Real-time synchrotron powder X-ray diffraction study of the antisite defect formation during sub- and supercritical synthesis of LiFePO4and LiFe1−xMnxPO4nanoparticles

Abstract

In situsynchrotron powder X-ray diffraction (PXRD) is used to study the formation of LiFePO4nanoparticles during hydrothermal synthesis from LiOH, H3PO4, and two different iron precursors, FeSO4and (NH4)2Fe(SO4)2. Furthermore, the synthesis of Li(Fe1−xMnx)PO4(x= 0.25, 0.50 and 0.75) from LiOH, H3PO4and FeSO4/MnSO4is studied. The reactions involve an unknown intermediate phase, which is not the previously observed intermediate NH4FePO4·H2O. The intermediate phase quickly transforms into LiFePO4and Li(Fe1−xMnx)PO4even at rather low temperatures. The presence of ammonium enhances the formation of LiFePO4, and it also leads to a significant reduction in the concentration of Li–Fe antisite defects. Thein situPXRD technique allows one to follow the influence of time, temperature and manganese doping on the antisite defect concentration, and it is shown that even under supercritical conditions a reaction time of several minutes is required to suppress the defects. This makes flow synthesis of defect-free LiFePO4and Li(Fe1−xMnx)PO4nanoparticles challenging.