A. Khelfa

Bio: A. Khelfa is an academic researcher from Pierre-and-Marie-Curie University. The author has contributed to research in topics: Thin film & Raman spectroscopy. The author has an hindex of 9, co-authored 13 publications receiving 428 citations.

Lithium intercalation in MoO3 : a comparison between crystalline and disordered phases

Abstract: We report properties of lithium-intercalated MoO3 crystalline and thin-film which are potential cathode materials for high energy density batteries. Discharge and charge reactions of MoO3 electrodes in a non-aqueous Li+-electrolyte have been studied. The kinetically accessible discharge range amounts to 0≤x≤1.5 for Li insertion in Li x MoO3. Transport parameters such as the Li+ chemical diffusion coefficient, thermodynamic factor and ionic conductivity are investigated during the Li+ insertion process and discussed with respect to the crystallinity of the cathode material.

Characterization of the ternary compounds AgGaTe2 and AgGa5Te8

Abstract: Optical and electrical properties of ternary compounds in the Ag-Ga-Te system are reported. Vibrational properties of AgGaTe2 and AgGa5Te8 single crystals were studied using Raman scattering and infrared absorption spectroscopy. Long-wavelength spectra are analysed and the symmetry of lattice modes are reported. The semiconducting character of Ag-Ga-Te compounds is confirmed by conductivity measurements.

Layered vanadium and molybdenum oxides: batteries and electrochromics

Abstract: The layered oxides of vanadium and molybdenum have been studied for close to 40 years as possible cathode materials for lithium batteries or electrochromic systems. The highly distorted metal octahedra naturally lead to the formation of a wide range of layer structures, which can intercalate lithium levels exceeding 300 Ah/kg. They have found continuing success in medical devices, such as pacemakers, but many challenges remain in their application in long-lived rechargeable devices. Their high-energy storage capability remains an encouragement to researchers to resolve the stability concerns of vanadium dissolution and the tendency of lithium and vanadium to mix changing the crystal structure on cycling the lithium in and out. Nanomorphologies have enabled higher reactivities to be obtained for both vanadium and molybdenum oxides, and with the latter show promise for electrochromic displays.

NMR studies of cathode materials for lithium-ion rechargeable batteries.

Abstract: Lithium intercalation or insertion materials have been widely investigated in the search for new electrode materials for use in high-voltage rechargeable batteries.1-6 The first commercial Li-ion rechargeable battery contains the layered materials LiCoO2 (Figure 1) and graphite as the cathode (or positive electrode) and anode (or negative electrode), respectively.7 Although this battery is the current standard in many applications including cell phones and laptops, its slow charge and discharge rates and cost have prevented its use in applications that require cheap high power and capacity, such as hybrid electric vehicles and electric vehicles. The toxicity of Co is also an issue. A wide variety of materials have been studied,5,6 which include doped LiCoO2 phases, layered compounds based on the LiCoO2 structure (e.g., LiNiO2 8 and LiNi0.5Mn0.5O2 9,10),

Fabrication of silver vanadium oxide and V2O5 nanowires for electrochromics.

Abstract: Silver vanadium oxide (SVO) and V2O5 nanowires have been hydrothermally synthesized. The as-made nanowires are over 30 µm long and 10–20 nm in diameter. The nanowires have a layered structure with a d-spacing of 1.07 nm. The nanowires can be fabricated into free-standing and flexible sheets by suction filtration. The electrical conductivity of the SVO nanowires is 0.5 S/cm, compared to 0.08 S/cm for the V2O5 nanowires. The Li ion diffusion coefficient in the SVO nanowires was 7 times higher than that in the V2O5 nanowires. An electrochromic device was fabricated from the SVO nanowires that displayed a color-switching time of 0.2 s from the bleached state (green) to the colored state (red-brown) and 60% transmittance contrast.

Indium selenides: structural characteristics, synthesis and their thermoelectric performances.

Abstract: Indium selenides have attracted extensive attention in high-efficiency thermoelectrics for waste heat energy conversion due to their extraordinary and tunable electrical and thermal properties. This Review aims to provide a thorough summary of the structural characteristics (e.g. crystal structures, phase transformations, and structural vacancies) and synthetic methods (e.g. bulk materials, thin films, and nanostructures) of various indium selenides, and then summarize the recent progress on exploring indium selenides as high-efficiency thermoelectric materials. By highlighting challenges and opportunities in the end, this Review intends to shine some light on the possible approaches for thermoelectric performance enhancement of indium selenides, which should open up an opportunity for applying indium selenides in the next-generation thermoelectric devices.

Photochromism of molybdenum oxide

Abstract: Molybdenum oxide can exhibit pronounced photochromism and thus might act as an excellent photonic material for a number of technical applications. In the early stage of the research, the attention was focused mainly on the (band) structure, photochromic mechanism and the behavior of the oxide. Later, many investigations were carried out on the factors that might influence the photochromic performance. At the same time, the photochromic response has been extended from UV light to visible light. In this review, the progress in all of these areas will be reviewed thoroughly.