Search

Understanding the reaction mechanism of olivine compounds as electrode materials for lithium lithium-ion batteries have has received much attention recently. The question whether olivine LiFePO4 undergoes two-phase or non-nonequilibrium single-phase reaction during electrochemical processes has taken center stage in the understanding of the faster reaction kinetics observed in this material. Here, the lithiation/delithiation mechanism of Mg Mg-substituted LiFePO4 using high high-resolution X-ray diffraction(XRD), transmission electron microscopy(TEM), and electrochemical measurements is reported. Ex situ partially (de)lithiated olivine- LiMg0.2Fe0.8PO4 show the existence of stable equilibrium intermediate phases as characterized by the presence of more than two phases and broadness of diffraction peaks. Electron energy loss spectroscopy profiles across individual nanoparticles further confirm uniform lithiation with a constant Fe-L3 energy measured across each nanoparticle, suggestive of solid solution behavior in individual particles. In addition, a continuous shift in the diffraction peak position is observed even in the 'two-phase' region in the ex situ electrochemical (de)lithiated electrodes. [ABSTRACT FROM AUTHOR]

Searching high capacity cathode materials is one of the most important fields of the research and development of sodium-ion batteries (SIBs). Here, we report a FeO0.7F1.3/C nanocomposite synthesized via a solution process as a new cathode material for SIBs. This material exhibits a high initial discharge capacity of 496 mAh g−1 in a sodium cell at 50 °C. From the 3rd to 50th cycle, the capacity fading is only 0.14% per cycle (from 388 mAh g−1 at 3rd the cycle to 360 mAh g−1 at the 50th cycle), demonstrating superior cyclability. A high energy density of 650 Wh kg−1 is obtained at the material level. The reaction mechanism studies of FeO0.7F1.3/C with sodium show a hybridized mechanism of both intercalation and conversion reaction. [ABSTRACT FROM AUTHOR]

Nanostructured MgAl2O4 spinel was synthesized by a direct conversion process from cubic γ-Al2O3. The effect of post-annealing temperature (300°, 500°, and 800°C) on MgAl2O4 phase formation was investigated using transmission electron microscopy, selected area electron diffraction (SAED), electron energy loss spectroscopy (EELS), and energy-dispersive spectroscopy (EDS). Relative diffraction intensities as well as lattice parameter measurements from SAED revealed that MgAl2O4 spinel structure starts forming at temperatures as low as 300°C. EELS and EDS spectrum images also revealed an increase in elemental homogeneity with increasing annealing temperature. The degree of ordering of Mg and Al between octahedral and tetrahedral sites has been determined from relative diffraction intensities. Results show that annealing to 800°C leads to a spinel phase with an order parameter of 0.78. [ABSTRACT FROM AUTHOR]

Nanostructured MgAl2O4 spinel was synthesized by a direct conversion process from cubic γ-Al2O3. The effect of post-annealing temperature (300°, 500°, and 800°C) on MgAl2O4 phase formation was investigated using transmission electron microscopy, selected area electron diffraction (SAED), electron energy loss spectroscopy (EELS), and energy-dispersive spectroscopy (EDS). Relative diffraction intensities as well as lattice parameter measurements from SAED revealed that MgAl2O4 spinel structure starts forming at temperatures as low as 300°C. EELS and EDS spectrum images also revealed an increase in elemental homogeneity with increasing annealing temperature. The degree of ordering of Mg and Al between octahedral and tetrahedral sites has been determined from relative diffraction intensities. Results show that annealing to 800°C leads to a spinel phase with an order parameter of 0.78. [ABSTRACT FROM AUTHOR]

Understanding the reaction mechanism of olivine compounds as electrode materials for lithium lithium-ion batteries have has received much attention recently. The question whether olivine LiFePO4 undergoes two-phase or non-nonequilibrium single-phase reaction during electrochemical processes has taken center stage in the understanding of the faster reaction kinetics observed in this material. Here, the lithiation/delithiation mechanism of Mg Mg-substituted LiFePO4 using high high-resolution X-ray diffraction(XRD), transmission electron microscopy(TEM), and electrochemical measurements is reported. Ex situ partially (de)lithiated olivine- LiMg0.2Fe0.8PO4 show the existence of stable equilibrium intermediate phases as characterized by the presence of more than two phases and broadness of diffraction peaks. Electron energy loss spectroscopy profiles across individual nanoparticles further confirm uniform lithiation with a constant Fe-L3 energy measured across each nanoparticle, suggestive of solid solution behavior in individual particles. In addition, a continuous shift in the diffraction peak position is observed even in the 'two-phase' region in the ex situ electrochemical (de)lithiated electrodes. [ABSTRACT FROM AUTHOR]