• A Levasseur

      Articles written in Bulletin of Materials Science

    • Study of lithium glassy solid electrolyte/electrode interface by impedance analysis

      A Karthikeyan P Vinatier A Levasseur

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      Cells of lithium ion conducting glassy electrolyte Li2SO4-Li2O-B2O3 with different combinations of electrodes (stainless steel blocking electrode, lithium non-blocking electrode and TiS2 electrode) have been prepared. The a.c. impedance measurements of the cells have been studied at elevated temperature as a function of time. The circuit elements such as bulk resistance, double layer capacitance and charge transfer resistance have been inferred and their time dependence studied. The results show that the electrolyte and the interface are chemically very stable with the different types of electrodes studied here.

    • Microwave synthesis of electrode materials for lithium batteries

      M Harish Bhat B P Chakravarthy P A Ramakrishnan A Levasseur K J Rao

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      A novel microwave method is described for the preparation of electrode materials required for lithium batteries. The method is simple, fast and carried out in most cases with the same starting material as in conventional methods. Good crystallinity has been noted and lower temperatures of reaction has been inferred in cases where low temperature products have been identified

    • Electrochemical properties of tungsten oxysulphide thin films as positive electrodes for lithium microbatteries

      I Martin-Litas P Vinatier A Levasseur J C Dupin D Gonbeau

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      Several WO𝑦S𝑧 tungsten oxysulphide thin films were tested as positive electrodes for lithium microbatteries. The amorphous WO1.05S2 thin film was found very promising. A capacity decrease occurred during the first few cycles, after which the films were able to intercalate reversibly up to 1.1 lithium ion per formula unit under high regime (75 𝜇A/cm2). They were tested for 250 charge–discharge cycles, between 3.0 V and 1.2 V. X-ray photoelectron spectroscopy measurements were performed on different compounds in both intercalated (Li1WO1.05S2, Li2.7WO1.05S2 and Li3.8WO1.05S2) and partially de-intercalated (Li1WO1.05S2) states in order to understand the redox processes occurring during the first discharge–charge cycle. The analysis of both the W4𝑓 and the S2𝑝 peaks has shown that the redox processes involve not only the tungsten atoms but also sulphur atoms. At the beginning of the intercalation, W6+ was first partially reduced into W5+, and then into W4+, but the important stage was the reduction of W4+ into W0. In W0, the electron binding energy was very close to that of metallic tungsten. At the same time, S$^{2-}_2$ ions were partially reduced into S2- ions. But only the reduction process of tungsten atoms appeared to be totally reversible.

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

      K J Rao B Pecquenard A Gies A Levasseur J Etourneau

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      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, Li𝑥 V2O5, become metallic for high values of 𝑥.

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      Posted on October 12, 2020

      Prof. Subi Jacob George — Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bengaluru
      Chemical Sciences 2020

      Prof. Surajit Dhara — School of Physics, University of Hyderabad, Hyderabad
      Physical Sciences 2020

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      Posted on July 25, 2019

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