Synthesis and properties of Co-doped LiFePO4 as cathode material via a hydrothermal route for lithium-ion batteries

Highlights: ► LiFe1−xCoxPO4/C cathode materials were synthesised by hydrothermal method under a reductive atmosphere. ► LiFe3/4Co1/4PO4 samples show a superior discharge capacity of 170 mAh/g at 0.1C. ► Co doping with large amount can increase the voltage of the Fe2+/3+ oxide couple. ► The amount of carbon coated onto the compound increases as Co doping amount rises. - Abstract: A series of olivine LiFe1−xCoxPO4 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 LiFe1−xCoxPO4. The electrochemical properties of the samples were studied by AC impedance spectroscopy and charge–discharge instruments at room temperature. The discharge capacity of LiFe3/4Co1/4PO4/C is 170 mAh/g at rate of 0.1 C. LiFe1−xCoxPO4 can achieve a higher discharge plateau (∼3.5 V) than does pure LiFePO4 (∼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–O band stabilises further as the doping amount increase, which is not beneficial to the lithium diffusion coefficient of the compound.