Philippe Poizot

On the Origin of the Extra Electrochemical Capacity Displayed by MO/Li Cells at Low Potential

and thegrowth of a polymer/gel-like film at high and low potentials, respectively, is extremely sensitive to cycling voltage ranges with thebest results obtained when the cells are fully discharged. The low-voltage process is quite reversible over the 0.02 to 1.8 V rangewith a sustained capacity of about 150 mAh/g over a few hundred cycles. Within such a range of potential the polymer/gel-like isbarely evolving while it vanishes as the oxidation potential is increased above 2 V. From the cyclic-voltammogram profiles weconclude that the origin of the low-voltage capacity is nested in the pseudocapacitive character of thein situ made polymeric/gelfilm. Tentative explanations based on comparisons with existing literature are made to explain such an unusual finding.© 2002 The Electrochemical Society. @DOI: 10.1149/1.1467947# All rights reserved.Manuscript submitted July 2, 2001; revised manuscript received November 14, 2001. Available electronically April 2, 2002.

Particle Size Effects on the Electrochemical Performance of Copper Oxides toward Lithium

The electrochemical reactivity of tailor-made Cu 2 O 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 Cu 2 O 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 I μm Cu 2 O and CuO particles. Ex situ transmission electron microscopy data and in situ X-ray experiments show that the reduction mechanism of Cu 2 O by Li first involved the formation of Cu nanograins dispersed into a lithia (Li 2 O) matrix, followed by the growth of an organic coating that partially dissolved upon the subsequent charge while Cu converted hack to Cu 2 O 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 Li 2 O upon subsequent cycles.

Conjugated dicarboxylate anodes for Li-ion batteries.

Present Li-ion batteries for portable electronics are based on inorganic electrodes. For upcoming large-scale applications the notion of materials sustainability produced by materials made through eco-efficient processes, such as renewable organic electrodes, is crucial. We here report on two organic salts, Li(2)C(8)H(4)O(4) (Li terephthalate) and Li(2)C(6)H(4)O(4)(Li trans-trans-muconate), with carboxylate groups conjugated within the molecular core, which are respectively capable of reacting with two and one extra Li per formula unit at potentials of 0.8 and 1.4 V, giving reversible capacities of 300 and 150 mA h g(-1). The activity is maintained at 80 degrees C with polyethyleneoxide-based electrolytes. A noteworthy advantage of the Li(2)C(8)H(4)O(4) and Li(2)C(6)H(4)O(4) negative electrodes is their enhanced thermal stability over carbon electrodes in 1 M LiPF(6) ethylene carbonate-dimethyl carbonate electrolytes, which should result in safer Li-ion cells. Moreover, as bio-inspired materials, both compounds are the metabolites of aromatic hydrocarbon oxidation, and terephthalic acid is available in abundance from the recycling of polyethylene terephthalate.

Size Effects on Carbon-Free LiFePO4 Powders The Key to Superior Energy Density

C-free LiFePO 4 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. 140 nm. A soft thermal treatment, typically at 500°C for 3 h under slight reducing conditions was shown to be necessary to obtain satisfactory electrochemical Li + 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 (147 mAh g -1 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.

A Transmission Electron Microscopy Study of the Reactivity Mechanism of Tailor-Made CuO Particles toward Lithium

The electrochemical reactivity of tailor-made CuO powders prepared according to a new low-temperature synthesis method was studied by a combination of transmission electron microscopy (TEM) and electrochemical techniques. All the processes involved during cycling were successfully identified. We show that the reduction mechanism of CuO by lithium involves the formation of a solid solution of Cu II 1x Cu I x O 1 1/2 :, 0 ≤ x ≤ 0.4, a phase transition into Cu 2 O, then the formation of Cu nanograins dispersed into a lithia matrix ( Li 2 O) followed by the growth of an organic-type coating. This one is responsible for the extra capacity observed on the voltage vs. composition curve. During the subsequent charge, the organic layer vanishes first, and then the Cu grains are partially or fully oxidized with a concomitant decomposition of Li 2 O. The formation of Li 2 O and Cu nanograins and then the one of Cu. CuO, and Cu 2 O nanograins on the first discharge and subsequent charge, respectively, were identified by high-resolution TEM studies. These results enabled a better understanding of the processes governing the reactivity of 3d metal oxides vs. lithium down to 0.02 V.

From biomass to a renewable LixC6O6 organic electrode for sustainable Li-ion batteries.

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.

Lithium Salt of Tetrahydroxybenzoquinone: Toward the Development of a Sustainable Li-Ion Battery

The use of lithiated redox organic molecules containing electrochemically active C=O functionalities, such as lithiated oxocarbon salts, is proposed. These represent alternative electrode materials to those used in current Li-ion battery technology that can be synthesized from renewable starting materials. The key material is the tetralithium salt of tetrahydroxybenzoquinone (Li(4)C(6)O(6)), which can be both reduced to Li(2)C(6)O(6) and oxidized to Li(6)C(6)O(6). In addition to being directly synthesized from tetrahydroxybenzoquinone by neutralization at room temperature, we demonstrate that this salt can readily be formed by the thermal disproportionation of Li(2)C(6)O(6) (dilithium rhodizonate phase) under an inert atmosphere. The Li(4)C(6)O(6) compound shows good electrochemical performance vs Li with a sustained reversibility of approximately 200 mAh g(-1) at an average potential of 1.8 V, allowing a Li-ion battery that cycles between Li(2)C(6)O(6) and Li(6)C(6)O(6) to be constructed.

Clean energy new deal for a sustainable world: from non-CO2 generating energy sources to greener electrochemical storage devices

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.

Evaluation of polyketones with N-cyclic structure as electrode material for electrochemical energy storage: case of pyromellitic diimide dilithium salt

Pyromellitic diimide dilithium salt was selected to complete our database on redox-active polyketones with a N-cyclic structure. Although never reported to date, such a lithiated salt was readily synthesized making its electrochemical evaluation in a Li battery possible. Preliminary data show that this novel material reversibly inserts two Li per formula unit at a relatively low potential giving a stable capacity value of 200 mAh g(-1).

Experimental evidence for electrolyte involvement in the reversible reactivity of CoO toward compounds at low potential

Characterization of different negative electrodes (Li or Li x C 6 ) cycled vs. CoO was performed on three-electrode cells by electrochemical impedance spectroscopy and cyclic voltammetry. The unexpected behavior of the negative electrode, especially the electrolyte reactivity occurring at the end of CoO discharge, was correlated with the reactions taking place at the positive electrode. This electrolyte involvement affects the electrochemical behavior of the negative electrode, and, more precisely, the charge transfer process, which becomes limited. Nevertheless, the latter is recovered on the following positive electrode oxidation. These observations are discussed and assumptions are made to explain the surprising and complex cobalt oxide system.