1,721,068 research outputs found
Closo-Hydroborate Sodium Salts as an Emerging Class of Room-Temperature Solid Electrolytes
Full text linkNa-based hydroborates, such as NaCB9H10, Na2B10H10, NaCB11H12, and Na2B12H12, are known for their high ionic conductivity above a phase transition, usually far from room temperature. Here, a systematic investigation to suppress this phase transition and thus to stabilize novel crystal structures is conducted by means of anion mixing. The obtained compounds crystallize either with hexagonal and cubic close packed (hcp and ccp) or body-centered cubic (bcc) arrangement of anions without polymorphic evolution in the temperature range 100 < T < 700 K. The high symmetry and the configurational ionic disorder, which characterize all crystals, give room-temperature Na+ conductivity close or above 1 mS cm−1. Finally, high oxidative electrochemical stability between 3 and 4 V versus Na+/Na results from the aromatic nature of the boron cage, making Na-based hydroborates potentially suitable as efficient solid electrolytes for next-generation, high-voltage, Na-ion batteries. Various drawbacks limit the development of solid electrolytes for sodium-based batteries as cheap and efficient alternatives to conventional Li-ion batteries. Brighi et al. present a strategy to stabilize hydroborate-based compounds with high sodium mobility, large electrochemical and thermal stability, and excellent mechanical properties
Metal hydroborates: From hydrogen stores to solid electrolytes
Full text linkThe last twenty years of an intense research on metal hydroborates as solid hydrogen stores and solid electrolytes are reviewed. It is shown that from the most promising application in hydrogen storage due to their high gravimetric and volumetric capacities, the focus has moved to solid electrolytes due to high cation mobility in disordered structures with rotating or tumbling anions-hydroborate clusters. Various strategies of overcoming the strong covalent bonding of hydrogen in hydroborates for hydrogen storage and disordering their structures at room temperature for solid electrolytes are discussed. The important role of crystal chemistry and crystallography knowledge in material design can be read in the cited literature
Room-temperature-operating Na solid-state battery with complex hydride as electrolyte
No full textAll-solid-state sodium batteries are potentially game-changer devices in the transition towards a fossil-fuel-free society. They combine better sustainability, switching from lithium, to the largely available sodium with enhanced safety, replacing the flammable liquid electrolyte by a more thermally stable solid material. Nonetheless, several challenges plague the development of highly performing cells, such as the electrochemical stability of the solid electrolyte vs. both sodium and positive electrode, and the fragile interfacial contact between the components of the cell. On the basis of a Na+ conductor recently developed by our group, Na4(CB11H12)2(B12H12), herein we report its superior performance as solid electrolyte in room-temperature-working batteries. This carbacloso-closohydroborate-based material shows stable Na plating/stripping with limited polarization. Galvanostatic tests in Na||NaCrO2 cells exhibit good electrochemical performance, owing to a specific capacity around 100 mAh g−1 up to a delivered current density of 24 mA g−1. These findings represent a step further towards viable Na-based solid-state batteries operating safely while keeping elevate performance even at room temperature
The Crystal Chemistry of Inorganic Hydroborates
No full textThe crystal structures of inorganic hydroborates (salts and coordination compounds with anions containing hydrogen bonded to boron) except for the simplest anion, borohydride BH4−, are analyzed regarding their structural prototypes found in the inorganic databases such as Pearson’s Crystal Data [Villars and Cenzual (2015), Pearson’s Crystal Data. Crystal Structure Database for Inorganic Compounds, Release 2019/2020, ASM International, Materials Park, Ohio, USA]. Only the compounds with hydroborate as the only type of anion are reviewed, although including compounds gathering more than one different hydroborate (mixed anion). Carbaborane anions and partly halogenated hydroborates are included. Hydroborates containing anions other than hydroborate or neutral molecules such as NH3 are not discussed. The coordination polyhedra around the cations, including complex cations, and the hydroborate anions are determined and constitute the basis of the structural systematics underlying hydroborates chemistry in various variants of anionic packing. The latter is determined from anion–anion coordination with the help of topology analysis using the program TOPOS [Blatov (2006), IUCr CompComm. Newsl. 7, 4–38]. The Pauling rules for ionic crystals apply only to smaller cations with the observed coordination number within 2–4. For bigger cations, the predictive power of the first Pauling rule is very poor. All non-molecular hydroborate crystal structures can be derived by simple deformation of the close-packed anionic lattices, i.e., cubic close packing (ccp) and hexagonal close packing (hcp), or body-centered cubic (bcc), by filling tetrahedral or octahedral sites. This review on the crystal chemistry of hydroborates is a contribution that should serve as a roadmap for materials engineers to design new materials, synthetic chemists in their search for promising compounds to be prepared, and materials scientists in understanding the properties of novel materials
Mechanical Behavior and Dendrite Resistance of closo-Hydroborate Solid Electrolyte
No full textStack pressure and mechanical robustness are two important parameters needed to tackle the interfacial instability of solid-state batteries. Here, the mechanical behavior of Na4(CB11H12)2(B12H12), as solid electrolyte at the interface with Na anode, is reported. The solid electrolyte is tested as function of stack pressure and different current densities, revealing a critical current density of 0.6 mA cm−2 at room temperature and an optimal stack pressure of 1.5 MPa. These findings are achieved, thanks to the adoption of a multilayer approach, demonstrating the powerfulness of hydroborates to compensate chemical and electrochemical instability, simply employing different complex hydride polyanions that change locally the electrochemical properties while preserving structural and chemical coherence
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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