Upadhyayula V Varadaraju

A new hydrogenophosphate Mn(H2PO4)2 has been synthesized from an aqueous solution. Its ab initio structure resolution shows that the original layered structure of this phase consists of PO 2(OH)2 tetrahedra and MnO5OH octahedra, sharing corners to form [MnP2O8H4]∞ layers, whose cohesion is ensured through hydrogen bonds. The excitation and emission spectra of this phase are characteristic of Mn2+ species. This phosphate is shown to be a good protonic conductor with a conductivity of 10-4.4 S/cm at 90°C (363 K). © 2008 American Chemical Society.

The exchange of lithium for proton in VO(H2PO4)2 has been studied. Beside the continuous exchange from VO(H2PO4)2 to Li2H2VO(PO4)2, a new cathode material Li4VO(PO4)2 has been synthesized, whose structure is closely related to that of VO(H2PO4)2. The electrochemical evaluation of Li4VO(PO4)2 vs. Li shows that it undergoes reversible lithium deintercalation/intercalation at high voltage, ∼4.0 V with a reversible capacity of ∼70 mAh/g. © 2006 Elsevier B.V. All rights reserved.

The exchange of lithium for univalent copper in CuNbO3 has been investigated. A new form of LiNbO3 with a lamellar structure has been synthesized from the topotactic reaction between CuNbO3 and a molten salt corresponding to the eutectic "LiCl/LiNO3". This compound crystallizes in the P21/a space group with a = 9.433 Å, b = 8.226 Å, c = 6.213 Å, and β = 90.2°. This new phase intercalates one lithium on the first discharge and shows reversibility of 0.7 lithium through a first-order transformation leading to a capacity of 120 mAh/g at a potential of 1.65 V vs Li+/Li. © 2011 American Chemical Society.

The electrochemical reactivity of the layered titanium hydrogeno phosphate Ti(HPO4)2·H2O versus lithium has been studied. Lithium intercalation occurs at ∼2.5 V with low polarization, leading to a new lithiated Ti(III) phase, LiTi(HPO4)2·H2O. Ti(HPO4)2·H2O exhibits a reversible capacity of 80 mAh g-1 in the voltage window 1.8-3.5 V at C/10 rate. The stable reversible capacity reveals that the presence of H2O lattice is not affecting the electrochemical reaction. The reversibility of the reaction is demonstrated by extracting lithium from LiTi(HPO4)2·H2O and the host structure is intact. The electrochemical behaviour of dehydrated phases Ti(HPO4)2 and TiP2O7 has also been investigated. © 2007 Elsevier B.V. All rights reserved.

A new vanadium diphosphate, Li2VOP2O7, has been synthesized by ion exchange from Na2VOP2O7, using an eutectic mixture of {0.4LiOH·H2O-0.6LiNO3} at 200 °C. It crystallizes in space group P21/c, with the lattice parameters a = 7.4674(8) Å, b = 12.442(2) Å, c = 6.2105(7) Å and β = 97.79(1)°. The crystal structure of Li2VOP2O7, refined by powder X-ray diffraction data, shows that the structure of the parent Na-phase is retained but a prominent decrease in the layer spacing is observed. Li2VOP2O7 has been tested as a cathode material for Li-ion battery. One lithium is deintercalated by charging to 4.6 V, however, on discharge only about 0.5 Li is re-intercalated. © 2007 Elsevier Masson SAS. All rights reserved.

The monoclinic form of FeOHSO4 was prepared by dehydration of FeSO4·7H2O. We show that reversible insertion of up to ∼1Li/f.u. is possible in this compound at an average voltage of 3.2 V. The insertion/deinsertion is a biphasic process. The high voltage plateau, a reversible capacity of 110 mAh/g after 20 cycles and good cycling behavior make this compound an attractive positive electrode material for rechargeable Li-ion batteries, suggesting also that transition metal sulphates need to be explored. © 2009 Elsevier B.V. All rights reserved.

A new V(III) lithium phosphate Li5VO(PO4)2 has been synthesized by electrochemical insertion of lithium into Li4VO(PO4)2. This phase, which crystallizes in the space group I4/mcm, exhibits a tunnel structure closely related to the layered structure of Li4VO(PO4)2 and to the tunnel structure of VO(H2PO4)2. The topotactic reactions that take place during lithium exchange and intercalation, starting from VO(H2PO4)2 and going to the final phase Li5VO(PO4)2 are explained on the basis of the flexible coordinations of V4+ and V3+ species. The electrochemical and magnetic properties of this new phase are also presented and explained on the basis of the structure dimensionality. © 2008.

Nanocrystalline rutile TiO2 is prepared at RT from acidic solution by sol-gel method using titanium tetraisopropoxide as precursor. Samples of varying crystallite sizes are prepared by post annealing the as synthesized rutile TiO2 at different temperatures. The absorption spectra of synthesized samples reveal a large blue shift (311 nm) vis a vis bulk rutile TiO2 (394 nm) indicating the nanocrystalline nature of the material. Electrochemical studies performed at RT show that one Li per formula unit is inserted into the nanocrystalline rutile TiO2. Variation in the voltage profiles is observed with respect to small changes in the crystallite sizes within the nanometric regime. © 2006 Elsevier B.V. All rights reserved.

Polycrystalline samples of VOMoO4 are prepared by a solid-state reaction method and their electrochemical properties are examined in the voltage window 0.005-3 V versus lithium. The reaction mechanism of a VOMoO4 electrode for Li insertion/extraction is followed by ex situ X-ray diffraction analysis. During initial discharge, a large capacity (1280 mAh g-1) is observed and corresponds to the reaction of ∼10.3 Li. The ex situ XRD patterns indicate the formation of the crystalline phase Li4MoO5 during the initial stages of discharge, which transforms irreversibly to amorphous phases on further discharge to 0.005 V. On cycling, the reversible capacity is due to the extraction/insertion of lithium from the amorphous phases. A discharge capacity of 320 mAh g-1 is obtained after 80 cycles when cycling is performed at a current density of 120 mA g-1. © 2007 Elsevier B.V. All rights reserved.