A complete study of amorphous iron phosphate structure

• The majority of Fe irons are in tetrahedral environments in amorphous FePO4.
• An MD model of amorphous FePO4 showed reasonable similarity to XRD results.
• The Fe environment in amorphous LiFePO4 is different than that in amorphous FePO4.
• The Li was found to be coordinated to an average of three oxygen atoms at ~ 1.9 Å.

In-depth structural studies have been carried out on amorphous FePO4 prepared by two different methods, and on amorphous LiFePO4 prepared by electrochemical insertion of Li. The local environment of Fe in these samples was investigated using Mössbauer spectroscopy and X-ray absorption spectroscopy. X-ray and neutron diffraction and transmission electron microscopy have been applied to elucidate the first complete structural study of these materials. The Fe environment in amorphous FePO4 was found to be similar to that in quartz FePO4 where every Fe is surrounded by four oxygen atoms. However, the Fe environment in amorphous LiFePO4 is affected by the appearance of Fe metal in this sample as a consequence of Li insertion. Small angle scattering measurements confirmed the presence of nm-scale internal structure in the amorphous FePO4 prepared by thermal decomposition and in amorphous LiFePO4.