7Li MAS NMR studies of Li4P2O7 and LiFePO4 materials

Abstract

7Li Magic Angle Spinning (MAS) NMR spectroscopy has been used to study the lithium local environments in Li4P2O7 and LiFePO4 materials. The purpose of this study was to know the structure of the solid electrolyte interphase (SEI) in lithium ion cells composed of LiFePO4 as cathode material. Li4P2O7 and LiFePO4 were prepared by a solid-state reaction. The 7Li MAS NMR experiments were carried out at variable temperatures in order to observe the local structure changes at the temperatures in Li4P2O7 system. The 7Li MAS NMR spectra of in Li4P2O7 indicate that the lithium local environments in Li4P2O7 were not changed in the temperature range between 27℃ and 97℃ . Through this work, we confirmed that the small amount of Li4P2O7 less than 5.0 wt% in LiFePO4 could be clearly measured by the 7Li MAS NMR spectroscopy at high spinning rate over than 11 kHz.