Sylvie Grugeon

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.

An update on the reactivity of nanoparticles Co-based compounds towards Li

Abstract In our comprehensive understanding of reactivity of CoO towards Li, we studied the effect of CoO electrode weight and composition (carbon-free or not) on the cycling performances of CoO/Li half-cells. Capacity and lifetime were measured as a function of the cycling rate and temperature. The lightest electrodes (2xa0mg/cm 2 ) were shown to behave the best, with sustained capacities as high as 600xa0mAh/g up to about 250 cycles at 20xa0°C, and with capacities that peaked up to 1700xa0mAh/g when cycling was performed at 75xa0°C. Searching for the origin of this huge “extra capacity” over the normal conversion process (Co 2+ O→Co 0 , 715xa0mAh/g), we dissociated phenomena by testing carbon-loaded and carbon-free CoO-based electrodes in CoO/Li half cells. We unravelled a temperature-driven capacity rate increase similar for both cells, although the initial reversible capacity was quite different. The carbon-free CoO/Li half cell showed limited initial reversible capacity due to the poor efficiency of the conversion process for non-conducting electrodes. This increase appears to be nested in the reversible growth of a polymeric gel-like film resulting from kinetically activated electrolyte degradation. Polymeric layers were also shown to form from the Li electrochemical reduction of numerous binary phases, differentiating either by the nature of the 3d-metal (Cu, Ni, Fe instead of Co) or that of the anion (S, F, N instead of O). Finally, purely coincidental or not, from comparative studies of CoO, CoSb 3 , and CoSb 2 Li half-cells, we found that, to a certain extent, the capacity amplitude associated with the growth of the polymer film scales with the surface developed by Co nano-particles. This fact would imply a possible catalytic role of 3d metals in assisting the electrolyte decomposition.

Rationalization of the Low-Potential Reactivity of 3d-Metal-Based Inorganic Compounds toward Li

The unusual low-potential Li reactivity toward simple 3d-metal oxides can be accounted for by classical thermodynamie predictions and simpe acid-basic considerations. The Smiths scale, defined in solids for acido-basic reactions involving O 2 species exchange, is successfully used to check that, among the numerous simple oxides, the basic ones such as MnO, FeO, CoO, NiO, and CuO should reversibly react with lithium. Besides the basicity criteria, we stressed that the nanometric character of the reduced composite electrode (e.g., metallic nanoparticles immersed in a highly divided Li 2 O media) is a must to enable the reversible reactivity of metal oxides toward Li. Such a simple approach was nally implemented to other compounds (sulfides, nitrides, vanadates....) and the predictions confronted with experimental data.

Synthesis of monodisperse Au, Pt, Pd, Ru and Ir nanoparticles in ethylene glycol

Au, Pt, Pd, Ru and Ir nanoparticles with a narrow size distribution have been synthesized by chemical reduction of their corresponding metal species in ethylene glycol. In all cases, the average particle size was found to be smaller than 10 nm. Particle size was mainly controlled by varying the initial total metal concentration, the reaction temperature, and the concentration of PVP. With the exception of Ir, metal particle agglomeration and sintering was prevented by the addition of PVP, a well known protective agent that also aids particle dispersion.

Searching for new anode materials for the Li-ion technology: time to deviate from the usual path

Abstract A brief review of our fundamental studies of the reversible reactivity mechanism of vanadates towards lithium is presented. This mechanism totally differs from the classical one based either on reversible insertion/deinsertion of lithium into host structures or on Li alloying reactions, and has led to the thought of using nanosized transition metal oxides as possible negative electrode materials for rechargeable Li-ion batteries. Electrochemical capacities, as high as 700xa0mAh/g with a 100% capacity retention up to 100 cycles and high rates, can be achieved with optimized metal oxides (MO, M=Co, Cu, Ni, Fe, etc.) powders. By combining transmission electron microscope (TEM), infrared (IR) and magnetic measurements we directly proved the formation of 10–50xa0A metal nanoparticles dispersed into a lithia (Li2O) matrix during the reduction step of MO with Li. Upon oxidation, the metal nanoparticles were shown to convert back to MO while Li2O was decomposed. The new opportunities provided by these metal oxides systems based on the reversible formation/decomposition of Li2O are discussed together with the positive attributes that nanoparticles could have to the field of energy storage.

XPS Identification of the Organic and Inorganic Components of the Electrode/Electrolyte Interface Formed on a Metallic Cathode

X-ray photoelectron spectroscopy (XPS) was used to determine the nature and composition of electrode/electrolyte interfaces forming during the 55°C cycling of Li-based cells in ethylene carbonate:dimethyl carbonate LiPF 6 electrolyte using a heat-treated stainless steel substrate as the positive electrode. From a classical analysis of the XPS C 1s, O 1s, F 1s, P 2p, and Li Is core peak spectra complemented by an unusual detailed interpretation of XPS valence spectra, we could follow, as a function of the cell cycling history, the evolution and nature of the species constituting the organic/inorganic layer as well as determine its approximate composition. We have shown that this surface layer mainly consists of PEO oligomers (-CH 2 -CH 2 -O-) n , carbonates Li 2 CO 3 and/or CH 3 OCO 2 Li, LiPF 6 salt, and of degradation products of the salt such as LiF and phosphates. Moreover, we give evidence that this layer does not only grow but also becomes richer in CH 3 OCO 2 Li and LiF species upon cycling.

Investigation on the fire-induced hazards of Li-ion battery cells by fire calorimetry

The use of the high energy Li-ion battery technology for emerging markets like electromobility requires precise appraisal of their safety levels in abuse conditions. Combustion tests were performed on commercial pouch cells by means of the Fire Propagation Apparatus also called Tewarson calorimeter in the EU, so far used to study flammability parameters of polymers and chemicals. Well-controlled conditions for cell combustion are created in such an apparatus with the opportunity to analyse standard decomposition/combustion gases and therefore to quantify thermal and toxic threat parameters governing the fire risk namely the rate of heat release and the effective heat of combustion as well as the toxic product releases. Using the method of O2 consumption, total combustion heats and its kinetic of production were determined as a function of the cell state of charge unveiling an explosion risk in the case of a charged cell. The resulting combustion heat is revealed to be consistent with cumulated contribution values pertaining to each organic part of the cell (polymers and electrolytes) as calculated from thermodynamic data. The first order evaluation of the dangerousness of toxic gases resulting from fire induced combustion such as HF, CO, NO, SO2 and HCl was undertaken and stressed the fact that HF is the most critical gas originating from F-containing cell components in our test conditions.

Electrochemical characterization of lithium 4,4′-tolane-dicarboxylate for use as a negative electrode in Li-ion batteries

Lithium 4,4′-tolane-dicarboxylate has been synthesized and examined for use as a negative electrode material in lithium ion batteries. Cycling studies in Swagelok cells, using lithium as a counter electrode, show a reversible capacity of ∼200 mAh g−1 at ∼0.65 V and minimal discharge/charge polarization (∼15 mV). XRD and SEM analyses reveal that the material crystallizes in two different ways depending on the type of solvent used in the synthesis. The changes in structural packing with methanol or ethanol dramatically affect the capacity of the material leading to electrodes that are able to intercalate almost two vs. one Li per unit formula, respectively.