Lithiated Phase Research Articles

Structural study of lithium insertion in vanadium oxides used as cathode materials

ABSTRACTCombined soft and solid state chemistry followed by precise XRD investigations allow us to determine the Li-V-O system as well as the structural modifications induced by Li insertion in silver vanadates. On the base of these studies we propose an interpretation of both Li//V2O5 and Li//Ag2V4O11 batteries electrochemical behavior. In the I<x<3 domain, disproportionation of V4+, occurs leading to the formation of different mixtures between lithium vanadates and vanadium oxides. The different domains are related to the different steps observed in the Li//V2O5 discharge curve. It is also demonstrated that the sprouting phenomenon occurring in the Ag1+xV3O8 vanadate induces the formation of a new phase Ag2V4O11 instead of the oxygen deficient form Ag2V4O11-y. According single crystal XRD structural determination this phase is shown to be isostructural with Li1+xV3O8. Electrochemical Li insertion starts with the reduction of Ag+ leading to the lithiated phase meaning that whatever the starting phase used, the main insertion process occurs in Li1+xV3O8.

Ramsdellite-MnO 2 for lithium batteries: the ramsdellite to spinel transformation

A pure and highly crystalline form of ramsdellite-MnO 2 has been synthesized by acid treatment of the spinels LiMn 2O 4 and Li 2Mn 4O 9 at 95°C. Although the ramsdellite—MnO 2 framework remains intact on lithiation at 70°C, the hexagonally-close-packed oxygen array buckles towards a cubic-close-packed structure to accommodate the inserted lithium ions. The reaction is reversible but the instability of the structure on cycling limits the utility of ramsdellite-MnO 2 as a rechargeable electrode in lithium cells. The ramsdellite structure can be stabilized by reaction with LiOH or LiNO 3 at 300–400°C; this reaction, which displaces manganese ions from the MnO 2 framework into interstitial octahedral sites generates spinel-related domains that coexist with the lithiated ramsdellite phase. At 300°C, under vacuum, the lithiated ramsdellite phase Li 0.5MnO 2 transforms to the spinel LiMn 2O 4; at 300–400°C, in air, it oxidizes slowly and transforms to a defect spinel LiMn 2O 4+δ (0 < δ ⩽ 0.5) via an intermediate compound. A mechanism for the ramsdellite—spinel transition is proposed.

Lithium insertion into YBa 2Cu 3O 7

Atomistic computer simulation techniques are used to investigate the effects of lithium insertion into YBa 2Cu 3O 7. Attention is focused on various possible lattice sites occupied by the inserted lithium ions and pathways for their migration. The square-planar position in the Cu(2) layer is calculated to be the most energetically favorable. This is supported by the structural modeling of the ordered lithiated phase Li 0.33YBa 2Cu 3O 7. The calculated activation energies derived from migration profiles are in accord with experimental values and suggest fairly mobile lithium ions.

Preparation and magnetic properties of Cu 6O 8·InCl and Li xCu 6O 8·InCl

The compounds Cu 6 O 8 ·InCl and Li 1.23 Cu 6 O 8 ·InCl were prepared. The powder X-ray diffraction pattern shows that both phases have the same cubic structure with a =9.144(5) A. The introduction of Li + lowers the average valence of copper. Neither phase superconducts above 5 K. Measurements of magnetic susceptibility show ferrimagnetic behavior for both phases, with an onset temperature of 125 K for the copper phase and 75 K for the lithiated phase. The copper phase shows a constant magnetization over the range 125–50 K that may be due to a two-sublattice antiferromagnetic interaction.

Mössbauer studies on high-temperature lithiated magnetite, Li xFe 3O 4

The influence of the insertion of lithium ions in magnetite by high-temperature techniques are studied by Mössbauer spectroscopy at room temperature. The results show: (i) the existence of two non-interacting phases, one corresponding to the pure magnetite and the other to a paramagnetic lithiated phase; (ii) that the mechanisms of electron hopping remain practically unaffected by the insertion of Li up to x ≈ 0.20. The results, when compared with those obtained by electrochemical Li insertion, show good agreement.

An iron-57 Moessbauer study of the intermediates formed in the reduction of iron disulfide in the lithium/iron disulfide battery system

{sup 57}Fe Moessbauer spectroscopy has been used to study the intermediates formed at the FeS{sub 2} cathode during room-temperature discharge in the Li{vert bar}LiClO{sub 4}-propylene carbonate {vert bar}FeS{sub 2} cell. Moessbauer spectra recorded at 4.2 K provided evidence for the formation of Li{sub 3}Fe{sub 2}S{sub 4} and another lithiated phase, similar to but not exactly the same as Li{sub 2}FeS{sub 2}. Small particles of superparamagnetic iron were also formed early in the discharge. When LiAsF{sub 6} was the electrolyte, no intermediates were detectable and rapid reduction to small particles of iron occurred. Chemical lithiation of FeS{sub 2} with n-Buli in hexane produced a mixture of reduction products similar to that observed for the Li{vert bar}LiClO{sub 4}-propylene carbonate{vert bar}FeS{sub 2} cell.

Redox processes in the Li xFeS 2/Li electrochemical system studied through crystal, Mössbauer, and EXAFS analyses

Li 2FeS 2 is a compound that can be de-intercalated, leading to a new FeS 2 cathodic material. The structure of the lithiated phase is developed from hexagonal-close-packing of S 2− anions with tetrahedral iron ions, constituting (2D) infinite sheets. Lithium fills some of the tetrahedral and octahedral voids of the host in equivalent proportion. The first lithium removal corresponds to the oxidation of iron and to an important shift from its tetrahedral sites to others in the structure, as evidenced by Mössbauer and EXAFS measurements. De-intercalation of the second lithium results in the oxidation of sulfur, the final structure of the completely oxidized phase being Fe 3+ ( T d ) S 2−(S 2) 2− 1 2 . As shown earlier, this charged material can be re-intercalated up to its original composition.

TG and DSC studies of lithium insertion in LiFe 5O 8

The chemical lithiation of LiFe 5-O 8 with n-butyl-lithium leads to the formation of Li 1+x Fe 5O 8, which is accompanied by unreacted α-LiFe 5O 8 and Li 2CO 3. The DSC traces of this material in air atmosphere show an exothermal effect at ca. 320°C which is associated with a weight increase, due to the decomposition of the lithiated phase to LiFe 5O 8 and Li 2O. A complex endotherm of low intensity and a weight loss effect are found at 430–550°C. These are interpreted in terms of the reaction of LiFe 5O 8 with Li 2CO 3 to give α-LiFeO 2. The thermal treatment of the material in vacuum leads to the reaction between LiFe 5O 8 and Li 1+x Fe 5O 8 to give a rock-salt phase with a = 8.362 Å.