Dominique Larcher

Electrochemical lithium reactivity with nanotextured anatase-type TiO2

Anatase TiO2 particles were synthesized by a two-step method consisting of the preparation of a solid precursor through hydrolysis of titanium alkoxide followed by heat treatment at different temperatures under ambient air. This simple method led to a highly porous material with a 200 nm homogenous particle size, while the BET specific surface area and crystallite sizes evolved between 49 m2 g−1 to 223 m2 g−1 and from 17.0 nm to 6.3 nm, respectively. Their electrochemical performances clearly revealed the beneficial influence of the divided texture of anatase-type TiO2 on the reactivity with lithium, namely in terms of reversibility. Furthermore, we showed that the TiO2 texture strongly affects the extent of the solid solution domain. Finally, through a simple chemical titration it was possible to clearly quantify the capacitive/faradaic contributions of the electrochemical reaction.

Combined XRD, EXAFS, and mossbauer studies of the reduction by lithium of alpha-Fe2O3 with various particle size.

The electrochemical reduction of hematite with various particle sizes by metallic lithium has been studied by means of X-ray diffraction (XRD) Mossbauer and extended X-ray absorption fine structure (EXAFS) spectroscopy. Previous in situ XRD analysis coupled with electrochemical data showed that lithium can be inserted in the nanosized sample up to 1 Li per Fe2O3 whereas bulk material undergoes an irreversible Li-driven transformation from an hexagonal anionic packing to a close cubic packed framework as soon as 0.03 Li is inserted in the corundum structure. The present data show that only 0.6 Li per formula unit are actually inserted in the structure of small particles. The remaining lithium (0.4) is engaged in irreversible reduction of surface groups, or capacitive behavior. Beyond the solid solution domains, both samples are multiphase, and consist of Li2Fe2O3, Fe0 clusters (10-15 A) and inserted -Fe2O3, which proportions are used to calculate the mean iron oxidation state in the electrode as the reaction proceeds. From these data, we found that electrolyte decomposition can occur at very different steps of the reduction depending on the texture of the active materials. In addition, during the reduction process, we evidenced a reaction of disproportionation (3Fe2+2Fe3+ + Fe0), an intense electrochemical grinding of the hematite particles and the formation of extremely fine metallic surface clusters. For the first time, the EXAFS/X-ray absorption near-edge structure signature of the divalent intermediate Li2Fe2O3 phase is obtained.

H2O2 Decomposition Reaction as Selecting Tool for Catalysts in Li – O2 Cells

The decomposition reaction of H 2 O 2 aqueous solutions (H 2 O 2 → H 2 O + 1/2O 2 ) catalyzed by transition metal oxide powders has been compared with the charging voltage of nonaqueous Li-O 2 cells containing the same catalyst. An inverse linear relationship between Ln k (rate constant for the H 2 O 2 decomposition) and the charging voltage has been found, despite differences in media and possible mechanistic differences. The results suggest that the H 2 O 2 decomposition may be a reliable, useful, and fast screening tool for materials that promote the charging process of the Li-O 2 battery and may ultimately give insight into the charging mechanism.

Comparison of the Reactivity of Various Carbon Electrode Materials with Electrolyte at Elevated Temperature

Using an accelerating rate calorimeter, the reaction between lithium-containing carbon samples and nonaqueous electrolyte has been studied. Six different carbons, differing in morphology (fiber, spheres, flakes), heat=treatment temperature (1,200 to 3,000 C), and surface area (0.4 to 9.2 m{sup 2}/g) were studied. The reaction processes for all six samples were similar, showing an initial activated process, associated with decomposition of metastable components of the solid electrolyte interface, followed by reaction of intercalated lithium with electrolyte. The activation energy for the first process if about 1.3 eV for the lithium-containing carbons in LiPF{sub 6} ethylene carbonate:diethyl carbonate electrolyte. The reaction rates, however, were strongly dependent on the surface area of the graphitized samples, increasing by about two orders of magnitude from the lowest to the highest surface area sample. Surprisingly, a petroleum coke sample, heated to only near 1,200 C, showed reaction rates an order of magnitude lower than expected based on its surface area. These results point the way to better carbons for safer Li-ion cells.

Hydrated Iron Phosphates FePO4 ⋅ n H 2 O and Fe4 ( P 2 O 7 ) 3 ⋅ n H 2 O as 3 V Positive Electrodes in Rechargeable Lithium Batteries

Hydrated Fe III phosphates were investigated as positive electrode materials in lithium batteries. Reversible lithium insertion into amorphous and crystalline FePO 4 .nH 2 O and Fe 4 (P 2 O 7 ) 3 .nH 2 O compositions was found at potentials between 3.5 and 2.5 V vs. Li + /Li. The roles of (i) specific surface area, (ii) amorphous vs. crystalline state, (iii) H 2 O content, and (iv) electronic contact between particles in the composite positive electrode, on the electrochemical performances of these materials are discussed. Very stable cycling was obtained for optimized FePO 4 .1.6H 2 O and Fe 4 (P 2 O 7 ) 3 .4H 2 O electrodes at an average voltage of 3.0 and 3.2 V vs. Li + /Li, respectively.

Biomineralized α-Fe2O3: texture and electrochemical reaction with Li

Sustainable batteries call for the development of new eco-efficient processes for preparation of electrode materials based on low cost and abundant chemical elements. Here we report a method based on bacterial iron biomineralization for the synthesis of α-Fe2O3 and its subsequent use as a conversion-based electrode material in Li batteries. This high-yield synthesis approach enlists (1) the room temperature formation of γ-FeOOH via the use of an anaerobic Fe(II)-oxidizing bacterium Acidovorax sp. strain BoFeN1 and (2) the transformation of these BoFeN1/γ-FeOOH assemblies into an alveolar bacteria-free α-Fe2O3 material by a short heat treatment under air. As the γ-FeOOH precursor particles are precipitated between the two membranes of the bacterial cell wall (40 nm-thick space), the final material consists of highly monodisperse nanometric ([similar]40 × 15 nm) and oriented hematite crystals, assembled to form a hollow shell having the same size and shape as the initial bacteria (bacteriomorph). This double level of control (nanometric particle size and particle organization at the micrometric scale) provided powders exhibiting (1) enhanced electrochemical reversibility when fully reacted with Li and (2) an impressive high rate capability when compared to non-textured primary α-Fe2O3 particles of similar size. This bacterially induced eco-efficient and scalable synthesis method opens wide new avenues to be explored at the crossroads of biomineralization and electrochemistry for energy storage.

Biosynthesis of Co3O4 electrode materials by peptide and phage engineering: comprehension and future

Biologically templated electrodes for Li-ion batteries are proposed. However, many questions regarding their practicality and their use on a large scale remain. Herein we revisit the phage-assisted synthesis of Co3O4 nanoparticles so as to identify the bio-chemistry/chemistry involved beyond this engineering phage synthetic approach and weigh its overall benefit. Various synthesis approaches to mimic the role of the phage which consist of using (i) wild or genetically modified phages made by insertions of specific peptides in the capsid protein, (ii) free peptides, and (iii) MWCNTs as the template were tried, and the resulting Co3O4 nanoparticles were checked for their morphology, size, organization, and electrochemical performances. We spotted the importance of a tetra-peptide motif in the Co3O4 nucleation/texturation process, whether this motif is part of the phage capsid or not, suggesting that the structure of the whole phage is not necessary for the production of the nanoparticles. In light of such findings the use of self-organized peptides or engineered bacteria for the templated synthesis of materials on a larger scale is proposed.

Formation of Nanometric HT-LiCoO2 by a Precipitation and Aging Process in an Alcoholic Solution

In this paper, we detailed the formation/evolution of precipitates in alcoholic media containing Co(II+) and Li(+) species, together with the evolution of the composition and structure/texture of the resulting solid phases during the aging process at controlled constant temperature. While the end product is found to be well-crystallized HT-LiCoO(2), its formation is shown to result from a two-step process enlisting the initial fast precipitation of β-HCoO(2) and then its slow dissolution followed by recrystallization of the lithium-containing material. These results were obtained through combined X-ray diffraction, Raman and IR spectroscopy, elemental and oxidation-state analysis, and high-resolution transmission electron microscopy/selected-area electron diffraction observations. Depending on the cationic concentration, the size of the precipitated material can be controlled within the nanometric range. The electrochemical performances of these aged materials are slightly improved compared to those of the directly precipitated ones that we previously reported. The main limitation of these materials remains the presence of surface protons.

The Lithium Ion

For more than a century, lithium was considered an oddity and a laboratory curiosity of very limited use. Now, however, lithium is regarded as one of the most critical of the elements. It is strategically and economically crucial in many sectors of human activity, including nuclear, medicine, energy, lubricants, metallurgy, polymers and glass sectors, among others. Increasing interest from a variety of fields has given rise to substantial demand for this element and triggered fears, among a few alarmists, about resources and the possibility of supply shortages. The reasons behind the increasing interest in lithium are mainly rooted in its unique atomic, physical and chemical properties, and it is these that this chapter presents.