We report on a particularly stable 3 V all-solid-state sodium–ion battery built using a closo-borate based electrolyte, namely Na2(B12H12)0.5(B10H10)0.5.

Thermoelectric properties vary dramatically between two boundary compositions of Ni-rich and Ni-poor TiNiSn, up to 25% in zT.

storage materials. [4] As SSEs for lithiumion batteries, they offer multiple advantages including the natural abundance of their constituent elements, their light weight, negligible electronic conduction, and low grain boundary resistance. [5] The prototypical example is LiBH 4 , whose Li + conductivity increases abruptly to >1 × 10 −3 S cm −1 above 100 °C due to a structural phase transition. [6] This superionic high-temperature phase can be stabilized at room temperature by incorporation of lithium halides (LiBH 4 -LiX, X = Cl, Br, I). Among these materials, the solid solution with lithium iodide displays the highest conductivity at room temperature of >10 −5 S cm −1 . [7] Conductivities reaching 10 −4 S cm −1 near room temperature have also been reported for two compounds of the lithium amide-borohydride Li(BH 4 ) 1−x (NH 2 ) x system, namely, for the cubic α phase (x = 3/4) and for the trigonal β phase (x = 1/2). [4,8] Here, we report the discovery of a transition to even higher Li + conductivities of up to 6.4 × 10 −3 S cm −1 near room temperature (40 °C) in BH 4 -rich lithium amide-borohydride (x = 2/3). We discuss the conduction mechanism in light of latent heat absorbed/released during the transition upon heating/cooling, respectively. We further demonstrate an allsolid-state Li 4 Ti 5 O 12 -based half-cell (employing the BH 4 -rich electrolyte) with excellent rate capability and cycling stability, comparable to a reference cell with standard liquid electrolyte representing an important step toward an all-solid-state amideborohydride-based battery. Results and DiscussionLi(BH 4 ) 1−x (NH 2 ) x powders, employing LiBH 4 and LiNH 2 precursors in amounts equivalent to x = 2/3, were prepared via reactive ball milling for 45 min and subsequent heat treatment at 120 °C for 12 h (see the Experimental Section for details). A reference sample with x = 3/4 (cubic α phase) and intermediate compositions were also synthesized.Ionic conductivities were determined for pellets pressed from the powders via temperature-dependent impedance spectroscopy. For low to intermediate conductivities, Nyquist plots take the typical form composed of a single semicircle and the electrode polarization tail (see Figure S1 in the Supporting Information for exemplary Nyquist plots). Conductivities as a High ionic conductivity of up to 6.4 × 10 −3 S cm −1 near room temperature (40 °C) in lithium amide-borohydrides is reported, comparable to values of liquid organic electrolytes commonly employed in lithium-ion batteries. Density functional theory is applied coupled with X-ray diffraction, calorimetry, and nuclear magnetic resonance experiments to shed light on the conduction mechanism. A Li 4 Ti 5 O 12 half-cell battery incorporating the lithium amide-borohydride electrolyte exhibits good rate performance up to 3.5 mA cm −2 (5 C) and stable cycling over 400 cycles at 1 C at 40 °C, indicating high bulk and interfacial stability. The results demonstrate the potential of lithium amide-borohydrides as solid-state electrolytes for high-power...

Three modifications of LiSr2Ge3 were prepared by solid state syntheses at high temperatures under inert conditions in sealed niobium ampoules. α‐LiSr2Ge3 [space group Pnnm (No. 58), a = 11.102(1), b = 11.862(1), c = 4.631(1) Å, Z = 2] is isostructural to LiCa2Tt3 (Tt = Si, Ge), containing a one‐dimensional infinite germanium chain in (tttctc)n conformation. β‐LiSr2Ge3 [space group Fmmm (No. 69), a = 8.733(1), b = 8.996(1), c = 15.045(2) Å, Z = 4] crystallizes with the AgCa2Si3 structure. The β‐phase shows a tendency for lithium deficiency, which may be as small as 6 % but can be larger. γ‐LiSr2Ge3 [space group Fddd (No. 70), a = 8.675(3), b = 15.066(5), c = 18.258(5) Å, Z = 8] is isostructural to LiBa2Tt3. The latter two structures contain planar and distorted Ge6‐rings, respectively. Comparison of the structures reveals significant changes of lattice parameters and bond lengths. β‐LiSr2Ge3 may be stabilized by a slightly smaller lithium content due to preparation procedure. This assumption is supported by the structure analysis and total energy calculations. LiSr2Ge3 can be formulated as (Li+)2(Sr2+)4[Ge6]10– according to the Zintl–Klemm concept, with each of the Zintl anions having a partially occupied delocalized π* system. Theoretical investigations indicate metallic properties since π* bands are crossing the Fermi level. Phase widths were explored for Ge/Si and Sr/Eu exchange and complete miscibility was found for both series. Mixed silicide germanides exclusively crystallize in form of the γ‐phase, whereas the Eu‐containing mixed phases prefer the α‐form, both throughout the series.

Alkaline earth monosilicides (AESi, AE ) Ca, Sr, Ba) are poor metals, and their transport properties are not solely determined by the Zintl anion, in contrast to their Zintl-type composition. Their conducting network is formed by the depopulated ∞ 1 [Si 2-] π system and AE-d states. This justifies the special local coordination of the metal atoms and the planarity of the silicon chains. The low density of carriers seems to be a playground for magnetic instabilities and the triangular prismatic arrangement of AE atoms responsible for the observed weak glassy behavior.