Etude et amélioration des batteries Lithium-Air via l’optimisation de l’électrode négative avec des alliages de silicium

Supplying the world energy demand while reducing the greenhouse gases emissions is one of the biggest challenges of the 21st century; this requires the development of efficient energy storage devices enabling the utilization of renewable energies. Among them, Lithium-Air batteries are very attractive due to their high theoretical energy density – 10 times that of the current Li-ion batteries – but their development is hindered by the complexity of the chemistry at play. In order to understand such chemistry, we designed a new electrochemical test cell that integrates a pressure sensor, thereby enabling an accurate in operando monitoring of the pressure changes during charge/discharge with high reproducibility and sensitivity. Its use is demonstrated by quantifying the parasitic reactions in Li-O2 cells for various electrolytes frequently encountered in the literature. Through this comparative study, we are able to observe the phenomena currently limiting the performances of Li-O2 batteries after a long cycling (> 1000 h), such as parasitic reactions and the instability of the Li anode. To address the later issue, Li was replaced by a prelithiated silicon electrode made of Si particles oxidized in surface. We demonstrated the feasibility of enhancing both their capacity and cycle life via a pre-formatting treatment that triggers the reduction of their SiO2 coating by liberating pure Si metal. The full LixSi-O2 cells using such treated electrodes exhibit performances competing with the best analogous systems reported in the literature (> 30 cycles; more than 400 h of cycling), but the development of practical prototypes still requires to improve the cycle-life.Face aux défis du XXIème siècle concernant l'approvisionnement mondial en énergie et le réchauffement climatique, il est capital de développer des systèmes de stockage d'énergie efficaces et compétitifs. Parmi eux, la technologie Lithium-Air fait l'objet de nombreuses recherches car elle présente une densité d'énergie théorique dix fois supérieure à celle des batteries Li-ion actuellement utilisées, mais la complexité des réactions chimiques mises en jeu la cantonne au stade de la recherche. Afin d'étudier de manière fiable et reproductible les batteries Li-Air, une nouvelle cellule de test électrochimique intégrant un capteur de pression a été développée. Elle permet d'estimer la quantité de réactions parasites associées à une configuration de batterie lors du cyclage à court et long terme (> 1000 h). Une étude comparative des différents électrolytes les plus utilisés a été réalisée, révélant la différence de comportement entre ces différentes espèces ainsi que l'instabilité de l'anode composée de lithium métallique. Nous avons donc abordé le remplacement de l'anode de lithium par une électrode de silicium pré-lithié. En étudiant l'influence de différentes techniques de pré-lithiation sur des électrodes contenant des particules de Si oxydées en surface, un phénomène de réduction de SiO2 en Si a été mis en évidence, apportant ainsi un gain substantiel en capacité. Les électrodes " activées " ont ensuite été utilisées en tant qu'anode dans les cellules complètes LixSi-O2. Après optimisation, la durée de vie obtenue est supérieure à 400 h (> 30 cycles), ce qui est comparable à la littérature actuelle mais toutefois limité par la présence de réactions parasites

Electrochemical Activation of Silica for Enhanced Performances of Si-Based Electrodes

International audienceThe negative electrodes in commercial Li-ion batteries are currently based primarily on the use of carbonaceous materials. Silicon stands as an attractive alternative; however, its implementation in complete Li-ion cells is limited by complexities inherent to handling this electrode, either as pure Si or Si/SiO2 composites. Herein, we revisit the use of Si-based electrodes and demonstrate the feasibility of enhancing both their capacity and cycle life via a pre-formatting treatment that triggers the reduction of the native SiO2 coating. Moreover, we show that such pretreatments can be applied to pure SiO2 particles to activate their reactivity with Li by liberating pure Si metal. In addition to its practical importance with regard to Si electrodes, this study also emphasizes the potential to harness new anode materials by strategically overcoming kinetic barriers. (C) 2016 The Electrochemical Society. All rights reserved

Controlling the Specific CO 2 Adsorption on Electrochemically Formed Metallic Copper Surfaces

International audienceThe recent demonstration of the reduced overpotential for the electrochemical conversion of CO2 to CO on the surface of oxidized copper films raised the question of possible interplay existing between the electroreduction of copper to its metallic form and the adsorption of CO2 on its surface. To study this effect and better understand the factor governing the CO2 adsorption on the surface of copper-based catalysts, we studied different copper vanadates oxides known for their ability to form metallic copper particles on their surface by electroreduction in Li+-containing salt. By controlling the vanadates framework, the potential at which metallic copper is formed can be controlled and selectively be varied around the CO2/CO standard potential. Studying the reduction behavior of these phases in CO2-saturated organic media containing Li+-salt, we demonstrate that the CO2 adsorption is correlated with the potential at which Cu particles are electrochemically formed. We further show that the CO2 adsorption is correlated with the oxidation of copper, indicating that the overpotential is controlled by the step corresponding to the formation of Cu(I)CO2− intermediate

Long-Time and Reliable Gas Monitoring in Li-O-2 Batteries via a Swagelok Derived Electrochemical Cell

International audienceLithium-oxygen batteries differ from other classical battery technologies because they involve reactions with gaseous species, for which valuable information can be gleaned from quantitative and qualitative investigations. In this study, we report a modified design for an electrochemical test cell that integrates a pressure sensor, thereby enabling accurate in operando monitoring of pressure changes during charge/discharge with high reproducibility and sensitivity and without disturbing the cell system. Its use is demonstrated by quantifying the parasitic reactions in Li-O-2 cells based on a carbon cathode, as a function of the various electrolytes frequently encountered in the literature, such as LiTFSI in DME, DEGDME and TEGDME, LiNO3 in DMA, and LiClO4 in DMSO. Through this comparative study, we are able to observe the phenomena currently limiting the performances of Li-O-2 batteries. Moreover, the long-term cycling behavior of the cells shows a similarity for all the electrolyte systems investigated - a formatting process occurring during the first cycles - which illustrates the importance of the set-up reported here, enabling easy gas monitoring over unlimited number of cycles. This technology is directly transferable to the study of every material whose electrochemical behavior enlists gas uptake and release such as Li-rich layered compounds, organic electrode materials and other metal-air batteries. (C) 2016 The Electrochemical Society. All rights reserved

Chemical vs Electrochemical Formation of Li 2 CO 3 as a Discharge Product in Li–O 2 /CO 2 Batteries by Controlling the Superoxide Intermediate

International audienc

Mesoscale Texturation of Organic-Based Negative Electrode Material through in Situ Proton Reduction of Conjugated Carboxylic Acid

International audienc

Chemical vs Electrochemical Formation of Li₂CO₃ as a Discharge Product in Li–O₂/CO₂ Batteries by Controlling the Superoxide Intermediate

The Li–O₂/CO₂ battery with high capacity has recently been proposed as a new protocol to convert CO₂. However, the fundamental mechanism for the reaction still remains hazy. Here, we investigated the discharge processes of Li–O₂/CO₂ (70%/30%) batteries in two solvents, dimethyl sulfoxide (DMSO) and 1,2-dimethoxyethane (DME). During discharge, both solvents initially show the reduction of oxygen. However, afterward, the solvent affects the reaction pathways of superoxide species by solvating Li⁺ with different strength, depending on the so-called donor number. More precisely, the initial formation of CO₄^•– is favored in DMSO at the expense of lithium superoxide formation that we observed in DME. Despite the different intermediate processes, X-ray diffraction showed that Li₂CO₃ was the final discharge product in both solvents. Moreover, we observed that CO₂ cannot be reduced within the electrochemical stability window of DMSO and DME

Fatal Invasive Infection with Fungemia Due to Microascus cirrosus after Heart and Lung Transplantation in a Patient with Cystic Fibrosis ▿

Scopulariopsis species are rarely but increasingly recognized as opportunistic pathogens in immunocompromised patients. We report on a patient suffering from cystic fibrosis who developed disseminated fungal infection due to a rare Scopulariopsis species, Microascus cirrosus, after heart and lung transplantation. Despite antifungal combination therapy with voriconazole and caspofungin, the patient died 4 weeks after transplantation. Diagnostic difficulties and optimal management of disseminated Scopulariopsis/Microascus infections are discussed

Active Surveillance Program to Increase Awareness on Invasive Fungal Diseases: the French RESSIF Network (2012 to 2018)

International audienceThe French National Reference Center for Invasive Mycoses and Antifungals leads an active and sustained nationwide surveillance program on probable and proven invasive fungal diseases (IFDs) to determine their epidemiology in France. Between 2012 and 2018, a total of 10,886 IFDs were recorded. The incidence increased slightly over time (2.16 to 2.36/10,000 hospitalization days, P = 0.0562) in relation with an increase of fungemia incidence (1.03 to 1.19/10,000, P = 0.0023), while that of other IFDs remained stable. The proportion of ≥65-year-old patients increased from 38.4% to 45.3% (P 60% of the cases) with a global mortality rate of 42.5% and 59.3%, respectively, at 3 months and significant changes in diagnosis procedure over time. More concurrent infections were also diagnosed over time (from 5.4% to 9.4% for mold IFDs, P = 0.0115). In conclusion, we observed an aging of patients with IFD with a significant increase in incidence only for yeast fungemia, a trend toward more concurrent infections, which raises diagnostic and therapeutic issues. Overall, global survival associated with IFDs has not improved despite updated guidelines and new diagnostic tools.IMPORTANCE The epidemiology of invasive fungal diseases (IFDs) is hard to delineate given the difficulties in ascertaining the diagnosis that is often based on the confrontation of clinical and microbiological criteria. The present report underlines the interest of active surveillance involving mycologists and clinicians to describe the global incidence and that of the main IFDs. Globally, although the incidence of Pneumocystis pneumonia, invasive aspergillosis, and mucormycosis remained stable over the study period (2012 to 2018), that of yeast fungemia increased slightly. We also show here that IFDs seem to affect older people more frequently. The most worrisome observation is the lack of improvement in the global survival rate associated with IFDs despite the increasing use of more sensitive diagnostic tools, the availability of new antifungal drugs very active in clinical trials, and a still low/marginal rate of acquired in vitro resistance in France. Therefore, other tracks of improvement should be investigated actively