Quenched Li0.6FePO4 As a Vehicle for Studying Phase Separation Kinetics in Li-Ion Battery Materials

Abstract

Olivine-type cathodes have asserted their ability to store energy efficiently in wide range of applications. Still, the phase transition process during charge and discharge raises questions regarding reactions rates, as the deintercallation/intercalation process via a phase transition mechanism is expected to affect ionic and electronic transport. In this study, the metastability of LixFePO4 solid solution is used to study the kinetics of the phase transition. Factors that affect the transformation of the metastable Li0.6FePO4 are reported, including preparation conditions and surface effects. Crystal structure dynamics were examined via X-ray diffraction (XRD) while more localized changes were revealed by attenuated total reflectance infrared spectroscopy (ATR-IR). These two techniques corroborate to distinguish the metastable solid solution phase relative to phase separation which emerges over time. Specifically, Reitveld refinement was used with the aim of detecting lithium rich and lithium poor phases as a function of time, resulting in a phase transition kinetic profile. In addition, lithium content was confirmed by flame emission spectrometry (AES). Recent results show how the phase separation is affected by the Li-ion battery chemistry as well as physical conditions. Importantly, surface effects were identified as crucial aspects in the kinetics of phase separation. The developed techniques serve as an experimental tool towards understanding Li0.6FePO4 solid solution.