The effect of ammonia concentration on the morphology and electrochemical properties of LiFePO4 synthesized by ammonia assisted hydrothermal route

The LiFePO4/C composites with different morphology are synthesized by an ammonia assisted hydrothermal method at various ammonia concentrations (from 0 to 1.6 mol L−1) using inexpensive Fe(NO3)3 and LiOH as raw materials. The influences of the ammonia concentration on the structure, morphology and electrochemical properties of the LiFePO4/C composite are investigated by X-ray diffraction (XRD), scanning electron microscope (SEM), galvanostatic charge/discharge tests and electrochemical impedance spectroscopy (EIS). The results demonstrate that the ammonia concentrations markedly impact the morphology and electrochemical properties of the LiFePO4/C. With the change of ammonia concentrations, the LiFePO4/C synthesized with 0.4 mol L−1 ammonia shows the smallest average particle size, the most uniform microsphere particle distribution and relatively high tap density (1.27 g cm−3). In addition, the sample appears a high discharge capacity of 153.9 mAh g−1 at the first cycle as well as stable cycling performance (the capacity was not almost changed till 100 cycles) at a rate of 1C (170 mA g−1). Moreover, it exhibits a good rate capability and still shows a high discharge capacity of over 125 mAh g−1 even at a rate of 5C.

► The LiFePO4/C is synthesized by a ammonia assisted hydrothermal method at various ammonia concentrations.
► The concentrations of ammonia affect the morphology and performance of samples.
► The LiFePO4/C microspheres synthesized with 0.4 mol L−1 ammonia exhibit excellent electrochemical performance.
► The ammonia assisted hydrothermal method is a promising process for preparing high performance LiFePO4/C.