Structure and Vibrational Dynamics of NASICON-Type LiTi₂(PO₄)₃

Abstract

Small single crystals of NASICON-type LiTi2(PO4)3 of high quality were grown by means of long-term annealing of polycrystalline specimens synthesized using conventional solid state reaction. A thorough study of their structural properties and vibrational dynamics was carried out by means of an integrated experimental and theoretical approach. A single-crystal X-ray diffraction analysis at room temperature allowed us to determine the precise crystal structure and the anisotropic displacement parameters of all atoms. In addition, all the 25 independent components of the polarizability tensor, expected on the basis of the group theory for the LiTi2(PO4)3 crystal, were observed using polarized Raman spectroscopy in backscattering geometry on a microcrystal, properly oriented by a micromanipulator. Thus, all the expected Raman modes have been unambiguously identified by determining both their wavenumber and symmetry throughout an accurate analysis of the spectral profiles observed in the different polarization configurations. Finally, these experimental findings were fully corroborated by the results of first-principles calculations performed to determine Raman and infrared vibrational modes

STEM‐EELS analysis of the interface structures of composite ASS‐LIB electrodes fabricated via aerosol deposition

“…In contrast, the spectral component (cʹ) suggested a smaller relative Ti/O ratio, and the O‐K ELNES of component (cʹ) exhibited a small pre‐peak with no characteristic shoulder at the lower energy side (the enlarged details are shown in Figure ) as was seen for component (aʹ) of pristine LATP particles (in Figure ). In addition, a characteristic peak appears in the low‐loss spectra (see Figure ), which has been reported to be a signature of partially or fully delithiated states in lithium iron phosphate olivine structures with tetrahedral PO 4 and octahedral TiO 6 units . It should be noted that the Ti‐L 2,3 white‐line peaks of Figure (cʹ) exhibited slight splitting (seen as small shoulders), suggesting partial crystallization rather than an amorphous structure, as also suggested by the nonuniform contrast of the Ti map in Figure and consistent with the selected area diffraction pattern in Figure .…”

“…In addition, a characteristic peak appears in the low-loss spectra (see Figure S3), which has been reported to be a signature of partially or fully delithiated states in lithium iron phosphate olivine structures 26 with tetrahedral PO 4 and octahedral TiO 6 units. 25 It should be noted that the Ti-L 2,3 white-line peaks of Figure 4(cʹ) exhibited slight splitting (seen as small shoulders), suggesting partial crystallization rather than an amorphous structure, as also suggested by the nonuniform contrast of the Ti map in Figure S2 and consistent with the selected area diffraction pattern in Figure S4. This phase is hereafter termed Li-deficient and partially crystallized LATP (Li def /pc-LATP).…”

“…The O‐K spectra of a series of representative LIB materials with different local structures were recently investigated and reported, which helped interpret the present results. The main component in the thicker region (spectrum (cʹ)) was derived from Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 , the NASICON structure having the tetrahedral PO 4 and octahedral TiO 6 units similar to LiFePO 4 or LiCoPO 4 olivine structures, where the tetravalent titanium (Ti 4+ ) is partially replaced by the equivalent amount of Al 3+ and Li + to ensure local electrical neutrality. The O‐K ELNES of (cʹ) exhibits a characteristic shoulder (indicated by an arrow) and no appreciable peak structure between ZLP and the first plasmon peak around 7 eV (Figure ), suggesting that Figure C and the spectrum (cʹ) correspond to a lithiated state …”

Solid-State Electrolytes for Lithium-Ion Batteries: Fundamentals, Challenges and Perspectives

“…Of these NASICON-type conductors, iso-structural LiM 2 (PO 4 ) 3 (M = Zr, Ti, Hf, Ge or Sn) was first reported in 1977 in which the skeletons consisting of MO 6 octahedra and PO 4 tetrahedra sharing oxygen atoms ( Fig. 3) [36]. These LiM 2 (PO 4 ) 3 series can further be divided into LiM 2 (PO 4 ) 3 (M = Ti, Ge) with rhombohedral symmetry and LiM 2 (PO 4 ) 3 (M = Zr, Hf, or Sn) with a triclinic phase and lower symmetry.…”

“…Reprinted with permission from Ref. [36]. Copyright 2017 American Chemical Society Reprinted with permission from Ref.…”