Preparation and characterization of LiFe0.975Rh0.025PO4 nanorods using the hydrothermal method

An effective method for the synthesis of LiFe0.975Rh0.025PO4 nanorods to serve as a cathode material for lithium-ion batteries is described. During their preparation, L-lysine was used as the growth director of nanorods. The contribution from chloride ions to the formation of the unique nanorods was also investigated. The samples were characterized using X-ray diffraction, X-ray photoelectron spectroscopy, Mossbauer measurements, scanning electron microscopy, electronic conductivity measurements, and transmission electron microscopy. The pH of the solution played a key role in controlling the particle size of the samples. The sample prepared at a pH of 9.5 exhibited excellent electrochemical performance. It delivered an initial discharge capacity of 143.1 mAh g(-1), and a capacity fade of only 7.7% was observed after 200 cycles at 2.5 C over a voltage range of 2.0-4.2 V. Furthermore, its discharge capacity remained stable for values as high as 20 C. The excellent electrochemical performance of LiFe0.975Rh0.025PO4 nanorods can be attributed their unique nanorod structure, which limits the distance of lithium ion diffusion in the electrode material to the radius of the nanorods and decreases the surface-film resistance for the charge-transfer process.