Synthesis of nanocrystals and morphology control of hydrothermally prepared LiFePO4

Abstract

Lithium transition metal phosphate olivines such as LiFePO₄ have been recognized as very promising electrodes for lithium-ion batteries because of their energy storage capacity combined with electrochemical and thermal stability. A key issue in these materials is to determine the synthetic conditions for optimum control of particle size and morphology, and ideally to find those that result in nanocrystalline products. Here, we report a full study that examines the synthesis of the material via hydrothermal methods to give single phase nanocrystalline materials for LiFePO₄ and LiMnPO₄, and their solid solutions with Mg²⁺. A reaction mechanism is proposed. Variation of the synthesis parameters showed that increasing reactant concentration strongly favours the formation of nanocrystalline products, but as less defect-free materials are formed at temperatures above 180 °C, and ideally above 200 °C, control of nucleation and growth can (and should) also be effected using polymeric or surfactant additives. The nature of the precursor and carbon-containing additives in the autoclave also have profound effects on morphology and the electrochemical properties.