Nanoscale characteristics of practical LiFePO4 materials - Effects on electrical, magnetic and electrochemical properties

LiFePO4 (LFP) is one of the important commercial battery materials, as such, many efforts have been made to understand its electrical and ionic conductivities and electrochemical properties. In this study, we have investigated electrochemical, electrical and magnetic properties of carbon coated LFP down to cryogenic temperatures. The fact that the practical material really consists of a core-shell structure with a shell of delithiated material and carbon coating determines the measured properties, which are often mistakenly attributed to pure LFP core behaviour. An electronic resistivity drop (11 ± 0.5% based on the resistivity at room temperature), preceded by a gradual increase feature between 100 and 30 K, was observed when the temperature was below the Néel temperature at low applied currents, indicating a likely interaction between the magnetic configuration of the core LFP and electronic transport mechanisms. Metallic Fe3P was precipitated on the samples surfaces after annealing at high temperature in Argon. The existence of Fe3P was found to significantly improve the electronic conductivity but it took a toll on the electrochemical performance.