Na-Ion Batteries Based on Na-Rich Layered Oxyde and Optimised Hard Carbon: An Study of the Electrode/Electrolyte Interphase

Sodium ion batteries (NIB) represent nowadays one of the most promising « beyond Li » technologies. However, and according to recent reviews [1], the development of a true market based on NIB strongly depends on optimizing positive/negative electrode couples delivering high potentials and with a suitable electrolyte. Research carried out in the PCM2E/GREMAN laboratories is focused on the synthesis and electrochemical characterization of positive electrodes based on new materials ascribed to the Na-rich oxide family, not containing expensive and toxic ions as cobalt. In a first time, sodium half-cells with very nice capacities, close to 140 mAh/g, have been successfully prepared in our laboratories. In order to ensure capacity retention, we have also studied different electrolytes by measuring their impact on the electrode/electrolyte interphase. Spectroscopic techniques as XPS and EIS are helpful for this goal. More recently, our laboratories are focusing on the building of full cells containing such oxides against optimized hard carbon-based composites as negative electrode, with increased conductivity. In this presentation we will show the first results on these full NIBs and analyze their cycling properties by the use of different physico-chemical and electrochemical techniques.  [1] </jats:p

Comparaison expérimentale à long terme du stockage de C et du bilan N de systèmes de culture alternatifs et conventionnel

CT3 ; EnjS4 ; Département EAComparaison expérimentale à long terme du stockage de C et du bilan N de systèmes de culture alternatifs et conventionnel. PIREN-SEIN

Similar mineralization rates of soil organic carbon and nitrogen in different alternative arable cropping systems

Similar mineralization rates of soil organic carbon and nitrogen in different alternative arable cropping systems. EGU 2018, European Geophysical Union General Assembly 201

Similar specific mineralization rates of organic carbon and nitrogen in incubated soils under contrasted arable cropping systems

International audienceNo tillage is often thought to mitigate greenhouse gas emissions from agricultural land by increasing soil carbon storage, because of a reduced mineralization of soil organic carbon (SOC) and nitrogen (SON). Regrettably, most available references on this topic come from laboratory incubations of disrupted soil from superficial soil layer. Here, we compare SOC and SON mineralization rates in the long-term experiment of La Cage (France) under conventional (CON), low input (LI), conservation agriculture (CA) or organic (ORG) management. Disturbed soil samples from the 0-27 cm soil layer of all treatments were laboratory incubated for four months, while undisturbed CON and CA soil cores were incubated to account for tillage effects. Physical disturbance decreased SOC and SON mineralization. Model fitting showed that the size of the C labile pool and the C and N mineralization rates of the slow pool were 1.5-2.3-fold greater in undisturbed soil cores than in disturbed ones, which may be due to a higher abundance of labile SOC (e.g. plant residues) in undisturbed soil cores. All cropping systems exhibited similar specific rate of mineralization, expressed per unit of SOC, SON or microbial biomass C, both for disturbed and undisturbed soils. Similar mineralization in CA and CON undisturbed soil cores may result from the balance between higher amount of labile OM and less favourable soil structure for decomposition in CA. Similar mineralization rates in disturbed soil cores suggest that OM decomposability and environmental conditions for decomposers were similar between cropping systems. Overall, these results confirmed the hypothesis previously made in silica to explain the differences in SOC storage in this experiment (Autret a al., 2016). Our results together with the increased SOC stocks observed in CA and ORG treatments suggest that increased biomass returns to soil or changes in microbial physiology may be the main drivers of SOC storage

Can alternative cropping systems mitigate nitrogen losses? Results from a 17-yr experiment in Northern France

CT3 ; EnjS4 ; Département EACan alternative cropping systems mitigate nitrogen losses? Results from a 17-yr experiment in Northern France. European Society of Agronomy 14 congres

Agricultural practices that store organic carbon in soils: is it only a matter of inputs ?

Increasing the world soils carbon stocks by a factor of 4 per mil annually would compensate the annual net increase of CO2 concentration in the atmosphere. This statement is the core of an initiative launched by the French government at the recent COP21, followed by many countries and international bodies, which attracts political attention to the storage potential of C in soils. Compared to forest and pasture soils, agricultural soils have a higher C storage potential, because they are often characterized by low C contents, and increasing their C content is associated with benefits in terms of soil properties and ecosystem services. Here we quantified, under temperate conditions, the additional C storage related to the implementation of two set of practices that are recognized to be in the framework of agroecology: conservation tillage on the one hand and agroforestry on the other hand. These studies were based on long-term experiments, a 16-years comparison on cropping systems on luvisols in the Paris area and a 18-year-old silvoarable agroforestry trial, on fluvisols in southern France, the main crops being cereals in both cases. C stocks were measured on an equivalent soil mass basis. Both systems allowed for a net storage of C in soils, which are, for the equivalent of the 0-30 cm tilled layer, of 0.55 ± 0.16 t ha‑ 1 yr‑ 1 for conservation agriculture (i.e. no tillage with permanent soil coverage with an associated plant, fescue or alfalfa) and of 0.25 ± 0.03 t ha-1 yr-1 for the agroforestry system. These results are in line with estimates proposed in a recent French national assessment concerning the potential of agricultural practices to reduce greenhouse gas emissions. Compared to recent literature, they further show that practices that increase C inputs to soil through additional biomass production would be more effective to store C in soil (tree rows, cover crops in conservation agriculture) than practices, such as no-tillage, that are assumed to reduce soil organic matter mineralisation rates. This questions our understanding of the stabilization processes of organic matter in soils and especially that of physical protection. The conditions and scale, both spatial and temporal, of physical protection of organic matter are discussed in light of recent literature

Agricultural practices to increase carbon storage in soils: is it only a matter of inputs ?

CT3 ; EnjS4 ; Département EAAgricultural practices to increase carbon storage in soils: is it only a matter of inputs ?. EcoSummit 2016. Ecological Sustainability: Engineering Chang

An Electrochemical Study of Fe1.18Sb1.82 as Negative Electrode for Sodium Ion Batteries

International audienceThe mechanism of the electrochemical reaction between FeSb2 and sodium in sodium half cells has been very recently reported [1,L.Baggetto, H.-Y. Hah, C. E. Johnson, C. A. Bridges, J. A. Johnson, G. M. Veith, Phys. Chem.Chem.Phys. 16 (2014) 9538]. Its electrochemical activity, initially limited, seems based on an incomplete desodiation of Na3Sb formed during the first discharge and the occurrence of a ``Fe4Sb'' alloy inactive in the cell. However, no more than two charge/discharge cycles were shown. With this work we shed light on the sodium ion battery electrode properties of another solid in the Fe-Sb system (Fe1.18Sb1.82). Capacity retention properties in two different electrolyte configurations containing NaClO4 as sodium salt and by setting two cycling voltage limits are shown. A discussion about the impact of an additive such as fluoroethylene carbonate (FEC) in the electrode performance is assisted by applying electrochemical impedance spectroscopy on the electrode/electrolyte interfaces. When the additive is not present in the electrolyte, the occurrence of a surface film onto the electrode particles due to the electrolyte decomposition is noticed at low voltage values (0.3 V vs. Na/Na+). Further discharge leads to the growth of this layer and conversely to decrease in the charge transfer resistance as several well dispersed metallic products are present in the discharged electrode. Upon charging, the film is firstly decomposed and/or dissolved and the charge transfer resistance increases. Beyond 1.05 V vs. Na/Na+, a second film, of a different nature from the first one appears onto fresh antimony or FexSby particles formed from desodiation of poorly crystallized Na3Sb. When FEC is added to the electrolyte, the interface is influenced at each stage of the discharge or the charge. FEC suppresses the growth of the surface film at low voltages and decreases the charge transfer resistance at any stage. Upon charging beyond 1.05 V vs. Na/Na+, the surface films are less resistive than in the absence of FEC. Therefore, the additive has a constructive effect on the cell capacity retention upon cycling. Finally setting the lowest limit voltage at 0.2 V vs. Na/Na+ does not result in an improvement in the capacity retention upon cycling, but halves the capacity values compared to the ones obtained at a 0 V vs. Na/Na+ limit voltage