Synthesis and properties of Co-doped LiFePO_4 as cathode material via a hydrothermal route for lithium-ion batteries

摘要

A series of olivine LiFe_(1-x)Co_xPO_4 composites were synthesised by a hydrothermal route under reductive atmosphere. The structure of the prepared samples was characterised by X-ray diffraction. Morphology, particle size, and elemental concentration were observed by scanning electron microscopy, high-resolution transmission electron microscopy, and corresponding EDS mapping, respectively. Raman spectroscopy was employed to study the surface information of the carbon-coated LiFe_(1-x)Co_xPO_4. The electrochemical properties of the samples were studied by AC impedance spectroscopy and charge-discharge instruments at room temperature. The discharge capacity of LiFe_(3/4)Co_(1/4)PO_4/C is 170mAh/g at rate of 0.1 C. LiFe_(1-x)Co_xPO_4 can achieve a higher discharge plateau (~3.5V) than does pure LiFePO_4 (~3.4 V). The results indicate that the Co-doped sample exhibits improved electrochemical performance at low discharge rates. However, XPS results show that the Li-0 band stabilises further as the doping amount increase, which is not beneficial to the lithium diffusion coefficient of the compound.