Anionic redox chemistry in Na-rich Na2Ru1−ySnyO3 positive electrode material for Na-ion batteries

The synthesis and Na- electrochemical activity of Na-rich layered Na2Ru1−ySnyO3 compounds is reported. Like their Li-analogue, Na2Ru1−ySnyO3 shows capacities that exceed theoretical capacity calculated from the cationic redox species. The high capacity was found, by means of XPS analysis, to be associated to the accumulation of both cationic (Ru4+/Ru5+) and anionic (O2−/O2n−) redox processes. The structural evolutions during cycling have been followed and found to be associated with the cation disordering and loss of crystallinity on cycling

Boron-Based Functional Additives Enable Solid Electrolyte Interphase Engineering in Calcium Metal Battery

Calcium-metal batteries have received growing attention recently after several studies reporting successful metal plating and stripping with organic electrolytes. Given the low redox potential of metallic calcium, its surface is commonly covered by a passivation layer grown by the accumulation of electrolyte decomposition products. The presence of borate species in this layer has been shown to be a key parameter allowing for Ca2+ migration and favoring Ca electrodeposition. Here, boron-based additives are evaluated in order to tune the SEI composition, morphology, and properties. The decomposition of a BF3-based additive is studied at different potentiostatic steps and the resulting SEI layer was thoroughly characterized. SEI growth mechanism is proposed based on both experimental data and DFT calculations pointing at the formation of boron-crosslinked polymeric matrices. Several boron-based adducts are explored as SEI-forming additives for calcium-metal batteries paving the way to very rich chemistry leading to Ca2+ conducting SEI.Funding from the European Union's Horizon 2020 research and innovation program H2020 are acknowledged: European Research Council (ERC-2016-STG, CAMBAT, grant agreement no. 715087 and ERC-2020-STG, HiPeR−F, grant agreement no. 950625) and H2020-MSCA-COFUND-2016 (DOC-FAM, grant agreement no. 754397). A.P. is grateful to the Spanish Ministry for Economy, Industry and Competitiveness Severo Ochoa Programme for Centres of Excellence in R&D (CEX2019-000917-S). D.F., C.C. and R.D. thank the French National Research Agency (STORE-EX Labex Project ANR-10-LABX-76-01) for financial support. K.R. and M.L. gratefully acknowledge the research funding by the Slovenian Research Agency (P1-0045, N1-0189). Alistore-European Research Institute is gratefully acknowledged for financial support through the postdoc grant to C.B. The SR-FTIR experiments were performed at MIRAS beamline at ALBA Synchrotron with the collaboration of ALBA staff. All DFT calculations were carried out at the Wroclaw Centre for Networking and Supercomputing within grant no. 346.With funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000917-S).Peer reviewe

Photocatalytic efficiency and self-cleaning properties under visible light of cotton fabrics coated with sensitized TiO2

International audienceA simple and reproducible one-pot process for the elaboration of cotton fabrics coated with sensitized TiO2 was developed. A molecular precursor [Ti(OR)3(O2C-AQ)] was prepared starting with anthraquinone-2-carboxylic acid (AQ-COOH) and characterized by FTIR, CPMAS NMR and XPS. Hydrolysis of mixtures of [Ti(OR)3(O2C-AQ)] and Ti(OR)4 at low temperature in an aqueous medium leads to pale yellow cotton fabrics together with the corresponding free P-TiO2/AQ powders. The diffuse reflectance UV spectra confirmed the shift of absorption towards the visible range. From FTIR, CPMAS NMR and XPS analysis of the samples (cotton pieces and powders), it was shown that AQ-COOH was not only adsorbed on Titania but tightly bond through a carboxylate complex as in the molecular precursor. Anatase polymorph was always characterized by XRD even in the absence of a calcination step. Examination by SEM of treated cotton tissues before and after washing showed stable and homogeneous coating of TiO2 particles on the cotton fibers.The photocatalytic properties of the samples were investigated, with special care to visible light activation. Under UV light, acetone mineralization was observed, while under filtered visible light, no acetone mineralization occurred. However efficient singlet oxygen addition to di-n-butyl sulfide was evidenced under visible light. Sulfoxide and sulfone were obtained in better yields using sensitized TiO2 than using un-modified TiO2 or Anthraquinone alone treated fabrics. Optimum results were obtained with low level of sensitizing AQ-COOH relative to TiO2 (8%) and no reactivity improvement was noticed with higher AQ-COOH levels. The cotton pieces coated with sensitized TiO2 also displayed self-cleaning properties towards wine stain, either under solar illumination or even in indoor light.The better efficiency of sensitized TiO2-coated cotton is accounted for by a synergy effect between TiO2 and AQ-COOH, enhancing the formation of Reactive Oxygen Species (singlet oxygen and/or superoxide radical-anion). However, under these conditions, the production of hydroxyl radical seems to be ruled out

Optimization of elemental selenium (Se(0)) determination in yeasts by anion-exchange HPLC-ICP-MS

International audienceAn analytical method was developed for the speciation of elemental selenium (Se(0)) in selenized yeasts by anion-exchange HPLC-ICP-MS after its chemical transformation into SeSO32− by reaction with sodium sulfite. The presence of Se(0) in the yeasts was further confirmed by single-particle ICP-MS. Indeed, Se nanoparticles, if present, are expected to be, at least partly, Se(0). X-ray photoelectron spectroscopy, a well-recognized technique for chemical element speciation in the solid state, was also used with this objective. Both methods were able to confirm the presence of Se(0) in the selenized yeasts but failed to provide reliable quantitative results. Analytical performances of the HPLC-ICP-MS method were then evaluated for Se(0) determination. Quantification limits of 1 mg/kg were reached. The recovery levels from an added quantity comprised between 93 and 101%. Within-run and between-run precisions were both below 8%. The procedure developed was finally applied to quantify Se(0) content in a series of seven yeast batches from different suppliers. Se(0) was found to be present in all the studied yeasts and represented on average 10–15% of the total S

Phase stability frustration on ultra-nanosized anatase TiO 2

cited By 8International audienceThis work sheds light on the exceptional robustness of anatase TiO 2 when it is downsized to an extreme value of 4â €‰nm. Since at this size the surface contribution to the volume becomes predominant, it turns out that the material becomes significantly resistant against particles coarsening with temperature, entailing a significant delay in the anatase to rutile phase transition, prolonging up to 1000â €‰°C in air. A noticeable alteration of the phase stability diagram with lithium insertion is also experienced. Lithium insertion in such nanocrystalline anatase TiO 2 converts into a complete solid solution until almost Li 1 TiO 2, a composition at which the tetragonal to orthorhombic transition takes place without the formation of the emblematic and unwished rock salt Li 1 TiO 2 phase. Consequently, excellent reversibility in the electrochemical process is experienced in the whole portion of lithium content

Direct Quantification of Anionic Redox over Long Cycling of Li-Rich NMC via Hard X-ray Photoemission Spectroscopy

International audienceCumulative anionic/cationic bulk redox processes lead to the outstanding specific energy (1000 Wh kg-1) of Li-rich Mn-based layered oxides as lithium-ion battery cathodes. Previous attempts to quantify redox processes in these materials were either limited to initial cycles or relied solely on the transition metals. It thus remains unclear to what extent does oxygen redox persist over cycling. This study provides an answer via synchrotron-based bulk-sensitive hard X-ray photoemission spectroscopy (HAXPES) by directly following the changes in the electronic state of lattice oxygen. We find that oxygen redox contribution stabilizes after initial cycles in Li1.2Ni0.13Mn0.54Co0.13O2 (Li-rich NMC), and even after 70 cycles, it accounts for more than one-third of the overall capacity. Consequently, we observe a gradual but limited growth of Mn3+/4+ redox, instead of a complete activation. Partial degradation of the Ni2+/3+/4+ redox is also detected. This fundamental study generates optimism for the concept of anionic redox in long-cycling batteries and also highlights the capability of HAXPES for understanding bulk versus surface effects in energy materials

Zero volt storage of Na-ion batteries: Performance dependence on cell chemistry!

International audienceSodium-ion batteries (NIBs) are regaining their importance in recent years as a sustainable complementary energy storage device for Li-ion batteries. Although, they cannot compete in terms of energy density with respect to Li-ion, they present a few advantages, namely the 0 V stability that makes them safe during external short and/or over-discharge. When the cell is discharged to 0 V, the negative electrode potential shoots up high during which the copper current collector in use for Li-ion cells could oxidize, dissolve and leads to internal short. In contrast, Na-ion cells utilize an aluminium current collector that is strongly resistant against oxidation, hence enabling their 0 V stability. However, apart from the current collector stability, the negative electrode potential rise could cause interphase instability which is not well elucidated. Hence, herein, we explored two different Na-ion chemistries, namely polyanionic Na3V2(PO4)2F3-hard carbon and sodium layered oxide-hard carbon using different electrolyte formulations. Combined impedance analyses, ex-situ X-ray photoelectron spectroscopy (XPS) and operando optical sensing indicate the 0 V discharge involves SEI degradation thereby deteriorating the cell performance, the extent of which depends on the positive electrode potential and the electrolyte in use. Overall, the 0 V stability is not an in-built property of Na-ion cells and a careful selection of cell chemistry is mandatory to achieve 0 V stable Na-ion cells

Electrode/electrolyte interface reactivity in high-voltage spinel LiMn 1.6Ni0.4O4/Li4Ti5O 12 lithium-ion battery

cited By 129International audienceHigh-voltage spinel oxides combined with Li4Ti5O 12 result in 3 V lithium-ion batteries with a high power capability; however, the electrochemical performances are limited by electrode/electrolyte interfacial reactivity at high potential. We have investigated electrode/electrolyte interfaces in LiMn1.6Ni0.4O 4/Li4Ti5O12 cells by X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectrocopy (EIS). EIS has shown that both electroadsorption and film-formation mechanisms occur at the positive electrode. XPS has revealed that very low amounts of lithiated species are deposited at the surface of the positive electrode, despite the high potential, but that great amounts of organic species are deposited. Interesting results were obtained for the Li4Ti 5O12 electrode. Whereas Li4Ti5O 12 is usually considered as a passivation-free electrode material, large amounts of organic and inorganic species were deposited at the surface of this electrode. The question of a possible interaction between both electrodes in the formation mechanisms of surface films is discussed. © 2010 American Chemical Society

Redox activity of argyrodite Li6PS5Cl electrolyte in all-solid-state Li-ion battery: An XPS study.

International audienceArgyrodite Li6PS5Cl is a good candidate as solid electrolyte for bulk all-solid-state Li-ion batteries due to its high ionic cond. and its good processability, although it shows some interface reactivity towards electrode active materials. In this work we have cycled LiCoO2/Li6PS5Cl/Li4Ti5O12 full cells and analyzed the interfacial mechanisms by surface-sensitive characterization techniques: Auger Electron Spectroscopy (AES) and XPS. We show that Li6PS5Cl has an electrochem. redox activity in the pos. electrode. It is partially oxidized into LiCl, P2S5 and polysulfides Li2Sn upon charge, with some reversibility upon discharge. Li6PS5Cl also reacts with LiCoO2 upon cycling, leading to the formation of phosphates at the interfac