C.M. Julien

Reduction Fe3+ of Impurities in LiFePO4 from Pyrolysis of Organic Precursor Used for Carbon Deposition

The structural properties of microcrystalline LiFePO4 prepared with and without carbon coating are analyzed with X-ray diffraction spectroscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, and magnetic measurements for comparison. While nanosized ferromagnetic particles (-Fe2O3 clusters) are evidenced from magnetic measurements in samples without carbon coating, such ferromagnetic clusters just do not exist in the carbon-coated sample. Ferromagnetic resonance experiments are a probe of the -Fe2O3 nanoparticles, and magnetization measurements as well, allowing for a quantitative estimate of the amount of Fe3+. While the fraction of iron in the Fe3+ configuration rises to 0.18% (in the form of -Fe2O3 nanoparticles) in the carbon-free sample, this fraction falls to a residual impurity concentration in the carbon-coated sample. Structural properties show that the carbon does not penetrate inside the LiFePO4 particles but has been very efficient in the reduction of Fe3+, preventing the -Fe2O3 clustering thus pointing out a gas phase reduction process. The carbon deposit characterized by Raman spectroscopy is an amorphous graphite deposit hydrogenated with a very small H/C ratio, with the same Raman characteristics as a-C carbon films obtained by pyrolysis technique at pyrolysis temperature 830±30°C. The impact of the carbon coating on the electrochemical properties is also reported.

Characterization of the carbon coating onto LiFePO4 particles used in lithium batteries

While nanosized ferromagnetic particles could poison the performance of the Li batteries containing phospho-olivine, the carbon-film coating the LiFePO4 particles has a beneficial effect on cycling life of the cells. In this paper, we present the properties of the carbon layer deposited at the surface of the LiFePO4 grains. Characteristics of the carbon layer are analyzed using scanning electron microscopy, high-resolution transmission scanning electron microscopy, Fourier transform infrared, and Raman scattering (RS) spectroscopy. The carbon deposit characterized by RS spectroscopy is hydrogenated with very small hydrogen/carbon ratio, so that it belongs to the family of the amorphous graphitic carbon. The carbon deposit is similar to that obtained by pyrolysis technique at high temperature. It is expected to have the same properties (small hardness, high electronic conductivity) that favor both the Li diffusion from the LiFePO4 bulk and the charge-discharge rate of the cell. A model for the Li-ion trans...

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.

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.

Electrochemical properties of sputter-deposited MoO3 films in lithium microbatteries

Molybdenum oxide (MoO3) films were prepared by magnetron sputtering using an Mo target. The films were sputtered in the reactive atmosphere of an argon–oxygen gas mixture under various substrate temperatures, Ts, and oxygen partial pressures, p(O2). The effects of the growth conditions on the microstructure were examined using reflection high-energy electron diffraction and x-ray photoelectron spectroscopy. The analyses indicate that stoichiometric and polycrystalline MoO3 films were obtained at Ts = 445 °C and p(O2) = 61%. The applicability of the sputtered MoO3 films for lithium microbattery application has been demonstrated. The discharge–charge profiles, the kinetics of lithium intercalation process in the film, and the cycling behavior have been investigated in detail to understand the effect of microstructure on the electrochemical performance.

Magnetic Properties of LiNi0.33Mn0.33Co0.33 as Positive Electrode for Li-Ion Batteries

In this work, we studied the magnetic properties of LiNi0.33Mn0.33Co0.33O2 synthesized by wet chemistry via oxalate route. Measurements included the temperature dependence of the magnetic susceptibility, χm(T) and magnetization M(H). The influence of the synthesis conditions on the magnetic and electronic properties is presented and discussed. Analysis of magnetic data allows the determination of the cationic disorder, i.e. the concentration of Ni ions in the 3a lithium sites.

Investigation of the reaction mechanism of lithium sulfur batteries in different electrolyte systems by in situ Raman spectroscopy and in situ X-ray diffraction

Lithium–sulfur batteries are of great interest owing to their high theoretical capacity of 1675 mA h g−1 and low cost. Their discharge mechanism is complicated and it is still a controversial issue. In the present work, in situ Raman spectroscopy is employed to investigate the poly-sulfide species in the sulfur cathode and in the electrolyte during the cycling of Li–S batteries. The aim is to understand the discharge mechanism and the influence of the electrolyte on the dissolution of sulfur and poly-sulfides. S8n− is identified as the main species in the high voltage plateau of discharge together with cycloocta S8, in the cell using 0.5 mol L−1 LiTFSI–PY13–FSI as the electrolyte. S42−, S22− and S2− are detected soon after the low voltage plateau is reached. A discharge mechanism in the PY13–FSI is proposed based on the identified species which provides important information for improving and designing cathodes. Electrolytes of 0.5 mol L−1 LiTFSI–PY13–FSI and 1 mol L−1 LiTFSI–DOL–DME are used in studying the dissolution of sulfur and poly-sulfides. The results demonstrate that the same poly-sulfide species are present in the two electrolytes. However, the rates of poly-sulfide formation and diffusion to the anode are slow in the ionic liquid compared to those in the ether-based electrolyte due to different ionic mobilities of various species in the two electrolytes. These differences are evidenced by the observation of poly-sulfide species in the DOL–DME from the very beginning of cell assembly even before starting the discharge whereas their appearances, in the ionic liquid, are delayed and only found at the end of the high voltage plateau. Notably, the soluble elemental sulfur is clearly observed in the ionic liquid electrolyte during the first discharge in the high voltage region, which is very different from the DOL–DME system where the elemental sulfur is quickly reduced to poly-sulfides due to self-discharge reactions. In addition, the elemental sulfur is also detected near the lithium anode in DOL–DME at the end of charge, for the first time to our knowledge, which suggests that the degradation of lithium metal is caused by the multiple reactions of the lithium metal surface with soluble poly-sulfides and/or elemental sulfur.

Design and Properties of LiFePO4 Nano-materials for High-Power Applications

This chapter presents a review of the structural and physicochemical properties of LiFePO4 which is considered as the most advanced positive electrode for lithium-ion batteries. Depending on the synthesis, the fundamental properties can be modified because impurities poison this material. These impurities are identified, and a quantitative estimate of their concentrations is deduced from the combination of analytical methods. An optimized preparation provides materials with carbon-coated particles free of any impurity phase, insuring structural stability and electrochemical performance that justify the use of this material as a cathode element in new generation of lithium secondary batteries operating for powering hybrid electric vehicles and full electric vehicles.

Structure and magnetic properties of nanophase-LiFe1.5P2O7

The structure and magnetic properties of lithium iron pyrophosphate, i.e., Li2Fe3(P2O7)2 or LiFe1.5P2O7, synthesized using a facile metal acetate approach for application in lithium-ion batteries, are investigated in detail. The high-resolution transmission electron microscopy, selected area electron diffraction, and x-ray diffraction measurements indicate that Li2Fe3(P2O7)2 is crystallized in the monoclinic structure, without any indication of crystallographic defects such as dislocations or misfits, and exhibit smooth surface morphology. The evaluated lattice parameters are a=0.698 76 nm, b=0.812 36 nm, c=0.964 22 nm, and β=111.83° (P21/c space group). Infrared spectroscopic measurements indicate the presence of P2O7 groups, which are formed by the two PO4 tetrahedral groups connected together. The magnetic measurements indicate that Li2Fe3(P2O7)2 is a weak antiferromagnetic material with TN=20 K exhibiting a Curie constant Cp=3.38 emu K/mol per Fe ion and a negative value of the Weiss temperature (Θp=−...