Samuel T. Lutta

Some transition metal (oxy)phosphates and vanadium oxides for lithium batteries

Iron and vanadium oxides have a rich structural chemistry when combined with phosphate groups; the transition metal most commonly in an octahedral coordination. The inductive effect increases the potential difference between Fe3+/Fe2+ and Li/Li+ couples in phosphate lattices relative to the pure iron oxides; a similar behavior is found for the corresponding vanadium compounds. Of the iron phosphates, the olivine phase LiFePO4 has high thermal and chemical stability, even when lithium-free; the challenges of low electronic conductivity are being overcome, but data is lacking on the true lithium diffusion behavior. The all-ferric lipscombite-type phase, Fe1.33PO4OH, shows the highest capacity of the iron phosphates for lithium intercalation. The e-VOPO4 material, formed by the oxidative de-intercalation of protons from H2VOPO4, can reversibly react with two lithium atoms in two steps. The face- and edge-sharing transition metal octahedra lead to a range of interesting and structurally revealing magnetic interactions. A number of vanadium oxide phases are known, with those containing VO6 octahedra showing the greatest stability when undergoing redox reactions. Such structures have been synthesized using xerogel, hydrothermal and electrochemical methods. The double-sheet delta structures show reversible lithium intercalation of up to one lithium ion per vanadium, leading to the highest storage capacities. However, the large potential width of discharge and the apparent low reaction rates will minimize their use unless improved.

Synthesis, crystal structures and magnetic properties of organically templated new layered vanadates: [C4H8NH2]V3O7, [(CH3)2NH2]V3O7, [C5H10NH2]V3O7 and [C2H5NH3]V3O7

Four new layered mixed-valance vanadium oxides, which contain the interlamellar organic cations pyrolidinium, dimethylammonium, piperidinium, and ethylammonium, have been prepared under hydrothermal conditions and their structures determined. All four structures contain vanadium oxide layers constructed from V5+O4 tetrahedra and pairs of V4+O5 square pyramids with the protonated organic amines occupying the interlayer space. The materials are further characterized by thermal analysis, FTIR and scanning electron microscopy. Magnetic susceptibility studies of the first three compounds reveal a spin-gap behavior explained by an isolated antiferromagnetic dimers model. Large values of the exchange constants J = 325 − 480 K were found and the dependence of J upon the structural parameters was analyzed assuming a kinetic exchange mechanism.

Solvothermal synthesis and characterization of a layered pyridinium vanadate, (C5H6N)V3O7

A new layered vanadium oxide, (C5H5NH)V3O7, has been synthesized by a solvothermal process at 200 °C; this is the first vanadium oxide to have an aromatic intercalate between the V3O7 sheets, and it has a monoclinic structure with space group P21 and lattice parameters a = 7.5296(6) A, b = 6.6592(8) A, c = 10.1513(12) A and β = 94.460(2)°.

Synthesis of Novel Vanadium Oxide Nanotubes and Nanofibers

Abstract : We are exploring the synthesis and properties of structured vanadium oxides mainly nanotubes and nanorods. Nanotubes initially formed with surfactant templates have been readily exchanged with simple cations without change of the basal-plane structure. These compounds contain delta-like vanadium oxide layers with the vanadium in VO6 octahedra. This structure is particularly suitable for redox reactions. In this paper we report on synthesis of vanadium oxide (NH4)(x)V2O(5-delta)(dot)nH2O rods using organic polymer as template. This compound has been synthesized by sol-gel reaction and subsequent hydrothermal treatment. TGA, SEM, XRD and FTIR were used to characterize this compound. Thermal analysis of this compound shows that the fibrous morphology is maintained when it is heated in nitrogen and oxygen above 300 deg. C. However, in both cases the size of the fibers decreases. Performance of this compound as cathode material in secondary electrolyte has been investigated using LiPF6 as electrolyte. A capacity of 140 mAh/g was obtained which remained fairly constant with up to at least 10 cycles. We also investigated electrochemical behavior of thermal products.

Vanadium Oxide Nanotubes: Characterization and Electrochemical Behavior

Abstract : Vanadium oxide nanotubes (VONT) were formed from vanadium (V) oxide and the dodecylamine templating agent by a sol-gel reaction and subsequent hydrothermal treatment. The nanotubes were characterized by transmission electron microscopy (TEM), electron diffraction, thermogravimetric analysis (TGA), infrared spectroscopy and powder X-ray diffraction (XRD). The nanotubes consist of VO2.4C12H28N0.27 and range in diameter from 100 nm to 150 nm. The study further reveals that the compound maintained the tubular morphology when heated at 430 deg C in an inert atmosphere. However, the tubular morphology is destroyed when the compound is heated at about 130 deg C in oxygen. Organic free manganese intercalated vanadium oxide nanotubes (MnVONT) were synthesized by an ion exchange reaction. The previously mentioned techniques were used to characterize MnVONT. Mn(0.86)V7O(16+sigma). nH2O layers have 2D tetragonal cell with a = 6.157(3) A, while interlayer spacing is 10.52 (3) A. VONT, heated VONT and Mn(0.86)V7C(16+sigma). nH2O are redox - active and can insert lithium reversibly. This study reveals that the electrochemical performance of VONT is enhanced by removing the organic template by heating in an inert atmosphere or exchanging with Mn(2+) ions.

Vanadium Oxide Nanofibers and Vanadium Oxide Polyaniline Nanocomposite: Preparation, Characterization and Electrochemical Behavior

The sol gel reaction of NH 4 VO 3 and polymethylmethacrylate (PMMA) template followed by hydrothermal treatment formed (NH 4 ) x V 2 O 5-Δ .nH 2 O rods. TGA, SEM, XRD and FTIR characterized this compound. Heating (NH 4 ) x V 2 O 5-Δ .nH 2 O in oxygen and nitrogen at 250 °C and 300 °C respectively resulted in the formation of vanadium oxides nanofibers of V 3 O 7 and V 2 O 5 . Performance of these compounds as cathode in rechargeable lithium battery was investigated in a LiPF 6 /mixed carbonate electrolyte. The materials show good cycling with capacity greater than 130mAh/g, which translates to the insertion of 0.5 moles of Li + per vanadium of the active material.