Comparison of Microwave Assisted Solvothermal and Hydrothermal Syntheses of LiFePO4/C Nanocomposite Cathodes for Lithium Ion Batteries

摘要

Highly crystalline LiFePO4 nanorods have been synthesized within a short reaction time of 5—15 min at <300 °C by a novel microwave-solvothermal (MW-ST) process and a microwave-hydrothermal (MS-HT) process. In order to improve the electrical conductivity, both an ex situ carbon coating by heating at 700 °C with sucrose the LiFePO4 obtained by the MW-ST method and an in situ carbon coating by carrying out the MW-HT process in presence of glucose (MW-HT carbonization) followed by heating at 700 °C have been pursued. The products have been characterized by X-ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, and charge—discharge measurements in hfhium cells. The MW-ST method offers smaller size nanorods (25 ± 6 nm width and up to 100 nm length) compared to the MW-HT method (225 ± 6 nm width and up to 300 nm length). Annealing at 700 °C improves the rate capability and cyclability significantly without much particle growth due to an improvement in the structural order of carbon and electronic conductivity. Moreover, the LiFePCVC nanocomposite obtained by the MW-ST method offers higher initial discharge capacity than that obtained by the MW-HT method due to a smaller particle size, illustrating that both lithium ion diffusion and electronic conductivity play a critical role in controlling the electrochemical properties.