Defect chemistry of phospho-olivine nanoparticles synthesized by a microwave-assisted solvothermal process

•LiFePO4 nanopowders synthesized by a microwave-assisted solvothermal process.•Defects directly observed by aberration-corrected HAADF STEM imaging.•Antisite defects present from synthesis at 255 and 275 °C.•Defects present from higher temperature synthesis than previously reported.•Powder diffraction data have been analyzed in detail for various defect models.

Nanocrystalline LiFePO4 powders synthesized by a microwave-assisted solvothermal (MW-ST) process have been structurally characterized with a combination of high resolution powder neutron diffraction, synchrotron X-ray diffraction, and aberration-corrected HAADF STEM imaging. A significant level of defects has been found in the samples prepared at 255 and 275 °C. These temperatures are significantly higher than what has previously been suggested to be the maximum temperature for defect formation in LiFePO4, so the presence of defects is likely related to the rapid MW-ST synthesis involving a short reaction time (∼5 min). A defect model has been tentatively proposed, though it has been shown that powder diffraction data alone cannot conclusively determine the precise defect distribution in LiFePO4 samples. The model is consistent with other literature reports on nanopowders synthesized at low temperatures, in which the unit cell volume is significantly reduced relative to defect-free, micron-sized LiFePO4 powders.

Graphical abstractTemperature-dependent antisite defect formation has been observed in nanocrystalline LiFePO4 powders synthesized by a microwave solvothermal process, using high resolution diffraction and STEM imaging.Figure optionsDownload full-size imageDownload as PowerPoint slide