Solid electrolytes with superionic conductivity are required as a main component for all-solid-state batteries. Here we present a novel solid electrolyte with three-dimensional conducting pathways based on "lithium-rich" phosphidosilicates with ionic conductivity of σ > 10 −3 S cm −1 at room temperature and activation energy of 30-32 kJ mol −1 expanding the recently introduced family of lithium phosphidotetrelates. Aiming towards higher lithium ion conductivities systematic investigations of lithium phosphidosilicates gave access to the so far lithium-richest compound within this class of materials. The crystalline material (space group Fm3 � m), which shows reversible thermal phase transitions, can be readily obtained by ball mill synthesis from the elements followed by moderate thermal treatment of the mixture. Lithium diffusion pathways via both, tetrahedral and octahedral voids, are analyzed by temperature-dependent powder neutron diffraction measurements in combination with maximum entropy method (MEM) and DFT calculations. Moreover, the lithium ion mobility structurally indicated by a disordered Li/Si occupancy in the tetrahedral voids plus partially filled octahedral voids, is studied by temperature-dependent impedance and 7 Li NMR spectroscopy.

Complexes in disguise: Homoleptic [Ln(AlMe4)3] (Ln=Y, Lu) complexes are effectively masked [LnMe3]n species, which are produced reversibly upon equimolar addition of a Lewis base to the former. Compounds [LnMe3]n are thermally stable and readily form peralkylated heterobimetallic complexes with alkylaluminum, ‐gallium, and ‐magnesium reagents (see scheme).

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The lithium phosphidosilicates LiSiP and LiSiP are obtained by high-temperature reactions of the elements or including binary Li-P precursors. LiSiP (P2/n, Z = 2, a = 7.2051(4) Å, b = 6.5808(4) Å, c = 11.6405(7) Å, β = 90.580(4)°) features edge-sharing SiP double tetrahedra forming [SiP] units with a crystal structure isotypic to NaSiP and NaGeP. LiSiP (P2/m, Z = 2, a = 6.3356(4) Å, b = 7.2198(4) Å, c = 10.6176(6) Å, β = 102.941(6)°) crystallizes in a new structure type, wherein SiP tetrahedra are linked via common vertices and which are further connected by polyphosphide chains to form unique [SiP] double layers. The two-dimensional Si-P slabs that are separated by Li atoms can be regarded as three covalently linked atoms layers: a defect α-arsenic type layer of P atoms sandwiched between two defect wurzite-type SiP layers. The single crystal and powder X-ray structure solutions are supported by solid-state Li,Si, and P magic-angle spinning NMR measurements.

A broad repertoire of potential solid-state electrolytes is a prerequisite for the development and optimization of high-energy-density all-solid-state batteries. An isovalent substitution of suitable elements is a very successful tool to get access to new materials with improved properties, which allow for a detailed investigation of structure−property relationships. Here, we present the two new lithium phosphidotetrelates Li 14 GeP 6 and Li 14 SnP 6 with ionic conductivities of σ ∼ 1 mS cm −1 at room temperature. To evaluate the rules for the structure−property relationships, all experimental data of lithium phosphidogermanate Li 14 GeP 6 and lithium phosphidostannate Li 14 SnP 6 are compared to the recently reported lithium phosphidosilicate Li 14 SiP 6 . The isotypic compounds Li 14 TtP 6 (Tt = Si, Ge, Sn) are accessible via a straightforward and simple synthesis, starting from ball milling of the elements, followed by annealing of the obtained mixtures. Because of the high Li and low Tt content, all of these compounds are considered as lightweight materials with a density of 1.644− 2.025 g cm −3 . The materials were analyzed applying powder X-ray diffraction, differential scanning calorimetry, 6 Li, 31 P, and 119 Sn solid-state magic angle spinning NMR as well as temperature-dependent 7 Li NMR experiments, and electrochemical impedance spectroscopy.