Surface effects on electrochemical properties of nano-sized LiFePO4

LiFePO4 has won the challenge to be the active element for the positive electrode of Li-ion batteries for electromobility. In an attempt to optimize the electrochemical performance, efforts have been made to reduce the size of the particles, so that the electrons and Li+ ions have a reduced path to travel inside the material. However, when the size decreases below 100 nm, surface effects become increasingly important, and can eventually dominate the physical and the chemical properties. The purpose of this work is to review them and their implications, involving sensitivity to exposure to humidity, and separate between surface disorder effects, impurities and intrinsic properties. This goal is achieved by the combination of different techniques to characterize the particles, including X-ray diffraction, electron microscope imaging, optical spectroscopy, and magnetism.