In situ Raman spectroscopy of LiFePO4: size and morphology dependence during charge and self-discharge.
Previous studies of the size dependent properties of LiFePO4 have focused on the diffusion rate or phase transformation pathways by bulk analysis techniques such as x-ray diffraction (XRD), neutron diffraction and electrochemistry. In this work, in situ Raman spectroscopy was used to study the surface phase change during charge and self-discharge on a more localized scale for three morphologies of LiFePO4: (1) 25 ± 6 nm width nanorods, (2) 225 ± 6 nm width nanorods and (3) ∼2 μm porous microspheres. Both the large nanorod and microsphere geometries showed incomplete delithiation at the end of charge, which was most likely caused by anti-site defects along the 1D diffusion channels in the bulk of the larger particles. Based on the in situ Raman measurements, all of the morphologies studied exhibited self-discharge with time. Among them, the smallest FePO4 particles self-discharged (lithiated) the fastest. While nanostructuring LiFePO4 can offer advantages in terms of lowering anti-site defects within particles, it also creates new problems due to high surface energies that allow self-discharge. The in situ Raman spectroscopy also showed that carbon coating did not provide significant improvement to the stability of the lithiated particles.
Department of Chemistry and Biochemistry, University of Texas at Austin, Austin, TX, USA.
Jing
J
Wu
Gopi Krishna Phani
GK
Dathar
Chunwen
C
Sun
Murali G
MG
Theivanayagam
Danielle
D
Applestone
Anthony G
AG
Dylla
Arumugam
A
Manthiram
Graeme
G
Henkelman
John B
JB
Goodenough
Keith J
KJ
Stevenson