Upadhyayula V Varadaraju

Lithium intercalation in phase-pure nanocrystalline brookite TiO2 is demonstrated for the first time. Galvanostatic studies show that 0.9 Li per formula unit can be intercalated into this phase in initial discharge. Ex situ X-ray diffraction studies on the electrodes at different levels of lithium intercalation show that the structure is stable toward lithium intercalation and deintercation. In the initial charge, an irreversible capacity loss is observed. However, on further cycling, the phase shows excellent cycling behavior. A reversible capacity of 170 mAhg-1 is observed even after 40 cycles. © 2006 The Electrochemical 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 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.

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.