Propylene oxide-assisted fast sol-gel synthesis of mesoporous and nano-structured LiFePO4/C cathode materials

LiFePO4/C nanocomposites are synthesized by a propylene oxide-assisted fast sol-gel method using FeCl3, LiNO3, NH4H2PO4, and sucrose as the starting materials. It was found that after adding propylene oxide into the solution containing the starting materials, a monolithic jelly-like FePO4 gel containing lithium and carbon source is generated in a few minutes without controlling the pH value of the solution and a time-consuming heating process. Propylene oxide plays a key role in the fast generation of the precursor gel. The final products of LiFePO4/C are obtained by sintering the dry precursor gel. The structures, micro-morphologies, and electrochemical properties of the LiFePO4/C composites are investigated using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, nitrogen adsorption-desorption analysis, electrochemical impedance spectrum, and charge-discharge cycling tests. The results indicate that the LiFePO4/C composite prepared by sintering the precursor gel at 680 A degrees C for 5 h is about 30 nm in size with a meso-porous structure (the main pore size distribution is around 3.4 nm). It delivers 166.7 and 105.8 mAh g(-1) at 0.2 and 30 C, respectively. The discharge specific capacity is 97.8 mAh g(-1) even at 40 C. The cycling performance of the prepared LiFePO4/C composite is stable. The excellent electrochemical performance of the LiFePO4/C composite is attributed to the nano-sized and mesoporous structure of LiFePO4/C and the in-situ surface coating of the carbon. It was also found that propylene oxide is crucial for the generation of mesoporous and nano-structured LiFePO4/C.