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

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 V2O5. It is proposed that the structure of amorphous films corresponds to a nanotextured mosaic of V2O5 and V2O4 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 V3+ even when V5+ has not been completely reduced to V4+ 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 V2O5 and its lithiated products, it is argued that the geometry of VOn 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, LixV2O5, become metallic for high values of x

Effect of substrate temperature on morphology and electrochemical performance of radio frequency magnetron sputtered lithium nickel vanadate films used as negative electrodes for lithium microbatteries

10.1021/jp0565554Journal of Physical Chemistry B11094301-4306JPCB

Structural and Electrochemical Behaviour of Sputtered Vanadium Oxide Films: Oxygen Non-stoichiometry and Lithium Ion Sequestration

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 $V_2O_5$. It is proposed that the structure of amorphous films corresponds to a nanotextured mosaic of $V_2O_5$ and $V_2O_4$ 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 $V_2O_5$ 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, $Li_xV_2O_5$, become metallic for high values of x

Perfect reversibility of the lithium insertion in FeS2: The combined effects of all-solid-state and thin film cell configurations

All-solid-state thin film batteries based on sputtered pyrite electrodes, a lithium phosphorus oxynitride electrolyte and a lithium anode were prepared and characterized. The successive reduction of both S22− and Fe2+ species led to an impressive volumetric discharge capacity, five times higher than the one for LiCoO2. Excellent reversibility and capacity retention were obtained during the first and the subsequent 800 charge–discharge cycles. A continuous cycling in the low voltage domain was found to be detrimental to the reversibility of the conversion reaction, suggesting a progressive evolution of the phase distribution inside the electrode. The initial capacity was easily recovered after few full oxidation cycles. Keywords: Pyrite, Thin film, Conversion reaction, Lithium microbattery, Solid-state batter

A study of the electrochemical mechanisms involved during lithium insertion into TiO0.6S2.8 thin film used as positive electrode in lithium microbatteries

International audienceAmorphous thin films were prepared by radio-frequency magnetron sputtering from TiS2 target under pure argon atmosphere. Two complementary techniques, X-ray Photoelectron Spectroscopy (XPS) and X-ray Absorption Spectroscopy (XAS), were used to investigate the local and electronic structure of the asprepared sample and to study the electrochemical mechanisms occurring during the first cycle. The results exhibit that the as-prepared TiO 0.6S2.8 thin film is close to bulk TiS3 (which may be viewed as Ti4+S22-S2-) with regard to the local and electronic structure. The electrochemical characterization of the film was performed in the Li/LiAsF6 (IM in EMC)/TiO0.6S2.8 cell. Upon lithium insertion, sulfur is first involved into the electrochemical reduction followed by titanium. The reduction of S22- to S2- is concomitant with the elongation of the distance between the two sulfur ions of the disulfide pair. At the end of the charge, the electrochemical processes appear to be reversible. This study clearly evidences the major contribution of sulfur atoms beside titanium

Caractérisation par RMN de la structure à l’échelle atomique des couches minces de LiPON utilisées comme électrolyte de microbatteries

International audienc

Improvement of the ionic conductivity of thin layers of LiPON used as electrolyte in microbatteries: Structural aspects studied by NMR

National audienc