Once lithium-ion battery (LIB) technology has reached a maturity level enough to be the battery of choice for consumer electronics and power tools, it will be very well positioned to take over transport applications while displacing, for instance, NiCd and Ni-MH technologies. However, a major challenge is waiting for us in the near term: large scale and low cost stationary energy storage. This will be crucial for boosting the efficiency, adaptability, and reliability of the next-generation power grid. The use of stationary energy storage systems coupled to the The urgent need for optimizing the available energy through smart grids and efficient large-scale energy storage systems is pushing the construction and deployment of Li-ion batteries in the MW range which, in the long term, are expected to hit the GW dimension while demanding over 1000 ton of positive active material per system. This amount of Li-based material is equivalent to almost 1% of current Li consumption and can strongly influence the evolution of the lithium supply and cost. Given this uncertainty, it becomes mandatory to develop an energy storage technology that depends on almost infinite and widespread resources: Na-ion batteries are the best technology for large-scale applications. With small working cells in the market that cannot compete in cost ($/W h) with commercial Li-ion batteries, the consolidation of Na-ion batteries mainly depends on increasing their energy density and stability, the negative electrodes being at the heart of these two requirements. Promising Na-based negative electrodes for large-scale battery applications are reviewed, along with the study of the solid electrolyte interphase formed in the anode surface, which is at the origin of most of the stability problems.

Na2Ti3O7 is considered a promising negative electrode for Na-ion batteries; however, poor capacity retention has been reported and the stability of the solid-electrolyte interphase (SEI) could be one of the main actors of this underperformance. The composition and evolution of the SEI in Na2Ti3O7 electrodes is hereby studied by means of X-ray photoelectron spectroscopy (XPS). To overcome typical XPS limitations in the photoelectron energy assignments, the analysis of the Auger parameter is here proposed for the first time in battery materials characterization. We have found that the electrode/electrolyte interface formed upon discharge, mostly composed by carbonates and semicarbonates (Na2CO3, NaCO3R), fluorides (NaF), chlorides (NaCl) and poly(ethylene oxide)s, is unstable upon electrochemical cycling. Additionally, solid state nuclear magnetic resonance (NMR) studies prove the reaction of the polyvinylidene difluoride (PVdF) binder with sodium. The powerful approach used in this work, namely Auger parameter study, enables us to correctly determine the composition of the electrode surface layer without any interference from surface charging or absolute binding energy calibration effects. As a result, the suitability for Na-ion batteries of binders and electrolytes widely used for Li-ion batteries is questioned here.

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Nowadays, the technological utilization of reactive hydride composites (RHC) as hydrogen storage materials is limited by their reaction kinetics. However, addition of transition-metal-based additives, for instance titanium isopropoxide (Ti-iso), to the 2LiBH4+MgH2 system, results in a significant improvement of sorption kinetics. In this work, the evolution of chemical state and local structure of the Ti-based additive has been investigated by means of X-ray absorption (XAS) and photoemission (XPS) spectroscopy. X-ray absorption near-edge structure (XANES) as well as extended X-ray absorption fine structure (EXAFS) analysis have been undertaken at the Ti K-edge. The measurements reveal the formation of a highly dispersed and disordered TiO2-like phase during ball milling. During first desorption reduced titanium oxide and titanium boride are formed and remain stable upon cycling. The surface analysis performed by XPS shows that the reduction processes of the Ti-based additive during first desorption is coupled to the migration of the Ti species from the surface to the bulk of the material. Several factors, related to favoring heterogeneous nucleation of MgB2 and the increase of interfacial area through grain refinement are proposed as potential driving force, among other effects, for the observed kinetic improvement.

Amongst post‐Li‐ion battery technologies, lithium–sulfur (Li–S) batteries have captured an immense interest as one of the most appealing devices from both the industrial and academia sectors. The replacement of conventional liquid electrolytes with solid polymer electrolytes (SPEs) enables not only a safer use of Li metal (Li°) anodes but also a flexible design in the shape of Li–S batteries. However, the practical implementation of SPEs‐based all‐solid‐state Li–S batteries (ASSLSBs) is largely hindered by the shuttling effect of the polysulfide intermediates and the formation of dendritic Li° during the battery operation. Herein, a fluorine‐free noble salt anion, tricyanomethanide [C(CN)3−, TCM−], is proposed as a Li‐ion conducting salt for ASSLSBs. Compared to the widely used perfluorinated anions {e.g., bis(trifluoromethanesulfonyl)imide anion, [N(SO2CF3)2)]−, TFSI−}, the LiTCM‐based electrolytes show decent ionic conductivity, good thermal stability, and sufficient anodic stability suiting the cell chemistry of ASSLSBs. In particular, the fluorine‐free solid electrolyte interphase layer originating from the decomposition of LiTCM exhibits a good mechanical integrity and Li‐ion conductivity, which allows the LiTCM‐based Li–S cells to be cycled with good rate capability and Coulombic efficiency. The LiTCM‐based electrolytes are believed to be the most promising candidates for building cost‐effective and high energy density ASSLSBs in the near future.

Abstract. Surface plasmon resonance and magnetic characterization have been carried out for two types of thiol-capped gold nanoparticles (NPs) with similar diameters between 2.0 and 2.5 nm and different organic molecules linked to the sulphur atom: dodecanethiol and tiopronin. In addition, Au NPs capped with tetraoctyl ammonium bromide have also been included in the investigation since such capping molecules weakly interact with the gold surface atoms and, therefore, this system can be used as a model for naked gold NPs; such particles presented a bimodal size distribution with diameters around 1.5 and 5 nm. The plasmon resonance is non-existent for tiopronin-capped NPs, whereas a trace of such a feature is observed for NPs covered with dodecanethiol molecules and, a bulk-like feature is measured for NPs capped with tetralkyl ammonium salts. These differences would indicate that the modification of the surface electronic structure of the Au NPs depends on the geometry and selfassembling capabilities of the capping molecules and, on the electric charge transferred between Au and S atoms. Regarding the magnetization, dodecanethiol-capped NPs have a ferromagnetic-like behaviour, while the NPs capped with tiopronin exhibit a paramagnetic behaviour and tetralkyl ammonium-protected NPs are diamagnetic across the studied temperature range; straight chains with a well defined symmetry axis can induce orbital momentum on surface electrons close to the binding atoms. The orbital momentum not only contributes to the magnetization but also to the local anisotropy giving rise to permanent magnetism. Due to the domain structure of the adsorbed molecules, orbital momentum is not induced for tiopronin-capped NPs and the charge transfer only induces a paramagnetic spin component.

Nanostructured coatings with variable contents of tungsten carbide (WC) and amorphous carbon (a-C) are prepared by controlling the sputtering power ratio using WC and graphite targets. XRD and TEM/ED analysis shows that increasing the C incorporation, the WC nanocrystalline phases evolve from γ-W 2 C to β-WC 1-x. Further C enrichment leads to a nanocomposite structure of small WC 1-x crystals dispersed in a-C matrix. The a-C at.% is estimated by XPS analysis and correlated with the observed tribo-mechanical properties. The hardness and friction properties vary from hard/high friction (36-40 GPa; µ=0.6-0.8) to moderate-hard/low friction (16-20 GPa; µ∼0.2) coatings depending on the film composition. The transition point is found for a-C content of 10 at.%. This correlates with a change from nanocrystalline WC to nanocomposite WC 1-x /a-C coatings. The overall study will help to understand the previous literature data and will serve as guide for a tailored synthesis of these WC/a-C nanocomposites.

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