Phonons and Thermodynamics of Unmixed and Disordered Li_0.6FePO₄

Abstract

The lithium-storage material Li(0.6)FePO(4) was studied by inelastic neutron scattering and differential scanning calorimetry. Li(0.6)FePO(4) undergoes a transformation from a two-phase mixture (heterosite and triphylite) to a disordered solid-solution at 200 degrees C. Phonon densities of states (DOS) obtained from the inelastic neutron scattering were similar for the two-phase sample measured at 180 degrees C and the disordered sample measured at 220 degrees C. The vibrational entropy of transformation is 1.8 +/-0.9 J/(K mol), which is smaller than the configurational entropy difference of approximately 3.1 J/(K mol). The measured enthalpy of the disordering transition was estimated as 2.5 kJ/mol. The phonon data show a small change in lattice dynamics upon disordering.

The Science of Electrode Materials for Lithium Batteries

“…The lithium-storage material Li 0.6 FePO 4 was studied by inelastic neutron scattering and differential scanning calorimetry [103]. Li 0.6 FePO 4 undergoes a transformation from a two-phase mixture (heterosite and triphylite) to a disordered solid-solution at 200 °C.…”

“…-22-Experimental phonon DOS curves for Li0.6FePO4 at 180 °C (solid) and 220 °C (dashed), normalized to unity [103].…”

“…The Li + ions cause changes in the local electronic structure in their immediate neighborhood, evidently changing the occupancy of nearby Fe-O molecular orbitals [103]. These changes are seen in the EELS studies on Fe and O absorption edges, and can be quantified with the assistance of electronic structure calculations.…”

Polaron-ion correlations inLixFePO4studied by x-ray nuclear resonant forward scattering at elevated pressure and temperature

“…The result, ∼ 10 13 Hz, is typical of optical phonon frequencies measured by inelastic neutron scattering and by Raman spectrometry. 49,50 For a second set of fits, we calculated the pressure dependence of the prefactor, ν exp(−2αR). We extrapolated the attempt frequency to elevated pressure using a typical Grüneisen parameter, γ = 2, and the compressibility, κ T ,…”

“…1. Constraining the prefactor to a reasonable range based on past measurements of optical phonons 49,50,52 gives an error in the magnitude of the activation enthalpies of approximately ±10%. The slope of the curve in Fig.…”