Karim Zaghib

Electrochemical study of Li4Ti5O12 as negative electrode for Li-ion polymer rechargeable batteries

Abstract Li4Ti5O12 a zero-strain insertion material was prepared by conventional method and by high energy ball milling (HEBM) of precursor to form nanocrystalline phases. The electrochemical performance of solid-state negative electrode was carried out using a solvent-free solid polymer electrolyte at 60°C and 80°C. A Li4Ti5O12 vs. lithium cell discharged at C/12 delivered 155 mA h g−1 for the conventional method and 157 mA h g−1 for the method using high ball energy milling, corresponding respectively to 97% and 96% first-cycle coulombic efficiency. The chemical diffusion coefficient of Li4Ti5O12 spinel-type compound is about 2×10−8 cm2 s−1. This is one order of magnitude higher than that of carbonaceous negative electrodes. Li4Ti5O12, which is a zero-strain insertion material, offers advantage for the SPE cell including safety, long life, and reliability.

Current density dependence of peroxide formation in the Li-O2 battery and its effect on charge†

We report a significant difference in the growth mechanism of Li2O2 in Li–O2 batteries for toroidal and thin-film morphologies which is dependent on the current rate that governs the electrochemical pathway. Evidence from diffraction, electrochemical, FESEM and STEM measurements shows that slower current densities favor aggregation of lithium peroxide nanocrystallites nucleated via solution dismutase on the surface of the electrode; whereas fast rates deposit quasi-amorphous thin films. The latter provide a lower overpotential on charge due to their nature and close contact with the conductive electrode surface, albeit at the expense of lower discharge capacity.

Electrochemistry of Anodes in Solid‐State Li‐Ion Polymer Batteries

An examination of the electrochemical performance of solid-state lithium-ion batteries was carried out using a solvent-free solid-polymer electrolyte at 60°C. We studied two different types of anode (negative electrode) material: graphite intercalation compound (GIC) or lithium-titanium oxide (Li 4 Ti 5 O 12 ), and LiCoO 2 was used as the cathode (positive electrode). Natural graphite and carbon fiber gave high reversible capacities of about 372 and 300 mAh/g, respectively. A Li 4 Ti 5 O 12 vs. lithium cell discharged at the C/15 rate delivered 155 mAh/g corresponding to a 97% first-cycle Coulombic efficiency. The irreversible capacity was high when carbon material was used as the negative electrode. However, this sacrificial capacity was very small when we replaced carbon with the spinel material. The crystallographic structure of Li 4 Ti 5 O 12 was analyzed by X-ray diffraction, and its stability was demonstrated by in situ scanning electron microscopy using Li 4 Ti 5 O 12 , which is a zero-strain insertion material that offers advantages for the solid-polymer electrolyte cell including safety, long life, and reliability.

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.

Effect of Carbon Source as Additives in LiFePO4 as Positive Electrode for Lithium-Ion Batteries

The electrochemical properties of LiFePO4 cathodes with different carbon contents were studied to determine the role of carbon as conductive additive. LiFePO4 cathodes containing from 0 to 12% of conductive additive ~carbon black or mixture of carbon black and graphite! were cycled at different C rates. The capacity of the LiFePO4 cathode increased as conductive additive content increased. Carbon increased the utilization of active material and the electrical conductivity of electrode, but decreased volumetric capacity of electrode. This composition ~LiFePO4 with 3 wt % of carbon and 3 wt % of Graphite! is suitable for HEV application.

Effect of Graphite Particle Size on Irreversible Capacity Loss

Electrolyte decomposition and irreversible capacity loss(ICL) occur on carbon electrodes in Li-ion cells. The nature of the surface sites and their role in the amount of electrolyte decomposition on carbon electrodes is not fully understood. Therefore, a study was undertaken to analyze the relationship between the ICL and the active sites on natural graphite of prismatic structure. The ICL was measured on natural graphite of predominantly two-dimensional platelets of average particle size varying from 2 to 40 μm. The fraction of edge and basal plane sites was determined for ideal prismatic structures of different particle size and used as a model for the natural graphite particles. This analysis permitted an analysis of the relationship between the electrolyte decomposition and the distribution of surface sites. From this analysis we conclude that these sites play an important role in the magnitude of the irreversible capacity loss on natural graphite.

Electrochemical and Thermal Studies of Carbon-Coated LiFePO4 Cathode

The carbon-coated LiFeP0 4 Li-ion cathode material was studied for its electrochemical and thermal performance. This electrode exhibited a reversible capacity corresponding to more than 90% of the theoretical capacity when cycled between 2.5 and 4.0 V. The material also showed good capacity retention at high powers, implying that the carbon coating improves the electronic conductivity and hence the cycling of this material. The diffusion coefficient of this material was calculated from its electrochemical impedance spectroscopy. The heat generation during charge and discharge was studied using an isothermal microcalorimeter. Thermal studies were also investigated by using a differential scanning calorimeter and an accelerating rate calorimeter, which showed that LiFePO 4 is safer than the commonly used lithium metal oxide cathodes with layered structures.

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.

Toward practical application of functional conductive polymer binder for a high-energy lithium-ion battery design.

Silicon alloys have the highest specific capacity when used as anode material for lithium-ion batteries; however, the drastic volume change inherent in their use causes formidable challenges toward achieving stable cycling performance. Large quantities of binders and conductive additives are typically necessary to maintain good cell performance. In this report, only 2% (by weight) functional conductive polymer binder without any conductive additives was successfully used with a micron-size silicon monoxide (SiO) anode material, demonstrating stable and high gravimetric capacity (>1000 mAh/g) for ∼500 cycles and more than 90% capacity retention. Prelithiation of this anode using stabilized lithium metal powder (SLMP) improves the first cycle Coulombic efficiency of a SiO/NMC full cell from ∼48% to ∼90%. The combination enables good capacity retention of more than 80% after 100 cycles at C/3 in a lithium-ion full cell.

LiFePO4/gel/natural graphite cells for the BATT program

LiFePO{sub 4}/gel/natural graphite (NG) cells have been prepared and cycled under a fixed protocol for cycle and calendar life determination. Cell compression of 10 psi was found to represent an optimal balance between cell impedance and the first cycle losses on the individual electrodes with the gel electrolyte. Cells with a Li anode showed capacities of 160 and 78 mAh/g-LiFePO{sub 4} for C/25 and 2C discharge rates, respectively. Rapid capacity and power fade were observed in the LiFePO{sub 4}/gel/NG cells during cycling and calendar life studies. Diagnostic evaluations point to the consumption of cycleable Li though a side reaction as the reason for performance fade with minimal degradation of the individual electrodes.