Synthesis, morphological analysis and electrochemical performance of iron hydroxyl phosphate as a cathode material for lithium ion batteries

Iron hydroxyl phosphate, with the formula Fe1.5(PO4)(OH), used as a cathode material in lithium ion batteries, is synthesised by a sample hydrothermal method. Scanning electron microscopy (SEM), X-ray diffraction and galvanostatical charge/discharge tests are employed to characterise the morphology, structure and electrochemical performance of the iron hydroxyl phosphate, respectively. FE-SEM shows that the morphologies are closely related to the hydrothermal temperatures at which they are synthesised. The morphologies, such as spherical, cubic, multi-armed and cross-like structures, could be easily regulated by adjusting the hydrothermal temperature. It is found that different morphologies of iron hydroxyl phosphate gave rise to different electrochemical performances. Compared to the others, iron hydroxyl phosphate spherical composites exhibit not only a high reversible capacity but also good cycling stability, with a reversible initial discharge specific capacity of around 176 mAh g−1 and a remaining 95% of the initial discharge specific capacity after 60 cycles at 0.1C. The improved electrochemical performance is attributed to the spherical morphology and smaller particle size, which increase the reaction interfaces and shorten the diffusion distance of the lithium ions.