materials have recently shown promise as high capacity stable electrodes for advanced rechargeable lithium batteries. Using first principles quantum mechanical energy computations we demonstrate that the stability of these materials is due to the particular valence distribution on the transition metals in this material. Spin density calculations indicate that the Mn ion has oxidation state independently of the Li content in the material, while Ni is oxidized from to upon removing Li. The high insertion voltage for the can be partly attributed to the change in Mn-Ni interaction upon Li cycling. © 2002 The Electrochemical Society. All rights reserved.

We have investigated the use of aluminum based amorphous metallic glass as the anode in lithium ion rechargeable batteries. Amorphous metallic glasses have no long-range ordered microstructure; the atoms are less closely packed compared to the crystalline alloys of the same compositions; they usually have higher ionic conductivity than crystalline materials, which make rapid lithium diffusion possible. Many metallic systems have higher theoretical capacity for lithium than graphite/carbon; in addition irreversible capacity loss can be avoided in metallic systems. With careful processing, we are able to obtain nano-crystalline phases dispersed in the amorphous metallic glass matrix. These crystalline regions may form the active centers with which lithium reacts. The surrounding matrix can respond very well to the volume changes as these nano-size regions take up lithium. A comparison study of various kinds of anode materials for lithium rechargeable batteries is carried out.

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A combination of ab initio calculations and experimental methods (high-resolution neutron and powder X-ray diffractions) was used to solve the crystal structure of MgxMo6S8 (x = 1 and 2). It was shown that at room temperature, the latter are similar to the crystal structure of classic Chevrel phases (CPs) such as CuxMo6S8: space group R3̄, ar = 6.494 Å, α = 93.43° for MgMo6S8 and ar = 6.615 Å, α = 95.16° for Mg2Mo6S8. For x = 1, one Mg2+ cation per formula unit is distributed statistically between inner sites. For x = 2, the second Mg2+ cation per formula unit is located in the outer sites. Peculiarities of the electrochemical behavior of the CPs as electrode materials for Mg batteries were understood on the basis of the analysis of the interatomic distances. It was shown that the circular motion of the Mg2+ ions between the inner sites in MgMo6S8 is more favorable than their progressive diffusion in the bulk of the material, resulting in relatively slow diffusion and Mg trapping in this phase. In contrast, in Mg2Mo6S8, the repulsion between the Mg2+ ions located in the inner and outer sites facilitates their transport through the material bulk.

To study material phenomena simultaneously at various length scales, descriptions in which matter can be coarse grained to arbitrary levels are necessary. Attempts to do this in the static regime (i.e., zero temperature) have already been developed. We present an approach that leads to a dynamics for such coarse grained models. This allows us to obtain temperature-dependent and transport properties. Renormalization group theory is used to create new local potential models between nodes, within the approximation of local thermodynamical equilibrium. Assuming that these potentials give an average description of node dynamics, we calculate thermal and mechanical properties. If this method can be sufficiently generalized it may form the basis of a multiscale molecular dynamics method with time and spatial coarse graining.

First-principles methods are used to calculate the miscibility of eight aluminum-doped transition-metal oxides in the layered alpha-NaFeO(2) structure. This study finds that for all Li(Al,M)O(2) compounds investigated(M = Ti, V, Cr, Mn, Fe, Co, Ni, Cu) the enthalpy of mixing is positive. In addition, detailed analyses were performed on LiA(1-x)Co(x)O(2) and LiA(1-x)Cr(x)O(2) by calculating full temperature-composition phase diagrams. For the Li(Al,Co)O(2) system, we find regions of immiscibility below - 173 degrees C and above 600 degrees C. For both Li(Al,Co)O(2) and Li(A1,Cr)O(2) above 600 degrees C, Al-doping is limited by the formation of gamma-LiAlO(2).

Abstract We have applied first principles computations to predict the properties of complex hydrides related to the alanate NaAlH 4 , a very promising class of systems for reversible hydrogen storage. The effect of partial substitution on the Na site (by Li or K), and on the Al site (by B or Ga) on the thermodynamic stability of NaAlH 4 and its decomposition product Na 3 AlH 6 is investigated and evaluated by means of qualitative van't Hoff plots. From the calculated results we infer that the most promising improved hydrides are Na 1−x Li x Al 1−y B y H 4 , obtained by a double substitution on the Na and on the Al sites of NaAlH 4 .

Ab Initio calculations suggest that partially lithiated layered LixMnO₂ transforms to spinel in a two-stage process. In the first stage, a significant fraction of the Mn and Li ions rapidly occupy tetrahedral sites, forming a metastable intermediate. The second stage involves a more difficult coordinated rearrangement of Mn and Li ions to form spinel. This behavior is contrasted to LixCoO₂. The susceptibility of Mn for migration into the Li layer is found to be controlled by oxidation state which suggests various means of inhibiting the transformation. These strategies could prove useful in the creation of superior Mn based cathode materials.

Using first-principles calculation and thermally equilibrated Li-vacancy configurations, we have calculated the monoclinicity, am/bm, as a function of lithium content in LixNiO2. In agreement with experimental data, maxima in am/bm are predicted around Li0.75NiO2 and Li0.4NiO2. We explain the monoclinicity maxima at Li0.75NiO2 in terms of a Jahn−Teller distortion assisted by the presence of lithium-vacancy ordering. The subsequent removal of lithium causes a decrease in the number of Ni3+ ions and therefore in the monoclinicity. However, the strong lithium-vacancy ordering at Li0.4NiO2 enables new maxima of monoclinicity despite the low Ni3+ content.

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