Henri Groult

Surface study of a titanium-based ceramic electrode material by X-ray photoelectron spectroscopy

The electrochemical behaviours of the Magneli phase titanium oxides with the general formula TixO2x-1 have been investigated. Surface analysis of these ceramic materials was performed using X-ray photoelectron spectroscopy in order to determine the surface composition. It was shown that the surface layers contain mainly TiIV. When these materials are used as an anode for oxygen evolution, in sulfuric acid, the XPS spectrum shows considerable modification in the O1s region, due to an important contribution of hydroxyl groups and the adsorption of sulfate anions.

Study of dry and electrogenerated Ta2O5 and Ta/Ta2O5/Pt structures by XPS

Two kinds of tantalum oxide films have been studied by XPS: dry and electrogenerated anodic oxides. XPS spectra of Ta4f and O1s have been used to determine the chemical composition of the different films. Ta2O5 is the main constituent of thick films (15 nm≤dox≤60 nm), although the concomitant presence of sub-oxides (mainly TaO) is observed. In thin films (dox<15 nm), the amount of TaII is larger and depends on the preparation procedure. Estimations of the thickness of the oxide layers are given. Ta/Ta2O5/Pt structures were prepared by depositing Pt by photoinduction. The XPS Pt4f spectra have shown the presence of Pt0, PtII and PtIV at the metal–oxide interface. On the contrary, the spectra of electrodeposited Pt present only the Pt04f doublet. Accordingly, these two kinds of structures have different electrochemical behaviours in the presence of a redox couple in solution. Ta/Ta2O5 structures exhibit a diode effect, whereas Ta/Ta2O5/Pt behave rather like Pt electrodes.

Inorganic electrolyte additives to suppress the degradation of graphite anodes by dissolved Mn(II) for lithium-ion batteries

Abstract It is well known that when the carbon/LiMn 2 O 4 -based cathode battery was operated at elevated temperatures, the severe capacity loss occurred in following cycles. As we recently described, the capacity loss is mainly due to the degradation on the carbon anode side caused by the deposition of manganese at the carbon followed by the irreversible decomposition at the graphite/deposited Mn/electrolyte interface. It was found that inorganic additives in electrolyte, such as LiI, LiBr, and NH 4 I, effectively suppressed the degradation of graphite anode to improve the battery performance. In case of LiI and LiBr, the irreversible reaction at the Mn/electrolyte interface was suppressed by specific adsorption of iodide or bromide anions on the metallic Mn surface. Further, the reduction of Mn(II) would be suppressed by adding NH 4 I into electrolyte which could be due to the formation of a stable amine complex of Mn(II).

Advanced Electrodes for High Power Li-ion Batteries

While little success has been obtained over the past few years in attempts to increase the capacity of Li-ion batteries, significant improvement in the power density has been achieved, opening the route to new applications, from hybrid electric vehicles to high-power electronics and regulation of the intermittency problem of electric energy supply on smart grids. This success has been achieved not only by decreasing the size of the active particles of the electrodes to few tens of nanometers, but also by surface modification and the synthesis of new multi-composite particles. It is the aim of this work to review the different approaches that have been successful to obtain Li-ion batteries with improved high-rate performance and to discuss how these results prefigure further improvement in the near future.

Polyacrylate modifier for graphite anode of lithium-ion batteries

Polyacrylates were applied as a binder of graphite electrode in a lithium-ion cell to modify the interface. Compared to a conventional binder, poly(vinylidene fluoride), the efficiency at the initial cycle was improved by poly(acrylic acid) and alkali polyacrylates in an ethylene carbonate (EC)-based electrolyte with highly reversible lithium intercalation. In a LiClO 4 propylene carbonate (PC) solution, the poly(vinylidene fluoride) electrode showed a huge irreversible capacity as is generally known. However, the polyacrylate-modified graphite demonstrated highly reversible lithium intercalation in the PC electrolyte containing no film-forming additives as well as in the EC electrolyte due to the interfacial modification with polyacrylates.

Electrochemical Study of Phase Transition Processes in Lithium Insertion in V 2 O 5 Electrodes

The lithium intercalation into a V 2 O 5 substrate was studied by chronopotentiometry. The samples were prepared by atomic layer chemical vapor deposition which provides homogenous and coherent layers at the surface of titanium plates. During the charge-discharge process, various phase transitions occurred in the system Li-V 2 O 5 which induced a large change in the diffusion coefficient of lithium. To obtain an accurate analysis of the intercalation mechanism, the diffusion equation with a variable diffusion coefficient was solved by digital simulation. The thermodynamic and kinetic properties of the system are represented by an analytical model based on the complementary error function. This procedure was useful for study of the electrode behavior in a large concentration range or in a large potential domain. The influence of various parameters. such as the thickness of the sample or the thermodynamic enhancement factor, were examined.

Preparation of Li–Mn–O thin films by r.f.-sputtering method and its application to rechargeable batteries

Spinel-LiMn2O4 thin films were fabricated on stainless steel substrate by the r.f.-sputtering method. They were annealed within the range 400–700 °C for 1 h in O2 and their electrochemical performance was compared to that of as-deposited film. The thin films were characterized by X-ray diffractometry and electron spectroscopy for chemical analysis (ESCA). Charge–discharge tests were carried out in an LiClO4/propylene carbonate solution. The films heat-treated at 400–700 °C exhibited excellent cyclability over a wide potential region from 2.0 to 4.3 V vs Li/Li+.

Vanadium Oxide Films Synthesized by CVD and Used as Positive Electrodes in Secondary Lithium Batteries

Vanadium oxide films were synthesized by chemical vapor deposition from pure or diluted VO(OC 3 H 7 ) 3 precursor. An annealing process at 500°C was required to obtain crystallized V 2 O 5 . X-ray diffraction patterns have pointed out the influence of the operating conditions for the vanadium oxide deposition on the crystallites sizes. No significant difference in the roughness factor was observed by atomic force microscopy measurements before and after annealing at 500°C. As-deposited V 6 O 13 films were also directly obtained by changing the operating conditions. The insertion/deinsertion of Li + into the host structure was investigated in 1 M LiClO 4 -propylene carbonate. V 2 O 5 films exhibit low irreversible capacity and high cyclability even for a deep lithium insertion ratio; in addition, only small amounts of γ-phases were formed during cycle life at low potential without significant effects on its electrochemical performance. After subsequent cycles between 3.8 and 2.2 V vs. Li/Li + . the reversible capacity is found to be 250 mAh g -1 (y 1.65) close to the theoretical one. V 6 O 13 films exhibit reversible capacity of about 410 mAh g -1 (y 7.9).

Electrochemical behaviour of platinum-coated Ta/Ta2O5 electrodes

Ta/Ta2O5/Pt electrodes were prepared by electrodeposition of platinum on Ta/Ta2O5 substrates. These electrodes were put in the presence of a redox couple in solution (Fe3+/Fe2+); it was shown that the rate of electron transfer strongly depends on the concentration of the electroactive species, the thickness dox of the oxide layer and the mode of platinum deposition.

Structural and electronic properties of the LiNiPO4 orthophosphate

Microcrystalline LiNiPO4 powders have been prepared by solid-state reaction using various precursors. Characterization of the structure and morphology of powders was performed using XRD, SEM, HRTEM, Raman, and FTIR. The electronic properties of materials were investigated by SQUID and ESR. The LiNiPO4 material adopts the olivine-like structure (Pnma S.G.). Analysis of the Raman and FTIR spectra figures out, with the aid of a molecular vibration model, the bonding between NiO6 octahedral and (PO4)3− tetrahedral groups. The electronic configuration and the local cationic arrangement are confirmed by magnetic susceptibility and electron spin resonance spectroscopy.