Laboratoire de Réactivité et Chimie des Solides

The increasing interest in energy storage for the grid can be attributed to multiple factors, including the capital costs of managing peak demands, the investments needed for grid reliability, and the integration of renewable energy sources. Although existing energy storage is dominated by pumped hydroelectric, there is the recognition that battery systems can offer a number of high-value opportunities, provided that lower costs can be obtained. The battery systems reviewed here include sodium-sulfur batteries that are commercially available for grid applications, redox-flow batteries that offer low cost, and lithium-ion batteries whose development for commercial electronics and electric vehicles is being applied to grid storage.

Energy storage is more important today than at any time in human history. Future generations of rechargeable lithium batteries are required to power portable electronic devices (cellphones, laptop computers etc.), store electricity from renewable sources, and as a vital component in new hybrid electric vehicles. To achieve the increase in energy and power density essential to meet the future challenges of energy storage, new materials chemistry, and especially new nanomaterials chemistry, is essential. We must find ways of synthesizing new nanomaterials with new properties or combinations of properties, for use as electrodes and electrolytes in lithium batteries. Herein we review some of the recent scientific advances in nanomaterials, and especially in nanostructured materials, for rechargeable lithium-ion batteries.

Despite the imminent commercial introduction of Li-ion batteries in electric drive vehicles and their proposed use as enablers of smart grids based on renewable energy technologies, an intensive quest for new electrode materials that bring about improvements in energy density, cycle life, cost, and safety is still underway. This Progress Report highlights the recent developments and the future prospects of the use of phases that react through conversion reactions as both positive and negative electrode materials in Li-ion batteries. By moving beyond classical intercalation reactions, a variety of low cost compounds with gravimetric specific capacities that are two-to-five times larger than those attained with currently used materials, such as graphite and LiCoO(2), can be achieved. Nonetheless, several factors currently handicap the applicability of electrode materials entailing conversion reactions. These factors, together with the scientific breakthroughs that are necessary to fully assess the practicality of this concept, are reviewed in this report.

We report that the room temperature cycling of CoO/Li cells involving two processes, the reduction of and the growth of a polymer/gel-like film at high and low potentials, respectively, is extremely sensitive to cycling voltage ranges with the best results obtained when the cells are fully discharged. The low-voltage process is quite reversible over the 0.02 to 1.8 V range with a sustained capacity of about 150 mAh/g over a few hundred cycles. Within such a range of potential the polymer/gel-like is barely evolving while it vanishes as the oxidation potential is increased above 2 V. From the cyclic-voltammogram profiles we conclude that the origin of the low-voltage capacity is nested in the pseudocapacitive character of the in situ made polymeric/gel film. Tentative explanations based on comparisons with existing literature are made to explain such an unusual finding. © 2002 The Electrochemical Society. All rights reserved.

For more than 20 years, most of the technological achievements for the realization of positive electrodes for practical rechargeable Li battery systems have been devoted to transition metal oxides such as LixMO2 (M = Co, Ni, Mn), LixMn2O4, LixV2O5, or LixV3O8. The first two classes of materials built on close-packed oxygen stacking adopt bidimensional and tridimensional crystal structures, respectively (Figure 1), from which lithium ions may be easily intercalated or extracted in a reversible manner. These oxides are reasonably good ionic and electronic conductors, and lithium insertion/extraction proceeds while operating on the M4+/M3+ redox couple, located between 4 and 5 V versus Li+/Li...

Functionalized multiwalled carbon nanotubes (CNTs) are coated with a 4-5 nm thin layer of V(2)O(5) by controlled hydrolysis of vanadium alkoxide. The resulting V(2)O(5)/CNT composite has been investigated for electrochemical activity with lithium ion, and the capacity value shows both faradaic and capacitive (nonfaradaic) contributions. At high rate (1 C), the capacitive behavior dominates the intercalation as 2/3 of the overall capacity value out of 2700 C/g is capacitive, while the remaining is due to Li-ion intercalation. These numbers are in agreement with the Trasatti plots and are corroborated by X-ray photoelectron spectroscopy (XPS) studies on the V(2)O(5)/CNTs electrode, which show 85% of vanadium in the +4 oxidation state after the discharge at 1 C rate. The cumulative high-capacity value is attributed to the unique property of the nano V(2)O(5)/CNTs composite, which provides a short diffusion path for Li(+)-ions and an easy access to vanadium redox centers besides the high conductivity of CNTs. The composite architecture exhibits both high power density and high energy density, stressing the benefits of using carbon substrates to design high performance supercapacitor electrodes.

Electrolytes are essential for the proper functioning of any battery technology and the emerging Na-ion technology is no exception. Hence, a major focus on battery research is to identify the most appropriate formulation so as to minimize interface reactions and enhance both cell performances and safety aspects. In order to identify suitable electrolyte formulations for Na-ion chemistry we benchmarked various electrolytes containing diverse solvent mixtures (cyclic, acyclic carbonates, glymes) and Na-based salts having either F-based or perchlorate anions and measured viscosity, ionic conductivity, and thermal and electrochemical stability. The binary EC:PC solvent mixture has emerged as the best solvent formulation and has been used to test the performance of Na/hard carbon cells with both NaClO4 and NaPF6 as dissolved salts. Hard carbon electrodes having reversible capacities of 200 mA h g−1 with decent rate capability and excellent capacity retention (>180 cycles) were demonstrated. Moreover, DSC heating curves demonstrated that fully sodiated hard carbon cycled in NaPF6–EC:PC exhibits the highest exothermic onset temperature and nearly the lowest enthalpy of reaction, thus making this electrolyte most attractive for the development of Na-ion batteries.

Na2Ti3O7 is found to reversibly uptake 2 Na ions per formula unit (200 mA h/g) at an average potential of 0.3 V and is hence a very promising negative electrode material for building sodium ion batteries working at room temperature.

Batteries are a major technological challenge in this new century as they are a key method to make more efficient use of energy. Although today's Li-ion technology has conquered the portable electronic markets and is still improving, it falls short of meeting the demands dictated by the powering of both hybrid electric vehicles and electric vehicles or by the storage of renewable energies (wind, solar). There is room for optimism as long as we pursue paradigm shifts while keeping in mind the concept of materials sustainability. Some of these concepts, relying on new ways to prepare electrode materials via eco-efficient processes, on the use of organic rather than inorganic materials or new chemistries will be discussed. Achieving these concepts will require the inputs of multiple disciplines.

The fundamental challenge of the 21st century that mankind has to face is definitely energy supply, its storage and conversion in a way that necessarily protects the environment. For 250 years, the tremendous development of humanity has been founded on the harnessing of fossil fuels (coal, crude oil then natural gas) as primary energy due to their high energy density values and the easiness of access. However, this global pattern of energy supply and use is unsustainable. Global warming and finite fossil-fuel supplies call for a radical change in the energy mix to favour renewable energy sources. Without being exhaustive, we tackle in this article the tricky energy question and associated environmental issues as personally perceived. The eminent role of electric energy produced from decarbonized sources in a future sustainable economy is particularly highlighted as well as the issues of its needed storage. The possible and foreseen hindrances of electrochemical energy storage devices, focusing on the lithium-ion technology, are presented in parallel with the possible pathways to make such a technology greener in synergy with the rise of a biomass-based industry.

In the race for better Li-ion batteries, research on anode materials is very intensive as there is a strong desire to find alternatives to carbonaceous negative electrodes. A large part of these studies is devoted to alloying reactions, which have been known for more than thirty years but that have regained great interest by downsizing particle sizes, moving to nano-textured/nanostructured composites, or designing new electrode concepts. It is not the scope of this review to retrace twenty-five years of research, but rather to highlight recent advances that have been made in the use of Sn or Si-based electrodes together with the remaining challenges to be addressed and issues to be solved prior to such electrodes being commercially implemented in Li-ion cells.

Integration of electrochemical capacitors with silicon-based electronics is a major challenge, limiting energy storage on a chip. We describe a wafer-scale process for manufacturing strongly adhering carbide-derived carbon films and interdigitated micro-supercapacitors with embedded titanium carbide current collectors, fully compatible with current microfabrication and silicon-based device technology. Capacitance of those films reaches 410 farads per cubic centimeter/200 millifarads per square centimeter in aqueous electrolyte and 170 farads per cubic centimeter/85 millifarads per square centimeter in organic electrolyte. We also demonstrate preparation of self-supported, mechanically stable, micrometer-thick porous carbon films with a Young's modulus of 14.5 gigapascals, with the possibility of further transfer onto flexible substrates. These materials are interesting for applications in structural energy storage, tribology, and gas separation.

The electrochemical reactivity of tailor-made or CuO powders prepared according to the polyol process was tested in rechargeable Li cells. To our surprise, we demonstrated that CuO, a material well known for primary Li cells, and could reversibly react with 1.1 Li and 2 Li ions per formula unit, respectively, leading to reversible capacities as high as 400 mAh/g in the 3-0.02 V range. The ability of copper oxide-based Li cells to retain their capacity upon numerous cycles was found to be strongly dependent on the particle size, and the best results (100% of the total capacity up to 70 cycles) were obtained with 1 μm and CuO particles. Ex situ transmission electron microscopy data and in situ X-ray experiments show that the reduction mechanism of by Li first involved the formation of Cu nanograins dispersed into a lithia matrix, followed by the growth of an organic coating that partially dissolved upon the subsequent charge while Cu converted back to nanograins. We believe that the key to the reversible reactivity mechanism of copper oxides or other transition metal oxides toward Li is the electrochemically driven formation of highly reactive metallic nanograins during the first discharge, which enables the formation-decomposition of upon subsequent cycles. © 2001 The Electrochemical Society. All rights reserved.

There's more to LiFe: When used as an electrode in a lithium half cell, the metal–organic framework [LixFeIIxFeIII1−x(OH)0.8F0.2L] (L=O2CC6H4CO2) shows a reversible redox process around 3.0 V versus Li+/Li0 with interesting capacity retention and rate capability (see voltage profile for a [LixFe(OH)0.8F0.2L] half cell; inset: representation of lithium insertion upon oxidation to Li+). Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2002/2007/z605163_s.pdf or from the author. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Reversible anionic redox has rejuvenated the search for high-capacity lithium-ion battery cathodes. Real-world success necessitates the holistic mastering of this electrochemistry's kinetics, thermodynamics, and stability. Here we prove oxygen redox reactivity in the archetypical lithium- and manganese-rich layered cathodes through bulk-sensitive synchrotron-based spectroscopies, and elucidate their complete anionic/cationic charge-compensation mechanism. Furthermore, via various electroanalytical methods, we answer how the anionic/cationic interplay governs application-wise important issues-namely sluggish kinetics, large hysteresis, and voltage fade-that afflict these promising cathodes despite widespread industrial and academic efforts. We find that cationic redox is kinetically fast and without hysteresis unlike sluggish anions, which furthermore show different oxidation vs. reduction potentials. Additionally, more time spent with fully oxidized oxygen promotes voltage fade. These fundamental insights about anionic redox are indispensable for improving lithium-rich cathodes. Moreover, our methodology provides guidelines for assessing the merits of existing and future anionic redox-based high-energy cathodes, which are being discovered rapidly.

Li-ion batteries presently operate on inorganic insertion compounds. The abundance and materials life-cycle costs of such batteries may present issues in the long term with foreseeable large-scale applications. To address the issue of sustainability of electrode materials, a radically different approach from the conventional route has been adopted to develop new organic electrode materials. The oxocarbon salt Li2C6O6 is synthesized through potentially low-cost processes free of toxic solvents and by enlisting the use of natural organic sources (CO2-harvesting entities). It contains carbonyl groups as redox centres and can electrochemically react with four Li ions per formula unit. Such battery processing comes close to both sustainable and green chemistry concepts, which are not currently present in Li-ion cell technology. The consideration of renewable resources in designing electrode materials could potentially enable the realization of green and sustainable batteries within the next decade.

C-free crystalline powders were prepared by a synthesis method based on direct precipitation under atmospheric pressure. The particle size distribution is extremely narrow, centered on ca. . A soft thermal treatment, typically at for under slight reducing conditions was shown to be necessary to obtain satisfactory electrochemical deinsertion/insertion properties. This thermal treatment does not lead to grain growth or sintering of the particles, and does not alter the surface of the particles. The electrochemical performances of the powders obtained by this synthesis method are excellent, in terms of specific capacity ( at 5C-rate) as well as in terms of cyclability (no significant capacity fade after more than 400 cycles), without the need of carbon coating.

The electrochemical reaction of lithium with crystallized (hematite) has been studied by means of in situ X-ray diffraction. When reacting large particles we observed the well-known transformation of the close-packed anionic array from hexagonal (hc) to cubic (ccp) stacking. At the early stage of the reduction, a very small amount of lithium can be inserted before this structural transformation occurs. Nanosize made of fine monolithic particles (200 Å) behaves very different, since up to one Li per formula unit can be inserted in the corundum structure without phase transformation. To our knowledge, this is the first time this phase is maintained for such large values. This cationic insertion was found to come with a small cell volume expansion evaluated to 1%. Unsuccessful attempts to increase the values on large particles by decreasing the applied discharge current density suggest that the particle size is the only parameter involved. The better structural reversibility of this monophasic process compared to the biphasic one was confirmed by electrochemical cycling tests conducted with hematite samples of various particle sizes. Therefore, by using nanosize particles, we can drastically increase the critical Li concentration required to observe the transition. This work demonstrates that a careful control of the texture/particle size of electrochemically active oxide particles is likely an important variable that has been largely disregarded for such properties. © 2002 The Electrochemical Society. All rights reserved.

To better understand the factors responsible for the poor electrochemical performances of the olivine-type , various experiments such as chemical delithiation, galvanostatic charge and discharge, cyclic voltamperometry, and impedance conductivity, were carried out on both and . Chemical delithiation experiments confirmed a topotactic two-phase electrochemical mechanism between and the fully delithiated phase (, , and ). We conclude that the limiting factor in the / electrochemical reaction is nested mostly in the ionic and/or electronic transport within the particles themselves rather than in charge transfer kinetics or structural instability of the phase. For instance, the electrical conductivity of ( at 573 K, ) was found to be several orders of magnitude lower than that of ( at 298 K, ).

Taking the shortcut: Spectroscopic data (see picture) provide direct evidence that in non-aqueous Li+ electrolyte, O2 is reduced to O2−, which then forms LiO2 on the electrode surface which disproportionates to Li2O2. On charging, Li2O2 decomposes directly, in a one-step reaction to evolve O2 and does not pass through LiO2 as an intermediate. Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.