Alain Mauger

Review of 5-V electrodes for Li-ion batteries: status and trends

Lithium-ion batteries have dominated the battery industry for the past several years in portable electronic devices due to their high volumetric and gravimetric energy densities. The success of these batteries in small-scale applications translates to large-scale applications, with an important impact in the future of the environment by improving energy efficiency and reduction of pollution. We present the progress that allows several lithium-intercalation compounds to become the active cathode element of a new generation of Li-ion batteries, namely the 5-V cathodes, which are promising to improve the technology of energy storage and electric transportation, and address the replacement of gasoline engine by meeting the increasing demand for green energy power sources. The compounds considered here include spinel LiNi0.5Mn1.5O4 and its related doped-structures, olivine LiCoPO4, inverse spinel LiNiVO4 and fluorophosphate Li2CoPO4F. LiNi0.5Mn1.5O4 thin films, nanoscale prepared materials and surface-modified cathode particles are also considered. Emphasis is placed on the quality control that is needed to guarantee the reliability and the optimum electrochemical performance of these materials as the active cathode element of Li-ion batteries. The route to increase the performance of Li-ion batteries with the other members of the family is also discussed.

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.

Surface modifications of electrode materials for lithium-ion batteries: status and trends

The research on the electrodes of Li-ion batteries aims to increase the energy density and the power density, improve the calendar and the cycling life, without sacrificing the safety issues. A constant progress through the years has been obtained owing to the surface treatment of the particles, in particular the coating of the particles with a layer that protects the core region from side reactions with the electrolyte, prevents the loss of oxygen, and the dissolution of the metal ions in the electrolyte, or simply improve the conductivity of the powder. The purpose of the present work is to review the different surface modifications that have been tried in the past for the different electrodes that are currently commercialized, or considered as promising, including the three families of positive electrodes (lamellar, spinel, and olivine families) and the three negative electrodes (carbon, Li4Ti5O12, and silicon). The role of the different coats used to improve either the surface conductivity, or the thermal stability, or the structural integrity is discussed. The limits in the efficiency of these different coats are also analyzed along with the understanding of the surface modifications that have been proposed.

UNIVERSAL FORMULAS FOR PERCOLATION THRESHOLDS

A power law is postulated for both site and bond percolation thresh- olds. The formula writes pc = p0((d 1)(q 1)) a d b , where d is the space dimension and q the coordination number. All thresholds up to d ! 1 are found to belong to only three universality classes. For first two classes b = 0 for site dilution while b = a for bond dilution. The last one associated to high dimensions is characterized by b = 2a 1 for both sites and bonds. Classes are defined by a set of value for {p0; a}. De- viations from available numerical estimates at d � 7 are within ±0.008 and ±0.0004 for high dimensional hypercubic expansions at d � 8. The formula is found to be also valid for Ising critical temperatures.

Overview of olivines in lithium batteries for green transportation and energy storage

We present the progress on the physical chemistry of the olivine compounds since the pioneering work of Prof. John Goodenough. This progress has allowed LiFePO4 to become the active cathode element of a new generation of Li-ion batteries that makes a breakthrough in the technology of the energy storage and electric transportation. This achievement is the fruit of about a decade of intensive research in the electrochemical community during which chemists, electrochemists, and physicists added there efforts to understand the properties of the material, to overcome the obstacles that were met on the way, and finally to reach the state of the art that allows its commercial use for worldwide applications in the industry today. These obstacles involved carbon coating, purification, control of the surface, the progressive decrease of the size of the particles down to nanoscale, and comprehensive investigation of surface effects. Nevertheless, heterogeneity in the quality of the product available on the market is damaging and may even be an obstacle to the development of new demanding technologies such as electric transportation. Emphasis is placed on the quality control that is needed to guarantee the reliability and the optimum electrochemical performance of this material as the active cathode element of Li-ion batteries. The route to increase the performance of Li-ion batteries with the other members of the family is also discussed. Since Prof. John Goodenough not only initiated the work but also played a major role in the research and development on these materials through the years, the present review is dedicated to him.

New Lithium metal polymer solid state battery for an ultra-high energy: Nano C-LiFePO4 versus Nano Li1.2V3O8

Novel lithium metal polymer solid state batteries with nano C-LiFePO4 and nano Li1.2V3O8 counter-electrodes (average particle size 200 nm) were studied for the first time by in situ SEM and impedance during cycling. The kinetics of Li-motion during cycling is analyzed self-consistently together with the electrochemical properties. We show that the cycling life of the nano Li1.2V3O8 is limited by the dissolution of the vanadium in the electrolyte, which explains the choice of nano C-LiFePO4 (1300 cycles at 100% DOD): with this olivine, no dissolution is observed. In combination with lithium metal, at high loading and with a stable SEI an ultrahigh energy density battery was thus newly developed in our laboratory.

On reducing terrorism power: a hint from physics

The September 11 attack on the US has revealed an unprecedented terrorism worldwide range of destruction. Recently, it has been related to the percolation of worldwide spread passive supporters. This scheme puts the suppression of the percolation effect as the major strategic issue in the fight against terrorism. Accordingly the world density of passive supporters should be reduced below the percolation threshold. In terms of solid policy, it means to neutralize millions of random passive supporters, which is contrary to ethics and out of any sound practical scheme. Given this impossibility we suggest instead a new strategic scheme to act directly on the value of the terrorism percolation threshold itself without harming the passive supporters. Accordingly we identify the space hosting the percolation phenomenon to be a multi-dimensional virtual social space which extends the ground earth surface to include the various independent terrorist-fighting goals. The associated percolating cluster is then found to create long-range ground connections to terrorism activity. We are thus able to modify the percolation threshold pc in the virtual space to reach p<pc by decreasing the social space dimension, leaving the density p unchanged. At once that would break down the associated world terrorism network to a family of unconnected finite-size clusters. The current world terrorism threat would thus shrink immediately and spontaneously to a local geographic problem. There, military action would become limited and efficient.

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.

Anomalous physical properties of cerium–lanthanum filled skutterudites

Abstract Thermoelectric materials generate an electromotive force when submitted to a thermal gradient with an efficiency scaled by the so-called figure of merit: Z = α 2 σ / κ , where α is the Seebeck coefficient, σ the electronic conductivity and κ the thermal conductivity. Theoretical considerations have shown that a large value of Z requires not only a small value of κ but also a large effective mass of charge carriers. The first condition is met in filled skutterudites, which have been studied extensively for this reason. The second condition suggests we focus our attention on skutterudites filled with an anomalous rare-earth element such as cerium, presenting heavy fermion characteristics. In this context, we report in this paper a study of the magnetic properties of CeFe 4 Sb 12 and their evolution upon cerium dilution.

Aging effects in free quantum Brownian motion

The two-time correlation function Cxx(t,t′) of the displacement x(t)−x(t0) of a free quantum Brownian particle with respect to its position at a given time t0 is calculated analytically in the framework of the Caldeira and Leggett ohmic dissipation model. As a result, at any temperature T,Cxx(t,t′) exhibits aging, i.e. it depends explicitly on both times t and t′ and not only on the time difference τ=t−t′, even in the limit of large age t′(t0⩽t′⩽t), in contrast with a dynamic variable in equilibrium such as the particle velocity. The equilibrium quantum fluctuation-dissipation theorem (QFDT) has to be modified in order to relate the response function χxx(t,t′) to Cxx(t,t′), since this latter quantity takes into account even those fluctuations of the displacement which take place during the waiting time tw=t′−t0. We describe the deviation from QFDT in terms of an effective inverse temperature βeff(τ,tw). The behaviour of this quantity as a function of τ for given values of T and tw is analysed. In the classical limit it is shown that βeff(τ,tw)=βD(τ)/[D(τ)+D(tw)], where D(t) denotes the time-dependent diffusion coefficient.