L.A. de Picciotto

Electrochemical extraction of lithium from LiMn2O4

Lithium has been removed electrochemically at 15 μA/cm2 from LiMn2O4 (spinel) to yield single phase Li1−xMn2O4 for 0 < × ⩽ 0.60. The electrochemical curve suggests that beyond x = 0.60 an electrochemical process other than lithium extraction occurs. Powder X-ray-diffraction spectra indicate that during the extraction process the [Mn2]O4 framework of the spinel structure remains intact. Previous results have shown that 1.2 Li+ ions can also be inserted into LiMn2O4, which suggests that lithium may be cycled in and out of the [Mn2]O4 framework of the spinel structure over a wide range of x, at least from Li0.4Mn2O4 to Li2Mn2O4. Discussion of the mechanism of formation of λ-MnO2 in an acidic environment is extended.

Structure refinement of the spinel-related phases Li2Mn2O4 and Li0.2Mn2O4

Abstract The crystal structures of the lithium-rich and lithium-deficient spinel phases Li2[Mn2]O4 and Li0.2[Mn2]O4 have been determined by neutron-diffraction techniques. Structure refinements confirm earlier reports that the [Mn2]O4 framework of the Li[Mn2]O4 spinel remains intact during both lithium insertion and extraction, but demonstrate unequivocally that in Li2[Mn2]O4 the Li+ ions reside in face-shared tetrahedra and octahedra of the cubic-close-packed oxygen-anion array; in Li0.2[Mn2]O4 the Li+ ions are located randomly on only the tetrahedral sites of the spinel structure.

Structural aspects of lithium-manganese-oxide electrodes for rechargeable lithium batteries

The structural characteristics of “LixMnOy” electrodes, prepared by reacting manganese oxides with lithium salts at 400°C–900°C, for ambient temperature, rechargeable lithium cells have been determined by powder X-ray and neutron diffraction studies. The identification of structure types and cyclic voltammetry data show that the rechargeability of the “LixMnOy” electrodes in Li“LixMnOy” cells can be attributed predominantly to a spinel component of the system LixMn2−zO4 (0≤x≤1.33 and 0≤z≤0.33) which includes the spinel phases LiMn2O4, Li2Mn4O9 and Li4Mn5O12.

Structural characterization of Li1+xV3O8 insertion electrodes by single-crystal X-ray diffraction

Abstract The crystal structures of Li1.2V3O8 and a lithiated product Li4.0V3O8 have been determined by single-crystal X-ray diffraction methods. The structure refinement of Li1.2V3O8 confirms that of Li1+xV3O8 (x ≈ 0) reported by Wadsley thirty-six years ago. However, unlike Wadsleys data, the refinement of Li1.2V3O8 demonstrates that the lithium ions are distributed over two independent crystallographic sites. One lithium ion, Li(1), is octahedrally coordinated; the other, Li(2), has tetrahedral coordination. Lithiation of Li1.2V3O8 with n-butyllithium at room temperature displaces Li(1) through an octahedral face into a neighbouring octahedral site, whereas Li(2) shifts its position very slightly to adopt octahedral coordination. During lithiation, the packing of the oxygen-ion array is adjusted slightly to adopt an arrangement that approaches cubic-close-packing. The lithiated product Li4V3O8 has a defect rock salt structure. The structural data provide a greater insight into the discharge mechanism that occurs in Li/Li1+xV3O8 electrochemical cells.

Defect spinels in the system Li2O.yMnO2 (y>2.5): A neutron-diffraction study and electrochemical characterization of Li2Mn4O9

Abstract The structure of the defect spinel Li2Mn4O9 which is a component of the system Li2O.yMnO2 (y = 4.0) has been determined by neutron diffraction analysis; it has the spinel notation (Li0.89□0.11) [Mn1.78□0.22]O4. The electrochemical properties of Li2Mn4O9 when used as an insertion electrode in rechargeable room-temperature lithium cells have been evaluated.

Lithium insertion into the spinel LiFe5O8

Lithium has been inserted into the spinel LiFe5O8 at both ambient and high temperature. At 50 °C two lithium ions per formula unit can be inserted into the structure; the inserted lithium ions displace the tetrahedral ferric ions of the spinel into neighbouring vacant octahedral sites to yield a rocksalt phase Li3Fe5O8. The long-range order of the lithium and iron ions on the B-sites of the Atet[B2]octX4 spinel (Fe[Li0.5Fe1.5]O4) is not affected by lithiation. At 400 °C electrochemical insertion of lithium is accompanied by iron extrusion from the oxide lattice. The reaction of two lithium ions per LiFe5O8 at this temperature results in a product consisting predominantly of a rocksalt phase of composition Li2Fe3O5 in which the lithium and iron ions are randomly distributed over all the octahedral sites of the structure, and metallic iron.

Spinel electrodes for lithium batteries — A review

Abstract This paper briefly reviews recent electrochemical data of several transition-metal oxide and sulphide spinel compounds of general formula A[B 2 ]X 4 that have been employed as cathode materials in both room-temperature and high-temperature (400 °C) lithium cells. Particular attention is given to the performance of the oxide spinels M 3 O 4 (M ue5fb Fe, Co, Mn) that have like A- and B-type cations, the lithium spinels Li[M 2 ]O 4 (M ue5fb Ti, V, Mn) and LiFe 5 O 8 , and the thiospinels CuCo 2 S 4 and CuTi 2 S 4 . Reaction processes and the structural characteristics of the reaction products are highlighted.

Transformation of delithiated LiVO2 to the spinel structure

Abstract Heat-treatment of Li 0.5 VO 2 obtained by chemical extraction of lithium from the layered LiVO 2 structure results in the spinel Li[V 2 ]O 4 . Similar treatment of Li 0.45 VO 2 results in a cation-deficient spinel Li 0.9 V 0.1 [V 1.9 ◊ 0.1 ]O 4 with vacancies on the octahedral B-sites of the spinel structure. Differential scanning calorimetric and powder X-ray diffraction data show that Li 0.45 VO 2 transforms irreversibly to spinel at ∼ 300 °C and that this phase is stable to ∼ 420 °C.

Synthesis and characterization of γ-MnO2 from LiMn2O4

Abstract γ-MnO 2 can be synthesized by acid treatment of the spinel LiMn 2 O 4 ; it is formed via an intermediate λ-MnO 2 phase. The γ-MnO 2 phase is significantly more crystalline and contains less occluded water than electrolytically prepared MnO 2 (EMD). Unlike EMD, the occluded water can be removed almost entirely by heating the γ-MnO 2 phase to 300 °C. Heating to 300 °C causes a transformation of the γ-MnO 2 structure to a predominantly β-MnO 2 phase. The discharge capacity of the β-phase in room-temperature lithium cells is comparable with the capacity of the γ/β-MnO 2 phase which is formed by heating EMD to 350 – 420 °C. Lithium-ion diffusion rates in the γ-MnO 2 and β-MnO 2 phases derived from the spinel precursor were determined to be 1 × 10 −9 cm 2 s −1 and 2 × 10 −10 cm 2 s −1 , respectively.

Structural refinement of delithiated LiVO2 by neutron diffraction

Abstract Lithium has been extracted from the layered compound LiVO 2 by chemical oxidation with bromine. Previous X-ray data have shown that in Li 1− x VO 2 lithium extraction beyond x ≈ 0.33 is accompanied by migration of one-third of the vanadium ions into the lithium-deficient layer to stabilize the structure; little information about the location of the lithium ions could be gathered from this data. The neutron diffraction data presented in this paper show that at a composition Li 0.22 VO 2 , determined by atomic absorption spectroscopy, the residual lithium ions are distributed over the octahedral sites of the original lithium layer; the possibility that a small fraction of the lithium ions partially occupy the tetrahedral sites in this layer cannot be discounted. No significant occupation by lithium of the tetrahedral or octahedral vacancies in the vanadium-rich layer could be detected.