Structural and electrochemical behaviour of sputtered vanadium oxide films: oxygen non-stoichiometry and lithium ion sequestration

Abstract

Structural and electrochemical aspects of vanadium oxide films recently reported from ICMCB/ ENSCPB have been examined using appropriate structural models. It is shown that amorphous films are nonstoichiometric as a result of pre-deposition decomposition of V 2 O 5. It is proposed that the structure of amorphous films corresponds to a nanotextured mosaic of V 2 O 5 and V 2 O 4 regions. Lithium intercalation into these regions is considered to occur sequentially and determined by differences in group electronegativities. Open circuit voltages (OCV) have been calculated for various stoichiometric levels of lithiation using available thermodynamic data with approximate corrections. Sequestration of lithium observed in experiments is shown to be an interfacial phenomenon. X-ray photoelectron spectroscopic observation of the formation of V 3+ even when V 5+ has not been completely reduced to V 4+ is shown to be entirely consistent with the proposed structural model and a consequence of initial oxygen nonstoichiometry. Based on the structural data available on V 2 O 5 and its lithiated products, it is argued that the geometry of VO n polyhedron changes from square pyramid to trigonal bipyramid to octahedron with increase of lithiation. A molecular orbital based energy band diagram is presented which suggests that lithiated vanadium oxides, Li x V 2 O 5 , become metallic for high values of x.

In Situ Ambient Pressure X-ray Photoelectron Spectroscopy Studies of Lithium-Oxygen Redox Reactions

“…The increasing Li 1s intensity was accompanied with the broadening and gradual shift of the V 2p peak to lower binding energy, indicating lowered valence state of vanadium ions upon discharge. The V 2p peak could be fitted to three peaks at 514.5 eV, 516.0 eV, and 517.4 eV, which are attributed to V 3+ , V 4+ and V 5+ in Li x V 2 O 5 , respectively 27 28 . The relative fractions of V 3+ and V 4+ ions were found to increase upon discharge while that of V 5+ decreased ( Supplementary Fig.…”

“…Three components centered at 530.2, 532.0 and 534.0 eV were used to describe lattice oxygen (O 2− ) in Li x V 2 O 5 27 28 , both oxygen doubly bound to phosphorus (P = O) 27 and oxygen in Li 2 CO 3 25 , and oxygen singly bound to two phosphorus (P-O-P) 27 in LiPON, respectively. Upon discharge, the lattice oxygen (O 2− ) in Li x V 2 O 5 27 28 , became increasingly pronounced and led to the gradual growth of the O 1s peak shoulder at the low binding energy side. In addition, there was a systematic shift in the binding energy of the O 2− lattice component in Li x V 2 O 5 to lower binding energy by 0.4 eV from 1.85 to 0 V cell , which is in agreement with decreased covalency of V-O bonds with decreasing vanadium valence state 28 .…”

“…Upon discharge, the lattice oxygen (O 2− ) in Li x V 2 O 5 27 28 , became increasingly pronounced and led to the gradual growth of the O 1s peak shoulder at the low binding energy side. In addition, there was a systematic shift in the binding energy of the O 2− lattice component in Li x V 2 O 5 to lower binding energy by 0.4 eV from 1.85 to 0 V cell , which is in agreement with decreased covalency of V-O bonds with decreasing vanadium valence state 28 .…”

Commitment Between Roughness and Crystallite Size in the Vanadium Oxide Thin Film opto-electrochemical Properties

“…The films voltammograms present three pairs of current peaks, corresponding to the reduction (intercalation), at potentials of 2.33, 3.20 and 3.41 V, and oxidation (deintercalation) at 2.64, 3.23 and 3.44 V (vs. Li|Li + ). The peaks can be attributed to different phase transitions of V 2 O 5 , due to the weak van der Waals forces between the adjacent layers, that are showed in the Figure 6 13,34,35 .…”

Controlled synthesis and electrochemical properties of vanadium oxides with different nanostructures

“…Of the family of metal oxides, vanadium oxides and their derived compounds as functional materials have received extensive attention because of their structures, novel electronic and optical properties, which make them have a wide range of practical applications, such as catalyst, gas sensor, cathode materials for reversible lithium batteries, electrochemical and optical devices, intelligent thermochromic * Author for correspondence (xxgyy@hotmail.com) windows, and so on (Chatterjee et al 2001;Parkin and Manning 2006;Rao et al 2006;Gao et al 2009;Strelcov et al 2009;Ye et al 2010). Vanadium usually forms a variety of binary oxides with the general formula, VO 2+x (-0 (B), have attracted more and more attention due to their specific magnetism, catalyst and electrochemistry (Hironori et al 1979;Liu et al 2004;Feyel et al 2006;Dong et al 2008).…”