Singular Structural and Electrochemical Properties in Highly Defective LiFePO₄ Powders

Highly defective LiFePO 4 powders were synthesized via a modified version of the coprecipitation in aqueous medium method using oxidizing experimental conditions. A pure olivine phase containing 44 at. % of Fe 3+ was obtained after only 10 min at 108 °C, and the evolution of the structure and purity was followed during reaction. The nature of the native defects and their influence on the crystallographic structure and on the electrochemical reaction mechanisms were thoroughly studied by a combination of ex situ and in situ methods, using high-resolution transmission electron microscopy, inductive coupled plasma, X-ray diffraction, and Mössbauer spectroscopy. The high concentration of defects induced a unit-cell volume 4 Å 3 smaller than that of stoichiometric LiFePO 4, with a complete cationic redistribution over the M1 and M2 crystallographic sites, as well as a completely new electrochemical signature. A precise structural model during electrochemical operation of the pristine defective LiFePO 4 was built.