Thermal annealing dynamics of carbon-coated LiFePO4 nanoparticles studied by in-situ analysis

The thermal behavior of core-shell carbon-coated lithium iron phosphate (LiFePO4-C) nanoparticles made by flame spray pyrolysis (FSP) during annealing was investigated by in-situ transmission electron microscopy (TEM), in-situ X-ray powder diffraction (XRD) as well as ex-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Crystallization of the initially glassy LiFePO4-C nanoparticles starts at quite low temperatures (T=400 degrees C), forming single crystals inside the confinement of the carbon shell. Upon increasing the temperature to T >= 700 degrees C, LiFePO4 starts to diffuse through the carbon shell resulting in cavities inside the mostly intact carbon shell. By increasing the temperature further to T >= 800 degrees C, the initial core-shell morphology converts into open carbon shells (flakes and cenospheres)and bulky LiFePO4 particles (diameter in the range 300-400 nm), in agreement with ex-situ experiments. (C) 2016 Elsevier Inc. All rights reserved.