Cellulose-Encapsulated Composite Electrolyte Design: Toward Chemically and Mechanically Enhanced Solid-Sodium Batteries.

Sulfide- and halide-based ceramic ionic conductors exhibit comparable ionic conductivity with liquid electrolytes and are candidates for high-energy- and high-power-density all-solid-state batteries. These materials, however, are inherently brittle, making them unfavorable for applications. Here, we report a mechanically enhanced composite Na+ conductor that contains 92.5 wt % of sodium thioantimonate (Na3SbS4, NSS) and 7.5 wt % of sodium carboxymethyl cellulose (CMC); the latter serves as the binder and an electrochemically inert encapsulation layer. The ceramic and binder constituents were integrated at the particle level, providing ceramic NSS-level Na+ conductivity in the NSS-CMC composite. The more than 5-fold decrease of electrolyte thickness obtained in NSS-CMC composite provided a 5-fold increase in Na+ conductance compared to NSS ceramic pellets. As a result of the CMC encapsulation, this NSS-CMC composite shows increased moisture resistivity and electrochemical stability, which significantly promotes the cycling performance of NSS-based solid-state batteries. This work demonstrates a well-controlled, orthogonal process of ceramic-rich, composite electrolyte processing: independent streams for ceramic particle formation along with binder encapsulation in a solvent-assisted environment. This work also provides insights into the interplay among the solvent, the polymeric binder, and the ceramic particles in composite electrolyte synthesis and implies the critical importance of identifying the appropriate solvent/binder system for precise control of this complicated process.

Are Selenides the Same as Sulfides? Structure, Spectroscopy, and Properties of Narrow-Gap Rare-Earth Semiconductors RE2Sn(S1-xSex)5 (RE = La, Ce; x = 0-0.8).

The ternary rare-earth sulfides RE2SnS5 (RE = La-Nd) and the partial solid solutions RE2Sn(S1-xSex)5 (RE = La, Ce; x = 0-0.8) were prepared in the form of polycrystalline samples by reaction of the elements at 900 °C and as single crystals in the presence of KBr flux. They adopt the La2SnS5-type structure (orthorhombic, space group Pbam, Z = 2) consisting of chains of edge-sharing SnCh6 octahedra separated by RE atoms. Although the cell parameters evolve smoothly in RE2Sn(S1-xSex)5, detailed structural analysis by single-crystal X-ray diffraction revealed a pronounced preference for the Se atoms to occupy two out of the three chalcogen sites, which offers a rationalization for why the all-selenide end-members RE2SnSe5 do not form. Solid-state 119Sn NMR spectra confirmed the nonrandom distribution of SnS6-nSen local environments, which could be resolved into individual resonances. The Raman spectra of RE2SnS5 compounds show an intense peak at 307-320 cm-1 assigned to a symmetric A1g mode, which is dominated by Sn-S bonds; the Raman peak intensities varied with Se substitution in La2Sn(S1-xSex)5. Optical diffuse reflectance spectra, band structure calculations, and electrochemical impedance spectra indicated that these compounds are narrow band gap semiconductors; the optical band gaps are insensitive to RE substitution in RE2SnS5 (0.7 eV) but they gradually decrease with greater Se substitution in RE2Sn(S1-xSex)5 (0.7-0.4 eV).

Mechanochemistry in Sodium Thioantimonate Solid Electrolytes: Effects on Structure, Morphology, and Electrochemical Performance.

Sodium thioantimonate (Na3SbS4) and its W-substituted analogue Na2.88Sb0.88W0.12S4 have been identified as potential electrolyte materials for all-solid-state sodium batteries due to their high Na+ conductivity. Ball milling mechanochemistry is a frequently employed synthetic approach to produce such Na+-conductive solid solutions; however, changes in the structure and morphology introduced in these systems via the mechanochemistry process are poorly understood. Herein, we combined X-ray absorption fine structure spectroscopy, Raman spectroscopy, solid-state nuclear magnetic resonance spectroscopy, powder X-ray diffraction, X-ray photoelectron spectroscopy and scanning electron microscopy characterization techniques to provide an in-depth analysis of these solid electrolytes. We report unique changes seen in the structure and morphology of Na3SbS4 and Na2.88Sb0.88W0.12S4 resulting from ball milling, inducing changes in the electrochemical performance of the solid-state batteries. Specifically, we observed a tetragonal-to-cubic crystal phase transition within Na3SbS4 following the ball mill, resulting in an increase in Na+ conductivity. In contrast, the Na+ conductivity was reduced in mechanochemically treated Na2.88Sb0.88W0.12S4 due to the formation and accumulation of a WS2 phase. In addition, mechanochemical treatment alters the surface morphology of densified Na2.88Sb0.88W0.12S4 pellets, providing intimate contact at the solid electrolyte/Na interface. This phenomenon was not observed in Na3SbS4. This work reveals the structural and morphological origin of the changes seen in these materials' electrochemical performance and how mechanochemical synthesis can introduce them.

An NHC-Stabilized H2 GeBH2 Precursor for the Preparation of Cationic Group 13/14/15 Hydride Chains.

The synthesis, characterization and reactivity studies of the NHC-stabilized complex IDipp ⋅ GeH2 BH2 OTf (1) (IDipp=1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene) are reported. Nucleophilic substitution of the triflate (OTf) group in 1 by phosphine or arsine donors provides access to the cationic group 13/14/15 chains [IDipp ⋅ GeH2 BH2 ERR1 R2 ]+ (2 E=P; R, R1 =H; R2 =t Bu; 3 E=P; R=H; R1 , R2 =Ph; 4 a E=P; R, R1 , R2 =Ph; 4 b E=As; R, R1 , R2 =Ph). These novel cationic chains were characterized by X-ray crystallography, NMR spectroscopy and mass spectrometry. Moreover, the formation of the parent complexes [IDipp ⋅ GeH2 BH2 PH3 ][OTf] (5) and [IDipp ⋅ GeH3 ][OTf] (6) were achieved by reaction of 1 with PH3 . Accompanying DFT computations give insight into the stability of the formed chains with respect to their decomposition.