layer ∼3.5 nm by a glucose solution impregnating-drying-sintering process. The electrochemical measurements show that the carbon coated LFP materials could exhibit high charge-discharge capacities of 158, 144, 125, 101, and even 72 mAh g^-1 at 0.1, 1, 5, 20, and 50 C, respectively. It could also maintain 80% of the initial discharge capacity after cycling for 2000 times at 20 C.