B. Zachau-Christiansen

Comparison of LiV3O8 cathode materials prepared by different methods

Lithium trivanadate, LiV{sub 3}O{sub 8}, can be prepared in a finely dispersed form by dehydration of aqueous lithium vanadate gels. Two methods of dehydration, both easily adaptable to large-scale production, are described in this work: freeze drying and spray drying. After heat-treatment of the dried gels (xerogels) to remove loosely bound water they show a high capacity for lithium insertion, approaching four additional lithium per formula unit, and good reversibility as electrode materials for high energy density lithium cells. How the heat-treatment temperature influences the crystal structure is demonstrated as well as the electrochemical properties of the vanadium oxide.

Lithium insertion in different TiO2 modifications

Abstract The insertion of Li into the three titanium dioxide modifications, anatase, rutile, and TiO2(B), is studied primarily by electrochemical techniques. At 25°C at potentials above 1.4 V versus Li/LiAsF6,PC the maximal Li uptake is 0.5 Li/Ti in anatase and TiO2(B), while rutile does not insert Li. At 120°C utilizing LiCF3SO3/PEO electrolyte an amount of 0.8, 0.5, and 0.5 Li/Ti, respectively, is inserted above 1.3 V. The different behaviour of the chemically identical, but structurally non-equivalent oxides, is discussed.

Vanadium oxide xerogels as electrodes for lithium batteries

Vanadium oxide xerogels V2O5 · nH2O are investigated as insertion electrode materials for secondary lithium batteries. Lithium insertion into these materials is shown to be fully reversible when all the loosely bound water is removed by proper heat treatments. The disordered xerogels obtained after heat treatment at 100°C in vacuum, where the reversibly bound water is removed, are able to insert nearly 1.5 Li/V2O5. The more crystalline films obtained after heat treatment at 300°C, where most of the chemically bound water is removed, insert up to 2 Li/V2O5 at potentials above 1.5 V vs. Li, corresponding to a stoichiometric energy density of 730 Wh kg−1. Analysis of differential capacity curves show that lithium ions are accommodated at sites in the xerogel host that are different from the sites occupied in orthorhombic V2O5. It is also noted that the xerogel host is more stable towards lithium insertion, retaining its structure after repeated cycling to a depth of 2 Li/V2O5.

Vanadium oxides as electrode materials for rechargeable lithium cells

Abstract Lithium insertion has been studied in a number of vanadium oxides with special regard to their application as the active component in rechargeable lithium cells. Very high stoichiometric energy densities for lithium insertion are found for several of these materials. As these oxides are poor electronic conductors, however, the high energy densities are partially offset by the addition of conductive material necessary for practical electrodes. Cycling results are reported for the three-dimensional oxide V 6 O 13 , the layered Li 1+ x V 3 O 8 , and the non-crystalline V 2 O 5 xerogel.

Electrochemical properties of non-stoichiometric V6O13

Non-stoichiometric V6O13±0.2 (VOy) prepared by thermal decomposition of NH4VO3 in N2 atmosphere is investigated cathode material for Li batteries. The maximum lithium composition is found to be Li2y-3VOy. The emf vs composition relationship of Li/LixVO2.144 is determined in the interval 0 < x < 1.3, yielding a theoretical energy density of 890 Wh kg−1. The kinetics and reversibility of the VOy electrode is investigated by cyclic voltammetry and cycling of test cells. The lithium diffusion coefficient and the electronic conductivity of the oxide is found to decrease with increasing lithium content. The cyclability of very thin electrodes is found to be excellent, but inferior results are obtained with practical cells, presumably due to degradation of electrode structure.

V6O13 As cathode material for lithium cells

Abstract The e.m.f. vs. composition relationship of Li/LixV6O13 has been studied at 25 °C and 155 °C by cyclic voltammetry using organic and polymeric electrolytes, respectively. At both temperatures the lithium insertion reaction is found to be reversible in the composition interval: 0 ⩽, x ⩽ 8. a.c.- impedance measurements on single crystals (25 °C) show that Li+ diffusion in LixV6O13 is one dimensional and proceeds along the channels in the b axis direction. Cycling of Li/LixV6O13 cells with organic and polymer electrolyte shows that high materials utilization and good cycling performance can be achieved with both systems. It is demonstrated that LixV6O13 is sensitive to discharge below 1 V vs. Li.

Lithium insertion into vanadium pentoxide bronzes

Abstract Lithium insertion has been studied in the α-, β- and γ - Li x V 2 O 5 bronzes at 100 °C. At this temperature the reversible lithium composition ranges can be expanded far beyond the thermodynamic stability interval. By electrochemical intercalation the composition parameter x can be varied between zero and nearly three in all three bronzes. The insertion reactions are, however, not reversible in the entire interval for the layerlike α- and γ-phases. They are converted into a weakly crystalline ω-phase when more than ≈ 1.8 Li per formula unit is inserted. As long as the discharge is limited to 2.25 V, lithium insertion is fully reversible in these materials. In contrast to the behaviour observed on cycling at room temperature we see no evidence for a structural rearrangement from α- to γ-phase upon cycling past x = 1. The 3-dimensional β-structure can be cycled reversibly throughout the entire interval 0 x

Determination of the differential capacity of intercalation electrode materials by slow potential scans

Abstract The differential capacity of an insertion electrode material and an estimate of the time constant for transport can be obtained directly from the linear sweep voltammograms at sufficiently low sweep-rates. A simple method of conducting sweep experiments at sweep-rates below 10 μV s −1 is outlined, and the use of this method as a tool in assessing the properties of intercalation electrode materials is demonstrated with results from the cell: Li/LiClO 4 in propylene carbonate/Li x TiS 2 .

Towards solid state lithium batteries based on ORMOCER electrolytes

Abstract ORMOCER polymer electrolytes have been tested both as separator electrolytes, and as binder elctrolyte in composite cathodes of lithium secondary batteries. The interface stability towards metallic lithium has been strongly improved by careful control of purity and conditions during polymerization. ∼900 cycles have been obtained with utilizations decreasing from 65 to 25%, with the total discharge capacity corresponding to 330 full discharges. The charge factor during long term cycling is very close to 1 (1.004±0.006), indicating that the amount of parasitic side reactions can be minimal.

Sodium insertion in vanadium oxides

Abstract Sodium insertion in three vanadium oxides is studied with regard to their use as cathode materials in solid-state sodium batteries. One channel structure ( β -Na x V 2 O 5 ) and two layered structures ( Na 1+ x V 3 O 8 and a -V 2 O 5 ) are investigated. The stoichiometric energy densities calculated from the first discharges were 245, 340, and 430 Wh/kg, respectively. Both Na 1+ x V 3 O 8 and β -Na x V 2 O 5 degraded gradually during cycling. The structure of α-V 2 O 5 changes after the first discharge, but the new phase exhibits excellent capacity retention upon cycling.