Ordering Of Lithium Ions Research Articles

Kinetics and structural changes of Li-rich layered oxide 0.5Li2MnO3·0.5LiNi(0.292)Co(0.375)Mn(0.333)O2 material investigated by a novel technique combining in situ XRD and a multipotential step.

Li-rich layered oxide 0.5Li2MnO3·0.5LiNi0.292Co0.375Mn0.333O2 was prepared by an aqueous solution-evaporation route. X-ray powder diffraction (XRD) showed that the as-synthesized material was a solid solution consisting of layered α-NaFeO2-type LiMO2 (M = Ni, Co, Mn) and monoclinic Li2MnO3. The superlattice spots in the selected area electron diffraction pattern indicated the ordering of lithium ions with transition metal (TM) ions in TM layers in this Li-rich layered oxide. Electrochemical performance testing showed that the as-synthesized material could deliver an initial discharge capacity of 267.7 mAh/g, with a capacity retention of 88.5% after 33 cycles. A new combination technique, multipotential step in situ XRD (MPS in situ XRD) measurement, was applied for the first time to investigate the Li-rich layered oxide. Using this approach, the relationships between kinetics and structural variations can be obtained simutaneously. In situ XRD results showed that the c parameter decreased from 3.70 to 4.30 V and increased from 4.30 to 4.70 V, whereas the a parameter underwent a decrease above 4.30 V during the first charge process. Below 3.90 V during the first discharge process, a slight decrease in the c parameter was found along with an increase in the a parameter. During the first charge process, the value of the coefficient of diffusion for lithium ions (DLi+) decreased to its mininum at 4.55 V, which might be associated with Ni(2+) migration, as indicated by both Ni occupancy in 3b sites (Ni3b%) in the Li(+) layers and complicated chemical reactions. Remarkably, a lattice distortion might occur within the local domain in the host stucture during the first discharge process, indicated by a slight splitting of the (003) diffraction peak at 3.20 V.

New Insight into the Atomic Structure of Electrochemically Delithiated O3-Li(1–x)CoO2 (0 ≤ x ≤ 0.5) Nanoparticles

Direct observation of delithiated structures of LiCoO(2) at atomic scale has been achieved using spherical aberration-corrected scanning transmission electron microscopy (STEM) with high-angle annular-dark-field (HAADF) and annular-bright-field (ABF) techniques. The ordered Li, Co, and O columns for LiCoO(2) nanoparticles are clearly identified in ABF micrographs. Upon the Li ions extraction from LiCoO(2), the Co-contained (003) planes distort from the bulk to the surface region and the c-axis is expanded significantly. Ordering of lithium ions and lithium vacancies has been observed directly and explained by first-principles simulation. On the basis of HAADF micrographs, it is found that the phase irreversibly changes from O3-type in pristine LiCoO(2) to O1-type Li(x)CoO(2) (x ≈ 0.50) after the first electrochemical Li extraction and back to O2-type Li(x)CoO(2) (x ≈ 0.93) rather than to O3-stacking after the first electrochemical lithiation. This is the first report of finding O2-Li(x)CoO(2) in the phase diagram of O3-LiCoO(2), through which the two previously separated LiCoO(2) phases, i.e. O2 and O3 systems, are connected. These new investigations shed new insight into the lithium storage mechanism in this important cathode material for Li-ion batteries.

Computer Modeling Study of the Lithium Ion Distribution in Quaternary Li–Mn–Fe–O Spinels

Computational and experimental techniques have been used to investigate the structural properties, especially the cation distribution, of spinel solid solutions formed between LiMn2O4 and LiFe5O8. The series of solid solutions of composition (1−x)LiMn2O4−xLi0.5Fe2.5O4 are single-phase products with the cubic spinel structure, with the lattice parameter increasing from 8.21 to 8.33 Å as x varies from 0 and 1. The variation of the unit cell parameter with x shows a distinct departure from Vegard's law, which is most pronounced for samples with the Fe:Mn molar ratio close to 1:1. With higher Fe content, the ordering of lithium ions in the octahedral spinel sites leads to the reduction of the crystal symmetry and to a strongly marked preference of Li+ ions to occupy the octahedral positions. Our lattice energy minimization results make clear predictions as to the Li+ ion content and distribution in these materials and thereby resolve confusions in the experimental data.

Effect of Trivalent Manganese on the Crystal Chemistry of some Lithium Spinels

Crystallographic properties of the spinel systems Li0.5Ga2.5−xMnxO4 (0≤x≤0.7), Li0.5Fe2.5−xMnxO4 (0≤x≤0.5), and Li0.5Al2.5−xMnxO4 (0≤x≤0.5) have been investigated in order to determine the effects of trivalent manganese substitution on the crystal chemistry of the ordered spinel hosts. In each system relatively small concentrations of Mn3+ removed long-range ordering of lithium ions on the octahedral sites. This loss of order was accompanied by anomalies in the dependence of lattice parameters on composition. These observations can be qualitatively interpreted by assuming that Mn3+ ions tend to cluster in order to reduce the elastic energies associated with Jahn-Teller stabilization. These effects may provide indirect evidence for lattice imperfections such as have been invoked to account for square B-H hysteresis loops in ferrite materials containing Jahn-Teller ions.